Research On Control Strategy Of Three-Phase Three-wire Vienna Rectifier

Electric vehicles can achieve zero emissions,no pollution,the use of electric vehicles has become the future trend of automotive development.In this trend,charging points will replace gas stations to provide new energy for cars.At present,charging points generally adopt AC/DC and DC/DC two-stage topology.The circuit structure of Vienna rectifier is simple,the output voltage is stable and adjustable,there is no dead time in the bridge arm through problem,and the switching stress is small.It is a suitable topology for the AC/DC of the front stage of charging point.Therefore,Vienna rectifier has high promotion value in the field of electric vehicles.The dynamic and steady state performance of the input and output of the three-phase three-wire Vienna rectifier will be affected by different operating conditions such as unbalanced grid voltage and abrupt load changes during operation.In view of the adverse effects of these conditions on the normal operation of the Vienna rectifier,a new double closed-loop control strategy is proposed.The inner loop adopts improved finite set predictive power control,and the outer loop adopts linear active disturbance rejection control.The normal operation of the Vienna rectifier under unbalanced grid conditions is achieved by introducing a redefined reactive power which enables both the instantaneous active power second harmonic and the instantaneous reactive power second harmonic to be effectively controlled in case of unbalanced grid.The linear active disturbance rejection control is adopted for the voltage outer loop,which overcomes the overvoltage and slow dynamic response problems associated with PI control,and provides better robustness and faster tracking performance under unbalanced grid conditions.The specific research contents of this paper include: The working principle of three-phase three-wire Vienna rectifier is analyzed,and the mathematical model of Vienna rectifier in static coordinate system is established.Based on the mathematical model,a new double closed loop control strategy in two phase static coordinate system is proposed.Based on the working principle of Vienna rectifier,the three-level space vector modulation strategy is introduced,and the three-two level transformation simplified modulation algorithm is implemented.The unbalance mechanism of point potential in Vienna rectifier is analyzed,and the problem of unbalance of point potential in Vienna rectifier is solved by space vector modulation.The mechanism of zero crossing distortion of input current modulated by seven-stage SVPWM is studied.A hybrid space vector modulation strategy is adopted to solve the problem of zero crossing distortion.In this paper,the SVPWM modulation strategy is used to output three voltage vectors in a switching cycle,and the switching frequency can also be fixed.MATLAB /Simulink simulation software was used to build the simulation model,and the experimental prototype of Vienna rectifier was designed and developed.Through theoretical simulation and experimental analysis,the correctness of the performance analysis of Vienna rectifier and the effectiveness of the proposed double closed-loop control strategy are verified.