Research And Design Of Three-phase PWM Rectifiers And Its Control Strategy Under Unbalanced Source Voltage

In this paper, the mathematical model was analysised and built under the balanced conditions, then analyzed the three-phase control strategy of VSR (Voltage Source PWM Rectifier) based on the model. When the operating conditions unbalanced, it is better to change the control strategy only to ensure operation of three-phase VSR is stable than to change the main circuit.The unbalanced is common phenomenon in the normal national grid.Using the traditional control strategy under such circumstances,it would add harmonics to AC current and DC voltage,so, the control strategy required to improve. In this paper, constructed mathematical model in the three-phase stationary coordinate system, and summarized two control strategies that was the suppress the AC side negative sequence current and the suppress the second order harmonic of DC side.and then simulated the control strategies by using SIMULINK toolbox of MATLAB.The calculation of positive and negative sequence voltage or current component is the top priority in the control system, so the paper presented a new positive and negative sequence calculation– the delay method. The feasibility and usability of the delay method was certificated by simulation and experiment, moreover, it can shorten the positive and negative sequence computing time.The traditional design for the main circuit,it is generally not considered the impact of inductance on the three-phase VSR when the power unbalance; the existing inductor design under unbalanced grid conditions not consider the affect of the balanced grid to the VSR system, therefore, the paper propose a design principle of the AC side inductance. When the network unbalanced, if unbalanced control strategy was adopted, that is need to consider the affect of inductance on the three-phase VSR system fully. The simulation and experimental verified the feasibility of this method.It has been confirmed through theoretical analysis and simulation, and then built up experimental platform, the control chip is TMS320LF2407. Experimental results have shown that the proposed positive and negative sequence computing method and inductive design methods are feasible.