Fuel cell system

Abstract

To propose a technique suppressing occurrence of component stress by reducing the frequency of a power supply stop operation of stopping power supply from a fuel cell to a battery.SOLUTION: A control unit of a fuel cell system performs a first operation of charging a battery with generated electric power while supplying air to the fuel cell when the target value of the generated electric power of the fuel cell is higher than the current value of the generated electric power, and performs a second operation of charging the battery with the generated electric power of the fuel cell while supplying the air with a lower flow rate than the first operation when the target value of the generated electric power is lower than the current value of the generated electric power. When an amount of charge in the battery is larger than a reference amount of charge, the control unit performs a power supply stop operation of stopping power supply from the fuel cell to the battery. The charging rate of the battery becomes slower in the second operation than in the first operation. As a result, the time required for the amount of charge in the battery to reach the reference amount of charge increases, so that the frequency of performing the power supply stop operation decreases.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The technology disclosed in this specification relates to a fuel cell system.

Background Art

[0002] The fuel cell system disclosed in Patent Document 1 has a fuel cell and an air compressor. The air compressor supplies air to the air flow path in the fuel cell. The fuel cell generates electricity according to the required power from the load. This fuel cell system stops supplying power to the load when the required power is below the reference value. Further, when this fuel cell system stops supplying power to the load, it controls the air compressor to reduce the supply amount of air to the air flow path. Thereby, the output voltage of the fuel cell is controlled below the upper limit value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, the fuel cell system disclosed in Patent Document 1 supplies air at a low flow rate to the air flow path by the air compressor when the power supply to the load is stopped. Thereby, an extreme decrease in the output voltage of the fuel cell is prevented. However, the operation of the air compressor may become unstable at low flow rates. For example, in an air compressor equipped with an air bearing, the air bearing floats due to the air flow, so the operation of the air compressor becomes unstable when the air flow rate is low. When the air compressor is operated with low-flow air, wear occurs in the air compressor. In this specification, in a fuel cell that charges a battery, a technique is proposed to reduce the frequency of the power supply stop operation and suppress the wear of the air compressor.

Means for Solving the Problems

[0005] The fuel cell system according to Embodiment 1 disclosed in this specification includes a fuel cell, an air flow path provided in the fuel cell, an air compressor that supplies air to the air flow path, a battery that is charged by the generated power generated by the fuel cell, and a control device. When the target value of the generated power is higher than the current value of the generated power, the control device performs a first operation of charging the battery with the generated power while supplying air to the air flow path by the air compressor. When the target value of the generated power is lower than the current value of the generated power, the control device performs a second operation of charging the battery with the generated power while supplying air to the air flow path at an air stoichiometry lower than that of the first operation by the air compressor. When the charged amount of the battery is greater than the reference charged amount, a power supply stop operation of stopping the power supply from the fuel cell to the battery is performed.

[0006] In the above fuel cell system, when the target value of the generated power is lower than the current value of the generated power, the control device executes the second operation, and the air compressor supplies air to the air flow path at an air stoichiometry lower than that of the first operation. Therefore, the power generation efficiency of the fuel cell decreases, and the charging speed of the battery slows down. For this reason, the time required for the charged amount of the battery to reach the reference charged amount increases, and the frequency of performing the power supply stop operation decreases. As a result, wear of the air compressor is suppressed.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0008] Following the above Aspect 1, additional configurations of the fuel cell system disclosed in this specification will be described below. (Aspect 2) The fuel cell has a plurality of cells, and when the target value of the power generation power is lower than the current value of the power generation power, the control device performs the first operation when the variation in the output voltages of the plurality of cells is greater than a reference value. The fuel cell system according to Aspect 1. (Aspect 3) The control device performs the first operation when the upper limit voltage is higher than the output voltage of the fuel cell when the target value of the power generation power is lower than the current value of the power generation power. The fuel cell system according to Aspect 1 or 2. (Aspect 4) The charge amount of the battery increases during the second operation. The fuel cell system according to any one of Aspects 1 to 3. (Aspect 5) The charge amount of the battery decreases during the power supply stop operation. The fuel cell system according to any one of Aspects 1 to 4.

[0009] According to Aspect 2, deterioration of the cells can be suppressed.

[0010] According to Aspect 3, deterioration of the cells can be suppressed.

[0011] The fuel cell system is mounted on a device powered by a fuel cell. The fuel cell system 10 of the embodiment shown in FIG. 1 is mounted on a fuel cell vehicle. The fuel cell system 10 has a fuel cell 12, a battery 18, and a motor 20. The motor 20 is a type of load that receives power supply from the fuel cell 12 and the battery 18. The motor 20 is driven by the power supplied from the fuel cell 12 and the battery 18 to rotate the drive wheels of the fuel cell vehicle.

[0012] The fuel cell 12 has a configuration in which a plurality of cells are stacked. Each cell is connected in series. The fuel cell 12 is connected to the battery 18 and the motor 20. Air is supplied to the fuel cell 12 by an air flow path 16 described later, and hydrogen is supplied by a hydrogen flow path (not shown). The fuel cell 12 generates electricity by reacting oxygen and hydrogen. The fuel cell 12 supplies power to the battery 18 and the motor 20.

[0013] The battery 18 is connected to the fuel cell 12 and the motor 20. The battery 18 is charged by the power supplied from the fuel cell 12. Also, the battery 18 supplies power to the motor 20.

[0014] The motor 20 is connected to the fuel cell 12 and the battery 18. The motor 20 is driven by receiving power supply from the fuel cell 12 and the battery 18.

[0015] The fuel cell system 10 has an air compressor 14 and an air flow path 16. The air compressor 14 and the air flow path 16 supply air to the fuel cell 12.

[0016] The air flow path 16 has an internal flow path 28 provided inside the fuel cell 12, a supply flow path 24 connected to the internal flow path 28, and a discharge flow path 26. The supply flow path 24 is connected to the upstream end of the internal flow path 28. The air compressor 14 is provided in the supply flow path 24. The air compressor 14 pressurizes the air in the supply flow path 24 and sends it to the downstream side. When the air compressor 14 is driven, air is supplied from the supply flow path 24 to the internal flow path 28. An air flow meter 34 is provided in the supply flow path 24. The air flow meter 34 detects the flow rate of the air flowing in the supply flow path 24. The discharge flow path 26 is connected to the downstream end of the internal flow path 28. The air that has passed through the internal flow path 28 is discharged to the outside through the discharge flow path 26. A pressure regulating valve 36 is provided in the discharge flow path 26. By adjusting the opening degree of the pressure regulating valve 36, the pressure in the internal flow path 28 is adjusted.

[0017] The air flow path 16 has a bypass flow path 30. The bypass flow path 30 is connected to the supply flow path 24 on the downstream side of the air compressor 14 and the discharge flow path 26 on the downstream side of the pressure regulating valve 36. A diverter valve 32 is provided in the bypass flow path 30. The diverter valve 32 opens and closes the flow path of the bypass flow path 30. When the diverter valve 32 is in the open state, the air in the supply flow path 24 branches and flows into the internal flow path 28 and the bypass flow path 30. When the opening degree of the diverter valve 32 is adjusted, the flow rate of the air flowing in the bypass flow path 30 is adjusted, so the flow rate of the air flowing in the internal flow path 28 is adjusted.

[0018] The air compressor 14 has an air compressor main body 14a, a motor 14b, and an inverter 14c. The air compressor main body 14a incorporates a rotor and an air bearing that supports the rotor. The motor 14b rotates the rotor of the air compressor main body 14a. The inverter 14c supplies current to the motor 14b to drive the motor 14b. When the motor 14b rotates the rotor, the air compressor 14 pressurizes the air in the supply flow path 24 and sends it to the downstream side. By controlling the rotational speed of the motor 14b, the flow rate of the air flowing through the air compressor 14 is controlled.

[0019] The fuel cell vehicle is equipped with an ECU (electronic control unit) 21. Further, the fuel cell system 10 has a control device 22.

[0020] Based on the operation amount of the accelerator, the operation amount of the brake, the operating state of the motor 20, the charge amount of the battery 18 (i.e., SOC: State Of Charge), etc., the ECU 21 calculates the target value Wt of the power generation power of the fuel cell 12. Note that the charge amount of the battery 18 (hereinafter sometimes referred to as the charge amount Qc) is calculated based on the charge and discharge current of the battery 18 in the past. The ECU 21 inputs the target value Wt of the power generation power of the fuel cell 12 to the control device 22.

[0021] The control device 22 is connected to the inverter 14c of the air compressor 14. The control device 22 controls the air compressor 14 by controlling the inverter 14c. The target value Wt, the charge amount Qc, etc. are input to the control device 22 from the ECU 21. The control device 22 executes a high air stoichiometry operation, a low air stoichiometry operation, and a power supply stop operation based on the charge amount Qc and the target value Wt. The low air stoichiometry operation is an operation in which power generation of the fuel cell 12 is performed with a lower air stoichiometry than the high air stoichiometry operation. The power supply stop operation is an operation in which power supply from the fuel cell 12 to the battery 18 is stopped. The fuel cell 12 selects an operation according to the flowchart of FIG. 2.

[0022] In step S2, the control device 22 determines whether the charge amount Qc is equal to or greater than the reference charge amount Qt.

[0023] When the charge amount Qc is equal to or greater than the reference charge amount Qt, the control device 22 performs a power supply stop operation in step S4. The power supply stop operation is an operation to stop the power supply from the fuel cell 12 to the battery 18. In the power supply stop operation, the control device 22 controls the air compressor 14 to control the flow rate of the air in the internal flow path 28 to an extremely low flow rate. Thereby, the generated power of the fuel cell 12 is reduced. For this reason, the power supply to the battery 18 is stopped, and the charging of the battery 18 is stopped. Note that in the power supply stop operation, the connection between the fuel cell 12 and the battery 18 may be interrupted by a switch (not shown), or the connection between the fuel cell 12 and the motor 20 may be interrupted. In the power supply stop operation, in order to suppress an extreme decrease in the output voltage of the fuel cell 12, low-flow air is caused to flow through the internal flow path 28. For this reason, the air compressor 14 operates in a state where the air flow rate is low, and wear occurs in the air compressor 14. In particular, wear occurs significantly in an air compressor having an air bearing. The control device 22 performs the power supply stop operation until the charge amount Qc falls below the lower limit charge amount Qmin (see FIG. 4).

[0024] When the charge amount Qc is less than the reference charge amount Qt (NO in step S2), the control device 22 makes determinations in steps S6, S10, and S14, and executes either a high air stoichiometry operation (step S18) or a low air stoichiometry operation (step S16) according to the determination result.

[0025] In step S6, the control device 22 determines whether the target value Wt is higher than the current value Wc of the generated power of the fuel cell 12. When the target value Wt is higher than the current value Wc, the control device 22 increases the generated power of the fuel cell 12 in step S8, and then performs a high air stoichiometry operation in step S18.

[0026] When the target value Wt is lower than the current value Wc, in step S10, the control device 22 determines whether the upper limit voltage Vd (see FIG. 3) of the fuel cell 12 is less than or equal to the output voltage Vc. FIG. 3 shows the relationship between the output current of the fuel cell 12 and the output voltage Vc. In FIG. 3, two graphs are shown for the case where the fuel cell 12 is operated at low air stoichiometry and high air stoichiometry, respectively. In either case, the lower the output current, the higher the output voltage Vc. Therefore, when the output current is low, the output voltage Vc may exceed the upper limit voltage Vd. Also, the higher the air stoichiometry, the easier it is for the output voltage Vc to increase. When the output voltage Vc exceeds the upper limit voltage Vd, the electrodes (e.g., carbon) inside the fuel cell 12 are likely to deteriorate. When the upper limit voltage Vd is higher than the output voltage Vc, the control device 22 increases the power generation of the fuel cell 12 in step S12, and then performs high air stoichiometry operation in step S18. In this case, since the upper limit voltage Vd is higher than the output voltage Vc, even if the power generation is increased, the output voltage Vc does not exceed the upper limit voltage Vd.

[0027] When the upper limit voltage Vd is less than or equal to the output voltage Vc, the control device 22 acquires the output voltage Vcell of each cell (i.e., cells connected in series) of the fuel cell 12 in step S14. Further, the control device 22 determines whether the variation in the output voltage Vcell is greater than a reference value. When the variation in the output voltage Vcell is greater than the reference value, the control device 22 performs high air stoichiometry operation in step S18. When the variation in the output voltage Vcell is less than or equal to the reference value, the control device 22 performs low air stoichiometry operation in step S16.

[0028] In the high air stoichiometry operation of step S18, the control device 22 generates power in the fuel cell 12 while supplying air to the internal flow path 28 at a high flow rate. That is, the control device 22 supplies air to the internal flow path 28 at a high flow rate by operating the air compressor 14 at a high output, and generates power in the fuel cell 12 at a high air stoichiometry. In the high air stoichiometry operation, power generation is performed with high power generation efficiency.

[0029] In the low air stoichiometry operation of step S16, the control device 22 generates power with the fuel cell 12 while supplying air to the internal flow path 28 at a flow rate lower than that in the high air stoichiometry operation. That is, the control device 22 supplies air to the internal flow path 28 at a low flow rate by reducing the output of the air compressor 14 below that in the high air stoichiometry operation, and generates power with the fuel cell 12 at low air stoichiometry. In the low air stoichiometry operation, power generation is performed with a power generation efficiency lower than that in the high air stoichiometry operation. Note that the flow rate of the air flowing through the air compressor 14 in the low air stoichiometry operation is larger than the flow rate of the air flowing through the air compressor 14 in the power supply stop operation. Therefore, wear of the air compressor 14 hardly occurs in the low air stoichiometry operation.

[0030] Next, the operation of the fuel cell system 10 when the target value Wt is higher than the current value Wc and when it is lower will be described. FIG. 4 shows changes in the generated power of the fuel cell 12 and the charge amount Qc when the target value Wt is higher than the current value Wc (that is, in the case of NO in step S6). In this case, when the charge amount Qc decreases, the control device 22 executes the high air stoichiometry operation. During the execution of the high air stoichiometry operation, the charge amount Qc increases at a high speed. When the charge amount Qc reaches the reference charge amount Qt, the control device 22 executes the power supply stop operation. During the power supply stop operation, the charge amount Qc decreases. Thus, when the target value Wt is higher than the current value Wc, the high air stoichiometry operation and the power supply stop operation are alternately performed. That is, charging of the battery 18 is intermittently executed.

[0031] FIG. 5 shows the changes in the power generation power of the fuel cell 12 and the charge amount Qc when the target value Wt is lower than the current value Wc (that is, when YES in step S6) and YES in step S10 and NO in step S16. In this case, when the charge amount Qc decreases, the control device 22 executes a low air stoichiometry operation. During the execution of the low air stoichiometry operation, the charge amount Qc increases at a lower rate than in the case of the high air stoichiometry operation. Therefore, in the low air stoichiometry operation, the arrival time T1 until the charge amount Qc reaches the reference charge amount Qt is longer than in the high air stoichiometry operation. When the charge amount Qc reaches the reference charge amount Qt, the control device 22 executes a power supply stop operation. During the power supply stop operation, the charge amount Qc decreases. Thus, when the target value Wt is lower than the current value Wc, the low air stoichiometry operation and the power supply stop operation are alternately performed.

[0032] The arrival time T1 is longer in the low air stoichiometry operation than in the high air stoichiometry operation. Therefore, when the low air stoichiometry operation is executed, the frequency of performing the power supply stop operation is lower than when the high air stoichiometry operation is executed. For this reason, wear of the air compressor 14 can be suppressed.

[0033] Also, if the air flow rate is reduced to the extent that variations in the output voltage Vcell occur, deterioration of the platinum catalyst in the cells of the fuel cell 12 occurs. On the other hand, as described above, the control device 22 performs a high air stoichiometry operation when the variation in the output voltage Vcell is greater than the reference value in step S14. Therefore, deterioration of the platinum catalyst can be suppressed.

[0034] Also, as described above, when the upper limit voltage Vd is higher than the output voltage Vc in step S10, the control device 22 increases the power generation amount and performs a high air stoichiometry operation. Thereby, power generation can be performed in a state where the output voltage Vc is close to the upper limit voltage Vd, and the power generation efficiency can be improved.

[0035] Further, in the above-described embodiment, the flow rate of the air in the internal flow path 28 was decreased by decreasing the output of the air compressor 14 in the low air stoichiometry operation. However, in the low air stoichiometry operation, the flow rate of the air in the internal flow path 28 may be decreased by increasing the opening degree of the flow dividing valve 32.

[0036] The high air stoichiometry operation of the embodiment is an example of the first operation. The low air stoichiometry operation of the embodiment is an example of the second operation.

[0037] As described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples exemplified above. The technical elements described in this specification or the drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Further, the technology exemplified in this specification or the drawings achieves a plurality of purposes simultaneously, and has technical utility by achieving one of those purposes itself.

Description of Reference Numerals

[0038] 10: Fuel cell system 12: Fuel cell 14: Air compressor 16: Air flow path 18: Battery 22: Control device 24: Supply flow path 26: Discharge flow path 28: Internal flow path 30: Bypass flow path 32: Flow dividing valve

Claims

1. A fuel cell system comprising: a fuel cell; an air flow path provided in the fuel cell; an air compressor that supplies air to the air flow path; a battery charged by the generated power generated by the fuel cell; a control device; and wherein: the control device: when the target value of the generated power is higher than the current value of the generated power, performs a first operation of charging the battery with the generated power while supplying air to the air flow path by the air compressor; when the target value of the generated power is lower than the current value of the generated power, performs a second operation of charging the battery with the generated power while supplying air to the air flow path at an air stoichiometry lower than that of the first operation by the air compressor; when the charge amount of the battery is greater than a reference charge amount, performs a power supply stop operation of stopping the power supply from the fuel cell to the battery. A fuel cell system.

2. wherein the fuel cell has a plurality of cells; and the control device performs the first operation when the variation in the output voltages of the plurality of cells is greater than a reference value when the target value of the generated power is lower than the current value of the generated power. The fuel cell system according to Claim 1.

3. The fuel cell system according to Claim 1 or 2, wherein the control device performs the first operation when the upper limit voltage is higher than the output voltage of the fuel cell when the target value of the generated power is lower than the current value of the generated power.

4. The fuel cell system according to Claim 1 or 2, wherein the charge amount of the battery increases during the second operation.

5. The fuel cell system according to Claim 1 or 2, wherein the charge amount of the battery decreases during the power supply stop operation.

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