JP2006260987A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system improved in both fuel efficiency by reducing reactive gas consumption and stability at a start. <P>SOLUTION: This fuel cell system comprises a fuel cell 20 receiving reactive gas supply for generation, a control part 50 controlling the reactive gas supply to the fuel cell 20 and power supply from the fuel cell 20 to loads 51, 52, M3 and M4 and a cell voltage monitor 11 measuring a cell voltage of the fuel cell 20. When it is detected that the cell voltage of the fuel cell 20 falles or in a situation to fall at the start, reactive gas is supplied to the fuel cell 20 while the power supply from the fuel cell 20 to the loads 51 and so on, and M4 is prohibited. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system including a fuel cell that generates power upon receiving a supply of a reaction gas, and more particularly to control at startup.

In recent years, a fuel cell system using a fuel cell that generates electric power by an electrochemical reaction between a fuel gas and an oxidizing gas as an energy source has attracted attention. With respect to the control of such a fuel cell system, for example, in Patent Document 1, when the power generation voltage of the fuel cell decreases during the warm-up operation after startup, the fuel gas is recovered so as to recover the temperature or voltage of the fuel cell. Techniques for controlling the supply device are disclosed.
JP 2004-165058 A

  However, since the technique disclosed in Patent Document 1 increases the amount of anode gas supplied to the fuel cell when it is determined that the power generation voltage of the fuel cell is low at the time of startup, the reduction in the power generation voltage is suppressed. Even if the stability at the time of starting the system can be improved, the consumption of the anode gas is increased and the fuel consumption may be deteriorated.

  Therefore, an object of the present invention is to provide a fuel cell system capable of achieving both improvement in fuel efficiency by reducing the amount of reaction gas consumption and improvement in stability at startup.

  The fuel cell system of the present invention controls a fuel cell that generates power upon receiving a reaction gas supply, a gas supply control unit that controls the supply of the reaction gas to the fuel cell, and a power supply from the fuel cell to a load. A power supply control unit, and a detection unit that detects that the power generation voltage (total voltage, cell voltage) of the fuel cell is reduced, or that detects that the power generation voltage can be reduced, and When the detection is made at the time of start-up, the reaction gas is supplied to the fuel cell in a state where power supply from the fuel cell to the load is prohibited.

  According to such a configuration, it is assumed that there is a load request (output request, power supply request) when the power generation state of the fuel cell is not yet stable, such as during startup (including restart immediately after system down). However, since power is not supplied from the fuel cell to the load, it is possible to suppress a decrease in the generated voltage without increasing the amount of reactant gas supplied to the fuel cell.

  When this fuel cell system is applied to, for example, a fuel cell vehicle, loads for which power supply from the fuel cell is prohibited include a traction motor that drives driving wheels, an auxiliary device, an accessory device, and the like. In addition, power storage devices such as secondary batteries and capacitors that charge power from the fuel cell and supply the charged power to other devices need to be charged because their remaining capacity (charged amount) is less than a predetermined amount. When there is a (charge request), it becomes a load on the fuel cell.

  The fuel cell system of the present invention includes a fuel cell that generates power upon receiving a supply of a reaction gas, a power storage device that can be charged from the fuel cell and discharged to a load, and a charge amount in the power storage device is a predetermined amount. As described above, a charge control unit that controls charging from the fuel cell to the power storage device, and detects that the power generation voltage (total voltage, cell voltage) of the fuel cell is decreased, or the power generation voltage decreases. A detection unit that detects that the current state is obtained, and when the detection is performed at the time of start-up, even if the charge amount of the power storage device does not reach the predetermined amount, the fuel cell to the power storage device Prohibit charging.

  According to such a configuration, when the power generation state of the fuel cell is not yet stable, such as at the time of start-up (including restart immediately after system down), the remaining capacity (charge amount) of the power storage device is small and the power storage Even if there is a situation where the device needs to be charged, charging (power supply) from the fuel cell to the power storage device is not performed, so the generated voltage can be generated without increasing the amount of reactant gas supplied to the fuel cell. Can be suppressed.

  In the fuel cell system, it may be detected that the power generation voltage can be lowered when the fuel cell system is stopped with the detection being performed during the previous drive.

  According to such a configuration, even when the power generation state of the fuel cell is not yet stable, the generated power is supplied to the load (including the power storage device) to start up (including restart). It is possible to prevent a system failure that may occur in the future.

  In the above fuel cell system, in order to detect that the generated voltage can be reduced, that is, to determine whether to reduce the generated voltage, a time-series change in the generated voltage (total voltage, cell voltage) (for example, Decrease or vibration) may be used. Moreover, since the generated voltage has a correlation with the amount of water in the fuel cell, a decrease in the generated voltage may be predicted based on the amount of water in the fuel cell.

  According to the present invention, when the power generation voltage of the fuel cell at the time of start-up is in a state where it can be lowered, even if there is a load request (including a charge request), the load (the power storage device is Therefore, it is possible to suppress a decrease in the generated voltage without increasing the amount of reaction gas supplied to the fuel cell. Therefore, it is possible to achieve both improvement in fuel consumption by reducing the reaction gas consumption and improvement in stability at startup.

  FIG. 1 is a schematic configuration diagram showing an embodiment of a fuel cell system according to the present invention. This fuel cell system can be applied to an in-vehicle power generation system of a fuel cell vehicle, and can be applied to, for example, a stationary power generation system.

  As shown in the figure, for example, air (outside air) as an oxidizing gas (reactive gas) is supplied to the cathode inlet side of the fuel cell 20 via an air supply path 71. The air supply path 71 is provided with an air filter A1 that removes particulates from the air, an air compressor A3 that pressurizes the air, a pressure sensor P4 that detects the supply air pressure, and a humidifier A21 that adds required moisture to the air. The air compressor A3 is driven by a compressor motor M controlled by a control unit (detection unit) 50.

  The air off gas discharged from the fuel cell 20 is discharged to the outside through the exhaust path 72. The exhaust path 72 is provided with a pressure sensor P1 for detecting the exhaust pressure, a pressure regulating valve A4, and a heat exchanger for the humidifier A21. The pressure sensor P <b> 1 is provided near the cathode side outlet of the fuel cell 20. The pressure adjustment valve A4 functions as a pressure regulator that sets the supply air pressure to the fuel cell 20 by adjusting the pressure on the cathode outlet side of the fuel cell 20.

  The detection signals of the pressure sensors P4 and P1 are sent to the control unit 50. The control unit 50 sets the supply air pressure and the supply air flow rate to the fuel cell 20 by adjusting the air compressor A3 and the pressure adjustment valve A4.

  For example, hydrogen gas as a fuel gas (reactive gas) is supplied from the hydrogen supply source 30 to the anode inlet side of the fuel cell 20 via the fuel supply path 74. The hydrogen supply source 30 corresponds to, for example, a high-pressure hydrogen tank, but may be a so-called fuel reformer, a hydrogen storage alloy, or the like.

  In the fuel supply path 74, a hydrogen supply valve H100 that supplies or stops supplying hydrogen from the hydrogen supply source 30, a pressure sensor P6 that detects a gas pressure downstream of the hydrogen supply valve 74, and a hydrogen gas supply pressure to the fuel cell 20 are reduced. A hydrogen pressure regulating valve H9 that adjusts the pressure, a pressure sensor P9 that detects a gas pressure downstream of the hydrogen pressure regulating valve H9, an FC inlet valve H21 that opens and closes between the anode inlet of the fuel cell 20 and the fuel supply path 74, and an anode inlet side of the fuel cell 20 A pressure sensor P5 for detecting the gas pressure is provided. Detection signals from the pressure sensors P5, P6 and P9 are supplied to the control unit 50.

  The hydrogen gas that has not been consumed in the fuel cell 20 is discharged as hydrogen off-gas to the hydrogen circulation path 75 and returned to the downstream side of the pressure regulating valve H9 in the fuel supply path 74. The hydrogen circulation path 75 includes a temperature sensor T31 that detects the temperature of the hydrogen off-gas, an FC outlet valve H22 that communicates / blocks the fuel cell 20 and the hydrogen circulation path 75, a gas-liquid separator H42 that collects moisture from the hydrogen off-gas, and a recovery A drain valve H41 that collects the generated water in a tank (not shown) outside the hydrogen circulation path 75, a hydrogen pump H50 that pressurizes hydrogen offgas, and a check valve H52 are provided.

  The FC inlet valve H21 and the FC outlet valve H22 close the anode side of the fuel cell. The detection signal of the temperature sensor T31 is supplied to the control unit 50. The hydrogen pump H50 is driven by a hydrogen pump motor M controlled by the control unit 50. The hydrogen off gas merges with the hydrogen gas in the fuel supply path 74 and is supplied to the fuel cell 20 for reuse. The check valve H52 prevents the hydrogen gas in the fuel supply path 74 from flowing back to the hydrogen circulation path 75 side. Various valves H100, H21, and H22 are driven by signals from the controller 50.

  The hydrogen circulation path 75 is connected to the exhaust path 72 by the purge flow path 76 via the purge valve H51. The discharge control valve H51 is an electromagnetic shut-off valve, and discharges (purges) hydrogen off-gas to the outside by operating according to a command from the control unit 50.

  The fuel cell 20 is configured as a fuel cell stack in which a required number of cells that are supplied with fuel gas and oxidizing gas to generate power are stacked. The cell includes an MEA (membrane-electrode assembly) and a pair of separators that sandwich the MEA, and has a laminated form as a whole. The MEA includes an electrolyte membrane made of an ion exchange membrane made of a polymer material and a pair of electrodes (anode and cathode) sandwiching the electrolyte membrane from both sides.

  The fuel cell 20 is connected to a measurement terminal from a cell voltage monitor (detection unit) 11 for each cell or for each predetermined number of cell groups, and a cell voltage (power generation voltage of the fuel cell) for each cell or cell group. Can be measured. The detection signal of the cell voltage monitor 11 is supplied to the control unit 50.

  Part of the DC power generated by the fuel cell 20 is stepped down by the DC / DC converter 53 and charged to the secondary battery (power storage device) 54. The secondary battery 54 plays a role as a regenerative energy storage source at the time of vehicle braking, and an energy buffer at the time of load fluctuation accompanying acceleration or deceleration of the vehicle, and includes a nickel / cadmium storage battery, a nickel / hydrogen storage battery, and a lithium secondary battery. Etc.

  Charging from the fuel cell 20 to the secondary battery 54 is controlled by the control unit 50 described later so that the remaining capacity (charge amount) SOC of the secondary battery 54 is equal to or greater than a predetermined amount. Is predicted or detected to be below a predetermined threshold value, even if the remaining capacity SOC of the secondary battery 54 has not reached the predetermined amount, the fuel cell 20 to the secondary battery 54 Power supply to, that is, charging is prohibited.

  A traction inverter (load) 51 and an auxiliary inverter (load) 52 convert DC power supplied from either or both of the fuel cell 20 and the secondary battery 54 into AC power, and a traction motor (load) M3. AC power is supplied to each auxiliary motor (load) M4. The auxiliary motor M4 is a generic term for a hydrogen pump motor M that drives a hydrogen pump H50, which will be described later, a compressor motor M that drives an air compressor A3, and the like.

  The control unit 50 is configured by a control computer system such as a CPU, ROM, RAM, HDD, input / output interface, and display, and controls the accelerator opening detected by an unillustrated accelerator sensor, the vehicle speed detected by an unillustrated vehicle speed sensor, and the like. Based on the system required power (the sum of the vehicle running power and the auxiliary power), the fuel cell 20 takes into account the remaining capacity SOC of the secondary battery 54 so that the output power of the fuel cell 20 matches the target power. Control the system.

  Specifically, the control unit 50 adjusts the rotation speed of the compressor motor M that drives the air compressor A3 to adjust the supply amount of the oxidizing gas, and adjusts the rotation speed of the hydrogen pump motor M that drives the hydrogen pump H50. Adjust the fuel gas supply. Further, the control unit 50 controls the DC / DC converter 53 to adjust the operation point (output voltage, output current) of the fuel cell 20 and adjust the output power of the fuel cell 20 to match the target power.

  However, the control unit 50 predicts or detects that the cell voltage of the fuel cell 20 measured at the time of start-up has fallen below a predetermined threshold (the power generation voltage is in a state where it can be lowered or can be lowered). For example, inverters 51 and 52, motors M3 and M4, vehicle accessory devices, secondary batteries 54 requiring charging, etc., in other words, Supplying reaction gas to the fuel cell 20 in a state where power supply to the load is prohibited;

  Start-up includes, for example, start-up after a certain period of time has elapsed since the system was stopped, such as start-up after parking and stopping, and restart that is performed immediately after a system down during start-up or driving Time is also included. Further, not only manual activation based on human operation but also automatic activation executed when a predetermined event occurs in the control program is included.

  As described above, the control unit 50 of the present embodiment is further provided as a gas supply control unit that controls the supply of the reaction gas to the fuel cell 20 and as a power supply control unit that controls the power supply from the fuel cell 20 to the load. Has a function as a charge control unit that controls charging from the fuel cell 20 to the secondary battery 54 so that the remaining capacity SOC of the secondary battery 54 becomes a predetermined amount. Further, the control unit 50 constitutes a detection unit together with the cell voltage monitor 11.

  FIG. 2 is a flowchart describing the contents of charge control at the time of activation. The routine shown in this flowchart is called when a predetermined event occurs in the main control program executed by the control unit 50, for example, when it is detected that the ignition is ON. In the following description, it is assumed that the reaction gas has already been supplied to the fuel cell 20.

  First, it is determined whether or not the remaining capacity SOC (charge amount) of the secondary battery 54 is equal to or greater than a predetermined threshold (for example, 50 to 80%) (step S1), and the remaining capacity SOC of the secondary battery 54 is determined. If it is equal to or greater than the predetermined threshold (step S1: YES), that is, if charging of the secondary battery 54 is not necessary, the subsequent processing is skipped and the routine returns to the routine from which this routine is read.

  On the other hand, when the remaining capacity SOC of the secondary battery 54 is less than the predetermined threshold (step S1: NO), charging of the secondary battery 54 is started under normal conditions (step S3). Thereafter, it is determined whether or not the cell voltage measured by the cell voltage monitor 11 is equal to or higher than a predetermined threshold (step S5). The cell voltage used for this determination is, for example, an average value or a minimum value of the measured cell voltages.

  When the cell voltage is equal to or higher than a predetermined threshold (step S5: YES), that is, even if normal charging to the secondary battery 54 is continued in the power generation state at that time, the fuel cell system is down (also called cell dropping). If there is no risk of this, the subsequent processing is skipped and the routine returns to the routine from which this routine is read. That is, normal charging to the secondary battery 54 is continued as it is.

  On the other hand, when the cell voltage is less than the predetermined threshold value (step S5: NO), the fuel cell system goes down (step S7), so the system is restarted (step S9). For example, per unit time Charging with limitation to the secondary battery 54 is started by setting an upper limit to the charge amount (step S11).

  Thereafter, it is determined whether or not the cell voltage measured by the cell voltage monitor 11 is equal to or higher than a predetermined threshold (step S13). The cell voltage used for this determination is, for example, an average value or a minimum value of the measured cell voltages.

  If the cell voltage is equal to or higher than the predetermined threshold (step S13: YES), that is, there is a possibility that the fuel cell system will be down even if the limited charging to the secondary battery 54 is continued in the power generation state at that time. If not, the subsequent processing is skipped and the routine returns to the routine from which this routine is read. That is, the limited charging to the secondary battery 54 is continued as it is.

  On the other hand, when the cell voltage is less than the predetermined threshold value (step S13: NO), the fuel cell system is down (step S15), so the system is restarted (step S17). Charging the secondary battery 54 is prohibited (stopped) (step S19). At this time, power supply to all loads viewed from the fuel cell 20, for example, the inverters 51 and 52, the motors M3 and M4, the accessory devices of the vehicle, and the like is also prohibited.

  Specifically, the connection between the fuel cell 20 and all the loads including the secondary battery 54 is electrically cut off to temporarily create an open circuit state. When the reaction gas is supplied to the fuel cell 20 in this state, a potential difference is generated in the fuel cell 20. Thereafter, when a predetermined charging permission (power supply permission) condition is satisfied (step S21: YES), charging to the secondary battery 54 is permitted (started) (step S23). At this time, power supply to the load may be permitted (started).

  The charging permission conditions in step S21 are, for example, when the temperature of the fuel cell 20 is equal to or higher than a predetermined temperature (for example, 60 ° C.), or the elapsed time since the restart in step S17 is equal to or longer than a predetermined time. This is the case. In the fuel cell 20, heat generated by a chemical reaction caused by supply of the reaction gas, a refrigerant for cooling the fuel cell 20, and a refrigerant for cooling the auxiliary motor M such as the air compressor A3 and the hydrogen pump H50 are shared. This is based on the fact that the cell voltage is gradually warmed by the endothermic heat from the auxiliary machine and the cell voltage is stabilized.

  If the cell voltage falls below a predetermined threshold during charging of the secondary battery 54, the air flow rate is increased by increasing the rotation speed of the compressor motor M that drives the air compressor A3 in order to increase the air stoichiometric ratio. May be increased.

  As described above, the fuel cell system according to the present embodiment has a cell voltage of a predetermined threshold at the time of system start-up including restart after system down because, for example, the power generation state of the fuel cell 20 is not yet stable. In the following cases, the reaction gas is supplied to the fuel cell 20 without being connected to all loads viewed from the fuel cell 20 as well as prohibiting charging of the secondary battery 54.

Therefore, according to this fuel cell system, even when the remaining capacity SOC of the secondary battery 54 is reduced at the time of starting the system and the secondary battery 54 needs to be charged, Even if there is a load demand on the fuel cell 20 when the power generation state is unstable, the decrease in cell voltage can be suppressed without increasing the amount of reaction gas supplied to the fuel cell 20, so that the amount of reaction gas consumption It is possible to improve both fuel efficiency by reducing the amount of fuel consumption and stability at startup.
<Other embodiments>

  The above-described embodiment is an example for explaining the present invention, and the present invention is not limited to this. Various components can be appropriately designed without departing from the gist thereof. For example, a capacitor may be used as a power storage device instead of the secondary battery 54.

  In addition, the control unit 50 of the above embodiment supplies power from the fuel cell 20 to all loads including the secondary battery 54 when detecting that the cell voltage has dropped below a predetermined threshold at the time of startup. Although it is prohibited, if the cell voltage of the fuel cell 20 has been lowered below the predetermined threshold during the previous drive, that is, if the system goes down in steps S7 and S15, the next restart will restart. It is predicted that the cell voltage has fallen below the predetermined threshold without measuring the cell voltage, and the power supply from the fuel cell 20 is immediately prohibited without performing the determination in steps S5 and S13. May be.

1 is a schematic configuration diagram showing an embodiment of a fuel cell system according to the present invention. The flowchart which shows the content of the process at the time of starting.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Cell voltage monitor (detection part), 20 ... Fuel cell, 50 ... Control part (gas supply control part, electric power supply control part, charge control part, detection part), 51 ... Traction inverter (load), 52 ... Auxiliary machine Inverter (load), 54 ... Secondary battery (power storage device), M ... Compressor motor, M ... Hydrogen pump motor (load), M3 ... Traction motor (load), M4 ... Auxiliary motor (load)

Claims (3)

A fuel cell that generates power upon receiving a supply of a reaction gas, a gas supply control unit that controls supply of the reaction gas to the fuel cell, a power supply control unit that controls power supply from the fuel cell to a load, and the fuel Detecting that the power generation voltage of the battery is reduced, or detecting that the power generation voltage can be reduced,
A fuel cell system that supplies a reactive gas to the fuel cell in a state where power supply from the fuel cell to a load is prohibited when the detection is made at the time of startup. A fuel cell that generates electric power upon supply of a reaction gas, a power storage device that can be charged from the fuel cell and discharged to a load, and the power storage from the fuel cell so that a charge amount in the power storage device is a predetermined amount A charge control unit that controls charging of the device, and a detection unit that detects that the power generation voltage of the fuel cell is reduced, or detects that the power generation voltage can be reduced,
A fuel cell system that prohibits charging from the fuel cell to the power storage device even when the charge amount of the power storage device has not reached the predetermined amount when the detection is made at the time of startup.   3. The fuel cell system according to claim 1, wherein it is detected that the generated voltage can be lowered when the detection is stopped with the detection being performed at the previous drive.

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