KR101879646B1 - System for fuel cell - Google Patents

Abstract

The present invention relates to a fuel cell system for detecting a state of a fuel cell in advance according to a voltage drop amount according to an amount of current and controlling the output of the fuel cell, Battery system.
A fuel cell system according to the present invention includes: a fuel cell that receives fuel containing hydrogen to produce electric power; A converter connected to the fuel cell and transforming a voltage output from the fuel cell; A battery connected to the output of the converter; And a control unit for calculating a voltage drop of the fuel cell and controlling an output of the fuel cell.

Description

[0001] SYSTEM FOR FUEL CELL [0002]

The present invention relates to a fuel cell system, and in particular, it relates to a fuel cell system, in which the state of a fuel cell can be grasped in advance in accordance with the amount of voltage drop according to an amount of current and output is controlled, and a deficient output is output from a battery, To a fuel cell system capable of supplying electric power.

Fuel cells are attracting attention as an energy source that can generate electricity and heat energy by replacing other energy sources. 2. Description of the Related Art In recent years, a fuel cell has been used as a small-sized self-power generation facility or as a power source of a moving object such as a vehicle in order to solve a power shortage due to an abrupt increase in electric power consumption.

Such a fuel cell is advantageous in that when a material capable of extracting hydrogen or hydrogen is injected into a raw material, heat and electricity are produced by hydrogen and oxygen reaction, and water is discharged to prevent air pollution. Particularly, when the fuel cell can continuously supply only fuel, it can be easily miniaturized, and it is easy to increase and decrease the desired power generation capacity, and the use place of the fuel cell is rapidly increasing.

However, the fuel cell has different characteristics from those of existing batteries, engines, and renewable energy generators, and therefore, there is no control method for efficiently controlling the fuel cell even though other control methods are required. It is a frequent occurrence.

Specifically, in the case of a fuel cell, when the voltage of the fuel cell is lowered to a certain level or lower due to various reasons such as the connection of the load and the supply of fuel mixed with impurities, the breakage of the membrane electrode assembly (MEA) There is a problem that occurs.

In addition, it has been difficult to rapidly change the output of the conventional fuel cell, and when the load increases greatly, breakage occurs frequently. Accordingly, a configuration has been developed in which a fuel cell is used in parallel or a fuel cell and a battery are used in parallel. However, when a fuel cell is used in parallel, there is a problem that a power generation cost is greatly increased.

Therefore, although a system mainly using a fuel cell and a battery in parallel is mainly used, it is difficult to control the load applied to the fuel cell even when the battery and the fuel cell are used in parallel, so that the damage of the fuel cell frequently occurs.

Korean Registered Patent No. 10-1382260 (Registration date April 04, 2014)

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fuel cell control apparatus and a fuel cell control method for controlling the output of the fuel cell in accordance with the amount of voltage drop according to the amount of current, Fuel cell system.

According to an aspect of the present invention, there is provided a fuel cell system including: a fuel cell that receives fuel containing hydrogen to produce electric power; A converter connected to the fuel cell and transforming a voltage output from the fuel cell; A battery connected to the output of the converter; And a control unit for calculating a voltage drop of the fuel cell and controlling an output of the fuel cell.

And the controller controls the converter to adjust the output of the fuel cell.

Wherein the control unit adjusts an output of the fuel cell by comparing a reference voltage variation rate determined in advance with a voltage variation rate of the fuel cell.

The control unit may stop the output of the fuel cell, restrict the current of the fuel cell, or adjust the output of the fuel cell so that the output of the fuel cell is normal.

And a plurality of reference voltage variation rates are provided.

And the reference voltage variation rate is provided according to the operating temperature of the fuel cell.

Wherein the control unit controls the output of the fuel cell using a reference voltage variation rate different from the reference voltage variation rate when the fuel is recirculated to the fuel cell, .

The control unit limits or stops the fuel recirculation when the output of the fuel cell system is stopped or the output is limited as a result of comparing the reference voltage variation rate with the voltage variation rate of the fuel cell.

The fuel cell system according to the present invention can grasp the state of the fuel cell in advance according to the amount of voltage drop according to the amount of current and control the output of the fuel cell system. Further, the insufficient output is output from the battery to prevent breakage of the fuel cell, This is possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a configuration of a fuel cell and its control system according to the present invention. FIG.
2 is an exemplary diagram showing the configuration of the control unit in more detail.
3 is a circuit diagram showing an example of a DC converter;
4 is an exemplary diagram showing a voltage curve of a fuel cell according to a current density and a cell temperature.
5 is an exemplary diagram for explaining control of a limited state;
6 is an exemplary diagram for explaining the control of the stop state;
7 is an exemplary view for explaining a voltage drop due to fuel recirculation;

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It should be noted that the drawings denoted by the same reference numerals in the drawings denote the same reference numerals whenever possible, in other drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. And certain features shown in the drawings are to be enlarged or reduced or simplified for ease of explanation, and the drawings and their components are not necessarily drawn to scale. However, those skilled in the art will readily understand these details.

FIG. 1 is a schematic view showing a configuration of a fuel cell and its control system according to the present invention, FIG. 2 is an exemplary view showing the configuration of the control unit in more detail, and FIG. 3 is an example of a DC converter Circuit diagram.

1 to 3, a fuel cell and its control system according to the present invention includes a battery 10, a fuel cell unit 20, and a control unit 80, and includes a fuel cell unit 20 and a battery 10 may be connected to a load 90. [

The battery 10 charges the electric power and supplies the charged electric power to the load under the control of the controller 80 when the load is connected. To this end, the battery 10 may be configured to include a circuit for charge / discharge and connection of a load. The battery 10 may be charged by electric power supplied from an external power source or by electric power produced by the fuel cell 21 by being connected to an external power source by a circuit. The battery 10 is composed of a battery that can be charged and discharged, such as a lead acid battery or a metal oxide battery. Here, the battery 10 may be replaced with another power source. For example, the battery 10 may be composed of a solar cell, a wind power generator, a hydraulic power generator, or another fuel cell, and the battery 10 may be included together with the battery 10, but the present invention is not limited thereto.

The fuel cell unit 20 is activated under the control of the control unit 80 to produce electric power and supplies the produced electric power to the load 80 or the battery 10 via the DC converter 26. [ The fuel cell unit 20 includes a supply device for supplying hydrogen or a fuel capable of extracting hydrogen to the fuel cell stack and a recirculation device 22 for recycling the used fuel to use the residual hydrogen contained in the used fuel ). ≪ / RTI > Also, the fuel cell stack may include a membrane electrode assembly (MEA), but it may be a fuel cell having other types of electrodes, and the present invention is not limited by the presented examples. The detailed structure and operation principle of such a fuel cell are disclosed in detail, and a detailed description thereof will be omitted.

DC converter 26 boosts or reduces the voltage of the electric power produced from the fuel cell 21 and transfers it to the external circuit or battery 10. [ In addition, the DC converter 26 regulates the current output from the fuel cell 21 under the control of the controller 80. This DC converter 26 can be implemented by a buck-boost circuit and controls the switching of the buck-boost circuit by PWM (Pulse Width Modulation) 21 are controlled. Here, the buck-boost (Sbuck) circuit is merely an example, and the present invention is not limited thereto.

The control unit 80 controls the operation of the fuel cell 21 and the DC converter 26. Specifically, the control unit 80 grasps the state of the fuel cell 21 according to the operation thereof, and controls the DC converter 26 to control the output from the fuel cell 21. The control unit 80 compares the operating temperature of the fuel cell 21 and the dynamic characteristic drop at the corresponding operating temperature and the current output voltage of the fuel cell 21, And 'stop', and performs output control according to each step. This step is not limited to the three steps shown as being able to be further increased as necessary, but for the sake of convenience of explanation, the explanation will be made by taking the case of three steps as an example.

Specifically, when the fuel cell 21 exhibits only a general dynamic drop according to the main operation temperature in the use state of the fuel cell 21, the control unit 80 maintains the normal output, that is, the output, to the external load 90 or the battery 10 . On the other hand, when the voltage drop is greater than a predetermined first ratio in a state where the dynamic characteristic drop is greater than the predetermined value, the output current is limited. In particular, when the voltage drop of the fuel cell 21 occurs at a predetermined second rate or more, the control unit releases the connection with the load for protection of the fuel cell 21 to reduce the load imposed on the fuel cell 21 . The control unit controls the DC converter 26 for this purpose. The controller 80 controls the current or voltage output through PWM (Pulse Width Modulation) control, and may include a proportional integral controller (PI control) and a fuzzy controller (Fuzzy Control) for PWM control, The present invention is not limited thereto. Such control will be described in more detail with reference to FIG. 4 and subsequent drawings.

The load 90 is operated by the power supplied from the battery 10 and the fuel cell unit 20. Such a load 90 may be a power source for various electronic devices, power engines such as vehicles. When the load 90 is an apparatus using AC power, for example, in the case of the motor 92, the inverter 91 for converting the DC power output from the battery 10 and the fuel cell unit 20 into AC, As shown in FIG.

FIGS. 4 to 7 are illustrations for explaining the current control by the control unit. FIG. 4 is an exemplary view showing the voltage curve of the fuel cell according to the current density and the cell temperature, and FIG. Fig. 6 is an exemplary diagram for explaining control of the stop state, and Fig. 7 is an exemplary diagram for explaining a voltage drop due to fuel recirculation.

Referring to FIGS. 4 to 7, as described above, the fuel cell control system according to the present invention adjusts the voltage drop rate of the fuel cell to a predetermined ratio to adjust the amount of current output from the fuel cell 21, The voltage of the fuel cell 21 is prevented from dropping to the breakdown voltage, thereby preventing the fuel cell 21 from being damaged.

The cell voltage of the fuel cell 21 varies depending on various conditions. 4, the ideal cell voltage of the fuel cell 21 is 1.2 V per cell, but a voltage of approximately 1 V is output for each cell of the fuel cell 21 in an actual reaction. At this time, when a load is applied to the cell of the fuel cell 21, the voltage drops due to the activation loss, and the amount of the voltage drop due to the activation loss depends on the temperature of the fuel cell 21 cell.

4, A represents the lossless voltage of the fuel cell 21 cell. However, in the actual cell voltage of the fuel cell 21, when the load is connected, an activation loss (section H) is generated, and a voltage drop of about 0.3 V is generated for each cell. As the amount of power supplied during the supply of power to the load 90 increases, a loss due to the internal resistance is generated and the voltage drop gradually increases (R section).

If the current demand exceeds the production amount due to the maximum reaction per unit area of the fuel cell 21, the cell voltage falls below the breakdown voltage and the MEA is broken. That is, it is possible to smoothly use the fuel cell 21 by maintaining the strategy amount supplied to the load in the R section.

Particularly, the output amount of the fuel cell 21 has a close relationship with temperature. Although the fuel cell 21 operates at a temperature of about 800 ° C, the fuel cell can operate at a lossless voltage. However, when it is used as a power source of an actual power unit, it is in a range of about 60 to 70 ° C Lt; / RTI >

In this case, as shown in Fig. 4, an activation loss H, a voltage drop R due to an internal resistance, and a voltage drop F due to an over capacity occur. Particularly, the voltage drop due to the ignition loss H, the voltage drop R due to the internal resistance, and the voltage drop F due to the excess capacity appear differently depending on the temperature of the fuel cell 21. Generally, when the cell temperature of the fuel cell 21 is low, the voltage drop becomes larger. Therefore, it is necessary to consider temperature and voltage drop for stable control.

To this end, the present invention performs multi-stage power control such as 'normal', 'limit', and 'stop' as described above. In the present invention, the case of limiting the current is described as an example, but the voltage control is also possible, and the present invention is not limited to the present invention.

First, the control unit 80 determines that the voltage drop of the fuel cell 21 is in the 'normal' state according to the power demand of the load 90 of the fuel cell 21, do. That is, when the voltage drop of the cell of the fuel cell 21 occurring during the supply of the power to the load 90 as shown in Fig. 4 is equal to the R period, the current is not limited to the load 90 or the battery 10, As shown in FIG.

To this end, the controller 80 compares the voltage variation rate? Vfc of the fuel cell 21 with a predetermined voltage variation rate? Vfc_pre1, and determines whether the current voltage variation rate? Vfc of the fuel cell 21 cell If it is equal to or less than the voltage variation rate (DELTA Vfc_pre1), it is determined as a normal state.

On the other hand, when the voltage variation rate? Vfc of the cell detected in the voltage variation amount detection period C exceeds the predetermined voltage variation rate? Vfc_pre1 as shown in FIG. 5, the amount of current output from the cell of the fuel cell 21 . For example, in FIG. 5, the amount of current is limited to 80%, and the current Is output to the stack after the detection period C is reduced compared with that before the detection period C. As a result, the fuel cell 21 supplies a current within a reaction amount per cell area to the load 90 and returns to the voltage in the stable period. At this time, among the electric power supplied to the load 90, the amount of electric power reduced by the fuel cell 21 is covered by the battery 10.

When the voltage variation rate (Vfc) of the cell detected in the detection period (C1) is greatly changed compared to the predetermined voltage variation rate (Vfc_pre0) as shown in Fig. 6, it is determined that the cell voltage is drastically lowered, The control for stopping the output is performed. As a result, in the section C2 after the detection period C1, the output of the current Is stops, and the stack voltage Vs returns to the normal state.

Here, the voltage variation rate (DELTA Vfc_pre0, 1), which is a level for comparing with the voltage variation rate of the current cell, can be variously provided according to the control level. In particular, the voltage variation rate (Vfc_pre) for comparison can be used by adjusting the calculated level value when calculating a value of one level and applying it to the voltage variation rate (Vfc_pre) of another level. That is, when the voltage variation rate (DELTA Vfc_pre0) for determining the driving stop is set to 1, the voltage variation rate (DELTA Vfc_pre1) for limiting the output of the current is set to a value of the stopped voltage variation rate DELTA Vfc_pre0 Can be calculated by multiplying by a constant, but the present invention is not limited thereto. In particular, the voltage variation rate (DELTA Vfc_pre0,1) may be provided for each operating temperature of the fuel cell.

FIG. 7 is an illustration showing the stack voltage at the time of supplying pure hydrogen and at the time of recycling.

Referring to FIG. 7, when the fuel cell 21 requires more power than the power produced by the maximum reaction amount as described above, a voltage drop below the breakdown voltage occurs, and the polymer membrane of the fuel cell is destroyed. It is closely related to temperature.

In addition to the temperature and the power, the amount of hydrogen required for the reaction also plays an important role in the fuel cell 21. In particular, recent fuel cell systems have a recirculation device 22 for the re-use of hydrogen and re-react the remaining hydrogen after the reaction.

In this case, the reaction rate of the fuel cell 21 is lowered in the section L where the recycled hydrogen is injected and the hydrogen density is lowered as shown in FIG. 7, so that a voltage drop occurs. Therefore, it is necessary to control the output of the fuel cell 21 in accordance with the amount of hydrogen.

That is, the voltage fluctuation rate? Vfc_pre, which is a criterion for comparison with the current voltage fluctuation rate? Vfc of the fuel cell 21, is a reference value for the recirculation hydrogen supply in consideration of the case where the fuel with low hydrogen density is supplied by recirculation It is necessary to calculate the voltage fluctuation rate (DELTA Vfc_pre_H) or to control to stop or reduce the supply of recirculated hydrogen at the time of voltage drop.

Therefore, when the fuel is supplied by the recirculation, the control unit 80 determines whether the reference voltage fluctuation rate (DELTA Vfc_pre0, 1) when the hydrogen dense fuel is not supplied or the recirculated hydrogen is supplied and the reference voltage fluctuation rate Vfc_pre_H). That is, when the recirculated hydrogen is not supplied, the control unit 80 determines 'normal', 'restricted', and 'stopped' by using the reference voltage variation rate (ΔVfc_pre0, 1) Quot; normal ", " restricted ", and " stopped " by using the voltage variation rate? Vfc_pre_H. The recirculation reference voltage variation rate (DELTA Vfc_pre_H) may also be set to various values depending on the temperature.

In particular, when the recirculating hydrogen is supplied in the 'restricted' and 'stopped' states in the 'normal', 'restricted' and 'stopped' controls, the controller 80 stops supplying the recycled hydrogen, , Or it is possible to control the supply amount of the recycle hydrogen.

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 the like. Accordingly, such modifications are deemed to be within the scope of the present invention, and the scope of the present invention should be determined by the following claims.

10: Battery 20: Fuel cell unit
21: Fuel cell 26: DC converter
80: control unit 90: load
91: Inverter 92: Motor

Claims (8)

1. A fuel cell system comprising: a fuel cell that receives fuel containing hydrogen to produce electric power;
A converter connected to the fuel cell and transforming a voltage output from the fuel cell;
A battery connected to the output of the converter;
A control unit for calculating a voltage drop of the fuel cell and controlling an output of the fuel cell; And
And a recirculation device for re-supplying the fuel reacted to the fuel cell,
Wherein,
Wherein the output of the fuel cell system is regulated by using a reference voltage variation rate different from a reference voltage variation rate when the fuel is recirculated. The method according to claim 1,
The control unit
And controls the converter to adjust the output of the fuel cell. 3. The method according to claim 1 or 2,
The control unit
Wherein the output of the fuel cell is controlled by comparing a predetermined reference voltage variation rate with a voltage variation rate of the fuel cell. The method of claim 3,
The control unit
Wherein the output of the fuel cell is controlled such that the output of the fuel cell is stopped or the current of the fuel cell is limited or output. The method of claim 3,
Wherein the plurality of reference voltage variation rates are provided. 6. The method of claim 5,
Wherein the reference voltage variation rate is provided in accordance with the operating temperature of the fuel cell. delete The method according to claim 1,
The control unit
If it is determined that the output is stopped or the output is limited as a result of comparing the reference voltage variation rate with the voltage variation rate of the fuel cell,
Thereby limiting or stopping the fuel recirculation.

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