Control Strategy for Flywheel Energy Storage Systems on a Three-Level Three-Phase Back-To-Back Converter

This paper studies the control structure for a flywheel energy storage system (FESS) used in the grid-connected applications. The power conversion structure uses a double conversion AC/AC through a three-phase thee level Neutral Point Clamp (NPC) inverter. The control structure allows a seamless connection of the FESS to the load and a simultaneous reduction of the current harmonic content to the load. A Fractional PI (FOPI) has been used to regulate the DC-link. Simulation results show excellent dynamic performance of the proposed control system, reducing both the DC-link voltage fluctuations and total harmonic distortion (THD) of the output currents.