A two-motor centre-driven winder drive fed by a five-leg voltage source inverter

Recent research has shown that it is possible to independently control two three-phase induction machines while supplying them via a single five-leg voltage source inverter (VSI). In such a two-motor drive system one phase of each motor is connected to a common inverter leg. Major shortcoming of this topology for general-purpose 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 VSI topology. Also, the semiconductors of the common leg have to withstand up to twice the operating current of the other inverter legs. This paper investigates the applicability of this topology for a specific constant-power two-motor drive of winder type, where these drawbacks can be to a large extent avoided. In particular, in two-motor centre-driven winders voltage requirements of two machines are hugely different during normal operation of the drive, so that the need for doubling the DC bus voltage does not take place. The current rating of the common leg does not need to be doubled either. Modelling of the centre-driven winder is summarised first. An appropriate PWM method for a two-motor drive with the common inverter leg is developed next, which allows control over how the available DC bus voltage is allocated to the two motors. Description of the five-leg inverter control scheme is further given. Detailed verification of the two-motor drive configuration is provided by simulating the operation of the centre-driven two-motor winder using the standard three-phase inverter topology and comparing the results with those obtained using the five-leg inverter configuration in conjunction with the developed PWM strategy.