JP2013218923A - Fuel cell system and fuel cell system activation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a fuel cell to be activated promptly from below a freezing point while restraining temperature distribution in the fuel cell from becoming nonuniform in a fuel cell system.SOLUTION: In the fuel cell system, the CPU of a control unit controls an LLC (long life coolant) circulation pump so that when a fuel cell stack is activated from below a freezing point, a circulation flow rate of the LLC circulating in the fuel cell stack is to be equal to a first circulation flow rate F1. The first circulation flow rate F1 is set within a range in which the nonuniformity of temperature distribution in the fuel cell stack can be restrained. Thereafter, if, when a current value I flowing from the fuel cell stack drops below a first threshold current value Ith1, a state where a temporal change rate dI/dt of the current value I is equal to or higher than a first threshold value TH1 and is less than 0 continues for a first period t1 in seconds or more, the CPU controls the circulation pump so that the circulation flow rate of the LLC circulating in the fuel cell stack is to be equal to a second circulation flow rate F2 which is smaller than the first circulation flow rate F1.

Description

  The present invention relates to a fuel cell system and a starting method of the fuel cell system.

  A fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas has attracted attention as an energy source. And since the said electrochemical reaction is an exothermic reaction, in a fuel cell system provided with a fuel cell, in order to generate electric power within a suitable temperature range in a fuel cell, a cooling medium is circulated through the fuel cell. Further, at the time of starting the fuel cell system, a warm-up operation for raising the temperature of the fuel cell to a temperature suitable for power generation is also performed. In consideration of the efficiency of the fuel cell system, this warm-up operation is often performed by self-heating of the fuel cell without using an external heater or the like for raising the temperature of the fuel cell.

  Conventionally, various techniques for quickly starting a fuel cell system have been proposed (see, for example, Patent Document 1 below). For example, in the fuel cell system described in Patent Document 1 below, the fuel cell stack voltage, the fuel cell stack temperature, and the fuel cell stack current from the fuel cell are determined based on whether the displacement amount with respect to time is positive or negative, respectively. The amount of heat release, for example, the amount of cooling fluid circulated in the fuel cell is controlled.

JP 2007-265930 A JP 2010-27468 A JP 2008-300197 A

  By the way, in a fuel cell, water (product water) is generated by a cathode reaction during power generation. This generated water freezes inside the fuel cell when the fuel cell system is started in a sub-freezing environment. When the generated water freezes inside the fuel cell, the power generation area decreases, the power generation amount decreases, and furthermore, power generation may not be possible.

  However, in the technique described in Patent Document 1, for example, since the power generation state of the fuel cell is determined based on the amount of displacement of the fuel cell stack current with respect to time, the change in the power generation state of the fuel cell is grasped in detail. I couldn't. That is, it has not been possible to grasp whether the power generation state of the fuel cell is changing rapidly or slowly. For this reason, with the technique described in the above-mentioned Patent Document 1, it is not possible to perform start-up control in accordance with the power generation state of the fuel cell. In the technique described in Patent Document 1, when the amount of displacement of the fuel cell stack voltage with respect to time is positive and the amount of displacement of the fuel cell stack temperature with respect to time is negative, the amount of heat released from the fuel cell is reduced. Although control to decrease is performed, such control cannot be applied when the fuel cell system is started from below freezing point.

  In addition, when the fuel cell system is started from below freezing point, the start-up control that reduces the circulation flow rate of the cooling medium circulated to the fuel cell or stops the circulation of the cooling medium in order to quickly raise the temperature of the fuel cell. If the power generation state of the fuel cell is not grasped in detail, the temperature distribution in the fuel cell may not be overlooked. If the generated water freezes inside the fuel cell and power is generated only locally, the temperature of the fuel cell rises locally, causing local deterioration of the electrolyte membrane included in the fuel cell. Invite. In addition, in a fuel cell stack in which a plurality of fuel cells are stacked, the temperature distribution in the stacking direction of the fuel cells becomes non-uniform due to the difference in the amount of heat released from each fuel cell, which causes deformation of the fuel cell stack. Invite.

  The present invention has been made to solve the above-described problems, and has an object to quickly start a fuel cell from below the freezing point while suppressing uneven temperature distribution in the fuel cell in the fuel cell system. And

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A fuel cell system,
A fuel cell;
A current value measuring unit for periodically measuring the current value of the current flowing from the fuel cell;
A cooling medium circulating section for circulating a cooling medium for cooling the fuel cell to the fuel cell;
A control unit,
The controller is configured to start the fuel cell from below freezing point.
Controlling the cooling medium circulating unit so that the circulating flow rate of the cooling medium circulating through the fuel cell becomes the first circulating flow rate;
Thereafter, when the current value becomes equal to or lower than the first threshold current value, and the state in which the time change rate of the current value is equal to or higher than the first threshold and lower than 0 continues for the first period. In addition, the cooling medium circulation unit is controlled so that the circulation flow rate becomes a second circulation flow rate that is smaller than the first circulation flow rate.
Fuel cell system.

  In the fuel cell system of Application Example 1, the control unit performs power generation by the fuel cell when starting the fuel cell from below the freezing point, so that the circulation flow rate of the cooling medium circulating through the fuel cell becomes the first circulation flow rate. The cooling medium circulation unit is controlled. The first circulation flow rate is set within a range in which uneven temperature distribution in the fuel cell can be suppressed. Immediately after the start of the fuel cell from below freezing point, the power generation state of the fuel cell deteriorates due to freezing of the generated water inside the fuel cell, and the current value of the current flowing from the fuel cell rapidly decreases and gradually decreases. To drop. Therefore, the control unit controls the coolant circulation unit based on the current value of the current flowing from the fuel cell and the time rate of change of the current value. Specifically, the control unit is a case where the power generation state of the fuel cell deteriorates and the current value of the current flowing from the fuel cell becomes equal to or less than the first threshold current value, and the time rate of change of the current value is When the state that is equal to or more than the first threshold and less than 0, that is, the state in which the current value decreases relatively slowly continues for the first period, the circulating flow rate of the cooling medium circulating through the fuel cell is the first. The cooling medium circulation unit is controlled so that the second circulation flow rate is smaller than the circulation flow rate. By reducing the circulating flow rate of the cooling medium circulating through the fuel cell to the second circulating flow rate, the amount of heat removed from the fuel cell by the cooling medium is reduced, and the temperature rise of the fuel cell by self-heating is promoted. . Then, the power generation state of the fuel cell is restored, and the current flowing from the fuel cell increases.

  Note that the first threshold current value is a value within a range where the current value of the current flowing from the fuel cell decreases relatively slowly, and is set to a value higher than the allowable lower limit value. The first threshold current value is expected to recover the power generation state of the fuel cell without reducing the circulating flow rate of the cooling medium circulated in the fuel cell, but the state below the first threshold current value is long. When the time continues, a value estimated to be further deteriorated is set without recovering the power generation state of the fuel cell. The first threshold current value, the first threshold value for the time rate of change of the current value, and the first period are, for example, the design of the fuel cell, the power generation conditions at the start of the fuel cell from below freezing point, The cooling medium circulation unit (for example, a circulation pump or a circulation pipe) can be appropriately changed according to the design. Further, the second circulating flow rate can also be set arbitrarily. The second circulation flow rate is set to 50 (%) of the first circulation flow rate, for example.

  When the current value of the current flowing from the fuel cell becomes equal to or lower than the first threshold current value, immediately, if the circulation flow rate of the cooling medium is reduced to the second circulation flow rate and the temperature rise of the fuel cell is promoted, Even if the flow rate is not reduced to the second circulation flow rate, there is a possibility that the temperature distribution in the fuel cell may become non-uniform even though there is a possibility that the power generation state of the fuel cell is recovered due to self-heating. On the other hand, in the fuel cell system of Application Example 1, the current value of the current flowing from the fuel cell is equal to or lower than the first threshold current value, and further, the time change rate of the current value is the first threshold value. As described above, when the state of less than 0, that is, the state in which the current value decreases relatively slowly continues for the first period, the circulating flow rate of the cooling medium is reduced to the second circulating flow rate. Even when the current value of the current flowing from the fuel cell becomes equal to or less than the first threshold current value, for example, when the rate of change of the current value with time is 0 or more, the power generation state of the fuel cell is It is determined that recovery is taking place and the circulating flow rate of the cooling medium is not reduced. By doing so, it is possible to suppress uneven temperature distribution in the fuel cell while waiting for recovery of the power generation state of the fuel cell due to self-heating.

  In the fuel cell system of Application Example 1, the power generation state of the fuel cell is grasped in detail based on the current value of the current flowing from the fuel cell and the time change rate of the current value, and in accordance with the power generation state of the fuel cell. The cooling medium circulation unit can be controlled. In addition, it is possible to quickly start the fuel cell from below the freezing point while suppressing uneven temperature distribution in the fuel cell.

[Application Example 2]
A fuel cell system according to Application Example 1,
The controller is configured to start the fuel cell from below freezing point.
After controlling the cooling medium circulation unit so that the circulation flow rate becomes the first circulation flow rate,
When the current value becomes equal to or less than a second threshold current value smaller than the first threshold current value, the cooling medium circulation unit is controlled so that the circulation flow rate becomes the second circulation flow rate. ,
Fuel cell system.

  In the fuel cell system of Application Example 2, the current value of the current flowing from the fuel cell is maintained in a state in which the time change rate of the current value is not less than the first threshold and less than 0 without continuing for the first period. Even when the value is equal to or less than the threshold current value of 2, the circulating flow rate of the cooling medium is reduced to the second circulating flow rate. The second threshold current value is also a value within a range in which the current value of the current flowing from the fuel cell decreases relatively slowly, similarly to the first threshold current value, and is higher than the allowable lower limit value. Value is set. The second threshold current value is not expected to recover the power generation state of the fuel cell by self-heating even if the power generation is continued with the circulating flow rate of the cooling medium kept at the first circulating flow rate. Is reduced to the second circulating flow rate, so that the power generation state of the fuel cell by self-heating can be restored within a sufficiently possible range. The second threshold current value also depends on, for example, the design of the fuel cell, the power generation conditions when starting from below the freezing point of the fuel cell, the design of the cooling medium circulation unit (for example, a circulation pump or a circulation pipe), and the like. It can be changed as appropriate. The fuel cell system according to Application Example 2 avoids that the power generation state of the fuel cell deteriorates when the fuel cell is started from below freezing point, and the current flowing from the fuel cell is excessively reduced, so that the fuel cell cannot generate power. Can do.

[Application Example 3]
A fuel cell system according to Application Example 1 or 2,
The controller is configured to start the fuel cell from below freezing point.
After controlling the cooling medium circulation unit so that the circulation flow rate becomes the second circulation flow rate,
The current value is equal to or greater than a third threshold current value that is greater than the first threshold current value, and the time change rate of the current value is greater than 0 and less than or equal to the second threshold value. When the state continues for a second period, the cooling medium circulation unit is controlled so that the circulation flow rate is higher than the second circulation flow rate.
Fuel cell system.

  When the circulating flow rate of the cooling medium circulating through the fuel cell is reduced from the first circulating flow rate to the second circulating flow rate when the fuel cell is started from below the freezing point, the amount of heat removed from the fuel cell by the cooling medium is reduced. The power generation state of the fuel cell is restored by self-heating. However, at this time, there is a possibility that the temperature distribution of the fuel cell becomes non-uniform due to the reduction of the circulating flow rate of the cooling medium. When the circulation flow rate of the cooling medium is reduced and power generation is continued for a long time while the temperature distribution of the fuel cell is not uniform, the temperature of the fuel cell rises excessively locally, and the electrolyte membrane included in the fuel cell becomes There is a risk of local degradation. Immediately after the circulating flow rate of the cooling medium is reduced, the power generation state of the fuel cell is restored, and the current value of the current flowing from the fuel cell increases rapidly and gradually increases.

  In the fuel cell system of Application Example 3, when the current value of the current flowing from the fuel cell is equal to or greater than the third threshold current value, the time rate of change of the current value is greater than 0, and the second When the state below the threshold value, that is, the state where the current value increases relatively slowly continues for the second period, the circulating flow rate of the cooling medium circulating in the fuel cell is increased. For example, the circulating flow rate of the cooling medium is increased to the first circulating flow rate. The third threshold current value is a value within a range in which the current value of the current flowing from the fuel cell increases relatively slowly, and is set to a value lower than the allowable upper limit value. In addition, the third threshold current value, the second threshold value for the time rate of change of the current value, and the second period are, for example, the design of the fuel cell, the power generation conditions at the start-up from below the freezing point of the fuel cell, The cooling medium circulation unit (for example, a circulation pump or a circulation pipe) can be appropriately changed according to the design. With the fuel cell system according to Application Example 3, it is possible to suppress local overheating due to uneven temperature distribution of the fuel cell and to suppress local deterioration of the electrolyte membrane included in the fuel cell.

[Application Example 4]
A fuel cell system according to Application Example 3,
The controller is configured to start the fuel cell from below freezing point.
After controlling the cooling medium circulation unit so that the circulation flow rate becomes the second circulation flow rate,
When the current value is equal to or greater than a fourth threshold current value that is greater than the third threshold current value, the cooling medium circulation unit is arranged so that the circulation flow rate is greater than the second circulation flow rate. Control,
Fuel cell system.

  In the fuel cell system of Application Example 4, the circulating flow rate of the cooling medium circulating through the fuel cell is reduced from the first circulating flow rate to the second circulating flow rate, and the current value of the current flowing from the fuel cell is the current value time. When the rate of change is greater than 0 and less than or equal to the second threshold, the circulating flow rate of the cooling medium is increased when the state exceeds the fourth threshold current value without continuing for the second period. Note that the fourth threshold current value is a value within a range in which the current value of the current flowing from the fuel cell increases relatively slowly, similarly to the third threshold current value, and is lower than the allowable upper limit value. Value is set. Further, the fourth threshold current value is set within a range in which the local overheating of the fuel cell can be sufficiently suppressed by increasing the circulating flow rate of the cooling medium. The fourth threshold current value also depends on, for example, the design of the fuel cell, the power generation conditions when starting from below the freezing point of the fuel cell, the design of the cooling medium circulation unit (for example, a circulation pump or a circulation pipe), and the like. It can be changed as appropriate. The fuel cell system according to Application Example 4 can more reliably suppress local overheating due to non-uniform temperature distribution of the fuel cell and more reliably suppress local deterioration of the electrolyte membrane included in the fuel cell. it can.

[Application Example 5]
The fuel cell system according to any one of Application Examples 1 to 4, further comprising:
A temperature sensor for measuring the temperature of the cooling medium at the inlet of the cooling medium flowing into the fuel cell;
The control unit stops the control of the cooling medium circulation unit that is executed when the fuel cell is started from below freezing point when the temperature of the cooling medium at the inlet of the cooling medium becomes 0 (° C.) or more. ,
Fuel cell system.

  Even when the temperature of the fuel cell becomes higher than 0 (° C.) by the above-described control at the time of starting the fuel cell from below the freezing point, the temperature of the cooling medium at the inlet of the cooling medium flowing into the fuel cell is 0 (° C.) or less. In such a case, there is a possibility that freezing of generated water inside the fuel cell may not be eliminated due to the removal of heat by the cooling medium. In the fuel cell system of the application example 5, the cooling medium circulating through the fuel cell is heated by the fuel cell, not when the temperature of the fuel cell becomes higher than 0 (° C.). When the temperature of the cooling medium at the inlet becomes higher than 0 (° C.), the above-described control executed when the fuel cell is started from below the freezing point is stopped. By doing so, it is possible to reduce the amount of heat taken away by the cooling medium and to eliminate the freezing of the generated water inside the fuel cell. In addition, after stopping the control executed at the time of starting the fuel cell from below the freezing point, the control executed when the temperature of the fuel cell is higher than 0 (° C.) may be appropriately performed.

  The present invention can be configured as an invention of a method for starting a fuel cell system in addition to the above-described configuration as a fuel cell system. Further, the present invention can be realized in various modes such as a computer program that realizes these, a recording medium that records the program, and a data signal that includes the program and is embodied in a carrier wave. In addition, in each aspect, it is possible to apply the various additional elements shown above.

  When the present invention is configured as a computer program or a recording medium storing the program, the entire program for controlling the operation of the fuel cell system may be configured, or only the portion that performs the function of the present invention is configured. It is good also as what to do. The recording medium includes a flexible disk, a CD-ROM, a DVD-ROM, a magneto-optical disk, an IC card, a ROM cartridge, a punch card, a printed matter on which a code such as a barcode is printed, a computer internal storage device (RAM or Various types of computer-readable media such as a memory such as a ROM and an external storage device can be used.

It is explanatory drawing which shows schematic structure of the fuel cell system 1000 as one Example of this invention. It is a flowchart which shows the flow of a starting control process.

Hereinafter, embodiments of the present invention will be described based on examples.
A. Configuration of fuel cell system:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell system 1000 as an embodiment of the present invention.

  The fuel cell stack 100 has a stack structure in which a plurality of fuel cell cells 40 that generate power by an electrochemical reaction between hydrogen and oxygen are stacked. Each fuel cell 40 generally has a structure in which a membrane electrode assembly formed by bonding an anode and a cathode is sandwiched between separators on both sides of an electrolyte membrane having proton conductivity. In this example, a solid polymer membrane was used as the electrolyte membrane. Each separator is provided with a flow path of hydrogen as a fuel gas to be supplied to the anode, a flow path of air containing oxygen as an oxidant gas to be supplied to the cathode, and a flow path of a cooling medium. Yes. The number of stacked fuel cells 40 can be arbitrarily set according to the output required for the fuel cell stack 100. Further, the fuel cell stack 100 is provided with a temperature sensor 42 for detecting the temperature of the fuel cell stack 100.

  The fuel cell stack 100 is formed by stacking the end plate 10a, the insulating plate 20a, the current collecting plate 30a, the plurality of fuel battery cells 40, the current collecting plate 30b, the insulating plate 20b, and the end plate 10b in this order from one end. It is configured. A supply manifold (hydrogen supply manifold, air supply manifold, cooling medium supply manifold) for distributing and supplying hydrogen, air, and a cooling medium to the fuel cell 40 is provided inside the fuel cell stack 100. The anode off-gas and cathode off-gas discharged from the anode and cathode of each fuel cell 40 and the exhaust manifold (anode off-gas exhaust manifold, cathode Off-gas discharge manifold, cooling medium discharge manifold) are formed.

  The end plates 10a and 10b are made of metal such as steel in order to ensure rigidity. The insulating plates 20a and 20b are formed of an insulating member such as rubber or resin. The current collector plates 30a and 30b are formed of dense carbon, a gas-impermeable conductive member such as a copper plate. The current collector plates 30a and 30b are each provided with an output terminal (not shown) so that the power generated by the fuel cell stack 100 can be output. A load 80 is connected to each output terminal. A current sensor 82 for detecting the current value of the current flowing from the fuel cell stack 100 is provided between the fuel cell stack 100 and the load 80.

  In addition, although illustration is abbreviate | omitted, in order for the fuel cell stack 100 to suppress the fall of the cell performance by the increase in the contact resistance in any part of a stack structure, or to suppress the leakage of gas, It is fastened by a fastening member with a fastening load applied in the stacking direction of the stack structure.

  Hydrogen as fuel gas is supplied to the anode of the fuel cell stack 100 from a hydrogen tank 50 that stores high-pressure hydrogen via a pipe 53. Instead of the hydrogen tank 50, a hydrogen-rich gas may be generated by a reforming reaction using alcohol, hydrocarbon, aldehyde or the like as a raw material, and supplied to the anode.

  The pressure and supply amount of the high-pressure hydrogen stored in the hydrogen tank 50 are adjusted by a shut valve 51 and a regulator 52 provided at the outlet of the hydrogen tank 50, and the fuel cell 40 of each fuel cell 40 is passed through the hydrogen supply manifold. Supplied to the anode. The anode off gas discharged from each fuel cell 40 can be discharged to the outside of the fuel cell stack 100 via a discharge pipe 56 connected to the anode off gas discharge manifold. Note that when the anode off gas is discharged to the outside of the fuel cell stack 100, hydrogen contained in the anode off gas is processed by a diluter or the like (not shown).

  Further, a circulation pipe 54 for recirculating the anode off gas to the pipe 53 is connected to the pipe 53 and the discharge pipe 56. An exhaust valve 57 is disposed on the downstream side of the connection portion between the discharge pipe 56 and the circulation pipe 54. The circulation pipe 54 is provided with a pump 55. By controlling the driving of the pump 55 and the exhaust valve 57, it is possible to appropriately switch whether the anode off gas is discharged to the outside or circulated through the pipe 53. By recirculating the anode off gas to the pipe 53, unconsumed hydrogen contained in the anode off gas can be efficiently used.

  Compressed air compressed by an air compressor 60 disposed in the pipe 61 is supplied to the cathode of the fuel cell stack 100 as an oxidant gas containing oxygen. The compressed air is supplied to the cathode of each fuel cell 40 via an air supply manifold connected to the pipe 61. Cathode off gas discharged from the cathode of each fuel cell 40 is discharged to the outside of the fuel cell stack 100 via a discharge pipe 62 connected to the cathode off gas discharge manifold. From the discharge pipe 62, the produced water generated by the electrochemical reaction between hydrogen and oxygen at the cathode of the fuel cell stack 100 is also discharged together with the cathode off gas.

  Since the fuel cell stack 100 generates heat by the above-described electrochemical reaction, the fuel cell stack 100 is also supplied with a cooling medium for cooling the fuel cell stack 100. In this embodiment, a long life coolant (LLC) that is an antifreeze liquid is used as the cooling medium. The LLC cooled by the radiator 71 is supplied to the cooling medium supply manifold of the fuel cell stack 100 through the piping 72 by the circulation pump 70 disposed in the piping 72. The LLC discharged from the fuel cell stack 100 circulates to the radiator 71 via a pipe 72 connected to the cooling medium discharge manifold. By controlling the output (rotation speed) of the circulation pump 70, the circulation flow rate of the LLC can be controlled. At this time, a flow meter that measures the circulating flow rate of LLC may be provided in the pipe 72, and the output of the circulation pump 70 may be controlled based on the detected value of the flow meter. A temperature sensor 73 for detecting the temperature of the LLC flowing into the fuel cell stack 100 is disposed at the inlet of the LLC to the fuel cell stack 100 in the pipe 72. Circulation pump 70, radiator 71, and pipe 72 correspond to the coolant circulation section in [Means for Solving the Problems].

  The operation of the fuel cell system 1000 is controlled by the control unit 90. The control unit 90 is configured as a microcomputer including a CPU, RAM, ROM, timer, and the like, and controls the operation of the system, such as driving various valves and pumps, according to a program stored in the ROM. . In addition, the control unit 90 executes activation control processing described below. The control unit 90 corresponds to the control unit in [Means for Solving the Problems].

B. Startup control processing:
FIG. 2 is a flowchart showing the flow of activation control processing. This process is a process executed by the CPU of the control unit 90 in order to raise the temperature Tfc of the fuel cell stack 100 to a temperature suitable for power generation when the fuel cell system 1000 is activated.

  First, the CPU acquires the temperature Tfc of the fuel cell stack 100 detected by the temperature sensor 42, and determines whether or not the temperature Tfc of the fuel cell stack 100 is higher than 0 (° C.) (step S100). When the temperature Tfc of the fuel cell stack 100 is higher than 0 (° C.) (step S100: YES), the CPU executes normal temperature activation control (step S110). Note that various types of conventionally known startup controls can be applied to the room temperature startup control, and description of the room temperature startup control is omitted in this specification.

  In step S100, when the temperature Tfc of the fuel cell stack 100 is 0 (° C.) or less (step S100: NO), the CPU starts below-freezing start control (step S120). In the present embodiment, hydrogen and air are introduced into the fuel cell stack 100, the open circuit voltage of the fuel cell stack 100 is checked, the circulation pump 70 is activated, and voltage control for below-freezing activation control is started. At this time, the CPU controls the output of the circulation pump 70 so that the circulation flow rate of the LLC circulating through the fuel cell stack 100 becomes the first circulation flow rate F1. The first circulation flow rate F1 is set within a range in which uneven temperature distribution in the fuel cell stack 100 can be suppressed. Immediately after the start of the below-freezing start control, the power generation state of the fuel cell stack 100 deteriorates due to the freezing of the generated water inside the fuel cell, and the current value of the current flowing from the fuel cell stack 100 rapidly decreases, Gradually decreases. Therefore, in the fuel cell system 1000 of the present embodiment, the following control is performed.

  After starting the below-freezing start control, the CPU periodically measures the current value I of the current flowing from the fuel cell stack 100 with the current sensor 82, and whether the current value I has become equal to or less than the first threshold current value Ith1. It is determined whether or not (step S130). When the current value I is larger than the first threshold current value Ith1 (step S130: NO), the CPU has the LLC temperature Tin at the inlet of the LLC flowing into the fuel cell stack 100 higher than 0 (° C.). Whether or not (step S132). When the temperature Tin is higher than 0 (° C.) (step S132: YES), the below-freezing start control is terminated and the normal temperature start control is executed (step S110). On the other hand, when the temperature Tin is 0 (° C.) or less (step S132: NO), the CPU returns the process to step S130.

  In step S130, when the current value I is equal to or less than the first threshold current value Ith1 (step S130: YES), the CPU has a time change rate dI / dt of the current value I equal to or greater than the first threshold value TH1. Then, it is determined whether or not the state of less than 0 continues for the first period t1 seconds or more (step S140). When the time rate dI / dt of the current value I is not less than the first threshold value TH1 and less than 0 continues for the first period t1 seconds or more (step S140: YES), the CPU The output of 70 is reduced, and the circulation flow rate of the LLC circulated in the fuel cell stack 100 is reduced to a second circulation flow rate F2 that is smaller than the first circulation flow rate F1 (step S150). By reducing the circulation flow rate of the LLC circulated through the fuel cell stack 100, the amount of heat removed from the fuel cell stack 100 by the LLC is reduced, and the temperature rise of the fuel cell stack 100 by self-heating is promoted. Then, the power generation state of the fuel cell stack 100 is recovered, and the current flowing from the fuel cell stack 100 increases.

  The first threshold current value Ith1 is a value within a range where the current value I of the current flowing from the fuel cell stack 100 decreases relatively slowly, and is set to a value higher than the allowable lower limit value. Further, although the first threshold current value Ith1 is expected to recover the power generation state of the fuel cell stack 100 without reducing the circulating flow rate of the LLC circulated in the fuel cell stack 100, the first threshold current value Ith1 When the following state continues for a long time, a value estimated to be further deteriorated is set without recovering the power generation state of the fuel cell stack 100. The first threshold current value Ith1, the first threshold value TH1 for the time rate of change dI / dt of the current value I, and the first period t1 seconds are, for example, the design of the fuel cell stack 100, the fuel cell The power generation condition at the time of starting the stack 100 from below the freezing point, the design of the circulation pump 70, the piping 72, and the like can be changed as appropriate. Further, the second circulating flow rate F2 can also be set arbitrarily. The second circulation flow rate F2 is set to 50 (%) of the first circulation flow rate F1, for example.

  When the current value I of the current flowing from the fuel cell stack 100 becomes equal to or less than the first threshold current value Ith1, the LLC circulation flow rate is immediately reduced to the second circulation flow rate F2 to raise the temperature of the fuel cell stack 100. In the fuel cell stack 100, the power generation state of the fuel cell stack 100 may be immediately recovered by self-heating without reducing to the second circulation flow rate F2. There is a risk of uneven temperature distribution. On the other hand, in the fuel cell system 1000 of the present embodiment, the current value I of the current flowing from the fuel cell stack 100 is less than or equal to the first threshold current value Ith1, and further, the current value I changes with time. When the rate is equal to or higher than the first threshold value TH1 and less than 0, that is, when the current value I decreases relatively slowly for the first period t1 seconds, the circulation flow rate of the LLC is set to the second flow rate. Reduce to circulation flow rate F2. Even when the current value I of the current flowing from the fuel cell stack 100 becomes equal to or less than the first threshold current value Ith1, for example, when the time change rate dI / dt of the current value I is equal to or greater than 0. Determines that the power generation state of the fuel cell stack 100 is recovering and does not reduce the circulating flow rate of the LLC. By doing so, it is possible to suppress uneven temperature distribution in the fuel cell stack 100 while waiting for the recovery of the power generation state of the fuel cell stack 100 due to self-heating.

  In step S140, when the time change rate dI / dt of the current value I is not less than the first threshold TH1 and smaller than 0 does not continue for the first period t1 seconds or more (step S140: NO). The CPU determines whether or not the current value I has become equal to or smaller than a second threshold current value Ith2 that is smaller than the first threshold current value Ith1 (step S142). When the current value I is larger than the second threshold current value Ith2 (step SS142: NO), the CPU returns the process to step S140. On the other hand, when the current value I becomes equal to or smaller than the second threshold current value Ith2 (step S142: YES), the CPU reduces the output of the circulation pump 70 and circulates the LLC to the fuel cell stack 100. The flow rate is reduced to the second circulation flow rate F2 (step S150). By doing so, it is possible to avoid that the power generation state of the fuel cell stack 100 is deteriorated, the current flowing from the fuel cell stack 100 is excessively reduced, and the fuel cell stack 100 cannot be generated.

  Note that the second threshold current value Ith2 is also a value within the range in which the current value I of the current flowing from the fuel cell stack 100 decreases relatively slowly, similarly to the first threshold current value Ith1. A value higher than the lower limit value is set. Further, the second threshold current value Ith2 is not expected to recover the power generation state of the fuel cell stack 100 due to self-heating even if power generation is continued with the LLC circulation flow rate being the first circulation flow rate F1. By reducing the circulating flow rate to the second circulating flow rate F2, the fuel cell stack 100 is set within a range where the power generation state of the fuel cell stack 100 can be sufficiently recovered by self-heating. The second threshold current value Ith2 is also determined according to, for example, the design of the fuel cell stack 100, the power generation conditions at the start of the fuel cell stack 100 from below the freezing point, the design of the circulation pump 70, the piping 72, and the like. It can be changed as appropriate.

  Here, when the circulation flow rate of the LLC circulating through the fuel cell stack 100 is reduced from the first circulation flow rate F1 to the second circulation flow rate F2, the amount of heat carried away from the fuel cell stack 100 by the LLC is reduced, and the self The power generation state of the fuel cell stack 100 is recovered by the heat generation. However, at this time, there is a possibility that the temperature distribution of the fuel cell stack 100 is non-uniform due to the reduction of the LLC circulation flow rate. When power generation is continued for a long time while the circulation flow rate of the LLC is reduced and the temperature distribution of the fuel cell stack 100 is not uniform, the temperature of the fuel cell stack 100 locally increases excessively, and the fuel cell stack 100 There is a possibility that the electrolyte membrane included in the is locally degraded. Immediately after reducing the circulating flow rate of the LLC, the power generation state of the fuel cell stack 100 is recovered, and the current value I of the current flowing from the fuel cell stack 100 increases rapidly and gradually increases gradually. Therefore, in the fuel cell system 1000 of the present embodiment, in step S150, after the circulation flow rate of the LLC circulating through the fuel cell stack 100 is reduced from the first circulation flow rate F1 to the second circulation flow rate F2, the following control is performed. Do.

  After step S150, the CPU periodically measures the current value I of the current flowing from the fuel cell stack 100 by the current sensor 82, and the current value I is larger than the first threshold current value Ith1, and the third threshold value. It is determined whether or not the current value is greater than or equal to Ith3 (step S160). When the current value I is smaller than the third threshold current value Ith3 (step S160: NO), the CPU has the LLC temperature Tin at the inlet of the LLC flowing into the fuel cell stack 100 higher than 0 (° C.). Whether or not (step S162). When the temperature Tin is higher than 0 (° C.) (step S162: YES), the below-freezing start control is terminated and the normal temperature start control is executed (step S110). On the other hand, when the temperature Tin is 0 (° C.) or less (step S162: NO), the CPU returns the process to step S160.

  In step S160, when the current value I is equal to or greater than the third threshold current value Ith3 (step S160: YES), the CPU has a time rate of change dI / dt of the current value I greater than 0, and It is determined whether or not the state of 2 or less of the threshold value TH2 has continued for the second period t2 seconds or more (step S170). A state in which the time change rate dI / dt of the current value I is greater than 0 and less than or equal to the second threshold value TH2, that is, a state in which the current value I increases relatively slowly continues for the second period t2 seconds or more. If so (step S170: YES), the CPU increases the output of the circulation pump 70 to increase the circulation flow rate of the LLC circulated in the fuel cell stack 100 (step S180). For example, the circulating flow rate of LLC is increased to the first circulating flow rate F1. By doing so, it is possible to suppress local overheating due to uneven temperature distribution of the fuel cell stack 100 and to suppress local deterioration of the electrolyte membrane provided in the fuel cell stack 100.

  The third threshold current value Ith3 is a value within a range where the current value I of the current flowing from the fuel cell stack 100 increases relatively slowly, and is set to a value lower than the allowable upper limit value. The third threshold current value Ith3, the second threshold value TH2 for the time rate of change dI / dt of the current value I, and the second period T2 seconds are, for example, the design of the fuel cell stack 100, the fuel cell The power generation condition at the time of starting the stack 100 from below the freezing point, the design of the circulation pump 70, the piping 72, and the like can be changed as appropriate.

  In step S170, when the time change rate dI / dt of the current value I is larger than 0 and not more than the second threshold value TH2, the state does not continue for the second period t2 seconds or more (step S170: NO), the CPU determines whether or not the current value I is equal to or greater than a fourth threshold current value Ith4 that is larger than the third threshold current value Ith3 (step S172). When the current value I is less than the fourth threshold current value Ith4 (step SS172: NO), the CPU returns the process to step S170. On the other hand, when the current value I becomes equal to or greater than the fourth threshold current value Ith4 (step S172: YES), the CPU increases the output of the circulation pump 70 and circulates the LLC to the fuel cell stack 100. The flow rate is increased (step S180). By doing so, it is possible to more reliably suppress local overheating due to uneven temperature distribution of the fuel cell, and more reliably suppress local deterioration of the electrolyte membrane included in the fuel cell.

  Note that the fourth threshold current value Ith4 is a value within the range in which the current value I of the current flowing from the fuel cell stack 100 increases relatively slowly, similar to the third threshold current value Ith3, and is acceptable. A value lower than the upper limit value is set. The fourth threshold current value Ith4 is also determined according to, for example, the design of the fuel cell stack 100, the power generation conditions at the start of the fuel cell stack 100 from below the freezing point, the design of the circulation pump 70, the piping 72, and the like. It can be changed as appropriate.

  In step S180, after increasing the circulation amount of LLC circulating in the fuel cell stack 100, the CPU returns the process to step S130.

  In the fuel cell system 1000 of the present embodiment described above, the current value I of the current flowing from the fuel cell stack 100 and the time change rate dI / dt of the current value I when the fuel cell stack 100 is started from below freezing point. Thus, the power generation state of the fuel cell stack 100 can be grasped in detail, and the circulation pump 70 (cooling medium circulation unit) can be controlled in accordance with the power generation state of the fuel cell stack 100. Then, it is possible to quickly start the fuel cell stack 100 from below the freezing point while suppressing uneven temperature distribution in the fuel cell stack 100.

C. Variations:
Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and can be implemented in various modes without departing from the scope of the present invention. For example, the following modifications are possible.

C1. Modification 1:
In the above embodiment, the state in which the time change rate dI / dt of the current value I is greater than or equal to the first threshold value TH1 and smaller than 0 in step S140 in the activation control process shown in FIG. 2 is the first period t1 seconds. When not continuing, the CPU performs the process of step S142, but this may be omitted.

C2. Modification 2:
In the above embodiment, the state in which the time change rate dI / dt of the current value I is larger than 0 and equal to or smaller than the second threshold value TH2 in step S170 in the start-up control process shown in FIG. When the CPU does not continue for t2 seconds or more, the CPU performs the process of step S172, but this may be omitted.

C3. Modification 3:
In the above embodiment, when the current value I is larger than the first threshold current value Ith1 in step S130 in the activation control process shown in FIG. 2, and in step S160, the current value I is the third threshold current value. When it is smaller than Ith3, the CPU determines whether or not the LLC temperature Tin at the inlet of the LLC flowing into the fuel cell stack 100 is higher than 0 (° C.). Not limited. In step S120, the CPU determines whether or not the temperature Tin of the LLC at the inlet of the LLC flowing into the fuel cell stack 100 is higher than 0 (° C.) after starting the below-freezing start control in step S120. When the temperature Tin is higher than 0 (° C.), the below-freezing start control may be terminated and the normal temperature start control may be executed.

C4. Modification 4:
In the above embodiment, when the LLC temperature Tin at the inlet of the LLC flowing into the fuel cell stack 100 is higher than 0 (° C.), the below-freezing start control is terminated and the normal temperature start control is executed. The present invention is not limited to this. For example, when the temperature Tfc of the fuel cell stack 100 reaches a temperature at which it is considered that the flooding or freezing of the generated water inside the fuel cell stack 100 can be eliminated, the below-freezing start control is terminated and the normal temperature start is performed. You may make it perform control.

C5. Modification 5:
In the above embodiment, the CPU performs the processes of steps S160, S162, S170, and S172 after step S150 in the activation control process shown in FIG. 2, but the present invention is not limited to this. Instead of performing the processes of steps S160, S162, S170, and S172 after step S150, for example, the CPU performs the process after a period during which the power generation state of the fuel cell stack 100 is expected to recover due to self-heating has elapsed. You may make it advance to S180.

DESCRIPTION OF SYMBOLS 1000 ... Fuel cell system 100 ... Fuel cell stack 10a, 10b ... End plate 20a, 20b ... Insulating plate 30a, 30b ... Current collecting plate 40 ... Fuel cell 42 ... Temperature sensor 50 ... Hydrogen tank 51 ... Shut valve 52 ... Regulator 53 ... Piping 54 ... Circulating pipe 55 ... Pump 56 ... Draining pipe 57 ... Exhaust valve 60 ... Air compressor 61 ... Piping 62 ... Draining pipe 70 ... Circulating pump 71 ... Radiator 72 ... Piping 73 ... Temperature sensor 80 ... Load 82 ... Current sensor 90 …Controller unit

Claims (6)

A fuel cell system,
A fuel cell;
A current value measuring unit for periodically measuring the current value of the current flowing from the fuel cell;
A cooling medium circulating section for circulating a cooling medium for cooling the fuel cell to the fuel cell;
A control unit,
The controller is configured to start the fuel cell from below freezing point.
Controlling the cooling medium circulating unit so that the circulating flow rate of the cooling medium circulating through the fuel cell becomes the first circulating flow rate;
Thereafter, when the current value becomes equal to or lower than the first threshold current value, and the state in which the time change rate of the current value is equal to or higher than the first threshold and lower than 0 continues for the first period. In addition, the cooling medium circulation unit is controlled so that the circulation flow rate becomes a second circulation flow rate that is smaller than the first circulation flow rate.
Fuel cell system. The fuel cell system according to claim 1, wherein
The controller is configured to start the fuel cell from below freezing point.
After controlling the cooling medium circulation unit so that the circulation flow rate becomes the first circulation flow rate,
When the current value becomes equal to or less than a second threshold current value smaller than the first threshold current value, the cooling medium circulation unit is controlled so that the circulation flow rate becomes the second circulation flow rate. ,
Fuel cell system. The fuel cell system according to claim 1 or 2, wherein
The controller is configured to start the fuel cell from below freezing point.
After controlling the cooling medium circulation unit so that the circulation flow rate becomes the second circulation flow rate,
The current value is equal to or greater than a third threshold current value that is greater than the first threshold current value, and the time change rate of the current value is greater than 0 and less than or equal to the second threshold value. When the state continues for a second period, the cooling medium circulation unit is controlled so that the circulation flow rate is higher than the second circulation flow rate.
Fuel cell system. The fuel cell system according to claim 3, wherein
The controller is configured to start the fuel cell from below freezing point.
After controlling the cooling medium circulation unit so that the circulation flow rate becomes the second circulation flow rate,
When the current value is equal to or greater than a fourth threshold current value that is greater than the third threshold current value, the cooling medium circulation unit is arranged so that the circulation flow rate is greater than the second circulation flow rate. Control,
Fuel cell system. The fuel cell system according to any one of claims 1 to 4, further comprising:
A temperature sensor for measuring the temperature of the cooling medium at the inlet of the cooling medium flowing into the fuel cell;
The control unit stops the control of the cooling medium circulation unit that is executed when the fuel cell is started from below freezing point when the temperature of the cooling medium at the inlet of the cooling medium becomes 0 (° C.) or more. ,
Fuel cell system. A method for starting a fuel cell system, comprising:
The fuel cell system includes:
A fuel cell;
A cooling medium circulating part for circulating a cooling medium for cooling the fuel cell to the fuel cell;
The fuel cell system activation method includes:
When starting the fuel cell from below freezing point,
Controlling the cooling medium circulation unit so that a circulation flow rate of the cooling medium circulating through the fuel cell becomes a first circulation flow rate;
Periodically measuring the current value of the current flowing from the fuel cell;
When the current value is equal to or lower than the first threshold current value, and when the time change rate of the current value is equal to or higher than the first threshold and lower than 0, the state continues for the first period. Controlling the cooling medium circulation unit so that the circulation flow rate becomes a second circulation flow rate smaller than the first circulation flow rate;
A method for starting a fuel cell comprising:

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