Analysis of current waveforms in permanent-magnet synchronous/stepping motors and synthesis of a stabilising signal

A comprehensive analytical study is presented of the current waveforms of a hybrid permanent-magnet synchronous/stepping motor exhibiting dynamic instability. It is shown that, in the stepping-motor mode, the lower-modulation envelope of the total intake-current waveform is the source of a suitable stabilising signal. A low-cost stabilisation scheme is developed which utilises this signal to frequency-modulate the supply voltage. Stable operation in 10000 step/s, under conditions of significant torque loading, is demonstrated for a 200 step/revolution bifilar-wound stepping motor