PWM Control of a Dual Inverter Drive Using an Open-Ended Winding Induction Motor

A dual pwm inverter drive operating an open-winding induction motor can be an attractive motor-drive system when operated from a dc battery source. Operating one of the inverters using a floating dc-link capacitor provides two main functions: reactive voltage support for the main bridge connected to the dc battery voltage source; voltage boosting to increase the motor terminal voltage. The latter feature eliminates the requirement to use a separate dc-dc converter to provide a voltage boost. The resultant drive system can provide several benefits such as: lowering the average battery current by operating the main bridge at unity power factor; improving the motor torque and efficiency over a wide operating speed range; compensation for battery voltage fluctuations; lowering the motor harmonic losses; elimination of common-mode circulating currents. This paper describes a pwm control scheme for the two inverters to regulate the floating bridge capacitor voltage over the entire dynamic speed range of the motor, whilst also providing the desired motor demand voltage. Experimental results are used to verify both the operation of the motor-drive system and the regulation of the floating capacitor voltage. Experimental results using an induction motor load confirm the practical feasibility of the motor-drive system.