DC-Bus Voltage Control for FESSs With Capacitor Energy Regulation and Tracking Differentiator

This article focuses on improving dc-bus voltage response performances in a permanent magnet synchronous machine (PMSM)-based flywheel energy storage system (FESS) facing with a rapid variation of speed, sudden change on dc-side load, and capacitance mismatch by proposing a tracking-differentiator-based energy indirect controller (TDEIC) and designing its coefficient selection region. Two parts constitute the proposed method: proportional control of capacitor energy estimation and feedforward compensation of consumed power estimation and speed. And these estimations are obtained via linear tracking differentiators. Besides, the boundaries of the designed coefficient region are derived through analyses of tracking performance, disturbance attenuation capacity for load variation, and robustness against capacitance variation. And these analyses are done via quasi-4-D illustrations of dominant poles, damping ratios, and maximal magnitudes. A simple control structure and robustness against variations of speed, load, and capacitance are, thus, achieved. The number of adjustable coefficients is only 2. Further, the following advantages are also ensured: fast response time, basic no influence on final voltage of speed variation, low voltage fluctuation under load step, and considerate small change on this fluctuation under capacitance mismatch. Finally, the effectiveness of the proposed scheme and coefficient selection region is validated experimentally.