JP4858746B2 - Fuel cell system and method for stopping operation - Google Patents

Description

  The present invention relates to a fuel cell system including a fuel cell that generates power upon receiving a supply of a reaction gas, and more particularly to control of a valve installed in an off-gas channel.

  As a fuel cell system, for example, one using a solid polymer electrolyte type fuel cell is configured by stacking cells composed of a membrane-electrode assembly (MEA) and a separator. Hydrogen (fuel gas) is supplied to the anode side electrode and oxygen (oxidizing gas) is supplied to the cathode side electrode, so that a power generation reaction is performed by an electrochemical reaction, and water is generated along with this power generation reaction. .

Therefore, in order to prevent the generated water from remaining in the gas distribution system including the fuel cell after the operation is stopped, in Patent Document 1, the generated water is discharged as follows. That is, when the fuel cell is stopped, the discharge passage on the cathode side is closed, the air is pressurized with an air compressor, and then the valve is opened when the pressure reaches a predetermined pressure to discharge the generated water.
JP 2002-305017 A

  However, if the discharge passage is suddenly opened while the upstream side of the valve is pressurized, the pressure in the air piping and the fuel cell is suddenly released, and the generated water is expelled from the discharge passage to the atmosphere. In particular, in a fuel cell system mounted on a vehicle, there is a problem that water is splashed around (flying water). In addition, there is a problem that noise is generated along with the discharge of generated water.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a fuel cell system capable of suppressing flying water and noise when the fuel cell is stopped.

  The fuel cell system of the present invention includes a fuel cell that generates power upon receiving a supply of a reaction gas, an off-gas passage through which a reaction off-gas discharged from the fuel cell flows, a valve installed in the off-gas passage, A control unit for controlling the opening of the valve, wherein the control unit is closed to a predetermined opening by a scavenging operation of the gas circulation system including the fuel cell and the off-gas passage. When the valve is opened, if the pressure difference between the upstream and downstream of the valve is equal to or greater than a predetermined value, the valve is gradually opened to the target opening.

  Here, the scavenging operation means that a valve is closed to a predetermined opening (including a fully closed state) in order to discharge the reaction gas and generated water remaining in the gas circulation system including the fuel cell and the off-gas flow path, and the upstream of the valve. After the pressurization, the reaction gas and the generated water are discharged by opening the valve when the upstream reaches a predetermined pressure.

  According to this configuration, it is possible to suppress flying water and noise from the off-gas flow path that are generated when the pressure is suddenly released during the scavenging operation because the valve is gradually opened. In other words, according to this configuration, when the valve opening speed until the valve reaches the target opening from the current opening is equal to or higher than the predetermined speed, the time until the valve opening reaches the target opening is delayed. In other words, by setting an upper limit on the valve opening speed, it is possible to suppress flying water and noise from the off-gas flow path.

  The control unit may set an opening command value of the valve according to a differential pressure upstream and downstream of the valve.

  The greater the differential pressure upstream and downstream of the valve, the more rapidly the pressure is released when the valve is opened. Therefore, for example, the larger the differential pressure, the smaller the amount of change in the opening area per hour of the valve. According to this, it is possible to appropriately suppress flying water and noise.

  The control unit may gradually open the valve to a target opening degree when stopping the operation of the fuel cell.

  According to this configuration, when the fuel cell is stopped, when the valve is gradually opened from a predetermined opening state, for example, when the valve is fully opened, the valve is gradually opened. The generated flying water and noise can be suppressed.

  The valve may be installed in an off-gas channel on the cathode side.

  Since the generated water is generated on the cathode side, it exists in the cathode off-gas channel more than the anode side. According to this configuration, the flying water generated when the off-gas is exhausted from the cathode off-gas channel Noise can be suppressed.

  A muffler may be provided in the off-gas flow path downstream of the valve.

  If a muffler is provided in the off-gas flow path, the generated water accumulates in the muffler, and when the valve is suddenly opened, it becomes easy to fly from the muffler. Can be suppressed.

  The control unit may set an opening command value of the valve according to a silencing characteristic of the muffler and a differential pressure between the upstream and downstream of the valve.

  The greater the pressure difference between the upstream and downstream of the valve, the more easily the noise is generated when the valve opening is increased, and noise is more likely to be generated. It is possible to control the opening command value of the valve so as to enter.

  The fuel cell system operation stop method of the present invention is installed in a fuel cell that generates power upon receiving supply of a reaction gas, an offgas passage through which a reaction offgas discharged from the fuel cell flows, and the offgas passage. A fuel cell system operation stop method comprising: a scavenging step of performing a scavenging operation of a gas flow system including the fuel cell and the off-gas flow path, and closing the valve at a predetermined opening in the scavenging operation When opening the valve, if the differential pressure between the upstream and downstream of the valve is equal to or greater than a predetermined value, the valve is gradually opened to the target opening.

  According to the present invention, it is possible to prohibit a rapid pressure release of the reaction off gas discharged from the fuel cell, and to suppress the generation of noise due to the scattered water around the generated water and the rapid pressure release.

  Next, an embodiment of a fuel cell system and an operation stop method thereof according to the present invention will be described. Hereinafter, the case where this fuel cell system is applied to an on-vehicle power generation system of a fuel cell vehicle will be described. However, the present invention is not limited to such an application example, and the present invention is not limited to such an application. For example, the present invention can be applied to a stationary power generation system in which a fuel cell is used as a power generation facility for buildings (housing, buildings, etc.)

  As shown in FIG. 1, air (outside air) as an oxidizing gas (reactive gas) is supplied to an air supply port of the fuel cell 20 via an air supply path 71. The air supply path 71 is provided with an air filter A1 that removes particulates from the air, a compressor A3 that pressurizes the air, a pressure sensor P4 that detects the supply air pressure, and a humidifier A21 that adds required moisture to the air. . The compressor A3 is driven by a motor (auxiliary machine). The motor is driven and controlled by a control unit 50 described later. The air filter A1 is provided with an air flow meter (flow meter) (not shown) that detects the air flow rate.

  The air off gas (reaction off gas) discharged from the fuel cell 20 is discharged to the outside through an exhaust path (off gas path) 72. The exhaust path 72 is provided with a pressure sensor P1 for detecting the exhaust pressure, a pressure regulating valve (valve) A4, a heat exchanger for the humidifier A21, and a muffler A22 for silencing noise generated by the exhaust. The pressure sensor P <b> 1 is provided in the vicinity of the air exhaust port of the fuel cell 20. The pressure adjustment valve A4 functions as a pressure regulator (pressure reduction) that sets the supply air pressure to the fuel cell 20.

  Detection signals (not shown) of the pressure sensors P4 and P1 are sent to the control unit 50. The control unit 50 sets the supply air pressure and the supply air flow rate to the fuel cell 20 by adjusting the motor rotation speed of the compressor A3 and the opening degree (opening area) of the pressure regulating valve A4.

  Hydrogen gas as a fuel gas (reactive gas) is supplied from the hydrogen supply source 30 to the hydrogen supply port of the fuel cell 20 via the fuel supply path 74. The hydrogen supply source 30 corresponds to, for example, a high-pressure hydrogen tank, but may be a so-called fuel reformer, a hydrogen storage alloy, or the like.

  The fuel supply path 74 includes a shutoff valve H100 that supplies or stops supplying hydrogen from the hydrogen supply source 30, a pressure sensor P6 that detects the supply pressure of hydrogen gas from the hydrogen supply source 30, and hydrogen gas to the fuel cell 20. The pressure regulating valve H9 for reducing and adjusting the supply pressure of the fuel, the pressure sensor P9 for detecting the hydrogen gas pressure downstream of the hydrogen pressure regulating valve H9, and the shutoff valve H21 for opening and closing between the hydrogen supply port of the fuel cell 20 and the fuel supply path 74. , And a pressure sensor P5 for detecting the inlet pressure of the hydrogen gas fuel cell 20 is provided.

  As the hydrogen pressure regulating valve H9, for example, a pressure regulating valve that performs mechanical pressure reduction can be used. However, a valve whose opening degree is linearly or continuously adjusted by a pulse motor may be used. Detection signals (not shown) of the pressure sensors P5, P6, and P9 are supplied to the control unit 50.

  The hydrogen gas that has not been consumed in the fuel cell 20 is discharged to the hydrogen circulation path 75 as a hydrogen off-gas and returned to the downstream side of the hydrogen pressure regulating valve H9 in the fuel supply path 74. The hydrogen circulation path 75 includes a temperature sensor T31 that detects the temperature of the hydrogen off-gas, a shutoff valve H22 that communicates / blocks the fuel cell 20 and the hydrogen circulation path 75, a gas-liquid separator H42 that collects moisture from the hydrogen off-gas, and a hydrogen A drain valve H41 that collects the generated water in a tank (not shown) outside the hydrogen circulation path 75, a hydrogen pump H50 that pressurizes the hydrogen off-gas, and a backflow prevention valve H52 are provided.

  The shutoff valves H21 and H22 close the anode side of the fuel cell 20. A detection signal (not shown) of the temperature sensor T31 is supplied to the control unit 50. The operation of the hydrogen pump H50 is controlled by the control unit 50. The hydrogen off gas merges with the hydrogen gas in the fuel supply path 74 and is supplied to the fuel cell 20 for reuse. The backflow prevention valve H52 prevents the hydrogen gas in the fuel supply path 74 from flowing back to the hydrogen circulation path 75 side. The shutoff valves H100, H21, and H22 are driven by a signal from the control unit 50.

  The hydrogen circulation path 75 is connected to the exhaust path 72 by the purge flow path 76 via the discharge control valve H51. The discharge control valve H51 is an electromagnetic shut-off valve, and discharges (purges) hydrogen off-gas to the outside by operating according to a command from the control unit 50. By performing this purge operation intermittently, it is possible to prevent the hydrogen off-gas circulation from being repeated, the impurity concentration of the hydrogen gas on the fuel electrode side being increased, and the cell voltage from being lowered.

  A cooling path 73 for circulating the cooling water is provided at the cooling water inlet / outlet of the fuel cell 20. In the cooling path 73, a temperature sensor T1 that detects the temperature of the cooling water drained from the fuel cell 20, a radiator (heat exchanger) C2 that radiates the heat of the cooling water to the outside, and a pump that pressurizes and circulates the cooling water. C1 and a temperature sensor T2 for detecting the temperature of the cooling water supplied to the fuel cell 20 are provided. The radiator C2 is provided with a cooling fan C13 that is rotationally driven by a motor.

  The fuel cell 20 is configured as a fuel cell stack in which a required number of cells that generate power upon receipt of fuel gas and oxidant gas are stacked. The electric power generated by the fuel cell 20 is supplied to a power control unit (not shown). The power control unit includes an inverter that drives a drive motor of a vehicle, an inverter that drives various auxiliary devices such as a compressor motor and a motor for a hydrogen pump, and charging to and from a power storage means such as a secondary battery. DC-DC converters for supplying power to the motors are provided.

  The control unit 50 receives control information from a requested load such as an accelerator signal of a vehicle (not shown) and sensors (pressure sensors, temperature sensors, flow sensors, output ammeters, output voltmeters, etc.) of each part of the fuel cell system. Control the operation of valves and motors.

  The control unit 50 is configured by a control computer system (not shown). The control computer system has a known configuration such as a CPU, ROM, RAM, HDD, input / output interface, and display, and is configured by a commercially available control computer system.

  In the present embodiment, when the operation of the fuel cell 20 is stopped, the pressure adjustment valve A4 installed in the exhaust passage 72 is controlled by the control unit 50 as follows.

  FIG. 2A is a time chart showing the target air pressure when the scavenging operation is performed at the end of the operation, more specifically, the target pressure at the air off-gas outlet of the fuel cell 20. FIG. 2B is a time chart showing an opening command value given to the pressure regulating valve A4 corresponding to the target pressure. Here, in the scavenging operation, in order to discharge generated water remaining in the oxidant gas circulation system including the fuel cell 20, the pressure regulating valve A4 is closed and the upstream thereof is pressurized, and then reaches a predetermined pressure. The generated water is discharged by opening the pressure regulating valve A4 at the time.

  Conventionally, as shown in FIG. 2A, in order to change the target pressure from the predetermined high pressure state to the atmospheric pressure at the end of the operation, as shown by the broken line in FIG. The opening of A4 is suddenly changed to 100% (fully open). For this reason, the pressure of the air off gas is suddenly released, and the generated water accumulated on the muffler A22 and the like is scattered around and noise is generated.

  In this embodiment, even when the target pressure is suddenly changed (decreased), as shown by the solid line in FIG. A4 is opened gently. Thereby, rapid pressure release of the air off gas is prohibited, and flying water and noise are suppressed. In detail, the control part 50 performs the following control according to the flow of FIG.

  First, scavenging operation is started in step ST1. In this scavenging operation, the pressure regulating valve A4 installed in the exhaust passage 72 is closed to a predetermined opening (for example, fully closed with an opening of 0%), and the upstream thereof is pressurized. At this time, since the downstream end of the pressure regulating valve A4 is opened to the atmosphere via the muffler A22, the differential pressure between the upstream and downstream of the pressure regulating valve A4 is the upstream pressure detected by the pressure sensor P1 and the atmospheric pressure. Differential pressure.

  Thereafter, in the conventional case, when the upstream pressure of the pressure adjustment valve A4 detected by the pressure sensor P1 reaches a predetermined pressure, or when a predetermined time has elapsed since the start of the scavenging operation, the pressure adjustment valve A4 When the opening is set to a target opening (for example, full opening of 100% opening) and discharge of generated water is promoted, in the present embodiment, the following processing is performed.

  First, in step ST3, the opening command value for the pressure regulating valve A4 is set to a predetermined target opening. After that, the opening command value is not immediately sent to the pressure adjustment valve A4, but before that, the opening until the pressure adjustment valve A4 shifts from the predetermined opening in step ST1 to the target opening set in step ST3. A valve speed (hereinafter referred to as a pressure regulating valve opening speed) is calculated (step ST5), and this pressure regulating valve opening speed is set to a predetermined flying water / noise danger speed that is set in advance according to the structure of the muffler A22, temperature rise characteristics, and the like. It is determined whether or not this is the case (step ST7).

  If the determination result in step ST7 is affirmative, that is, if the pressure regulating valve opening speed is equal to or higher than the flying water or noise danger speed (step ST5: YES), in step ST9, the opening command value for the pressure regulating valve A4 is set. A so-called annealing process for gradually increasing the target opening is performed, and the pressure adjustment valve A4 is gradually opened until the target opening is reached.

  That is, the opening of the pressure regulating valve A4 is shortened by performing a process of limiting the opening speed of the pressure regulating valve to the flying water / noise dangerous speed or less and delaying the time until the pressure regulating valve A4 reaches the target opening. Avoid sudden changes over time. During the annealing process in step ST9, the opening command value from the control unit 50 to the pressure regulating valve A4 changes gently and linearly with a predetermined gradient as shown by the solid line in FIG.

  On the other hand, if the determination result in step ST7 is negative, that is, if the pressure regulating valve opening speed is less than the flying water or noise danger speed (step ST7: NO), the opening command value set in step ST3 is pressure adjusted. The pressure adjustment valve A4 is opened to reach the target opening degree.

  As described above, in the fuel cell system of the present embodiment, during the scavenging operation that is performed when the operation is stopped, the pressure adjustment valve A4 is controlled as described above, thereby preventing rapid pressure release of the air off gas. In addition, it is possible to suppress the generation of generated water accumulated on the muffler A22 and the like and the generation of noise due to rapid pressure release.

  The opening command value for the pressure regulating valve A4 is not only increased linearly as shown in FIG. 2 (b), but, for example, as shown by reference symbols a and b in FIG. (Rate) may be changed in a curvilinear manner (eg, exponential). In the curve of symbol a, the increasing speed of the opening command value is gradually decreased with time, whereas in the curve of symbol b, it is increased. Furthermore, as shown in FIG. 5, the opening command value may be gradually increased while periodically increasing and decreasing slightly.

  Further, the larger the differential pressure between the upstream and downstream of the pressure regulating valve A4, the easier it is to release the pressure when the valve opening degree of the pressure regulating valve A4 is shifted to the target opening degree. The amount of change in the opening area of the pressure regulating valve A4 per time may be reduced.

  It is also possible to combine the valve opening patterns after limiting the valve opening of the pressure regulating valve A4 so that it does not suddenly reach the target opening. Furthermore, if the opening degree of the pressure regulating valve A4 rises gently as a whole until the target opening degree is reached, the opening degree is temporarily reduced like the peak portion of the wave pattern shown in FIG. It may be raised rapidly.

  The above-described pattern selection of the opening increase speed, the increase / decrease speed, and the flying water / noise danger speed can be determined according to the state of the upstream pressure of the pressure regulating valve A4 (pressure measured by the pressure sensor P1). This is because noise is likely to occur when the differential pressure between the upstream pressure and the downstream pressure (atmospheric pressure) of the pressure regulating valve A4 is large.

  In addition, the pattern selection of the opening increase speed, the magnitude of the ascent speed, and the danger level of flying water / noise can be determined according to the structure or the silencing performance of the muffler A22 so that the generated noise enters the muffler characteristics of the muffler A22. . Thereby, it is possible to implement appropriate noise suppression according to the muffler A22.

  Next, another embodiment of the present invention will be described. In the present embodiment, as shown by the solid line in FIG. 6, at the end of the operation of the fuel cell 20, the upper limit opening of the pressure adjustment valve A <b> 4 is in a range of, for example, 80% or less with respect to the fully open state (opening 100%). The pressure is set based on the differential pressure between the upstream pressure of the pressure regulating valve A4 detected by the pressure sensor P1 and the atmospheric pressure.

  Specifically, the control unit 50 performs the following control according to the flow shown in FIG. First, scavenging operation is started in step ST11. In this scavenging operation, as described above, the opening of the pressure adjustment valve A4 installed in the exhaust passage 72 is closed to a predetermined opening (for example, a fully closed opening of 0%) and the upstream thereof is pressurized.

  Thereafter, in the conventional case, when the upstream pressure of the pressure adjustment valve A4 detected by the pressure sensor P1 reaches a predetermined pressure, or when a predetermined time has elapsed since the start of the scavenging operation, the pressure adjustment valve A4 In the present embodiment, the upper limit of the opening command value for the pressure regulating valve A4 is limited when the opening degree is set to a target opening degree (for example, full opening of the opening degree of 100%) and discharge of generated water is promoted.

  The upper limit of the opening command value is set based on the differential pressure between the upstream pressure of the pressure regulating valve A4 detected by the pressure sensor P1 and the atmospheric pressure, and is set to, for example, 80% or less. Then, the limited opening command value is sent to the pressure regulating valve A4, and the pressure regulating valve A4 is opened.

  As described above, also in the fuel cell system of the present embodiment, when the scavenging operation is performed when the operation is stopped, the upper limit opening of the pressure regulating valve A4 is limited to a predetermined opening as described above. Abrupt pressure release of the air off-gas can be prohibited, and generation of noise accumulated around the muffler A22 and the like and noise generation due to the sudden pressure release can be suppressed.

  The scavenging operation is not limited to the operation only when the operation is stopped. For example, when the fuel cell 20 is operating, the scavenging operation is performed, for example, at idling, at low speed, or during regenerative braking. As described above, the operation may be executed when the power generation of the fuel cell 20 is temporarily stopped during the low load operation and the operation mode (intermittent operation) in which the vehicle is driven by the electric power supplied from the power storage means such as a battery or a capacitor is entered.

1 is a system configuration diagram schematically illustrating an embodiment of a fuel cell system according to the present invention. (A) is the target air pressure at the time of scavenging operation at the end of the operation of the fuel cell, (b) is a diagram showing the opening command value given to the pressure regulating valve corresponding to the target pressure. It is a control flow of the pressure regulating valve when the operation of the fuel cell is stopped. It is the figure shown about the other example which restrict | limits an opening degree command value. It is the figure shown about the other example which restrict | limits an opening degree command value. It is the figure shown about the restriction | limiting of the opening degree command value in other embodiment. It is a control flow of the pressure regulating valve when the operation of the fuel cell is stopped.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Fuel cell, 50 ... Control part, 71 ... Air supply path (part of gas distribution system), 72 ... Exhaust path (off-gas flow path, part of gas distribution system), A3 ... Compressor, A4 ... Pressure control valve (Valve), A22 ... muffler, P1-P9 ... pressure sensor

Claims (7)

A fuel cell that generates power upon receiving the supply of a reaction gas, an off-gas passage through which a reaction off-gas discharged from the fuel cell flows, a valve installed in the off-gas passage, and a control that controls the opening of the valve A fuel cell system comprising:
When the control unit opens the valve closed at a predetermined opening in the scavenging operation of the gas flow system including the fuel cell and the off-gas flow path, the differential pressure between the upstream and downstream of the valve is predetermined. When the value is equal to or greater than the value, the fuel cell system is characterized in that the valve is gradually opened to a target opening.   2. The fuel cell system according to claim 1, wherein the control unit sets an opening command value of the valve in accordance with a differential pressure between the upstream side and the downstream side of the valve.   3. The fuel cell system according to claim 1, wherein the control unit gradually opens the valve to a target opening degree when stopping the operation of the fuel cell. 4.   4. The fuel cell system according to claim 1, wherein the valve is installed in an off-gas channel on a cathode side. 5.   The fuel cell system according to any one of claims 1 to 4, wherein a muffler is provided in the off-gas channel downstream of the valve.   6. The fuel cell system according to claim 5, wherein the control unit sets an opening command value of the valve according to a muffler characteristic of the muffler and a differential pressure between the upstream side and the downstream side of the valve. . Stopping the operation of a fuel cell system comprising a fuel cell that generates power upon receiving a supply of a reaction gas, an offgas passage through which a reaction offgas discharged from the fuel cell circulates, and a valve installed in the offgas passage A method,
A scavenging step of performing a scavenging operation of a gas flow system including the fuel cell and the off-gas flow path;
When opening the valve closed to a predetermined opening in the scavenging operation, if the differential pressure between the upstream and downstream of the valve is greater than or equal to a predetermined value, gradually open the valve to the target opening A method for stopping the operation of a fuel cell system.