Fast Frequency Regulation of Virtual Power Plants Via Droop Reset Integral Control

We consider the frequency regulation problem for a Virtual Power Plant (VPP) consisting of inverter-interfaced distributed energy resources connected to a power grid, modelled macroscopically, by a conventional generator connected to multiple time-varying loads. To improve the transient performance (settling time, overshoot, etc.) of the frequency response under load disturbances, we introduce a novel Droop Reset Integral Control (DRIC) law that synergistically combines resetting integrators with integral droop controllers (also referred to as proportional integral (PI) control in the literature). We prove the stability of the proposed control scheme, and its robustness to external disturbances, using conditions based on Linear matrix inequalities (LMI) that can be numerically verified a priori. Furthermore, we validate the proposed approach using both learned voltage source inverter dynamics and a high-fidelity Simscape model developed by Sandia National Laboratories. Our results show that the DRIC algorithm is able to significantly reduce overshoot, induce zero steady-state error, and decrease settling times up to $7$ times that of standard droop and PI control. We also provide heuristic tuning guidelines for the proposed controller, which can be particularly useful for system operators whenever a detailed model of the virtual power plant is unavailable.