Fuel cell system and its control method

Abstract

To suppress the decrease in the drainage performance of a fuel cell during the transitional period when the fuel cell load decreases from high load to low load. [Solution] The fuel cell system comprises a fuel cell stack, an injector provided in a hydrogen introduction pipe connecting the anode gas circulation channel, which includes the anode channel of the fuel cell stack, to a hydrogen tank, and an ECU that opens and closes the injector at a cycle corresponding to the required output current for the fuel cell stack, intermittently injecting hydrogen gas from the hydrogen tank into the anode channel. During the load reduction transition from high load to low load of the fuel cell stack, if hydrogen gas is not injected from the start of this load reduction transition until a waiting time determined based on the decrease in the required output current between high load and low load has elapsed, the ECU opens the injector and injects additional hydrogen gas.

Description

【Technical Field】 , , , , 【0006】 , , 【0005】 , , , 【0001】 The present invention relates to a fuel cell system and a control method thereof. 【Background Art】 【0002】 In recent years, in order to enable more people to access affordable, reliable, sustainable, and advanced energy, research and development have been conducted on fuel cells that contribute to energy efficiency. 【0003】 In recent fuel cell systems, the pressure in the anode gas flow path (hereinafter also referred to as "anode pressure") is often controlled by an injector provided in the flow path from the supply source of the anode gas (for example, a hydrogen tank) to the anode gas flow path of the fuel cell. In the invention described in Patent Document 1, the injector is driven to open and close under a cycle corresponding to the required power generation amount of the fuel cell, and the anode gas is intermittently injected. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2008-146923 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 However, when the injection cycle of the anode gas is changed according to the required power generation amount in this way, in the transient period when the load on the fuel cell decreases from a high load to a low load, the anode gas consumed by power generation rapidly decreases, so a large amount of anode gas remains in the fuel cell, and as a result, the off-time of the injector (that is, the time to close the injector) becomes long, and ultimately, the drainage performance of the fuel cell may deteriorate. 【0006】 The present invention aims to achieve a fuel cell system that can suppress the decrease in the drainage performance of a fuel cell during the transition period when the fuel cell load decreases from high load to low load, and thereby contribute to energy efficiency. [Means for solving the problem] 【0007】 (1) The fuel cell system according to the present invention (for example, the fuel cell system 1 described later) comprises a fuel cell (for example, the fuel cell stack 2 described later) that generates electricity when anode gas and cathode gas are supplied, an injector (for example, the injector 362 described later) provided in a flow path (for example, the hydrogen introduction pipe 36 described later) that connects an anode gas circulation flow path including the anode gas flow path of the fuel cell (for example, the anode flow path 21 described later) to an anode gas supply source (for example, the hydrogen tank 31 described later), and under a period corresponding to the required amount of power generated by the fuel cell (for example, the required output current described later) The system includes a control means (e.g., ECU6 described later) that opens and closes the injector to intermittently inject anode gas from the anode gas supply source into the anode gas flow path, wherein the control means is characterized in that, during a transition period from high load to low load of the fuel cell (e.g., a load reduction transition period described later), if anode gas is not injected from the start of the transition period until a set time (e.g., a waiting time described later) determined based on the decrease in the required power generation between the high load and low load periods has elapsed, the injector is opened and additional anode gas is injected. 【0008】 (2) In this case, it is preferable that the control means set the setting time to be shorter the smaller the reduction amount. 【0009】 (3) In this case, it is preferable that the control means set the setting time to be shorter as the required amount of power generation during high load increases. 【0010】 (4) In this case, it is preferable that the control means make the opening time of the injector in the additional injection shorter than the opening time of the injector during steady-state operation when the load of the fuel cell is constant and during the transition period from low load to high load of the fuel cell. 【0011】 (5) In this case, the fuel cell system further comprises an anode pressure detection means (for example, an anode pressure sensor 25 described later) for detecting the anode pressure in the anode gas flow path and a cathode pressure detection means (for example, a cathode pressure sensor 27 described later) for detecting the cathode pressure in the cathode gas flow path of the fuel cell, and the control means preferably sets the valve opening time of the injector in the additional injection based on the difference between the anode pressure detected by the anode pressure detection means and the cathode pressure detected by the cathode pressure detection means. 【0012】 (6) In this case, it is preferable that the control means set the valve opening time of the injector in the additional injection to the minimum valve opening time specified for the injector. 【0013】 (7) The control method according to the present invention is a method for controlling a fuel cell system (e.g., a fuel cell stack 2 described later) comprising a fuel cell that generates electricity when anode gas and cathode gas are supplied (e.g., a fuel cell stack 2 described later), and an injector (e.g., an injector 362 described later) provided in a flow path connecting an anode gas circulation flow path including the anode gas flow path of the fuel cell (e.g., an anode flow path 21 described later) and an anode gas supply source (e.g., a hydrogen tank 31 described later), wherein the method controls the required amount of power generated for the fuel cell (e.g., The system comprises the steps of obtaining the required output current (described later) and opening and closing the injector at a cycle corresponding to the required power generation amount, thereby intermittently injecting anode gas from the anode gas supply source into the anode gas flow path. The system is characterized in that, during the transition period from high load to low load of the fuel cell, if anode gas is not injected between the start of the transition period and the elapsed time determined based on the decrease in the required power generation amount between the high load and low load periods, the injector is opened and additional anode gas is injected. [Effects of the Invention] 【0014】 (1) The control means, during the transition period from high load to low load of the fuel cell, that is, the period when the required amount of power generation suddenly decreases, opens the injector and injects additional anode gas if anode gas is not injected from the start of this transition period until a set time determined based on the decrease in the required amount of power generation between high load and low load has elapsed.Therefore, according to the present invention, it is possible to suppress the decrease in the drainage performance of the fuel cell caused by the injector being closed for a long time during the transition period from high load to low load, and thereby contribute to energy efficiency. 【0015】 (2) The control means can shorten the set time as the decrease in the required power generation amount decreases, thereby enabling additional injection to be performed at an appropriate timing according to the power generation state of the fuel cell, and thus suppressing a decrease in the drainage performance of the fuel cell. 【0016】 (3) The control means can shorten the set time as the required amount of power generation at high load increases, thereby enabling additional injection to be performed at an appropriate timing according to the power generation state of the fuel cell, and thus suppressing a decrease in the drainage performance of the fuel cell. 【0017】 (4) The control means makes the valve opening time of the injector during additional injection performed during the transition from high load to low load shorter than the valve opening time of the injector during steady-state operation when the load is constant and during the transition from low load to high load, thereby preventing an excessive rise in anode pressure associated with additional injection, and thus ensuring the drainage capacity of the fuel cell while maintaining the upper limit of the differential pressure between anode pressure and cathode pressure. 【0018】 (5) The control means sets the valve opening time of the injector during the additional injection performed during the transition from high load to low load based on the difference between the detected anode pressure and the detected cathode pressure, thereby preventing an excessive rise in anode pressure associated with the additional injection, and thus ensuring the drainage of the fuel cell while maintaining an upper limit on the differential pressure between anode pressure and cathode pressure. 【0019】 (6) The control means can prevent an excessive rise in anode pressure associated with additional injection by setting the valve opening time of the injector during the additional injection performed during the transition from high load to low load to the minimum valve opening time specified for the injector, thereby ensuring the drainage of the fuel cell while maintaining the upper limit of the differential pressure between the anode pressure and the cathode pressure. 【0020】 (7) According to the control method for a fuel cell system of the present invention, it is possible to suppress the decrease in the drainage performance of the fuel cell caused by the prolonged time of closing the injector during the transition from high load to low load, and thereby contribute to energy efficiency. [Brief explanation of the drawing] 【0021】 [Figure 1] This is a diagram showing the configuration of a fuel cell system according to one embodiment of the present invention. [Figure 2]It is a flowchart showing the specific procedure of hydrogen gas injection control. [Figure 3] It is a diagram showing an example of a map for determining the waiting time. [Figure 4] It is a time chart showing the change in anode voltage realized by hydrogen gas injection control. 【Mode for Carrying Out the Invention】 【0022】 Hereinafter, a fuel cell system according to an embodiment of the present invention will be described with reference to the drawings. 【0023】 FIG. 1 is a diagram showing the configuration of a fuel cell system 1 according to the present embodiment. The fuel cell system 1 includes a fuel cell stack 2 that generates power when supplied with anode gas and cathode gas, an anode gas supply device 3 that supplies hydrogen to the fuel cell stack 2 as anode gas, a cathode gas supply device 4 that supplies air to the fuel cell stack 2 as cathode gas, a cooling system 5 that cools the fuel cell stack 2, a battery B that stores the power generated by the fuel cell stack 2, a traveling motor M that rotates tires (not shown) by the power supplied from the fuel cell stack 2 and the battery B, a power circuit 7 that electrically connects the battery B, the traveling motor M, and the fuel cell stack 2, and an ECU 6 that is a computer for controlling these. Hereinafter, the case where this fuel cell system 1 is mounted on a fuel cell vehicle that travels with the above tires as drive wheels will be described. 【0024】 The fuel cell stack 2 is, for example, a stack structure in which tens to hundreds of fuel cell cells are stacked. Each fuel cell is constructed by sandwiching a membrane electrode structure (MEA) between a pair of separators. The membrane electrode structure consists of two electrodes, an anode electrode (cathode) and a cathode electrode (anode), and a solid polymer electrolyte membrane sandwiched between these electrodes. Typically, both electrodes are formed from a catalyst layer that performs oxidation-reduction reactions in contact with the solid polymer electrolyte membrane, and a gas diffusion layer in contact with this catalyst layer. In this fuel cell stack 2, when hydrogen is supplied to the anode channel 21 formed on the anode electrode side and oxygen-containing air is supplied to the cathode channel 22 formed on the cathode electrode side, electricity is generated by these electrochemical reactions. The electricity generated by the fuel cell stack 2 is supplied to loads such as the driving motor M and battery B via the power circuit 7. 【0025】 The anode gas supply device 3 includes a hydrogen tank 31 for storing hydrogen gas at high pressure, a hydrogen supply pipe 32 connected to the inlet of the anode flow path 21 of the fuel cell stack 2, a hydrogen discharge pipe 33 leading from the outlet of the anode flow path 21 to a diluent (not shown) provided in the cathode gas supply device 4, a hydrogen reflux pipe 34 branching from the hydrogen discharge pipe 33 to the hydrogen supply pipe 32, and a hydrogen introduction pipe 36 connecting the hydrogen tank 31 and the hydrogen supply pipe 32. 【0026】 The hydrogen introduction piping 36 is equipped with a shut-off valve 361 and an injector 362, arranged in order from the high-pressure hydrogen tank 31 side to the low-pressure hydrogen supply pipe 32 side. The shut-off valve 361 is a solenoid valve that opens and closes in response to a command signal from the ECU 6. The injector 362 also opens and closes in response to a command signal from the ECU 6. When the injector 362 is opened, high-pressure hydrogen gas supplied from the hydrogen tank 31 is injected into the hydrogen supply pipe 32. When the injector 362 is closed, the injection of hydrogen gas into the hydrogen supply pipe 32 is stopped. 【0027】 An ejector 323 is provided in the hydrogen supply pipe 32. The ejector 323 mixes the fresh hydrogen gas injected from the injector 362 with the gas discharged from the anode flow path 21 of the fuel cell stack 2 via the hydrogen discharge pipe 33 and the hydrogen reflux pipe 34 (hereinafter also referred to as "anode off gas") and circulates it back to the fuel cell stack 2. 【0028】 A hydrogen circulation pump 341 is provided in the hydrogen reflux pipe 34. The hydrogen circulation pump 341 pumps anode-off gas from the hydrogen discharge pipe 33 side to the ejector 323 side, thereby circulating hydrogen-containing gas within the circulation path composed of the hydrogen supply pipe 32, anode flow path 21, hydrogen discharge pipe 33, hydrogen reflux pipe 34, and ejector 323. The hydrogen circulation pump 341 operates in response to command signals from the ECU 6. 【0029】 The hydrogen discharge pipe 33 is equipped with a catch tank 331 for storing water contained in the anode off gas and a purge valve 332 for discharging the anode off gas to the cathode gas supply device 4, in that order from the fuel cell stack 2 side toward the cathode gas supply device 4 side. The catch tank 331 is also provided with a drain pipe 35 for discharging the accumulated water. This drain pipe 35 runs from the catch tank 331 to the downstream side of the hydrogen discharge pipe 333 beyond the purge valve 332. The drain pipe 35 is equipped with a drain valve 351. When this drain valve 351 is opened, the water accumulated in the catch tank 331 is discharged through the hydrogen discharge pipe 33 to a diluent (not shown). The purge valve 332 and the drain valve 351 are solenoid valves that open and close in response to command signals from the ECU 6. 【0030】 The cathode gas supply device 4 includes an air compressor 41, an air supply passage 42 from the air compressor 41 to the inlet of the cathode passage 22, an air discharge pipe 43 from the discharge of the cathode passage 22 to a diluent (not shown), an air return pipe 45 that branches off from the air discharge pipe 43 to the air supply pipe 42, and a humidifier 46 that connects the air discharge pipe 43 and the air supply pipe 42. 【0031】 The air compressor 41 supplies outside air to the cathode channel 22 of the fuel cell stack 2 via the air supply pipe 42. The air compressor 41 operates in response to command signals from the ECU 6. The humidifier 46 recovers water contained in the gas discharged from the cathode channel 22 (hereinafter also referred to as "cathode-off gas") and uses the recovered water to humidify the air supplied by the air compressor 41. Due to the function of this humidifier 46, the MEA of the fuel cell stack 2 during power generation is maintained in a state suitable for power generation. 【0032】 The air supply pipe 42 is provided with a bypass pipe 47 that bypasses the humidifier 46. This bypass pipe 47 is provided with a bypass valve 471. When the bypass valve 471 is opened, most of the air supplied from the air compressor 41 bypasses the humidifier 46 and is supplied to the fuel cell stack 2. The bypass valve 471 is a solenoid valve that opens and closes in response to a command signal from the ECU 6. The air discharge pipe 43 is provided with a back pressure control valve 432 for adjusting the back pressure in the cathode flow path of the fuel cell stack 2. The back pressure control valve 432 is a solenoid valve that opens and closes in response to a command signal from the ECU 6. 【0033】 Furthermore, the air supply pipe 42 and the air discharge pipe 43 are equipped with an inlet sealing valve 421 and an outlet sealing valve 431, respectively. When these sealing valves 421 and 431 are closed, the inside of the cathode flow path 22 is isolated from the outside air. These sealing valves 421 and 431 are solenoid valves that open and close in response to command signals from the ECU 6. 【0034】 The air recirculation pipe 45 is equipped with an EGR pump 48 that pressurizes the gas from the air discharge pipe 43 to the air supply pipe 42 and circulates the oxygen-containing gas within the oxygen circulation channel. The EGR pump 48 operates in response to command signals from the ECU 6. The rotation speed of the EGR pump 48 is controlled by the ECU 6. When this EGR pump 48 is driven, a portion of the gas discharged from the outlet side of the cathode channel 22 of the stack 2 is recirculated to the inlet side of the cathode channel 22. Therefore, this EGR pump 48 is used when it is desired to reduce the oxygen concentration of the gas in the cathode channel 22, etc. 【0035】 The cooling system 5 includes a refrigerant circulation path 51 that includes the inside of the fuel cell stack 2 as part of its flow path, a cooling pump 52 that circulates refrigerant within the refrigerant circulation path 51, a radiator 53 provided upstream of the cooling pump 52 in the refrigerant circulation path 51, a thermovalve 54 provided downstream of the cooling pump 52 in the refrigerant circulation path 51, and a bypass pipe 55 that connects the thermovalve 54 to the upstream side of the radiator 53 in the refrigerant circulation path 51. 【0036】 The fuel cell stack 2 is cooled by heat exchange with the refrigerant flowing through its internal passages. The radiator 53 cools the refrigerant by heat exchange with the outside air. The cooling pump 52 operates in response to command signals from the ECU 6. The rotational speed of the cooling pump 52 is controlled by the ECU 6. Increasing the rotational speed of the cooling pump 52 increases the flow rate of the refrigerant circulating in the refrigerant circulation path 51, which includes the fuel cell stack 2 and the radiator 53 in its refrigerant passages, thereby increasing the cooling capacity of the fuel cell stack 2. 【0037】 The thermovalve 54 is a three-way valve that opens and closes in response to a command signal from the ECU 6. The opening ratio of the thermovalve 54 (the ratio of the opening on the refrigerant circulation path 51 side (100% to 0%) to the opening on the bypass pipe 55 side (0% to 100%)) is controlled by the ECU 6. When the opening ratio of the thermovalve 54 is set to the maximum (i.e., "1"), all the refrigerant discharged from the cooling pump 52 is supplied to the fuel cell stack 2, thereby increasing the cooling capacity of the fuel cell stack 2. When the opening ratio of the thermovalve 54 is set to the minimum (i.e., "0"), all the refrigerant discharged from the cooling pump 52 is supplied to the bypass pipe 55. 【0038】 Battery B is a secondary battery capable of both discharging, which converts chemical energy into electrical energy, and charging, which converts electrical energy into chemical energy. In the following description, a so-called lithium-ion battery, which charges and discharges by the movement of lithium ions between electrodes, is used as Battery B, but the present invention is not limited to this. Battery B may also be a capacitor, for example. 【0039】 The power circuit 7 consists of power lines connecting the fuel cell stack 2 to the drive motor M and battery B, a DC-DC converter installed in these power lines to step up or step down the DC power output from the fuel cell stack 2, and an inverter installed in these power lines to convert the DC power output from the DC-DC converter into three-phase AC power for supply to the drive motor M, and to convert the three-phase AC power supplied from the drive motor M into DC power for supply to the battery B. Multiple switching elements constituting these DC-DC converters and inverters are driven on / off according to gate drive signals generated at predetermined timings from a gate drive circuit (not shown) of the ECU 6. Therefore, the ECU 6 can control the flow of power between the fuel cell stack 2, battery B, and drive motor M in the power circuit 7 by operating the DC-DC converters and inverters using the gate drive circuit. 【0040】 The ECU6 is a computer equipped with multiple functions, including a requested power generation acquisition function, a power generation control function, a temperature control function, and an output control function. The requested power generation acquisition function refers to the function in which the ECU6 acquires the requested power generation amount for the fuel cell stack 2 based on the amount of operation by the driver, such as the accelerator pedal or brake pedal (not shown). In the following description, the case in which the ECU6 acquires the requested output current as the requested power generation amount, which corresponds to the request for the output current supplied from the fuel cell stack 2 to loads such as the drive motor M or battery B via the power circuit 7, will be explained, but the present invention is not limited to this. The ECU6 may also acquire the requested output power as the requested power generation amount, which corresponds to the request for the output power supplied from the fuel cell stack 2 to loads such as the drive motor M or battery B via the power circuit 7. 【0041】 The power generation control function refers to the function by which the ECU 6 controls the power generation state of the fuel cell stack 2 to a state corresponding to the required power generation amount by performing anode gas supply control (for example, hydrogen gas injection control as shown in Figure 2 below) which operates the anode gas supply device 3 based on the required power generation amount, and cathode gas supply control which operates the cathode gas supply device 4 based on the required power generation amount. 【0042】 The temperature control function refers to the function in which the ECU 6 controls the temperature of the fuel cell stack 2 by operating the cooling system 5. The output control function refers to the function in which the ECU 6 controls the output current, output power, etc., of the fuel cell stack 2 so that the required power generation amount is met by operating the DC-DC converter and inverter of the power circuit 7. 【0043】 The ECU6 is connected to several sensors, including a cell voltage sensor 24, an anode pressure sensor 25, a current sensor 26, and a cathode pressure sensor 27, to monitor the state of the fuel cell stack 2 during power generation. 【0044】 The cell voltage sensor 24 detects the voltage (so-called cell voltage) of each fuel cell constituting the fuel cell stack 2 and transmits a signal approximately proportional to the detected value to the ECU 6. The anode pressure sensor 25 is installed, for example, in the hydrogen supply pipe 32. The anode pressure sensor 25 detects the pressure (so-called anode pressure) of the anode gas supplied to the anode flow path 21 and transmits a signal approximately proportional to the detected value to the ECU 6. 【0045】 The current sensor 26 detects the output current of the fuel cell stack 2, more specifically the current output from the fuel cell stack 2 to loads such as the drive motor M and battery B via the power circuit 7, and transmits a signal approximately proportional to the detected value to the ECU 6. The cathode pressure sensor 27 is installed, for example, in the air supply pipe 42. The cathode pressure sensor 27 detects the pressure of the cathode gas supplied to the cathode flow path 22 (so-called cathode pressure) and transmits a signal approximately proportional to the detected value to the ECU 6. 【0046】 Figure 2 is a flowchart showing the specific procedure for controlling hydrogen gas injection by the injector 362. This hydrogen gas injection control is repeatedly performed by the ECU 6 at a predetermined control cycle while the fuel cell stack 2 is generating power. 【0047】 First, in step ST1, the ECU 6 obtains the requested output current for the fuel cell stack 2 and then proceeds to step ST2. In step ST2, the ECU 6 sets a target anode pressure value based on the requested output current obtained in step ST1, which is the target value for the anode pressure sensor 25 (hereinafter referred to as the "anode pressure detection value"), and then proceeds to step ST3. The larger the requested output current, the larger the anode pressure target value the ECU 6 sets. 【0048】 In step ST3, the ECU6 determines whether the fuel cell stack 2 is in a load reduction transition period from high load to low load. Here, a load reduction transition period refers to a period in which the requested output current is decreasing. More specifically, a load reduction transition period is defined as a period starting when the requested output current begins to decrease and ending when the detected anode pressure reaches the anode pressure target value set in step ST2. The ECU6 determines whether it is in a load reduction transition period based on the history of the requested output current for the past few cycles and the deviation between the detected anode pressure value and the anode pressure target value. 【0049】 If the result of step ST3 is YES, in other words, if it is a transition period from high load to low load for fuel cell stack 2, ECU6 proceeds to step ST5. If the result of step ST3 is NO, in other words, if it is a steady-state operation where the load of fuel cell stack 2 is approximately constant, or if it is a transition period of load increase from low load to high load for fuel cell stack 2, ECU6 proceeds to step ST4. 【0050】 In step ST4, the ECU 6 performs normal injection control and terminates the hydrogen gas injection control shown in Figure 2. In this normal injection control, the ECU 6 intermittently injects high-pressure hydrogen gas supplied from the hydrogen tank 31 into the anode gas circulation channel by opening and closing the injector 362 so that the detected anode pressure value is maintained at the anode pressure target value calculated in step ST2. 【0051】 As described above, when the injector 362 is opened, high-pressure hydrogen gas supplied from the hydrogen tank 31 is injected into the anode gas circulation channel, causing the anode pressure to rise. When the injector 362 is closed, the injection of hydrogen gas stops. When the injection of hydrogen gas stops, the anode pressure decreases due to power generation in the fuel cell stack 2. Therefore, in this normal injection control, by intermittently injecting hydrogen gas from the injector 362, the detected anode pressure can be maintained near the anode pressure target value. Also, the larger the output current of the fuel cell stack 2, the faster the anode pressure decreases. Therefore, during the execution of this normal injection control, the hydrogen gas injection cycle by the injector 362 tends to become shorter as the output current of the fuel cell stack 2 and the anode pressure target value increase. 【0052】 In step ST5, the ECU6 determines whether or not the additional injection described in step ST10 below has already been performed. If the result of the determination in step ST5 is YES, the ECU6 proceeds to step ST4 and performs normal injection control. If the result of the determination in step ST5 is NO, the ECU6 proceeds to step ST6. 【0053】 In step ST6, the ECU6 calculates the decrease in the required output current between high load and low load conditions, and then proceeds to step ST7. Here, the required output current under high load conditions refers more specifically to the required output current immediately before the start of the load reduction transient. The required output current under low load conditions refers to the current required output current during the load reduction transient. The ECU6 calculates the positive decrease by subtracting the required output current under low load conditions from the required output current under high load conditions. 【0054】 In step ST7, the ECU6 sets a waiting time based on the decrease in the requested output current and the requested output current under high load conditions calculated in step ST5, and then proceeds to step ST8. Here, the waiting time corresponds to the time spent waiting for the execution of additional injection, as described later, during the load reduction transient. The ECU6 sets the waiting time by searching a map as shown in Figure 3, based on the decrease in the requested output current and the requested output current under high load conditions. 【0055】 Figure 3 shows an example of a map that determines the waiting time according to the decrease in the requested output current and the detected current value. As shown in Figure 3, it is preferable for the ECU 6 to set a shorter waiting time as the decrease in the requested output current decreases. It is also preferable for the ECU 6 to set a shorter waiting time as the requested output current increases under high load. 【0056】 Returning to Figure 2, in step ST8, the ECU6 determines whether the waiting time defined in step ST7 has elapsed from the start of the load reduction transient period being targeted. If the result of the determination in step ST8 is NO, the ECU6 proceeds to step ST4 and continues to perform normal injection control. If the result of the determination in step ST8 is YES, the ECU6 proceeds to step ST9. 【0057】 In step ST9, the ECU6 determines whether or not hydrogen gas was injected from the injector 362 during the period from the start of the load reduction transient to the end of the waiting time. As described above, the ECU6 continues to perform normal injection control from the high load period until the end of the waiting time. On the other hand, during this load reduction transient, the anode pressure target value drops sharply, so the injection cycle under normal injection control tends to become longer, and hydrogen gas may not be injected during the period from the start of the load reduction transient to the end of the waiting time. Furthermore, if the time during which the injector 362 is closed and hydrogen gas injection is stopped (hereinafter also referred to as the "breath-holding time") is prolonged, the drainage performance of the fuel cell stack 2 may deteriorate. 【0058】 If the result of step ST9 is YES, that is, if hydrogen gas has already been injected between the start of the load reduction transient and the expiration of the waiting period, ECU6 proceeds to step ST4 and continues to perform normal injection control. 【0059】 Furthermore, if the result of step ST9 is NO, that is, if hydrogen gas was not injected between the start of the load reduction transient and the end of the waiting period, ECU6 proceeds to step ST10. 【0060】 In step ST10, the ECU 6 performs an additional injection and terminates the hydrogen gas injection control shown in Figure 2. More specifically, the ECU 6 opens the injector 362 for a predetermined valve opening time and injects hydrogen gas into the anode gas circulation path. 【0061】 As described above, the ECU6 can suppress the deterioration of the drainage performance of the fuel cell stack 2 by performing an additional injection in response to the fact that no hydrogen gas was injected between the start of the load reduction transient and the end of the waiting period. However, performing an additional injection at such a timing may cause the anode pressure to rise excessively, and consequently, the differential pressure between the anode pressure and the cathode pressure may exceed a predetermined upper limit. 【0062】 Therefore, in order to prevent an excessive rise in anode pressure associated with the additional injection, the ECU 6 prefers to make the opening time of the injector 362 during additional injection shorter than the opening time of the injector 362 during normal injection control. 【0063】 The ECU 6 may also set the valve opening time of the injector 362 during additional injection to the minimum valve opening time specified for the injector 362. This minimizes the increase in anode pressure associated with additional injection. 【0064】 The ECU 6 may also set the valve opening time of the injector 362 during additional injection based on the difference between the anode pressure detection value and the cathode pressure sensor 27 detection value (hereinafter referred to as the "cathode pressure detection value"). This prevents the differential pressure between the anode pressure and cathode pressure from exceeding the upper limit due to additional injection. 【0065】 Figure 4 is a time chart showing the change in anode pressure achieved by the hydrogen gas injection control shown in Figure 2. In Figure 4, the upper panel shows the time change of the requested output current, and the lower panel shows the time change of the anode pressure. In Figure 4, the solid line shows the detected anode pressure value, and the dashed line shows the target anode pressure value. Figure 4 also shows the case where the load changes from high to low in response to a sharp decrease in the requested output current at time t0. 【0066】 As explained with reference to Figure 2, until time t0 when the requested output current drops sharply, the ECU 6 performs normal injection control, intermittently injecting high-pressure hydrogen gas into the anode gas circulation channel (see step ST4 in Figure 2). Therefore, until time t0, the detected anode pressure repeatedly increases and decreases, and is maintained near the anode pressure target value. 【0067】 At time t0, the system transitions to a load reduction transient as the requested output current decreases. In the example shown in Figure 4, time t0 marks the start of the load reduction transient. The ECU 6 then sets a waiting time based on the decrease in the requested output current and the requested output current under high load (i.e., the requested output current immediately before time t0) in response to the transition to the load reduction transient. After time t0, the anode pressure target value also begins to decrease as the requested output current decreases. Thus, after time t0, as the difference between the detected anode pressure value and the anode pressure target value widens, the hydrogen gas injection cycle under normal injection control becomes longer than before time t0, and as a result, hydrogen gas injection is temporarily stopped. Therefore, after time t0, the anode pressure gradually begins to decrease. 【0068】 Subsequently, at time t1, in response to the fact that no hydrogen gas was injected from injector 362 between the start of the load reduction transient and the expiration of the waiting time, the ECU 6 performs additional hydrogen gas injection to suppress deterioration of the drainage performance of the fuel cell stack 2 (see step ST10 in Figure 2). As a result, after time t1, the detected anode pressure temporarily rises and then decreases again toward the anode pressure target value. Subsequently, at time t2, in response to the detected anode pressure falling to the anode pressure target value, the load reduction transient ends. Thus, in the hydrogen gas injection control shown in Figure 2, by performing additional injection in response to the expiration of the waiting time at time t1, the time it takes for the detected anode pressure to fall toward the anode pressure target value is longer compared to the case where no additional injection is performed, but deterioration of drainage performance due to the breath-holding time exceeding the waiting time can be suppressed. 【0069】 The fuel cell system 1 according to this embodiment provides the following effects. (1) In the load reduction transition period of the fuel cell stack 2 from high load to low load, if hydrogen gas is not injected from the start of this load reduction transition period until a waiting time determined based on the decrease in the required output current between high load and low load has elapsed, the ECU 6 opens the injector 362 and injects additional hydrogen gas. Therefore, according to this embodiment, it is possible to suppress the decrease in the drainage performance of the fuel cell stack 2 caused by the prolonged time of closing the injector 362 during the transition period from high load to low load, and thereby contribute to energy efficiency. 【0070】 (2) The ECU 6 can perform additional injection at an appropriate timing according to the power generation state of the fuel cell stack 2 by setting the waiting time to be shorter as the decrease in the requested output current is smaller, thereby suppressing a decrease in the drainage performance of the fuel cell stack 2. 【0071】 (3) The ECU 6 can perform additional injection at an appropriate timing according to the power generation state of the fuel cell stack 2 by setting the standby time to be shorter as the required output current under high load is larger, thereby suppressing a decrease in the drainage performance of the fuel cell stack 2. 【0072】 (4) The ECU 6 can prevent an excessive rise in anode pressure associated with additional injection by shortening the valve opening time of the injector 362 during the load reduction transition from high load to low load compared to the valve opening time of the injector 362 during normal injection control. This ensures the drainage of the fuel cell stack 2 while maintaining the upper limit of the differential pressure between the anode pressure and the cathode pressure. 【0073】 (5) The ECU 6 can prevent an excessive rise in anode pressure associated with additional injection by setting the valve opening time of the injector 362 during the load reduction transition from high load to low load based on the difference between the detected anode pressure and the detected cathode pressure, thereby ensuring the drainage of the fuel cell stack 2 while maintaining the upper limit of the differential pressure between the anode pressure and the cathode pressure. 【0074】 (6) The ECU 6 can prevent an excessive rise in anode pressure associated with additional injection by setting the valve opening time of the injector 362 during the load reduction transition from high load to low load to the minimum valve opening time specified for the injector 362, thereby ensuring the drainage of the fuel cell stack 2 while maintaining the upper limit of the differential pressure between the anode pressure and the cathode pressure. 【0075】 Although one embodiment of the present invention has been described above, the present invention is not limited thereto. Within the scope of the spirit of the present invention, the details of the configuration may be modified as appropriate. [Explanation of symbols] 【0076】 1…Fuel cell system 2…Fuel cell stack 21... Anode channel 22... Cathode channel 24... Cell voltage sensor 25…Anode pressure sensor (anode pressure detection means) 27… Cathode pressure sensor (cathode pressure detection means) 3…Anode gas supply device 31…Hydrogen tank (anode gas supply source) 362... Injector 4… Cathode gas supply device 5…Cooling system 6…ECU (Control Unit) 7…Power circuit B... Battery M... Driving motor

Claims

[Claim 1] A fuel cell system comprising a fuel cell that generates electricity when anode gas and cathode gas are supplied, An injector is provided in a flow path connecting the anode gas circulation flow path, which includes the anode gas flow path of the fuel cell, and the anode gas supply source. The system includes a control means that opens and closes the injector at a cycle corresponding to the required power generation amount for the fuel cell, and intermittently injects anode gas from the anode gas supply source into the anode gas flow path, The control means is characterized in that, during the transition period from high load to low load of the fuel cell, if anode gas is not injected from the start of the transition period until a set time has elapsed based on the decrease in the required power generation between the high load and low load periods, the injector is opened and additional anode gas is injected. [Claim 2] The fuel cell system according to claim 1, characterized in that the control means sets the setting time shorter as the decrease amount decreases. [Claim 3] The fuel cell system according to claim 2, characterized in that the control means sets the setting time to be shorter as the required amount of power generation during high load increases. [Claim 4] The fuel cell system according to claim 1 or 2, characterized in that the control means makes the valve opening time of the injector in the additional injection shorter than the valve opening time of the injector during steady-state operation when the load of the fuel cell is constant and during the transition period from low load to high load of the fuel cell. [Claim 5] Anode pressure detection means for detecting the anode pressure in the anode gas flow path, The fuel cell further comprises a cathode pressure detection means for detecting the cathode pressure in the cathode gas flow path, The fuel cell system according to claim 1 or 2, characterized in that the control means sets the valve opening time of the injector in the additional injection based on the difference between the anode pressure detected by the anode pressure detection means and the cathode pressure detected by the cathode pressure detection means. [Claim 6] The fuel cell system according to claim 1 or 2, characterized in that the control means sets the valve opening time of the injector in the additional injection to the minimum valve opening time specified for the injector. [Claim 7] A control method for a fuel cell system comprising a fuel cell that generates electricity when anode gas and cathode gas are supplied, and an injector provided in a flow path connecting an anode gas circulation flow path, which includes the anode gas flow path of the fuel cell, and an anode gas supply source, wherein The steps include obtaining the required power generation amount for the fuel cell, The method includes the step of opening and closing the injector at a cycle corresponding to the required power generation amount, thereby intermittently injecting anode gas from the anode gas supply source into the anode gas flow path, A control method for a fuel cell system, characterized in that, during the transition period from high load to low load of the fuel cell, if anode gas is not injected from the start of the transition period until a set time determined based on the decrease in the required power generation between the high load and low load periods has elapsed, the injector is opened and additional anode gas is injected.

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