Design of an adaptive frequency control for flywheel energy storage system based on model predictive control to suppress frequency fluctuations in microgrids

Frequency fluctuations are brought on by power imbalances between sources and loads in microgrid systems. The flywheel energy storage system (FESS) can mitigate the power imbalance and suppress frequency fluctuations. In this paper, an adaptive frequency control scheme for FESS based on model predictive control (MPC) is proposed to suppress the frequency fluctuation in microgrids. Firstly, a linear-fuzzy control is proposed and employed in a frequency regulation controller (FRC) to carry out adaptive frequency control according to the frequency fluctuation and the energy of the FESS, which improves the utilization rate of the FESS, and at the same time avoid the power oscillation caused by overcharging and over-discharging situations. Secondly, a voltage regulation controller (VRC) for dynamic power balance is designed to improve the speed of FESS power balance and suppress the large fluctuation of DC bus voltage. In addition, a MPC based on quadratic programming method is proposed to make the actual current quickly follow the reference current, speed up the power response, and respond to system changes in time through real-time feedback state variables to improve system stability. Finally, the stability of the proposed control system is verified by simulation and experiment.