Study On Control Strategy Of VIENNA Rectifier

Under the background of the large-scale application of traditional rectifier devices,there are some problems,such as the increase of power loss and the decrease of equipment service life caused by harmonic pollution.As a power correction device,VIENNA rectifier has become one of the hot spots in the field of power electronics.Compared with other three-level topologies,VIENNA rectifier has the advantages of less voltage stress on power devices and no leg through problem.However,the VIENNA rectifier has problems such as the internal coupling of the system and the inherent midpoint potential fluctuation of the three-level topology,which adds difficulty to the design of the control system.But the quality of its control strategy is the key to improve the power quality and increase the reliability of the system,so it is of great practical significance to study the control strategy of VIENNA rectifier.This paper takes VIENNA rectifier as the research object and power electronics technology as the theoretical basis to study its control strategy under the condition of grid voltage balance and imbalance.Based on the analysis of the topology principle of VIENNA rectifier,the mathematical model is derived by coordinate transformation.Under the condition of three-phase grid voltage balance,the current and voltage double closed-loop control strategy based on PI controller is adopted,so that the rectifier can operate in the unit power factor state,and the DC side can output stable voltage;in order to solve the inherent neutral point potential fluctuation problem of three-level,a control strategy based on SVPWM modulation is adopted to adjust the action time of positive and negative small vectors,so that the neutral point potential is balanced.Under the condition of unbalanced three-phase power grid voltage,because the AC side current contains third harmonic and the DC side output voltage is unstable,aiming at the problem that the harmonic is still large and the parameter setting is difficult in the traditional double closed-loop control based on PI controller,a negative sequence current control strategy based on VPI controller is proposed.The negative sequence component of AC current is controlled to zero by VPI controller,thus the harmonic content of AC current is reduced and the control performance of rectifier is enhanced.In order to fully illustrate the correctness and effectiveness of the control strategy studied in this paper,the control strategy under the condition of grid voltage balance and imbalance is studied on the MATLAB/Simulink simulation software.The simulation results show the correctness of the control strategy adopted in this paper;the experimental results on the hardware platform verify the effectiveness of the current voltage double closed-loop control and neutral point potential balance control strategy under the condition of grid voltage balance.