A robust GPS-based control scheme for power sharing and quality improvement in microgrid

Frequency droop control is commonly used to maintain coordination and share load power among distributed generation (DG) units in microgrid (MG). While no communication links are required in conventional frequency droop control method, undesired frequency fluctuation and poor dynamic responses are inevitable. Recently, fresh control methods with fixed frequency operation and fast dynamics are widely reported based on global positioning system (GPS) synchronization technology. However, GPS based control methods are vulnerable to nonlinear or unbalanced loads due to low inertial essence. This paper presents a novel a robust H-infinity voltage control algorithm with angle droop scheme to address these concerns. The voltage controller design is specifically formulated on rotating reference frames in order to minimize the adverse impact of harmonics and negative-sequence disturbance caused by nonlinear and unbalanced loads. The adverse effects caused by parameter variation, model uncertainty and unmodelled dynamics are evaluated in H-infinity form and considered as a constraint in the optimization problemoptimal target to improve the robustness of the overall system. The controller optimization is then translated to H-infinity optimization problem and necessary conversions are executed to form a set of linear matrix inequality (LMI) conditions which can be conveniently solved with LMI theories. Eigenvalue analysis of a sample microgrid is conducted to investigate the stability margin and robustness of the voltage controller due to the variation of angle droop parameters. Theoretical interpretation and simulation results are presented to verify the efficacy of the proposed control algorithm. Hardware-in-the-Loop (HIL) experiments are conducted to further test and analyze the performance of the proposed controller in practical application situations.