Computation and measurements of the DC link current in six-phase voltage source PWM inverters for AC motor drives

Multiphase AC motor drives (with more than three phases) have some potential advantages as widely discussed in the literature. The DC-link capacitor size depends on the current RMS value, in particular, if the drive is supplied by a DC source, the current requested to the capacitor is basically determined by inverter input current AC component. The analytical computation of the capacitor current RMS value in the DC link of a voltage source PWM inverter, driving an induction motor, is extended from the common 3-phase systems to multiphase systems in general. In particular the six-phase-double star case has been analyzed in detail. The consistency of the analytical results have been tested through digital simulations. Furthermore, a 6-phase voltage source PWM inverter prototype has been designed and built to supply a multiphase induction motor drive: the experimental results confirm the validity of the mathematical/simulation approach.