KR101020200B1 - Power controlling method of Fuel cell and Fuel cell system - Google Patents

Abstract

The present invention relates to a power control method for a fuel cell and a fuel cell system thereof. In the present invention, three or more fuel cells, that is, the first to third fuel cells 30, 40, 50 are provided. In order to supply the DC power supplied from the first to third fuel cells 30, 40 and 50, respectively, to the power system, a power converter 60 is provided. The power converter 60 senses output voltages of the first to third fuel cells. As a result of the sensing, it is determined whether the output voltages of the first to third fuel cells 30, 40, 50 belong to a normal voltage, a minimum voltage, and a limit voltage. When all of the first to third fuel cells 30, 40 and 50 belong to a normal voltage, the output power of the first to third fuel cells 300 (40 and 50) is equally controlled, respectively. When the output voltage of at least one of the first to third fuel cells 30, 40 and 50 is sensed to the lowest voltage, the first to third power is supplied to the load required power of the power system. The output of the fuel cells 30, 40 and 50 is output at a predetermined predetermined output power, and at least one of the first to third fuel cells 30, 40 and 50 of the fuel cell. When the output voltage is sensed as the threshold voltage, the control unit does not output power from the fuel cell outputting the threshold voltage, in which case the output power of the fuel cell outputting the minimum voltage or the limit voltage is maintained as it is and the remaining fuel The battery is controlled to compensate for the load demand power and to be output. According to the invention, such as, it is possible to stably load the required power in accordance with the output voltage of the plurality of the fuel cell has the advantage that prevent damage to the fuel cell and to improve the efficiency of the overall system operation.

Fuel cell, steady voltage, peak voltage, limit voltage, power converter

Description

Power control method of fuel cell and fuel cell system thereof

The present invention relates to a fuel cell system, and more particularly, to a fuel cell power control method and a fuel cell system thereof for stably controlling the output power of three or more fuel cells arranged in parallel.

Due to the depletion of fossil fuels and the crisis of energy, global demands and interests on renewable energy are increasing, and fuel cells are at the center. The fuel cell has a very high power generation efficiency for directly converting chemical energy of a hydrocarbon-based fuel such as natural gas, naphtha and methanol into electrical energy. In addition, there are very few pollution factors, so it can be installed near power demand or distributed in areas where power demand is close, and can also be used as a large capacity power generation facility if necessary. For this reason, it is a technology that is already entering the commercialization stage in many application fields as one of the next major power generation technologies. In particular, molten carbonate fuel cells (MCFCs) are distributed and deployed in the power system for the power generation business and are being put into practical use.

The fuel cells are connected in series or in parallel in order to supply power required by various devices using the fuel cells as energy sources. 1 shows a configuration diagram of a fuel cell system in which a plurality of fuel cells are arranged in parallel.

1, the first to n th fuel cells are connected in parallel. Hereinafter, three fuel cells will be described, which will be referred to as first to third fuel cells 11, 12, and 13.

A power converter (PCS) 20 for converting DC power DC, which is an output of the first to third fuel cells 11, 12, 13, into AC power AC is provided. . The power converter 20 converts the DC power of the low voltage state output from the first to third fuel cells 11, 12, 13 to a predetermined level from the first to third DC-DC converters 21. (22) (23) and a DC-AC inverter for converting each DC power obtained in the first to third DC-DC converters 21, 22, 23 into an AC power source for use in a power system ( 25).

According to such a configuration, the DC power generated in the first to third fuel cells 11, 12, 13 is transferred to the power converter 20. The first to third DC-DC converters 21 and 22 and 23 of the power converter 20 convert the DC power to a predetermined level and transfer the DC power to the DC-AC inverter 25. The DC-AC inverter 25 converts the converted DC power into AC power that can be actually used, and then transfers the converted DC power to the power system.

In this case, the output characteristics of the first to third fuel cells 11, 12, 13 must be the same so that the power conversion in the power converter 25 can be stably performed. However, the output characteristics of the first to third fuel cells 11, 12, 13 may vary due to various variables and long time use of the fuel cell in manufacturing the fuel cell. As a result, output voltages of the first to third fuel cells 11 and 12 and 13 are different from each other, and thus output power also varies.

In order to solve this problem, a method of controlling the output current of the first to third fuel cells 11, 12, 13 evenly is conventionally used. For example, the output current of each of the first to third fuel cells 11, 12, 13 is sensed, and the output current of another fuel cell is increased based on the largest output current therefrom, thereby increasing the first current. The output currents of the third to third fuel cells 11, 12 and 13 are equally controlled so that the output power is supplied as much as the load demand power in the power system.

However, even if the output currents of the first to third fuel cells 11, 12 and 13 are equalized, the output voltage of any one of the plurality of fuel cells becomes less than or equal to a predetermined minimum voltage, and the other The output voltage and deviation of the fuel cell may be severe. The lowest voltage refers to a lower limit at which effective power can be output from the fuel cell. If the operation of the fuel cell system is maintained in this state, the fuel cell below the minimum voltage will be overloaded, resulting in damage to the fuel cell. Therefore, the life of the fuel cell is reduced and the efficiency of the entire fuel cell system is reduced.

This can be confirmed through the simulation result waveform diagram of FIG. 2. 2 illustrates that when the two fuel cells are connected in parallel, the output voltage of the fuel cell falls below the minimum voltage when there is a deviation. Since the result is the same in the configuration of connecting two fuel cells and connecting three or more fuel cells, the simulation was performed in a state in which two fuel cells were connected in parallel.

2A shows the DC-DC converter output voltage Vo when the voltage deviation of the first and second fuel cells is 3.2%, the output currents I1 and I2 of the fuel cell, and the output voltage of the fuel cell ( Vf1, Vf2) is a waveform diagram, and FIG. 2B shows the DC-DC converter output voltage Vo when the first and second fuel cells have a voltage deviation of 24%, the output currents I1 and I2 of the fuel cell, and The waveforms of the output voltages Vf1 and Vf2 of the fuel cell. Here, the minimum voltage of the fuel cell is set to about 100v.

2A, the fuel cell output voltages Vf1 and Vf2 are maintained at about 140v during the rated operation of the fuel cell system, and the output currents I1 and I2 are controlled equally within an error range of about 3%. It can be seen.

However, when the voltage deviation is relatively large, that is, when the voltage deviation is 24%, the output voltage Vf2 of the second fuel cell is falling below the minimum voltage of 100v at the point 'A' as shown in FIG. 2B. . The 24% voltage deviation may be a case in which the output voltage of any one fuel cell is suddenly lowered and may fall to the lowest voltage.

Further, when the fuel cell provided in the fuel cell system outputs a lower range than the lowest voltage at which active power can be output from the fuel cell, for example, a threshold voltage at which the active power cannot be output, the minimum voltage is output. Fuel cells are more damaged than they are, and operating efficiency is also relatively poor.

Accordingly, an object of the present invention is to solve the above-mentioned problems, so that three or more fuel cells can be controlled in different operation modes according to the output voltage state of the fuel cells in a system configured in parallel so as to stably supply the load demand power. To provide a method for controlling power of a fuel cell and a fuel cell system thereof.

According to a feature of the present invention for achieving the above object, a sensing step of sensing the fuel cell output voltage during the conversion and supply of power supplied from a plurality of fuel cells; Determining whether the output voltage of at least one of the fuel cells among the fuel cells is a minimum voltage at which the effective power can be output from the fuel cell or a threshold voltage at which the effective power cannot be output; And a control step of controlling the output of the fuel cell outputting the minimum voltage or the threshold voltage as a result of the determination.

In the controlling step, if the output voltage is the lowest voltage, each of the fuel cells is output at a predetermined constant output power.

In the control step, if the output voltage is a threshold voltage, the control unit so that power is not output in the fuel cell outputting the threshold voltage.

The output power of the fuel cell outputting the minimum voltage or the limit voltage may be maintained as it is, and the remaining fuel cell may be controlled to compensate for the load required power.

According to another feature of the invention, a plurality of fuel cells connected in parallel; A power converter for converting the output of the fuel cell; The output voltage of the fuel cell is sensed when the output voltage of the fuel cells is sensed, and the output voltage of the fuel cell reaches a minimum voltage at which the effective power can be output from the fuel cell or a threshold voltage at which the effective power cannot be output. It is configured to include a control unit for controlling the power converter operation limited.

An operation mode setting unit for setting an operation mode of the system including the fuel cell is further included. The operation mode setting unit includes a first operation mode that is set when the output voltage becomes a minimum voltage and the output voltage is a threshold voltage. It has a second operation mode set when this.

The first operation mode is a constant power operation mode in which the power converter operation is controlled such that each of the fuel cells is output at a predetermined constant output power.

The second operation mode is a power limiting operation mode in which the output power is limited in the power converter so that the fuel cell outputting the threshold voltage is no longer generated.

According to the present invention, in a fuel cell system in which three or more fuel cells are configured in parallel, the output voltage of the fuel cell is sensed. It controls the output to be constant, and when the limit voltage is reached, the fuel cell is no longer generated and the remaining fuel cell shares the load demand power, thereby preventing damage to the fuel cell and improving its life and reliability. There is an effect that can be improved, and the load demand power can be stably supplied.

Hereinafter, a power control method of a fuel cell and a fuel cell system thereof according to the present invention will be described in detail with reference to the accompanying drawings.

3 is a diagram illustrating an overall configuration of a fuel cell system according to an exemplary embodiment of the present invention.

3, at least three fuel cells connected in parallel are provided. In the present embodiment, it will be described that the first to third fuel cells 30, 40, and 50 are provided. The first to third fuel cell controllers 32 and 42 may receive power available signal (PAS) information of the fuel cell in the first to third fuel cells 30 and 40 and 50. 52 are provided, respectively. The first to third fuel cells 30 and 40 and 50 may be output by changing the output voltage according to the usage time of the fuel cell. The output voltage is divided into a normal voltage, a lowest voltage which is a lower limit at which active power can be output from the fuel cell, and a threshold voltage at which no effective power can be output from the fuel cell. In general, the normal voltage refers to the rated voltage of the fuel cell, the lowest voltage refers to a voltage in the range lower than the normal voltage, the limit voltage refers to a voltage in the range lower than the minimum voltage. This voltage division is not always the same, but may be applied differently according to the specifications and characteristics of the fuel cell.

A power converter 60 is connected to the first to third fuel cells 30 and 40 and 50. The power converter 60 converts the DC power DC of the first to third fuel cells 30, 40, 50 into an AC power AC. To this end, the power converter 60 includes first to third DC-DC converters 62 and 64 for converting a low voltage output from the first to third fuel cells 30, 40 and 50 to a predetermined level. 66 is provided. The first to third DC-DC converters 62 and 64 and 66 may output the constant power to the first to third fuel cells 30 and 40 and 50 according to an operation mode described later. Or, it plays a role of limiting the output power so as not to generate a specific fuel cell. In addition, a DC-AC inverter 68 for converting each DC power obtained in the first to third DC-DC converters 62, 64, 66 into an AC power source for use in a load of a power system is provided. .

The power converter 60 is provided with a power conversion controller 70 for controlling the operation of the power converter 60. The power conversion controller 70 outputs power information (PAS) of the first to third fuel cells 30, 40, 50 from the first to third fuel cell controllers 32, 42, 52. ), And senses the output voltage of the first to third fuel cells 30, 40, 50 input to the power converter 60. Thus, the power conversion controller 60 may perform operation state information of the first to third fuel cells 30, 40, 50 based on the output power information PAS of the fuel cell and the sensed output voltage. Monitor it.

An operation mode setting unit 80 for setting an operation mode of the fuel cell system including the first to third fuel cells 30, 40 and 50 is provided. The operation mode setting unit 80 may set the first operation mode and the output voltage when the output voltages of the first to third fuel cells 30, 40 and 50 become the minimum voltage. Has a second operation mode which is set when In the first operation mode, the output power of the fuel cell outputting the lowest voltage among the first and third fuel cells 30, 40, 50 is maintained as it is, and the remaining fuel cells compensate for the load required power. A constant power control mode in which the operations of the first to third DC-DC converters 62, 64 and 66 are controlled to be output. The second operation mode is a power limiting operation mode for limiting the output power in the first to third DC-DC converters 62, 64, 66 so that the fuel cell outputting the threshold voltage is no longer generated. Refers to (Power Limit Control MODE).

Next, a power control method of a fuel cell according to an exemplary embodiment of the present invention will be described.

4 is a flowchart illustrating a power control method of a fuel cell according to an exemplary embodiment of the present invention.

First, when the fuel cell system configured as shown in FIG. 3 starts to operate (s90), the first to third fuel cells 30 and 40 and 50 output a DC power source in accordance with a preset output characteristic thereof. s91). If so, the output DC power is transmitted to the power converter 60. The first to third DC-DC converters 62, 64 and 66 provided in the power converter 60 determine the DC power of the first to third fuel cells 30, 40 and 50. Step up or down by level to convert. Each DC power converted by the first to third DC-DC converters 62, 64, 66 is transferred to the DC-AC inverter 68. The DC-AC inverter 68 converts the DC power into AC power required by the load of the power system, and supplies the converted AC power to the power system. At this time, the power conversion controller 70 compares with the load demand on the output side of the power converter 60, and controls the first to third DC-DC converters 62, 64, 66 according to the comparison result. Allow the power to be supplied as much as the load requirement. This is because the power conversion controller 70 continuously senses the output voltage and current of the first to third fuel cells 30 and 40 and 50, and the first to third fuel cell controller 32. (42) 52 receives the outputable power (PAS) information of the first to third fuel cells 30 and 40 and 50, based on which the first to third fuel cells 30 are received. This is because it is possible to grasp the state of the (40) (50).

In such a state, the power conversion controller 70 continuously senses the output voltage of the DC power output from the sensed first to third fuel cells 30, 40, 50 (S92).

As a result of the sensing, the power conversion controller 70 determines in step 93 whether the output voltages of the first to third fuel cells 30 and 40 and 50 are output in the normal voltage range. The steady voltage range refers to the rated voltage of the first to third fuel cells 30, 40, 50. As a result of the determination, if the output voltage of the first to third fuel cells 30, 40 and 50 belongs to the normal voltage, the process proceeds to step 94 to operate in the normal operation mode. That is, the output power of the first to third fuel cells 300 (40, 50) is equally controlled to provide the load demand power.

In operation 95, it is determined whether at least one output voltage of the output voltages of the first to third fuel cells 30, 40 and 50 falls within the lowest voltage range. As a result of the determination, if the output voltage is within the lowest voltage range, the operation mode setting unit 80 receiving the control operation of the power conversion controller 70 proceeds to step 96 and the first to third DC-DCs. The corresponding DC-DC converter among the converters 62, 64 and 66 is set to operate in a constant power control mode which is the first operation mode. For example, when one of the fuel cells outputs the lowest voltage, the first to third fuel cells 30 and 40 and 50 allow the output power to be constantly output in accordance with the load demand power. Alternatively, if the output voltage of the first fuel cell 30 is sensed as the lowest voltage, the power conversion controller 70 controls the first DC-DC converter 62 to only the lowest voltage from the first fuel cell 32. The second and third DC-DC converters 64 and 66 to control the second and third DC-DC converters 64 and 66 so that the second fuel cell 40 and the third fuel cell 50 share the required power among the load demand powers. do.

As such, even if the output voltage of at least one of the first to third fuel cells 30, 40, 50 falls to the lowest voltage range, all of the fuel cells 30, 40, 50 remain constant power. By controlling only the DC-DC converters 62, 64 and 66 so that only the output, or some fuel cells are limited, and the remaining fuel cells compensate for the output power, the required load driving power can be stably supplied.

This will be described by way of example with reference to FIG. 5. FIG. 5 illustrates waveform diagrams of the DC-DC converter output voltage Vo, the fuel cell output currents I1 and I2, and the fuel cell output voltages Vf1 and Vf2 under the same conditions as those of FIG. 2B. Here, the results are the same in the configuration of connecting two fuel cells and connecting three or more fuel cells. Therefore, the simulation was performed in a state in which two fuel cells were connected in parallel. Referring to FIG. 5, when the output voltage of the second fuel cell is controlled to the first operation mode while the output voltage of the second fuel cell is dropped to the lowest voltage, the output voltage of the second fuel cell is maintained at about 100v, which is the lowest voltage, and the insufficient load is achieved. It can be seen that the required power is output from the first fuel cell.

In operation 97, it is determined whether at least one output voltage among the output voltages of the first to third fuel cells 30, 40 and 50 falls within the limit voltage range. As a result of the determination, if the output voltage is within the lowest voltage range, the operation mode setting unit 80 receiving the control operation of the power conversion controller 70 proceeds to step 98 and the first to third DC-DCs. A corresponding DC-DC converter among the converters 62, 64 and 66 is set to operate in a power limit control mode which is a second operation mode.

Accordingly, the power conversion controller 70 limits the output power in the DC-DC converter so that the fuel cell that has fallen to the limit voltage is no longer generated. Therefore, the fuel cell having the limit voltage is stopped driving, and the remaining fuel cell supplies the load driving power. This stops the driving of the fuel cell, thereby preventing damage to the fuel cell that may occur due to the fuel cell being continuously driven under overload.

In the above embodiment, the output voltages of the first to third fuel cells 30, 40 and 50 are sensed to fall in the order of the normal voltage, the lowest voltage, and the limit voltage. The output voltages of the first to third fuel cells 30 and 40 and 50 may drop directly from the normal voltage to the limit voltage. In this case, the operation mode setting unit 80 immediately operates the first to third DC-DC converters 62 and 64 and 66 to operate in a power limit control mode which is a second operation mode. Will be set.

The scope of the present invention is not limited to the embodiments described above, but is defined by the claims, and various changes and modifications can be made by those skilled in the art within the scope of the claims. It is self evident.

That is, although the illustrated embodiment illustrates a fuel cell system as an example, the present invention may be applied to a renewable energy system and a distributed power supply system to which a power converter including a DC-DC converter may be applied.

In addition, it is described that three fuel cells are provided, but the number of fuel cells may be configured in various numbers so as to supply power required by a load.

1 is a configuration diagram of a fuel cell system in which a plurality of fuel cells are configured in parallel.

2A and 2B are graphs for explaining that the output voltage of the fuel cell falls below the minimum voltage when the fuel cell has two deviations in parallel.

3 is an overall configuration diagram of a fuel cell system according to a preferred embodiment of the present invention.

4 is a flowchart of a method for controlling power of a fuel cell according to an exemplary embodiment of the present invention.

FIG. 5 is a graph showing waveform diagrams of a DC-DC converter output voltage Vo, a fuel cell output current I1 and I2 and a fuel cell output voltage Vf1 and Vf2 according to an exemplary embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

30, 40, 50: fuel cell 32, 42, 52: fuel cell controller

60: power converter 62, 64, 66: DC-DC converter

68: DC-AC inverter 70: power conversion controller

80: operation mode setting unit

Claims (8)

A sensing step of sensing an output voltage of a fuel cell by a power conversion controller controlling an operation of the power converter while a power converter converts and supplies power supplied from a plurality of fuel cells; Determining, by the power conversion controller, whether the output voltage of at least one of the fuel cells is the lowest voltage at which the effective power can be output from the fuel cell or the threshold voltage at which the effective power is not output. ; And, And a control step of controlling the output power of the fuel cell to be restricted when the lowest voltage or the limit voltage is outputted, as a result of the determination, wherein the operation mode setting unit under the control operation of the power conversion controller is output. Power control method. The method of claim 1, In the control step, if the output voltage is the lowest voltage, the output power of the fuel cell outputting the minimum voltage is maintained as it is, and the remaining fuel cell is controlled to compensate for the load required power output of the fuel cell, characterized in that Power control method. The method of claim 1, In the control step, if the output voltage is a threshold voltage, the power control method of the fuel cell, characterized in that for controlling the power is not output in the fuel cell outputting the threshold voltage. The method of claim 3, wherein The fuel cell outputting the threshold voltage stops driving, and controls the remaining fuel cell to be output by compensating for the load required power. A plurality of fuel cells connected in parallel; A power converter for converting the output of the fuel cell; And, The output voltage of the fuel cell is sensed when the output voltage of the fuel cells is sensed, and the output voltage of the fuel cell reaches a minimum voltage at which the effective power can be output from the fuel cell or a threshold voltage at which the effective power cannot be output. And a control unit for controlling the power converter operation to be limited. The method of claim 5, An operation mode setting unit for setting an operation mode of the system including the fuel cell is further included. And the operation mode setting unit comprises a first operation mode set when the output voltage reaches a minimum voltage and a second operation mode set when the output voltage reaches a threshold voltage. The method of claim 6, The first operation mode is a constant power control mode in which the output power of the fuel cell outputting the lowest voltage is maintained as it is, and the remaining fuel cells are controlled to be output by compensating for the load required power. Fuel cell system. The method of claim 6, The second operation mode is a fuel cell system, characterized in that the power limit operation mode (Power Limit Control Mode) for limiting the output power in the power converter so that the fuel cell outputting the limit voltage is no longer generated.

Images