JP2011210405A - Fuel cell system, and control method of fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system in which a fuel cell is operated in a state immediately before flooding by reducing flow-rate of air with a simple structure.SOLUTION: The fuel cell system 10 is provided with a fuel cell 100, an air pump 220 which supplies air to the fuel cell, a voltage measuring unit 410 which acquires a voltage of the fuel cell, and a control unit 500 which controls driving of the air pump and controls a flow-rate of air to be supplied to the fuel cell. Upon starting the fuel cell, the control unit reduces gradually the flow-rate of air and, when a voltage of the fuel cell drops for a predetermined time or more and to a predetermined voltage or less, determines that a flooding condition has happened, and thereafter, increases the flow-rate of air to the flow-rate immediately before the flooding condition has happened, and thereby, controls the flow-rate of the air to be supplied to the fuel cell so that the condition immediately before the flooding may be maintained.

Description

  The present invention relates to control of air supply in a fuel cell system.

  In the fuel cell, the fuel cell is stably operated by increasing the air stoichiometric ratio at each load in consideration of variations in shape and sensor. Here, the AC impedance of the specific cell that is easily dried is measured, the average moisture content of the fuel cell stack is estimated based on the measured AC impedance of the specific cell, and the average moisture content is calculated based on the average moisture content. There is known a fuel cell system including water content control means for maintaining an average water content of a fuel cell within an appropriate range (for example, Patent Document 1).

JP 2009-4299 A

  In the fuel cell system, it is desired to reduce the air flow rate in consideration of the storage capacity, power consumption, and durability of the air compressor in a small compartment. However, if the air flow rate is excessively reduced, flooding occurs, causing a problem that the power generation capacity is reduced. In the prior art, it has been difficult to operate the fuel cell in a state immediately before flooding by reducing the air flow rate.

  The present invention has been made to solve at least a part of the above-described problems, and has an object of reducing the air flow rate and operating the fuel cell in a state immediately before flooding with a simple configuration. .

  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, an air pump that supplies air to the fuel cell, a voltage measurement unit that acquires a voltage of the fuel cell, and an air that controls driving of the air pump and is supplied to the fuel cell A control unit for controlling the flow rate of the fuel cell, wherein the control unit gradually decreases the flow rate of the air when the fuel cell is started, so that the voltage of the fuel cell is maintained in advance for a predetermined time or more. When the voltage drops below a predetermined voltage, it is determined that the flooding state has occurred, and then the air flow rate is increased to a flow rate immediately before the flooding state occurs, so that the state immediately before the flooding occurs. A fuel cell system that controls a flow rate of air supplied to the fuel cell so that the above is maintained.
According to this application example, it is possible to easily detect the occurrence of flooding with a simple configuration, reduce the flow rate of air, and operate the fuel cell immediately before flooding.

[Application Example 2]
The fuel cell according to Application Example 1 further includes an impedance measurement device that measures the impedance of the fuel cell, and the control unit stores the impedance in a state immediately before the occurrence of flooding as a target impedance value. Then, when the impedance measured thereafter becomes larger than the target impedance value, the amount of air supplied to the fuel cell is decreased, and the impedance measured thereafter becomes smaller than the target impedance value. A fuel cell system for increasing the amount of air supplied to the fuel cell.
According to this application example, it is possible to easily control the fuel cell to operate in the state immediately before flooding by using the impedance as a parameter and easily reducing the air flow rate.

[Application Example 3]
A control method for a fuel cell system, comprising: (a) supplying air to the fuel cell when the fuel cell is started; and (b) gradually reducing the amount of air supplied to the fuel cell, A step of determining that the flooding state has occurred when the voltage of the battery drops below a predetermined voltage for a predetermined time or more; and (c) the flow rate of the air after the flooding state has occurred. And (d) controlling the flow rate of air supplied to the fuel cell so that the state immediately before the occurrence of flooding is maintained. Control method of fuel cell system.

  The present invention can be realized in various forms. For example, in addition to the fuel cell system, the present invention can be realized in various forms such as a control method of the fuel cell system.

It is explanatory drawing which shows the fuel cell system of a present Example. It is an operation | movement flowchart at the time of starting of a fuel cell system. It is explanatory drawing which shows an example of the measurement method and measurement result of an impedance measurement. It is explanatory drawing which shows the relationship between the moisture content of the cell of a fuel cell, and an impedance. It is an operation | movement flowchart of the fuel cell system after restart.

  FIG. 1 is an explanatory view showing a fuel cell system of the present embodiment. The fuel cell system 10 includes a fuel cell 100, an oxidizing gas supply pipe 200, an oxidizing gas exhaust pipe 250, a fuel gas supply pipe 300, a fuel gas exhaust pipe 350, a cell monitor 410, an impedance measuring instrument 420, and an ECU 500 ( Electronic Control Unit) and barometer 401. The fuel cell 100 includes a plurality of single cells (not shown). A cell monitor 410 is connected to each single cell, and the voltage and current of each single cell can be monitored. An impedance measuring device 420 is connected to some unit cells, and the impedance of the unit cell can be measured. The single cell for measuring impedance may be, for example, a single cell arranged at both ends. Single cells arranged at both ends are more likely to be flooded or dry-up than other single cells. The barometer 401 acquires atmospheric pressure, and may not be connected to the oxidizing gas supply pipe 200.

  The oxidizing gas supply pipe 200 is connected to the fuel cell 100. In this embodiment, air is used as the oxidizing gas. The oxidizing gas supply pipe 200 is provided with an air cleaner 210, an air pump 220, an intercooler 230, a filter 235, and air flow meters 201 to 203. The air cleaner 210 removes dust and dirt in the air when taking in air in the atmosphere. The air pump 220 compresses the air and supplies it to the fuel cell 100. The intercooler 230 cools air that has become hot due to compression. The motor 221 of the intercooler 230 and the air pump 220 is cooled by the FC cooling system. The filter 235 removes fine dust and dust that could not be removed by the air cleaner 210. Air flow meters 201-203 measure the flow rate of air.

  The fuel gas supply pipe 300 is connected to the fuel cell 100. In this embodiment, hydrogen is used as the fuel gas. A hydrogen tank 310 and a pressure adjustment valve 311 are connected to the oxidizing gas supply pipe 200. The pressure adjustment valve 311 adjusts the pressure of hydrogen supplied to the fuel cell 100.

  The oxidizing gas exhaust pipe 250 is connected to the fuel cell 100. The oxidizing gas exhaust pipe 250 is provided with a diluter 260, a muffler 270, a pressure regulating valve 280, a shut valve 281, and a pressure gauge 402. The oxidizing gas exhaust pipe 250 is connected to the oxidizing gas supply pipe 200 by a bypass pipe 290. A bypass valve 291 is provided in the bypass pipe 290. The fuel gas exhaust pipe 350 is connected to the fuel cell 100 and the diluter 260. The fuel gas exhaust pipe 350 is provided with an exhaust drain valve 381.

  The diluter 260 mixes the fuel exhaust gas discharged from the fuel cell 100 and the oxidation exhaust gas discharged from the fuel cell 100 to reduce the concentration of the fuel exhaust gas. The muffler 270 reduces exhaust noise when exhaust gas is exhausted. The pressure regulating valve 280 adjusts the pressure of the oxidizing gas supplied to the fuel cell. The shut valve 281 is open when the fuel cell 100 is operating, and is closed when the fuel cell 100 is stopped. The bypass valve 291 is used when excess oxidizing gas flows through the oxidizing gas exhaust pipe 250 without passing through the fuel cell 100.

  FIG. 2 is an operation flowchart when starting the fuel cell system. In step S <b> 200, ECU 500 supplies air of a predetermined flow rate to fuel cell 100. The predetermined flow rate of air may be any flow rate as long as the fuel cell 100 does not cause flooding or dry-up when the fuel cell 100 is operated with this amount of air. For example, this predetermined amount of air can be determined at the time of fuel cell design.

  In step S210, ECU 500 measures the current, voltage and impedance of the single cell. FIG. 3 is an explanatory diagram illustrating an example of a measurement method and a measurement result of impedance measurement. FIG. 3A is an explanatory diagram showing a method for measuring the impedance of a fuel cell. The impedance measuring device 420 causes the voltage drawn from the fuel cell 100 to have a minute amplitude (V ± ΔV) at the frequency f, and measures the current I flowing through the fuel cell 100 at that time. The current I has a small amplitude (I ± ΔI), similar to a minute change in voltage. The impedance measuring instrument 420 applies a voltage in the same manner by changing the frequency, and measures the current. Next, ECU 500 calculates impedance Z using fast Fourier transform with frequency, voltage, and current as parameters. FIG. 3B shows an example of the calculation result of the impedance Z. The impedance Z has a real component and an imaginary component. Further, the value of the impedance Z varies depending on the frequency. In this embodiment, the real component R at the target frequency is used. Hereinafter, the real component R is also referred to as “impedance R”. Note that the target frequency is obtained in advance by experiments.

  FIG. 4 is an explanatory diagram showing the relationship between the water content of the fuel cell and the impedance. This graph can be obtained in advance by, for example, design parameters of the fuel cell 100 or experiments. In step S220 of FIG. 2, ECU 500 determines point R3 on the graph of FIG. 4 based on the impedance obtained in step S210. The position of this point R3 is a position where neither flooding nor dry-up occurs with respect to the fuel cell 100.

  In step S230 in FIG. 2, the ECU 500 decreases the amount of air that flows to the fuel cell 100. When the amount of air flowing to the fuel cell 100 is reduced, the amount of water carried away by the air is reduced, so that the water content of the cells of the fuel cell 100 is increased. That is, it moves in the lower right direction along the graph of FIG. The air flow rate is preferably decreased stepwise. This is because if the amount of air is suddenly reduced, the operation of the fuel cell 100 may fluctuate rapidly. Further, the smaller the air flow rate, the lower the power consumption in the air pump 220, so the fuel efficiency of the fuel cell system 10 is better. In step S240, the ECU 500 measures the amount of air, the current of the single cell, the voltage, and the impedance at each stage.

  In step S250, ECU 500 determines whether fuel cell 100 is flooded or not. In the flooding state, the oxidizing gas hardly reaches the electrolyte membrane, so the electromotive force of the single cell is greatly reduced. Therefore, ECU 500 measures the voltage of the single cell, and can determine that the flooding state has occurred when the voltage of the single cell falls below a predetermined value for a predetermined time or more. When the fuel cell 100 is not in the flooding state, the ECU 500 moves the process to step S230 and further reduces the air flow rate. On the other hand, when the fuel cell 100 is flooded, the ECU 500 moves the process to step S260.

  In step S260, ECU 500 determines point R2 on the graph of FIG. 4 based on the impedance value in the flooding state. In step S270, ECU 500 increases the air flow rate by a predetermined amount ΔV from the air flow rate in the flooding state. The air flow rate may be the air flow rate immediately before the flooding state occurs when the air flow rate is decreased. ECU 500 stores this flow rate. In step S280, ECU 500 measures and stores the current, voltage, and impedance of the single cell when the air flow rate is increased by ΔV. In step S290, a point R4 on the graph of FIG. 4 is determined based on the impedance value. ECU 500 adjusts the air flow rate with the impedance at point R4 as a target. The operating point from the start in FIG. 4 moves from the start state (A) to the lower right direction along the graph, enters the flooding occurrence state (B), returns to the upper left direction, and reaches the target value (C). Moving.

  FIG. 5 is an operation flowchart of the fuel cell system after restart. In step S500, the ECU 500 supplies the fuel cell 100 with the air having the flow rate stored in step S270 of FIG. In step S510, ECU 500 measures the current, voltage and impedance of the single cell.

  In step S520, ECU 500 determines whether or not the impedance value measured in step S510 in FIG. 5 is greater than the target value (impedance value stored in step S280 in FIG. 2). If the impedance value measured in step S510 in FIG. 5 is greater than the target value by a predetermined value or more, ECU 500 reduces the air flow rate. That is, it is considered that the impedance is increased as a result of air being taken away too much by the air flow.

  In step S540, ECU 500 determines whether or not the impedance value measured in step S510 in FIG. 5 is smaller than the target value (impedance value stored in step S280 in FIG. 2). When the impedance value measured in step S510 in FIG. 5 is smaller than the target value by a predetermined value or more, ECU 500 increases the flow rate of air. That is, it is considered that the impedance is lowered as a result of the water not being sufficiently removed by the air flow. When the impedance value measured in step S510 in FIG. 5 is substantially the same as the target value, ECU 500 moves the process to step S560 and maintains the air flow rate at the same flow rate.

  As described above, according to the present embodiment, the flow rate of air supplied to the fuel cell can be adjusted with a simple configuration so that the flow rate of air is slightly higher than that in the flooding state. Further, since the impedance is acquired using the impedance value immediately before flooding as a target value and the flow rate of air (air pump operation) is controlled based on the impedance value, the control is simple. Further, it is possible to easily detect the occurrence of flooding based on the voltage of the single cell.

  In the present embodiment, the ECU 500 does not have to perform the flow shown in FIG. 2 every time the fuel cell system is activated, and may be performed every certain period and every certain number of activations. Further, ECU 500 may execute the flow shown in FIG. 2 a plurality of times instead of only once at the time of one activation.

  In the present embodiment, the fluctuation of the impedance value due to temperature and pressure is not described, but the fluctuation of the impedance value due to temperature and pressure may be mapped in advance and the impedance may be corrected using this map.

  In the second and subsequent activations, the air flow rate in step S200 of FIG. 2 may be used as the air flow rate immediately before the first flooding (step S270). In this case, there may be a flooding state at the time of startup. In such a case, the air flow rate is once increased to obtain the air flow rate in step S200 in FIG. 2, and then the flow in FIG. 2 is executed. That's fine. That is, the operation at point R3 may be executed once.

  In the present embodiment, the flow rate of air is measured as a parameter, but the driving force of the air pump 220 may be used as a parameter instead. The air flow rate is a function of the driving force of the air pump 220, and the ECU 500 can directly control not the amount of air but the driving force of the air pump 220.

  The embodiments of the present invention have been described above based on some examples. However, the above-described embodiments of the present invention are for facilitating the understanding of the present invention and limit the present invention. It is not a thing. The present invention can be changed and improved without departing from the spirit and scope of the claims, and it is needless to say that the present invention includes equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 100 ... Fuel cell 200 ... Oxidizing gas supply pipe 201-203 ... Air flow meter 210 ... Air cleaner 220 ... Air pump 221 ... Motor 230 ... Intercooler 235 ... Filter 250 ... Oxidizing gas exhaust pipe 260 ... Diluter 270 ... Muffler 280 ... Pressure regulating valve 281 ... Shut valve 290 ... Bypass pipe 291 ... Bypass valve 300 ... Fuel gas supply pipe 310 ... Hydrogen tank 311 ... Pressure regulating valve 350 ... Fuel gas exhaust pipe 381 ... Exhaust drain valve 401 ... Atmospheric pressure gauge 402 ... Pressure Total 410 ... Cell monitor 420 ... Impedance measuring instrument 500 ... ECU

Claims (3)

A fuel cell system,
A fuel cell;
An air pump for supplying air to the fuel cell;
A voltage measuring unit for obtaining a voltage of the fuel cell;
A control unit that controls driving of the air pump to control a flow rate of air supplied to the fuel cell;
With
The control unit gradually decreases the flow rate of the air when the fuel cell is started up, and when the voltage of the fuel cell falls below a predetermined voltage for a predetermined time or more, It is determined that a flooding state has occurred, and then the flow rate of the air is increased to a flow rate immediately before the occurrence of the flooding state, thereby supplying the fuel cell with the state immediately before the occurrence of the flooding. Control the air flow,
Fuel cell system. The fuel cell according to claim 1, further comprising:
Comprising an impedance measuring device for measuring the impedance of the fuel cell;
The controller is
Storing the impedance in the state immediately before the flooding occurs as a target impedance value;
When the impedance measured after that becomes larger than the target impedance value, the amount of air supplied to the fuel cell is decreased, and the impedance measured thereafter becomes smaller than the target impedance value. When the fuel cell system increases the amount of air supplied to the fuel cell. A control method for a fuel cell system, comprising:
(A) supplying air to the fuel cell when starting the fuel cell;
(B) The amount of air supplied to the fuel cell is gradually decreased, and the flooding state occurs when the voltage of the fuel cell drops below a predetermined voltage for a predetermined time or more. The process of judging that
(C) after the flooding state occurs, increasing the flow rate of the air to a flow rate immediately before the flooding state occurs;
(D) controlling the flow rate of air supplied to the fuel cell so that the state immediately before the occurrence of flooding is maintained;
A control method for a fuel cell system.

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