| The mathematical model of PWM rectifier are analyzed in this paper, according to the model analyzed the control strategy of the three-phase voltage source PWM rectifier, and designed the main circuit parameters of a three-phase VSR.Further more, analysis of the unbalance in power grid, if use the control strategy of balanced grid can make the AC side of PWM rectifier contains a large number of odd harmonics, and the DC side contains a lot of even harmonics, so the control strategy needs to improve for unbalanced power. Considering the unbalanced grid containing positive and negative sequence components,so use the dual current inner loops for control positive and negative sequence independent. Due to the currents are coupling in the dq coordinate system, so the current loop using feed-forward decoupling control based on SVPWM.This paper adopts two kinds of methods to analyzed and compared the control method of AC side negative sequence current suppression and ten control method of DC side voltage harmonic suppression.Through the simulation experiments verify the feasibility of two methods, and find that the second way is better than the first way.Due to the dual current loops are controlling the positive and negative sequence components, whether quickly and accurately detect the grid voltage positive and negative sequence components, directly affect the control performance is good or bad. Comprehensive consideration, proposed that use DSOGI-FLL to detect the positive and negative sequence components, and also to phase lock the grid. The simulation and experimental results show, DSOGI-FLL can achieve fast, accurate detection and tracking stability for unbalanced grid voltage, at the same time improved control system enables PWM rectifier under unbalanced grid, Grid side have the AC sine input current, and the DC side have a stable DC output voltage. |
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