Kan Akatsu

• Doctor of Philosophy
• Professor at Yokohama National University

Technical innovations for the downsizing of motor systems are necessary to realize energy savings and roomy and comfortable car interior space in electric vehicles. In this paper, a novel motor drive system with multiple high‐speed motors and a magnetic multiple spur gear (MMSG) is proposed for electric vehicles. Furthermore, the factors leading to...

Technical innovations for the downsizing of motor systems are necessary to realize energy savings and roomy and comfortable car interior space in electric vehicles. In this paper, a novel motor drive system with multiple high speed motors and a Magnetic Multiple Spur Gear (MMSG) is proposed for electric vehicles. Furthermore, the factors leading to...

The dynamic eccentricity of rotors is a significant obstacle in their manufacturing process. This obstacle causes an imbalanced electromagnetic force and generates unexpected vibrations and acoustic noise. In this study, the effects of dynamic eccentricity on the temporal and spatial harmonic distributions of gap magnetic flux density and electroma...

Dual three-phase motors offer numerous advantages, including the elimination of 6th-order torque ripple. However, they have the drawback of generating large harmonic currents when driven because of their small inductance for specific harmonics. In this study, inductance, which depends on the winding structure and harmonics, is formulated using the...

Over the years, wireless power transfer has been increasing attention. With the development of high-speed switching devices, research on wireless power transfer system using megahertz bands has been increasing. The size and weight of the coupler can be reduced using megahertz bands. However, the loss of the coupler owing to the skin effect and the...

Permanent magnet synchronous machines (PMSMs) are widely used in a variety of applications. The static eccentricity of the rotor is a common fault in the fabrication process. These faults cause imbalanced electromagnetic force and exert unexpected vibration and acoustic noise during the design process. In the worst case, it causes bearing or motor...

Dual three-phase motors have the problem of a large generation of harmonic currents while driving due to small inductance for certain harmonics. The purpose of this paper is to theoretically clarify the effect of the winding structure of dual three-phase motors on harmonic currents. Analytical calculations considering the spatial harmonics of the m...

Permanent magnet synchronous motors (PMSMs) are widely utilized for many purposes owing to their high efficiency. Such frequent applications require less noise and fewer vibrations. This work focuses on multi-three-phase PMSMs that can independently control the current among winding groups to suppress the vibrations caused by air gap imbalances, wh...

In recent years, progress in power semiconductor switching devices has created more additional advantages that can be realized using multi-phase inverter-fed motors. The authors propose a MATRIX motor to realize electric motors with higher functionalities than conventional electric motors. Since the MATRIX motor is driven by H-bride inverters conne...

It is known that the harmonic current of a motor affects torque ripple. Therefore, to take into account the harmonic current in finite element analysis, the voltage input needs to be evaluated however, voltage input analysis is more time-consuming than current input analysis. In this paper, we propose a method to predict the harmonic current and to...

It is predicted that the maximum speed of EV traction motors will increase in the future due to reductions in size and weight. The high-speed motors are required to have high mechanical strength of the rotor for high-speed rotation, in addition to satisfying the required output and high efficiency in the wide operation area. Therefore, it is necess...

The switched reluctance motor (SRM) has generated considerable attention because of its lack of magnets and lower cost structure compared to the permanent magnet synchronous motor (PMSM) structure. In addition, SRM can achieve high speed rotation because of its simple structure and high robustness. However, SRM has lower torque density than that of...

In this article, we investigate the optimal carrier phase-shift angle to reduce harmonic iron loss under various operating conditions, such as torque, speed, dc voltage, and carrier frequency, on a dual three-phase-winding permanent-magnet synchronous motor (PMSM). We calculate the carrier harmonic voltage by theoretical analysis and relate it to t...

Permanent-magnet synchronous motors (PMSMs) are used for traction application in electric vehicles (EVs) and hybrid electric vehicles (HEVs). However, PMSMs generate vibration and acoustic noise in the connected load due to torque ripple. Torque ripple reduction techniques require accurate modeling of torque ripple and estimation of motor parameter...

In this study, an effective combination of methods to estimate the magnet operating points in a permanent magnet synchronous motor (PMSM) is proposed. First, the magnet temperature estimation is compensated with the initial temperature and magnet loss based on the error between the estimated temperature obtained using the thermal equivalent circuit...

The main limitation of magnetic gears is their relatively low torque density. Therefore, a novel structured high torque density magnetic-geared permanent magnet (MGPM) machine, which combines the advantages of a conventional MGPM machine and magnetic gear to enhance the torque considerably and achieve low-speed high-torque operation, is proposed in...

This paper presents some techniques for driving novel 5 phase dual winding PMSM (Permanent Magnet Synchronous Motor) for the in-wheel motor. The motor realizes winding change over characteristics that can expand driving area from high-torque mode to high-speed mode due to the dual winding construction. However, the dual winding structure makes a hi...

Permanent magnet synchronous motors (PMSMs) are widely used as an automotive motor, and there has been a demand for their further technological advance. A harmonic current control method has been used as a controllable approach for realizing its low vibration of PMSMs. In addition, a dual inverter system has attracted attention as an automotive mot...

1. Power conversion system: requirements and solution 2. Challenges for power modules 3. Failures and malfunctions caused in power module 4. Improvements 5. “Highly reliable and compact half-bridge SiC power module” as implementation example 6. Summery

Electric hand tools must be low cost and require minimal maintenance. To achieve these demands, a switched reluctance motor (SRM) is expected to be used as an electric hand tool motor as an alternative to a brushless DC Motor (BLDCM). The SRM is suitable for electric hand tools owing to its low manufacturing cost. However, the SRM has a disadvantag...

This paper proposes a self-sensing control method considering a position sensor fault detection and algorithm transition, which can be applied to a self-sensing control based on back-electromotive force (back-EMF) estimation for an interior permanent magnet synchronous motor (IPMSM). An adaptive threshold method is derived to accomplish not only th...

This paper presents an air-cooled in-wheel motor integrated with an SiC inverter having high torque density, high gear ratio, and fault tolerant characteristics. Air-cooling is achieved using an integrated SiC power module, which utilizes a volume of only 5 cc for one phase, thus reducing the inverter loss. Additionally, a 5-phase permanent magnet...

Magnetic gears realize the characteristics such as low acoustic noise and low vibration, maintenance-free by contact-less power transformation. However, conventional magnetic gears are not suitable for high-speed motor drive systems because of their low mechanical strength, which results from the permanent magnets of the input rotor. This paper pro...

The high speed motor is effective to realize downsizing motor in an electric vehicle (EV). Switched Reluctance Motor (SRM) is possible to the high speed drive because the rotor structure has simple and robust. However, the vibration and the acoustic noise are large from the drive principle. Moreover, the conventional complicated current excitation...

RECENT global warming issue is a serious problem. One of the key solutions is to spread Electric Vehicle and/or Hybrid Vehicle. Due to high torque density and efficiency, permanent magnet machines have been used for the traction motors for Electric Vehicle and Hybrid Vehicle. The torque density has been improved for this decade, almost two times to...

Rotor position and speed in sensorless control based on back-electromotive force (back-EMF) estimation can be estimated from back-EMF estimator and rotor position estimator in an interior permanent magnet synchronous motor (IPMSM). Even if the rotor position and speed are correctly estimated by these estimators in the steady state, the performance...

This paper discusses a magnetization state (MS) manipulation method at high speeds with low vehicle vibration for variable flux permanent magnet synchronous machines (VF-PMSMs). VF-PMSMs can achieve lower driving cycle losses compared to conventional PMSMs by changing the MS in the medium speed and medium torque range. To maximize this advantage fo...

Magnetic gears are expected as the system with maintenance-free, low noise and low vibration characteristics by contact-less power transformation. However, conventional magnetic gears are not suitable system for high speed motors because the mechanical strength is weak due to permanent magnets of the high speed rotor. Adding that, the magnet eddy c...