Capacitance Energy Control for FESSs: Tracking Performance Analysis and Robust Design Against Variations of Speed, Load and Capacitance

This paper focuses on the dc voltage control based on capacitance energy (E C ) for a flywheel energy storage system (FESS) with the permanent magnet synchronous machine (PMSM) as the energy transformation device. For EC - based PI controller, performance degradation occurs due to the rapid speed change, potential dc-side load step and parameter mismatch. To address this, system properties containing stability, tracking performance and robustness against the aforementioned factors are revealed for E C -based dc voltage control methods. It is derived through illustrations of dominant poles and maximal magnitudes with respect to speed, capacitance and coefficients. Moreover, a linear-tracking-differentiator-based energy controller (LTDEC) is presented to achieve fast tracking performance and foregoing robustness of dc voltage. It includes proportional control for direct feedback of E C and feedforward of speed and indirectly calculated total consumed power. A selection region for coefficients of LTDEC is designed to enhance stability, tracking performance and robustness. Experiments have verified the effectiveness of the proposed control method and designed coefficient selection region.