A contactless power transfer system using a repeater coil (Repeater Coil topology) has been proposed as a method of suppressing overcurrent without power control during misalignment or no-load. By installing a repeater coil between the primary and secondary coils, it is possible to increase the input impedance in the case of misalignment of the secondary coil or no-load condition. In addition, another a contactless power transfer system using primary parallel and secondary series resonance capacitors (PS Capacitor topology) has been proposed. In the PS Capacitor topology, the input impedance can be increased during misalignment of the secondary coil or no-load condition similar to the Repeater Coil topology. In this paper, we evaluated the characteristics of both these topologies. First, we conducted a circuit analysis of the Repeater Coil topology and proposed a design method. In addition, we theoretically clarified the characteristic difference of the two topologies and experimentally evaluated the characteristics.

A sensorless angle estimation method for brushed DC motor is proposed in this paper. In order to estimate the angle of the rotor without any mechanical sensors, the proposed method uses impedance variation by contact switching. In usual sensorless angle estimation methods, the angle of the rotor is estimated by the counter electromotive force (EMF). However, methods based on the counter EMF cannot estimate the angle accurately during standstill and at low speed. Furthermore, estimation errors occur due to the modeling error. In the proposed method, the angle of the rotor is estimated by using angle-dependent impedance. This paper focuses on the pulse variation due to contact switching. The impedance is measured by high-frequency signal injection and discrete Fourier transform. This method can be used to estimate the angle of the rotor directly. Therefore, it is possible to estimate the angle accurately at low speeds. The validity of the proposed method is verified through experiments.

High-frequency switching techniques enable the miniaturization of inductors in non-isolated DC/DC converters. However, higher frequency converters cause large switching power losses. This paper proposes a design method for a high-frequency, non-isolated buck DC/DC converter with a passive soft-switching circuit. The calculation results of the converter revealed decrease in power losses compared to that of a hard switching converter, for over 50kHz. A 2.1kW prototype was designed for reification, and it achieved a power efficiency of 95.6%.

This paper presents a variable magnetic flux PM motor in which space harmonic power is utilized for weakening the magnetic flux, automatically. The stator has a toroidally-concentrated winding structure, and the torque generation surfaces are composed of three air-gaps, including one single radial gap and two axial gaps. The radial-gap rotor is a constant-magnetized PM rotor and the axial-gap rotors are self-excited wound-field rotors. These rotors are coaxially fastened with opposite magnetic pole positions. The magnetomotive force of axial-gap rotor can automatically retrieve space harmonic power, which is inevitably generated by the concentrated winding structure. In this study, the effect of relative angle of the magnetic pole between the radial-gap rotor and the axial-gap rotors on the drive performance, e.g., current phase-vs.-torque characteristics, adjustable speed drive characteristics, and variable-magnetic-flux range, are experimentally demonstrated with a prototype machine.