JP2005063909A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the degree of cross leakage of cells to be determined in a short time. <P>SOLUTION: In a normal cell with no cross leakage, whether or not there is a differential pressure between fuel gas and oxidation gas, an open circuit voltage is generally constant. In a defective cell with much cross leakage, when there is a differential pressure, the open circuit voltage drops. Thus, on the basis of the open circuit voltage every cell in a state that a predetermined differential pressure is produced between the fuel gas and the oxidation gas, the degree of cross for leakage every cell is determined. As a result, because it is not necessary to purge hydrogen and oxygen in a fuel cell 10 as in the conventional example, the degree of cross leakage can be determined in a short time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell system including a fuel cell that generates electric energy by a chemical reaction between hydrogen and oxygen, and is effective when applied to a moving body such as a vehicle, a ship, and a portable generator.

  2. Description of the Related Art Conventionally, a fuel cell system including a fuel cell that generates power using an electrochemical reaction between hydrogen and oxygen (air) is known. For example, in a polymer electrolyte fuel cell that is considered as a driving source for vehicles and the like, the voltage per cell is around 1 V, so that the cells are stacked and used as a stack. In a fuel cell used as a stack, the cells are connected in series.Therefore, there is a problem that if one cell fails, the power generation of the fuel cell itself stops. It is necessary to electrically bypass the failed cell portion.

There is a cross leak method as a method for diagnosing a cell failure, and a system has been proposed in which a constant concentration of fuel gas and oxidant gas is supplied and the amount of cross leak is detected from the change over time in the flow rate and cell voltage change (for example, , See Patent Document 1).
JP-A-9-27336

  However, the above system has a problem that it takes a long time to diagnose a cross leak. Specifically, it is necessary to purge hydrogen and oxygen in the fuel cell before flowing the fuel gas and the oxidizing gas at a constant concentration, and a time for purging is required. In addition, since the voltage change of the cell is measured while changing the flow rate, the time required for the measurement becomes long.

  An object of the present invention is to make it possible to determine the degree of cross leak in a short time.

  In order to achieve the above object, according to the first aspect of the present invention, a solid polymer electrolyte fuel cell that generates electricity by electrochemically reacting hydrogen in fuel gas and oxygen in oxidizing gas in a number of cells. (10) A differential pressure setting means (32) for generating a predetermined differential pressure (ΔP1) between the fuel gas and the oxidizing gas, and a voltage for detecting an open circuit voltage for each cell. Detection means (17) and determination means for determining a deteriorated cell by determining the degree of cross leak for each cell based on the open circuit voltage for each cell in a state where the predetermined differential pressure is generated ( 50).

  By the way, in a normal cell having no cross leak, the open circuit voltage is substantially constant regardless of whether or not there is a differential pressure between the fuel gas and the oxidizing gas. On the other hand, in a degraded cell with many cross leaks, the open circuit voltage when a differential pressure is applied between the fuel gas and the oxidizing gas is lower than the open circuit voltage when a differential pressure is not applied between the fuel gas and the oxidizing gas. To do. Therefore, according to the first aspect of the present invention, it is possible to determine the degree of cross leak for each cell based on the open circuit voltage for each cell in a state where the predetermined differential pressure is generated.

  Further, in the first aspect of the invention, it is only necessary to apply a predetermined differential pressure to the fuel gas and the oxidizing gas to measure the cell voltage, so that it is not necessary to purge hydrogen and oxygen in the fuel cell as in the prior art. Furthermore, in the invention of claim 1, since only the cell voltage at the predetermined differential pressure is measured, in other words, the number of conditions is larger than the case of measuring the cell voltage while changing the flow rate as in the prior art. The time required for measurement is shorter than when the cell voltage is measured below. Therefore, according to the first aspect of the present invention, it is possible to determine the degree of cross leak in a short time due to the fact that purging is not necessary and the time required for measurement is shortened.

  The invention described in claim 2 is characterized by comprising storage means (50) for storing information on the deteriorated cell specified by the determination means. According to this, the deteriorated cells to be replaced at the time of maintenance can be easily selected based on the information on the deteriorated cells stored in the storage means. In addition, the degree of cell degradation is likely to vary depending on the arrangement position in the fuel cell. Therefore, if the deteriorated cell stored in the storage means has a deterioration level that is still usable, the deterioration of the deteriorated cell can be suppressed by rotating the deteriorated cell and the normal cell.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  1st Embodiment of this invention is described based on FIGS. In this embodiment, the fuel cell system is applied to an electric vehicle (fuel cell vehicle) that runs using the fuel cell as a power source.

  FIG. 1 shows the overall configuration of the fuel cell system of the present embodiment. FIG. 2 is a schematic diagram showing the configuration of the fuel cell 10 in detail. As shown in FIG. 1, the fuel cell system of the present embodiment includes a fuel cell (FC stack) 10 that generates electric power by utilizing an electrochemical reaction between hydrogen and oxygen. The fuel cell 10 is configured to supply electric power to electric devices such as a motor generator 11, a secondary battery 12, and an auxiliary machine 16 for running the vehicle.

  In the fuel cell 10, the following electrochemical reaction between hydrogen and oxygen occurs to generate electric energy.

(Hydrogen electrode side) H ₂ → 2H ⁺ + 2e ⁻
(Oxygen electrode side) 2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O
In this embodiment, a solid polymer electrolyte fuel cell is used as the fuel cell 10, and a plurality of cells serving as basic units are stacked. Each cell has a configuration in which an electrolyte membrane is sandwiched between a pair of electrodes.

  As shown in FIG. 2, the fuel cell 10 includes a plurality of (three in this example) cell blocks 101 to 103 in which electrode plates 10a are arranged between a plurality of stacked cells at a fixed number. It is divided into Relays 61, 62, and 63 such as semiconductor relays are disposed between the electrode plates 10a. The relays 61, 62, and 63 are configured to electrically open between the electrode plates 10a when the fuel cell 10 is in a normal state.

  As shown in FIG. 1, the fuel cell system includes an air supply path 20 a for supplying air (oxidizing gas) to the oxygen electrode side of the fuel cell 10, and an air discharge for discharging air from the fuel cell 10. A path 20b, a hydrogen supply path 30a for supplying hydrogen (fuel gas) to the hydrogen electrode side of the fuel cell 10, and a hydrogen discharge path 30b for discharging unreacted hydrogen gas and the like from the fuel cell 10 are provided. It has been.

  The air supply path 20a is provided with a blower 21 for air pressure feeding. The blower 21 is driven by an electric motor 22. The air discharge path 20b is provided with an air discharge path opening / closing valve 23 for opening and closing the air discharge path 20b. When supplying air to the fuel cell 10, the air discharge path opening / closing valve 23 is opened and the blower 21 is driven by the electric motor 22.

  A humidifier 24 is provided in the air supply path 20a and the air discharge path 20b. The humidifier 24 humidifies the air discharged from the blower 21 using moisture contained in the humid exhaust air discharged from the fuel cell 10, and thereby the solid polymer electrolyte in the fuel cell 10. The membrane is in a wet state containing moisture so that the electrochemical reaction can be satisfactorily performed during power generation operation.

  The hydrogen supply path 30a includes a hydrogen cylinder 31 filled with hydrogen gas, a hydrogen pressure regulating valve 32 that adjusts the pressure of hydrogen supplied to the fuel cell 10, and a hydrogen supply path opening / closing valve 33 that opens and closes the hydrogen supply path 30a. Is provided. The hydrogen discharge path 30b is provided with a hydrogen discharge path on / off valve 34 that opens and closes the hydrogen discharge path 30b. When supplying hydrogen to the fuel cell 10, the hydrogen supply path opening / closing valve 33 is opened and adjusted to a desired hydrogen pressure by the hydrogen pressure regulating valve 32. The hydrogen discharge path 30b is opened and closed by a hydrogen discharge path opening / closing valve 34 in accordance with operating conditions. The hydrogen discharge path 30b discharges unreacted hydrogen gas, steam (or water), nitrogen, oxygen, and the like mixed through the solid polymer electrolyte membrane from the oxygen electrode. The hydrogen pressure regulating valve 32 corresponds to the differential pressure setting means of the present invention.

  The fuel cell 10 generates heat with power generation. For this reason, the fuel cell system is provided with cooling systems 40 to 45 that cool the fuel cell 10 so that the operating temperature becomes a temperature suitable for the electrochemical reaction (about 80 ° C.).

  The cooling system includes a cooling water path 40 that circulates cooling water (heat medium) in the fuel cell 10, a water pump 41 that circulates the cooling water, an electric motor 42 that drives the water pump 41, and a radiator 43 that includes a fan 44, A temperature sensor 45 that detects the coolant temperature at the outlet of the fuel cell 10 is provided. The heat generated in the fuel cell 10 is discharged out of the system by the radiator 43 through the cooling water. With such a cooling system, the cooling amount control of the fuel cell 10 can be performed by the flow rate control by the water pump 41 and the air volume control by the fan 44.

  The fuel cell 10 and the secondary battery 12 and the secondary battery 12 and the motor generator 11 are electrically connected via a DC-DC converter 13 capable of transmitting power in both directions. The DC-DC converter 13 controls the flow of electric power from the fuel cell 10 to the secondary battery 12 or from the secondary battery 12 to the fuel cell 10.

  An inverter 14 is arranged between the fuel cell 10 and the secondary battery 12 and the motor generator 11. The inverter 14 switches the function of the motor generator 11, that is, the function as an electric motor and the function as a generator.

  When the DC-DC converter 13 and the inverter 14 are operated, for example, when a large amount of electric power is suddenly required during sudden acceleration, the motor generator 11 is not only from the fuel cell 10 but also from the secondary battery 12. Can be powered. Further, the surplus power during the power generation of the fuel cell 10 and the power regenerated by the motor generator 11 can be stored in the secondary battery 12.

  The auxiliary machine 16 includes the electric motor 22 of the blower 21, the electric motor 42 of the water pump 41, and the like, and is connected to the secondary battery 12 via the inverter 15.

  The fuel cell system includes a cell monitor 17 that detects a voltage for each cell, a voltage detector 18 that detects a power generation voltage of the fuel cell 10 as a whole, and a current detector 19 that detects a power generation current of the fuel cell 10. Is provided. The cell monitor 17 corresponds to the voltage detection means of the present invention.

  The fuel cell system is provided with a control unit (ECU) 50 that performs various controls. The control unit 50 includes a well-known microcomputer including a CPU, ROM, RAM, EEPROM and the like (not shown), and performs arithmetic processing according to a program stored in the microcomputer.

  The control unit 50 is input with required power signals from various loads, voltage signals from the cell monitor 17, voltage signals from the voltage detector 18, current signals from the current detector 19, and temperature signals from the temperature sensor 45. The Further, the control unit 50 includes the secondary battery 12, the DC-DC converter 13, the inverters 14 and 15, the electric motor 22, the air discharge path opening / closing valve 23, the hydrogen pressure regulating valve 32, the hydrogen supply path opening / closing valve 33, and the hydrogen discharge path opening / closing. A control signal is output to the valve 34, the electric motor 42, the fan 44, the relays 61, 62, 63, and the like. The control unit 50 corresponds to the determination unit and the storage unit of the present invention.

  FIG. 3 is a characteristic diagram showing the relationship between the cell open circuit voltage (hereinafter referred to as OCV) and the inter-gas differential pressure ΔP in the polymer electrolyte fuel cell 10. The inter-gas differential pressure ΔP is a difference between the pressure Pa of air supplied to the fuel cell 10 and the pressure Ph of hydrogen supplied to the fuel cell 10 (however, in this embodiment, Pa <Ph and To do).

  In FIG. 3, in a normal cell having no cross leak, the OCV is substantially constant regardless of the inter-gas differential pressure ΔP as indicated by the solid line. On the other hand, in the deteriorated cell in which cross leak occurs, the OCV decreases as the inter-gas differential pressure ΔP increases as shown by the one-dot chain line and the two-dot chain line, and the degree of the OCV decrease is the cross indicated by the one-dot chain line. The heavily deteriorated cell with a large amount of cross leak indicated by a two-dot chain line is larger than the lightly deteriorated cell with a small amount of leak.

  In the present embodiment, the degree of cross leak of each cell is determined using such a relationship between the OCV and the differential pressure ΔP between gases. Specifically, the gas pressure difference ΔP is set to a predetermined differential pressure ΔP1 by adjusting the hydrogen pressure by the hydrogen pressure regulating valve 32, and the OCV for each cell is generated by the cell monitor 17 in a state where the predetermined differential pressure ΔP1 is generated. To detect. And if OCV exceeds the 1st setting voltage V1, it will determine with the normal cell without a cross leak. If the OCV is equal to or lower than the first set voltage V1 and equal to or higher than the second set voltage V2 (however, V1> V2), it is determined that the cell is a lightly deteriorated cell with a small amount of cross leak and still usable. Furthermore, if the OCV is less than the second set voltage V2, it is determined that the cell is a heavily deteriorated cell that has a large amount of cross leak and cannot be used.

  Next, the operation of the fuel cell system configured as described above will be described with reference to FIG. FIG. 4 is a flowchart showing processing executed by the control unit 50. The determination of the degree of cross leak and the control of the moisture in the cell based on the determination result will be described.

  When the key switch of the vehicle is turned on, the control shown in FIG. 4 is started. First, the operation of the auxiliary machine 16 is started to start the fuel cell system (step 101, step is hereinafter abbreviated as S).

  Next, the OCV for each cell is detected by the cell monitor 17 in a state where the predetermined differential pressure ΔP1 is generated, and the degree of cross leak for each cell is determined based on the OCV (S102). If the OCV of all cells exceeds the first set voltage V1, it is determined that all the cells are in the normal state, and the process proceeds to S103. If there is no cell whose OCV is less than the second set voltage V2, and there is even one cell whose OCV is the first set voltage V1 or less and the second set voltage V2 or more, that is, one lightly deteriorated cell, the process proceeds to S107. Further, if there is even one cell whose OCV is less than the second set voltage V2, that is, one heavily deteriorated cell, the process proceeds to S108.

  When it is determined that all the cells are in the normal state and the process proceeds from S102 to S103, power generation according to the load is performed in S103. While the key switch is on (S104 is YES) and there is a request for power generation (S105 is YES), the control of S103 is continued. When the key switch is turned off (NO in S104), the fuel cell system is stopped (S106). If there is no request for power generation (NO at S105), the process returns to S102 to determine the degree of cross leak again.

  When it is determined that there is no heavy deteriorated cell but there is a light deteriorated cell and the process proceeds from S102 to S107, in S107, which cell among the many cells is the light deteriorated cell, and the OCV of the light deteriorated cell, It is stored in the EEPROM of the control unit 50. Then, it progresses to S103 and performs the electric power generation according to load.

  When it is determined that there is a heavily deteriorated cell and the process proceeds from S102 to S108, in S108, the fact that there is a heavily deteriorated cell and maintenance is required is displayed on, for example, the meter section of the vehicle and a warning is issued. Further, which of the many cells is the heavily deteriorated cell and the OCV of the heavily deteriorated cell are stored in the EEPROM of the control unit 50 (S109).

  If there is a heavily deteriorated cell, the power generation of the fuel cell 10 itself may stop. Therefore, for example, as illustrated in FIG. 2, when there is a heavily deteriorated cell 10 </ b> X in the second cell block 102, the second cell 62 is bypassed by operating the second relay 62 to bypass the first cell block 102. 101 and the third cell block 103 are directly connected (S110), so that the fuel cell 10 can be operated.

  In addition, if the second cell block 102 is bypassed and the power generation is about the same as the maximum power generation amount under normal conditions, the cells of the first cell block 101 and the third cell block 103 are overloaded and cannot generate power. Therefore, the power generation according to the load is performed while limiting the power generation amount below a preset power generation amount (S111).

  Next, while the key switch is on (S112 is YES) and there is a request for power generation (S113 is YES), the control of S111 is continued. When the key switch is turned off (NO in S112), the fuel cell system is stopped (S106). If there is no request for power generation (NO at S112), the process returns to S102 to determine the degree of cross leak again.

  According to the present embodiment, when determining the degree of cross leak of each cell, it is only necessary to measure the cell voltage by applying a predetermined differential pressure ΔP1 to air and hydrogen. Or purging hydrogen. Furthermore, since only the cell voltage at the predetermined differential pressure ΔP1 is measured, in other words, the cell voltage is measured under a large number of conditions than when the cell voltage is measured while changing the flow rate as in the prior art. The time required for measurement is shorter than in the case of measurement. Therefore, it is possible to determine the degree of cross leak in a short time due to the fact that purging is not necessary and the time required for measurement is shortened.

  In addition, when there is a deteriorated cell, information indicating which cell has deteriorated to what extent is stored in the EEPROM of the control unit 50, so that the deteriorated cell to be replaced at the time of maintenance based on the stored information on the deteriorated cell. Can be easily selected. Further, the degree of cell deterioration tends to vary depending on the arrangement position in the fuel cell 10. Therefore, if the degree of deterioration is such that the deteriorated cell is still usable, the deterioration of the deteriorated cell can be suppressed by rotating the deteriorated cell and the normal cell.

  In addition, a large number of cells are divided into a plurality of cell blocks 101 to 103, and a cell block in which a heavily deteriorated cell exists is electrically bypassed to directly connect other cell blocks. The fuel cell 10 can be brought into emergency operation. Further, during the emergency operation, since the power generation amount is limited to a preset power generation amount or less, it is possible to prevent the normal cell block from being overloaded and unable to generate power.

(Other embodiments)
In the above embodiment, the fuel cell system is applied to the fuel cell vehicle. However, the fuel cell system of the present invention can be applied to other than the fuel cell vehicle, for example, a home fuel cell system. Can be applied.

1 is a conceptual diagram showing an overall configuration of a fuel cell system according to an embodiment of the present invention. It is a schematic diagram which shows the structure of the fuel cell 10 of FIG. 1 in detail. FIG. 2 is a characteristic diagram showing a relationship between a cell open circuit voltage (OCV) and an inter-gas differential pressure ΔP in the fuel cell 10 of FIG. 1. It is a flowchart which shows the process performed in the control part 50 of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 17 ... Cell monitor (voltage detection means), 32 ... Hydrogen pressure regulation valve (differential pressure setting means), 50 ... Control part (determination means).

Claims (2)

A fuel cell system comprising a solid polymer electrolyte type fuel cell (10) for generating electricity by electrochemically reacting hydrogen in fuel gas and oxygen in oxidizing gas in a number of cells,
Differential pressure setting means (32) for generating a predetermined differential pressure (ΔP1) between the fuel gas and the oxidizing gas;
Voltage detection means (17) for detecting an open circuit voltage for each cell;
Determination means (50) for determining the degree of cross leak for each cell and identifying a deteriorated cell based on the open circuit voltage for each cell in a state where the predetermined differential pressure is generated. A fuel cell system. The fuel cell system according to claim 1, further comprising storage means (50) for storing information on a deteriorated cell specified by the determination means.

Images