Medium voltage flywheel energy storage system employing dual three-phase induction machine with machine-side series-connected converters

Flywheels as energy storage systems are good candidates for numerous power system applications such as voltage support, serving fluctuating loads, frequency regulation and renewable energy utilization. Most of these applications utilize flywheel energy storage systems (FESSs) at medium voltage ranges. This paper discusses the optimization of the medium voltage high power converters interfacing the FESS with the grid. A dual three phase induction machine (IM) is proposed to drive the flywheel and is controlled via two series-connected three phase voltage source front end converters (VSCs). The proposed configuration is believed to reduce the converters ratings by a half compared to the conventional configuration where three-phase IM with single three-phase VSC is employed. The machine modelling and control are presented, in addition to converters DC links balancing technique. The performance of the proposed system is verified via simulation using MATLAB/Simulink.