LQG Based Augmented Control for Stability Enhancement of a Grid Tied Inverter

This paper proposes an augmented controller to the existing grid tied inverter (GTI) control system, to deal with the instability arising during weak grid condition. The proposed linear feedback controller is a linear-quadratic-gaussian (LQG) regulator which helps in loop-shaping of the conventional feedback control to attain stability at the point of common coupling (PCC) during varying grid condition. The LQG design also involves the reduction of states which makes the synthesis realizable in low cost processors and also plays a successful role in the loop shaping. Time domain simulation results validate the loop-shaping in the frequency domain and show that the proposed approach successfully brings stability to a GTI system at PCC. A trade-off between stability and current reference tracking performance has also been discussed.