Piezoelectric transducers are widely used, for example, in distance sensing applications. Recently, there have been many studies on the application of piezoelectric transducers to antennas used for very low frequency radio wave communication, especially those used for underwater communications and IoT applications. These transducers are essentially narrow-band electromechanical resonators. In order to drive these transducers efficiently, accurate electrical equivalent circuits are required when designing the drive circuit. This paper introduces a method for determining the values of equivalent circuit components over a relatively wide frequency range, taking into account two series resonating circuits. We use evolutionary programming to find the circuit constants. Although the algorithm does not calculate the constant values analytically, the resulting equivalent circuit is evaluated in terms of the residual admittance over the range of frequencies, and it is shown to emulate the actual circuits reasonably well.

A brush-slip ring system enables the transfer of electrical current between stationary and moving parts. It is widely used mainly in the excitation mechanism of AC rotating machines. In recent years, various brush-slip ring systems have been developed. Their uses range from automotive alternators to grounding mechanisms for electric railways. Therefore, brush-slip ring systems require maintenance-saving features and improved reliability.

Until now, copper materials have been used for slip rings. In recent years, considering their mechanical strength and cost, the use of steel slip rings is increasing. However, the sliding contact energization characteristics of steel slip rings have not yet been elucidated.

In this study, we examined the V-I characteristics of a steel slip ring (S45C) and a Ag graphite brush (Ag content 50, 60, 70, 80, and 90wt%). As a result, the electrical characteristic of the steel slip ring was found to be unique. In addition, the effect of the Ag content of the brush on this characteristic cannot be ignored. Therefore, we estimated the contact point temperature for each brush Ag content using the φ-θ theory. Based on this, the current-carrying characteristics of the steel slip ring and Ag graphite brushes were clarified for each brush Ag content.

This paper presents a control scheme for smooth torque production in permanent-magnet synchronous motor drives. The proposed control scheme consists of two techniques: a feedforward compensation for torque ripple minimization and an online parameter estimation technique for harmonic fluxes. The feedforward compensation is constructed on a position-sensorless vector control system and generates voltage commands to suppress torque ripples. The command calculation process requires the parameters of the harmonic fluxes; therefore, the proposed control scheme includes their estimator and calculates them from detected current information. These techniques are simpler than existing ones and can be implemented on a computational device with a small amount of calculation load. The proposed control scheme is verified by performing simulations and experiments.

This paper describes the methods for improving the performance of an active common-noise canceler (ACC) that suppresses the common-mode (CM) voltage generated by inverters. Whereas the already proposed ACC (ACC0) compatible with space vector pulse width modulation requires two emitter follower circuits, this paper proposes an improved ACC (ACC1) that requires a single emitter follower. In addition, an ACC (ACC2) that improves the CM voltage suppression performance by adding a feedback circuit to ACC1 is also proposed. The experimental results show that ACC1 improved the CM voltage attenuation by -10dB compared to ACC0, and ACC2 improved the CM voltage attenuation by -20dB compared to ACC1. ACC2 has a large CM voltage attenuation of up to -53dB in the wide frequency range from 100kHz to 5MHz.

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 motor system considering its fault tolerant function. In this study, an open-winding structure PMSM driven by dual three-phase inverters, which share a DC bus source, is used for the proposed third harmonic current control. By using third harmonic current control, it is possible to reduce both the sixth order torque ripple component and the second order radial force. The performance of the third harmonic current control of the open-winding PMSM is verified through FEA and experimental results.

This paper describes a 680W output switching power supply using a flying capacitor type 3-level PFC for single-phase 200V or 400V input. With this input specification, because the voltage and current range of the PFC converter is wider than that of a conventional power supply, the PFC inductor has a large inductance and current capacity, which leads to an increase in size. The adoption of a 3-level circuit can suppress the inductor size increase. The circuit is configured by connecting a flying capacitor type three-level chopper to the diode bridge. Like the conventional PFC, this circuit can make the reference potential of the control circuit the same as that of the DC output negative terminal. This configuration simplifies the gate drive and current detection circuits compared to other three-level circuits. In the DC/DC converter, a neutral point clamp type three-level circuit is used as a means to apply power devices whose rated voltage is lower than the circuit voltage in series. The control method, prototype, and evaluation results are demonstrated. At the rated load, efficiency exceeding 87% was obtained at both 200V and 400V inputs.

This paper reports on a study of the electromagnetic force with respect to excitation frequency changes in a three-phase annular linear electromagnetic pump, assuming pumping of molten aluminum. A prototype of a small-scale proof-of-principle machine that simulates aluminum melt with an aluminum pipe was fabricated, and the electromagnetic force generated in the aluminum pipe was measured using a pure sinusoidal power supply while changing the excitation frequency. The results clarified experimentally that the electromagnetic force characteristics with respect to the magnetomotive force changed from a linear increase to a quadratic increase as the excitation frequency increased. In addition, the results were analyzed using an equivalent circuit method.

Overheating due to the screw slackening of a circuit breaker, an electromagnetic switch, a terminal, or a plug-receptacle in a distribution panel or an electric apparatus is one of the main causes of fire accidents originating from electrical equipment in industrial and domestic environments. In this study, we propose a novel screw slackening sensing method for a commercially available 100V blanch circuit breaker. Attention is paid to the conducted emission spectrum obtained during discharge, which occasionally occurs in a small gap between the slackened connected conductors. An investigation of the screw slackening is conducted based on a convolutional neural network. Thus, the proposed approach serves as a potentially effective method for the prevention of fire accidents due to screw slackening.

To increase the power density of power converters, it is crucial to not only utilize SiC and GaN power devices but also to reduce loss and volume of the passive components. High-dielectric-constant-type ceramic capacitors having high current capacity with small volume are good candidates to be used in high-frequency and high-power-density converters. In terms of a practical designing process, accurate evaluation of the loss characteristics of passive components is critical. However, accurate loss evaluation of ceramic capacitors under practical operating conditions, such as nonsinusoidal high-current conditions, has not been reported. In this study, the loss characteristics of a high-dielectric-constant-type ceramic capacitor are measured by a custom-developed capacitor loss analyzer. As a result of extracting the characteristics of loss from the measurement results, it is suggested that the loss of the sample is dominated by dielectric loss. A new loss calculation method is also studied.