Optimal Damping Recovery Scheme for Droop-Controlled Inverter-Based Microgrids

Inverter-based microgrids may experience small-signal stability issues as the generation, loading or network topology change in real-time. This paper presents an event-triggered damping recovery scheme to improve the stability of a system with droop-controlled inverters and synchronous machines in the event of poorly damped power flows. The droop coefficients of the controllable inverters are manipulated in real-time based on their node sensitivities so as to obtain the maximum damping effort per unit additional power injected. This prevents the overloading of any one inverter or group of inverters in the system and reduces the power sharing disparity that arises from the damping recovery process. For determining the node sensitivities, a novel damping sensitivity formula is presented as an alternative to conventional sensitivity analysis. This enables the reduction of computation complexity from O(n^3) to O(n), making the proposed algorithm scalable to large systems. Experimental and simulation case studies are presented to demonstrate the effectiveness of the proposed control scheme in restoring damping, as well as its robustness to communication failure.