KR100906993B1 - Power control system for fuel cell hybrid power system and Power control method - Google Patents

Abstract

The present invention is to control the power flow between the fuel cell hybrid power generation system and the load, to meet the power demand of the load and to prevent the battery from being overcharged or discharged, and to prevent the fuel cell from being overloaded. The present invention relates to a power control system of a fuel cell hybrid power generation system.

The present invention is supplied with a fuel controlled through a fuel cell controller, a fuel cell for generating electricity by the reaction of the supplied fuel, a battery connected in parallel with the fuel cell, and controls the output of the fuel cell and battery A power control system of a fuel cell hybrid power generation system including a power controller, the power control system comprising: a DC-DC converter for converting an output voltage of the fuel cell and a low harmonic current output from the fuel cell; It is characterized by further comprising a digital controller for DC-DC converter to prevent overload of the fuel cell by limiting.

Fuel Cell, Hybrid, Power Control, Predictive Current Limiter, Moving Average Digital Filter

Description

Power control system for fuel cell hybrid power system and Power control method

The present invention relates to a power control system of a fuel cell hybrid power generation system, and more particularly, to control the power flow between a fuel cell hybrid power generation system and a load, to correspond to the power demand of the load and to overcharge or discharge the battery. The present invention relates to a power control system of a fuel cell hybrid power generation system which can prevent and prevent an overload of a fuel cell.

Fuel cells are attracting attention as a major energy source because they are environmentally friendly and have higher efficiency than existing power generation facilities. The load connected to such a fuel cell exhibits a pulse train pattern and has a peak-to-average ratio of 9 or more, so that only the fuel cell can satisfy this load pattern. Therefore, fuel cell-battery hybrid power generation system is widely used, and this fuel cell hybrid reversal system can maintain high power density and high efficiency while satisfying peak power demand.

The fuel cell of the fuel cell hybrid power generation system supplies power to the load and the battery, and the battery supplies supplementary power to the peak load.

That is, the power generated from the fuel cell is continuously supplied to the load and the battery to drive the load and at the same time to charge the battery, and the power charged to the battery is supplied to supply the power of the fuel cell when the load increases rapidly.

In such a fuel cell hybrid power generation system, the fuel cell has a slow dynamic response characteristic, and thus, the fuel cell alone cannot sufficiently cope with overload or peak load. Accordingly, it is necessary to appropriately control the flow of power between the power generation system and the load.

That is, while controlling the power flow between the fuel cell hybrid power generation system and the load, it must be able to meet the power demand of the load and to prevent the battery from being overcharged or discharged.

In addition, the current output from the fuel cell is low harmonic current, especially in the case of single-phase alternating current 120Hz harmonic current is induced, and such low harmonic current not only makes the control of the DC-DC converter difficult, but also the amount of fuel supplied to the fuel electricity. There was a problem that the fuel cell overloaded by outputting more current than the battery can output.

As described above, the fuel cell hybrid power generation system of the fuel cell hybrid power generation system, which controls the power flow between the fuel cell hybrid power generation system and the load, must correspond to the power demand of the load and prevent the battery from being excessively charged or discharged. It is an object to provide a power control system.

In particular, a moving average digital filter is installed in the voltage feedback loop of the digital controller for the DC-DC converter of the power control system to remove low harmonic currents from the fuel cell, and the output current of the fuel cell is limited using the predictive current controller. It is an object of the present invention to provide a power control system of a fuel cell hybrid power generation system that prevents the fuel cell from being overloaded so that the fuel cell can operate in an optimal state.

The power control system of the fuel cell hybrid power generation system of the present invention for achieving the above object is supplied with a fuel controlled through a fuel cell controller, a fuel cell for generating electricity by the reaction of the supplied fuel, and the fuel cell and A reversal system comprising a battery connected in parallel, and a power controller for controlling the output of the fuel cell and the battery, the low-harmonic current output from the fuel cell and the DC-DC converter for converting the output voltage of the fuel cell; It is characterized in that it further comprises a digital controller for DC-DC converter to remove and limit the output current to within the current limit to prevent overload of the fuel cell.

According to another aspect of the present invention, there is provided a method for controlling power of a hybrid fuel cell hybrid power generation system, including calculating a fuel cell output (P _fc ) from a state of charge (SoC) and a load power (P _load ) of a battery. ; Comparing the calculated fuel cell output P _fc with the minimum power P _{min that} can be output from the fuel cell; When the output of the fuel cell P _fc is smaller than the minimum power P _min , the fuel cell is turned off and the battery power is supplied to the load, and the output of the fuel cell P _fc is the minimum power P _min. Comparing the maximum power P _max that the output of the fuel cell P _fc can output from the fuel cell if greater than; If the output of the fuel cell (P _fc ) is greater than the maximum power (P _max ), the power corresponding to the maximum output of the fuel cell is supplied to the load and the insufficient power is supplied by the battery, and the output of the fuel cell (P _fc ) is maximum. If it is smaller than the power P _max , the fuel cell output P _fc is supplied to the load, and the battery is charged or discharged by the difference between the load power P _load and the fuel cell output P _fc depending on the state of charge (SoC). It is characterized by consisting of steps.

The present invention not only facilitates control of the DC-DC converter by removing the low harmonic current of the current output from the fuel cell by the moving average digital filter constituting the digital controller for the DC-DC converter, but also limits the prediction current. By limiting the output current of the fuel cell to within the current limit through the gas can be prevented from overloading the fuel cell.

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

1 is a block diagram of a fuel cell hybrid power generation system according to the present invention, Figure 2 is a block diagram for explaining a digital controller for a DC-DC converter constituting a power control system of a fuel cell hybrid power generation system according to the present invention. 3 is a voltage-current characteristic curve and a power density curve of a fuel cell in a fuel cell system, FIG. 4 is an efficiency curve of a fuel cell, and FIG. 5 is power control of a fuel cell hybrid power generation system according to the present invention. 6 is a graph illustrating the operation principle of the moving average digital filter of the digital controller for the DC-DC converter constituting the system, and FIG. 6 is for the DC-DC converter constituting the power control system of the fuel cell hybrid power generation system according to the present invention. Figure 7 is a graph of the inductor current waveform of the DC-DC converter for explaining the predictive current limiter of the digital controller, Figure 7 is a fuel according to the present invention It is a flowchart for demonstrating the power control method of the power controller which comprises the power control system of a battery hybrid power generation system.

As shown, the power control system of the fuel cell hybrid power generation system according to the present invention efficiently utilizes a DC-DC converter 120 that converts the output of the fuel cell as a means for allowing the fuel cell 100 to operate with high efficiency. It is configured to include a digital controller (1) to operate.

The power control system of the fuel cell hybrid power generation system of the present invention receives a fuel controlled through the fuel cell controller 110 as shown in FIG. 1, and generates electricity by reaction of the supplied fuel. A power control system including a 100, a battery 200 connected in parallel with the fuel cell 100, and a power controller 300 for controlling outputs of the fuel cell 100 and the battery 200. DC-DC converter 120 for converting the output of the fuel cell 100 and DC-DC converter digital to remove the low harmonic current output from the fuel cell and to limit the output current within the current limit to prevent the overload of the fuel cell It is configured by installing more controllers.

The digital controller 1 includes a moving average digital filter 1a for removing low harmonic currents, and a predictive current limiter 1b for limiting the output current of the fuel cell to within the current limit to prevent overload of the fuel cell. .

The low harmonic current from the fuel cell due to the load, especially when the load is a single-phase AC load, outputs a harmonic current of 120 Hz, which not only makes the control of the DC-DC converter 120 difficult but also the fuel by the amount of fuel supplied to the fuel cell. This requires more current output than the cell can output, and this load demand overloads the fuel cell.

The moving average digital filter 1a serves to remove low harmonics from the output of the fuel cell to prevent the fuel cell 100 from being overloaded.

After the low harmonics are removed by the moving average digital filter 1a, the output of the fuel cell is limited by the predictive current limiter 1b.

That is, the predictive current limiter 1b limits the current output from the fuel cell within the limit value of the output current of the fuel cell calculated by the amount of fuel supplied to the fuel cell, thereby preventing the fuel cell from being driven in an overloaded state. It is possible to increase the durability of the fuel cell.

As described above, an object of the present invention is to enable the fuel cell 100 to be operated with high efficiency. The voltage-current characteristics and the power density characteristics of the fuel cell 100 are drawn as shown in FIG. 3. The efficiency of the fuel cell is obtained by the ratio of the output electricity and the fuel consumed (hereinafter, 'hydrogen' will be described as an example), and is obtained by the following equation (1).

식(1)

Formula (1)

는 소비된 수소의 에너지,

는 수소의 고위발열량(286kjmool^-1)here

Is the energy of hydrogen consumed,

Is the high calorific value of hydrogen (286kjmool ^-1 )

In the efficiency curve of FIG. 4, it can be seen that the efficiency of the fuel cell 100 is much lower outside the range between the minimum power density P ₁ and the maximum power density P ₂ due to power consumption by peripheral devices and electrical characteristics of the cell. Therefore, in order to drive the fuel cell 100 with high efficiency in consideration of such a situation, it is necessary to operate the fuel cell to avoid such a low efficiency region. The minimum power density P ₁ and the maximum power density P ₂ of the fuel cell are determined by Equation (1) above and the voltage current characteristic curve and power density curve of the cell of FIG. 3.

That is, the output power P _fc of the fuel cell is controlled based on the state of charge of the battery 200 and the load power P _load , but the output of the fuel cell is set to a minimum power so that the battery 200 maintains a sufficiently charged state. And control in the range between and maximum power.

This control method is performed by the process as shown in FIG.

That is, calculating the output of the fuel cell P _fc from the power P _b1 and the load power P _{load that} can be output from the battery when the state of charge (SoC) and the state of charge of the battery is 1; ; Comparing the calculated fuel cell output P _fc with the minimum power P _min of the fuel cell; When the output of the fuel cell P _fc is smaller than the minimum power P _min , the fuel cell is turned off and the battery power is supplied to the load, and the output of the fuel cell P _fc is the minimum power P _min. Comparing the maximum power P _max that the output of the fuel cell P _fc can output from the fuel cell if greater than; If the output of the fuel cell (P _fc ) is greater than the maximum power (P _max ), the power corresponding to the maximum output of the fuel cell is supplied to the load and the insufficient power is supplied by the battery, and the output of the fuel cell (P _fc ) is maximum. is less than the power (P _max) fed the output of the fuel cell (P _fc) to the load and the battery is charged, or by the difference between load power (P _load) and the fuel cell output (P _fc) according to the state of charge (SoC) Discharging step. The minimum power P _min and the maximum power P _max of the fuel cell are calculated from the minimum power density P ₁ and the maximum power density P ₂ of the cell, respectively.

The output power of the fuel cell is obtained by the following equation (2).

식(2)

Formula (2)

Here, the state of charge (SOC) is the state of charge of the battery, P _b1 is the power that can be output from the battery when the SoC is 1.

When the output power P _fc of the fuel cell calculated as described above is less than the minimum power P _min , the fuel cell is turned off and the power is supplied from the battery 200.

The calculated output power P _fc and battery output P _bat of the fuel cell are sent to the fuel cell controller 110 and the bidirectional DC-DC converter 210, respectively, and the output of the fuel cell 100 is calculated. The amount of fuel supplied to the fuel cell 100 is controlled based on the output power P _fc of the fuel cell 100. Accordingly, the fuel cell always has a high efficiency section, that is, a minimum power P _min and a maximum power P _min . Will work in between.

The DC-DC converter 120 for the fuel cell is configured by employing any one of the commonly used converters, as shown in Figure 2 is configured to include an input inductor, a power switching device, an output filter capacitor, etc. The output current of the fuel cell 100 and the subsequent DC bus voltage are controlled.

In order to enable the fuel cell 100 pursued by the present invention to be operated with high efficiency, the digital controller 1 for efficiently operating the DC-DC converter 120 for converting the output of the fuel cell is required as described above. The moving average digital filter 1a constituting the digital controller 1 controls the DC-DC converter 120 to remove low harmonic currents as shown in FIG. 2.

As shown, when a single phase AC load is connected to the power generation system of the present invention through a DC-AC converter, a low harmonic current appears on the DC bus, and a series of voltage ripples of the same frequency occurs in the DC bus voltage.

The low ripple current is induced from the fuel cell by the voltage ripple and the voltage control loop characteristic of the DC-DC converter 120. The low harmonic current size is determined by the characteristics of the control loop and the capacitor of the DC bus.

In the present invention, the moving average digital filter 1a is configured in a voltage feedback loop as a means for removing such low harmonics, and the moving average digital filter 1a is expressed by the following equation, and is shown in FIG. It works with the same operating principle.

식(3)

Formula (3)

After the low harmonics are removed by the moving average digital filter 1a as described above, the output current of the fuel cell is limited using the predictive current limiter 1b to prevent the fuel cell 100 from being overloaded.

The current limit value of the predictive current limiter 1b based on the amount of air supplied to the fuel cell 100 by the fuel cell controller 110 is as follows.

식(4)

Formula (4)

Formula (5)

Where n is the number of cells of the fuel cell, and I _max is the current upper limit of the high efficiency operating section of the fuel cell, and the voltage-current characteristic curve is shown by P ₁ and P ₂ of the efficiency curve (Fig. 4) of the fuel cell. ), V ₂ , I ₁ and V ₁ , I ₂ are determined, and I _max is calculated from I ₂ .

The prediction current limiter 1b may control the peak current to be less than or equal to the current limit value during each switching period. The maximum duty rate for the next switching period is the current measurement of the current cycle, the output voltage of the fuel cell (V _fc ) between the cycles, the output voltage of the DC-DC converter, that is, the DC bus voltage (V _d ), Calculated based on the duty cycle of the preceding period, the calculated maximum duty ratio (D _max ) effectively limits the peak current of the inductor constituting the converter during each switching cycle as well as during overload.

FIG. 6 shows current waveforms of the inductor constituting the DC-DC converter 12. The inductor current i _L [n + 1] and the inductor peak current I _p [n + 1] of the n + 1 th cycle are illustrated in FIG. ]) Is expressed as

식(7)

Formula (7)

식(8)

Formula (8)

Here, it can be assumed that the output voltage V _d [n} is constant for successive switching periods, but the fuel cell output voltage V _fc [n} is not constant because the fuel cell 100 is a current control voltage source. .

From the above two equations, the maximum duty ratio (d _{L, max} [n]) of the inductor current in the n + 1th switching period is calculated as follows.

식(9)

Formula (9)

Where f _s is the switching frequency.

The maximum duty ratio (d _{L, max} [n]) for the inductor current (i _L1 ) limits the peak current (I _p [n + 1]) of the n + 1th cycle below the current limit, thereby overloading the fuel cell. To prevent it.

1 is a configuration diagram of a fuel cell hybrid power generation system according to the present invention,

2 is a block diagram illustrating a digital control method of a power control system of a fuel cell hybrid power generation system according to the present invention;

3 is a voltage-current characteristic curve and a power density curve of a fuel cell in a fuel cell system,

4 is an efficiency curve of a fuel cell in a fuel cell system,

5 is a graph for explaining the operation principle of the moving average digital filter in the power control system of the fuel cell hybrid power generation system according to the present invention,

6 is a graph of an inductor current waveform of a predictive current limiter in a power control system of a fuel cell hybrid power generation system according to the present invention;

7 is a flowchart illustrating a power control method of a power controller constituting a power control system of a fuel cell hybrid power generation system according to the present invention.

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

1: Digital Controller

1a: Moving Average Digital Filter

1b: Predictive current limiter

Claims (4)

A fuel cell 100 that receives fuel controlled through the fuel cell controller 110 and generates electricity by a reaction of the supplied fuel, a battery 200 connected in parallel with the fuel cell 100, and power It includes a power controller 300 for controlling the output of the fuel cell 100 and the battery 200 with a control program and a DC-DC converter 120 for converting the output voltage of the fuel cell 100 In a hybrid fuel cell power generation system, It characterized by further comprising a digital controller (1) for the DC-DC converter to remove the low harmonic current output from the fuel cell 100 and to limit the output current to within the current limit to prevent the overload of the fuel cell Power control system of battery hybrid power generation system. The method of claim 1, The digital controller 1 includes a moving average digital filter 1a for removing low harmonic currents and a predictive current limiter 1b for limiting the output current of the fuel cell to within the current limit to prevent overload of the fuel cell. A power control system for a fuel cell hybrid power generation system, characterized in that. A fuel cell 100 that receives fuel controlled through the fuel cell controller 110 and generates electricity by a reaction of the supplied fuel, a battery 200 connected in parallel with the fuel cell 100, and power A power controller 300 for controlling the output of the fuel cell 100 and the battery 200 and a DC-DC converter 120 for converting the output voltage of the fuel cell 100 with a control program, and the DC A control method using a hybrid fuel cell power generation system comprising a digital controller (1) for a DC converter (120), Calculating an output P _fc of the fuel cell from a power P _b1 and a load power P _{load outputable} from the battery when the state of charge (SoC) and the state of charge of the battery is 1; Comparing the calculated fuel cell output P _fc with the minimum power P _min of the fuel cell; When the output of the fuel cell P _fc is smaller than the minimum power P _min , the fuel cell is turned off and the battery power is supplied to the load, and the output of the fuel cell P _fc is the minimum power P _min. Comparing the maximum power P _max that the output of the fuel cell P _fc can output from the fuel cell if greater than; If the output of the fuel cell (P _fc ) is greater than the maximum power (P _max ), the power corresponding to the maximum output of the fuel cell is supplied to the load and the insufficient power is supplied by the battery, and the output of the fuel cell (P _fc ) is maximum. If it is smaller than the power P _max , the fuel cell output P _fc is supplied to the load, and the battery is charged or charged by the difference between the load power P _load and the fuel cell output P _fc depending on the state of charge (SoC). A power control method for a fuel cell hybrid power generation system, characterized in that the step of discharging. The method of claim 3, wherein The output of the fuel cell (P _fc ) is a formula

Power control method of a fuel cell hybrid power generation system, characterized in that calculated by. Here, the state of charge (SOC) is the state of charge of the battery, P _b1 is the power that can be output from the battery when the SoC is 1.

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