Study Of Unbalanced Compensation Strategy In Three-phase Four-wire System

In recent years,with the rapid development of modern power electronic devices,the higher requirement of power quality has been required by electricity users.The exist of instantaneous reactive power increases the reactive power load system losses,and even seriously affect power quality.It is of great significance for power quality optimization to reactive power compensate in time.However,traditional compensation of reactive power compensation device has been unable to meet the needs of modern power compensation.Due to the advantages of fast response,high precision and reliability can be achieved inductive and capacitive reactive power compensation.The effective suppression system voltage fluctuations,and gradually developed into a transmission and distribution systems ideal compensation device.This paper first briefly introduces the reactive power compensation of power system development and current situation,the principle of SVG is analyzed.A low voltage distribution network of phase four-wire SVG studied.From the basic circuit topology view of dynamic reactive power compensation system,SVG basic circuit topology and working principle is detailed analyzed,the complete mathematical model is built for the simulation research and device development.In view of the negative impact coursed by the grid voltage harmonic voltage component for reactive current detection and control performance,using traditional control strategy is difficult to meet the higher system performance.Voltage feed-forward control method is adopted in this paper to improve the tracking precision of compensation current voltage and speed up the response.Meanwhile,in order to ensure reliable operation of the switching device,the actual circuit systems need to set dead time.However,dead time often have a greater impact to current waveform,and even cause serious distortion of the output waveform.The effect of the traditional dead-elimination policy and shortcomings is analyzed,as well as to avoid the influence of inverter dead time.A new method based on the pulse width is put forward to achieve a reasonable optimization between dead band compensation and net current.Based on PSIM simulation platform,the complete system simulation model of voltage feed forward compensation and dead time control strategy is built,simulation results show that the current waveform distortion significantly improved system dynamic and static characteristics.To further verify the correctness of control strategy,a ±70kVar SVG prototype is built,detailed parametric design principles is given out,and use the high-performance DSP TMS320F28335 as the core of SVG control system.Experimental results show that performance of control strategy is good,verify the effectiveness of proposed strategy.