Fuel cell system

Abstract

This fuel cell system is provided with: a plurality of fuel cell stacks; an oxidizing gas supply unit having a turbo compressor for supplying oxidizing gas to each of the plurality of fuel cell stacks; and a control device that determines, on the basis of the requested output, a requested number of operations for the plurality of fuel cell stacks, and a target supply pressure and a target supply flow rate for the oxidizing gas to be commanded to the oxidizing gas supply means. The oxidizing gas supply means has an adjustment means for adjusting the supply rate, which is the ratio of the supply flow rate supplied to the plurality of fuel cell stacks to the discharge flow rate of the turbo compressor. The control device monitors the pressure ratio in the turbo compressor, and when the pressure ratio is greater than a predetermined threshold value, the control device controls the adjustment mechanism to reduce the supply rate.

Description

Technical Field

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

[0002] Japanese Patent Application Laid-Open No. 2022-156906 describes a fuel cell system comprising a plurality of fuel cell stacks, an oxidizing gas supply unit for supplying oxidizing gas to each of the plurality of fuel cell stacks, a cooling unit for supplying a coolant for cooling each of the plurality of fuel cell stacks, and a control device for determining a target supply flow rate of the oxidizing gas to be commanded to the oxidizing gas supply unit and a target supply flow rate of the coolant to be commanded to the cooling unit.

[0003] In a fuel cell stack, the supply pressure and supply flow rate of the oxidizing gas to be supplied to the fuel cell stack are determined based on the required output (i.e., generated power) and the temperature of the fuel cell stack. For example, if the temperature of the fuel cell stack is constant, the greater the output required of the fuel cell stack, the greater the supply pressure and supply flow rate of the oxidizing gas need to be. At this time, if a turbo compressor is used for the supply of the oxidizing gas, surge may occur due to the increase in the pressure ratio in the compressor. In particular, in a fuel cell system having multiple fuel cell stacks, there is a situation where the number of fuel cell stacks in operation is reduced according to the output required of the entire system. In this case, since the output required of the fuel cell stack that continues to operate rises sharply, the risk of surge occurring becomes higher. Summary of the Invention

[0004] In view of the above-mentioned practical situation, this specification provides a technology for avoiding surge of a turbo compressor.

[0005] As mentioned above, if the output required of the fuel cell stack increases, it is necessary to increase the supply pressure and supply flow rate of the oxidant gas to the fuel cell stack. To this end, in the turbo compressor, it is necessary to increase the pressure ratio and the exhaust flow rate of the oxidant gas. In this regard, in the turbo compressor, the risk of surge due to the pressure ratio exceeding a certain upper limit value increases. Among them, this upper limit value is not constant, and the higher the exhaust flow rate of the turbo compressor, the higher the upper limit value becomes. Therefore, if the pressure ratio in the turbo compressor increases, the exhaust flow rate of the oxidant gas in the compressor can also be increased, and the surge of the compressor can be avoided. Moreover, if the ratio of the supply flow rate to the fuel cell stack to the exhaust flow rate of the oxidant gas in the compressor can be adjusted, an appropriate amount of oxidant gas can be supplied to the fuel cell stack.

[0006] Based on the above findings, the technology disclosed in this specification is embodied as a fuel cell system. In its first embodiment,

[0007] The fuel cell system has:

[0008] multiple fuel cell stacks;

[0009] an oxidizing gas supply unit having a turbo compressor for supplying oxidizing gas to each of the plurality of fuel cell stacks; and

[0010] The control device determines the required operation number of the plurality of fuel cell stacks and the target supply pressure and target supply flow rate of the oxidizing gas to be instructed to the oxidizing gas supply unit based on the required output.

[0011] The oxidizing gas supply unit includes an adjusting mechanism that adjusts a supply rate, which is a ratio of a supply flow rate to the plurality of fuel cell stacks relative to a discharge flow rate of the turbo compressor.

[0012] The control device monitors a pressure ratio in the turbo compressor, and controls the adjustment mechanism to reduce the supply rate when the pressure ratio exceeds a predetermined threshold value.

[0013] According to the above configuration, when the pressure ratio in the turbo compressor increases, for example, by reducing the number of fuel cell stacks in operation (i.e., generating electricity), the discharge flow rate of the oxidizing gas from the turbo compressor can be preferentially increased, thereby preventing turbo compressor surge.

[0014] The second method is proposed based on the above-mentioned first method, wherein:

[0015] The adjustment mechanism has:

[0016] a return flow path interconnecting the discharge side and the suction side of the turbo compressor; and

[0017] The flow regulating valve is installed in the return flow path.

[0018] According to such a configuration, the oxidizing gas can be sent from the discharge side to the suction side via the return path, and the discharge flow rate of the oxidizing gas in the turbo compressor can be preferentially increased.

[0019] The third aspect is proposed based on the first or second aspect, wherein:

[0020] The oxidizing gas supply unit further includes an intercooler that cools the oxidizing gas discharged from the turbo compressor.

[0021] In this case, the return path may connect the discharge side and the suction side of the turbo compressor to each other at a position upstream of the intercooler.

[0022] According to this configuration, since the oxidizing gas sent from the discharge side to the intake side does not pass through the intercooler, only the oxidizing gas supplied to the fuel cell stack can be cooled by the intercooler.

[0023] The fourth aspect is proposed based on the first or second aspect, wherein:

[0024] The oxidizing gas supply unit further includes an intercooler that cools the oxidizing gas exhausted from the turbo compressor.

[0025] In this case, the return path may connect the discharge side and the suction side of the turbo compressor to each other at a position downstream of the intercooler.

[0026] According to such a configuration, the temperature of the oxidizing gas sucked into the turbo compressor is lowered, and the energy required to achieve a predetermined pressure ratio in the compressor can be reduced.

[0027] The fifth aspect is proposed based on any one of the first to fourth aspects, wherein:

[0028] The oxidizing gas supply unit has:

[0029] an oxidizing gas supply path for supplying oxidizing gas from the turbo compressor to the plurality of fuel cell stacks; and

[0030] The exhaust gas discharge path discharges the exhaust gas of the oxidizing gas from the plurality of fuel cell stacks.

[0031] In this case, the adjustment mechanism may include a branch path connecting the oxidation gas supply path and the exhaust gas discharge path to each other, and a flow rate adjustment valve provided in the branch path.

[0032] According to such a configuration, the oxidizing gas can be discharged from the oxidizing gas supply path to the exhaust gas discharge path via the branch path, and the discharge flow rate of the oxidizing gas in the turbo compressor can be preferentially increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention are described below with reference to the accompanying drawings, in which like reference numerals represent like elements, wherein:

[0034] Figure 1 This is a diagram schematically showing the configuration of the fuel cell system 10 according to the first embodiment.

[0035] Figure 2 This diagram shows the relationship between the target supply pressure and the target supply flow rate of the oxidizing gas instructed by the control device 36 to the oxidizing gas supply unit 20 in accordance with the output required of the fuel cell stacks 12 and 14 .

[0036] Figure 3 2 is a diagram showing a surge limit line SL of the compressor 22 .

[0037] Figure 4 This is a flowchart showing the first process executed by the control device 36 .

[0038] Figure 5 express Figure 4 The temporal changes of various parameters in the first process are shown.

[0039] Figure 6 This is a flowchart showing the second process executed by the control device 36 .

[0040] Figure 7 This is a diagram schematically showing the configuration of a fuel cell system 110 according to the second embodiment.

[0041] Figure 8 This is a diagram schematically showing the configuration of a fuel cell system 210 according to the third embodiment. DETAILED DESCRIPTION

[0042] Example 1

[0043] The fuel cell system 10 of this embodiment will be described with reference to the accompanying drawings. The fuel cell system 10 is a power generation system that is mounted on a mobile object (e.g., an automobile, bus, truck, train, ship, airplane), a stationary fuel cell device, or the like, and outputs power in response to an external output request.

[0044] like Figure 1 As shown, the fuel cell system 10 includes a plurality of fuel cell stacks 12 and 14. Each fuel cell stack 12 and 14 has a structure in which a plurality of fuel cell cells are stacked. Each fuel cell stack 12 and 14 includes an anode side supply port (not shown), a cathode side supply port 16a, an anode side exhaust port (not shown), and a cathode side exhaust port 16b. The anode side supply port and the cathode side supply port 16a of each fuel cell stack 12 and 14 are connected to the plurality of fuel cell cells in the fuel cell stack 12 and 14, respectively. Each fuel cell stack 12 and 14 generates electricity by chemically reacting the fuel gas taken in from the anode side supply port and the oxidizing gas taken in from the cathode side supply port 16a in the plurality of fuel cell cells. The gas (i.e., exhaust gas) that has passed through the plurality of fuel cell stacks 12 and 14 is discharged to the outside from the anode side exhaust port and the cathode side exhaust port 16b.

[0045] The plurality of fuel cell stacks 12 and 14 include a first fuel cell stack 12 and a second fuel cell stack 14. In this embodiment, the first fuel cell stack 12 and the second fuel cell stack 14 are electrically connected in parallel. However, the number of the plurality of fuel cell stacks 12 and 14 is not particularly limited, as long as there are two or more. In the fuel cell system 10 of this embodiment, hydrogen is used as the fuel gas, and air is used as the oxidizing gas. Air contains oxygen as an oxidant.

[0046] like Figure 1 As shown, the fuel cell system 10 further includes multiple power control units 18. In this embodiment, the power control units 18 include boost converters. The power control units 18 are electrically connected to each of the fuel cell stacks 12 and 14. The power control units 18 are capable of boosting the power generated by the fuel cell stacks 12 and 14 and outputting it externally. Although not particularly limited, the power control units 18 may include an inverter in addition to the boost converters.

[0047] like Figure 1 As shown, the fuel cell system 10 further includes an oxidizing gas supply unit 20 and a control device 36. The oxidizing gas supply unit 20 is a unit for supplying oxidizing gas (air) to each of the plurality of fuel cell stacks 12 and 14. The oxidizing gas supply unit 20 includes a compressor 22, an intercooler 50, an oxidizing gas supply path 24, a plurality of inlet valves 26, an exhaust gas discharge path 28, a plurality of outlet valves 30, a flow diversion path 32, and a flow diversion valve 34. The control device 36 can start and stop the operation of the fuel cell stacks 12 and 14.

[0048] The compressor 22 is a turbine-type compressor. The compressor 22 is provided in the oxidizing gas supply path 24 and compresses air obtained from the outside to supply the air to the plurality of fuel cell stacks 12 and 14. The oxidizing gas supply path 24 is a path for supplying the oxidizing gas discharged from the compressor 22 to the plurality of fuel cell stacks 12 and 14. The oxidizing gas supply path 24 includes a first oxidizing gas supply path 24a and a second oxidizing gas supply path 24b. The first oxidizing gas supply path 24a is connected to the cathode-side supply port 16a of the first fuel cell stack 12 and supplies the oxidizing gas from the compressor 22 to the first fuel cell stack 12. The second oxidizing gas supply path 24b is connected to the cathode-side supply port 16a of the second fuel cell stack 14 and supplies the oxidizing gas from the compressor 22 to the second fuel cell stack 14. The first oxidizing gas supply path 24a and the second oxidizing gas supply path 24b are connected to each other at a branch point B1.

[0049] The oxidizing gas supply path 24 further includes a third oxidizing gas supply path 24c and a fourth oxidizing gas supply path 24d. The third oxidizing gas supply path 24c extends between the branch point B1 and the compressor 22, connecting the compressor 22 to the first oxidizing gas supply path 24a and the second oxidizing gas supply path 24b. The third oxidizing gas supply path 24c is located on the discharge side of the compressor 22 and supplies the oxidizing gas discharged from the compressor 22 to the first oxidizing gas supply path 24a and the second oxidizing gas supply path 24b. The fourth oxidizing gas supply path 24d is located on the intake side of the compressor 22 and supplies air obtained from the outside to the compressor 22. Although not particularly limited, the fuel cell system 10 may further include an air purifier that removes foreign matter such as dust and dirt from the air obtained from the outside.

[0050] The exhaust gas discharge path 28 is a path for discharging exhaust gas of the oxidizing gas from the plurality of fuel cell stacks 12 and 14. The exhaust gas discharge path 28 is connected to the cathode-side exhaust port 16b in each of the plurality of fuel cell stacks 12 and 14.

[0051] An intercooler 50 is provided in the third oxidizing gas supply path 24c. The intercooler 50 cools the oxidizing gas discharged from the compressor 22. Thus, the oxidizing gas discharged from the compressor 22 is cooled by the intercooler 50 before being supplied to the plurality of fuel cell stacks 12 and 14. The intercooler 50 may be water-cooled or air-cooled.

[0052] The plurality of inlet valves 26 are provided at the cathode supply port 16a in each of the plurality of fuel cell stacks 12 and 14. The plurality of outlet valves 30 are provided at the cathode exhaust port 16b in each of the plurality of fuel cell stacks 12 and 14.

[0053] The bypass path 32 connects the oxidation gas supply path 24 and the exhaust gas exhaust path 28 to each other. As an example, the bypass path 32 in this embodiment branches from the third oxidation gas supply path 24c and is connected to the exhaust gas exhaust path 28. A bypass valve 34 is provided in the bypass path 32. The inlet valve 26, the outlet valve 30 and the bypass valve 34 are control valves capable of adjusting the opening. The operation (opening) of the inlet valve 26, the outlet valve 30 and the bypass valve 34 is controlled by the control device 36. The control device 36 can adjust the supply pressure and supply flow rate of the oxidation gas supplied to the multiple fuel cell stacks 12 and 14 respectively by controlling the operation of the compressor 22, each inlet valve 26, each outlet valve 30 and the bypass valve 34.

[0054] like Figure 1As shown, the oxidizing gas supply unit 20 also includes a reflux path 52 and a reflux valve 54. The reflux path 52 connects the fourth oxidizing gas supply path 24d located on the suction side of the compressor 22 and the third oxidizing gas supply path 24c located on the discharge side of the compressor 22. A reflux valve 54 is provided in the reflux path 52. The operation (opening) of the reflux valve 54 is controlled by the control device 36. By controlling the operation of the reflux valve 54, the control device 36 can send a portion of the oxidizing gas discharged from the compressor 22 from the third oxidizing gas supply path 24c to the fourth oxidizing gas supply path 24d. Thus, the control device 36 can adjust the ratio of the supply flow rate supplied to the multiple fuel cell stacks 12 and 14 to the discharge flow rate of the compressor 22, that is, the supply rate (hereinafter, there is a case where it is simply referred to as the supply rate).

[0055] Although not shown in the figure, the fuel cell system 10 further includes a fuel gas supply unit. The fuel gas supply unit is a unit for supplying fuel gas (hydrogen gas) to the fuel cell stacks 12 and 14 .

[0056] like Figure 1 As shown, the fuel cell system 10 further includes a cooling unit 38. The cooling unit 38 is a unit for cooling each of the plurality of fuel cell stacks 12 and 14. The cooling unit 38 includes a radiator 40, a circulation path 42, a pump 44, and a plurality of temperature sensors 46 and 48. The radiator 40 releases heat from the refrigerant circulating in the circulation path 42. The circulation path 42 includes an outgoing path 42a that supplies refrigerant from the radiator 40 to the fuel cell stacks 12 and 14, and a return path 42b that returns the refrigerant from the fuel cell stacks 12 and 14 to the radiator 40. The pump 44 is provided on the outgoing path 42a.

[0057] The multiple temperature sensors 46 and 48 include a first temperature sensor 46 and a second temperature sensor 48. The first temperature sensor 46 is provided at the outlet of the first fuel cell stack 12 in the loop 42b to detect the temperature of the refrigerant after passing through the first fuel cell stack 12. The second temperature sensor 48 is provided at the outlet of the second fuel cell stack 14 in the loop 42b to detect the temperature of the refrigerant after passing through the second fuel cell stack 14. The refrigerant absorbs heat from the fuel cell cells when passing through the multiple fuel cell cells in each fuel cell stack 12 and 14. Therefore, the detection value of each temperature sensor 48, that is, the temperature of the refrigerant at the outlet of each fuel cell stack 12 and 14, is correlated with the actual temperature of the fuel cell stacks 12 and 14. Here, the actual temperature of the fuel cell stacks 12 and 14 refers to the actual temperature of the fuel cell stacks 12 and 14.

[0058] The control device 36 determines the target cooling temperature for the fuel cell stacks 12 and 14, which is instructed to the cooling unit 38. Furthermore, the control device 36 controls the pump 44 based on the detection values of the temperature sensors 46 and 48 to adjust the flow rate of the refrigerant supplied to the fuel cell stacks 12 and 14. Thus, the control device 36 cools the fuel cell stacks 12 and 14 so that the temperature of the fuel cell stacks 12 and 14 reaches the target cooling temperature. As an example, the refrigerant is water. Furthermore, in another embodiment, the fuel cell system 10 may include a separate cooling unit 38 for each fuel cell stack 12 and 14.

[0059] like Figure 1 As shown, the fuel cell system 10 further includes a first pressure sensor 56 and a second pressure sensor 58. The first pressure sensor 56 is provided in the fourth oxidizing gas supply path 24d and detects the pressure of the oxidizing gas (air) being drawn into the compressor 22. The second pressure sensor 58 is provided in the third oxidizing gas supply path 24c and detects the pressure of the oxidizing gas (air) discharged from the compressor 22. The control device 36 obtains the detection values of the pressure sensors 56 and 58. The control device 36 calculates and monitors the pressure ratio in the compressor 22 based on the detection values of the pressure sensors 56 and 58.

[0060] like Figure 1 As shown, the fuel cell system 10 further includes a third temperature sensor 60 and a flow sensor 62. The third temperature sensor 60 is provided on the outlet side of the intercooler 50 in the third oxidizing gas supply path 24c. Thus, the third temperature sensor 60 detects the temperature of the oxidizing gas after being cooled by the intercooler 50. The flow sensor 62 is provided in the fourth oxidizing gas supply path 24d and detects the flow rate of the oxidizing gas drawn by the compressor 22. The detection values of these sensors 60 and 62 are obtained by the control device 36.

[0061] The control device 36 can change the number of fuel cell stacks 12 and 14 to be operated based on the output required of the fuel cell system 10. For example, if the output required of the fuel cell system 10 is relatively low, the control device 36 stops the operation of one of the two fuel cell stacks 12 and 14. This can avoid a decrease in power generation efficiency.

[0062] Once the number of fuel cell stacks 12 and 14 to be operated is determined, the output required of each fuel cell stack 12 and 14 is determined. The supply pressure and flow rate of the oxidizing gas to each fuel cell stack 12 and 14 are determined based on the required output (i.e., generated power) and the temperature of the fuel cell stack 12 and 14. Figure 2It shows the relationship between the target supply pressure and target supply flow of the oxidizing gas that the control device 36 instructs the oxidizing gas supply unit 20 according to the output required for the fuel cell groups 12 and 14. The solid lines U1 to U4 respectively show the relationship between the supply flow of the oxidizing gas and the supply pressure of the oxidizing gas for different temperatures of the fuel cell groups 12 and 14. The dotted lines P1 to P5 respectively show the relationship between the supply flow of the oxidizing gas and the supply pressure of the oxidizing gas for different currents (i.e., generated power) of the fuel cell groups 12 and 14. Among them, the larger the number, the higher the temperature, or the greater the power. As shown in FIG. Figure 2 As shown, for example, if the temperature of the fuel cell stacks 12 and 14 is constant, the greater the output required of the fuel cell stacks 12 and 14, the greater the supply pressure and flow rate of the oxidizing gas needs to be. In particular, when the number of operating fuel cell stacks 12 and 14 decreases, the output required of the fuel cell stacks 12 (or 14) that continue to operate increases sharply, so the supply pressure and flow rate of the oxidizing gas also need to be significantly increased.

[0063] In this regard, in the fuel cell system 10 of the present embodiment, a turbo compressor 22 is used to supply the oxidizing gas. Figure 3 The surge limit line SL of the compressor 22 is shown. The dotted lines L1 to L5 respectively represent the relationship between the discharge flow rate of the oxidizing gas and the pressure ratio in the compressor 22 for different rotation speeds of the compressor 22. The larger the number, the higher the rotation speed. If the pressure ratio in the compressor 22 is increased in order to increase the supply pressure of the oxidizing gas to the fuel cell stacks 12 and 14, there is a risk of surge in the compressor 22. Therefore, if Figure 3 As shown, in the fuel cell system 10, surge limit lines SL1 and SL2 are defined for the operating point (combination of pressure ratio and discharge flow rate) of the compressor 22. Specifically, if the operating point of the compressor 22 exceeds the surge limit lines SL1 and SL2, there is a risk of surge occurring in the compressor 22. In particular, when the output required of the fuel cell stack 12 (or 14) increases rapidly, such as when the number of operating fuel cell stacks 12 and 14 decreases, the risk of the compressor 22 operating point exceeding the surge limit lines SL1 and SL2 increases.

[0064] In order to avoid surge of the compressor 22, it is necessary to maintain the operating point of the compressor 22 below the surge limit line SL1 (or SL2). Here, as shown by the surge limit line SL1 (or SL2), in the compressor 22, the risk of surge due to the pressure ratio exceeding a certain upper limit value increases. However, this upper limit value is not constant, and the higher the discharge flow rate of the compressor 22, the higher the upper limit value becomes. Therefore, when the pressure ratio in the compressor 22 increases, if the discharge flow rate of the oxidant gas in the compressor 22 is also increased, the surge of the compressor 22 can be avoided. Moreover, even when the discharge flow rate of the oxidant gas in the compressor 22 is increased, if the ratio of the supply flow rate to the fuel cell stacks 12 and 14 relative to the discharge flow rate can be adjusted, an appropriate amount of oxidant gas can be supplied to the fuel cell stacks 12 and 14.

[0065] Based on this knowledge, the control device 36 of this embodiment is configured to repeatedly execute Figure 4 The control device 36 can adjust the supply rate, which is the ratio of the supply flow rate to the plurality of fuel cell stacks 12 and 14 to the discharge flow rate of the compressor 22, by repeatedly executing the first process.

[0066] like Figure 4 As shown, the control device 36 obtains the output PR required from the outside (S10). Based on the output PR obtained in S10, the control device 36 calculates the required operating number of the fuel cell groups 12 and 14 (S12). In addition, the control device 36 calculates the target current (i.e., target generated power) for each fuel cell group 12 and 14 (S14). The control device 36 calculates the target supply pressure of the oxidizing gas instructed to the oxidizing gas supply unit 20 based on the target current determined in S14 (S16), and calculates the target supply flow rate of the oxidizing gas instructed to the oxidizing gas supply unit 20 (S18). The control device 36 of this embodiment pre-stores the relationship between the target supply pressure and the target supply flow rate of the oxidizing gas instructed to the oxidizing gas supply unit 20 (refer to Figure 2 ) map. Therefore, the control device 36 calculates the target supply pressure and target supply flow rate of the oxidizing gas corresponding to the actual number of operations based on the relationships described in the pre-stored map. The control device 36 then controls each component based on the calculated values.

[0067] The control device 36 obtains the discharge flow rate of the compressor 22 (S20). As described above, the intake flow rate of the oxidizing gas sucked into the compressor 22 is detected by the flow sensor 62. For example, when the pressure of the oxidizing gas in the third oxidizing gas supply path 24c rises, the discharge flow rate of the oxidizing gas by the compressor 22 decreases. In addition, when the oxidizing gas in the third oxidizing gas supply path 24c decreases, the discharge flow rate of the oxidizing gas by the compressor 22 increases. Moreover, the control device 36 can infer the discharge flow rate of the compressor 22 based on the detection value of the second pressure sensor 58 and the detection value of the flow sensor 62. However, as another embodiment, the fuel cell system 10 may further include a flow sensor for detecting the discharge flow rate of the compressor 22, and the control device 36 obtains the detection value of the flow sensor.

[0068] The control device 36 obtains the pressure ratio CP in the compressor 22 (S22). As described above, the control device 36 calculates the pressure ratio in the compressor 22 based on the detection values of the pressure sensors 56 and 58 and monitors the pressure ratio.

[0069] Next, the control device 36 obtains the opening WR of the return valve 54 ( S24 ). As described above, the opening WR of the return valve 54 is controlled by the control device 36 , so the control device 36 can obtain the opening WR of the return valve 54 .

[0070] The control device 36 determines whether the transition to reduce the number of fuel cell groups 12 and 14 in operation is in progress (S26). Here, the transition to reduce the number of fuel cell groups 12 and 14 in operation refers to the period from the state where both fuel cell groups 12 and 14 are in operation to the state where only one fuel cell group 12 and 14 is in operation (i.e., the state where only one fuel cell group 12 and 14 is in operation). During this period, if Figure 5 As shown in the range from time R1 to time R3 , various parameters such as the discharge flow rate of the oxidizing gas from the compressor 22 vary greatly, and surge of the compressor 22 is likely to occur. Figure 5 Graphs A to I show Figure 4 The changes of various parameters in the first process with time are shown in FIG. Figure 5 In the graph B of FIG. 1 , the curve I1 represents the current of the first fuel cell group 12, and the curve I2 represents the current of the second fuel cell group 14. Figure 5 In the graph E of FIG. 1 , the curve OV1 represents the opening degree of the outlet valve 30 of the first fuel cell stack 12, and the curve OV2 represents the opening degree of the outlet valve 30 of the second fuel cell stack 14. Figure 5 In the graph F of , a curve IV1 represents the opening degree of the inlet valve 26 of the first fuel cell stack 12 , and a curve IV2 represents the opening degree of the inlet valve 26 of the second fuel cell stack 14 .

[0071] If the answer is NO in S26, the control device 36 sets the first pressure value A1 as the surge limit pressure SP (S30). In S30, the control device 36 first adopts Figure 3 The first surge limit line SL1 shown is the surge limit line SL. The control device 36 determines the pressure value corresponding to the discharge flow rate of the compressor 22 acquired in S20 on the first surge limit line SL1 as the first pressure value A1.

[0072] On the other hand, if the answer is yes in S26, the control device 36 sets the second pressure value A2 as the surge limit pressure SP (S28). In S28, the control device 36 first adopts the second surge limit line SL2 as the surge limit line SL. The control device 36 determines the pressure value of the discharge flow rate of the compressor 22 obtained in S20 on the second surge limit line SL2 as the second pressure value A2. The second pressure value A2 is a value smaller than the first pressure value A1. Figure 3 As shown, the second surge limit line SL2 corresponds to the first surge limit line SL1 shifted downward. Therefore, if the discharge flow rate of the compressor 22 is constant, when the second surge limit line SL2 is used, the surge limit pressure SP is set lower than when the first surge limit line SL1 is used. This makes it possible to more reliably avoid surge in the compressor 22.

[0073] The control device 36 determines whether the pressure ratio CP in the compressor 22 obtained in S22 is greater than the surge limit pressure SP set in S28 or S30 (S32). If the answer is yes in S32, the control device 36 sets the target opening WT of the return valve 54 to be greater than the opening WR of the return valve 54 obtained in S24 (S34). This increases the opening of the return valve 54, increasing the amount of oxidizing gas discharged from the compressor 22 that is sent from the third oxidizing gas supply path 24c to the fourth oxidizing gas supply path 24d. In other words, the supply rate decreases. If the answer is no in S32, the control device 36 sets the target opening WT of the return valve 54 to be less than the opening WR of the return valve 54 obtained in S24 (S36).

[0074] The control device 36 calculates the target opening degree of the inlet valve 26 of the oxidizing gas supply unit 20 (S38), and calculates the target opening degree of the outlet valve 30 of the oxidizing gas supply unit 20 (S40). Next, the control device 36 calculates the target speed of the compressor 22 (S42). The control device 36 controls each part according to the calculated values and ends. Figure 4 One cycle of the first process is shown.

[0075] According to the above configuration, when the pressure ratio in the compressor 22 increases due to the reduction in the number of fuel cell stacks 12, 14 in operation (i.e., generating electricity), the discharge flow rate of the oxidizing gas in the compressor 22 can be increased preferentially. This can avoid surging of the compressor 22. Figure 4 In the first process shown, the oxidizing gas can be sent from the discharge side to the suction side via the return path 52, thereby enabling the discharge flow rate of the oxidizing gas in the compressor 22 to be increased preferentially (see Figure 5 ). The return path 52 and the return valve 54 in this specification are examples of adjustment mechanisms in the present technology. The first pressure value A1 and the second pressure value A2 in this specification are examples of predetermined threshold values for the pressure ratio in the turbo compressor in the present technology.

[0076] In this embodiment, the oxidizing gas supply unit 20 includes an intercooler 50 for cooling the oxidizing gas discharged from the compressor 22. Furthermore, a return path 52 connects the fourth oxidizing gas supply path 24d located on the intake side of the compressor 22 with the third oxidizing gas supply path 24c located on the discharge side of the compressor 22. In particular, the return path 52 is connected to the third oxidizing gas supply path 24c upstream of the intercooler 50. With this configuration, the oxidizing gas sent from the discharge side to the intake side does not pass through the intercooler 50, allowing the intercooler 50 to cool only the oxidizing gas supplied to the fuel cell stacks 12 and 14.

[0077] In the first process described above, in the transition to reduce the number of operations of the fuel cell stacks 12 and 14, the threshold value (here, the second pressure value A2) relative to the pressure ratio in the compressor 22 is set low. In the transition to reduce the number of operations of the fuel cell stacks 12 and 14, surge is more likely to occur due to large fluctuations in the discharge flow rate of the oxidizing gas in the compressor 22, the pressure ratio in the compressor 22, and the like. Therefore, according to the above-mentioned configuration, even in the transition to reduce the number of operations of the fuel cell stacks 12 and 14, surge of the compressor 22 can be avoided more reliably. In addition, in Figure 4 In the first process shown, the control device 36 may omit the processes of S26 to S30. That is, in another embodiment, the control device 36 may not set the threshold value for the pressure ratio in the compressor 22 to a low value when the number of operations of the fuel cell stacks 12 and 14 is reduced.

[0078] In addition, based on the same concept, the control device 36 of this embodiment is configured to repeatedly execute Figure 6 In the second process, instead of Figure 4The bypass path 32 and bypass valve 34 are used instead of the return path 52 and return valve 54 shown in the first process. This allows adjustment of the supply rate, which is the ratio of the flow rate supplied to the plurality of fuel cell stacks 12 and 14 to the discharge flow rate of the compressor 22. Steps S50 to S82 in the second process correspond to steps S10 to S42 in the first process. In the second process, the third pressure value A3 or the fourth pressure value A4 is set as the surge limit pressure SP (S78, S80). The fourth pressure value A4 is a value smaller than the third pressure value A3.

[0079] With this configuration, when the pressure ratio in the compressor 22 increases due to a decrease in the number of operating (i.e., generating electricity) fuel cell stacks 12 and 14, the oxidizing gas can be discharged from the oxidizing gas supply path 24 to the exhaust gas discharge path 28 via the bypass path 32. This allows the discharge flow rate of the oxidizing gas from the compressor 22 to be preferentially increased. The bypass path 32 and bypass valve 34 in this specification are examples of adjustment mechanisms in the present technology. The third pressure value A3 and the fourth pressure value A4 in this specification are examples of predetermined threshold values for the pressure ratio in the turbo compressor in the present technology.

[0080] Although not particularly limited, the control device 36 may also be configured to Figure 4 In the first process shown, the bypass path 32 and the bypass valve 34 are used in addition to the return path 52 and the return valve 54 to preferentially increase the discharge flow rate of the oxidizing gas in the compressor 22 .

[0081] Example 2

[0082] Reference Figure 7 , the fuel cell system 110 of Example 2 is described. Figure 7 As shown, in the fuel cell system 110 of the second embodiment, the position of the return path 152 is changed compared to the fuel cell system 10 of the first embodiment. The remaining structure is the same as that of the fuel cell system 10 of the first embodiment, and therefore, repeated description is omitted here.

[0083] like Figure 7 As shown, the return path 152 connects the fourth oxidizing gas supply path 24d located on the suction side of the compressor 22 and the third oxidizing gas supply path 24c located on the discharge side of the compressor 22. In particular, the return path 152 is connected to the third oxidizing gas supply path 24c at a position downstream of the intercooler 50.

[0084] Even in the above configuration, the control device 36 can repeatedly execute the first and / or second processes of the first embodiment. This prevents surging of the compressor 22. In particular, as described above, since the return path 152 is connected downstream of the intercooler 50, the temperature of the oxidizing gas drawn into the compressor 22 is lowered. Consequently, the energy required to achieve a predetermined pressure ratio in the compressor 22 can be reduced.

[0085] Example 3

[0086] Reference Figure 8 , the fuel cell system 210 of Example 3 is described. Figure 8 As shown, in the fuel cell system 210 of the third embodiment, a plurality of fuel cell stacks 12 and 14 are electrically connected in series, compared to the fuel cell system 10 of the first embodiment. The remaining structure is the same as that of the fuel cell system 10 of the first embodiment, and therefore repeated description is omitted here.

[0087] like Figure 8 As shown, the fuel cell system 210 further includes a first relay 64 and a second relay 66. The first relay 64 is provided between one pole of the first fuel cell stack 12 and one pole of the power control unit 18, and the second relay 66 is provided between the other pole of the second fuel cell stack 14 and the other pole of the power control unit 18. Figure 8 As shown, when both the first relay 64 and the second relay 66 are in the first state, the first fuel cell stack 12 and the second fuel cell stack 14 are electrically connected in series. When the first relay 64 is in the first state and the second relay 66 is in the second state (the dotted line position), the fuel cell system 10 supplies only the output from the first fuel cell stack 12 to the outside. When the second relay 66 is in the first state and the first relay 64 is in the second state (the dotted line position), the fuel cell system 10 supplies only the output from the second fuel cell stack 14 to the outside.

[0088] In the above-described configuration, the control device 36 can also repeatedly execute the first process and / or the second process in Embodiment 1. This can avoid surging of the compressor 22 .

[0089] Furthermore, the location of the return path 52 can also be changed in the fuel cell system 210 of Example 3. Specifically, as another embodiment, a fuel cell system can be employed in which a plurality of fuel cell stacks 12 and 14 are electrically connected in series, as compared to the fuel cell system 110 of Example 2. In this configuration, the control device 36 can also repeatedly execute the first process and / or the second process of Example 1, thereby preventing surging of the compressor 22.

[0090] While several specific examples have been described in detail above, these are merely illustrative and do not limit the technical solution. The technology described in the technical solution includes various modifications and variations of the specific examples described above. The technical elements described in this specification or the accompanying drawings may be used individually or in combination to achieve technical usefulness.

Claims

1. A fuel cell system, wherein: The fuel cell system comprises: multiple fuel cell stacks; an oxidizing gas supply unit having a turbo compressor for supplying oxidizing gas to each of the plurality of fuel cell stacks; and A control device determines the required operating frequency of the plurality of fuel cell stacks and the target supply pressure and target supply flow rate of the oxidizing gas to be instructed to the oxidizing gas supply unit based on the required output. The oxidizing gas supply unit includes an adjusting mechanism for adjusting a supply rate, which is a ratio of a supply flow rate to the plurality of fuel cell stacks relative to a discharge flow rate of the turbo compressor. The control device monitors a pressure ratio in the turbo compressor, and controls the adjustment mechanism to reduce the supply rate when the pressure ratio exceeds a predetermined threshold value.

2. The fuel cell system according to claim 1, wherein: The adjustment mechanism comprises: a return flow path interconnecting the discharge side and the suction side of the turbo compressor; and The flow regulating valve is provided in the return path.

3. The fuel cell system according to claim 2, wherein: The oxidizing gas supply unit further includes an intercooler for cooling the oxidizing gas discharged from the turbo compressor. The return path connects the discharge side and the suction side of the turbo compressor to each other at a position upstream of the intercooler.

4. The fuel cell system according to claim 2, wherein: The oxidizing gas supply unit further includes an intercooler for cooling the oxidizing gas discharged from the turbo compressor. The return path connects the discharge side and the suction side of the turbo compressor to each other at a position downstream of the intercooler.

5. The fuel cell system according to claim 1, wherein: The oxidizing gas supply unit includes: an oxidizing gas supply path for supplying the oxidizing gas from the turbo compressor to the plurality of fuel cell stacks; and an exhaust gas discharge path for discharging the exhaust gas of the oxidizing gas from the plurality of fuel cell stacks, The adjustment mechanism includes a branch path connecting the oxidation gas supply path and the exhaust gas discharge path to each other, and a flow rate adjustment valve provided in the branch path.

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