Research On A Multifunction Power Quality Fusion Control System For Low-voltage Distribution Network

Three-phase four wire loads such as single-phase loads,nonlinear loads,reactive power loads occupy a heavy proportion in the current low-voltage distribution network in China,which bring a serious problems of power quality to the distribution network,such as harmonic current,low power factor,three phase unbalance,neutral line current.In order to solve those problems,a multifunction power quality fusion control system is proposed which is based on compound repetitive control strategy.Firstly,the paper introduces the working principle of multifunction power quality fusion control system.The three level diode clamped topology of split capacitor is chosen according to the analysis and comparison of the existing three-phase four wire converter topology.The mathematical model of the system in the abc coordinate system is derived,according to which comes to a conclusion that the three-phase current is independent of each other in the three phase four wire system.Secondly,acording to the capacity of the transformer in the three-phase four wire low-voltage distribution network and the compensation property of the multifunction power quality fusion control system,a reasonable capacity of the system is determined.And then design the main circuit parameters of the system.On the basis of previous research,the parameters of LCL filter for this research are designed.Thirdly,a series combined current tracking controller based on PI control and repetitive control is designed in this paper,which is on account of mathematical model of multifunction power quality fusion control system based on abc stationary coordinate system.It combines the advantages of the PI control strategy and the repetitive control strategy.In addition,the DC bus voltage controller and the DC bus midpoint potential controller are designed.Finaly,the simulation experiment of the design scheme is carried out by using Matlab simulation in this paper.The result of simulation proves the reasonable of the proposed scheme and control strategy.