The Active Filter Control Strategies And Characteristics

In recent years, along with the rapid development of power electronics technology, variable nonlinear devices have obtained wide applications. Because of the nonlinear electronic devices characteristics and diversity, a lot of harmonic and reactive currents are injected into the power system, which cause low system efficiency and bad power factor and disturbance other devices and applications. As a result, power quality and safe operation of utility equipment have been suffered serious threaten. Active Power Filter (APF) can compensate harmonics reactive power and asymmetry load dynamically, and its' compensation is not influenced by power system impedance. The parasitic oscillation question that may be caused by passive filters can also be avoided. Research and development of control strategies and character of APF is very important to the applications in reality.Firstly, the basic concepts of APF are introduced in this paper. APF is a new power electronic device that can carry out dynamic compensation of harmonics and reactive power. It can compensate the harmonics that both frequency and amplitude are all variable. It can also compensate the time variable reactive power. Secondly, the cause and production of hannonic and the necessity of APF are described in this paper. Nonlinear power electronic devices play an important role in energy conservation, in productivity enhancement, and in people's life quality, however, a lot of harmonic and reactive currents injected into the power grid, which cause low system efficiency and bad power factor, and other equipment and devices result in disturbances, due to the nonlinear and diversity of power electronic devices. As a result, power quality and safe operation of utility equipment have been suffered serious threaten.This paper detailed describes the basic principle, basic structure and classify of APF. APF system consists of two major components, namely, command current calculating circuit and compensation current producing circuit. The core of command current calculating circuit is to detect the compensating object, such as harmonic and reactive current components, which is also known as harmonic and reactive currentdetection circuit. The function of current compensation circuit is to produce the real compensating currants according to command currents.The first control work of APF is the obtainment of compensation command. This part will have a direct impact on the performance of the APF, because if we can not accurately obtain command signal, the current control will be fruitless. This paper has discussed variable detection methods and constructed testing and sample model, and focus on instantaneous reactive harmonic detection method and the theory of adaptive harmonic detection method in MATLAB simulation environment. This confirmed the feasibility and characteristics of this several harmonic detection work in theory.The performance of APF depends on main circuit and its control system. When the main circuit is determined, control methods will become the key to the performance and efficiency of their performance. In this paper, the characteristic of APF control strategy is deeply study. Comprehensive analysis of APF control strategy is discussed, and their advantages and disadvantages of various control strategies is also been analyzed. Common SPWM parallel-type APF, hysteresis parallel-type APF and control model of UPQC are also analyzed in this paper. Lastly, this paper prospects the development of new control strategies.This paper also has an in-depth analysis of APF parallel connection. The mathematical model is established according to the results of simulation and the stability of the mathematic model is analyzed in this paper.