JP2008021611A - Voltage measuring system and method of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily, surely calculate a value closely approximated to the actual lowest unit cell voltage, appropriately control the whole fuel cell, and enhance reliability and durability. <P>SOLUTION: A voltage measuring system includes a fuel cell 14 formed by electrically connecting a plurality of unit cells 12a-12j in series; a first cell monitor 18a to a fifth cell monitor 18e for dividing the fuel cell 14 into 5 groups 16a-16e containing two unit cells and measuring group voltage of the divided groups 16a-16e; an average unit cell voltage calculating device 22 for calculating average unit cell voltage by dividing the total voltage of the whole fuel cells by the total number of unit cells; a lowest group voltage detecting device 24 for detecting the lowest group voltage among the group voltages of the groups 16a-16e; and a lowest unit cell voltage decision device 26 for calculating the lowest unit cell voltage from the lowest cell voltage obtained by subtracting the average unit cell voltage from the lowest group voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell voltage measurement system and a voltage measurement method for detecting a minimum unit cell voltage in a fuel cell in which a plurality of unit cells are electrically connected in series.

  For example, a polymer electrolyte fuel cell employs an electrolyte membrane made of a polymer ion exchange membrane. An electrolyte membrane / electrode structure in which an anode side electrode and a cathode side electrode are disposed on both sides of the electrolyte membrane includes a unit cell sandwiched between separators, and a plurality of the unit cells are electrically stacked in series. Thus, a stacked fuel cell (also referred to as a fuel cell stack) is configured.

  By the way, in this type of fuel cell, it is necessary to detect whether each unit cell has a desired power generation performance. This is because if the power generation performance of any unit cell is reduced, control based on the voltage of the unit cell (minimum unit cell voltage) is required. For this reason, usually, an operation of detecting a cell voltage for each unit cell during power generation by connecting a cell voltage terminal provided in the separator to a voltage detection device (cell voltage monitor) is performed.

  However, for example, in a fuel cell used for in-vehicle use, several tens to several hundreds of unit cells are stacked, and it is not realistic to detect a cell voltage for every unit cell. Therefore, a fuel cell performance monitoring method and apparatus disclosed in Patent Document 1 are known.

  In Patent Document 1, as shown in FIG. 7, a stack 2 in which 20 fuel cells 1a to 1t are electrically connected in series is provided, and five fuel cells 1a to 1e, 1f to 1j, and 1k are respectively provided. It is divided into four groups 1 to 4 composed of ˜1o and 1p to 1t. In order to measure the output voltage of each group 1 to group 4, independent voltage measurement units V1 to V4 are provided.

  The voltage measuring unit V1 measures the voltage generated from the five series-connected fuel cells 1a to 1e constituting the group 1, and the voltage measuring unit V2 is generated by the fuel cells 1f to 1j constituting the group 2. The voltage measuring unit V3 measures the voltage generated by the fuel cells 1k to 1o constituting the group 3, and the voltage measuring unit V4 is determined by the fuel cells 1p to 1t constituting the group 4. The voltage that is generated is measured.

  In the stack 2 described above, for example, a result obtained by dividing the total voltage of the fuel cells 1a to 1t in the stack 2 (that is, the sum of the voltages of the groups 1 to 4) by the number of groups is used as the group reference voltage. ing.

  Next, the voltages of the fuel cells 1a to 1e obtained by the voltage measurement unit V1 are compared with the group reference voltage. Further, in the order of the voltage measurement units V2, V3 and V4, the voltages detected by these are compared with the group reference voltage. Has been.

Japanese Patent Publication No. 5-502973 (Fig. 1)

  However, in the above-mentioned Patent Document 1, even if, for example, a voltage drop in the group 2 is detected by comparison with the group reference voltage, the minimum unit cell voltage of the fuel cells 1f to 1k cannot be accurately calculated. There is.

  Specifically, when the cell voltage of the fuel cell 1f is 0.2V and the cell voltages of the other fuel cells 1g to 1j are 0.6V, the minimum unit set for performing protection control of the entire stack 2 The cell voltage is a normalized unit cell voltage, and is (0.2V + 0.6V × 4) /5=0.52V.

  Accordingly, there is a problem that a value close to the actual minimum unit cell voltage (0.2V) cannot be set, and proper control based on the actual minimum unit cell voltage is not performed. As a result, the entire stack is controlled on the higher voltage side than the actual minimum unit cell voltage, and the fuel cell 1f may not be protected.

  The present invention solves this type of problem, and can easily and reliably calculate a value approximating the actual minimum unit cell voltage, so that proper control of the entire fuel cell can be performed satisfactorily, and reliability It is another object of the present invention to provide a voltage measuring system and a voltage measuring method for a fuel cell capable of improving durability.

  The present invention divides a fuel cell in which a plurality of unit cells are electrically connected in series, and the fuel cell into at least two groups including two or more unit cells, and the divided voltages for each group A group voltage measuring device that measures the group voltage, an average unit cell voltage calculating device that calculates an average unit cell voltage by dividing the total voltage of the entire fuel cell by the total number of unit cells, and each of the groups The lowest group cell voltage is calculated from the lowest group voltage detection device for detecting the lowest group voltage and the lowest group voltage-average unit cell voltage × (number of unit cells in group-1) = lowest unit cell voltage. A minimum unit cell voltage determining device.

  The group preferably includes two unit cells. This is because the arithmetic processing of the lowest unit cell voltage determination device is simplified at once.

  Further, according to the present invention, a fuel cell in which a plurality of unit cells are electrically connected in series is divided into at least two groups including two or more unit cells, and a group is a voltage for each divided group. A step of measuring a voltage; a step of calculating an average unit cell voltage by dividing the total voltage of the entire fuel cell by the total number of unit cells; and detecting the lowest group voltage among the group voltages of each group And a step of calculating the lowest unit cell voltage from the lowest group voltage−average unit cell voltage × (number of unit cells in group−1) = lowest unit cell voltage.

  In the present invention, since the lowest unit cell voltage is calculated based on the lowest group voltage, the average unit cell voltage, and the number of unit cells in the group, it is possible to easily and reliably calculate a value that approximates the actual lowest unit cell voltage. Can do. As a result, proper control of the entire fuel cell can be satisfactorily performed, and a protective operation such as output control can be reliably performed to improve reliability and durability.

  FIG. 1 is a schematic configuration explanatory diagram of a voltage measurement system 10 according to the first embodiment of the present invention, and FIG. 2 is a schematic main part explanatory diagram of the voltage measurement system 10.

  As shown in FIG. 2, the voltage measurement system 10 includes a fuel cell 14 in which a plurality of, for example, ten unit cells 12 a to 12 j are electrically connected in series. In practice, in the in-vehicle fuel cell, several tens to several hundreds of unit cells are electrically connected in series. However, for the sake of simplicity of explanation, ten unit cells 12a to 12j are used for convenience. A fuel cell 14 having the following is adopted.

  The fuel cell 14 is divided into at least two, for example, five groups 16a to 16e each including two or more unit cells 12a and 12b, 12c and 12d, 12e and 12f, 12g and 12h, and 12i and 12j. Is done. The fuel cell 14 includes a first cell voltage monitor (group voltage measuring device) 18a to a fifth cell voltage monitor (group voltage) for measuring a group voltage (Vass) that is a voltage for each of the divided groups 16a to 16e. Measuring device) 18e is connected.

  The first cell voltage monitor 18 a to the fifth cell voltage monitor 18 e are connected to the control unit 20. The control unit 20 divides the total voltage (Vall) of the entire fuel cell 14 by the total number of unit cells 12a to 12j, thereby calculating an average unit cell voltage calculation device (circuit) 22 that calculates an average unit cell voltage (Vav). Among the group voltages (Vass) of the groups 16a to 16e, the lowest group voltage detection device (circuit) 24 for detecting the lowest group voltage (Vasslow), and the lowest group voltage (Vasslow) -average unit cell voltage (Vuav) × (The number of unit cells in the group −1) = the lowest unit cell voltage determination device (circuit) 26 for calculating the lowest unit cell voltage (Vlow) from the lowest unit cell voltage (Vlow).

  As shown in FIG. 1, each of the unit cells 12 a to 12 j includes an electrolyte membrane / electrode structure 28. The electrolyte membrane / electrode structure 28 includes, for example, a solid polymer electrolyte membrane 30 in which a perfluorosulfonic acid thin film is impregnated with water, and an anode side electrode 32 and a cathode side electrode that sandwich the solid polymer electrolyte membrane 30. 34. The electrolyte membrane / electrode structure 28 is interposed between separators (not shown) and stacked in the direction of arrow A.

  The fuel cell 14 is provided with a fuel gas supply device 36 and an oxidant gas supply device 38. The fuel gas supply device 36 includes a hydrogen supply unit 40 connected to the control unit 20, and hydrogen derived from the hydrogen supply unit 40 constitutes each electrolyte membrane / electrode structure 28 through a hydrogen supply path 42. Supplied to the anode side electrode 32. A hydrogen discharge path 44 is connected to the discharge side of the anode side electrode 32, and a purge valve 46 is disposed in the hydrogen discharge path 44. The purge valve 46 is controlled to be opened and closed by the control unit 20.

  The oxidant gas supply device 38 includes an air compressor 48 connected to the control unit 20, and the air led out from the air compressor 48 constitutes each electrolyte membrane / electrode structure 28 through an air supply path 50. It is supplied to the cathode side electrode 34. An air discharge path 52 is connected to the discharge side of the cathode side electrode 34, and a pressure adjusting valve 54 is disposed in the air discharge path 52. The opening of the pressure adjustment valve 54 is controlled by the control unit 20.

  For example, a load 56 such as a traveling motor is connected to the fuel cell 14, and a current obtained by power generation of the fuel cell 14 is supplied to the load 56. Although not shown, the fuel cell 14 is provided with a cooling medium supply device for circulatingly supplying the cooling medium.

  The operation of the voltage measurement system 10 configured as described above will be described below along the flowchart shown in FIG. 3 in relation to the voltage measurement method of the present invention.

  First, the fuel gas supply device 36 and the oxidant gas supply device 38 are driven via the control unit 20. In the fuel gas supply device 36, hydrogen is led out from the hydrogen supply unit 40 to the hydrogen supply path 42, and this hydrogen is supplied to the anode side electrode 32 of each electrolyte membrane / electrode structure 28 constituting the fuel cell 14. The hydrogen is discharged to the hydrogen discharge path 44.

  On the other hand, in the oxidant gas supply device 38, when air is led out from the air compressor 48 to the air supply path 50, this air is supplied to the cathode side electrode 34 of each electrolyte membrane / electrode structure 28 and then air. It is discharged to the discharge path 52. Accordingly, in each electrolyte membrane / electrode structure 28, the fuel gas (hydrogen) supplied to the anode side electrode 32 and the oxidant gas (oxygen) supplied to the cathode side electrode 34 are contained in an electrode catalyst layer (not shown). In this way, it is consumed by an electrochemical reaction to generate electricity.

  Therefore, as shown in FIG. 2, power is generated in the unit cells 12a to 12j constituting the fuel cell 14, and the group voltages (16a to 16e) of the groups 16a to 16e (via the first cell voltage monitor 18a to the fifth cell voltage monitor 18e) Vass) is calculated (step S1 in FIG. 3).

  The first cell voltage monitor 18 a to the fifth cell voltage monitor 18 e are connected to the control unit 20, and the group voltage (Vass) measured by these is sent to the lowest group voltage detection device 24. The lowest group voltage detection device 24 detects the lowest group voltage (Vasslow) having the lowest voltage among all the group voltages (Vass) (step S2).

  The group voltage (Vass) of each group 16 a to 16 e is sent to the average unit cell voltage calculation device 22. In this average unit cell voltage calculation device 22, the total voltage (Vall) of the entire fuel cell 14, which is the sum of the group voltages (Vass) of the groups 16 a to 16 e, is divided by the total number of unit cells (10). A voltage (Vav) is calculated (step S3).

  Next, in the lowest unit cell voltage determination device 26, the lowest unit cell voltage (Vasslow) −average unit cell voltage (Vuav) × (number of unit cells in group−1) = the lowest unit cell voltage (Vulow) to the lowest unit cell voltage (Vulow) Vulow) is calculated (step S4).

  Here, in the first embodiment, the number of unit cells in each of the groups 16a to 16e is two, and in the lowest unit cell voltage determination device 26, the lowest group voltage (Vasslow) -average unit cell voltage. The minimum unit cell voltage (Vlow) is calculated from (Vuav) = the minimum unit cell voltage (Vlow).

  Further, the process proceeds to step S5, and based on the calculated minimum unit cell voltage (Vlow), for example, output limitation of the fuel cell 14, air increase or decrease, pressure increase or decrease, hydrogen increase or decrease, pressure increase Alternatively, various stack protection controls such as decompression and idle stop determination are performed.

  In this case, in the first embodiment, the lowest unit cell voltage (Vlow) is calculated based on the lowest group voltage (Vasslow) and the average unit cell voltage (Vuav). Therefore, a value approximate to the actual minimum unit cell voltage (Vlow) can be easily and reliably calculated.

  Specifically, as shown in FIG. 4, for example, when the output voltage of the unit cell 12d is lowered to 0.2V, the lowest group voltage (via the second cell voltage monitor 18b connected to the group 16b) Vasslow) = 0.8V is detected. On the other hand, when the total voltage (Vall) = 5.6V of the whole fuel cell 14 is obtained and this total voltage (Vall) is divided by the total number of unit cells (10), the average unit cell voltage (Vuav) = 0.56V. Is calculated. Next, by subtracting the average unit cell voltage (Vuav) = 0.56V from the lowest group voltage (Vasslow) = 0.8V, the lowest unit cell voltage (Vulow) = 0.24V is calculated.

  On the other hand, when the respective group voltages (Vass) detected by the first cell voltage monitor 18a to the fifth cell voltage monitor 18e are normalized to the voltages of the unit cells 12a to 12j, the unit cells 12a, 12b, and 12e. ˜12j, 1.2V / 2 = 0.6V, respectively, while unit cells 12c and 12d have 0.8V / 2 = 0.4V. Therefore, the lowest unit cell voltage (Vlow) = 0.4V.

  Therefore, in the first embodiment, a value (0.24V) approximate to the actual minimum unit cell voltage (Vulow) = 0.2V is obtained, and the minimum unit is more accurate than the conventional normalization method. A cell voltage (Vlow) calculation process is performed. As a result, proper control of the entire fuel cell 14 is satisfactorily performed, protection operation such as output limitation is performed reliably, and the reliability and durability of the fuel cell 14 can be improved satisfactorily. The effect is obtained.

  FIG. 5 is a schematic explanatory diagram of a main part of a voltage measurement system 60 according to the second embodiment of the present invention. The same components as those of the voltage measurement system 10 according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The voltage measurement system 60 includes a fuel cell 62 in which a plurality of, for example, 20 unit cells 12a to 12t are electrically connected in series. The fuel cell 62 is divided into five or more groups 64a to 64e including, for example, four unit cells 12a to 12d, 12e to 12h, 12i to 12l, 12m to 12p, and 12q to 12t, respectively.

  The fuel cell 62 includes a first cell voltage monitor (group voltage measuring device) 66a to a fifth cell voltage monitor (group voltage) for calculating a group voltage (Vass) that is a voltage for each of the divided groups 64a to 64e. Measuring device) 66e is connected.

  The voltage measurement system 60 configured in this way operates according to the flowchart shown in FIG.

  The voltage generated from the unit cells 12a to 12t will be specifically illustrated, and will be described below. Among the unit cells 12a to 12t, for example, the voltage of the unit cell 12e is 0.2V, and other unit cells The voltages at 12a to 12d and 12f to 12t are 0.6V.

  First, after the group voltage (Vass) of each of the groups 64a to 64e is calculated (step S11), the lowest group voltage (Vasslow) = 2.0V is detected (step S12). In step S13, the total voltage (Vall) of the entire fuel cell 62 is calculated as 2.4V × 4 + 2.0V = 11.6V, and the total voltage 11.6V is divided by 20 which is the number of unit cells. The lowest unit cell voltage (Vlow) = 0.58V is calculated.

  In step S14, the lowest group voltage (Vasslow) − (average unit cell voltage (Vuav) × (number of unit cells in group−1) = 2.0V−0.58V × 3 = 0.26V, that is, the lowest The unit cell voltage (Vulow) is calculated, and various stack protection controls are performed based on the lowest unit cell voltage (Vulow) = 0.26 V (step S15).

  Here, for example, when the unit cells 12e to 12h constituting the group 64b are normalized, 2.0V ÷ 4 = 0.5V is obtained, and the minimum unit cell voltage (Vlow) = 0.5V is obtained. It will be considerably larger than.

  Therefore, in the second embodiment, the minimum unit cell voltage (Vulow) = 0.26 V approximate to the actual value of 2.2 V is obtained, and proper protection control of the entire fuel cell 62 is satisfactorily performed, and reliability is improved. In addition, the same effects as those of the first embodiment can be obtained, such as improvement of durability.

1 is a schematic configuration explanatory diagram of a fuel cell voltage measurement system according to a first embodiment of the present invention. FIG. It is a principal part schematic explanatory drawing of the said voltage measurement system. It is a flowchart explaining the voltage measurement method by the said voltage measurement system. It is explanatory drawing of the specific example of the said voltage measurement method. It is a principal part schematic explanatory drawing of the voltage measurement system of the fuel cell which concerns on the 2nd Embodiment of this invention. It is a flowchart explaining the voltage measurement method by the said voltage measurement system. FIG. 2 is an explanatory diagram of a fuel cell performance monitoring method and apparatus disclosed in Patent Document 1;

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 60 ... Voltage measurement system 12a-12t ... Unit cell 14, 62 ... Fuel cell 16a-16e, 64a-64e ... Group 18a-18e, 66a-66e ... Cell voltage monitor 20 ... Control part 22 ... Average unit cell voltage calculation Device 24 ... Minimum group voltage detection device 26 ... Minimum unit cell voltage determination device 28 ... Electrolyte membrane / electrode structure 30 ... Solid polymer electrolyte membrane 32 ... Anode side electrode 34 ... Cathode side electrode 36 ... Fuel gas supply device 38 ... Oxidation Agent gas supply device

Claims (4)

A fuel cell in which a plurality of unit cells are electrically connected in series;
A group voltage measuring device that divides the fuel cell into at least two groups including two or more unit cells, and measures a group voltage that is a voltage for each of the divided groups;
An average unit cell voltage calculation device for calculating an average unit cell voltage by dividing the total voltage of the entire fuel cell by the total number of unit cells;
Among the group voltages of each group, the lowest group voltage detection device for detecting the lowest group voltage,
Lowest group voltage-average unit cell voltage × (number of unit cells in group−1) = lowest unit cell voltage determination device for calculating the lowest unit cell voltage from lowest unit cell voltage
A voltage measurement system for a fuel cell, comprising:   The voltage measurement system according to claim 1, wherein the group includes the two unit cells. Dividing a fuel cell in which a plurality of unit cells are electrically connected in series into at least two groups including two or more unit cells, and measuring a group voltage that is a voltage for each divided group; ,
Calculating an average unit cell voltage by dividing the total voltage of the entire fuel cell by the total number of unit cells;
Detecting the lowest group voltage among the group voltages of each group;
Calculating the lowest unit cell voltage from the lowest group voltage−average unit cell voltage × (number of unit cells in group−1) = lowest unit cell voltage;
A method for measuring a voltage of a fuel cell, comprising:   4. The voltage measuring method according to claim 3, wherein the group includes the two unit cells.

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