Grid active filter structure and its application - Power Circuit - Circuit Diagram

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In non-linear load AC networks, active filtering has become a mature technology for suppressing harmonic and reactive power compensation. This paper comprehensively introduces the structural characteristics and applications of active filters in AC power grids, and forecasts the development direction of active filter technology. Descriptor: active filter; harmonic; reactive power compensation; passive filter Abstract: Active power filtering of electric power has now become a mature technology for harmonic and reactive power compensation in nonlinear loads. This paper presents a comprehensive review of Active power filter (APF) configurations. It aims to provide a broad perspective on the status of APF topology technology, and the prospects of the application of APF as well. Keyword:active power filters; harmonic; reactive power compensation; passive filter 1 1 Introduction With the rapid development and maturity of power electronics technology, large-scale power electronic devices in power systems are increasing. While improving the level and efficiency of industrial automation, it is a large-capacity non-linear load using traditional phase-controlled rectifier technology. The high harmonics and low power factor operating conditions generated during operation seriously jeopardize the safety of the power system and the quality of the power grid.
The traditional method of harmonic suppression and reactive power compensation is to connect the power passive filter in parallel with the non-linear load to be compensated, to provide a low resistance path for the harmonics and also to provide the reactive power required by the load. The passive filter (PF) has the advantages of simple structure, convenient use, mature technology and low cost. At the same time, its shortcomings are also obvious: 1) Its compensation characteristics are greatly affected by the power grid and load, its filtering effect depends on the parameters of the power grid and load, and the filtering characteristics are poor; 2) it brings certain hidden dangers to the power grid, which may occur. Series and parallel resonance between power grid and filter; 3) can only compensate for fixed reactive power, can not accurately compensate for changing reactive power, can not achieve dynamic compensation for harmonics and reactive power; 4) required storage The energy component is bulky. Active Power Filter (APF) effectively solves the shortcomings of passive filters. The compensation characteristics of the active filter are greatly affected by the power grid and the load, which not only avoids the danger of series and parallel resonance with the power grid, but also suppresses the occurrence of series-parallel resonance; realizes dynamic compensation, which can change both frequency and size. The harmonics and the varying reactive power perform rapid dynamic tracking compensation; the harmonics and reactive power can be compensated at the same time, and the compensation reactive power can be continuously adjusted, which can be used for one harmonic and reactive power alone. Compensation can also comprehensively compensate multiple harmonics and reactive sources; the active filter does not need energy storage components when compensating for reactive power, and the capacity of energy storage components required for compensation of harmonics is not large.
Based on the introduction of the basic principle and structural characteristics of the active filter, this paper introduces the development status and application of the active filter topology, and finally forecasts the development prospect of the active filter.
2 Principle of Active Filter and Its Structure The active filter consists of a set of switching devices and passive energy storage components such as inductors and capacitors. The system consists of two parts: the command current calculation circuit and the compensation current generation circuit. The active filter structure is shown in Figure 1. Set the higher harmonic content of the load current to be. Its basic working principle is: detecting the current (or voltage) of the compensation object, and obtaining a command signal for compensating the current through the instruction operation circuit. The signal is obtained by the compensation current generating circuit via the controller, and the compensation current is offset by the harmonic current in the load.

The current of the grid is restored to a pure sinusoidal waveform; at the same time, the active filter emits a fundamental reactive current for reactive compensation.

Figure 1 Structure of the active filter

3 Active filter topology and its application
According to the way that the active power filter is connected to the grid, the system structure can be divided into three categories, namely parallel type [2-4], series type [5, 6] and hybrid type.
3.1 Parallel Active Filters In general, shunt active filters are used in three ways, single use, mixed with PF, and injected current.
3.1.1 Parallel APF Single Use Mode Figure 2 shows the configuration topology of the parallel active filter system in a single use mode. It is the most basic form of active filter, which produces a compensation current equal in magnitude and opposite direction to the load harmonics, thereby compensating the supply side current to a sine wave. The shunt active filter is mainly used for the compensation of inductive current source type load. It is also the one that has been put into operation most in the industry. However, since the power supply voltage is directly applied to the inverter bridge, the voltage level requirement of the switching element is required. High; when the load harmonic current content is high, the capacity of the APF is required to be large, and it is difficult to have a large compensation capacity and a wide compensation band.