Low-Speed Drive of PWM-VSI-Fed Brushless Self-Excited Synchronous Motor

The brushless self-excited synchronous motor with halfwave rectified field circuits has been invented already by Nonaka. For the low-speed drive of the motor a new method of the voltage supply which superimposes a higher-order harmonic component on sinusoidal low-frequency voltage by a pulsewidth modulated (PWM) GTO inverter is presented. The amplitude and frequency of the fundamental component and those of the harmonic component are controlled independently by a microcomputer-based PWM strategy. It is confirmed from the experimental results that controllable brushless self-excitation and smooth low-speed operation without torque pulsation are achieved by the proposed scheme.