Study on Optimum Design of Multi-Pole Interior Permanent Magnet Motor with Concentrated Windings: —Motor Volume Minimization of IPM Motor for Low-Speed, High Torque Applications—@@@—低速大トルク用途への小型最適化—

Because of the high torque density and high efficiency, the Permanent Magnet (PM) motors having rare-earth magnet are widely used in many industrial applications. Among various types of the PM motors, the multi-pole PM motor with similar slot and pole numbers and concentrated windings is promising as a low-speed, high torque motor. Moreover, the buried magnet rotor structure will make the motors more attractive from the standpoints of higher torque density and efficiency. However, unlike the traditional surface PM motors, the Interior PM (IPM) motors has a complex magnetic circuit for analysis, which makes it difficult to design the optimum motor dimensions for the given requirements. Since the Finite Element Analysis (FEA) has enabled easy and accurate analysis of all nonlinear magnetic properties in terms of flux density and torque in the motors, FEA is commonly used in the IPM motor design. However, it is still difficult to apply FEA for the repeated-calculation required to obtain fitness evaluation in the computer aided design approaches because of long CPU times. This paper presents a simple non-linear magnetic analysis for an IPM motor as a preliminary design tool of FEA. The proposed analysis consists of the geometric-flux-tube-based equivalentmagneticcircuit model. Fig. 1 shows the equivalent magnetic circuit for the IPM motor. In the model, the magnet is assumed as an ideal mmf source and the notations Hmh, Hm are the mmf of magnet. The concentrated winding is used and the notation NI is the mmf of the stator winding. Most parts of the core in the motor are represented by the corresponding saturable permeances. Py is saturble permeance in the stator yoke. PS is the saturable permeance in the stator pole trunk. PaA ∼ PaD, PbA ∼ PbD, PiA and PiB are the saturable tip permeances in the pointed end of the stator poles for considering the local magnetic saturation. PtA and PtB are the stator pole horn permeances. On the other hand, Pr1 ∼ Pr4, Pb and PR are the saturable permeances in the magnet retaining bridge. All saturable permeances are determined by solving the equivalent magnetic circuit while considering the magnetic non-linearity of the core under the given winding excitation. As a result, the proposed analysis is capable of calculating the flux distribution and the torque characteristics in the presence of magnetic saturation. To verify the accuracy of the proposed analysis, the calculated flux-linkage distributions and maximum torque vs. current characteristics of test motor are shown in Figs. 2 and 3, respectively. As shown in Figs. 2 and 3, the analytical results of the proposed analysis are in good agreement with those of the FEA. In addition, the required computational time per step in 2D-FEA is 9.63 minutes, whereas in the proposed non-linear magnetic analysis it is 1.1 seconds using the same PC. Despite employing the reasonable mesh configuration in 2D-FEA, the proposed analysis shows the significant reduce in the computational time by 1/500. Therefore, the proposed analysis is very useful for the preliminary design tool of FEA. Moreover, the proposed analysis-based optimum design is examined, by which the minimization of motor volume is realized while satisfying the maximum torque for target applications.