This paper presents a basic design method for the surface-mounted permanent magnet synchronous motor (SPMSM) for both distributed and concentrated windings. The design is based on the air-gap magnetic flux density distribution focusing on the image magnetic pole. The calculus equation of the air-gap magnetic flux density distribution is analytically derived by supposing the magnetic pole is located on the magnet surface and image planes. In this study, a three-phase and double-layer stator winding SPMSM that has a linear demagnetizing characteristic magnet, such as a ferrite or rare-earth magnet is considered. From the required specifications and design conditions, the design target values of the parameters that appear in the voltages equations of the d-q axis coordinate system are calculated. Then, the relational equations for the torque constant, d-axis inductance, copper loss, and the maximum current density are presented as a function of three design parameters under i_d=0 control. They are the stator stack length, the number of coil turns in series in a phase, and the slot bottom length. Hence, this approach reduces the SPMSM basic design to the problem with these design parameters has to be solved. The proposed method makes it possible to address the concentrated winding as a special case of the distributed winding. The FEA results confirm the validity of the proposed basic design method for both distributed and concentrated windings.

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A reluctance network analysis (RNA), which is an improved magnetic circuit method, has some advantages: the analytical model is simple, the calculation accuracy is relatively high, and a coupled analysis with an electric circuit, a heat circuit, a motion equation, etc. is fundamentally easy. The RNA has been applied to the dynamic analysis of several motors such as a surface permanent magnet (SPM) motor, an interior permanent magnet (IPM) motor, and a switched reluctance (SR) motor. The dynamic characteristics of these motors including starting and a sudden load change can be calculated by an RNA. However, the torque calculation methods for these motors are different from each other. This paper presents a unified calculation method for the motor torque in an RNA, which does not depend on the types and structures of motors. The validity and availability of the proposed method are demonstrated by a finite element method (FEM) and an experiment.

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This paper presents a novel type of flux-modulating synchronous machine (FMSM) in which permanent magnets (PMs) are embedded in the stator back-iron. The rotor has neither windings nor PMs. A prototype machine with an outer-rotor configuration was designed and manufactured to validate the operating principle of the FMSM. The characteristics in the motor mode of the prototype machine were also investigated with a vector control system. The results of the investigations show that, as in surface-mounted PM motors, the torque of the FMSM is predominantly generated by the PM flux and can be controlled using the armature current.

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This paper proposes a novel variable flux reluctance motor without DC-field coils. The stator of this motor has only armature coils. The proposed motor can control the torque-speed characteristics by increasing or decreasing the field voltage that is superimposed on the armature currents. In this paper, the operational principle of the motor is described, and the N-T characteristics are computed by finite element analysis under vector control. In addition, the N-T characteristics are compared with a conventional variable flux reluctance machine with armature and DC-field coils.

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We propose a novel variable-field motor with toroidal windings to achieve both miniaturization and high efficiency. The proposed motor is characterized by a structure that uses a three-dimensional (3D) magnetic flux to increase the number of torque-generation faces. The 3D structure has prevented an increase of the motor volume due to the addition of the variable field. We investigated the principle of variable field by finite element analyses and experiments. We verified that the induced voltage and the torque can be changed by changing the direct current in the field-excitation winding. Moreover, the efficiency can be improved by changing the direct current.

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This paper presents a novel single-phase switched reluctance motor (SRM) that can be directly driven by a commercial AC power supply without any switching circuit and sensor. This proposed SRM is optimized based on a simple design technique. The optimized machine has higher motor efficiency compared with conventional induction motors. In addition, the novel SRM can start-up with direct commercial AC power supply. In this paper, the performance of the prototype single-phase SRM is verified through simulations and experiments.

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A magnetic gear has advantages with respect to noise and maintainability, and the so-called PM (Permanent Magnet) magnetic gear has been studied, which consists of two magnet rotors and a ferromagnetic pole-piece rotor. In this study, we research a novel magnetic gear that we call a VR (Variable Reluctance) magnetic gear. It consists of a magnet rotor and two ferromagnetic pole-piece rotors to improve its performance. First, we describe the operating principle and compare the charactericstics of the VR magnetic gear with those of the PM magnetic gear by using a finite element analysis. Next, we prototype a VR magnetic gear and demonstrate its validity by experiment.

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The electrical steel sheets of motors are often stamped with dies in order to raise productivity. The magnetic characteristics of electrical steel sheets under the strained and stressed conditions due to stamping are known to be inferior to those under normal conditions. In this paper, we propose an accurate finite-element analysis for estimating motor characteristics that focuses on elasto-plastic deformation in the magnetic core. The calculated results were compared with observations of a rectangular test piece in order to validate the methods. Based on the results, the method that considers the maximum principal stress is suitable rather than the method that considers the von Mises stress. This is because the maximum principal stress can be used to distinguish the magnetic properties under compressive stress from the properties under tensile stress. In addition, the proposed method is applicable to motor analysis. The cogging torque waveform and iron loss differ depending on the strain and stress distribution in the magnetic core when the stator core of the motor is stamped out from electric steel sheets with a die.

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A closed-loop control system is commonly used in electromagnetic actuators to ensure operating performance. However, this system frequently leads to high costs. We developed a swing electromagnetic actuator with an integrated eddy current brake to reduce the operating time and improve the stopping accuracy. The developed actuator is a three-position cylindrical actuator moving within a ±120-degree angle without closed-loop control. The rotor is composed of a bulk and thin metal laminations and the stator has three sets of pairs of coils. The rotor is stopped at an intermediate position by magnetic force generated by the coils. This paper describes the electromagnetic design and its evaluation by using an FEM simulation to predict its operating characteristics and measure its performance on a test bench. The superiority of our actuator design is verified by comparing these measurements. The operating time is reduced to one-sixth of that of a laminated rotor and the over-travel is compressed to zero. In addition, this actuator has the advantage that it is electrically robust against variations in the power supply.

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This paper proposes a torque control method for interior permanent magnetic synchronous motors (IPMSMs). The proposed method controls the voltage amplitude and phase based on a new n-t coordinate system. The t-axis is a tangent line of a constant voltage ellipse, and the n-axis is a normal line of the ellipse. On the n-t coordinate system, the n-axis current is not affected by the voltage phase. The n-axis current is utilized to reduce the mutual coupling between the voltage amplitude controller and phase controller. The proposed method realizes a high torque response for the linear range and over-modulation range of the inverter, including six-step mode. The effectiveness of the proposed method was verified by simulation and experimental results.

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Fractional-slot windings are widely used in rotating machines in order to improve the output voltage waveform, increase the design flexibility, and gain many other advantages. However, fractional-slot windings are known to produce different harmonic components such as an even order and/or fractional number of space flux harmonics compared to integral-slot windings. These harmonics may increase stray losses and cause stator core vibration.  This paper describes an analysis of space flux harmonics and proposes new winding methods such as “novel interspersed windings” to reduce these harmonic components. The proposed winding methods were verified by numerical analysis and model tests.

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