Research On Soft Start Of Thyristors To Suppress Start-up Inrush Current Of VIENNA Rectifier

With the widespread use of power electronic equipment in human society,it brings great economic benefits and convenient life style to people.At the same time,it will inject a lot of harmonic and reactive power into the power grid,reducing the power quality and utilization ratio of the power grid,and creating a serious burden to the power grid.Therefore,it is essential to increase the power factor of power electronic equipment,especially the rectifiers,decrease the total harmonic distortion(THD)of input current,and research the rectifiers used in high voltage and high power applications.Three-phase VIENNA rectifier is a promising three-level rectifier.Compared with traditional rectifiers,It has the superiorities of high power factor,low current harmonic distortion rate,low switching stress,no need for switching tube dead zone setting,and fewer switching devices.There is a tendency to gradually replace traditional rectifiers in the fields of aviation power supply,wind power generation and electric vehicle chargers.This article takes the three-phase three-level six-switch LCL filter VIENNA rectifier as the research object,and studies its working principle,mathematical model,control strategy and soft start control.Firstly,the working principle of VIENNA rectifier is introduced,and the parameter design of LCL filter is briefly introduced.According to Kirchhoff's law of current and voltage,respectively establish the VIENNA rectifier's mathematical models in abc,??and dq coordinate system,which lays the foundation for the follow-up work.Then,according to the mathematical model,the control strategy of VIENNA rectifier is designed,and the double closed-loop PI control strategy of current inner loop and voltage outer loop is adopted;the current inner loop uses current feedforward decoupling control,and the PI controller of current inner loop and voltage outer loop is designed with typical type I system and typical type II system respectively.Next,the space vector modulation method of the VIENNA rectifier is analyzed,the four basic space vectors of the VIENNA rectifier are introduced,and the simplified algorithm of the three-level SVPWM modulation is analyzed.Aiming at the problem of capacitor neutral point potential imbalance,it puts forward a solution by dynamically adjusting the action time of positive and negative small vectors;Aiming at the problem of excessive inrush current during the startup process of the VIENNA rectifier,a two-stage start control strategy with thyristors as precharge circuit and slow curve signalas the DC bus voltage is proposed in order to achieve the soft start of the entire system.Finally,the simulation model of the system was established by Matlab/Simulink software and an experimental prototype was built on the hardware platform.The software simulation and experimental analysis verified the correctness and feasibility of the theoretical analysis and control strategy proposed in this paper.