JP2006092801A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent lowering of fuel cell output voltage due to deficiency of water in a fuel cell system or drying of solid electrolyte. <P>SOLUTION: A controller 23 calculates water balance management temperature for each output current on the basis of fuel cell operating pressure and the amount of air flow supplied to a fuel cell 1. When the temperature of a cathode egress detected by a cathode egress thermometer 22 is higher than the water balance management temperature, and an output current value detected by an ammeter 26 is below a specified value; supplying of air from an air supplying apparatus 2 to the fuel cell stack 1 is temporarily stopped in the fuel cell system. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system.

  In a fuel cell, a fuel gas such as hydrogen gas and an oxidizing gas containing oxygen are electrochemically reacted through an electrolyte, and electric energy is directly taken out between electrodes provided on both surfaces of the electrolyte. In particular, a polymer electrolyte fuel cell using a polymer electrolyte has attracted attention as a power source for electric vehicles because of its low operating temperature and easy handling. That is, a fuel cell vehicle is equipped with a hydrogen storage device such as a high-pressure hydrogen tank, a liquid hydrogen tank, or a hydrogen storage alloy tank in the vehicle, and reacts by supplying hydrogen supplied therefrom and air containing oxygen to the fuel cell. This is the ultimate clean vehicle that drives the motor connected to the drive wheels with the electric energy extracted from the fuel cell, and the only exhaust material is water.

  It is known that when the fuel cell system has a low output, the auxiliary machine power consumption is relatively larger than the power generation output and the power generation efficiency is lowered. Particularly in a fuel cell vehicle or the like, since the load range is wide from an idle state to a full load, fuel consumption performance can be improved by stopping power generation of the fuel cell and supplying power from a secondary battery or a capacitor during idling.

As a conventional fuel cell system that performs idle stop, there is a fuel cell vehicle that performs idle stop when it is determined that the power generation can be stopped based on the motor speed, the brake operation state, and the remaining capacity of the power storage device ( For example, Patent Document 1).
JP 2001-359204 A (page 5, FIG. 1)

  However, in the above conventional technique, the fuel cell operation is simply stopped during the idling operation. Therefore, in the low load region where the excess air ratio (SR) supplied to the cathode is large, the water balance becomes negative. However, there is a problem that the water in the fuel cell system is insufficient or the output voltage of the fuel cell is lowered due to drying of the solid electrolyte.

  In order to solve the above-described conventional problems, the present invention provides a fuel gas supply means for supplying a hydrogen-rich fuel gas, an air supply means for supplying air, and a fuel cell that generates electric power using the fuel gas and air. And a thermometer for detecting the cathode outlet temperature of the fuel cell, a current sensor for detecting the output current of the fuel cell, and a water balance management for each output current based on the fuel cell operating pressure and the air flow rate supplied to the fuel cell. A water balance calculating means for calculating a temperature, and an output current value detected by the current sensor when the cathode outlet temperature detected by the thermometer is higher than the water balance management temperature calculated by the water balance calculating means. And a control means for temporarily stopping the air supply from the air supply means to the fuel cell when the value is equal to or less than a predetermined value.

  According to the present invention, when the cathode outlet temperature is higher than the water balance management temperature, the air supply is stopped, so that moisture is not taken out from the fuel cell by the cathode exhaust, and the solid electrolyte membrane is dried. There is an effect that the output voltage of the fuel cell can be prevented from decreasing.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. Each embodiment described below is a fuel cell system suitable for a fuel cell vehicle, although not particularly limited thereto.

  FIG. 1 is a system configuration diagram showing the configuration of Embodiment 1 of the fuel cell system according to the present invention. In FIG. 1, hydrogen is supplied as fuel gas from a hydrogen supply device 3 such as a high-pressure hydrogen tank, and the fuel cell system is determined within a range in which the fuel cell system can be operated by a hydrogen pressure regulating valve 13 provided in a hydrogen supply pipe 14 via a hydrogen cutoff valve 12. After being adjusted to a predetermined pressure, the fuel cell stack (fuel cell body) 1 flows into the anode inlet 1a.

  The fuel cell system includes a hydrogen circulation pipe 16 that circulates hydrogen discharged from the anode outlet 1b of the fuel cell stack 1 to the anode inlet 1a, and the hydrogen circulation pipe 16 includes a hydrogen circulation device 15 such as a pump and an ejector. . By making the hydrogen flow rate supplied to the anode inlet 1a of the fuel cell stack 1 larger than the reaction hydrogen flow rate corresponding to the output current, the fuel hydrogen stack without any shortage is provided in each cell of the fuel cell stack composed of a plurality of cells. Is configured to supply.

  The air is compressed and heated by an air supply device 2 such as a compressor, but is cooled by a cooling pipe (not shown), for example, a cooler 4 that cools using a cooling liquid common to the fuel cell stack 1. A humidifier 5 is provided downstream of the cooler 4 and upstream of the fuel cell stack 1 to humidify the air supplied to the fuel cell stack 1.

  In the humidifier 5, for example, air in exhaust air discharged from the cathode outlet 1 d of the fuel cell stack 1 is supplied to the cathode inlet 1 c through a film made of a material having high moisture permeability such as polyimide. A humidifier having a water vapor exchanging function is used.

  An air pressure adjustment valve 6 is provided downstream of the exhaust air side flow path of the humidifier 5 and is adjusted so that the cathode pressure of the fuel cell stack 1 is maintained within a range where the fuel cell can be operated.

  In order to detect the operating state of the fuel cell system, the cathode inlet 1c has a cathode flow meter 24 for detecting the air flow rate at the cathode inlet, and the cathode outlet 1d has a cathode outlet thermometer 22 for detecting the gas temperature at the cathode outlet. A cathode pressure gauge 25 for detecting the gas pressure at the cathode outlet is provided.

  The fuel cell system includes an ammeter 26 that detects the output current of the fuel cell stack 1, a secondary battery 28 that is a power auxiliary device that compensates for the shortage of the output power of the fuel cell stack 1, and the secondary battery 28. An SOC detector 27 that detects a state of charge (SOC) and a load device 29 that is supplied with power from the fuel cell stack 1 and / or the secondary battery 28 are provided.

  When such a fuel cell system is used for a device with a wide load range such as a power source of a vehicle, the reaction gas is distributed to all the plurality of flow paths of the plurality of cells in the fuel cell stack, and is generated by a reaction. As shown in FIG. 2, the ratio of the flow rate that needs to flow through the fuel cell stack to the air flow rate required for the reaction (hereinafter referred to as SR) is low as shown in FIG. It must be increased in the load area.

  Since the condition for establishing the water balance of the fuel cell system can be expressed by the following equation (1), the water balance becomes difficult at a low load that increases the air side SR, and the cathode outlet of the fuel cell stack that can maintain the water balance The temperature goes down.

[Equation 1]
(Moisture amount contained in compressor intake air) + (humidified moisture amount) + (generated water accompanying reaction) ≧ (water amount contained in cathode exhaust air−water amount recovered by humidifier) (1)
Therefore,
(Water content contained in compressor intake air) + (humidified water content) + (product water generated by reaction) ≥ (water content discharged from humidifier outlet) (2)
In this,
Moisture amount discharged from humidifier outlet カ ソ ー ド Cathode exhaust air flow rate 空 気 Air side SR… (3)
On the high load side, the pressure loss of the air flow path increases, so the pressure at the outlet of the humidifier decreases, and as a result, the amount of moisture discharged from the humidifier outlet to the outside increases, so the water balance temperature Gradually decreases.

  Therefore, the cathode outlet temperature at which the water balance is balanced has a temperature characteristic as shown by the solid line in the graph of FIG. 3, and the water balance is not established at a temperature higher than this solid line, and the water balance is established at a temperature below this solid line. Thus, the fuel cell can be operated without water supply.

  FIG. 4 is a flowchart illustrating a control procedure performed by the controller in the first embodiment.

  First, in Step 2, the fuel cell output current value from the ammeter 26, the fuel cell cathode gas flow value from the cathode flow meter 24, the fuel cell cathode outlet pressure value from the cathode pressure gauge 25, and the secondary battery SOC value from the SOC detector 27. Is read into the controller 23.

  In step 3, based on the fuel cell output current value, the fuel cell cathode gas flow rate value, and the fuel cell cathode outlet pressure value, the upper limit temperature value of the gas temperature at the cathode outlet where the water balance is established (hereinafter simply referred to as the water balance management temperature). Call). This calculation is performed, for example, using the fuel cell output current value, the fuel cell cathode gas flow rate value, and the fuel cell cathode outlet pressure value as parameters, and the cathode outlet temperature at which the water balance is balanced in the fuel cell system obtained in advance experimentally. You can search the map to find the water balance management temperature.

  In step 4, in parallel with the calculation in step 3, the fuel cell cathode outlet temperature value is read into the controller.

  In step 5, the water balance management temperature value derived in step 3 is compared with the fuel cell cathode outlet temperature value read in step 4.

  In step 5, when the fuel cell cathode outlet temperature value> the water balance management temperature value, the controller determines that the water balance is established, and proceeds to step 7.

  In step 5, when the fuel cell cathode outlet temperature value ≦ the water balance management temperature value, the process proceeds to step 6 to determine whether or not to continue the system operation and return to step 2.

  In step 7, it is determined whether or not the fuel cell output current value is less than a predetermined value. This predetermined value is a minimum current management threshold value that permits fuel cell power generation, and is recorded in advance in the controller as a current upper limit value that can be supplied by the secondary battery.

  If it is determined in step 7 that the fuel cell output current value is less than the predetermined value, the process proceeds to step 9. If it is determined in step 7 that the fuel cell output current value is equal to or greater than a predetermined value, the process proceeds to step 8 to determine whether or not to continue system operation.

  In step 9, it is determined whether or not the secondary battery SOC value read in step 2 exceeds the SOC management lower limit value.

  If the secondary battery SOC value exceeds the SOC management lower limit value in the determination in step 9, the idle stop in step 12 and thereafter is performed.

  If it is determined in step 9 that the secondary battery SOC value does not exceed the SOC management lower limit value, the process proceeds to step 10, where it is determined that the operation of the fuel cell system is to be continued. The secondary battery is charged by adding up the secondary battery charge.

  In step 12 and subsequent steps, an operation for reducing the open-circuit voltage of the fuel cell stack during the idle stop is performed.

  First, in step 12, the operation of the hydrogen circulation pump is continued or started to perform hydrogen circulation. After waiting until the circulation flow rate can be ensured, in step 13, the air supply device is stopped and the air supply to the fuel cell stack is stopped.

  In step 14, the hydrogen shutoff valve 12 is closed to stop the hydrogen supply. After waiting until the gas supply can be stopped for both the anode and the cathode, in step 15, power is taken out from the fuel cell stack, and stack output voltage control is performed to lower the fuel cell voltage to a predetermined voltage. In step 16, the idle stop control is bypassed.

  The return from the idle stop state to the operating state of the fuel cell system is performed by operating the stopped air supply device when the following condition (1) or (2) is satisfied.

  (1) When the required output to the fuel cell system increases and it is estimated that the cathode outlet temperature calculated from the cooling water temperature will be below the water balance management temperature when power is generated with this required output.

  (2) The cooling water temperature is lowered, and the cathode outlet temperature calculated from the cooling water temperature can be estimated to be lower than the water balance management temperature.

  Next, the effect of Example 1 is demonstrated. With reference to FIG. 2, it is confirmed that the operation shifts to the idle stop according to the change of the operation condition.

  First, when the output current of the fuel cell stack is decreased from the operating state of the rated output current such as point B, point C is reached. The point C is a condition that coincides with the water balance management temperature, and the control shown in FIG. 5 starts toward the idle stop from here.

  At the idle point D, since the cathode outlet temperature is higher than the water balance temperature and the water balance is not established, the process proceeds from step 5 to step 7 in the control shown in FIG. Point E reaches step 16 through the current check in step 7 and the secondary battery SOC check in step 9. By stopping power generation, the stack does not generate heat, and the temperature of the entire system can be lowered.

  Further, when the temperature of the system decreases and reaches point F due to the stoppage of power generation, the fuel cell is returned to idle operation. When returning to idle operation and reaching point G, the water balance can be positive because it is within the water balance management temperature.

  Next, the effect of the present embodiment will be described with reference to the flowchart of FIG.

  In step 5, the water balance of the stack at that time can be determined by comparing the cathode outlet temperature of the fuel cell stack with the water balance management temperature value and determining whether the water balance is established or not.

  Next, in step 7, the output current value is compared with the predetermined current value, and it can be determined whether the water balance is not established at high load or the water balance is not established at idle or low load.

  In step 8, the heat generation of the stack can be reduced by limiting the output in response to the determination of failure of water balance at high load.

  In step 9, after determining whether the water balance is not established at the time of idling or low load, it is determined whether the SOC value of the secondary battery as the stack alternative power source can sufficiently cover the auxiliary machine power during idling stop, It is possible to prevent power shortage during idle stop.

  In step 16, the heat generation of the stack can be reduced by performing idling stop in response to the determination of water balance failure at high load.

  Next, a second embodiment of the present invention will be described. FIG. 5 is a system configuration diagram illustrating the configuration of a second embodiment of the fuel cell system according to the present invention. The description of the same configuration as in the first embodiment is omitted.

  The difference between the present embodiment and the first embodiment is that the fuel cell stack of the present embodiment is composed of an internal humidification type fuel cell stack 1, and in order to circulate pure water therethrough, a water storage tank 7, a hydraulic pump 8, a pure water supply pipe 9, a pure water recovery pipe 10, and a water level sensor 11 are added. As the fuel gas and oxidant gas are supplied to the fuel cell stack 1 and power is generated by taking out the load, the water pressure pump 8 is driven to start circulation.

  Since the water balance of the fuel cell system shown in the second embodiment can be expressed by the following equation (4), the water balance becomes difficult at a low load where the air side SR is increased, and the fuel cell stack outlet can maintain the water balance. The temperature goes down.

[Equation 2]
(Moisture content in compressor intake air) + (humidified moisture content) + (water produced by reaction)
+ (Circulating water amount) ≧ (Moisture content in cathode exhaust air) (4)
In this,
Moisture amount discharged from humidifier outlet カ ソ ー ド Cathode exhaust air flow rate 側 Air side SR… (5)
Therefore, when the water balance is positive, the generated water is circulated to the water storage tank 7, and the indicated value of the water level sensor 11 increases.

  On the other hand, when the water balance is negative, the amount of water taken out from the water storage tank 7 increases with respect to the amount collected in the water storage tank 7, and the indicated value of the water level sensor 11 decreases.

  Therefore, the capacity of the water storage tank 7 can be increased to increase the capacity between the upper and lower limits of the water level and the time allowed for the water balance to be negative.

  Further, in the fuel cell system shown in the second embodiment, the water balance can be directly determined by the change in the detection value of the water level sensor 11, so that the water balance can be managed with higher accuracy.

  FIG. 6 is a flowchart illustrating a control procedure by the controller in the second embodiment.

  First, in step 22, the fuel cell output current value from the ammeter 26, the fuel cell cathode gas flow value from the cathode flow meter 24, the fuel cell cathode outlet pressure value from the cathode pressure gauge 25, and the secondary battery SOC value from the SOC detector 27. Is read into the controller 23.

  In step 23, the water balance management temperature value is calculated based on the fuel cell output current value, the fuel cell cathode gas flow rate value, and the fuel cell cathode outlet pressure value. This calculation is performed, for example, using the fuel cell output current value, the fuel cell cathode gas flow rate value, and the fuel cell cathode outlet pressure value as parameters, and the cathode outlet temperature at which the water balance is balanced in the fuel cell system obtained in advance experimentally. You can search the map to find the water balance management temperature.

  In step 24, in parallel with the calculation in step 23, the fuel cell cathode outlet temperature value is read into the controller.

  In step 25, the water balance management temperature value derived in step 23 is compared with the fuel cell cathode outlet temperature value read in step 24.

  In step 25, when the fuel cell cathode outlet temperature value> the water balance management temperature value, the controller determines that the water balance is established, and proceeds to step 27.

  In step 25, when the fuel cell cathode outlet temperature value ≦ the water balance management temperature value, the routine proceeds to step 26, where the system operation continuation determination is performed, and the routine returns to step 22.

  In step 26, the detected value of the water level sensor 11 for detecting the water level of the water storage tank 7 is read into the controller, and compared with the predetermined lower limit value of the water level of the water storage tank 7, the sensor detected value is less than the lower limit value of the water level. If there is, the idle stop control is continued and the process proceeds to step 28.

  In step 28, it is determined whether or not the fuel cell output current value is less than a predetermined value. This predetermined value is a minimum current management threshold value that permits fuel cell power generation, and is recorded in advance in the controller as a current upper limit value that can be supplied by the secondary battery.

  If it is determined in step 28 that the fuel cell output current value is less than the predetermined value, the process proceeds to step 30. If it is determined in step 28 that the fuel cell output current value is greater than or equal to a predetermined value, the process proceeds to step 29 to determine whether or not to continue system operation.

  In step 30, it is determined whether or not the secondary battery SOC value read in step 22 exceeds the SOC management lower limit value.

  If it is determined in step 30 that the secondary battery SOC value exceeds the SOC management lower limit value, an idle stop in step 33 and subsequent steps is performed.

  If it is determined in step 30 that the secondary battery SOC value does not exceed the SOC management lower limit value, the process proceeds to step 31 where it is determined that the operation of the fuel cell system is to be continued. The secondary battery is charged by adding up the secondary battery charge.

  In step 33 and subsequent steps, an operation for suppressing the open end voltage of the fuel cell stack during the idling stop is performed.

  First, in step 33, the operation of the hydrogen circulation pump is continued or started to perform hydrogen circulation. After waiting until the circulation flow rate can be secured, in step 34, the air supply device is stopped and the air supply to the fuel cell stack is stopped.

  In step 35, the hydrogen shutoff valve 12 is closed to stop the hydrogen supply. After waiting for the time when gas supply can be stopped for both the anode and cathode, stack output voltage control is performed in step 36 to extract power from the fuel cell stack and lower the fuel cell voltage to a predetermined voltage. In step 37, the idle stop control is bypassed.

  The effect is demonstrated about the flowchart of FIG.

  According to the second embodiment, even when it is determined that the temperature is lower than the water level management temperature, if the water level is equal to or lower than the lower limit, the idle stop control is advanced.

  As the stack power generation time elapses, fuel cell characteristics such as IV characteristics change. As a result, the water balance also changes, and the water balance management temperature curve built in the controller in advance and the condition that the water balance is actually established in the stack at that time may be uneven, and the water balance may become negative. is assumed.

  According to the present embodiment, the water balance can be controlled more accurately by the direct measurement of the water level using the water level sensor value without causing the water balance to become negative.

1 is a system configuration diagram illustrating the configuration of a first embodiment of a fuel cell system according to the present invention. FIG. It is a figure which shows the relationship between a fuel cell output current and cathode SR. It is a figure which shows the water balance management curve in a fuel cell output current and cathode exit temperature. 5 is a flowchart illustrating idle stop permission determination and a system control procedure for shifting to idle stop in the first embodiment. It is a system block diagram explaining the structure of Example 2 of the fuel cell system which concerns on this invention. 10 is a flowchart illustrating permission determination for idling stop and a system control procedure for shifting to idling stop in the second embodiment.

Explanation of symbols

1: Fuel cell stack 2: Air supply device 3: Hydrogen supply device 4: Cooler 5: Humidification device 6: Air pressure adjustment valve 7: Water storage tank 8: Water pressure feed pump 9: Pure water supply pipe 10: Pure water recovery Pipe 11: Water level sensor 12: Hydrogen shutoff valve 13: Hydrogen pressure regulating valve 14: Hydrogen supply pipe 15: Hydrogen circulation device 16: Hydrogen circulation pipe 17: Purge valve 20: Radiator 21: Cooling water pump 22: Cathode outlet thermometer 23 :controller

Claims (6)

Fuel gas supply means for supplying hydrogen-rich fuel gas;
Air supply means for supplying air;
A fuel cell body that generates power using the fuel gas and air;
A thermometer for detecting the cathode outlet temperature of the fuel cell body;
An ammeter that detects the output current of the fuel cell body;
A water balance calculating means for calculating a water balance management temperature for each output current based on the fuel cell operating pressure and the air flow rate supplied to the fuel cell body;
When the cathode outlet temperature detected by the thermometer is higher than the water balance management temperature calculated by the water balance calculating means, and when the output current value detected by the current sensor is less than a predetermined value, the air Control means for temporarily stopping air supply from the supply means to the fuel cell body;
A fuel cell system comprising: A hydrogen circulation device that circulates unused fuel gas discharged from the anode of the fuel cell main body to the anode inlet,
2. The fuel cell system according to claim 1, wherein when the air supply is temporarily stopped by the control means, the operation of the hydrogen circulation device is continued.   The current output from the fuel cell main body is continued so that the cell voltage of all cells or partial cells of the fuel cell main body becomes a predetermined voltage or lower when air supply is temporarily stopped by the control means. The fuel cell system according to claim 1 or 2. It has a power auxiliary device that supplements the output power of the fuel cell body,
The fuel cell system according to any one of claims 1 to 3, wherein a predetermined current value for temporarily stopping the air supply is equal to or less than a current that can be supplied by the power auxiliary device.   When the required output to the fuel cell system increases and power is generated with this required output, it is stopped when the cathode outlet temperature calculated from the cooling water temperature can be estimated to be below the water balance management temperature. The fuel cell system according to any one of claims 1 to 4, wherein the air supply means that has been operated is operated.   After the air supply is temporarily stopped by the control means, the cooling water temperature is lowered, and when it is estimated that the cathode outlet temperature calculated from the cooling water temperature is lower than the water balance management temperature, it is stopped. The fuel cell system according to any one of claims 1 to 5, wherein the air supply means is operated.

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