Novel modular and retractable permanent magnet motor/generator for flywheel applications with reduced iron losses in stand-by mode

The no-load losses represent one of the most important problems for flywheels energy storage systems (FESS) which produce electrical energy from the kinetic energy stored with long waiting times between charging and discharging. This study presents a novel modular stator for use in synchronous permanent magnet (PM) electrical machine coupled to a FESS. The modular stator includes several sections of retractable yoke stator, displaceable in the radial direction. Each stator segment is composed of several coils, teeth and its corresponding back iron section. A removable back iron yoke stator allows reducing the iron losses in the ferromagnetic core of the PM motor/generator during stand-by operation mode in FESS. In stand-by mode, with the stator in a retracted position, the iron losses are reduced up to 95% when the air gap length is increased 20 mm.