A 2-kW, 6.78-MHz, Capacitive Power Transfer and Position Resolver System for Synchronous Machine Rotor Excitation

Wound field synchronous machines (WFSMs) are power dense, have outstanding field weakening performance, and avoid rare-earth (RE) element market volatility; these are important for electric vehicle traction applications. Current research focuses on reducing the cost and complexity of the brushless rotor excitation system while maintaining performance and efficiency. This article presents the design of a series resonant capacitive power transfer (CPT) mechanism combined with a capacitive position resolver to reduce the drive system cost. The resolver is integrated within the printed circuit board (PCB)-based capacitive coupler and uses the main power pathway for its carrier signal. A 6.78-MHz industrial, scientific, medical (ISM) band GaN inverter designed with analytical and FEA techniques drives the system. Measurements demonstrate up to 2.3-kW peak power transfer to the field windings at >88% efficiency, while the unfiltered resolver gives the shaft position with a maximum error of ±10° or 2.8% out of 360°. The fully integrated system is shown to be compact with a minimal parts count.