Virtual Power Injection for Optimal Adjustment of Droop-Controlled Inverters

As the penetration of inverter-based renewable energy sources increases, maintaining grid stability with a satisfactory frequency response will become more challenging. This needs to be addressed in order to maintain resilience to system disturbances while having desirable steady-state behavior. Among a variety of solutions proposed to compensate for the loss of system inertia, re-design of controllers could be very cost effective in mitigating the anticipated frequency deviations in the event of system disturbances. This paper proposes a novel method to virtually emulate inertial power compensation by modulating the behavior of a droop-controlled inverter. This is accomplished by adding a static output feedback controller to an otherwise conventionally droop-controlled voltage source inverter. This method provides additional degrees of freedom to optimize the primary response of a droop-controlled inverter to minimize the worst-case frequency deviation in the event of a sudden power loss. The design has been tested on a 14-bus and 24-bus power system to demonstrate that the proposed droop adjustment can substantially reduce the effect of sudden power imbalances on frequency response with a minimal increase in the energy cost.