Fuel cell system

Abstract

To provide a technology that makes it possible to secure a hydrogen amount necessary for operation of a fuel cell in an output amount range of the fuel cell, when the fuel cell includes a circulation system for fuel gas that uses an injector, a linear solenoid valve, and an ejector.SOLUTION: An injector 40 of a fuel cell system 100 operates when an output amount of a fuel cell 10 is within a first output region which is equal to or smaller than a first output amount threshold, and a linear solenoid valve 50 operates when the output amount of the fuel cell 10 is within a second output region which is larger than a first output amount threshold. When the output amount of the fuel cell 10 is within a third output region that is within the second output region, which is larger than the first output amount threshold and is equal to or smaller than a second output amount threshold, the linear solenoid valve opens at such a degree that fuel gas and fuel off-gas that are necessary to secure a hydrogen amount threshold can be introduced from the ejector 60 into the fuel cell 10, the hydrogen amount threshold being a smallest hydrogen amount necessary for operation of the fuel cell 10.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] A fuel cell uses fuel gas for power generation, but also uses fuel gas for draining and scavenging inside the fuel cell. When the output of the fuel cell is low, it is desirable to increase the circulation amount of the fuel off-gas while suppressing the usage amount of the fuel gas as much as possible to perform draining and the like.

[0003] In order to increase the circulation amount of the fuel off-gas, it has been proposed to provide an ejector that sucks the fuel off-gas and introduces it into the fuel cell together with the fuel gas (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the fuel gas circulation system of a fuel cell, when the output power of the fuel cell is small, the injector may be operated, and when the output power is above a certain level, it may be switched to a linear solenoid valve for operation. The injector supplies fuel gas by an intermittent flow based on the opening and closing operation of the valve by pulse control, and the linear solenoid valve supplies fuel gas by a steady flow proportional to the opening degree of the solenoid valve by linear control. When fuel gas is injected by such an intermittent flow or steady flow, the ejector sucks the fuel off-gas according to the injection pressure, mixes it with the fuel gas, and introduces it into the fuel cell.

[0006] As described above, injectors and linear solenoid valves operate differently. Therefore, in the power range where the linear solenoid valve is used, in the region where the fuel cell output is low and the linear solenoid valve is at a low opening, the fuel gas injection pressure tends to be lower than the injection pressure when the injector is operating. Consequently, in this low-opening region, the amount of fuel off-gas drawn in by the ejector decreases, which can make it impossible to secure a sufficient amount of circulating gas. If the amount of circulating gas cannot be secured, as a result, it may become impossible to secure the amount of hydrogen necessary for the operation of the fuel cell. If the amount of hydrogen is insufficient, the performance of the fuel cell may deteriorate due to oxidation of the electrode material, etc.

[0007] This specification provides a technology that ensures the amount of hydrogen necessary for the operation of a fuel cell throughout the fuel cell's power output range, when the fuel cell is equipped with a fuel gas circulation system using an injector, a linear solenoid valve, and an ejector. [Means for solving the problem]

[0008] The fuel cell system disclosed herein includes a fuel gas circulation system in the fuel cell. This circulation system includes a fuel gas injector, a fuel gas linear solenoid valve arranged in parallel with the injector, and an ejector that introduces fuel off-gas discharged from the fuel cell along with the fuel gas from the injector and the linear solenoid valve into the fuel cell. The injector operates when the output of the fuel cell is in a first output region where it is less than or equal to a first output threshold, and the linear solenoid valve operates when the output of the fuel cell is in a second output region where it exceeds the first output threshold. When the output of the fuel cell is in a third output region where it is above the first output threshold in the second output region but less than or equal to the second output threshold, the linear solenoid valve opens to the extent that it can introduce fuel gas and fuel off-gas from the ejector into the fuel cell to secure a hydrogen threshold, which is the minimum amount of hydrogen required to operate the fuel cell.

[0009] By doing so, even when using an injector and a linear solenoid valve, the hydrogen threshold of the gas circulating in the fuel cell is maintained, thereby suppressing fuel cell degradation. In addition, the circulation flow rate of the fuel off-gas introduced from the ejector to the fuel cell is also ensured, enabling proper scavenging and other processes. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing an example of the configuration of a fuel cell system according to an embodiment. [Figure 2] This shows the relationship between the operating ranges of the injector and linear solenoid valve within the output range of the fuel cell in the fuel cell system of the embodiment, and the circulation flow rate of the fuel off-gas by the ejector 60. [Figure 3] This figure shows an example of the process for a fuel gas and fuel off-gas flow rate control program in a fuel cell system according to an embodiment. [Figure 4] This figure shows an example of a time chart in a fuel cell system according to an embodiment. [Modes for carrying out the invention]

[0011] The fuel cell system disclosed herein includes a fuel gas circulation system in the fuel cell, the circulation system comprising a fuel gas injector, a fuel gas linear solenoid valve (hereinafter simply referred to as LSV) arranged in parallel with the injector, and an ejector that introduces fuel off-gas (hereinafter simply referred to as off-gas) discharged from the fuel cell along with the fuel gas from the injector and the linear solenoid valve into the fuel cell, wherein the injector operates when the output of the fuel cell is in a first output region where it is less than or equal to a first output threshold, and the linear solenoid valve operates when the output of the fuel cell is in a second output region where it exceeds the first output threshold. When the output of the fuel cell is in a third output region where it is greater than the first output threshold in the second output region but less than or equal to the second output threshold, the linear solenoid valve opens to the extent that it can introduce fuel gas and off-gas from the ejector into the fuel cell to secure a hydrogen threshold, which is the minimum amount of hydrogen required to operate the fuel cell.

[0012] In one embodiment of the present disclosure, the LSV may be configured to open at a larger opening than a predetermined opening relative to the fuel cell output when the fuel cell output is within a third output region. This increases the amount and pressure of fuel gas supplied to the ejector and increases the off-gas circulation flow rate in the ejector, thereby easily securing the hydrogen quantity threshold.

[0013] In one embodiment of this disclosure, the LSV may be configured such that, when the fuel cell output is within a third output region, the smaller the fuel cell output, the wider the opening than the predetermined opening. This allows for effective maintenance of the hydrogen quantity threshold and an increase in the off-gas circulation flow rate, which is difficult to achieve when the output is low in the third output region due to the decrease in off-gas circulation flow rate.

[0014] In one embodiment of the present disclosure, the second power threshold may be the power level at which the circulating flow rate of the fuel off-gas reaches a target flow rate due to the predetermined opening of the linear solenoid valve relative to the power output of the fuel cell. This makes it easy to control the LSV to operate while maintaining the hydrogen amount threshold from the low power range to the higher power range when using the injector and LSV together.

[0015] In one embodiment of the present disclosure, the LSV may open at a predetermined opening degree relative to the fuel cell output after the fuel cell output exceeds a third output region. By opening the LSV at a predetermined opening degree, a suitable amount of hydrogen and off-gas circulation flow rate can be secured according to the fuel cell output.

[0016] In this specification, the terms "greater than or equal to," "greater than," "less than or equal to," and "less than" are defined in relation to a numerical value. Depending on the numerical value of the threshold, it may be expressed as "greater than or equal to" or "greater than," and similarly as "less than or equal to" or "less than." Therefore, "greater than or equal to" and "greater than" can mutually encompass the meaning of the other, and the same applies to "less than or equal to" and "less than."

[0017] The following description will explain the circulation control of fuel gas and off-gas in the fuel cell systems disclosed herein, with reference to the drawings as appropriate.

[0018] The fuel cell system described below comprises a fuel cell with a stack of multiple fuel cell cells arranged in series, a circulation system for circulating fuel gas (hydrogen), and a control device. The fuel cell system also includes an oxidant gas supply system for supplying oxidant gas (air), and a cooling system consisting of a cooling water pump, cooling water channels, etc. The application of the fuel cell system is not particularly limited. For example, it may be a mobile fuel cell system mounted on a moving object such as a vehicle or ship, or a stationary fuel cell system used in a stationary power generation facility.

[0019] The outline of the configuration of the fuel cell system 100 according to the embodiments disclosed in this specification is shown in FIG. 1. The fuel cell system 100 includes a fuel cell 10, a fuel gas circulation system 20 through which fuel gas circulates, an oxidant gas supply system (not shown), and a control device 80. The fuel cell system 100 also includes a cooling water circulation system (not shown) for cooling the fuel cell 10, although not shown in the figure.

[0020] The fuel cell 10 is a conventionally known one and is not particularly limited. For example, a solid polymer fuel cell (PEFC) may be used. The fuel cell 10 is provided with a sensor (not shown) for obtaining the hydrogen stoichiometric ratio of the gas circulating inside, and the detection value by the sensor is transmitted to the control device 80 to calculate the hydrogen stoichiometric ratio inside the fuel cell 10.

[0021] The fuel gas circulation system 20 includes a fuel gas tank 30, a supply flow path 32 for supplying fuel gas to the fuel cell 10, an injector 40, a LSV 50, and an ejector 60.

[0022] The tank 30 may be any hydrogen storage device, and various known forms such as a compressed hydrogen cylinder, a liquid hydrogen tank, and a hydrogen storage alloy can be adopted. Downstream of the tank 30, a regulator 34 for adjusting the flow rate of the fuel gas from the tank and a pressure sensor (not shown) are provided. The opening degree of the valve or the like of the regulator 34 is adjusted by a control signal transmitted from the control device 80 described later, and the pressure value detected by the pressure sensor is transmitted to the control device 80.

[0023] The injector 40 is arranged downstream of the tank 30 and injects and supplies fuel gas to the ejector 60 at a predetermined flow rate. The injector 40 has, for example, an on-off valve that can adjust the flow rate and pressure of the fuel gas from the primary side (tank 30) to the secondary side (ejector 60) by driving a valve body away from the valve seat at a predetermined driving cycle by an electromagnetic driving force or the like.

[0024] The injector 40 is controlled by pulse control, in accordance with the amount of output (current or output) required by the fuel cell 10, based on a control signal from the control device 80, to open and close a valve and intermittently inject a predetermined amount of fuel gas towards the ejector 60.

[0025] The injector 40 has a specific critical pressure ratio at which it switches between non-choke flow (subsonic flow) and choke flow (sonic flow). From the viewpoint of the accuracy of fuel gas flow rate control, the fuel cell system 100 may be configured, for example, to operate the injector 40 primarily in the choke flow region of the injector 40.

[0026] The LSV50 controls the opening of the valve from the primary side (tank 30) to the secondary side (ejector 60) by a plunger driven by a solenoid, to any opening between the maximum opening and the closed valve, thereby arbitrarily controlling the fuel gas flow rate in proportion to the opening of the solenoid valve. The structure of the LSV50 is not particularly limited, and a known LSV structure can be adopted.

[0027] The LSV50 is arranged in parallel with the injector 40. In the fuel gas supply passage 32, the fuel gas supply destination can be switched between the injector 40 and the LSV50 by a control signal from the control device 80.

[0028] The LSV50 also has its own critical pressure ratio, and the flow switches between non-choke flow and choke flow around this critical pressure ratio. The fuel cell system 100 may be configured to primarily operate the LSV50 in the choke flow region at pressure ratios exceeding the critical pressure ratio, from the viewpoint of the accuracy of fuel gas flow rate control.

[0029] The LSV50 adjusts the plunger operation and solenoid valve operation by linear control according to the output amount (current amount) required by the fuel cell 10 based on a control signal from the control device 80, and injects a predetermined amount of fuel gas toward the ejector 60.

[0030] The ejector 60 is located between the fuel cell 10 and the injection devices of the injector 40 and LSV 50 on the fuel gas supply passage 32. The ejector 60 is connected to a circulation passage 70 for off-gas, which is introduced into the fuel cell 10 from the fuel gas inlet 10a and discharged from the fuel gas outlet 10b. The circulation passage 70 is configured to recirculate the off-gas back to the fuel gas inlet 10a. The circulation passage 70 may, if necessary, be equipped with a circulation pump driven by a motor or the like to compress the off-gas to an appropriate gas pressure and recirculate it back to the supply passage 32. An exhaust passage 74 is branched from the circulation passage 70 to exhaust the off-gas to the outside of the fuel cell system 100 via a gas-liquid separator 72. An exhaust valve (not shown) is installed in the exhaust passage 74, and the off-gas is exhausted by opening and closing the valve.

[0031] The ejector 60 draws in off-gas from the circulation path 70 using fuel gas flowing into the ejector 60 via the injector 40 or LSV 50, and introduces it into the fuel cell 10 together with the fuel gas. The amount of off-gas drawn in by the ejector 60 (circulation flow rate) increases as the amount and pressure of fuel gas supplied from the injector 40 or LSV 50 increases.

[0032] Downstream of the ejector 60 and between it and the fuel gas inlet 10a of the fuel cell 10, there is a pressure sensor 62 that detects the pressure of the mixed gas of fuel gas and off-gas injected from the ejector 60 and introduced into the fuel cell 10. The pressure value detected by the pressure sensor 62 is transmitted to the control device 80.

[0033] Next, the operation of the injector and LSV will be described. Figure 2 shows the relationship between the operating range of the injector 40 and LSV 50 within the power output range of the fuel cell 10 and the amount of off-gas drawn in and circulated by the ejector 60. As shown in Figure 2, the injector 40 operates in the lower power output range (injector operating range) of the power output range of the fuel cell 10. The LSV 50 operates in the higher power output range (LSV operating range). In other words, the injector 40 operates in the lower flow rate range of the fuel gas flow rate range corresponding to the power output range of the fuel cell 10, and the LSV 50 operates in the higher flow rate range of the power output range of the fuel cell 10. For example, the injector 40 may mainly operate in the flow rate range corresponding to the choke flow range of the injector 40, and the LSV 50 may mainly operate in the flow rate range corresponding to the choke flow range of the LSV 50, beyond the operating range of the injector 40. This enables highly precise flow control over a wide range of fuel cell output levels, or in other words, a wide range of fuel gas flow rates.

[0034] The upper limit output P1 of the fuel cell 10 on which the injector 40 operates can be, for example, an output corresponding to the maximum fuel gas flow rate at which the injector 40 can stably achieve choke flow.

[0035] The injector operating region, which is the range of output levels of the fuel cell 10 in which the injector 40 operates, is an example of a first output region in this specification. The upper limit output level P1 of the fuel cell 10 in which the injector 40 operates is an example of a first output level threshold in this specification. The LSV operating region, which is the range of output levels of the fuel cell 10 in which the LSV 50 operates beyond the upper limit output level P1, is an example of a second output region in this specification.

[0036] On the other hand, as shown in Figure 2, when the injector 40 and LSV 50 are switched between and used within the output range of the fuel cell 10, in the low-power range of the LSV 50's operating range, when the output of the fuel cell 10 exceeds the upper limit output P1 and the LSV 50 is started to be used, the off-gas circulation flow rate decreases compared to the amount of off-gas drawn in (circulation flow rate) by the injector 40 up to that point. This is because, in the LSV 50, which continuously injects fuel gas, the planned opening of the solenoid valve is small relative to the output of the fuel cell 10, and as a result, the fuel gas injection pressure is lower than that of the injector 40, reducing the off-gas suction force in the ejector 60. Subsequently, as the output of the fuel cell 10 increases, the planned opening of the solenoid valve specified for that output also increases, and the off-gas circulation flow rate gradually increases, becoming equivalent to the off-gas circulation flow rate when the injector 40 is operating (when the on / off valve is open) at output P2. After that, the off-gas circulation amount increases according to the planned opening of the solenoid valve.

[0037] Thus, in the low-power range where the fuel cell 10 is above its upper limit output P1 and below output P2, the amount of off-gas circulated and introduced into the fuel cell 10 decreases. As a result, the amount of hydrogen that relies on the off-gas becomes insufficient to meet the minimum amount of hydrogen required for the operation of the fuel cell 10 (minimum hydrogen amount: hydrogen concentration or hydrogen stoichiometric ratio).

[0038] Therefore, in the low-power range of the LSV operating region, the LSV50 operates to open the solenoid valve more than the planned opening for the fuel cell 10 relative to its output. By opening the valve more than the planned opening, more fuel gas is supplied to the ejector 60 than planned, increasing the hydrogen concentration in the gas supplied to the fuel cell 10. At the same time, by increasing the amount of fuel gas supplied to the ejector 60, more off-gas than planned is drawn in by the ejector 60 and circulated to the fuel cell 10. As a result, even in the low-power range, the decrease in the hydrogen stoichiometric ratio in the fuel cell 10 can be suppressed. For example, at least the minimum amount of hydrogen concentration necessary for the operation of the fuel cell 10 can be secured, and deterioration of electrodes and other components of the fuel cell 10 due to hydrogen deficiency can be suppressed.

[0039] In the low-power range of the LSV50, the output amount P2 at which the circulating flow rate of the injector 40 is equivalent to that of the fuel cell 10 at the planned valve opening is an example of a second output threshold in this specification. The circulating flow rate of the off-gas at the time of injector 40 operation is an example of a target flow rate in this specification. The low-power range, which is above the upper limit output amount P1 and below the output amount P2, is an example of a third output range in this specification. The minimum amount of hydrogen required to operate the fuel cell 10 is an example of a hydrogen amount threshold in this specification.

[0040] The control device 80 is configured as a computer equipped with a processor and memory such as RAM and ROM. It controls the operation of each part of the fuel cell system 100 according to the program stored in ROM or the like.

[0041] Furthermore, the control device 80 is connected to the regulator 34, injector 40, linear solenoid valve 50, and ejector 60 downstream of the tank 30, respectively, and controls their operation based on the values ​​detected by various sensors in the fuel cell system 100. In addition, the control device 80 is connected to the input section of the power supply target equipment (external equipment) to which the fuel cell system 100 is connected, and acquires the output amount required for the fuel cell 10 from the input section.

[0042] The control device 80 determines the circulation flow rate of the off-gas that the ejector 60 draws in and circulates back to the fuel cell 10, based on the structure of the ejector 60 and other pre-acquired parameters, as well as the valve opening of LSV50 and other valves, the amount of fuel gas supplied, and the hydrogen stoichiometric ratio detected in the fuel cell 10.

[0043] When the control device 80 executes a fuel gas flow rate control program that controls the flow rate of fuel gas, it outputs control signals to the injector 40 and LSV 50 to control their operation.

[0044] Next, the process and operation of controlling the flow rates of fuel gas and off-gas in the fuel cell system 100 will be explained with reference to Figures 3 and 4. When the processor of the control device 80 detects an input related to the output amount of the fuel cell 10 from the input section of an external device, it repeatedly executes the process defined in the fuel gas flow rate control program. Figure 3 shows an example of the flow of this process, and Figure 4 shows the operation of each part of the fuel cell system 100 as a time chart by this process. In Figure 4, the operation by this process is shown with a solid line, and the conventional operation is shown with a dotted line.

[0045] First, the processor calculates the required output for the fuel cell 10 based on the input amount obtained from the input section of the external device (step S10). For example, if the external device is a vehicle, the output is calculated based on the accelerator opening by the driver and the condition of the vehicle.

[0046] Furthermore, the processor determines whether this output amount is within the output range in which the injector 40 should be used, that is, whether the output amount is less than or equal to the upper limit output amount P1 (step S20). If it is within the output range in which the injector 40 should be used (when the output amount is less than or equal to the upper limit output amount P1), the processor controls the opening and closing of the valve body of the injector 40, which is scheduled to supply a fuel gas flow rate corresponding to the input output amount to the fuel cell 10, thereby supplying fuel gas to the fuel cell 10 (step S30), and then terminates this process.

[0047] When fuel gas is supplied to the fuel cell 10 using the injector 40, as shown in Figure 4, in the injector operating region, the pressure downstream of the ejector 60 changes in accordance with the intermittent injection of fuel gas from the injector 40. Also, the circulation flow rate of the off-gas in the ejector 60 changes in accordance with the intermittent injection of fuel gas from the injector 40. Furthermore, the hydrogen stoichiometric ratio is maintained at a level well above the minimum amount of hydrogen required for the operation of the fuel cell 10 by the fuel gas and off-gas.

[0048] On the other hand, if the processor determines that this output amount exceeds the upper limit output amount P1 and is in an output range where LSV50 should be used, it further determines whether this output amount is in a low output range of less than or equal to output amount P2, or in an output range exceeding that (step S40). If the processor determines that the output amount is in a low output range, it operates the LSV50 to open wider than the predetermined opening angle set in advance for the output amount, in order to satisfy the minimum amount of hydrogen while satisfying the output amount, and supplies fuel gas to the fuel cell 10 (step S50), and then terminates this process.

[0049] The processor can determine the LSV 50 opening degree that satisfies the output amount and hydrogen amount threshold based on the required output amount, the relationship between the LSV opening degree and the fuel gas flow rate, the fuel gas flow rate or pressure and the off-gas circulation flow rate, the amount of hydrogen in the fuel cell 10 and in the off-gas, etc. The off-gas circulation flow rate can be uniquely calculated from operating conditions such as the fuel gas flow rate and the parameters of the ejector 60 itself.

[0050] By controlling the opening of the solenoid valve of the LSV50 in the low-power range, the fuel gas flow rate increases beyond the planned flow rate. As shown in Figure 4, conventionally, when the LSV50 was open at the planned opening, the outlet pressure of the ejector 60 was significantly lower than the outlet pressure in the injector operating range. In contrast, with the control of the LSV50 in the low-power range, for example, the outlet pressure of the ejector 60 is increased to the point where it exceeds the outlet pressure of the injector 40 due to the increased fuel gas flow rate. Also, conventionally, the off-gas circulation flow rate in the ejector 60 was significantly lower than the circulation flow rate in the operating range of the injector 40, but with this control, the increased fuel gas flow rate can compensate for the decrease in the off-gas circulation flow rate. Furthermore, conventionally, the hydrogen amount threshold required for the operation of the fuel cell 10 in the operating range of the injector 40 could not be met, whereas with this control, the minimum amount of hydrogen required for the operation of the fuel cell 10 is met by the increased fuel gas flow rate and off-gas circulation flow rate.

[0051] On the other hand, when the processor determines that this output amount is in a region beyond the low output range, it operates the LSV 50 at a predetermined opening degree set in advance for the output amount to supply fuel gas to the fuel cell 10 (step S60), and terminates this process.

[0052] As explained above, the fuel cell system 100 allows for highly accurate flow control over the wide output range of the fuel cell 10, according to the characteristics of each injection device, by using the injector 40 and LSV 50 interchangeably depending on the required output of the fuel cell 10. Furthermore, in the low output range within the operating range of the LSV 50, the fuel gas flow rate is increased by opening the LSV 50 to a larger opening than the planned opening. This increases the off-gas circulation flow rate in the ejector 60. By increasing the fuel gas flow rate and the off-gas circulation flow rate, the minimum amount of hydrogen required to operate the fuel cell 10 can be secured. This suppresses the degradation of the fuel cell 10. In addition, the total circulation flow rate (fuel gas supply amount and off-gas circulation flow rate) in the fuel cell 10 can be secured, avoiding problems caused by insufficient total circulation flow rate.

[0053] This specification includes the following components: [1] A fuel cell system, The fuel cell is equipped with a fuel gas circulation system, and the circulation system is: The fuel cell comprises a fuel gas injector, a linear solenoid valve for the fuel gas arranged in parallel with the injector, and an ejector for introducing fuel off-gas discharged from the fuel cell along with the fuel gas from the injector and the linear solenoid valve into the fuel cell. The injector operates when the output of the fuel cell is within a first output region with a first output threshold as the upper limit, and the linear solenoid valve operates when the output of the fuel cell is within a second output region with an output exceeding the first output threshold. A system wherein, when the output of the fuel cell is within a third output region where the output exceeds the first output threshold in the second output region but is less than or equal to the second output threshold, the linear solenoid valve opens to the extent that the fuel gas and fuel off-gas necessary to secure a hydrogen threshold, which is the minimum amount of hydrogen required to operate the fuel cell, can be introduced from the ejector into the fuel cell. [2] The system according to [1], wherein the linear solenoid valve opens to a larger opening than a predetermined opening for the output of the fuel cell when the output of the fuel cell is within the third output region. [3] The linear solenoid valve opens wider than the planned opening when the output of the fuel cell is within the third output region, the smaller the output of the fuel cell is. [4] The system according to any one of [1] to [3], wherein the second output threshold is the output amount at which the circulation flow rate of the fuel off-gas reaches a target flow rate due to the predetermined opening of the fuel cell with respect to the output amount. [5] The linear solenoid valve opens at the predetermined opening degree relative to the output amount of the fuel cell after the output amount of the fuel cell exceeds the third output region, according to any one of [2] to [4].

[0054] The above provides a detailed description of specific examples of the technologies disclosed herein, but these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the examples described above, such as a control method for a fuel cell. The technical elements described herein or in the drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. The technologies illustrated herein or in the drawings can achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness in itself. [Explanation of Symbols]

[0055] 10 Fuel cell, 20 Fuel gas circulation system, 30 Tank, 32 Fuel gas supply path, 34 Regulator, 40 Injector, 50 Linear solenoid valve, 60 Circulation path, 62 Pressure sensor, 70 Ejector, 72 Gas-liquid separator, 74 Exhaust path, 80 Control device, 100 Fuel cell system

Claims

1. A fuel cell system, The fuel cell is equipped with a fuel gas circulation system, and the circulation system is: The fuel cell comprises a fuel gas injector, a linear solenoid valve for the fuel gas arranged in parallel with the injector, and an ejector for introducing fuel off-gas discharged from the fuel cell along with the fuel gas from the injector and the linear solenoid valve into the fuel cell. The injector operates when the output of the fuel cell is within a first output region with a first output threshold as the upper limit, and the linear solenoid valve operates when the output of the fuel cell is within a second output region with an output exceeding the first output threshold. A system wherein, when the output of the fuel cell is within a third output region where the output exceeds the first output threshold in the second output region but is less than or equal to the second output threshold, the linear solenoid valve opens to the extent that the fuel gas and fuel off-gas necessary to secure a hydrogen threshold, which is the minimum amount of hydrogen required to operate the fuel cell, can be introduced from the ejector into the fuel cell.

2. The system according to claim 1, wherein the linear solenoid valve opens to a larger opening than a predetermined opening that is set in advance for the output amount of the fuel cell when the output amount of the fuel cell is within the third output region.

3. The system according to claim 2, wherein the linear solenoid valve opens wider than the predetermined opening when the output amount of the fuel cell is within the third output region, and the smaller the output amount of the fuel cell is.

4. The system according to claim 3, wherein the second output threshold is the output amount at which the circulation flow rate of the fuel off-gas reaches a target flow rate due to the predetermined opening degree with respect to the output amount of the fuel cell.

5. The system according to claim 4, wherein the linear solenoid valve opens at the predetermined opening degree relative to the output amount of the fuel cell after the output amount of the fuel cell exceeds the third output region.

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