Analysis of time and space harmonics in symmetrical multiphase induction motor drives by means of vector space decomposition

Abstract

The use of multiphase motor drives, i.e., with a phase number higher than three, is an increasingly important trend nowadays. The common procedure to analyze or to design the control algorithm for multiphase motors is to use a decoupling transformation method that transforms the model from the original phase-variable reference frame, where the electrical variables are cross-coupled, into a model decoupled in orthogonal subspaces. One of such transformations is the vector space decomposition (VSD), in which each variable is represented by a complex number called spatial vector. When the multiphase induction motor model is decoupled by means of the VSD, different types of subspaces are obtained. The main type of subspace is the one where there is coupling between the rotor and the stator, i.e., the electromechanical energy conversion happens. There are other types of subspaces in which there is no coupling between the stator and the rotor; these planes do not produce electromechanical energy conversion and their impedance can be very high (in case of homopolar components with isolated neutral points) or low.