UPS前置四桥臂PWM整流器控制策略

Control Scheme for Front-End Four-Leg PMW Rectifier in UPS

分析了无变压器的双变换式UPS的功率流动。根据瞬时功率理论,当UPS带不平衡负载时,逆变器需要提供平均功率和二次脉动功率。为了保证功率平衡,由整流器提供平均功率,而母线电容提供二次脉动功率。而由此产生的母线电压脉动会使得整流器三相输入电流耦合低次谐波。本文提出了一种滑动平均的算法来滤除母线电压反馈中的二次脉动分量,使得整流器能有效的提供平均功率。并针对UPS中前置四桥臂PWM整流器提出了一种基于abc坐标系下的双环控制策略。该方法可以有效抑制公共桥臂上的电流对整流器的影响,在电网某一相故障时,其余两相也能继续正常工作。仿真研究和实验结果验证了理论分析结论。

This paper presents power flow of the double conversion transformerless UPS.The inverter has to supplying average power and oscillating power if the load is unbalanced according to instantaneous power theory.In this paper,the rectifier provides the average power and the DC-bus capacitor provides the oscillating power for the aim of power balance.However,the oscillating DC-bus voltage will lead to input currents coupling with low order harmonic.Therefore,a moving average algorithm is adopted to attenuating the oscillating component,which has a considerable impact on rectifier.This paper presents a dual-loop control scheme for three-phase four-leg PWM rectifier in UPS based on abc coordinate.This control method could effectively attenuate the impact on rectifier which is caused by the current in common leg.Thus,if one of inputs is failed,the others can be operating properly.The simulation and experimental results are in close agreement with the theoretical predictions.