KR101867917B1 - Current Control Method of Fuel Cell Stack and Fuel Cell System Using the Method - Google Patents

Abstract

A method of controlling current in a fuel cell stack is disclosed. The method may include setting a maximum current limit of the stack, monitoring a rate of voltage change with time of the cells included in the stack, and performing a corresponding control if the rate of voltage change is less than or equal to a predetermined value have. Thus, the device efficiency can be improved.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of controlling current in a fuel cell stack,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a fuel cell system, and more particularly, to a method of controlling current in a fuel cell stack and a fuel cell system using the same.

The fuel cell vehicle includes a fuel cell stack in which a plurality of fuel cell cells to be used as a power source are stacked, a fuel supply system for supplying hydrogen as fuel to the fuel cell stack, an air supply system for supplying oxygen, A water and thermal management system for controlling the temperature of the fuel cell stack, and the like.

In a conventional vehicle fuel cell system, a hydrogen supply device supplies high-pressure hydrogen stored in a hydrogen tank to a fuel cell stack by regulating pressure through a regulator. The air supply device humidifies air supplied by an air blower through a humidifier, To the battery stack. The fuel cell vehicle also has an inverter that uses an electric motor as a driving source for running and converts the direct current voltage of the fuel cell stack or the battery into an alternating current voltage to drive the electric motor.

The fuel supply system decompresses the compressed hydrogen in the hydrogen tank to supply it to the fuel electrode (anode) of the stack, and the air supply system operates the air blower to supply the sucked external air to the cathode (cathode) of the stack.

When hydrogen is supplied to the fuel electrode of the stack and oxygen is supplied to the air electrode, the hydrogen ions are separated through the catalytic reaction at the fuel electrode. The separated hydrogen ions are transferred to the oxidizing electrode, which is an air electrode, through the electrolyte membrane. In the oxidizing electrode, hydrogen ions separated from the fuel electrode, electrons and oxygen are electrochemically reacted together to obtain electrical energy. Specifically, the electrochemical oxidation of hydrogen takes place in the anode, and the electrochemical reduction of oxygen occurs in the air electrode. At this time, electricity and heat are generated due to the movement of the generated electrons. By the chemical action of hydrogen and oxygen, Is generated.

A discharge device for discharging hydrogen, oxygen and the like which is not reacted with by-products such as water and heat generated in the electric energy generation process of the fuel cell stack, and gases such as water vapor, hydrogen and oxygen, Lt; / RTI >

On the other hand, the fuel cell system must manage the current value and the voltage value inside the stack to a predetermined level. If the current value or the voltage value is lowered by a predetermined value, the output is lowered, and the stack durability is scratched, so that deterioration of the fuel cell may occur.

Further, the fuel cell system has a current limiting logic such that when the voltage of a specific cell of the stack falls below a target voltage (the cell's minimum threshold voltage) while the fuel cell system is being driven, the current can no longer rise. If the performance of a specific cell included in the stack becomes lower than the limit of the available current, the current limit will occur due to the specific cell, which may cause a shock during operation, which may cause degradation of operability. 1 (a) to 1 (d) illustrate a current control method of a fuel cell stack according to the prior art.

According to Fig. 1 (a), the X axis is the operating time at which the fuel cell is driven. The first Y-axis is the current, and the second Y-axis is the voltage. The first line 11 represents the fuel cell maximum current limit. The first line (11, maximum current limit of the stack) is an ideal current value that can be limited to a maximum when the voltage of the fuel cell falls.

The second line 12 represents the current fuel cell current. The vehicle is driven to the full accelerator from the second line 12 to the point where the second line 12 rapidly reaches the first line 11 at 0 amperes.

The third line 13 indicates a current limit that can be supplied to the fuel cell. If the first line 11 is an ideal value, the third line 13 may correspond to a current limit value of a realistic fuel cell. The fourth line 14 represents the minimum cell voltage. It corresponds to the minimum voltage at which each cell voltage in the stack can be lowered. If any one of the cells in the stack falls below the minimum fourth line 14, a loss in stack durability occurs.

1 (b) to 1 (d) are graphs showing voltage values for the stack cells of the first point 110, the second point 120, and the third point 130. Each thin bar shape represents each voltage value of the stack cell. The current limit value becomes lower while the current flows from the first point 110 to the third point 130.

First, the first point 110 is the point where the third line 13 and the first line 11 meet. Therefore, all the cells in the stack do not fall below the target voltage (below the current limit), and all cells in the stack are stable without exceeding the maximum current limit (Cur Limit 1) as shown in the figure.

Since the second point 120 has a current limit after the average cell (Min Cell) of the second cell 120 drops, the control time is delayed to have a value lower than the target voltage in the specific cell 120-1 as shown in FIG. . That is, even if the voltage of the specific cell 120-1 drops below the target voltage and the current is limited, a problem arises in the stack durability.

The third point 130 is a case where the specific cell 130-1 is repeatedly below the target voltage (Cur Lim 3) after the second point 120. Even in this case, a problem arises even if the current is controlled after the specific cell 130-1 has already fallen below the target voltage.

In this way, a drop in the cell voltage is caused and a constant lowering of the minimum cell voltage demands a lower current limit value. The output of the fuel cell is stepwise limited after the performance of the fuel cell system has deteriorated (when the cell voltage reaches the minimum target voltage, and when the wet state indicator value is detected). In this case, when the fuel cell is operated after reaching the limit performance of the fuel cell, if such a situation is repeated, deterioration of the fuel cell accelerates and when the cell voltage reaches the minimum target voltage, May occur.

Therefore, a more improved current limiting method is required.

Japanese Patent Application Laid-Open No. 10-2016-0007826 (Publication date 201.01.201)

It is an object of the present invention to provide a fuel cell system that adjusts a maximum current limit before a fuel cell cell voltage reaches a minimum target voltage.

It is another object of the present invention to provide a fuel cell system that prevents sudden current limitation to prevent vehicle shock.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, unless further departing from the spirit and scope of the invention as defined by the appended claims. It will be possible.

A method of controlling current in a fuel cell stack according to an embodiment of the present invention includes: setting a maximum current limit value of a stack; Monitoring a voltage change rate with time of a cell included in the stack; And performing a control corresponding to the voltage change rate when the voltage change rate is equal to or less than a predetermined value.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, And can be understood and understood.

According to various embodiments of the present invention, there are the following advantages.

First, device stability and device efficiency can be improved by providing a fuel cell system that adjusts the maximum current limit before the fuel cell cell voltage reaches the minimum target voltage.

Second, user safety and device efficiency can be improved by providing a fuel cell system that prevents sudden current limitation and prevents vehicle shock.

The effects obtained by the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the following description will be.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. It is to be understood, however, that the technical features of the present invention are not limited to the specific drawings, and the features disclosed in the drawings may be combined with each other to constitute a new embodiment.
Figs. 1 (a) to 1 (d) are diagrams for explaining adjustment of the current limit of the fuel cell stack after the minimum cell voltage according to the prior art falls below the target voltage.
2 is a block diagram of a fuel cell system according to an embodiment.
3 is a sequence diagram showing a method of adjusting the current limit of the fuel cell stack before the minimum cell voltage according to the embodiment falls below the target voltage.
4 is a diagram for explaining adjusting the current limit of the fuel cell stack before the minimum cell voltage according to the embodiment falls below the target voltage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an apparatus and various methods to which embodiments of the present invention are applied will be described in detail with reference to the drawings. The suffix "module" and " part "for the components used in the following description are given or mixed in consideration of ease of specification, and do not have their own meaning or role.

In the description of the embodiment, in the case of being described as being formed on the "upper or lower", "before" or "after" of each component, (Lower) "and" front or rear "encompass both that the two components are in direct contact with each other or that one or more other components are disposed between the two components.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected to or connected to the other component, It should be understood that an element may be "connected," "coupled," or "connected."

It is also to be understood that the terms such as " comprises, "" comprising," or "having ", as used herein, mean that a component can be implanted unless specifically stated to the contrary. But should be construed as including other elements. All terms, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used terms, such as predefined terms, should be interpreted to be consistent with the contextual meanings of the related art, and are not to be construed as ideal or overly formal, unless expressly defined to the contrary.

2 is a block diagram illustrating a fuel cell system according to an embodiment.

2, the fuel cell system 220 may include a sensor unit 210, a stack cell 220, a hydrogen valve 240, and a fuel control unit (FCU) 250. The fuel cell system 220 may include an inverter including a drive motor 300, a valve heater, an LDC, a main / auxiliary battery module, a radiator, and the like, but for the sake of clarity of description, Will be mainly described.

The hydrogen valve 240 may include a drain hydrogen valve and a purge hydrogen valve, respectively. The drain hydrogen valve collects the condensed water and discharges it to the humidifier. In the humidifier, the air can be humidified using the condensed water and then supplied to the air electrode. A purge hydrogen valve can be used to release impurities.

The stack cell 220 may be a core component of a fuel cell, which is a unit of a plurality of cells.

The control unit 250 is a module for controlling the overall operation of the system 200.

3 is a sequence diagram showing a method of adjusting the current limit of the fuel cell stack before the minimum cell voltage according to the embodiment falls below the target voltage.

Once the control unit 250 sets the maximum current limit value of the fuel cell stack (S310).

The controller 250 sets a maximum current limit value to set a maximum value at which the current value increases when the voltage drops. For example, the control unit 250 can set the maximum current limit value to 350A.

Next, the controller 250 determines whether DELTA (minimum cell voltage / average cell voltage) exceeds a predetermined value (S315).

The controller 250 may calculate a value? (MinCell / AveCell) that is? (Minimum cell voltage / average cell voltage). The minimum cell voltage (MinCell) is the voltage value of the cell having the lowest voltage value among the cells included in the stack. The average cell voltage (AveCell) is a voltage value representing an average voltage of all the cells included in the stack.

The control unit 250 can continuously measure the minimum cell voltage / average cell voltage according to the time variation of the minimum cell voltage / average cell voltage at a preset period or a set time unit. The controller 250 monitors the value of DELTA (minimum cell voltage / average cell voltage) and can perform current control when the value exceeds a predetermined value.

According to the present invention, by monitoring Δ (minimum cell voltage / average cell voltage), it is possible to control the current so that any one of the cells in the stack does not reach the minimum reference voltage (target voltage). This can overcome the problems of vehicle shock and stack deterioration caused by controlling the current after the reference voltage of the cell drops from the target voltage in the prior art.

The controller 250 continuously monitors DELTA (minimum cell voltage / average cell voltage) when DELTA (minimum cell voltage / average cell voltage) exceeds a predetermined value (S315).

If the minimum cell voltage / average cell voltage is less than or equal to the predetermined value (S315), the controller 250 determines how many times it is less than the predetermined value. This is because the control method differs depending on the number of times.

First, when the minimum cell voltage / average cell voltage is less than a predetermined value (S320), the controller 250 limits the output of the air vent and the hydrogen vent or controls the humidity of the generated water drain ( S335). This is because the cell voltage drop can be improved. The control unit 250 may control the air vent, oxygen and hydrogen of the hydrogen vent to be discharged or the humidity of the generated water drain to be increased or decreased.

Then, the control unit 250 returns to step S315 and repeats step S315.

If the difference Δ (minimum cell voltage / average cell voltage) is equal to or less than the predetermined value (S325), the control unit 250 resets the maximum current limit again. For example, the control unit 250 may reset the maximum current limit by A (S340). For example, the controller 250 may set the maximum current limit to 320 A, but this is an example.

Then, the control unit 250 returns to step S315 and repeats step S315.

If the minimum cell voltage / average cell voltage is equal to or more than the predetermined value (S325), the controller 250 subtracts the maximum current limit by B (S330) The current limit warning lamp is blinked (S350). Where B may be 20A, but this is not limiting. Accordingly, the user can visit the repair shop and receive the service.

As described above, when Δ (minimum cell voltage / average cell voltage) is monitored before the minimum cell voltage reaches the target voltage or less, the fuel cell system is protected rather than the current limit after the cell voltage reaches the target voltage or lower , Deterioration of the fuel cell system can be prevented.

In addition, since the minimum cell voltage is adjusted to the maximum current limit, the drying condition due to the supercharged air and the overload are prevented, so that the constant voltage can be maintained and the operability can be improved.

4 is a diagram for explaining adjusting the current limit of the fuel cell stack before the minimum cell voltage according to the embodiment falls below the target voltage.

Referring to FIG. 4, as in FIG. 1, the X axis is the operating time at which the fuel cell is driven. The first Y-axis is a current value, and the second Y-axis is a voltage value.

The first line 11 represents the fuel cell maximum current limit. The first line (11, maximum current limit of the stack) is an ideal current value that can be limited to a maximum when the voltage of the fuel cell falls.

The second line 12 represents the current fuel cell current. The vehicle is driven to the full accelerator from the second line 12 to the point where the second line 12 rapidly reaches the first line 11 at 0 amperes.

The third line 13 indicates a current limit that can be supplied to the fuel cell. If the first line 11 is an ideal value, the third line 13 may correspond to a current limit value of a realistic fuel cell. The fourth line 14 represents the minimum cell voltage. It corresponds to the minimum voltage at which each cell voltage in the stack can be lowered. If any one of the cells in the stack falls below the minimum fourth line 14, a loss in stack durability occurs.

The present invention aims at adjusting the current limit so that the voltage of one of the stack cells does not drop below the target voltage. The goal is to minimize the number of times if it is difficult for one of the stack cells to fall below the target voltage.

4 (b) to 4 (d) are graphs showing voltage values of the fourth point 310, the fifth point 320, and the sixth point 330 for each stack cell. Each thin bar shape represents each voltage value of the stack cell. The maximum current limit (current value, not voltage value) is displayed in yellow. The maximum current limit becomes smaller as it proceeds from the fourth point 310 to the sixth point 330.

4 (b), the fourth point 310 is the point where the third line 13 and the first line 11 meet. Therefore, all the cells in the stack do not fall below the target voltage, and all the cells in the stack are in a stable state that do not exceed the maximum current limit (Cur Limit 1) as shown in the figure.

According to the present invention, the control unit 250 monitors Δ (minimum cell voltage / average cell voltage) and monitors the state of the stack.

4 (c) shows that the control unit 250 adjusts the current limit value in advance before the specific cell 320-1 falls below the target voltage. Thus, deterioration of the stack durability can be prevented.

4 (d) again shows that the control unit 250 adjusts the current limit value before the specific cell 330-1 falls below the target voltage. Thus, deterioration of the stack durability can be prevented.

According to the present invention, it is confirmed that the voltage of a specific cell does not fall below a minimum voltage (target voltage) by calculating a voltage ratio of the fuel cell cell as a rate of change with time and applying a current limit in advance. As a result, the vehicle output is constant and no vehicle shock is generated. In addition, it is possible to prevent voltage drop repetition of a specific cell, thereby preventing battery deterioration starting from a specific cell having low durability.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the above description should not be construed in a limiting sense in all respects and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention.

The method according to the above-described embodiments may be implemented as a program to be executed by a computer and stored in a computer-readable recording medium. Examples of the computer-readable recording medium include a ROM, a RAM, a CD- , Floppy disks, optical data storage systems, and the like.

The computer readable recording medium may be distributed over a networked computer system so that computer readable code can be stored and executed in a distributed manner. And, functional program, code, and code segments for implementing the above-described method can be easily inferred by programmers in the technical field to which the embodiment belongs.

Claims (15)

A method of controlling current in a fuel cell stack,
Setting a maximum current limit value of the stack;
Monitoring a voltage change rate with time of a cell included in the stack; And
And performing control corresponding to the voltage change rate if the voltage change rate is equal to or less than a predetermined value,
Wherein when the voltage change rate is equal to or less than a predetermined value,
And performing control corresponding to the number of times that the voltage change rate is less than or equal to a predetermined value,
The step of performing control corresponding to the number of times may include:
And resetting the maximum current limit value of the stack if the number is second or third. The method according to claim 1,
The voltage change rate with time is? (Minimum cell voltage / average cell voltage)
Wherein the step of monitoring the voltage change rate comprises:
And determining whether the voltage change rate exceeds a predetermined reference value. delete The method according to claim 1,
The step of performing control corresponding to the number of times may include:
Performing at least one of limiting the output of the air vent, limiting the output of the hydrogen vent, and controlling the humidity of the generated water drain when the frequency is the first time. The method according to claim 1,
Wherein resetting the maximum current limit value of the stack comprises:
And the number of times is a second time. The method according to claim 1,
Wherein resetting the maximum current limit value of the stack comprises:
And resetting the maximum current limit value of the stack by subtracting a certain value from the maximum current limit value of the stack when the number is greater than or equal to the third number. The method according to claim 6,
Further comprising: if the number of times is greater than or equal to a third number, providing a warning indication if the maximum current limit value of the stack exceeds a predetermined value. 1. A fuel cell system for controlling current in a fuel cell stack,
Fuel cell stack;
And a controller for setting a maximum current limit value of the stack, monitoring a voltage change rate with time of a cell included in the stack, and performing control corresponding to the voltage change rate when the voltage change rate is less than a predetermined value,
Wherein,
Wherein the control unit performs control corresponding to the number of times that the voltage change rate is less than or equal to a predetermined value and resets the maximum current limit value of the stack when the number is second or third. 9. The method of claim 8,
The voltage change rate with time is? (Minimum cell voltage / average cell voltage)
Wherein,
And determines whether the voltage change rate exceeds a predetermined reference value. delete 9. The method of claim 8,
Wherein,
And performs at least one of limiting the output of the air vent, limiting the output of the hydrogen vent, and controlling the humidity of the generated water drain when the frequency is the first time. 9. The method of claim 8,
Wherein,
And performs the reset if the number of times is the second time. 9. The method of claim 8,
Wherein,
Wherein the maximum current limit value of the stack is reset by subtracting a certain value from the maximum current limit value of the stack when the number is greater than or equal to the third number. 14. The method of claim 13,
Wherein,
And provides a warning notification when the maximum current limit value of the stack exceeds a preset value when the number of times is a third or more. A program recorded on a recording medium, characterized by realizing a method of controlling the current of the fuel cell stack according to claim 1 through being executed by a processor.

Images