A Novel Phase-Locked Loop based Four-leg Converter Control for Unbalanced Load Compensation under Distorted and Unbalanced Grid Condition

This paper presents a new reduced-order generalized integrator (ROGI) based synchronization technique, namely ROGI-PLL for unbalanced non-linear load compensation using four-leg converter under distorted and unbalanced grid condition. In this approach, the phase angle of fundamental frequency positive sequence component of distorted and unbalanced grid voltage can be estimated accurately and rapidly by using ROGI along with conventional PLL. Such scheme enables to increase the open-loop bandwidth of PLL and improve the dynamic performance of synchronization. A Triple-ROGI (TROGI) based control algorithm is proposed to compensate unbalanced non-linear loads using four-leg converter under distorted grid voltage conditions. The compensation and rectification modes of the four-leg converter are decoupled, which adds more flexibility and selectivity in terms of control methods. The effectiveness of the proposed PLL and control strategy is verified through simulation and experimental results.