JP2009259519A - Fuel cell system and cross leak detecting method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system and a cross leak detecting method using the same which can accurately detect a cross leak even in detecting a summed cell voltage of a plurality of cells. <P>SOLUTION: The system is characterized in that comparison is made between a first minimum cell-pair voltage and a second cell-pair voltage, and if the second cell-pair voltage is lower than the first minimum cell-pair voltage, it is determined that the cross leak is caused. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell system and a cross leak detection method using the same.

In a fuel cell, a membrane electrode structure is formed by sandwiching a solid polymer electrolyte membrane between an anode electrode and a cathode electrode from both sides, and a pair of separators are arranged on both sides of the membrane electrode structure to form a flat unit fuel. A battery (hereinafter referred to as “unit cell”) is configured, and a plurality of unit cells are stacked to form a fuel cell stack.
In this fuel cell, hydrogen gas is supplied as a fuel gas to a fuel gas passage formed between the anode electrode and the anode-side separator, and an oxidizing gas passage formed between the cathode electrode and the cathode-side separator. Is supplied with air as an oxidizing gas. As a result, hydrogen ions generated by the catalytic reaction at the anode electrode permeate the solid polymer electrolyte membrane and move to the cathode electrode, and the cathode electrode causes an electrochemical reaction with oxygen in the air to generate power.

  In this type of fuel cell, a cross leak may occur as the solid polymer electrolyte membrane deteriorates. Cross-leakage means that when power generation is stopped, hydrogen gas on the anode side remaining in the fuel cell passes through the solid polymer electrolyte membrane to the cathode side, and oxygen gas and nitrogen gas in the air on the cathode side are solid high. This is a phenomenon that passes through the molecular electrolyte membrane and moves to the anode side. When this cross leak occurs, hydrogen and oxygen react on the anode side and the solid polymer electrolyte membrane may be damaged.

Therefore, for example, as shown in Patent Document 1, fuel gas is supplied into a pipe connected to the fuel cell stack, the pipe is sealed, and a cross leak is determined based on a pressure change of the pipe or an open voltage. The configuration is known. Specifically, the open circuit voltages of all the cells of the fuel cell stack are detected, and it is determined whether or not the lowest cell voltage among these is greater than 0 during a predetermined monitoring time. Then, when the detected minimum cell voltage is 0 or less, that is, a reverse potential is detected, it is determined that there is a cross leak.
JP 2007-5266 A

By the way, in the above-described prior art, voltage sensors (cell voltage detection means) are installed for each unit cell. Therefore, the cost of the fuel cell is increased by increasing the cost of the voltage sensor itself and the number of assembly steps. I was invited.
Therefore, in recent years, in order to reduce the cost of the fuel cell, instead of installing a voltage sensor for each cell, a plurality of unit cells (for example, two) are made into one cell group, and these cell groups On the other hand, a configuration in which one voltage sensor is installed is known. In this case, the voltage detected by the voltage sensor is detected as a voltage for each cell group, that is, a total cell voltage of a plurality of unit cells.

  However, when determining the cross leak based on the total cell voltage, it is determined whether or not the cross leak actually occurs even if the cross leak occurs in any of the unit cells. There is a problem that it is difficult. For example, in the case of a configuration in which two unit cells are used as a cell pair and the total cell voltage (hereinafter referred to as total cell pair voltage) is detected for each cell pair, the total cell pair voltage is less than half of the average value (hereinafter referred to as average cell pair voltage). However, the cause of this voltage drop cannot be determined.

Specifically, there is a problem that it is difficult to determine whether the cause of the voltage drop is actually due to a cross leak or simply due to a decrease in power generation performance such as the generated water covers the power generation surface. In other words, there are cases where the total cell-pair voltage can be the same in the case where only one cell is at a reverse potential due to cross leakage and the case where the voltage of both cells is reduced to less than half due to the decrease in power generation performance. is there.
Then, by replacing the unit cell in which the cross leak does not occur accidentally, the unit cell replacement work or the unit cell itself is lost. On the other hand, if the unit cell in which the cross leak occurs is left unattended, There is a problem that the damage is gradually increased and the surrounding unit cells are also damaged.

  Accordingly, the present invention has been made in view of the above-described circumstances, and a fuel cell system capable of accurately detecting a cross leak even when the total cell voltage of a plurality of cells is detected. A cross leak detection method using the same is provided.

  In order to solve the above-described problem, the invention described in claim 1 is a cell that generates electricity by supplying an anode gas (for example, hydrogen gas in the embodiment) and a cathode gas (for example, the oxidizing gas in the embodiment). For example, a fuel cell stack (for example, the fuel cell 1 in the embodiment) configured by stacking the cells 55) in the embodiment, and a cathode gas supply unit (for example, the embodiment) that supplies the cathode gas to the fuel cell stack. And an air pump 7) and a cell voltage detection means (for example, a cell pair voltage in the embodiment) for detecting a total cell voltage (for example, a total cell pair voltage in the embodiment) for each cell group. For example, the cell voltage monitor 41 in the embodiment, and a fuel cell system (for example, the fuel in the embodiment) A cathode gas supply stop means (for example, cathode gas supply stop means 67 in the embodiment) for stopping supply of the cathode gas to the fuel cell stack, and the cathode gas supply stop means, When the supply of the cathode gas is stopped, a cathode gas removing unit (for example, the cathode gas removing unit 68 in the embodiment) that removes the cathode gas existing at the cathode electrode, and the cathode gas removing unit removes the cathode gas. When the gas is removed, first lowest cell voltage detection means (for example, implementation) detects the total cell voltage of the specific cell group having the lowest total cell voltage among the plurality of cell groups as the first lowest cell voltage. First lowest cell voltage detection means 64) in the form and a cross-rear based on the first lowest cell voltage There is a possibility that a cross leak has occurred due to the first determination means (for example, the first determination means 61 in the embodiment) for determining whether or not there is a possibility that the occurrence of the occurrence of the crossover has occurred. A second cell voltage detecting means for detecting the total cell voltage of the specific cell group as a second cell voltage after a predetermined time has elapsed since the detection of the first lowest cell voltage (for example, the embodiment). The second cell voltage detecting means 65) and the first lowest cell voltage and the second cell voltage are compared, and if the second cell voltage is lower than the first lowest cell voltage, the specific cell Second judging means for judging that cross leak has occurred in the group (for example, second judging means 62 in the embodiment), and cross leak signal output means for outputting an abnormal signal according to the result of the second judging means (example The cross-leak signal output means 63) in the embodiment.

  The invention described in claim 2 is an average cell voltage detecting means for calculating an average cell group voltage of the fuel cell stack based on the total cell voltage for each cell group (for example, the average cell voltage detecting means in the embodiment). 66), wherein the first determination means is the case where the number of the cells in the cell group is n and the first lowest cell voltage is not more than (n−1) / n of the average cell group voltage. It is characterized in that it is determined that there is a possibility that a cross leak has occurred.

  The invention described in claim 3 is characterized in that the cathode gas removing means removes the cathode gas by discharging the cathode gas remaining inside the fuel cell stack.

  According to a fourth aspect of the present invention, the second determination means compares the first lowest cell voltage with the second cell voltage, and the second cell voltage is equal to or higher than the first lowest cell voltage. Is characterized in that it is determined that no cross leak occurs.

  According to a fifth aspect of the present invention, when the cross leak signal output unit determines that the cross leak has occurred a predetermined number of times or more by the second determination unit, the cross leak signal is generated in the specific cell group. It is determined and an abnormal signal is output.

  According to a sixth aspect of the present invention, when the cross leak signal output means detects that the second cell voltage is lower than the first lowest cell voltage by a predetermined value or more by the second determination means. Is characterized in that the occurrence of cross leak in the specific cell group is determined and an abnormal signal is output even if it is not determined by the second determination means that the cross leak has occurred more than the predetermined number of times. .

  The invention described in claim 7 is a fuel cell stack configured by stacking cells for generating power by supplying anode gas and cathode gas, and cathode gas supply means for supplying the cathode gas to the fuel cell stack. A cross leak detection method for detecting a cross leak of the cell using a fuel cell system having a plurality of cells as a cell group, and a cell voltage detection means for detecting a total cell voltage for each cell group. A cathode gas supply stop step for stopping the supply of the cathode gas to the fuel cell stack, and a cathode gas removal for removing the cathode gas present at the cathode electrode when the supply of the cathode gas is stopped And when the cathode gas is removed by the cathode gas removal step, the combination of the plurality of cell groups is combined. A first lowest cell voltage detecting step for detecting the total cell voltage of the specific cell group having the lowest cell voltage as a first lowest cell voltage; and the first lowest cell voltage detected in the first lowest cell voltage detecting step. A first determination step for determining whether or not there is a possibility of occurrence of a cross leak based on the first determination step, and when the first determination step determines that there is a possibility of occurrence of a cross leak, A second cell voltage detecting step of detecting the total cell voltage of the specific cell group as a second cell voltage after a predetermined time has elapsed since the detection of the first lowest cell voltage; and the first lowest cell voltage and the second cell A second determination step of determining that a cross leak has occurred in the specific cell group when the second cell voltage is lower than the first lowest cell voltage by comparing with a voltage; A cross leak signal output step of outputting an abnormality signal in accordance with a result of decision, and having a.

  According to the first and seventh aspects of the present invention, the first lowest cell voltage and the second cell voltage are compared, and when the second cell voltage is lower than the first lowest cell voltage, that is, the amount of change in the lowest cell voltage. The occurrence of cross leak can be determined based on the above. Specifically, if the cause of the voltage drop is a decrease in power generation performance, the cathode gas enters the cathode electrode from the outside and power generation is performed again, or the power generation performance is restored. The second cell voltage increases compared to the voltage. On the other hand, when a cross leak occurs, the influence of the cross leak increases as time elapses. Therefore, the reaction between the anode gas and the cathode gas on the anode electrode side is promoted, and the reverse potential increases. Therefore, the second cell voltage is lower than the first lowest cell voltage. Thereby, even if it is the structure which detects a total cell voltage for every cell group which consists of a several cell, the voltage fall which generate | occur | produces by cross leak can be detected correctly.

  According to the invention described in claim 2, when the first lowest cell voltage is (n−1) / n or less of the average cell group voltage, a reverse potential is generated in any cell of the cell group. Therefore, the occurrence of cross leak can be accurately determined. This eliminates the need for wasteful detection of cross leaks, thereby reducing energy consumption for cross leak detection.

  According to the third aspect of the present invention, the cathode gas remaining in the fuel cell stack is consumed by discharging, so that the fuel cell stack can be kept at a low potential, for example, during idling stop. Thereby, it is possible to prevent the deterioration of the solid polymer electrolyte membrane of the cell, which is caused by maintaining the fuel cell stack at a high potential during idle stop or the like. Furthermore, since the cross leak is detected during the discharge, it is not necessary to perform a wasteful discharge for the cross leak detection.

  According to the fourth aspect of the present invention, when the cross leak occurs, the second cell voltage is rarely higher than the first cell voltage. That is, when the second cell voltage is equal to or higher than the first lowest cell voltage, that is, when the voltage is recovered, it is possible to prevent erroneous detection of cross leak by determining that the cause is other than cross leak.

  According to the fifth aspect of the present invention, it is possible to eliminate the influence of errors and accurately detect the occurrence of cross leaks.

  According to the invention described in claim 6, when a large hole is opened in the solid polymer electrolyte membrane of the cell, that is, when the cross leak is large, the amount of voltage drop is large. At this time, if the voltage drop amount is greater than or equal to a predetermined value, it is possible to detect the cross leak early without detecting the cross leak a predetermined number of times by determining the occurrence of the cross leak at that time. Therefore, when a cross leak occurs, it is possible to prevent damage to surrounding cells.

Next, embodiments of the present invention will be described with reference to the drawings.
(Fuel battery cell)
FIG. 2 is a cross-sectional view of the cell.
As shown in FIG. 2, the fuel cell 1 of the present embodiment is a solid polymer electrolyte membrane type fuel cell, and includes a fuel cell stack configured by stacking a plurality of cells 55 as unit fuel cells. The cell 55 includes, for example, a solid polymer electrolyte membrane 51 made of a solid polymer ion exchange membrane such as perfluorosulfonic acid polymer (registered trademark “Nafion”) or the like sandwiched between an anode 52 and a cathode 53 from both sides, and a pair of outer sides thereof. It is formed by being sandwiched between separators 54, 54. Each cell 55 is supplied with a hydrogen gas passage 56 to which hydrogen gas (anode gas) is supplied as a fuel gas, an air passage 57 to which air containing oxygen (cathode gas) is supplied as an oxidizing gas, and a coolant is supplied. The coolant passage 58 is provided. Then, hydrogen ions generated by the catalytic reaction at the anode 52 permeate the solid polymer electrolyte membrane 51 and move to the cathode 53, causing an electrochemical reaction with oxygen at the cathode 53 to generate power. In order to prevent the fuel cell 1 from exceeding a predetermined temperature due to heat generated by this power generation, the cooling liquid flowing through the cooling liquid passage 58 is deprived of heat and cooled.

  Further, in this fuel cell 1, the cell voltage monitor (V) 41 for detecting the output voltage of the cell 55 includes n (where n ≧ 2) cells 55 (in this embodiment, n = 2). ). Specifically, one end of the cell voltage monitor 41 is connected to the separator 54 outside the one cell 55, and the other end is connected to the separator 54 outside the other cell 55. That is, in the fuel cell 1 of the present embodiment, the two cells 55 are configured as one cell pair (cell group), and each cell voltage monitor 41 detects the total cell voltage of each cell pair (hereinafter, total cell pair voltage). To do. The output signal of the cell voltage monitor 41 is input to voltage detection means 60 (described later) of the ECU 39 as cell voltage information (see FIG. 1).

(Fuel cell system)
FIG. 1 is a schematic configuration diagram of a fuel cell system according to the present embodiment.
As shown in FIG. 1, the fuel cell 1 in the fuel cell system 100 is mounted on a fuel cell vehicle (not shown), and is composed of the fuel cell stack described above. In FIG. 1, only one cell voltage monitor 41 described above is shown.
The fuel cell system 100 includes an air pump 7 such as a supercharger that pressurizes air, which is an oxidizing gas, to a predetermined pressure. The air pump 7 is connected to the inlet of the fuel cell 1 through the oxidizing gas supply path 8. The oxidizing gas supply path 8 is preferably provided with an air cooling device, a humidifier or the like (all not shown). On the other hand, a cathode offgas discharge passage 9 having a back pressure control valve 10 is connected to the oxidizing gas discharge (exit) side of the fuel cell 1. The air used for power generation in the fuel cell 1 is supplied to the diluter 30 through the cathode offgas discharge passage 9 together with the generated water on the cathode 53 (see FIG. 2) side.

  The fuel cell system 100 also includes a hydrogen tank (cathode gas supply means) 15 in which hydrogen gas that is fuel gas is stored. The hydrogen tank 15 is connected to the inlet of the fuel cell 1 through a fuel gas supply path 17. The fuel gas supply path 17 is provided with a fuel gas cutoff valve 20, a pressure reducing valve (not shown) for reducing the hydrogen gas to a predetermined pressure, and an ejector 19 for joining the anode off-gas to the fuel gas supply path 17. .

On the other hand, an anode off-gas circulation path 18 is connected to the fuel gas discharge (exit) side of the fuel cell 1. Unreacted hydrogen gas that has not been consumed in the fuel cell 1 is sucked into the ejector 19 through the anode off-gas circulation path 18 and supplied again to the fuel gas supply path 17 of the fuel cell 1.
Further, an anode off-gas discharge path 22 having a hydrogen discharge valve 21 is branched from the anode off-gas circulation path 18. The hydrogen discharge valve 21 is opened as necessary to discharge the anode off-gas when the concentration of impurities (water, nitrogen, etc.) in the hydrogen gas circulating through the fuel cell 1 becomes high. The anode off gas discharged from the hydrogen discharge valve 21 is discharged to the diluter 30 and is diluted by the cathode off gas in the diluter 30.

  The fuel cell 1 is connected to a power consuming device 42 such as an audio or a battery via a discharge output lead wire 43. The discharge output lead wire 43 is supplied with the electric power generated by the fuel cell 1 when discharging the fuel cell 1 while the vehicle is idle, regenerative, or when the cathode gas supply is stopped such as when the ignition is off. It is like that.

  Discharge means that the oxidizing gas remaining at the cathode 53 is reacted and removed to lower the potential of the fuel cell 1. Thereby, it is possible to prevent the solid polymer electrolyte membrane 51 from being loaded by the oxidizing gas remaining on the cathode 53 while the cathode gas supply is stopped. Then, the electric power generated by the fuel cell 1 by the discharge is supplied to the power consuming device 42 so that the audio is reproduced or stored in the battery. In the discharge lead wire 43, an ammeter 55 is connected between the fuel cell 1 and the power consuming device 42. The ammeter 55 detects a current (power) supplied to the power consuming device 42, and an output signal of the ammeter 55 is input to the ECU 39 as current information.

(ECU)
The cell voltage monitor 41 and the ammeter 55 described above are connected to an ECU 39 that controls the fuel cell system 100 in an integrated manner.
FIG. 3 is a block diagram of the ECU.
As shown in FIG. 3, the ECU 39 detects the occurrence of cross leak in the fuel cell 1 while the cathode gas supply is stopped, so that the voltage detection means 60, the first determination means 61, the second determination means 62, , A cross leak signal output means 63, a cathode gas supply stop means 67, and a cathode gas removal means 68. Although not shown, the ECU 39 also includes a memory unit that stores each cell pair voltage and each determination result described later.

The voltage detection means 60 receives an output signal (cell voltage information in FIG. 1) output from the above-described cell voltage monitor 41, and includes a first lowest cell voltage detection means 64 and a second cell voltage detection means 65. And an average cell voltage detecting means 66.
The first lowest cell voltage detection means 64 calculates the total cell pair voltage out of the total cell pair voltage of each cell pair detected by each voltage sensor 40 based on the output signal output from the cell voltage monitor 41 after completion of the above-described discharge. The total cell pair voltage of the lowest cell pair (specific cell pair) is detected as the first lowest cell pair voltage. Then, an output signal of the detected first lowest cell pair voltage is output toward the first determination means 61 and the second determination means 62.

The average cell voltage detection unit 66 calculates an average cell pair voltage (hereinafter referred to as an average cell pair voltage) in the fuel cell 1 based on the total cell pair voltage of the entire fuel cell 1, that is, the total cell pair voltage of each cell pair. Then, the output signal of the calculated average cell pair voltage is output toward the first determination means 61.
The second cell voltage detection means 65 is based on the output signal output from the cell voltage monitor 41 after the first lowest cell pair voltage is detected or after a predetermined time (time T3 in FIGS. 5 to 7) has elapsed since the completion of the discharge. Among the total cell pair voltages detected by each voltage sensor 40, the total cell pair voltage of the specific cell pair described above is detected as the second cell pair voltage. Then, the output signal of the detected second cell pair voltage is output toward the second determination means 62.

The cathode gas supply stopping means 67 outputs an air stop command signal to the air pump 7 when the vehicle is in an idle stop, during regeneration, or when the ignition is turned off, and stops the supply of cathode gas by the air pump 7. .
The cathode gas removing unit 68 outputs a discharge command signal to the power consuming device 42 when the cathode gas supply is stopped, and causes the power consuming device 42 to perform the above-described discharge. That is, in a state where the supply of the cathode gas is stopped, power is taken out from the fuel cell 1 and is consumed by the power consuming device 42.

  The first determination unit 61 determines whether or not a cross leak has occurred in the fuel cell 1 based on the output signal of the first minimum cell pair voltage output from the first minimum cell voltage detection unit 64. Specifically, when the first lowest cell pair voltage after completion of the discharge is equal to or less than 1 / 2−α (α: detection error) of the average cell pair voltage, it is determined that there is a possibility that a cross leak has occurred. To do.

  The second determination means 62 compares the output signal of the first lowest cell pair voltage and the output signal of the second cell pair voltage output from each of the first lowest cell voltage detection means 64 and the second cell voltage detection means 65. . Then, when the value of the second cell pair voltage is lower than the value of the first lowest cell pair voltage, occurrence of cross leak is determined. Then, the output signal of the determination result in the second determination unit 62 is output toward the cross leak signal output unit 63.

  The cross leak signal output means 63 outputs an abnormal signal of cross leak occurrence such as a warning sound or a warning display to the driver based on the output signal of the cross leak occurrence output from the second determination means 62. is there. Specifically, when the difference between the second cell pair voltage calculated by the second determination unit 62 and the first lowest cell pair voltage is smaller than a predetermined value, this state is changed every time the cathode gas supply is stopped (for example, every idle stop). Occurrence of a cross leak is determined when it is detected a plurality of times (for example, five times) continuously. On the other hand, if the difference between the second cell pair voltage and the first lowest cell pair voltage is greater than or equal to a predetermined value, the occurrence of cross leak is determined at that time. When the occurrence of the cross leak is confirmed, an abnormal signal such as a warning sound or a warning display is output to the driver.

(Cross leak detection method)
Next, a cross leak detection method according to this embodiment will be described. FIG. 4 is a flowchart showing a cross leak detection method. The detection of the cross leak in this embodiment is performed when the cathode gas supply is stopped, that is, when the vehicle is idling or regenerating, when the ignition is OFF, or the like.
First, when the vehicle is idle stopped, regenerated, or when the ignition is off, an air stop command signal is output from the cathode gas supply stop means 67 to the air pump 7 and the supply of cathode gas by the air pump 7 is stopped. Let

Then, as shown in FIG. 4, the ECU 39 determines whether or not the supply of the cathode gas (oxidizing gas) is stopped (step S1). If the determination result in step S1 is “NO” (when cathode gas is being supplied, that is, while the vehicle is traveling, etc.), the cross leak is not detected and the flow ends.
On the other hand, when the determination result of step S1 is “YES”, it is determined that the cathode gas supply is stopped, and the process proceeds to step S2.

Next, the ECU 39 determines whether or not the cathode 53 side is in a cathode gas deficient state (step S2). At this point, the anode gas (hydrogen gas) is sufficiently present on the anode 52 side. When the determination result in step S2 is “NO” (when the cathode gas remains on the cathode 53), a discharge command signal is output from the cathode gas removing means 68 to the power consuming device. Then, the power consuming device 42 that has received the discharge command signal performs the above-described discharge. The determination of the completion of the discharge is made based on the current information output from the ammeter 55. Further, in order to remove the cathode gas remaining on the cathode 53 side, the anode gas existing on the anode 52 side after being left for a predetermined time (for example, about 2 to 3 seconds to 10 seconds) and the cathode gas remaining on the cathode 53 are left. It is also possible to carry out the reaction. Thereby, the oxidizing gas remaining on the cathode 53 side is removed.
On the other hand, if the determination result in step S2 is “YES”, it is determined that the cathode 53 side is in a cathode gas deficient state, and the process proceeds to step S3.

Next, the total cell pair voltage of the entire fuel cell 1 is detected. Specifically, the total cell pair voltage of each cell pair (between two cells 55) is detected by each voltage sensor 40, and the output signal (cell voltage information) of the detection result is detected from the cell voltage monitor 41 to the voltage detected by the ECU 39. Output to means 60. Based on the detection result of the total cell pair voltage of each cell pair, the average cell pair voltage of the fuel cell 1 is calculated by the average cell voltage detector 66.
On the other hand, the first lowest cell pair voltage is detected by the first lowest cell voltage detection means 64 based on the detection result of the total cell pair voltage. Specifically, the lowest total cell pair voltage among the total cell pair voltages of each cell pair is detected as the first lowest cell pair voltage. Then, the average cell pair voltage and the first lowest cell pair voltage are stored in the memory unit of the ECU 39 (step S3).

  Thus, by detecting the total cell pair voltage after completion of the discharge (the cathode 53 side is in a cathode gas deficient state), the total cell pair voltage of each cell pair can be detected under the same conditions. That is, when there is a cell pair in which some abnormality has occurred, a change in the total cell pair voltage appears significantly. This makes it easy to determine a change between a cell pair that maintains good voltage performance and a cell pair that has some abnormality.

5 to 7 are time charts showing the cell voltage (cell pair voltage) with respect to time T. FIG. 5 is normal, FIG. 6 is when the cell pair voltage is lowered due to the influence of generated water, and FIG. 7 is cross leak. The cell pair voltage drop due to occurrence is shown.
As shown in FIGS. 5 to 7, at time T <b> 1, after the cathode gas supply is stopped, by performing discharge or the like, the cathode gas remaining on the cathode 53 side is consumed, and the average cell pair voltage and the minimum cell pair voltage are lowered. (Time T2).
As shown in FIG. 5, in the normal state, that is, when there is no influence of generated water or cross leak, as the time further elapses from time T2 (for example, T3 in FIG. 5), the cathode gas is externally applied to the cathode 53. Since power is generated again after entering, the average cell pair voltage and the minimum cell pair voltage increase.

  Subsequently, returning to the flowchart of FIG. 4, at time T <b> 2 (see FIGS. 5 to 7), the first determination unit 61 causes the first lowest cell pair voltage to be equal to or less than 1 / 2−α (α: detection error) of the average cell pair voltage. It is determined whether or not (step S4). In a state where the supply of the cathode gas is stopped, a potential of 0 V or a reverse potential is generated in the cell 55 where the cross leak has occurred. That is, if the first lowest cell pair voltage is 1 / 2−α or less of the average cell pair voltage, there is a possibility that the potential of one cell 55 of the cell pair is 0 V or a reverse potential. Note that the reverse potential is a potential generated by the reaction between oxygen that has moved from the cathode 53 side to the anode 52 side due to cross leak and hydrogen present on the anode 52 side, and is generated by this reaction. It is a phenomenon that reverses the potential that occurs at times.

  As described above, when the first lowest cell pair voltage is ½−α or less of the average cell pair voltage, it is highly possible that a reverse potential is generated in one cell 55 of the cell pair. Can be accurately determined. That is, the fact that the first lowest cell pair voltage is ½−α or less of the cell pair of the average cell pair voltage is a case where a reverse potential is generated due to cross leakage, or both cells in the cell pair due to a decrease in power generation performance. This is a case where the voltage of 55 has dropped to half or less. This eliminates the need for wasteful detection of cross leaks, thereby reducing energy consumption for cross leak detection.

If the determination result in step S4 is “NO” (the first lowest cell pair voltage is equal to or greater than 1 / 2−α of the average cell pair voltage), the process proceeds to step S8 to determine that there is no possibility of a cross leak failure. If it is determined that there is no possibility of a cross leak failure, the cross leak detection flow is terminated.
On the other hand, if the determination result of step S4 is “YES”, it is determined that there is a possibility of cross leak, and the process proceeds to step S5.

Next, it is determined whether or not a predetermined time (time T3 in FIGS. 5 to 7) has elapsed since the detection of the first lowest cell pair voltage (time T2) by the first lowest cell voltage detection means 64 (step S5). If the determination result in step S5 is “NO” (not reaching time T3 in FIGS. 5 to 7), the process waits until a predetermined time elapses.
On the other hand, when the determination result of step S5 is “YES”, it is determined that a predetermined time has elapsed after the detection of the first lowest cell pair voltage, and the process proceeds to step S6.

  Next, the second cell voltage detection means 65 detects the second cell pair voltage. Specifically, based on the cell pair voltage output signal (cell voltage information) output from the cell voltage monitor 41 at time T3 (see FIGS. 5 to 7), the total cell pair of the specific cell pair described above among the total cell pair voltages. The voltage is detected as the second cell pair voltage. And the detected 2nd cell pair voltage is memorize | stored in the memory part of ECU39 (step S6).

  By the way, when determining the cross leak based on the total cell pair voltage, it is difficult to determine whether or not the cross leak actually occurs even if the cross leak occurs in any of the plurality of cells. There's a problem. For example, in the configuration for detecting the total cell pair voltage, even if the total cell pair voltage decreases to half or less, the cause of this voltage decrease cannot be determined. Specifically, there is a problem that it is difficult to determine whether the cause of the voltage drop is actually due to a cross leak or due to a drop in power generation performance such as the generated water covers the power generation surface. In other words, as described above, the total cell pair voltage is the same between the case where only one cell is at a reverse potential due to cross leakage and the case where the voltage of both cells is reduced to half or less due to a decrease in power generation performance. It may be possible.

Here, in the present embodiment, it is determined whether or not the second cell pair voltage detected in step S6 is equal to or lower than the first lowest cell pair voltage detected in step S4 (step S7).
If the determination result in step S7 is “NO” (the second cell pair voltage is equal to or higher than the first lowest cell pair voltage), the process proceeds to step S8 and it is determined that there is no cross leak failure. If it is determined that there is no cross leak failure, the cross leak detection flow is terminated.

  That is, when the cross leak occurs, the second cell pair voltage is unlikely to be higher than the first cell pair voltage. When the cross leak occurs, the influence of the cross leak increases as time elapses. Therefore, the reaction between the anode gas and the cathode gas on the anode 52 side is promoted, and the reverse potential increases. Therefore, the second cell voltage is lower than the first lowest cell pair voltage.

On the other hand, as shown in FIG. 6, when the cause of the decrease in the cell pair voltage from the time T1 to the time T2 is a decrease in the power generation performance due to the generated water or the like, power is If the generated water present on the surface is removed, the power generation performance recovers at time T3. As a result, the second cell pair voltage increases compared to the first lowest cell pair voltage. In addition, as described above, the second cell pair voltage is increased compared to the first lowest cell pair voltage also when the cathode gas enters the cathode 53 from the outside and power generation is performed again.
As described above, when the lowest cell pair voltage at time T3 is increased as compared with the lowest cell pair voltage at time T2, that is, when the lowest cell pair voltage is recovered, the decrease in the lowest cell pair voltage at time T2 is generated water or the like. Judged that the power generation performance was reduced.

On the other hand, when the determination result of step S7 is “YES” (the second cell pair voltage is equal to or lower than the first lowest cell pair voltage), the process proceeds to step S9.
That is, as shown in FIG. 7, when the cause of the decrease in the total cell pair voltage at time T2 is due to cross leakage, the reaction on the anode 52 side increases as time passes as described above, and the reverse potential is increased. Becomes larger. Accordingly, when the total cell pair voltage at time T3 is further reduced as compared with the total cell pair voltage at time T2, it is determined that the decrease in the total cell pair voltage is not due to the decrease in power generation performance but due to cross leak. can do.

  Next, the occurrence of a cross leak failure is determined based on the determination result of step S7 (step S9). To confirm the occurrence of the cross leak, the above-described flow is performed every time the cathode gas supply is stopped (for example, every time the idle gas is stopped). Confirm that it occurred. In other words, when cross leaks are detected multiple times in succession, by confirming the occurrence of cross leaks, it is possible to eliminate the effects of errors and prevent false detection of cross leaks. A leak can be detected accurately.

  In step S7, if the difference between the second cell pair voltage and the first lowest cell pair voltage is greater than or equal to a predetermined value, it is determined that a cross leak failure has occurred at that time. For example, when a large hole is opened in the solid polymer electrolyte membrane 51 of the cell 55, that is, when the cross leak is large, the amount of voltage drop increases. At this time, if the voltage drop amount is greater than or equal to a predetermined value, it is possible to detect the cross leak early without detecting the cross leak a predetermined number of times by determining the occurrence of the cross leak failure at that time. Therefore, it is possible to prevent damage to the surrounding cells 55 when a cross leak failure occurs.

When the occurrence of the cross leak failure is determined, an abnormal signal such as a warning sound or a warning display is output from the cross leak signal output means 63 to the driver. When the abnormal signal is received, the cell 55 in which the cross leak has occurred is immediately replaced. Therefore, even if a cross leak has occurred in a plurality of cells 55, the presence or absence of a cross leak in another cell 55 may be confirmed when the cell 55 is replaced. Therefore, it is sufficient to detect the cell 55 in which the cross leak occurs first by detecting the lowest cell pair voltage.
This completes the cross leak detection flow.

Thus, according to the above-described embodiment, the first lowest cell pair voltage is compared with the second cell pair voltage, and the occurrence of cross leakage is determined when the second cell pair voltage is lower than the first lowest cell pair voltage. It was. That is, the occurrence of cross leak can be determined based on the amount of change in the minimum cell pair voltage. Specifically, when the cause of the voltage drop in the first determining means 61 is a decrease in power generation performance, the cathode gas enters the cathode 53 from the outside and power generation is performed again, or the power generation performance is restored. Thus, the second cell pair voltage increases compared to the first lowest cell pair voltage. On the other hand, when the cross leak occurs, the influence of the cross leak increases as time elapses. Therefore, the reaction between the anode gas and the cathode gas on the anode 52 side is promoted, and the reverse potential increases. Therefore, the second cell voltage is lower than the first lowest cell pair voltage. Thereby, even if it is the structure which detects a total cell pair voltage for every cell pair which consists of several cells 55, the voltage fall which generate | occur | produces by cross leak can be detected correctly.
When the second cell pair voltage is higher than the first lowest cell pair voltage, that is, when the total cell pair voltage is recovered, it is possible to prevent erroneous detection of cross leak by determining that the cause is other than cross leak.

Further, by consuming the cathode gas remaining in the fuel cell 1 by discharging, the fuel cell 1 can be kept at a low potential, for example, during idling stop. Thereby, deterioration of the solid polymer electrolyte membrane 51 of the cell 55 caused by maintaining the fuel cell 1 at a high potential during idle stop or the like can be prevented. Furthermore, since the cross leak is detected during the discharge that is performed during idle stop or the like, it is not necessary to wastefully discharge for the cross leak detection.
Therefore, it is possible to reduce damage to the cell 55 due to cross leak while reducing the cost of the fuel cell 1.

By the way, as a cross leak detection method, for example, a configuration in which a hydrogen sensor is provided on the cathode outlet side (diluter outlet side) and the amount of hydrogen gas leaked from the cathode side is detected by this hydrogen sensor is also conceivable. However, in this configuration, since the oxidizing gas discharged from each cell flows out to the cathode outlet side, a cross leak cannot be determined unless a large amount of hydrogen gas leaks. In addition, the location where the cross leak occurs cannot be determined.
On the other hand, in this embodiment, since it is not necessary to provide a hydrogen sensor by determining the cross leak based on the amount of change in the cell pair voltage, the cost of the fuel cell 1 can be reduced. Further, it is possible to determine the cross leak more quickly and accurately than the detection by the hydrogen sensor.

It should be noted that the technical scope of the present invention is not limited to the above-described embodiments, and includes those in which various modifications are made to the above-described embodiments without departing from the spirit of the present invention. In other words, the configuration described in the above-described embodiment is merely an example, and can be changed as appropriate.
For example, in the above-described embodiment, the configuration in which two cells are used as a cell pair and the total cell pair voltage for each cell pair is detected has been described. However, a plurality of cells are used as one cell group, and the total cell for each cell group is described. You may make it the structure which detects a voltage. In this case, assuming that the number of cells is n, the determination in step S4 described above is that there is a possibility of cross leak when the first lowest cell voltage is (n-1) / n-α of the average cell voltage. to decide.

  Further, in the above-described embodiment, the case where the discharge is performed when the cathode side is not in a cathode gas deficient state in step S2 or the case where the cathode side is left for a predetermined time has been described. A configuration that draws air is also possible.

1 is a schematic configuration diagram of a fuel cell system in an embodiment of the present invention. It is sectional drawing of the cell of the fuel cell in embodiment of this invention. It is a block diagram of ECU in the embodiment of the present invention. It is a flowchart which shows the cross leak detection method in embodiment of this invention. It is a time chart which shows the cell voltage with respect to time T at the time of normal in embodiment of this invention. It is a time chart which shows the cell voltage with respect to time T at the time of the cell voltage fall by the generated water in embodiment of this invention. It is a time chart which shows the cell voltage with respect to time T at the time of the voltage fall by the cross leak generation in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell (fuel cell stack) 42 ... Electric power consumption device (cathode gas removal means) 52 ... Anode 53 ... Cathode 55 ... Cell 61 ... First judgment means 62 ... Second judgment means 63 ... Cross leak signal output means 64 ... First lowest cell voltage detection means 65 ... second cell voltage detection means 66 ... average cell voltage detection means

Claims (7)

A fuel cell stack configured by stacking cells for supplying power by supplying anode gas and cathode gas;
Cathode gas supply means for supplying the cathode gas to the fuel cell stack;
A plurality of the cells as a cell group, and a cell voltage detection means for detecting a total cell voltage for each cell group, and a fuel cell system comprising:
Cathode gas supply stop means for stopping supply of the cathode gas to the fuel cell stack;
A cathode gas removing means for removing the cathode gas present in the cathode electrode when the supply of the cathode gas is stopped by the cathode gas supply stopping means;
When the cathode gas is removed by the cathode gas removing means, a first lowest cell voltage that detects the total cell voltage of a specific cell group having the lowest total cell voltage among the plurality of cell groups as a first lowest cell voltage. Cell voltage detection means;
First determination means for determining whether or not there is a possibility of occurrence of a cross leak based on the first lowest cell voltage;
When it is determined by the first determining means that there is a possibility that a cross leak has occurred, the total cell voltage of the specific cell group is set to a first value after a predetermined time has elapsed since the detection of the first lowest cell voltage. A second cell voltage detecting means for detecting as a two-cell voltage;
The first lowest cell voltage and the second cell voltage are compared, and if the second cell voltage is lower than the first lowest cell voltage, it is determined that a cross leak has occurred in the specific cell group. Second judging means for
And a cross leak signal output means for outputting an abnormal signal in accordance with a result of the second determination means. Based on the total cell voltage for each cell group, an average cell voltage detection means for calculating an average cell group voltage of the fuel cell stack,
The first determination means generates a cross leak when the number of the cells in the cell group is n and the first lowest cell voltage is (n−1) / n or less of the average cell group voltage. The fuel cell system according to claim 1, wherein the fuel cell system is determined to be possible.   3. The fuel cell system according to claim 1, wherein the cathode gas removing unit removes the cathode gas by discharging the cathode gas remaining in the fuel cell stack. 4.   The second determination means compares the first lowest cell voltage with the second cell voltage, and if the second cell voltage is equal to or higher than the first lowest cell voltage, there is no occurrence of cross leak. The fuel cell system according to any one of claims 1 to 3, wherein a determination is made.   The cross leak signal output means determines an occurrence of cross leak in the specific cell group and outputs an abnormal signal when the second determination means determines that the cross leak has occurred a predetermined number of times or more. The fuel cell system according to any one of claims 1 to 4, wherein:   When the second determination unit detects that the second cell voltage is lower than the first lowest cell voltage by the second determination unit, the cross leak signal output unit detects the cross leak signal output unit by the second determination unit. 6. The fuel cell system according to claim 5, wherein even if it is not determined that the cross leak has occurred a predetermined number of times or more, the occurrence of the cross leak in the specific cell group is confirmed and an abnormal signal is output. . A fuel cell stack configured by stacking cells for supplying power by supplying anode gas and cathode gas;
Cathode gas supply means for supplying the cathode gas to the fuel cell stack;
A cross leak detection method for detecting a cross leak of the cell using a fuel cell system having a plurality of the cells as a cell group, and a cell voltage detecting means for detecting a total cell voltage for each cell group. ,
A cathode gas supply stop step of stopping supply of the cathode gas to the fuel cell stack;
A cathode gas removing step for removing the cathode gas present in the cathode electrode when the supply of the cathode gas is stopped;
When the cathode gas is removed by the cathode gas removal step, a first lowest cell voltage that detects the total cell voltage of a specific cell group having the lowest total cell voltage among the plurality of cell groups as a first lowest cell voltage. A cell voltage detection step;
A first determination step of determining whether or not there is a possibility of occurrence of a cross leak based on the first minimum cell voltage detected in the first minimum cell voltage detection step;
When it is determined by the first determination step that there is a possibility that a cross leak has occurred, the total cell voltage of the specific cell group is changed to a first value after a predetermined time has elapsed since the detection of the first lowest cell voltage. A second cell voltage detection step for detecting as a two-cell voltage;
The first lowest cell voltage and the second cell voltage are compared, and if the second cell voltage is lower than the first lowest cell voltage, it is determined that a cross leak has occurred in the specific cell group. A second determining step,
And a cross leak signal output step of outputting an abnormal signal in accordance with the result of the second determination step.

Images