Split Rotor Concept for Permanent Magnet Electrical Machines

Abstract

This paper discusses a field weakening method for permanent magnet electrical machines. The proposed method can be an alternative to complex mechanical field weakening methods for safety critical applications. The developed concept is based on a split rotor in which a permanent magnet rotor is split into two parts to achieve two states of field excitation; either maximum flux output or the least flux output, depending on alignments between the rotor parts, having a degree of freedom to rotate on the shaft. The stator of the permanent magnet (PM) machine exposes two magnetic fluxes by the split rotor sections. Thus, the fixed nature of the PM excitation can be altered by this concept to achieve a wide speed range, which is a key concern in PM electrical machines at higher speeds. A number of 3D finite element (FE) simulations and a Simulink/Matlab model have been implemented to investigate the dynamic behavior of the system. Although it is challenging to computationally investigate the behavior of the split rotor at different operating conditions due to complex torque interactions, altering the relative angular position of the free-to-rotate rotor on a shaft, the proposed method might eliminate the complex implementation of mechanical field weakening apparatus for PM electrical machines. Thus, a PM machine with split rotor would be used over a wide speed range without excessive voltages at high speeds in fault tolerant aerospace applications.