Source-voltage-sensorless scheme for PWM rectifier under voltage unbalance condition

A simple and robust source-voltage-sensorless scheme for a PWM rectifier considering voltage unbalance conditions is proposed. When a voltage unbalance occurs in a three-phase system, the unbalance component deteriorates the performance of the voltage source estimator by generating AC disturbances. Since the the source voltage information is used to control the real/reactive power flow, the inaccurate information causes voltage fluctuation in the DC-link, the increase of reactive power, and furthermore, instability in a PWM rectifier. In this work, the proposed sensorless scheme estimates the normal components and the unbalance components of the source voltage separately by using a modified reduced-dimensional estimator. The use of the measurement´s derivative quantity sensitizing the estimator to measurement noises is avoided by introducing an auxiliary variable. Thus, the proposed sensorless scheme yields better robustness to measurement noises, and it works well even in the transient state. The feasibility of the proposed sensorless scheme is confirmed through computer simulations and experiments.