Study Of Anti-disturbance Three Phase Voltage PWM Rectifier

Three-phase PWM rectifier is a kind of high performance AC/DC converter, which is widely used in uninterruptible power supply, active power filter, and renewable energy generation. The traditional PWM rectifier is easily disturbed by the biased grid during grid-connected operation. The three-phase unbalance, voltage dip, harmonic and frequency deviation are the common disturbance conditions for the grid. Among them, the unbalance disturbance is a serious harm to the PWM rectifier, which will lead to current distortion for the AC side of the PWM rectifier, and low frequency pulse for the output DC voltage. As the traditional way cann't solve these problems, the anti-disturbance control strategies under unbalance grid are mainly studied.Several common PWM rectifier topologies, the working principle of them and some control strategies have been presented first. Then an improved mathematical model for the anti-disturbance PWM rectifier has been established with reference to the unbalance grid model which has been decomposed into positive and negative sequence components. It has been concluded that the key to suppress the unbalance disturbance is to control the positive and negative sequence components separately.Based on the established model, the voltage oriented vector control strategy has been analyzed. Afterwards, the dual current control and proportional-resonant control strategies have been proposed. All of these strategies have adopted the double close-loop control structures. Their outer voltage loops have adopted PI controllers to adjust DC bus voltage. The difference of them lies in the inner current loops. In the voltage oriented vector control strategy, a PI controller has been employed for the inner loop. In order to suppress the unbalance disturbance, the dual current control strategy has employed two PI controllers to adjust the positive and negative sequence components which have been decomposed from the PWM rectifier system. To simplify the controller design, the proportional-resonant control strategy has been raised to track the AC variable under stationary coordinate communication directly. In addition, several design methods of two important modules which are positive and negative sequence decomposition and grid voltage phase-locked loop have been proposed. The simulation results have shown that the time delay method has the best comprehensive performance.To verify the feasibility and validity of the proposed strategies, an experimental prototype has been built based on STM32's rich on-chip resources. The design methods of hardware circuits and control programs have been given in particular. The experimental and simulation results have shown that the anti-disturbance performance of the proposed PWM rectifier has been improved obviously.