| Today’s power electronic devices are quickly booming in all walks of life.They have brought a shocking experience in comfort and production and living efficiency.However,the harmonics produced by them threaten the safety and economic operation of the equipment,and even cause accidents.As a device which can quickly and efficiently control harmonics and purify the power grid,Active power filter(APF)has great research value and application prospects.NPC(Neutral-Point Clamped)three-level APF has attracted much more attention due to its high DC bus voltage utilization,smaller output current ripple.In this dissertation,based on the parallel NPC three level APF,the modulation strategy of the three-phase three wire active power filter,the middle point potential balance control method,the harmonic current detection,the compensation current tracking control and other key technologies are studied.SVPWM(Space Vector Pulse Width Modulation)strategy is used for NPC three-level APF in this dissertation.Different from the traditional SVPWM control algorithm,this dissertation divided the sector detailed to make the control algorithm more accurate,then based on it,the DC side neutral potential balance control of three-level active filter based on charge balance principle is introduced.The detection and tracking control technology of harmonic current are two key technologies of APF,which determines the compensation ability and compensation precision of APF.In the detection of harmonic current,based on the ip-iq detection method,this paper proposes an improved integral detection method,which uses integral and delay links instead of LPF,effectively shortening the time when APF put into operation.For the tracking control of the reference harmonic current,this dissertation adopts an improved repeated-prediction deadbeat control strategy,which can improve the prediction accuracy of the system in the steady state and the response speed in the transient state.Therefore,the simulation platform of a NPC three-level APF is built,and the device parameters of the main circuit are determined according to the theoretical analysis and condition.The simulation results prove the feasibility and superiority of the control scheme. |
