This paper proposes a neutral point (NP) voltage balancing control technique for 3-level inverters operating at high modulation ratios. Compared to 2-level inverters, 3-level inverters offer lower output voltage total harmonic distortion by generating three level output voltages through a NP clamped by DC-link capacitors. However, NP voltage imbalance occur due to current flow through the NP. While various NP voltage balancing methods have been developed, their performance typically degrades at high modulation ratios. To address this issue, this paper introduces a new pulse-width modulation (PWM) technique designed to enhance NP voltage balancing performance under high modulation conditions.

Japan, a country prone to disasters, frequently experiences large-scale power outages caused that disrupts business operations. As a result, resilient office buildings equipped with photovoltaic power generation and storage batteries are gaining attention for their potential to enhance business continuity. To support advance planning of business continuity plans (BCPs), numerous mathematical models have been developed to optimize building operations during power outages. However, accuracy can lead to operational failures during actual disasters, resulting in extensive damage. Therefore, it is essential that these models incorporate economic viability, realistic operational strategies, and disaster-related uncertainties. Despite this need, no existing model integrates all of these factors. This study proposes an operational optimization model for office buildings during power outages that accounts for economic usefulness, realistic operation, and disaster uncertainty. The effectiveness of the proposed model will be evaluated based on its economic benefits and the practicality of its operational plans.

A double-track railway terminus often becomes a bottleneck under high train frequency owing to longer dwell times and frequent conflicts between trains moving in both directions. This study evaluates the track layout at the terminus by optimizing the order of arrivals and departures to achieve the highest train frequency. Based on the result of our initial analysis which indicated that this optimization problem closely resembles the “Asynchronous Travelling Salesman Problem”, an NP-hard problem, we applied genetic algorithm and obtained satisfactory optimisation results. We believe that this technique holds potential for improving the performance of urban railways.

This paper proposes a novel capacitor current reduction method in dual three-phase permanent magnet synchronous motor (PMSM) drive system. Using model predictive control and considering the dead time, the method modifies the three-phase voltage command generated by the proportional integral(PI) current controller for the current reduction. The effectiveness is verified by simulations and experiments.

To enable efficeint vibration diagnosis of rotating machinery in industry settings, we investigate a spectral analysis approach for accurately estimating the envelope spectrum from short-duration vibration signals, thereby reducing data traffic. We propose the use of the maximum entropy method as the spectral estimation algorithm for short-record vibration data and demonstrate that it achieves significantly higher accuracy than the commonly used Fast Fourier Transform. Through analysis of both simulated and measured vibration data, we show that this approach can reduce the data required for vibration diagnosis to approximately one-tenth of that required by conventional methods.

Interlocking is a promising technique for assembling laminated electrical steel sheets in electrical machines. However, it can create short circuits along the lamination direction, leading to additional eddy-current loss. For a better prediction of the efficiency of electrical machines, the additional loss should be calculated accurately. In this study, we have estimated the electrical resistance of the short circuits caused by interlocking. First, we measured the resistance between various points in a laminated core. Next, using a circuit simulator, we calculated the resistance of the short circuits. The value of resistance obtained in this study will be used for the calculations of eddy-current loss in electrical machines.

A new minimum total loss trajectory is derived and analyzed based on the novel mathematical model of permanent-magnet synchronous motor proposed by Shinnaka in 2024, which required considering the iron loss. The analysis shows that the new trajectory has the following characteristics: (a) The new trajectory exhibits zero-point passing characteristics at zero torque regardless of speed. (b) The new trajectory is identical to the conventional trajectory in the high torque region.

This article introduces Power Electronics Laboratory at Department of Electrical and Electronic Engineering, Hokkaido University of Science. Our laboratory focuses on loss reduction of air-core inductors, precise loss measurement of high-frequency transformers, and mitigation methods of electromagnetic noise generated in power converters.