LQ current control for three-phase PWM rectifiers under unbalanced grid voltage conditions

This paper presents a synthesis of a control system of a three-phase three-level PWM rectifier operated under unbalanced grid voltage conditions. The main goal is to obtain balanced grid currents. The proposed control method contains a PI dc-link voltage controller and an inner state feedback current controller coordinated in synchronous reference frame. The state-space model, which describes the dynamics of an input L-type filter of the rectifier, is augmented by a disturbance model that contains integral and oscillatory terms. Moreover, two approaches of reference tracking are considered. In order to determine the current controller gains, linear-quadratic (LQ) optimization is used. The discussed issues are illustrated by experimental results to validate the accuracy of the proposed control design.