Reseaechn Of Modulation Strategy Of VIENNA Rectifier

With the gradual depletion of fossil energy,new energy sources have gradually emerged and developed rapidly.Various switching power supplies have been widely used in many fields,which indirectly or directly improve people’s quality of life,but the harmonic pollution of switching power supplies has gradually become more problematic.Aroused people’s attention,relevant staff have conducted in-depth research on related issues such as controlling grid pollution,and PWM rectifiers are favored by people due to their small current harmonic content.PWM rectifiers can work in a unit power factor state,and the input current is sinusoidal.The VIENNA rectifier uses a small number of power switches,there is no bridge arm through problem,and there is no need to consider the dead zone,so the cost is lower,and the reliability is higher,so the VIENNA rectifier has a wider application.The improvement of the modulation strategy is of great significance for improving the performance of the VIENNA rectifier.In this paper,the modulation method of the VIENNA rectifier is deeply studied.This paper first compares the characteristics of some modulation strategies,then introduces the development process of the three-phase rectifier and the characteristics and advantages of the VIENNA rectifier.This article analyzes the working principle of the VIENNA rectifier.According to the equivalent switch model,the mathematical model of the VIENNA rectifier in the dq coordinate system is obtained through coordinate transformation.On this basis,the control system is designed,and the specific tuning method of PI parameters is given.After considering the influence of parasitic parameters and absorption circuit,the relationship between the terminal voltage and the input current of the VIENNA rectifier is analyzed.This paper also analyzes the influence of terminal voltage error on current quality.In order to improve the current quality of the conventional SPWM modulation,A zero-crossing clamp SPWM is adopted to suppress the terminal voltage error,which improves the quality of the current waveform.Simulations and experiments have been carried out.The result of experimental proves the effectiveness of the improved method.The space vector control of the VIENNA rectifier is studied,the synthesis of the target vector is analyzed,and the selection of the basic vector and its action time are deduced and calculated.The influence of different basic vectors on the balance of the midpoint is analyzed,and the balance of the midpoint can be adjusted by controlling the length of the action time of the small vector.The input current distortion caused by space vector control is studied,and the reason for the distortion is analyzed because of the wrong selection of the vector.In order to improve the current waveform,a hybrid modulation strategy is proposed.This method adopts five-stage and seven-stage methods.The hybrid modulation can improve the current distortion phenomenon,and the modulation algorithm simplifies the calculation,which is conducive to the realization of the program.The simulation and experiment are compared with the traditional space vector control effect to verify the correctness of the proposed strategy.