KR20080044429A - Fuel cell system and emergency driving method - Google Patents

Abstract

A fuel cell system is provided to prevent degradation of the quality of a stack (particularly an electrolyte membrane) caused by long-term shut-down and to enable emergency driving. A fuel cell system comprises: a timer(210) for measuring a time interval from the endpoint of the last driving of the fuel cell system; and an operation managing and controlling section(220), which causes the fuel cell system to be in an emergency driving state for a predetermined period, if the time measured by the timer reaches a predetermined reference value, and resets the endpoint of the driving of the fuel cell system so that the timer is reoperated.

Description

Fuel Cell System and Emergency Driving Method {Fuel Cell System and Emergency Driving Method}

1 is a block diagram showing a configuration of a fuel cell system to which the present invention can be applied.

Figure 2 is a detailed block diagram showing a structure for performing emergency operation according to the spirit of the present invention.

3 is a flow chart illustrating an emergency driving method according to the spirit of the present invention.

* Explanation of symbols for the main parts of the drawings

130: drive control unit

150: battery

210: timer

220: operation management control unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system for performing emergency operation for maintaining performance during a driving stop, and more particularly, to a fuel cell system and a method for emergency driving that periodically run during a driving stop to prevent drying of the stack electrolyte membrane. will be.

A fuel cell is a power generation system that generates electrical energy by a balanced electrochemical reaction between hydrogen contained in a hydrocarbon-based material such as methanol, ethanol and natural gas and oxygen in the air.

Fuel cells are classified into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, polymer electrolyte fuel cells, alkaline fuel cells, and the like, depending on the type of electrolyte used. Each of these fuel cells basically operates on the same principle, but differs in the type of fuel used, operating temperature, catalyst, and electrolyte.

Among them, the polymer electrolyte fuel cell (PEMFC) has a much higher output characteristic, lower operating temperature, and faster start-up and response characteristics than other fuel cells. It has a wide range of applications such as transportation power sources such as power sources and automotive power sources, as well as distributed power sources such as stationary power plants in houses and public buildings. The polymer electrolyte fuel cell performs power generation using a gaseous fuel (mainly hydrogen molecules).

Meanwhile, a fuel cell includes a direct methanol fuel cell (DMFC), which is similar to a polymer electrolyte fuel cell but can directly supply a liquid methanol fuel, typically a fuel in an aqueous methanol solution, to a stack. Direct methanol fuel cells, unlike polymer electrolyte fuel cells, are more advantageous for miniaturization because they do not use a reformer to obtain hydrogen from the fuel.

The above-described direct methanol fuel cell includes, for example, a stack, a fuel tank and a fuel pump. The stack generates electrical energy by electrochemically reacting a fuel containing hydrogen with an oxidant such as oxygen or air. Such a stack typically has a structure in which several to tens of unit fuel cells including a membrane electrode assembly (MEA) and a separator are stacked. Here, the membrane-electrode assembly has a structure in which an anode electrode (also called "fuel electrode" or "oxide electrode") and a cathode electrode (also called "air electrode" or "reduction electrode") are attached with a polymer electrolyte membrane interposed therebetween. Has

By the way, the longer the downtime the fuel cell is idle, the lower the performance of the stack of fuel cells, especially in the case of a stack of DMFCs using liquid methanol as fuel.

In order to prevent this, when it is determined that the fuel cell system is not used for a long time, a predetermined long-term storage procedure is performed during the termination of the fuel cell system. For example, in the case of DMFC, the stacked electrolyte membrane is filled with methanol of a predetermined concentration, or filled with water or a specific liquid.

However, if the user does not use for a long time after a short time stop, the storage procedure is not performed, and even if the storage procedure is performed, the liquid filled in the electrolyte membrane of the stack is likely to dry naturally. In addition, the storage procedure may not be performed in order to reduce the complexity of the implementation and the termination time.

In such a case, a means for preventing the performance deterioration of the fuel cell stack suspended for a long time has been desired.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a fuel cell system and an emergency driving method thereof capable of preventing performance degradation of a stack (particularly, an electrolyte membrane) due to prolonged stoppage.

A fuel cell system according to the present invention for achieving the above object comprises a timer for measuring the time elapsed since the last operation end of the fuel cell system; And an operation management control unit configured to emergencyly operate the fuel cell system for a predetermined time and update an operation end time of the fuel cell system to restart the timer when the time measured by the timer reaches a predetermined reference value.

Emergency operation method of the fuel cell system according to the present invention for achieving the above object comprises the steps of counting the elapsed time after the stop of the fuel cell system; Checking whether the counted elapsed time exceeds the reference time; Driving the fuel cell system if the reference time has been exceeded; Counting an elapsed time after driving the fuel cell system; Checking whether the counted elapsed time exceeds the minimum drive time; And stopping the fuel cell system if the minimum drive time has been exceeded.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

For example, in the following examples, the idea of the present invention is described by embodying a direct methanol fuel cell and a PEM fuel cell, but any fuel cell such as a solid methanol fuel cell and a hydrogen storage solution fuel cell may be used as long as it is a fuel cell for preventing drying of the stack. Of course, also applicable to.

In addition, in the description of the following embodiments, the power generation unit of the fuel cell is collectively referred to as a stack, but this is merely for convenience of use of the term. In the following description, the stack includes a single cell as well as a stacked cell.

(Example)

1 illustrates a fuel cell system in a simplified structure to which the spirit of the present invention can be applied. The illustrated fuel cell system has a structure for directly supplying fuel from a fuel tank to a stack, but in the case of a direct methanol fuel cell, a structure for supplying methanol instead of hydrogen to a stack and a recycling tank for recovering unreacted fuel of the cathode are further provided. The PEM fuel cell may further include a reformer for generating hydrogen gas from butane and a hydration unit for hydrating hydrogen gas supplied to the stacked electrolyte membrane.

The illustrated battery system includes a fuel tank 120 for storing hydrogen-containing fuel; A fuel cell stack 110 generating electricity by an electrochemical reaction of hydrogen and oxygen; A power converter (140) for delivering the output of said fuel cell stack (110) to an external load (18); A battery 150 made of a secondary battery; And a drive controller 130 that controls the operation of each component of the fuel cell system, including the pump 160 from the fuel tank 120 to the stack 110.

The fuel cell stack 110 has a structure in which a unit fuel cell including a membrane electrode assembly (MEA) and a separator is stacked to several tens to several tens. Here, the membrane-electrode assembly has a structure in which an anode electrode (also called "fuel electrode" or "oxide electrode") and a cathode electrode (also called "air electrode" or "reduction electrode") are attached with a polymer electrolyte membrane interposed therebetween. Has The separator is for electrically separating each of the plurality of membrane-electrode assemblies, and may be omitted depending on the implementation.

Referring to FIG. 1, the membrane-electrode assembly 20 of the fuel cell stack 110 includes the polymer electrolyte membrane 12, the anode catalyst layer 14, and the cathode catalyst layer 16. When hydrogen gas or a fuel containing hydrogen is supplied to the anode catalyst layer 14 in the fuel cell 10, an electrochemical oxidation reaction occurs in the anode catalyst layer 14 and ionized with hydrogen ions (H ⁺ ) and electrons (e ⁻ ). And oxidize. Ionized hydrogen ions move from the anode catalyst layer 14 through the polymer electrolyte membrane 12 to the cathode catalyst layer 16, and electrons move from the anode catalyst layer 14 through the outer wire 18 to the cathode catalyst layer 16. Done. The hydrogen ions transferred to the cathode catalyst layer 16 cause an electrochemical reduction reaction with oxygen supplied to the cathode catalyst layer 16 to generate heat of reaction and water. And electric energy is generated by the movement of electrons.

Representative electrochemical reactions of the above-described polymer electrolyte fuel cell and direct methanol fuel cell are shown in Schemes 1 and 2 below.

The ^{_{anode: H 2 → 2H + + 2e}} -

^{_{Cathode: 1 / 2O 2 + 2H +}} + 2e - → H 2 O

_{Anode: CH 3 OH + H 2 O} → CO 2 + 6H + + 6e -

^{_{Cathode: 3 / 2O 2 + 6H +}} + 6e - → 3H 2 O

Meanwhile, the fuel cell stack 110 supplies the external load 18 with electrical energy having a predetermined potential difference through current collectors (not shown) positioned at both ends or the outermost sides. For example, the external load 200 includes a portable electronic device such as a notebook computer, a personal digital assistant (PDA), a portable multimedia player (PMP), or the like. The fuel cell stack 110 then discharges the remaining fuel and reaction products. The remaining fuel can be recycled to fuel by recycling means, and reaction products such as carbon dioxide are discharged into the atmosphere.

In this embodiment, although the power converter 140 is used as a power converter for transferring the power produced by the fuel cell stack 110 to an external load, in the case of the implementation where stabilization of the output voltage is not important, LDO (Low) It can be replaced by a simpler output stage circuit such as Drop Output Regulator. In general, the power converter 140 may be replaced by a DC / DC converter or a DC / AC converter when the external load is a device using an AC power source.

The power conversion device 140 is to maintain a constant DC voltage power source and output it to the external load 18 irrespective of fluctuations in the stack output voltage. In some embodiments, the power converter 140 may not only output the external load. The battery 150 and / or the driving controller 130 may also be supplied with a charging power or driving power having a constant voltage. The power converter 140 may be configured to generate an output terminal voltage lower than the fuel cell stack 110 voltage or to generate an output terminal voltage higher than the stack 110 voltage. In the latter case, a direct current output from the stack 100 may be used. It can be implemented by a variety of known methods such as switching to make an alternating current, and boosting the alternating current using a coil, transformer, capacitance, etc., and then rectifying it to output DC directly, or switching the STEP-UP method.

The battery 150 may be a secondary battery capable of charging and discharging at least once, but in order to ensure smooth operation of the fuel cell system of the present invention, it is preferable to apply a sufficient number of charge / discharge cycles. The battery 150 may be implemented as a variety of secondary batteries known in the art, such as lithium-ion batteries, lithium-poly batteries, nickel-hydrogen batteries, lead acid batteries, large capacity capacitors, or electrolytic capacitors.

The charging of the battery 150 may be performed by directly connecting the output of the fuel cell stack 110, or may be implemented to be performed by the power converter 140 as illustrated. For more stable charging operation, the power converter 140 may further include a battery charging circuit 150 for charging the battery 130 with the power generated by the stack 110.

Although the power transfer path between the fuel cell stack 110 and the power converter 140 and the power transfer path between the power converter 140 and the external load 18 are shown as one line in the drawing, in practice, It is implemented with a pair of lines, plus and minus lines.

2 illustrates a structure for supporting emergency driving to maintain stack performance during stoppages according to the spirit of the present invention. Although the illustrated structure may be implemented as some modules of the driving controller 130 of FIG. 1, it is easy to manage the driving power by implementing it as a separate module as shown in FIG. 2.

That is, the fuel cell system having the emergency driving structure for maintaining the stack performance during the driving stop according to the spirit of the present invention, the timer 210 for measuring the time elapsed since the last operation of the fuel cell system; And an operation management controller 220 for operating the fuel cell system for a predetermined time, updating the end point of operation of the fuel cell system to restart the timer when the time measured by the timer 210 reaches a predetermined reference value. do.

Since the timer 210 and the driving management controller 220 must be operated even while the fuel cell system is stopped, the timer 210 and the driving management controller 220 are implemented to receive power from the battery 150. The battery 150 of FIG. 1 is a battery for initial startup of a fuel cell system that is charged with the power generation of the fuel cell stack 110. In FIG. 2, the battery 150 of FIG. 1 is operated with the timer 210. Although used as a driving power supply means of the management control unit 220, depending on the implementation may be applied to a separate means such as a battery.

When the operation management control unit 220 determines that the fuel cell system should be emergency operated, the driving control unit 130 may be activated to implement the entire fuel cell system to operate, and to minimize the emergency operation part. It may be implemented to drive only a pump for supplying fuel to the stack, or only to drive a charging circuit for the pump and a battery for supplying fuel to the fuel cell stack. Here, the charging circuit is a part of the power converter 140 of FIG.

In addition, the timer counts the elapsed time from the emergency operation time of the fuel cell system, and the operation management control unit may be configured to stop the fuel cell system when the elapsed time exceeds the predetermined minimum operation time from the emergency operation time. Can be. This is to use the timer and the operation management control unit not only to determine and perform the emergency operation during the suspension, but also to determine and perform the emergency operation after the start.

FIG. 3 illustrates a specific emergency driving method according to the emergency driving structure of FIG. 2.

The emergency driving method may include: counting an elapsed time after stopping (S10) the fuel cell system (S20); Checking whether the counted elapsed time exceeds the reference time (S30); If the reference time is exceeded, driving the fuel cell system (S40); Counting an elapsed time after driving the fuel cell system (S50); Checking whether the counted elapsed time exceeds the minimum driving time (S60); And stopping the fuel cell system if the minimum driving time is exceeded (S70).

In operation S20, when the timer of FIG. 2 determines the stop of the fuel cell system, counting is started. In operation S30, the operation management controller of FIG. 2 compares the elapsed time counted by the timer with a previously recorded reference time.

In operation S40, only a pump for supplying fuel to the fuel cell stack may be driven or only a charging circuit for the pump and a battery for supplying fuel to the fuel cell stack may be driven to minimize an emergency running portion. The latter is an implementation to avoid wasting power generated by emergency operations.

In the case of the direct methanol fuel cell in step S40, the fuel pump refers to a pump for supplying a dilute methanol solution to the anode of the stack, and drying of the stack electrolyte membrane is prevented by the dilute methanol solution supplied to the stack.

In the case of the PEM fuel cell in the step S40, the fuel pump refers to a pump for supplying hydrogen gas hydrated to the anode of the stack, the drying of the stack electrolyte membrane is prevented by the water vapor molecules supplied with the hydrogen gas supplied to the stack do.

The steps S50 and S60 are to ensure a minimum driving time which is a minimum driving time sufficient to maintain moisture of the stack electrolyte membrane during emergency driving.

The step S70 may be performed in the same manner as the stop (S10) process of the normal operation of the fuel cell system, and may include, for example, filling the fuel cell stack with a fuel aqueous solution having a predetermined concentration to protect the fuel cell stack. The predetermined concentration is generally lower than the fuel concentration supplied to the stack during normal operation, and in order to achieve this, a method of developing the stack without supplying additional fuel until the aqueous solution of fuel filled in the stack becomes a predetermined concentration may be used. Alternatively, if there is a mixing tank, it is also possible to use a method in which the concentration of the aqueous solution in the mixing tank is supplied to the stack according to the predetermined concentration.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the scope of the invention.

By implementing the fuel cell system of the present invention according to the above configuration, even if the fuel cell system stops running for a long time, fuel is supplied to the stack at a time when the stack electrolyte membrane is dried, thereby preventing the performance degradation of the stack due to long stop operation. It can be effective.

Claims (9)

A timer for measuring the time elapsed since the last operation termination of the fuel cell system; And When the time measured by the timer reaches a predetermined reference value, Emergency operation of the fuel cell system, Update the end point of the fuel cell system to restart the timer. A driving management controller; Fuel cell system comprising a. According to claim 1, wherein the operation management control unit, And, when the fuel cell system is emergency run for a predetermined time, only a pump for supplying fuel to the fuel cell stack is driven. According to claim 2, The operation management control unit, And driving a charging circuit for a battery and a pump for supplying fuel to a fuel cell stack when the fuel cell system is operated for a predetermined time. The method of claim 1, The timer counts the elapsed time from the emergency operation time of the fuel cell system, And the operation management control unit stops the fuel cell system when the elapsed time exceeds the predetermined minimum operation time from the emergency operation time point. The method of claim 1, And a power supply means for supplying driving power to the timer and the operation management control part while the fuel cell system is stopped. The method of claim 5, wherein the power supply means, A fuel cell system, characterized in that the battery is charged by the generated power of the fuel cell stack. (a) counting elapsed time after stopping of the fuel cell system; (b) checking whether the counted elapsed time exceeds the reference time; (c) driving the fuel cell system if the reference time has been exceeded; (d) counting an elapsed time after driving the fuel cell system; (e) checking whether the counted elapsed time exceeds the minimum drive time; And (f) stopping the fuel cell system if the minimum run time has been exceeded Emergency operation method of the fuel cell system comprising a. The method of claim 7, wherein in step (c), A method of emergency operation of a fuel cell system, characterized by driving only a pump for supplying fuel to the fuel cell stack. The method of claim 7, wherein in step (c), A method of emergency operation of a fuel cell system, characterized in that it only drives a charging circuit for a pump and a battery for supplying fuel to the fuel cell stack.

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