JP2006190571A - Control device for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate a flooding at anode side without switching a flow passage between an anode and a cathode. <P>SOLUTION: On the control device for the fuel cell generating power by fuel gas supplied to anode side of a membrane-electrode assembly and oxidizer supplied to cathode side, when it is judged that a flooding is generated at anode side while operating the fuel cell 20, the fuel cell 20 is operated in a state of reducing the actual supply amount of the air below that corresponding to a target power supply amount. At this time, hydrogen generated at cathode side of the fuel cell 20 may be circulated toward anode side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for a fuel cell, and more particularly to a technique effective for eliminating flooding on the anode side.

For example, in a solid polymer electrolyte fuel cell, hydrogen is converted into hydrogen ions and electrons on the anode side, the hydrogen ions move to the cathode side through the electrolyte membrane, and oxygen, hydrogen ions and electrons on the cathode side. The reaction to produce water from is performed. When this generated water diffuses (moves) to the anode side through the electrolyte membrane and the diffusion water on the anode side becomes excessive (flooding), the cell voltage particularly at the end in the cell stacking direction is lowered and power generation becomes impossible. Patent Document 1 discloses a technique for forming a moisture distribution optimal for restarting between an anode and a cathode.
JP 2004-179086 A

  Since the technology of this Patent Document 1 uses the movement of water associated with the movement of hydrogen ions to move the generated water on the cathode side to the anode side, the fuel gas supply to the fuel cell is normally operated. There is a problem that a pipe line and a valve for switching from the anode side to the cathode side are necessary, and the configuration of the fuel cell system becomes complicated.

  Therefore, an object of the present invention is to provide a fuel cell control device that can eliminate flooding on the anode side without switching the flow path between the anode and the cathode.

  The fuel cell control device according to the present invention is a fuel cell control device that generates power by supplying fuel gas to the anode side of the membrane-electrode assembly and oxidant to the cathode side, and the fuel cell is in operation. When it is determined that the fuel cell is in the predetermined state, the fuel cell is caused to generate power in a state where the actual oxidant supply amount is lower than the oxidant supply amount corresponding to the target power generation amount.

  Further, another fuel cell control device according to the present invention is a fuel cell control device for generating power by supplying fuel gas to the anode side of the membrane-electrode assembly and supplying an oxidant to the cathode side. The fuel cell in a state where the oxidant supply amount is reduced so that the ratio of the oxidant supply amount / fuel gas supply amount is lower than the setting during operation when it is determined that the fuel cell is in a predetermined state during the stoppage. To generate electricity.

  In these configurations, the predetermined state is, for example, a state in which flooding occurs on the anode side of the fuel cell, or a state in which flooding is expected to occur. The state where flooding occurs on the anode side is, for example, when the measured voltage (cell voltage) of the fuel cell drops below a predetermined value, or when a voltage change with an amplitude exceeding the predetermined value is repeated irregularly. Is determined.

  On the other hand, a state where flooding is expected to occur on the anode side is determined, for example, when a predetermined time or more has passed since the fuel cell was stopped. When it is determined that the fuel cell is in these predetermined states, not only the oxidant supply to the cathode side is reduced, but the oxidant supply may be completely cut off. The amount (absolute amount) of fuel gas supplied to the anode side of the fuel cell may be the same regardless of the result of the determination.

  According to the above configuration, without switching the flow path between the anode and the cathode, water existing on the anode side (for example, diffusion water in which the produced water on the cathode side diffuses to the cathode side) is supplied to the cathode side as electric accompanying water. It can be moved. For example, when hydrogen gas is used as the fuel gas, as shown in FIG. 2, a reaction for converting hydrogen into hydrogen ions and electrons is performed on the anode side, and the hydrogen ions pass through the membrane-electrode assembly to the cathode side. Move to. At that time, the water on the anode side moves to the cathode side as the electric accompanying water.

  In the fuel cell control device according to the present invention, hydrogen generated on the cathode side of the fuel cell in accordance with power generation in a state where the oxidant supply amount is reduced may be recirculated to the anode side.

  When hydrogen gas is used as the fuel gas, as described above, a reaction for converting hydrogen into hydrogen ions and electrons is performed on the anode side, and the hydrogen ions move to the cathode side through the membrane-electrode assembly. On the cathode side, in the normal fuel cell reaction shown in FIG. 3, a reaction for generating water from hydrogen ions, an oxidant and electrons is performed. In the present invention, an oxidant corresponding to a target power generation amount is used. Since the actual supply amount of the oxidant is reduced rather than the supply amount, surplus hydrogen ions and electrons react to generate hydrogen. Therefore, if this hydrogen is recirculated to the anode side, it becomes possible to reuse a part of the hydrogen supplied to the anode side during the operation of the fuel cell, and when the fuel cell is stopped, It is possible to suppress wasteful hydrogen consumption.

  A fuel cell control device according to the present invention is a fuel cell control device that generates power by receiving supply of fuel gas on the anode side of the membrane-electrode assembly and supply of oxidant on the cathode side. Is greater than a predetermined amount, and if the result of the determination is negative, the oxidant and fuel gas are adjusted so that the ratio of oxidant supply amount / fuel gas supply amount becomes the first ratio. If the determination result is affirmative, the oxidant and the fuel gas are supplied at a second ratio in which the ratio of the oxidant supply amount / fuel gas supply amount is smaller than the first ratio. Also good.

  Even with such a configuration, water existing on the anode electrode side can be moved to the cathode electrode side as electric accompanying water without switching the flow path between the anode and the cathode.

  According to the present invention, water existing on the anode side can be moved to the cathode side as electric accompanying water without switching the flow path between the anode and the cathode. As a result, flooding on the anode side is eliminated, and power generation performance is prevented from being lowered.

  FIG. 1 is a schematic configuration diagram showing a fuel cell system including a fuel cell control device according to an embodiment of the present invention. This fuel cell system can be applied to an in-vehicle power generation system of a fuel cell vehicle, and can be applied to, for example, a stationary power generation system.

  As shown in the figure, for example, air (outside air) as an oxidizing gas (oxidant) is supplied to the cathode inlet side of the fuel cell 20 via the air supply path 11. The air supply path 11 is provided with an air filter that removes particulates from the air, a compressor 12 that pressurizes the air, an air supply valve 13 that supplies air to the fuel cell 20 or stops supply, and the like. The compressor 12 is driven by an auxiliary motor (load). The exhaust passage 15 is provided with a pressure sensor for detecting the exhaust pressure, a pressure adjusting valve, and the like.

  For example, hydrogen gas as the fuel gas is supplied from the hydrogen supply source 30 to the anode inlet side of the fuel cell 20 through the fuel supply path 31. The hydrogen supply source 30 corresponds to, for example, a high-pressure hydrogen tank, but may be a so-called fuel reformer, a hydrogen storage alloy, or the like.

  The fuel supply path 31 includes a hydrogen supply valve that supplies hydrogen from the hydrogen supply source 30 or stops the supply, at least one pressure adjustment valve that adjusts the supply pressure of hydrogen gas to the fuel cell 20 by reducing the pressure, and the fuel cell 20. An FC inlet valve for communicating / blocking the anode side inlet and the fuel supply path 31 is provided.

  The hydrogen gas that has not been consumed in the fuel cell 20 is discharged as a hydrogen off-gas to the hydrogen circulation path 35 and returned to the fuel supply path 31. The hydrogen circulation path 35 includes an FC outlet valve for communicating / blocking the anode outlet of the fuel cell 20 and the hydrogen circulation path 35, a gas-liquid separator for recovering moisture from the hydrogen off gas, a hydrogen pump 36 for pressurizing the hydrogen off gas, and the like. Is provided. The hydrogen circulation path 35 is connected to an exhaust path via a purge valve, and the hydrogen off-gas is appropriately discharged (purged) to the outside.

  The hydrogen circulation path 35 is connected to a reflux path 41 for refluxing the hydrogen gas contained in the exhaust path 15 to the anode side of the fuel cell 20. The off-gas from the cathode side of the fuel cell 20 is discharged to the outside as it is through the exhaust path 15 by a flow path switching valve (not shown), and is joined to the hydrogen circulation path 35 from the reflux path 41 to the fuel supply path 31. May be refluxed. The flow path switching valve is controlled by the control unit 60.

  The fuel cell 20 is configured as a fuel cell stack in which a required number of cells that generate electric power by electrochemical reactions of the following formulas 1 and 2 (see FIG. 3) when a fuel gas and an oxidizing gas are supplied are stacked. The cell includes an MEA (membrane-electrode assembly) and a pair of separators that sandwich the MEA. The MEA includes an electrolyte membrane made of an ion exchange membrane made of a polymer material and a pair of electrodes (anode and cathode) sandwiching the electrolyte membrane from both sides.

Anode side: H ₂ → 2H ⁺ + 2e- ... Formula 1
Cathode side: 2H ⁺ + 2e− (1/2) O ₂ → H ₂ O Formula 2
The fuel cell 20 is provided with a cell voltage monitor 50 for making a cell voltage for each cell or a predetermined number of cell groups. The detection signal of the cell voltage monitor 50 is sent to the control unit 60.

  The electric power generated by the fuel cell 20 is supplied to a power control unit (not shown). The power control unit consists of an inverter that drives the drive motor (load) of the vehicle, an inverter that drives various auxiliary machines (loads) such as a compressor motor and a motor for a hydrogen pump, and charging and recharging of the secondary battery. DC-DC converter etc. which supply electric power to motors from are provided. In FIG. 1, these loads are collectively shown as a load 71, and are connected to the fuel cell 20 by a cutoff switch 72.

  The control unit (control device) 60 is configured by a control computer system such as a CPU, ROM, RAM, HDD, input / output interface, and display. The control unit 60 determines the output distribution between the fuel cell 20 and the battery according to the output request, and each part of the system so that air and hydrogen gas corresponding to the target power generation amount of the fuel cell 20 are supplied to the fuel cell 20. Control the operation of valves and motors.

  Based on the detection signal from the cell voltage monitor 50, the control unit 60 detects that flooding has occurred on the anode side, or, for example, when the operation is stopped and left for a long time. When the cell voltage drop is expected, the air supply valve 13 is closed and the air supply from the compressor 12 to the cathode side of the fuel cell 20 is stopped. On the anode side of the fuel cell 20, the supply of hydrogen gas corresponding to the target power generation amount to the fuel cell 20 is continued.

  Then, on the anode side of the fuel cell 20, hydrogen ions are generated by the reaction of the above formula 1. On the anode side, water on the cathode side generated by the reaction of the above formula 2 during steady operation moves through the electrolyte membrane and diffuses to the anode side, and hydrogen ions on the anode side are transferred from the cathode side to the anode side. The diffused water diffused in the water moves to the cathode side through the electrolyte membrane as electric accompanying water.

  On the other hand, on the cathode side, hydrogen is generated by the reaction of the following formula 3 by hydrogen ions that have moved from the anode side through the electrolyte membrane and electrons that have moved from the anode side through the external circuit 73 including the load 71. Power generation is performed.

Cathode side: 2H ⁺ + 2e− → H ₂ Formula 3
At this time, since air is not supplied to the cathode side (see FIG. 2), the reaction of the above formula 2 does not occur, and water is not generated on the cathode side. In other words, there is no diffusion (movement) of the generated water from the cathode side to the anode side due to the concentration difference as in the steady operation, so that the generated water on the anode side is sequentially supplied to the cathode side as electric accompanying water in the fuel cell 20. Moving.

  While monitoring the output signal of the cell voltage monitor 50, the control unit 60 causes the fuel cell 20 to continue the reaction (power generation) of Formula 3 to the extent that the anode-side diffusion water does not cause a voltage drop due to flooding. . Thereby, it is possible to prevent the cell voltage from decreasing. In addition, the electric power generated by the power generation may be supplied to a secondary battery in the vehicle or supplied as a household power source when the vehicle is parked in a house garage.

  In addition, by switching a not-shown flow path switching valve based on a control command from the control unit 60, the off-gas from the cathode side of the fuel cell 20, that is, the off-gas containing hydrogen generated by the reaction of Equation 3 is recirculated. It may be joined from the path 41 to the hydrogen circulation path 35 and refluxed from the fuel supply path 31 to the anode of the fuel cell 20. In such a case, the hydrogen consumption can be reduced.

<Other embodiments>
The above embodiment is an example for explaining the present invention, and the present invention is not limited to this. Various components can be appropriately designed without departing from the gist thereof. For example, in the above embodiment, in order to move the diffusion water on the anode side to the cathode side as the electric accompanying water, the air supply to the cathode is completely cut off, but the actual air supply amount to the cathode is changed to the fuel cell 20. The air supply amount corresponding to the target power generation amount may be reduced.

  In such a configuration, although water is generated on the cathode side according to the above equation 2, if the amount of air supplied to the cathode is reduced, the amount of generated water on the cathode side is also reduced. It can be moved to the cathode side as accompanying water. This is the same even if the supply oxygen concentration (oxidant concentration) is lowered instead of reducing the air supply amount to the cathode.

  In the above embodiment, when it is determined that the fuel cell 20 is in a predetermined state during its operation, power generation is performed in a state where the actual air supply amount is lower than the air supply amount corresponding to the target power generation amount. However, when it is determined that the fuel cell is in the same state during its stoppage, the fuel gas is supplied to the anode side of the fuel cell while the oxidant supply amount / fuel gas is supplied to the cathode side. The fuel cell may be caused to generate electric power in a state where the oxidant is supplied or not supplied at all so that the ratio of the supply amount becomes lower than the setting at the time of operation.

  Furthermore, the air supply valve 13 is not necessarily an essential configuration. In a configuration without the air supply valve 13, the air supply to the cathode may be stopped by stopping the compressor 12. Further, instead of providing the air supply valve 13, a bypass flow path provided with a film, a filter or the like for reducing the oxidant concentration is provided in the air supply path 11, and the oxidant from the oxidant supply source is circulated through the bypass flow path. The fuel cell may be supplied.

  Furthermore, the control unit (control device) 60 determines whether or not the amount of moisture on the anode electrode side is larger than a predetermined amount based on, for example, the detection signal of the cell voltage monitor 50, and the determination result is negative. In this case, the oxidant and the fuel gas are supplied so that the ratio of the oxidant supply amount / fuel gas supply amount becomes the first ratio. If the determination result is affirmative, the oxidant supply amount / fuel gas is supplied. A configuration may be adopted in which the oxidant and the fuel gas are supplied at a second ratio in which the ratio of the supply amounts is smaller than the first ratio. In this configuration, the amount (absolute amount) of fuel gas supplied to the anode side of the fuel cell may be the same regardless of the determination result.

1 is a schematic configuration diagram of a fuel cell system including a fuel cell control device according to an embodiment of the present invention. The schematic diagram explaining the principle which can eliminate the flooding of the anode side by this invention. The schematic diagram which shows the electrochemical reaction of the fuel cell at the time of steady operation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Fuel cell, 12 ... Compressor, 13 ... Air supply valve, 30 ... Hydrogen supply source, 41 ... Recirculation path, 50 ... Cell voltage monitor, 60 ... Control part

Claims (5)

A fuel cell control device for generating power by supplying fuel gas to the anode side of the membrane-electrode assembly and supplying an oxidant to the cathode side,
When the fuel cell is determined to be in a predetermined state during its operation, the fuel cell causes the fuel cell to generate power in a state where the actual oxidant supply amount is lower than the oxidant supply amount corresponding to the target power generation amount Control device. A fuel cell control device for generating power by supplying fuel gas to the anode side of the membrane-electrode assembly and supplying an oxidant to the cathode side,
A state in which the oxidant supply amount is reduced so that the ratio of the oxidant supply amount / fuel gas supply amount becomes lower than the setting during operation when it is determined that the fuel cell is in a predetermined state during the stoppage. A fuel cell control device for generating power from a fuel cell.   3. The fuel cell control device according to claim 1, wherein the predetermined state is a state in which flooding occurs on the anode side of the fuel cell or a state in which flooding is expected to occur. 4.   The fuel cell control device according to claim 1, wherein hydrogen generated on the cathode side of the fuel cell accompanying the power generation is recirculated to the anode side. A fuel cell control device for generating power by receiving supply of fuel gas on the anode side of the membrane-electrode assembly and supply of oxidant on the cathode side,
Determine whether the amount of moisture on the anode side is greater than a predetermined amount,
When the determination result is negative, the oxidant and the fuel gas are supplied so that the ratio of the oxidant supply amount / fuel gas supply amount becomes the first ratio,
When the determination result is affirmative, the control device for the fuel cell supplies the oxidant and the fuel gas at a second ratio in which the ratio of the oxidant supply amount / fuel gas supply amount is smaller than the first ratio. .