The Research On Key Technologies Of Active Power Quality Combined Compensator

With the rapid development of power electronics technology,the promotion and use of various power electronic devices will seriously pollute the power quality of grid system.APQCC can effectively compensate the harmonic current,reactive current and three-phase power unbalance current existing in the power grid,and improve the power quality.Moreover,it has the advantages of high compensation precision,fast dynamic response speed,flexible compensation mode,and not generating resonance with the power grid.Therefore the theoretical study of the active power quality comprehensive compensator has attracted wide attention from domestic and foreign scholars.For this reason this paper discusses and studies the key technical issues such as the extraction of instruction current,phase-locking method and the current loop controller.This paper adopts Neutral Point Clamp(NPC)three-level as the topology of active power quality integrated compensator.Firstly,the operation principle of the NPC three-level converter is analyzed,and its mathematical model is established.Based on the analysis of the DC offset of Neutral Point,a simple and easy to implement method for effectively balancing the DC offset is given.By analyzing the working principle and deficiencies of several commonly used modulation strategies,a pulse width modulation method that can effectively suppress AC ripple of Neutral Point is proposed.Secondly,in order to solve the shortcomings of traditional methods based on instantaneous reactive power theory,a transient reactive power theory instruction extraction method can used in three-phase four-wire system is presented,which can effectively extract specific subharmonic current and zero sequence current.A positive and negative sequence separation method based on grid rotation transformation and a phase angle correction method based on forgetting iterative filtering are given for grid phase-locked phase,which effectively improves the accuracy of phase-locking.The current tracking control method using the deadbeat control as the active power quality comprehensive compensator is adopted,and the control performance of the current inner loop is improved by predicting the current correction and the current error compensation method.Finally,an experimental platform of active power quality comprehensive compensator was built in the laboratory,and relevant experiments were carried out to verify the feasibility of the proposed control method.