JP2007220355A - Fuel cell system and low temperature startup method of fuel cell - Google Patents

Abstract

It is possible to promote warm-up without operating a compressor at a high load at low temperature startup.
A fuel cell system supplies a reaction gas to generate power, a supply pressure control means for controlling a supply pressure of the reaction gas to the fuel cell, and a temperature of the fuel cell. A temperature sensor 23, a low temperature start determination means for determining whether or not to start at a low temperature based on the temperature of the fuel cell 1 detected by the temperature sensor 23, and a fuel cell when the low temperature start determination means determines that the start is a low temperature Low temperature starting supply pressure changing means for changing the supply pressure of the reaction gas to 1 to a pressure lower than the supply pressure of the reaction gas at room temperature.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell system and a fuel cell cold start method.

In a fuel cell that generates power by reacting with a reaction gas, the effective power generation area decreases when water freezes inside the fuel cell. Therefore, if the reaction gas is supplied under the same conditions as at room temperature, the consumption of hydrogen will be lower than at room temperature. The amount of power generation decreases. Conventionally, in order to compensate for this decrease in power generation, when the fuel cell is started below freezing point, the contact pressure of hydrogen and oxygen to the electrode is increased by increasing the supply pressure of the reaction gas compared to when starting at room temperature. At the same time, the amount of power generation is increased, and at the same time, the supply flow rate of the reaction gas is increased compared with that at the normal temperature startup, thereby improving the water discharge performance and promptly warming up the fuel cell (for example, patents) Reference 1).
JP 2005-44795 A

However, in order to increase or increase the reaction gas, auxiliary equipment such as a compressor must be operated at a high load, and in that case, noise of these auxiliary equipment may increase, which may impair commerciality.
In addition, it is disadvantageous in terms of energy management to operate an auxiliary machine such as a compressor at a high load when the power generation state of the fuel cell is not in a steady state.
Therefore, the present invention provides a fuel cell system and a low temperature start method for a fuel cell that can promote warm-up without operating an auxiliary machine at a high load during low temperature start.

The fuel cell system according to the present invention employs the following means in order to solve the above problems.
The invention according to claim 1 is a fuel cell (for example, a fuel cell 1 in an embodiment described later) that is supplied with a reaction gas to generate power, and a supply pressure control that controls a supply pressure of the reaction gas to the fuel cell. Detected by means (for example, pressure control valve 10 and regulator 16 in the embodiment described later), state detection means for detecting the state of the fuel cell (for example, temperature sensor 23 in the embodiment described later), and state detection means The low temperature start determination means (for example, step S101 in the embodiment described later) for determining whether or not the low temperature start is performed based on the state of the fuel cell, and when the low temperature start determination means determines the low temperature start, the fuel Low temperature starting supply pressure changing means (for example, described later) for changing the supply pressure of the reaction gas to the battery to a pressure lower than the supply pressure of the reaction gas at room temperature That the step S102) in the embodiment is a fuel cell system comprising: a.
The fuel cell has an IV characteristic in which the overvoltage increases when the reaction gas supply pressure is reduced, and the amount of heat generated by the fuel cell is substantially proportional to the overvoltage. Therefore, when the reaction gas is supplied to the fuel cell at a lower temperature than the supply pressure of the reaction gas to the fuel cell at normal temperature at low temperature startup, the amount of heat generated by power generation can be increased.

According to a second aspect of the present invention, in the first aspect of the present invention, the supply flow rate control means for controlling the supply flow rate of the reaction gas to the fuel cell (for example, the compressor 7 and the hydrogen pump 27 in the embodiments described later). And a low temperature start supply flow rate that changes the supply flow rate of the reaction gas to the fuel cell to a flow rate larger than the supply flow rate of the reaction gas at room temperature when the low temperature start determination means determines that the start is low temperature. Changing means (for example, step S102 in the embodiment described later).
By configuring in this way, the water inside the fuel cell (product water before freezing and thawed water before freezing) can be reliably blown off at low temperature startup, improving the water discharge performance, Can be prevented from refreezing.

Moreover, in the low temperature starting method of the fuel cell according to the present invention, the following means are adopted in order to solve the above problems.
The invention according to claim 3 supplies the reaction gas to the fuel cell at normal temperature when starting a fuel cell (for example, a fuel cell 1 in an embodiment described later) that is supplied with the reaction gas to generate power at a low temperature. A method for starting a fuel cell at a low temperature, comprising supplying a reaction gas to the fuel cell at a pressure lower than a pressure.
The fuel cell has an IV characteristic in which the overvoltage increases when the reaction gas supply pressure is reduced, and the amount of heat generated by the fuel cell is substantially proportional to the overvoltage. Therefore, if the reaction gas is supplied to the fuel cell at a temperature lower than the supply pressure of the reaction gas to the fuel cell at room temperature when starting at a low temperature, the amount of heat generated by the power generation can be increased. The temperature of the fuel cell can be increased rapidly.

According to the first aspect of the present invention, since the amount of heat generated by the power generation of the fuel cell can be increased at the time of low temperature startup, the self-heating of the fuel cell can be promoted and the temperature of the fuel cell can be raised quickly.
According to the invention which concerns on Claim 2, the discharge | emission property of water improves and it can prevent that water refreezes inside a fuel cell at the time of starting.
According to the third aspect of the present invention, since the amount of heat generated by the power generation of the fuel cell can be increased at the time of low temperature startup, the self-heating of the fuel cell can be promoted and the temperature of the fuel cell can be quickly raised.

Embodiments of a fuel cell system and a fuel cell cold start method according to the present invention will be described below with reference to the drawings of FIGS. Note that the fuel cell system in this embodiment is an embodiment mounted on a fuel cell vehicle.
First, a schematic configuration of a fuel cell system according to the present invention will be described with reference to FIG.
The fuel cell 1 is of a type that obtains electric power by chemically reacting a reaction gas. For example, a plurality of cells formed by sandwiching a solid polymer electrolyte membrane made of a solid polymer ion exchange membrane or the like between an anode and a cathode from both sides. The fuel gas flow passage (reaction gas flow passage) 5 on the anode side is supplied with hydrogen gas as fuel gas, and the oxidant gas flow passage (reaction gas flow passage) 6 on the cathode side is supplied with oxidant. When air containing oxygen is supplied as a gas, hydrogen ions generated by a catalytic reaction at the anode move through the solid polymer electrolyte membrane to the cathode, and cause an electrochemical reaction with oxygen at the cathode to generate electricity, Is generated. Part of the generated water generated on the cathode side permeates the solid polymer electrolyte membrane and back diffuses to the anode side, so that the generated water also exists on the anode side.

  The air is pressurized to a predetermined pressure by a compressor 7 such as a supercharger and supplied to the oxidant gas flow passage 6 of the fuel cell 1 through the air supply passage 8. The flow rate of air supplied to the fuel cell 1 is controlled by the compressor 7, and the rotation speed of the compressor 7 is controlled by an electronic control unit (ECU) 30. After the air supplied to the fuel cell 1 is used for power generation, it is discharged from the fuel cell 1 together with the produced water on the cathode side to the air discharge passage 9 and is not shown via the pressure control valve (supply pressure control means) 10. It is discharged to the exhaust treatment device. The pressure of the air supplied to the fuel cell 1 is controlled by the pressure control valve 10, and the opening degree of the pressure control valve 10 is controlled by the ECU 30. A cathode outlet pressure sensor 24 that detects the pressure of the air discharged from the fuel cell 1 is provided in the air discharge passage 9 upstream of the pressure control valve 10.

  On the other hand, the hydrogen gas supplied from the hydrogen tank 15 flows through the hydrogen gas supply flow path 17 and the shutoff valve 20, is reduced to a predetermined pressure by a regulator (supply pressure control means) 16, passes through the ejector 19, and the fuel cell 1. It is supplied to the fuel gas flow passage 5. The unreacted hydrogen gas that has not been consumed is discharged from the fuel cell 1 as an anode off-gas, passes through the anode off-gas passage 18, is boosted by the hydrogen pump 27, and then is sucked into the ejector 19, from the hydrogen tank 15. The fresh hydrogen gas supplied is merged and supplied again to the fuel gas flow passage 5 of the fuel cell 1. That is, the anode off gas discharged from the fuel cell 1 circulates in the fuel cell 1 through the anode off gas passage 18 and the hydrogen gas supply passage 17 downstream of the ejector 19.

The hydrogen pump 27 is a variable flow rate type pump. The flow rate of hydrogen gas supplied to the fuel cell 1 is controlled by the hydrogen pump 27, and the hydrogen pump 27 is controlled by the ECU 30.
Further, the regulator 16 includes a secondary pressure changing device, and the secondary pressure can be changed by a command from the ECU 30. In this fuel cell system, the pressure of the hydrogen gas supplied to the fuel cell 1 can be controlled by changing the secondary pressure of the regulator 16.
An anode inlet pressure sensor 25 that detects the pressure of the hydrogen gas supplied to the fuel cell 1 is provided in the hydrogen gas supply channel 17 downstream of the ejector 19.

The anode off gas flow path 18 is provided with a temperature sensor (state detection means) 23 for detecting the temperature of the anode off gas discharged from the fuel cell 1. In this embodiment, the anode off-gas temperature detected by the temperature sensor 23 is regarded as the internal temperature (system temperature) of the fuel cell 1.
An anode off-gas discharge channel 22 having a discharge valve 21 branches off from the anode off-gas channel 18. The 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 discharge valve 21 is discharged to the exhaust treatment device, and the anode off gas is diluted by the air discharged from the pressure control valve 10 in the exhaust treatment device.
The output signals of the temperature sensor 23, the cathode outlet pressure sensor 24, and the anode inlet pressure sensor 25 are input to the ECU 30, and the ECU 30 based on the input signals from these sensors 23 to 25, the required output, etc. The secondary pressure change device of the regulator 16, the pressure control valve 10, the discharge valve 21 and the like are controlled.

By the way, in this fuel cell system, when starting at a low temperature, the reaction gas is supplied to the fuel cell 1 at a pressure lower than the supply pressure of the reaction gas to the fuel cell 1 at room temperature, thereby promoting self-heating of the fuel cell 1. And we are trying to warm up early.
The principle will be described with reference to the IV characteristic diagram of the fuel cell 1 shown in FIG.
When a load is connected to the fuel cell 1 and a current flows, the voltage of the fuel cell 1 decreases from the open circuit voltage by an overvoltage according to the magnitude of the current, and the fuel cell 1 generates heat. The amount of heat generated at this time is almost proportional to the magnitude of the overvoltage.

  The IV characteristic diagram shown in FIG. 2 changes only the reaction gas supply pressure (hereinafter sometimes abbreviated as the reaction gas supply pressure) supplied to the fuel cell 1, and the reaction gas supply flow rate (hereinafter referred to as the reaction gas supply flow rate). This is a result obtained experimentally under the same conditions as in other cases. In this figure, the IV characteristic of “low supply pressure” indicated by a solid line is an IV characteristic when the reaction gas supply pressure to the fuel cell 1 is lowered when the power generation state of the fuel cell 1 is normal, and is indicated by a broken line. The “supply pressure high” IV characteristic is an IV characteristic when the reaction gas supply pressure to the fuel cell 1 is higher than when the fuel cell 1 is in a normal power generation state than when the “supply pressure is low”. From this experimental result, when the load is applied to the fuel cell 1 with the same current value, the overvoltage is larger when the reaction gas supply pressure to the fuel cell 1 is lower than when the reaction gas supply pressure is high. . For example, at the current value i, the overvoltage β in the case of “low supply pressure” is larger than the overvoltage α in the case of “high supply pressure”.

As a result, as described above, the amount of heat generated by the fuel cell 1 is proportional to the magnitude of the overvoltage. Therefore, when compared with when the fuel cell 1 is loaded with the same current value, the reaction gas supply pressure to the fuel cell 1 is When the reaction gas supply pressure is low, the amount of heat generated by the fuel cell 1 is larger than when the reaction gas supply pressure is high.
Therefore, by making the reaction gas supply pressure to the fuel cell 1 at the low temperature start-up lower than the reaction gas supply pressure at the normal temperature start-up, the self-heat generation amount of the fuel cell 1 at the start-up can be increased.
Therefore, in this fuel cell system, when starting at a low temperature, the reaction gas is supplied to the fuel cell 1 at a pressure lower than the reaction gas supply pressure to the fuel cell 1 at room temperature, thereby promoting self-heating of the fuel cell 1. In addition, the temperature of the fuel cell 1 can be quickly raised so that the fuel cell 1 can be quickly shifted to a normal operation state (normal temperature start-up, normal temperature operation). At the same time, at the time of low temperature startup, the reaction gas is supplied to the fuel cell 1 at a flow rate larger than the flow rate of supply of the reaction gas to the fuel cell 1 at room temperature. (The generated water before freezing and the thawed water) can be surely blown off, the water discharge performance is improved, and the water is prevented from refreezing inside the fuel cell 1. did.

Next, an embodiment of a method for starting the fuel cell 1 will be described with reference to a flowchart shown in FIG. The activation control routine shown in the flowchart of FIG. 3 is executed by the ECU 30 with the ON signal input of the ignition switch 26 as a start condition.
First, in step S101, it is determined whether or not the temperature of the fuel cell 1 detected by the temperature sensor 23 is lower than 0 ° C. (that is, below freezing point). If the determination result in step S101 is “YES” (lower than 0 ° C.), the process proceeds to step S102, and the required load is referred to by referring to the supply pressure map (solid line) for low temperature startup in the supply pressure map shown in FIG. Calculate the reaction gas supply pressure according to the required load while calculating the reaction gas supply pressure according to the (required current) and referring to the supply flow map (solid line) for starting at low temperature in the supply flow map shown in FIG. To do.

  The reaction gas supplied to the fuel cell 1 includes hydrogen gas supplied to the anode side of the fuel cell 1, that is, the fuel gas flow passage 5, and air supplied to the cathode side, that is, the oxidant gas flow passage 6. There are a supply pressure map for hydrogen gas, a supply flow map for hydrogen gas, a supply pressure map for air, and a supply flow map for air. However, since the trend of the change in supply pressure with respect to the extraction current is the same for both the hydrogen gas map and the air map, both the hydrogen gas supply pressure map and the air supply pressure map are shown in FIG. Show. Further, since the trend of the change in the supply flow rate with respect to the extraction current is the same for both the hydrogen gas map and the air map, both the hydrogen gas supply flow rate map and the air supply flow rate map are shown in FIG. Show.

  The supply pressure map in FIG. 4 includes a supply pressure map for low temperature startup (solid line), a supply pressure map for normal temperature startup (broken line), and a supply pressure map for normal temperature operation (dashed line). Yes. In any supply pressure map, the reaction gas supply pressure increases as the extraction current increases. However, when compared with the same extraction current value, the supply pressure for starting at room temperature is higher than the supply pressure for operating at room temperature. The supply pressure for starting at low temperature is set smaller than the supply pressure for normal temperature operation.

  The supply flow rate map shown in FIG. 5 includes a supply flow rate map for low temperature startup (solid line), a supply flow rate force map for normal temperature startup (broken line), and a supply flow rate map for normal temperature operation (one-dot chain line). ing. In any supply flow map, the reaction gas supply flow rate increases as the extraction current increases. However, when compared with the same extraction current value, the supply flow rate for starting at room temperature is larger than the supply flow rate for normal temperature operation. The supply flow rate for low temperature startup is set to be larger than the supply flow rate for normal temperature startup. The supply flow rate map for cold start is set in the range of the allowable extraction current.

  And after performing the process of step S102, it progresses to step S103 and performs cold start operation control. In the low-temperature start-up operation control, the hydrogen gas supplied to the fuel gas flow passage 5 of the fuel cell 1 is set to the low-temperature start-up control target value using the supply pressure and supply flow rate of the hydrogen gas calculated in step S102 as the low-temperature start-up control target value. The regulator 16 and the hydrogen pump 27 are feedback-controlled so that the supply pressure and the supply flow rate of the air flow coincide with each other, and the low-temperature start-up control target value is set with the air supply pressure and supply flow calculated in step S102 as the low-temperature start-up control target value Further, the compressor 7 and the pressure control valve 10 are feedback-controlled so that the supply pressure and supply flow rate of the air supplied to the oxidant gas flow passage 6 of the fuel cell 1 coincide.

After performing the process of step S103, it progresses to step S104 and it is determined whether the temperature of the fuel cell 1 detected with the temperature sensor 23 is higher than 0 degreeC.
If the determination result in step S104 is “NO” (0 ° C. or less), the process returns to step S103 to continue the low temperature start-up operation control.
If the determination result in step S104 is “YES” (higher than 0 ° C.), the process proceeds to step S105, and the required load is referenced with reference to the supply pressure map for starting at room temperature (broken line) in the supply pressure map shown in FIG. Calculate the reaction gas supply pressure according to the required load while calculating the reaction gas supply pressure according to the (required current) and referring to the supply flow map for starting at room temperature (broken line) in the supply flow map shown in FIG. To do. If the determination result in step S101 is “NO” (0 ° C. or higher), it is not necessary to execute the low-temperature start-up operation control. In this case, too, the process proceeds to step S105 to supply the reaction gas at the normal temperature start-up. Calculate pressure and supply flow rate.

  Next, it progresses to step S106 from step S105, and normal temperature starting driving | operation control is performed. In the normal temperature start-up operation control, the hydrogen gas supply pressure and supply flow rate calculated in step S105 are set as the normal temperature start control target value, and the hydrogen gas supplied to the fuel gas flow passage 5 of the fuel cell 1 is set to the normal temperature start control target value. The regulator 16 and the hydrogen pump 27 are feedback-controlled so that the supply pressure and the supply flow rate of the air flow coincide with each other, and the normal temperature start control target value is set with the air supply pressure and supply flow calculated in step S105 as the normal temperature start control target value. Further, the compressor 7 and the pressure control valve 10 are feedback-controlled so that the supply pressure and supply flow rate of the air supplied to the oxidant gas flow passage 6 of the fuel cell 1 coincide.

After performing the process of step S106, it progresses to step S107 and it is determined whether the temperature of the fuel cell 1 detected with the temperature sensor 23 is higher than TC. This temperature T is a temperature for determining completion of activation, and is set in advance to a predetermined temperature higher than 0 ° C. The determination of whether or not the start is complete may be made based on the IV characteristics of the fuel cell 1 at that time. For example, the voltage of the fuel cell 1 is determined in advance according to the supply conditions of the reaction gas and the extraction current. The determination can be made based on whether or not the preset predetermined voltage is exceeded.
If the determination result in step S107 is “NO” (T ° C. or lower), the process returns to step S106 to continue the normal temperature activation operation control.
If the determination result in step S107 is “YES” (higher than T ° C), the process proceeds to step S108, and the request is made with reference to the supply pressure map (one-dot chain line) for normal temperature operation in the supply pressure map shown in FIG. While calculating the reaction gas supply pressure according to the load (required current) and referring to the supply flow map (one-dot chain line) for normal temperature operation in the supply flow map shown in FIG. 5, the reaction gas supply flow according to the required load Is calculated.

  Next, it progresses to step S108, normal temperature starting operation control is performed, and execution of this routine is complete | finished. In the normal temperature operation control, the supply pressure and supply flow rate of the hydrogen gas calculated in step S108 are set as the normal temperature operation control target values, and the normal temperature operation control target values are set to the hydrogen gas supplied to the fuel gas flow passage 5 of the fuel cell 1. The regulator 16 and the hydrogen pump 27 are feedback-controlled so that the supply pressure and the supply flow rate coincide with each other, and the supply pressure and supply flow rate of air calculated in step S108 are used as the normal operation control target values. The compressor 7 and the pressure control valve 10 are feedback-controlled so that the supply pressure and supply flow rate of the air supplied to the oxidant gas flow passage 6 of the fuel cell 1 coincide.

In this embodiment, the temperature sensor 23 that detects the temperature of the fuel cell 1 constitutes a state detection unit that detects the state of the fuel cell 1. In the embodiment, the anode off-gas temperature is substituted as the temperature of the fuel cell, but the temperature of the air discharged from the fuel cell may be substituted, or the temperature of the fuel cell may be directly detected.
The state detection means is not limited to the temperature sensor 23 that detects the temperature of the fuel cell 1. For example, when the ignition switch 26 is turned on, a reaction gas is supplied to the fuel cell 1 at a preset initial flow rate and initial pressure to generate power, and a load is applied to the fuel cell 1, and a preset current is applied to the load. And the state of the fuel cell 1 may be detected based on the overvoltage value (hereinafter referred to as the initial overvoltage) detected at that time. In this case, the state detection means is detected by the initial overvoltage detection process. Is configured.

In this embodiment, the ECU 30 executes the process of step S101 to realize the cold start determination means, and the process of step S102 realizes the cold start supply pressure changing means and the cold start supply flow rate changing means. .
In this embodiment, the supply pressure map for starting at normal temperature and the supply pressure map for operating at normal temperature are prepared separately, but these maps may be used in the same manner, and similarly, the supply flow rate for starting at normal temperature The map and the supply flow rate map for normal temperature operation may be made the same.
Furthermore, the fuel cell system is not limited to being mounted on the vehicle, and may be mounted on another moving body or may be fixed.

1 is a schematic configuration diagram of a fuel cell system according to the present invention. It is IV characteristic of a fuel cell. It is a flowchart which shows the starting control of the fuel cell in the Example of this invention. It is the supply pressure map of the reactive gas used in the starting control of the said Example. It is the supply flow rate map of the reactive gas used in the starting control of the said Example.

Explanation of symbols

1 Fuel cell 7 Compressor (Supply flow control means)
10 Pressure control means (supply pressure control means)
16 Regulator (Supply pressure control means)
23 Temperature sensor (status detection means)
27 Hydrogen pump (supply flow rate control means)

Claims (3)

A fuel cell that is supplied with a reaction gas to generate power;
Supply pressure control means for controlling the supply pressure of the reaction gas to the fuel cell;
State detecting means for detecting the state of the fuel cell;
Low temperature start determination means for determining whether or not the low temperature start based on the state of the fuel cell detected by the state detection means;
Low temperature start supply pressure changing means for changing the reaction gas supply pressure to the fuel cell to a pressure lower than the reaction gas supply pressure at room temperature when the low temperature start determination means determines that the start is low temperature. When,
A fuel cell system comprising: Supply flow rate control means for controlling the supply flow rate of the reaction gas to the fuel cell;
Low temperature start supply flow rate changing means for changing the supply flow rate of the reaction gas to the fuel cell to a flow rate larger than the supply flow rate of the reaction gas at room temperature when the low temperature start determination means determines that the start is low temperature. When,
The fuel cell system according to claim 1, comprising:   When starting a fuel cell that generates power by being supplied with a reactive gas at a low temperature, the reactive gas is supplied to the fuel cell at a pressure lower than a pressure for supplying the reactive gas to the fuel cell at room temperature. Low temperature startup method for fuel cells.

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