Design and Testing of Reduced Order Adaptive VSG Control in a Three-Phase Four-Wire Standalone Microgrid

Isolated microgrids (MGs) have emerged as possible alternatives for power supply to the places without a utility grid. Standalone MGs often encounter several operational challenges, including the intermittent nature of solar generation, low system inertia, DC link voltage fluctuations, supply-demand imbalance, unpredictable behavior of power electronic converter switching, and the presence of non-linear/unbalanced loads. To conquer the above challenges, this work proposes a reduced order control structure for the voltage source converter (VSC), ensuring frequency and voltage regulation. In the proposed scheme, inverter's internal voltage is controlled collectively, through an adaptive virtual synchronous generator (VSG) and Q-V droop combined with a single controller. The moment of inertia and damping coefficient in the VSG are designed to be adaptive based on the variation in frequency and rate of change of frequency, using fuzzy logic rules. The performance of the proposed strategy is evaluated against the conventional VSG schemes, with constant and adaptive parameters, employed in conventional double loop control. Stability and sensitivity of the system with proposed single loop structure are ensured through small signal stability and sensitivity analysis for parametric uncertainties. The effectiveness of the proposed control scheme is verified through comprehensive MATLAB/Simulink simulations and also through a detailed comparative analysis with the existing VSG control schemes. Further, a controller hardware in the loop (CHIL) testbed, based on OPAL-RT and TMS320F28379D control card, is developed and efficacy of the proposed control technique is validated.