JP2009004243A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of stabilizing power generation of a fuel cell at low-temperature startup. <P>SOLUTION: A control device 7, when it judges that a temperature of the fuel cell 2 exceeds a first threshold temperature (for instance, 0°C), detection of an anode-system pressure loss is carried out with the use of a circulation system anode pressure sensor P2. In case abnormalities such as freezing do not take place in a fuel gas piping system 4, an anode-system pressure loss falls within a standard pressure loss range. The control device, if it confirms that the anode-system pressure loss detected goes beyond the standard pressure loss range, judges that a freezing abnormality has occurred in the fuel gas piping system 4 to continue a warm-up operation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system capable of rapidly heating a fuel cell by self-heating of the fuel cell.

  A polymer electrolyte fuel cell generates electric power by a chemical reaction between hydrogen in a fuel gas supplied to an anode and oxygen in an oxidizing gas supplied to a cathode. In general, this type of fuel cell has a temperature range of 70 to 80 ° C. that is optimal for power generation. Depending on the use environment, it may take a long time to reach this temperature range after the fuel cell is started.

  In addition, when the external temperature is low, there is a problem that water generated inside the fuel cell system is frozen after the fuel cell system is stopped, and pipes and valves are damaged. In general, fuel cells have poor startability compared to other power sources, and in particular, there has been a problem that a desired voltage / current cannot be supplied and the device cannot be started at a low temperature.

In view of such circumstances, in the fuel cell system described in Patent Document 1, the current extracted from the fuel cell at the time of low temperature start is increased, and the self-heat generation accompanying the power generation of the fuel cell is promoted (that is, the heat generation amount is increased). The warm-up operation is performed to raise the temperature of the fuel cell in a shorter time than the normal operation. In such prior art, when the internal temperature of the fuel cell exceeds 0 ° C., the warm-up operation is terminated and the normal operation is started.
JP 2006-100093 A

  However, even when the internal temperature of the fuel cell exceeds 0 ° C., the warm-up is not sufficient, and the piping for supplying the fuel gas may be frozen. As described above, when the normal operation is performed with insufficient warm-up, the power generation of the fuel cell may become unstable.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a fuel cell system capable of stabilizing the power generation of the fuel cell at the time of cold start.

  In order to achieve the above object, a fuel cell system according to the present invention performs a warm-up operation in which a fuel cell self-heats, thereby increasing the temperature of the fuel cell in a shorter time than in a normal operation. In the battery system, after starting the warm-up operation, a determination unit that determines whether or not the related temperature of the fuel cell has exceeded a first threshold temperature, and a pipe through which the reaction gas is circulated based on the determination result Detection means for detecting pressure loss, and operation control means for determining whether the detected pressure loss is within a standard pressure loss range and controlling the warm-up operation based on the determination result. Features.

  According to this configuration, the warm-up operation is controlled based on not only the temperature related to the fuel cell (outside air temperature, cooling water temperature, etc.) but also the pressure loss of the piping through which the reaction gas such as fuel gas flows. For this reason, even when the internal temperature of the fuel cell exceeds 0 ° C., if the piping for supplying the fuel gas is frozen, the warm-up operation can be continued to stabilize the power generation of the fuel cell. it can.

  Here, in the above configuration, the reaction gas is a fuel gas containing hydrogen supplied to the anode of the fuel cell, and the detection means is configured to reduce a pressure loss of a pipe that forms a circulation path of the fuel gas. Preferably, the operation control means detects and detects that the detected pressure loss is not within the standard pressure loss range, and continues the warm-up operation.

  In the above configuration, when the operation control unit determines that the detected pressure loss is not within the standard pressure loss range, the warm-up operation is performed at the second threshold temperature higher than the first threshold temperature. It is further preferable that the warm-up operation is continued so that the temperature is increased to about 1.

  As described above, according to the fuel cell system of the present invention, it is possible to stabilize the power generation of the fuel cell at the low temperature start.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. First, the outline of the fuel cell system of the present invention will be described, and then control in the case of performing warm-up operation will be described.

A. FIG. 1 is a configuration diagram of a fuel cell system 1.
The fuel cell system 1 can be mounted on a vehicle 100 such as a fuel cell vehicle (FCHV), an electric vehicle, or a hybrid vehicle. However, the fuel cell system 1 can also be applied to various mobile bodies (for example, ships, airplanes, robots, etc.) other than the vehicle 100, stationary power sources, and portable fuel cell systems.

  The fuel cell system 1 includes a fuel cell 2, an oxidizing gas piping system 3 that supplies air as an oxidizing gas to the fuel cell 2, a fuel gas piping system 4 that supplies hydrogen gas as a fuel gas to the fuel cell 2, A refrigerant piping system 5 that supplies refrigerant to the fuel cell 2, a power system 6 that charges and discharges the power of the system 1, and a control device 7 that performs overall control of the operation of the system 1 are provided. Oxidizing gas and fuel gas can be collectively referred to as reaction gas.

  The fuel cell 2 is formed of, for example, a solid polymer electrolyte type and includes 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 electrochemical reaction in the fuel cell 2 is an exothermic reaction, and the temperature of the solid polymer electrolyte fuel cell 2 is approximately 60 to 80 ° C.

  The oxidizing gas piping system 3 includes a supply path 11 through which the oxidizing gas supplied to the fuel cell 2 flows, a discharge path 12 through which the oxidizing off gas discharged from the fuel cell 2 flows, and the oxidizing gas flows bypassing the fuel cell 2. And a bypass path 17. The supply path 11 communicates with the discharge path 12 via the oxidizing gas flow path 2a. The oxidizing off gas is in a highly moist state because it contains moisture generated by the cell reaction of the fuel cell 2.

  The supply path 11 is provided with a compressor 14 that takes in outside air via an air cleaner 13, and a humidifier 15 that humidifies the oxidizing gas pumped to the fuel cell 2 by the compressor 14. 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 on the air electrode side of the fuel cell 2 is adjusted by a back pressure adjusting valve 16 disposed in the discharge path 12 near the cathode outlet. In the vicinity of the back pressure adjustment valve 16, a pressure sensor P1 for detecting the pressure in the discharge passage 12 is provided. The oxidizing off gas passes through the back pressure regulating valve 16 and the humidifier 15 and is finally exhausted into the atmosphere outside the system as exhaust gas.

  The bypass path 17 connects the supply path 11 and the discharge path 12. A supply side connection B between the bypass path 17 and the supply path 11 is located between the compressor 14 and the humidifier 15. Further, the discharge side connection portion C between the bypass path 17 and the discharge path 12 is located on the downstream side of the humidifier 15. The bypass passage 17 is provided with a bypass valve 18 which is an on-off valve (shut valve) driven by a motor or a solenoid. The bypass valve 18 is connected to the control device 7 and opens and closes the bypass path 17. In the following description, the oxidizing gas that is bypassed downstream of the bypass passage 17 through the bypass valve 18 by opening the bypass valve 18 is referred to as “bypass air”.

  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. 22, a circulation path 23 for returning to the junction point A of 22, a pump 24 that pumps the hydrogen off-gas in the circulation path 23 to the supply path 22, and a purge path 25 that is branched and connected to the circulation path 23. 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 passage 25 is provided with a purge valve 33 for discharging the hydrogen off gas to a hydrogen diluter (not shown).

  The circulation path 23 is provided with a circulation system anode pressure sensor (detection means) P2. The circulation system anode pressure sensor P <b> 2 detects the pressure of hydrogen gas at a low temperature start (described later) under the control of the control device 7. The control device 7 detects a change in the pressure loss (hereinafter referred to as anode system pressure loss) of the fuel gas piping system 4 based on the sensor value from the circulation system anode pressure sensor P2 (details will be described later).

  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 refrigerant flow path 41 has a temperature sensor 46 provided in the vicinity of the refrigerant inlet of the fuel cell 2 and a temperature sensor 47 provided in the vicinity of the refrigerant outlet of the fuel cell 2. The refrigerant temperature detected by the temperature sensor 47 reflects the internal temperature of the fuel cell 2 (hereinafter referred to as the temperature of the fuel cell 2). 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 output voltage of the fuel cell 2 is controlled by the high voltage DC / DC converter 61.

  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 (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 device 7 is configured as a microcomputer having a CPU, ROM, and RAM therein. The CPU executes a desired calculation according to the control program, and performs various processes and controls such as control of normal operation and control of low efficiency operation described later. 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 device 7 includes various pressure sensors (P 1, P 2) and temperature sensors (46, 47), an outside air temperature sensor 51 that detects the outside air temperature in the environment where the fuel cell system 1 is placed, and the accelerator opening of the vehicle 100. Detection signals from various sensors such as an accelerator opening sensor are detected, and a control signal is output to each component (compressor 14, back pressure adjusting valve 16, bypass valve 18, etc.). In addition, when it is necessary to warm up the fuel cell 2 such as when starting at a low temperature, the control device 7 performs a warm-up operation using various maps stored in the ROM.

  The voltage sensor 72 detects the voltage generated by the fuel cell 2. Specifically, a voltage generated by each of a large number of single cells of the fuel cell 2 (hereinafter referred to as “cell voltage”) is detected by a voltage sensor 72. Thereby, the state of each single cell of the fuel cell 2 is grasped.

  Here, the warm-up operation refers to an operation capable of raising the temperature of the fuel cell 2 in a shorter time than the normal operation by causing the fuel cell 2 to self-heat. Such a warm-up operation is a low-efficiency operation in which the reaction gas is insufficient compared to the normal operation and the power loss is increased, that is, a low-efficiency operation in which the power generation efficiency of the fuel cell 2 is reduced to increase the heat generation amount In addition, there is an operation in which the output current of the fuel cell 2 is increased to increase the amount of heat generated by power generation. In other words, the normal operation is an operation with a relatively high power generation efficiency, and the low efficiency operation is an operation with a relatively low power generation efficiency. Hereinafter, the warm-up operation will be described by taking a low efficiency operation as an example.

  FIG. 2 is a diagram showing the relationship between the output current (hereinafter referred to as “FC current”) of the fuel cell 2 and the output voltage (hereinafter referred to as “FC voltage”). FIG. 2 shows a solid line when the fuel cell system 1 performs normal operation, and a dotted line when the fuel cell system 1 performs low efficiency operation.

  When the fuel cell system 1 is normally operated, the fuel cell 2 is operated in a state where the air stoichiometric ratio is set to 1.0 or more (theoretical value) so that high power generation efficiency can be obtained while suppressing power loss (see FIG. (See solid line part 2). Here, the air stoichiometric ratio means an oxygen surplus ratio, and indicates how much oxygen is supplied to oxygen necessary for reacting with hydrogen without excess or deficiency.

  On the other hand, when the fuel cell 2 is warmed up, the fuel cell 2 is set with the air stoichiometric ratio set to less than 1.0 (theoretical value) in order to increase the power loss and raise the temperature of the fuel cell 2. (See the dotted line portion in FIG. 2). When the air stoichiometric ratio is set to be low and the low efficiency operation is performed, the power loss (that is, the heat loss) is positively increased in the energy that can be extracted by the reaction between hydrogen and oxygen. For this reason, if low-efficiency operation is performed, the temperature of the fuel cell 2 can be increased in a shorter time than in normal operation, and the warm-up time can be shortened.

Here, the control at the end of the operation of the fuel cell system 1 will be briefly described.
When the operation stop of the fuel cell system 1 is instructed by the ignition switch OFF operation or the like by the driver of the vehicle 100, the control device 7 ends the normal operation of the fuel cell system 2 and executes the scavenging process.

  The scavenging process refers to scavenging the inside of the fuel cell 2 by discharging the moisture in the fuel cell 2 to the outside at the end of the operation of the fuel cell system 2. In the scavenging process of the cathode system (oxidizing gas piping system 3), the supply of hydrogen gas to the fuel cell 2 is stopped, the oxidizing gas is supplied to the oxidizing gas flow path 2a by the compressor 14, and the supplied oxidizing gas is used. This is done by discharging the water containing the generated water remaining in the oxidizing gas flow path 2 a to the discharge path 12. Then, after the exhaust process is completed, the operation stop of the fuel cell system 1 is completed, and the fuel cell system 1 waits for the next start. A scavenging process of the anode system (fuel gas piping system 4) is also performed, but detailed description thereof is omitted here.

FIG. 3 is a flowchart showing the starting process executed by the control device 7.
As shown in FIG. 3, when the start of operation of the fuel cell system 1 is instructed, for example, by turning on an ignition switch by the driver of the vehicle 100, the control device 7 causes the rapid increase in temperature of the fuel cell 2 by low temperature start Is determined (step S10).

  Here, the determination as to whether or not rapid heating is necessary is made based on at least one of the outside air temperature and the temperature of the fuel cell 2. For example, when the temperature detected by the outside air temperature sensor 51 or the temperature sensor 46 exceeds a predetermined low temperature (for example, 0 ° C. or less), it is determined that rapid temperature increase is not necessary (Step S10; No). Ready On "(step S60). That is, the control device 7 permits the traction motor 64 to be driven, ends the low efficiency operation, and starts the normal operation. “Ready On” means permitting driving of the traction motor 64, that is, permitting the vehicle 100 to start running (start).

  On the other hand, when the temperature detected by the outside air temperature sensor 51 or the temperature sensor 46 is equal to or lower than a predetermined low temperature (for example, 0 ° C.), it is determined that rapid temperature increase is necessary (step S10; Yes), and the warm-up operation is performed. It starts (step S20). The reason for performing the warm-up operation in such a case is to improve the initial output characteristics of the fuel cell 2. As the warm-up operation, the low-efficiency operation is executed, and the temperature of the fuel cell 2 is gradually raised.

  When a predetermined time has elapsed since the start of the warm-up operation, the control device (determination means) 7 determines whether or not the temperature (related temperature) of the fuel cell 2 has exceeded the set first threshold temperature (step). S30). The first threshold temperature may be arbitrarily set, for example, set to a freezing point (0 ° C.) that can prevent the remaining water of the fuel cell 2 from freezing. The first threshold temperature is stored in a memory (not shown) of the control device 7 at the time of manufacture and shipment. Further, instead of the temperature of the fuel cell 2, the outside air temperature or the temperature of parts around the fuel cell 2 (related temperature) may be detected to determine whether or not these temperatures have exceeded the first threshold temperature.

  When the temperature of the fuel cell 2 is lower than the first threshold temperature (step S30; No), the control device 7 returns to step S20 and continues the warm-up operation.

  On the other hand, when the control device (detection means) 7 determines that the temperature of the fuel cell 2 exceeds the first threshold temperature (step S30; Yes), the control system (detection means) 7 uses the circulation system anode pressure sensor P2 to reduce the anode system pressure loss. Detection is performed (step S40). FIG. 4 is a diagram illustrating the relationship between the pump speed and the pressure loss. The horizontal axis indicates the speed of the pump 24 and the vertical axis indicates the anode system pressure loss. Here, when there is no abnormality such as freezing (hereinafter referred to as “freezing abnormality”) in the fuel gas piping system 4, the anode system pressure loss is within the region surrounded by the dotted line in FIG. 4 (hereinafter referred to as “standard pressure loss region”). It will fit. The standard pressure loss region may be obtained in advance by experiments or the like and stored in the memory of the control device 7 as a pressure loss abnormality determination map as shown in FIG.

  When the control device (operation control means) 7 confirms that the detected anode system pressure loss is out of the standard pressure loss region, for example, as shown at P1 in FIG. 4 (step S50; No), the fuel gas piping system 4 determines that a freezing abnormality has occurred, and returns to step S20 to continue the warm-up operation.

  On the other hand, when the control device (operation control means) 7 confirms that the detected anode system pressure loss is within the standard pressure loss region (step S50; Yes), "Ready On" is finished and the warm-up operation is finished. (Step S60), and normal operation is started.

  As described above, according to the present embodiment, when warming up (rapid temperature rise) in low-efficiency operation, the anode system pressure loss is monitored and whether or not a freezing abnormality has occurred in the fuel gas piping system 4. Judge whether or not. By controlling the switching between warm-up operation and normal operation based on the determination result, problems such as normal operation can be suppressed while the pipe is frozen, and the warm-up operation ends. It becomes possible to stabilize the power generation of the later fuel cell 2.

B. Modification <Modification 1>
In this embodiment, the anode system pressure loss is monitored and it is determined whether or not a freezing abnormality has occurred in the fuel gas piping system 4. Instead of (or in addition to) this, the cathode system pressure loss is monitored. Further, it may be determined whether or not a freezing abnormality has occurred in the oxidizing gas piping system 3, and the switching between the warm-up operation and the normal operation may be controlled based on the determination result.

<Modification 2>
FIG. 5 is a flowchart of the starting process according to the second modification.
The start process shown in FIG. 5 is obtained by adding steps S31, S32, and S51 to the start process shown in FIG. Since the other steps are the same, the corresponding steps are denoted by the same reference numerals, and detailed description thereof is omitted.

  When the control device 7 determines that the temperature of the fuel cell 2 exceeds the first threshold temperature (step S30; Yes), the control device 7 proceeds to step S31 and determines whether or not the anode system pressure abnormality flag is “ON”. To do. The anode system pressure abnormality flag is a flag for determining whether the anode system pressure loss is within the standard pressure loss region (see FIG. 4) or not. The anode system pressure loss is within the standard pressure loss region. When it is within the range, it is set to “OFF” by the control device 7, and when the anode system pressure loss is out of the standard pressure loss region, it is set to “ON” by the control device 7. In the initial state, the anode pressure abnormality flag is set to “OFF”.

  If the control device 7 determines that the anode system pressure abnormality flag is set to “OFF” because of the initial state (step S31; No), the control device 7 proceeds to step S40 and detects the anode system pressure loss. The control device 7 determines whether or not the detected anode system pressure loss is within the standard pressure loss region (step S50). If the control device 7 determines that the anode pressure loss is within the standard pressure loss region, the control device 7 proceeds to step S60, “Ready On”, ends the warm-up operation, and starts the normal operation.

  On the other hand, when the control device 7 determines that the anode system pressure loss is out of the standard pressure loss region, the control device 7 switches the anode system pressure abnormality flag from “OFF” to “ON” (step S51), and then returns to step S20. Continue the warm-up operation. Thereafter, the control device 7 proceeds from step S20 to step S30 to step 31, and when determining that the anode system pressure abnormality flag is set to “ON”, the control device 7 proceeds to step S32, where the temperature of the fuel cell 2 is the second. It is determined whether or not a threshold temperature has been exceeded. The second threshold temperature is higher than the first threshold temperature (for example, 0 ° C.), and is preferably set to a temperature included in the temperature range (approximately 60 to 80 ° C.) of the fuel cell 2 in normal operation. For example, it is set to 70 ° C.

When it is determined that the temperature of the fuel cell 2 is lower than the second threshold temperature (step S32; No), the control device (operation control means) 7 returns to step S20 and repeatedly executes the series of processes described above. . On the other hand, if the control device 7 determines that the temperature of the fuel cell 2 has exceeded the second threshold temperature (step s32; Yes), the control device 7 assumes that the freezing abnormality of the fuel gas piping system 4 has been resolved, and proceeds to step S60. “Ready On” ends the warm-up operation and starts the normal operation.
Thus, after the anode system pressure abnormality is recognized, the warm-up operation may be continued up to the temperature range (approximately 60 to 80 ° C.) of the fuel cell 2 during the normal operation.

<Modification 3>
In the present embodiment, the case has been described in which the anode system pressure loss is detected using the sensor value of the circulation system anode pressure sensor P2, but instead of (or in addition to) this, the anode system pressure is determined from the power value of the pump 24. Loss may be detected.

1 is a configuration diagram of a fuel cell system according to an embodiment. It is a graph which shows the relationship between FC electric current and FC voltage which concern on embodiment. It is a flowchart which shows the starting process which concerns on embodiment. It is the figure which illustrated the relationship between the pump rotation speed and pressure loss which concerns on embodiment. It is a flowchart which shows the starting process which concerns on the modification 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Fuel cell, 4 ... Fuel gas piping system, 7 ... Control apparatus, 23 ... Circulation path, 24 ... Pump, P2 ... Circulation system Anode pressure sensor.

Claims (3)

In the fuel cell system configured to raise the temperature of the fuel cell in a short time as compared with the normal operation by performing a warm-up operation that self-heats the fuel cell,
A determination means for determining whether or not an associated temperature of the fuel cell has exceeded a first threshold temperature after starting the warm-up operation;
Detecting means for detecting a pressure loss of the piping through which the reaction gas is circulated based on the determination result;
An operation control means for determining whether or not the detected pressure loss is within a standard pressure loss range, and for controlling the warm-up operation based on the determination result. A fuel cell system comprising: The reaction gas is a fuel gas containing hydrogen supplied to the anode of the fuel cell,
The detection means detects a pressure loss of a pipe forming the fuel gas circulation path,
2. The fuel cell system according to claim 1, wherein the operation control unit continues the warm-up operation when determining that the detected pressure loss is not within a standard pressure loss range.   When the operation control means determines that the detected pressure loss is not within the standard pressure loss range, the operation control means increases the warm-up operation to a second threshold temperature higher than the first threshold temperature. The fuel cell system according to claim 1 or 2, wherein the machine operation is continued.

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