Fuel battery system
The fuel cell system addresses power output limitations by using a control unit to calculate and control power based on stack and auxiliary equipment losses, enabling efficient and reliable power delivery to external loads.
Patent Information
- Application Number
- JP2024041271
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-03-15
- Publication Date
- 2025-09-29
AI Technical Summary
Existing fuel cell systems face challenges in accurately calculating and controlling the power output to external loads due to limitations imposed by the fuel cell stack and auxiliary equipment, leading to inefficiencies and potential overloading.
A fuel cell system that includes a control unit capable of calculating a power limit value based on the maximum output power of the fuel cell stack and auxiliary equipment losses, using a map or calculated values to determine a system power target value, and controlling the fuel cell system to ensure the output current follows this target, thereby accounting for both stack and auxiliary power consumption.
This approach allows for precise calculation of the maximum power that can be supplied to external loads, preventing overloading and ensuring efficient operation throughout the designed life of the fuel cell stack by considering degradation and auxiliary equipment losses.
Smart Images
Figure 2025141373000001_ABST
Abstract
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 unit. The control unit supplies anode gas from the anode system to the fuel cell stack. The control unit 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 unit may limit the output power of the fuel cell stack. In this case, the control unit sets a stack power limit value. The control unit 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 an external load provided outside the fuel cell system, it may be necessary to calculate the power that can be supplied to this external load. [Means for solving the problem]
[0005] A fuel cell system that solves the above problem comprises a fuel cell stack electrically connected to an external load, auxiliary equipment that operates using the power generated by the fuel cell stack, and a control unit, wherein the control unit calculates a power limit value for the fuel cell stack based on the maximum output power of the fuel cell stack and a limit value, determines a power limit value for the fuel cell system from the power limit value of the fuel cell stack, sets the smaller of a command value from the external load that commands the output power of the fuel cell system and the power limit value of the fuel cell system as a system power target value, calculates a current target value for the fuel cell stack from the power supplied to the external load and the system power target value, and controls the fuel cell system so that the output current of the fuel cell stack follows the current target value, and when determining the power limit value for the fuel cell system from the power limit value of the fuel cell stack, determines the power limit value for the fuel cell system based on a map based on the correlation between the power limit value of the fuel cell stack and losses in the auxiliary equipment, or based on a value calculated from the power limit value of the fuel cell stack.
[0006] The output power of the fuel cell stack is also consumed by the auxiliary equipment. Therefore, the power consumed by the auxiliary equipment cannot be output to an external load. The control unit determines the power limit value of the fuel cell system based on a map or a calculated value. This makes it possible to determine the maximum power that can be supplied from the fuel cell system to an external load.
[0007] In the above fuel cell system, when the control unit calculates the power limit value of the fuel cell system from the power limit value of the fuel cell stack, the control unit may calculate the power limit value of the fuel cell system based on the output current of the fuel cell stack over the design life of the fuel cell stack.
[0008] In the above fuel cell system, the control unit may transmit a power limit value of the fuel cell system to the external load. [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 calculation logic for the power limit value of the fuel cell stack. [Figure 3] FIG. 3 is a diagram showing the calculation logic for the current target value of the fuel cell stack. [Figure 4] FIG. 4 is a diagram showing a map in which stack power limit values and system power limit values are associated with each other. [Figure 5] FIG. 5 is a diagram showing the correspondence relationship between the stack power limit value and the post-degradation current. [Figure 6] FIG. 6 is a diagram showing the correspondence relationship between the stack power limit value and the power consumption of the compressor. [Figure 7] FIG. 7 is a diagram showing the correspondence relationship between the stack power limit value and the DC / DC power consumption. [Figure 8] FIG. 8 is a diagram showing the correspondence relationship between the stack power limit value and the WP power consumption. [Figure 9] FIG. 9 is a diagram showing the correspondence relationship between the stack power limit value and the HP power consumption. [Figure 10] FIG. 10 is a diagram showing the correspondence relationship between the stack power limit value and 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 an external load 200, a heat exchanger 82, a fan 83, and a fuel cell system 20.
[0012] The external load 200 includes a load 201, a supply source 202, and a host controller 203. The external load 200 is provided outside the fuel cell system 20. As will be described later, the load 201 of the external load 200 operates when power generated by the fuel cell stack 21 is supplied to it via a DC / DC converter 91. 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 controller 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 unit 110 .
[0015] The fuel cell stack 21 includes a plurality of fuel cell units 22. Each fuel cell unit 22 is a solid polymer membrane fuel cell. Each fuel cell unit 22 includes an anode electrode, a cathode electrode, and an electrolyte membrane. Each fuel cell unit 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 DC / DC converter 91 , a stack current sensor 93 , a stack voltage sensor 94 , a system current sensor 96 , and a system voltage sensor 97 . The DC / DC converter 91 is connected to the fuel cell stack 21. The DC / DC converter 91 transforms the output power of the fuel cell stack 21 and outputs the transformed power. The DC / DC converter 91 transforms the output power of the fuel cell stack 21 to, for example, 350 V and outputs the transformed power. The DC / DC converter 91 includes a switching element 92. The DC / DC converter 91 performs the transformation by controlling the switching of the switching element 92. The DC / DC converter 91 is electrically connected to the load 201, the electric compressor 42, the circulation pump 67, and the refrigerant pump 84. The output power from the DC / DC converter 91 is supplied to the load 201, the electric compressor 42, the circulation pump 67, and the refrigerant pump 84.
[0038] 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.
[0039] 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 auxiliary equipment, 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 auxiliary equipment from the output current of the fuel cell stack 21. Examples of the auxiliary equipment include the electric compressor 42, the circulation pump 67, the refrigerant pump 84, and the DC / DC converter 91. The auxiliary equipment operates using the power generated by the fuel cell stack 21.
[0040] 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 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 DC / DC converter 91.
[0041] The control unit 110 includes a processor 111 and a memory unit 112. The memory unit 112 includes a random access memory (RAM) and a read-only memory (ROM). The memory unit 112 stores program code or instructions configured to cause the processor 111 to execute processes. The memory unit 112, i.e., a computer-readable medium, includes any available medium accessible by a general-purpose or special-purpose computer. The control unit 110 may be configured with a hardware circuit such as an ASIC or FPGA. The control unit 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 unit 110 causes the fuel cell stack 21 to generate electricity.
[0042] The control unit 110 is configured to be able to communicate with the upper control device 203. The control unit 110 controls the output power of the fuel cell system 20 in response to commands from the upper control device 203. A command value from the upper control device 203 that commands the output power of the fuel cell system 20 is referred to as a system power command value. The output power of the fuel cell system 20 is referred to as system output power. The system output power is the power supplied to the external load 200. The output power of the fuel cell stack 21 is referred to as stack output power.
[0043] <Output restriction by the control unit> The control unit 110 limits the output of the fuel cell stack 21. The output of the fuel cell stack 21 is limited, for example, when an abnormality occurs in the fuel cell system 20. The abnormality in the fuel cell system 20 is, 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 unit 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 unit 110 determines that a power generation failure of the fuel cell stack 21 has occurred when there is a fuel cell 22 whose voltage is below a predetermined voltage threshold.
[0044] As shown in FIG. 2 , the control unit 110 calculates the power limit value [kW] of the fuel cell stack 21 by multiplying the maximum output power [kW] of the fuel cell stack 21 by the limit rate [%]. The maximum output power of the fuel cell stack 21 is the maximum value of power that the fuel cell stack 21 can output. The limit rate can take a value of 100% or less. When the output of the fuel cell stack 21 is not limited, the limit rate is 100%. When the output of the fuel cell stack 21 is limited, the limit rate is a value less than 100%. The lower the limit rate, the lower the power limit value of the fuel cell stack 21. The limit rate is calculated according to the state of the fuel cell system 20. For example, the higher the temperature detected by the temperature sensor 87 is above the temperature threshold, the lower the limit rate is set by the control unit 110. The limit rate is an example of a limit value. The power limit value of the fuel cell stack 21 is the maximum value of output power permitted for the fuel cell stack 21. The power limit value of the fuel cell stack 21 is appropriately referred to as a stack power limit value. The control unit 110 controls the output power of the fuel cell stack 21 so that it does not exceed the stack power limit value.
[0045] As shown in Fig. 3, the control unit 110 controls the system output power [kW] by using both feedforward control and feedback control. More specifically, the control unit 110 controls the system output power by controlling the target current value of the fuel cell stack 21. The feedback control in this embodiment is PI control. The feedback control may also be PID control.
[0046] The control unit 110 includes a system power limiting unit 121. The system power limiting unit 121 is a functional element included in the control unit 110. The system power limiting unit 121 calculates a power limit value for the fuel cell system 20. The power limit value for the fuel cell system 20 is the maximum power that the fuel cell system 20 can output. The power limit value for the fuel cell system 20 is set as the system power limit value as appropriate. The system power limiting unit 121 compares a system power command value input from the upper control device 203 with the system power limit value calculated by the system power limiting unit 121. If the system power command value is greater than the system power limit value, the system power limiting unit 121 replaces the system power command value with the system power limit value and outputs it. If the system power command value is smaller than the system power limit value, the system power limiting unit 121 outputs the system power command value. If appropriate, the system power command value or the system power limit value output from the system power limiting unit 121 is set as the system power target value. The smaller of the system power command value and the system power limit value becomes the system power target value.
[0047] The control unit 110 obtains a FF term (feedforward term) from the system power target value. The FF term can be obtained from, for example, the current-voltage characteristics of the fuel cell stack 21 and a feedforward gain.
[0048] The control unit 110 calculates an FB term (feedback term) from the system output power and the system power target value. The system output power can be calculated from the detection results of the system current sensor 96 and the system voltage sensor 97. The control unit 110 calculates the difference between the system output power and the system power target value as the output deviation. The control unit 110 calculates the FB term from the output deviation, proportional gain, and integral gain. More specifically, the control unit 110 calculates the proportional term from the output deviation and proportional gain, and calculates the integral term from the output deviation and integral gain. The control unit 110 determines the sum of the proportional term and the integral term as the FB term.
[0049] The control unit 110 adds the FF term and the FB term. The value obtained by this addition is the current target value of the fuel cell stack 21. The control unit 110 controls the fuel cell system 20 so that the output current of the fuel cell stack 21 follows the current target value. More specifically, the control unit 110 controls the electric compressor 42 and the injector 63 to make the output current of the fuel cell stack 21 follow the current target value. The current target value is a value calculated to reduce the output deviation. Therefore, the system output power is controlled to follow the system power target value.
[0050] <System power limiter> The system power limiting unit 121 will now be described in detail. The system power limiting unit 121 obtains a system power limit value from the stack power limit value. In this embodiment, the system power limiting unit 121 obtains the system power limit value from a one-dimensional map M1 that indicates the correspondence between the stack power limit value and the system power limit value. The map M1 is stored in a storage device that stores data that can be read by the control unit 110. The storage device may be the storage unit 112, or may be an external storage device provided separately from the storage unit 112.
[0051] As shown in Fig. 4, map M1 associates system power limit values with specified stack power limit values. In the example shown in Fig. 4, the specified values are 10, 15, 20, 30, 40, 50, 60, and 70 kW. When the stack power limit value is a specified value, the system power limiting unit 121 obtains the system power limit value corresponding to the specified value from map M1. When the stack power limit value is a value different from the specified value, the system power limiting unit 121 obtains a value obtained by linear interpolation from map M1. For example, if the stack power limit value is 12 kW, the system power limit value corresponding to the stack power limit value of 12 kW can be obtained by linear interpolation between the system power limit value when the stack power is 10 kW and the system power limit value when the stack power is 15 kW.
[0052] When the control unit 110 determines the system power limit value, it transmits the system power limit value to the external load 200 , more specifically, to the upper control device 203 . <Map> The method for creating the map M1 will now be described.
[0053] The difference between the stack output power and the system output power is caused by losses due to the auxiliaries. Therefore, the system power limit value corresponding to the stack power limit value can be obtained by subtracting the losses due to the auxiliaries when the stack power limit value is being output from the stack power limit value. In this embodiment, the map M1 is created assuming a case where the losses due to the auxiliaries are at their maximum. The losses due to the auxiliaries will be referred to as "auxiliary loss" where appropriate.
[0054] As the fuel cell stack 21 deteriorates, the output voltage of the fuel cell stack 21 decreases. When the output voltage of the fuel cell stack 21 decreases, it is necessary to increase the output current of the fuel cell stack 21 in order to output the same amount of power. When the output current of the fuel cell stack 21 increases, the auxiliary loss increases. Therefore, when assuming a case where the auxiliary loss is at its maximum, the auxiliary loss is calculated assuming the output current from the fuel cell stack 21 after deterioration. The deteriorated fuel cell stack 21 is, for example, the fuel cell stack 21 after a predetermined period has passed since manufacture. The predetermined period is, for example, the design life set by the manufacturer of the fuel cell stack 21. The design life is, for example, 10 years from manufacture and 20,000 hours of use.
[0055] 5 shows the output current of the fuel cell stack 21 after deterioration that is required to output a specified stack power limit value. The output current of the fuel cell stack 21 after deterioration can be obtained, for example, by experiment. The output current of the fuel cell stack 21 after deterioration will be referred to as the post-deterioration current [A] as appropriate.
[0056] The post-degradation current is the current required to output the specified stack power limit value. Therefore, this post-degradation current can be used to determine the auxiliary device drive amount required to output the specified stack power limit value. Then, the auxiliary device loss can be calculated using the drive amount required to drive the auxiliary device and the post-degradation current.
[0057] <Losses caused by electric compressor> As shown in Fig. 6, the loss due to the electric compressor 42 is calculated for each specified value of the stack power limit value. The loss due to the electric compressor 42 is defined as compressor power consumption [kW]. The loss due to the electric compressor 42 is an example of auxiliary machine loss.
[0058] 6, the minimum air flow rate required to achieve the target value of the output power of the fuel cell stack 21 is denoted as the required air St1.0 flow rate [NL / min]. The required air St1.0 flow rate can be calculated based on, for example, the current flowing from the fuel cell stack 21, the number of fuel cell units 22, Faraday's constant, the volume occupied by 1 mole of oxygen, etc.
[0059] The air stoichiometry of the fuel cell stack 21 varies depending on the temperature of the refrigerant circulating through the refrigerant circuit 81. The air stoichiometry is the ratio of the actual air flow rate to the minimum air flow rate required to achieve the target value of the output power of the fuel cell stack 21.
[0060] The lower the temperature of the refrigerant, the higher the air stoichiometry needs to be. The higher the air stoichiometry, the higher the rotation speed of the electric compressor 42 needs to be. The rotation speed of the electric compressor 42 is the rotation speed of the electric motor 43. In this embodiment, the lowest possible temperature of the refrigerant is assumed, and the air stoichiometry required for that temperature is assumed.
[0061] The target air flow rate [NL / min] required to achieve air stoichiometry can be calculated by multiplying the required air St1.0 flow rate by the air stoichiometry. The pressure of the air supplied to the fuel cell stack 21 varies depending on the temperature of the refrigerant circulating through the refrigerant circuit 81. The higher the temperature of the refrigerant, the higher the air pressure required for power generation in the fuel cell stack 21 must be. The higher the air pressure required for power generation in the fuel cell stack 21, the higher the rotation speed of the electric compressor 42 must be. In this embodiment, the highest possible temperature of the refrigerant is assumed, and the air pressure required for that temperature is assumed. The air supplied to the fuel cell stack 21 is air that has passed through the intercooler 45, so the air pressure referred to here is the pressure at the outlet of the intercooler 45. This pressure is referred to as IC outlet air pressure in Figure 6.
[0062] The compressor power consumption is calculated based on the target air flow rate required to achieve air stoichiometry and the IC outlet air pressure. The rotational speed of the electric compressor 42 required to achieve the target air flow rate and the IC outlet air pressure required to achieve air stoichiometry is acquired as acquired data. The acquired data can be obtained, for example, by experiment or simulation. The power consumption when the electric compressor 42 is driven at the rotational speed obtained from the acquired data is then defined as the compressor power consumption. The power consumption when the electric compressor 42 is driven at the rotational speed obtained from the acquired data can be obtained, for example, by experiment or simulation.
[0063] As an example, we will explain how to calculate the compressor power consumption X11 when the stack power limit value is 10 kW. The required air St1.0 flow rate Y1 required to output 10 kW of output power is calculated. The air stoichiometry Y11 required to output 10 kW of output power when the refrigerant temperature is at its lowest is calculated. The target air flow rate Y21 is calculated by multiplying the required air St1.0 flow rate Y1 by the air stoichiometry Y11. The IC outlet air pressure Y31 required to output 10 kW of output power when the refrigerant temperature is at its highest is calculated. The rotational speed of the electric compressor 42 required to achieve the target air flow rate Y21 and the IC outlet air pressure Y31 is calculated as acquired data Y41. Then, the compressor power consumption X11 required to achieve the rotational speed of the electric compressor 42 represented by the acquired data Y41 using the post-degradation current X1 is calculated. The compressor power consumptions X12 to X18 can be calculated similarly for the other specified values.
[0064] <Losses from other auxiliary equipment> As shown in FIG. 7, the loss due to the DC / DC converter 91 is calculated for each specified value of the stack power limit value. The loss due to the DC / DC converter 91 is an example of auxiliary equipment loss. The loss due to the DC / DC converter 91 is defined as DC / DC power consumption [kW]. The loss due to the DC / DC converter 91 can be obtained, for example, by experiment or simulation. It has been found through experiment that the DC / DC converter 91 in this embodiment loses approximately 5% of the output power of the fuel cell stack 21. Therefore, the specified value multiplied by 0.05 can be used as the DC / DC power consumption. In the example shown in FIG. 7, X21 is 10×0.05, which is 0.5 [kW].
[0065] As shown in Fig. 8, the loss due to the refrigerant pump 84 is calculated for each specified value of the stack power limit value. The loss due to the refrigerant pump 84 is an example of auxiliary machine loss. The loss due to the refrigerant pump 84 is defined as the WP power consumption [kW]. In this embodiment, the power consumption when the refrigerant pump 84 has the maximum rotation speed is defined as the WP power consumption. Therefore, the WP power consumptions X31 to X38 corresponding to the specified values are the same value. If the maximum possible rotation speed of the refrigerant pump 84 differs depending on the specified value, the WP power consumptions X31 to X38 may be different values.
[0066] As shown in Fig. 9, the loss due to the circulation pump 67 is calculated for each specified value of the stack power limit value. The loss due to the circulation pump 67 is an example of auxiliary machine loss. The loss due to the circulation pump 67 is defined as HP power consumption [kW]. In this embodiment, the power consumption of the circulation pump 67 when the system output power is at its maximum is defined as the HP power consumption. Therefore, the HP power consumptions X41 to X48 corresponding to the specified values are the same value. If the maximum possible rotation speed of the circulation pump 67 differs depending on the specified value, the HP power consumptions X41 to X48 may be different values.
[0067] <Map Selection> As shown in FIG. 10, the compressor power consumption, DCDC power consumption, WP power consumption, and HP power consumption can be obtained from the above results corresponding to the specified values. Then, by adding up the compressor power consumption, DCDC power consumption, WP power consumption, and HP power consumption corresponding to each specified value, the auxiliary loss when outputting the stack power limit value corresponding to the specified value can be obtained. In the example shown in FIG. 10, if the specified value is 10 kW, the auxiliary loss is X11 + X21 + X31 + X41. The previous system power limit value is the value obtained by subtracting the auxiliary loss corresponding to each specified value from each specified value. In other words, the previous system power limit value is a calculated system power limit value.
[0068] The system output power has a lower limit. A system output power lower than the lower limit cannot be output. Therefore, if the previous system power limit value falls below the lower limit of the system output power, the system power limit value is set to 0. For example, if X51 shown in FIG. 10 falls below the lower limit of the system output power, X61 is set to 0. Furthermore, even if the previous system power limit value is not below the lower limit of the system output power, if the value is within a predetermined range from the lower limit, the system power limit value may be set to 0. For example, if X52 is within a predetermined range from the lower limit of the system output power, X62 may be set to 0. If the previous system power limit value is greater than the lower limit of the system output power and is outside the predetermined range from the lower limit, the system power limit value is set to the same value as the previous system power limit value. For example, if X53 is greater than the lower limit of the system output power and is outside the predetermined range from the lower limit, X63 is set to the same value as X53.
[0069] In this way, the system power limit value is obtained corresponding to the specified value of the stack power limit value. The system power limit value corresponding to 10 [kW] is X61. The system power limit value corresponding to 15 [kW] is X62. The system power limit value corresponding to 20 [kW] is X63. The system power limit value corresponding to 30 [kW] is X64. The system power limit value corresponding to 40 [kW] is X65. The system power limit value corresponding to 50 [kW] is X66. The system power limit value corresponding to 60 [kW] is X67. The system power limit value corresponding to 70 [kW] is X68. This relationship is then determined as map M1.
[0070] The system power limit value is the stack power limit value minus the auxiliary equipment loss, and therefore the map M1 is based on the correlation between the stack power limit value and the auxiliary equipment loss. [Operation of this embodiment] If an abnormality occurs in the fuel cell system 20, the control unit 110 limits the output power of the fuel cell stack 21. At this time, the control unit 110 sets a stack power limit value. The auxiliary equipment operates using the output power of the fuel cell stack 21. Therefore, when power is supplied from the fuel cell system 20 to the external load 200, the power that can be supplied to the external load 200 becomes lower than the stack power limit value.
[0071] The control unit 110 may wish to calculate the maximum value of power that can be supplied to the external load 200, i.e., the system power limit value. For example, the control unit 110 controls the fuel cell stack 21 according to the output deviation between the system power target value and the system output power. When the output of the fuel cell stack 21 is limited, the system power command value may become larger than the maximum value of the system output power that can be output. In this case, the output deviation cannot be reduced. In contrast, by setting a system power limit value, if the system power command value is larger than the system power limit value, the system power target value can be set to the system power limit value. This makes it possible to prevent situations in which the output deviation cannot be reduced.
[0072] [Effects of this embodiment] (1) The control unit 110 can obtain a system power limit value corresponding to the stack power limit value. The system power limit value is the maximum power that can be supplied from the fuel cell system 20 to the external load 200. Therefore, the maximum power that can be supplied from the fuel cell system 20 to the external load 200 can be obtained.
[0073] (2) Map M1 is created based on the post-degradation current. As a result, when calculating the system power limit value, the system power limit value is calculated based on the post-degradation current. If the system power limit value is calculated based on the post-degradation current, the value of the auxiliary equipment loss will be large. As a result, it is possible to prevent the system power limit value from exceeding the power that the fuel cell system 20 can actually output until the end of the designed life of the fuel cell stack 21.
[0074] (3) The control unit 110 transmits the system power limit value to the external load 200. This allows the system power limit value to be used for control in the external load 200. For example, the upper control device 203 can perform control so that the system power command value does not exceed the system power limit value.
[0075] [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.
[0076] The map M1 does not have to be created using the post-deterioration current. For example, the map M1 may be created using the output current at the time of manufacturing the fuel cell stack 21. Furthermore, multiple maps M1 may be provided depending on the time that has elapsed since the fuel cell stack 21 was manufactured. In this case, the map M1 may be switched depending on the time that has elapsed since the fuel cell stack 21 was manufactured.
[0077] Instead of using map M1, the control unit 110 may calculate the auxiliary loss from the stack power limit value to obtain the system power limit value. In this case, a calculation formula for calculating the auxiliary loss from the stack power limit value may be stored in advance in the storage unit 112 or the like. Then, the control unit 110 may set the value obtained by subtracting the auxiliary loss from the stack power limit value as the system power limit value.
[0078] The control unit 110 may set the stack power limit value to a value obtained by subtracting the limit value from the maximum output power of the fuel cell stack 21. In this case, the control unit 110 may increase the limit value as the temperature detected by the temperature sensor 87 increases above the temperature threshold value.
[0079] The control unit 110 does not have to transmit the system power limit value to the external load 200 . The map M1 may associate the stack power limit value with the auxiliary loss. In this case, when the control unit 110 determines the system power limit value from the stack power limit value, the control unit 110 determines the auxiliary loss corresponding to the stack power limit value from the map M1. Then, the control unit 110 determines the system power limit value by subtracting the auxiliary loss from the stack power limit value.
[0080] Among the compressor power consumption, DC / DC power consumption, WP power consumption, and HP power consumption, those that account for a small proportion of the total auxiliary loss do not need to be included in the auxiliary loss when calculating the system power limit value. In other words, auxiliary devices with low power consumption do not need to be taken into consideration.
[0081] The map M1 may be created assuming a case where the auxiliary loss is not maximum. For example, the map M1 may be created assuming a case where the auxiliary loss is an average value. [Explanation of symbols]
[0082] M1...map, 20...fuel cell system, 21...fuel cell stack, 42...electric compressor which is an example of auxiliary equipment, 67...circulation pump which is an example of auxiliary equipment, 84...refrigerant pump which is an example of auxiliary equipment, 91...DC / DC converter which is an example of auxiliary equipment, 110...control unit, 200...external load.
Claims
1. a fuel cell stack electrically connected to an external load; an auxiliary device that operates using the power generated by the fuel cell stack; A fuel cell system comprising: The control unit calculating a power limit value of the fuel cell stack based on the maximum output power of the fuel cell stack and a limit value; determining a power limit value for the fuel cell system from the power limit value for the fuel cell stack; a command value from the external load that commands the output power of the fuel cell system and a power limit value of the fuel cell system, the smaller of which is set as a system power target value; calculating a current target value of the fuel cell stack from the power supplied to the external load and the system power target value; controlling the fuel cell system so that the output current of the fuel cell stack follows the current target value; A fuel cell system in which, when calculating the power limit value of the fuel cell system from the power limit value of the fuel cell stack, the power limit value of the fuel cell system is calculated based on a map based on the correlation between the power limit value of the fuel cell stack and losses in the auxiliary equipment, or based on a value calculated from the power limit value of the fuel cell stack to calculate the losses.
2. 2. The fuel cell system according to claim 1, wherein when the control unit determines the power limit value of the fuel cell system from the power limit value of the fuel cell stack, the control unit determines the power limit value of the fuel cell system based on the output current of the fuel cell stack over the design life of the fuel cell stack.
3. 3. The fuel cell system according to claim 1, wherein the control unit transmits a power limit value of the fuel cell system to the external load.
Citation Information
Patent Citations
Fuel cell system
JP2023045620A