Research On Control Strategy Of VIENNA-type Rectifier

VIENNA rectifier is a three level PWM rectifier with high power factor,low current harmonic and controllable output voltage,it transmits active power to DC side while avoiding injecting too much reactive power and harmonic to the power grid,so far it has received much attention from scholars at home and abroad,how to better control VIENNA rectifier is the focus of the study.This paper researches this topology's control strategy to promote practical using in engineering.Firstly established the mathematical model,then introdudced in-pahse disposition carrier modulation strategy,analysised voltage oriented current decoupling dual closed control based on the PLL(Phase-Locked Loop),designed digital controller and the inductor filter in grid side,completed the development of 10 k W VIENNA rectifier.Secondly,in allusion to the problem of traditional PI controller's failure to trace the AC signals and the bad dynamic performance with a single DC voltage loop in DC side,PR(Proportional Resonant)controller was firstly expanded to the current loop of VIENNA rectifier to achieve the performance that zero-error tracing the AC signals,at the same time load current feed-forward was introduced to enhance the ability of anti-load disturbance.Derived the feed-forward expression,analyzed feed-forward factor on system dynamic performance and gave how feed-forward factor was selected.The simulation and experiment results proved the correctness and feasibility of expressed theories.Finally,For the common problems of three level topology,a novel method to suppress neutral point potential based on the dynamic regulation factor was improved,it can grearly eliminate the three times fundamental frequency fluctuation of the neutral point potential,at the same time suppressed the DC bias,even in special conditions(asymmetric capacitance and load parameter)could effectively inhibit the unbalance of neutral point potential.Simulated the scheme by PSIM 9.03,and build a VIENNA rectifier prototype for experiments to verify the scheme.Simulation and experimental results show that:(1)The control strategy that voltage oriented current decoupling dual closed loop has high grid power factor,harmonic characteristics and good output stabilized voltage characteristic;(2)The control strategy that proportional resonant current control strategy with load current feed-forward control could change the closed-loop dynamic equivalent impedance,had better anti load disturbance performance while keeping unit power factor t in grid side;(3)The improved novel method to suppress neutral point potential based ondynamic regulation factor could greatly deduce the midpoint fluctuation.