An alternator with field-form envelope control

Consideration is given to a method of waveform synthesis by changing the generated waveform envelope as an alternative to the more usual procedure in which the desired non-sinusoidal waveform is obtained by mixing selected constituent harmonics. A rotating machine is used and continuous variation of the shape of the generated waveform may be made with the machine in motion. A preliminary version of this apparatus has been constructed from a modified induction motor, but owing to the inherent heteropolar form of the magnetic circuit, this machine will synthesize only waveshapes containing the odd harmonic series. For convenience in observation and measurement a fundamental frequency of 50c/s has been selected for the prototype, but with suitable modification of the magnetic circuits, higher frequencies and also waveforms containing both odd and even harmonic series could be obtained.