Three Phase-locked Loop Design And Research On Three-phase Four-wire DSTATCOM System

In the low voltage power supply system esxits nonlinear load,so it is appears some problems about harmonic and current unbalancing in power grid.According to these problems,the grid synchronization technology,harmonic elimination,reactive power compensation and other problems in the three-phase four-wire system have been researched in thsis.The research significance of DSTATCOM is introduced and its research background and current situation is explained.Then this thesis states the features of different reactive power compensation devices.The principle of power compensation device is analyzed,and the main circuit in the thesis is determined.Grid synchronization technology under unbalanced grid voltage is investigated in DSTATCOM device.The working principles and faults of the single synchronous reference frame software phase locked loop(SRF-PLL)is analyzed.Given the disadvantages of conventional method,The decoupled double synchronous reference frame expressions under positive and negative sequence components of the voltage vectors are derived.Acquiring the decoupling network through formual,and this network leads to DDSRF-PLL structure which can detect the positive sequence voltage components accurately and quickly.Insteading of PLL,frequency locked loop which based on the structure of dual second order generalized integrator frequency is researched.DSOGI-FLL can optimize the dynamic response of the system.Based on the MATLAB platform,the simulation models of the three techniques are established,and their performance are compared under the normal or the faulty grid voltage.Because the DSOGI-FLL method has the relatively best capability of detecting the grid frequent and phase,thsis chooses DSOGI-FLL as the grid synchronization link in the system of DSTATCOM.For the contorl system of three-phase four-wire three-leg DSTATCOM,in order to stable the voltage of DC side,PI controller is designed in voltage loop.It combines the PI controller,which has the capability of quick response,with the repetitive controller,which has periodic signal control,and applies this method in the inner current loop of DSTATCOM to track the current.This method can improve the tracking accuracy of the harmonic reference current.An optimized 3D-SVPWM is adopted to produce the PWM signal in DSTATCOM.The optimized algorithm can achieve good performance.Comparing with conventional method,this algorithm effectively reduced the calculated amount.based on the software of MATLAB,the DSATATCOM system simulation model according to the design of control strategy in the thesis is builded.Through the simulation,we can conclude that this system can be able to achieve the desired compensation reactive power result.Through research on control system,The hardware circuit and software of the system based on TMS320F2812 are designed.