Symmetrical components-based robust stabilizing control of a grid-connected inverter under unbalanced voltage sag

This study presents an approach for robust current and power control for a three-phase grid-connected inverter set up with an L-filter that operates under an unbalanced AC grid-voltage source. This control method consists of two paralleled current control for the positive and negative sequences to accomplish one of three selective control targets: a) supplying balanced three-phase current; b) supplying non-oscillated real power; and c) supplying non-oscillated imaginary power to the AC grid for a given reference value utilizing the identical control gains. The real and imaginary power references, together with the measured grid voltages, are used in the computation of the reference current for each control target. In addition, the proposed dual-current control system has a control law that comprises state feedback to offer stability and an integral effect to get rid of the offset error in the dq-frame. To reduce settling time under uncertain system conditions, an optimization problem based on linear matrix inequalities is solved to determine a set of robust stabilizing gains. Simulation and experimental results using a TMS320F28377D digital signal processor validate the proposed control performance under three control targets.