KR100726877B1 - Fuel cell system and control method thereof - Google Patents

Abstract

A fuel cell system according to the present invention includes a fuel cell stack that generates electricity by reacting with a humidified fuel, and is installed at a rear end of the fuel cell stack to periodically retain fuel and condensate in the fuel cell stack for a predetermined time and to the outside. The discharge key is configured to include a hydrogen vent valve and the method for controlling a fuel cell system according to the present invention includes closing the valve so that fuel and condensed water stays in the fuel cell stack for a predetermined time, and after the step, the condensed water and the fuel The step of opening the valve to be discharged to the outside of the fuel cell stack is performed periodically, there is an advantage that the fuel can be used efficiently.

Fuel Cell, Valve Control, PWM Control, Hydrogen, Humidification Condition, Fuel Cell Stack

Description

Fuel cell system and control method thereof

1 is a schematic diagram illustrating a fuel line of a fuel cell system for a vehicle according to the prior art.

2 is a schematic view showing a fuel line of a fuel cell system for automobiles according to the present invention.

3 is a graph showing the average voltage of the fuel cell stack when the hydrogen vent valve of the fuel cell system according to the present invention is closed.

4 is a waveform showing the hydrogen vane valve opening period and the opening time of the fuel cell system according to the present invention.

5 is a hydrogen vane valve control system diagram of a vehicle equipped with a fuel cell system according to the present invention.

6 is a graph showing fuel consumption of a fuel cell system according to the present invention.

<Explanation of symbols for the main parts of the drawings>

10: hydrogen storage tank 20: regulator

30: humidifier 40: fuel cell stack

50: valve 61: accelerated lung moon

62: signal converter 63: load current summed up for a certain time

64: average load current

65: function of hydrogen vane valve opening time versus load current

66: hydrogen vent valve opening time 67: actuator controller

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid polymer fuel cell system and a method of controlling the fuel cell system for application to an automobile engine configured to obtain high efficiency by controlling fuel emissions.

In general, a fuel cell is defined as a cell having a capability of producing direct current by converting chemical energy of fuel (hydrogen) directly into electrical energy, and unlike fuel cells, fuel and air are supplied from the outside. It has the characteristic of producing electricity continuously.

Hydrogen, the fuel of the fuel cell, uses pure hydrogen or hydrogen produced through a reforming process using hydrocarbons such as methane or ethanol. Pure oxygen as an oxidant of a fuel cell can increase the efficiency of the fuel cell, but there is a problem in that cost and weight increase due to oxygen storage. Therefore, the air contains a lot of oxygen, so the efficiency is slightly lower, but directly use the air.

For chemical reactions in fuel cell stacks applied to automobiles, hydrogen or air must be kept at an appropriate humidity level.

The fuel cell system is equipped with a humidifier to supply pure hydrogen as a fuel and air as an oxidant to humidify the reaction gas.

The humidification of the reaction gas increases the ion conductivity of the ion exchange membrane constituting the membrane electrode assembly in the fuel cell stack to easily move proton ions produced from the anode to the cathode, and to the air supplied to the cathode. Water is produced through the reaction of oxygen and the electrons that come from work outside and electrochemical reactions.

The relative humidity of hydrogen should be maintained at around 70% to prevent dry-out phenomenon of the membrane electrode assembly.The more the humidification of the ion exchange membrane, the higher the ion conductivity, the higher the efficiency of the fuel cell stack. do. On the contrary, the high humidification condition is such that the liquefaction process of the water vapor supplied from the humidifier together with the reactant gas in the fuel cell stack becomes easy to interfere with the contact between the catalyst and the reactant gases, thereby reducing the efficiency of the fuel cell stack.

Therefore, in the fuel cell system, it is very important to find an appropriate point of the two opposite effects in consideration of the appropriate humidification conditions for the above reasons.

1 is a schematic diagram illustrating a fuel line of a fuel cell system for a vehicle according to the prior art.

Referring to the drawings, pure hydrogen is mainly used as fuel supplied to the fuel cell system according to the prior art, which is supplied from a hydrogen storage tank 10 mounted in an automobile. The compression pressure in the hydrogen storage tank 10 is quite high, but the pressure of hydrogen supplied to the atmospheric pressure fuel cell system is lowered to about 0.2 barg (Gauge bar) using the regulator 20. The hydrogen thus supplied is humidified through the humidifier 30, enters the fuel cell stack 40, and generates electricity through an electrochemical reaction, and the surplus remaining after the reaction is discharged to the outside of the fuel cell stack.

At this time, the surplus discharged increases in proportion to the supplied pressure, and when the fuel cell stack 40 having an inlet / outlet pressure difference of 0.12 barg is supplied at a supply pressure of about 0.2 barg, the amount of hydrogen released is 1 minute. It is about 1200 liters. Therefore, increasing the efficiency of fuel in such a system is difficult to expect, and it is virtually impossible to mount such a system in an automobile.

Finding an appropriate humidification condition of the fuel cell stack 40 is a matter to be considered from the design stage of the fuel cell stack. When the fuel cell stack is defined as a system, the amount of water supplied from the humidifier 30 and the stack ( The amount of water produced by the electrochemical reaction in 40 and the amount of water exiting the stack 40 should be adjusted to an appropriate amount.

If the water balance is not properly adjusted, the fuel cell stack will have a flooding and condensate generated by this process will block dead channels in the membrane electrode assembly by blocking the channel through which the reaction gas passes or covering the catalyst surface. area).

In the case of the cathode through which air passes, the pressure difference between the blower and the compressor supplying the air in the air is slightly adjusted to increase the pressure difference between the inlet and the outlet of the stack, so that the water condensed in the stack can be easily discharged. The amount of fuel supplied to the anode is directly related to the fuel efficiency of the system and the emissions must be limited.

However, if the discharge of the fuel is limited for the above reason, the water contained in the humidified reaction gas and the water diffused back from the cathode through the ion exchange membrane are easily condensed in the anode, and the condensate causes the stack performance. A dead area is generated that reduces the dead space.

Therefore, there is an urgent need to develop a fuel cell system that efficiently controls humidification conditions and efficient emission of fuel used for the popularization of automobiles using fuel cells, which have many advantages as low pollution and new energy sources. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides a fuel cell system and a method of controlling the same, which can efficiently use fuel by adjusting the opening time and opening period of a hydrogen vane valve that is responsible for discharging fuel. There is a purpose.

A fuel cell system according to the present invention for achieving the above object is installed at the rear of the fuel cell stack and the fuel cell stack to generate electricity by reacting with the humidified fuel periodically to fuel and condensate inside the fuel cell stack Retention key for a certain time and the discharge key to the outside is characterized in that it comprises a hydrogen valve.

On the other hand, the fuel cell system control method according to the present invention comprises closing the valve so that the fuel and condensed water stays for a predetermined time in the fuel cell stack that generates electricity by reacting with the humidified fuel and the condensed water and the fuel after the step The step of opening the valve to be discharged to the outside of the fuel cell stack is characterized in that it is performed periodically.

The closing and opening of the valve may be performed by opening the valve when the cell average voltage of the fuel cell stack is lower than or equal to a range of values to maintain a constant opening time (a) and closing the valve when the valve is greater than or equal to a range of values. In addition, it is characterized in that it is executed by defining a time point of opening the valve again as a period (T).

The predetermined range of the value is characterized in that the voltage value of 80% ~ 99% of the voltage immediately after the minimum cell voltage or the hydrogen vane valve opening.

The opening / closing period T of the valve sets the period at the maximum load current among each load current transmitted to the fuel cell system to the same value for all the load currents, and the opening time of the valve according to the period T a) converts the opening time in each period calculated according to the respective load currents to the duty rate (T / a), and converts the converted value in the opening period (T) calculated by the maximum load current ( A method of controlling a fuel cell system, wherein each opening time a is set to a different value in the same period T for all load currents in terms of a).

On the other hand, the opening time (a) of the valve is set to the same arbitrary value for all the load current, and the opening time (a) of the valve according to the period (T) in each cycle calculated according to each load current Is converted into a duty rate (T / a), and the converted value is converted into a period (T) at the same arbitrary value of the opening time (a) to convert each period (T) to all load currents. It is characterized by setting different values at the same arbitrary opening time (a).

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention, and to those skilled in the art to fully understand the scope of the invention. It is provided to inform you. Like reference numerals in the drawings refer to like elements.

2 is a schematic diagram showing a fuel line of a fuel cell system for automobiles according to the present invention, and FIG. 3 is a graph showing an average voltage of the fuel cell stack when the hydrogen vane valve of the fuel cell system according to the present invention is closed. .

The fuel cell system according to the present invention is provided with a fuel cell stack 40 which generates electricity by reacting with the humidified fuel and a control signal to periodically retain the fuel and condensed water inside the fuel cell stack for a predetermined time and discharge it to the outside. It is configured to include a hydrogen vent valve 50.

Hydrogen compressed to a high pressure in the hydrogen storage tank 10 is supplied to the atmospheric pressure fuel cell system using a regulator 20, usually down to about 0.2 barg (Gauge bar). The hydrogen supplied is humidified through the humidifier 30, enters the fuel cell stack 40, and generates electricity through an electrochemical reaction, and the remaining surplus is released to the outside of the fuel cell stack. At this time, the surplus discharged increases in proportion to the supplied pressure, and when the fuel cell stack 40 having an inlet / outlet pressure difference of 0.12 barg with a supply pressure of about 0.2 barg is used, the amount of hydrogen released is 1 minute. At about 1200 liters.

After the hydrogen vent valve 50 is mounted at the rear end of the line where hydrogen is discharged from the fuel cell stack 40 so as to limit the discharge of hydrogen used as fuel, the opening time of the hydrogen vent valve 50 and By controlling the opening period, the cell voltage in the fuel cell stack 40 is kept constant, thereby limiting the amount of hydrogen released.

The method for controlling a fuel cell system according to the present invention includes closing the valve 50 such that the fuel and condensed water in the fuel cell stack 40 generating electricity by reacting with the humidified fuel stays for a predetermined time. The step of opening the valve 50 so as to discharge condensate and fuel out of the fuel cell stack 40 is performed periodically.

One embodiment of the control method for controlling the fuel cell system of the present invention equipped with the hydrogen vane valve 50 as described above is as follows.

When the fuel cell system is operated while the rear end of the hydrogen line discharged from the fuel cell stack 40 is closed with the hydrogen vane valve 50, the average voltage of the fuel cell stack maintains a constant voltage as shown in FIG. 3. It keeps down and then decreases drastically.

In order for the fuel cell system to produce electrical energy, the area of the membrane electrode assembly corresponding thereto is required. That is, since a large area of the membrane electrode assembly is required to output a high current, the cell average voltage is kept constant until the required area in the anode of the membrane electrode assembly required for high current is obscured. However, if the required area of the anode of the membrane electrode assembly is obscured by humidified water and water diffused back from the cathode, the cell voltage is drastically reduced so that the average voltage of the fuel cell stack remains constant for a certain time. .

Accordingly, before the cell voltage of the fuel cell stack 40 decreases to the shutdown condition, the operation of restoring the cell average voltage again by opening the hydrogen vane valve 50 to discharge water condensed in the anode through the discharge flow of the fuel need. In order to open the hydrogen ban valve 50 to discharge the condensed water condensed in the anode of the stack through the pressure difference between the stack inlet and outlet generated from the flow of fuel, the hydrogen ban valve must be closed for some time and opened for some time. You have to decide if it is.

4 is a waveform showing the hydrogen vane valve opening period and the opening time of the fuel cell system according to the present invention.

Two variables as shown to control the amount of fuel discharged from the fuel cell system according to the present invention, that is, the opening and closing period (T) of the hydrogen vane valve and the opening time (a) of the hydrogen vane valve are amplitude modulation control method ( Similar to the control elements of PWM (Pulse Width Modulation).

In order to apply the control method as described above, a maximum period in which the minimum voltage of the stack in the fuel cell system is maintained is determined first. Here, the cycle means the same as the opening / closing period T of the hydrogen vane valve described above, and the hydrogen vane valve is opened and closed after maintaining the predetermined time (a) at the time when the cell average voltage starts to decrease. It is then defined as the point at which the hydrogen vant valve is opened again.

The period T is determined as the period T until the cell average voltage reaches a limit value or when the average voltage decreases. The limit value may be a minimum cell voltage that does not shut down the fuel cell. It can be a percentage of the voltage. However, in the case of automobiles, it is often accompanied by a sudden load change, so it is appropriate to decide until the cell average voltage decreases in the range of 80% to 99% of the initial voltage. Here, the initial voltage refers to the voltage immediately after the hydrogen vane valve is opened.

In a process of restoring the cell average voltage by opening the hydrogen vant valve at each determined period T, a time a for maintaining the opening of the hydrogen vant valve 50 is also important. When the opening time of the hydrogen vane valve is long, the condensed water covering the area of the membrane electrode assembly in the anode may sufficiently escape and the cell voltage may be recovered, but the amount of hydrogen discharged may increase, thereby decreasing fuel utilization. Conversely, shortening the opening time (a) of the hydrogen ban valve increases fuel utilization, but fails to discharge enough condensate accumulated inside the anode of the fuel cell stack, resulting in a decrease in cell voltage, resulting in a shutdown of the fuel cell system. do.

The opening time (a) of the hydrogen vant valve may be defined as a time at which the cell voltage is recovered, and the period T of each load current and the hydrogen vane valve opening time (a) may be defined.

The cycle T and the hydrogen vane valve opening time a defined for each load current may be converted into a duty rate T / a. This is used for operation by converting the hydrogen vane valve opening time to the cycle at the maximum load current among the reference load currents used for measurement, or setting a certain hydrogen vane valve opening time constant, and then converting the period to duty rate. Applicable to the system.

FIG. 5 is a schematic diagram of a hydrogen vent valve control system for an automobile equipped with a fuel cell system according to the present invention, and FIG. 6 is a graph showing fuel consumption of the fuel cell system according to the present invention.

The period T is executed by setting the period at the maximum load current of each load current transmitted to the fuel cell system to the same value for all load currents.

In this case, the opening time (a) according to the period (T) is a step of converting the opening time in each cycle calculated according to each load current to the duty rate, and the value converted in the step by the maximum load current The step of setting each opening time a to a different value in the same period T for all load currents in terms of the opening time a in the calculated period T is executed.

On the other hand, the opening time (a) according to the period (T) is a step of converting the opening time in each cycle calculated according to each load current to the duty rate, and the value converted in the step at any constant opening time Converting the period T of (a) to set each period T to different values for all the load currents may be performed.

For example, the position of the acceleration pedal month 61 is changed by the signal converter 62 according to the load signal required by the driver according to the degree of the driver stepping on the acceleration pedal moon 61. At this time, the load current required for the fuel cell system is determined and the determined current signal is transmitted to the fuel cell system. The load current thus transferred is the energy for driving the motor through a motor controller (not shown) that drives the vehicle, and on the other hand it is summed (63) over a period of time and averaged (64) and then the hydrogen vant relative to the load current. The hydrogen vane valve opening time 66 is determined through a function 65 of the valve opening time, and the hydrogen vane valve is controlled through the actuator controller 67 in accordance with the determined hydrogen vane valve opening time a.

At this time, the time for summing the loads is the same as the period determined at the maximum peak current because the condensed water accumulates in the anode of the fuel cell stack will be the fastest when the maximum peak, the period determined at this maximum peak This is because it is time to maintain the stabilized minimum current at the fastest accumulation rate of condensate.

The period (T) measured by the above method in the operation of a 100 cell stack fabricated from a 250 cm ² membrane electrode assembly was 60 seconds at a load current of 50 A, 36 seconds at 100 A, 28 seconds at 150 A, 17 seconds at 200 A, and 9 seconds at 250A. In addition, the hydrogen vane valve opening time (a) at each load current is 1.6 seconds at 50 A, 1.2 seconds at 100 A, 1 second at 150 A, 0.8 seconds at 200 A, and 0.5 seconds at 250 A. The respective duty rates are calculated from the data obtained as described above, 37.5 at 50A, 30 at 100A, 28 at 150A, 21.25 at 200A and 18 at 250A. Using the obtained duty rate, the hydrogen valve opening time (a) was calculated for each load current with a period of 9 seconds of 250 A. 0.24 seconds at 50 A, 0.3 seconds at 100 A, 0.32 seconds at 150 A, 0.42 seconds at 200 A, 0.5 at 250 A. Seconds. Therefore, if the period T is set to 9 seconds and then the valve opening time a is set to different values described above, FIG. 5 shows a case of a fuel cell equipped with a 232 연료 fuel cell stack. As such, the efficiency of the fuel can be increased.

On the other hand, the hydrogen vent valve opening time (a) may be set to a predetermined value and the period (T) may be calculated using the obtained duty rate according to each load current. The shorter the opening time (a) of the hydrogen valve, the higher the fuel efficiency. However, if the short time is too short, the response of the valve may be short and the reaction rate may be slow.

The straight line marked open operation in FIG. 5 indicates the case where the hydrogen vane valve is operated continuously while it is open during operation, that is, according to the prior art, and the hydrogen supply pressure in front of the humidifier is 0.2 barg. In addition, the dotted line marked the opening / closing control operation is an illustration of the operation of controlling the hydrogen vant valve using the system of the present invention. Both operations were driven using the same load profile, and it can be seen that there are significant differences and fuel savings as shown.

The present invention has been described in detail by way of examples, but the rights of the present invention are not limited to the above-described embodiments but are defined by the claims, and those of ordinary skill in the art of the present invention It is obvious that various modifications and adaptations can be made within the scope of the rights described.

The fuel cell system and its control method according to the present invention prevent the dry-out phenomenon of the membrane electrode assembly and adjust the ion conductivity of the ion exchange membrane by adjusting the opening time and opening period of the hydrogen vane valve which is responsible for discharging fuel. As a result, the fuel can be used efficiently.

Claims (7)

delete delete Closing the valve so that the fuel and condensate stays inside the fuel cell stack for generating electricity by reacting with the humidified fuel, and opening the valve to discharge the condensate and fuel to the outside of the fuel cell stack after the step. In the fuel cell system control method, wherein the step of performing the periodically The step of closing and opening the valve, When the cell average voltage of the fuel cell stack is less than or equal to a range of values, the valve is opened to maintain a certain opening time (a), and when the cell average voltage is greater than or equal to the range of values, the valve is closed and then the valve is opened again. A method for controlling a fuel cell system, characterized in that executed as defined by T). The method of claim 3, wherein the predetermined range of values is a minimum cell voltage.  The method according to claim 3, wherein the predetermined range of values is a voltage value in the range of 80% to 99% of the voltage immediately after the hydrogen vane valve is opened. The method according to any one of claims 3 to 5, wherein the opening / closing period T of the valve sets the period at the maximum load current of each load current transmitted to the fuel cell system to the same value for all load currents, The opening time (a) of the valve is set in terms of the period (T) at each load current and the duty rate (T / a) calculated according to each load current. 6. The valve according to any one of claims 3 to 5, wherein the opening time (a) of the valve is set to the same predetermined value for all load currents, and the period (T) at that load current is open at each load current. And a duty rate (T / a) calculated according to the time (a) and the respective load currents.

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