JP7359605B2 - fuel cell system - Google Patents

Description

The present invention relates to a fuel cell system.

Conventionally, a regenerative braking device for a vehicle as described in Patent Document 1 is known.
The above regenerative braking device for a vehicle is installed in a fuel cell vehicle. The fuel cell vehicle includes a fuel cell stack, a driving motor that generates driving force for driving using the electric power generated by the fuel cell stack, and a high-voltage power storage device that stores electricity to be supplied to the driving motor. A fuel cell system is used that includes a battery and a fuel cell ECU as a control unit that controls the operation of a fuel cell stack.

The above regenerative braking device for a vehicle includes a regenerative brake, the above battery, and a heater. The regenerative brake, battery, and heater are electrically connected. Regenerative braking generates braking force during regenerative braking. Regenerative power generated by regenerative braking during regenerative braking is stored in a battery. When regenerative electric power is generated by regenerative braking, surplus electric power exceeding the amount of electricity stored in the battery is supplied to the heater. Therefore, the heater generates heat by converting electrical energy into thermal energy.

Further, the vehicle regenerative braking device includes a vehicle hot water circuit. Water is flowing through the vehicle hot water circuit, and the heat generated by the heater is stored in the vehicle hot water circuit. Further, the regenerative braking device for a vehicle includes a cooling circuit through which cooling water flows to cool the fuel cell stack. The cooling circuit is provided with a radiator for dissipating heat contained in the cooling water, a rotary valve as an auxiliary device, and a fuel cell pump as an auxiliary device. A fuel cell pump is a circulation pump for circulating cooling water through a cooling circuit. The rotary valve adjusts the flow rate of cooling water flowing into the radiator. Note that the auxiliary equipment generally includes an electric compressor and the like for supplying oxygen to the fuel cell stack.

JP2017-93154A

Incidentally, surplus power exceeding the amount stored in the battery is converted from electrical energy to thermal energy by a heater, but there is a risk that energy loss may occur when changing from electrical energy to thermal energy. Note that this problem does not only occur in a fuel cell vehicle as a vehicle, but can also occur in a unit that is equipped with a fuel cell system and stores regenerated power in a battery.

The present invention has been made in view of the problems that exist in the conventional technology, and its purpose is to provide a fuel cell system that can efficiently store regenerated power.

A fuel cell system that solves the above problems is a load that includes a fuel cell stack and a motor that functions as an electric motor that generates driving force using the electric power generated by the fuel cell stack and also functions as a generator that generates regenerated electric power. a high-voltage power storage device that stores power for the motor to generate driving force and regenerated power generated by the motor; a control unit that controls the operation of the fuel cell stack; and an auxiliary device. a low-voltage power storage device that is charged with power for operation and is set to have a lower voltage when storing power than the high-voltage power storage device;
a step-down converter that is electrically connected to the low-voltage power storage device and steps down the voltage of power when stored in the high-voltage power storage device, and the control unit controls the motor to generate regenerative power. In this case, when the high-voltage power storage device reaches a specified voltage value, the regenerative power is stored in the low-voltage power storage device via the step-down converter.

According to this, regenerative power generated by a motor is stored in a high-voltage power storage device, and when the high-voltage power storage device reaches a specified voltage value, the voltage of the regenerated power is stepped down by a step-down converter and the power is stored in a low-voltage power storage device. . Therefore, for example, if the specified voltage value is the voltage value when the high-voltage power storage device is fully charged, surplus power exceeding the amount of power stored in the high-voltage power storage device is stored in the low-voltage power storage device. Therefore, surplus power when the high-voltage power storage device reaches a specified voltage value is stored in the low-voltage power storage device without being converted into energy. Therefore, in the above fuel cell system, regenerated power can be efficiently stored without causing energy loss due to energy conversion.

In the above fuel cell system, the step-down converter includes an inverter circuit having a three-phase switching element, and is electrically connected to the inverter circuit and the low-voltage power storage device, and the voltage of the power supplied to the low-voltage power storage device. a smoothing circuit that stabilizes the inverter circuit, the inverter circuit includes a positive electrode bus, a negative electrode bus that is electrically connected to the low voltage power storage device, and a first smoothing circuit that electrically connects the positive electrode bus and the negative electrode bus. a relay wiring consisting of a wiring, a second wiring, and a third wiring, and an upper arm switching element as the switching element and a lower arm switching element as the switching element are connected in series to each of the relay wiring. , and a diode for preventing reverse flow of current from the positive busbar side toward the negative busbar side is connected in antiparallel to the upper arm switching element and the lower arm switching element on the relay wiring. The smoothing circuit includes a first smoothing wiring electrically connected between the negative electrode bus bar, the upper arm switching element and the lower arm switching element in the second wiring, and the third wiring. A second smooth wiring electrically connected between the upper arm switching element and the lower arm switching element, and the first smooth wiring and the second smooth wiring are formed in the low voltage storage battery. an integrated smooth wiring that is electrically connected to the device, a smooth relay wiring that electrically connects the negative electrode bus and the integrated smooth wiring, a capacitor provided in the smooth relay wiring, the first smooth wiring and the a reactor provided in each of the second smooth wirings, and regenerative power generated by the motor is input between the upper arm switching element and the lower arm switching element in the first wiring. A regeneration wiring is electrically connected to the first wiring, and the control unit is configured to be connected to the first wiring when the high voltage power storage device reaches a predetermined voltage value when the motor is generating regenerative power. In a state where the switching element provided in the second wiring and the lower arm switching element provided in the third wiring are maintained in an open state, the switching element provided in the second wiring and the third wiring It is preferable to open and close the upper arm switching element.

The load typically includes an inverter that drives a motor. Therefore, the fuel cell system must use a step-down converter and an inverter.
In this respect, according to this, the step-down converter includes an inverter circuit. That is, the step-down converter has the same configuration as the inverter included in the load, but with a smoothing circuit added. Therefore, since there is no need to newly use a step-down converter, the cost of the fuel cell system can be reduced.

In the above fuel cell system, when the motor is generating regenerative power, when the high-voltage power storage device reaches a specified voltage value, the control unit controls the switching element provided in the first wiring of the inverter circuit. and the lower arm switching elements provided in the second wiring and the third wiring are maintained in an open state, and the upper arm switching elements provided in the second wiring and the third wiring are opened and closed. For example, consider a case where the upper arm switching element provided in the third wiring is placed in the closed state.

The regenerative power generated by the motor is transmitted to the first wiring through the regeneration wiring, and is transmitted to the second wiring via a diode connected in antiparallel to the upper arm switching element provided in the first wiring. It is supplied to the third wiring. The regenerated power supplied to the third wiring is supplied to the integrated smooth wiring via the reactor of the second smooth wiring, and is then supplied to the low voltage power storage device. When the upper arm switching element provided in the third wiring is in a closed state, the reactor provided in the second smooth wiring is magnetized. As a result, a back electromotive force is generated in the reactor provided in the second smoothing wiring in a direction that prevents a current from flowing from the third wiring through the second smoothing circuit. Therefore, when the upper arm switching element provided in the third wiring is in a closed state, the voltage of the regenerated power is stepped down by the reactor provided in the second smooth wiring. The same applies when the upper arm switching element provided in the second wiring is in the closed state, and the reactor provided in the first smooth wiring is magnetized, so that the upper arm switching element provided in the first smooth wiring is magnetized. A back electromotive force is generated in the reactor in a direction that obstructs the current flowing from the second wiring through the first smooth wiring. Therefore, when the upper arm switching element provided in the second wiring is in a closed state, the voltage of the regenerated power is stepped down by the reactor provided in the first smooth wiring. Here, when the upper arm switching elements provided in the second wiring and the third wiring are opened and closed, the capacitor provided in the smooth relay wiring is charged. The capacitor is charged with regenerated power that has been stepped down by each reactor. Even if the upper arm switching element provided in the second wiring and the third wiring is in an open state, the capacitor is connected in antiparallel to the lower arm switching element provided in the second wiring and third wiring. A freewheeling current is generated that flows toward each reactor through the diodes in the reactor. Therefore, even if the upper arm switching elements provided in the second wiring and the third wiring are in an open state and regenerative power does not flow to the low-voltage power storage device, the time of the voltage of the power stored in the low-voltage power storage device due to the return current from the capacitor. physical changes are reduced. Therefore, it is possible to stabilize the voltage of the power stored in the low-voltage power storage device while lowering the voltage of the regenerated power by the smoothing circuit of the step-down converter.

In the above fuel cell system, when the motor is generating regenerative power, when the high-voltage power storage device reaches a prescribed voltage value, the control unit controls the upper arm provided in the second wiring. It is preferable that the switching element and the upper arm switching element provided on the third wiring are alternately opened and closed.

For example, consider a case where the upper arm switching elements provided in the second wiring and the third wiring are simultaneously opened and closed. When regenerative power is supplied from the regeneration wiring to the second wiring and the third wiring via the diode connected in antiparallel to the upper arm switching element provided in the first wiring, the regenerative power is regenerated toward the capacitor. There are periods when there is no power. Depending on the timing of opening and closing the upper arm switching elements provided in the second wiring and the third wiring, there is a risk that the voltage of the power stored in the low-voltage power storage device may increase over time due to the return current caused by the capacitor.

In this respect, according to this, the upper arm switching elements provided in the second wiring and the third wiring are alternately opened and closed. Therefore, the period during which regenerative power does not flow toward the capacitor can be shortened. Therefore, the voltage stored in the low-voltage power storage device can be made more stable.

In the above fuel cell system, the positive electrode of the fuel cell stack is electrically connected to the positive electrode bus of the inverter circuit, and the negative electrode of the fuel cell stack is electrically connected to the negative electrode bus of the inverter circuit. , a high-voltage converter that steps down the power generated by the fuel cell stack to a voltage that can be stored in the high-voltage power storage device, and the high-voltage converter and the motor send the power stepped down by the high-voltage converter to the load. The regeneration wiring is electrically connected to the positive electrode side of the high voltage side conversion wiring, and the control unit controls the motor when the motor is not generating regenerative power. , in a state where the switching element provided in the first wiring and the lower arm switching element provided in the second wiring and the third wiring are maintained in an open state, the second wiring and the When step-down control is performed to step down the voltage of the power generated by the fuel cell stack by opening and closing the upper arm switching element provided in the third wiring, and the motor is generating regenerative power; When the high-voltage power storage device reaches a specified voltage value, the operation of the fuel cell stack is stopped, and the timing for opening and closing the upper arm switching element provided in the second wiring and the third wiring is determined by the step-down step. It is preferable to implement regenerative pressure reduction control that is faster than control.

According to this, when the motor is not generating regenerated power, the step-down converter can perform the function of stepping down the electric power generated by the fuel cell stack by the step-down control of the control section. When the motor is generating regenerative power, the step-down converter can perform a function of stepping down the regenerative power by the regenerative step-down control of the control unit when the high-voltage power storage device reaches a specified voltage value. That is, there is no need to separately prepare a converter that steps down the power generated by the fuel cell stack and a converter that steps down the regenerated power. Therefore, the cost of the fuel cell system can be reduced.

Furthermore, in the above fuel cell system, when the motor is generating regenerative power, the control unit stops the operation of the fuel cell stack when the high voltage power storage device reaches a specified voltage value. This makes it possible to distinguish between a function when the buck converter performs voltage step-down control and a function when it performs regenerative voltage step-down control.

Further, the voltage step-down width is different depending on whether the power generated by the fuel cell stack is stepped down or the regenerated power is stepped down. The reason why the regenerated power can be stepped down is the back electromotive force generated by the magnetization of the reactor. Therefore, in order to change the step-down width, it is necessary to change the magnitude of the back electromotive force generated in the reactor.

In this regard, according to this, the control unit opens and closes the upper arm switching elements provided in the second wiring and the third wiring earlier when performing the regenerative voltage step-down control compared to the voltage step-down control. There is. When the upper arm switching elements provided in the second wiring and the third wiring are in an open state for a long period of time, the reactor stores a large amount of magnetic energy due to the return current generated by the capacitor. Therefore, when the upper arm switching element provided in the second wiring and the third wiring is closed and the reactor is magnetized, the back electromotive force generated in the reactor increases. That is, when performing regenerative voltage step-down control, the timing for opening and closing the upper arm switching elements provided in the second wiring and third wiring is made earlier than that in voltage step-down control, thereby reducing the magnetic energy stored in the reactor. This makes it possible to reduce the back electromotive force generated in the reactor. Therefore, the step-down width is appropriately changed by step-down control that steps down the power generated by the fuel cell stack to a voltage that can be stored in the low-voltage power storage device, and regenerative step-down control that steps down the regenerated power to a voltage that can be stored by the low-voltage power storage device. be able to.

According to this invention, regenerated power can be efficiently stored.

FIG. 1 is a block diagram showing the configuration of a fuel cell system. FIG. 2 is a schematic diagram showing the configuration of a first low voltage converter. The schematic diagram which shows the structure of the 1st low voltage converter in the example of a change. The schematic diagram which shows the structure of the 1st low voltage converter in the example of a change.

An embodiment of a fuel cell system will be described below with reference to FIGS. 1 and 2.
As shown in FIG. 1, a fuel cell system 1 of this embodiment is applied to a towing tractor. The fuel cell system 1 is a system that generates electric power to be supplied to a load mounted on a vehicle. The fuel cell system 1 includes a fuel cell stack 10. The fuel cell stack 10 is a stack of a plurality of fuel cells. The fuel cell is, for example, a fixed molecule fuel cell. The fuel cell stack 10 generates electricity through a chemical reaction between fuel gas and oxidant gas. In this embodiment, power generation is performed using hydrogen gas as a fuel gas and oxygen in the air as an oxidant gas. That is, the fuel cell system 1 is a system that drives a load using electric power generated by the fuel cell stack 10. Note that the voltage value of the electric power generated by the fuel cell stack 10 is, for example, 140V.

The load in this embodiment includes a running motor 70 as a motor that generates a driving force for driving the vehicle. Although not shown, the load includes an inverter for driving the travel motor 70. The traveling motor 70 is also used as a regenerative brake that generates braking force when the towing tractor stops. Therefore, the driving motor 70 functions as an electric motor that generates driving force using the electric power generated by the fuel cell stack 10, and also functions as a generator that generates braking force and regenerated power during regenerative braking. Note that the traveling motor 70 is a three-phase AC rotating electrical machine.

The fuel cell system 1 includes a high voltage power storage device 20, a high voltage converter 30, a first low voltage power storage device 40 as a low voltage power storage device, and a first low voltage converter 50 as a step down converter.

A lithium ion capacitor is employed in the high voltage power storage device 20. The high-voltage power storage device 20 has a function of storing electric power for the driving motor 70 to generate driving force, and also storing regenerated electric power generated by the driving motor 70. The high voltage power storage device 20 can store power with a voltage value of 80V, for example.

For example, a DC/DC converter is employed as the high voltage converter 30. The high voltage converter 30 has a function of reducing the voltage of the electric power generated by the fuel cell stack 10. The high voltage converter 30 has a function of reducing the voltage of the electric power generated by the fuel cell stack 10 to, for example, 80V. The positive electrode of the fuel cell stack 10 and the positive electrode on the input side of the high voltage converter 30 are electrically connected by a high voltage side supply positive electrode wiring L1. The negative electrode of the fuel cell stack 10 and the input side negative electrode of the high voltage converter 30 are electrically connected by a high voltage side supply negative electrode wiring L2. The high-voltage side supply positive electrode wiring L1 and the high-voltage side supply negative electrode wiring L2 are provided to send the electric power generated by the fuel cell stack 10 to the high-voltage converter 30. The high voltage side supply negative electrode wiring L2 is a ground wiring. Note that the high-voltage side supply positive electrode wiring L1 is provided with a diode 105 that prevents backflow of power toward the fuel cell stack 10.

The output-side positive electrode of high-voltage converter 30 and the positive electrode of high-voltage power storage device 20 are electrically connected by high-voltage side conversion positive electrode wiring L3. The output-side negative electrode of high-voltage converter 30 and the negative electrode of high-voltage power storage device 20 are electrically connected by high-voltage side conversion negative electrode wiring L4. The high voltage side conversion negative electrode wiring L4 is a ground wiring. Further, the positive and negative electrodes on the output side of the high voltage converter 30 and the driving motor 70 are electrically connected by a high voltage side conversion positive electrode wiring L3 and a high voltage side conversion negative electrode wiring L4. The high-voltage side conversion positive electrode wiring L3 and the high-voltage side conversion negative electrode wiring L4 are provided in order to send the power stepped down by the high-voltage converter 30 to the load and the high-voltage power storage device 20. Therefore, the electric power generated by the fuel cell stack 10 is stored in the high voltage power storage device 20 while being supplied from the high voltage converter 30 to the driving motor 70 via the high voltage side conversion positive electrode wiring L3 and the high voltage side conversion negative electrode wiring L4. . That is, the high-voltage power storage device 20 stores surplus power generated by supplying the power generated by the fuel cell stack 10 to the driving motor 70. The electric power stored in the high-voltage power storage device 20 is also used, for example, as electric power for driving the travel motor 70 when the amount of power generation is insufficient in the initial stage of power generation by the fuel cell stack 10. Note that the high voltage side conversion positive electrode wiring L3 and the high voltage side conversion negative electrode wiring L4 are examples of high voltage side conversion wiring, and the high voltage side conversion positive electrode wiring L3 is an example of the positive electrode side of the high voltage side conversion wiring.

The first low-voltage power storage device 40 employs a lithium ion capacitor. The first low-voltage power storage device 40 is charged with power for operating the first auxiliary device 60 as an auxiliary device, and is set to have a lower voltage than the high-voltage power storage device 20 when storing power. The first low-voltage power storage device 40 can store power with a voltage value of 48V, for example. Here, the first auxiliary machine 60 indicates, for example, a solenoid valve and an electric compressor that assist the operation of the fuel cell stack 10. The solenoid valve is provided in a hydrogen supply pipe that connects a hydrogen tank (not shown) and the fuel cell stack 10, and has a function of opening and closing the hydrogen supply pipe. The electric compressor has a function of supplying air containing oxygen to the fuel cell stack 10 in a compressed state.

Here, the fuel cell system 1 includes an FCECU 65 as a control section. The FCECU 65 controls the operation of the fuel cell stack 10. The FCECU 65 controls the operation of the fuel cell stack 10 by controlling the operations of the electromagnetic valve and electric compressor described above. Specifically, the FCECU 65 adjusts the opening degree of the hydrogen supply pipe by operating a solenoid valve according to a preset drive cycle and valve opening time. That is, the FCECU 65 controls the operation of the electromagnetic valve and adjusts the opening degree of the hydrogen supply pipe, thereby adjusting the amount of hydrogen supplied from the hydrogen tank to the fuel cell stack 10. Furthermore, the amount of air supplied to the fuel cell stack 10 is controlled by controlling the torque of an electric motor provided in the electric compressor. Therefore, the FCECU 65 controls the amount of power generated by the fuel cell stack 10 by controlling the operations of the electromagnetic valve and the electric compressor, and controlling the amount of hydrogen and air supplied.

The first low voltage converter 50 is, for example, a DC/DC converter. The first low voltage converter 50 has a function of reducing the voltage of the electric power generated by the fuel cell stack 10. The first low voltage converter 50 has a function of reducing the voltage of the electric power generated by the fuel cell stack 10 to, for example, 48V. The positive electrode of the fuel cell stack 10 and the positive electrode on the input side of the first low voltage converter 50 are electrically connected by a high voltage side supply positive electrode wiring L1. The negative electrode of the fuel cell stack 10 and the input side negative electrode of the first low voltage converter 50 are electrically connected by a high voltage side supply negative electrode wiring L2. The high voltage side supply positive electrode wiring L1 and the high voltage side supply negative electrode wiring L2 are provided not only to the above-described high voltage converter 30 but also to send the electric power generated in the fuel cell stack 10 to the first low voltage converter 50.

The output side positive electrode of the first low voltage converter 50 and the positive electrode of the first low voltage power storage device 40 are electrically connected by the first low voltage side conversion positive electrode wiring L5. The negative electrode of the output side of the first low voltage converter 50 and the negative electrode of the first low voltage power storage device 40 are electrically connected by the first low voltage side conversion negative electrode wiring L6. Moreover, the positive and negative electrodes on the output side of the first low voltage converter 50 and the first auxiliary machine 60 are electrically connected by the first low voltage side conversion positive electrode wiring L5 and the first low voltage side conversion negative electrode wiring L6. The first low-voltage side conversion positive electrode wiring L5 and the first low-voltage side conversion negative electrode wiring L6 are provided to send the power stepped down by the first low-voltage converter 50 to the first auxiliary device 60 and the first low-voltage power storage device 40. There is. Therefore, the electric power generated in the fuel cell stack 10 is supplied from the first low voltage converter 50 to the first auxiliary equipment 60 via the first low voltage side conversion positive electrode wiring L5 and the first low voltage side conversion negative electrode wiring L6. 1. Electricity is stored in the low-voltage electricity storage device 40. That is, surplus power generated by supplying the power generated by the fuel cell stack 10 to the first auxiliary machine 60 is stored in the first low-voltage power storage device 40 . The electric power stored in the first low-voltage power storage device 40 is also used as electric power for driving the first auxiliary device 60, for example, when the amount of power generation is insufficient in the initial stage of power generation by the fuel cell stack 10.

Fuel cell system 1 includes a second low voltage power storage device 80 and a second low voltage converter 90. The second low voltage power storage device 80 employs a 12V battery. The second low-voltage power storage device 80 is charged with power for operating the second auxiliary device 95 and is set to have a lower voltage than the first low-voltage power storage device 40 when storing power. As described above, the second low-voltage power storage device 80 can store power with a voltage value of 12V. Here, the second auxiliary equipment 95 indicates, for example, an air conditioner, a navigation system, a light, or the like. Note that the FCECU 65 in this embodiment is a part of the second auxiliary machine 95.

The second low voltage converter 90 is, for example, a DC/DC converter. The second low-voltage converter 90 has a function of further reducing the voltage of the electric power reduced by the first low-voltage converter 50. The second low voltage converter 90 has a function of reducing the voltage of the power reduced by the first low voltage converter 50 to, for example, 12V. A first low voltage side conversion positive electrode wiring L5 and a first low voltage side conversion negative electrode wiring L6 are electrically connected to the second low voltage converter 90. The first low-voltage side conversion positive electrode wiring L5 and the first low-voltage side conversion negative electrode wiring L6 are not limited to the first auxiliary equipment 60 and the first low-voltage power storage device 40 described above. It is provided for sending to the low voltage converter 90. Therefore, the power stepped down by the first low voltage converter 50 is supplied to the first auxiliary machine 60 and also to the second low voltage converter 90. The output-side positive electrode of the second low-voltage converter 90 and the positive electrode of the second low-voltage power storage device 80 are electrically connected by a second low-voltage side conversion positive electrode wiring L7. The output side negative electrode of the second low voltage converter 90 and the negative electrode of the second low voltage power storage device 80 are electrically connected by a second low voltage side conversion negative electrode wiring L8. Further, the positive and negative electrodes on the output side of the second low voltage converter 90 and the second auxiliary machine 95 are electrically connected by a second low voltage side conversion positive electrode wiring L7 and a second low voltage side conversion negative electrode wiring L8. The second low-voltage side conversion positive electrode wiring L7 and the second low-voltage side conversion negative electrode wiring L8 are provided to send the power stepped down by the second low-voltage converter 90 to the second auxiliary device 95 and the second low-voltage power storage device 80. There is. Therefore, the electric power stepped down by the first low voltage converter 50 is supplied from the second low voltage converter 90 to the second auxiliary machine 95 via the second low voltage side conversion positive wiring L7 and the second low voltage side conversion negative wiring L8. Power is stored in the second low voltage power storage device 80. That is, the second low-voltage power storage device 80 stores surplus power obtained by supplying the second auxiliary device 95 with the power stepped down by the second low-voltage converter 90 . The electric power stored in the second low-voltage power storage device 80 is also used as electric power for driving the second auxiliary machine 95, for example, when the amount of power generation is insufficient at the beginning of power generation by the fuel cell stack 10.

In the fuel cell system 1 configured as described above, when the fuel cell system 1 is started, the FCECU 65 operates the electromagnetic valve and the electric compressor, so that the fuel cell stack 10 starts generating electricity. The electric power generated by the fuel cell stack 10 is supplied to the load (the inverter and the driving motor 70) via the high voltage converter 30, while the surplus electric power not used to drive the load is transferred to the high voltage side conversion positive wiring L3. The high voltage power storage device 20 is charged via the high voltage side conversion negative electrode wiring L4. Similarly, the electric power generated by the fuel cell stack 10 is supplied to the first auxiliary machine 60 via the first low voltage converter 50, while the surplus electric power not used to drive the first auxiliary machine 60 is supplied to the first auxiliary machine 60. The first low voltage power storage device 40 is charged via the first low voltage side conversion positive electrode wiring L5 and the first low voltage side conversion negative electrode wiring L6. Further, the power stepped down by the first low voltage converter 50 is supplied to the second auxiliary machine 95 via the second low voltage converter 90, while the surplus power that is not used to drive the second auxiliary machine 95 is supplied to the second auxiliary machine 95. The second low voltage power storage device 80 is charged via the second low voltage side conversion positive electrode wiring L7 and the second low voltage side conversion negative electrode wiring L8.

The FCECU 65 controls the operation of the fuel cell stack 10 while checking the charging capacity of the high voltage power storage device 20, the charging capacity of the first low voltage power storage device 40, and the charging capacity of the second low voltage power storage device 80. Specifically, the FCECU 65 determines whether the voltage value detected by the voltage sensor 101 provided near the high voltage power storage device 20 in the high voltage side conversion positive electrode wiring L3 and the high voltage side conversion negative electrode wiring L4 is the first specified value. I'm checking to see if it's true. Further, the FCECU 65 determines that the voltage value detected by the voltage sensor 102 provided near the first low voltage power storage device 40 in the first low voltage side conversion positive electrode wiring L5 and the first low voltage side conversion negative electrode wiring L6 is a second specified value. I'm checking to see if it is. Furthermore, the FCECU 65 determines that the voltage value detected by the voltage sensor 103 provided near the second low voltage power storage device 80 in the second low voltage side conversion positive electrode wiring L7 and the second low voltage side conversion negative electrode wiring L8 is a third specified value. I'm checking to see if it is. The FCECU 65 operates until the voltage value of the high voltage power storage device 20 satisfies the first specified value, the voltage value of the first low voltage power storage device 40 satisfies the second specified value, and the voltage value of the second low voltage power storage device 80 satisfies the third specified value. By continuing the operation of the fuel cell stack 10, charging of the high voltage power storage device 20, the first low voltage power storage device 40, and the second low voltage power storage device 80 is continued.

Here, the first specified value is set so that the electric power stored in the high-voltage power storage device 20 can maintain the followability of the operation of the travel motor 70 when the output state of the fuel cell stack 10 suddenly changes. ing. A sudden change in the output of the fuel cell stack 10 indicates that, for example, the towing tractor and the fuel cell system 1 are activated and the operation of the travel motor 70 is suddenly changed. In order to suddenly change the operation of the traveling motor 70, it is necessary to suddenly change the output state from a low output state to a high output state so as to increase the amount of power generated by the fuel cell stack 10. However, depending on the amount of power generated by the fuel cell stack 10, there may be a shortage of electric power to suddenly change the operation of the travel motor 70. In this case, the power stored in the high-voltage power storage device 20 is discharged toward the load to compensate for the lack of power generation. Therefore, the first specified value is set to such an extent that the followability of the operation of the traveling motor 70 can be maintained even when the output state of the fuel cell stack 10 suddenly changes. The second specified value is set so that the first auxiliary machine 60 (electromagnetic valve, electric compressor, and FCECU 65) can be driven stably. That is, the second specified value is set so that the first auxiliary machine 60 can be stably driven when the amount of power generation is insufficient in the initial stage of power generation by the fuel cell stack 10. Similar to the second specified value, the third specified value is set so that the second auxiliary machine 95 can be stably driven when the amount of power generation is insufficient in the initial stage of power generation by the fuel cell stack 10.

Furthermore, the fuel cell system 1 has a function of storing regenerated power in the high-voltage power storage device 20 when the driving motor 70 is generating the regenerated power. When the traveling motor 70 is generating regenerative power, the fuel cell system 1 operates the first low voltage converter 50 when the voltage value of the power stored in the high voltage power storage device 20 reaches a specified voltage value. It has a function of storing surplus power exceeding a prescribed voltage value of the high voltage power storage device 20 in the first low voltage power storage device 40 via the first low voltage power storage device 40 . Note that the prescribed voltage value of the high voltage power storage device 20 is preferably set in consideration of the amount of charge required of the high voltage power storage device 20 according to the specifications of the fuel cell system 1. For example, when a large amount of electric power is used for the driving motor 70 in the fuel cell system 1, it is considered preferable to charge the high voltage power storage device 20 with as much regenerated electric power as possible. In that case, it is preferable that the prescribed voltage value of the high voltage power storage device 20 is, for example, the voltage value when the high voltage power storage device 20 is fully charged. Further, when more power is used for the first auxiliary machine 60 than for the driving motor 70, it is considered preferable to charge the first low-voltage power storage device 40 with as much regenerative power as possible. In this case, it is preferable that the specified voltage value of the high voltage power storage device 20 be the first specified value of the high voltage power storage device 20, for example. Further, the specified voltage value of the high voltage power storage device 20 may be set between the first specified value and the voltage value at full charge.

In the fuel cell system 1, the FCECU 65 receives a current detected by the current sensor 104 connected in series to the high voltage side conversion positive wiring L3 connecting the high voltage converter 30 and the driving motor 70. The FCECU 65 determines the direction of the current flowing through the high-voltage side conversion positive wiring L3 based on the current input from the current sensor 104, and confirms whether or not the travel motor 70 is generating regenerative power. The FCECU 65 stops the operation of the fuel cell stack 10 when the travel motor 70 is generating regenerative power. Specifically, when the driving motor 70 is generating regenerative power, the FCECU 65 stops energizing the solenoid valve and closes the hydrogen supply pipe to supply hydrogen from the hydrogen tank to the fuel cell stack 10. supply will be stopped. Furthermore, the FCECU 65 stops the supply of air containing oxygen to the fuel cell stack 10 by stopping the operation of the electric compressor. Thereby, the FCECU 65 stops the operation of the fuel cell stack 10.

In the fuel cell system 1, a regeneration wiring Lr is electrically connected to the first low voltage converter 50. The regeneration wiring Lr is electrically connected to the high voltage side conversion positive electrode wiring L3. Regenerative power generated by the travel motor 70 is input to the regeneration wiring Lr via the high voltage side conversion positive electrode wiring L3, and is input to the first low voltage converter 50. The first low voltage converter 50 has a function of stepping down the regenerative power generated by the driving motor 70 when the high voltage power storage device 20 reaches a specified voltage value when the driving motor 70 is generating regenerative power. are doing. Although not shown, the regeneration wiring Lr is provided with, for example, a relay. When the driving motor 70 is not generating regenerated power, the FCECU 65 opens the relay to prevent the power reduced by the high voltage converter 30 from being input to the first low voltage converter 50. When the driving motor 70 is generating regenerative power, the FCECU 65 closes the relay when the high voltage power storage device 20 reaches a specified voltage value, and connects the high voltage side conversion positive wiring L3 and the regenerative wiring Lr. to input regenerated power to the first low voltage converter 50. That is, when the driving motor 70 is generating regenerated power, the FCECU 65 transfers the regenerated power to the first low voltage power storage device 40 via the first low voltage converter 50 when the high voltage power storage device 20 reaches a specified voltage value. is used to store electricity. Furthermore, when the traveling motor 70 is generating regenerative power, the FCECU 65 stops the operation of the fuel cell stack 10, but the high voltage state of the fuel cell stack 10 continues for a short period of time. That is, there is a period in which the electric power (140 V) generated by the fuel cell stack 10 and the regenerated electric power (80 V) act on the first low-voltage converter 50 at the same time. However, since air containing oxygen is not supplied to the fuel cell stack 10, the high voltage state of the fuel cell stack 10 is quickly resolved when regenerated power is input to the first low voltage converter 50, and the high voltage state of the fuel cell stack 10 is quickly resolved. Regenerative power is superior to electric power. Therefore, even if the high voltage state of the fuel cell stack 10 continues for a short period of time, the function of the first low voltage converter 50 to step down the regenerated power will not be hindered.

Next, the configuration of the first low voltage converter 50 will be explained in detail.
As shown in FIG. 2, the first low voltage converter 50 includes an inverter circuit 51 and a smoothing circuit 52. The inverter circuit 51 is the same as the inverter circuit included in the load inverter. The inverter circuit 51 has six switching elements Q1 to Q6 as three-phase switching elements. For example, insulated gate bipolar transistors (IGBT) and MOSFETs are used as the switching elements Q1 to Q6. The inverter circuit 51 includes a positive bus Lp, a negative bus Ln, and a relay line Lm. The positive electrode bus line Lp is electrically connected to the high voltage side supply positive electrode wiring L1. Therefore, the positive electrode bus line Lp is electrically connected to the positive electrode of the fuel cell stack 10. The negative electrode bus line Ln is electrically connected to the high voltage side supply negative electrode wiring L2. Therefore, the negative electrode bus line Ln is electrically connected to the negative electrode of the fuel cell stack 10. The negative electrode bus line Ln is electrically connected to the first low voltage side conversion negative electrode wiring L6. Therefore, the negative electrode bus Ln is electrically connected to the first low voltage power storage device 40. The relay wiring Lm includes a first wiring Lm1, a second wiring Lm2, and a third wiring Lm3 that electrically connect the positive electrode bus Lp and the negative electrode bus Ln.

In the first wiring Lm1, a switching element Q1 as an upper arm switching element constituting the u-phase upper arm and a switching element Q2 as a lower arm switching element constituting the u-phase lower arm are connected in series. In the second wiring Lm2, a switching element Q3 as an upper arm switching element constituting the v-phase upper arm and a switching element Q4 as a lower arm switching element constituting the v-phase lower arm are connected in series. In the third wiring Lm3, a switching element Q5 as an upper arm switching element constituting the w-phase upper arm and a switching element Q6 as a lower arm switching element constituting the w-phase upper arm are connected in series. Additionally, six diodes D1 to D6 for preventing reverse flow of current from the positive bus Lp side toward the negative bus Ln on the relay wiring Lm constitute a switching element Q1 that constitutes an upper arm switching element and a lower arm switching element, respectively. - Q6 are connected in antiparallel to each other.

The smoothing circuit 52 is electrically connected to the inverter circuit 51 and the first low-voltage power storage device 40, and has a function of stabilizing the voltage of the power supplied to the first low-voltage power storage device 40. Like the inverter circuit 51, the smoothing circuit 52 has a negative bus Ln. The smoothing circuit 52 shares the negative bus Ln with the inverter circuit 51. The smoothing circuit 52 includes a first smoothing wiring Ls1, a second smoothing wiring Ls2, an integrated smoothing wiring Lst, a smoothing relay wiring Lsm, a capacitor 53, and reactors 54 and 55. The first smooth wiring Ls1 is electrically connected between the switching element Q3 and the switching element Q4 in the second wiring Lm2. The second smooth wiring Ls2 is electrically connected between the switching element Q5 and the switching element Q6 in the third wiring Lm3. The integrated smooth wiring Lst is formed by combining the first smooth wiring Ls1 and the second smooth wiring Ls2. The integrated smooth wiring Lst is electrically connected to the first low voltage side conversion positive electrode wiring L5. Therefore, the integrated smooth wiring Lst is electrically connected to the first low voltage power storage device 40. The smooth relay wiring Lsm electrically connects the negative electrode bus Ln and the integrated smooth wiring Lst. The capacitor 53 is provided in the smooth relay wiring Lsm. The reactor 54 is provided in the first smooth wiring Ls1. The reactor 55 is provided in the second smooth wiring Ls2. Here, a regeneration wiring Lr is electrically connected between the switching element Q1 and the switching element Q2 in the first wiring Lm1. Note that the reactors 54 and 55 are passive elements such as inductors, and in this embodiment, are composed of coils. Note that the first low-voltage converter 50 of the present embodiment is a non-insulated converter that is electrically connected to the input side (fuel cell stack 10 side) and the output side (first low-voltage power storage device 40 side).

Here, the control of the first low voltage converter 50 by the FCECU 65 will be described, and the operation of the first low voltage converter 50 will also be described.
As shown in FIGS. 1 and 2, when the driving motor 70 is not generating regenerative power, the FCECU 65 performs voltage step-down control to step down the power generated by the fuel cell stack 10. In step-down control, the FCECU 65 controls switching elements Q1 and Q2 provided on the first wiring Lm1 in the inverter circuit 51 of the first low voltage converter 50, and switching elements provided on the second wiring Lm2 and third wiring Lm3. Elements Q4 and Q6 are always kept open. Then, the FCECU 65 performs voltage step-down control by opening and closing switching elements Q3 and Q5 while switching elements Q1, Q2, Q4, and Q6 are maintained in an open state. More specifically, during voltage step-down control, the FCECU 65 alternately opens and closes the switching elements Q3 and Q5.

For example, consider a case where the switching element Q5 provided in the third wiring Lm3 is brought into a closed state. Electric power generated by the fuel cell stack 10 is supplied to the second wiring Lm2 and the third wiring Lm3 through the high voltage side supply positive electrode wiring L1 and the positive electrode bus line Lp. The power supplied to the third wiring Lm3 is supplied to the integrated smooth wiring Lst via the reactor 55 of the second smooth wiring Ls2, and then to the first low voltage power storage device 40. When the switching element Q5 provided in the third wiring Lm3 is in a closed state, the reactor 55 provided in the second smooth wiring Ls2 is magnetized. As a result, a back electromotive force is generated in the reactor 55 provided in the second smooth wiring Ls2 in a direction that obstructs the current flowing from the third wiring Lm3 via the second smooth wiring Ls2. Therefore, when the switching element Q5 provided in the third wiring Lm3 is in the closed state, the voltage of the power generated in the fuel cell stack 10 is reduced by the reactor 55 provided in the second smooth wiring Ls2, and the fuel cell The electric power generated by the stack 10 is stepped down. Further, the same applies when the switching element Q3 provided in the second wiring Lm2 is in the closed state, and the reactor 54 provided in the first smooth wiring Ls1 is magnetized, so that the switching element Q3 provided in the first smooth wiring Ls1 is magnetized. A back electromotive force is generated in the reactor 54 which is located in a direction that obstructs the current flowing from the second wiring Lm2 through the first smooth wiring Ls1. Therefore, when the switching element Q3 provided in the second wiring Lm2 is in the closed state, the voltage of the electric power generated in the fuel cell stack 10 is reduced by the reactor 54 provided in the first smooth wiring Ls1, and the fuel cell The electric power generated by the stack 10 is stepped down. Here, when the switching elements Q3 and Q5 provided in the second wiring Lm2 and the third wiring Lm3 are opened and closed, the capacitor 53 provided in the smooth relay wiring Lsm is charged. The capacitor 53 is charged with the power of the fuel cell stack 10 whose voltage is lowered by the reactors 54 and 55. Even if the switching elements Q3 and Q5 provided in the second wiring Lm2 and the third wiring Lm3 are in an open state, the switching elements Q4 and Q6 provided in the second wiring Lm2 and the third wiring Lm3 are connected from the capacitor 53. A return current is generated that flows toward each reactor 54, 55 via the diodes D4, D6 connected in antiparallel to the reactor 54, 55. Therefore, even if the switching elements Q3 and Q5 provided in the second wiring Lm2 and the third wiring Lm3 are in an open state and the power generated in the fuel cell stack 10 does not flow to the first low-voltage power storage device 40, the capacitor 53 Due to the return current caused by this, temporal changes in the voltage of the power stored in the first low-voltage power storage device 40 are reduced. Therefore, it is possible to stabilize the voltage of the power stored in the first low-voltage power storage device 40 while lowering the voltage of the power generated by the fuel cell stack 10 by the smoothing circuit 52 of the first low-voltage converter 50 .

As shown in FIGS. 1 and 2, when the driving motor 70 is generating regenerative power, the FCECU 65 performs regenerative step-down control to step down the regenerated power when the high-voltage power storage device 20 reaches a specified voltage value. implement. In the regenerative pressure reduction control, the FCECU 65 stops the operation of the fuel cell stack 10 as described above. In addition, the FCECU 65 includes a switching element Q1 and a switching element Q2 provided on the first wiring Lm1 in the inverter circuit 51 of the first low voltage converter 50, and a lower arm switching element provided on the second wiring Lm2 and the third wiring Lm3. The switching elements Q4 and Q6 are always kept open. Then, the FCECU 65 performs regenerative voltage step-down control by opening and closing switching elements Q3 and Q5 while switching elements Q1, Q2, Q4, and Q6 are maintained in an open state. More specifically, during regenerative voltage step-down control, the FCECU 65 alternately opens and closes the switching elements Q3 and Q5. In addition, in the regenerative voltage step-down control, the FCECU 65 opens and closes the switching elements Q3 and Q5 provided in the second wiring Lm2 and the third wiring Lm3 earlier than in the step-down control described above.

For example, consider a case where the switching element Q5 provided in the third wiring Lm3 is brought into a closed state. The regenerative power generated by the driving motor 70 is transmitted to the first wiring Lm1 through the regeneration wiring Lr, and is connected to the diode D1 which is connected in antiparallel to the switching element Q1 provided in the first wiring Lm1. It is supplied to the second wiring Lm2 and the third wiring Lm3 via the wiring. The regenerated power supplied to the third wiring Lm3 is supplied to the integrated smooth wiring Lst via the reactor 55 of the second smooth wiring Ls2, and then to the first low voltage power storage device 40. When the switching element Q5 provided in the third wiring Lm3 is in a closed state, the reactor 55 provided in the second smooth wiring Ls2 is magnetized. As a result, a back electromotive force is generated in the reactor 55 provided in the second smooth wiring Ls2 in a direction that obstructs the current flowing from the third wiring Lm3 via the second smooth wiring Ls2. Therefore, when the switching element Q5 provided in the third wiring Lm3 is in a closed state, the voltage of the regenerated power is stepped down by the reactor 55 provided in the second smooth wiring Ls2. Further, the same applies when the switching element Q3 provided in the second wiring Lm2 is in the closed state, and the reactor 54 provided in the first smooth wiring Ls1 is magnetized, so that the switching element Q3 provided in the first smooth wiring Ls1 is magnetized. A back electromotive force is generated in the reactor 54 which is located in a direction that obstructs the current flowing from the second wiring Lm2 through the first smooth wiring Ls1. Therefore, when the switching element Q3 provided in the second wiring Lm2 is in a closed state, the voltage of the regenerated power is stepped down by the reactor 54 provided in the first smooth wiring Ls1. Here, when the switching elements Q3 and Q5 provided in the second wiring Lm2 and the third wiring Lm3 are opened and closed, the capacitor 53 provided in the smooth relay wiring Lsm is charged. The capacitor 53 is charged with the regenerated power lowered by the reactors 54 and 55. Even if the switching elements Q3 and Q5 provided in the second wiring Lm2 and the third wiring Lm3 are in an open state, the switching elements Q4 and Q6 provided in the second wiring Lm2 and the third wiring Lm3 are connected from the capacitor 53. A return current is generated that flows toward each reactor 54, 55 via the diodes D4, D6 connected in antiparallel to the reactor 54, 55. Therefore, even if the switching elements Q3 and Q5 provided in the second wiring Lm2 and the third wiring Lm3 are in an open state and the regenerative power does not flow to the first low-voltage power storage device 40, the return current from the capacitor 53 causes the first low-voltage power storage device to Temporal changes in the voltage of the power stored in the battery 40 are reduced. Therefore, the voltage of the power stored in the first low-voltage power storage device 40 can be stabilized while reducing the voltage of the regenerated power by the smoothing circuit 52 of the first low-voltage converter 50.

Here, the reason why switching elements Q3 and Q5 are opened and closed earlier in regenerative voltage step-down control than during voltage step-down control will be explained.
The voltage step-down width is different between when the power generated by the fuel cell stack 10 is stepped down and when the regenerated power is stepped down. The reason why the regenerated power can be stepped down is the back electromotive force generated by the magnetization of the reactors 54 and 55. Therefore, in order to change the step-down width, it is necessary to change the magnitude of the back electromotive force generated in the reactors 54 and 55. Therefore, when performing the regenerative voltage step-down control, the FCECU 65 opens and closes the switching elements Q3 and Q5 earlier than when performing the voltage step-down control. When the switching elements Q3 and Q5 remain open for a long time, the reactors 54 and 55 store a large amount of magnetic energy due to the return current generated by the capacitor 53. Therefore, when the switching elements Q3 and Q5 are closed and the reactors 54 and 55 are magnetized, the back electromotive force generated in the reactors 54 and 55 increases. That is, by opening and closing the switching elements Q3 and Q5 earlier than in the step-down control when performing the regenerative step-down control, it is possible to reduce the magnetic energy stored in the reactors 54 and 55. The generated back electromotive force can be reduced. Therefore, the reason why the switching elements Q3 and Q5 are opened and closed earlier in the regenerative voltage step-down control than in the voltage step-down control is to appropriately change the voltage step-down width between the voltage step-down control and the regenerative voltage step-down control.

Here, the FCECU 65 determines that when the voltage value detected by the voltage sensor 102 reaches a specified voltage value, even if the driving motor 70 is in a state where the regenerative power is being generated, the regenerative power is transferred to the high voltage power storage device 20 and Regeneration stop control is performed to prevent the flow from flowing toward the first low-voltage power storage device 40. For example, in implementing regeneration stop control, a relay may be provided as a power cutoff section downstream of the high voltage power storage device 20 in the high voltage side conversion positive wiring L3. Then, when the first low-voltage power storage device 40 reaches a specified voltage value, the FCECU 65 opens the relay to prevent the regenerated power from flowing toward the high-voltage power storage device 20 and the first low-voltage power storage device 40. Make it. Note that the regeneration stop control introduced here is an example, and if it is possible to prevent the regenerative power from flowing to the high voltage power storage device 20 and the first low voltage power storage device 40 when the first low voltage power storage device 40 reaches a specified voltage value, You can change it however you like. Furthermore, the specified voltage value of the first low-voltage power storage device 40 takes into account the amount of charge required for the first low-voltage power storage device 40 according to the specifications of the fuel cell system 1, similar to the specified voltage value of the high-voltage power storage device 20. It is preferable to set the Therefore, the specified voltage value of the first low-voltage power storage device 40 is, for example, the voltage value when the first low-voltage power storage device 40 is fully charged, the second specified value of the first low-voltage power storage device 40, or the voltage value of the first low-voltage power storage device 40 when the first low-voltage power storage device 40 is fully charged. The voltage value may be set between the voltage value at full charge and the second specified value.

In this embodiment, the following actions and effects can be obtained.
(1) In the present embodiment, the regenerative power generated by the driving motor 70 is stored in the high voltage power storage device 20, and when the high voltage power storage device 20 reaches a specified voltage value, the first low voltage converter 50 converts the regenerated power into a voltage The voltage is lowered and the first low voltage power storage device 40 stores electricity. Therefore, for example, if the specified voltage value is the voltage value when the high-voltage power storage device 20 is fully charged, surplus power exceeding the amount of power stored in the high-voltage power storage device 20 is stored in the first low-voltage power storage device 40. Therefore, surplus power when the high voltage power storage device 20 reaches a specified voltage value is stored in the first low voltage power storage device 40 without being converted into energy. Therefore, the fuel cell system 1 can efficiently store regenerated power without causing energy loss due to energy conversion.

(2) In this embodiment, the first low voltage converter 50 includes an inverter circuit 51. That is, the first low voltage converter 50 has the same configuration as the inverter included in the load, but a smoothing circuit 52 is added. Therefore, since there is no need to newly use a step-down converter, the cost of the fuel cell system 1 can be reduced.

(3) For example, consider a case where switching elements Q3 and Q5 provided in the second wiring Lm2 and the third wiring Lm3 are simultaneously opened and closed. When regenerative power is supplied from the regeneration wiring Lr to the second wiring Lm2 and the third wiring Lm3 via the diode D1 which is connected in antiparallel to the switching element Q1 provided in the first wiring Lm1, the capacitor 53, there is a period in which regenerative power does not flow. Although it depends on the timing of opening and closing the switching elements Q3 and Q5 provided in the second wiring Lm2 and the third wiring Lm3, the return current from the capacitor 53 causes a temporal change in the voltage of the power stored in the first low-voltage power storage device 40. There is a risk that it will become larger.

In this regard, in this embodiment, the switching elements Q3 and Q5 provided in the second wiring Lm2 and the third wiring Lm3 are alternately opened and closed. Therefore, the period during which regenerative power does not flow toward the capacitor 53 can be shortened. Therefore, the voltage stored in the first low voltage power storage device 40 can be made more stable.

(4) In this embodiment, when the driving motor 70 is not generating regenerative power, the first low voltage converter 50 performs the function of lowering the voltage of the electric power generated by the fuel cell stack 10 by the step-down control of the FCECU 65. be able to. When the driving motor 70 is generating regenerative power, the first low voltage converter 50 performs a function to step down the regenerative power by the regenerative step-down control of the FCECU 65 when the high voltage power storage device 20 reaches a specified voltage value. able to demonstrate. That is, there is no need to separately prepare a converter that steps down the power generated by the fuel cell stack 10 and a converter that steps down the regenerated power. Therefore, the cost of the fuel cell system 1 can be reduced.

Further, in the fuel cell system 1 described above, when the driving motor 70 is generating regenerative power, the FCECU 65 stops the operation of the fuel cell stack 10 when the high voltage power storage device 20 reaches a specified voltage value. Thereby, the function when the first low voltage converter 50 implements the voltage step-down control and the function when the first low voltage converter 50 performs the regenerative voltage step-down control can be distinguished.

Further, when performing regenerative voltage step-down control, the FCECU 65 opens and closes the switching elements Q3 and Q5 provided in the second wiring Lm2 and third wiring Lm3 earlier than when performing the voltage step-down control. Therefore, the step-down control that steps down the power generated by the fuel cell stack 10 to a voltage that can be stored in the first low-voltage power storage device 40 and the regenerative step-down control that steps down the regenerated power to a voltage that can be stored in the first low-voltage power storage device 40 are performed. The step-down width can be changed appropriately.

(5) Conventionally, the high-voltage power storage device 20 has a large charging capacity in order to store regenerated power, but in this embodiment, when the high-voltage power storage device 20 reaches a specified voltage value, the first The low voltage power storage device 40 can be charged. Therefore, the high-voltage power storage device 20 does not have to have an unnecessarily large charging capacity. Therefore, it is possible to employ the high voltage power storage device 20 with an appropriate charging capacity, so that the fuel cell system 1 can be downsized and the cost can be reduced.

Note that this embodiment can be implemented with the following modifications. This embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
The fuel cell stack 10 may be operated until the high voltage power storage device 20 reaches a specified voltage value. Even in this case, since the relay provided in the regeneration wiring Lr is in the open state, the electric power generated by the fuel cell stack 10 and the regenerative electric power generated by the driving motor 70 are simultaneously input to the first low voltage converter 50. It will not be done.

In the present embodiment, the operation of the fuel cell stack 10 is stopped when the traveling motor 70 is generating regenerative power, but the present invention is not limited to this. For example, in order to suppress the voltage of the fuel cell stack 10 from increasing or decreasing between high voltage and low voltage, the operation of the fuel cell stack 10 is restricted even when the travel motor 70 is generating regenerative power. It is preferable to continue. In this case, for example, if a relay is provided in the high voltage side supply positive wiring L1 and the traveling motor 70 is generating regenerative power, the FCECU 65 may open the relay. With this change, when the driving motor 70 is generating regenerative power, the power generated by the fuel cell stack 10 and the regenerative power are transferred to the first low-voltage converter 50 while the fuel cell stack 10 continues to operate. They will no longer be input at the same time. Therefore, while distinguishing between the function of the first low voltage converter 50 in step-down control and the function of the first low-voltage converter 50 in regenerative step-down control, it is possible to increase or decrease the voltage of the fuel cell stack 10 between high voltage and low voltage. can be suppressed.

In the present embodiment, the first low-voltage converter 50 performs the step-down control and the regenerative step-down control, but the present invention is not limited to this. For example, a step-down converter that performs step-down control may be newly provided, and the first low-voltage converter 50 may be changed to perform only regenerative step-down control. In this modification example, a step-down converter that performs step-down control is arranged at the position of the first low-voltage converter 50 of the present embodiment, and the first low-voltage converter includes a regeneration wiring Lr and a first low-voltage side conversion positive electrode wiring L5. , and the first low-voltage side conversion negative electrode wiring L6 may be changed to a state where they are electrically connected.

Although the FCECU 65 alternately opens and closes the switching elements Q3 and Q5 during voltage step-down control and regenerative voltage step-down control, the present invention is not limited thereto. For example, the FCECU 65 may open and close switching elements Q3 and Q5 at the same time.

〇 As shown in FIG. 3, the switching elements Q1, Q2, Q4, and Q6 are omitted, and the first low-voltage converter 50 is replaced with the positive electrode bus Lp, the negative electrode bus Ln, the relay wiring Lm, the switching elements Q3, Q5, and the smoothing circuit 52. It may be changed so that it is configured by In this case, the regeneration wiring Lr is electrically connected between the diodes D1 and D2 provided in the first wiring Lm1. The first smooth wiring Ls1 is electrically connected between the switching element Q3 and the diode D4 in the second wiring Lm2. The second smooth wiring Ls2 is electrically connected between the switching element Q5 and the diode D6 in the third wiring Lm3.

〇 The first low voltage converter 50 may be modified as follows.
As shown in FIG. 4, the first low voltage converter 50 includes a positive bus Lp, a negative bus Ln, one relay wiring Lm, and a smoothing circuit that stabilizes the voltage of the power supplied to the first low voltage power storage device 40. 56. A switching element Q7 is provided in the relay wiring Lm closer to the positive electrode bus Lp. The relay wiring Lm is provided with a diode D7 connected in antiparallel to the switching element Q7 in order to prevent reverse flow of current from the positive bus Lp side to the negative bus Ln side. Further, the relay wiring Lm is provided with a diode D8 close to the negative electrode bus Ln to prevent current from flowing backward from the positive electrode bus Lp side toward the negative electrode bus Ln side. Diode D8 is connected in series with switching element Q7. The regeneration wiring Lr is electrically connected to the positive electrode bus Lp. The regeneration wiring Lr is provided with a diode D9 for preventing current from flowing backward from the positive bus Lp side toward the regeneration wiring Lr.

The smoothing circuit 56 includes a negative bus Ln, one smoothing wiring Ls, a smoothing relay wiring Lsm, a reactor 57, and a capacitor 53. The smooth wiring Ls is electrically connected between the switching element Q7 and the diode D8 in the relay wiring Lm. The smooth wiring Ls is electrically connected to the first low voltage side conversion positive electrode wiring L5. Therefore, the smooth wiring Ls is electrically connected to the first low voltage power storage device 40. The smooth relay wiring Lsm is electrically connected to the negative electrode bus Ln and the smooth wiring Ls. The reactor 57 is provided on the smooth wiring Ls. The reactor 57 is the same as the reactors 54 and 55 of this embodiment.

In the first low voltage converter 50 configured in this way, the FCECU 65 performs step-down control to step down the power generated by the fuel cell stack 10 by opening and closing the switching element Q7, and performs regenerative step-down control to step down the regenerated power. It may be changed to implement. Furthermore, even if the first low-voltage converter 50 of this modified example is adopted, the timing at which the FCECU 65 opens and closes the switching element Q7 in the regenerative step-down control can be made earlier than the timing at which the switching element Q7 opens and closes in the step-down control. preferable.

〇 The first low voltage converter 50 is not limited to a non-insulated converter, but may also be an isolated converter in which the input side (fuel cell stack 10 side) and the output side (first low voltage power storage device 40 side) are not electrically connected. May be adopted.

Although the FCECU 65 maintains the switching elements Q1, Q2, Q4, and Q6 in the open state, they may be kept in the open state mechanically. Therefore, the FCECU 65 only needs to open and close the switching elements Q3 and Q5.

The first low voltage converter 50 may be changed to be electrically connected to the high voltage side conversion positive wiring L3 and the high voltage side conversion negative wiring L4. In this case, when carrying out voltage step-down control, the function of the first low-voltage converter 50 is changed to a function of further stepping down the voltage stepped down by the high-voltage converter 30. Furthermore, since the regenerated power is input to the first low voltage converter 50 via the high voltage side conversion positive electrode wiring L3, it is preferable to omit the regeneration wiring Lr.

In the present embodiment, the first low voltage power storage device 40 is used as an example of the low voltage power storage device, but the present invention is not limited to this. For example, the second low voltage power storage device 80 may be used as an example of the low voltage power storage device. In this case, for example, the second low-voltage converter 90 may be changed to have the same configuration as the first low-voltage converter 50 and used as an example of a step-down converter. At this time, the second auxiliary machine 95 is an example of an auxiliary machine. Then, the regeneration wiring Lr is changed to be electrically connected to the second low voltage converter 90.

Further, the first low-voltage power storage device 40 and the second low-voltage power storage device 80 may be an example of a low-voltage power storage device. In this case, the configuration of the second low-voltage converter 90 is changed to be the same as that of the first low-voltage converter 50, and the regeneration wiring Lr is electrically connected to both the first low-voltage converter 50 and the second low-voltage converter 90. Change it to connect to. At this time, the first auxiliary machine 60 and the second auxiliary machine 95 are examples of auxiliary machines.

In the present embodiment, the FCECU 65 performs regeneration stop control when the first low-voltage power storage device 40 reaches a specified voltage value, but the present invention is not limited to this. For example, when the first low voltage power storage device 40 reaches a specified voltage value, the second low voltage power storage device 80 may be charged with surplus power that exceeds the specified voltage value of the first low voltage power storage device 40. Note that, for example, the FCECU 65 controls whether the regenerative power is generated by the high-voltage power storage device 20 or Regeneration stop control may be implemented to prevent the flow from flowing toward the first low-voltage power storage device 40 and the second low-voltage power storage device 80. Note that the specified voltage value of the second low-voltage power storage device 80 is the same as the specified voltage value of the high-voltage power storage device 20 and the specified voltage value of the first low-voltage power storage device 40, and the specified voltage value of the second low-voltage power storage device 80 depending on the specifications of the fuel cell system 1. It is preferable to set the amount of charge in consideration of the amount of charge required for the low-voltage power storage device 80. Therefore, the specified voltage value of the second low-voltage power storage device 80 is, for example, the voltage value when the second low-voltage power storage device 80 is fully charged, the third specified value of the second low-voltage power storage device 80, or the voltage value of the second low-voltage power storage device 80. The voltage value may be set between the voltage value at full charge and the third specified value.

〇 The high voltage power storage device 20 and the first low voltage power storage device 40 used lithium ion capacitors, but for example, other capacitors such as electric double layer capacitors, or secondary batteries such as nickel metal hydride batteries and lithium ion secondary batteries A battery may also be used. Furthermore, although a 12V battery is used as the second low-voltage power storage device 80, a capacitor such as a lithium ion capacitor may be used instead.

〇 In this embodiment, the fuel cell system 1 is applied to a towing tractor, but the invention is not limited to this. For example, it may be applied to industrial vehicles such as forklifts. Further, the fuel cell system 1 may be applied to a fuel cell vehicle.

〇 In the present embodiment, the load includes an inverter and the traveling motor 70, but the load is not limited to this. For example, consider a case where the fuel cell system 1 is applied to a forklift. In this case, the load may include a cargo handling motor. The cargo handling motor is a motor that generates driving force that drives a cargo handling pump that supplies hydraulic oil to the hydraulic mechanism of the forklift. In the cargo handling motor, for example, when a forklift unloads a load, hydraulic oil is returned from the hydraulic mechanism to the cargo handling pump, thereby rotating the cargo handling motor and generating regenerative power. Therefore, the cargo handling motor functions as an electric motor that generates driving force using the electric power generated by the fuel cell stack 10, and also functions as a generator that generates regenerative power during unloading.

〇 The voltage value of the power generated by the fuel cell stack 10 is 140V, the voltage value of the power that can be stored in the high-voltage power storage device 20 is 80V, the voltage value of the power that can be stored in the first low-voltage power storage device 40 is 48V, and the voltage value of the power that can be stored in the first low-voltage power storage device 40 is 48V. Although the voltage value of the power that can be stored in the device 80 was 12V, the magnitude of the voltage value may be changed as appropriate. For example, the voltage value of the power generated by the fuel cell stack 10 is changed to 80V, the voltage value of the power that can be stored in the high-voltage power storage device 20 is changed to 48V, and the voltage value of the power that can be stored in the first low-voltage power storage device 40 is changed to 24V. Good too. The voltage value of the power that can be stored in the second low-voltage power storage device 80 may also be changed as appropriate.

Next, technical ideas that can be understood from the above embodiment and other examples will be additionally described below.
(1) A fuel cell stack, a load including a motor that functions as an electric motor that generates driving force using the electric power generated by the fuel cell stack, and also generates regenerated electric power, and a load that includes a motor that generates regenerative electric power by the motor. a power storage device that stores electric power and regenerated power generated by the motor; a control section that controls the operation of the fuel cell stack; and a power storage device that is charged with electric power that operates the auxiliary equipment, and that is stored in the high-voltage power storage device. a low-voltage power storage device whose voltage is set low when storing power; a step-down converter electrically connected to the low-voltage power storage device and which steps down the voltage of power when stored in the high-voltage power storage device; If the motor is generating regenerative power, the control unit causes the low-voltage power storage device to store the regenerative power via the step-down converter when the high-voltage power storage device reaches a prescribed voltage value. , when the motor is generating regenerative power, perform regeneration stop control so that the regenerative power does not flow to the high voltage power storage device and the low voltage power storage device when the low voltage power storage device reaches a specified voltage value. A fuel cell system characterized by:

Generally, power storage devices may deteriorate due to overcharging, but according to this, the high voltage power storage device reaches the specified voltage value while the motor is generating regenerative power, and the low voltage power storage device reaches the specified voltage value. When the voltage value reaches the voltage value, the control unit performs regeneration stop control so that the regenerated power does not flow to the high voltage power storage device and the low voltage power storage device. Therefore, overcharging in the high voltage power storage device and the low voltage power storage device can be suppressed.

DESCRIPTION OF SYMBOLS 1... Fuel cell system, 10... Fuel cell stack, 20... High voltage power storage device, 30... High voltage converter, 40... First low voltage power storage device, 50... First low voltage converter, 51... Inverter circuit, 52... Smoothing circuit, 53... Capacitor, 54, 55... Reactor, 60... First auxiliary machine, 65... FCECU, 70... Traveling motor, 80... Second low voltage power storage device, 90... Second low voltage converter, 95... Second auxiliary machine, L3... High voltage Side conversion positive electrode wiring, L4... High voltage side conversion negative electrode wiring, Lr... Regeneration wiring, Q1, Q2, Q3, Q4, Q5, Q6... Switching element, D1, D2, D3, D4, D5, D6... Diode, Lp... Positive electrode bus, Ln...Negative electrode bus, Lm...Relay wiring, Lm1...First wiring, Lm2...Second wiring, Lm3...Third wiring, Ls1...First smooth wiring, Ls2...Second smooth wiring, Lst...Integrated smooth wiring , Lsm...Smooth relay wiring.

Claims (3)

fuel cell stack,
a load including a motor that functions as an electric motor that generates driving force using the electric power generated by the fuel cell stack and also functions as a generator that generates regenerated electric power;
a high-voltage power storage device that stores power for the motor to generate driving force and stores regenerative power generated by the motor;
a control unit that controls the operation of the fuel cell stack;
a low-voltage power storage device that is charged with power for operating an auxiliary device and is set to have a lower voltage when storing power than the high-voltage power storage device;
a step-down converter that is electrically connected to the low-voltage power storage device and that steps down the voltage of power when stored in the high-voltage power storage device;
The step-down converter is
an inverter circuit having a three-phase switching element;
a smoothing circuit that is electrically connected to the inverter circuit and the low-voltage power storage device and stabilizes the voltage of the power supplied to the low-voltage power storage device;
The inverter circuit is
a positive electrode bus;
a negative electrode bus electrically connected to the low voltage power storage device;
Relay wiring consisting of a first wiring, a second wiring, and a third wiring that electrically connects the positive electrode bus and the negative electrode bus,
An upper arm switching element as the switching element and a lower arm switching element as the switching element are connected in series to each of the relay wirings, and on the relay wiring from the positive busbar side to the negative busbar side. A diode for preventing reverse current flow is connected in antiparallel to the upper arm switching element and the lower arm switching element,
The smoothing circuit is
the negative electrode busbar;
a first smooth wiring electrically connected between the upper arm switching element and the lower arm switching element in the second wiring;
a second smooth wiring electrically connected between the upper arm switching element and the lower arm switching element in the third wiring;
an integrated smooth wiring formed by combining the first smooth wiring and the second smooth wiring and electrically connected to the low voltage power storage device;
smooth relay wiring that electrically connects the negative electrode bus and the integrated smooth wiring;
a capacitor provided in the smooth relay wiring;
a reactor provided in each of the first smooth wiring and the second smooth wiring,
A regeneration wiring to which regenerative power generated by the motor is input is connected between the upper arm switching element and the lower arm switching element in the first wiring,
The control unit includes:
When the motor is generating regenerative power, when the high-voltage power storage device reaches a specified voltage value , the switching element installed in the first wiring, the second wiring, and the third wiring The regenerative power is transferred to the low voltage by opening and closing the upper arm switching elements provided in the second wiring and the third wiring while the lower arm switching element provided in the second wiring and the third wiring are maintained in an open state. A fuel cell system characterized by storing electricity in a power storage device. The control unit includes:
When the motor is generating regenerative power, when the high voltage power storage device reaches a specified voltage value, the upper arm switching element provided in the second wiring and the upper arm switching element provided in the third wiring 2. The fuel cell system according to claim 1 , wherein the upper arm switching element is alternately opened and closed. The positive electrode of the fuel cell stack is electrically connected to the positive electrode bus of the inverter circuit,
The negative electrode of the fuel cell stack is electrically connected to the negative electrode bus of the inverter circuit,
A high-voltage converter that steps down the power generated by the fuel cell stack to a voltage that can be stored in the high-voltage power storage device,
The high voltage converter and the motor are electrically connected by high voltage side conversion wiring for sending the electric power stepped down by the high voltage converter to the load,
The regeneration wiring is electrically connected to the positive electrode side of the high voltage side conversion wiring,
The control unit includes:
When the motor is not generating regenerative power, the switching element provided in the first wiring and the lower arm switching elements provided in the second wiring and the third wiring are maintained in an open state. In this state, step-down control is performed to step down the voltage of the electric power generated by the fuel cell stack by opening and closing the upper arm switching element provided in the second wiring and the third wiring,
When the motor is generating regenerative power, the high-voltage power storage device stops the operation of the fuel cell stack when the voltage reaches a predetermined voltage value, and is provided in the second wiring and the third wiring. 3. The fuel cell system according to claim 1 , wherein regenerative voltage step-down control is performed in which the timing of opening and closing the upper arm switching element is earlier than that of the voltage step-down control.