Daiki Matsuhashi

Method for Evaluating the Eddy Current Loss of a Permanent Magnet in a PM Motor Driven by an Inverter Power Supply Using Coupled 2-D and 3-D Finite Element Analyses

To evaluate eddy current losses of permanent magnets (PMs) in motors driven by inverter power supplies in less computation time, we propose the coupled 2-D analysis of the motor and 3-D eddy current analysis of only the PM. In the proposed method, we carry out 2-D nonlinear magnetostatic analysis of the PM motor by rotating the rotor. We then perform 3-D eddy current analysis of only the PM using the temporally varying flux distributions in the PM obtained from the 2-D analysis. For 3-D eddy current analysis, we investigate methods that do and do not consider the compensation field generated by eddy currents. Moreover, for the case in which the compensation field is considered, we demonstrate the method of considering the reluctance of the motor core by the equivalent gap. Finally, we verify the proposed method by comparing results obtained using the proposed method and results obtained by full 3-D analysis for an interior PM motor. We show that the eddy current loss can be estimated in 1/15 of the computation time required for full 3-D analysis when the proposed method takes both the compensation field and the reluctance of motor core into account.

Coupled 2-D and 3-D Eddy Current Analyses for Evaluating Eddy Current Loss of a Permanent Magnet in Surface PM Motors

To evaluate the eddy current losses of permanent magnets (PMs) in interior PM (IPM) motors accurately within the practical CPU time, we have already proposed a scheme to carry out the 3-D eddy current analysis of only the PM using the temporally varying flux distribution obtained from the 2-D magnetostatic analysis of the motor. In the 3-D eddy current analysis, the compensation field Hc generated by the eddy currents in PM itself only is taken account of. Moreover, the reluctance of the motor except the PM obtained from the 2-D magnetostatic analysis is also taken into account by adding a uniform equivalent gap on the PM. The effectiveness of the coupled 2-D and 3-D analyses was shown using an actual IPM motor. In this paper, the coupled analyses are improved to apply to a surface PM (SPM) motor. Namely, the uniform equivalent gap is improved to a variable equivalent gap in space to take account of the space variation of the gap width between the PM and the stator core. Moreover, the 2-D magnetostatic analysis of the motor is replaced to the 2-D eddy current analysis to take account of not only the Hc by PM itself but also that by the neighboring PM. It is shown that the proposed coupled 2-D and 3-D eddy current analyses can improve the accuracies of the eddy current loss distribution in PMs of a SPM motor without increasing the CPU time.

Magnetic Field Analysis Using Voxel Modeling With Nonconforming Technique

To establish a large-scale magnetic field analysis, the magnetic field analysis with the voxel modeling is investigated. To reduce the number of elements, the nonconforming technique is introduced. The accuracy of flux densities, eddy current densities, and forces obtained from the nonconforming voxel modeling is verified by comparing with those obtained from the ordinary voxel modeling in a simple 2-D model. Moreover, the proposed method is applied to a 3-D eddy current model as well as to a 2-D nonlinear IPM motor model. It is shown that the results obtained from the proposed method sometimes converge to true values slowly, whereas it provides acceptable results.

Comparison study of various motors for EVs and the potentiality of a ferrite magnet motor

This paper presents a comparison study of various motors for application to an electric vehicle (EV) and the potentiality of a ferrite magnet motor as a candidate for rare-earth-less motor for an EV. The rotor shape of the proposed ferrite magnet motor is based on a spoke-type shape. Further, we developed two types of prototypes: one has a large magnetic torque equivalent to a conventional rare-earth permanent magnet motor for an equal volume, and another has a wide variable-speed range suitable for an EV.

Prototype and characteristics measurement of bearingless motor with wide air gap structure

Nowadays, more and more applications have been developed along with continuous research on magnetic suspension. In these applications, wide air gap structure always plays an important role. Therefore, bearingless motor with such structure which can provide large magnetic suspension force was proposed. This paper shows the experimental results of such bearingless motor based on a prototype model and high efficiency and stabilized transitional characteristic were specified.

Effects of Stress and Magnetostriction on Loss and Vibration Characteristics of Motor

A method of 3-D finite element magnetomechanical analysis is developed to investigate the effect of magnetostriction (MS) and stress on the core loss and vibration of motors. Shrink-fit stress calculation is carried out using static structural analysis and equivalent thermal force calculated by a novel method using the thermal stress tensor. A method of core loss calculation is proposed to take account of the 3-D stress in the core loss calculation. The methods are applied to the core loss and the vibration analysis of a permanent magnet motor. Numerical results show that the stator core loss increases significantly due to the shrink-fit stress. However, the radial velocity of the housing surface slightly decreases due to the MS and further decreases due to the shrink-fit stress because the MS increases under compressive stress.

Operational characteristics of an IPM-type bearingless motor with 2-pole motor windings and 4-pole suspension windings

A bearingless motor (BelM) integrates the characteristics of an electric motor and a magnetic bearing. Typically, a surface-mounted permanent magnet (SPM)-type BelM with a ring magnet magnetized in parallel is employed for high-speed operation. It is noteworthy that a carbon fiber bandage is needed to fix the ring magnet. However, when an SPM-type BelM is applied to a high-output motor, it becomes difficult to generate sufficient suspension force because of the wide magnetic gap arising from the carbon fiber bandage and the ring magnet. In addition, the manufacturing cost for the large-scale ring magnet and the carbon fiber bandage is high. Therefore, to realize a high-output and high-speed BelM at a low cost, we have focused on an interior permanent magnet (IPM)-type BelM with 2-pole motor windings and 4-pole suspension windings. Moreover, a rotor structure for suppressing suspension force ripple arising in the IPM-type BelM has been proposed based on three-dimensional finite element analysis. In this study, a prototype of the IPM-type BelM with the proposed rotor structure is produced. Experiments with this prototype show that the proposed rotor structure is effective in reducing suspension-force ripple. Additionally, the operational characteristics of the prototype are shown in detail.

Novel Structure of Three-Axis Active-Control-Type Magnetic Bearing for Reducing Rotor Iron Loss

Magnetic bearings (MBs) are useful for suspending the rotor shaft of a high-speed, high-output motor because they can do so without mechanical contact. In [2], we have proposed a three-axis active-control-type MB (3-axis AMB) with a cylindrical rotor whose diameter is equal to that of the rotor of a radial MB (RMB) or a motor. The proposed 3-axis AMB integrates an RMB and a thrust MB in one unit. However, the assembly of the conventional 3-axis AMB is complex, and the rotor iron loss is large. Thus, in order to simplify the assembly of the 3-axis AMB and to reduce rotor iron loss, this paper discusses a novel structure for the 3-axis AMB in which small auxiliary permanent magnets (PMs) are inserted in the radial winding slots. The suspension force and the rotor iron loss of the proposed device are evaluated by 3-D finite-element analysis in comparison with a 3-axis AMB without small auxiliary PMs.

Operational Characteristics of an IPM-Type Bearingless Motor With 2-Pole Motor Windings and 4-Pole Suspension Windings

A bearingless motor (BelM) integrates the characteristics of an electric motor and a magnetic bearing. Typically, a surface-mounted permanent magnet (SPM)-type BelM with a ring magnet magnetized in parallel is employed for high-speed operation. It is noteworthy that a carbon fiber bandage is needed to fix the ring magnet. However, when an SPM-type BelM is applied to a high-output motor, it becomes difficult to generate sufficient suspension force because of the wide magnetic gap arising from the carbon fiber bandage and the ring magnet. In addition, the manufacturing cost for the large-scale ring magnet and the carbon fiber bandage is high. Therefore, to realize a high-output and high-speed BelM at a low cost, we have focused on an interior permanent magnet (IPM)-type BelM with 2-pole motor windings and 4-pole suspension windings. Moreover, a rotor structure for suppressing suspension force ripple arising in the IPM-type BelM has been proposed based on a three-dimensional finite element analysis. In this study, a prototype of the IPM-type BelM with the proposed rotor structure is produced. Experiments with this prototype show that the proposed rotor structure is effective in reducing suspension-force ripple. Additionally, the operational characteristics of the prototype are shown in detail.

New technical trends on adjustable speed AC motor drives

Adjustable speed AC Motor drives have been used extensively in modern industry and transportation which calls for electrical and mechanical energy conversion with wide output power range applications. Because of its modularity and scalability, the drive system can be extended to many different application areas. More recently, adjustable speed AC motor drive applications are spreading not only in industry applications, but also sky and the marine. In this paper, after summarizing the history of adjustable speed AC motor drives and applications, the main issues of AC drive technologies are reviewed and investigated in the paper. Technical issues of adjustable speed AC motor drives including its standardization are surveyed and analyzed for more advancement. Finally, the paper provides the latest technical trends on adjustable speed AC motor drives technologies, and discusses the development of high speed high power PM motor.