Fuel battery system

Abstract

To calculate a maximum value of a power that can be output to a load.SOLUTION: A fuel battery system includes: a fuel battery stack; an auxiliary device for driving the fuel battery stack; and a control device for causing the fuel battery stack to generate a power. The control device calculates a difference between a stack actual power and a system actual power as an accessory loss. The control device calculates a ratio of the auxiliary accessory loss to the stack actual power as the auxiliary accessory loss ratio. The control device calculates, as a system power limit value that is a maximum value of the power that can be output to a load, a value that takes into consideration an accessory loss ratio with respect to a stack power limit value that is the maximum value of the power that can be output from the fuel battery stack.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to fuel cell systems. [Background technology]

[0002] The fuel cell system disclosed in Patent Document 1 includes a fuel cell stack, a cathode system, an anode system, and a control device. The control device supplies anode gas from the anode system to the fuel cell stack. The control device supplies cathode gas from the cathode system to the fuel cell stack. The fuel cell stack generates electricity through a chemical reaction between the cathode gas supplied from the cathode system and the anode gas supplied from the anode system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-45620 Summary of the Invention [Problem to be solved by the invention]

[0004] The control device may limit the output power of the fuel cell stack. In this case, the control device sets a stack power limit value. The control device then controls the output power of the fuel cell stack so that it does not exceed the stack power limit value. When the output power of the fuel cell stack is supplied to a load provided outside the fuel cell system, it may be necessary to calculate the power that can be supplied to this load. [Means for solving the problem]

[0005] A fuel cell system that solves the above problem comprises a fuel cell stack, a stack power detection unit that detects the stack actual power, which is the output power of the fuel cell stack, an auxiliary device for driving the fuel cell stack, and a control device that causes the fuel cell stack to generate power, and the system power detection unit detects the system actual power, which is the power output from the fuel cell system to a load located outside the fuel cell system, and the control device calculates the difference between the stack actual power and the system actual power as auxiliary loss, calculates the ratio of the auxiliary loss to the stack actual power as an auxiliary loss ratio, and calculates a value that takes into account the auxiliary loss ratio with respect to a stack power limit value, which is the maximum value of power that the fuel cell stack can output, as a system power limit value, which is the maximum value of power that can be output to the load.

[0006] The control device calculates a value that takes into account the auxiliary equipment loss ratio with respect to the stack power limit value as the system power limit value. The output power of the fuel cell stack is also consumed by the auxiliary equipment. Therefore, the power consumed by the auxiliary equipment out of the output power of the fuel cell stack cannot be output to the load. The control device calculates the auxiliary equipment loss ratio, which is the ratio of the auxiliary equipment loss to the actual stack power. Using this, it is possible to calculate the system power limit value, which is the maximum power that can be output to the load.

[0007] The fuel cell system may include a power conversion device connected to the fuel cell stack, a first filter that reduces noise in the system actual power, and a second filter that reduces noise in the stack actual power, and the control device may measure the impedance of the fuel cell stack by controlling the power conversion device to superimpose an AC voltage on the DC voltage output by the fuel cell stack.

[0008] In the fuel cell system, when the stack actual power is 0, the control device may replace the stack actual power with a numerical value other than 0 when calculating the auxiliary equipment loss rate. [Effects of the Invention]

[0009] According to the present invention, it is possible to calculate the maximum value of power that can be output to a load. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a fuel cell system. [Figure 2] FIG. 2 is a diagram showing the relationship between the system actual power, the system power limit value, the system power command value, and the on / off state of the power generation limit flag. [Figure 3] FIG. 3 is a diagram for explaining the process of calculating the system power limit value. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of a fuel cell system will now be described. As shown in FIG. 1, the drive system 10 includes a host system 200, a heat exchanger 82, a fan 83, and a fuel cell system 20.

[0012] The host system 200 includes a load 201, a supply source 202, and a host control device 203. The load 201 is provided outside the fuel cell system 20. The load 201 is driven by power supplied from the fuel cell system 20. The supply source 202 supplies anode gas to the fuel cell system 20. The supply source 202 includes, for example, a storage unit that stores the anode gas, and a valve that adjusts the pressure of the anode gas supplied from the storage unit. The host control device 203 issues commands to the fuel cell system 20. The drive system 10 is a system that drives the load 201 by power supplied from the fuel cell system 20.

[0013] A refrigerant can flow inside the heat exchanger 82. The refrigerant is, for example, water, antifreeze, or air. A fan 83 blows air toward the heat exchanger 82. This cools the refrigerant inside the heat exchanger 82.

[0014] <Fuel cell system> The fuel cell system 20 includes a fuel cell stack 21 , a cathode system 40 , an anode system 60 , a diluter 71 , a cooling system 80 , an electrical system 90 , and a control device 110 .

[0015] The fuel cell stack 21 includes a plurality of fuel cell cells 22. The fuel cell cells 22 are polymer membrane fuel cell cells. Each fuel cell 22 includes an anode electrode, a cathode electrode, and an electrolyte membrane. The fuel cell 22 generates electricity through a chemical reaction between anode gas and cathode gas. The anode gas is hydrogen. The cathode gas is oxygen in the air.

[0016] The fuel cell stack 21 includes a cathode flow path 30 and an anode flow path 33. Air flows through the cathode flow path 30. Hydrogen flows through the anode flow path 33. The cathode flow path 30 includes an inlet 31 and an outlet 32. Air flows into the cathode flow path 30 through the inlet 31 and flows out through the outlet 32. The anode flow path 33 includes an inlet 34 and an outlet 35. Hydrogen flows into the anode flow path 33 through the inlet 34 and flows out through the outlet 35.

[0017] The cathode system 40 includes an intake port 41 , an electric compressor 42 , an inverter 44 , an intercooler 45 , a cathode supply channel 46 , a cathode discharge channel 49 , a first valve 51 , and a second valve 52 .

[0018] The intake port 41 draws air into the fuel cell system 20. The intake port 41 may be open to the atmosphere or may be connected to a gas cylinder. The electric compressor 42 includes an electric motor 43. The electric compressor 42 is driven by the electric motor 43. The electric compressor 42 supplies air to the fuel cell stack 21. Specifically, the electric compressor 42 compresses the air supplied from the intake port 41 and supplies the compressed air to the fuel cell stack 21. The air supplied from the electric compressor 42 to the fuel cell stack 21 flows through the cathode flow path 30.

[0019] The inverter 44 is connected to the electric motor 43. The inverter 44 converts DC power into AC power and supplies it to the electric motor 43. In this way, the electric motor 43 is driven.

[0020] The intercooler 45 is supplied with air discharged from the electric compressor 42. The intercooler 45 cools the air supplied from the electric compressor 42. The air supplied to the fuel cell stack 21 is the air that has been cooled by the intercooler 45.

[0021] The cathode supply path 46 connects the electric compressor 42 and the cathode flow path 30. More specifically, the cathode supply path 46 connects the electric compressor 42 and the inlet 31 of the cathode flow path 30. The cathode supply path 46 includes a first supply path 47 and a second supply path 48. The first supply path 47 connects the electric compressor 42 and the intercooler 45. The second supply path 48 connects the intercooler 45 and the cathode flow path 30.

[0022] The cathode discharge channel 49 connects the cathode flow path 30 and the diluter 71. More specifically, the cathode discharge channel 49 connects the outlet 32 ​​of the cathode flow path 30 and the diluter 71. The cathode discharge channel 49 is a passage through which the cathode exhaust gas flows. The cathode exhaust gas is air discharged from the fuel cell stack 21 and contains produced water. The produced water is water produced by power generation in the fuel cell stack 21.

[0023] The first valve 51 is provided in the cathode supply passage 46. In the present embodiment, the first valve 51 is provided in the second supply passage 48, i.e., between the intercooler 45 and the cathode flow passage 30. The first valve 51 may also be provided in the first supply passage 47, i.e., between the intercooler 45 and the electric compressor 42.

[0024] The second valve 52 is provided in the cathode discharge passage 49. The second valve 52 is a valve whose opening degree is adjustable. The anode system 60 includes a supply path 61, a circulation path 65, a gas-liquid separator 66, a circulation pump 67, an inverter 69, and an exhaust / drain valve .

[0025] The supply channel 61 connects the supply source 202 and the inlet 34 of the anode flow channel 33 . The injector 63 is provided in the supply path 61. The injector 63 injects the hydrogen supplied from the supply source 202 toward the fuel cell stack 21.

[0026] The circulation path 65 connects the outlet 35 of the anode flow path 33 and the supply path 61. The anode exhaust gas flows through the circulation path 65. The anode exhaust gas contains unreacted hydrogen and generated water. The circulation path 65 is a passage for returning the unreacted hydrogen contained in the anode exhaust gas to the supply path 61.

[0027] The gas-liquid separator 66 is provided in the circulation path 65. The gas-liquid separator 66 separates the anode exhaust gas into hydrogen and produced water. The produced water separated from the anode exhaust gas is stored in the gas-liquid separator 66.

[0028] The circulation pump 67 is provided in the circulation path 65. The circulation pump 67 includes an electric motor 68. The circulation pump 67 is driven by the electric motor 68. The circulation pump 67 supplies the hydrogen separated from the anode exhaust gas by the gas-liquid separator 66 to the supply path 61. This causes the hydrogen to circulate.

[0029] The inverter 69 is connected to the electric motor 68. The inverter 69 converts DC power into AC power and supplies it to the electric motor 68. In this way, the electric motor 68 is driven.

[0030] The exhaust / drain valve 70 is connected to the gas-liquid separator 66. The exhaust / drain valve 70 can be switched between an open state and a closed state. When the exhaust / drain valve 70 is in the open state, the produced water is discharged from the gas-liquid separator 66. In addition, exhaust is performed from the circulation path 65. When the exhaust / drain valve 70 is in the closed state, the produced water cannot be discharged from the gas-liquid separator 66. In other words, when the exhaust / drain valve 70 is in the closed state, the produced water accumulates in the gas-liquid separator 66. The exhaust / drain valve 70 is switched from the closed state to the open state at predetermined valve opening intervals.

[0031] The gas-liquid separator 66 is connected to a diluter 71. When the exhaust / drain valve 70 is opened, the produced water stored in the gas-liquid separator 66 and the anode exhaust gas are supplied to the diluter 71. The diluter 71 dilutes the anode exhaust gas with the cathode exhaust gas and discharges it into the atmosphere.

[0032] The cooling system 80 includes a refrigerant circulation path 81 , a refrigerant pump 84 , an inverter 86 , and a temperature sensor 87 . The refrigerant circulation path 81 connects the fuel cell stack 21 and the heat exchanger 82. In the refrigerant circulation path 81, a refrigerant circulates.

[0033] The refrigerant pump 84 circulates the refrigerant through the refrigerant circulation path 81. This causes the refrigerant to circulate between the fuel cell stack 21 and the heat exchanger 82. The refrigerant, whose temperature has increased due to heat exchange with the fuel cell stack 21, is cooled by heat exchange in the heat exchanger 82. The refrigerant cooled in the heat exchanger 82 is then supplied to the fuel cell stack 21, thereby cooling the fuel cell stack 21.

[0034] The refrigerant pump 84 includes an electric motor 85. The refrigerant pump 84 is driven by the electric motor 85. The refrigerant cooled in the heat exchanger 82 is supplied to the fuel cell stack 21 through the refrigerant circulation path 81, thereby cooling the fuel cell stack 21.

[0035] The inverter 86 is connected to the electric motor 85. The inverter 86 converts DC power into AC power and supplies it to the electric motor 85. In this way, the electric motor 85 is driven.

[0036] The temperature sensor 87 detects the temperature of the coolant. The temperature sensor 87 may be provided to detect the temperature of the coolant before heat exchange with the fuel cell stack 21, or may be provided to detect the temperature of the coolant after heat exchange with the fuel cell stack 21.

[0037] The electrical system 90 includes a first DC / DC converter 91 , a stack current sensor 93 , a stack voltage sensor 94 , a second DC / DC converter 95 , a system current sensor 96 , and a system voltage sensor 97 .

[0038] The first DC / DC converter 91 is connected to the fuel cell stack 21. The first DC / DC converter 91 is an example of a power conversion device. The first DC / DC converter 91 transforms the output power of the fuel cell stack 21 and outputs the transformed power. For example, the first DC / DC converter 91 transforms the output power of the fuel cell stack 21 to 48 V and outputs the transformed power. The first DC / DC converter 91 includes a switching element 92. The first DC / DC converter 91 performs the transformation by controlling the switching of the switching element 92. The output power from the first DC / DC converter 91 is supplied to a load 201 and 48 V system auxiliaries. The 48 V system auxiliaries are, for example, the electric compressor 42, the circulation pump 67, and the refrigerant pump 84.

[0039] The stack current sensor 93 detects the output current of the fuel cell stack 21 . The stack voltage sensor 94 detects the output voltage of the fuel cell stack 21. The stack voltage sensor 94 used can detect the voltages of the multiple fuel cell cells 22 individually. For example, the stack voltage sensor 94 has multiple ports, and the positive and negative electrodes of the fuel cell cells 22 are connected to each of the multiple ports. This allows the stack voltage sensor 94 to detect the voltages of the fuel cell cells 22 individually. The stack voltage sensor 94 can also detect the output voltage of the fuel cell stack 21.

[0040] The second DC / DC converter 95 is connected to the first DC / DC converter 91. The second DC / DC converter 95 transforms the output power of the first DC / DC converter 91 and outputs the transformed power. For example, the second DC / DC converter 95 transforms the output power of the first DC / DC converter 91 to 12 V and outputs the transformed power. The output power from the second DC / DC converter 95 is supplied to 12 V auxiliaries. The 12 V auxiliaries are, for example, the fan 83, the first valve 51, and the second valve 52.

[0041] The system current sensor 96 detects the output current of the fuel cell system 20. Because the output current of the fuel cell stack 21 also flows to the accessories, a difference may occur between the output current of the fuel cell stack 21 and the output current of the fuel cell system 20. The system current sensor 96 detects the current obtained by subtracting the current flowing to the accessories from the output current of the fuel cell stack 21. The accessories are devices for driving the fuel cell stack 21 and include 48V accessories and 12V accessories.

[0042] The system voltage sensor 97 detects the output voltage of the fuel cell system 20. Because the output voltage of the fuel cell stack 21 is transformed by the first DC / DC converter 91, a difference may occur between the output voltage of the fuel cell stack 21 and the output voltage of the fuel cell system 20. The system voltage sensor 97 detects the voltage output by the first DC / DC converter 91.

[0043] The control device 110 includes a processor 111 and a storage unit 112. The storage unit 112 includes a random access memory (RAM) and a read-only memory (ROM). The storage unit 112 stores program code or instructions configured to cause the processor 111 to execute processes. The storage unit 112, i.e., a computer-readable medium, includes any available medium accessible by a general-purpose or special-purpose computer. The control device 110 may be configured with hardware circuits such as an ASIC or FPGA. The control device 110, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or FPGA, or a combination thereof. The control device 110 causes the fuel cell stack 21 to generate electricity.

[0044] <Impedance measurement performed by the control device> The control device 110 measures the impedance of the fuel cell stack 21 by impedance spectroscopy. The control device 110 superimposes an AC voltage on the DC voltage of the fuel cell stack 21 by controlling the switching element 92 of the first DC / DC converter 91. The control device 110 acquires detection results from the stack current sensor 93 and the stack voltage sensor 94. The control device 110 extracts AC components from the output current and output voltage of the fuel cell stack 21. The control device 110 measures the impedance of the fuel cell stack 21 using AC impedance spectroscopy. The frequency of the AC voltage applied to the fuel cell stack 21 by the control device 110 is set so that the electrolyte membrane resistance can be measured. The electrolyte membrane resistance is a resistance value resulting from ion movement in the electrolyte membrane.

[0045] <Output limit performed by the control device> As shown in FIGS. 2(a) and 2(b), the control device 110 switches the power generation limit flag between on and off. The power generation limit flag is turned on, for example, when an abnormality occurs in the fuel cell system 20, and is turned off when no abnormality occurs in the fuel cell system 20. An abnormality in the fuel cell system 20 may be, for example, overheating of a component constituting the fuel cell system 20 or a power generation failure of the fuel cell stack 21. Overheating of a component constituting the fuel cell system 20 can be determined from the detection result of the temperature sensor 87. For example, the control device 110 may determine that overheating has occurred when the temperature detected by the temperature sensor 87 exceeds a predetermined temperature threshold. A power generation failure of the fuel cell stack 21 can be determined, for example, from the detection result of the stack voltage sensor 94. For example, the control device 110 determines that a power generation failure has occurred in the fuel cell stack 21 when there is a fuel cell 22 whose voltage is below a predetermined voltage threshold.

[0046] The control device 110 is configured to be able to communicate with the upper control device 203. The control device 110 controls the output power of the fuel cell system 20 in response to a command from the upper control device 203. A target value of the output power of the fuel cell system 20 instructed to the control device 110 by a command from the upper control device 203 is set as a system power command value.

[0047] When the power generation limit flag is off, the control device 110 controls the fuel cell stack 21 so that the output power of the fuel cell system 20 follows the system power command value. For example, the control device 110 calculates the actual system power from the detection results of the system current sensor 96 and the system voltage sensor 97. The control device 110 performs feedback control so that the actual system power follows the system power command value. The actual system output is the output power output from the fuel cell system 20 to a load 201 provided outside the fuel cell system 20. The system current sensor 96 and the system voltage sensor 97 are examples of a system power detection unit.

[0048] When the power generation limit flag is on, the control device 110 sets a system power limit value. When the system power command value is greater than the system power limit value, the control device 110 controls the system actual power so that it follows the system power limit value. When the system power command value is smaller than the system power limit value, the control device 110 controls the system actual power so that it follows the system power command value. In other words, when the power generation limit flag is on, output is limited so that the system actual power does not exceed the system power limit value. The system power limit value is the maximum value of power that can be output from the fuel cell system 20 to the load 201.

[0049] <Calculating the system power limit value> When limiting the output, the control device 110 calculates a system power limit value. As shown in FIG. 3, the fuel cell system 20 includes a first filter 121 and a second filter 122. The first filter 121 and the second filter 122 are first-order response delay filters. The time constants of the first filter 121 and the second filter 122 are, for example, 100 ms. The control device 110 inputs the system actual power to the first filter 121. The first filter 121 filters the system actual power and outputs it. This reduces noise in the system actual power. The control device 110 inputs the stack actual power to the second filter 122. The second filter 122 filters the stack actual power and outputs it. This reduces noise in the stack actual power. The stack actual power can be calculated from the detection results of the stack current sensor 93 and the stack voltage sensor 94. The stack current sensor 93 and the stack voltage sensor 94 are examples of a stack power detection unit.

[0050] The fuel cell system 20 includes a subtractor 123. The subtractor 123 receives the system actual power output from the first filter 121 and the stack actual power output from the second filter 122. The subtractor 123 subtracts the system actual power from the stack actual power. This provides an auxiliary loss, which is the difference between the stack actual power and the system actual power. The auxiliary loss is the power consumed by the auxiliary equipment out of the stack actual power.

[0051] The fuel cell system 20 includes a divider 124. The divider 124 receives the stack actual power and the auxiliary loss output from the second filter 122. The divider 124 divides the auxiliary loss by the stack actual power. The value obtained as a result is the auxiliary loss ratio. The auxiliary loss ratio is the ratio of the power consumed by the auxiliary to the stack actual power. If the stack actual power is 0, the control device 110 replaces the stack actual power with a value other than 0 and inputs it to the divider 124. For example, the control device 110 inputs the maximum value that the stack actual power can take to the divider 124. For example, if the stack actual power is expressed in 16 bits, the maximum value of 16 bits can be input to the divider 124.

[0052] The fuel cell system 20 includes an upper and lower limit guard unit 125. An auxiliary equipment loss rate is input to the upper and lower limit guard unit 125. The upper and lower limit guard unit 125 corrects the auxiliary equipment loss rate when an abnormal value occurs in the auxiliary equipment loss rate. When the auxiliary equipment loss rate exceeds a predetermined upper limit value, the upper and lower limit guard unit 125 corrects the auxiliary equipment loss rate to the upper limit value and outputs it. When the auxiliary equipment loss rate is below a predetermined lower limit value, the upper and lower limit guard unit 125 corrects the auxiliary equipment loss rate to the lower limit value and outputs it. When the auxiliary equipment loss rate is a value between the upper limit value and the lower limit value, the upper and lower limit guard unit 125 outputs the input auxiliary equipment loss rate without correcting it.

[0053] The fuel cell system 20 includes a subtractor 126. The subtractor 126 receives the auxiliary equipment loss rate output from the upper / lower limit guard unit 125 and 1 as input. The subtractor 126 subtracts the auxiliary equipment loss rate from 1 and outputs the result. The value obtained in this way is the rate of power that is not consumed by the auxiliary equipment out of the stack actual power. In other words, it is the rate of power that can be output from the fuel cell system 20 out of the stack actual power. The value output from the subtractor 126 is the system output rate.

[0054] The fuel cell system 20 includes a multiplier 127. The multiplier 127 receives as input a stack power limit value and a system output rate. The stack power limit value is the maximum value of power that the fuel cell stack 21 can output when limiting the output. The stack power limit value is calculated by the control device 110. The control device 110 calculates the stack power limit value in response to, for example, overheating of components that make up the fuel cell system 20 or a power generation failure of the fuel cell stack 21.

[0055] The control device 110 multiplies the stack power limit value by the system output rate to obtain the system power limit value. In this way, the rate excluding the auxiliary equipment loss rate from the stack power limit value becomes the system power limit value. The control device 110 transmits the system power limit value to the upper control device 203.

[0056] [Operation of this embodiment] If an abnormality occurs in the fuel cell stack 21, the control device 110 limits the output power of the fuel cell stack 21. At this time, the control device 110 sets a stack power limit value. The auxiliary equipment is driven by the output power of the fuel cell stack 21. Therefore, when power is supplied from the fuel cell system 20 to a load 201 external to the fuel cell system 20, the power that can be supplied to the load 201 will be lower than the stack power limit value.

[0057] The control device 110 may wish to calculate the power that can be supplied to the load 201, i.e., the system power limit value. For example, the control device 110 may wish to notify the upper control device 203 of the system power limit value. When the upper control device 203 transmits a system power command value to the control device 110, if the upper control device 203 does not recognize the system power limit value, the control device 110 may transmit a system power command value that is higher than the system power limit value. By the control device 110 notifying the upper control device 203 of the system power limit value, the upper control device 203 can transmit a system power command value that is equal to or less than the system power limit value to the control device 110.

[0058] In this embodiment, the system power limit value is calculated by taking into account the auxiliary equipment loss rate with respect to the stack power limit value. Specifically, the control device 110 multiplies the stack power limit value by 100 [%] minus the percentage [%] of the auxiliary equipment loss rate, and calculates the system power limit value, which is the maximum value of power that can be output to the load 201. By reflecting the auxiliary equipment loss rate, it is possible to calculate a system power limit value that takes into account the power consumption by the auxiliary equipment.

[0059] It is also possible to use the value obtained by subtracting the auxiliary loss from the stack power limit as the system power limit. However, because the auxiliary loss varies depending on the stack actual power and the system actual power, if the system power limit and the system actual power do not match, the correct system power limit may not be calculated. For example, assume that the system power command value from the upper control device 203 is 3 [kW]. In this case, the auxiliary loss for the system actual power of 3 [kW] is calculated. In this case, if the stack power limit is 11 [kW], the system power limit is calculated based on the auxiliary loss for the system actual power of 3 [kW]. If the auxiliary loss for the system actual power of 3 [kW] does not correspond to the auxiliary loss for the stack power limit of 11 [kW], a difference will occur between the calculated auxiliary loss and the actual auxiliary loss. If the system power limit calculated based on this auxiliary loss is 7 [kW], the upper control device 203 may set the system power command value to 7 [kW]. Then, the auxiliary loss for the system actual power of 7 [kW] is calculated. In this case, the increased system power command value increases the auxiliary loss, causing the system power limit value to be lower than 7 kW. As a result, the system power limit value becomes lower in a short period of time, which may reduce the stability of the fuel cell system 20.

[0060] In contrast, in the embodiment, the system power limit value is calculated using the auxiliary loss ratio. By calculating the auxiliary loss as a ratio, even if the system power limit value and the system actual power do not match, it is possible to calculate a system power limit value with less error. More specifically, the auxiliary loss ratio is less likely to fluctuate due to fluctuations in the stack actual power and the system actual power. Therefore, it is possible to calculate a system power limit value with less error.

[0061] [Effects of this embodiment] (1) The control device 110 calculates the system power limit value by multiplying the stack power limit value by 100 [%] - the auxiliary equipment loss rate [%]. The output power of the fuel cell stack 21 is also consumed by the auxiliary equipment. Therefore, the power consumed by the auxiliary equipment out of the output power of the fuel cell stack 21 cannot be output to the load 201. The control device 110 calculates the auxiliary equipment loss rate, which is the rate of the auxiliary equipment loss to the stack actual power. Using this, it is possible to calculate the system power limit value, which is the maximum value of power that can be output to the load 201.

[0062] (2) The control device 110 controls the first DC / DC converter 91 to superimpose an AC voltage on the DC voltage output by the fuel cell stack 21, and measures the impedance of the fuel cell stack 21. By superimposing an AC voltage, the stack actual power and system actual power contain AC components as noise. By reducing noise using the first filter 121 and the second filter 122, it is possible to suppress the influence of noise generated during impedance measurement. This makes it possible to reduce errors in auxiliary loss.

[0063] (3) When the stack actual power is 0, the control device 110 replaces the stack actual power with a value other than 0 when calculating the auxiliary equipment loss ratio. This makes it possible to calculate the auxiliary equipment loss ratio even when the stack actual power is 0.

[0064] In the embodiment, the maximum value that the stack actual power can take is used as a numerical value other than 0. When the stack actual power is 0, the auxiliary loss is 0. By calculating the auxiliary loss ratio using the maximum value that the stack actual power can take, the auxiliary loss ratio can be made closer to 0. Therefore, the difference between the actual auxiliary loss ratio and the calculated auxiliary loss ratio can be made smaller.

[0065] [Example of change] The embodiment can be modified as follows: The embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0066] The fuel cell system 20 does not have to include the first filter 121 and the second filter 122. In this case, the control device 110 may measure the impedance of the fuel cell stack 21 using a method that does not superimpose an AC voltage on a DC voltage.

[0067] The fuel cell system 20 does not have to include the upper and lower limit guard units 125. [Explanation of symbols]

[0068] 20...fuel cell system, 21...fuel cell stack, 91...first DC / DC converter which is a power conversion device, 93...stack current sensor, 94...stack voltage sensor, 96...system current sensor, 97...system voltage sensor, 110...control device, 121...first filter, 122...second filter, 201...load.

Claims

1. a fuel cell stack; a stack power detection unit that detects a stack actual power, which is the output power of the fuel cell stack; an auxiliary device for driving the fuel cell stack; a control device that causes the fuel cell stack to generate power, a system power detection unit that detects a system actual power, which is power output from the fuel cell system to a load provided outside the fuel cell system; The control device A difference between the stack actual power and the system actual power is calculated as an auxiliary loss; Calculating a ratio of the auxiliary loss to the stack actual power as an auxiliary loss ratio; A fuel cell system that calculates a system power limit value, which is the maximum power that can be output to the load, by taking into account the auxiliary equipment loss rate with respect to a stack power limit value, which is the maximum power that can be output by the fuel cell stack.

2. The fuel cell system includes: a power conversion device connected to the fuel cell stack; a first filter for reducing noise in the system real power; a second filter for reducing noise in the stack real power; 2. The fuel cell system according to claim 1, wherein the control device measures the impedance of the fuel cell stack by controlling the power conversion device to superimpose an AC voltage on a DC voltage output from the fuel cell stack.

3. 3. The fuel cell system according to claim 1, wherein when the stack actual power is zero, the control device replaces the stack actual power with a value other than zero when calculating the auxiliary equipment loss rate.

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