Research On VIENNA Rectifier Control Strategy Under Unbalanced Power Grid Based On LCL Filter

VIENNA rectifier as a three-level boost type AC/DC converter,from its topology structure and the working characteristic,it compared with the conventional three-level rectifier,high power density,do not need to set the dead zone,simple topology and control circuit,input and output harmonic advantages of excellent performance,so it is widely used in industrial inverters,aerospace,electric vehicle charging piles and other fields,VIENNA rectifier has high research significance.Most studies on VIENNA rectifier are focused on the grid balance.However,when the grid voltage is unbalanced,the normal operation of VIENNA rectifier will be adversely affected,resulting in the instability of the dc side voltage,the generation of secondary ripple,affecting the operation of unit power factor,or even directly stopping the operation.Therefore,the control method of VIENNA rectifier in the case of unbalanced three-phase power grid voltage is studied in this paper.First of all,based on the operating principle of VIENNA rectifier,the mathematical model of voltage balance and unbalance of power grid is derived by formula,which lays a foundation for the following introduction of LCL filter design and rectifier control method research.Secondly,the double closed-loop control method based on PI control obtained by VIENNA rectifier through feedforward decoupling is introduced.This method can achieve the control of VIENNA rectifier well when the grid voltage is balanced,but when the three-phase voltage of the grid is unbalanced,Problems such as secondary voltage fluctuations on the DC side,poor current waveforms on the grid side,and large harmonics occur.In this paper,the three-phase voltage imbalance of the power grid is studied in the background.Through derivation,a method is proposed to first separate the positive and negative sequence components by the positive and negative sequence separation method based on the double second-order generalized integrator in the αβ coordinate system.A quasi-PR control strategy is used to track the reference current.This method is simple to control and can better suppress the secondary fluctuation of the DC side voltage,and has less harmonic content.The space vector modulation method of VIENNA rectifier and the midpoint potential balance control method based on SVPWM method are introduced.Finally,in order to improve the power density of VIENNA rectifiers,the use of LCL filters instead of single L filters is proposed,and the simplified LCL filter parameter calculation method is introduced.In order to verify the method discussed,this paper builds a simulation model of VIENNA rectifier using simulink simulation system,and establishes a system experimental platform based on TMS320D28377,and debugs the software and hardware.The analysis of the simulation model and the experimental results verify the effectiveness and feasibility of the proposed method.