This paper discusses the factors for reducing torque ripple in a topology-optimized shape of a synchronous reluctance motor (SynRM) considering multiple driving points. To fairly compare the torque characteristics of the proposed SynRM with those of conventional SynRMs with multiple-flux barriers and the topology-optimized shape considering a single driving point, we discuss magnetic properties for wide driving points. In this work, we use the Fourier components of a magnetic force density (MFD) in the air gap for discussing the difference in the torque ripple of the proposed and conventional SynRMs. Moreover, we modify the flux barrier shape in the proposed SynRM to verify the effectiveness for torque ripple reduction of the topology-optimized shape. We observe that the proposed SynRM not only reduces the spatial higher harmonics of MFDs for minimum and maximum torques but also matches their phases to reduce the torque ripple.

We proposed a two-phase PWM scheme using one variable switching pause period to equalize device losses in unbalance three-phase inverters. However, the two-phase PWM scheme did not effectively equalize losses of unbalanced three-phase inverter. Therefore, we propose a two-phase PWM scheme utilizing 2-degrees-of-freedom (2-DOF) variable switching pause periods. Some experimental results demonstrate that the proposed PWM scheme successfully equalizes the device losses of unbalance three-phase inverter.

In this study, we aimed to accurately measure the current passing through a planer conductor with rectangular cross section in electronic circuits such as those of power converters, which feature increasingly high frequencies. Recently, the authors invented an optical-probe current sensor based on the Faraday-effect employing a very small sensor head with low insertion impedance. We investigated a method for measuring the magnetic field on conductor surface using this sensor, and a method for inversely analyzing the current distribution in planer conductors such as surface wiring on printed circuit boards, transistor outline package leads, and busbars. Furthermore, we discuss the inverse analysis method for current distribution using gradient descent based on the measured magnetic field distribution. Finally, we present the transient response of current distribution and total current analyzed by gradient descent.

The impedance-based method for stability analysis evaluates the stability of the entire power system using only measured data. It maintains the confidentiality of design details of distributed energy resource (DERs) while ensuring system stability prior to operation. However, the need for large and expensive devices capable of inducing small voltage or current perturbations across a wide bandwidth hinders the broader adoption of this method. To address this challenge, this study explores the potential integration of analysis devices within the DERs themselves, focusing on the development of a perturbation generator and a corresponding algorithm that leverages a compact power converter to generate perturbation voltages. The proposed approach enables precise impedance measurements, including the control algorithms of both the power system and the connected DERs.

When railway line sections are partially disrupted due to damage from large-scale natural disasters, it is necessary to prepare crew schedule plans for temporary timetables. In such a case, a crew schedule plan ensures that duties once assigned to crew members are not changed. As this task is time-consuming for schedule planners, an automatic crew scheduling method for supporting planners is desired. In this paper, we focus on crew scheduling following a large-scale natural disaster. The proposed algorithm is based on mathematical programming and column generation. In addition, we show the results of computational experiments based on a real disaster case, which indicate that the proposed algorithm can generate an efficient schedule plan in a short time.

This paper proposes a rapid initial rotor-position estimation technique that simultaneously identifies the magnetic polarity and position of a permanent-magnet synchronous motor (PMSM), based on the magnetic saturation and saliency characteristics using the motor current caused by the voltage injection. The method is verified experimentally using an electric-vehicle motor. The experimental results show that the method rapidly and accurately estimates the initial rotor position.

Localized wear of pantograph contact strips is a significant problem affecting current-collecting systems in electric railways, given that it can lead to fusion of the pantograph head and cause severe damage to the overhead contact wire. However, the causes of localized wear of carbon-based contact strips have not been fully clarified, making it difficult to establish effective prevention measures. In this study, we aimed to clarify the progression mechanism of localized wear in copper-impregnated carbon-based contact strips. We conducted on-track observations of the progression process of the localized wear, wear experiments and an analysis of the restraint behavior of the contact wire at the worn position of contact strips. As a result, it is suggested that rapid progression of localized wear may occur owning to repeated arc discharge occurring at the worn position and the subsequent restraint of the contact wire at that position.

In this study, a motor was developed with a target output of 55kW and IE5-level efficiency. To reduce harmonic losses that increase at high speeds, a low-loss structure using amorphous metal was investigated. The rotor adopts an IPM structure, and the core shape was designed as durable via stress analysis. A prototype was developed with the aforementioned structure, and the fundamental performance of the motor was evaluated to verify the validity of the design. An efficiency of 95% was confirmed at 20kr/min and 55kW, and thereby, the target efficiency was achieved.

The magnetic properties of electrical steel sheets, which are used for the magnetic cores of motors, are known to deteriorate with stress. To assess these deteriorations, it is necessary to measure magnetic properties because the degree of deterioration with stress varies depending on the grades of electrical steel sheets. In this report, an estimation method is proposed for the magnetization curve under elastic stress, and its estimation accuracy is verified through magnetic field analysis.

In this paper, we propose a new type of hybrid excited motor called “doubly-excited variable-flux consequent pole motor (DeVFCM)”. The DeVFCM consists of a three-phase double Y-connected armature winding with two neutral points, O₁ and O₂, and field poles with alternating permanent magnet and iron poles. When a DC voltage for supplying the field current is applied across O₁ and O₂ in such a configuration, the armature winding also acts as a field winding, and the magnetic flux through the iron poles can be adjusted. To validate the principle of this DeVFCM, a prototype machine was fabricated, and the basic characteristics of the prototype machine were investigated through three-dimensional finite element analysis and experiments. The results show that both high torque generation and loss reduction at high speeds can be achieved by adjusting the field current.