CN112886593A

CN112886593A - Mixed type active filter circuit structure

Info

Publication number: CN112886593A
Application number: CN202110344907.XA
Authority: CN
Inventors: 张�成; 朱东柏
Original assignee: Harbin University of Science and Technology
Current assignee: Harbin University of Science and Technology
Priority date: 2021-03-31
Filing date: 2021-03-31
Publication date: 2021-06-01

Abstract

The invention provides a novel parallel hybrid active power filter based on a magnetic flux compensation principle and a harmonic current shunt technology, and the capacity of the active filter of the novel parallel hybrid active power filter is smaller than that of active filters required by other parallel hybrid power filtering schemes at present; in the aspect of passive filter, adopt double-tuned filter, its advantage is: the cost is low compared with the cost of using two single-tuned filters; the hybrid active filter fully exerts the advantages of the passive filter and the active filter, improves the filtering performance of the passive filter, and enables the active filter not to bear fundamental voltage any more, thereby reducing the capacity of the active filter to the maximum extent and enabling the active power filter to be applied to high-power occasions.

Description

Mixed type active filter circuit structure

Technical Field

The invention relates to the field of active filtering, in particular to a circuit structure of a hybrid active filter.

Background

Harmonic pollution is a prominent problem in the quality of electric energy in recent years, and effective treatment of the harmonic pollution is of great significance to electric power systems and power users; for high-voltage and high-capacity harmonic sources, an LC passive filter is mainly adopted for compensation at home and abroad, although the LC passive filter has the advantages of small initial investment, simple structure and the like, the filtering performance of the LC passive filter is extremely sensitive to parameter changes such as system impedance frequency and the like, and the expected filtering effect is difficult to achieve; although the active power filter can overcome the defects of the passive filter, the installation capacity of the active power filter is limited by the level of a switching device; the hybrid active power filter formed by combining the passive filter and the active filter can make up the defects of the passive filter and the active filter, is beneficial to reducing the initial investment of a harmonic compensation system, improves the cost performance, and achieves the purposes of practicability of the active filter and harmonic suppression.

The common structural forms of the hybrid active filter are three types: the parallel active filter is connected with the passive filter in parallel, the active filter is connected with the parallel passive filter in series, and the series active filter is connected with the passive filter in parallel; the active filter compensates the residual harmonic current after the passive filter acts in the structure that the parallel active filter and the passive filter are connected in parallel, and the passive filter can filter most of harmonic waves, so the required active filter has smaller capacity; however, in this structure, there are harmonic channels between the power supply and the active filter and between the active filter and the passive filter, and especially, the harmonic channel between the active filter and the passive filter may cause the harmonic current of the active filter to flow into the passive filter and the filter capacitor connected to other nodes in the power grid, because a large-scale power supply and distribution station usually wants to perform reactive power compensation while filtering out the harmonic, the structure of the parallel connection type active filter and the passive filter in series is adopted to cause the fundamental wave reactive current to flow through the active filter under the coupling action of the transformer, so that the capacity of the active filter is increased, and the technical difficulty and cost of the converter implementation are increased, thereby limiting the application of the active filter in a large-scale transformer substation.

In the structure that the series active filter and the passive filter are connected in parallel, harmonic waves are basically compensated by the passive filter, the active filter can be regarded as variable impedance, the impedance of fundamental waves is approximately zero, the harmonic waves present high impedance, harmonic wave current is prevented from flowing into a power grid and flowing into the passive filter, meanwhile, the resonance which possibly occurs between the power grid and the passive filter can be restrained, the filtering characteristic of the passive filter is improved, and the structure is not easy to install.

Disclosure of Invention

The present invention provides a mixed type active filter circuit structure for solving the above problems.

Technical scheme

In order to solve the problems, the invention adopts the technical scheme that: a mixed active filter circuit structure is composed of a tuned filter, a three-winding transformer, an air-core reactor connected in parallel with the primary side of the three-winding transformer, a capacitor connected in series with a secondary winding of the three-winding transformer, an active power filter connected to the secondary winding of the transformer, and a switch for switching a filtering branch.

The double-tuned filter is used for compensating specific harmonic current generated by a load harmonic source; one side of the capacitor C is led out from the power grid in parallel, and the other side of the capacitor C is connected to one side of the three-winding transformer and forms a harmonic current shunting branch with the tuning filter to shunt harmonic current generated by a load; the air-core reactor is connected in parallel with the primary side of the three-winding transformer, the L-shaped inductive reactance is utilized to limit the fundamental voltage and harmonic voltage born by the active power filter, and the defect of increased magnetic leakage of the air-gap transformer in the traditional parallel hybrid active power filter can be effectively overcome; in addition, the reactor L and the transformer are used for inhibiting the impact current when the series capacitor C is switched, and the reactor L is also used for limiting the voltage when the harmonic magnetic fluxes generated by the primary and secondary high-order harmonic currents are greatly different; the active filter main circuit adopts a voltage type PWM converter, a large capacitor is connected to the direct current side of the PWM converter, overvoltage can be effectively inhibited, and the active filter is used for improving the filtering performance of the whole filtering system and enabling grid side current not to contain harmonic components.

Drawings

Fig. 1 is a circuit configuration diagram of a hybrid active filter of the present invention.

In the figure: 1-double tuning filter, 2-active filter, 3-three winding transformer, 4-air core reactor, 5-capacitor, 6-breaker.

Detailed Description

As shown in fig. 1, the operation principle of the hybrid active filter circuit in the present invention is described, which includes the following operation stages: when the active filter 2 is not put into operation, harmonic current is shunted through the capacitor 5, the double-tuned filter 1 and the three branches of the grid impedance, and the flow direction of each harmonic current on the air-core reactor 4 depends on the selection of circuit parameters; regardless of the direction, the voltage of a certain harmonic wave borne at the moment when the active filter 2 is not put into operation or the active filter 2 is put into operation is the voltage drop across the air-core reactor 4; due to the small shunt inductance, the voltage experienced by the active filter 2 during the transition is small.

After the active filter 2 is put into operation, the method for reducing the fundamental wave voltage borne by the active filter 2 by the hybrid active power filter is based on the fundamental wave magnetic flux compensation principle; the fundamental current in the power grid flows into the three-winding transformer 3 through the C1 and the capacitor 5, and as can be seen from the labels of the same-name ends of the transformer coils in the figure, the directions of the currents in the transformers are opposite, so that the generated fundamental magnetic fluxes compensate each other, and when the fundamental magnetic flux is zero (i.e. the fundamental demagnetization condition is satisfied), the fundamental voltage borne by the active filter 2 is zero; when the fundamental wave degaussing condition is not met, the fundamental wave voltage borne by the active filter 2 is mainly determined by the air-core reactor 4, and the fundamental wave voltage borne by the active filter 2 is very small because the air-core reactor 4 is small; after the active filter 2 is put into steady state operation, the non-tuned subharmonic current is shunted through the double tuned filter and the capacitor 5.

After the active filter 2 is put into operation, a transition is required from a steady-state process in which the active filter 2 is not put into operation to a steady-state process in which the voltage applied to the active filter 2 smoothly transitions from the voltage before the transition to its steady-state voltage value after the active filter 2 is put into operation.

Although the present invention has been described with reference to the accompanying drawings, it will be understood by those skilled in the art that equivalents may be substituted for elements thereof without departing from the scope of the present invention, and that the hybrid active filter circuit configuration according to the present invention may ultimately reduce the capacity of the active filter 2 by way of flux compensation and harmonic splitting, thereby enabling the active power filter to be used in high power applications.

Claims

1. A hybrid active filter circuit structure comprising: the active power filter comprises a group of double-tuned filters (1), an active filter (2), a three-winding transformer (3), an air-core reactor (4), a capacitor (5) and a circuit breaker (6), and is characterized in that the filters enable harmonic magnetic fluxes generated by currents flowing into the three-winding transformer (3) to compensate each other on the basis of a magnetic flux compensation principle and a harmonic current technology, the incompletely compensated parts are compensated by the harmonic currents generated by the active filter (2), and finally the capacity of the active filter (2) is reduced, so that the active power filter can be applied to high-power occasions.