記述言語：英語   掲載種別：研究論文（学術雑誌）

This article presents the mathematical derivation of the current waveform that flattens the radial-force sum in switched reluctance motors. The proposed current waveform is mathematically derived, thus no numerical computation is required. Additionally, the proposed current waveform contains the phase shifts of the harmonic components. The proposed current makes the radial-force sum flat, in addition to reducing the torque ripple and the current rms value compared to previously proposed waveforms. The mathematical derivation of the proposed method imposes a negative part of the current, hence current flipping is introduced. Since the proposed method is mathematically derived, it is applicable to various switched reluctance motors. The proposed method was validated by finite element analysis and was experimentally verified on an 18/12 switched reluctance motor designed as a generator for hybrid vehicle applications.

DOI： 10.1109/TIA.2023.3321589

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper compares the electromagnetic and vibroacoustic performances of the dual three-phase and the five-phase surface permanent magnet motors when changing a teeth pitch of stator core. 3D-finite element analysis indicates that the five-phase motor exhibited superior performance compared to the dual three-phase motor in terms of torque and vibration performance, while the dual three-phase motor had advantageous of the efficiency and acoustic noise. Additionally, by injection of third harmonic current to enhance torque performance for the five-phase motor, electromagnetic and vibroacoustic comparison is performed. Although the average torque is increased by approximately 17%, the acoustic noise and vibration is more inferior than that without the harmonic current injection.

DOI： 10.23919/ICEMS60997.2024.10921160

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

The authors have proposed an inverter-less drive of thrust magnetic suspension in a 5-axis actively controlled bearingless motor. In the method, thrust suspension winding is connected between the neutral points of the three-phase motor windings and the three-phase radial suspension windings. The current flowing in the thrust winding is called as zero-sequence current. This paper addresses the voltage disturbance compensation for the thrust suspension using zero-sequence current in the above system. First, experimental results showed that the zero-sequence current fluctuated at higher rotational speed. Then, the motor neutral-point-potential was theoretically derived considering the zero-sequence current and the harmonics of motor back-emf and consequently, it was fond that the fluctuation was caused by the variation in the motor neutral-point potential owing to the motor back-emf with harmonics of third order multiple. To suppress the fluctuation, the voltage disturbance compensation was implemented as a feedforward control. Experimental result demonstrated that the fluctuation of the zero-sequence current was significantly reduced by the voltage disturbance compensation.

DOI： 10.1109/ECCE55643.2024.10861268

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper presents a 2-DOF actively controlled consequent-pole-permanent magnet (CPM) type bearingless single-phase motor. In the proposed bearingless CPM motor with 6-poles/6-slots, the combined windings, which integrates functions of both the single-phase motor and radial suspension windings into one, is wound on the stator, and thereby the system can be driven by one three-phase four wire inverter. Furthermore, the CPM structure does not require a rotational angle for the suspension force regulation and consequently the proposed system is small size and low-cost. First, the constraint regarding the combined windings using zero-sequence motor current is theoretically derived and then based on the above constraint, a bearingless CPM single-phase motor is proposed. Finally, design of the proposed motor is conducted with 3D-finite element analysis.

DOI： 10.23919/ICEMS60997.2024.10921105

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper proposes a one-axis actively positioned bearingless motor with 1 kW output power using a zero-sequence current. The axial suspension winding is connected between the neutral point of the motor windings and the midpoint of the capacitors in the DC link. The zero-sequence current flowing into the axial suspension winding produces active axial force, while the motor is driven by dq-axis currents. In the proposed bearingless motor, the flux of bias PMs for the axial magnetic suspension does not pass through the motor stator core, and therefore the motor design is not constrained from the bias flux. Additionally, the flux, which is produced by the zero-sequence current flowing into the motor winding, contributes to boost the axial force. To demonstrate the performance of both the motor and magnetic suspension, FEA and experiment were conducted. The rotor was successfully levitated and, the proposed bearingless motor system has a potential to achieve both stable magnetic suspension and 1 kW-output.

DOI： 10.23919/ICEMS60997.2024.10921071

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Magnetic-geared motors have many advantages over mechanical gearboxes, such as reduced maintenance and overload protection. However, the limited life of the mechanical bearings, which hold a high-speed rotor, is problematic in terms of durability. In this paper, a magnetic-geared motor with an integrated bearingless high-speed rotor having a novel structure is proposed to solve this problem. The proposed magnetic-geared motor has an additional three-phase winding to achieve magnetic suspension for the high-speed rotor. In addition, the proposed structure has a consequent-pole high-speed rotor for simplified suspension control, and it can reduce the number of sensors. This paper presents the principles of magnetic suspension and torque generation. In addition, a comparison of the magnetic suspension characteristics and torque capabilities of different motor topologies determined by finite element analysis is discussed.

DOI： 10.1541/ieejjia.23008015

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

記述言語：英語   掲載種別：研究論文（学術雑誌）

This article presents a novel method for vibration and acoustic noise reduction in a three-phase 6/10 switched reluctance motor (SRM). The test machine has major vibration and acoustic noise at the 2nd, 4th, 5th, 7th, and 8th harmonics. Accordingly, a novel method called 'selective radial force harmonics reduction' is proposed. The proposed method selectively reduces the specific radial force harmonics at the stator teeth. By reducing the specific radial force harmonics such as 2nd, 4th, 5th, 7th, and 8th, the corresponding vibration and acoustic noise can be reduced significantly in the test machine. In this study, a current calculation for the proposed method is introduced. In addition, finite element analysis and experiments are conducted to verify the effectiveness of the proposed method. Compared with a conventional square current, the experimental results show that the overall sound pressure level is reduced by 7.1 dBA using the proposed method at the rated speed and torque. The dynamic conditions of the test machine using the proposed method are also presented. As a result, the proposed method is effective in reducing vibration and acoustic noise in the three-phase 6/10 SRM.

DOI： 10.1109/OJIA.2022.3229849

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The torque density improvement of a low-speed high-torque swirling actuator is presented in this article. The swirling actuator is driven by the electromagnetic radial force and integrated mechanical gears. The electromagnetic radial force generates the circular motion of the swirler, which is converted into the low-speed rotor rotation by the mechanical gears. First, the dimensions of the swirler with 12-pole permanent magnets are optimized to enhance the electromagnetic radial force by analytical calculation and three-dimensional finite-element analysis. Second, an improved gear set with a reduced pressure angle and an increased transmission ratio is designed. The gear efficiency and torque are investigated analytically considering the friction loss. Two prototypes are designed, and the experimental results exhibit that the peak torque density is improved from 27 to 64 Nm/L with a small volume of 0.16 L.

DOI： 10.1109/OJIA.2022.3232119

Scopus

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Five-degree-of-freedom controlled bearingless motor needs at least four inverters for levitation and rotation. For simplification of the system, this paper proposes inverter-less drive of thrust magnetic suspension. In the proposed method, the thrust suspension winding is connected between the neutral points of the three-phase motor windings and the three-phase radial suspension windings. The current flowing in the thrust winding is defined as zero-sequence current, resulting in generating thrust force without inverter for thrust suspension. The influence of zero-sequence current on the radial suspension force is investigated through theoretical equations and FEA, and can be suppressed by adopting small third-winding coefficient in radial suspension. The test machine was fabricated, and experimental results demonstrated that the thrust suspension was successfully performed by the zero-sequence current while four-axis motions are regulated in a non-contact manner during rotation.

DOI： 10.1109/ECCE53617.2023.10362858

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記述言語：英語   掲載種別：研究論文（学術雑誌）

This article investigates a bearingless motor with passive electrodynamic axial suspension. The axial suspension force is generated by a specific coil configuration called a figure-eight coil. Radial directions and tilting angles are stabilized by passive permanent magnet bearings. Since axial electrodynamic force increases with rotational speed, it must overcome a certain minimum threshold speed to compensate for the rotor weight and the unstable axial force caused by the permanent magnet bearing. Theoretical equations are derived for the braking torque caused by the suspension current and for the steady-state axial equilibrium position at constant rotational speed. A method based on the braking torque equation is proposed for correcting the mismatch between the magnetic center of the bearingless motor and the middle point of the axial clearance. This method sets the middle point between upper and lower touchdown positions in the same place where the motor current is minimum during passive axial suspension. Axial suspension is confirmed in the experiment with a noncontact laser sensor.

DOI： 10.1109/OJIA.2023.3236984

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記述言語：英語   掲載種別：研究論文（学術雑誌）

This study estimates the axial magnetic suspension loss and efficiency of a one-axis actively positioned single-drive bearingless motor in the rotational speeds of 1000 to 30 000 r/min. Bearingless motors have the advantage of enhanced efficiency owing to the absence of friction loss caused by mechanical ball bearings. In this study, the input powers of a bearingless motor with radial passive magnetic suspension and that of a motor with ball bearings were measured. Moreover, the mechanical ball bearing loss was also measured. Furthermore, the axial magnetic suspension loss in the single-drive bearingless motor was estimated. The efficiencies of both test motors were compared. Additionally, the ratios of the axial magnetic suspension loss and the ball bearing loss with respect to their input powers were evaluated.

DOI： 10.1541/ieejjia.22007118

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

The concerns about the acoustic noise, vibration, and harshness of electric machines are ever-growing in traction applications for electric vehicles. Among various motor topologies, interior permanent magnet synchronous machines are adopted in most commercial products for advantages including high efficiency and high torque density. However, the severe acoustic noise and vibration excited by the electromagnetic forces acting on the stator remain an issue. In this paper, a method using strain gauges is proposed to measure the radial electromagnetic force in an interior permanent magnet synchronous machine for electric vehicle applications. The method is first verified in finite element analysis. Additionally, an interior permanent magnet synchronous motor installed with strain gauges is fabricated for experimental verification. The experiment results show that the radial force estimated by using the strain gauges has a good correspondence in terms of phase and shape, whereas a significant difference in amplitude is observed.

DOI： 10.1109/IEMDC55163.2023.10238785

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）

This study experimentally investigates the acoustic noise, vibration, and power consumption in a one-degree-of-freedom actively positioned single-drive bearingless motor, which has radial passive magnetic bearings (RPMBs) and compared to an identical stator part and rotor shaft with radial mechanical ball bearings. For the experiment, three test motors were set up: (a) a bearingless motor with two RPMB, (b) a motor with two ball bearings without an axial preload, and (c) a motor with two ball bearings with an axial preload. Motor (a) under test had one-axis active positioning and the radial movements were supported by RPMB made of cylindrical permanent magnets. Conversely, in motors (b) and (c), the radial and axial movements were supported by ball bearings, and there was no production of active axial force. The experimental results confirmed that the levels of acoustic noise, stator vibration, and input power consumption were significantly lower in motor (a) than those in motors (b) and (c). In the analysis section, dynamic models of the bearingless motor with RPMB and motor with ball bearings were designed and simulated using MATLAB backslash Simulink. The low radial stiffness in RPMB was found to contribute to acoustic noise and vibration reductions. Thus, this article presents an example of a one-degree-of-freedom actively positioned bearingless motor with RPMB that realizes reductions of acoustic noise, stator vibration, and input power consumption.

DOI： 10.1109/OJIA.2022.3232116

Scopus

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper proposes a novel derivation for radial-force sum flattening in a switched reluctance motor. The main objective of the proposed method is the reduction of the acoustic noise by flattening the radial-force sum, while having the lowest current rms. The proposed method is applicable to any switched reluctance motor as long as the zeroth-mode vibration is dominant, such as the case in which the stator pole-number is sufficiently high with a large stator outer diameter. Since the proposed method is analytical, no computational burden is imposed from applying the method. The proposed method was validated by electromagnetic finite element analysis, followed by mechanical and acoustic finite element analyses that show significant reduction in the acceleration and sound pressure level compared to the conventional square current excitation.

DOI： 10.1109/IEMDC55163.2023.10238907

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper focuses on acoustic noise reduction by the injection of the third and ninth harmonics into the zero-sequence current in surface permanent motors. In the proposed method, the sixth and tenth radial force components are reduced significantly by the injected third and ninth harmonics, respectively. The finite element analysis results show that the main component of the acoustic noise, the sixth, is reduced by the injection of the third zero-sequence current harmonics. However, this injection leads to the increase of another acoustic noise component, the tenth. Thereby, this component is reduced by the third and ninth zero-sequence current harmonics injections simultaneously. As a result, it is demonstrated that the acoustic noise performance was significantly improved.

DOI： 10.1109/ICEMS59686.2023.10344341

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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper introduces a novel analytical force-shaping method based on the Heaviside function for radial-force sum flattening in switched reluctance motors. The purpose of the proposed method is suppressing mode 0 vibration and acoustic noise reduction. The proposed method relies on radial force estimation, where the estimated force is compared against a proposed reference radial force. The reference radial-force sum is mathematically devised to be entirely DC and void from harmonics, significantly reducing the vibration and acoustic noise. The proposed method was simulated on model-base design software platforms, and was validated through 3D finite element analysis.

DOI： 10.1109/ECCE53617.2023.10362579

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The induction machine has proven to be one of the most difficult motor technologies to transform into a bearingless motor due to currents that are induced in the squirrel cage rotor by the suspension field. This paper develops a new rotor for use in a bearingless induction motor to solve this problem. The rotor is described as 'pole-specific' because its winding couples to the motor field but not the suspension field. This new structure uses a common end-ring to reduce the rotor's axial length, solving rotor dynamic challenges present in previous efforts to develop a pole-specific rotor. This paper presents the new rotor concept and leverages traditional cage rotor design theory to develop equivalent circuit models and a theoretical framework that reveals which combinations of poles and slots can be used to implement the new rotor. Experimental results validate the new rotor concept and demonstrate its performance improvement over the classical squirrel cage rotor. A case study is presented of a high performance 50 kW, 30,000 r/min design for an industrial compressor with a modeled efficiency of 96.8%.

DOI： 10.1109/TEC.2022.3172017

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

A novel one-axis actively positioned single-drive bearingless motor topology with enhanced torque density is presented. The torque density is improved as follows: (i) The lower stator core was eliminated to cancel negative motor torque. (ii) The upper stator core was made of soft magnetic composite material (SMC) and integrated with supplementary windings. (iv) Wide air-gap length was also adopted to avoid radial touchdown. (iii) High residual flux density (Br) material was adapted for the rotor permanent magnets (PM). Motor torque of the proposed machine was improved up to 23% compared to the initial design.

DOI： 10.1109/ECCE50734.2022.9947459

Scopus

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

In this paper, a calculation method is proposed for the radial suspension force of a bearingless motor with a surface-mounted permanent magnet (SPM) rotor, a consequent-pole permanent magnet (CPM) rotor, and a homopolar permanent rotor (HPM). The radial suspension forces are calculated mathematically and analytically using the airgap flux density. It was confirmed that the proposed radial force equations are practical to calculate the suspension force based on the airgap flux density. The CPM bearingless motor and bearingless AC HPM have salient pole rotors that interact with the 2-pole Magnetomotive force (MMF) to generate 6- and 10-pole components. As a result, the radial suspension force of the CPM bearingless motor is generated by 8- and 6-pole, and 8- and 10-pole magnetic flux, whereas the bearingless AC HPM produces the radial suspension force by DC and 2-pole components. The shaft torque, the suspension force, and efficiency were also compared for SPM, CPM bearingless motors, and bearingless AC HPM. Consequently, the torque value of the CPM bearingless motor is quite close to SPM bearingless motor. Moreover, the suspension force of the CPM bearingless motor is quite close to bearingless AC HPM.

DOI： 10.1541/ieejias.142.506

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper focuses on the reduction of torque ripple and radial-force harmonics of a consequent-pole permanent magnet (CPM) motor by harmonic current injection based on dq-axis frame without skewing the rotor or stator so that the CPM motor can be applied to electric power steering (EPS) applications. In the proposed method, the 6th and 12th radial-force components are reduced by the 6th and 12th d-axis current harmonics, respectively, whereas the 6th and 12th torque components are reduced by the 6th and 12th q-axis current harmonics, respectively. Finite element analysis (FEA) results demonstrated that the electromagnetic and acoustic noise performances of the CPM motor with harmonic current injection were significantly improved and were competitive with those of the surface permanent magnet motor.

DOI： 10.1109/ICEMS56177.2022.9982893

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Bearingless motors have several advantages, and their designs and characteristics have been studied. However, stator vibration acceleration has not yet been reported experimentally. This study investigated stator vibration reduction using a small permanent magnet (PM) bearingless motor with repulsive passive magnetic bearings. The dynamic modeling of motors with ball bearings and repulsive passive magnetic bearings was introduced to examine the difference in the vibrations via MATLAB/Simulink simulation. Two test machines were used as part of the experimental setup: (a) bearingless motors with repulsive passive magnetic bearings, and (b) a motor with ball bearings. The experimental results confirmed that the stator vibration acceleration levels of the bearingless motor were significantly reduced, by up to 98.7%, compared with those of the motor with ball bearings.

DOI： 10.1109/ICEMS56177.2022.9983182

Scopus

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper addresses reduction of 6f 6 times of electrical frequency, f-radial force harmonics with zero-order mode in an interior permanent magnet synchronous motor by injection of the zero-sequence third-harmonic current, which has only little influence on the motor performance. The injection frequency for reduction of 6f-radial force harmonics in the proposed method is half of that for conventional dq-harmonic current injection. Thus, the control of current injection can be easier. Furthermore, the proposed system with a three-phase four-wire inverter enables providing the zero-sequence current without additional power electronics circuit. To demonstrate the effectiveness of the proposed method, three-dimensional FEM analysis was performed using an IPM motor with 8-pole/48slots distributed winding. The analysis results indicated that the 6f radial force harmonics and sound pressure were reduced by injection of the zero-sequence third-harmonic current while the torque ripple is largely not changed.

DOI： 10.1109/SPEEDAM53979.2022.9842205

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記述言語：英語   掲載種別：研究論文（学術雑誌）

This article proposes a swirling actuator that uses the electromagnetic radial force and mechanical gears to generate rotational torque. The proposed actuator generates a rotating radial force between an inner stator and a swirler. The gears on the swirler and outer rotor convert the circular motion of the swirler to low-speed rotor rotation. Thus, the proposed actuator is aimed at low-speed high-torque applications. In this study, the air-gap radial flux density and electromagnetic radial force are investigated analytically and verified through finite-element analysis. The static radial force and output torque are measured in a prototype of the actuator. The system efficiency and the gear efficiency are evaluated. A peak torque density of 27 Nm/L with a small volume of 0.16 L is realized in the prototype.

DOI： 10.1109/TIA.2022.3142118

Scopus

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

In this paper, an axial-gap magnetic levitation PM motor with a magnetic bearing consisting of a pyrolytic graphite and a ring Halbach array permanent magnet is proposed. A full-passive magnetic levitation motor with a diamagnetic disk has been proposed with no mechanical contact between the rotor and the stator. to avoid radial touchdown. Experimental validation is conducted on the proposed motor and the maximum rotational speed is measured.

DOI： 10.1109/ICEMS56177.2022.9983088

Scopus

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Switched reluctance motors generate a variation of radial forces upon the stator poles, causing considerable vibration and acoustic noise. This paper introduces a novel mathematical derivation of the current waveform to flatten the radial-force sum. The proposed mathematical method takes into consideration the phase shifts of three current components, hence providing a comprehensive flattening solution. The proposed method was implemented and validated through 3D finite element analysis, on an 18/12 switched reluctance motor. The results illustrated an effective correspondence between the proposed mathematical method and the simulation model, as well as reducing the acoustic noise components, especially the third and sixth components.

DOI： 10.1109/ECCE50734.2022.9947423

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This study compares the estimated magnetic suspension loss, the mechanical ball bearing loss, the input power, and efficiency in the proposed bearingless motor and a ball-bearing-supported motor. Bearingless motors have the advantage of enhanced efficiency owing to their operation without mechanical ball bearings. In the experiments, input power related to speeds from 1000 to 30 000 r/min of the ball-bearing-supported motor and the bearingless motor were measured. Mechanical loss of ball bearing was measured as well; then, magnetic suspension loss of the proposed bearingless motor can be estimated. In addition, the efficiencies of both motors are evaluated.

DOI： 10.23919/IPEC-Himeji2022-ECCE53331.2022.9807210

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記述言語：英語   掲載種別：研究論文（学術雑誌）

A novel electromagnetic force estimation using strain gauges attached to a laminated iron core method is proposed. Based on the strain gauge output, the electromagnetic force that occurs on the air-gap surface of the core is estimated with compensations for magnetostriction and nonuniform strain distribution. The proposed method is validated by comparing the electromagnetic force calculated in the finite element analysis and an experiment on a pair of C-shaped laminated iron cores. This article focuses on the force estimation in a pair of simple C-shaped cores, which are aimed at being a part of the stator and rotor of a switched reluctance machine. In future research, this basic approach will be extended to the estimation of the radial forces in switched reluctance motors to reduce the vibration and acoustic noise.

DOI： 10.1109/TIA.2022.3195188

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

記述言語：英語   掲載種別：研究論文（学術雑誌）

The bearingless version of the induction motor (IM) has unacceptable performance for high speed or significant power applications. This is due to design challenges that are unique to the bearingless IM, including fundamental topology differences, rotor current induced by the suspension field, and a lack of techniques that can rapidly and accurately model the machine. This article presents a complete investigation into the design topology, modeling, and optimization of bearingless IMs to identify high-efficiency, power-dense designs for a high speed industrial compressor system. Key differences in the design of the bearingless IM from that of the classical line-fed IM are explored and an analytic design approach is proposed. A pole-specific rotor and a combined stator winding are used to improve the machine performance. Computationally efficient finite element modeling techniques are proposed and evaluated based on their ability to accurately calculate bearingless IM design performance metrics. An optimization framework is developed around these advancements using the multiobjective evolutionary algorithm based on decomposition. This article exercises this framework to explore the design space of four different slot-pole combination bearingless IMs for a 50 kW, 30 000 r/min compressor. High performance designs are identified that achieve >96% efficiency with a torque density competitive with high performance servo motors that use contact bearings.

DOI： 10.1109/TIA.2020.3044970

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記述言語：英語   掲載種別：研究論文（学術雑誌）

This article presents a novel structure of a bearingless motor with integrated passive axial electrodynamic suspension. The simple initial structure has been improved in three steps. The structure was upgraded by including additional rings of permanent magnets and rotating back iron yokes in a double rotor structure that embraces the stator. Electrodynamic force generated in the final model was several times higher than that of the initial one. A prototype machine of the final structure was built. The suspension currents and axial electrodynamic forces were validated through an experiment under quasi-static condition, that is, constant rotational speed and fixed axial displacement. Theoretical equations for the axial electrodynamic force were derived. The force equation was compared to the finite-element analysis and experimental results.

DOI： 10.1109/TIA.2021.3091415

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

This article aimed to simplify magnetically levitated motor system by implementing the voltage sensorless control of the split capacitor potential for a three-phase four-wire motor system with a zero-sequence suspension winding. In the system, the suspension winding for magnetic suspension is connected between the neutral point of the Y-connected three-phase motor winding and the midpoint of two capacitors of direct-current (dc) link, thereby enabling simultaneous control of a three-phase interior permanent magnet synchronous motor and an axial magnetic bearing (iron-ball magnetic suspension, in this article), with only six power switches. However, the split capacitor potential is unbalanced by the dc component of the zero-sequence current, owing to the offset detection error of the current sensor and the bias current of the magnetic suspension. For suppressing the imbalance, we propose a voltage sensorless control. In the proposed method, the split capacitor potential is controlled without voltage detection by utilizing the zero-sequence voltage reference in the controller. The experimental results demonstrated that the split capacitor potential was successfully balanced while the iron-ball magnetic suspension and motor drive were performed. For further improvement of voltage sensorless control, a simplified control system was configurated with a filter controller based on an equivalent block diagram. The results indicated that the use of the filter controller improved the positioning accuracy of the magnetic suspension for the sensorless control system.

DOI： 10.1109/TIA.2021.3088767

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper investigates a bearingless motor with full passive suspension. The axial direction is stabilized by an electrodynamic force generated by a specific coil configuration called a figure-eight coil. Radial directions and tilting angles are stabilized by passive permanent magnet bearings. Since the electrodynamic force increases with rotational speed, it must overcome a certain minimum threshold speed to compensate the rotor weight and the unstable axial force caused by the permanent magnet bearing. A weight relief structure with a pair of permanent magnets in attractive configuration is designed to reduce the axial load by the rotor weight. This weight relief structure reduces the balance axial position at steady state. With a smaller axial displacement, the suspension current, and, consequently, the copper losses at rated operation are reduced. An external inductor is connected in series with the coils, resulting in enhanced electrodynamic stiffness at low rotational speed. Through theoretical equations derived in a previously published manuscript, an appropriate external inductor is chosen. Forces in the radial permanent magnet bearings and weight relief structures are calculated through Finite Element Analysis. The steady state balance position and the minimum rotational speed required for full passive suspension are estimated through the theoretical equation. It is found that both the external inductance and the weight relief structure improve the axial stiffness performance for rotational speeds below 5000 rpm.

DOI： 10.1109/ECCE47101.2021.9595427

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper proposes a novel full passive magnetic levitation motor without active magnetic suspension. It has a magnetic levitation unit and a motor unit. The Halbach array permanent magnets and a pyrolytic graphite (PG) disk realize the full passive magnetic levitation. The rotational motor torque is generated by a coreless motor. The axial and radial stable forces are calculated by the diamagnetic equation based with magnetic field distribution given by the 3-D FEM analysis. In experiment, the static levitation force and axial vibrations are measured and speed control test is conducted as high as 4000 r/min.

DOI： 10.1109/ECCE47101.2021.9595636

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記述言語：英語   掲載種別：研究論文（学術雑誌）

A novel structure design and experimental results of a one-Axis actively positioned single-drive bearingless motor is proposed. This new single-drive bearingless motor is proposed by adapting the 4-pole 2-layer permanent magnet rotor and a wide air-gap length for high rotational speed operation. It is found that the rotational speed of 30 000 r/min is experimentally possible, although around 16 000 r/min top speeds were reported in the literature in only one-Axis active magnetic suspension. In the machine design stage, it is shown that a wide gap length provides an efficiency improvement with a reduced risk of possible radial position touchdown.

DOI： 10.1109/TIA.2021.3090736

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記述言語：英語   掲載種別：研究論文（学術雑誌）

In this article, three test motors are fabricated with different iron materials, conventional steel, high silicon steel, and amorphous iron. Among the three materials, the high silicon steel has the lowest magnetostriction and the amorphous iron has the highest magnetostriction and the lowest saturated flux density. Hammer test is carried out to identify the respective resonant frequency and the optimum Young's modulus and Poisson ratio are identified from the measured resonant frequency for each core. Furthermore, the acoustic noise is measured in load test and it is found that the high silicon steel has the lowest acoustic noise. Then, the electromagnetic finite element analysis (FEA) and acoustic noise analysis are carried out. According to the FEA results, the acoustic noise of the amorphous iron motor is the lowest, while it is the highest in an experiment. This discrepancy is considered to be resulted from the magnetostriction property of the magnetic materials that are ignored in FEA so far. Therefore, the magnetostriction of three iron sheets is measured and the FEAs that take magnetostriction into consideration are carried out. From the results of the improved FEAs, it is found that the magnetostriction plays an important role in acoustic noise analysis.

DOI： 10.1109/TIA.2021.3108948

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記述言語：英語   掲載種別：研究論文（学術雑誌）

A novel consequent-pole bearingless motor is proposed with a unique combined winding structure of parallel motor windings for mixing applications, such as agitators used to mix fluids in the pharmaceutical or food industry. Bearingless motors can be used to achieve high purity and no contamination in these mixing applications. The principles of the magnetic suspension force and torque generation are presented by calculating the magnetomotive force (MMF) distributions with two different magnetic field. In addition, the error angle of the suspension force is evaluated in several pole/slot combinations with the proposed combined winding using 3-D finite element analysis. As a result, 20-pole/24-slot was found to be the best configuration, because it has the least direction and amplitude variations in the radial suspension force generation. A prototype of the proposed 20-pole/24-slot bearingless motor was built and tested. The stable magnetic suspension start-up and rotation can be successfully achieved in the experiment. The measured waveforms of the rotor displacement and the U-phase current while the rotor is magnetically suspended and rotated are shown. It is confirmed by calculations and experiments that the proposed combined winding is effective for stable radial magnetic suspension and rotation.

DOI： 10.1109/TIA.2021.3096485

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担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

DOI： https://doi.org/10.1299/transjsme.19-00403

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

We have proposed a driving method for both a three-phase permanent magnet motor drive and one-degree-of-freedom controlled magnetic suspension using only one three-phase inverter. The suspension winding is connected between the neutral-point of the Y-connected motor winding and the middle point of the voltage sources. Hence, the suspension force is actively controlled by the zero-sequence current. The experimental result showed that the vibration of the magnetic suspension increased under the loaded condition of the motor compared with that under no load. The vibration mainly includes the fundamental and 3rd components of the driving frequency, 1 f and 3 f. This paper focuses on the positioning accuracy improvement of this magnetic suspension system. We have found that the vibration 1 f is caused by the detection error of the current sensor and the three-phase unbalanced resistance and inductance values, and the vibration 3 f is caused by the PWM drive. To improve the positioning accuracy, we investigated both the current detection method and the observer-based voltage disturbance compensation. The experimental results demonstrated that these compensations improved the positioning accuracy of the magnetic suspension.

DOI： 10.1541/ieejias.139.322

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

日本   新潟  

DOI： https://doi.org/10.23919/ipec.2018.8506671

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： https://doi.org/10.1299/mej.15-00116

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

受賞国：日本国

受賞国：日本国