Fuel cell system

Abstract

Provided is a fuel cell system having a fuel cell and a battery that is connected to the fuel cell and that charges with power generated by the fuel cell, the fuel cell system being a system in which the current of the fuel cell depends on the voltage of the battery, wherein: a control to start power generation in the fuel cell is performed when the SOC of the battery becomes equal to or less than an SOC lower limit value; and the SOC lower limit value is changed in accordance with the current of the fuel cell or in accordance with the deterioration state of the battery.

Description

fuel cell system

[0001] The present disclosure relates to a fuel cell system having a fuel cell that generates electricity when supplied with a fuel gas and an oxidant gas.

[0002] Patent Document 1 discloses a fuel cell system having a fuel cell that receives a supply of fuel gas from a fuel gas system and a supply of oxidant gas from an oxidant gas system to generate electricity.

[0003] Japanese Patent Application Laid-Open No. 2022-185247

[0004] In a fuel cell system that does not have a device (e.g., a DC-DC converter) that converts the fuel cell voltage (i.e., the voltage of the power generated by the fuel cell), the fuel cell current (i.e., the current of the power generated by the fuel cell) and voltage depend on the battery voltage. Therefore, if the battery deteriorates and the battery voltage drops, the fuel cell voltage also drops, and there is a risk that the fuel cell current will become excessive. This could result in problems such as deterioration due to excessive current being applied to the fuel cell. However, Patent Document 1 does not disclose or suggest anything about the issues that arise in a fuel cell system that does not have a device that converts the fuel cell voltage.

[0005] Therefore, the present disclosure has been made to solve the above-mentioned problems, and aims to provide a fuel cell system that can form a simple system configuration that does not have equipment that converts the voltage of the fuel cell, while suppressing the occurrence of fuel cell malfunctions due to battery deterioration.

[0006] One aspect of the present disclosure made to solve the above problem is a fuel cell system having a fuel cell and a battery connected to the fuel cell and charged with power generated by the fuel cell, wherein the fuel cell system is a system in which the current of the fuel cell depends on the voltage of the battery, and is characterized in that when the SOC of the battery falls below an SOC lower limit value, control is performed to start power generation of the fuel cell, and the SOC lower limit value is changed depending on the current of the fuel cell or the deterioration state of the battery.

[0007] According to this aspect, the fuel cell system can be configured with a simple system configuration that does not include a device that converts the fuel cell voltage supplied to the battery. Furthermore, when the fuel cell current becomes excessive or the battery deteriorates, the lower limit of the SOC, which is the threshold value at which the fuel cell starts to generate power, can be changed to reduce the number of times the fuel cell generates power. Therefore, while forming a simple system configuration that does not include a device that converts the fuel cell voltage, it is possible to prevent fuel cell malfunctions, such as deterioration caused by excessive current being applied to the fuel cell due to battery deterioration.

[0008] In the above aspect, it is preferable that the SOC lower limit value is increased when the current of the fuel cell remains at or above a first predetermined current value for a predetermined period of time, or when deterioration of the battery is detected.

[0009] According to this aspect, if the fuel cell current remains excessive for a predetermined period of time, or if battery degradation is confirmed, the lower limit of the SOC, which is the threshold for starting fuel cell power generation, can be raised to reduce the number of times the fuel cell generates power, thereby more reliably preventing fuel cell malfunctions due to battery degradation.

[0010] In the above aspect, it is preferable that the SOC lower limit be reduced if the maximum value of the current of the fuel cell when the SOC is equal to or lower than a predetermined SOC value is equal to or lower than a second predetermined current value.

[0011] According to this aspect, when there is little risk of the fuel cell current becoming excessive, the opportunities for the fuel cell to generate power can be increased, thereby ensuring a sufficient SOC for the battery.

[0012] The fuel cell system of the present disclosure can form a simple system configuration that does not include a device for converting the voltage of the fuel cell, while suppressing the occurrence of malfunctions in the fuel cell due to battery degradation.

[0013] Fig. 1 is a configuration diagram of a fuel cell system of the present embodiment. Fig. 2 is a diagram showing an example of FC current, FC voltage, battery current, and battery voltage when there is power consumption in an inverter in a DCDC converter-less fuel cell system. Fig. 3 is a diagram showing an example of FC current, FC voltage, battery current, and battery voltage when there is no power consumption in an inverter in a DCDC converter-less fuel cell system. Fig. 4 is a flowchart showing the content of control for maintaining the SOC of a battery within a predetermined range. Fig. 5 is a time chart showing an example of the time course of each value of the inverter output, SOC, battery output, FC output, FC voltage, battery voltage, FC current, and battery current. Fig. 6 is a flowchart showing the content of control for learning the lower limit value of SOC.

[0014] An embodiment of a fuel cell system according to the present disclosure will now be described.

[0015] 1, in the fuel cell system 1 of this embodiment, an FC stack 11, a battery 12, and an inverter 13 (or a motor) are connected in parallel, forming a simple system configuration that does not include a DC-DC converter. In other words, the fuel cell system 1 is a DC-DC converter-less system.

[0016] The DC-DC converter is a device that converts the FC voltage supplied to the battery 12. The FC stack 11 is an example of a "fuel cell" in the present disclosure. The FC voltage is an example of a "fuel cell voltage" in the present disclosure, and is the voltage of the power generated by the FC stack 11.

[0017] The fuel cell system 1 also has a hydrogen system 21 and an air system 22 .

[0018] The FC stack 11 generates power by receiving a supply of fuel gas and an oxidant gas. In this embodiment, the fuel gas is hydrogen gas, and the oxidant gas is air. That is, the FC stack 11 generates power by receiving a supply of hydrogen gas from a hydrogen system 21 and a supply of air from an air system 22. The power generated by the FC stack 11 is then supplied to the battery 12 and the inverter 13.

[0019] The battery 12 is connected to the FC stack 11 and is charged with the power generated by the FC stack 11. The battery 12 is also connected to the inverter 13 and supplies the charged power to the inverter 13.

[0020] The hydrogen system 21 is provided on the anode side of the FC stack 11. The hydrogen system 21 includes a hydrogen supply passage 31, a hydrogen discharge passage 32, a filling passage 33, and a circulation passage .

[0021] The hydrogen supply passage 31 is a passage for supplying hydrogen gas from a hydrogen tank 41 in which hydrogen gas is stored to the FC stack 11. The hydrogen discharge passage 32 is a passage for discharging hydrogen gas (i.e., hydrogen off-gas) discharged from the FC stack 11.

[0022] The filling passage 33 is a passage for filling hydrogen gas into the hydrogen tank 41 from the filling port 51. The circulation flow path 34 is a passage that connects the hydrogen discharge passage 32 (more specifically, the gas-liquid separator 71) and the ejector 64, and is a passage for circulating and supplying hydrogen off-gas to the ejector 64.

[0023] The hydrogen system 21 also includes a valve 61, a pressure reducing valve 62, an injector 63, and an ejector 64 in this order from the hydrogen tank 41 side in the hydrogen supply passage 31.

[0024] The valve 61 switches between supplying and blocking hydrogen gas from the hydrogen tank 41 to the hydrogen supply passage 31. The pressure reducing valve 62 is a pressure regulating valve for reducing the pressure of hydrogen gas. The injector 63 is a device that injects hydrogen gas introduced from the hydrogen tank 41 downstream. The ejector 64 is a device that generates negative pressure in the hydrogen gas injected from the injector 63, sucks in hydrogen off-gas from the circulation flow path 34, mixes it with the hydrogen gas, and discharges it downstream.

[0025] In addition, the hydrogen system 21 has a gas-liquid separator 71 and an exhaust / drain valve 72 arranged in this order from the FC stack 11 side in the hydrogen discharge passage 32. The gas-liquid separator 71 is a device that separates moisture from the hydrogen off-gas. The exhaust / drain valve 72 is a valve that switches between discharging and blocking the hydrogen off-gas and moisture from the gas-liquid separator 71.

[0026] On the other hand, the air system 22 is provided on the cathode side of the FC stack 11. This air system 22 includes an air supply passage 81 and an air discharge passage 82. The air supply passage 81 is a passage for supplying air from outside the fuel cell system 1 to the FC stack 11. The air discharge passage 82 is a passage for discharging air (i.e., air off-gas) discharged from the FC stack 11.

[0027] The air system 22 also includes an air compressor 91 and a supply-side air valve 92 in the air supply passage 81. The air compressor 91 is a device that supplies air to the FC stack 11. The supply-side air valve 92 is a valve that switches between supplying and blocking air from the air supply passage 81 to the FC stack 11.

[0028] The air system 22 also has a discharge-side air valve 101 disposed in the air discharge passage 82. The discharge-side air valve 101 is a valve that switches between discharging and blocking the air off-gas from the FC stack 11 to the air discharge passage 82.

[0029] The fuel cell system 1 also has a fan 111 that cools the FC stack 11 .

[0030] The fuel cell system 1 further includes a control unit 14. The control unit 14 is a device having, for example, an arithmetic processing unit such as a CPU, a memory unit such as a ROM for storing control programs and control data processed by the CPU and a RAM used as various work areas for control processing, and an input / output interface unit. The control unit 14 performs various controls of the fuel cell system 1 in accordance with the control programs stored in the memory unit.

[0031] In this embodiment, the control unit 14 controls various components of the fuel cell system 1, such as the inverter 13, valve 61, pressure reducing valve 62, injector 63, ejector 64, gas-liquid separator 71, exhaust drain valve 72, air compressor 91, supply side air valve 92, discharge side air valve 101, and fan 111.

[0032] (Operation of Fuel Cell System) In the fuel cell system 1 configured as described above, hydrogen gas supplied from the hydrogen supply passage 31 to the FC stack 11 is used for power generation in the FC stack 11, and then discharged from the FC stack 11 as hydrogen off-gas via the hydrogen discharge passage 32 to the outside of the fuel cell system 1. In addition, air supplied from the air supply passage 81 to the FC stack 11 is used for power generation in the FC stack 11, and then discharged from the FC stack 11 as air off-gas via the air discharge passage 82 to the outside of the fuel cell system 1.

[0033] The electric power generated by the FC stack 11 is supplied to the battery 12 to charge the battery 12, or is supplied to the inverter 13 to drive the inverter 13. The inverter 13 is also supplied with electric power from the battery 12.

[0034] (Regarding a DCDC converter-less system) As shown in FIG. 1 , the fuel cell system 1 of this embodiment is a so-called DCDC converter-less system in which a DCDC converter is not disposed between the FC stack 11 and the battery 12. Therefore, in the fuel cell system 1, the FC voltage is equal to (or approximately equal to) the battery voltage, and the FC current depends on the battery voltage. In other words, the fuel cell system 1 supplies the power generated in the FC stack 11 to the battery 12 and the inverter 13 without converting the FC voltage. Note that the FC current is an example of the "fuel cell current" in this disclosure, and is the current of the power generated in the FC stack 11. Note that the battery voltage is the voltage of the battery 12.

[0035] In the fuel cell system 1, the FC voltage becomes equal to the battery voltage in this way, so the FC stack 11 generates electricity as it goes according to the battery voltage. When the SOC (i.e., the charging rate) of the battery 12 becomes high, the supply-side air valve 92 and the discharge-side air valve 101 are closed to reduce the FC voltage below the battery voltage, and power generation by the FC stack 11 is stopped intermittently.

[0036] For example, as shown in FIG. 2, when there is power consumption in the inverter 13, if the battery voltage is 47 V, the FC voltage will be equal to the battery voltage, 47 V. As a result, the FC current will be 50 A. Therefore, the FC output = 47 V × 50 A = 2.3 kW, and the battery output = 47 V × 100 A = 4.7 kW. By adding up these FC output and battery output, the power consumption in the inverter 13 = 47 V × 150 A = 7.0 kW can be obtained. The FC output is the power generated by the FC stack 11 and output from the FC stack 11. The battery output is the power output from the battery 12.

[0037] 3, if there is no power consumption in the inverter 13 and the battery voltage is 49 V, the FC voltage will be equal to the battery voltage, 49 V. This will result in the FC current being 30 A. Therefore, the FC output = 49 V x 30 A = 1.5 kW, and the battery output = 49 V x -30 A = -1.5 kW.

[0038] (Regarding control to maintain the SOC of the battery within a predetermined range) In the fuel cell system 1 of this embodiment, the control unit 14 performs control to maintain the SOC of the battery 12 within a predetermined range, for example, as shown in FIG. 4.

[0039] As shown in FIG. 4, first, the control unit 14 determines whether the SOC is equal to or greater than an upper limit value UL (for example, 90%) (step S1).

[0040] If the SOC is equal to or greater than the upper limit value UL (step S1: YES), the control unit 14 closes both the supply side air valve 92 and the discharge side air valve 101 to intermittently stop power generation by the FC stack 11 (step S2).

[0041] Next, the control unit 14 determines whether the SOC is equal to or lower than a lower limit value LL (step S3). As will be described later, in this embodiment, the lower limit value LL of the SOC is a learned value.

[0042] Then, if the SOC is equal to or lower than the lower limit LL (step S3: YES), the control unit 14 opens both the supply-side air valve 92 and the discharge-side air valve 101, and performs FC power generation as the situation demands (step S4). In this way, the control unit 14 starts power generation in the FC stack 11 when the SOC becomes equal to or lower than the lower limit LL. Note that "performing FC power generation as the situation demands" means that the FC voltage becomes equal to the battery voltage, and power generation in the FC stack 11 is performed in accordance with the battery voltage.

[0043] In step S1, if the SOC is less than the upper limit UL (step S1: NO), the control unit 14 maintains the previous state (step S5). In step S3, if the SOC is greater than the lower limit LL (step S3: NO), the control unit 14 maintains the previous state (step S6).

[0044] In steps S5 and S6, "the control unit 14 maintains the previous state" means that if the control unit 14 terminates the processing in a state where the power generation of the FC stack 11 was stopped intermittently in the previous routine processing, the control unit 14 will continue to stop the power generation of the FC stack 11 intermittently, and if the control unit 14 terminates the processing in a state where the power generation of the FC stack 11 was continuing as it was in the previous routine processing, the control unit 14 will continue to continue the power generation of the FC stack 11 as it was in the previous routine processing.

[0045] Furthermore, by performing the control shown in FIG. 4, the values ​​of the inverter output, SOC, battery output, FC output, FC voltage, battery voltage, FC current, and battery current will be as shown in the time chart in FIG. 5, for example.

[0046] As shown in Figure 5, when the SOC becomes equal to or lower than the lower limit LL, the intermittent stop is ended, the uninterrupted power generation is started, and the FC output increases. On the other hand, when the SOC becomes equal to or higher than the upper limit UL, the uninterrupted power generation is ended, and the intermittent stop is started. The battery current is the current of the battery 12.

[0047] In this way, the fuel cell system 1 can control the SOC within a predetermined range (for example, 30% to 90%).

[0048] (Regarding control for learning the lower limit value of SOC) In this embodiment, the control unit 14 learns the lower limit value LL of SOC by changing the lower limit value LL of SOC according to the FC current or the deterioration state of the battery 12.

[0049] As shown in FIG. 6, first, the control unit 14 determines whether the FC current has been at or above a predetermined value Ia (e.g., 70 A) for a predetermined time (e.g., 3 seconds) or whether deterioration of the battery 12 has been detected (step S101).

[0050] Then, if the FC current remains at or above a predetermined value Ia for a predetermined time, or if deterioration of the battery 12 is detected (step S101: YES), the control unit 14 adds a predetermined value ΔS1 (e.g., 0.5%) to the SOC lower limit value LL (step S102).

[0051] In this way, if the state in which the FC current is equal to or greater than the predetermined value Ia continues for a predetermined time, or if deterioration of the battery 12 is detected, the control unit 14 can raise the lower limit LL of the SOC to reduce the opportunities for power generation by the FC stack 11, since there is a risk of malfunctions such as deterioration due to excessive current being applied to the FC stack 11 as a result of deterioration of the battery 12. The predetermined value Ia is an example of the "first predetermined current value" in this disclosure.

[0052] On the other hand, if the FC current has not remained above the predetermined value Ia for a predetermined time and deterioration of the battery 12 has not been detected (step S101: NO), the control unit 14 proceeds directly to the control processing of step S103.

[0053] Next, the control unit 14 determines whether the FC current MAX value is equal to or less than a predetermined value Ib (e.g., 60 A) when the SOC is equal to or less than a predetermined value S (e.g., 40%) (step S103). Note that the predetermined value S is an example of the "predetermined SOC value" in the present disclosure.

[0054] Then, when the SOC is below a predetermined value S, if the FC current MAX value becomes below a predetermined value Ib (step S103: YES), the control unit 14 reduces the SOC lower limit value LL by a predetermined value ΔS2 (e.g., 0.1%) (step S104).

[0055] In this way, if the FC current MAX value when the SOC is equal to or less than the predetermined value S is equal to or less than the predetermined value Ib, there is little risk of the FC current becoming excessive, so the lower limit value LL of the SOC can be lowered to increase the opportunities for power generation in the FC stack 11 and ensure a sufficient SOC for the battery 12. The predetermined value Ib is an example of the "second predetermined current value" in the present disclosure.

[0056] On the other hand, when the SOC is equal to or less than the predetermined value, if the FC current MAX value is greater than the predetermined value Ib (step S103: NO), the control unit 14 ends the control process.

[0057] (Operational Effects of the Present Embodiment) According to the present embodiment, the fuel cell system 1 is a DCDC converter-less system in which the FC current depends on the battery voltage. In such a DCDC converter-less system, when the control unit 14 controls the FC stack 11 to start power generation when the SOC of the battery 12 falls below the lower limit LL, the control unit 14 changes (i.e., learns) the lower limit LL of the SOC in accordance with the FC current or the deterioration state of the battery 12.

[0058] As described above, the fuel cell system 1 is a DCDC converter-less system, and therefore the fuel cell system 1 can be configured with a simple DCDC converter-less system configuration. In such a DCDC converter-less system, when the FC current becomes excessive or the battery 12 deteriorates, the lower limit LL of the SOC, which is the threshold value for starting power generation in the FC stack 11, can be changed to reduce the number of times the FC stack 11 generates power. Therefore, while forming a simple DCDC converter-less system configuration, it is possible to prevent malfunctions in the FC stack 11, such as deterioration caused by excessive current being applied to the FC stack 11 due to deterioration of the battery 12.

[0059] Furthermore, when the state in which the FC current is equal to or greater than the predetermined value Ia continues for a predetermined time, or when deterioration of the battery 12 is detected, the control unit 14 increases the lower limit value LL of the SOC.

[0060] In this way, if an excessively large FC current continues for a predetermined time, or if degradation of the battery 12 is confirmed, the lower limit LL of the SOC, which is the threshold value for starting power generation in the FC stack 11, can be increased to reduce the number of opportunities for power generation in the FC stack 11. This makes it possible to more reliably prevent malfunctions in the FC stack 11 due to degradation of the battery 12.

[0061] Furthermore, if the FC current MAX value (that is, the maximum value of the FC current) when the SOC is equal to or less than the predetermined value S is equal to or less than the predetermined value Ib, the lower limit value LL of the SOC is lowered.

[0062] This increases the opportunities for power generation by the FC stack 11 when there is little risk of the FC current becoming excessive, making it possible to ensure a sufficient SOC for the battery 12 .

[0063] It should be noted that the above-described embodiments are merely examples and do not limit the present disclosure in any way. It goes without saying that various improvements and modifications are possible within the scope of the gist of the present disclosure.

[0064] REFERENCE SIGNS LIST 1 fuel cell system 11 FC stack 12 battery 13 inverter (or motor) 14 control unit 21 hydrogen system 22 air system 31 hydrogen supply passage 32 hydrogen discharge passage 41 hydrogen tank 81 air supply passage 82 air discharge passage 91 air compressor UL upper limit value (of SOC) LL lower limit value (of SOC) Ia predetermined value Ib predetermined value S predetermined value ΔS1 predetermined value ΔS2 predetermined value

Claims

1. A fuel cell system having a fuel cell and a battery connected to the fuel cell and charged with power generated by the fuel cell, wherein the current of the fuel cell depends on the voltage of the battery, and the fuel cell system performs control to start power generation by the fuel cell when the SOC of the battery falls below an SOC lower limit, and changes the SOC lower limit according to the current of the fuel cell or the deterioration state of the battery.

2. A fuel cell system according to claim 1, wherein the lower limit of SOC is increased when the current of the fuel cell remains at or above a first predetermined current value for a predetermined period of time, or when deterioration of the battery is detected.

3. A fuel cell system according to claim 1 or 2, characterized in that, when the maximum value of the current of the fuel cell when the SOC is equal to or lower than a predetermined SOC value is equal to or lower than a second predetermined current value, the SOC lower limit value is lowered.

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