JP5080876B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  In the fuel cell system, a back pressure valve is provided in a cathode off gas pipe through which the cathode off gas discharged from the fuel cell circulates, and the opening of the back pressure valve is controlled, so that the fuel cell is provided with an output required for the fuel cell. The supply pressure of the supplied cathode gas is changed.

Fuel cells have the characteristic that the power generation performance increases when the cathode gas supply pressure is increased. When the required output for the fuel cell is high, such as when accelerating in a fuel cell vehicle, the back pressure valve should be almost fully closed. Thus, the supply pressure of the cathode gas is increased (see, for example, Patent Document 1).
JP 2005-38691 A

  However, when the back pressure valve is substantially fully closed, the cathode gas stops flowing (especially at the outlet side of the fuel cell). If power generation is continued in this state, the fuel cell will be in an oxygen-deficient state and the power generation performance will be reduced. In addition to lowering, there is a risk of causing deterioration of the solid polymer electrolyte membrane of the fuel cell.

  FIG. 5 is a time chart showing the voltage drop of the fuel cell when the fuel cell is required to have a high output and the back pressure valve is controlled to be fully closed. The voltage suddenly increases with the back pressure valve being fully closed. It turns out that it falls to. In this figure, FC is the fuel cell, FC voltage is the output voltage of the fuel cell, FC current is the output current of the fuel cell, the target CG pressure is the target cathode gas pressure in the fuel cell, and the actual COG pressure is the actual cathode off-gas pressure. Indicates.

  Therefore, the present invention provides a fuel cell system that can suppress a decrease in power generation performance during high-power operation of the fuel cell.

The fuel cell system according to the present invention employs the following means in order to solve the above problems.
According to the first aspect of the present invention, a fuel cell (for example, a fuel cell 1 in an embodiment to be described later) that supplies an anode gas and a cathode gas to generate power, and a cathode gas supplied to the fuel cell are disposed outside the fuel cell. A back pressure valve (for example, a back pressure valve 15 in an embodiment to be described later) installed in a discharge cathode off gas flow path (for example, a cathode off gas channel 13 in an embodiment to be described later), and a valve opening degree of the back pressure valve are controlled. Thus, a pressure control unit (for example, ECU 70 in the embodiment described later) for adjusting the cathode gas pressure inside the fuel cell, and a load (for example, a traveling motor 43 in the embodiment described later) that consumes the electric power generated by the fuel cell. ), A required output detector that detects a required output required by the load to the fuel cell (for example, a rear Step S101) in the embodiment to be performed, and a minimum valve opening setting unit for setting the minimum valve opening of the back pressure valve in accordance with the requested output detected by the requested output detecting unit (for example, step S104 in the embodiment described later) ), A cathode gas pressure detection unit (for example, a pressure sensor 37 in an embodiment described later) for detecting the cathode gas pressure inside the fuel cell , and a target cathode gas according to the required output detected by the required output detection unit A target pressure calculation unit (for example, step S102 in an embodiment to be described later) for calculating the pressure, and the pressure control unit calculates the target pressure based on the cathode gas pressure detected by the cathode gas pressure detection unit. The valve opening of the back pressure valve is feedback controlled so that the target cathode gas pressure calculated by the When the opening command value for the back pressure valve by the feedback control is less than or equal to the minimum valve opening set by the minimum valve opening setting unit, the valve opening of the back pressure valve does not fall below the minimum valve opening. The feedback control includes an integral term, and when the opening command value is equal to or less than the minimum valve opening, the pressure control unit is configured to increase the opening command value beyond the minimum valve opening. While canceling the integral term, the minimum valve opening during the cancellation period of the integral term is changed according to the change in the required output of the load, the minimum valve opening setting unit, the required output of the load The minimum valve opening is set so as to increase as it increases .
By configuring in this way, the minimum valve opening of the back pressure valve is set according to the required output of the load, so that the back pressure valve is not fully closed even when the cathode gas pressure is increased due to a high output request. Thus, the flow of the cathode gas inside the fuel cell can be ensured.

Further , even when the demand output of the load increases and the demands of the supply pressure and the supply flow rate of the cathode gas increase, the cathode gas flow rate corresponding to the demand output of the load can be secured.

Furthermore , even when the valve opening degree of the back pressure valve is feedback-controlled, the valve opening degree of the back pressure valve can be prevented from becoming less than the minimum valve opening degree.

  In addition, the integral term can be canceled while the opening command value for the back pressure valve by feedback control is less than or equal to the minimum valve opening.

According to the first aspect of the present invention, the cathode gas flow inside the fuel cell can be secured even when the fuel cell has a high output demand. Degradation of the molecular electrolyte membrane can be prevented.
Further , even when the required load output increases, the cathode gas flow rate corresponding to the required load output can be secured.
Furthermore , even when feedback control is performed on the valve opening of the back pressure valve, it is possible to prevent the valve opening of the back pressure valve from becoming less than the minimum valve opening. The valve opening degree of the back pressure valve can be controlled by feedback control while ensuring.
In addition , since the integral term can be canceled while the opening command value for the back pressure valve by feedback control is less than the minimum valve opening, when the integral term cancellation period ends, that is, the opening command value is When the minimum valve opening is exceeded, overshoot due to feedback control of the integral term can be prevented, and responsiveness can be improved.

  Embodiments of a fuel cell system 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.

A schematic configuration of the fuel cell system will be described with reference to FIG.
The fuel cell 1 is a type that obtains electric power by chemically reacting a reaction gas. For example, a solid polymer electrolyte membrane made of a solid polymer ion exchange membrane or the like is sandwiched from both sides by an anode and a cathode to form a membrane electrode structure. A plurality of cells each having an anode gas channel 3 and a cathode gas channel 5 are stacked on both sides of the membrane electrode structure. Hydrogen gas is supplied to the anode gas channel 3 as an anode gas. When oxygen-containing air is supplied to the cathode gas channel 5 as a cathode gas, hydrogen ions generated by the catalytic reaction at the anode move through the solid polymer electrolyte membrane to the cathode, and oxygen and electrochemistry are produced at the cathode. It reacts and generates electricity, producing water. 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. In FIG. 1, the anode gas channel 3 and the cathode gas channel 5 of a single cell are shown as representatives.

  The cathode gas (air) is pressurized to a predetermined pressure by a compressor 7 such as a supercharger, and supplied to the cathode gas channel 5 of the fuel cell 1 through the cathode gas supply channel 9 and the humidifier 11. After the cathode gas supplied to the fuel cell 1 is used for power generation, it is discharged from the fuel cell 1 together with the water produced on the cathode side as cathode offgas to the cathode offgas flow path 13, passes through the humidifier 11, and passes through the back pressure valve 15. Are discharged to an exhaust treatment device (not shown). The humidifier 11 includes, for example, a water permeable membrane. When the cathode gas and the cathode off gas are circulated with the water permeable membrane interposed therebetween, moisture contained in the cathode off gas permeates the water permeable membrane and becomes cathode. It moves to gas and the cathode gas is humidified.

  On the other hand, the anode gas (hydrogen gas) supplied from the hydrogen tank 21 is supplied to the anode gas passage 3 of the fuel cell 1 through the anode gas supply passage 23, the shutoff valve 25, and the ejector 27. The unreacted anode gas that has not been consumed is discharged from the fuel cell 1 as an anode off-gas, sucked into the ejector 27 through the anode off-gas passage 29, and merged with the fresh anode gas supplied from the hydrogen tank 21. Then, it is supplied again to the anode gas flow path 3 of the fuel cell 1. That is, the anode off-gas discharged from the fuel cell 1 circulates through the fuel cell 1 through the anode off-gas passage 29, the ejector 27, and the anode gas supply passage 23 downstream from the ejector 27.

  An anode offgas discharge channel 33 having a discharge valve 31 branches off from the anode offgas channel 29. The discharge valve 31 is normally closed when the fuel cell 1 generates power, and opens when a predetermined condition is satisfied, and discharges the anode off-gas to the exhaust treatment device. The anode off gas is diluted with the cathode gas discharged from the back pressure valve 15 in the exhaust treatment device.

  The cathode offgas passage 13 between the humidifier 11 and the back pressure valve 15 is provided with a pressure sensor 37 for detecting the pressure of the cathode offgas, and the pressure sensor 37 outputs an output signal corresponding to the detected value to the electronic control device. (Hereinafter abbreviated as ECU) 70. In this embodiment, the cathode off-gas pressure detected by the pressure sensor 37 is regarded as the cathode gas pressure inside the fuel cell 1 and used for opening degree control of the back pressure valve 15. Therefore, in this embodiment, the pressure sensor 37 constitutes a cathode gas pressure detector.

The fuel cell 1 can charge the power storage device 45, and the fuel cell 1 and the power storage device 45 are connected to the travel motor 43 via a power drive unit (hereinafter abbreviated as PDU) 41 having an inverter. . The traveling motor 43 is driven by power supplied from the fuel cell 1 or the power storage device 45. That is, the traveling motor 43 is a load that consumes the power generated by the fuel cell 1.
The fuel cell 1 includes a voltmeter 47 and an ammeter 49 that detect an output voltage and an output current, and these output an output signal corresponding to the detected value to the ECU 70.
Further, the ECU 70 receives an output signal corresponding to the depression amount from the accelerator pedal sensor 35 that detects the depression amount of the accelerator pedal.

The ECU 70 controls the back pressure valve 15, the discharge valve 31, the PDU 41, the travel motor 43, and the like based on input signals from various sensors and instruments.
For example, the ECU 70 calculates the required output of the traveling motor 43 based on the depression amount of the accelerator pedal detected by the accelerator pedal sensor 35, and calculates the required output of the fuel cell 1 according to the required output of the traveling motor 43. Further, the target cathode gas pressure inside the fuel cell 1 is calculated according to the required output of the fuel cell 1, and the back pressure valve 15 is opened so that the cathode offgas pressure detected by the pressure sensor 37 becomes the target cathode gas pressure. PID feedback control including a proportional term (P term), an integral term (I term), and a differential term (D term) is performed.
Further, the ECU 70 performs control to periodically open the discharge valve 31 and discharge the anode off-gas in order to suppress an increase in the concentration of impurities (moisture, nitrogen, etc.) in the anode gas circulating through the fuel cell 1. .
Further, the ECU 70 controls the PDU 41 according to the required output of the traveling motor 43 and controls the power distribution between the fuel cell 1 and the power storage device 45.

As described above, when the required output to the fuel cell 1 is high, such as when accelerating the fuel cell vehicle, if the back pressure valve is fully closed, the cathode gas does not flow in the fuel cell 1 and the fuel cell 1 There is a risk that the inside will be in an oxygen-deficient state and power generation performance will be reduced, or the solid polymer electrolyte membrane of the fuel cell 1 will be deteriorated.
Therefore, in the fuel cell system of this embodiment, the minimum valve opening of the back pressure valve 15 is set according to the required output to the fuel cell 1, and control is performed so that the valve opening of the back pressure valve 15 does not become less than the minimum valve opening. As a result, the flow of the cathode gas in the fuel cell 1 is always ensured so that the power generation performance does not deteriorate even during the high output operation of the fuel cell 1, and the solid polymer electrolyte membrane of the fuel cell 1 is deteriorated. I try to prevent it.

Next, the opening degree control of the back pressure valve 15 in this embodiment will be described with reference to the flowchart of FIG.
The back pressure valve opening control routine shown in the flowchart of FIG. 2 is repeatedly executed by the ECU 70 at regular intervals.
First, in step S101, an output required for the traveling motor 43 (that is, a requested output of the traveling motor 43) is calculated based on the depression amount of the accelerator pedal detected by the accelerator pedal sensor 35. The required output of the fuel cell 1 corresponding to the required output of the motor 43 is calculated. In other words, the travel motor 43 that is the load of the fuel cell 1 calculates (detects) the required output that the fuel cell 1 requires.

Next, the process proceeds to step S102, and an optimum cathode gas pressure (target cathode gas pressure) in the fuel cell 1 for efficiently outputting the required output of the fuel cell 1 calculated in step S101 is calculated.
Next, proceeding to step S103, the valve opening degree of the back pressure valve 15 (that is, opening) when performing PID feedback control so that the cathode offgas pressure detected by the pressure sensor 37 becomes the target cathode gas pressure calculated in step S102. Degree command value) A1 is calculated.

  Next, proceeding to step S104, the minimum valve opening degree A2 of the back pressure valve 15 corresponding to the required output of the fuel cell 1 calculated at step S101 is calculated with reference to the minimum valve opening degree map shown in FIG. The minimum valve opening map shown in FIG. 3 is created based on the results of experiments performed in advance and stored in the ROM. The minimum valve opening A2 is set according to the required output of the fuel cell 1, and is set so that the minimum valve opening A2 increases as the required output increases. This is because it is necessary to increase the cathode gas flow rate supplied to the fuel cell 1 as the required output of the fuel cell 1 increases. The minimum valve opening A2 is set to a valve opening that can ensure the cathode gas pressure required for each required output of the fuel cell 1.

Next, it progresses to step S105 and it is determined whether the valve opening degree A1 by PID feedback control calculated at step S103 is smaller than the minimum valve opening degree A2 calculated at step S104.
If the determination result in step S105 is “NO” (A1 ≧ A2), the process proceeds to step S106, the valve opening degree of the back pressure valve 15 is set to the valve opening degree A1 calculated in step S103, and execution of this routine is temporarily performed. finish. That is, in this case, since the valve opening A1 by the PID feedback control is not less than the minimum valve opening A2 corresponding to the required output of the fuel cell 1, the opening of the back pressure valve 15 is opened by the PID feedback control. The degree A1 is adopted as the valve opening degree of the back pressure valve 15.

On the other hand, if the determination result in step S105 is “YES” (A1 <A2), the process proceeds to step S107, where the valve opening of the back pressure valve 15 is set to the minimum valve opening A2 calculated in step S104. The integral term (I term) of the PID control set when calculating the valve opening A1 in S103 is reset to zero (that is, canceled), and the execution of this routine is once ended.
That is, in this case, if the valve opening A1 by PID feedback control is adopted as the valve opening of the back pressure valve 15, the minimum valve opening A2 corresponding to the required output of the fuel cell 1 will be below, so the minimum valve opening The minimum valve opening A2 is adopted as the valve opening of the back pressure valve 15 so as not to be less than the degree A2.

  Further, by resetting (cancelling) the integral term (I term) of the PID control set when calculating the valve opening degree A1 in step S103, the valve opening degree A1 by the feedback control becomes the minimum valve opening degree A2. Since the integral term can be canceled during the following period (hereinafter referred to as the I term cancellation period), when the I term cancellation period ends, that is, the valve opening A1 by PID feedback control is the minimum valve opening. When the degree A2 is exceeded, overshoot due to feedback control of the integral term can be prevented, and responsiveness can be improved.

  In this embodiment, the ECU 70 constitutes a pressure control unit, and the request output detection unit is realized by the ECU 70 executing the process of step S101, and the target pressure calculation unit is changed by executing the process of step S102. The minimum valve opening setting unit is realized by executing the process of step S104.

FIG. 4 is a time chart when the back pressure valve opening degree control is executed as described above, and shows a case where a high output is requested from the fuel cell 1 because the vehicle is requested to accelerate.
In this figure, the FC voltage is the output voltage of the fuel cell 1 detected by the voltmeter 47, and the FC current is the output current of the fuel cell 1 detected by the ammeter 49. The target CG pressure is the target cathode gas pressure in the fuel cell 1, and the actual COG pressure is the cathode offgas pressure detected by the pressure sensor 37.

In FIG. 4, when a high output is required for the fuel cell 1, the back pressure valve 15 is controlled so as to close the valve opening. In the initial stage, the valve opening A 1 by the PID feedback control of the back pressure valve 15 is When it is larger than the minimum valve opening A2, the valve opening of the back pressure valve 15 is set to the valve opening A1 by PID feedback control.
When the valve opening A1 by the PID feedback control becomes equal to or smaller than the minimum valve opening A2, the valve opening of the back pressure valve 15 is set to the minimum valve opening A2, and then the valve opening A1 by the PID feedback control is again the minimum valve. Until the opening degree A2 is exceeded (that is, the I term cancellation period), the opening degree of the back pressure valve 15 is set to the minimum valve opening degree A2. However, the minimum valve opening A2 during the I term cancellation period is changed according to the change in the required output of the fuel cell 1.
When the valve opening degree A1 by PID feedback control exceeds the minimum valve opening degree A2, the valve opening degree of the back pressure valve 15 is set again to the valve opening degree A1 by PID feedback control.
FIG. 4 shows that when the valve opening of the back pressure valve 15 is controlled in this way, the decrease in the output voltage (FC voltage) of the fuel cell 1 immediately after the required output of the fuel cell 1 increases is smaller than in the prior art. It is clear from the transition of FC voltage.

  As described above, in the fuel cell system in this embodiment, the minimum valve opening A2 of the back pressure valve 15 is set according to the required output required by the traveling motor 43 for the fuel cell 1, so that the high output request is met. Even when the cathode gas pressure is increased, the back pressure valve 15 is not fully closed, and the flow of the cathode gas inside the fuel cell 1 can be secured. As a result, it is possible to prevent a decrease in power generation performance and deterioration of the solid polymer electrolyte membrane due to a shortage of cathode gas in the fuel cell 1.

  Further, since the minimum valve opening A2 is set so as to increase as the required output of the fuel cell 1 increases, the required output of the fuel cell 1 increases, and the demand for the supply pressure and supply flow rate of the cathode gas increases. However, the cathode gas flow rate according to the required output can be secured.

  Further, even when the valve opening degree of the back pressure valve 15 is controlled by PID feedback, the valve opening degree of the back pressure valve 15 can be prevented from being less than the minimum valve opening degree A2, thereby preventing a decrease in power generation performance. The valve opening degree of the back pressure valve 15 can be controlled by feedback control while ensuring a predetermined power generation performance.

  Furthermore, since the integral term is reset (cancelled) while the valve opening A1 with respect to the back pressure valve 15 by the PID feedback control is equal to or less than the minimum valve opening A2 (I term cancellation period), the I term cancellation period has ended. Sometimes, overshoot due to feedback control of the integral term can be prevented, and responsiveness can be improved.

  Further, during the power generation operation of the fuel cell 1, the valve opening of the back pressure valve 15 does not become the minimum valve opening A2 or less, and the minimum valve opening A2 is appropriately set according to the required output of the fuel cell 1. Therefore, for example, even when there is an abnormality in a flow rate sensor (not shown) that detects the flow rate of the cathode gas supplied to the fuel cell 1, the back pressure valve 15 is not closed excessively. Therefore, an abnormal pressure increase in the fuel cell 1 and the fuel cell system can be prevented.

[Other Examples]
The present invention is not limited to the embodiment described above.
For example, in the embodiment described above, the load that consumes the electric power generated by the fuel cell 1 is the traveling motor 43, but this is merely an example, and the load is not limited to this. For example, the compressor 7 and other auxiliary machines can be used as the load of the fuel cell 1. When there are a plurality of loads as described above, the required output required by the load to the fuel cell 1 can be the sum of the required outputs required by the individual loads to the fuel cell 1.

It is a schematic block diagram in one Example of the fuel cell system concerning this invention. It is a flowchart which shows the back pressure valve opening degree control of the fuel cell system in the said Example. It is a figure which shows an example of the minimum valve opening degree map used in the back pressure valve opening degree control in the said Example. It is a time chart of the output voltage etc. of a fuel cell when back pressure valve opening degree control of the said Example is performed. It is a time chart of the output voltage etc. of the fuel cell in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 13 Cathode off-gas flow path 15 Back pressure valve 37 Pressure sensor (cathode gas pressure detection part)
43 Motor for travel (load)
70 ECU (pressure control unit)

Claims (1)

A fuel cell that supplies anode gas and cathode gas to generate electricity;
A back pressure valve installed in a cathode offgas flow path for discharging the cathode gas supplied to the fuel cell to the outside of the fuel cell;
A pressure control unit for adjusting the cathode gas pressure inside the fuel cell by controlling the valve opening of the back pressure valve;
A load that consumes the power generated by the fuel cell;
In a fuel cell system having
A request output detector for detecting a request output required by the load to the fuel cell;
A minimum valve opening setting unit that sets a minimum valve opening of the back pressure valve in accordance with the required output detected by the required output detection unit;
A cathode gas pressure detector for detecting a cathode gas pressure inside the fuel cell;
A target pressure calculator that calculates a target cathode gas pressure according to the required output detected by the required output detector,
The pressure control unit feedback-controls the valve opening of the back pressure valve so that the cathode gas pressure detected by the cathode gas pressure detection unit becomes the target cathode gas pressure calculated by the target pressure calculation unit, When the opening command value for the back pressure valve by feedback control is less than or equal to the minimum valve opening set by the minimum valve opening setting unit, the valve opening of the back pressure valve does not fall below the minimum valve opening. Control to
The feedback control includes an integral term, and the pressure control unit determines the integral term until the opening command value exceeds the minimum valve opening when the opening command value is less than or equal to the minimum valve opening. Canceling, and changing the minimum valve opening during the cancellation period of the integral term according to the change in the required output of the load,
The minimum valve opening setting unit sets the minimum valve opening so that the minimum valve opening increases as the required output of the load increases .

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