JP2009037762A - Control device of fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of a fuel cell system suitably preventing dry-up of an electrolyte film. <P>SOLUTION: The control device (25) of the fuel cell system includes a reference determining means determining a reference gas stoichiometric ratio corresponding to a demand power generation volume concerning gas supplied to a fuel cell, a temperature detecting means (21) detecting temperature of the fuel cell, a state decision means deciding an operating state of the fuel cell, a calculating means calculating a temperature changing rate of the fuel cell from the temperature detected by the temperature detecting means, and, if the fuel cell is decided to be in an operating state for the electrolyte film easily getting dry by the state decision means, a correcting means for correcting the above reference gas stoichiometric ratio in accordance with the temperature changing rate calculated by the calculating means so that temperature of the fuel cell is stabilized. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for a fuel cell system, and more particularly to a technique for preventing drying of an electrolyte membrane in a fuel cell.

  In order to maintain power generation efficiency in each cell of the fuel cell, it is necessary to keep the electrolyte membrane wet in order to ensure the movement of protons (hydrogen ions). Drying the electrolyte membrane also leads to deterioration of the electrolyte membrane. Therefore, the fuel cell system is configured to supply a gas humidified by a humidifier to a cell composed of the electrolyte membrane, gas diffusion electrode (fuel gas electrode (anode) and oxidant gas electrode (cathode)), and the like. There is something to be done.

  On the other hand, when the fuel cell system is mounted on a vehicle, it is desired that the fuel cell system be light and small and inexpensive. Thereby, in a fuel cell system, the structure which does not have a humidifier, or the structure which has a humidifier with a small capacity | capacitance is taken. In such a fuel cell system, a gas in a non-humidified state or a low humidified state is supplied to the fuel cell, so that another configuration for keeping the electrolyte membrane moist is required.

In Patent Document 1 below, when it is determined that the electrolyte membrane is dry in the fuel cell system, the amount of air supplied to the cathode is controlled to be smaller than usual, thereby suppressing moisture evaporation. A technique for preventing the electrolyte membrane from drying is proposed. In Patent Document 2 below, the drying of the electrolyte membrane is determined based on the detected values of the flow rate, pressure, and temperature of the oxidant gas, and the electrolyte membrane is dried by reducing the supply amount, pressure, and temperature of the oxidant gas. Methods to prevent it have been proposed. Patent Document 3 below proposes a method for preventing the electrolyte membrane from being dried by determining the drying of the electrolyte membrane from the cell voltage or the like in the fuel cell system and increasing the air pressure in the air passage of the cell from that during normal operation. Has been.
JP 2004-47427 A JP 2006-351506 A JP 2006-210004 A

  However, in the conventional methods as described above, in the method of preventing the drying by controlling the air supply amount to be small, if the air supply amount is too small, the drying of the electrolyte membrane may be promoted conversely. . When the air supply amount decreases, the generated voltage decreases due to the lack of hydrogen or oxygen, and the heat generation amount of the cell increases. Furthermore, since the air supply amount is small, the heat dissipation effect to the exhaust gas is also reduced. As a result, if the air supply amount becomes too small, the stack temperature may rise and promote cell drying. As described above, there are scenes where the conventional technique as described above cannot appropriately prevent the electrolyte membrane from being dried.

  Further, even in a fuel cell system having a configuration in which a gas in a non-humidified state or a low humidified state as described above is supplied to the fuel cell, cell drying does not become prominent in all operating states. In an operating state where cell drying becomes significant, problems such as a decrease in power generation efficiency and deterioration of the electrolyte membrane are likely to occur. Therefore, the conventional method has a problem that the operation state becomes unstable.

  In view of such problems, an object of the present invention is to provide a control device for a fuel cell system that appropriately prevents the electrolyte membrane from drying.

  The present invention employs the following means in order to solve the above-described problems. That is, the present invention relates to a control device for a fuel cell system. This control device relates to a gas supplied to the fuel cell, a standard determination means for determining a standard gas stoichiometric ratio corresponding to a required power generation amount, and a fuel cell. Temperature detection means for detecting the temperature of the fuel cell, state determination means for determining the operating state of the fuel cell, calculation means for calculating the temperature change rate of the fuel cell from the temperature detected by the temperature detection means, and the state determination means If it is determined that the fuel cell is in an operating state in which the electrolyte membrane is easy to dry, the standard gas stoichiometric ratio is corrected according to the rate of temperature change calculated by the above calculation means so that the temperature of the fuel cell is stabilized. And a correcting means for performing.

  In the present invention, the temperature change rate of the fuel cell is calculated by the calculating means. This temperature change rate indicates, for example, the ratio of the temperature change amount with respect to a predetermined elapsed time. Further, the standard gas stoichiometric ratio corresponding to the required power generation amount is determined by the standard determining means. The standard gas stoichiometric ratio indicates a ratio of an actual supply amount including an error or the like to an ideal supply amount determined so as to correspond to a required power generation amount for the gas supplied to the fuel cell. The gas stoichiometric ratio is controlled, for example, by changing the gas supply amount. Further, the operating state of the fuel cell is determined by the state determining means. In the present invention, when it is determined by the correcting means that the fuel cell is in an operating state in which the electrolyte membrane is easily dried, the standard gas stoichiometric ratio is corrected so that the temperature of the fuel cell is stabilized.

  When the fuel cell is in an operating state in which the electrolyte membrane can be easily dried, the temperature of the fuel cell may rise rapidly and promote the drying of the electrolyte membrane even if the gas stoichiometric ratio is too high or too low. The same applies to the case where power is generated using the standard gas stoichiometric ratio determined so as to correspond to the required power generation amount. Thus, in the present invention, when the fuel cell is in an operation state where the electrolyte membrane is easy to dry, it is distinguished from the case where the electrolyte membrane is in an operation state where the electrolyte membrane is easy to dry. By correcting the standard gas stoichiometric ratio used for the fuel cell, the temperature of the fuel cell is controlled to be stable.

  Therefore, according to the present invention, since the gas stoichiometric ratio is more finely controlled in the operating state in which the electrolyte membrane is easily dried, drying of the electrolyte membrane accompanying the operating state can be appropriately prevented. This is the same whether the fuel cell system is equipped with another device for controlling the humidity of gas such as a humidifier or not, but is equipped with another device for controlling the humidity of gas. Not more noticeable in fuel cell systems.

  In the present invention, preferably, the calculation means obtains a difference between the temperature change rate calculated last time and the temperature change rate calculated this time, and the correction means sets the temperature so that the temperature of the fuel cell is stabilized. The standard gas stoichiometric ratio is increased or decreased according to the difference in change rate.

  According to such a configuration, the standard gas stoichiometric ratio may be increased or decreased depending on the difference in temperature change rate. By correcting the standard gas stoichiometric ratio in this way, the temperature change rate is controlled to be small, and drying of the electrolyte membrane can be prevented beforehand.

  In such a configuration, more preferably, the correction means determines an increase / decrease width according to the difference in temperature change rate, and increases / decreases the standard gas stoichiometric ratio by the determined increase / decrease width.

According to such a configuration, when the temperature change rate difference is large, for example, the increase / decrease range can be increased, and when the temperature change rate difference is small, the increase / decrease range can be decreased, for example. Thereby, the corrected value of the gas stoichiometric ratio can be brought closer to the ideal value for preventing the electrolyte membrane from drying more quickly. Therefore, it is possible to further prevent the electrolyte membrane from being dried in any operating state.

  In the present invention, preferably, the apparatus further comprises power measuring means for measuring the power generation amount of the fuel cell, and the state determination means detects the power generation amount measured by the power measurement means and the temperature detection means. Based on the measured temperature, it is configured to determine whether or not the fuel cell is in an operation state in which the electrolyte membrane is easily dried. In such a configuration, the state determination means may determine that the fuel cell is in an operation state in which the electrolyte membrane is easily dried when the power generation is low and the temperature of the fuel cell is high.

  The fuel cell has such characteristics that the higher the stack temperature or the higher the gas stoichiometric ratio, the greater the amount of water vapor that is taken away and the more the electrolyte membrane is dried. By determining whether or not the fuel cell is in an operation state in which the electrolyte membrane is easy to dry using such characteristics as a criterion, it is possible to accurately determine the operation state in which the standard gas stoichiometric ratio is to be corrected.

  Therefore, according to the present invention, the operating state in which the drying of the electrolyte membrane is likely to be promoted is appropriately determined, and the temperature of the fuel cell is controlled to be stable in such an operating state. Drying can be prevented.

  ADVANTAGE OF THE INVENTION According to this invention, the control apparatus of the fuel cell system which prevents the electrolyte membrane from drying appropriately can be provided.

  Hereinafter, a fuel cell system according to an embodiment of the present invention will be described with reference to the drawings. The configuration of the embodiment described below is an exemplification, and the present invention is not limited to the configuration of the following embodiment.

[Outline of the embodiment of the present invention]
First, before describing the details of the embodiment of the present invention, the outline of the embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing an operation state and a normal operation state in which drying of the electrolyte membrane becomes significant in the fuel cell system based on the relationship between the stack temperature and the power generation amount. The stack temperature shown in FIG. 1 is the temperature of the fuel cell stack.

  The drying of the cell (drying of the electrolyte membrane) occurs when the amount of water vapor carried away is large, that is, when the amount of water evaporated by the gas flowing in the cell is larger than the amount of water generated in the cell during power generation. That is, the higher the stack temperature or the higher the gas stoichiometric ratio, the greater the amount of water vapor that is taken away, and the more the electrolyte membrane is dried. The gas stoichiometric ratio indicates the ratio of the actual supply amount to the required supply amount of the oxidant gas or fuel gas to the fuel cell. Generally, the gas stoichiometric ratio tends to be high during low power generation operation of the fuel cell system. On the other hand, if the amount of power generation is large, the amount of water produced at the cathode of the cell increases, so that even if the stack temperature is high, cell drying may not be significant.

  Further, in a fuel cell system including a cooling water circulation system (a radiator, a cooling water circulation pump, etc.), generally, when the amount of power generation is small, the heat radiation to the cooling water is small and the stack temperature is low. However, when the outside air temperature is extremely high or when the amount of ventilation to the radiator is small, such as when there is a traffic jam, the cooling water temperature rises even when the amount of power generation is low, so the stack temperature rises and cell drying occurs.

Thereby, it can be said that the operation state in which cell drying becomes remarkable among all the operation states of the fuel cell system is located in a region 1 surrounded by a broken line in FIG. 1 and the normal operation state is located in a region 2 surrounded by a solid line. . That is, cell drying becomes significant in an operation state where the stack temperature is high to some extent during low power generation operation. Hereinafter, such an operation state in which cell drying becomes significant (region 1 surrounded by a broken line in FIG. 1) is referred to as a dry attention state 1. In the fuel cell system according to the embodiment of the present invention, whether or not the operating state is included in the dry caution state 1 determines whether or not the current operating state is an operating state in which cell drying becomes significant. Determine whether.

  FIG. 2 is a diagram showing the relationship between the gas stoichiometric ratio and the cooling water temperature change rate during normal operation. The cooling water temperature change rate shown in FIG. 2 indicates the ratio of the temperature change amount with respect to a predetermined elapsed time. The normal gas stoichiometric ratio in the normal state in FIG. Gas stoichiometric ratio determined. In general, the standard gas stoichiometric ratio is more than the required supply amount (gas stoichiometric ratio = 1), taking into account the variations in output characteristics in each cell and the characteristics of a device (such as an air compressor) that controls the gas supply amount. It is determined to be a large value.

  As shown in FIG. 2, during normal operation, even when the gas stoichiometric ratio is high, the power generation amount is large and the amount of generated water is large, and the heat dissipation effect to the exhaust gas is improved, so that the stack temperature is stabilized. If the stack temperature is stabilized, the cooling water temperature is naturally also stabilized. Therefore, during normal operation, the fuel cell system may be controlled so as to achieve the determined standard gas stoichiometric ratio. If the gas stoichiometric ratio is too low, the power generation voltage decreases due to the lack of hydrogen or oxygen, the amount of heat generated by the cell increases, and the effect of heat dissipation to the exhaust gas also decreases due to the small amount of gas supply. As a result, when the gas stoichiometric ratio becomes too low, the stack temperature rises, so the rate of increase in the coolant temperature increases.

  FIG. 3 is a diagram showing the relationship between the gas stoichiometric ratio and the cooling water temperature change rate in an operating state where the drying of the electrolyte membrane becomes significant. When the operating state is a dry caution state, unlike the scene of FIG. 2, the cooling water temperature change rate increases even when the gas stoichiometric ratio becomes too high. That is, when the operation state is in the dry attention state 1, the stack temperature change rate increases and causes the electrolyte membrane to be dried even if the gas stoichiometric ratio is too high or too low. Therefore, when the operation state is the dry caution state 1, it is necessary to control the gas stoichiometric ratio more precisely than during normal operation so that the cooling water temperature is stabilized. In such an operating state, the standard gas stoichiometric ratio at the normal time is slightly higher than the value at which the cooling water temperature is most stable.

  Therefore, when the fuel cell system according to the embodiment of the present invention is in an operation state in which cell drying becomes significant, the standard gas stoichiometric ratio determined at the normal time is set so that the cooling water temperature becomes stable, that is, the cooling water temperature change rate. Correct so that becomes lower. Specifically, the control is performed so as to shift from the control point A during power generation using the standard gas stoichiometric ratio shown in FIG. 3 to the control point B at which the cooling water temperature change rate is the lowest.

  In the fuel cell system according to the embodiment of the present invention, the stack temperature is stabilized and the electrolyte membrane is prevented from drying by controlling in this way. Note that the controlled gas stoichiometric ratio may be for both the fuel gas and the oxidant gas, or may be for either one. In addition, the dry prevention control executed in the present embodiment corrects the gas stoichiometric ratio, but it goes without saying that the same applies even if the gas supply amount is used. In this case, the standard gas supply amount may be obtained and the standard gas supply amount may be corrected.

[First embodiment]
The fuel cell system according to the first embodiment of the present invention will be described below.

〔System configuration〕
The configuration of the fuel cell system according to the first embodiment of the present invention will be described with reference to FIG. FIG. 4 is a diagram showing a configuration example of the fuel cell system as the first embodiment of the present invention. The fuel cell system in the present embodiment includes a fuel cell 10, an air compressor 11, pressure adjusting valves 13 and 17, a fuel gas supply device 15, a flow rate adjusting valve 16, a fuel gas circulation pump 18, a cooler 20, and an ECU (Electric Control Unit). ) 25 (corresponding to the control device of the present invention), temperature sensor 21, watt-hour meter 23, and the like.

  The air compressor 11 compresses a predetermined amount of air taken from the atmosphere via an air filter or the like as an oxidant gas, and sends the compressed air to the pipe 41. In the present invention, the oxidant gas delivered from the air compressor 11 is not limited to such compressed air. Accordingly, the oxidant gas is supplied to the fuel cell 10 through the oxidant gas supply pipe 41 connected to the oxidant gas inlet of the fuel cell 10.

  The fuel gas supply device 15 supplies, for example, hydrogen gas, a hydrogen mixed gas, or the like as the fuel gas. The flow rate of the fuel gas supplied from the fuel gas supply device 15 is controlled by the flow rate adjusting valve 16 and is sent out to the pipe 51.

  The flow rate adjusting valve 16 sends out the fuel gas supplied from the fuel gas supply device 15 by a predetermined flow rate according to the required power generation amount of the fuel cell 10. The fuel gas that has passed through the flow rate adjustment valve 16 is supplied to the fuel cell 10 through a fuel gas supply pipe 51 that is connected to the fuel gas inlet of the fuel cell 10.

  The fuel cell 10 is formed such that both surfaces of the electrolyte membrane are sandwiched between gas diffusion electrodes (fuel gas electrode (anode) and oxidant gas electrode (cathode)) and both sides are sandwiched between separators provided with gas supply paths. A plurality of cells are stacked. In this cell, MEA (Membrane Electrode Assembly) or MEGA (Membrane Electrode & Gas Diffusion Layer Assembly) may be used as an assembly of the electrolyte membrane, the fuel gas electrode, and the oxidant gas electrode. May be.

  The fuel cell 10 generates electric power by reacting the fuel gas and the oxidant gas supplied in this manner through the electrolyte membrane in each cell. The fuel gas that has not been used for power generation (hereinafter referred to as anode offgas) is discharged from the anode offgas outlet, and the oxidant gas that has not been used for power generation (hereinafter referred to as cathode offgas) is discharged from the cathode offgas outlet. Is done.

  The pressure adjustment valve 13 is disposed between a pipe 44 and a pipe 46 connected to the cathode offgas outlet of the fuel cell 10 and adjusts the back pressure of the cathode offgas. The cathode off gas that has passed through the pressure regulating valve 13 is sent out to the piping 46 and sent out to an exhaust path (not shown) or the like.

  On the other hand, the pressure regulating valve 17 is arranged in the pipe 52 connected to the anode off gas outlet. The pressure adjusting valve 17 adjusts the back pressure of the anode off gas. The anode off gas that has passed through the pressure regulating valve 17 is sent to the pipe 54 and sent to the fuel gas circulation pump 18.

  The fuel gas circulation pump 18 includes a rotation driving motor and the like, and is disposed between a pipe 54 connected to the pressure regulating valve 17 and a pipe 57 for circulating the anode off gas to the fuel cell 10 again. The fuel gas circulation pump 18 sends the anode off gas to the pipe 57 in order to resupply the anode off gas passing through the pipe 54 to the fuel cell 10. The anode off-gas passing through the pipe 57 is mixed with the fuel gas supplied from the fuel gas supply device 15 by the pipe 51 and supplied again to the fuel cell 10.

Thus, in the fuel cell system according to the present embodiment, an anode off-gas circulation path is formed in which the anode off-gas sent from the fuel cell 10 without being used for power generation is supplied to the fuel cell 10 again. However, the present invention is not limited to a fuel cell system having such an anode off-gas circulation path, and the fuel cell system may be configured not to have an anode off-gas circulation path.

  Further, a coolant (cooling water) is supplied to the fuel cell 10 in order to operate the fuel cell at an appropriate temperature. In the fuel cell 10, for example, when the cooling water passes through a cooling plate provided between the cells, the heat generated by the cells is taken and is sent out of the fuel cell 10 from the cooling water outlet. The cooling water sent out from the cooling water outlet passes through the piping 61 connected to the cooling water outlet and is sent to the cooler 20.

  The cooler 20 takes in the cooling water heated by taking heat from each cell of the fuel cell 10 from the pipe 61 and cools the taken-in cooling water. The cooler 20 cools the cooling water taken from the pipe 61 by wind sent from a cooling fan or the like provided inside, and sends the cooled cooling water to the pipe 62. The cooling water sent to the pipe 62 is supplied again to the fuel cell 10.

  As described above, the fuel cell system according to the present embodiment has a cooling water circulation system in which the heat of each cell in the fuel cell 10 is removed and the heated cooling water is cooled by the cooler 20 and supplied to the fuel cell 10 again. Have.

  In the fuel cell system in the present embodiment, a temperature sensor 21 is installed in the vicinity of the outlet of the fuel cell 10 in such a cooling water circulation system in order to estimate the operating temperature of the fuel cell 10. The temperature sensor 21 detects the temperature of the cooling water that is heated by taking heat from each cell of the fuel cell 10 and is discharged from the fuel cell 10. The detected temperature of the cooling water is sent to the ECU 25.

  The present invention does not limit the installation position of the temperature sensor 21 or the temperature detection principle as long as the temperature of the cooling water reflecting the heat generated by each cell of the fuel cell 10 can be measured. Therefore, the temperature sensor 21 may be provided in a discharge path through which the cooling water that has passed through each cell in the fuel cell 10 flows. Furthermore, the present invention does not have to be the temperature of the cooling water as long as the operating temperature of the fuel cell 10 can be measured, and the temperature in the fuel cell 10 or the temperature of a predetermined location of the fuel cell 10 itself is measured. You may make it do.

  The fuel cell system in the present embodiment further includes a watt-hour meter 23 for measuring the amount of power generated in the fuel cell 10. For example, the watt hour meter 23 is installed on a power line that connects the output terminal of the fuel cell 10 and a load device (not shown). The measured electric energy is sent to the ECU 25. Note that the present invention does not limit the installation position, measurement principle, and the like of the watt-hour meter 23 as long as the power generation amount of the fuel cell 10 can be measured. Further, as the power generation amount of the fuel cell 10, the current or voltage output from the fuel cell 10 may be measured.

The ECU 25 includes a CPU (Central Processing Unit), a memory, an input / output interface, and the like. The ECU 25 performs dry prevention control by causing the CPU to execute a control program stored in the memory. The drying prevention control executed by the ECU 25 is as described in the above [Body of the embodiment of the present invention]. That is, the ECU 25 determines whether or not the operating state of the fuel cell 10 is the dry caution state 1 based on the coolant temperature sent from the temperature sensor 21 and the power generation amount sent from the watt hour meter 23. When the ECU 25 determines that the operating state of the fuel cell 10 is the dry attention state 1, the ECU 25 corrects the standard gas stoichiometric ratio according to the cooling water temperature change rate, and continues the power generation of the fuel cell 10 with the corrected gas stoichiometric ratio.

  The control object of the gas stoichiometric ratio by the ECU 25 may be for both the fuel gas and the oxidant gas, or may be for either one. When controlling the stoichiometric ratio of the oxidant gas, the ECU 25 may change the flow rate of the oxidant gas output from the air compressor 11 or change the flow rate of the cathode off gas passing through the pressure regulating valve 13. You may make it make it. When controlling the stoichiometric ratio of the fuel gas, the ECU 25 may change the flow rate of the anode off-gas circulated by controlling the number of revolutions of the motor of the fuel gas circulation pump 18, or the flow rate adjusting valve 16. Thus, the fuel gas supply flow rate may be changed, or the anode off-gas flow rate passing through the pressure regulating valve 17 may be changed. Since the present invention does not limit the method for realizing the determined gas stoichiometric ratio, any one of the above methods may be adopted, or all the methods may be executed together. A method other than the above may be adopted. The above-described system configuration also changes depending on the method for realizing the gas stoichiometric ratio.

[Operation example]
Hereinafter, an operation example of the fuel cell system in the present embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing the operation of the fuel cell system in the first embodiment.

  The ECU 25 receives a request for a required amount of power sequentially or at a predetermined cycle from a control device (not shown) that controls the load device or the like (S401). In response to this request, the ECU 25 determines the amount of power to be generated by the fuel cell 10 (S402). At this time, the ECU 25 determines the amount of power to be supplied by the fuel cell 10 from the relationship with the amount of power supplied by another power source, for example.

  When the ECU 25 determines the power generation amount to be supplied in the fuel cell 10, the ECU 25 determines a standard gas stoichiometric ratio corresponding to the power generation amount (S403). For example, the ECU 25 determines the standard gas stoichiometric ratio from the relationship with the required power generation amount based on a control map or the like held in a memory or the like. In addition, this invention does not limit the determination method of this standard gas stoichiometric ratio. The ECU 25 controls the power generation of the fuel cell based on the standard gas stoichiometric ratio thus determined. Of course, elements other than such a gas stoichiometric ratio may be used together in order to generate the required amount of power in the fuel cell 10. At this time, the fuel cell system in the present embodiment is controlled so that the air compressor 11, the pressure regulating valves 13 and 17, the fuel gas circulation pump 18 and the flow rate regulating valve 16 satisfy the above standard gas stoichiometric ratio. To work.

  The air compressor 11 compresses the oxidant gas by a predetermined flow rate and sends it out to the pipe 41. The oxidant gas is supplied to the cathode of each cell in the fuel cell 10 through the pipe 41. The pressure regulating valve 13 regulates the back pressure of the cathode off gas sent from the fuel cell 10. On the other hand, the flow rate adjustment valve 16 adjusts the flow rate of the fuel gas supplied from the fuel gas supply device 21 and sends it out to the pipe 51. The fuel gas is supplied to the anode of each cell in the fuel cell 10 through the pipe 51. The pressure adjustment valve 17 adjusts the back pressure of the anode off gas delivered from the fuel cell 10. The fuel gas circulation pump 18 sends the anode off gas that has passed through the pressure regulating valve 17 to the pipe 57 at a predetermined pressure. The anode off gas passing through the pipe 57 is mixed with the fuel gas supplied from the fuel gas supply device 15 by the pipe 51 and re-supplied to the fuel cell 10.

  In each cell in the fuel cell 10, the fuel gas and the oxidant gas supplied in this manner react with each other through the electrolyte membrane to generate power. The watt hour meter 23 measures the amount of power generated by the fuel cell 10 in this way, and sends the measurement result to the ECU 25 sequentially or at a predetermined cycle.

Each cell in the fuel cell 10 generates heat with power generation. Cooling water cooled by the cooler 20 is fed into the fuel cell stack 10 in order to prevent the cell from becoming hot due to this heat generation and drying the electrolyte membrane of the cell. The cooling water takes heat generated by each cell in the fuel cell 10 and is discharged from the fuel cell 10. The temperature sensor 21 detects the temperature of the cooling water sent from the fuel cell 10 and sends the detection result to the ECU 25 sequentially or at a predetermined cycle.

  The ECU 25 acquires the output signal from the temperature sensor 21 and the output signal from the watt hour meter 23 (S404). The ECU 25 holds the coolant temperature indicated by the output signal from the temperature sensor 21 in a memory or the like each time. The maintained cooling water temperature is used to calculate a cooling water temperature change rate described later.

  The ECU 25 determines whether or not the operating state of the fuel cell 10 is a dry caution state based on the coolant temperature and the power generation amount indicated by the output signal from the watt hour meter 23 (S405). Specifically, based on the information of FIG. 1 held in a memory or the like, the ECU 25 determines whether or not the acquired cooling water temperature (stack temperature) and the power generation amount are included in the region 1 indicating the dry caution state. Determine whether. When the ECU 25 determines that the operating state of the fuel cell 10 is not the dry caution state (S405; NO), the ECU 25 continues the power generation using the standard gas stoichiometric ratio as it is (S430). Even if it does in this way, as FIG. 2 shows, it is because a cooling water temperature change rate does not rise so much that the dry state of an electrolyte membrane becomes remarkable.

  When the ECU 25 determines that the operating state of the fuel cell 10 is a dry caution state (S405; YES), the ECU 25 corrects the previously determined standard gas stoichiometric ratio as follows. At this time, the relationship between the cooling water temperature change rate and the gas stoichiometric ratio is located in the vicinity of the control point A in FIG. The ECU 25 corrects the standard gas stoichiometric ratio so that the control point A is transferred to the control point B.

First, the ECU 25 calculates the rate of change (T _N ) in the coolant temperature (S406).
At this time, the history data of the coolant temperature information sent from the temperature sensor 21 and held is used. The ECU 25 holds the calculated change rate (T _N ) of the cooling water temperature in a memory or the like each time. The ECU 25 obtains a difference (T _N −T _N-1 ) between the previous cooling water temperature change rate (T _N-1 ) held in this way and the currently calculated cooling water temperature change rate (T _N ) ( S407).

Subsequently, the ECU 25 determines whether or not the continuous processing flag is ON (S408). The initial value of the continuous processing flag is OFF. When the ECU 25 determines that the continuous processing flag is OFF (S408; NO), the ECU 25 compares the difference in cooling water temperature change rate (T _N −T _N-1 ) with the first threshold (S420).

When the ECU 25 determines that the difference (T _N −T _N−1 ) in the cooling water temperature change rate is smaller than the first threshold (S420; YES), the ECU 25 increases the standard gas stoichiometric ratio by a predetermined amount (S421), and sets the continuous processing flag. Set to ON (S422). Conversely, if the ECU 25 determines that the difference (T _N −T _N−1 ) in the cooling water temperature change rate is not smaller than the first threshold (S420; NO) and is larger than the second threshold (S423; YES), the standard The gas stoichiometric ratio is decreased by a predetermined amount (S424). At this time, the continuous processing flag remains OFF.

On the other hand, the ECU 25 determines that the continuous processing flag is set to ON (S408; YES), and that the difference in cooling water temperature change rate (T _N −T _N-1 ) is smaller than the first threshold (S410; YES). ), The standard gas stoichiometric ratio is decreased by a predetermined amount (S411), and the continuous processing flag is set to OFF (S412). When the ECU 25 determines that the difference in the cooling water temperature change rate (T _N −T _N−1 ) is not smaller than the first threshold (S410; NO) and larger than the second threshold (S413; YES), the ECU 25 sets the standard gas stoichiometric ratio. A predetermined amount is increased (S414). At this time, the continuous processing flag remains ON.

  When the standard gas stoichiometric ratio is corrected in this way, the ECU 25 performs control so that electric power is generated with the corrected gas stoichiometric ratio (S435). The first threshold value, the second threshold value, and the predetermined amount for increasing or decreasing the gas stoichiometric ratio are determined in advance according to the output characteristics of the cells constituting the fuel cell 10 and the characteristics of other devices used for controlling the gas stoichiometry. , And can be adjusted and held in a memory or the like. When such a process is completed, the process is repeated from S401.

<Operation and effect of the first embodiment>
The operation and effect of the fuel cell system as the first embodiment described above will be described below.

  In the fuel cell system according to the present embodiment, the amount of electric power generated by the fuel cell 10 is measured by the watt hour meter 23, and the temperature of the cooling water sent from the fuel cell 10 after heat exchange with each cell is detected by the temperature sensor 21. Is done.

  The ECU 25 calculates a cooling water temperature change rate based on the detected cooling water temperature. Further, the ECU 25 controls the gas stoichiometric ratio and the like so that the fuel cell 10 generates the required amount of power. The gas stoichiometric ratio determined at this time is a standard gas stoichiometric ratio determined by the required power amount.

  In the fuel cell system according to the present embodiment, it is determined whether or not the operation state of the fuel cell 10 is a dry caution state based on the power generation amount and the cooling water temperature. If the dry caution state is satisfied, the previously determined standard gas stoichiometric ratio is determined. Is corrected according to the cooling water temperature change rate. On the other hand, when the operating state of the fuel cell 10 is not in a dry caution state, power generation is continued with the standard gas stoichiometric ratio.

  Thus, according to the fuel cell system of the present embodiment, when the electrolyte membrane is in an operating state where the drying of the electrolyte membrane is significant, the standard gas stoichiometric ratio determined during normal operation is controlled to further prevent the electrolyte membrane from drying. The Therefore, even in such an operating state, the gas stoichiometric ratio is controlled more finely, so that it is possible to prevent the drying of the electrolyte membrane from being promoted and to prevent the electrolyte membrane from being dried to a problem.

[Second Embodiment]
The fuel cell system according to the second embodiment of the present invention will be described below. In the fuel cell system according to the first embodiment described above, the gas stoichiometric ratio is increased or decreased by a predetermined amount. The fuel cell system according to the second embodiment acquires the amount by which the gas stoichiometric ratio is increased or decreased according to the difference in the cooling water temperature change rate.

〔System configuration〕
The configuration of the fuel cell system according to the second embodiment of the present invention is the same as that of the first embodiment shown in FIG. Therefore, the description is omitted here. Since the content of the cell drying prevention control by the ECU 25 changes, this change will be described in the following [Operation Example] section.

[Operation example]
Hereinafter, an operation example of the fuel cell system in the second embodiment will be described with reference to FIG. FIG. 6 is a flowchart showing the operation of the fuel cell system in the second embodiment. The process is the same as that in the first embodiment until the ECU 25 calculates the difference (T _N −T _N−1 ) from the previous cooling water temperature change rate (S407).

In the fuel cell system according to the second embodiment, the ECU 25 determines the increase / decrease width (γ) of the gas stoichiometric ratio based on the calculated difference ( _TN - _TN-1 ) in the coolant temperature change rate (S601). At this time, the ECU 25 determines the difference (T _N −
T _N-1 ) and the gas stoichiometric ratio increase / decrease width (γ) are used. FIG. 7 is a diagram showing an example of the relationship between the difference in the cooling water temperature change rate (T _N −T _N−1 ) and the gas stoichiometric ratio increase / decrease width (γ). In the example of FIG. 7, the relationship between the difference in the cooling water temperature change rate (T _N −T _N−1 ) and the gas stoichiometric ratio increase / decrease width (γ) is a proportional relationship. For example, the ECU 25 calculates the increase / decrease width (γ) of the gas stoichiometric ratio using such a relational expression.

  When correcting the standard gas stoichiometric ratio, the ECU 25 decreases (S411, S424) or increases (S414, S421) the gas stoichiometric ratio using the determined increase / decrease width (γ) of the gas stoichiometric ratio. The ECU 25 greatly corrects the standard gas stoichiometric ratio when the difference in the cooling water temperature change rate from the previous time is large, that is, in the state away from the control point B shown in FIG. Is small, that is, in a state close to the control point B shown in FIG. 3, the standard gas stoichiometric ratio is corrected to be small.

  The fuel cell system according to the second embodiment can be brought closer to an ideal control point as compared with the first embodiment by controlling in this way, and thus the electrolyte membrane can be appropriately prevented from drying.

<Operation and effect of the second embodiment>
The operation and effect of the fuel cell system as the second embodiment described above will be described below.

In the fuel cell system according to the present embodiment, the gas stoichiometric ratio increase / decrease width (T _N −T _N−1 ) corresponding to the difference (T _N −T _N−1 ) between the previously calculated cooling water temperature change rate and the currently calculated cooling water temperature change rate. γ) is determined. When the operating state of the fuel cell 10 is in a dry caution state, the previously determined standard gas stoichiometric ratio is corrected by this gas stoichiometric ratio increase / decrease width (γ).

  As a result, according to the fuel cell system of the present embodiment, the gas stoichiometric ratio is controlled to be finer and closer to the ideal point when the electrolyte membrane is in an operation state where the drying of the electrolyte membrane becomes significant compared to the normal operation. Therefore, drying of the electrolyte membrane can be prevented in advance.

[Modification]
In the fuel cell systems in the first embodiment and the second embodiment described above, the correction of the standard gas stoichiometric ratio is executed in the same cycle as the control cycle in which the standard gas stoichiometric ratio corresponding to the required power generation amount in the fuel cell 10 is determined. It was. That is, regarding the standard gas stoichiometric ratio, the determination cycle and the correction cycle are the same.

  However, the correction period may be controlled to be shorter than the determination period. Specifically, in the processing flows of FIGS. 5 and 6, S404 to S435 may be looped a plurality of times. In this case, after being controlled to generate power at the corrected gas stoichiometric ratio (S435), the process returns to S404, and if the operating state of the fuel cell 10 is dry again, the standard gas stoichiometric ratio is corrected again.

  In this way, even when the operating state of the fuel cell 10 is in a dry caution state and the required power generation amount is kept constant for a long time, the standard gas stoichiometry is maintained until the control point B shown in FIG. Since the ratio is corrected, drying of the electrolyte membrane can be prevented in advance.

Further, in the fuel cell systems in the first and second embodiments described above, the difference (T _N −T _N−1 ) between the previously calculated cooling water temperature change rate and the currently calculated cooling water temperature change rate. Based on the above, the increase / decrease or increase / decrease width (γ) of the standard gas stoichiometric ratio was determined.

  However, the increase / decrease or increase / decrease width (γ) of the standard gas stoichiometric ratio may be determined based on the cooling water temperature change rate (change amount) at that time. When the cooling water temperature change amount is large, the same processing as that when the difference in the cooling water temperature change rate from the previous time is large may be used.

It is a figure which shows the driving | running state in which drying of an electrolyte membrane becomes remarkable in a fuel cell system, and a normal driving | running state based on the relationship between stack temperature and electric power generation amount. It is a figure which shows the relationship between the gas stoichiometric ratio at the time of normal driving | operation, and a cooling water temperature change rate. It is a figure which shows the relationship between the gas stoichiometric ratio and the cooling water temperature change rate in the driving | running state in which drying of an electrolyte membrane becomes remarkable. It is a figure which shows the structural example of the fuel cell system as 1st embodiment of this invention. It is a flowchart which shows operation | movement of the fuel cell system in 1st embodiment. It is a flowchart which shows operation | movement of the fuel cell system in 2nd embodiment. It is a figure which shows the example of the relationship between the difference ( _TN - _TN-1 ) of a cooling water temperature change rate, and a gas stoichiometric ratio increase / decrease width ((gamma)).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel cell 11 Air compressor 13, 17 Pressure adjustment valve 15 Fuel gas supply apparatus 16 Flow rate adjustment valve 18 Fuel gas circulation pump 20 Cooler 21 Temperature sensor 23 Electricity meter 25 ECU (Electric Control Unit)
41, 44, 46, 51, 52, 54, 57, 61, 62 Piping

Claims (5)

Standard determination means for determining a standard gas stoichiometric ratio corresponding to the required power generation amount with respect to the gas supplied to the fuel cell;
Temperature detecting means for detecting the temperature of the fuel cell;
State determining means for determining an operating state of the fuel cell;
Calculation means for calculating a temperature change rate of the fuel cell from the temperature of the fuel cell detected by the temperature detection means;
When it is determined by the state determination means that the fuel cell is in an operating state in which the electrolyte membrane is easily dried, the temperature change rate calculated by the calculation means is adjusted so that the temperature of the fuel cell is stabilized. Correction means for correcting the standard gas stoichiometric ratio,
A control device for a fuel cell system comprising: The calculation means obtains a difference between the temperature change rate calculated last time and the temperature change rate calculated this time,
The correction means increases or decreases the standard gas stoichiometric ratio according to the difference in the temperature change rate so that the temperature of the fuel cell is stabilized.
The control apparatus for a fuel cell system according to claim 1.   3. The fuel cell system according to claim 2, wherein the correction unit determines an increase / decrease width corresponding to a difference in the temperature change rate, and increases / decreases the standard gas stoichiometric ratio by the determined increase / decrease width. Control device. Further comprising power measuring means for measuring the amount of power generated by the fuel cell;
The state determination unit determines whether or not the fuel cell is in an operation state in which the electrolyte membrane is easily dried based on the amount of power generation measured by the power measurement unit and the temperature detected by the temperature detection unit. ,
The fuel cell system control device according to any one of claims 1 to 3, wherein the control device is a fuel cell system control device.   5. The fuel cell system according to claim 4, wherein the state determination unit determines that the fuel cell is in an operation state in which the electrolyte membrane is easily dried when the power generation is low and the temperature of the fuel cell is high. Control device.

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