A two-motor centre-driven winder drive with a reduced switch count

Industrial applications often require two (or more) variable speed electric drives, which have to be controlled independently. An example is a centre-driven two-motor winder, where ac machines are traditionally supplied from their individual three-phase voltage source inverters (VSIs). Over the past decade research efforts have been made to reduce the number of power electronic devices required in multi-motor drive systems in order to reduce the complexity and hence cost of the drive. One such configuration consists of two three-phase induction machines, supplied using a five-leg VSI, with one inverter leg being common to both machines. A PWM method for the five-leg VSI control, which enables an arbitrary distribution of the available dc link voltage between the two machines, has been recently developed and its suitability for application in a two-motor centre-driven winder has been demonstrated by simulation. This paper reports results of the practical realization of this drive system. In the first stage the two-motor drive supplied from a five-leg VSI is built and tested by performing the winder emulation experiments under no-load conditions. Suitability of the configuration for real winder system is thus demonstrated. In the second stage the complete two-motor centre-driven paper winder is built and results of the experimental testing are provided. The advantages of the analyzed solution over the standard one are also addressed.