The Research About VIENNA Rectifier

From the perspective of topology design and operating characteristics,compared to the traditional rectification topology with power factor correction,the Vienna Rectifier topology of one of the three-level converter topologies embodies the following advantages:1)Simpler power and control circuits;2)Less input current harmonics and lower output voltage ripple;3)The voltage stress applied to the power device is half of the output DC voltage;4)The output voltage pass-through phenomenon does not exist between the bridge arms in the topology,and there is no need to set the dead zone.Particularly,it satisfies some application requirements for higher power density and higher power quality requirements,and gradually leads to extensive research and attention.In order to facilitate the analysis and design of the control system,the mathematical model of the Vienna rectifier is deduced in two different coordinate systems,which provides a theoretical basis for the design of the control system.Then,the multi-loop control structure with feedforward decoupling was designed in the rotating coordinate system.This method is easy to implement,with excellent control performance and high engineering application value.This thesis analyzes the modulation principle of different carrier cascaded PWM modulation methods and proposes an improved single-carrier pulse width modulation modulation algorithm for DSP control systems.A carrier-based PWM with synchronous switching technique for a Vienna Rectifier proposed in this thesis have the advantage of reducing the PWM signal from six to three.However,compared with the traditional CB-P WM switching method,the current distortion in the zero-crossing region under the synchronous switching method is severe,which does not meet the important constraints of the power grid phase current and phase voltage under the unit power factor work conditions.The thesis analyzes the reasons of the waveform distortion of the zero-crossing region of the power grid caused by the multi-loop control and the improved single-carrier pulse width modulation method in the synchronous rotating coordinate system.Based on above analysis,this thesis proposes a reactive current injection technology,which makes the distortion of the grid current at each zero-crossing point become suppressed,and the power quality is significantly optimized.In order to solve the problem of neutral point potential balance in Vienna rectifier,this thesis reveals the essence of mid-point potential fluctuation.A balance control strategy based on the zero-sequence component injection is adopted to suppress the fluctuation of the midpoint potential and achieve the purpose of midpoint potential balance control.The rectifier model is established under the Matlab/Simulink simulation environment.The simulation model analyzes and compares the variation of the current waveform distortion rate of the grid before and after adding the compensation component,and verifies the correctness of the theoretical analysis.Based on TMS320F2812,the hardware circuit and software program were designed to build a Vienna rectifier experimental platform.Finally,the obtained experimental waveforms and data confirm the feasibility of the design program.