Robust Dual-Current Control of a Three-Phase Grid-Tied Inverter under Unbalanced Grid Voltage Using LMI Approach

In this paper, a robust dual-current control is proposed for a three-phase grid-tied inverter under unbalanced grid voltage. To compensate the unbalanced grid current rooted by the grid voltage dips or faults, an additional negative sequence compensator is considered in this proposed controller. The current control for both positive and negative sequence utilizes state feedback with integral control to archive fast reference tracking without steady-state error. The robust control gain is computed by solving a linear matrix inequality-based optimization problem to obtain fast convergence rate in the presence of the uncertainty of the system. The positive sequence current reference is used to regulate the amount of current flow from DC source to the grid, and the zero negative sequence reference is used to compensate the unbalanced grid current. To verify the efficacy of this control method, a comparison between the proposed robust dual-current control and robust current control without negative sequence compensator is conducted using simulation.