Research On Control Strategy Of Three-phase Voltage Source PWM Rectifier

The research of PWM rectification technology has become more important for the problems of high harmonic content on the AC side caused by uncontrollable and phase-controlled rectification.The PWM rectifier can achieve bidirectional flow of energy,reduce the harmonic content of the input current on the AC side,and control the DC side output voltage.The three-phase voltage source PWM rectifier has been widely studied because of its high power factor on the grid side,simple topology of the main circuit,and fast dynamic response of the control strategy.In this paper,the existing research results are improved on the control strategy.The specific research contents are as follows:(1)Simple analysis of the working principle and operating characteristics of the PWM rectifier.The main circuit structure,current loop and mathematical model of the three-phase voltage source PWM rectifier are analyzed.Through the coordinate transformation,the mathematical model under the two-phase rotating coordinate system is established,which provides theoretical support for the design of the later control strategy.(2)According to the mathematical model under the two-phase rotating coordinate system,the control strategy based on current feedforward decoupling is designed by means of the traditional PI control principle.Through the coordinate transformation,the three-phase AC control variable is converted into a two-phase DC control variable;through the current inner loop decoupling,the input current active and reactive components are separately controlled.The PI parameters are adjusted,according to the voltage outer loop and current inner loop running characteristics.(3)The parameters of the AC side filter inductor and the DC side voltage regulator capacitor are calculated in the main circuit,and the PWM wave modulation mode is analyzed,the space vector modulation technique is used to modulate the reference voltage signal which generated by the control strategy to generate a PWM signal.The current feedforward decoupling control strategy is simulated and analyzed by Matlab/Simulink simulation platform.The various working states of the rectifier are simulated,and the control strategy is used to verify the rationality of the control strategy.(4)The advantages and disadvantages of current feedforward decoupling control strategy are analyzed.For the existing research,the optimal control strategy is designed under the condition that the main circuit parameter design is unchanged.The traditional predictive current control is improved,the voltage outer loop sliding mode control andphase-locked loop technology are used to provide a reference current for the current inner loop.Through the phase compensation,the AC side input current and the grid voltage static error are eliminated,and the reference voltage signal is modulated by the improved space vector modulation technique.Using the Matlab/Simulink simulation platform,the traditional predictive current control and improved control strategy are simulated,and the same working state as the current feedforward decoupling control strategy is simulated.By simulating the waveform,while verifying the rationality of the control strategy,the simulation waveforms of the two control strategies are compared.The improved control strategy has better stability and faster dynamic response speed when the harmonic content of the power grid is met.