JP2008034309A - Fuel battery system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently scavenge a fuel battery according to the output capacity of a secondary battery at power generation stoppage. <P>SOLUTION: A fuel battery system 10 includes a fuel battery stack 30, an air compressor which supplies a scavenging gas to the fuel battery stack 30 at power generation stoppage, the secondary battery 76 which supplies operation power to the air compressor, and a temperature sensor 93 which detects the temperature of the secondary battery 76. A controller 20 estimates a scavenging time set for supplying the scavenging gas to the fuel battery stack 30 at power generation stoppage on the basis of the temperature of the secondary battery 76, and estimates a scavenging start temperature set for scavenging residual water content in the fuel battery stack 30 within the scavenging time. A cooling unit 60 increases the temperature of the fuel battery stack 30 to the scavenging start temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system that supplies a scavenging gas to a fuel cell when power generation is stopped, and drains water inside the fuel cell.

  In recent years, low-pollution vehicles have been developed as part of efforts to deal with environmental problems, and one of them is a fuel cell vehicle using a fuel cell system as an on-vehicle power source. A fuel cell system causes an electrochemical reaction by supplying a reaction gas to a membrane-electrode assembly in which an anode electrode is disposed on one surface of an electrolyte membrane and a cathode electrode is disposed on the other surface, and chemical energy is generated. Is an energy conversion system that converts electricity into electrical energy. In particular, a solid polymer electrolyte fuel cell system using a solid polymer membrane as an electrolyte is easy to downsize at low cost and has a high output density, so that it is expected to be used as an in-vehicle power source. Yes.

  Inside the gas flow path of the fuel cell, water generated by the electrochemical reaction of the reaction gas, humidified water for humidifying the reaction gas, etc. remain, and if power generation is stopped while leaving this residual water, Under a low temperature environment, the residual water freezes, the reaction gas is prevented from diffusing into the membrane-electrode assembly, and the low temperature startability is lowered.

In view of such problems, Japanese Patent Application Laid-Open No. 2005-317224 discloses a fuel cell in which the temperature of the refrigerant circulating inside the fuel cell is raised when power generation is stopped, and the air compressor is driven while the fuel cell is warmed up. There has been proposed a fuel cell system configured to supply scavenging gas inside and drain water remaining in the gas flow path.
JP 2005-317224 A

  However, the technology described in the publication does not take into account the remaining capacity of the secondary battery that supplies operating power to the air compressor or the decrease in output performance due to the temperature decrease of the secondary battery. There is a possibility that the fuel cell will not be sufficiently drained due to insufficient supply. In particular, in cold regions, the output performance is likely to deteriorate due to the temperature decrease of the secondary battery. Therefore, it is necessary to take measures to sufficiently scavenge the inside of the fuel cell in consideration of the output performance of the secondary battery.

  Accordingly, an object of the present invention is to propose a fuel cell system capable of sufficiently scavenging the inside of the fuel cell according to the output performance of the secondary battery when power generation is stopped.

  In order to solve the above problems, a fuel cell system according to the present invention includes a fuel cell that generates electricity by electrochemically reacting a fuel gas and an oxidizing gas, and a scavenging gas supply means that supplies the scavenging gas to the fuel cell when power generation is stopped. A secondary battery that supplies operating power to the scavenging gas supply means, a detection means that detects the temperature or remaining capacity of the secondary battery, and a scavenging time when the scavenging gas is supplied to the fuel cell when power generation is stopped. Scavenging time estimating means for estimating based on the temperature or remaining capacity of the battery; and temperature estimating means for estimating a scavenging start temperature when scavenging residual moisture inside the fuel cell within the scavenging time estimated by the scavenging time estimating means; Temperature adjusting means for raising the temperature of the fuel cell until the scavenging start temperature estimated by the temperature estimating means is reached.

  By estimating the scavenging time based on the temperature or remaining capacity of the secondary battery and increasing the scavenging gas scavenging capability by warming up the fuel cell so that the scavenging process is completed within the scavenging time, Even when the operating power that can be supplied to the scavenging means is limited, the inside of the fuel cell can be sufficiently scavenged.

  Here, it is preferable that the temperature estimation means corrects the scavenging start temperature based on any one of the moisture content, temperature, and operating conditions inside the fuel cell. By estimating the amount of residual water inside the fuel cell with higher accuracy based on these parameters, waste of energy required to warm up the fuel cell can be suppressed.

  The temperature adjusting means preferably raises the temperature of the fuel cell to the scavenging start temperature on the condition that the temperature or remaining capacity of the secondary battery when power generation is stopped is less than a predetermined value. This is because when the temperature or remaining capacity of the secondary battery is equal to or higher than a predetermined value, sufficient power necessary for the scavenging process can be supplied from the secondary battery, and it is not necessary to warm up the fuel cell during the scavenging process. .

  According to the present invention, the scavenging time is estimated based on the temperature or remaining capacity of the secondary battery, and the scavenging gas scavenging ability is increased by warming up the fuel cell so that the scavenging process is completed within the scavenging time. Thus, even if the operating power that can be supplied from the secondary battery to the scavenging means is limited, the inside of the fuel cell can be sufficiently scavenged.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a system configuration of a fuel cell system 10 according to the present embodiment. The fuel cell system 10 is an in-vehicle power generation system mounted on a fuel cell vehicle, and includes a fuel cell stack 30 that generates chemical power by converting chemical energy into electric energy. The fuel cell stack 30 is formed by stacking a plurality of cells in series. The cell has a membrane-electrode assembly in which an anode electrode is disposed on one surface of an electrolyte membrane and a cathode electrode is disposed on the other surface, and a reaction gas (fuel gas, oxidizing gas) is applied to the membrane-electrode assembly. It consists of a gas channel for flowing (anode gas channel, cathode gas channel) and a separator in which a refrigerant channel for flowing refrigerant is formed. The fuel cell stack 30 is, for example, a polymer electrolyte fuel cell stack. The fuel cell stack 30 is supplied with fuel gas (hydrogen gas) from the hydrogen tank 80 to the anode electrode, and receives an oxidizing gas (air) from the air compressor 50 to the cathode electrode. Generate electricity by receiving supply.

  In the fuel gas supply system, a hydrogen tank 80, a shut-off valve 81, a regulator 82, and the like are disposed on the fuel gas supply path. When the shut-off valve 81 is opened, the high-pressure hydrogen gas stored in the hydrogen tank 80 is regulated to a predetermined pressure by the regulator 82 and then supplied to the anode electrode of the fuel cell stack 30.

  In the oxidizing gas supply system, an air compressor 50, a humidifier 51, and the like are disposed on the oxidizing gas supply path 41. The air taken in from the atmosphere by the air compressor 50 is pressurized to a predetermined gas pressure, moderately humidified by the humidifier 51, and then supplied to the cathode electrode of the fuel cell stack 30.

  In the fuel cell stack 30, an oxidation reaction of the formula (1) occurs at the anode electrode, and a reduction reaction of the equation (2) occurs at the cathode electrode. The fuel cell stack 30 as a whole undergoes an electromotive reaction of the formula (3).

H ₂ → 2H ⁺ + 2e ⁻ (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

  The communication passage 43 is a gas passage that branches off from the oxidizing gas supply passage 41 and merges with the fuel gas supply passage 42. A shutoff valve 83 is disposed on the communication passage 43, and the shutoff valve 83 is closed during normal operation. In the gas flow path inside the fuel cell stack 30, moisture such as generated water generated by the reduction reaction shown in the equation (2) and humidified water contained in the reaction gas remains. When the system is stopped (when power generation is stopped), pressurized air (scavenging gas) supplied from the air compressor 50 is introduced into the cathode electrode of the fuel cell stack 30 and remains in the cathode gas flow path in the fuel cell stack 30. The drained water is drained out of the fuel cell stack 30 and the shut-off valve 83 is further opened, and a part of the pressurized air flowing through the oxidizing gas supply passage 41 is connected to the anode electrode of the fuel cell stack 30 via the communication passage 43. The moisture remaining in the anode gas flow path in the fuel cell stack 30 is drained out of the fuel cell stack 30. At this time, the air compressor 50 functions as a scavenging means for scavenging residual moisture.

  The cooling device 60 functions as a temperature adjusting unit that adjusts the operating temperature of the fuel cell stack 30. The cooling device 60 includes a pump 62 for circulating the refrigerant in the fuel cell stack 30 along the refrigerant passage 61, a radiator 63 for adjusting the refrigerant temperature, and a heater 64. In the refrigerant passage 61, three-way valves 65 and 66 are arranged so that the flow of the refrigerant can be controlled. During normal operation, the ports P1 and P3 of the three-way valve 65 are opened and the port P2 is closed. Similarly, the ports P4 and P6 of the three-way valve 66 are opened, and the port P5 is closed. Then, the heat generated by the fuel cell stack 30 is absorbed, and the heated refrigerant is cooled by the cooling action of the radiator 63 and circulates on the refrigerant passage 61 while repeating the cycle of absorbing the heat generated by the fuel cell stack 30 again. .

  A plurality of inverters 71 and 73 and a DC / DC converter 75 are connected in parallel to the output terminal of the fuel cell stack 30 via power lines 77 and 78, respectively. The inverters 71 and 73 include, for example, a three-phase bridge circuit composed of six power transistors, and direct current power supplied from the fuel cell stack 30 or the secondary battery 76 is converted into alternating current power by switching operation of the power transistors. Convert to (three-phase AC). The inverter 71 supplies AC power to the traction motor 72 for obtaining vehicle driving propulsion power. The traction motor 72 is an electric motor such as a three-phase motor. The inverter 73 supplies AC power to the compressor motor 74 for driving the air compressor 50.

  Connected to the DC / DC converter 75 is a secondary battery 76 for storing power generated by the fuel cell stack 30 or regenerative energy during vehicle braking. The secondary battery 76 is a power storage device capable of storing and discharging electric power, and functions as a regenerative energy storage source during brake regeneration and an energy buffer during load fluctuations accompanying acceleration or deceleration of the fuel cell vehicle. As the secondary battery 76, for example, a nickel / cadmium storage battery, a nickel / hydrogen storage battery, a lithium secondary battery, or the like is suitable.

  When the fuel cell vehicle is powered by the traction motor 72, the DC / DC converter 75 boosts the output voltage of the secondary battery 76 and supplies DC power to the inverter 71, while the fuel cell vehicle is regenerated by the traction motor 72. When braking, the regenerated DC voltage is stepped down to charge the secondary battery 76. The DC / DC converter 75 can charge the secondary battery 75 by reducing the output voltage of the fuel cell stack 30 in order to store the surplus power generated by the fuel cell stack 30.

  The controller 20 is a control unit (ECU) including a central processing unit (CPU), a storage device (ROM, RAM), an input / output interface, and the like. The controller 20 controls the fuel cell system 10 based on various control programs and data (for example, secondary battery temperature-outputtable time map data 101, scavenging start temperature-scavenging time map data 102, etc.) stored in the memory 21. (Details of the map data 101 and 102 will be described later).

  For example, when the controller 20 receives an activation signal output from the ignition switch 22, the controller 20 starts operation of the fuel cell system 10, and an accelerator opening signal output from the accelerator sensor 24 or a vehicle speed output from the vehicle speed sensor 23. Based on the signal and the like, the required power of the entire system (the sum of vehicle travel power and auxiliary power) is obtained. Auxiliary power includes, for example, 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 device). , And suspension devices), and power consumed by devices (such as air conditioners, lighting fixtures, and audio) disposed in the passenger space.

  Then, the controller 20 determines the distribution of the output power of the fuel cell stack 30 and the secondary battery 76, and the rotation speed of the air compressor 50 and the regulator 82 are adjusted so that the power generation amount of the fuel cell stack 30 matches the target power. The operating point of the fuel cell stack 30 is adjusted by adjusting the valve opening, adjusting the supply amount of the reaction gas to the fuel cell stack 30, and controlling the DC / DC converter 75 to adjust the output voltage of the fuel cell stack 30. (Output voltage, output current) is controlled. Furthermore, the controller 20 outputs, for example, each U-phase, V-phase, and W-phase AC voltage command value to the inverter 71 as a switching command so that the target vehicle speed according to the accelerator opening is obtained, and the traction motor 72. The output torque and rotation speed of the motor are controlled.

  The controller 20 receives signals from various sensors provided in the fuel cell system 10 and controls the power generation operation. As various sensors, for example, a temperature sensor 91 for detecting the temperature of the fuel cell stack 30 (for example, a refrigerant temperature), an internal resistance measuring device 92 for detecting the internal resistance of the fuel cell stack 30, and the temperature of the secondary battery 76 There are a temperature sensor 93 that detects the remaining battery capacity and an SOC sensor 94 that detects the remaining capacity of the secondary battery 76.

  The internal resistance measuring device 92 is, for example, a high frequency impedance measuring device capable of obtaining the internal resistance of the fuel cell stack 30 by applying a high frequency current to the fuel cell stack 30 and detecting the voltage response. Since the internal resistance of the fuel cell stack 30 has a correlation with the amount of water remaining in the fuel cell stack 30, the residual water amount can be estimated to some extent by detecting the internal resistance.

  Here, an outline of the control process for scavenging the water inside the fuel cell stack 30 when the system is stopped will be described. FIG. 2 shows the secondary battery temperature-outputtable time map data 101. The horizontal axis indicates the temperature of the secondary battery 76, and the vertical axis indicates the time during which power can be discharged from the secondary battery 76 (output possible time). Auxiliary power required for scavenging water inside the fuel cell stack 30 (operating power of auxiliary equipment such as the air compressor 50 and the heater 64) varies slightly depending on the amount of residual water and temperature. However, here, it is considered as a constant value for convenience, and the output possible time at the temperature T can be obtained by dividing the power that can be output from the secondary battery 76 at a certain temperature T by the auxiliary power per unit time. In order to avoid a shortage of scavenging due to a shortage of power supply from the secondary battery 76, it is preferable to calculate the available output time based on the auxiliary machine power per unit time assuming that there is a large amount of residual moisture. It is.

  When the output possible time of the secondary battery 76 at various temperatures T is obtained by experiments, secondary battery temperature-output possible time map data 101 as shown in FIG. 2 can be obtained. Referring to FIG. 2, it can be seen that at a certain temperature T0 or lower, the possible output time gradually decreases as the temperature of the secondary battery 76 decreases. Particularly in a cold region, there is a possibility that sufficient power cannot be supplied to the compressor motor 74 due to a decrease in output characteristics due to a decrease in temperature of the secondary battery 76, and moisture in the fuel cell stack 30 may not be sufficiently scavenged.

  Therefore, in the present embodiment, the fuel cell is configured so that the water inside the fuel cell stack 30 can be sufficiently scavenged even when the power that can be supplied from the secondary battery 76 whose output characteristics are reduced in a low temperature environment is limited. Warm up the stack 30. When the fuel cell stack 30 is warmed up, the scavenging gas flowing in the fuel cell stack 30 absorbs heat and expands, so that the volumetric flow rate increases compared to the scavenging gas having the same mass flow rate at a low temperature, and the residual water removal capability Can be increased. Further, when the scavenging gas is warmed, the amount of saturated water vapor increases (in other words, the relative humidity of the scavenging gas decreases), and the amount of residual water carried away can be increased even at the same volume flow rate. Therefore, the amount of scavenging gas required for the scavenging process can be reduced, and the energy consumed for scavenging can be suppressed. As a result, even if the power that can be supplied from the secondary battery 76 whose output characteristics have deteriorated in a low temperature environment is limited, sufficient scavenging processing can be performed.

  As a method for warming up the fuel cell stack 30, for example, the ports P1 and P2 of the three-way valve 65 are opened and the port P3 is closed. Similarly, the ports P4 and P5 of the three-way valve 66 are opened, and the port P4 is closed. Then, the refrigerant circulating inside the fuel cell stack 30 is heated by the heat generation action of the heater 64, and the fuel cell stack 30 can be warmed up. As another warm-up method, for example, in a state where the cooling capacity of the cooling device 60 is reduced (specifically, the pump 62 is stopped or the rotation speed is reduced), the reaction gas is supplied to the fuel cell stack 30. It may be supplied to implement low-efficiency power generation. At this time, the reaction gas supply amount is adjusted so that the temperature inside the fuel cell stack 30 raised by low-efficiency power generation does not exceed the heat resistance temperature of the polymer electrolyte membrane.

  FIG. 3 shows the scavenging start temperature-scavenging time map data 102. The horizontal axis represents the temperature at which the scavenging process starts (scavenging start temperature), and the vertical axis represents the time required for the scavenging process (scavenging time). Here, on the assumption that the output possible time shown in FIG. 2 and the scavenging time shown in FIG. 3 are the same, when the scavenging start temperature required for completing the scavenging process within the scavenging time is experimentally determined, FIG. As shown in FIG. 3, scavenging start temperature-scavenging time map data 102 can be obtained. For example, in order to complete the scavenging process within the scavenging time t0, it is understood that the scavenging start temperature needs to be set within the range of T1 to T2. Here, when the scavenging time is set to t0, which temperature should be specifically set within the range of T1 to T2 depends on the amount of residual moisture in the fuel cell stack 30. The amount of water in the fuel cell stack 30 can be estimated to some extent by the internal resistance value obtained by the internal resistance measuring device 92. However, when the amount of water increases, the correct amount of water is estimated only by the internal resistance value. I can't.

  Therefore, in addition to the internal resistance value obtained by the internal resistance measuring device 92, the amount of residual moisture inside the fuel cell stack 30 is estimated based on the temperature and operating conditions, and the scavenging start temperature is corrected. The operation condition refers to an operation history indicating how much power is output for how long under what temperature environment. For example, when a high output operation is performed for a long time in a low temperature environment, the residual moisture amount becomes extremely large. The scavenging start temperature can be corrected to an optimum value within the range of T1 to T2 by taking into consideration the temperature and operating conditions in addition to the internal resistance value.

  In the above description, the output possible time is obtained based on the temperature of the secondary battery 76, and the configuration for obtaining the scavenging start temperature at which the scavenging process can be completed within the output possible time (= scavenging time) is exemplified. A configuration may be adopted in which the output possible time is obtained based on the remaining capacity of the secondary battery 76 and the scavenging start temperature at which the scavenging process can be completed within the output possible time (= scavenging time). The remaining capacity of the secondary battery 76 can be detected based on the output value of the SOC sensor 94.

  Further, when the temperature of the secondary battery 76 is equal to or higher than T0, or when the remaining capacity is equal to or higher than a predetermined value (for example, the remaining capacity is about 30%), the power supply from the secondary battery 76 will not be insufficient. The warm-up process of the fuel cell stack 30 described above may be performed when the temperature of the secondary battery 76 is less than T0 or the remaining capacity is less than a predetermined value.

Next, scavenging control when the system is stopped will be described with reference to FIG.
When the controller 20 detects that the ignition switch 22 has been switched from on to off (step 401; YES), the controller 20 measures the temperature of the secondary battery 76 based on the output value of the temperature sensor 93 (step 402). It is determined whether or not the temperature of the secondary battery 76 is less than a predetermined value T0 (step 403).

  If the temperature of the secondary battery 76 is less than the predetermined value T0 (step 403; YES), the controller 20 refers to the secondary battery temperature-output possible time map data 101 to determine the output possible time of the secondary battery 76. Estimate (step 404).

  Next, the controller 20 estimates the scavenging start temperature with reference to the scavenging start temperature-scavenging time map data 102 (step 405). At this time, the residual moisture amount is estimated based on the internal resistance, temperature, operating conditions, etc. of the fuel cell stack 30, and the scavenging start temperature is corrected to an appropriate value.

  Next, the controller 20 controls the cooling device 60 and the like to adjust the temperature of the fuel cell stack 30 to reach the scavenging start temperature (step 406), and when the temperature of the fuel cell stack 30 reaches the scavenging start temperature. Then, the scavenging process is started (step 407). At this time, the shut-off valve 43 is opened, and the pressurized air supplied from the air compressor 50 flows into the anode gas channel and the cathode gas channel inside the fuel cell stack 30 to scavenge residual moisture.

  When the scavenging time has elapsed since the start of the scavenging process (step 408; YES), the scavenging process ends.

  On the other hand, if the temperature of the secondary battery 76 is equal to or higher than the predetermined value T0 (step 403; NO), the controller 20 executes the scavenging process for a predetermined time (step 409). At this time, since sufficient power necessary for the scavenging process can be supplied from the secondary battery 76, there is no need to warm up the fuel cell stack 30, and sufficient time for the scavenging process can be secured.

  According to the present embodiment, the scavenging time is estimated based on the temperature or remaining capacity of the secondary battery 76, and the fuel cell stack 30 is warmed up so that the scavenging gas scavenging is completed within the scavenging time. By increasing the capacity, the inside of the fuel cell stack 30 can be sufficiently scavenged even when the operating power that can be supplied from the secondary battery 76 to the air compressor 50 is limited.

1 is a system configuration diagram of a fuel cell system according to an embodiment. FIG. It is explanatory drawing of secondary battery temperature-output possible time map data. It is explanatory drawing of scavenging start temperature-scavenging time map data. It is a flowchart which shows the scavenging control at the time of a system stop.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 20 ... Controller 30 ... Fuel cell stack 50 ... Air compressor 60 ... Cooling device 101 ... Secondary battery temperature-output possible time map data 102 ... Scavenging start temperature-scavenging time map data

Claims (3)

A fuel cell that generates electricity by electrochemically reacting fuel gas and oxidizing gas; and
Scavenging gas supply means for supplying scavenging gas to the fuel cell when power generation is stopped;
A secondary battery for supplying operating power to the scavenging gas supply means;
Detecting means for detecting the temperature or remaining capacity of the secondary battery;
Scavenging time estimation means for estimating a scavenging time when supplying scavenging gas to the fuel cell when power generation is stopped based on the temperature or remaining capacity of the secondary battery;
Temperature estimating means for estimating a scavenging start temperature when scavenging residual moisture inside the fuel cell within the scavenging time estimated by the scavenging time estimating means;
Temperature adjusting means for raising the temperature of the fuel cell until the scavenging start temperature estimated by the temperature estimating means is reached;
A fuel cell system comprising: The fuel cell system according to claim 1,
The fuel cell system, wherein the temperature estimation means corrects the scavenging start temperature based on any one of water content, temperature, and operating conditions inside the fuel cell. The fuel cell system according to claim 1 or 2, wherein
The fuel cell system, wherein the temperature adjusting means raises the temperature of the fuel cell to the scavenging start temperature on condition that the temperature or remaining capacity of the secondary battery when power generation is stopped is less than a predetermined value.

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