Nine-Phase Six-Terminal Induction Machine Modeling Using Vector Space Decomposition

The nine-phase six-terminal induction machine (IM) has been recently proposed as a promising contender to the conventional asymmetrical six-phase type in terms of torque density, stator winding simplicity, and fault-tolerant capability. The stator is composed of nine phases, which are connected in a fashion to only provide six stator terminals. Therefore, this connection combines the high performance of a nine-phase winding with the terminal behavior of a six-phase machine. This paper introduces the machine mathematical model based on the vector space decomposition (VSD) modeling approach. The required current and voltage sequence transformation matrices are derived such that the machine is mathematically regarded as an equivalent six-phase IM with only three decoupled subspaces. This way, the same VSD-based controller structures conventionally applied to six-phase-based systems can be preserved. A 1.5-hp prototype IM is used to experimentally validate the machine model under both healthy and open-phase conditions.

I. Introduction

The growing demand for high fault-tolerant capability in modern drive systems has, in turn, provoked the upward proliferation of multiphase machines in many industrial applications. Considerable effort has, therefore, been devoted in the literature to investigate different types of multiphase machines [1]. Multiphase machines with multiple three-phase winding sets have demonstrated their attractiveness, especially in high-power drives and multimegawatt wind energy conversion systems [2]. Standard three-phase converters can still be used to supply these machines.