The Research On Control Strategy Of Hybrid Active Filter

With the wide application of power electronic devices, harmonic problems in the power system are becoming serious. Hybrid active filter can be used to achieve real-time tracking and dynamic management of harmonic currents with the advantages of low cost of passive filter and good performance of active filter. It is of significance to study hybrid active filter control strategies to ensure the filtering effect and make full use of advantages of active filter and passive filter.Four major hybrid active filter topologies are analyzed, indicating that the hybrid active filter topology with APF in parallel with the inductor of PF is of good topological advantages, with better comprehensive performance. Four control strategies of this hybrid active filter are analyzed. And a novel control strategy based on output voltage correction is proposed with the advantages of stable, high filtering rate, unaffected by background harmonics and simple parameter selection, which the existing control strategies do not have. To control the amplitude of each order current of APF effective, control strategy based on output voltage correction is proposed. Control link of APF output current is added to achieve the control of each order APF output current. In order to reduce fundamental current APF in hybrid active filter, a DC voltage control method based on power control is proposed. With this method, the APF can output minimum fundamental current with the same active power, which further reduces the capacity of APF. According to the calculation characteristics of APF output voltage reference in the proposed control strategies, sliding window DFT method is utilized to detect system harmonic current, based on which two methods to calculate the reference value of APF output voltage are given:trigonometry calculation and recursive calculation.Two problems of the hybrid power filter when put into operation alone are analyzed: short-term amplification of 5th harmonic and the difficulty to control DC voltage. Joint operation of HAPF and 5th passive filter (PF) is proposed to solve these problems. It is pointed out that an appropriate increase in quality factor of passive filter reduces the fundamental current of APF. Simulation results show that a 5th passive filter with relatively small capacity can effectively reduce the short-term amplification of 5th harmonic and realize stable control of DC voltage and that an appropriate increase in quality factor of passive filter reduces the fundamental current of APF.