Invertor-fed synchronous motors with induced excitation

Invertor-fed brushless synchronous motors are described, in which the harmonic content of typical invertor-supply waveforms is utilised to produce rotor excitation in wound rotors with shaft-mounted diodes. Particular attention is paid to a 3-phase star-connected rotor, connected to two diodes, and a salient-pole rotor with a single diode. Approximate analyses of synchronous performance are presented which provide a clear understanding of the special modes of operation of these systems, and results of full digital simulations are shown to be in excellent agreement with measured performance characteristics. Practical developments are reported which demonstrate the influence of design features, including saturation and skew, and which typify the high levels of performance attained with these motors.