Research Of The Three-phase VSR PWM Rectifier System Based On Double Closed Loop Control

Traditional uncontrollable or phase-controlled rectifiers have wasted thePower System because of the drawbacks of low power factor, high harmonic andso on. That has drawn the attention of academia. However, PWM rectifiersovercome these shortcomings and can achieve adjustable power factor, unitypower factor, sinusoidal input currents, bi-direction power flowing, directcurrent control convenient for the design of the control system, fast dynamicsresponse and steady DC voltage. So they have been adored by academia usedwidely in high-performance power electronic cases and devices. In this paper,some relating issues on PWM rectifier system are researched on.Based on the steady-state ac vectors of three-phase VSR PWM rectifier,theory of PWM rectifier is analyzed. After the topology structure of the system isset to three-phase half-bridge, the switch mode is analyzed. Eight modes aredetermined and the variables of the circuit are analyzed. The mathematicalmodels of three-phase VSR PWM rectifier in three-phase static coordinate andd-q coordinate are studied and the improved mathematical model of VSR in d-qcoordinate is studied as well. The direct current control of three-phase VSRPWM rectifier is studied, and the arithmetic expression with fixed switchingfrequency is studied as well.The theory and algorithm of SVPWM are studied, and the simulation modelis set up based on the algorithm. As to the inductance on AC side and thecapacitance on DC side, the design principles are analyzed and several modelsare simulated with varieties of parameters. The double closed-loop controlstrategy is adopted. The double closed-loop control strategy of PWM rectifiersystem is composed of inner current-loop and external voltage-loop. It realizesthe energy passing balance between AC side and DC side with the aid ofstabilizing the bus voltage. In order to assure the grid-side converter runningsafely and reliably, phase-locked loop method used for obtaining the grid voltagephase quickly and accurately is proposed. Feedforward control is adopted torestrain possible ripples of the Power System and the load.The simulation model of PWM rectifier system is set up in Simulink and thewaveforms when the Power System and the load are steady or have fluctuationsare obtained.At last, in order to verify the validity of the control strategy and topology ofthree-phase VSR PWM rectifier, the complete test platform is developed. System responses when the Power System and the load are steady or have fluctuationsare obtained and the results are analyzed.