A Novel Five-leg Inverter PWM Technique for Two-Motor Centre-Driven Winders

Two three-phase motors can be controlled independently using a five-leg inverter as the supply, with one leg being common to both machines. Major shortcoming of this topology for general applications is the need to double the DC bus voltage in order to achieve the same speed control range as with the standard dual three-phase voltage source inverter (VSI) supply. Further, the semi-conductors of the common leg have to withstand up to twice the operating current of the other legs. This paper investigates use of the five-leg inverter topology for a specific constant-power two-motor centre-driven winder drive, where the listed drawbacks can be either fully avoided or at least reduced. A PWM method is developed, which enables control over how the available DC bus voltage is allocated to the two motors. This PWM technique, when used for two-motor winder control, enables operation without any increase in the required DC link voltage. The increase of the switch current rating in the common inverter leg can be kept at 50%, meaning that the five-leg topology enables a saving in the capital cost when compared to the standard dual three-phase topology.