KR101644455B1 - Multi-Purpose Active Filter for Compensating Reactive Power and Harmonic Distortion - Google Patents

Abstract

The present invention relates to a multipurpose active filter which performs a reactive power compensation and harmonic compensation at the same time. There is disclosed a multipurpose active filter according to the present invention, comprising: a sensor unit which measures a voltage and a current of a three-phase power system; a control unit which outputs a voltage command value for minimizing reactive power and harmonics based on the voltage and the current measured at the sensor unit; and a modular multilevel converter (MMC) unit which receives the voltage command value from the control unit and supplies a voltage/current for minimizing reactive power and harmonics to the three-phase power system. According to the present invention, reactive power and harmonics can be minimized in a system by using one device, which minimizes a loss occurring in the system due to the reactive power and harmonics. Also, cost saving is accomplished since reactive power and harmonics are minimized by using one device.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a multipurpose active filter for reactive power and harmonic compensation,

The present invention relates to an active filter, and more particularly, to a multipurpose active filter that simultaneously performs reactive power compensation and harmonic compensation.

When AC power is supplied to the boiler or power plant with inductive reactance (L) characteristics, a counter electromotive force is generated which interrupts the current flow to the coil. The back electromotive force generated at this time acts in the direction opposite to the original voltage, so that the flow of current is suppressed. In this case, the phases of the current and the voltage are different, and the positive and negative electric currents cross each other at regular intervals, so that the positive and negative electric power are canceled. As a result of these canceling effects, power that does not work is generated, which is called reactive power.

Such reactive power deteriorates the utilization rate of electric power facilities, hinders smooth current flow, generates additional heat to the electric circuit, and causes electric loss. Also, if the reactive power is large, the power to be actually transmitted is decreased, and the transmission loss is increased and the utilization ratio of the generator and the transformer is decreased. Therefore, if the reactive power is reduced, the ratio of the active power is increased, and the amount of work performed by the same energy is increased.

In addition, harmonic components can be included in the current / voltage waveform due to the nonlinear characteristics of various semiconductor power conversion equipments such as advanced control devices, power electronic devices, and the like, which have rapidly increased in use recently, and basic power devices. When harmonics are included, voltage / current distortion occurs, which affects the power facilities in the system, which can lead to power quality problems such as overheating of power equipment, iron core magnetic saturation of the instrument, power factor reduction, and noise / vibration.

In order to eliminate the reactive power problem and the distortion caused by harmonics, the reactive power is a reactive power compensation device such as a TSC (Thyristor Switched Capacitor), and the harmonics are separately performed using a passive filter or an active filter including an inductor and a capacitor come.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a multipurpose active filter based on a modular multi-level converter capable of simultaneously performing reactive power and harmonic elimination.

According to an aspect of the present invention, there is provided a multipurpose active filter for reducing reactive power and harmonics of a three-phase power system, comprising: a sensor unit for measuring voltage and current of the three-phase power system; A control unit for outputting a voltage command value for minimizing reactive power and harmonics on the basis of the measured voltage and current, and a control unit for receiving a voltage command value of the control unit and outputting a voltage / current for minimizing reactive power and harmonics to the three- And an MMC unit for supplying the MMC unit to the system.

Here, the controller may include a PI controller for generating a first voltage command value for canceling the reactive power present in the three-phase power system, a second voltage command value for canceling the harmonics present in the three-phase power system And a summer for adding the second voltage command value generated by the PR controller to the first voltage command value generated by the PI controller.

The PI control unit includes a PLL for outputting a signal synchronized with the voltage measured by the sensor unit, a DQ axis corresponding to a phase difference of the current measured by the sensor unit with respect to the voltage based on a synchronized signal from the PLL, A comparator for comparing the current on the DQ axis output from the DQ converter with a current command value on the DQ axis and outputting the difference value; a comparator for receiving the difference value output from the comparator, A PI controller for generating a DQ axis control signal for controlling the DQ axis control signal in a direction that minimizes a value of the DQ axis control signal, and an abc converter for outputting the first voltage command value by performing inverse DQ conversion on the DQ axis control signal, A comparator for comparing the current measured by the sensor and the three-phase current command value to output a difference value for each higher-order frequency; And a resonance controller that outputs a voltage command value to make the difference value of each high frequency by zero. In this case, the higher frequency may be a third order, a fifth order, and a seventh order frequency.

According to another aspect of the present invention, there is provided a method of compensating power supply of a multipurpose active filter for minimizing reactive power and harmonics of a three-phase power system, comprising: measuring a voltage and a current of the three- Generating a first voltage command value for compensating for reactive power using the PI control based on the measured voltage and current, calculating a first voltage command value for compensating harmonics using resonance control based on the measured current, Generating a voltage command value for a modular multi-level converter by summing the first voltage command value and the second voltage command value, and generating a voltage command value for the modular multi-level converter based on the voltage command value, And supplying a voltage / current for harmonic compensation to the three-phase power system.

The generating of the first voltage command value may include generating a synchronization signal from the measured voltage, DQ-converting the current measured based on the generated synchronization signal, and outputting the DQ axis current command value and the DQ Extracting an error value by comparing the converted currents, and generating a first voltage command value based on the error value.

According to the present invention, it is possible to minimize the losses caused by the reactive power and the harmonics in the system by simultaneously solving the reactive power and the harmonic in the system by one apparatus, and by solving the reactive power and the harmonic problem as one device, Effect can be obtained.

FIG. 1 is a diagram showing a multi-purpose active filter according to an embodiment of the present invention connected on a power system.
2 is a diagram illustrating the configuration of an MMC unit according to an embodiment of the present invention.
3 is a diagram showing an example of a half-bridge type sub-module.
4 is a diagram illustrating the configuration of a control unit according to an embodiment of the present invention.
5 is a diagram illustrating a method for simultaneously compensating for reactive power and harmonics according to an embodiment of the present invention.
6 is a diagram illustrating a method of generating the first voltage command value for reactive power compensation according to an embodiment of the present invention.

In the following description, well-known functions or constructions are not described in detail to avoid unnecessarily obscuring the subject matter of the present invention.

Although the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, But should be understood to include all modifications, equivalents, and alternatives.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description with reference to the accompanying drawings, the same or corresponding components will be denoted by the same reference numerals, and redundant description thereof will be omitted.

FIG. 1 is a diagram showing a multi-purpose active filter according to an embodiment of the present invention connected on a power system.

1, a multi-purpose active filter according to an exemplary embodiment of the present invention includes a controller 100, an MMC unit (not shown), and a controller 100 to compensate for reactive power and harmonics on a power system of three phases connected to a power unit 1000 and a load 2000 200, and a sensor unit 300.

The sensor unit 300 measures the voltage and current flowing through the three-phase line on the system and transmits the measured voltage and current to the controller 100. At this time, the sensor unit 300 may convert the high voltage / high current flowing on the line to the corresponding low voltage / low current in proportion thereto and transmit the same to the controller 100.

The MMC unit 200 provides a voltage / current capable of canceling reactive power and harmonics to the three-phase line on the system in accordance with a reference signal provided by the control unit 100, based on a modular multilevel converter .

FIG. 2 is a diagram illustrating a configuration of an MMC unit 200 according to an embodiment of the present invention.

Referring to FIG. 2, the MMC unit 200 may be configured in three phases corresponding to three phases of a power system, and each phase includes an upper arm 210 and a lower arm 230, And a plurality of sub modules 220. And an MMC controller 240 for generating a control signal for controlling the switch of the sub-module 220 to generate a voltage / current according to an input voltage command value.

FIG. 3 is a diagram showing an example of a half-bridge type sub-module 220. FIG.

3, the half-bridge type submodule 220 includes two insulated gate bipolar transistor (IGBT) switches 221 and 223, two diodes 225 and 227, and an energy storage element 229 such as a capacitor consist of. The MMC unit 200 may control ON / OFF of the IGBT switches 221 and 223 in the submodule 220 so that AC power of a sinusoidal waveform can be generated in AC terminals of each phase.

2, the MMC unit 200 receives a voltage command value, and the MMC controller 240 generates a control signal in accordance with the voltage command value and outputs the control signal to the IGBT switches 511 and 513 in the submodule 220 of each arm. Off power of the system can be controlled so as to minimize the reactive power and the harmonics of the system.

The control unit 100 extracts reactive power and harmonic components present on the system based on the measured current / voltage from the sensor unit 300, and generates a voltage / current capable of canceling the voltage / ). This reference signal may be a voltage command value for each phase.

FIG. 4 is a diagram illustrating a configuration of a control unit 100 according to an embodiment of the present invention.

Referring to FIG. 4, the controller 100 includes a PI controller 110 for generating a voltage command value for canceling reactive power, and a PR controller 120 for generating a voltage command value for canceling harmonics.

)는 다음 [수학식 1]을 이용하여 구할 수 있는데, 여기서

는 전압 주기의 시작점과 전류 주기의 시작점 간의 차이고, T는 전압과 전류의 주기이다. The PI control unit 110 receives the voltage V and the current I flowing in the three phases measured by the sensor unit 300 and outputs a synchronous signal with the measured voltage from the PLL 111. More specifically, the input voltage is a sinusoidal periodic signal and the PLL outputs the period starting point of the periodic sinusoidal signal. The phase difference between the voltage ( V ) and the current ( I )

) Can be obtained using the following equation (1), where

Is the difference between the start point of the voltage cycle and the start point of the current cycle, and T is the period of the voltage and current.

)를 정확히 구하기 위해서는 전압 주기의 시작점을 정확히 알아내어야 할 필요가 있고 PLL(111)은 전압 주기의 시작점을 정확히 알아내기 위하여 사용된다.The above-

), It is necessary to accurately determine the starting point of the voltage cycle, and the PLL 111 is used to accurately determine the starting point of the voltage cycle.

로 회전하는 직교 좌표계의 d축, q축 변수로 변환하는 것으로, DQ변환에 의하여 측정 전압(V)에 동기화된 DQ축 상의 전류가 구해진다. 일반적으로 전류와 전압에 동일한 위상차가 발생하므로 상기 DQ축 상의 전류는 위상차와 대응되는 상수값이 될 수 있다. 이렇게 구해진 DQ 축 상의 전류는 비교기(116)에서 전류지령값(115)과 비교되고, 그 비교 결과에 따른 차이값이 비교기(116)에서 출력된다. 이렇게 출력된 차이값은 PI제어기(117)로 들어가고, PI제어기(117)는 상기 차이값을 최소화하는 방향으로 제어를 한다. PI제어기(117)는 상기 차이값을 최소화하기 위해 예컨대 [수학식 2]의 전달함수를 적용할 수 있다.The PI control unit 110 performs DQ conversion of the current measured by the DQ converter 113. [ The DQ conversion is performed by converting the three-phase variable of the abc coordinate system to an arbitrary angular velocity

Axis, and the d-axis and q-axis variables of the orthogonal coordinate system rotated by the DQ conversion, thereby obtaining the current on the DQ axis synchronized with the measured voltage V by the DQ conversion. Generally, since the same phase difference is generated between the current and the voltage, the current on the DQ axis can be a constant value corresponding to the phase difference. The thus obtained current on the DQ axis is compared with the current command value 115 in the comparator 116 and the difference value according to the comparison result is outputted from the comparator 116. [ The difference value thus outputted enters the PI controller 117, and the PI controller 117 controls the direction to minimize the difference value. The PI controller 117 may apply the transfer function of Equation (2), for example, to minimize the difference value.

는 비례제어게인이고,

적분제어게인이다.here

Is a proportional gain gain,

It is an integral regulator.

 Since the value output from the PI controller 117 is a current value synchronized with the voltage on the DQ axis, the abc converter 119 converts the DQ axis data into the three-phase abc current / voltage.

The PR control unit 121 includes a comparator 122 and a resonant controller 123. The comparator 122 compares the measured current I and the current command value 121 for each higher frequency and outputs the difference value. The resonance controller 123 outputs a voltage command value, which is a control signal for making the difference value 0 for each higher frequency based on the difference value inputted. Since the PR control is performed on each of the three phases rather than on the DQ axis, the converters of the PI control unit 110 are unnecessary. At this time, the control logic used in the resonance controller 123 can use, for example, the transfer function of [Equation 3].

는 비례제어게인이고,

은 비례공진게인이며,

은 차수를 나타내는 것으로, 3, 5, 7, 9 등의 값을 가질 수 있다.

는 기본 각 주파수이다. 우리나라 전력 계통이 일반적으로 60Hz를 사용하므로

는

가 될 수 있다. 그리고 고조파는 짝수차수에서는 거의 발생하지 않고 홀수차수에서만 주로 발생하고 차수가 높을수록 그 기여도는 줄어들게 된다. here

Is a proportional gain gain,

Is a proportional resonance gain,

Represents the order, and can have values of 3, 5, 7, 9, and so on.

Is the fundamental angular frequency. Since our power system generally uses 60Hz

The

. Harmonics occur only in the odd order and not in the even order, and the higher the order, the less the contribution.

The voltage command values generated by the PI control unit 110 and the PR control unit 120 are added to each other by a summer 130 and transmitted as a voltage command value for controlling the MMC unit 200.

5 is a diagram illustrating a method for simultaneously compensating for reactive power and harmonics according to an embodiment of the present invention.

5, the multipurpose active filter measures the voltage and current of the power system to be compensated (S510), generates a first voltage command value for compensating for reactive power using Proportional Integral (PI) control (S520) And generates a second voltage command value for harmonic component compensation using resonance control (S530). Then, the MMC voltage command value is generated by adding the first voltage command value and the second voltage command value (S540). The MMC section of the multipurpose active filter receives the MMC voltage command value and supplies voltage / current for reactive power and harmonic compensation to the system (S550).

6 is a diagram illustrating in more detail a method for generating the first voltage command value for reactive power compensation.

Referring to FIG. 6, in order to generate a first voltage command value for reactive power compensation, a synchronization signal is generated from a voltage measured using a PLL (S610). Then, the measurement current is DQ converted (S620) on the basis of the generated synchronizing signal, the error value is extracted by comparing the measured current with the DQ axis current command value (S630), and based on this error value, (S640).

In order to generate a second voltage command value for harmonic compensation, the PR controller 120 compares the current measured in the three-phase conductor with the three-phase current command value to output a difference value according to the higher frequency, The second voltage command value can be output so that the difference value of each higher frequency can be zero.

As described above, the multipurpose active filter according to an embodiment of the present invention generates a first voltage command value for canceling the reactive power using the PI control unit 110, and generates a second voltage command value for canceling the reactive power using the PR control unit 120 The voltage command value is generated and transmitted to the MMC unit 200, so that the reactive power and the harmonics can be simultaneously removed.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims and their equivalents. Only. It is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. .

Claims (8)

A multipurpose active filter for reducing reactive power and harmonics of a three-phase power system,
A sensor unit for measuring voltage and current of the three-phase power system;
A first voltage command value for canceling the reactive power present in the three-phase power system and a second voltage command for canceling the harmonics present in the three-phase power system based on the voltage and the current measured by the sensor unit; And outputs a summed voltage command value; And
A MMC (Modular Multilevel Converter) unit for receiving a voltage command value of the control unit and supplying a voltage / current for minimizing reactive power and harmonics to the 3-phase power system;
Wherein the active filter is a multi-purpose active filter. The apparatus of claim 1,
A PI controller for generating a first voltage command value for canceling the reactive power present in the three-phase power system;
A PR controller for generating a second voltage command value for canceling harmonics present in the three-phase power system; And
A summer for summing the first voltage command value generated by the PI controller and the second voltage command value generated by the PR controller;
Wherein the active filter is a multi-purpose active filter. 3. The apparatus of claim 2,
A PLL (Phase Locked Loop) for outputting a signal synchronized with the voltage measured by the sensor unit;
A DQ converter for outputting a current on a DQ axis corresponding to a phase difference of a current measured by the sensor unit with respect to the voltage based on a synchronized signal from the PLL;
A comparator for comparing the current on the DQ axis output from the DQ converter with a current command value on the DQ axis and outputting the difference value;
A PI controller for receiving the difference value output from the comparator and generating a DQ axis control signal for controlling the difference value to be minimized; And
An abc converter for performing inverse DQ conversion on the DQ axis control signal to output the first voltage command value;
Wherein the active filter is a multi-purpose active filter. 3. The apparatus of claim 2, wherein the PR control unit comprises:
A comparator for comparing the current measured by the sensor unit with a three-phase current command value and outputting a difference value according to a higher-order frequency; And
A resonance controller for outputting a second voltage command value to make the difference value of each higher frequency frequency to be 0 based on the difference value by the higher frequency;
Wherein the active filter is a multi-purpose active filter. 5. The method of claim 4,
Wherein the higher order frequency comprises at least a third order, a fifth order,
Multipurpose active filter. A method of compensating power supply of a multipurpose active filter for minimizing reactive power and harmonics of a three-phase power system,
Measuring voltage and current of the three-phase power system;
Generating a first voltage command value for compensating reactive power using PI control based on the measured voltage and current;
Generating a second voltage command value for compensating harmonics using the resonance control based on the measured current;
Generating a modulo multilevel converter voltage command value by summing the first voltage command value and the second voltage command value; And
Supplying a voltage / current for reactive power and harmonic compensation to the three-phase power system based on the voltage command value;
/ RTI > 7. The method of claim 6, wherein generating the first voltage command value comprises:
Generating a synchronization signal from the measured voltage of the system;
DQ converting the current measured based on the generated synchronization signal;
Comparing the DQ-axis current command value with the DQ-converted current to extract an error value;
Generating a first voltage command value based on the error value;
/ RTI > 7. The method of claim 6, wherein generating the second voltage command value comprises:
Comparing the measured current with a three-phase current command value and outputting a difference value by higher-order frequency; And
And outputting a second voltage command value based on the higher frequency difference value so that the difference value of each higher frequency frequency becomes zero;
/ RTI >

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