JP2008053112A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system, capable attaining both freezing suppression of an exhaust system and ensuring of requested power generation. <P>SOLUTION: The fuel cell system comprises a fuel cell 2 which receives supply of fuel gas and oxidizer gas and performs power generation by electrochemical reaction thereof; a plurality of exhaust systems (discharge path 12, discharge path 38) for carrying oxidation offgas discharged from the fuel cell 2; and a control part 7 selectively switching the plurality of exhaust systems to carry the oxidation offgas according to the system state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a fuel cell that receives a supply of a reaction gas and generates power by an electrochemical reaction.

In the fuel cell system, an oxidizing gas (for example, air) and a fuel gas (for example, hydrogen) are supplied to the fuel cell, and power generation is performed by an electrochemical reaction of these reaction gases. Water generated in the fuel cell due to this electrochemical reaction is discharged outside through the exhaust system of the fuel cell during operation of the system, but when the outside air temperature is low, the water in the exhaust system is frozen, It may be impossible to continue operation or resume operation after stopping operation.
JP 2005-228634 A

  In Patent Document 1, by providing two exhaust systems having a small passage cross-sectional area, even if one exhaust system is frozen, an exhaust path is secured by the other exhaust system, It can be resumed. However, since exhaust is always performed in two systems, there is a problem that the required power generation amount for the fuel cell cannot be secured depending on the state of the fuel cell system.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel cell system capable of achieving both suppression of freezing of an exhaust system and securing of a required power generation amount.

  In order to achieve the above object, a fuel cell system of the present invention includes a fuel cell that receives a supply of a reaction gas and generates electric power by an electrochemical reaction, a plurality of exhaust systems that flow a reaction off gas discharged from the fuel cell, And a control unit that selects an exhaust system through which the reaction off gas flows from among a plurality of exhaust systems in accordance with a system state.

  According to this configuration, since there are a plurality of exhaust systems, the reaction off-gas flow rate per exhaust system decreases, and the amount of water remaining per exhaust system also decreases. Thereby, freezing can be suppressed. In addition, the required power generation amount can be ensured by selectively switching the exhaust system through which the reaction off gas flows according to the system state.

  The fuel cell system of the present invention includes at least a main exhaust system and a sub exhaust system as the plurality of exhaust systems, and the control unit allows the reaction off gas to flow only to the main exhaust system during normal operation. Accordingly, the reaction off gas may be additionally supplied to the auxiliary exhaust system.

  According to this configuration, the reaction off gas is allowed to flow through the auxiliary exhaust system as necessary, so that the required power generation amount can be easily ensured as compared with the case where the reaction gas is always discharged from a plurality of exhaust systems.

  In the fuel cell system of the present invention, the system state may be determined by a required power generation amount for the fuel cell or a parameter correlated therewith (for example, a throttle valve opening degree when mounted on a vehicle).

  For example, when there is a rapid output increase request such as when WOT (Wide Open Throttle) when the fuel cell system is mounted on a vehicle, the number of exhaust systems through which reaction off-gas flows is increased. Then, compared with the case where the opening of the pressure regulating valve and the rotation speed of the pump are controlled by one exhaust system, the reaction gas supply amount can be increased with higher responsiveness, and the rise of the output can be accelerated.

  In the fuel cell system of the present invention, the control unit may be configured to flow the reaction off gas to another exhaust system that is not closed when at least one of the plurality of exhaust systems is closed. .

  According to this configuration, even when a specific exhaust system becomes unusable due to freezing or the like, for example, another exhaust system can be used as a backup.

  The fuel cell system of this invention WHEREIN: The said control part may be comprised so that the exhaust system which flows the said reaction off gas among these several exhaust systems may be switched continuously according to a system state.

  According to this configuration, it is possible to cause pulsation in the reaction off gas flowing through the exhaust system, and when moisture is present in the exhaust system, the moisture is easily discharged by the pulsation. Such scavenging operation by pulsation is performed, for example, after receiving a stop command for the fuel cell system from the user, and thereby, freezing of the exhaust system after the system is stopped can be suppressed.

  In the fuel cell system of the present invention, a humidifier for humidifying a reaction gas supplied to the fuel cell may be provided in at least one of the exhaust systems.

  In such a case, a valve is provided in at least one of the plurality of exhaust systems provided with the humidifier, and the control unit controls the open / closed state of the valve, The reaction off gas may be selectively flowed to any of the exhaust systems provided with the humidifier.

  According to this configuration, it is possible to control the flow rate of the reaction gas passing through the humidifier, that is, to control the humidification amount of the reaction gas, by selecting the number of exhaust systems through which the reaction gas flows.

  In the fuel cell system of the present invention, a valve is provided in each of the plurality of exhaust systems provided with the humidifier, and the back pressure of the fuel cell is controlled according to the open / closed state of these valves. It may be configured.

  According to this configuration, it is possible to eliminate the pressure regulating valve arranged on the upstream side of the humidifier and adjusting the back pressure of the fuel cell from the exhaust system, and the back is more responsive than the pressure regulating valve. Pressure adjustment is possible.

  According to the present invention, it is possible to achieve both suppression of freezing of the exhaust system and securing of the required power generation amount by providing a plurality of exhaust systems and selectively switching the exhaust system through which the reaction off-gas flows.

  Hereinafter, a fuel cell system according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings. The fuel cell system of the present embodiment can be mounted on a vehicle such as a fuel cell vehicle (FCHV), an electric vehicle, or a hybrid vehicle. However, the present invention is not limited to such an application example, and may be a ship, an aircraft, The present invention can be applied to all moving objects such as trains and walking robots, and can also be applied to stationary power generation systems in which fuel cells are used as power generation equipment for buildings (housing, buildings, etc.).

  The fuel cell system 1 includes a fuel cell 2, an oxidizing gas piping system 3 that supplies air (oxygen) as an oxidizing gas (reactive gas) to the fuel cell 2, and hydrogen gas as a fuel gas (reactive gas). 2, a fuel gas piping system 4 that supplies fuel to the fuel cell 2, a refrigerant piping system 5 that supplies the refrigerant to the fuel cell 2 to cool the fuel cell 2, a power system 6 that charges and discharges the power of the system 1, and the overall system control And a control unit 7 that performs.

  The fuel cell 2 is formed of, for example, a solid polymer electrolyte type and has a stack structure in which a large number of single cells are stacked. The single cell has an air electrode (cathode) on one surface of an electrolyte made of an ion exchange membrane, a fuel electrode (anode) on the other surface, and a pair of the air electrode and the fuel electrode sandwiched from both sides. Of separators. An oxidizing gas is supplied to the oxidizing gas channel 2a of one separator, and a fuel gas is supplied to the fuel gas channel 2b of the other separator. The fuel cell 2 generates electric power by the electrochemical reaction of the supplied fuel gas and oxidizing gas.

  The oxidizing gas piping system 3 includes a supply path 11 through which the oxidizing gas supplied to the fuel cell 2 flows, and a discharge path (main exhaust system) 12 through which the oxidizing off gas discharged from the fuel cell 2 flows. The downstream end of the supply path 11 communicates with the upstream end of the oxidizing gas flow path 2a, and the upstream end of the discharge path 12 communicates with the downstream end of the oxidizing gas flow path 2a. Further, the oxidizing off gas is in a highly moist state because it contains moisture generated by the electrochemical reaction of the fuel cell 2.

  The supply path 11 is provided with a compressor 14 (compressor) that takes in the oxidizing gas (outside air) via the air cleaner 13, and a humidifier 15 that humidifies the oxidizing gas pumped to the fuel cell 2 by the compressor 14. Yes. The humidifier 15 exchanges moisture between the low-humidity oxidizing gas flowing in the supply passage 11 and the high-humidity oxidizing off-gas flowing in the discharge passage 12, and appropriately supplies the oxidizing gas supplied to the fuel cell 2. Humidify.

  The back pressure of the oxidizing gas supplied to the fuel cell 2 is regulated by a back pressure control valve 16 disposed in the discharge path 12 near the cathode outlet. The back pressure control valve 16 is a valve driven by, for example, a step motor, and is electrically connected to the control unit 7. The valve opening degree of the back pressure control valve 16 is configured to be adjustable by the control unit 7 in an arbitrary range including full open, half open, and full close.

  In the vicinity of the back pressure control valve 16, a pressure sensor (not shown) that detects the pressure in the discharge path 12 is provided. The oxidizing off gas passes through the back pressure control valve 16 and the humidifier 15 and is finally exhausted into the atmosphere outside the system as exhaust gas.

  The fuel gas piping system 4 includes a hydrogen supply source 21, a supply path 22 through which hydrogen gas supplied from the hydrogen supply source 21 to the fuel cell 2 flows, and a supply path for supplying hydrogen offgas (fuel offgas) discharged from the fuel cell 2. A circulation path 23 for returning to the junction A of 22, a gas-liquid separator 29 that recovers moisture from the hydrogen off-gas, and a pump 24 that pumps the hydrogen off-gas in the circulation path 23 to the supply path 22. Yes.

  The fuel gas piping system 4 further includes a discharge path (discharge pipe) 25 that guides the generated water separated by the gas-liquid separator 29, an exhaust path 30 that guides the gas separated by the gas-liquid separator 29, and a discharge path 25. And a purge valve 33B provided in the exhaust passage 30.

  The hydrogen gas flowing out from the hydrogen supply source 21 to the supply path 22 by opening the main valve 26 is supplied to the fuel cell 2 through the pressure regulating valve 27 and other pressure reducing valves and the shutoff valve 28. The purge valves 33A and 33B are appropriately opened when the fuel cell system 1 is operated, so that impurities and generated water in the hydrogen off-gas are discharged out of the system as described later.

  By opening the purge valves 33A and 33B, the concentration of impurities in the hydrogen off-gas in the circulation path 23 is lowered, and the hydrogen concentration in the hydrogen off-gas supplied in circulation is increased. Hydrogen off-gas and oxidizing off-gas are discharged to the outside through the muffler 36. Generated water, oxidizing off gas, and hydrogen off gas are led to the muffler 36 from the discharge path 25, the discharge path 12, and the exhaust path 30, respectively.

  In the present embodiment, in addition to the discharge path 12 forming the main exhaust system, a discharge path 38 forming the sub exhaust system is provided. The discharge path 38 branches from between the fuel cell 2 and the back pressure control valve 16 in the discharge path 12, and introduces the oxidizing off gas branched from the discharge path 12 to the muffler 39. The oxidizing off gas is released to the atmosphere through the muffler 39. A sub valve 40 is provided in the discharge path 38. The sub valve 40 is, for example, an electromagnetically driven on / off valve having higher responsiveness than the back pressure control valve 16.

  The refrigerant piping system 5 includes a refrigerant channel 41 communicating with the cooling channel 2 c 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 bypass passage 44 that bypasses the radiator 43, and a switching valve 45 that sets the flow of cooling water to the radiator 43 and the bypass passage 44. The cooling pump 42 circulates and supplies the refrigerant in the refrigerant channel 41 to the fuel cell 2 by driving the motor.

  The power system 6 includes a high-voltage DC / DC converter 61, a battery 62, a traction inverter 63, a traction motor 64, and various auxiliary inverters 65, 66, and 67. The high-voltage DC / DC converter 61 is a direct-current voltage converter that 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.

  The charge / discharge of the battery 62 is realized by these functions of the high-voltage DC / DC converter 61. Further, the traction inverter 63 in which the output voltage of the fuel cell 2 is controlled by the high voltage DC / DC converter 61 converts a direct current into a three-phase alternating current and supplies it to the traction motor 64. The traction motor 64 (power generation device) is, for example, a three-phase AC motor.

  The traction motor 64 constitutes, for example, a main power source of the vehicle 100 on which the fuel cell system 1 is mounted, and is connected to the wheels 101L and 101R of the vehicle 100. The auxiliary machine inverters 65, 66, and 67 control the driving of the motors of the compressor 14, the pump 24, and the cooling pump 42, respectively.

  The control unit 7 is configured as a microcomputer including a CPU, a ROM, and a RAM inside. The CPU executes a desired calculation according to the control program and performs various processes and controls. The ROM stores control programs and control data processed by the CPU. The RAM is mainly used as various work areas for control processing.

  The control unit 7 includes a pressure sensor and a temperature sensor used in the gas system (3, 4) and the refrigerant system 5, an outside air temperature sensor that detects an outside air temperature in the environment where the fuel cell system 1 is placed, and an accelerator opening of the vehicle 100. Detection signals from various sensors such as an accelerator opening sensor for detecting the degree are input, and control signals are output to each component (compressor 14, back pressure control valve 16, sub valve 40, etc.).

  During operation of the fuel cell system 1 configured as described above, generated water is generated by the electrochemical reaction of the fuel cell 2. The produced water flows from the circulation path 23 through the gas-liquid separator 29 and into the discharge path 25 when the purge valve 33A is opened.

  Further, in the present embodiment, the oxidizing off gas exhaust system is divided into a discharge path 12 that is a main exhaust system and a discharge path 38 that is a sub exhaust system. These switching operations are performed by the control unit 7 as follows. First, during normal operation, the sub-valve 40 is closed and only the discharge path 12 that is the main exhaust system is used. The back pressure of the oxidizing off gas is adjusted by the back pressure control valve 16 and is released to the atmosphere through the humidifier 15 and the muffler 36.

  On the other hand, when the control unit 7 detects the possibility of freezing in the discharge path 12 based on the outside air temperature, for example, the sub valve 40 is opened and the discharge path 38 is used together with the discharge path 12. As a result, the flow amount of oxidizing off gas per exhaust system decreases, and as a result, the amount of generated water remaining per exhaust system also decreases. Freezing can be suppressed.

  Even if one of the discharge passages 12 and 38 is frozen, the oxidizing off gas can be continuously exhausted using the discharge passages 12 and 38 that are not frozen, so that the operation is not disabled. . Whether or not the discharge passages 12 and 38 are frozen is detected by the control unit 7 by monitoring the output of a pressure sensor (not shown) provided in the gas system 3 and the rotational speed of the compressor 14. Is possible.

  Further, the control unit 7 detects a sudden increase request for the required power generation amount (required output) for the fuel cell 2 based on the operation state (system state), for example, at the time of WOT (Wide Open Throttle). In that case, the sub-valve 40 is opened to allow the oxidizing off gas to flow also into the discharge passage 38. As a result, the back pressure of the fuel cell 2 can be lowered, so that the rise of the output can be accelerated without waiting for the response of the compressor 14 and the back pressure control valve 16.

  Further, in the present embodiment, the discharge path 38 that is a sub exhaust system is configured to exhaust the oxidizing off gas by bypassing the humidifier 15, so that it is supplied to the fuel cell 2 by switching the opening and closing of the sub valve 40. The humidification amount of the oxidizing gas by the humidifier 15 can be controlled.

  In this embodiment, since there are two exhaust systems for oxidizing off gas, the back pressure can be reduced by opening the sub valve 40 and exhausting the oxidizing off gas using both exhaust systems. Thus, the power of the compressor 14 can be reduced. Therefore, driving with improved fuel efficiency can be performed.

  The above control may be controlled by the control unit 7 based on the driving state (system state) or the external environment (outside temperature, etc.), or may be switched by the control unit 7 according to an instruction from the user (driver). Also good.

  Further, the control unit 7 can generate exhaust gas pulsation in the discharge passages 12 and 38 by alternately and continuously switching the use of the discharge passages 12 and 38. Thereby, the drainage of the water | moisture content in the discharge paths 12 and 38 improves, and freezing of the discharge paths 12 and 38 can be suppressed. In addition, since the exhaust sound can be changed by the exhaust pulsation, the exhaust sound is alerted to the driver or a nearby person by an exhaust sound (for example, a warning sound approaching the vehicle, a driving state of the vehicle by the user). It is also possible to use it as a warning sound to be notified.

  Thus, in the fuel cell system 1 according to the present embodiment and the fuel cell vehicle equipped with the fuel cell system 1, two exhaust systems are provided, and these exhaust systems can be selectively switched according to the operating state. Therefore, it is possible to achieve both suppression of freezing of the exhaust system and securing of the required power generation amount for the fuel cell 2.

  Next, a second embodiment of the present invention will be described. In the fuel cell system 1 of the present embodiment, as shown in FIG. 2, the discharge path 50 branches from between the back pressure control valve 16 of the discharge path 12 and the humidifier 15, and the discharge path 50 is humidified. It passes through the vessel 15. A sub valve 40 is provided in the discharge path 50.

  In the humidifier 15, the oxidant gas supplied to the fuel cell 2 through the supply path 11 is humidified by moisture contained in the oxidizing off gas in the discharge path 12 and the discharge path 50. The oxidizing off gas guided by the discharge path 50 is discharged to the atmosphere through the muffler 39 as in the above embodiment. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  According to the fuel cell system 1 of the present embodiment, the oxidation supplied to the fuel cell 2 by the oxidizing off gas guided to both the discharge path 12 and the discharge path 50 in the humidifier 15 by opening the sub valve 40. Since the gas is humidified, the humidifying capacity of the humidifier 15 can be increased.

  Next, a third embodiment of the present invention will be described. As shown in FIG. 3, the fuel cell system 1 of the present embodiment is not provided with a back pressure control valve 16 (see FIGS. 1 and 2) in the discharge path 12, and instead of this back pressure control valve 16. Are provided with valves 46, 53, 54.

  Further, discharge passages 51 and 52 as sub-exhaust systems branch from between the valve 46 of the discharge passage 12 and the fuel cell 2, and sub-valves 53 and 54 are provided in the discharge passages 51 and 52, respectively. ing. These valves 46, 53, 54 are, for example, electromagnetically driven on-off valves that have higher responsiveness than the back pressure control valve 16.

  The discharge paths 51 and 52 guide the oxidant off-gas through the humidifier 15 and the muffler 39, respectively, and release them to the atmosphere. In the humidifier 15, humidification of the oxidizing gas supplied to the fuel cell 2 through the supply path 11 is performed by moisture contained in the oxidizing off gas in the discharge paths 12, 51, 52. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  In the fuel cell system 1 of the present embodiment, the back pressure control valve 16 is not provided, and the control unit 7 performs back pressure adjustment by opening and closing the valves 46, 53, and 54. Therefore, high responsiveness can be obtained as compared with the fuel cell system including the back pressure control valve 16.

1 is a system configuration diagram schematically illustrating a first embodiment of a fuel cell system according to the present invention. FIG. 3 is a system configuration diagram schematically showing a second embodiment of the fuel cell system according to the present invention. It is the system block diagram which showed schematically 3rd Embodiment of the fuel cell system which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Fuel cell, 7 ... Control part, 12 ... Discharge path (main exhaust system), 15 ... Humidifier, 38 ... Discharge path (sub exhaust system), 50 ... Discharge path (sub exhaust system) , 51 ... Discharge path (sub exhaust system), 52 ... Discharge path (sub exhaust system)

Claims (8)

A fuel cell that receives a supply of reactive gas and generates power by an electrochemical reaction;
A plurality of exhaust systems for flowing a reaction off gas discharged from the fuel cell;
A control unit that selects an exhaust system for flowing the reaction off-gas among the plurality of exhaust systems according to a system state;
A fuel cell system. As the plurality of exhaust systems, at least a main exhaust system and a sub exhaust system are provided,
2. The fuel cell system according to claim 1, wherein the control unit causes the reaction off gas to flow only to the main exhaust system during normal operation, and additionally causes the reaction off gas to flow to the sub exhaust system according to a system state.   The fuel cell system according to claim 1 or 2, wherein the system state is determined by a required power generation amount for the fuel cell or a parameter correlated therewith.   4. The fuel cell system according to claim 1, wherein, when at least one of the plurality of exhaust systems is blocked, the control unit causes the reaction off gas to flow to another exhaust system that is not blocked. 5.   The fuel cell system according to any one of claims 1 to 4, wherein the control unit continuously switches an exhaust system through which the reaction off gas flows, among the plurality of exhaust systems, according to a system state.   The fuel cell system according to any one of claims 1 to 5, wherein at least one of the exhaust systems is provided with a humidifier for humidifying a reaction gas supplied to the fuel cell. A valve is provided in at least one of the plurality of exhaust systems provided with the humidifier;
The fuel cell system according to claim 6, wherein the control unit selectively causes the reaction off gas to flow to any one of an exhaust system provided with the humidifier by controlling an open / close state of the valve. All of the plurality of exhaust systems provided with the humidifier are provided with valves,
The fuel cell system according to claim 7, wherein a back pressure of the fuel cell is controlled according to an open / close state of the valves.

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