System-Level Optimization of Flux-Switching Machines With Multiple Excitation Sources in a Long-Term Flywheel Energy Storage System

This paper presents the optimization of a LongTerm Flywheel Energy Storage System (LT-FESS) whose electromechanical converter is a Flux-Switching Machine (FSM). Three topologies of FSM that differ with their excitation source are investigated: the Permanent Magnet FSM (PM-FSM), Wound-Field FSM (WF-FSM) and the Hybrid-Excited FSM (HEFSM). The design parameters of the machines, as well as those of the power electronics and of the rotor of a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10 k W$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10 k W h$</tex> LTFESS, are optimized according to energy and economic metrics. The maximization of the energy efficiency of storage cycles of increasing storage durations shows that the HE-FSM is the bestsuited topology for intermediate storage durations with energy efficiencies above 70 % for storage cycles shorter than 7 hours. Beyond, the WF-FSM becomes more efficient thanks to its lower idling losses. The PM-FSM is never observed as the best-suited topology regardless of the storage duration.