PWM switching strategies for current-fed inverter drives

Quasi-square-wave current-fed inverter drives suffer from low-speed torque pulsations, which can cause mechanical resonances and speed ripple problems. Attempts to minimise these problems, using PWM switching strategies based on harmonic elimination techniques, have been reported. It is shown that these PWM switching strategies are based on unnecessarily restrictive modulation rules, and that these rules may be relaxed to allow more versatile PWM switching strategies to be used to improve system performance. New, more flexible, modulation rules are presented, based on the duality relationship which exists between the PWM voltage-fed inverter and the PWM current-fed inverter. These new modulation rules are confirmed using practical results obtained from an experimental microprocessor-based PWM current-fed inverter drive.