Methods and verification of loss breakdown in an AC brushless PM soft magnetic composite machine

Improving the efficiency and power density of permanent magnet machines has been of growing interest because of the large potential energy and material savings. Accurate and reliable methods of loss separation are required to identify the most significant machine losses to target for reduction in order to increase the efficiency. Machines made with stators of soft magnetic composites can offer higher power density. However, in such machines, the proximity of the rotor and stator windings to the end-caps may elevate the induced eddy-currents in the endcaps, increasing the machine losses. This study investigates the losses of a 9 slot, 8 pole, 400 W, 3,000 rpm surface permanent magnet soft magnetic composite machine with a bonded rare-earth magnet ring rotor. Using a combination of analytical and finite-element modelling, and laboratory experimentation, the losses are characterised. The methods used to determine and separate the losses are described, and the results are then applied to prediction of the machine efficiency. The loss characterisation methodology presented in this paper can be used to analyse and hence improve the performance of other brushless permanent magnet machines.

I. Introduction

I N the past decades, permanent magnet (PM) machines have been of increasing interest because of their various advantages, including high efficiency, power density and power factor. These advantages are particularly important when high and variable speed operation in machines of smaller size and weight is desirable in some applications, such as in turbine generators and automotive propulsion [1]–[2]. Improving the efficiency of electric machines has also been of interest recently since higher energy efficiency classes for electric motors have been put in place by the International Electrotechnical Commission (IEC) [3].