The insulation and magnetic properties of epoxy composed of pure iron powders were studied as a function of iron powder volume fraction (R_Fe) in the range of 0-70vol% to achieve a good balance between the insulation and magnetic properties. Frequency-dependent impedance measurement revealed that the relative permittivity, ε_r', at 10kHz increased from 4.2 to 278.4 with increasing R_Fe up to 50vol%. The loss factor, ε_r”, increased from 0.2 to 86.1 and the electric conductivity, σ, increased from 9.9 × 10^-8S/m to 4.8 × 10^-5S/m at 10kHz with increasing R_Fe up to 50vol%. The dependence of σ on R_Fe was explained by the equivalent serial capacitor-resistor (CR) connection model. The initial maximum relative permeability, μ_{r_max}, increased from 3.7 to 8.9 with increasing R_Fe up to 70vol%. These data were compared with those for the “Reference” sample which has been in practical use in industrial electric machine applications.

Magnetic-geared motors (MGMs) have attracted attention owing to their ability to offer higher torque densities than conventional permanent magnet (PM) motors. An MGM consist of a magnetic gear (MG) part and a PM motor part, which are shared one high-speed-rotor (HSR). An interior permanent magnet (IPM) type and a surface permanent magnet (SPM) type has been proposed as a structure of HSR. In the IPM-type HSR, the PM motor part and MG part are magnetically coupled to each other, which is called a magnetic interaction. However, the torque equation considering this magnetic interaction has not been studied thus far. This paper presents the torque equation of an IPM-type MGM (IPM-MGM). The torque equation considering the magnetic interaction is derived based on the proposed vector diagram, and the parameter identification is conducted by using a two-dimensional finite element method. Moreover, the validity of the torque equation is proved through comparison with experimental results.

This study proposes a novel approach that employs the kernel method as a regression model to demonstrate the dependency of magnet flux linkage on the applied current, which is suitable for magnet temperature estimation. This model can estimate the flux linkage with a mean relative error of less than 2% in comparison with that obtained using finite element analysis. The magnet temperature is estimated by comparing the magnet flux linkage under loading conditions with the values obtained from the regression models built under fixed temperatures. The accuracy of the results obtained using the magnet temperature estimation method is approximately the same as that of the results obtained using the look-up table, suggesting that the proposed approach is suitable for non-linear motor property modeling.

Recently, high-efficiency permanent magnet synchronous motors (PMSMs) have been used in various fields as the performances of permanent magnets have improved rapidly. PMSM position sensorless control based on high-frequency (HF) voltage injection is investigated herein, where the HF voltage is injected into the fundamental voltage. The HF current response, which includes information on the rotor position, is used for position estimation. There are two problems with this approach: the control becomes unstable as the speed increases and estimated position errors occur under load condition. The study considers the impact of speed and load on position estimation. Based on the consideration, a speed independent detection of HF current amplitude and estimated position error compensations under load condition are proposed. Further, an estimated position error compensation method is proposed by considering the impact of speed and load. Finally, experiments are conducted with an interior PMSM to demonstrate the validity of the proposed methods.

Magnetic gears have beneficial features such as low vibration and maintenance-free owing to no mechanical contacts. Among the several types of the magnetic gears, a flux-modulated type magnetic gear has a higher torque density than the other types. Thus, it is expected to be put into practical use. Previous studies have verified that an interior permanent magnet (IPM) structure rotor can reduce the eddy current loss in magnets. In this study, IPM rotor structures proper to a flux-modulated type axial-flux magnetic gear (AFMG) were investigated. Two types of IPM low-speed rotor structures, one is a spoke-shape and the other is a segment-shape, were compared in terms of torque and efficiency. Furthermore, to prove the validity of the proposed rotor structure, prototype tests were conducted.

Flywheel energy storage systems (FESSs) store kinetic energy corresponding to the rotation of an object as Jω²/2, where J is the moment of inertia, and ω is the angular rotation speed. Conventional FESSs implement charging and discharging by varying ω. In contrast, the authors have proposed a fixed-speed FESS that implements charging and discharging by varying not ω but J. However, the net power output in the discharge operation for a fixed-speed FESS was not positive owing to the low efficiency of the mechanism of varying J. This paper reports on the prototype development of a self-inertia-varying fixed-speed FESS that varies J by using the rotational inertia force of the flywheel itself. In the prototype test, actual charging and discharging operations were demonstrated, and a net mechanical power generation was observed during the discharge operation.

This paper presents a current control and mover design method for a linear synchronous motor with half-wave-rectified self-excitation to improve its thrust characteristics. First, we propose the current control method to improve the ratio of thrust to current in a maximum thrust/current control for this linear synchronous motor. Experiments are then performed to demonstrate that the proposed current control method is effective at increasing thrust and that the current and input power required to drive this linear motor can be reduced. Next, we propose a new mover that applies the principle of half-wave-rectified self-excitation to the mover with a multi-flux barrier structure. We design the structure of the proposed mover using finite element method. As a result, it is experimentally shown that the thrust density of this linear synchronous motor with the newly designed mover is approximately 30% higher than that of the previously fabricated mover.

To satisfy the demand for more compact medium-voltage motor drive systems, it is desirable to increase the frequencies of cascaded H-bridge inverters used in high-speed motor systems. However, in asynchronous pulse-width modulation (PWM) systems, as the output frequency increases, the command voltage and triangular wave carrier frequencies become closer, making it impossible to output the command voltage accurately. This manifests in the form of increased current harmonics, increased surge voltage at the motor terminals, and increased low-frequency ripple current owing to the asynchronous nature of the system. In this study, we adopt a fixed pulse pattern modulation method to address these problems. In our method, a low-distortion output voltage without multiple simultaneous changes is compiled into a table in advance, and subsequently output in synchronization with the fundamental voltage phase. We were able to confirm the effectiveness of the proposed method via simulations and mini-model experiments at fundamental wave frequencies of 700Hz and 1000Hz.

Noise is a key asset in air management applications. The use of slotless motors is an effective solution to mitigate the noise due to magnetic forces on teeth. In this paper, we propose a topology of slotless motors with toroidal winding that enables noise reduction and that simplifies the manufacturing process. With prototypes of this technology, we have been able to reduce the acoustic noise by 5dB in comparison with existing classical slotted motors.

Electric vehicles (EVs) and hybrid electric vehicles (HEVs) have electric motor drive systems, and these systems possess an advantage of quick and smooth response. In use the potential performance of control response, this study introduces multi sampling deadbeat control (MSDB) of permanent magnet synchronous motor (PMSM) drive systems for EVs and HEVs using a field programmable gate array (FPGA). The proposed deadbeat control using an FPGA can realize good response and robustness, especially for electric motor drive systems using a low carrier frequency of pulse width modulation (PWM) inverter used in EVs and HEVs.

Irreversible demagnetization analysis is complicated in motors with bonded magnets that have unique B-H curves and do not exhibit distinct knee points. We have proposed a permanent magnet assisted synchronous motor (PMASynRM) with bonded magnets and examined its demagnetization characteristics by assuming the relative recoil permeability (μ_rec) as constant to simplify the analysis. However, the present recoil loop measurements of bonded magnets show that μ_rec has different characteristics depending on the magnitude of the reverse magnetic field intensity at the working point of the magnet and temperature. Therefore, this study presents a demagnetization analysis method based on these measurement results and investigates the demagnetization characteristics of a PMASynRM considering the variation in μ_rec for bonded magnets. The results of the demagnetization analysis considering the variation in μ_rec are compared with those where μ_rec is assumed to be constant. The comparison results indicate that there is no problem with assuming a constant μ_rec of 1.15 in the demagnetization analysis of a motor with bonded magnets.

Recently, high step-up DC-DC converters have been widely used in several applications. Previously, we proposed a novel high step-up DC-DC converter, which consisted of a single-switch and a three-winding coupled inductor. Our previous report only highlighted the CCM operation and steady state principle of the proposed converter. This study aimed to investigate the switching frequency characteristics including the CCM and DCM operations of the proposed converter.

Induction machines are used in a wide range of industrial applications due to their simplicity, ruggedness, and low price. Despite their robustness, induction machines eventually fail due to a variety of mechanisms. Most faults exhibit specific frequency components in the motor current spectrum, which allows for fault detection. Many classical fault detection methods have been developed for grid-connected machines with relatively fixed operating points. In inverter-driven machines with a wide operating range, these methods cannot reliably detect and classify faults. Machine learning methods have been successfully used for various classification tasks. This study therefore combines classical fault detection approaches with various fault classification algorithms to reliably detect induction machine faults over a wide operating range.

The developed fault classification method is evaluated using steady-state measurements on an inverter-fed 5.5 kW induction machine. The algorithm shows promising fault detection and classification capabilities, achieving an accuracy of 97.4% over a wide load range.

When the force to be calculated is very small, it is not easy to determine this force with high accuracy using the nodal force method because of the discretization errors that may occur in the finite element analysis (FEA). In this study, we investigate a technique to calculate the force with high accuracy based on the magnetic levitation force and the torque analysis of a diamagnetic material. The levitation force can be calculated with high accuracy using the extreme fine mesh in the domain integration of the nodal force. Extremely small torque values can be calculated with high accuracy by symmetrizing the mesh in the domain of integration of the nodal force.

This paper proposes a combination of two methods to reduce the conductive noise in power factor correction (PFC) circuits. The two methods do not involve large additional components.

The first method achieves noise cancellation with an additional circuit using general-purpose transistors. It reduces the noise voltage by injecting a current of equal magnitude and opposite polarity to the leakage current generated by the switching device, which is the noise source, according to its operation. This is effective for not only average (AV) values but also quasi-peak (QP) values since the changes in the noise waveform are tracked.

The second method applies a control signal with a spread spectrum. The application of the spread spectrum for PFC has conventionally been effective only for AV values. This paper shows the conditions required to be effective for QP values as well.

The combination of these methods is confirmed to reduce the conductive noise by about 30dB in the frequency range below 1MHz, which is the dominant factor affecting sizing of EMI filters. This is equal to the attenuation achieved by a single LC filter stage.

A switched reluctance (SR) motor is simple and robust, and it is less expensive than a permanent magnet (PM) motor as it does not use rare earth magnets. Thus, the SR motor is one of the best in-wheel motors for electric vehicles (EVs). In previous works, a compact EV equipped with two 16/20-pole SR motors in rear wheels was prototyped. This paper proposes a novel control method for the in-wheel SR motor to implement a torque vectoring control for the prototyped EV. Furthermore, the proposed method is validated experimentally.

This paper presents the servomotor structure suitable for sensorless drives based on high-frequency injection method. The position estimation accuracy is related to the saliency ratio of the motor. Although the motor with increasing saliency ratio with the load has been reported, the mechanism of the phenomenon has not been explained.

In this paper, the improvement in the saliency ratio in a conventional servomotor structure is explained with respect to the magnetic flux distribution. Moreover, the increase in the saliency ratio through further structural improvement is examined, and the effect is confirmed by experiments.

High step-down DC-DC converters and rectifiers are required for large applications such as battery chargers. We previously proposed a dual 2-stage Cockcroft-Walton (CW) circuit as a high step-down all-passive rectifier. The rectifier provides the output voltage subject to circuit parameters. This study investigates the proposed circuit's operation through numerical simulations and an experimental prototype system focusing on the input source's duty ratio. Both the numerical and experimental procedures confirm that the output voltage of the proposed dual 2-stage CW circuit is sensitive to the input source's duty ratio.

This is the first study to experimentally perform the magnetic characterization of 4μm-thick electrical steel sheet based on the sinusoidal excitation technique at high frequencies of up to 1MHz. The steel is made of pure iron, fabricated using a high-precision continuous rolling process, which is a suitable and effective method for mass production. One ring core in which the steel part is appropriately fixed on a plastic cylindrical chassis is fabricated for measurements, whereas another ring core without the steel part is fabricated to serve as a reference. In addition, a method for effectively estimating the magnetic flux density and relative permeability of the steel part in the first ring core from the measured data of the two ring cores is presented as a key contribution of this study. This method can also be applied in the magnetic characterization of other thin steels at high frequencies. The magnetic flux density-field intensity (B-H) curve, relative permeability, and iron loss per weight of the examined 4μm-thick steel are measured and evaluated through experiments. The measured results and Steinmetz approximation indicate that the eddy current loss in the investigated steel is relatively considerable at high frequencies of 500kHz and above.

Synchronous optimal pulse width modulation is commonly applied when the ratio between the fundamental frequency and the switching frequency is low. Offline computed pulse patterns are optimized in terms of the harmonic distortion in phase currents. Typically, the underlying optimization problem is based on a simple inductor model representing the harmonic behavior of one phase of a nonsalient machine. This paper proposes an alternative formulation of the optimization problem, which generalizes it for salient machine types. An investigation of the optimization results' sensitivity to operating point-dependent parameters is presented.

Owing to the robust structure of switched reluctance machines, high-speed operations are preferred to achieve higher power densities. Generally, at high speeds, single pulse control is applied. However, its control parameter set is not unique. This paper proposes an algorithm based on design of experiments that simultaneously allows the calculation of optimal control parameters for an operating area and the minimization of the total machine losses. The designed experiments are finite-element analyses (FEAs) considering both iron and copper losses. A Pareto search algorithm solves the proposed multi-objective optimization problem. The results for different response surfaces are compared considering the errors in torque production and machine loss prediction. A reduced response surface based on 15 FE-runs shows a mean error of 1.9%, whereas the maximum error is 6.3% for machine losses within the validation operating area.

NANOMET is one of the several nanocrystalline soft magnetic alloys⁽¹⁾. The authors already reported about the prototype motor with NANOMET stator cores⁽²⁾. In this paper, the authors reported that NANOMET core motor has low iron loss characteristics which cannot be achieved with 35A360 core motor, while maintaining the torque density comparable to that of 35A360 core motor. In order to reduce the mass production cost of the currently expensive NANOMET stator cores and promote its practical application, we have devised molding of crushed NANOMET into a stator core. This paper describes about crushed NANOMET toroidal core, and presents the evaluation results of the iron loss characteristics.

This paper addresses power quality compensation with a constant DC-capacitor voltage-control (CDCVC)-based reactive power control method for a three-leg pulse-width modulated (PWM) rectifier in a bidirectional battery charger (BBC) for electric vehicles (EVs) in commercial single-phase three-wire low-voltage feeders, considering two domestic consumers. The instantaneous power flowing into the three-leg PWM rectifier demonstrates that the balanced and sinusoidal source currents, with a predetermined power factor (PF), are obtained in the domestic consumer equipped with the BBC, whereas the unbalanced and distorted source currents remain in the domestic consumers without the BBC. The simulation and experimental results show that the balanced and sinusoidal source currents at a PF of 0.90, which is a predetermined value, are obtained in the domestic consumer with the BBC, whereas the unbalanced and distorted source-side currents remain in those without the BBC. These simulation and experimental results demonstrate that controlling the reactive power on the source side with the CDCVC-based strategy reduces the capacity of the three-leg PWM rectifier in the BBC for EVs.

More reliable motor drive systems are expected in the realization of automated driving. The redundant motor drive system with two voltage supplies, two inverters, and a dual winding motor is one of the strong candidates since the two systems that construct the motor drive system are electrically independent. The dual winding motor has a characteristic of cancelling the 6^th harmonic produced in the overmodulation drive. However, it loses its characteristic when there is a voltage difference in the two voltage supplies. In this paper, it is proposed to control only the sum of the current during the overmodulation to maintain the characteristic of cancellation even if there is voltage difference in the two voltage supplies. Furthermore, the current difference of the two windings is controlled in the sinusoidal wave region to suppress the deviation of currents and turned off during the overmodulation to reduce 6^th harmonic. The maintained characteristic during voltage supply unbalance is confirmed with the experiment.

This paper presents a general set of transformations of stationary and rotating reference frames for all types of symmetrical multi-phase machines, as well as a generic approach for developing detailed electrical models of such machines. The electrical multi-phase model of an example 50 kW interior permanent-magnet synchronous machine (IPMSM) is developed. The transformations and model development procedures are illustrated in context of this example machine. The transformations are also used to reduce the computational complexity of obtaining model parameters via finite element (FEM) analysis. The results for the example machine are presented and the implications for model validity and associated challenges are discussed.

We have been studying the application of amorphous metals, which have a significantly lower loss than electrical steel sheets, to motors. Thus far, we have studied simple-shaped iron cores that can be machined only by shearing for radial motors. However, it is considered that the loss can be further reduced if the iron core is entirely made of amorphous metal. Here in this report, we report the results of a trial evaluation of a motor in which an amorphous metal is punched using a press die to form a stator core.