E-Gear Functionality Based on Mechanical Relays in Permanent Magnet Synchronous Machines

Permanent magnet synchronous machines (PMSMs) are still the first choice for use in electric vehicles, due to their unparalleled efficiency and power density. However, they suffer from an inherently limited speed range. As field weakening or the addition of a mechanical gearbox deteriorates the efficiency of the drive, it is suggested in this paper to equip the drive with reconfiguration switches, giving rise to a so-called e-gear. The switches—which are implemented by means of mechanical relays—allow to change the winding connection of the electric machine from a series to a parallel connection and hence to double its efficient speed range. Simulations and experimental results on a 4-kW axial-flux PMSM confirm the feasibility of the concept and prove that the reconfiguration can be conducted in less than 35 ms.