A robust control strategy for a grid-connected multi-bus microgrid under unbalanced load conditions

The increasing presence of inverter-based distributed generation (DG) units in microgrid application requires control methods that achieve high performance not only during normal operating conditions, but also under unbalanced conditions. These conditions can occur permanently due to distribution of unbalanced loads on the three phases of the microgrid. This paper proposes a robust control strategy for a grid-connected multi-bus microgrid containing several inverter-based DG units. Each of the DG units can supply a combination of balanced and unbalanced local loads. The proposed control strategy employs an adaptive Lyapunov function based control scheme to directly compensate the negative-sequence current components caused by unbalanced loads in some part of microgrid; and a sliding mode based control scheme to directly regulate the positive-sequence active and reactive power injected by DG units to the microgrid. The control method proposed in this paper is shown to be robust and stable under load disturbances and microgrid parameter uncertainties even in the presence of nonlinear and timevariant unbalanced loads. The effectiveness of the presented controller is validated through time-domain simulation studies, under the MATLAB/Simulink software environment. (C) 2015 Elsevier Ltd. All rights reserved.