Adaptive droop control strategy for Flywheel Energy Storage Systems: A Power Hardware-in-the-Loop validation

Abstract

Low-inertia power systems can suffer from high rates of change of frequency during imbalances between the generation and the demand. Fast-reacting storage systems such as a Flywheel Energy Storage System (FESS) can help maintain the frequency by quickly reacting to frequency disturbances, with no concern over its lifetime. While a modern high-speed FESS has a significantly higher energy density than the conventional low-speed ones, the capacity of this storage technology is still limited. Therefore, this paper proposes a new adaptive droop controller for a FESS, considering the practical advantages and also limitations of this storage technology. The proposed controller increases the contribution of the FESS for frequency support during the first instances of a disturbance, while it reduces its output when the frequency is recovering. To verify the advantages of the proposed control strategy, the controller is implemented on a real 60 kW high-speed FESS using the concept of rapid control prototyping. Next, the performance of the FESS with the new controller is tested using Power Hardware-in-the-Loop simulations in a low-voltage microgrid. The PHIL simulation results show that the proposed adaptive controller improves the performance of the FESS in terms of limiting the frequency deviations, while preserving more energy in the FESS.