JP2006202696A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose a fuel cell system capable of impressing a high load immediately after the start-up of the system. <P>SOLUTION: The fuel cell system (10) that is a system carrying out an output limit of the fuel cell (20) at the start-up of the system is provided with a storage system (42) storing output limit characteristics (51, 52) of the fuel cell (20), a measurement means (41) measuring a soak standing time of the fuel cell (20), and an output limiting means (40) limiting outputs of the fuel cell (20) based on the soak standing time measured by the measurement means (41) and the output limiting characteristics (51, 52) stored in the storage device (42). Since an output limit can be changed in accordance with the soak standing time of the fuel cell (20), an optimum output limit can be obtained in accordance with inner conditions of the fuel cell (20) changing from time to time in response to the soak standing time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system, and more particularly to output restriction control at system startup.

The fuel cell system is a power generation system capable of taking out electric energy from electrodes provided on both surfaces of an electrolyte by electrochemically reacting a fuel gas and an oxidizing gas via an electrolyte. A fuel cell vehicle is equipped with a hydrogen storage source such as a high-pressure hydrogen tank in the vehicle, and hydrogen supplied from the vehicle and the air taken from outside air are sent to the fuel cell to react with each other. The motor is driven. Since the output voltage of the cell is as low as about 1V, in order to use the fuel cell system as a power source for driving the vehicle, it is configured as a fuel cell stack in which several hundred cells are connected in series. When operating the fuel cell system, it is necessary to detect local reaction gas shortage and flooding and other deterioration of the fuel cell system in advance to prevent damage to the fuel cell due to overcurrent and to obtain sufficient output. It is necessary to restore the state of the battery. In Patent Document 1, when the cell voltage falls below a predetermined value, the output of the fuel cell is restricted, and when the cell voltage recovers beyond the average cell voltage before the output restriction, the output restriction of the fuel cell is released. Technology has been proposed.
JP 2004-152604 A

  However, in a fuel cell vehicle, if the fuel cell is suddenly accelerated immediately after starting the fuel cell after it has been stopped for a certain period of time and then suddenly demanded a large power generation, the cell voltage drops. There is a case. When the cell voltage drops, the system may be stopped to prevent the fuel cell from being damaged. In view of such circumstances, conventionally, a preset output restriction characteristic is stored as map data, and after the system is started, output restriction is performed based on this map data. Therefore, the internal state of the fuel cell is good. In some cases, the power output may be limited even though stable power generation is possible, and driving performance (drivability) has deteriorated.

  By the way, it has been confirmed that when the fuel cell is stopped and left soaked for a long time beyond a certain time, the cell voltage decrease tendency is improved. If this characteristic is used, after leaving the soak for a long time, the fuel cell can be operated without limiting the output, so that it is possible to improve the running performance.

  Accordingly, an object of the present invention is to solve the above-described problems and to propose a fuel cell system that can apply a high load immediately after the system is started.

  In order to solve the above-described problems, a fuel cell system according to the present invention is a fuel cell system that limits the output of a fuel cell at the time of system startup, and includes a storage device that stores output limitation characteristics of the fuel cell, and a soak of the fuel cell Measuring means for measuring the leaving time, and output limiting means for limiting the output of the fuel cell based on the soak leaving time measured by the measuring means and the output limiting characteristic stored in the storage device. Since the output limit can be changed according to the soaking time of the fuel cell, the optimum output limit can be realized according to the internal state of the fuel cell which changes every moment according to the soaking time.

  The output limiting means preferably sets the output limit value of the fuel cell based on the soaking time and the output limiting characteristic. The output limit value is, for example, a power generation allowable current value or a power generation allowable power value.

  In addition to the above-described configuration, the fuel cell system of the present invention may further include learning control means for correcting the output limiting characteristic based on the soaking time of the fuel cell and the cell voltage reduction margin at the time of system startup. Through learning control, it is possible to perform optimum output restriction according to the characteristics of individual fuel cells.

  The output limiting means may limit the output of the fuel cell based on a relational characteristic curve between the soaking time of the fuel cell and the cell voltage drop at the time of starting the system. By limiting the output of the fuel cell based on the relationship characteristic curve between the soaking time of the fuel cell and the cell voltage drop at the time of starting the system, it is possible to implement the optimum output limitation according to the characteristics of the individual fuel cells.

  The output restricting means suppresses execution of the output restriction of the fuel cell when the soak leaving time of the fuel cell is less than the first time, and when the soaking time of the fuel cell is not less than the first time and less than the second time. It is preferable to limit the output of the fuel cell, and to suppress the output limitation of the fuel cell when the soaking time of the fuel cell is equal to or longer than the second time. When the soak standing time is less than the first time, the condensed water hardly moves to the anode side, so that almost no flooding occurs. When the soak standing time is equal to or longer than the second time, most of the condensed water moved to the anode side disappears due to natural drying or the like, so that almost no flooding occurs. That is, when the soak leaving time is less than the first time or in the range of the second time or more, almost no decrease in the cell voltage at the time of starting the system is observed, so it is preferable to suppress the output restriction of the fuel cell. However, the second time is longer than the first time.

  According to the present invention, since the output limit can be changed according to the soak leaving time of the fuel cell, the optimum output limit can be realized according to the internal state of the fuel cell that changes every moment according to the soak leaving time.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a system configuration diagram centering on an electric system of a fuel cell electric vehicle according to the present embodiment. The fuel cell system 10 mainly includes a fuel cell (cell stack) 20 in which a plurality of cells are stacked in series, a fuel gas supply device 21 that supplies fuel gas (hydrogen gas) to the anode of the fuel cell 20, An oxidizing gas supply device 22 that supplies an oxidizing gas (air) to the cathode of the fuel cell 20, a cell voltage detection device 23 that detects a cell voltage of the fuel cell 20, and a regenerative energy generated by the fuel cell 20 or when braking the vehicle , A DC / DC converter 33 that controls the power supply distribution between the fuel cell 20 and the secondary battery 34 by adjusting the output voltage of the fuel cell 20, and the fuel cell 20. Or the inverter 31 which converts the direct current power supplied from the secondary battery 34 into alternating current power, and supplies it to the traction motor (vehicle drive motor) 32, and the whole system are controlled. It is configured to include a control device 40. The measuring means 41 is a means for measuring the soaking time (or operation stop time) of the fuel cell 20, for example, the time from when the system stop signal is input to the control device 40 until the next system start signal is input. Measure. The storage device 42 stores two pieces of map data 51 and 52 having the output limit value of the fuel cell 20 (output limit characteristics such as a power generation allowable current value or a power generation allowable power value) as map values. The first map data 51 is output restriction map data having low output characteristics assuming that the fuel cell 20 is operated in a state where the cell voltage tends to decrease. The second map data 52 is output limit map data having a high output characteristic assuming that the fuel cell 20 is operated in a state where the cell voltage is unlikely to decrease.

  The fuel gas supply device 21 is, for example, a hydrogen gas from a high-pressure hydrogen tank filled with hydrogen gas at a high pressure, a hydrogen storage tank in which hydrogen is stored in a hydrogen storage alloy, or a reformed raw fuel (methane, ethane, propane, butane, etc.). It is comprised by the reformer etc. which produce | generate. The oxidizing gas supply device 22 is configured by, for example, an air compressor that compresses air taken from outside air. The cell voltage detection device 23 detects the cell voltage of each cell constituting the fuel cell 20 or the cell voltage of a cell group composed of a plurality of cells. In this specification, not only the output voltage of a single cell but also the output voltage of a cell group composed of a plurality of cells is referred to as a cell voltage.

  The control device 40 obtains the required power of the entire system (the sum of vehicle travel power and auxiliary power) based on the accelerator opening, the vehicle speed, and the like. Next, the distribution of the output power of the fuel cell 20 and the secondary battery 34 is determined, and the fuel gas supply device 21 and the oxidizing gas supply device 22 are controlled so that the power generation amount of the fuel cell 20 matches the target power. While adjusting the supply amount of the reaction gas to the battery 20, the DC / DC converter 33 is controlled to adjust the operation point (output voltage, output current) of the fuel cell 20. Furthermore, the control device 40 controls the inverter 31 so as to obtain the target vehicle speed according to the accelerator opening, and adjusts the rotational speed and rotational torque of the traction motor 32.

  FIG. 3 shows a relationship characteristic curve between the soaking time of the fuel cell and the cell voltage drop at the time of system startup. As shown in the figure, when the soak leaving time T is in the range of the time t1 or more and less than the time t2, the cell voltage drop at the time of starting the system is large. The cell voltage drop is the voltage difference between the average cell voltage and the lowest cell voltage. The minimum cell voltage refers to the minimum value of the cell voltage when a certain load such as rapid acceleration is applied at the time of system startup. In this way, when the battery operation is stopped for a while and then the battery operation is started again, the condensed water or the like generated at the cathode permeates the electrolyte membrane and moves to the anode side. The water droplets covering the anode hinder the supply of hydrogen to the anode when the system is started up, resulting in insufficient supply of the reaction gas and a decrease in cell voltage (flooding). However, when the soak leaving time T is less than the time t1, the condensate is not sufficiently moved to the anode side, so that almost no flooding occurs. When the soak standing time T is longer than the time t2, most of the condensed water that has moved to the anode side disappears due to natural drying or the like, so that almost no flooding occurs. In other words, when the soak leaving time T is less than the time t1 or in the range of t2 or more, there is almost no decrease in the cell voltage at the system startup.

  FIG. 4 shows a characteristic curve between the soaking time of each of the fuel cells A and B and the cell voltage drop at the time of starting the system. As shown in the figure, the fuel cell A has a large cell voltage drop margin at the time of starting the system even if the soak time is short, whereas the fuel cell B has a cell voltage at the time of starting the system if the soak time is not more than a certain level. It has the characteristic that no deterioration occurs. In this way, since the relationship characteristics between the soak time and the cell voltage drop at system startup are different for each fuel cell, appropriate processing that reflects the characteristics of the individual fuel cells is also applied to the output limiting process. It is desirable to do.

  The output limitation of the fuel cell 20 at the time of starting the system is to limit the execution of power generation control corresponding to the power generation request value even when there is a power generation request from a load connected to the fuel cell 20 at the time of fuel cell startup. Say. In other words, until the fuel cell 20 can stably generate power at the time of starting the system, it refers to control for quickly shifting to a state where power generation can be stably performed by limiting or ignoring the power generation request to the fuel cell 20.

  FIG. 2 shows a control routine describing the output limiting process of the fuel cell 20. This control routine is repeatedly executed at regular intervals by the control device 40 when the system is activated. When this control routine is called, the control device 40 determines whether or not the soak leaving time T of the fuel cell 20 is t1 ≦ T <t2, that is, when a certain high load is applied at the time of starting the system. It is determined whether or not it is in a state where it is easy to decrease (S1). If t1 ≦ T <t2 (S1; YES), the cell voltage is likely to decrease. Therefore, the output limit value is determined based on the first map data 51, and the output current and output of the fuel cell 20 are determined. The operating point of the fuel cell 20 is adjusted so that the electric power does not exceed the output allowable value (S2). Next, the control unit 40 determines whether or not the cell voltage has decreased (S3). If the cell voltage has decreased (S3; YES), the output restriction of the fuel cell 20 is insufficient, so that the output is performed. The first map data 51 is corrected (map adjustment) so that the limit value becomes lower (S4). If the cell voltage has not decreased (S3; NO), the output limit of the fuel cell 20 is sufficient, and the control routine is exited. On the other hand, when T <t1 or t2 ≦ T (S1; NO), since the cell voltage is difficult to decrease, an output limit value is determined based on the second map data 52, and the fuel cell 20 The operation point (output voltage, output current) is adjusted (S5).

  The control device 40 functions as output limiting means (S2, S5) for limiting the output of the fuel cell 20, and by repeatedly executing this control routine, the first map data 51 is converted into optimum output limit map data. It also functions as a learning control means (S4) for correction.

  According to the present embodiment, since the output restriction of the fuel cell 20 is performed according to the soak leaving time, the optimum output restriction can be realized according to the internal state of the fuel cell 20 that changes every moment according to the soak leaving time. Further, according to the present embodiment, it is possible to obtain optimum output restriction map data suitable for the characteristics of the fuel cell 20 by repeatedly executing the output restriction processing routine, so that it is possible to travel at a high load immediately after the system is started. Therefore, the driving performance can be improved.

1 is a system configuration diagram of a fuel cell electric vehicle according to an embodiment. It is a flowchart describing an output restriction processing routine. It is a characteristic curve between a soak leaving time and a cell voltage reduction allowance. It is a comparison figure of the relational characteristic curve of soak leaving time and cell voltage drop margin.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 20 ... Fuel cell 21 ... Fuel gas supply apparatus 22 ... Oxidation gas supply apparatus 23 ... Cell voltage detection apparatus 31 ... Inverter 32 ... Traction motor 33 ... DC / DC converter 34 ... Secondary battery 40 ... Control apparatus 41 ... Measuring means 42 ... Storage device 51 ... First map data 52 ... Second map data

Claims (5)

  A fuel cell system for limiting the output of a fuel cell at system startup, a storage device for storing output limitation characteristics of the fuel cell, measuring means for measuring the soaking time of the fuel cell, and the soak measured by the measuring means A fuel cell system comprising: an output limiting unit that limits the output of the fuel cell based on a standing time and an output limiting characteristic stored in the storage device.   2. The fuel cell system according to claim 1, wherein the output limiting unit sets an output limit value of the fuel cell based on the soak leaving time and the output limiting characteristic. 3.   The fuel cell system according to claim 1 or 2, further comprising learning control means for correcting the output limiting characteristic based on a soaking time of the fuel cell and a cell voltage reduction margin at the time of starting the system. Fuel cell system.   The fuel cell system according to any one of claims 1 to 3, wherein the output limiting means has a relational characteristic curve between a soaking time of the fuel cell and a cell voltage reduction margin at the time of starting the system. A fuel cell system that limits the output of the fuel cell based on the fuel cell system.   2. The fuel cell system according to claim 1, wherein the output restriction unit suppresses execution of the output restriction when the soak leaving time is less than a first time, and the soak leaving time is a first time. The fuel cell system that executes the output restriction when the time is less than the second time and suppresses the output restriction when the soak leaving time is the second time or more.

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