JP7590205B2 - Fuel Cell Systems - Google Patents

Description

This disclosure relates to a fuel cell system.

The fuel cell system disclosed in Patent Document 1 includes a fuel cell stack, a power storage device, and a control device. The fuel cell stack supplies power to a load. The power storage device is connected in parallel to the load. When the power generated by the fuel cell stack exceeds the power required by the load, the surplus power is charged to the power storage device. When the power generated by the fuel cell stack falls below the power required by the load, the shortage of power is discharged from the power storage device. The control device transitions the power generation state of the fuel cell stack according to the charging rate of the power storage device. The power generation state includes a low power generation state, a medium power generation state, and a high power generation state. The power generation power in the low power generation state is smaller than the power generation power in the medium power generation state. The power generation power in the medium power generation state is smaller than the power generation power in the high power generation state. By transitioning the power generation state, the control device can change the power generation power in stages according to the charging rate of the power storage device. By changing the power generation power of the fuel cell stack in stages, fluctuations in the power generation power of the fuel cell stack are suppressed. Fluctuations in the power generation power of the fuel cell stack are one of the factors that cause the fuel cell stack to deteriorate. By suppressing fluctuations in the power generated by the fuel cell stack, deterioration of the fuel cell stack can be suppressed.

JP 2018-73722 A

There is variation in the power required by the load. This results in a difference between the power generated by the fuel cell stack and the power required by the load. When the power generated by the fuel cell stack exceeds the power required by the load, the charging rate of the power storage device increases. When the power generated by the fuel cell stack falls below the power required by the load, the charging rate of the power storage device decreases. In either case, the change in the charging rate of the power storage device causes a transition in the power generation state. As a result, the fluctuation in the power generated by the fuel cell stack is one of the causes of deterioration of the fuel cell stack.

The fuel cell system that solves the above problem includes a fuel cell stack that supplies power to a load, a power storage device connected in parallel to the load, a charge state detection unit that detects the charge state of the power storage device, a generated power detection unit that detects the generated power of the fuel cell stack, and a control device that controls the generated power of the fuel cell stack by switching the power generation state of the fuel cell stack based on the charge state of the power storage device detected by the charge state detection unit, the power generation state including a first power generation state in which the fuel cell stack generates a first generated power, a second power generation state in which the fuel cell stack generates a second generated power greater than the first generated power, and a third power generation state in which the fuel cell stack generates a third generated power greater than the second generated power, and the control device includes a power reference value calculation unit that calculates a power reference value indicating the actual power generation performance of the fuel cell stack from the generated power detected by the generated power detection unit, and an update unit that updates the second generated power based on the power reference value.

The update unit updates the second generated power based on a power reference value that indicates the actual power generation of the fuel cell stack. This sets the second generated power according to the usage status of the fuel cell stack. This makes it possible to prevent the generated power of the fuel cell stack from becoming insufficient or excessive. Because there is little change in the charging state of the power storage device, the power generation state of the fuel cell stack is unlikely to transition from the second power generation state to the first power generation state, or from the second power generation state to the third power generation state. This makes it possible to suppress fluctuations in the generated power of the fuel cell stack due to the transition of the power generation state, and to suppress deterioration of the fuel cell stack.

For the above fuel cell system, the update unit may calculate the difference between the power reference value and the current value of the second generated power, and may divide the difference by a predetermined time, add the result to the current value of the second generated power, and use the result as the new second generated power.

Even if the power generation of the fuel cell stack temporarily becomes excessively large or excessively small, this effect can be suppressed and a second power generation value corresponding to the actual power generation performance can be calculated.

The present invention can suppress deterioration of the fuel cell stack.

FIG. 1 is a schematic diagram of a fuel cell vehicle. FIG. 1 is a circuit diagram of a DC/DC converter. FIG. 13 is a state transition diagram of the power generation state. 13 is a flowchart showing a medium power generation setting process. 11 is a diagram showing an example of the relationship between the power generation time of a fuel cell stack, the value of medium power generation, and the number of transitions of the power generation state of the fuel cell stack; FIG.

An embodiment of a fuel cell system will now be described.
As shown in Fig. 1, a fuel cell vehicle 10 includes a hydrogen tank 11, a valve 12, a compressor 13, a vehicle load 15, and a fuel cell unit 20. The fuel cell vehicle 10 may be a passenger car or an industrial vehicle. The fuel cell vehicle 10 of this embodiment is an industrial vehicle. Examples of industrial vehicles include a forklift and a towing tractor. Alternatively, the hydrogen tank 11, the valve 12, the compressor 13, and the fuel cell unit 20 may form a stationary generator that supplies power to a connected load.

The fuel cell unit 20 includes an auxiliary device 14 and a fuel cell system 21. The fuel cell system 21 includes a fuel cell stack 22, a voltage sensor 23, a current sensor 24, a DC/DC converter 30, a power storage device 25, a charge state detection unit 26, and a control device 40.

Hydrogen gas is stored in the hydrogen tank 11. The hydrogen gas discharged from the hydrogen tank 11 is supplied to the fuel cell stack 22.
The valve 12 is a component for adjusting the amount of hydrogen gas supplied from the hydrogen tank 11 to the fuel cell stack 22. The valve 12 is an electromagnetically driven on-off valve in which a valve body is electromagnetically driven in accordance with a drive cycle and a valve open time. The amount of hydrogen gas supplied to the fuel cell stack 22 can be adjusted by controlling the drive cycle and valve open time of the valve 12.

The compressor 13 is an electric compressor driven by an electric motor. The compressor 13 supplies air to the fuel cell stack 22. The amount of air supplied to the fuel cell stack 22 can be adjusted by controlling the voltage (rotation speed) of the electric motor.

The fuel cell stack 22 is a stack of multiple fuel cell cells. The fuel cell cells are, for example, solid polymer fuel cells. The fuel cell stack 22 generates electricity through a chemical reaction between a fuel gas and an oxidant gas. In this embodiment, electricity is generated using hydrogen gas as the fuel gas and oxygen in the air as the oxidant gas. The fuel cell stack 22 generates electricity using hydrogen gas supplied from the hydrogen tank 11 and oxygen supplied from the compressor 13.

The voltage sensor 23 measures the voltage of the fuel cell stack 22. The measurement result of the voltage sensor 23 is acquired by the control device 40.
The current sensor 24 measures the current of the fuel cell stack 22. The measurement result of the current sensor 24 is acquired by the control device 40.

The DC/DC converter 30 is connected to the fuel cell stack 22. The DC/DC converter 30 boosts the DC power generated by the fuel cell stack 22 and outputs the boosted power.
As shown in FIG. 2 , the DC/DC converter 30 includes a positive wiring Lp, a negative wiring Ln, six switching elements Q1, Q2, Q3, Q4, Q5, and Q6, six diodes D1, D2, D3, D4, D5, and D6, three reactors 31, 32, and 33, and a capacitor C.

The first switching element Q1 and the second switching element Q2 are connected in series. The third switching element Q3 and the fourth switching element Q4 are connected in series. The fifth switching element Q5 and the sixth switching element Q6 are connected in series. The first switching element Q1, the third switching element Q3, and the fifth switching element Q5 are connected to the positive electrode wiring Lp. The second switching element Q2, the fourth switching element Q4, and the sixth switching element Q6 are connected to the negative electrode wiring Ln. The first switching element Q1, the third switching element Q3, and the fifth switching element Q5 form an upper arm. The second switching element Q2, the fourth switching element Q4, and the sixth switching element Q6 form a lower arm. MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) are used as the six switching elements Q1 to Q6. IGBTs (Insulated Gate Bipolar Transistors) may also be used as the six switching elements Q1 to Q6.

The diodes D1 to D6 are connected in parallel to the switching elements Q1 to Q6. The diodes D1 to D6 are parasitic diodes of the switching elements Q1 to Q6. The cathodes of the diodes D1, D3, and D5 connected in parallel to the switching elements Q1, Q3, and Q5 constituting the upper arm are connected to the positive wiring Lp. The anodes of the diodes D1, D3, and D5 connected in parallel to the switching elements Q1, Q3, and Q5 constituting the upper arm are connected to the midpoint of the two switching elements Q1 to Q6 connected in series to each other. The cathodes of the diodes D2, D4, and D6 connected in parallel to the switching elements Q2, Q4, and Q6 constituting the lower arm are connected to the midpoint of the two switching elements Q1 to Q6 connected in series to each other. The anodes of the diodes D2, D4, and D6 connected in parallel to the switching elements Q2, Q4, and Q6 constituting the lower arm are connected to the negative wiring Ln.

Reactors 31, 32, and 33 are connected to the midpoints of the switching elements Q1, Q3, and Q5 that make up the upper arm and the switching elements Q2, Q4, and Q6 that make up the lower arm. The reactors 31, 32, and 33 are connected to the fuel cell stack 22.

The capacitor C is connected to the positive electrode wiring Lp and the negative electrode wiring Ln.
In the above-described DC/DC converter 30, voltage is boosted by the switching operation of the switching elements Q1 to Q6. The DC/DC converter 30 outputs a DC voltage in the voltage range of the power storage device 25, for example.

1, the auxiliary device 14 is connected to a DC/DC converter 30. The auxiliary device 14 is an electrical component that is driven by the electric power generated by the fuel cell stack 22.
The vehicle load 15 is connected to the DC/DC converter 30. The vehicle load 15 includes electrical components that are driven by the power generated by the fuel cell stack 22, and a driving motor that drives the fuel cell vehicle 10. The accessories 14 and the vehicle load 15 are loads. The fuel cell stack 22 supplies power to the loads via the DC/DC converter 30. In the following description, the accessories 14 and the vehicle load 15 will be collectively referred to as the load, where appropriate.

The power storage device 25 is connected in parallel to the load. Any type of power storage device 25 may be used as long as it is capable of being charged and discharged. Examples of the power storage device 25 include a secondary battery and a capacitor. When the power generated by the fuel cell stack 22 exceeds the power required by the load, the surplus power is charged to the power storage device 25. When the power generated by the fuel cell stack 22 is below the power required by the load, the shortage of power is discharged from the power storage device 25. The power generated by the fuel cell stack 22 can also be referred to as the output power of the fuel cell stack 22.

The charge state detection unit 26 detects the charge state of the power storage device 25. Examples of the charge state include the charge rate of the power storage device 25, the remaining capacity of the power storage device 25, and the open circuit voltage of the power storage device 25. In this embodiment, the charge state detection unit 26 detects the charge rate of the power storage device 25. The charge state detection unit 26 includes a sensor and an estimation unit that estimates the charge state from the detection result of the sensor. The sensor includes at least one of a current sensor and a voltage sensor. The estimation unit estimates the charge rate of the power storage device 25 using a current integration method that integrates the charge/discharge current of the power storage device 25, a method that uses the correlation between the open circuit voltage of the power storage device 25 and the charge rate of the power storage device 25, or a combination of these. The open circuit voltage may be estimated from the closed circuit voltage.

The control device 40 includes a processor 41 and a storage unit 42. Examples of the processor 41 include a central processing unit (CPU), a graphics processing unit (GPU), and a digital signal processor (DSP). The storage unit 42 includes a random access memory (RAM), a read-only memory (ROM), and a rewritable non-volatile memory. Examples of the non-volatile memory include an electrically erasable programmable read-only memory (EEPROM) and a flash memory. The storage unit 42 stores program code or instructions configured to cause the processor to execute a process. The storage unit 42, i.e., the computer-readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The control device 40 may be configured by a hardware circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The control device 40, which is a processing circuit, may include one or more processors that operate according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

The control device 40 controls the power generated by the fuel cell stack 22. The power generated by the fuel cell stack 22 varies depending on the amount of hydrogen gas supplied to the fuel cell stack 22 and the amount of oxygen supplied to the fuel cell stack 22. The control device 40 controls the amount of hydrogen gas supplied to the fuel cell stack 22 by controlling the valve 12. The control device 40 controls the amount of oxygen supplied to the fuel cell stack 22 by controlling the compressor 13.

The control device 40 controls the DC/DC converter 30. The control device 40 controls the switching elements Q1 to Q6 so that the fuel cell stack 22 outputs power according to the load's required power. During power generation in the fuel cell stack 22, the voltage of the fuel cell stack 22 becomes lower than the voltage of the power storage device 25. In this embodiment, when power generation in the fuel cell stack 22 is stopped, the voltage of the fuel cell stack 22 becomes higher than the voltage of the power storage device 25. The control device 40 performs a switching operation of the switching elements Q1 to Q6 during power generation in the fuel cell stack 22, thereby boosting the voltage. The control device 40 does not perform a switching operation of the switching elements Q1 to Q6 when power generation in the fuel cell stack 22 is stopped. In this case, a current flows to the power storage device 25 from the diodes D1, D3, and D5, which are parasitic diodes of the switching elements Q1, Q3, and Q5 that constitute the upper arm. The diodes D1, D3, and D5 can step down the voltage of the fuel cell stack 22 while charging the power storage device 25.

As shown in FIG. 3, the control device 40 switches the power generation state of the fuel cell stack 22 in stages according to the charging rate of the power storage device 25. The power generation states in this embodiment include a power generation stop state ST1, a low power generation state ST2, a medium power generation state ST3, and a high power generation state ST4. The power generation stop state ST1, the low power generation state ST2, the medium power generation state ST3, and the high power generation state ST4 are each associated with a power generation electric power [kW] of the fuel cell stack 22. The control device 40 controls the power generation electric power of the fuel cell stack 22 by switching the power generation state. The power generation electric power associated with the power generation state is a target value of the power generation electric power. The control device 40 controls the power generation electric power of the fuel cell stack 22 so that it follows the target value.

The power generation stop state ST1 is a state in which no power is generated by the fuel cell stack 22. The generated power in the power generation stop state ST1 is 0 [kW].
The low power generation state ST2 is a state in which the fuel cell stack 22 generates power. The power generated by the fuel cell stack 22 in the low power generation state ST2 is referred to as low generated power. The low generated power is, for example, 3 kW. The low power generation state ST2 is a first power generation state. The low generated power is the first generated power.

The medium power generation state ST3 is a state in which the power generation of the fuel cell stack 22 is greater than in the low power generation state ST2. The power generation of the fuel cell stack 22 in the medium power generation state ST3 is referred to as the medium power generation. The medium power generation is a variable value that changes depending on the usage status of the fuel cell stack 22. The medium power generation state ST3 is the second power generation state. The medium power generation is the second power generation.

The high power generation state ST4 is a state in which the fuel cell stack 22 generates the power required by the load when the fuel cell vehicle 10 is operating at maximum load. The power generated by the fuel cell stack 22 in the high power generation state ST4 is the high power generation. The high power generation is, for example, 12 kW. The high power generation state ST4 is the third power generation state. The high power generation is the third power generation.

When the fuel cell stack 22 is in the power generation stop state ST1, if the charging rate of the power storage device 25 becomes equal to or lower than a power generation start threshold _VD , the control device 40 transitions the fuel cell stack 22 to a low power generation state ST2. The power generation start threshold _VD can be, for example, 50%.

When the fuel cell stack 22 is in the low power generation state ST2, if the charging rate of the power storage device 25 becomes equal to or lower than the medium power generation switching threshold V _M , the control device 40 transitions the fuel cell stack 22 to the medium power generation state ST3. The medium power generation switching threshold V _M can be, for example, 45%.

When the fuel cell stack 22 is in the medium power generation state ST3, if the charging rate of the power storage device 25 becomes equal to or lower than the high power generation switching threshold _VH , the control device 40 transitions the fuel cell stack 22 to the high power generation state ST4. The high power generation switching threshold _VH can be, for example, 30%.

When the fuel cell stack 22 is in the high power generation state ST4, if the charging rate of the power storage device 25 becomes equal to or higher than the medium power generation switch threshold V _M , the control device 40 transitions the fuel cell stack 22 to the medium power generation state ST3.

When the fuel cell stack 22 is in the medium power generation state ST3, if the charging rate of the power storage device 25 becomes equal to or higher than the low power generation switching threshold _VL , the control device 40 transitions the fuel cell stack 22 to the low power generation state ST2. The low power generation switching threshold _VL can be, for example, 60%.

When the fuel cell stack 22 is in the low power generation state ST2, if the charging rate of the power storage device 25 becomes equal to or higher than the power generation stop threshold value V _S , the control device 40 transitions the fuel cell stack 22 to the power generation stop state ST1. The power generation stop threshold value V _S can be, for example, 70%.

The control device 40 performs a medium power generation setting process. The medium power generation setting process is a process for setting a medium power generation. The medium power generation setting process is repeatedly performed at a predetermined control period when the fuel cell vehicle 10 is in an activated state. The activated state is a state in which the fuel cell vehicle 10 can be driven. The activated state is also called a key-on state.

As shown in FIG. 4, in step S1, the control device 40 determines whether the fuel cell stack 22 is generating electricity. Whether the fuel cell stack 22 is generating electricity can be determined from the power generation state of the fuel cell stack 22. If the fuel cell stack 22 is in a power generation stop state ST1, the control device 40 determines that the fuel cell stack 22 is not generating electricity. If the fuel cell stack 22 is in a low power generation state ST2, a medium power generation state ST3, or a high power generation state ST4, the control device 40 determines that the fuel cell stack 22 is generating electricity. If the determination result of step S1 is positive, the control device 40 performs the process of step S2. If the determination result of step S1 is negative, the control device 40 performs the process of step S6.

In step S2, the control device 40 stores the value of the generated power of the fuel cell stack 22 in the memory unit 42. More specifically, the control device 40 calculates the generated power of the fuel cell stack 22 from the detection results of the current sensor 24 and the voltage sensor 23. The control device 40 then stores the value of the generated power in the memory unit 42. The current sensor 24 and the voltage sensor 23 are a generated power detection unit that detects the generated power of the fuel cell stack 22.

Next, in step S3, the control device 40 determines whether the counter has expired. The control device 40 counts the number of times the process of step S2 has been performed. The control device 40 determines that the counter has expired when the number of times the process of step S2 has been performed reaches a preset number of times. In other words, the control device 40 determines that the counter has expired when the number of times the value of the generated power of the fuel cell stack 22 has been stored in the memory unit 42 reaches a preset number of times. If the determination result of step S3 is negative, the control device 40 returns to the process of step S2. If the determination result of step S3 is positive, the control device 40 performs the process of step S4. It can be said that the control device 40 performs the process of step S2 until the counter expires.

Next, in step S4, the control device 40 calculates a power reference value [kW]. The power reference value is a value that indicates the actual power generation of the fuel cell stack 22. In this embodiment, the average value of the power generated by the fuel cell stack 22 is used as the power reference value. The control device 40 calculates the average value of the power generated by the fuel cell stack 22 that is stored in the memory unit 42 by the processing of steps S2 and S3. The control device 40 sets this average value as the power reference value. By performing the processing of step S4, the control device 40 functions as a power reference value calculation unit.

Next, in step S5, the control device 40 updates the medium power generation power. The control device 40 calculates the difference between the power reference value and the initial value, and divides this difference by a predetermined time period [h]. The value thus obtained is added to the initial value to calculate the medium power generation power. That is, the medium power generation power is calculated from the following formula (1).

Medium power generation = initial value + (power reference value - initial value) / predetermined time ... (1)
The initial value is a preset setting value when the process of step S5 is performed for the first time. When the process of step S5 is performed for the first time, it can be said that the medium power generation power has not been updated. The setting value can be set to any value within the range between the low power generation power and the high power generation power. When the process of step S5 is performed for the second or subsequent times, the initial value is the value of the medium power generation power calculated in the previous control cycle. In other words, the initial value is the current value of the medium power generation power.

Any value can be used as the predetermined time. For example, the predetermined time is set to a value that allows calculation of the medium power generation according to the load usage over a one-week period. In this case, assuming that the fuel cell vehicle 10 operates for 8 hours per day for 5 days per week, the predetermined time is 40 hours.

As can be seen from equation (1), the medium power generation power gradually approaches the average value of the power reference value for a given time as the time during which the fuel cell stack 22 is generating power passes. In other words, the medium power generation power can be considered to be the average value of the power generated by the fuel cell stack 22 in the most recent given time. The control device 40 sets the value calculated by equation (1) as the new medium power generation power, and ends the medium power generation power setting process. By performing the process of step S5, the control device 40 functions as an update unit. The medium power generation power is set between the low power generation power and the high power generation power. It can be said that the medium power generation power is greater than the low power generation power and less than the high power generation power.

In step S6, the control device 40 sets the medium generated power as the previous value. That is, the control device 40 maintains the medium generated power calculated in the previous control cycle.
The value of the medium generated power is stored in the non-volatile memory of the storage unit 42 so that it is retained even when the fuel cell vehicle 10 is in the key-off state.

The operation of this embodiment will be described.
The usage status of the fuel cell stack 22 changes depending on the usage status of the fuel cell vehicle 10. The usage status of the fuel cell stack 22 differs for each customer. For example, the usage status of the fuel cell stack 22 differs depending on factors such as differences in the operation method of the fuel cell vehicle 10 by the operator of the fuel cell vehicle 10, the environment in which the fuel cell vehicle 10 is used, whether there is a busy season or the timing of the busy season, etc. In other words, the appropriate medium power generation power differs for each customer. The appropriate medium power generation power is a power that reduces the transition from the medium power generation state ST3 to a power generation state different from the medium power generation state ST3.

In this embodiment, the medium power generation is updated based on a power reference value indicating the actual power generation of the fuel cell stack 22. This sets the medium power generation according to the usage status of the fuel cell stack 22. It is possible to prevent the fuel cell stack 22 from generating insufficient or excessive power. If the medium power generation is a constant value of 5 [kW] and the load requires an average of 4 [kW] of power, 1 [kW] of power is charged to the storage device 25. As the charging rate of the storage device 25 increases, the medium power generation state ST3 transitions to the low power generation state ST2. If the medium power generation is a constant value of 5 [kW] and the load requires an average of 6 [kW] of power, 1 [kW] of power is discharged from the storage device 25. As the charging rate of the storage device 25 decreases, the medium power generation state ST3 transitions to the high power generation state ST4. In contrast, when the medium power generation power is set based on the power reference value, the charging and discharging of the power storage device 25 can be suppressed compared to when the medium power generation power is set to a constant value. Since the power generation state of the fuel cell stack 22 transitions according to the charging rate of the power storage device 25, the number of transitions in the power generation state can be reduced by reducing the fluctuation in the charging rate of the power storage device 25.

Figure 5 shows an example of the relationship between the power generation time during which the fuel cell stack 22 generates power, the number of transitions in the power generation state of the fuel cell stack 22, and the medium power generation power. In the example shown in Figure 5, the time when the initial value of formula (1) is the set value, that is, the time when the actual power generation of the fuel cell stack 22 is not reflected in the medium power generation power, is set to 0. As can be seen from Figure 5, the medium power generation power is updated every time the time during which the fuel cell stack 22 generates power elapses. Every time the time during which the fuel cell stack 22 generates power elapses, the actual power generation of the fuel cell stack 22 is accumulated, and the medium power generation power that reflects the tendency due to the load usage status is set. After a predetermined time has elapsed, the medium power generation power that fully reflects the load usage status is set. As the medium power generation power is updated, the number of transitions in the power generation state of the fuel cell stack 22 also decreases.

Fuel cell stack 22 has a characteristic that the current increases as the generated power increases, and the voltage decreases as the generated power increases. The theoretical voltage of fuel cell stack 22 is 1.23 [V], and the greater the deviation of the voltage of fuel cell stack 22 from the theoretical voltage, the greater the loss of fuel cell stack 22. The theoretical voltage is the voltage when all the chemical energy of hydrogen gas can be converted into electrical energy. When the generated power of fuel cell stack 22 increases and the voltage of fuel cell stack 22 decreases, the difference between the voltage of fuel cell stack 22 and the theoretical voltage increases, and the loss of fuel cell stack 22 increases. In the example shown in FIG. 5, the medium generated power gradually decreases. In this way, by setting the medium generated power based on the actual power generation of fuel cell stack 22, it is possible to prevent the generated power of fuel cell stack 22 from becoming excessively high. This makes it possible to reduce the loss of fuel cell stack 22.

The effects of this embodiment will be described.
(1) The medium power generation power is set based on the power reference value. Since there is little change in the charging rate of the power storage device 25, the fuel cell stack 22 is unlikely to transition from the medium power generation state ST3 to the low power generation state ST2, or from the medium power generation state ST3 to the high power generation state ST4. This makes it possible to suppress fluctuations in the power generation power of the fuel cell stack 22 caused by the transition of the power generation state, and thus makes it possible to suppress deterioration of the fuel cell stack 22.

(2) The control device 40 calculates the difference between the power reference value and the initial value, and divides this difference by a predetermined time. The value thus obtained is added to the initial value to calculate a new medium-level generated power. The medium-level generated power gradually decreases or increases depending on the actual power generation performance of the fuel cell stack 22. Even if the power generation performance of the fuel cell stack 22 temporarily becomes excessively large or small, this effect can be suppressed and the medium-level generated power according to the actual power generation performance can be calculated.

In addition, the amount of data stored in the memory unit 42 is smaller than when the power generated by the fuel cell stack 22 for a specified time is stored in the memory unit 42 and the average power generated for the specified time is set as the medium power generation power. Therefore, the capacity of the memory unit 42 can be prevented from increasing.

(3) The power generation state of the fuel cell stack 22 does not easily transition from the medium power generation state ST3, so the power generation of the fuel cell stack 22 does not easily fluctuate. When fluctuating the power generation of the fuel cell stack 22, it is necessary to control the compressor 13 and the valve 12 to adjust the amount of hydrogen gas supplied and the amount of oxygen supplied. In this case, the driving force of the compressor 13 and the driving cycle and opening time of the valve 12 change, which causes a decrease in the quietness of the fuel cell vehicle 10. By making the power generation of the fuel cell stack 22 less likely to fluctuate, the quietness of the fuel cell vehicle 10 can be improved.

The embodiment can be modified as follows: The embodiment and the following modified examples can be combined with each other to the extent that there is no technical contradiction.
The control device 40 may set the value of the low power generation power to a variable value. In this case, the value of the low power generation power is changed according to the value of the medium power generation power. For example, the control device 40 may set the value of the low power generation power to 1/2 of the value of the medium power generation power.

The control device 40 may also set a lower limit and an upper limit for the value of the low power generation power, and vary the value of the low power generation power within a range between the lower limit and the upper limit. The values of the lower limit and the upper limit are arbitrary. The lower limit may be, for example, the lower limit of the voltage conversion limit value. The upper limit may be, for example, the upper limit of the voltage conversion limit value.

The upper limit of the voltage conversion limit value is the generated power when the voltage of the fuel cell stack 22 becomes the minimum voltage that can be input to the DC/DC converter 30. The DC/DC converter 30 has a set input voltage range. By setting the upper limit of the voltage conversion limit value as described above, it is possible to prevent the voltage input to the DC/DC converter 30 from falling below the lower limit of the input voltage.

The lower limit of the voltage conversion limit value is the voltage at which the voltage of the fuel cell stack 22 matches the voltage of the power storage device 25. When the voltage of the fuel cell stack 22 exceeds the voltage of the power storage device 25, the voltage is stepped down using diodes D1, D3, and D5. When the voltage is stepped down using diodes D1, D3, and D5, losses occur due to this step-down. By setting the lower limit of the voltage conversion limit value as described above, it is possible to prevent the voltage from being stepped down by diodes D1, D3, and D5, and to suppress losses due to step-down.

The control device 40 may set a lower limit and an upper limit for the value of the medium power generation. The lower limit of the medium power generation and the upper limit of the medium power generation may be set arbitrarily. The lower limit of the voltage conversion limit value may be used as the lower limit of the medium power generation, and the upper limit of the voltage conversion limit value may be used as the upper limit of the voltage conversion limit value.

The medium power generation may be calculated by a method other than that of formula (1) as long as it is a value corresponding to the power reference value. For example, the medium power generation may be a moving average of the power generation for a specified time. The control device 40 acquires the power reference value for the specified time at a specified cycle and stores it in the memory unit 42. The control device 40 divides the sum of the power reference values for the specified time by the number of times the power reference value was acquired. The control device 40 may use the value obtained in this way as the medium power generation.

The power reference value may be the median of the power generation of the fuel cell stack 22 stored in the memory unit 42 by the processing of steps S2 and S3. The control device 40 may obtain the power generation of the fuel cell stack 22 only once in one control cycle, and use this power generation as the power reference value. The power reference value may be a moving average of the power generation for a predetermined period of time. In other words, the power reference value may be any value that indicates the actual power generation of the fuel cell stack 22.

The configuration of the DC/DC converter 30 may be changed arbitrarily. The DC/DC converter 30 may be an insulated type or a non-insulated type.
The power generation state may include three states with different power generation power. For example, the low power generation state ST2 of the embodiment may be omitted, and three states, a power generation stop state ST1, a medium power generation state ST3, and a high power generation state ST4, may be transitioned. In this case, the power generation stop state ST1 is the first power generation state, the medium power generation state ST3 is the second power generation state, and the high power generation state ST4 is the third power generation state.

The power generation state may include five or more states with different power generation. In this case, the state corresponding to the average value of the power generation of the fuel cell stack 22 is the second power generation state. The first power generation state is a state in which the power generation is one step lower than the second power generation state. The third power generation state is a state in which the power generation is one step higher than the second power generation state.

The power generated by the fuel cell stack 22 may be calculated by dividing the power supplied to the vehicle load 15 by (1-ratio of auxiliary losses). In this case, the current sensor 24 and the voltage sensor 23 are provided so as to be able to measure the power supplied to the vehicle load 15. The auxiliary losses include losses occurring in the DC/DC converter 30 and power consumed by the auxiliary 14.

The device that controls the power generated by the fuel cell stack 22 and the device that controls the DC/DC converter 30 may be separate devices. In other words, the control device 40 may be a unit composed of multiple devices.

ST2...low power generation state as the first power generation state, ST3...medium power generation state as the second power generation state, ST4...high power generation state as the third power generation state, 14...auxiliary equipment as load, 15...vehicle load as load, 23...voltage sensor as generated power detection unit, 24...current sensor as generated power detection unit, 25...electricity storage device, 26...charge state detection unit, 40...power reference value calculation unit, and control device as update unit.

Claims (2)

a fuel cell stack for supplying power to a load;
A power storage device connected in parallel to the load;
a charge state detection unit that detects a charge state of the power storage device;
a generated power detection unit that detects the generated power of the fuel cell stack;
a control device that controls the generated power of the fuel cell stack so as to generate power according to the state of charge of the power storage device by switching the power generation state of the fuel cell stack based on the state of charge of the power storage device detected by the state of charge detection unit,
the power generation states include a first power generation state in which the fuel cell stack generates a first generated power, a second power generation state in which the fuel cell stack generates a second generated power greater than the first generated power, and a third power generation state in which the fuel cell stack generates a third generated power greater than the second generated power,
The control device includes:
a power reference value calculation unit that calculates a power reference value indicating the actual power generation performance of the fuel cell stack from the generated power detected by the generated power detection unit;
an update unit that updates the second generated power based on the power reference value. The update unit is
Calculating a difference between the reference power value and a current value of the second generated power;
2. The fuel cell system according to claim 1, wherein a value obtained by dividing the difference by a predetermined time and adding the value to a current value of the second generated power is set as a new second generated power.