JP2019040819A - Fuel cell system - Google Patents

Abstract

To provide a fuel cell system capable of precisely determining presence of an air bubble in the cooling water flow path of a fuel cell stack, where unit cells are placed in such a posture that the lamination direction is substantially vertical direction.SOLUTION: In a fuel cell system 1, out of multiple single cells 10-1 through 10-n of a fuel cell stack 10, a second cell 10-4 located anywhere between a first cell 10-1 placed on the vertically uppermost side and 1/10-th of the total number of the multiple single cells is provided with a first detector V1, and a second detector V2 is provided at a part other than the second cell 10-4. Any one of the output voltage, temperature and impedance is detected, any one of a representative voltage, a representative temperature and a representative impedance is acquired based on the detection results from the second detector V2, and then presence of an air bubble in the cooling water flow path is determined based on the comparison results of the detection results from the first detector V1 and the representative value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell system.

  A fuel cell stack in which a plurality of single cells are stacked is known. In such a fuel cell stack, a cooling water flow path is formed, and if bubbles exist in the cooling water flow path, the cooling efficiency to the fuel cell stack decreases. Here, the single cell around the bubble may not be sufficiently cooled due to the presence of the bubble, and the temperature may increase and the output voltage may decrease. It can be considered that the presence or absence of bubbles in the cooling water flow path of the fuel cell stack is determined based on such a decrease in the output voltage of the single cells around the bubbles.

  Since the cells in which the output voltage decreases due to the presence of bubbles are not always the same, it is conceivable to provide a voltage sensor for every single cell and detect the output voltage for each single cell. However, in this case, the same number of voltage sensors as single cells are required, and the configuration becomes complicated. In Patent Document 1, a single cell arranged at an end portion in a stacking direction among a plurality of single cells is detected by a voltage sensor, and an entire output of the remaining plurality of single cells arranged in the vicinity of the central portion in the stacking direction is disclosed. It is described that the voltage is detected by a single voltage sensor. As a result, the number of voltage sensors can be reduced and the configuration can be simplified, but when bubbles are present around the single cell near the center in the stacking direction, the entire plurality of single cells near the center There is a possibility that the accuracy of determining the presence / absence of air bubbles may be reduced without greatly reducing the output voltage.

JP 2005-285692 A

  By the way, a fuel cell stack may be arrange | positioned with the attitude | position in which the lamination direction of the single cell followed the substantially perpendicular direction. Even when arranged in such a posture, it is desired that the presence or absence of bubbles in the cooling water flow path of the fuel cell stack can be accurately determined with a simple configuration.

  The present invention provides a fuel cell system capable of accurately determining the presence or absence of bubbles in a cooling water flow path of a fuel cell stack arranged in a posture in which the stacking direction of a plurality of single cells is substantially along the vertical direction. The purpose is to provide.

  The object is to form a fuel cell stack in which a direction in which a plurality of single cells are stacked is arranged in a substantially vertical direction, and at least a part of the fuel cell stack so as to penetrate the plurality of single cells. The cooling water flow path and the second one between the first cell arranged on the most vertically upper side of the plurality of single cells and the tenth sheet of the total number of the plurality of single cells. A first detector that detects any one of the output voltage, temperature, and impedance of the cell; and a second detector that detects any of the output voltage, temperature, and impedance at a portion other than the second cell of the plurality of single cells. A detection unit; an acquisition unit that acquires any one of a representative output voltage, a representative temperature, and a representative impedance based on a detection result of the second detection unit; and presence / absence of bubbles in the cooling water flow path of the fuel cell stack. Judgment part to judge The determination unit includes a difference between the detected output voltage of the second cell and the representative output voltage that is greater than a first threshold, and the detected temperature of the second cell and the representative temperature. If the difference is larger than the second threshold or the difference between the detected impedance of the second cell and the representative impedance is larger than the third threshold, there is a bubble in the cooling water flow path. Can be achieved by the fuel cell system.

  According to the present invention, a fuel cell capable of accurately determining the presence or absence of bubbles in a cooling water flow path of a fuel cell stack arranged in a posture in which the stacking direction of a plurality of single cells is substantially along the vertical direction. Can provide a system.

FIG. 1A is a schematic diagram of a fuel cell system, and FIG. 1B is a graph showing the output voltage of each single cell when bubbles are present in the cooling water flow path of the fuel cell stack. 2A and 2B are graphs showing the temperature and impedance of each single cell when bubbles exist in the cooling water flow path of the fuel cell stack.

  FIG. 1A is a schematic diagram of a fuel cell system (hereinafter referred to as a system) 1. The system 1 is mounted on a vehicle, for example. The system 1 includes a fuel cell stack (hereinafter referred to as a stack) 10, a cooling system 20, voltage sensors V1 and V2, a control device 50, and the like. The control device 50 is a computer including a CPU, a ROM, a RAM, and the like, and is electrically connected to each device described later, and controls the entire system 1. The system 1 includes a hydrogen gas supply system (not shown) that supplies hydrogen gas as an anode gas to the stack 10, an air supply system (not shown) that supplies air containing oxygen as a cathode gas to the stack 10, and the stack 10 A power control system (not shown) for controlling the generated power is included.

  In the stack 10, a plurality of single cells 10-1, 10-2 to 10-n are stacked, and the stacked direction of these single cells is arranged in a posture along a substantially vertical direction. N single cells are stacked. The single cell 10-1 is located on the uppermost vertical side among the plurality of single cells. The single cell 10-n is located on the lowest vertical side among the plurality of single cells. Each single cell has a membrane electrode gas diffusion layer assembly (MEGA), an insulating member that supports the MEGA, and a pair of separators that sandwich the MEGA and the insulating member. The MEGA has an electrolyte membrane, a catalyst layer formed on each side of the electrolyte membrane, and a pair of gas diffusion layers respectively joined to the catalyst layer. Although not shown, a pair of current collecting plates, a pair of insulating plates, and a pair of end plates are arranged so as to sandwich the plurality of single cells. A cooling water flow path is formed in the stack 10.

  The cooling system 20 cools the stack 10 by circulating cooling water through a predetermined path. The cooling water flows through the circulation path 21 by the circulation pump 22, is heat-exchanged by the radiator 24, is cooled, and is supplied to the stack 10. The circulation pump 22 is electrically connected to the control device 50 and controlled.

  A cooling water supply manifold 12 and a cooling water discharge manifold 14 (hereinafter both referred to as a manifold) are formed inside the stack 10, and both the manifolds 12 and 14 are formed through a plurality of single cells. Yes. The manifolds 12 and 14 communicate with the circulation path 21. The cooling water is supplied to the manifold 12 from the circulation path 21, passes through between the separators of adjacent single cells from the manifold 12, and flows to the manifold 14. As a result, the plurality of single cells are cooled. The manifolds 12 and 14 are formed so as to penetrate the current collector plate, the insulating plate, and the end plate arranged on the single cell 10-n side. In this specification, all the flow paths formed between the manifolds 12 and 14 and the adjacent single cells are referred to as a cooling water flow path of the stack 10.

  The voltage sensors V1 and V2 are electrically connected to the control device 50 and detect output voltages of different single cells. Specifically, the voltage sensor V1 detects the output voltage of the single cell 10-4, and the voltage sensor V2 detects the voltage of the single cell 10- (n / 2) that is a single cell arranged in the center in the stacking direction. To detect. The control device 50 executes bubble determination control for determining the presence or absence of bubbles in the cooling water flow path of the stack 10 based on the output voltages detected by the voltage sensors V1 and V2. The bubble determination control is executed by an acquisition unit and a determination unit that are functionally realized by the CPU, ROM, RAM, and the like of the control device 50.

  Next, the characteristics of the output voltage of each single cell when bubbles are present in the cooling water flow path of the stack 10 will be described. FIG. 1B is a graph showing the output voltage of each single cell when bubbles are present in the cooling water flow path of the stack 10. In FIG. 1B, the vertical axis represents the output voltage, the horizontal axis represents each single cell, and the single cells are shown in order from the vertical upper side from the left side to the right side of the horizontal axis. Therefore, the leftmost single cell on the horizontal axis is the single cell 10-1 located on the uppermost vertical side. FIG. 1B shows the position of the single cell 10- (n / 10) corresponding to the n / 10th number of single cells from the vertically upper side when the total number of single cells is n. Yes. FIG. 1B shows a case where the output voltage of the single cell 10-4 is the lowest.

  When bubbles are mixed into the cooling water flow path of the stack 10, the bubbles rise to the vertically upper side and stay in the vicinity of the single cell 10-1 located on the most vertically upper side. Specifically, although it depends on the size and amount of the bubbles, the bubbles in the vicinity of the single cells 10-1 to 10-4 in the manifold 12 or 14 or between the single cells 10-1 to 10-4. Stays. Due to the presence of the bubbles, the single cells around the bubbles are not sufficiently cooled, and the temperature of the single cells around the bubbles rises as compared with the temperatures of the other single cells. For this reason, drying progresses in the electrolyte membrane of the single cell around the bubbles as compared with the electrolyte membranes of the other single cells. As a result, the output voltage of the single cell around the bubble is lower than the output voltage of the other single cells. Here, as shown in FIG. 1B, the output voltage of the single cell 10-1 positioned on the uppermost vertical side is not the lowest, but the output voltage of the single cell 10-4 on the lower side is the lowest. It has become. The reason for this is that the single cell 10-1 is located on the outermost side of the stack 10, so that it is easily radiated to the outside of the stack 10 and cooled, and accordingly, the single cell 10 adjacent to the single cell 10-1. -2 and the single cell 10-3 adjacent to the single cell 10-2 are considered to be easily cooled. The reason why the output voltage of the single cells after the single cell 10-4 is recovered is that there are no bubbles around the single cells after the single cell 10-4, and the heat radiation effect by the cooling water gradually increases. This is thought to be increasing. In this embodiment, the single cell 10-4 is selected as the single cell whose output voltage is most likely to drop when bubbles are present in the cooling water flow path. As described above, the voltage sensor V1 is the single cell. The output voltage of the cell 10-4 is detected. Further, the single cell 10- (n / 2) is selected as a single cell whose output voltage does not substantially change even when bubbles are present in the cooling water flow path. As described above, the voltage sensor V2 The output voltage of the single cell 10- (n / 2) is detected. In addition, since the drying of the electrolyte membrane of the single cell around the bubble proceeds as time passes, it is considered that the output voltage of the single cell around the bubble decreases as time passes.

  The control device 50 accurately determines the presence or absence of bubbles in the cooling water flow path of the stack 10 based on the detection results of the voltage sensors V1 and V2. Specifically, the determination is performed as follows. First, the representative output voltage is acquired based on the detection result of the voltage sensor V2. Here, the output voltage of the single cell 10- (n / 2) detected by the voltage sensor V2 is acquired as the representative output voltage. Next, it is determined whether or not the difference between the detected output voltage of the single cell 10-4 and the representative voltage is greater than the first threshold value. In the case of negative determination, this control is terminated on the assumption that bubbles do not exist in the cooling water flow path of the stack 10. In the case of an affirmative determination, it is determined that bubbles are present in the cooling water flow path of the stack 10.

  In the example of FIG. 1B, assuming that the difference between the output voltage of the single cell 10-4 and the output voltage of the single cell 10- (n / 2) is larger than the first threshold, bubbles exist in the cooling water flow path of the stack 10. It is determined that The single cell 10-1 is an example of a first cell arranged on the uppermost vertical side. The single cell 10-4 is 10 minutes of the total number of the single cells 10-1 to 10-n to the single cell 10-1 disposed on the most vertically upper side among the multiple single cells 10-1 to 10-n. It is an example of the 2nd cell in any one to the 1st sheet | seat. The voltage sensor V1 is an example of a first detection unit that detects any of the output voltage, temperature, and impedance of the single cell 10-4. The voltage sensor V2 is an example of a second detection unit that detects any of the output voltage, temperature, and impedance at a portion other than the single cell 10-4 of the plurality of single cells 10-1 to 10-n. In this way, the presence or absence of bubbles in the cooling water flow path of the stack 10 can be accurately determined with a simple configuration by the two voltage sensors V1 and V2.

  When it is determined that bubbles are present in the cooling water flow path of the stack 10 as described above, the output of the circulation pump 22 may be increased to discharge the bubbles from the cooling water flow path of the stack 10. Then, it may be notified that bubbles are present in the cooling water flow path of the stack 10 by means of a diagnosis display or a monitor display.

  The manifolds for supplying and discharging the cathode gas and the anode gas formed in the stack 10 are also formed to extend in a substantially vertical direction so as to pass through the plurality of single cells, and thus are generated in the stack 10. The generated water is discharged to the outside of the stack 10 through the manifold by the action of gravity.

  In the above embodiment, the voltage sensor V2 detects the output voltage of the single cell 10- (n / 2) arranged in the center in the stacking direction, but the single cell from which the voltage sensor V2 detects the output voltage is limited to this. Alternatively, the output voltage of the single cell may be detected at a portion other than the single cell 10-4 where the output voltage is detected by the voltage sensor V1. For example, the voltage sensor V2 may detect the output voltage of the single cell 10-n. Further, the voltage sensor V2 may detect the output voltage across the plurality of single cells. For example, the voltage sensor V2 may detect the total output voltage of the single cells 10-1 to 10-n, or a plurality of continuous single cells among the single cells 10-1 to 10-n. The total output voltage may be detected. In this case, as a representative output voltage, the average value of the output voltages of a single cell per sheet obtained by dividing the total output voltage detected by the voltage sensor V2 by the number of single cells that are the detection target of the voltage sensor V2. May be used. The representative output voltage is acquired by the control device 50 calculating as described above.

  Next, the bubble determination control of the first modification will be described. The bubble determination control of the first modification is executed based on the temperature, not the output voltage of each of the single cells 10-4 and 10- (n / 2). The control apparatus 50 acquires the temperature of these single cells by the temperature sensor which detects the temperature of the single cell 10-4, and the temperature sensor which detects the temperature of the single cell 10- (n / 2). FIG. 2A is a graph showing the temperature of each single cell when bubbles are present in the cooling water flow path of the stack 10, and corresponds to FIG. 1B. As described above, the temperature of the single cells around the bubbles rises compared to the temperature of the other single cells, but the single cells 10-1 and 10-2, 10- arranged outside the stack 10 3 is easily cooled, so the temperature of the single cell 10-4 is the highest.

  The control device 50 accurately determines the presence or absence of bubbles in the cooling water flow path of the stack 10 based on the detection results of the temperature sensors that detect the temperatures of the single cells 10-4 and 10- (n / 2). To do. Specifically, the determination is made as follows. First, the representative temperature is acquired based on the detection result of the temperature sensor that detects the temperature of the single cell 10- (n / 2). Here, the temperature of the single cell 10- (n / 2) detected by the temperature sensor is acquired as the representative temperature. Next, it is determined whether or not the difference between the detected temperature of the single cell 10-4 and the representative temperature is greater than the second threshold value. In the case of negative determination, this control is terminated on the assumption that bubbles do not exist in the cooling water flow path of the stack 10. In the case of an affirmative determination, it is determined that bubbles are present in the cooling water flow path of the stack 10.

  In the example of FIG. 2A, assuming that the difference between the temperature of the single cell 10-4 and the temperature of the single cell 10- (n / 2) is larger than the second threshold, there are bubbles in the cooling water flow path of the stack 10. It is determined that In this way, the presence or absence of bubbles in the cooling water flow path of the stack 10 can be accurately determined with a simple configuration by the two temperature sensors.

  In the first modified example, one of the two temperature sensors detects the temperature of the single cell 10- (n / 2) disposed in the center in the stacking direction, and this single temperature sensor detects the temperature. However, the temperature of the single cell may be detected at a site other than the single cell 10-4. For example, one of the two temperature sensors may detect the temperature of the single cell 10-n. Further, a temperature sensor may be arranged downstream of the stack 10 in the cooling water circulation path 21 and upstream of the radiator 24 to detect the temperature of the cooling water, and this may be used as the representative temperature.

  Next, the bubble determination control of the second modification will be described. The bubble determination control of the second modification is executed based on the impedance instead of the output voltage and temperature of each of the single cells 10-4 and 10- (n / 2). The control apparatus 50 acquires the impedance temperature of these single cells with the sensor which detects the impedance of the single cell 10-4, and the sensor which detects the impedance of the single cell 10- (n / 2). The impedance is measured by, for example, an AC impedance method. FIG. 2B is a graph showing the impedance of each single cell when bubbles are present in the cooling water flow path of the stack 10, and corresponds to FIG. 1B. As described above, the single-cell electrolyte membrane around the bubbles has a lower humidity than the other single-cell electrolyte membranes. Thereby, the impedance of the single cell around the bubble is increased as compared with the impedance of the other single cells. For the same reason as described above, the impedances of the single cell 10-1 and the single cells 10-2 and 10-3 are not increased as much as the impedance of the single cell 10-4.

  The control device 50 accurately determines the presence or absence of bubbles in the cooling water flow path of the stack 10 based on the detection results of the sensors that detect the respective impedances of the single cells 10-4 and 10- (n / 2). . Specifically, the determination is made as follows. First, the representative impedance is acquired based on the detection result of the sensor that detects the impedance of the single cell 10- (n / 2). Here, the impedance of the single cell 10- (n / 2) detected by this sensor is acquired as the representative impedance. Next, it is determined whether or not the difference between the detected impedance of the single cell 10-4 and the representative impedance is greater than a third threshold value. In the case of negative determination, this control is terminated on the assumption that bubbles do not exist in the cooling water flow path of the stack 10. In the case of an affirmative determination, it is determined that bubbles are present in the cooling water flow path of the stack 10.

  In the example of FIG. 2B, assuming that the difference between the impedance of the single cell 10-4 and the impedance of the single cell 10- (n / 2) is larger than the third threshold, there are bubbles in the cooling water flow path of the stack 10. It is determined that In this manner, the presence or absence of bubbles in the cooling water flow path of the stack 10 can be accurately determined with a simple configuration by the two sensors.

  In the second modified example, one of the two sensors detects the impedance of the single cell 10- (n / 2) arranged in the center in the stacking direction, but the single cell that this sensor detects the impedance is limited to this. Instead, the impedance of the single cell at a portion other than the single cell 10-4 may be detected. For example, one of the two sensors may detect the impedance of the single cell 10-n. Moreover, the sensor which detects the impedance in parts other than the single cell 10-4 may detect the impedance in the whole several single cell. For example, this sensor may detect the total impedance of the single cells 10-1 to 10-n, or the total impedance of a plurality of continuous single cells among the single cells 10-1 to 10-n. May be detected. In this case, as the representative impedance, an average value of the impedance of each single cell obtained by dividing the total impedance detected by this sensor by the number of single cells to be detected by this sensor may be used. . The representative impedance is acquired by the control device 50 calculating as described above.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

  In the stack 10, the stacking direction of the single cells does not necessarily coincide with the vertical direction. In the “almost along the vertical direction” in the present application, the stacking direction of the single cells is 20 degrees from the vertical direction. Including those that are inclined to the extent.

10 Fuel Cell Stack 10-1 to 10-n Single Cell 10-1 Single Cell (First Cell)
10-4 Single cell (second cell)
12 Cooling water supply manifold (cooling water flow path)
14 Cooling water discharge manifold (cooling water flow path)
20 Cooling system 50 Control device (acquisition unit and determination unit)
V1 voltage sensor (first detector)
V2 voltage sensor (second detector)

Claims (1)

A fuel cell stack in which a direction in which a plurality of single cells are stacked is arranged in a posture along a substantially vertical direction;
A coolant flow path formed in the fuel cell stack so that at least a portion penetrates the plurality of single cells;
The output voltage, temperature of the second cell in any one of the plurality of the single cells between the first cell arranged on the uppermost vertical side to the first tenth of the total number of the plurality of single cells, And a first detection unit for detecting either of the impedance,
A second detection unit for detecting any one of an output voltage, temperature, and impedance at a portion other than the second cell of the plurality of single cells;
An acquisition unit that acquires one of the representative output voltage, the representative temperature, and the representative impedance based on the detection result of the second detection unit;
A determination unit for determining the presence or absence of bubbles in the cooling water flow path of the fuel cell stack,
The determination unit
A difference between the detected output voltage of the second cell and the representative output voltage is greater than a first threshold;
A difference between the detected temperature of the second cell and the representative temperature is greater than a second threshold;
A difference between the detected impedance of the second cell and the representative impedance is greater than a third threshold;
A fuel cell system that determines that air bubbles are present in the cooling water flow path when either of the above is satisfied.

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