Concentrated winding axial flux permanent magnet motor with plastic bonded magnets and sintered segmented magnets

Abstract

Direct drive axial flux permanent magnet (PM) motors are a cost effective and an energy saving choice for industrial use. Open slots make concentrated winding machines a favourable configuration with respect to manufacturing. However, open slots expose rotor surface magnets to large flux pulsations and the losses of sintered magnets may not be neglected. Plastic bonded magnets have very low eddy current losses but other magnetic properties of such magnet materials are not satisfactory at the moment. Divided sintered neodymium iron boron (NdFeB) may be used instead but the magnet configuration must be carefully analyzed to attain an acceptable eddy current losses level in the magnets. This paper addresses permanent magnet rotor constructions, which eliminate or remarkably reduce eddy-current losses in the magnets of a 2500 min-1 / 3000 min-1, 37 kW permanent magnet synchronous motor with concentrated windings. Different magnet materials, such as plastic-bonded Neo-magnets and sintered segmented NdFeB-magnets are evaluated. Also a prototype motor with plastic bonded magnets has been built. Analytical Matlabtrade- and finite-element-method-based (Flux2D/3Dtrade by Cedrat) programs are used in the calculations. The permanent magnets should be segmented into many small sections in the Machine which the flux pulsations in the magnets are high.