JP2008103201A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system which can surely detect an abnormality of a cell voltage even in a low-load operation. <P>SOLUTION: The fuel cell system judges whether power generation is possible or not in a low-load operation in which a state quantity of hydrogen gas supply or the like concerning power generation of a fuel cell stack 1 is controlled, and if power generation in a low-load operation in which a state quantity is controlled is judged as possible, power generation in a low-load operation is performed, and a cell voltage of the fuel cell stack 1 where power generation is performed in a low-load operation in which a state quantity is controlled is detected by a voltage sensor 15, and based on the detected cell voltage, it is judged if the cell voltage is abnormal or not. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system having improved cell voltage abnormality detection.

  Conventionally, in a fuel cell system including a fuel cell that generates an electric energy by electrochemically reacting an oxidant gas mainly containing oxygen and a fuel gas mainly containing hydrogen in a large number of cells, the cell voltage For example, a technique described in the following literature is known as a technique for estimating the factor of the output fluctuation of the system (see Patent Document 1).

In the technique described in this document, a large number of cells of the fuel cell system are divided into a plurality of cell groups, the output voltage for each cell group is measured, the average voltage of the output voltage and the variation of the output voltage are calculated, and the output Based on the voltage, the average voltage of the output voltage, and variations in the output voltage, it is estimated whether or not the moisture in the gas flow path in the fuel cell is excessive and the wet state of the electrolyte membrane.
JP2004-127915

  In conventional fuel cells, power generation efficiency and cell voltage are higher at lower load operation (low load power generation). Therefore, even if some cell voltage abnormality occurs during low load operation, The cell voltage may not appear as a clear difference from the cell voltage of a normal cell. For this reason, when determining abnormal cell voltage based on the output voltage of a cell (or cell group) in low-load operation, there is a risk of erroneous determination if the determination condition is tightened, while if the determination condition is relaxed It becomes difficult to reliably detect the abnormality.

  Here, the cause of the abnormal cell voltage is that moisture stays in the gas flow path of the fuel cell, resulting in excessive moisture and flooding (water clogging), while the moisture is insufficient and dryout (drying of the electrolyte membrane) ), Or due to insufficient stoichiometry due to insufficient fuel gas or oxidant gas.

  Furthermore, when the system switches from a low load operation to a high load operation transiently, even if the cell voltage abnormality cannot be detected in the low load operation, the high load operation is easily affected by the cell voltage abnormality. That is, there has been a problem that the cell voltage of the cell in which the cell voltage abnormality has occurred suddenly decreases and the reliability of the system decreases.

  Accordingly, the present invention has been made in view of the above, and an object of the present invention is to provide a fuel cell system capable of reliably detecting an abnormality in a cell voltage even in a low load operation.

  In order to achieve the above object, a means for solving the problems of the present invention is to generate power by an electrochemical reaction between a fuel gas supplied by a fuel gas supply means and an oxidant gas supplied by an oxidant gas supply means. In a fuel cell system including a fuel cell to be performed, voltage detection means for detecting a cell voltage of each cell constituting the fuel cell or a cell group voltage of a cell group including a plurality of cells, and power generation of the fuel cell The limited power generation determination means for determining whether or not the fuel cell system is capable of generating power in a low load operation with a limited amount of state, and the fuel cell system is capable of generating power in a low load operation with a limited amount of state. If it is determined by the limited power generation determination means, the limited power generation control means for generating power at a low load operation with a limited state quantity, and the state power is limited by the limited power generation control means. The cell voltage or cell group voltage of the fuel cell that is generating power is detected by the voltage detection means, and it is determined whether the cell voltage is abnormal based on the detected cell voltage or cell group voltage And a cell voltage abnormality determining means.

  According to the present invention, a state voltage is limited to intentionally generate an unstable power generation state, and a cell (or cell group) voltage variation is amplified, so that an abnormal cell voltage can be obtained even in a low-load operation state. Can be detected with high accuracy.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best embodiment for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a fuel cell system according to Embodiment 1 of the present invention. The system of Embodiment 1 shown in FIG. 1 includes a fuel cell stack 1 and a hydrogen system (anode system) configured to supply and discharge hydrogen gas as a fuel gas to the fuel cell stack 1. A main valve 3, a pressure reducing valve 4, a hydrogen supply valve 5, a hydrogen circulation pump 6, a purge valve 7, a dilution device 8, a pressure sensor 9, and a temperature sensor 10 are provided. Further, a compressor 11, an air pressure regulating valve 12, a pressure sensor 13, and a temperature sensor 14 are provided as an air system (cathode system) configuration for supplying and discharging oxidant gas air to and from the fuel cell stack 1. The system further includes a voltage sensor 15, a power manager 16, a secondary battery 17, a battery controller 18, an atmospheric pressure sensor 19, and a controller 20.

In the fuel cell stack 1, hydrogen gas is supplied as fuel gas to the anode, and air (oxygen) is supplied as oxidant gas to the cathode, and the electrode reaction shown below proceeds to generate electric power.
Anode (hydrogen) electrode reaction: H ₂ → 2H ⁺ + 2e ⁻
Cathode (oxygen) electrode reaction: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O

  Hydrogen is supplied from the hydrogen tank 2 to the anode of the fuel cell stack 1 through the hydrogen tank main valve 3, the pressure reducing valve 4, and the hydrogen supply valve 5. The high-pressure hydrogen supplied from the hydrogen tank 2 is mechanically reduced to a predetermined pressure by the pressure reducing valve 4, and the hydrogen pressure at the fuel cell inlet at the hydrogen supply valve 5 satisfies a desired hydrogen supply amount. Control is performed based on the pressure measured by the pressure sensor 9 provided on the fuel cell inlet side so that the hydrogen pressure is obtained.

  The hydrogen supply valve 5 is configured such that the valve opening is adjusted using, for example, electromagnetic force generated in the drive coil, and the current flowing through the drive coil is changed according to the temperature, or the friction of the mechanical system is changed. It has the characteristic that the actual opening degree with respect to changes. For this reason, the representative temperature of the hydrogen supply valve 5 is measured by the temperature sensor 10, and the command opening is set corresponding to the actual opening based on the measured temperature.

  In other words, the relationship between the commanded opening and the actual opening with respect to the temperature is obtained in advance through simulations of experiments and desk studies, etc., and the obtained relationship is stored in a storage device or the like as a map, and hydrogen is supplied with reference to this map. The opening degree of the valve 5 is adjusted and controlled. The basic characteristics of temperature and opening tend to reduce the error of the actual opening with respect to the command opening as the temperature rises.

  The hydrogen circulation pump 6 is installed to recycle hydrogen that has not been consumed at the anode. Since air is supplied to the cathode side, nitrogen that is contained in the air and does not chemically react passes through the electrolyte membrane of the fuel cell stack 1 and accumulates in the hydrogen path. If the accumulated amount of nitrogen becomes too large, hydrogen cannot be circulated by the hydrogen circulation pump 6, so it is necessary to manage the amount of nitrogen in the circulation path. Therefore, the nitrogen in the circulation path is discharged to the outside through the purge valve 7, and the amount of nitrogen existing in the hydrogen path is managed to such an extent that the circulation performance can be maintained.

  The diluting device 8 introduces unused air discharged from the fuel cell stack 1 before releasing the hydrogen discharged simultaneously with the purge valve 7 when nitrogen is discharged to the outside of the system. And hydrogen are stirred to dilute and exhausted out of the system.

  Air pressurized by the compressor 11 is supplied to the cathode of the fuel cell stack 1, the air pressure regulating valve 12 adjusts the pressure of the air supplied to the cathode, and the pressure of the air is a pressure sensor provided in the compressor 11. The pressure is adjusted based on the pressure measured at 13. For example, when it is desired to increase the electric power extracted from the fuel cell stack 1, the reaction efficiency in the fuel cell stack 1 is increased to an energy density that can be extracted by pressurizing the air supplied to the fuel cell stack 1.

  The compressor 11 has such characteristics that volumetric efficiency deteriorates due to temperature rise, and flow rate characteristics with respect to the rotational speed deteriorate. For this reason, the temperature of the air discharged from the compressor 11 is measured by the temperature sensor 14 provided at the cathode inlet of the fuel cell stack 1, and the measured temperature of the air is set as the representative temperature of the compressor 11, and based on this representative temperature. The rotational drive of the compressor 11 is controlled. That is, the relationship between the rotational speed with respect to the temperature and the discharge flow rate is obtained in advance through simulations of experiments and desktop examinations, etc., and the obtained relationship is prepared as a map stored in a storage device or the like. Control the drive.

  Further, the compressor 11 has such characteristics that the air density to be sucked in is reduced due to the drop in the atmospheric pressure, and the flow rate characteristic with respect to the rotational speed is deteriorated. For this reason, the atmospheric pressure is measured by the atmospheric pressure sensor 19, and the rotational drive of the compressor 11 is controlled based on the measured atmospheric pressure. That is, the relationship between the rotational speed with respect to the atmospheric pressure and the discharge flow rate is obtained in advance through simulations of experiments and desk studies, and the obtained relationship is stored as a map in a storage device or the like. Controls rotational drive.

  The voltage sensor 15 is provided in the fuel cell stack 1 and measures a cell voltage for each of a large number of cells constituting the fuel cell stack 1 or a predetermined number of cells.

  The power manager 16 takes out electric power from the fuel cell stack 1 and supplies it to a drive motor (not shown) that drives a moving body such as a fuel cell vehicle that mainly consumes the taken out electric power. The power manager 16 has a function of measuring a current taken out from the fuel cell stack 1 for power take-out control.

  The secondary battery 17 supplies power necessary for driving auxiliary machinery necessary for generating power in the fuel cell system, and the generated power of the fuel cell stack 1 with respect to the power required for the fuel cell system. When there is a shortage of power, supply the power for the shortage. Conversely, the secondary battery 17 stores surplus power when the generated power of the fuel cell stack 1 becomes surplus. Further, when the consumer that mainly consumes the electric power obtained by the fuel cell stack 1 is a drive motor, the secondary battery 17 charges the regenerative power of the drive motor.

  The battery controller 18 measures the charge amount of the secondary battery 17 and controls charging / discharging of the secondary battery.

  The controller 20 functions as a control center for controlling the operation of the system, and includes, for example, a microcomputer having resources such as a CPU, a storage device, and an input / output device necessary for a computer that controls various operation processes based on a program. It is realized by. The controller 20 reads signals from the sensors (not shown) that collect information necessary for operation of the system, such as the above-mentioned sensors and other pressures, temperatures, concentrations, voltages, and currents that cannot be obtained by these sensors. Based on the read various signals and the control logic (program) stored in advance in the interior, a command is sent to the components requiring control of the system including the actuators of the valves, and the cell voltage abnormality determination operation described below is performed. All the operations necessary for operation / stop of this system are managed and controlled.

  As shown in FIG. 2, the controller 20 detects a driving force value requested by the driver of the fuel cell vehicle, and based on the detected value and the suppliable power of the secondary battery 17 as means for determining cell voltage abnormality. The generated power determining means 201 for determining the target generated power of the fuel cell stack 1 and the normal power generation operation in which no restriction is added based on the target generated power determined by the generated power determining means 201 A power generation mode switching determination unit 202 is provided that determines switching from the power generation mode to the limited power generation mode that is a power generation operation in which the state quantity of the system is limited, and vice versa.

  Here, the state quantity of the system restricted in the limited power generation mode is the state quantity of the anode system, such as the amount of generated power, the amount of hydrogen supply, and the like, and the state quantity of the cathode system, such as the amount of air supply.

  Further, the controller 20 is based on the target power generation and the state of the fuel cell system, based on the normal power generation mode control means 203 for controlling the auxiliary devices of the fuel cell system in the normal power generation mode, and on the state of the fuel cell system, And a limited power generation mode control means 204 for controlling the auxiliary devices of the fuel cell system in the limited power generation mode.

  Further, the controller 20 reads a cell (group) voltage in the normal power generation mode, calculates a parameter using the voltage variation index, determines a cell voltage abnormality in the normal power generation mode based on the obtained parameter, and the limited power generation mode. A voltage variation determination unit 205 that reads a cell (group) voltage from time to time and calculates a parameter that uses a voltage variation index as a parameter and determines a cell voltage abnormality in the limited power generation mode based on the parameter is provided.

  The generated power determination means 201 is based on the moving speed of the moving body, the driver's required driving force value (the amount of accelerator operation in the case of a vehicle), the remaining amount of the secondary battery 17 and the suppliable power in the fuel cell stack 1. Determine the target generated power.

  The power generation mode switching determination means 202 is a target generated power in the fuel cell stack 1 determined by the generated power determination means 201, a moving speed of the moving body, an operation state of the driver (in the case of a vehicle, an operation amount of an accelerator or a brake), Based on the remaining amount of the secondary battery 17 and the suppliable power, it is determined whether or not the power generation operation with the limited amount of state is possible from the viewpoint of securing the driving performance of the moving body, and whether or not to switch the power generation mode. To do. The power generation mode switching determination unit 202 determines whether or not a power generation operation with a limited amount of state is necessary based on the cell voltage abnormality determination result of the voltage variation determination unit 205 in the normal power generation mode, and determines whether or not to switch the power generation mode. judge.

  The normal power generation mode control unit 203 compensates for the power generation of the fuel cell system in the normal power generation mode based on the target generated power in the fuel cell stack 1 determined by the generated power determination unit 201 and the state quantity of the fuel cell system. It determines how to control the hydrogen supply valve 5, hydrogen circulation pump 6, purge valve 7, dilution device 8, compressor 11, air pressure regulating valve 12, etc.

  The limited power generation mode control means 204 is based on the state quantity of the fuel cell system, the hydrogen supply valve 5, the hydrogen circulation pump 6, the purge valve 7, and the diluting device of auxiliary equipment related to power generation of the fuel cell system in the limited power generation mode. 8. Decide how to control the compressor 11, the air pressure regulating valve 12, and the like.

  The voltage variation determination unit 205 reads the cell (group) voltage periodically (for example, every 10 msec), and based on the difference between the read average value of the cell voltages and each cell voltage, a parameter serving as a variation index, For example, the lowest cell voltage, standard deviation value, variance value, etc. are calculated, and one of these parameters, or the average value of the cell voltage, the highest cell voltage is added to the parameter, and a combination of two or more parameters and the judgment threshold And whether or not the cell voltage is abnormal is determined based on the comparison result.

  In such a configuration, a process for determining whether or not the cell voltage is abnormal is executed according to the procedure shown in the flowchart of FIG.

  In FIG. 3, first, the required driving force of the driver of the moving body is detected by the generated power determining means 201, and the power consumption of the auxiliary devices is estimated based on data obtained by measurement or experiments in advance. The target generated power is determined by subtracting the power that can be supplied from the secondary battery 17 from the sum of the required driving force and the power consumption of the auxiliary devices required to maintain the power generation state (step S301).

  Subsequently, the power generation mode switching determination means 202 determines whether or not the target generated power is equal to or less than a predetermined determination threshold value (Pa), and permits the transition from the normal power generation mode to the limited power generation mode. The permission determination flag to be checked is confirmed (step S302).

Here, the determination threshold value (Pa) of the target generated power that shifts to the limited power generation mode is obtained and set in advance by experiments or the like. The permission determination flag is a flag that is permitted (turned on) when it is determined that the limited power generation is necessary and the limited power generation is allowable based on the determination result of the power generation mode switching determination unit 202. For example, in the case of a mobile object such as a fuel cell vehicle, it is determined that the limited power generation can be permitted (the permission flag is turned on), for example.
(1) This is a case where rapid reacceleration of the vehicle is not recognized, for example, when it is determined that low load operation is continued.
(2) This is a case where there is no possibility of promoting deterioration of the fuel cell stack 1.
(3) This is a case where the cell voltage abnormality is not determined in the normal power generation mode. This is because when the cell voltage abnormality occurs in the normal power generation mode, the abnormality is further promoted in the limited power generation mode.

  As a result of the determination, if the target generated power is equal to or greater than the determination threshold value (Pa), it is possible to easily detect a cell voltage abnormality even in the normal power generation mode, so there is no need to perform limited power generation. Therefore, the system is operated for power generation in the normal power generation mode (step S304).

  On the other hand, when the target generated power is equal to or less than the determination threshold value (Pa), the system determines that the system is in a low load operation state. For this reason, there is a possibility that a cell voltage abnormality that cannot be detected by normal power generation may occur. Therefore, the limited power generation permission determination (refer to the permission flag) is performed. Limited power generation is performed under control (step S303). A specific method of how to limit power generation by limiting which state quantity related to power generation is described later.

  On the other hand, if the limited power generation is not permitted, normal power generation is performed under the control of the normal power generation mode control means 203 (step S304).

  When the limited power generation is permitted, the cell voltage for each cell (or cell group) of the fuel cell stack 1 measured by the voltage sensor 15 is subsequently controlled by the controller 20 under the control of the voltage variation determination means 205. (Step S305).

After that, based on the read cell voltage, the average cell voltage, the highest cell voltage, and the lowest cell voltage are first calculated as an indicator of cell voltage abnormality determination, and the standard deviation σ and variance σ ² are calculated as voltage variations between cells. To do. A cell voltage abnormality is determined based on these indices. Here, in order to facilitate understanding, the above average voltage and minimum cell voltage will be described for convenience. Of course, other combinations of the above-described determination indexes may be used, and the technical idea of the present invention is not limited.

  When the average voltage and the minimum cell voltage are obtained, whether or not the difference (Vave−Va) between the average cell voltage Vave and the determination threshold value Va set in advance by experiment or the like is positive (> 0), and the minimum cell It is determined whether the difference (Vmin−Vb) between the voltage Vmin and the determination threshold value Vb set in advance through experiments or the like is positive (> 0) or less (step S306).

  If (Vave−Va)> 0 and (Vmin−Vb)> 0 as a result of the determination, whether the target generated power is equal to or higher than the previous determination threshold Pa and refer to the previous permission flag Whether or not the limited power generation is being performed, and the determination result that (Vave−Va)> 0 and (Vmin−Vb)> 0 is obtained in the low load, medium, or high load operation state And whether the result is obtained by amplifying the voltage variation between cells by intentionally creating an unstable power generation state by limiting the state quantity (step) S307).

  As a result of the verification, if the target generated power is equal to or higher than the determination threshold Pa and the determination result is obtained in the middle and high load operation state of the fuel cell system, the determination result is (Vave−Va)> 0 and (Vmin Since −Vb)> 0, it is determined that the cell voltage is normal, and the determination result is stored in the controller 20 (step S308). Further, when the determination result is obtained in the state where the limited power generation is performed, the determination result is (Vave−Va)> 0 and (Vmin−Vb)> 0, and therefore the cell voltage is normal. It determines with a thing, and a determination result is preserve | saved at the controller 20 (step S308).

  On the other hand, if the determination result is obtained with low load operation and normal power generation, it is determined that the determination result was obtained in an environment where the cell voltage abnormality is not accurately determined. Then, the determination result is invalidated, it is determined that it is unknown whether or not the cell voltage is abnormal, and the result is stored in the controller 20 (step S309).

  In the determination result of the previous step S306, when (Vave−Va)> 0 and (Vmin−Vb)> 0 are not satisfied, that is, (Vave−Va) ≦ 0, (Vmin−Vb) ≦ 0, or (Vave− If Va) ≦ 0 and (Vmin−Vb) ≦ 0, it is determined that the cell voltage is abnormal, and the result is stored in the controller 20 (step S310). Furthermore, by storing the cause of the abnormality described below together, it is possible to select recovery control from the abnormal state based on the cause of the abnormality, and it is possible to perform an appropriate abnormality recovery operation.

  As a result of the determination, when (Vave−Va)> 0 and (Vmin−Vb) ≦ 0, it is estimated that only a specific cell has a cell voltage drop. This can be presumed that water has accumulated (flooded) in the gas flow path of the fuel cell stack 1 and gas supply has become insufficient. In addition, when (Vave−Va) ≦ 0 and (Vmin−Vb)> 0, it is estimated that the voltage drops almost uniformly in many cells. This is presumably because the cell voltage was reduced due to an increase in resistance (IR drop) due to drying (dryout) of the electrolyte membrane. Further, when (Vave−Va) ≦ 0 and (Vmin−Vb) ≦ 0, it is presumed that the voltage decreases in many cells and the voltage variation between the cells increases. The cause of this is presumed that the voltage has decreased due to the shortage of the fuel gas SR (stoichiometric ratio).

  The determination thresholds Va and Vb are variable values using parameters such as fuel gas temperature, oxidant gas temperature, cooling water temperature for cooling the fuel cell stack 1, and stack temperature of the fuel cell stack 1 as parameters. It is also possible to set. In this case, the relationship between the determination threshold value and the temperature is obtained in advance by an experiment or a simulation of desk study, and the obtained relationship is stored in a storage device or the like as a map, and the determination is made with reference to this map. After the threshold values Va and Vb are set, determination processing is executed. By doing so, the determination process can be performed more accurately.

  Next, referring to FIG. 4, a control method for limiting the state quantity to which a limit is applied when performing the limited power generation described above will be described.

  The amount of state to be limited includes the amount of generated power, the amount of air supply, the amount of hydrogen circulation, the amount of hydrogen supply, the hydrogen supply pressure and the air supply pressure. Any one of these state amounts, or two or more items Select in combination. Further, the amount to be limited may be limited at a predetermined ratio with respect to the target command value at the time of normal power generation operation given from the controller 20 to each corresponding auxiliary device, or may be limited by subtracting the predetermined amount. But you can. Further, the state limitation includes an operation of pausing.

(Restriction of power generation)
The limitation on the amount of generated power limits the power that is sent from the fuel cell stack 1 by sending a command from the controller 20 to the power manager 16. In the operation of limiting the amount of generated power, the target generated power is compared with the power that can be supplied from the secondary battery 17, and the target generated power is limited to the point where insufficient power is supplied by the power generation of the fuel cell stack 1. Is included.

(Air supply limit)
The air supply amount is limited by sending a command from the controller 20 to the compressor 11 and adjusting and controlling the rotation speed of the compressor. The operation of limiting the air supply amount includes limiting the target air supply amount to the target dilution air flow rate required for diluting the hydrogen amount discharged through the purge valve 7 by the diluting device 8. . Further, the limiting operation includes stopping the rotation of the compressor 11 when the purge valve 7 is closed.

(Restriction of hydrogen circulation rate)
Restriction of the hydrogen circulation amount is performed by sending a command from the controller 20 to the hydrogen circulation pump 6 and adjusting and controlling the rotation speed of the hydrogen circulation pump 6. In the limitation of the hydrogen circulation amount, the hydrogen circulation amount is limited to an amount that allows a predetermined excess amount of hydrogen consumption corresponding to the target extraction current determined based on the target generated power to be re-supplied to the fuel cell stack 1 by the circulation amount. Is included.

  When the generated current can be reduced to 0, the rotation driving of the hydrogen circulation pump 6 may be stopped. Nitrogen accumulates in the anode due to nitrogen cross-leakage between the anode and the cathode through the electrolyte membrane of the fuel cell stack 1. Therefore, when the hydrogen concentration is unevenly distributed in the anode circulation system, The circulation pump 6 may be rotated to level the hydrogen concentration distribution at the anode.

  Further, the anode circulation system is provided with nitrogen concentration estimation means (or nitrogen concentration measurement means), and when the nitrogen concentration obtained by these means reaches a predetermined concentration or more, power generation with limited hydrogen circulation is terminated. Then, it may be returned to the normal power generation operation. In this way, by adjusting and controlling the nitrogen concentration in the anode circulation system, when the fuel cell system shifts from a low load operation to a high load operation due to the accelerator operation of the driver of the fuel cell vehicle, the power generation response is improved. Degradation is avoided, and the reliability of the system is not reduced.

(Limitation of hydrogen supply)
Restriction of the hydrogen supply amount is performed by sending a command from the controller 20 to the hydrogen supply valve 5 and adjusting and controlling the valve opening. The hydrogen supply valve 5 fuels the hydrogen consumption corresponding to the target extraction current determined by the target generated power and the reference I (current) -V (voltage) characteristics of the fuel cell stack 1 stored in the storage device of the controller 20. Since the battery stack 1 is supplied, the hydrogen supply amount can be limited together with the generated power limit.

(Restriction of hydrogen supply pressure)
The restriction of the hydrogen pressure is performed by sending a command from the controller 20 to the hydrogen supply valve 5 and the purge valve 7 to adjust and control the respective valve openings. The hydrogen supply valve 5 can increase or decrease the hydrogen pressure by increasing or decreasing the hydrogen supply flow rate with respect to the hydrogen consumption in the fuel cell stack 1. Accordingly, the hydrogen pressure can be lowered by reducing the hydrogen supply amount by a predetermined amount or a proportion from the hydrogen consumption.

(Air supply pressure limit)
The restriction of the air supply pressure is performed by sending a command from the controller 20 to the air pressure regulating valve 12 and adjusting and controlling the valve opening. Limiting the air supply pressure includes limiting to at least approximately atmospheric pressure when the air pressure regulating valve 12 is not a closed valve.

  As described above, in Example 1 described above, in a low-load operation that is a stable power generation state and in an environment where the state quantity can be restricted, the state quantity is limited and intentionally unstable. By generating a power generation state and amplifying voltage variations between cells (or cell groups), it is possible to accurately detect a cell voltage abnormality even in a low-load operation state.

  The fuel cell system can be reduced by limiting any one of the power generation amount, air supply amount, hydrogen circulation amount, hydrogen supply amount, hydrogen supply pressure, and air supply pressure, or a combination of two or more of these. Even in the load operation state, it is possible to intentionally create an unstable power generation state.

  Cell voltage abnormality is accurately detected by determining cell voltage abnormality based on one of cell voltage variation, variance, standard deviation, difference between average and minimum values, or a combination of two or more of these. be able to.

  By determining a cell voltage abnormality based on any one of a dispersion, standard deviation, average value, minimum value, or a combination of two or more of output voltage of a specific cell (or cell group) set in advance, The system configuration can be reduced in size and simplified.

  Next, a second embodiment of the present invention will be described.

  In the first embodiment, the state quantity is intentionally limited to determine the cell voltage abnormality. On the other hand, the feature of the second embodiment is an idle stop state in which power generation is intermittently stopped. Is provided with an idle stop control means for controlling the fuel cell system, and under the control of the idle stop control means, a cell voltage abnormality is determined when the fuel cell system enters an idle stop state. Is the same as in the first embodiment.

  Here, the “idle operation” of the fuel cell stack refers to a state in which power is not supplied to an external load, and the minimum load necessary for operation (power generation) is supplied by itself, It is a concept that includes standby operation (Japanese Industrial Standard Number: JISC8800).

  On the other hand, the “idle stop state” of the fuel cell stack is a state in which only the power generation of the fuel cell stack is stopped from the idle operation or each auxiliary machine constituting the fuel cell system other than the fuel cell stack from the idle operation. It is a concept that includes a state in which the operation of a kind is also stopped. In addition to the fuel cell stack, the operation of each auxiliary device is also stopped when the auxiliary device related to the supply of fuel gas, the auxiliary device related to the supply of oxidizing gas, or the auxiliary device related to the supply of water for humidifying the reaction gas. It is a concept including a state in which at least one of the operations is stopped.

  Next, the operation procedure of the second embodiment will be described with reference to the flowchart of FIG. The feature of the operation procedure of the second embodiment shown in FIG. 5 is that the processing of step S302 shown in FIG. 3 is shown by step S501 in FIG. 5 in comparison with FIG. 3 showing the operation procedure of the first embodiment. Instead of the process, the process of step S303 shown in FIG. 3 is replaced with the process shown in step S502 of FIG. 5, the process of step S307 shown in FIG. 3 is replaced with the process shown in step S503 of FIG. The procedure is the same as that shown in FIG.

  That is, instead of referring to the flag that permits the restriction of the state quantity, a flag indicating whether or not the idle stop state is permitted is referred to (step S501), and when the idle stop is permitted, the idle stop control means Under this control, the fuel cell system is controlled to the idle stop state (step S502). After that, instead of referring to the flag for permitting the restriction of the state quantity, the flag indicating whether or not the idle stop state is permitted is referred to (step S503), and the same verification as step S307 shown in FIG. 3 is performed. .

  In place of the determination processing shown in step S306 of FIG. 5, a standard deviation σ representing a cell voltage variation index is calculated, and determination is made to determine normality / abnormality of the cell voltage set in advance based on the result of an experiment or the like. The threshold voltage (Vt) may be compared with the standard deviation σ, and it may be determined whether the cell voltage is abnormal based on the comparison result.

  When the fuel cell system enters the idle stop state, for example, the following state varies depending on the system, and the state is the same as when the state quantity of the first embodiment is limited. In idle stop state, generated power: stop, air supply amount: compressor stop, hydrogen circulation flow rate: hydrogen circulation pump stop or weak rotation (in non-idle stop state: normal control rotation), hydrogen supply pressure: approximately atmospheric pressure or negative pressure (Non-idle stop state: pressurization), hydrogen supply amount: Slightly supplied by stop or pressure control, air pressure: pressure control stop, equivalent to atmospheric pressure (non-idle stop state: about the same as hydrogen supply pressure) Pressure regulation).

  FIG. 6 shows the average cell voltage (Vave), the minimum cell voltage (Vmin), the maximum cell voltage (Vmax), and the standard deviation σ that is an indicator of the variation in cell voltage when the non-idle stop state is shifted to the idle stop state. It is a figure which shows a time change, the figure (a) shows the case where a cell voltage is normal, and the figure (b) shows the case where a cell voltage is abnormal.

  In FIG. 6, a method of determining a cell voltage abnormality based on the comparison result between the standard deviation σ of the cell voltage described above and the determination threshold voltage (Vt) is adopted.

  6A, when the idle stop is permitted at time t1 and the fuel cell system shifts from the non-idle stop state to the idle stop state, the cell voltage abnormality determination process is started.

  When the fuel cell system is in an idle stop state, it is consumed by a chemical reaction in the cathode by hydrogen leaked from the anode side of the fuel cell stack 1, and the oxygen partial pressure at the cathode is lowered and the cell voltage is lowered. Go. As shown in FIG. 6A, each voltage gradually decreases with time. In addition, the standard deviation σ of the cell voltage gradually increases. However, the increase in the standard deviation σ is slight, and the standard deviation σ does not exceed the determination threshold voltage (Vt) even at the end time t3 when the determination process ends, and the cell voltage is thereby normal. It is determined.

  On the other hand, in FIG. 6B, when the idle stop state is entered, each cell voltage decreases with time. Further, the standard deviation σ of the cell voltage increases sharply as compared with FIG. 5A, and the variation in the cell voltage becomes remarkable. This is because, for example, the normal power generation seems to be clogged with water, and the system shifts to the idle stop state. It is done. Therefore, the standard deviation σ exceeds the determination threshold voltage (Vt) at time t2 before the determination end time t3, and it is determined that the cell voltage is abnormal at this time.

  As described above, in Example 2 described above, by determining a cell voltage abnormality after the fuel cell system has shifted to the idle stop state, without intentionally generating an unstable power generation state in low-load operation, It becomes possible to amplify voltage variations between cells (or cell groups), and it is possible to accurately detect cell voltage abnormality even in a low-load operation state.

  In the first and second embodiments, the elapsed time from the start of power generation with a limited amount of state or the elapsed time after shifting to the idle stop state is measured, and the elapsed time for storing the measured elapsed time is stored. A detection means may be provided in the controller 20, and a method of determining a cell voltage abnormality when the elapsed time measured and stored by the elapsed time detection means reaches a predetermined time set in advance may be adopted.

  By adopting such a method, it becomes possible to determine the cell voltage abnormality in a state where the abnormality of the cell voltage is almost determined, and the determination accuracy can be improved.

  Further, when the above method is adopted, the determination threshold value in the determination may be changed according to the elapsed time for determining the cell voltage abnormality. In such a case, erroneous determination can be prevented and cell voltage abnormality can be accurately determined in a short time.

It is a figure which shows the structure of the fuel cell system which concerns on Example 1 of this invention. It is a figure which shows the structure of the controller shown in FIG. It is a flowchart which shows the procedure of the process which concerns on Example 1 of this invention. It is a figure which shows the process of step S303 shown in FIG. It is a flowchart which shows the procedure of the process which concerns on Example 2 of this invention. It is a figure which shows the time change of the cell voltage and the standard deviation of a cell voltage at the time of normal and abnormal cell voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell stack 2 ... Hydrogen tank 3 ... Hydrogen tank main valve 4 ... Pressure-reducing valve 5 ... Hydrogen supply valve 6 ... Hydrogen circulation pump 7 ... Purge valve 8 ... Dilution device 9, 13 ... Pressure sensor 10, 14 ... Temperature sensor 11 Compressor 12 Air pressure regulating valve 15 Voltage sensor 16 Power manager 17 Secondary battery 18 Battery controller 19 Atmospheric pressure sensor 20 Controller 201 Power generation determining means 202 Power generation mode switching determining means 203 Normal power generation mode Control unit 204... Limited power generation mode control unit 205... Voltage variation determination unit

Claims (7)

In a fuel cell system including a fuel cell that generates power by an electrochemical reaction between a fuel gas supplied by a fuel gas supply unit and an oxidant gas supplied by an oxidant gas supply unit,
Voltage detection means for detecting a cell voltage of each cell constituting the fuel cell, or a cell group voltage of a cell group composed of a plurality of cells;
Limited power generation determination means for determining whether or not the fuel cell system is capable of generating power in a low load operation in which a state quantity related to power generation of the fuel cell is limited;
A limited power generation control unit configured to generate power in a low load operation with a limited amount of state, when the limited power generation determination unit determines that the fuel cell system can generate power in a low load mode with a limited amount of state; ,
The cell voltage or cell group voltage of the fuel cell that is generating power in a low load operation with the state quantity being limited by the limited power generation control unit is detected by the voltage detection unit, and the detected cell voltage or cell group voltage is detected. And a cell voltage abnormality determining means for determining whether or not the cell voltage is abnormal based on the above. In a fuel cell system including a fuel cell that generates power by an electrochemical reaction between a fuel gas supplied by a fuel gas supply unit and an oxidant gas supplied by an oxidant gas supply unit,
Voltage detection means for detecting a cell voltage of each cell constituting the fuel cell, or a cell group voltage of a cell group composed of a plurality of cells;
Idle stop control means for limiting the state quantity related to power generation of the fuel cell, intermittently stopping power generation of the fuel cell, and controlling the fuel cell system to an idle stop state;
The cell voltage or cell group voltage of the fuel cell in the idle stop state under the control of the idle stop control means is detected by the voltage detection means, and based on the detected cell voltage or cell group voltage, the cell voltage And a cell voltage abnormality determining means for determining whether or not the fuel cell is abnormal. The state quantity restricted by the limited power generation control means or the state quantity restricted by the idle stop control means is the fuel gas pressure, the oxidant gas pressure, the fuel gas supply amount, the oxidant gas supply amount, and the fuel gas circulation amount. 3. The fuel cell system according to claim 1, wherein any one of the generated power amounts, or a combination of two or more thereof. Elapsed time since the start of power generation with a limited amount of state in the fuel cell system,
Alternatively, it includes an elapsed time detecting means for measuring and storing the elapsed time that has elapsed since the fuel cell system shifted to the idle stop state,
4. The cell voltage abnormality determining means determines an abnormality of the cell voltage when the elapsed time detected by the elapsed time detecting means reaches a predetermined time set in advance. The fuel cell system according to claim 1. 5. The fuel according to claim 4, wherein the cell voltage abnormality determination unit changes a determination threshold value when determining abnormality of the cell voltage according to the elapsed time detected by the elapsed time detection unit. Battery system. The cell voltage abnormality determining means is one or more of a cell voltage detected by the cell voltage detecting means or a dispersion value, a standard deviation value, a maximum value, an average value, and a minimum value of a cell group voltage. 6. The fuel cell system according to claim 1, wherein an abnormality in the cell voltage is determined based on the combination of the above. The cell voltage abnormality determination means is any one of a cell voltage detected by the cell voltage detection means in a specific cell selected in advance, or a dispersion value, standard deviation value, maximum value, average value, and minimum value of a cell group voltage. The fuel cell system according to any one of claims 1 to 5, wherein an abnormality of the cell voltage is determined based on one or a combination of two or more.

Images