JP2008282778A - Fuel cell system and scavenging processing method for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the amount of water of a fuel cell to be accurately ascertained in the case of an antifreeze liquid being used for cooling the fuel cell. <P>SOLUTION: The system includes: an antifreeze liquid temperature measurement device 44 for measuring a temperature of an antifreeze liquid; an antifreeze liquid concentration measurement device 45 for measuring a concentration of the antifreeze liquid; and an arithmetic processing section 7a for calculating a weight of the antifreeze liquid in a fuel cell 2 from the results of the temperature and concentration of the antifreeze liquid, wherein scavenging processing is started after operational halt of the fuel cell 2, and the scavenging processing is stopped when the remaining amount of water in the fuel cell 2 is less than a predetermined amount. The remaining amount of water of the fuel cell 2 can be obtained by subtracting a stack weight of the fuel cell 2 and the calculated weight of the antifreeze liquid from the total weight. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system and a scavenging method for a fuel cell. More specifically, the present invention relates to improved control in a fuel cell system.

  In general, a fuel cell (for example, a solid polymer electrolyte fuel cell) is configured by stacking a plurality of cells each having an electrolyte sandwiched between separators.

  In such a fuel cell, if generated water or condensed water remains in the flow path in the separator, it freezes at a low temperature and may damage the electrolyte membrane, separator, piping, valve, etc. . Furthermore, if the frozen water blocks the gas flow path, there may be a problem that the gas supply is hindered at the next startup and the electrochemical reaction does not proceed sufficiently. Therefore, for example, at the end of the operation, a so-called scavenging process is performed so that moisture does not remain in the fuel cell by sending dry air or the like so as to optimize the amount of moisture in the fuel cell.

In carrying out such a scavenging process, it is desired to grasp the water content of the fuel cell as accurately as possible. Conventionally, as a technique for grasping the moisture content, there is a technique in which the weight of the fuel cell stack is detected by a strain gauge during scavenging, and the scavenging is stopped when it is determined that the moisture content in the fuel cell is appropriate. Further, there is a technique for correcting the gas weight in the fuel cell in accordance with the gas pressure and temperature (see, for example, Patent Document 1).
JP 2004-158274 A

  However, when antifreeze is used for cooling the fuel cell, it may be difficult to accurately grasp the amount of water in the fuel cell.

  Therefore, the present invention provides a fuel cell system and a scavenging method for a fuel cell that can more accurately grasp the water content of the fuel cell when antifreeze is used for cooling the fuel cell. Objective.

  In order to solve this problem, the present inventor has made various studies and obtained new knowledge. The present invention is based on such knowledge, and in a fuel cell system including a fuel cell that generates electric power by an electrochemical reaction of a reaction gas and an antifreeze liquid as a cooling medium for the fuel cell, an antifreeze liquid temperature for measuring the temperature of the antifreeze liquid A measurement device; an antifreeze concentration measuring device that measures the concentration of the antifreeze; and an arithmetic processing unit that calculates the weight of the antifreeze in the fuel cell from the temperature and concentration measurement results of the antifreeze. The scavenging process is started later, and the scavenging process is stopped when the remaining water amount in the fuel cell becomes smaller than a predetermined amount.

  The present invention also relates to a scavenging method after stopping the operation of the fuel cell, which is performed on a fuel cell in which an antifreeze is used as a cooling medium, and the temperature and concentration of the antifreeze after the scavenging process is started. The weight of the antifreeze liquid in the fuel cell is calculated from the measurement results of the temperature and concentration of the antifreeze liquid, and the scavenging process is stopped when the remaining water amount in the fuel cell becomes less than a predetermined amount. is there.

An antifreeze liquid may be used as a medium for cooling the fuel cell in consideration of operation in a sub-freezing environment. However, since the weight of the antifreeze solution changes depending on the temperature and concentration, an error (shift) may occur if the amount of water in the fuel cell is managed only by weight. The inventor who has focused on this point has come up with a technique for grasping the amount of remaining water in the fuel cell by using parameters such as temperature and concentration. That is, in the present invention, the weight of the antifreeze liquid is calculated using these parameters, and the remaining water amount in the fuel cell is obtained from the calculation result. Thus, by considering parameters such as temperature and concentration, it becomes possible to correct the weight of the antifreeze liquid itself and manage the remaining water amount more accurately. The amount of remaining water in the fuel cell is, for example, the amount of remaining water in the fuel cell = the total weight-(stack weight + antifreeze liquid weight)
It can be calculated by the formula.

  ADVANTAGE OF THE INVENTION According to this invention, when the antifreeze is utilized for cooling of a fuel cell, it becomes possible to grasp | ascertain the moisture content of the said fuel cell more correctly.

  Hereinafter, the configuration of the present invention will be described in detail based on an example of an embodiment shown in the drawings.

  1 to 3 show an embodiment of a fuel cell system and a scavenging method for a fuel cell according to the present invention. A fuel cell system 1 according to the present invention is a system that includes a fuel cell that generates electric power by an electrochemical reaction of a reaction gas, and an antifreeze as a cooling medium for the fuel cell. Further, the fuel cell system 1 of the present embodiment includes an antifreeze liquid temperature measurement device that measures the temperature of the antifreeze liquid, an antifreeze liquid concentration measurement device that measures the concentration of the antifreeze liquid, and the measurement result of the temperature and concentration of the antifreeze liquid. An arithmetic processing unit 7a for calculating the weight of the antifreeze liquid, and starts the scavenging process after the operation of the fuel cell 2 is stopped, and stops the scavenging process when the remaining water amount in the fuel cell 2 becomes smaller than a predetermined amount. It has become.

  In the following, the overall configuration of the fuel cell system 1 will be described first, and then the configuration for scavenging the fuel cell 2 and the control contents will be described.

  1 and 2 show a schematic configuration of a fuel cell system 1 mounted on a fuel cell vehicle. Here, an example of a system applicable as an on-vehicle power generation system of a fuel cell vehicle (Fuel Cell Hybrid Vehicle) is shown, but the fuel cell system 1 is self-propelled such as various mobile bodies (for example, ships and airplanes) and robots. It can also be used as a power generation system mounted on a possible one, or as a stationary power generation system.

  The fuel cell system 1 in the present embodiment includes a fuel cell 2 that generates electric power by an electrochemical reaction upon receiving supply of reaction gas (oxidation gas and fuel gas), and an oxidation that supplies air as the oxidation gas to the fuel cell 2. A gas piping system 3, a fuel gas piping system 4 for supplying hydrogen gas as a fuel gas to the fuel cell 2, a refrigerant piping system 5 for supplying a refrigerant to the fuel cell 2 and cooling the fuel cell 2, and a system An electric power system 6 that charges and discharges electric power and a control unit 7 that performs overall control of the entire system are provided.

  The fuel cell 2 is, for example, a solid polymer electrolyte fuel cell, and has a stack structure in which a large number of single cells are stacked. The single cell has an air electrode on one surface of an electrolyte composed of an ion exchange membrane, a fuel electrode on the other surface, and a pair of separators so that the air electrode and the fuel electrode are sandwiched from both sides. It has become. The fuel gas is supplied to the fuel gas flow path of one separator, the oxidizing gas is supplied to the oxidizing gas flow path of the other separator, and further, each of these reaction gases generates a chemical reaction, thereby generating electric power. The fuel cell 2 is provided with a current sensor 2a for detecting a current during power generation.

  The oxidizing gas piping system 3 has an air supply passage 11 through which oxidizing gas supplied to the fuel cell 2 flows, and an exhaust passage 12 through which oxidizing off-gas discharged from the fuel cell 2 flows. The air supply flow path 11 is provided with a compressor 14 that takes in the oxidizing gas via the filter 13 and a humidifier 15 that humidifies the oxidizing gas fed by the compressor 14. The compressor 14 takes in the oxidizing gas in the atmosphere by driving a motor (not shown). Further, the oxidizing off gas flowing through the exhaust passage 12 passes through the back pressure regulating valve 16 and is subjected to moisture exchange by the humidifier 15, and is finally exhausted into the atmosphere outside the system as exhaust gas.

  The fuel gas piping system 4 includes a fuel tank 21 as a hydrogen supply source, a hydrogen supply passage 22 through which hydrogen gas supplied from the fuel tank 21 to the fuel cell 2 flows, and hydrogen off-gas (fuel) discharged from the fuel cell 2. Off-gas) to the junction A1 of the hydrogen supply flow path 22, a hydrogen pump 24 for pumping the hydrogen off-gas in the circulation flow path 23 to the hydrogen supply flow path 22, and a branch to the circulation flow path 23 And an exhaust drainage flow path 25 connected thereto.

  The fuel tank 21 is composed of, for example, a high-pressure tank or a hydrogen storage alloy and is mounted on the fuel cell vehicle in the present embodiment, and is configured to be able to store, for example, 35 MPa or 70 MPa of hydrogen gas. When a shut-off valve 26 described later is opened, hydrogen gas flows out from the fuel tank 21 to the hydrogen supply passage 22. The hydrogen gas is finally depressurized to about 200 kPa, for example, by a regulator 27 and an injector 28 described later, and supplied to the fuel cell 2. In this embodiment, such a fuel tank 21 is used as a hydrogen supply source. In addition, a reformer that generates hydrogen-rich reformed gas from a hydrocarbon-based fuel, and a reformer that is generated by this reformer. It is also possible to configure the hydrogen supply source by a high-pressure gas tank that stores the reformed gas in a high-pressure state.

  The hydrogen supply channel 22 is provided with a shutoff valve 26 that shuts off or allows the supply of hydrogen gas from the fuel tank 21, a regulator 27 that adjusts the pressure of the hydrogen gas, and an injector 28. A pressure sensor 29 that detects the pressure of the hydrogen gas in the hydrogen supply flow path 22 is provided on the downstream side of the injector 28 and upstream of the junction A1 between the hydrogen supply flow path 22 and the circulation flow path 23. It has been. Further, a pressure sensor and a temperature sensor (not shown) for detecting the pressure and temperature of the hydrogen gas in the hydrogen supply flow path 22 are provided on the upstream side of the injector 28. Information regarding the gas state (pressure, temperature) of the hydrogen gas detected by the pressure sensor 29 or the like is used for feedback control and purge control of an injector 28 described later.

  The regulator 27 is a device that regulates the upstream pressure (primary pressure) to a preset secondary pressure. In this embodiment, a mechanical pressure reducing valve that reduces the primary pressure is employed as the regulator 27. The mechanical pressure reducing valve has a structure 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. Thus, a publicly known configuration for the secondary pressure can be employed.

  The injector 28 is an electromagnetically driven on-off valve capable of adjusting the gas flow rate and gas pressure by driving the valve body directly with a predetermined driving cycle with an electromagnetic driving force and separating it from the valve seat. The injector 28 includes a valve seat having an injection hole for injecting gaseous fuel such as hydrogen 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 movably accommodated and opens and closes the injection hole. For example, in the present embodiment, the valve body of the injector 28 is driven by a solenoid that is an electromagnetic drive device, and the opening area of the injection hole is increased in two stages by turning on and off the pulsed excitation current supplied to the solenoid. , Or can be switched steplessly. Furthermore, the flow rate and pressure of hydrogen gas are controlled with high accuracy by controlling the gas injection time and gas injection timing of the injector 28 by the control signal output from the control unit 7. Thus, the injector 28 directly opens and closes the valves (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.

  Since the gas flow rate is adjusted by opening and closing the valve body of the injector 28 and the gas pressure supplied downstream of the injector 28 is reduced from the gas pressure upstream of the injector 28, the injector 28 is controlled by a pressure regulating valve (pressure reducing valve, Regulator). Further, in the present embodiment, a variable pressure control valve capable of changing the pressure adjustment amount (pressure reduction amount) of the upstream gas pressure of the injector 28 so as to match the required pressure within a predetermined pressure range according to the gas requirement. Can also be interpreted.

  In the present embodiment, such an injector 28 is arranged on the upstream side of the junction A1 between the hydrogen supply channel 22 and the circulation channel 23 (see FIG. 1). In addition, as shown by a broken line in FIG. 1, when a plurality of fuel tanks 21 are used as a fuel supply source, a portion where hydrogen gas supplied from these fuel tanks 21 merges (hydrogen gas joining portion A2). The injector 28 is arranged on the downstream side.

  An exhaust / drain channel 25 is connected to the circulation channel 23 via a gas / liquid separator 30 and an exhaust / drain valve 31. The gas-liquid separator 30 collects moisture from the hydrogen off gas. The exhaust / drain valve 31 operates in response to a command from the control unit 7, so that moisture collected by the gas-liquid separator 30 and hydrogen off-gas (fuel off-gas) containing impurities in the circulation channel 23 are externally provided. It is to be discharged (purged). When the exhaust / drain valve 31 is opened, the concentration of impurities in the hydrogen off-gas in the circulation passage 23 decreases and the concentration of hydrogen in the hydrogen off-gas supplied in circulation increases. An upstream pressure sensor 32 and a downstream pressure sensor 33 for detecting the pressure of the hydrogen off gas are provided at the upstream position (on the circulation flow path 23) and the downstream position (on the exhaust drain flow path 25) of the exhaust drain valve 31, respectively. It has been.

  Although not shown in detail, the hydrogen off-gas discharged through the exhaust / drain valve 31 and the exhaust / drain passage 25 is diluted by a diluter (not shown) and merges with the oxidizing off-gas in the exhaust passage 12. It is supposed to be. The hydrogen pump 24 circulates and supplies the hydrogen gas in the circulation system to the fuel cell 2 by driving a motor (not shown). The hydrogen gas circulation system is constituted by a downstream channel of the junction A1 of the hydrogen supply channel 22, a fuel gas channel formed in the separator of the fuel cell 2, and a circulation channel 23. Become.

  The refrigerant piping system 5 includes a refrigerant channel 41 communicating with the cooling channel in the fuel cell 2, a cooling pump 42 provided in the refrigerant channel 41, and a radiator 43 that cools the refrigerant discharged from the fuel cell 2. And a temperature sensor 44 for detecting the temperature of the refrigerant discharged from the fuel cell 2. The cooling pump 42 circulates and supplies the refrigerant in the refrigerant passage 41 to the fuel cell 2 by driving a motor (not shown). The temperature of the refrigerant detected by the temperature sensor 44 (= temperature of hydrogen off-gas discharged from the fuel cell 2) is used for purge control described later.

  The power system 6 includes a high-voltage DC / DC converter 61, a battery 62, a traction inverter 63, a traction motor 64, various auxiliary machine inverters not shown, and the like. The high-voltage DC / DC converter 61 is a direct-current voltage converter, which adjusts the direct-current voltage input from the battery 62 and outputs it to the traction inverter 63 side, and the direct-current input from the fuel cell 2 or the traction motor 64. And a function of adjusting the voltage and outputting it to the battery 62. With such a function of the high voltage DC / DC converter 61, charging / discharging of the battery 62 is realized. Further, the output voltage of the fuel cell 2 is controlled by the high voltage DC / DC converter 61.

  The battery 62 is configured such that battery cells are stacked and a constant high voltage is used as a terminal voltage, and surplus power can be charged or power can be supplementarily supplied under the control of a battery computer (not shown). The traction inverter 63 converts a direct current into a three-phase alternating current and supplies it to the traction motor 64. The traction motor 64 is, for example, a three-phase AC motor, and constitutes a main power source of a fuel cell vehicle on which the fuel cell system 1 is mounted.

  The auxiliary inverter is an electric motor control unit that controls driving of each motor, converts a direct current into a three-phase alternating current, and supplies the three-phase alternating current to each motor. The auxiliary inverter is, for example, a pulse width modulation type PWM inverter, which converts a DC voltage output from the fuel cell 2 or the battery 62 into a three-phase AC voltage in accordance with a control command from the control unit 7 and is generated by each motor. To control the rotational torque.

  The control unit 7 detects an operation amount of an operation member (accelerator or the like) for acceleration provided in the vehicle, and receives control information such as an acceleration request value (for example, a required power generation amount from a load device such as the traction motor 64). To control the operation of various devices in the system. In addition to the traction motor 64, the load device includes auxiliary devices (for example, motors for the compressor 14, the hydrogen pump 24, and the cooling pump 42) necessary for operating the fuel cell 2, and is involved in the running of the vehicle. Power consumption devices including actuators used in various devices (transmissions, wheel control units, steering devices, suspension devices, etc.), air conditioning devices (air conditioners) for passenger spaces, lighting, audio, and the like can be included.

  Such a control part 7 is comprised by the computer system which is not shown in figure. Such a computer system is provided with a CPU, ROM, RAM, HDD, input / output interface, display, and the like. The CPU reads various control programs recorded in the ROM and executes desired calculations to perform feedback control and purge. Various processes and controls such as control are performed.

  Next, a description will be given of the configuration and control for making it possible to more accurately grasp the moisture content of the fuel cell when antifreeze is used for cooling the fuel cell 2 (see FIGS. 2 and 3).

  In the fuel cell 2, moisture and heat are generated by a chemical reaction during power generation. At this time, in order to achieve high power generation efficiency of the fuel cell 2, it is maintained at an appropriate temperature (for example, about 80 ° C.) during operation. Need to be. In the present embodiment, the refrigerant piping system 5 described above is used to cool the heat generated in the fuel cell 2 by releasing it out of the system.

  Here, as the cooling medium used in the refrigerant piping system 5 of the present embodiment, an antifreeze liquid added with a solvent or a liquid containing such an antifreeze liquid is used to prevent freezing at low temperatures. As an example of the antifreeze, for example, a freezing point depressant such as ethylene glycol or cooling water containing the same can be used.

  Here, the temperature sensor 44 provided in the refrigerant piping system 5 functions as an antifreeze liquid temperature measuring device capable of measuring the temperature of the antifreeze liquid (see FIGS. 1 and 2). Further, a concentration sensor 45 is further provided, for example, in the refrigerant tank 46 of the refrigerant piping system 5 (see FIG. 2). The concentration sensor 45 functions as an antifreeze concentration measuring device that measures the concentration of the antifreeze.

  The arithmetic processing unit 7 a calculates the weight of the antifreeze liquid in the fuel cell 2 from the measurement result of the temperature and concentration of the antifreeze liquid by the temperature sensor 44 and the concentration sensor 45. The arithmetic processing unit 7a is constituted by a CPU built in the control unit 7, for example.

  Next, the content of the early processing method after stopping the operation of the fuel cell 2 in the present embodiment will be described using a flowchart (see FIG. 3).

  The temperature and concentration of the antifreeze liquid in the fuel cell system 1 are measured at any time by the temperature sensor 44 and the concentration sensor 45 described above (steps S11 and S12). In addition, the arithmetic processing unit 7a calculates the weight of the antifreeze liquid from the temperature and concentration measurement results (step S13).

  On the other hand, when the operation of the fuel cell 2 is stopped (step S1), the scavenging process is started (step S2). At this time, the amount of remaining water in the fuel cell 3 is calculated using the above-described weight calculation result of the antifreeze (step S3). In general, since the weight of the antifreeze varies depending on the temperature and concentration, an error may occur when trying to grasp and manage the amount of water in the fuel cell 2 only by weight. In the present embodiment, these parameters such as temperature and concentration are considered. Since the weight of the antifreeze is calculated, the amount of remaining water in the fuel cell 2 can be calculated with higher accuracy by correcting the influence due to temperature change and concentration change.

Subsequently, it is determined whether or not the remaining water amount obtained by the calculation is less than a predetermined amount (step S4). If it is still greater than the predetermined amount, the scavenging process is continued (No in step S4), and if it is less than the predetermined amount (Yes in step S4), the scavenging process is stopped (step S5). The amount of remaining water in the fuel cell is, for example, the amount of remaining water in the fuel cell = total weight-(stack weight + antifreeze liquid weight)
It can be calculated by the formula. The predetermined amount is preset as a certain target value.

  As described above, according to this embodiment, in the fuel cell system 1 in which the antifreeze is used for cooling the fuel cell 2, when the remaining water amount during scavenging is managed by weight, Management can be optimized. That is, when the water content of the fuel cell 2 is calculated from the weight, the weight is corrected according to the temperature and concentration of the antifreeze, so that the remaining water amount during scavenging can be further increased regardless of the temperature when the fuel cell 2 is shut down. It is possible to accurately grasp and accurately determine the end of the scavenging process.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention.

It is a figure which shows the structural example of the fuel cell system in one Embodiment of this invention. It is a figure which shows schematically the structure of the principal part of the fuel cell system in this embodiment. It is a flowchart which shows an example of the flow of a scavenging process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Fuel cell, 7a ... Arithmetic processing part, 44 ... Temperature sensor (antifreeze liquid temperature measuring device), 45 ... Concentration sensor (antifreeze liquid concentration measuring device)

Claims (4)

In a fuel cell system including a fuel cell that generates electricity by an electrochemical reaction of a reaction gas, and an antifreeze as a cooling medium for the fuel cell,
An antifreeze liquid temperature measuring device for measuring the temperature of the antifreeze liquid;
An antifreeze concentration measuring device for measuring the concentration of the antifreeze,
An arithmetic processing unit that calculates the weight of the antifreeze liquid in the fuel cell from the measurement results of the temperature and concentration of the antifreeze liquid;
A scavenging process is started after the fuel cell is stopped, and the scavenging process is stopped when the amount of remaining water in the fuel cell becomes smaller than a predetermined amount.   2. The fuel cell system according to claim 1, wherein the remaining water amount of the fuel cell is obtained by subtracting the stack weight of the fuel cell and the calculated weight of the antifreeze from the total weight. A scavenging method after stopping the operation of the fuel cell, which is performed on a fuel cell in which antifreeze is used as a cooling medium,
After the start of the scavenging process, measure the temperature and concentration of the antifreeze,
From the measurement results of the temperature and concentration of the antifreeze, calculate the weight of the antifreeze in the fuel cell,
A scavenging process method for a fuel cell, wherein the scavenging process is stopped when the amount of remaining water in the fuel cell becomes smaller than a predetermined amount.   The scavenging method for a fuel cell according to claim 3, wherein the remaining water amount of the fuel cell is obtained by subtracting the stack weight of the fuel cell and the calculated weight of the antifreeze from the total weight.

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