An improved discharge control strategy with load current and rotor speed compensation for High-Speed Flywheel Energy Storage System

This paper proposes an improved discharge control strategy with load current and rotor speed compensation to suppress the fluctuation of DC bus voltage in High-speed Flywheel Energy Storage System (FESS). Mathematical model of FESS is built at first and conventional discharge control strategy with pure PI controller is analyzed. Then a load current and rotor speed compensation module is added to the outer DC bus voltage loop to recalculate the reference value of q-axis current with the DC bus voltage, load current, rotor speed and motor flux considered. In addition, feedforward decoupling strategy is utilized in the inner-current-loop to realize the independent control of the d-axis and q-axis currents. Simulation results with MATLAB/Simulink verify the proposed strategy improves the tracking capability of the d-q axis current, accelerates the DC bus voltage recovery speed and eliminates the fluctuation of the DC bus voltage caused by abrupt change of load current.