Novel Brushless Wound Rotor Synchronous Machine With Zero-Sequence Third-Harmonic Field Excitation

This paper introduces a novel topology for generating a spatial third-harmonic current component to excite the rotor field winding of a wound rotor synchronous machine to achieve brushless operation. In this topology, each of the three-phase windings on the stator is connected with a switch in parallel. In particular, two antiparallel thyristors are used to switch during positive and negative half cycles. Two windings are mounted on the rotor of the machine: 1) the harmonic winding and 2) the field winding. Zero-sequence currents are generated, when the switches are closed near zero crossing for a short time interval. Consecutive operation of the switches creates an additional spatial third-harmonic current pulsating in the stator winding. The number of poles of the stator winding and the field winding is the same (four-poles in this case) to intercept the torque generation component of the air-gap flux, whereas, the number of poles of the harmonic windings is adjusted (12-poles in this case) to intercept the harmonic component of the air-gap flux and develop voltage across the harmonic windings. Harmonic voltage is rectified through a rotating rectifier to feed dc current to the field windings. Results verify the proposed topology simulated by a 2-D finite-element method.