Brushless Excitation for Wound-field Synchronous Machines using Multi-harmonic Windings

Wound-field synchronous machines (WFSM) are promising alternatives to electric machines with permanent magnets (PM). The ability to control the rotor field in these machines makes them well-suited to safety-critical applications, while the absence of rare-earth permanent magnets makes these machines sustainable. The WFSM rotor excitation schemes have traditionally used carbon brushes, which significantly reduces the reliability of these machines, limiting their widespread adoption. To overcome this limitation and improve the reliability of WFSMs, several brushless rotor excitation schemes have been developed. However, most of these systems require additional windings or dedicated power electronics, making them expensive and limiting achievable power density. In this paper a brushless excitation scheme is proposed based on a multiphase, multiharmonic stator winding. This winding can independently control two sets of spatial harmonics in the airgap of the machine: the first to create torque and the second to wirelessly transfer power to the rotor to excite it. Two windings are designed, and their performance is evaluated using FEA simulations.