JP2002289235A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To feed hydrogen and oxygen to a fuel cell while preventing significant degradation of the overall efficiency of a fuel cell system. SOLUTION: An excess rate is changed (learning control) so as to set the dispersion value ΔV of cell voltage to a predetermined value Vo or less. Thereby, while preventing a blocked air passage and a blocked hydrogen passage in the fuel cell 1, consumption of electric power (energy) generated by the fuel cell 1 for feeding hydrogen and oxygen can be prevented. Accordingly, hydrogen and oxygen can be fed to the fuel cell 1 while preventing the significant degradation of the overall efficiency of the fuel cell system. Even if the fuel cell changes over aging, the excess rate is so selected as to be optimum in that state, so that the remarkable degradation of the overall efficiency of the fuel cell system can be prevented over a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system having a fuel cell for generating electric power from hydrogen and oxygen, and is effective when applied to an electric vehicle.

[0002]

2. Description of the Prior Art FIG. 2 is a schematic view of a (solid polymer type) fuel cell for a vehicle. In general, a fuel cell has an electrolyte membrane having a platinum catalyst carried on the surface. 1a, Supplying air (oxygen) and hydrogen to electrolyte membrane 1
a, a carbon cloth (diffusion layer) 1b for diffusing so as to spread over the entirety, a separator 1c made of carbon which separates each electrolyte membrane 1a and forms an electrode, a cooling water passage 1d through which cooling water flows, and air (oxygen) flowing And a hydrogen passage 1f through which hydrogen flows.

By the way, in a fuel cell, as described above,
Electric power is extracted through a chemical reaction with hydrogen and oxygen. Water (condensed water) generated at that time and water (condensation) generated by condensation of hydrogen (hydrogen-rich gas) and water vapor contained in oxygen (air) are supplied. Water) may block the air passage 1e and the hydrogen passage 1f.

Therefore, conventionally, more hydrogen (hydrogen-rich gas) and oxygen (air) than the theoretical amount of hydrogen and oxygen necessary to obtain the required amount of electric power are supplied to flow through the air passage 1e. The flow rate of air flowing through the hydrogen passage 1f and the flow rate of hydrogen flowing through the hydrogen passage
And the water accumulated in the hydrogen passage 1f was discharged (blown off).

However, in order to increase the flow rate of the air flowing through the air passage 1e and the flow rate of the hydrogen flowing through the hydrogen passage 1f, it is necessary to increase the work of a pump for supplying air and hydrogen. Since power is supplied from the fuel cell (via the battery), if the work of the pump is increased, the amount of power consumed by the pump out of the power generated by the fuel cell increases. The ratio of the amount of power that can be supplied from the battery to the traveling motor decreases, and the efficiency of the entire fuel cell system decreases.

On the other hand, if the work of the pump is excessively reduced, water accumulates in the air passage 1e and the hydrogen passage 1f, so that hydrogen and oxygen cannot be sufficiently supplied to the electrolyte membrane 1a. May not function (power generation).

[0007] In view of the above, it is an object of the present invention to supply hydrogen and oxygen to a fuel cell while preventing the efficiency of the entire fuel cell system from being greatly reduced.

[0008]

According to the present invention, in order to achieve the above object, the present invention comprises a plurality of fuel cells which generate electric power by a chemical reaction between hydrogen and oxygen. Fuel cell (1), cell voltage detecting means (8) for detecting electromotive voltage of fuel cell, and fuel cell (1)
And a fuel supply amount control means (7) for controlling the amount of hydrogen and oxygen supplied to the fuel cell. The fuel supply amount control means (7) controls a variation value of the detection value detected by the cell voltage detection means (8). The amount of hydrogen and the amount of oxygen supplied to the fuel cell (1) are controlled so that ΔV) is equal to or less than a predetermined value.

This prevents the power (energy) generated by the fuel cell (1) from supplying hydrogen and oxygen while preventing the air (oxygen) passage and the hydrogen passage in the fuel cell (1) from being blocked. Consumption can be suppressed.
Therefore, it is possible to supply hydrogen and oxygen to the fuel cell 1 while preventing the efficiency of the entire fuel cell system from being greatly reduced.

The relationship between the variation value and the excess rate (the ratio of the amount of supplied hydrogen and oxygen to the theoretical amount of hydrogen and oxygen required to obtain the required amount of power) is shown in FIG. As shown in (1), there is variation among the fuel cells due to individual differences of the fuel cells (1). For this reason, if the excess ratio is set to a fixed value, it is necessary to consider individual differences of the fuel cell (1), so that a large value must be necessarily selected.

On the other hand, if the excess rate is changed (learning control) so that the variation value (ΔV) becomes equal to or less than a predetermined value as in the present invention, the excess rate can be made a relatively small value. Therefore, it is possible to supply hydrogen and oxygen to the fuel cell (1) while preventing the efficiency of the entire fuel cell system from being greatly reduced.

Further, even if the fuel cell changes over time, the excess ratio is selected so as to be optimal in that state, so that the efficiency of the entire fuel cell system is prevented from greatly decreasing over a long period of time. And hydrogen and oxygen to the fuel cell (1).

According to the second aspect of the present invention, the fuel supply amount control means (7) stores the amount of hydrogen and the amount of oxygen previously supplied to the fuel cell (1), and stores the amount of hydrogen and the amount of oxygen stored therein. Controlling the amount of hydrogen and the amount of oxygen supplied to the fuel cell (1) so that the variation value (ΔV) of the detection values detected by the plurality of cell voltage detection means (8) is equal to or less than a predetermined value. Features.

Thus, when the excess ratio is determined next time, the excess ratio is quickly converged to an appropriate value as compared with the case where an appropriate excess ratio is determined from the initial value (the excess ratio at the time of factory shipment). Can be done.

Incidentally, the reference numerals in parentheses of the above means are examples showing the correspondence with specific means described in the embodiments described later.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In this embodiment, the fuel cell system according to the present invention is applied to an electric vehicle. FIG. 1 shows a fuel cell system according to the embodiment (power system for driving an electric vehicle). FIG.

In FIG. 1, reference numeral 1 denotes a fuel cell (FC stack) which generates electric power by utilizing a chemical reaction between hydrogen and oxygen and supplies electric power to electric equipment such as an electric motor for driving or a battery. As shown in FIG. 2, the fuel cell 1 has an electrolyte membrane 1a having a platinum catalyst supported on its surface, and a carbon cloth (diffusion layer) for diffusing supplied air (oxygen) and hydrogen so as to spread throughout the electrolyte membrane 1a. 1) 1b, a carbon separator 1 that separates each electrolyte membrane 1a and constitutes an electrode
c, a plurality of fuel cells including a cooling water passage 1d through which cooling water flows, an air (oxygen) passage 1e through which air (oxygen) flows, and a hydrogen passage 1f through which hydrogen flows are electrically connected in series. It is a known solid polymer type.

In FIG. 1, reference numeral 2 designates a fuel rich by producing (generating) a hydrogen-rich gas containing a large amount of hydrogen from a mixed solution of water and methanol (hereinafter, this mixed solution is referred to as a methanol mixed solution). A hydrogen generator (hydrogen supply means) for supplying a hydrogen-rich gas to the battery 1;
Is a fuel evaporator for hydrogen production (not shown) for evaporating a methanol mixed solution, and a chemical reaction between methanol vapor evaporated and vaporized by the fuel evaporator for hydrogen production, and hydrogen and carbon dioxide. A hydrogen reforming fuel reformer (not shown) for reforming the fuel into a small amount of carbon monoxide, and a pump (not shown) for supplying the produced hydrogen-rich gas to the fuel cell 1. Have been.

Reference numeral 3 denotes an air pump (oxygen supply means) for supplying oxygen (air) to the fuel cell 1.
Inhales air (oxygen) from the atmosphere into the fuel cell 3
To supply. Note that hydrogen (hydrogen-rich gas) and air (oxygen) supplied to the fuel cell 1 are supplied to the fuel cell 1 in a humidified state by the humidifiers 2a and 3a.

Reference numeral 4 denotes a chargeable / dischargeable battery (secondary battery). The battery 4 is charged by the power supplied from the fuel cell 1 and the power generated during regenerative braking. ) And other electric accessories (such as the air pump 3 and a control device described later).

Reference numeral 5 denotes a traveling electric motor (hereinafter abbreviated as a motor). Reference numeral 6 denotes a motor control device (power controller) for controlling the motor 5.
Controls the power supplied to the motor 5 in response to a control signal from a system controller (system controller) 7 for controlling the entire fuel cell system (power system for traveling).

A detection value of a cell voltage monitoring device (cell voltage detecting means) 8 for detecting an electromotive voltage of each fuel cell is input to the system control device 7. The amount of hydrogen and the amount of oxygen supplied to the fuel cell 1 are controlled based on the detection value of the monitor device 8, the electric power required by the motor 5, and the like.

Next, the characteristic operation of the fuel cell system according to this embodiment and its effects will be described.

FIG. 3 is a flowchart showing the characteristic operation of the fuel cell system according to the present embodiment. When the fuel cell system starts, the detected value of the cell voltage monitoring device 8 is read, and the read detected value varies. It is determined whether or not the value ΔV is equal to or less than a predetermined value Vo (S100).

Here, the variation ΔV of the detected value is the difference between the maximum value and the minimum value of the detected cell voltage, and
As more hydrogen (hydrogen-rich gas) and oxygen (air) are supplied than the theoretical amount of hydrogen and oxygen required to obtain the required amount of power, the variation value ΔV tends to decrease.

Hereinafter, the ratio of the amount of supplied hydrogen and the amount of oxygen to the theoretical amount of hydrogen and oxygen required to obtain the required amount of power is referred to as an excess ratio. Therefore, as the excess rate increases, as shown in FIG.
Becomes smaller.

As described above, as the excess ratio increases, water accumulated in the air passage 1e and the hydrogen passage 1f can be discharged as described in the section of "Problems to be Solved by the Related Art and the Invention". Therefore, each fuel cell has a sufficient power generation capability, and the influence of individual differences between the fuel cells is reduced.

When it is determined in S100 that the variation value ΔV is larger than the predetermined value Vo, as shown in FIG. 3, the excess ratio is increased to reduce the variation value ΔV (S110), while the variation value is decreased. When ΔV is smaller than the predetermined value Vo, the excess ratio is reduced to increase the variation value ΔV (S120). When the variation value ΔV matches the predetermined value Vo, the current excess ratio is maintained and the excess ratio Is stored (S130, S140).

When the variation value .DELTA.V is smaller than the predetermined value Vo, the excess ratio is reduced, but when the excess ratio is smaller than the predetermined minimum excess ratio, the excess ratio is set to the minimum excess ratio.

Thus, in the present embodiment, the amount of hydrogen and the amount of oxygen supplied to the fuel cell 1 are controlled such that the excess rate becomes equal to or less than the predetermined value Vo, so that the air passage 1e and the hydrogen passage 1f are closed. It is possible to prevent an increase in the amount of power consumed by the air pump 3 and the hydrogen supply pump out of the power generated by the fuel cell 1 while preventing the occurrence of such a situation. Therefore, it is possible to supply hydrogen and oxygen to the fuel cell 1 while preventing the efficiency of the entire fuel cell system from being greatly reduced.

When the variation value ΔV matches the predetermined value Vo, the current excess ratio is maintained and the excess ratio is stored, so that the next time the excess ratio is determined,
As compared with the case where an appropriate excess rate is determined from an initial value (excess rate at the time of factory shipment), the excess rate can be quickly converged to an appropriate value.

In the present embodiment, when the variation value ΔV is smaller than the predetermined value Vo, the excess ratio is reduced to increase the variation value ΔV. However, similarly to the case where the variation value ΔV matches the predetermined value Vo, The current excess rate may be maintained.

Incidentally, the relationship between the variation value and the excess rate is as follows:
As shown in FIG. 5, there is variation among the fuel cells due to individual differences of the fuel cells 1. For this reason, if the excess ratio is set to a fixed value, it is necessary to consider individual differences of the fuel cell 1, so that a large value is necessarily selected.

On the other hand, when the excess ratio is changed (learning control) so that the variation value ΔV of the cell voltage becomes equal to or less than the predetermined value Vo as in the present embodiment, the excess ratio is set to a relatively small value. Therefore, it is possible to supply hydrogen and oxygen to the fuel cell 1 while preventing the efficiency of the entire fuel cell system from being greatly reduced.

Further, even if the fuel cell changes over time, the excess ratio is selected so as to be optimal in that state, so that the efficiency of the entire fuel cell system is prevented from greatly decreasing over a long period of time. And hydrogen and oxygen to the fuel cell 1.

(Other Embodiments) In the above embodiment, the difference between the maximum value and the minimum value of the detected cell voltage is adopted as the variation value ΔV. However, the present invention is not limited to this. For example, the average value or the variance of the detected cell voltages may be used.

In the above-described embodiment, the hydrogen supply unit 2 is used as the hydrogen supply means for reforming the hydrocarbon fuel to produce a hydrogen-rich gas containing a large amount of hydrogen.
The present invention is not limited to this, and a high-pressure hydrogen tank or a hydrogen tank using a hydrogen storage alloy that can supply pure hydrogen gas may be used as the hydrogen supply means.

In the above-described embodiment, the present invention is applied to an electric vehicle. However, the present invention is not limited to this, and can be applied to a stationary fuel cell system.

In the above embodiment, the variation value Δ
Although the predetermined value Vo as the threshold value of V is a constant value, it may be a value having a predetermined range.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a fuel cell system according to an embodiment of the present invention.

FIG. 2 is a structural diagram of a fuel cell.

FIG. 3 is a flowchart showing an operation of the fuel cell system according to the embodiment of the present invention.

FIG. 4 is a graph showing a relationship between a cell voltage variation of a fuel cell and an excess ratio.

FIG. 5 is a graph showing a relationship between a cell voltage variation of a fuel cell and an excess ratio.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fuel cell, 2 ... Hydrogen production device (hydrogen supply means), 3 ...
Air pump (oxygen supply means), 4 ... battery, 5 ... motor, 6 ... motor control equipment, 7 ... system control device.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Kawai 1-1-1, Showa-cho, Kariya-shi, Aichi Pref. F-term (reference) 5H026 AA06 CC03 HH02 HH06 5H027 AA06 BA01 BA13 DD03 KK54 MM04 MM09

Claims (2)

[Claims] 1. A fuel cell comprising a plurality of fuel cells for generating electric power by a chemical reaction between hydrogen and oxygen.
And a cell voltage detecting means (8) for detecting an electromotive voltage of the fuel cell, and a fuel supply amount controlling means (7) for controlling an amount of hydrogen and an amount of oxygen supplied to the fuel cell (1). The fuel supply amount control means (7) controls the amount of hydrogen supplied to the fuel cell (1) such that the variation (ΔV) of the detection value detected by the cell voltage detection means (8) is equal to or less than a predetermined value. And a fuel cell system for controlling the amount of oxygen. 2. The fuel supply amount control means (7) stores a hydrogen amount and an oxygen amount previously supplied to the fuel cell (1), and based on the stored hydrogen amount and oxygen amount. The amount of hydrogen and the amount of oxygen supplied to the fuel cell (1) are controlled so that the variation value (ΔV) of the detection values detected by the cell voltage detection means (8) becomes equal to or less than a predetermined value. The fuel cell system according to claim 1.