Comparison of 2D and 3D FEM analysis of the magnetic field in a PM servo motor

Nowadays, the applications of the electrical machines with permanent magnets become very common, because of the outstanding properties of these devices in comparison with the induction machines. PM machines do not indicate electrical losses with the field excitation, which means increasing of their efficiency. This is a very important factor considering the urgent need of the energy conservation. Although, numerical methods for a field computation are time consuming, they provide accurate results without making any simplification of the geometry. The paper presents a comparison of 2D and 3D magnetic analysis of a PM servo motor. The analyzed servo motor is designed with a surface magnet rotor and produced by the VUES Brno company. The applied PM material is of rare earth type NdFeB. This material is characterized by a very high energy product. 2D model of this servo motor is created using AutoCAD program. The 2D magnetic analysis is computed using FEMM (finite element method magnetics). The 3D magnetic analysis is computed using a modem technique in the field of magnetic analysis of electrical machines. 3D model of the servo motor is generated using RMxprt program. The 3D magnetic analysis of the generated 3D model is computed using Maxwell 3D program. The program Maxwell 3D generates fine mesh automatically with a high accuracy. The distribution of the magnetic field inside the servo motor is computed for the case of the nominal current in both of 2D and 3D magnetic analysis. The distribution of the magnetic flux density according to the air gap length is presented too. The FEM (finite element method) is used for both 2D and 3D magnetic analysis of this servo motor.