Filter Deballasting Control of Droop-Controlled Inverters

In microgrids with droop-controlled inverters, the supervisory controller must the tune the droop gains in real time to maintain stability as the system topology or the number of inverters change. Stability could be compromised due to delays in the dispatch of supervisory control inputs or due to communication link failures. This article proposes a filter deballasting control (FDC) method for maintaining stability in the interim period until the supervisory inputs become available. FDC employs a quasi-open-loop control structure to leverage the inductance of the LC filter as a stability ballast, which under normal operation does not contribute to the dynamic behavior of the system. To further improve the stability, a lead-lag compensator is implemented to compensate the lagging dynamics of the deballasted system. The proposed method does not affect the steady-state active and reactive power share of the inverters, enabling a smooth transition between the conventional and FDC operating modes. The effectiveness of the proposed control strategy is verified through theoretical and experimental means.