JP6444456B2 - Starting method of fuel cell system - Google Patents

Description

  The present invention relates to a method for starting a fuel cell system.

  Patent Document 1 discloses a method for starting a fuel cell system, in particular, a method for starting a fuel cell system in a sub-freezing environment where the temperature of the refrigerant is 0 ° C. or lower. In the fuel cell system of Patent Document 1, it is shown that at the time of starting below freezing point, the circulation of the refrigerant for adjusting the temperature of the fuel cell is stopped and the temperature rise by power generation of the fuel cell is promoted.

JP 2010-257635 A

  In the fuel cell system of Patent Document 1, as described above, the circulation of the refrigerant is temporarily stopped at the time of starting below the freezing point, and the circulation of the refrigerant is started after the internal temperature of the fuel cell rises to a predetermined temperature or higher. However, in this case, as shown in FIG. 5, the temperature of the fuel cell can be quickly raised while the refrigerant circulation is stopped. However, as soon as the circulation of the cooled refrigerant is started, the total voltage of the fuel cell stack and the minimum cell Both voltages may drop significantly.

  An object of the present invention is to provide a start-up method of a fuel cell system capable of starting refrigerant circulation at an appropriate timing without excessively reducing the voltage of the fuel cell.

  (1) A fuel cell system (for example, a fuel cell system 1 described later) includes a fuel cell (for example, a fuel cell stack 2 described later) that generates power when a reaction gas is supplied, and a heat medium circuit ( For example, a temperature adjusting device (for example, a water pump 52 described later) that circulates the heat medium in a refrigerant circulation path 51 described later is provided. The fuel cell system activation method includes a power generation step (for example, a system activation process described later) for starting supply of a reactive gas to the fuel cell in response to a predetermined activation command, a temperature inside the fuel cell, A temperature difference estimation step (for example, the processing of S6 in FIG. 3 to be described later) for estimating a difference (for example, an internal / external temperature difference to be described later) from the temperature inside the heat medium circuit, and the power generation step is started at low temperature startup. The heat medium circulation step (for example, the processing of S7 to S9 in FIG. 3 described later) for starting the circulation of the heat medium in response to the temperature difference exceeding a predetermined value (for example, introduction determination temperature difference described later) from And comprising.

  (2) A fuel cell system activation method includes a power generation step (for example, a system activation process described later) for starting supply of a reactive gas to the fuel cell in response to a predetermined activation command, and a target current value of the fuel cell. And determining whether or not the engine is in an idle state based on the target current value (for example, the process of S3 in FIG. 3 to be described later) A heat medium circulation step (for example, processing of S3 to S9 in FIG. 3 described later) for starting circulation of the heat medium in response to the determination that the state is an idle state.

  (3) In this case, in the heat medium circulation step, it is preferable to increase the circulation amount of the heat medium per unit time as the temperature inside the fuel cell increases.

  (1) In the present invention, when the fuel cell system is started, the supply of the reaction gas is started first, and the circulation of the heat medium is stopped. As a result, it is possible to prevent the temperature increase of the fuel cell due to power generation from being disturbed by the cooled heat medium flowing through the fuel cell immediately after the start of startup, and thus the state in which the fuel cell can be promptly output as required. Can be. Further, when the circulation of the heat medium is stopped in this manner, the internal temperature of the fuel cell quickly rises, but the difference between the internal temperature of the fuel cell and the internal temperature of the heat medium circuit also spreads quickly. Therefore, in the present invention, the circulation of the heat medium is started in response to the temperature difference between the inside of the fuel cell and the inside of the heat medium circuit exceeding a predetermined value. In other words, in the present invention, the circulation of the heat medium is started before the temperature difference becomes excessively large. Thereby, since the fall of the voltage of the fuel cell by starting the circulation of the cold heat medium can be reduced, it is possible to improve the power generation stability at the time of starting the fuel cell system at a low temperature.

  (2) In the present invention, when starting the fuel cell system, the supply of the reaction gas is started first, and the circulation of the heat medium is stopped. Thereby, similarly to (1), it is possible to prevent the temperature rise of the fuel cell due to power generation from being hindered, and as a result, the fuel cell can be promptly put into a state where output according to the request is possible. Further, in the present invention, it is determined whether or not the engine is in the idle state based on the target current value of the fuel cell. When it is determined that the fuel cell is in the idle state, circulation of the heat medium is started accordingly. When the circulation of the heat medium is started, the temperature increase rate of the fuel cell is lowered. However, in the idle state, no large current is taken out from the fuel cell in the first place, so there is no problem even if the temperature rise rate of the fuel cell is slow. Rather, the circulation of the heat medium is started in a state where the difference between the internal temperature of the fuel cell and the heat medium circuit is widened, and this adversely affects that the temperature of the fuel cell is greatly lowered and power generation becomes unstable. Is big. In the present invention, in the idling state, such an adverse effect can be prevented by starting the circulation of the heat medium immediately before the temperature difference widens.

  (3) In the present invention, as the internal temperature of the fuel cell becomes higher, the circulation amount of the heat medium per unit time is increased. That is, at first, the circulation amount of the heat medium is decreased and the circulation amount is gradually increased. As a result, it is possible to prevent the temperature of the fuel cell from greatly decreasing due to a large amount of the cooled heat medium being introduced into the fuel cell, and thus the voltage from being greatly decreased.

It is a figure which shows the structure of the fuel cell system which concerns on one Embodiment of this invention. It is an example of the map which determines the duty ratio of the drive current of a water pump. It is a flowchart which shows the procedure which determines the timing which turns on / off a water pump. It is a time chart which shows the change of the refrigerant | coolant circulation amount when a water pump is turned on / off according to the procedure of FIG. It is a figure which shows the change of the voltage of a fuel cell when the timing which introduce | transduces a refrigerant | coolant is determined according to the conventional starting method.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a fuel cell system 1 according to the present embodiment.
The fuel cell system 1 includes a fuel cell stack 2, an anode system 3 that supplies hydrogen as a reaction gas to the fuel cell stack 2, and a cathode system 4 that supplies air containing oxygen as a reaction gas to the fuel cell stack 2. And a cooling device 5 that cools the fuel cell stack 2, a battery B that stores electric power generated by the fuel cell stack 2, and a tire (not shown) is driven by the supply of electric power from the fuel cell stack 2 and the battery B A travel motor M and an ECU 6 as these electronic control units are provided. The fuel cell system 1 is mounted on a fuel cell vehicle (not shown) using the tire as a driving wheel.

  The fuel cell stack (hereinafter simply referred to as “stack”) 2 has a stack structure in which, for example, several tens to several hundreds of cells are stacked. Each fuel cell is configured by sandwiching a membrane electrode structure (MEA) between a pair of separators. The membrane electrode structure is composed of two electrodes, an anode electrode (cathode) and a cathode electrode (anode), and a solid polymer electrolyte membrane sandwiched between these electrodes. Usually, both electrodes are formed of a catalyst layer that performs an oxidation / reduction reaction in contact with the solid polymer electrolyte membrane and a gas diffusion layer in contact with the catalyst layer. In the stack 2, when hydrogen is supplied to the anode flow path 21 formed on the anode electrode side and oxygen-containing air is supplied to the cathode flow path 22 formed on the cathode electrode side, these electrochemical reactions occur. To generate electricity.

  The output current taken out from the stack 2 during power generation is input to the battery B and the load (travel motor M, air compressor 41, etc.) via the current controller 29. The ECU 6 calculates a target current value corresponding to a target value for the output current of the stack 2 based on an output signal from an accelerator opening sensor that detects the opening of the accelerator pedal (not shown). The current controller 29 uses these target current values calculated by the ECU 6 to control the output current of the stack 2 during power generation so that this is realized.

  The battery B stores electric power generated by the stack 2 and electric energy recovered as a regenerative braking force by the traveling motor M. Further, for example, when the output current of the stack 2 is limited at the start of the fuel cell system 1 or when the vehicle is operating at a high load, the power stored in the battery B supplements the output of the stack 2. Supplied to the load.

  The anode system 3 includes a hydrogen tank 31 that stores hydrogen gas at a high pressure, a hydrogen supply pipe 32 that extends from the hydrogen tank 31 to the introduction portion of the anode flow path 21 of the stack 2, and a discharge system that discharges the anode flow path 21 to the cathode system 4. A hydrogen discharge pipe 33 extending to a diluter (not shown) provided in FIG. 5 and a hydrogen reflux pipe 34 branched from the hydrogen discharge pipe 33 to the hydrogen supply pipe 32 are configured. The hydrogen circulation flow path for the gas containing hydrogen is constituted by a hydrogen supply pipe 32, an anode flow path 21, a hydrogen discharge pipe 33 and a hydrogen reflux pipe 34.

  In the hydrogen supply pipe 32, in order from the hydrogen tank 31 side to the stack 2 side, a shutoff valve 321 and an injector 322 for injecting new hydrogen gas supplied through the shutoff valve 321 toward the stack 2, An ejector 323 for circulating the gas refluxed from the hydrogen reflux pipe 34 to the stack 2 is provided. The shut-off valve 321 is an electromagnetic valve that opens and closes in response to a command signal from the ECU 6. The injection amount of hydrogen gas from the injector 322 is controlled by PWM control by the ECU 6.

  In the hydrogen discharge pipe 33, a catch tank 331 for storing water discharged together with the gas from the anode flow path 21 in order from the stack 2 side to the cathode system 4 side, and the gas in the hydrogen circulation flow path are supplied to the cathode system 4. And a purge valve 332 for discharging to the side. The purge valve 332 is an electromagnetic valve that opens and closes in response to a command signal from the ECU 6.

  The catch tank 331 is provided with a drain pipe 35 for discharging the accumulated water. The drain pipe 35 extends from the catch tank 331 to the downstream side of the purge valve 332 in the hydrogen discharge pipe 33. A drain valve 351 is provided in the drain pipe 35. When the drain valve 351 is opened, the water accumulated in the catch tank 331 is discharged to a diluter (not shown) of the cathode system 4 through the hydrogen discharge pipe 33. The drain valve 351 is an electromagnetic valve that opens and closes in response to a command signal from the ECU 6.

  The cathode system 4 includes an air compressor 41, an air supply pipe 42 extending from the air compressor 41 to the introduction section of the cathode flow path 22, an air discharge pipe 43 extending from the discharge section of the cathode flow path 22 to a diluter (not shown), An air recirculation pipe 45 that branches from the discharge pipe 43 and reaches the air supply pipe 42 and a humidifier 46 that connects the air discharge pipe 43 and the air supply pipe 42 are configured. The oxygen circulation flow path of the gas containing oxygen is constituted by the air supply pipe 42, the cathode flow path 22, the air discharge pipe 43 and the air reflux pipe 45.

  The air compressor 41 supplies outside air to the cathode flow path 22 of the stack 2 through the air supply pipe 42. The air compressor 41 operates in response to a command signal from the ECU 6. The rotational speed of the air compressor 41 is controlled by the ECU 6.

  The humidifier 46 collects water contained in the gas discharged from the cathode channel 22 and humidifies the air supplied from the air compressor 41 using the collected water. With the function of the humidifier 46, the MEA of the stack 2 during power generation is maintained in a wet state suitable for power generation.

  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 is supplied to the stack 2 via the bypass pipe 47, that is, bypassing the humidifier 46. The bypass valve 471 is an electromagnetic valve that opens and closes in response to a command signal from the ECU 6.

  The air supply pipe 42 and the air discharge pipe 43 are provided 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 of the stack 2 is blocked from outside air. These sealing valves 421 and 431 are electromagnetic valves that open and close in response to a command signal from the ECU 6.

  The cooling device 5 includes a refrigerant circulation path 51 including the inside of the stack 2 as a part of the flow path, a water pump 52 provided in the refrigerant circulation path 51 for circulating the refrigerant in the circulation path 51, and the refrigerant circulation path 51. And a radiator 53 as a part. The cooling device 5 circulates the refrigerant by the water pump 52 and promotes heat exchange between the stack 2 and the refrigerant, and cools the refrigerant by the radiator 53, thereby exceeding the upper limit temperature defined for protecting the stack 2. Do not.

  The circulation amount of the refrigerant circulating in the refrigerant circulation path 51 per unit time is controlled by the rotation speed of the water pump 52. Further, the on / off of the water pump 52 or the rotational speed thereof is adjusted by controlling the duty ratio of the drive current supplied from the battery B to the water pump 52 by the ECU 6. The ECU 6 determines whether the water pump 52 is turned on / off according to the procedure shown in FIG. 3 described later. When the water pump 52 is turned on, the ECU 6 estimates the internal temperature of the stack 2 according to the procedure described later. The duty ratio of the water pump 52 is determined by searching a map as shown in FIG. 2 based on the temperature. According to the map shown in FIG. 2, the circulation amount of the refrigerant per unit time increases as the internal temperature of the stack 2 increases.

  A plurality of sensors for grasping the state of the fuel cell system 1 such as the refrigerant temperature sensor 24, the stack air temperature sensor 25, and the current sensor 26 are connected to the ECU 6.

  The refrigerant temperature sensor 24 is provided in the refrigerant circulation path 51 and transmits a signal substantially proportional to the temperature of the refrigerant flowing through the refrigerant circulation path 51 to the ECU 6. The ECU 6 acquires the refrigerant temperature based on the output of the refrigerant temperature sensor 24.

  The current sensor 26 detects the output current of the stack 2 and transmits a signal substantially proportional to the detected value to the ECU 6. The stack air temperature sensor 25 is provided on the outlet side of the cathode channel 22, detects the temperature of the gas discharged from the cathode channel 22, and transmits a signal substantially proportional to the detected value to the ECU 6. The ECU 6 estimates the internal temperature of the stack 2 by using the detected values of the current sensor 26 and the stack air temperature sensor 25. The internal temperature of the stack 2 varies depending on the power generation state. The ECU 6 accurately refers to the output current history of the stack 2 using the current sensor 26 or refers to the temperature of the gas discharged from the inside of the stack 2 using the stack air temperature sensor 25. The internal temperature of the stack 2 can be estimated.

  A driver's seat of a vehicle (not shown) is provided with an ignition switch IG that can be operated by the driver to start and stop the fuel cell system 1. The ignition switch IG outputs a start command signal for the fuel cell system 1 to the ECU 6 when turned on by the driver. Upon receiving this start command signal, the ECU 6 triggers a system start process (not shown) for starting the supply of hydrogen and air to the stack and a process for determining the timing for starting or stopping the refrigerant circulation (described later) Etc.). The ignition switch IG outputs a stop command signal for the fuel cell system 1 to the ECU 6 when turned off by the driver. The ECU 6 starts a system stop process (not shown) upon receiving this stop command signal.

  FIG. 3 is a flowchart showing a procedure for determining the timing for starting or stopping the circulation of the refrigerant, that is, the timing for turning on / off the water pump. As described above, the duty ratio of the water pump is controlled to an appropriate value according to the internal temperature of the stack with reference to the map as shown in FIG. The process shown in FIG. 3 is repeatedly executed at a predetermined cycle from when the ignition switch is turned on by the driver until the predetermined system warm-up time elapses.

  First, in S1, the ECU determines whether or not the current system activation is below freezing. More specifically, the ECU acquires the refrigerant temperature based on the output of the refrigerant temperature sensor, and when the refrigerant temperature is equal to or lower than a predetermined temperature (for example, 0 ° C.), determines that the engine is operating below freezing point, and proceeds to S2. If the refrigerant temperature is higher than the predetermined temperature, it is determined that the operation is not below freezing, and the process proceeds to S8. In S8, the ECU turns on the water pump and circulates the refrigerant.

  In S2, the ECU acquires the target current value of the stack, and proceeds to S3. In S3, the ECU determines whether or not the current stack is in an idle state. More specifically, the ECU determines that the stack is in an idle state when the target current value of the stack acquired in the previous step is equal to or less than a predetermined value, and proceeds to S8 to turn on the water pump and circulate the refrigerant. Let If the target current value is larger than the predetermined value, it is determined that the engine is not in the idle state (that is, it is determined that the vehicle is in the accelerated state), and the process proceeds to S4.

  Here, the effect of circulating the refrigerant will be described when the engine is in the idle state even at the time of starting below freezing. When the refrigerant is circulated at the time of starting below the freezing point, since the cooled refrigerant is introduced into the stack during power generation, the temperature increase rate decreases. However, in the idle state, since a large output is not required for the stack in the first place, it is not necessary to quickly raise the stack temperature. Instead, it delays the timing of starting the circulation of the refrigerant at the time of starting below freezing point, and the temperature of the stack is greatly reduced by introducing the cooled refrigerant in a state where the temperature difference between the stack and the refrigerant is large, As a result, the negative effect of a large drop in voltage is greater. In the process of FIG. 3, in order to prevent such an adverse effect, the refrigerant immediately starts to circulate in the idle state.

  Returning to the description of the flowchart, in S4, the ECU estimates the internal temperature of the stack by using the outputs of the current sensor and the stack air temperature sensor, and proceeds to S5. In S5, the ECU acquires the refrigerant temperature based on the output of the refrigerant temperature sensor, and proceeds to S6. In S6, the ECU calculates the internal / external temperature difference by subtracting the refrigerant temperature from the acquired stack internal temperature, and proceeds to S7. In S7, the ECU determines whether the internal / external temperature difference is higher than a predetermined introduction determination temperature difference. When the determination in S7 is NO (that is, when the internal / external temperature difference is equal to or smaller than the introduction determination temperature difference), the ECU turns off the water pump and stops the circulation of the refrigerant (S9). When the determination in S7 is YES (that is, when the internal / external temperature difference is higher than the introduction determination temperature difference), the ECU turns on the water pump and starts circulating the refrigerant (S8). In the process of FIG. 3, at the time of starting below freezing point, the refrigerant is started to circulate in response to the difference between the internal and external temperatures exceeding the introduction determination temperature difference, so that the cooled refrigerant is introduced into the stack, and thus the temperature is increased. Can be prevented from deteriorating and the power generation of the stack becomes unstable.

  FIG. 4 is a time chart showing changes in the refrigerant circulation rate when the water pump is turned on / off according to the flowchart of FIG. FIG. 4 shows changes in stack output current value, refrigerant circulation rate, and internal / external temperature difference when starting below freezing (IG-ON) at time 0 and continuing to draw a predetermined current from the stack. Show. FIG. 4 shows the case where the load on the stack is changed in three stages, with different line types. More specifically, the solid line indicates a high load, the broken line indicates a medium load, and the alternate long and short dash line indicates a low load (idle state).

  As shown by a solid line and a broken line in FIG. 4, when starting below freezing, the refrigerant circulation is stopped until the internal / external temperature difference exceeds the introduction determination temperature difference, and when the internal / external temperature difference exceeds the introduction determination temperature difference, Circulation begins. At this time, if a large current is continuously drawn from the stack (in the case of a high load), the internal temperature of the stack rises quickly, and the internal / external temperature difference also increases rapidly. Therefore, the timing at which the refrigerant starts to be circulated is earlier at a higher load than at a middle load.

  In addition, as shown by the one-dot chain line in FIG. 4, when the load is always low after starting below freezing, the difference between the internal and external temperature is less than the introduction determination temperature difference, compared to the case of high load or medium load. The circulation of the refrigerant is started immediately. This is because, as described with reference to FIG. 3, since no large current is drawn in the idle state, it is not necessary to quickly raise the internal temperature of the stack.

  Although one embodiment of the present invention has been described above, the present invention is not limited to this. Within the scope of the gist of the present invention, the detailed configuration may be changed as appropriate.

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 2 ... Fuel cell stack 51 ... Refrigerant circuit (heat medium circuit)
52 ... Water pump (temperature control device)
6 ... ECU

Claims (8)

A fuel cell system start-up method comprising: a fuel cell that generates power when a reaction gas is supplied; and a pump that circulates the heat medium in a heat medium circuit including the fuel cell.
An activation determination step of determining whether or not the fuel cell has been activated below freezing ;
An idle determination step for determining whether or not the fuel cell is in an idle state after it is determined that the fuel cell has been activated below freezing ;
A method for starting a fuel cell system , comprising: turning off the pump from off and starting circulation of the heat medium when it is determined in the idle determination step that the fuel cell is in an idle state. A start condition determining step for determining whether or not a predetermined start condition regarding the internal temperature of the fuel cell and the internal temperature of the heat medium circuit is satisfied after it is determined that the fuel cell has been activated below freezing ;
If it is determined in the idle determination step that the fuel cell is not in an idle state, the pump is kept off until the start condition is determined to be satisfied in the start condition determination step. The circulation is not started , and after that, when it is determined in the start condition determination step that the start condition is satisfied, the pump is turned from OFF to ON and circulation of the heat medium is started. 2. A method for starting a fuel cell system according to 1.   3. The fuel cell according to claim 2, wherein in the start condition determining step, it is determined whether the start condition is satisfied based on an internal temperature of the fuel cell and an internal temperature of the heat medium circuit. How to start the system.   The method for starting a fuel cell system according to claim 3, wherein the start condition is that a difference between an internal temperature of the fuel cell and an internal temperature of the heat medium circuit is a predetermined value or more.   5. The fuel cell system activation method according to claim 1, wherein in the idle determination step, it is determined whether or not the engine is in the idle state based on a target current value of the fuel cell. 6. The circulation amount of the heat medium per unit time increases as the temperature inside the fuel cell increases after the pump is turned on and the heat medium is started to circulate. A method for starting a fuel cell system according to any one of the above. A fuel cell system start-up method comprising: a fuel cell that generates power when a reaction gas is supplied; and a pump that circulates the heat medium in a heat medium circuit including the fuel cell.
An idle determination step of determining whether or not the fuel cell is in an idle state;
A start condition determining step for determining whether or not a predetermined start condition regarding the internal temperature of the fuel cell and the internal temperature of the heat medium circuit is satisfied;
After the fuel cell is started below freezing point, the pump is turned from off to on according to the determination result of the idle determination step or the combination of the determination result of the idle determination step and the determination result of the start condition determination step , and the heat And a heat medium circulation step for starting the circulation of the medium. In the heat medium circulation step, when it is determined in the idle determination step that the fuel cell is in an idle state, the heat medium is started to circulate by turning the pump from OFF to ON. If it is determined in the step that the fuel cell is not in an idle state, the start condition determination step is executed. If it is determined in the start condition determination step that the start condition is satisfied , the pump is turned off. The fuel cell system start-up method according to claim 7, wherein the heat medium is started to circulate by being turned on .

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