On the Advantages of Symmetrical Over Asymmetrical Multiphase AC Drives With Even Phase Number Using Direct Controllers

Multiphase electric drives offer attractive advantages over conventional three-phase systems. Some of the benefits are shared by all multiphase configurations, but the performance can be highly affected by the specific location of the stator windings. While the asymmetrical configuration has been traditionally a popular choice, the symmetrical disposition in even-phase machines has a main advantage: it is possible to generate alpha-beta voltages without any contribution in different x-y subspaces. This article explains and demonstrates this feature for the general case of distributed-winding symmetrical n-phase machines, with it being an even number. Fortunately, direct controllers can benefit from this characteristic by exclusively selecting voltage states with only alpha-beta voltage production. To illustrate this capability, a finite-control-set model predictive control (FCS-MPC) using these special voltage states is also suggested in this work for symmetrical six-phase electric drives. This approach provides a greater simplicity and much less current distortion than in standard FCS-MPC for the asymmetrical configuration. Comparative experimental results confirm the minimal x-y injection of symmetrical configurations thanks to the proposed control actions (i.e., voltage states).