Brushless wound field synchronous machine with third-harmonic field excitation using a single inverter

This paper proposes an inverter scheme to generate an additional third-harmonic component alongside the fundamental component of the current. The generated third-harmonic component is used to achieve the brushless operation in a wound field synchronous machine (WFSM). Contrary to the traditional schemes used, i.e., dual inverter, single inverter with extra switches schemes, and single inverter with four transistor legs, the proposed scheme comprises a single inverter with three transistor legs that utilizes a modified third-harmonic injection pulse-width modulation. The brushless operation in WFSM requires two windings on the rotor periphery, i.e., harmonic winding and field winding that are interconnected through a rotating diode bridge rectifier. To maximize the usage of generated third-harmonic component, the selection of pole-slot combinations of the machine is carried out considering the winding factors. The proposed inverter scheme is verified in MATLAB, and a 2-D finite element analysis is used to validate the brushless operation of the machine along with its electromagnetic performance.