The maximum power transfer theorem (MPT) for the inductive resonant coupling (IRC) of information transfer (IT) circuits was extended more than half a century ago. In that extension, the mutual inductance of the coupling was used as the optimization parameter, and the equality of the primary circuit resonance frequency with the secondary circuit resonance frequency was assumed. Hence the extension is not applicable to a general (i.e., composed by elements of arbitrary circuit constants) inductive resonant coupling (GIRC). A new method “the dual optimization” is introduced to derive an extended maximum power transfer theorem (EMPT) for a GIRC. By applying the EMPT to a GIRC, a maximum power condition (such as the values of circuit reactances) that causes a unified resonance is given.

The use of linear motors has been rapidly increasing in recent years in response to the rising demand for drive mechanisms with higher speed and acceleration to improve the throughput of semiconductor production equipment, machine tools, and so on. In this study, we have developed a new type of linear motor with an opposed magnetic pole structure and twin movers. To achieve higher acceleration of a linear motor, it is necessary to satisfy both large thrust and low inertia. In our proposed new type linear motor, the thrust is improved by increasing the facing area between the permanent magnets and magnetic pole teeth by using multistage movers. Furthermore, the magnetic leakage flux is reduced by multiplexing the magnetic flux path. In a short stroke (approximately 210mm) drive, the high acceleration of 1670m/s² and maximum velocity of 14.2m/s is demonstrated using a prototype linear motor (maximum thrust =25kN).

In this paper, a technique is proposed to reduce the carrier noise of pulse width modulation (PWM) inverters for a permanent magnet motor drive. The carrier noise is generated by the motor and the reactor driven by the inverter and affected by the switching frequency. When a motor rotates and drives a machine, the carrier noise is hidden by the machine noise. However, when the motor speed is approximately zero, the carrier noise becomes dominant and raucous. The typical method to reduce the noise employs a switching frequency higher than the audible frequency of human hearing. However, the increase in switching frequency results in the inverter suffering a higher switching loss and lower efficiency. In particular, when the permanent magnet motor operates at approximately zero speed and full-load, for example, in the hill-start conditions of electric vehicles and the start and stop conditions of elevators, the current flows in specific power devices and the switching loss further increases. The proposed technique uses a zero-sequence voltage, which is generated randomly with the M-sequence signal, and diffuses the frequency components of the ripple contained in the current. The technique is able to reduce the noise without increasing the switching frequency of the inverter when the motor speed is almost zero. Simulation and experimental results show that the proposed technique can diffuse the carrier noise and the cycle of the M-sequence signal changes the diffusion effect of the carrier noise.

This paper presents local vector magnetic properties in a three-phase induction-motor model core under sinusoidal and PWM excitation. The distributions of the vector magnetic properties were measured using a small sized vector magnetic sensor (V-H sensor). The results show a clear influence of the magnetic anisotropy due to rolling, although the core material was the non-oriented silicon steel sheet. In case of PWM excitation, iron loss due to a high-frequency component was generated because the excitation current waveform includes higher frequency components caused by the modulation frequency. In this paper, effects of the higher harmonics on the magnetic property distributions are discussed in detail.

Vehicle detectors play an indispensable role in traffic management and control systems (TMCS). The data collected via vehicle detectors are used to fulfill various functions such as signal control and traffic information provision. In Japan, TMCS use mainly ultrasonic detectors. Owing to their aged deterioration, their detection accuracy gradually reduces over many years, and thus their efficient operation and maintenance requires accomplished engineers. In recent years, it has become difficult to maintain great numbers of ultrasonic detectors because of the financial constraints in public resources and shortfall of accomplished engineers. In this paper, we propose failure detection methods, and confirm their validity by using actual data. First, we propose an aggregation method of detector data for classifying installation positions, and validate the method by using large amount of data. Moreover, we propose a few failure detection methods with the aggregated data, and compare their decision results by using the actual data.

Wireless Power Transfer (WPT), such as magnetic resonant coupling using a magnetic field is being studied and discussed for a wide variety of applications. When the transmission distances are large, very large transmitters and receivers need to be considered. However, in the early stages of an investigation, it might be prohibitive to manufacture and evaluate coils of such a large size. To reduce costs and effort, a scaling law can be used to estimate the WPT efficiency of very large coils using the results of smaller coils. In this paper, a scaling law is proposed that relates the coil size to the coupling coefficient, assuming the ratio between the coil diameter and coil length remains constant. The coupling coefficient is one of the parameters that determine the maximum efficiency of magnetic field WPT. The proposed method was verified by an electromagnetic field simulator and experiment. The results of this study provide an easy method for estimating the WPT efficiency of very large coils.

In this study, we developed a converter based on SiC-MOSFET for use in ultra-high-speed elevators, with a reduced volume of 15% compared with the conventional converter. We succeeded in reducing the power loss of the converter unit by 56% compared to the conventional converter in one round trip under high temperature condition. Recently, because of their useful characteristics, wide-gap semiconductors, such as SiC and GaN, have gained considerable attention for use in various application in the power electronics systems. Therefore, we studied the use of a converter in elevator systems based on SiC-MOSFET. We used a 1200V/800A SiC-MOSFET module for the converter unit. We developed a prototype of the converter unit and the control panel by applying for the SiC-MOSFET module for an ultra high-speed elevator. As a result, the setting area of the control panel (main part) becomes less than 43% of the conventional panel. We tried to demonstrate the working of a 68kW elevator by applying the prototype control panel. Because of the characteristic of the switching loss of SiC-MOSFET, the power loss of the converter unit has almost no dependence on temperature. An energy-saving effect of approximately 17% was acheived in the total elevator system in one round trip under high temperature condition.

Feedback controllers are used to suppress disturbances and modelling error. In particular, position control error depends on feedback control performance. Therefore, extensive research has been devoted to the development of feedback control design. However, mechanical systems have many resonant modes, which disturb system stability and limit feedback control performance. Generally, notch filters are used to suppress resonant modes at the expense of phase delay, which also restricts bandwidth. In this paper, a method for the simultaneous design of a feedback controller and phase stabilization and gain stabilization compensators using the generalized KYP lemma is proposed. The generalized KYP lemma enables feedback control performance to be optimized while considering system stability. First, the structures of the feedback controllers and stabilization compensators are defined. Various control performances are formulated using frequency domain inequalities. Using the generalized KYP lemma, the feedback controller is optimized while considering various types of control performance. The effectiveness of the proposed design method is verified in application examples on the HDD benchmark problem.

In contactless power transformers, the electric power is transmitted at a high frequency. Therefore, the skin and proximity effects much increase the AC resistance. In this paper, the influence of the magnetic field and frequency on the equivalent resistance of the coils is evaluated. In addition, the iron loss characteristics are evaluated by considering the excitation voltage. The iron and copper losses due to the skin and proximity effects in a 300kW CPT transformer were estimated. Based on the results, the temperature rise characteristics were predictively studied using heat equivalent circuits. The results of this study contribute to the thermal design efforts of high power contactless power transformer coils.

As a simple vector control method for sensorless drives of permanent-magnet synchronous motors (PMSMs), a self-tuning power-factor-based vector control (PFVC) method has been reported. It can perform simultaneously three functions such as current limit, efficiency, and wide-speed range drive under a practical voltage limit. This method is realized in the stator current reference frame where the phase of the frame is identical to that of the stator current. This paper proposes a new self-tuning PFVC method realized in the voltage reference frame where the phase of the frame is identical to that of the stator voltage rather than the stator current. The proposed self-tuning PFVC method can perform simultaneously the three functions. The effectiveness and usefulness of the new method are verified through extensive experiments.

Voltage-fed converters have dead-time to protect the short-phenomenon of the DC-link voltage. However, this dead-time distorts the AC-output voltage and decreases the DC-link voltage utilization. To overcome these problems, the authors propose a PWM method without voltage error caused by the dead-time for a voltage-fed three-level converter. In this letter, the principle and theoretical operation of the proposed PWM method are described in detail and the theory is confirmed through experiments.