Reaserch And Implemention Of Three-phase Four-wire Three-level APF

Three-phase and four-wire power distribution systems are mostly used in our country,and the harmonic problem is becoming more and more serious with the development of power electronics technology.At present,the main measure to solve the power quality problem is to use active power filter(APF).In the case of high voltage and high power,the three-level topology has a broader research and application prospects due to its unique advantages compared to the two-level topology.In this paper,three-phase four-wire threelevel active power filter is taken as the research object,The control strategy is mainly studied and an experimental prototype is built.The main contents are as follows:Firstly,the principle of three-phase four-wire three-level APF is analyzed,and its mathematical model is deduced.Aiming at the problems of harmonics and unbalanced current components widely existing in three-phase four-wire distribution system,a harmonic detection method of ip-iq based on second-order generalized integrator is proposed,and a PI+ repetitive composite current controller is designed.Secondly,the modulation strategy and neutral-point potential balance control strategy are studied.A simplified 3D-SVPWM modulation strategy is proposed by mathematically transforming the traditional 3D-SVPWM modulation strategy.Based on this,a neutral-point potential balance control strategy called multi-phase control is proposed which assigns the neutral-point potential offset to the phase with neutral-point potential balance ability to compensate.Specifically,the strategy proposes the concept of midpoint compensation capability factor,and uses this to determine the phase and balance capability with neutral-point potential balance capability,and assigns the neutral-point potential offset according to the weight of factor.Lastly,the compensation of the midpoint potential offset is completed by reconstructing the actuation duration of O state.Finally,a three-phase four-wire three-level APF system is designed.Based on the Matlab/Simulink simulation platform,a three-phase four-wire three-level APF simulation model is built.The simulation raserch is carried out under balanced and unbalanced load conditions.And the experimental platform is built for experimental research.The simulation and experimental result prove the effectiveness and feasibility of the proposed control strategy.