JP5454556B2 - Fuel cell system and control method of fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system and a control method for the fuel cell system.

  It is known that the startability of a fuel cell at the time of restarting below freezing point (at starting below freezing point) decreases when water such as generated water exists in the battery after operation is stopped to some extent. Therefore, a fuel cell system that performs a scavenging process for discharging water inside the battery after the operation of the fuel cell is stopped is known. Further, when performing the scavenging process, a fuel cell system that estimates the amount of water present in the battery (water content) and changes the scavenging content such as the scavenging time and the flow rate of the scavenging gas according to the estimated water content It has been known.

  As a method of estimating the water content of a fuel cell, a method of estimating from the impedance of a fuel cell has been conventionally known (Patent Document 1). In addition, there are known methods for estimating from the flow rate, pressure, temperature, and the like of the gas supplied to the fuel cell and the gas discharged from the fuel cell during the operation of the fuel cell (Patent Documents 2 and 3).

JP 2010-135341 A JP 2007-052936 A JP 2007-052937 A Japanese Patent Laying-Open No. 2005-085537

  However, in order to estimate the water content based on the impedance of the fuel cell, it is necessary to dry the inside of the fuel cell sufficiently. Therefore, it takes time to dry and the power consumption required for drying is large. In addition to the problem of reducing the efficiency (fuel consumption) of the entire system, there was a problem of degrading the electrolyte membrane and the like due to excessive drying. Also, in the fuel cell system that estimates the water content from the flow rate, pressure, temperature, etc. of the gas supplied to the fuel cell and the gas discharged from the fuel cell during the operation of the fuel cell, the estimated water content and actual There was a problem that an error was likely to occur between the moisture content. If there is an error between the estimated water content and the actual water content, there will be problems such as excessive power consumption due to excessive scavenging, deterioration of the electrolyte membrane, etc., and insufficient scavenging. As a result, there was a problem that startability below freezing point decreased. As described above, in the fuel cell system that performs the scavenging process when the operation of the fuel cell is stopped, the operation (operation stop operation) that is executed when the operation of the fuel cell is stopped still has room for improvement.

  The present invention has been made to solve the above problems, and in a fuel cell system that performs a scavenging process when the fuel cell operation is stopped, a reduction in the efficiency (fuel consumption) of the entire fuel cell system due to the operation stop operation, It aims at providing the technique which suppresses generation | occurrence | production of malfunctions, such as deterioration of an electrolyte membrane.

In order to solve at least a part of the above problems, the present invention can be realized as the following aspects or application examples.
[First aspect of the present invention]
A fuel cell system,
A fuel cell;
A measurement unit for measuring electrical characteristics of the fuel cell;
A control unit for controlling the fuel cell,
The controller is
When a signal for stopping the operation of the fuel cell is received, a scavenging process for discharging moisture present inside the fuel cell to the outside of the fuel cell is performed, and after the scavenging process, the voltage of the fuel cell The process of lowering
(I) a first process for measuring a current generated when the voltage of the fuel cell is lowered and calculating an electric quantity from an integrated value of the measured current;
(Ii) a second process for calculating a substance amount of the reaction gas existing inside the fuel cell immediately before the voltage drop based on the amount of electricity;
(Iii) a third process for calculating the volume of the gas present inside the fuel cell from the amount of the reactant gas;
(Iv) a fourth process for estimating the water content indicating the amount of liquid water present in the fuel cell by calculating the volume of liquid water present in the fuel cell from the volume of the gas; Run the fuel cell system.
According to this configuration, since the fuel cell system estimates the water content of the fuel cell by lowering the voltage of the fuel cell after performing the scavenging process, it is possible to suppress the occurrence of problems due to the shutdown operation. . Moreover, since the water content of the fuel cell is estimated by integrating the current generated when the voltage of the fuel cell is lowered after the scavenging process is performed, it is possible to suppress the occurrence of problems due to the operation stop operation.

[Application Example 1]
A fuel cell system,
A fuel cell;
A measurement unit for measuring electrical characteristics of the fuel cell;
A control unit for controlling the fuel cell,
When the control unit receives a signal for stopping the operation of the fuel cell, the control unit performs a scavenging process for discharging moisture existing inside the fuel cell to the outside of the fuel cell, and after the scavenging process, Decreasing the voltage of the fuel cell, measuring the electrical characteristics when the voltage drops, and using the measurement result to estimate the water content indicating the amount of liquid water present in the fuel cell, Fuel cell system.

  According to this configuration, since the fuel cell system estimates the water content of the fuel cell by lowering the voltage of the fuel cell after performing the scavenging process, it is possible to suppress the occurrence of problems due to the shutdown operation. .

[Application Example 2]
In the fuel cell system according to Application Example 1,
The controller is
When the water content exceeds the allowable value, further scavenging treatment is performed,
A fuel cell system that stops without performing a scavenging process if the water content is below an allowable value.

  According to this configuration, since the fuel cell system performs the scavenging process according to the estimated water content, it is possible to suppress the occurrence of problems due to the operation stop operation.

[Application Example 3]
In the fuel cell system according to Application Example 1 or Application Example 2,
The controller is
(I) a first process for measuring a current generated when the voltage of the fuel cell is lowered and calculating an electric quantity from an integrated value of the measured current;
(Ii) a second process for calculating a substance amount of the reaction gas existing inside the fuel cell immediately before the voltage drop based on the amount of electricity;
(Iii) a third process for calculating the volume of the gas present inside the fuel cell from the amount of the reactant gas;
(Iv) A fuel cell system that performs a fourth process of estimating the water content by calculating the volume of liquid water existing inside the fuel cell from the volume of the gas.

  According to this configuration, since the fuel cell system estimates the water content of the fuel cell by accumulating the current generated when the voltage of the fuel cell is lowered after performing the scavenging process, Can be suppressed.

[Application Example 4]
In the fuel cell system according to Application Example 3,
The controller is
Obtain information on the operating state of the fuel cell, including the current generated from the fuel cell and the amount of gas flowing into the fuel cell, and according to the information, the composition ratio of air present in the fuel cell Make corrections,
In the third process, the volume of the gas existing inside the fuel cell is calculated from the substance amount of the reaction gas using the corrected composition ratio.

  According to this configuration, the fuel cell system corrects the composition ratio of the air used for the estimation of the moisture content according to the operating state of the fuel cell before the estimation of the moisture content. The decrease can be suppressed.

[Application Example 5]
In the fuel cell system according to Application Example 3 or Application Example 4,
The controller is
According to the difference between the water content estimated by the first method using the first to fourth treatments and the water content estimated by the second method different from the first method, Correct the amount of electricity generated by the reduction of the catalyst contained in the fuel cell,
A fuel cell system that calculates a substance amount of a reaction gas existing inside the fuel cell by using the corrected electric quantity in the second processing.

  According to this configuration, the fuel cell system corrects the amount of electricity used for the estimation of the moisture content according to the difference between the two moisture contents estimated by different estimation methods. Can be suppressed.

[Application Example 6]
In the fuel cell system according to Application Example 5,
The second method is a fuel cell system in which the water content is estimated based on resistance of a constituent member of the fuel cell including an electrolyte.

  According to this configuration, since the fuel cell system estimates the water content based on the resistance of the constituent members of the fuel cell including the electrolyte, it is possible to improve the correction accuracy of the amount of electricity generated by the reduction of the catalyst.

[Application Example 7]
In the fuel cell system according to any one of Application Example 3 to Application Example 6,
The controller is
According to the pressure loss of the gas flow path provided inside the fuel cell, correct the volume of the gas flow path,
In the third process, the volume of the gas existing in the fuel cell is calculated from the substance amount of the reaction gas using the corrected volume of the gas flow path.

  According to this configuration, since the fuel cell system corrects the gas flow path volume used for estimating the water content according to the pressure loss of the gas flow path, it is possible to suppress a decrease in the estimation accuracy of the water content.

[Application Example 8]
In the fuel cell system according to any one of Application Example 1 to Application Example 7,
The control unit obtains information on the operating state of the fuel cell including the temperature of the fuel cell and the amount of gas flowing into the fuel cell, estimates the water content before the scavenging process from the information, and A fuel cell system that changes the content of scavenging according to the water content estimated before the scavenging process when performing the process.

  According to this configuration, the fuel cell system estimates the water content of the fuel cell by a method other than the method of estimating the water content of the fuel cell by lowering the voltage of the fuel cell before performing the scavenging process. In addition, it is possible to suppress the occurrence of problems due to the operation stop operation.

[Application Example 9]
In the fuel cell system according to any one of Application Example 1 to Application Example 7,
The said control part is a fuel cell system which changes the content of scavenging according to the resistance of the structural member of the said fuel cell containing electrolyte, when performing the said scavenging process.

  According to this configuration, the fuel cell system estimates the water content of the fuel cell by a method other than the method of estimating the water content of the fuel cell by lowering the voltage of the fuel cell before performing the scavenging process. In addition, it is possible to suppress the occurrence of problems due to the operation stop operation.

[Application Example 10]
In the battery system according to Application Example 9,
The controller is
When the resistance is equal to or less than a predetermined value, the scavenging process is performed, and after the scavenging process, the water content is estimated,
When the resistance exceeds a predetermined value, the scavenging process is not performed.

  According to this configuration, the fuel cell system performs a scavenging process for discharging moisture present inside the fuel cell to the outside of the fuel cell when the resistance of the constituent members of the fuel cell including the electrolyte exceeds a predetermined value. Since this is not performed, it is possible to suppress the occurrence of problems due to the operation stop operation.

[Application Example 11]
In the battery system according to any one of Application Examples 1 to 10,
When the fuel cell operation is stopped, when the speed of the voltage drop caused by the fuel gas passing through the electrolyte membrane inside the fuel cell is the first voltage drop speed,
The said control part is a fuel cell system which makes the 2nd voltage drop speed which is a speed | rate at the time of dropping the voltage of the said fuel cell the speed of 2 times or more of the said 1st voltage drop speed.

  According to this configuration, in the fuel cell system, the voltage drop speed when estimating the water content is more than twice the voltage drop speed caused by the crossover when the fuel cell is stopped. The estimation accuracy can be improved.

  The present invention can be realized in various modes, and can be realized in the form of, for example, a vehicle including a fuel cell system, a control device that controls the fuel cell, a control method of the fuel cell system, and the like. . Further, the fuel cell system and the like according to the present invention can be applied in combination with other members as appropriate.

It is explanatory drawing which shows schematic structure of the fuel cell system which concerns on 1st Example. It is explanatory drawing for demonstrating the estimation method of the moisture content at the time of the voltage drop used by a present Example. It is a flowchart for demonstrating the flow of a moisture content estimation process. It is a flowchart for demonstrating the flow of operation stop operation. It is explanatory drawing for demonstrating an example of the effect of a present Example. It is a flowchart for demonstrating the flow of the exercise | movement stop operation | movement in a prior art example. It is explanatory drawing which shows schematic structure of the fuel cell system which concerns on 2nd Example. It is a flowchart for demonstrating the flow of the operation stop operation in 2nd Example. It is a flowchart for demonstrating the flow of the operation stop operation in the modification of 2nd Example. It is explanatory drawing which shows schematic structure of the fuel cell system which concerns on 3rd Example. It is a flowchart for demonstrating the flow of the driving | running operation | movement of a fuel cell system including the operation | movement stop operation | movement in 3rd Example. It is explanatory drawing which shows schematic structure of the fuel cell system which concerns on 4th Example. It is explanatory drawing for demonstrating OCV avoidance driving | operation. It is a flowchart for demonstrating the flow of the driving | running operation | movement of a fuel cell system including the operation | movement stop operation | movement in 4th Example. It is explanatory drawing which shows schematic structure of the fuel cell system which concerns on 5th Example. It is a flowchart for demonstrating the flow of the operation stop operation in 5th Example. It is explanatory drawing for demonstrating the relationship between the fall factor of the specific surface area of a catalyst, and a fall rate. It is a flowchart for demonstrating the flow of the correction process in the modification of 5th Example. It is explanatory drawing which shows schematic structure of the fuel cell system which concerns on 6th Example. It is explanatory drawing for demonstrating the reduction | decrease of the volume of a cathode gas flow path. It is explanatory drawing for demonstrating the relationship between the flow volume of the air supplied to a fuel cell, and the pressure loss of a cathode gas flow path. It is explanatory drawing for demonstrating the relationship between the cross-sectional area of a cathode gas flow path, and the pressure loss of a cathode gas flow path. It is a flowchart for demonstrating the flow of the operation stop operation in 6th Example. It is explanatory drawing for demonstrating the estimation method of the moisture content which concerns on the modification 1. FIG. It is explanatory drawing for demonstrating the voltage drop speed | rate in a voltage drop process.

A. First embodiment:
A-1. Configuration of fuel cell system:
FIG. 1 is an explanatory diagram showing a schematic configuration of the fuel cell system according to the first embodiment. The fuel cell system 10 is mounted and used in a fuel cell vehicle or an electric vehicle as a system for supplying driving power. The fuel cell system 10 includes a fuel cell 100, a fuel gas supply / discharge system 200, an oxidizing gas supply / discharge system 300, a fuel cell circulation cooling system 400, a power charge / discharge system 500, and a control device 600. .

  The fuel cell 100 has a stack structure in which a plurality of fuel cells 110 are stacked. The fuel battery cell 110 is configured to generate electricity between a fuel gas (hydrogen) supplied to an anode-side catalyst electrode layer provided with an electrolyte membrane interposed therebetween and an oxidizing gas (oxygen contained in air) supplied to a cathode-side catalyst electrode layer. Electricity is generated by chemical reaction. The fuel cell 100 can be composed of fuel cells using various electrolyte membranes such as a solid polymer electrolyte membrane. In this example, a fuel cell using a solid polymer electrolyte membrane is used. The catalyst electrode layer includes a catalyst, for example, carbon particles supporting platinum (Pt) and an electrolyte. In the fuel cell 100, two terminal plates 111 serving as total electrodes are disposed at both ends of the stacked fuel cells 110.

  The fuel gas supply / discharge system 200 includes a hydrogen tank 210, a flow rate adjustment unit 220, a circulation compressor 240, a gas-liquid separation unit 250, and a switching valve 260. The fuel gas supply / discharge system 200 is connected to the anode side catalyst electrode layer (hereinafter also simply referred to as “anode”) of each fuel cell 110 constituting the fuel cell 100 from the hydrogen tank 210, the fuel gas supply unit 220, and the fuel gas supply. Hydrogen, which is a fuel gas, is supplied through the flow path 231. At this time, the flow rate adjustment unit 220 supplies hydrogen to the anode of the fuel cell 100 at a flow rate and pressure according to instructions from the control device 600.

  In addition, the fuel gas supply / discharge system 200 opens the switching valve 260 so that hydrogen that has not been used at the anode of the fuel cell 100 passes through the fuel gas discharge channel 232, the gas-liquid separation unit 250, and the switching valve 260. To the outside of the fuel cell system 10. In addition, the fuel gas supply / discharge system 200 closes the switching valve 260 to remove hydrogen that has not been used at the anode of the fuel cell 100 from the fuel gas discharge channel 232, the gas-liquid separation unit 250, the circulation channel 233, and the circulation compressor. It returns to the fuel gas supply flow path 231 via 240, and uses again as fuel gas. Circulation compressor 240 adjusts the circulation amount and pressure of hydrogen in accordance with instructions from control device 600.

  The oxidizing gas supply / discharge system 300 includes an air cleaner 310, a compressor 320, a sealing valve 340, and a pressure sensor 350. This oxidizing gas supply / discharge system 300 includes an air cleaner 310, a compressor 320, and an oxidizing gas supply flow in the cathode side catalyst electrode layer (hereinafter, also simply referred to as “cathode”) of each fuel cell 110 constituting the fuel cell 100. Air containing an oxidizing gas (oxygen) is supplied through the path 331. At this time, the compressor 320 sends out the air taken in from the air cleaner 310 toward the fuel cell 100 at a pressure according to an instruction from the control device 600.

  Further, the oxidizing gas supply / discharge system 300 discharges the exhaust gas discharged from the fuel cell 100 to the outside of the fuel cell system 10 via the oxidizing gas discharge channel 332 and the sealing valve 340. The oxidant gas supply / discharge system 300 stops the compressor 320 and closes the sealing valve 340 in accordance with an instruction from the control device 600, whereby the cathode gas flow path between the compressor 320 and the sealing valve 340 is obtained. Can be in a sealed state. Here, the “cathode gas flow path” refers to the oxidizing gas supply flow path 331 between the compressor 320 and the fuel cell 100, the oxidizing gas supply manifold inside the fuel cell 100, the gas flow path inside the single cell, and the oxidizing gas discharge. A manifold and a flow path including an oxidizing gas discharge flow path 332 between the fuel cell 100 and the sealing valve 340 are referred to. The “gas flow path inside the single cell” refers to a space in which the oxidizing gas can flow inside the single cell, and the space between the separator and the cathode side catalyst electrode layer and the inside of the cathode side catalyst electrode layer. Consists of voids.

  The pressure sensor 350 is provided in the vicinity of the connection portion of the oxidizing gas discharge flow path 332 with the fuel cell 100 and measures the pressure Pc [Pa] inside the oxidizing gas discharge flow path 332. In this embodiment, it is used to measure the pressure inside the sealed cathode gas flow path. The pressure sensor 350 is electrically connected to the control device 600 and outputs a measurement result to the control device 600. For various sensors described later, the measurement results are output to the control device 600 in the same manner as the pressure sensor 350.

  The fuel cell circulation cooling system 400 includes a radiator 410, a refrigerant temperature sensor 420, and a refrigerant circulation pump 430. The radiator 410 supplies the cooling medium to the fuel cell 100 via the refrigerant supply channel 441, and receives the cooling medium after being supplied from the fuel cell 100 via the refrigerant discharge channel 442, thereby cooling the radiator 410. The medium is circulated to cool the fuel cell 100. Water, air, or the like can be used as the cooling medium. The refrigerant temperature sensor 420 is provided in the vicinity of the connection portion of the refrigerant discharge passage 442 with the fuel cell 100 and measures the refrigerant temperature Tf [° C.] flowing out from the fuel cell 100. In this embodiment, the refrigerant temperature Tf is used as the temperature Tc inside the cathode gas channel.

  The power charging / discharging system 500 includes a load device 510, an inverter 520, a current sensor 530, a voltage sensor 540, a battery 550, and a DC-DC converter 560. The load device 510 is a vehicle driving motor, various catchers, and the like, and is connected to the terminal plate 111 on the positive electrode side and the negative electrode side of the fuel cell 100, respectively. The inverter 520 is connected in parallel to the fuel cell 100 and the battery 550, converts a direct current supplied from the fuel cell 100 or the battery 550 into an alternating current, and supplies the alternating current to the load device 510. The current sensor 530 is connected in series with the fuel cell 100 and measures the current If [A] flowing through the fuel cell 100. The voltage sensor 540 is connected in parallel with the fuel cell 100 and measures the voltage Ef [V] of the fuel cell 100.

  The battery 550 is connected in parallel with the load device 510 and the fuel cell 100 via the DC-DC converter 560. The DC-DC converter 560 boosts the output voltage of the battery 550 and supplies the boosted voltage to the inverter 520. Further, the DC-DC converter 560 steps down the output voltage and supplies it to the battery 550 in order to store the surplus power generated by the fuel cell 100.

  The control device 600 includes a microcomputer including a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The control device 600 is electrically connected to each component of the fuel cell system 10 and controls the operation of each component based on information received from each component. The control device 600 stores a control program (not shown) for controlling the fuel cell system 10 in the ROM. The CPU functions as an operation control unit 610 and a water content estimation unit 620 by executing a control program while using the RAM. In addition, the ROM stores various maps used for a moisture content estimation process described later.

  In the fuel cell system 10 configured as described above, the operation control unit 610 performs a voltage drop process that is a process for reducing the voltage Ef of the fuel cell 100. Further, the water content estimation unit 620 performs a water content estimation process, which is a process for estimating the amount of water Wc existing in the cathode gas flow path of the fuel cell 100 (hereinafter also referred to as “water content Wc”).

  When performing the voltage drop process, the operation control unit 610 can decrease the voltage Ef of the fuel cell 100 by controlling the DC-DC converter 560 and the inverter 520, for example. In addition, the operation control unit 610 controls the compressor 320 to stop the supply of air to the fuel cell 100 and controls the sealing valve 340 to seal the cathode gas flow path when performing the voltage drop process. Put it in a state.

  The moisture content estimation unit 620 executes the moisture content estimation process when the operation control unit 610 is executing the voltage drop process. That is, the water content estimation unit 620 estimates the water content Wc using the current If, the pressure Pc, and the temperature Tf when the voltage Ef of the fuel cell 100 is decreasing (during voltage decrease) by the voltage drop process. Details of the estimation method and details of the water content estimation process will be described later.

FIG. 2 is an explanatory diagram for explaining a method for estimating the water content at the time of voltage drop used in the present embodiment. The current If generated when a voltage drop process for dropping the voltage is performed on the fuel cell in which the fuel gas is supplied to the anode of the fuel cell 100 and the cathode gas flow path is sealed. Two currents are considered to be included.
(I) Current Ir [A] generated by reduction of the oxide film formed on the catalyst (hereinafter also referred to as “reduction current Ir”)
(Ii) Current Io [A] generated by consumption of oxygen present in the sealed cathode gas flow path (hereinafter also referred to as “consumption current Io”)

  The reduction current Ir is a current generated when an oxide film formed on the catalyst (Pt) included in the cathode side catalyst electrode layer is reduced. The reduction reaction of the catalyst is represented by the following formulas (1) and (2).

The consumption current Io is the oxygen (O ₂ ) contained in the air that is supplied to the cathode gas flow channel before sealing the cathode gas flow channel and is present inside the sealed cathode gas flow channel, and the hydrogen of the anode. This is a current generated by an electrochemical reaction with (H ₂ ). The reaction at the cathode at this time is represented by the formula (3), and the reaction at the anode is represented by the formula (4).

  The current If during the voltage drop can be considered to be the sum (If = Ir + Io) of the reduction current Ir and the consumption current Io (FIG. 2). In addition, the electric quantity Cf [A · s] calculated by integrating the current If at the time of voltage drop with time t [s] is the electric quantity Cr [A · s] obtained by integrating the reduction current Ir with time. It can be considered as the sum (Cf = Cr + Co) of the electric quantity Co [A · s] obtained by integrating the current Io with time. Note that the length of the time t [s] integrated to calculate the amount of electricity Cf can be arbitrarily set. For example, it may be an arbitrary time between 1 and 3 seconds from the start of the voltage drop.

Since the amount of electricity Cr is proportional to the surface area of the catalyst (Pt), it can be considered constant in the fuel cell 100 if the surface area does not change due to deterioration of the catalyst. This amount of electricity Cr can be calculated in advance by a known method. For example, from the formula (1), it can be seen that if the amount Mpto [mol] of PtO contained in the cathode side catalyst electrode layer is calculated, electric charges of twice the molar amount are generated. The amount Mpto of PtO can be calculated from the Pt oxide coating ratio CR, the number of effective Pt sites Ns [mol / cm ² ], and the specific surface area As [cm ² ] of Pt.

After calculating the amount of electricity Cf from the current If, the amount of electricity Co can be calculated by subtracting the known amount of electricity Cr from the amount of electricity Cf (Co = Cf−Cr). Using the above equation (3) and the Faraday constant, it is possible to calculate the amount of oxygen n _O2 [mol] of oxygen present in the cathode gas channel after sealing from the amount of electricity Co. In addition, since the composition ratio Ro of air (outside air) is known (O ₂ : N ₂ = 21: 79), the amount of oxygen existing in the sealed cathode gas flow channel n _{O2 is} sealed. The amount of nitrogen n _O2 [mol] of nitrogen present inside the stopped cathode gas flow path can be calculated.

  Since it is considered that only the above-described gas composed of air and water vapor and liquid water including generated water generated by power generation or the like exist in the cathode gas flow channel, the volume Vc of the cathode gas flow channel is determined as follows. Can be considered as the sum (Vc = Vcg + Vcl) of the gas volume Vcg which is the volume of the gas existing inside the liquid water volume Vcl which is the volume of the liquid water existing inside the cathode gas flow path. The gas volume Vcg can be calculated from the equation of state shown in the following equation (5).

ここで、Ｐｃは、カソードガス流路の内部の圧力であり、ｎ_H2Oは、カソードガス流路の内部に存在する水蒸気の物質量である。また、Ｒは、気体定数であり、Ｔｃは、カソードガス流路の内部の温度である。水蒸気の物質量ｎ_H2Oは、温度Ｔｃにおける飽和水蒸気量Ａから算出することができる。

Here, Pc is the pressure inside the cathode gas channel, and n _H2O is the amount of water vapor present inside the cathode gas channel. R is a gas constant, and Tc is the temperature inside the cathode gas flow path. The substance amount n _H2O of water vapor can be calculated from the saturated water amount A at the temperature Tc.

  Since the volume Vc of the cathode gas channel is known, the liquid water volume Vcl can be calculated from the gas volume Vcg (Vcl = Vc−Vcg). Further, the water content Wc can be calculated by multiplying the liquid water volume Vcl by the density.

A-2. Water content estimation process:
FIG. 3 is a flowchart for explaining the flow of the water content estimation process. First, a voltage drop process is performed by the operation control unit 610. The voltage drop speed here can be set to an arbitrary speed. When the voltage Ef of the fuel cell 100 decreases, the water content estimation unit 620 obtains the voltage Ef, current If, pressure Pc, and temperature Tf from the voltage sensor 540, current sensor 530, refrigerant temperature sensor 420, and pressure sensor 350. (Step S110). At this time, the water content estimation unit 620 continuously acquires the current If for a time (for example, 1 second) preset as the voltage drop time.

  Thereafter, the water content estimation unit 620 calculates the amount of electricity Cf (step S120). As described above, the water content estimation unit 620 calculates the amount of electricity Cf by integrating the current If with time. Further, the electric quantity Co is calculated by subtracting the electric quantity Cr (set value) from the electric quantity Cf. The water content estimation unit 620 may calculate the electrical quantity Co from the electrical quantity Cf using a map indicating the relationship between the electrical quantity Cf and the electrical quantity Co. The map can be obtained in advance experimentally or by simulation.

Subsequently, the moisture content estimation unit 620 calculates the oxygen substance amount n _O2 present in the sealed cathode gas flow path (step S130). As described above, the water content estimation unit 620 calculates the oxygen substance amount n _O2 from the electric quantity Co. Further, the amount of nitrogen n _{O2 of} nitrogen existing inside the sealed cathode gas flow path is calculated.

Thereafter, the gas volume Vcg is calculated by the water content estimation unit 620 (step S140). The water content estimation unit 620 calculates the gas volume Vcg from the state equation of the above equation (5) using the pressure Pc and the refrigerant temperature Tf. At this time, the water content estimation unit 620 uses the refrigerant temperature Tf as the temperature Tc inside the fuel cell 100. The water content estimation unit 620 may calculate the gas volume Vcg using a map showing the relationship between the oxygen substance amount n _O2 inside the cathode gas flow path and the gas volume Vcg. The map can be obtained in advance experimentally or by simulation.

  Thereafter, the water content estimation unit 620 calculates the water content Wc (step S150). The water content estimation unit 620 calculates the liquid water volume Vcl, which is the volume of liquid water inside the cathode gas flow path, by subtracting the calculated gas volume Vcg from the known cathode gas flow path volume Vc. The water content Wc is calculated by multiplying the calculated liquid water volume Vcl by the density. The above is the content of the water content estimation process.

A-3. Stop operation:
Hereinafter, an operation (operation stop operation) when the operation (power generation) of the fuel cell 100 is stopped in the fuel cell system 10 will be described. This operation stop operation is executed, for example, when a vehicle (FC vehicle) equipped with the fuel cell system 10 stops. Here, “stop” means a state in which the ignition switch of the vehicle is turned off (ignition off), the vehicle ignition switch is on (ignition on), and the vehicle is temporarily stopped. This is called “temporary stop”. When the vehicle stops, the fuel cell system 10 scavenges the fuel cell 100 and then performs a voltage drop process and a water content estimation process.

  FIG. 4 is a flowchart for explaining the flow of the operation stop operation. When the vehicle changes from the temporary stop state to the stop state due to the ignition off, the fuel cell system 10 starts the operation stop operation. First, the operation control unit 610 receives an ignition-off signal and performs a scavenging process (step S210). The scavenging process is a process of discharging moisture inside the fuel cell 100 to the outside of the fuel cell 100 by sending a gas such as oxidizing gas or fuel gas into the fuel cell 100. In the oxidizing gas supply / discharge system 300, the operation control unit 610 controls the sealing valve 340 to be in an open state, controls the compressor 320, and supplies air to the cathode of the fuel cell 100. As a result, moisture present inside the cathode gas flow channel is discharged from the sealing valve 340. Further, in the fuel gas supply / discharge system 200, the switching valve 260 is controlled to be opened, and the flow rate adjusting unit 220 is controlled to supply the fuel gas to the anode of the fuel cell 100. As a result, moisture present in the anode gas flow path is discharged from the switching valve 260.

  In the present embodiment, the operation control unit 610 controls the compressor 320 and the flow rate adjustment unit 220 so as to have preset scavenging contents (scavenging time, scavenging gas flow rate, etc.). The scavenging content can be set arbitrarily. Further, the operation control unit 610 estimates the water content Wc immediately before executing the scavenging process, and controls the compressor 320 and the flow rate adjustment unit 220 to change the scavenging content according to the estimated water content Wc. Good. As a method for estimating the water content Wc immediately before executing the scavenging process, any method other than the above-described method for estimating the water content by voltage drop may be used. This configuration will be exemplified in the second and third embodiments.

  After the scavenging process, a voltage drop process is performed by the operation control unit 610, and a water content estimation process is performed by the water content estimation unit 620 (step S220). Specifically, the operation control unit 610 controls the DC-DC converter 560 and the inverter 520 to decrease the voltage Ef. Further, the compressor 320 is controlled to stop the supply of air to the fuel cell 100, and the sealing valve 340 is controlled to bring the cathode gas flow path into a sealed state. The water content estimation unit 620 executes a water content estimation process when the voltage drops, and estimates the water content Wc from the voltage Ef, current If, pressure Pc, and temperature Tf.

  When the moisture content Wc is estimated by the moisture content estimation unit 620, the operation control unit 610 determines whether or not the moisture content Wc is equal to or less than the threshold value Th1 (step S230). The threshold value Th1 is stored in advance in the control device 600 and can be set to an arbitrary value. When the water content Wc is less than or equal to the threshold Th1 (step S230: YES), the fuel cell system 10 ends the operation stop operation. This is because the interior of the fuel cell 100 is considered to be substantially free of moisture by the scavenging process in step S210.

  On the other hand, when the water content Wc is higher than the threshold Th1 (step S230: YES), the scavenging process is performed again by the operation control unit 610 (step S240). This is because it is considered that moisture still remains in the fuel cell 100 even after the (first) scavenging process in step S210. The scavenging process (second time) in step S230 may be the same as or different from the first scavenging process (scavenging time, scavenging gas flow rate, etc.). After the second scavenging process, the operation control unit 610 performs a voltage drop process (step S250). This is because the voltage Ef increased by the scavenging process is decreased again. Thereafter, the fuel cell system 10 ends the operation stop operation. The above is the content of the operation stop operation.

  FIG. 5 is an explanatory diagram for explaining an example of the effect of the present embodiment. The upper part of FIG. 5 shows the relationship between the water content [g / cell] of the fuel cell and the start time [s] of the fuel cell at −20 ° C. below the freezing point. The lower part of FIG. 5 shows the relationship between the water content [g / cell] of the fuel cell and the impedance of the fuel cell. When the fuel cell has a large water content inside the fuel cell, the startability below freezing point decreases (FIG. 5, water content X4˜). For this reason, conventionally, a fuel cell that performs a scavenging process in order to bring the water content after the operation of the fuel cell to a range that is easy to start below freezing (FIG. 5, water content X1 to X4, hereinafter also referred to as “target range”). The system is known.

  As a method for confirming whether or not the water content of the fuel cell after the scavenging process has decreased to the target range, a method for estimating the water content from the impedance of the fuel cell after the scavenging process is conventionally known. . However, as shown in the lower part of FIG. 5, the range of water content that can be estimated by impedance is limited to the dry side (water content X1 to X2) of the target range, and the wet side (water content X3) of the target range. In ~ X4), it was difficult to estimate the water content. Therefore, when checking whether the moisture content is within the target range by impedance, it is necessary to dry the inside of the fuel cell sufficiently, which takes time to dry and the power consumption required for drying is large. Therefore, there is a problem that the efficiency (fuel consumption) of the entire fuel cell system is lowered, and there is a problem that the electrolyte membrane is deteriorated by drying.

  According to the fuel cell system 10 of the present embodiment, since the water content Wc is estimated from the voltage drop, the water content Wc can be detected on the wet side (water content X3 to X4) in the target range. Therefore, it is possible to suppress the time and power consumption required for drying (scavenging treatment) while ensuring sub-freezing startability, and to suppress deterioration of the electrolyte membrane and the like due to drying.

  FIG. 6 is a flowchart for explaining the flow of the motion stop operation in the conventional example. In a fuel cell system that performs a voltage drop process and a water content estimation process, when a motion stop operation is started, in order to determine the scavenging content, first, a voltage drop process and a water content estimation process are performed to estimate the water content (step S310). Thereafter, a scavenging process is executed according to the estimated water content (step S320). After executing the scavenging process, in order to confirm whether or not the water content is within the target range, the voltage drop process and the water content estimation process are performed again to estimate the water content (step S330). As described above, it is common to perform voltage drop processing and water content estimation processing multiple times.

  The estimation of the moisture content at the time of voltage drop has the advantage that the moisture content Wc can be detected on the wet side (moisture content X3 to X4) of the target range (FIG. 5). Due to the voltage drop, there is a problem that the catalyst (Pt) included in the fuel cell is likely to deteriorate. Therefore, unlike the fuel cell system 10 of the present embodiment, if the moisture content estimation based on the voltage drop is not performed before scavenging, and the moisture content estimation based on the voltage drop is performed only after scavenging, the number of voltage drop processes can be reduced. it can. Thereby, generation | occurrence | production of the deterioration of the catalyst by a voltage drop can be suppressed.

  When the fuel cell is disconnected from the load device when the operation is stopped and the voltage rises to a value close to the open circuit voltage (OCV), the catalyst deteriorates due to oxidation, and thus the voltage drop process is performed when the operation is stopped. Is common. That is, in the conventional fuel cell system, the voltage drop process is performed when the operation of the fuel cell is stopped. Since the fuel cell system 10 of this embodiment estimates the water content using this voltage drop process, it is not necessary to perform the voltage drop process again for the estimation of the water content. Therefore, it is possible to suppress the deterioration of the catalyst due to the voltage drop process.

B. Second embodiment:
B-1. Configuration of fuel cell system:
FIG. 7 is an explanatory diagram showing a schematic configuration of the fuel cell system according to the second embodiment. In the second embodiment, a fuel cell that estimates the water content Wc immediately before executing the scavenging process by the AC impedance method and changes the scavenging content (scavenging time, scavenging gas flow rate, etc.) according to the estimated water content Wc. The system 12 will be described.

  Compared with the fuel cell system 10 of the first embodiment, the fuel cell system 12 of the second embodiment includes an impedance measurement unit 545 in the power charge / discharge system 502 and an IMP water content estimation unit in the control device 602. The difference is that 630 functions are added. Similar to the voltage sensor 540 (FIG. 1) of the first embodiment, the impedance measuring unit 545 has a function of measuring the voltage Ef of the fuel cell 100 and also superimposes an alternating current on the fuel cell 100 to thereby generate fuel. The internal impedance of battery 100 (hereinafter simply referred to as “impedance”) can be measured. The IMP moisture content estimation unit 630 estimates the moisture content Wc from the impedance of the fuel cell 100.

  It is known that the impedance of the fuel cell 100 changes depending on the wet state of the electrolyte. In general, a fuel cell is an equivalent circuit composed of a cell resistance Rc that is an electric resistance of an electrolyte membrane, a separator, etc., a reaction resistance Rr that is required to cause an electrochemical reaction, and an electric double layer capacitance Cd that is a capacitance. Can be represented. The wet state of the electrolyte has a correlation with the cell resistance Rc, and the cell resistance Rc increases as the electrolyte becomes dry. Therefore, there is a correlation between the impedance of the fuel cell 100 (specifically, the cell resistance Rc) and the water content Wc, and a map showing the relationship between the impedance and the water content Wc is created by experiments and simulations. be able to. The ROM of the control device 602 stores a map showing the relationship between the impedance and the water content Wc.

B-2. Stop operation:
FIG. 8 is a flowchart for explaining the flow of the operation stop operation in the second embodiment. When the operation stop operation of the fuel cell system 12 is started, first, the water content Wc is estimated by the IMP water content estimation unit 630 (step S400). Specifically, the IMP water content estimation unit 630 controls the impedance measurement unit 545 to measure the impedance of the fuel cell 100. Thereafter, the IMP moisture content estimation unit 630 estimates the moisture content Wc from the impedance with reference to a map showing the relationship between the measured impedance and the moisture content Wc. The map can be obtained in advance experimentally or by simulation, and is stored in the control device 600.

  After the moisture content Wc is estimated, the operation control unit 610 performs a scavenging process (step S410). At this time, the operation control unit 610 controls the compressor 320 so that the scavenging content corresponds to the water content Wc estimated from the impedance. The control device 600 according to the present embodiment stores data indicating the relationship between the water content Wc and the control content of the compressor 320, and controls the compressor 320 by referring to this data. The subsequent processes from step S420 to S450 are the same as steps S220 to S250 of the operation stop operation (FIG. 4) of the first embodiment, and thus description thereof is omitted. When the fuel cell system 12 stores a map showing the relationship between the impedance and the scavenging content in the control device 600, the scavenging content is directly estimated without estimating the water content Wc from the measured impedance. May be determined.

  According to the fuel cell system 12 of the second embodiment described above, since the scavenging content can be changed according to the water content Wc, it is possible to suppress the occurrence of problems such as scavenging more than necessary. . Further, since the voltage drop process is not executed when the water content Wc for determining the scavenging content is estimated, the number of voltage drop processes can be reduced in the entire operation of stopping operation. On the other hand, since the water content Wc after the scavenging process is estimated by the voltage drop, as described with reference to FIG. 5, it is possible to suppress the time and power consumption required for the scavenging process while ensuring the startability below the freezing point. it can. In addition, deterioration of the electrolyte membrane and the like due to drying can be suppressed.

B-3. Modification of the second embodiment:
FIG. 9 is a flowchart for explaining the flow of the operation stop operation in the modification of the second embodiment. Here, a configuration will be described in which it is determined whether or not the fuel cell 100 is in a dry state from the water content Wc estimated from the impedance, and when the fuel cell 100 is in a dry state, the operation of stopping the operation is terminated without performing the scavenging process.

  When the operation of stopping the operation of the fuel cell system 12 is started, first, the impedance of the fuel cell 100 is measured by the IMP water content estimation unit 630 (step S401). At this time, the IMP moisture content estimation unit 630 of the present embodiment estimates the moisture content Wc from the estimated impedance, but does not need to estimate the moisture content Wc.

  Thereafter, the operation control unit 610 determines whether or not the inside of the fuel cell 100 is in a dry state (step S402). As shown in the lower part of FIG. 5, since there is a correlation between the wet state inside the fuel cell 100 and the impedance, the fuel cell depends on whether or not the measured impedance exceeds a preset threshold value Th2. It can be determined whether or not the inside of the is dry. In step S401, when the IMP moisture content estimation unit 630 estimates the moisture content Wc, it may be determined from the moisture content Wc whether or not the inside of the fuel cell 100 is in a dry state.

  When the inside of the fuel cell 100 is in a dry state (step S402: YES), predetermined scavenging is performed by the operation control unit 610 (step S403). The predetermined scavenging is scavenging for sweeping out dust and the like in the flow path, and the scavenging content is set in advance. Since the inside of the fuel cell 100 is in a dry state, the scavenging process for drying the inside is not performed. This step S403 can be omitted. That is, the scavenging process may not be performed after the inside of the fuel cell 100 is determined to be in a dry state. Thereafter, a voltage drop process is performed by the operation control unit 610 (step S404), and the fuel cell system 12 ends the operation stop operation.

  On the other hand, when the inside of the fuel cell 100 is not in a dry state (step S402: NO), the scavenging process is performed by the operation control unit 610 (step S410). This is for drying the inside of the fuel cell 100. Since the processes of steps S420 to S450 after the scavenging process are the same as steps S420 to S450 of the second embodiment described above, description thereof will be omitted.

  According to the fuel cell system 12 according to the modification of the second embodiment described above, when the inside of the fuel cell 100 is in a dry state, the scavenging process for drying the inside is not performed. In addition to shortening the stop operation, power consumption required for the operation stop operation can be suppressed. In addition, deterioration of the electrolyte membrane and the like due to drying can be suppressed.

  In the present embodiment, the impedance of the fuel cell 100 is measured by the AC impedance method. However, the fuel cell 100 can be used as long as the change in the cell resistance Rc, which varies depending on the wet state of the electrolyte, can be detected. The configuration for measuring the impedance of is not essential. For example, the fuel cell system 12 may be configured to detect a change in the cell resistance Rc by a current interruption method or the like.

C. Third embodiment:
C-1. Configuration of fuel cell system:
FIG. 10 is an explanatory diagram showing a schematic configuration of the fuel cell system according to the third embodiment. In the third embodiment, the water content Wc is estimated by monitoring the balance of water inside the fuel cell 100 during operation of the fuel cell 100, and the scavenging content (scavenging time and scavenging is determined according to the estimated water content Wc. The fuel cell system 13 for changing the gas flow rate and the like will be described.

  Compared with the fuel cell system 10 of the first embodiment, the fuel cell system 13 of the third embodiment includes a flow sensor 361, a humidity sensor 362, a pressure sensor 363, and a temperature sensor 364 in the oxidizing gas supply / discharge system 303. And the point that the function of the RTM water content estimation unit 640 is added to the control device 602 is different. The flow sensor 361, the humidity sensor 362, and the pressure sensor 363 are provided in the oxidizing gas supply flow path 331, respectively, and the flow rate Fci [l / min] of air supplied to the fuel cell 100, the humidity Hci [g / l], The pressure Pci [Pa] is measured. The temperature sensor 364 is provided in the oxidizing gas discharge flow path 332 and measures the temperature Tco [° C.] of the air discharged from the fuel cell 100. The pressure sensor 350 measures the pressure Pco [Pa] of the air discharged from the fuel cell 100. The RTM water content estimation unit 640 monitors the water balance (inflow, outflow, generation, etc.) inside the fuel cell 100 during operation of the fuel cell 100 and estimates the water content Wc from the water balance. .

  A method for monitoring the balance of water inside the fuel cell 100 by the RTM water content estimation unit 640 will be described. The change amount ΔWc per unit time of the water content Wc can be calculated by the following equation (6).

ここで、ΔＷｃｖは、水蒸気としてカソードガス流路に流入し、または、水蒸気としてカソードガス流路から流出した水の総和量である。ΔＷｃｇは、発電によって生成された水の量である。ΔＷｃａは、カソード側からアノード側へ移動した水の量である。ΔＷｃｌは、液水としてカソードガス流路から排出された水の量である。

Here, ΔWcv is the total amount of water flowing into the cathode gas channel as water vapor or flowing out from the cathode gas channel as water vapor. ΔWcg is the amount of water generated by power generation. ΔWca is the amount of water moved from the cathode side to the anode side. ΔWcl is the amount of water discharged from the cathode gas flow path as liquid water.

  ΔWcv is calculated by subtracting the outflow amount ΔWcvo per unit time of the water vapor flowing out from the cathode gas flow path from the inflow amount ΔWcvi per unit time of the water vapor flowing into the cathode gas flow path (ΔWcv = ΔWcvi−ΔWcvo). Can do. The inflow amount ΔWcvi can be calculated from the inflow rate Fci of the air flowing into the cathode gas flow path, the inflow pressure Pci, and the inflow humidity Hci.

The outflow amount ΔWcvo can be calculated from the discharge flow rate Fco of air discharged from the cathode gas flow path, the discharge pressure Pco, and the saturated water vapor amount A at the discharge temperature Tco of the discharged air. The exhaust flow rate Fco can be calculated by subtracting the consumption flow rate Fcr of air (oxygen) consumed by power generation from the inflow rate Fci of air flowing into the cathode gas flow path (Fco = Fci-Fcr). The air consumption flow rate Fcr can be calculated from the current If which is the generated current and the ratio of oxygen contained in the air (O ₂ : N ₂ = 21: 79). This is because the current If generated by the electrochemical reaction and the amount of oxygen consumed by the electrochemical reaction have a correlation as shown in Expression (3).

  ΔWcg can be calculated from the current If. This is because there is a correlation between the amount of water generated by the electrochemical reaction and the current If generated by the electrochemical reaction. ΔWca is the amount of water diffused to the anode side through the electrolyte membrane among the produced water generated at the cathode, and ΔWcg is calculated from the diffusion rate (migration rate) of the produced water from the cathode side to the anode side and the elapsed time. Can be calculated. The diffusion rate can be obtained in advance by experiments or the like.

  ΔWcl can be calculated by a map showing the relationship between the current If and ΔWcl, a map showing the relationship between the air discharge flow rate Fco and ΔWcl, or the like. These maps can be obtained by experiments or the like. Note that ΔWcl is applied only when the water vapor is saturated in the cathode gas flow path, and is preferably 0 when the water vapor is not saturated. That is, in equation (6), it is preferable to apply ΔWcl only when the amount of change ΔWc when ΔWcl is 0 is positive.

C-2. Driving behavior:
FIG. 11 is a flowchart for explaining the flow of the operation operation of the fuel cell system including the operation stop operation in the third embodiment. In FIG. 11, the operation from start to step S502 is an operation during the operation of the fuel cell 100, and the operation after step S510 is an operation stop operation. During the operation of the fuel cell 100, the fuel cell system 13 monitors the water content Wc by the RTM water content estimation unit 640 (step S501). Specifically, the RTM water content estimation unit 640 includes a flow sensor 361, a humidity sensor 362, a pressure sensor 363, a temperature sensor 364, a pressure sensor 350, and a current sensor 530, and an inflow flow rate Fci, an inflow pressure Pci, an inflow humidity Hci, The current If, the discharge pressure Pco, and the discharge temperature Tco are acquired, and ΔWcv, ΔWcg, ΔWca, ΔWcl are calculated as needed. The RTM water content estimation unit 640 calculates the change amount ΔWc by applying Equation (5) to ΔWcv, ΔWcg, ΔWca, ΔWcl, and updates the water content Wc as needed.

  When the ignition control is detected by the operation control unit 610 (step S502: YES), a scavenging process is performed (step S510). At this time, the operation control unit 610 controls the compressor 320 so that the scavenging content corresponds to the water content Wc estimated by the RTM water content estimation unit 640. The control device 600 controls the compressor 320 by referring to data indicating the relationship between the water content Wc and the control content of the compressor 320. The subsequent processes from step S520 to S550 are the same as steps S220 to S250 of the operation stop operation (FIG. 4) of the first embodiment, and thus description thereof is omitted.

  According to the fuel cell system 13 of the third embodiment described above, the scavenging content can be changed according to the water content Wc, as in the second embodiment. Can be suppressed. Further, since the voltage drop process is not executed when the water content Wc for determining the scavenging content is estimated, the number of voltage drop processes can be reduced in the entire operation of stopping operation. On the other hand, since the water content Wc after the scavenging process is estimated by a voltage drop, the occurrence of an error with the actual water content is suppressed as compared with the case where the water balance is estimated by monitoring the water balance. be able to.

D. Fourth embodiment:
D-1. Configuration of fuel cell system:
FIG. 12 is an explanatory diagram showing a schematic configuration of the fuel cell system according to the fourth embodiment. In the fourth embodiment, a fuel cell system 14 that performs the OCV avoidance operation when the connection between the fuel cell and the load device is disconnected will be described. The fuel cell system 14 of the fourth embodiment is different from the fuel cell system 10 of the first embodiment in that the oxidizing gas supply / discharge system 304 includes a flow sensor 361. The flow sensor 361 is provided in the oxidizing gas supply channel 331 and measures the flow rate Fci [l / min] of the air supplied to the fuel cell 100.

  FIG. 13 is an explanatory diagram for explaining the OCV avoidance operation. The OCV avoidance operation is to prevent the voltage Ef of the fuel cell 100 from becoming an open circuit voltage (OCV) when the fuel cell 100 and the load device 510 are disconnected in the fuel cell system 14. Driving.

  A vehicle (FC vehicle) equipped with the fuel cell system 14 disconnects the fuel cell 100 from the load device 510 (particularly, a vehicle driving motor) when temporarily stopped or stopped, and thus the voltage Ef increases. When the voltage Ef becomes a value close to the open circuit voltage (OCV) (Ef≈OCV) due to the increase of the voltage Ef, there is a problem that the catalyst included in the fuel cell 100 deteriorates. Therefore, when the vehicle is temporarily stopped or stopped, the current If is drawn from the fuel cell 100 by using the power of the fuel cell 100 for charging the battery 550 instead of disconnecting the connection between the fuel cell 100 and the load device 510 ( If> 0) and the voltage Ef is maintained in a state lower than OCV (Ef <OCV). The method for drawing the current If from the fuel cell 100 is not limited to charging the battery, and power may be supplied to an auxiliary machine other than the vehicle drive motor. The OCV avoidance operation is performed by the operation control unit 610 controlling the DC-DC converter 560 and the inverter 520.

D-2. Driving behavior:
FIG. 14 is a flowchart for explaining the flow of the operation operation of the fuel cell system including the operation stop operation in the fourth embodiment. In FIG. 14, the operation up to step S603 is the operation during the operation of the fuel cell 100, and the operation after step S610 is the operation stop operation. When the FC vehicle equipped with the fuel cell system 14 stops temporarily (step S601: YES), the operation control unit 610 starts the OCV avoidance operation (step S602). Thereafter, when the ignition control is detected by the operation control unit 610 (step S603: YES), the scavenging process is performed while continuing the OCV avoiding operation (step S610).

After the scavenging process, a voltage drop process is performed by the operation control unit 610, and a water content estimation process is performed by the water content estimation unit 620 (step S620). In this embodiment, since the OCV avoidance operation is performed before the water content estimation process, the composition ratio Rm (O ₂ : N ₂ ) of the air inside the cathode gas flow path is set to the outside air when the water content estimation process is executed. Composition ratio Ro (O ₂ : N ₂ = 21: 79). Therefore, the moisture content estimation process calculates the composition ratio Rm of the air inside the cathode gas flow channel at the time of moisture content measurement.

  The amount of oxygen in the air consumed by the OCV avoidance operation can be calculated from the current If (FIG. 13) during the OCV avoidance operation, as shown in Equation (3). Therefore, the composition of the air inside the cathode gas channel after the OCV avoidance operation is calculated from the inflow flow rate Fci of the air (outside air, composition ratio Ro) flowing into the cathode gas channel during the OCV avoidance operation and the amount of oxygen consumed. The ratio Rm can be calculated. The water content estimation unit 620 calculates the water content Wc using the composition ratio Rm. The subsequent processes from step S630 to S650 are the same as steps S230 to S250 of the operation stop operation (FIG. 4) of the first embodiment, and thus description thereof is omitted. According to the fuel cell system 14 of the fourth embodiment described above, even if the OCV avoidance operation is performed before performing the water content estimation due to the voltage drop, the decrease in the estimation accuracy of the water content Wc is suppressed. Can do.

E. Example 5:
E-1. Configuration of fuel cell system:
FIG. 15 is an explanatory diagram showing a schematic configuration of the fuel cell system according to the fifth embodiment. In the fifth embodiment, a description will be given of a fuel cell system 15 that corrects the set value of the amount of electricity Cr used at the time of water content estimation after operation stop. The amount of electricity Cr is the amount of electricity generated by the reduction of the oxide film formed on the catalyst (Pt). Compared with the fuel cell system 10 of the first embodiment, the fuel cell system 15 of the fifth embodiment includes an impedance measuring unit 545 in the power charge / discharge system 505, and the control device 605 includes a correction processing unit 650. The difference is that a function is added. The impedance measurement unit 545 is the same as the impedance measurement unit 545 of the second embodiment. The correction processing unit 650 corrects the set value of the electric quantity Cr stored in the control device 600 by a method described later.

  Since the amount of electricity Cr is proportional to the surface area of the catalyst (Pt), it can be considered constant in the fuel cell 100 if the surface area does not change due to deterioration of the catalyst. However, when the catalyst gradually deteriorates due to the operation of the fuel cell 100, a difference occurs between the set value of the electric quantity Cr and the actual electric quantity Cr due to a decrease in the specific surface area. Specifically, the actual amount of electricity Cr is smaller than the set value. When this difference increases, an error occurs between the estimated water content Wc and the actual water content Wc. That is, the estimated water content Wc is larger than the actual water content Wc. Therefore, in the fuel cell system 15 of the present embodiment, when the inside of the cathode gas flow path is in a dry state, that is, when the water content Wc is considered to be almost 0 (Wc≈0), the water content Wc is estimated by a voltage drop. The amount of electricity Cr (set value) is corrected by making the generated water content Wc an error from the actual one.

E-2. Stop operation:
FIG. 16 is a flowchart for explaining the flow of the operation stop operation in the fifth embodiment. When the operation of stopping the operation of the fuel cell system 15 is started, first, the impedance of the fuel cell 100 is measured by the correction processing unit 650 (step S701). Thereafter, the operation control unit 610 determines whether or not the inside of the fuel cell 100 is in a dry state (step S702).

  When the inside of the fuel cell 100 is in a dry state (step S702: YES), predetermined scavenging is performed by the operation control unit 610 (step S703). The scavenging here is scavenging for sweeping out dust and the like in the flow path, not scavenging for drying the inside. This step S703 can be omitted. Thereafter, a voltage drop process is performed by the operation control unit 610, and a water content estimation process is performed by the water content estimation unit 620 (step S704). Thereby, the water content Wc using the electric quantity Cr (set value) is estimated.

  Thereafter, the correction processing unit 650 determines whether or not the estimated water content Wc is smaller than the threshold value Th3 (step S705). Here, the threshold value Th3 is a value set in advance as the water content Wc when the fuel cell 100 is in a dry state, and is a value close to 0 (Th3≈0). When the estimated water content Wc is equal to or less than the threshold Th3 (step S705: YES), the fuel cell system 15 ends the operation stop operation. This is because there is no error between the water content Wc estimated using the electric amount Cr (set value) and the actual water content Wc, or it is considered that there is no problem even if it occurs.

  On the other hand, when the estimated water content Wc is larger than the threshold value Th3 (step S705: NO), the correction processing unit 650 performs a correction process for the electric quantity Cr (set value) (step S706). The correction processing unit 650 calculates a new set value of the electrical quantity Cr by back-calculating the electrical quantity Cr when the moisture content Wc becomes 0 in the method for estimating the moisture content Wc described in the first embodiment. be able to.

Specifically, the correction processing unit 650 calculates the gas volume Vcg by setting the liquid water volume Vcl to 0 (Vcl≈0) in the method for estimating the water content Wc of the first embodiment (Vcg = Vc−Vcl). To do. Thereafter, the amount of oxygen n _O2 in the cathode gas flow path is calculated from the calculated gas volume Vcg using Equation (5). After that, the correction processing unit 650 calculates the amount of electricity Co generated by the consumption of oxygen from the calculated oxygen substance amount n _O2 using Equation (3). Then, the amount of electricity Cr is calculated from the amount of electricity Co (Co = Cf−Cr). The correction processing unit 650 stores the calculated amount of electricity Cr in the control device 600 as a new set value. After the correction process, the fuel cell system 15 ends the operation stop operation.

  In step S701, when the inside of the fuel cell 100 is not in a dry state (step S702: YES), processing in steps S710 to S750 is performed. Since these processes are the same as steps S210 to S250 of the first embodiment, description thereof will be omitted. According to the fuel cell system 15 of the fifth embodiment described above, even if the catalyst deteriorates due to the operation of the fuel cell 100, it is possible to suppress a decrease in the estimation accuracy of the water content Wc.

E-3. Modification of the fifth embodiment:
Here, the fuel cell system 15 for correcting the specific surface area As of the catalyst (Pt) used for calculating the amount of electricity Cr will be described. Specifically, the fuel cell system 15 that measures a reduction factor that reduces the specific surface area As of the catalyst during or after the operation of the fuel cell and corrects the specific surface area As according to the measurement result will be described.

  FIG. 17 is an explanatory diagram for explaining the relationship between the reduction factor of the specific surface area of the catalyst and the reduction rate. In FIG. 17A, the horizontal axis represents the fluctuation range (potential fluctuation width) ΔEf of the voltage Ef in the fuel cell 100, and the vertical axis represents the reduction rate RAs of the specific surface area As of the catalyst (Pt). FIG. 17A shows the relationship between the potential fluctuation range ΔEf and the specific surface area reduction rate RAs for each temperature Tf of the fuel cell 100. In FIG. 17B, the horizontal axis represents time (elapsed time) t, and the vertical axis represents the specific surface area reduction rate RAs of the catalyst (Pt). FIG. 17B shows the relationship between time t and specific surface area reduction rate RAs for each voltage Ef of the fuel cell 100.

  The catalyst (Pt) deteriorates as the fluctuation range (potential fluctuation range) ΔEf of the voltage Ef during operation or stop of the fuel cell 100 increases. That is, the specific surface area As decreases as the potential fluctuation range ΔEf increases. This is because, when the potential fluctuation range ΔEf is large, the potential at which the catalyst is oxidized / reduced is crossed and Pt is easily deformed (condensed). Further, the decrease in the specific surface area As due to the fluctuation of the voltage Ef becomes more remarkable as the temperature Tc of the fuel cell 100 is higher. For these reasons, as shown in FIG. 17A, the decrease rate RAs of the specific surface area As increases as the potential fluctuation width ΔEf increases and as the temperature Tc increases.

  Further, the catalyst (Pt) deteriorates as it is exposed to a high potential for a long period of time. That is, the higher the voltage Ef and the longer the time, the lower the specific surface area As. This is because the oxidation of Pt proceeds as the catalyst is exposed to a higher potential. From this, as shown in FIG. 17B, the rate of decrease in the specific surface area As increases as the voltage Ef increases and the elapsed time increases. The fuel cell system 15 of the present embodiment stores two maps shown in FIGS. 17A and 17B in the control device 600.

  FIG. 18 is a flowchart for explaining the flow of correction processing in a modification of the fifth embodiment. The fuel cell system 15 of the present embodiment performs the correction process shown in FIG. 18 when the fuel cell 100 is operated and stopped. First, the correction processing unit 650 monitors the voltage Ef (step S801). The correction processing unit 650 calculates the potential fluctuation range ΔEf from the voltage Ef measured at any time. The potential fluctuation range ΔEf can be a change amount of the voltage Ef at an arbitrary timing and period. For example, it may be the amount of voltage drop during the voltage drop process, or may be the difference between the maximum value and the minimum value of the voltage Ef during a preset period when the fuel cell 100 is in operation.

  After calculating the potential fluctuation width ΔEf, the correction processing unit 650 determines whether or not the potential fluctuation width ΔEf is larger than the threshold Th4 (step S802). The threshold Th4 can be set arbitrarily. The threshold value Th4 is preferably set to a fluctuation range that is considered to cause oxidation of the catalyst. When the potential fluctuation range ΔEf is larger than the threshold Th4 (step S802: YES), the correction processing unit 650 controls the refrigerant temperature sensor 420 to measure the temperature Tc, and then corrects the specific surface area As (step S804). Here, the specific surface area reduction rate RAs is calculated by fitting the temperature Tc and the potential fluctuation width ΔEf to the map shown in FIG. The correction processing unit 650 corrects the set value of the specific surface area As by multiplying the set value of the specific surface area As by the specific surface area reduction rate RAs. The correction processing unit 650 may correct the amount of electricity Cr together with the correction of the specific surface area As. On the other hand, when the potential fluctuation range ΔEf is equal to or smaller than the threshold Th4 in step S802 (step S802: NO), the correction processing unit 650 skips steps S803 and S804 described above.

  The correction processing unit 650 also determines whether or not the monitored voltage Ef has exceeded the threshold Th5 (step S805). The threshold value Th5 can also be set arbitrarily. The threshold Th5 is preferably set to a voltage value at which it is considered that oxidation of the catalyst starts to occur. When the voltage Ef exceeds the threshold value Th5 (step S805: YES), the correction processing unit 650 measures the time t that exceeds the threshold value (step S806). Thereafter, the correction processing unit 650 corrects the specific surface area As (step S807). Here, the specific surface area reduction rate RAs is calculated by applying the voltage Rf and the time t to the map shown in FIG. The correction processing unit 650 corrects the set value of the specific surface area As using the specific surface area reduction rate RAs. In addition, the amount of electricity Cr may be corrected. According to the fuel cell system 15 according to the modified example of the fifth embodiment described above, it is possible to correct the electric quantity Cr even after the system is not stopped.

F. Example 6:
F-1. Configuration of fuel cell system:
FIG. 19 is an explanatory diagram showing a schematic configuration of the fuel cell system according to the sixth embodiment. In the sixth embodiment, a fuel cell system 16 that corrects the set value of the volume Vc of the cathode gas flow path used when estimating the water content after the operation is stopped will be described. Compared with the fuel cell system 10 of the first embodiment, the fuel cell system 16 of the sixth embodiment has a point that the power charge / discharge system 506 includes an impedance measuring unit 545 and a flow rate to the oxidizing gas supply / discharge system 306. The difference is that the sensor 361 and the pressure sensor 363 are provided, and the function of the correction processing unit 660 is added to the control device 606. The impedance measurement unit 545 is the same as the impedance measurement unit 545 of the second embodiment. The flow sensor 361 and the pressure sensor 363 are provided in the oxidizing gas supply channel 331, respectively, and measure the flow rate Fci [l / min] and the pressure Pci [Pa] of the air supplied to the fuel cell 100. The pressure sensor 350 measures the pressure Pco [Pa] of the air discharged from the fuel cell 100. The correction processing unit 650 corrects the set value of the volume Vc of the cathode gas flow path stored in the control device 600 by a method described later.

  FIG. 20 is an explanatory diagram for explaining a decrease in the volume of the cathode gas flow path. In the cathode gas channel, the gas diffusion layer (GDL) may bite into the gas channel side with time, and the gas channel cross-sectional area (channel cross-sectional area) Sc may decrease. Then, since the actual cathode gas flow channel volume Vc is smaller than the set value of the volume Vc, an error occurs between the estimated water content Wc and the actual water content Wc. That is, the estimated water content Wc is larger than the actual water content Wc. Therefore, in the fuel cell system 16 of the present embodiment, when the inside of the cathode gas channel is in a dry state, that is, when the water content Wc is considered to be substantially 0 (Wc≈0), the pressure loss ΔPc inside the cathode gas channel is Measurement is performed, and the volume Vc (set value) of the cathode gas flow path is corrected from the measured value.

  FIG. 21 is an explanatory diagram for explaining the relationship between the flow rate of air supplied to the fuel cell and the pressure loss of the cathode gas passage. The horizontal axis of FIG. 21 indicates the flow rate Fci of air supplied to the fuel cell 100, and the vertical axis indicates the pressure loss ΔPc of the cathode gas flow path. FIG. 21 shows the relationship between the flow rate Fci and the pressure loss ΔPc when the liquid water is present inside the cathode gas flow path and when it is not present. As can be seen from FIG. 21, the pressure loss ΔPc of the cathode gas flow channel differs in the relationship between the pressure loss ΔPc and the flow rate Fci depending on the presence or absence of liquid water inside the flow channel. Therefore, in order to calculate the channel cross-sectional area Sc from the pressure loss ΔPc, it is necessary to keep the water content Wc constant. Hereinafter, the relationship between the pressure loss ΔPc and the flow path cross-sectional area Sc when the water content Wc is considered to be substantially 0 (Wc≈0) will be described.

  FIG. 22 is an explanatory diagram for explaining the relationship between the cross-sectional area of the cathode gas channel and the pressure loss of the cathode gas channel. The horizontal axis in FIG. 22 indicates the flow path cross-sectional area Sc, and the vertical axis indicates the pressure loss ΔPc. As can be seen from FIG. 22, when the water content is constant (here, Wc≈0), the pressure loss ΔPc decreases as the flow path cross-sectional area increases. The fuel cell system 16 of this embodiment stores the map shown in FIG.

F-2. Stop operation:
FIG. 23 is a flowchart for explaining the flow of the operation stop operation in the sixth embodiment. When the operation of stopping the operation of the fuel cell system 16 is started, first, the impedance of the fuel cell 100 is measured by the correction processing unit 660 (step S901). Thereafter, the operation control unit 610 determines whether or not the inside of the fuel cell 100 is in a dry state (step S902).

  When the inside of the fuel cell 100 is in a dry state (step S902: YES), the operation control unit 610 performs predetermined scavenging for sweeping out dust and the like in the flow path (step S903). This step S903 can be omitted. Thereafter, the operation control unit 610 measures the pressure loss ΔPc (step S904). Specifically, the operation control unit 610 controls the pressure sensor 363 and the pressure sensor 350 to measure the pressure Pci of air flowing into the fuel cell 100 and the pressure Pco of air discharged from the fuel cell 100. Thereafter, the operation control unit 610 sets a difference between the pressure Pci and the pressure Pco as a measured value of the pressure loss ΔPc.

  The correction processing unit 660 determines whether or not the measured pressure loss ΔPc is smaller than the threshold Th6 (step S905). The threshold Th6 here is calculated in advance using the set value of the volume Vc stored in the control device 600 and the map shown in FIG. Specifically, since the length of the cathode gas channel is known, the set value of the channel cross-sectional area Sc can be calculated from the set value of the volume Vc. The set value of the pressure loss ΔPc can be calculated from the set value of the channel cross-sectional area Sc and the map. The correction processing unit 660 sets the set value of the pressure loss ΔPc to Th6.

  When the pressure loss ΔPc measured in step S904 is equal to or smaller than the threshold Th6 (step S905: YES), the fuel cell system 16 ends the operation stop operation. This is because a reduction in the cross-sectional area Sc of the cathode gas flow path does not occur, or it is considered that there is no problem even if it occurs.

  On the other hand, when the estimated measured pressure loss ΔPc is larger than the threshold Th6 (step S905: NO), the correction processing unit 660 performs a correction process of the volume Vc (set value) (step S906). The correction processing unit 660 uses the map of FIG. 22 to calculate the channel cross-sectional area Sc from the actually measured pressure loss ΔPc and multiply the known cathode gas channel length to obtain a new set value of the volume Vc. Can be calculated. The correction processing unit 660 stores the calculated Vc in the control device 600 as a new set value. After the correction process, the fuel cell system 16 ends the operation stop operation.

  In step S901, when the inside of the fuel cell 100 is not in a dry state (step S902: NO), the processes of steps S910 to S950 are performed. Since these processes are the same as steps S210 to S250 of the first embodiment, description thereof will be omitted. According to the fuel cell system 16 of the sixth embodiment described above, even if the volume Vc of the cathode gas flow path changes due to a temporal change or the like, it is possible to suppress a decrease in the estimation accuracy of the water content Wc. it can.

E. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

E1. Modification 1:
FIG. 24 is an explanatory diagram for describing a method for estimating water content according to the first modification. In FIG. 24A, the horizontal axis indicates the current If of the fuel cell 100, and the vertical axis indicates the voltage Ef. The horizontal axis of FIG. 24 (b) shows the current change amount (increase amount) ΔIf per unit voltage drop amount (0.1V) at the time of voltage drop of the fuel cell 100, and the vertical axis shows the water content Wm of MEA. Show. The method for estimating the water content Wc due to the voltage drop is not limited to the method described in the first embodiment, and other methods may be used. For example, as another first method, the water content Wc of the cathode gas channel may be estimated from the current change amount ΔIf per unit voltage drop amount (for example, 0.1 V) at the time of pressure drop.

  Specifically, as shown in FIG. 24A, in the fuel cell 100, when the water content Wm of the membrane electrode assembly (MEA) is large, the voltage Ef decreases due to flooding at high load. It has been known. Therefore, as shown in FIG. 24 (b), the water content Wm of the MEA can be estimated from the change amount (increase amount) ΔIf of the current If per unit drop amount when the voltage Ef of the fuel cell 100 is lowered. it can. Since there is a correlation between the water content Wm of the MEA and the water content Wc of the cathode gas flow path, if a map showing the relationship between the water content Wm and the water content Wc is prepared in advance, from the water content Wm of the MEA, The water content Wc of the cathode gas channel can be calculated. If this method is used, it is not necessary to stop the supply of air to the cathode gas flow path, so that it can be used even when the operation is not performed.

As another second method, the cathode gas is determined by the time Te until the open circuit voltage (OCV) becomes 0 when the fuel cell 100 is left in a state where the cathode gas flow path is sealed, and the crossover speed X. You may estimate the water content Wc of a flow path. When the fuel cell 100 is left in a state where the cathode gas channel is sealed, the OCV is initially in a high state, but hydrogen (H ₂ ) moves from the anode side to the cathode side, and the sealed cathode gas flow By reacting with residual oxygen (O ₂ ) present in the path, the OCV gradually decreases. When all the residual oxygen is consumed, the OCV becomes almost zero. Therefore, if the moving speed (crossover speed) X of hydrogen from the anode side to the cathode side and the time Te until the OCV becomes approximately 0 are known, the substance amount n _O2 of residual oxygen can be estimated.

Specifically, assuming that the crossover speed is X [mol / sec], the residual oxygen of the cathode is consumed at a speed of 1 / 2X [mol / sec]. If the time from when the fuel cell 100 is left in a state where the cathode gas channel is sealed until the open circuit voltage (OCV) becomes 0 is Te [sec], the amount of residual oxygen substance n _O2 [mol] is 1 / 2X / Te. If the substance amount of residual oxygen is known, the water content Wc can be estimated by the same method as in the first embodiment.

E2. Modification 2:
FIG. 25 is an explanatory diagram for explaining a voltage drop speed in the voltage drop process. In FIGS. 25A and 25B, the horizontal axis indicates time t, and the vertical axis indicates voltage Ef. As described in the first modification, the voltage Ef of the fuel cell 100 with the cathode gas flow path sealed is gradually reduced due to crossover. Therefore, the voltage drop amount during the voltage drop processing is the sum of the voltage drop amount due to the voltage drop processing and the voltage drop amount due to the crossover. Since the amount of oxygen consumed by the crossover does not appear in the current If, when the water content is estimated, the amount of oxygen remaining in the cathode gas flow path is calculated to be smaller than the actual amount, resulting in an error in the water content Wc. There is a fear. As shown in FIG. 25A, the error of the water content Wc increases as the voltage drop rate by the voltage drop process is closer to the voltage drop rate by the crossover. Therefore, by making the voltage drop speed by the voltage drop process sufficiently faster than the voltage drop speed by the crossover, the influence of the voltage drop by the crossover can be suppressed. Here, the sufficiently high speed means that the voltage drop speed by the voltage drop process is set to be twice or more the voltage drop speed by the crossover. In addition, it is more preferable to set it as 5 times or more.

E3. Modification 3:
In the first to sixth embodiments, the fuel cell system for calculating the water content Wc of the cathode gas flow path has been described. However, the first to sixth embodiments described above are also applied to the estimation of the water content Wa of the anode gas flow path. can do. At this time, the fuel cell system 10 preferably includes a pressure sensor in the vicinity of the connection portion of the fuel gas discharge passage 232 with the fuel cell 100. In addition, the operation control unit 610 controls the flow rate adjustment unit 220 to stop the supply of hydrogen to the fuel cell 100 and controls the switching valve 260 to seal the anode flow path during the voltage drop process. It is preferable to be in a state.

E4. Modification 4:
In the first to sixth embodiments, the water content Wc is estimated using the voltage Ef and current If of the entire fuel cell 100, but the water content Wcc of each single cell is determined from the voltage Ec and current Ic for each single cell. May be estimated. Further, the water content Wc of the entire fuel cell 100 may be estimated from the water content Wcc of the single cell.

E5. Modification 5:
The contents of the first to sixth embodiments and the contents of the first to fourth modifications can be realized by appropriately combining them. For example, the fuel cell system that performs the scavenging process of the second and third embodiments may perform the correction process of the fifth and sixth embodiments, and the fuel cell system of the second, third, fifth, and sixth embodiments The water content may be estimated by the method of the fourth embodiment.

DESCRIPTION OF SYMBOLS 10, 12-16 ... Fuel cell system 100 ... Fuel cell 110 ... Fuel cell 111 ... Terminal plate 200 ... Fuel gas supply discharge system 210 ... Hydrogen tank 220 ... Flow rate adjustment part 231 ... Fuel gas supply flow path 232 ... Fuel gas discharge Flow path 233 ... Circulation flow path 240 ... Circulation compressor 250 ... Gas-liquid separator 260 ... Switching valve 300, 303, 304, 306 ... Oxidation gas supply / discharge system 310 ... Air cleaner 320 ... Compressor 331 ... Oxidation gas supply flow path 332 ... Oxidation Gas discharge flow path 340 ... Sealing valve 350 ... Pressure sensor 361 ... Flow rate sensor 362 ... Humidity sensor 363 ... Pressure sensor 364 ... Temperature sensor 400 ... Fuel cell circulation cooling system 410 ... Radiator 420 ... Refrigerant temperature sensor 430 ... Refrigerant circulation pump 441 ... refrigerant supply flow path 442 ... refrigerant discharge flow 500, 502, 505, 506 ... Power charge / discharge system 510 ... Load device 520 ... Inverter 530 ... Current sensor 540 ... Voltage sensor 545 ... Impedance measurement unit 550 ... Battery 600, 602, 605, 606 ... Control device 610 ... Operation control unit 620 ... moisture content estimation unit 650, 660 ... correction processing unit

Claims (11)

A fuel cell system,
A fuel cell;
A measurement unit for measuring electrical characteristics of the fuel cell;
A control unit for controlling the fuel cell,
The controller is
When a signal for stopping the operation of the fuel cell is received, a scavenging process for discharging moisture present inside the fuel cell to the outside of the fuel cell is performed, and after the scavenging process, the voltage of the fuel cell a process of Ru lowering the,
(I) a first process for measuring a current generated when the voltage of the fuel cell is lowered and calculating an electric quantity from an integrated value of the measured current;
(Ii) a second process for calculating a substance amount of the reaction gas existing inside the fuel cell immediately before the voltage drop based on the amount of electricity;
(Iii) a third process for calculating the volume of the gas present inside the fuel cell from the amount of the reactant gas;
(Iv) a fourth process for estimating the water content indicating the amount of liquid water present in the fuel cell by calculating the volume of liquid water present in the fuel cell from the volume of the gas; Run the fuel cell system. The fuel cell system according to claim 1, wherein
The controller is
When the water content exceeds the allowable value, further scavenging treatment is performed,
A fuel cell system that stops without performing a scavenging process if the water content is below an allowable value. The fuel cell system according to claim 1 or 2 ,
The controller is
Obtain information on the operating state of the fuel cell, including the current generated from the fuel cell and the amount of gas flowing into the fuel cell, and according to the information, the composition ratio of air present in the fuel cell Make corrections,
In the third process, the volume of the gas existing inside the fuel cell is calculated from the substance amount of the reaction gas using the corrected composition ratio. The fuel cell system according to any one of claims 1 to 3 ,
The controller is
According to the difference between the water content estimated by the first method using the first to fourth treatments and the water content estimated by the second method different from the first method, Correct the amount of electricity generated by the reduction of the catalyst contained in the fuel cell,
A fuel cell system that calculates a substance amount of a reaction gas existing inside the fuel cell by using the corrected electric quantity in the second processing. The fuel cell system according to claim 4 , wherein
The second method is a fuel cell system in which the water content is estimated based on resistance of a constituent member of the fuel cell including an electrolyte. A fuel cell system according to any one of claims 1 to 5,
The controller is
According to the pressure loss of the gas flow path provided inside the fuel cell, correct the volume of the gas flow path,
In the third process, the volume of the gas existing in the fuel cell is calculated from the substance amount of the reaction gas using the corrected volume of the gas flow path. The fuel cell system according to any one of claims 1 to 6 ,
The control unit obtains information on the operating state of the fuel cell including the temperature of the fuel cell and the amount of gas flowing into the fuel cell, estimates the water content before the scavenging process from the information, and A fuel cell system that changes the content of scavenging according to the water content estimated before the scavenging process when performing the process. The fuel cell system according to any one of claims 1 to 6 ,
The said control part is a fuel cell system which changes the content of scavenging according to the resistance of the structural member of the said fuel cell containing electrolyte, when performing the said scavenging process. The battery system according to claim 8 , wherein
The controller is
When the resistance is equal to or less than a predetermined value, the scavenging process is performed, and after the scavenging process, the water content is estimated,
When the resistance exceeds a predetermined value, the scavenging process is not performed. The battery system according to any one of claims 1 to 9 ,
When the fuel cell operation is stopped, when the speed of the voltage drop caused by the fuel gas passing through the electrolyte membrane inside the fuel cell is the first voltage drop speed,
The said control part is a fuel cell system which makes the 2nd voltage drop speed which is a speed | rate at the time of dropping the voltage of the said fuel cell the speed of 2 times or more of the said 1st voltage drop speed. A control method for a fuel cell system, comprising:
Receiving a signal for stopping the operation of the fuel cell, performing a scavenging process for discharging moisture present inside the fuel cell to the outside of the fuel cell; and
After the scavenging process, the steps of Ru lowering the voltage of the fuel cell,
Measuring a current generated when the voltage of the fuel cell is lowered, and calculating an electric quantity from an integrated value of the measured current;
Calculating the amount of reactant gas present in the fuel cell immediately before the voltage drop based on the amount of electricity;
Calculating the volume of gas present in the fuel cell from the amount of substance of the reaction gas;
And a step of estimating a water content indicating an amount of liquid water present in the fuel cell by calculating a volume of liquid water present in the fuel cell from the volume of the gas .

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