JP2013105635A - Fuel cell system and fuel cell vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system capable of promptly restarting power supply when intermittent operation is completed in a short period and preventing a fuel cell from being deteriorated while improving operation efficiency when intermittent operation is performed over a long period.SOLUTION: A fuel cell system 10, when it is estimated that intermittent operation is completed within a first period, executes voltage recovery control for maintaining a stack voltage Vc of a fuel battery stack 20 so that the stack voltage is not less than a first lower limit threshold value and does not execute voltage recovery control when it is estimated that intermittent operation is continued beyond the first period.

Description

  The present invention relates to a fuel cell system and a fuel cell vehicle equipped with the same.

  The fuel cell stack constituting the fuel cell system directly converts energy released in the oxidation reaction into electric energy by oxidizing fuel by an electrochemical process. This fuel cell stack has a membrane-electrode assembly in which both side surfaces of a polymer electrolyte membrane for selectively transporting hydrogen ions are sandwiched by a pair of electrodes made of a porous material. Each of the pair of electrodes is mainly composed of a carbon powder carrying a platinum-based metal catalyst, and is formed on the surface of the catalyst layer in contact with the polymer electrolyte membrane and a gas having both air permeability and electronic conductivity. And a diffusion layer.

  It is known that such a fuel cell system has a higher power generation efficiency in principle as the output is lower, but in an actual system, the power generation efficiency is lower at a lower output due to a loss of auxiliary machine power or the like. For this reason, for example, in a fuel cell vehicle equipped with a fuel cell system, the fuel cell stack is caused to generate power in a high output region, and power is supplied to the traction motor from both the fuel cell stack and the secondary cell or only the fuel cell stack On the other hand, in the low output region, power generation of the fuel cell stack is temporarily stopped, and operation control is performed to supply power to the traction motor only from the secondary battery.

  Thus, suppressing the power generation of the fuel cell stack in a low load region where the power generation efficiency of the fuel cell system is low is referred to as intermittent operation. In the low load region where the power generation efficiency of the fuel cell system is reduced, intermittent operation can be performed to operate the fuel cell stack within a range of high energy conversion efficiency, thereby improving the efficiency of the entire fuel cell system. Can do.

  In the fuel cell system that performs the intermittent operation as described above, when the transition is made from the low load region to the high load region, it is required to quickly restart the power supply from the state of the intermittent operation. However, since the voltage of the fuel cell stack decreases during intermittent operation, a certain period of time is required until the voltage is recovered and power supply is resumed.

  In the fuel cell system described in Patent Document 1 below, the stack voltage of the fuel cell is monitored during intermittent operation, and if the stack voltage drops below a predetermined threshold, the cell stack is temporarily placed in the cell stack. The stack voltage is recovered by supplying fuel gas or the like. As a result, the stack voltage during the intermittent operation is always maintained at the above threshold value or more, so that it is possible to quickly restart the power supply from the intermittent operation state.

  Further, Patent Document 1 described below also describes a control method of lowering the threshold value in a situation where the state of intermittent operation is expected to be long. By reducing the threshold voltage of the stack voltage, the frequency at which the voltage recovery process is executed is limited, and the operation efficiency of the fuel cell system is improved.

JP 2008-52937 A

  By the way, in a fuel cell, the phenomenon that an electrode deteriorates by the fluctuation | variation of a stack voltage and the power generation performance of a fuel cell falls is known. As the stack voltage fluctuates, a part of the catalyst supported on the electrode of the fuel cell elutes and the effective area of the catalyst decreases. It is known that the rate at which the effective area of the catalyst decreases due to the elution of the catalyst increases as the fluctuation range of the stack voltage increases and the number of fluctuations of the stack voltage increases.

  In the fuel cell system described in Patent Document 1, the stack voltage is constantly reduced and recovered during intermittent operation. In particular, in a situation where the state of intermittent operation is expected to be long, the threshold voltage of the stack voltage is lowered, so that the voltage fluctuation range becomes large. In addition, the stack voltage is decreased and recovered repeatedly over a long period of time, thereby increasing the number of stack voltage fluctuations. As a result, as described above, the rate at which the effective area of the catalyst decreases is increased, and the power generation performance of the fuel cell decreases in a short period of time.

  The present invention has been made in view of such a problem, and the object thereof is to quickly restart the power supply in the case where the intermittent operation is completed in a short period, while the intermittent operation is performed for a long time. In such a case, an object is to provide a fuel cell system capable of preventing the deterioration of the fuel cell while improving the power generation efficiency.

  In order to solve the above problems, a fuel cell system according to the present invention is a fuel cell system including a fuel cell stack including a plurality of cells each having an anode and a cathode, and a fuel gas supply means for supplying fuel gas to the anode. And an oxidant gas supply means for supplying an oxidant gas to the cathode, a control means for controlling the fuel gas supply means and the oxidant gas supply means to cause the fuel cell stack to generate electric power according to required power And the control means performs intermittent operation for temporarily stopping supply of the fuel gas and suppressing power generation of the fuel cell stack in a state where the required power is a predetermined value or less. When the intermittent operation is predicted to end within the first period during the intermittent operation, the output terminal voltage of the fuel cell stack is the first While performing the voltage recovery control to maintain the threshold value to be equal to or higher than the limit threshold, the voltage recovery control is not performed when the intermittent operation is predicted to continue beyond the first period. .

  According to the present invention, when the intermittent operation is predicted to end within the first period, the voltage recovery control is performed to maintain the output terminal voltage of the fuel cell stack to be equal to or higher than the first lower limit threshold. When the intermittent operation is predicted to continue beyond the first period, the voltage recovery control is not performed. Thus, whether to perform voltage recovery control according to the length of a period during which intermittent operation is predicted to be continued, i.e., a period during which the required power is predicted to continue below a predetermined value is determined. Has been decided.

  When it is predicted that the intermittent operation will be completed within the first period, the output terminal voltage of the battery stack is maintained to be equal to or higher than the first lower limit threshold by performing voltage recovery control. For this reason, when the required power becomes equal to or greater than a predetermined value, the intermittent operation can be terminated and the power supply from the fuel cell stack can be restarted quickly. In particular, a situation in which intermittent operation ends in a short period of time has a high frequency of occurrence, and thus prompt restart of power supply is required. According to the present invention, such a request can be met.

  On the other hand, when the intermittent operation is predicted to continue beyond the first period, the voltage recovery control is not performed. That is, even if the stack voltage decreases during intermittent operation, no control is performed to increase the stack voltage. As a result, the decrease and recovery of the stack voltage are not repeated, so that the elution of the electrode catalyst is suppressed. In addition, since it is not necessary to supply fuel gas for increasing the stack voltage or supply of oxidant gas, the operation efficiency of the fuel cell system can be improved. It should be noted that, by not performing the voltage recovery control, it takes time until the power supply is resumed. However, since the occurrence frequency is low in a situation where intermittent operation continues for a long period of time, the fuel cell system The influence on the driving (for example, the adverse effect on the drivability of the fuel cell vehicle) is small.

  In the fuel cell system according to the present invention, when the intermittent operation is predicted to continue beyond the first period, the supply of the fuel gas to the anode and the oxidant gas to the cathode It is also preferable to stop the supply.

  In this preferred embodiment, when the intermittent operation is predicted to continue beyond the first period, the supply of the fuel gas to the anode and the supply of the oxidant gas to the cathode are stopped. In addition to not performing the voltage recovery control, both the fuel gas supply and the oxidant gas supply are stopped, so that the operation efficiency of the fuel cell system can be further improved.

  In the fuel cell system according to the present invention, when the intermittent operation is predicted to end within a second period shorter than the first period, the control device outputs the output terminal voltage of the fuel cell stack. It is also preferable to maintain such that is equal to or greater than a second lower limit threshold value that is greater than the first lower limit threshold value.

  In this preferable aspect, when the intermittent operation is predicted to end within the second period shorter than the first period, the control device causes the output terminal voltage of the fuel cell stack to be greater than the first lower limit threshold. Maintain at or above the two lower thresholds. The situation where the intermittent operation ends in a shorter time than the first period has a higher occurrence frequency. In such a case, since the stack voltage is maintained to be equal to or higher than the second lower limit threshold value that is larger than the first lower limit threshold value, the power supply can be restarted more quickly.

  In the fuel cell vehicle equipped with the fuel cell system according to the present invention, it is also preferable to predict that the intermittent operation will be completed within the first period based on the shift position of the fuel cell vehicle.

  Although it is difficult to accurately predict the length of the period during which intermittent operation continues, for example, when the shift position of the vehicle is P (parking) or N (neutral), compared to D (drive) Therefore, there is a high possibility that intermittent operation will continue for a long time. In this preferred embodiment, the prediction that the intermittent operation is completed within the first period is performed based on the shift position of the fuel cell vehicle. As a result, the possibility of appropriately determining whether or not to perform voltage recovery control during intermittent operation increases, so that deterioration of the fuel cell can be suppressed and the operating efficiency of the fuel cell system can be improved.

  In the fuel cell vehicle equipped with the fuel cell system according to the present invention, it is also preferable to predict that the intermittent operation will be completed within the second period based on the vehicle speed of the fuel cell vehicle.

  Although it is difficult to accurately predict the period during which the intermittent operation continues, for example, when the vehicle is stopped (the vehicle speed is 0), the intermittent operation is longer for a longer period than when the vehicle is traveling. It is likely to continue. In this preferred embodiment, the prediction that the intermittent operation is completed within the second period is performed based on the vehicle speed of the fuel cell vehicle. This increases the possibility that the lower limit value of the stack voltage is appropriately set during intermittent operation, so that the drivability of the fuel cell vehicle can be improved by the rapid start of power supply.

  According to the present invention, when intermittent operation is completed in a short period of time, power supply can be resumed quickly, while in the case where intermittent operation is performed over a long period of time, the operation efficiency is improved. A fuel cell system capable of preventing deterioration of the fuel cell can be provided.

It is the figure which showed the system configuration | structure of the fuel cell vehicle carrying the fuel cell system which is one Embodiment of this invention. 2 is a flowchart for explaining a flow of processing for determining whether to shift to intermittent operation, which is performed in the fuel cell vehicle shown in FIG. 1. 2 is a flowchart for explaining a specific processing flow of intermittent operation performed in the fuel cell vehicle shown in FIG. 1. 5 is a graph for explaining a change in stack voltage with time during intermittent operation in a fuel cell system according to an embodiment of the present invention. It is a graph explaining the relationship between the frequency | count of a cell voltage fluctuation | variation, and the effective area maintenance factor of a catalyst.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same constituent elements in the drawings will be denoted by the same reference numerals as much as possible, and redundant description will be omitted.

  FIG. 1 is a diagram showing a system configuration of a fuel cell vehicle equipped with a fuel cell system 10 according to an embodiment of the present invention. The fuel cell system 10 functions as an in-vehicle power supply system mounted on a fuel cell vehicle. The fuel cell stack 20 generates electric power by receiving supply of reaction gas (fuel gas, oxidant gas), and oxidant gas. An oxidant gas supply system 30 (oxidant gas supply means) for supplying the air to the fuel cell stack 20 and a fuel gas supply system 40 (fuel for supplying hydrogen gas as fuel gas to the fuel cell stack 20) Gas supply means), a power system 50 for controlling charge / discharge of power, and a controller 60 (control means) for overall control of the entire system.

  The fuel cell stack 20 is a solid polymer electrolyte cell stack formed by stacking a large number of cells in series. In the fuel cell stack 20, the oxidation reaction of the formula (1) occurs at the anode electrode, and the reduction reaction of the equation (2) occurs at the cathode electrode. In the fuel cell stack 20 as a whole, the electromotive reaction of the formula (3) occurs.

H2 → 2H ++ 2e- (1)
(1/2) O2 + 2H ++ 2e-> H2O (2)
H2 + (1/2) O2 → H2O (3)

  A voltage sensor 71 for detecting the output terminal voltage (stack voltage Vc) of the fuel cell stack 20 and a current sensor 72 for detecting the output current (stack current) are attached to the fuel cell stack 20.

  The oxidant gas supply system 30 has an oxidant gas passage 33 through which the oxidant gas supplied to the cathode electrode of the fuel cell stack 20 flows and an oxidant off gas passage 34 through which the oxidant off-gas discharged from the fuel cell stack 20 flows. doing. The oxidant gas passage 33 has an air compressor 32 that takes in the oxidant gas from the atmosphere via the filter 31, a humidifier 35 for humidifying the oxidant gas pressurized by the air compressor 32, and a fuel cell stack. A shutoff valve A1 for shutting off the oxidant gas supply to 20 is provided. In the oxidizing off gas passage 34, a shutoff valve A2 for shutting off the oxidizing off gas discharge from the fuel cell stack 20, a back pressure adjusting valve A3 for adjusting the oxidizing gas supply pressure, and an oxidizing gas (dry gas). And a humidifier 35 for exchanging moisture between the gas and the oxidizing off gas (wet gas).

  The fuel gas supply system 40 includes a fuel gas supply source 41, a fuel gas passage 43 through which fuel gas supplied from the fuel gas supply source 41 to the anode electrode of the fuel cell stack 20 flows, and fuel discharged from the fuel cell stack 20. A circulation passage 44 for returning off-gas to the fuel gas passage 43, a circulation pump 45 for pressure-feeding the fuel off-gas in the circulation passage 44 to the fuel gas passage 43, and an exhaust / drain passage 46 branched and connected to the circulation passage 44 Have.

  The fuel gas supply source 41 is composed of, for example, a high-pressure hydrogen tank or a hydrogen storage alloy, and stores high-pressure (for example, 35 MPa to 70 MPa) hydrogen gas. When the shut-off valve H1 is opened, the fuel gas flows out from the fuel gas supply source 41 into the fuel gas passage 43. The fuel gas is decompressed to about 200 kPa, for example, by the regulator H2 and the injector 42, and supplied to the fuel cell stack 20.

  The fuel gas supply source 41 includes a reformer that generates a hydrogen-rich reformed gas from a hydrocarbon-based fuel, and a high-pressure gas tank that stores the reformed gas generated by the reformer in a high-pressure state. It may be configured.

  In the fuel gas passage 43, a shutoff valve H1 for shutting off or allowing the supply of the fuel gas from the fuel gas supply source 41, a regulator H2 for adjusting the pressure of the fuel gas, and a fuel gas supply to the fuel cell stack 20 An injector 42 for controlling the amount, a shutoff valve H3 for shutting off the supply of fuel gas to the fuel cell stack 20, and a pressure sensor 74 are provided.

  The regulator H2 is a device that regulates the upstream side pressure (primary pressure) to a preset secondary pressure, and includes, for example, a mechanical pressure reducing valve that reduces the primary pressure. The mechanical pressure reducing valve has a housing in which a back pressure chamber and a pressure adjusting chamber are formed with a diaphragm therebetween, and the primary pressure is reduced to a predetermined pressure in the pressure adjusting chamber by the back pressure in the back pressure chamber. It has a configuration for the next pressure. By arranging the regulator H2 upstream of the injector 42, the upstream pressure of the injector 42 can be effectively reduced. For this reason, the design freedom of the mechanical structure (a valve body, a housing, a flow path, a drive device, etc.) of the injector 42 can be increased. Further, since the upstream pressure of the injector 42 can be reduced, it is possible to prevent the valve body of the injector 42 from becoming difficult to move due to an increase in the differential pressure between the upstream pressure and the downstream pressure of the injector 42. be able to. Therefore, it is possible to widen the adjustable pressure width of the downstream pressure of the injector 42 and to suppress a decrease in responsiveness of the injector 42.

  The injector 42 is an electromagnetically driven on-off valve capable of adjusting the gas flow rate and gas pressure by driving the valve body directly at a predetermined driving cycle with an electromagnetic driving force and separating it from the valve seat. The injector 42 includes a valve seat having an injection hole for injecting gaseous fuel such as fuel gas, a nozzle body for supplying and guiding the gaseous fuel to the injection hole, and an axial direction (gas flow direction) with respect to the nozzle body. And a valve body that is slidably accommodated and opens and closes the injection hole.

  In the present embodiment, the valve element of the injector 42 is driven by a solenoid that is an electromagnetic drive device, and the opening area of the injection hole can be switched in two stages by turning on and off the pulsed excitation current supplied to the solenoid. it can. By controlling the gas injection time and gas injection timing of the injector 42 by the control signal output from the controller 60, the flow rate and pressure of the fuel gas are controlled with high accuracy. The injector 42 directly opens and closes the valve (valve body and valve seat) with an electromagnetic driving force, and has a high responsiveness because its driving cycle can be controlled to a highly responsive region. The injector 42 changes its downstream area by changing at least one of the opening area (opening) and the opening time of the valve provided in the gas flow path of the injector 42 in order to supply the required gas flow rate downstream. The gas flow rate (or hydrogen molar concentration) supplied to the side is adjusted.

  The circulation passage 44 is connected to a shutoff valve H4 for shutting off the fuel off-gas discharge from the fuel cell stack 20 and an exhaust drainage passage 46 branched from the circulation passage 44. An exhaust / drain valve H5 is disposed in the exhaust / drain passage 46. The exhaust / drain valve H <b> 5 is operated according to a command from the controller 60, thereby discharging the fuel off-gas containing impurities in the circulation passage 44 and moisture to the outside. By opening the exhaust / drain valve H5, the concentration of impurities in the fuel off-gas in the circulation passage 44 decreases, and the hydrogen concentration in the fuel off-gas circulating in the circulation system can be increased.

  The fuel off-gas discharged through the exhaust / drain valve H5 is mixed with the oxidizing off-gas flowing through the oxidizing off-gas passage 34 and diluted by a diluter (not shown). The circulation pump 45 circulates and supplies the fuel off gas in the circulation system to the fuel cell stack 20 by driving the motor.

  The power system 50 includes a DC / DC converter 51, a battery 52, a traction inverter 53, a traction motor 54, and auxiliary machinery 55. The fuel cell system 10 is configured as a parallel hybrid system in which a DC / DC converter 51 and a traction inverter 53 are connected to the fuel cell stack 20 in parallel. The DC / DC converter 51 boosts the DC voltage supplied from the battery 52 and outputs it to the traction inverter 53, and the DC power generated by the fuel cell stack 20, or the regenerative power collected by the traction motor 54 by regenerative braking. And a function of charging the battery 52 by stepping down the voltage. The charge / discharge of the battery 52 is controlled by these functions of the DC / DC converter 51. Further, the operation point (output voltage, output current) of the fuel cell stack 20 is controlled by voltage conversion control by the DC / DC converter 51.

  The battery 52 functions as a surplus power storage source, a regenerative energy storage source during regenerative braking, and an energy buffer during load fluctuations associated with acceleration or deceleration of the fuel cell vehicle. As the battery 52, for example, a secondary battery such as a nickel / cadmium storage battery, a nickel / hydrogen storage battery, or a lithium secondary battery is suitable. An SOC sensor 73 for detecting SOC (State of charge) is attached to the battery 52.

  The traction inverter 53 is, for example, a PWM inverter driven by a pulse width modulation method, and converts a DC voltage output from the fuel cell stack 20 or the battery 52 into a three-phase AC voltage in accordance with a control command from the controller 60. The rotational torque of the traction motor 54 is controlled. The traction motor 54 is a three-phase AC motor, for example, and constitutes a power source of the fuel cell vehicle.

  Auxiliary machines 55 are motors (for example, power sources such as pumps) arranged in each part in the fuel cell system 10, inverters for driving these motors, and various on-vehicle auxiliary machines. (For example, an air compressor, an injector, a cooling water circulation pump, a radiator, etc.) is a general term.

  The controller 60 is a computer system including a CPU, a ROM, a RAM, and an input / output interface, and controls each part of the fuel cell system 10. For example, when the controller 60 detects that the state of the ignition switch IG is ON, the controller 60 starts the operation of the fuel cell system 10 and is output from the accelerator opening signal ACC output from the accelerator sensor or the vehicle speed sensor. Based on the vehicle speed signal VV and the like, the required power of the entire system is obtained. The required power of the entire system is the total value of the vehicle running power and the auxiliary machine power. The controller 60 also receives the state of the shift position SP of the fuel cell vehicle.

  Here, auxiliary electric power includes electric power consumed by in-vehicle auxiliary equipment (humidifier, air compressor, hydrogen pump, cooling water circulation pump, etc.), and equipment required for vehicle travel (transmission, wheel control device, steering) Power consumed by devices, suspension devices, etc.), power consumed by devices (air conditioners, lighting equipment, audio, etc.) disposed in the passenger space, and the like.

  Then, the controller 60 determines the distribution of the output power of each of the fuel cell stack 20 and the battery 52, and the oxidant gas supply system 30 and the fuel gas so that the power generation amount of the fuel cell stack 20 matches the target power. The operating point (output voltage, output current) of the fuel cell stack 20 is controlled by controlling the supply system 40 and the DC / DC converter 51 to adjust the output voltage of the fuel cell stack 20. Further, the controller 60 outputs, for example, each of the U-phase, V-phase, and W-phase AC voltage command values to the traction inverter 53 as a switching command so as to obtain a target torque corresponding to the accelerator opening, The output torque of the motor 54 and the rotation speed are controlled.

  In the fuel cell system 10 of the present embodiment, the controller 60 determines whether to perform intermittent operation or normal operation based on the fuel cell system 10 and the vehicle speed signal VV. The intermittent operation mode is a mode in which power generation (power supply) by the fuel cell stack 20 is stopped and the traction motor 54 is driven only by the battery 52. The intermittent operation mode is not limited to completely stopping power generation (power supply) by the fuel cell stack 20, and may be an operation mode in which a small amount of power generation is continued while suppressing power generation. The normal operation mode is a mode in which power is generated by the fuel cell stack 20 and the traction motor 54 is driven using the electric power. In the normal operation mode, the battery 52 may be used together.

  With reference to FIG. 2, the flow of processing performed inside the controller 60 in order to determine whether or not the fuel cell system 10 shifts to intermittent operation will be described. FIG. 2 is a flowchart for explaining the flow of the processing. The series of processing shown in FIG. 2 is repeatedly executed by the controller 60 every time a predetermined time elapses.

  First, in step S101, the state of the ignition switch IG is confirmed. If the state of the ignition switch IG is OFF, the fuel cell system 10 is in a stopped state, so it is not necessary to determine whether or not to shift to intermittent operation, and the process ends. If the state of the ignition switch IG is ON, the process proceeds to step S102.

  In step S102, the state of the intermittent flag is confirmed. The intermittent flag is flag information indicating whether or not intermittent operation is being performed, and is stored in the controller 60. The state where the intermittent flag is ON indicates the intermittent operation mode. The state where the intermittent flag is OFF indicates the normal operation mode. In step S102, if the intermittent flag is ON, the process proceeds to step S104. If the intermittent flag is OFF, the process proceeds to step S103, and after the normal operation mode is started (or continued), the process proceeds to step S104.

  In step S104, the state of the accelerator opening signal ACC is confirmed. If the accelerator opening signal ACC is OFF, that is, if the accelerator is not depressed and the accelerator opening is 0, the process proceeds to step S105. When the accelerator opening signal ACC is not OFF, it is estimated that electric power for running the fuel cell vehicle is required and the electric power is likely to further increase. That is, there is a possibility that high-load operation is performed, and it is assumed that intermittent operation is not appropriate. For this reason, after moving to step S107 and setting the intermittent flag to OFF, the process ends.

  In step S105, the vehicle speed of the fuel cell vehicle is confirmed based on the vehicle speed signal VV. When the vehicle speed is 3 km / h or less, the process proceeds to step S106. When the vehicle speed is higher than 3 km / h, it is estimated that the fuel cell vehicle is traveling on the road and may accelerate thereafter. That is, there is a possibility that high-load operation is performed, and it is assumed that intermittent operation is not appropriate. For this reason, after moving to step S108 and setting the intermittent flag to OFF, the process is terminated.

  In step S106, since the accelerator opening signal ACC is OFF and the vehicle speed is 3 km / h or less, it is estimated that the fuel cell vehicle has already stopped or will stop within a short time. . For this reason, after that, there is a high possibility that low load operation will be performed, and it is determined that it is appropriate to shift to intermittent operation. For this reason, the process is terminated after the intermittent flag is set to ON.

  Next, a specific processing flow of intermittent operation will be described with reference to FIG. FIG. 3 is a flowchart for explaining a specific processing flow of intermittent operation. The series of processes shown in FIG. 3 is repeatedly executed by the controller 60 every time a predetermined time elapses.

  First, in step S201, the state of the intermittent flag is confirmed. If the intermittent flag is in an OFF state, it is not necessary to perform intermittent operation, and the process ends. If the intermittent flag is ON, the process proceeds to step S202.

  In step S202, the supply of the oxidant gas to the cathode electrode of the fuel cell stack 20 and the supply of the fuel gas to the anode electrode of the fuel cell stack 20 are both stopped. Further, the supply of power from the fuel cell stack 20 to the battery 52 and the supply of power from the fuel cell stack 20 to the traction inverter 53 (and the traction motor 54) are both stopped. In the intermittent operation mode, the traction motor 54 is driven only by the electric power supplied from the battery 52.

  In step S203, it is determined from the vehicle speed signal VV whether or not the fuel cell vehicle is stopped (whether or not the vehicle speed is 0). If the fuel cell vehicle is stopped, the process proceeds to step S207. If the fuel cell vehicle is not stopped, the process proceeds to step S204.

  When the process proceeds to step S204, the fuel cell vehicle is traveling at a low vehicle speed of 3 km / h or less. As already described with respect to step S105 and step S106, when the vehicle speed is low, such as 3 km / h or less, it is estimated that the fuel cell vehicle will stop thereafter. However, compared with the case where the fuel cell vehicle is completely stopped and the vehicle speed is 0, it can be said that the possibility that the fuel cell vehicle will accelerate in a short time is relatively high. In other words, the time (second period) during which the intermittent operation is predicted to continue can be said to be relatively short.

  Therefore, in step S204, V2 (second lower limit threshold) higher than the voltage V1 (first lower limit threshold) described later is set as the threshold Vth of the stack voltage Vc, and the process proceeds to step S205. In step S205, it is determined whether or not the stack voltage Vc has decreased to a voltage lower than the threshold value Vth. If the stack voltage Vc is equal to or higher than the threshold value Vth, the process is terminated. When the stack voltage Vc is lower than the threshold value Vth, the process proceeds to step S206.

  In step S206, voltage recovery control is performed to recover the stack voltage Vc to the threshold value Vth or higher. Specifically, the air compressor 32 is temporarily operated to supply the oxidant gas to the fuel cell stack 20, and control is performed so that the stack voltage Vc exceeds the threshold value Vth and rises to a predetermined voltage target value. .

  The time change of the stack voltage Vc at this time is shown in FIG. FIG. 4 is a graph for explaining the time change of the stack voltage Vc during intermittent operation. As indicated by Vc1 in FIG. 4, when the stack voltage Vc decreases to the threshold value Vth, the voltage recovery process in step S206 is performed and the stack voltage Vc increases. Thereafter, while the intermittent operation mode continues, the stack voltage Vc is maintained at the threshold value Vth or higher while repeatedly decreasing to the threshold value Vth and increasing to the voltage target value by the voltage recovery control. .

  As described above, when the vehicle speed is not 0, the threshold voltage Vth is set higher than when the vehicle speed is 0, and the voltage recovery control is performed. Therefore, when the intermittent operation ends thereafter, power supply is started quickly. be able to. In other words, in situations where intermittent operation is relatively likely to continue for a long period of time, it is more likely that it is appropriate to set the lower limit value of the stack voltage higher. Drivability can be improved.

  Returning again to FIG. 3, the description will be continued. If the fuel cell vehicle is stopped in step S203, the process proceeds to step S207. In step S207, it is determined whether or not the shift position SP of the vehicle is P (parking).

  In step S207, if the shift position SP is P (parking), the process is terminated. For this reason, the intermittent operation mode is maintained without performing the voltage recovery control in step S206. Since voltage recovery control is not performed, the stack voltage Vc gradually decreases as shown by Vc2 in FIG. 4, and finally becomes a constant voltage value.

  When the shift position SP is P (parking), it is unlikely that the fuel cell vehicle will immediately start traveling, and it is estimated that intermittent operation continues for a long time by stopping. For this reason, in the fuel cell system 10 according to the present embodiment, the voltage recovery control is not performed as described above.

  If the shift position SP is not P (parking) in step S207, it is determined in the subsequent step S208 whether the shift position SP is N (neutral). When the shift position SP is not N (neutral), the process proceeds to step S209.

  When the process proceeds to step S209, the shift position SP is not P (parking) and is not N (neutral). For this reason, it is highly possible that the fuel cell vehicle is temporarily stopped, and it is estimated that the vehicle starts to travel and ends the intermittent operation within a relatively short time. However, the time (first period) is estimated to be longer than the time (second period) during which intermittent operation is expected to continue during low-speed traveling at 3 km / h or less. For this reason, in step S209, V1 (first lower limit threshold) lower than the voltage V2 (second lower limit threshold) described above is set as the threshold Vth of the stack voltage Vc, and the process proceeds to step S205. Thereafter, as described above, the voltage recovery control in step S206 is performed as necessary, and the stack voltage Vc is maintained at or above the threshold value Vth.

  If the shift position SP is N (neutral) in step S208, it is then determined whether or not the state where the shift position SP is N (neutral) continues for 120 seconds. Specifically, the process proceeds to step S <b> 210, and elapsed time measurement is started inside the controller 60. Thereafter, in step S211, it is determined whether or not the shift position SP remains N (neutral). When the shift position is changed to other than N (neutral), the process proceeds to step S209. If the shift position SP remains N (neutral) in step S211, the process proceeds to step S212, and it is determined whether the elapsed time measured in the controller 60 has exceeded 120 seconds. If it does not exceed 120 seconds, the process returns to step S210, and the determination as to whether or not the shift position SP remains N (neutral) is repeated.

  If it is determined in step S212 that the shift position SP remains N (neutral) and 120 seconds have elapsed, the process ends in the same manner as in step S207 where the shift position SP is P (parking). For this reason, the intermittent operation mode is maintained without performing the voltage recovery control in step S206. Since the voltage recovery control is not performed, the stack voltage Vc gradually decreases and finally becomes a constant voltage value.

  Even when the shift position SP remains N (neutral) and 120 seconds elapse, it is also unlikely that the fuel cell vehicle immediately starts running, and it is assumed that intermittent operation continues for a long time by stopping. The For this reason, in the fuel cell system 10 according to the present embodiment, the voltage recovery control is not performed as described above.

  Thus, in the intermittent operation mode, the fuel cell vehicle stops both when the shift position SP is P (parking) and when the shift position SP is N (neutral) continues for 120 seconds. It is estimated that intermittent operation continues for a long time. This time is longer than the time (first period) during which the fuel cell vehicle is completely stopped and the vehicle speed is 0, and the shift position SP is predicted to continue intermittent operation in a state other than the above. It is estimated to be even longer. For this reason, in the fuel cell system 10 according to the present embodiment, voltage recovery control is not performed in such a case.

  Here, the influence of the fluctuation of the stack voltage Vc on the effective area of the electrode catalyst will be described with reference to FIG. FIG. 5 is a graph for explaining the relationship between the number of fluctuations of the cell voltage and the effective area maintenance ratio of the catalyst (the ratio of the area of the catalyst that effectively functions as the catalyst in the surface area of the catalyst).

  E1 in FIG. 5 shows the relationship between the number of fluctuations and the effective area maintenance ratio of the catalyst when the voltage between the electrodes of the single cells constituting the fuel cell stack 20 is varied in the range of 0.8V to 0.9V. Showing the relationship. E2 in FIG. 5 shows the relationship between the number of fluctuations and the effective area maintenance ratio of the catalyst when the voltage between the electrodes of the single cell is varied in the range of 0.1 V to 0.9 V. .

  As shown in FIG. 5, in both E1 and E2, the effective area maintenance ratio of the catalyst decreases as the number of cell voltage fluctuations increases. This indicates that the greater the number of cell voltage (stack voltage) fluctuations, the higher the rate at which the effective area of the catalyst decreases. Further, E2 has a larger reduction amount of the effective area maintenance rate of the catalyst than E1. This shows that even when the number of fluctuations of the cell voltage (stack voltage) is the same, the greater the fluctuation range of the cell voltage (stack voltage), the higher the rate at which the effective area of the catalyst decreases.

  In the fuel cell system 10 according to the present embodiment, the voltage recovery control is not performed when the shift position SP is P (parking) in the intermittent operation mode, or when 120 seconds have elapsed with N (neutral). As a result, the elution of the electrode catalyst is suppressed because the decrease and recovery of the stack voltage Vc (such as Vc1 in FIG. 4) are not repeated. Further, since it is not necessary to supply fuel gas for increasing the stack voltage Vc or supply of oxidant gas, the operation efficiency of the fuel cell system 10 can be improved. Note that, by not performing the voltage recovery control, it takes time to restart the power supply, but the situation where the shift position SP is P (parking) and the shift position SP is N (neutral). In any situation where 120 seconds elapses, the occurrence frequency is low, so it can be said that the adverse effect on the drivability of the fuel cell vehicle is small.

  Further, when the shift position SP is other than the above in the intermittent operation mode, the voltage recovery control is performed so as to maintain the stack voltage Vc at or above the threshold value Vth. This threshold value Vth is set to be a higher threshold value (second lower limit threshold value) when the intermittent operation mode is predicted to end in a short time. As a result, since the fluctuation range of the stack voltage Vc is reduced, the elution of the electrode catalyst is suppressed.

  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. In other words, those specific examples that have been appropriately modified by those skilled in the art are also included in the scope of the present invention as long as they have the characteristics of the present invention. For example, the elements included in each of the specific examples described above and their arrangement, materials, conditions, shapes, sizes, and the like are not limited to those illustrated, but can be changed as appropriate. Moreover, each element with which each embodiment mentioned above is provided can be combined as long as technically possible, and the combination of these is also included in the scope of the present invention as long as it includes the features of the present invention.

10: Fuel cell system 20: Fuel cell stack 30: Oxidant gas supply system 31: Filter 32: Air compressor 33: Oxidant gas passage 34: Oxidation off-gas passage 35: Humidifier 40: Fuel gas supply system 41: Fuel gas supply Source 42: Injector 43: Fuel gas passage 44: Circulation passage 45: Circulation pump 46: Exhaust drain passage 50: Electric power system 51: Converter 52: Battery 53: Traction inverter 54: Traction motor 55: Auxiliary machinery 60: Controller 71: Voltage sensor 72: Current sensor 73: Sensor 74: Pressure sensor A2: Shut-off valve A3: Back pressure adjustment valve ACC: Accelerator opening signal H1: Shut-off valve H2: Regulator H3, H4: Shut-off valve H5: Exhaust drain valve IG: Ignition Switch SP: Shift position Vc: Stud Voltage VV: vehicle speed signal Vth: threshold

Claims (5)

A fuel cell system comprising a fuel cell stack comprising a plurality of cells having an anode and a cathode,
Fuel gas supply means for supplying fuel gas to the anode;
An oxidant gas supply means for supplying an oxidant gas to the cathode;
Control means for controlling the fuel gas supply means and the oxidant gas supply means, and causing the fuel cell stack to generate power according to required power,
The control means performs an intermittent operation for temporarily stopping the supply of the fuel gas and suppressing the power generation of the fuel cell stack in a state where the required power is a predetermined value or less,
During the intermittent operation,
When the intermittent operation is predicted to end within the first period, while performing the voltage recovery control to maintain the output terminal voltage of the fuel cell stack to be equal to or higher than the first lower limit threshold,
The fuel cell system is characterized in that the voltage recovery control is not performed when the intermittent operation is predicted to continue beyond the first period.   When the intermittent operation is predicted to continue beyond the first period, the supply of the fuel gas to the anode and the supply of the oxidant gas to the cathode are stopped. The fuel cell system according to claim 1.   When the intermittent operation is predicted to end within a second period shorter than the first period, the control device is configured to output a first output terminal voltage of the fuel cell stack greater than the first lower limit threshold. The fuel cell system according to claim 1 or 2, wherein the fuel cell system is maintained so as to be equal to or more than a second lower limit threshold value.   A fuel cell vehicle equipped with the fuel cell system according to any one of claims 1 to 3, wherein the prediction that the intermittent operation ends within a first period is based on a shift position of the fuel cell vehicle. A fuel cell vehicle comprising:   A fuel cell vehicle equipped with the fuel cell system according to claim 3, wherein the intermittent operation is predicted to be completed within the second period based on a vehicle speed of the fuel cell vehicle. Fuel cell vehicle.

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