Study On Control System Of Three-phase Active Power Filter

As harmonic contamination increasingly severity, so the introduction of active power filter (APF) is an important development trend. As far as principles of APF are concerned, harmonic currents of compensated target are detected first, then APF generates compensating currents which are equal to harmonic currents in amplitude and converse in polarity to purify power currents. After compensation, the power currents only contain fundamental components. When frequency and amplitude of harmonic currents vary, this kind of filter can compensate harmonics effectively. Moreover, the compensation performance is not affected by power impedance. So, it is more and more acceptable. This studies applications of one –cycle control in APF. The main contents are as follows:The method based on instantaneous reactive power theory is used as harmonic currents detecting method of APF, triangular wave modulation method and hysteresis control method are applied to currents tracing control circuit of APF. And simulations of three-phase APF are performed under symmetrical power source voltage condition. Furthermore, comparison is drawn between above simulations and simulations of three-phase three-wire APF with one-cycle control under symmetrical power source voltage condition. In order to solve its disadvantages, this thesis presents a APF based on both detecting method and one-cycle control for the first time. The key control equations are derived and model of APF is set up. Simulations are carried out under symmetrical power source voltage for harmonic compensation, reactive power compensation, and both harmonic compensation and reactive power compensation respectively. In addition, simulations for harmonic compensation are performed under asymmetrical power source voltage condition as well. And comparison is drawn between the above simulations and simulations of three-phase three-wire APF with one-cycle control under asymmetrical power source voltage condition. The simulation results verify APF presented in this thesis not only achieves multi-function, but also acquires simple structure, high control accuracy and fast response speed. Moreover, under symmetrical power source voltage condition, three-phase power source current are proportional to three-phase power source voltage after compensation and almost symmetrical.This thesis applies vector operation of Unified Constant Frequency Integration(UCI)control to three-phase four-wire APF for the first time. Based on the analysis of UCI controlled four-arm three-phase four-wire APF, and simulations are performed. By comparison with one-cycle control, this scheme decreases switches operating at high frequency and reduces switching losses.