A load torque control system using an electromagnetic motor with a reduction gear, a spring, and motor/load-side encoders is designed. Frequency analysis indicates that the control system with a low-stiffness spring has high robustness against backlash modeling error and high disturbance suppression characteristics. However, the control system has low target tracking characteristics and frequently causes current saturation. Therefore, this study addresses this problem by optimizing not only parameters of the controller but also the stiffness of the spring. The validity of the optimized control system is verified by simulations and experiments.

Electrochemical machining (ECM) is a processing method for metals that uses a DC power supply and flowing electrolyte. In some cases, discharge occurs during ECM when the gap between the electrode and workpiece, whose distance is rather small, is filled with hydrogen generated via electrolysis. We attempt to utilize a DC inductor placed between the DC supply and the electrochemical machining load in order to limit di/dt of the short or discharge current, which damages both the electrode and workpiece. When the output current surges, that is, when discharge occurs, the output voltage is suppressed by the DC inductance. In this paper, we propose a method for designing a PWM rectifier to reduce the discharge current, establish a linear approximation model for use in the PWM rectifier, describe a control method of the PWM rectifier, and demonstrate the efficacy of the model via simulations and experiments.

In electric turbocharger systems, in which the permanent magnet synchronous motor (PMSM) is driven by the power generated by the permanent magnet synchronous generator (PMSG) connected to the internal combustion engine to assist the drive power of the compressor, it is required to reduce the capacitance of the DC-link capacitor between the PWM rectifier and the inverter. However, if a DC-link capacitor with small capacitance is used, the DC-link voltage fluctuates in transient conditions such as when the engine speed fluctuates. Therefore, this study investigates the suppression control of the DC-link voltage in the transient state. In addition, an experimental system with a diesel engine and an electric turbocharger is constructed. Using this experimental system with an 870µF film capacitor, the DC-link voltage fluctuation could be suppressed by maximum of 17.5 and 16.5 points during turbine acceleration and deceleration, respectively. This was achieved by feed-forward control of the generator-side current. The results revealed that the DC-link voltage fluctuation could be suppressed by a maximum of 17.5 points during turbine acceleration and 16.5 points during turbine deceleration.

This paper proposes a novel method for building multi-type air-conditioners, wherein the power management control system can automatically adapt to various air-conditioning environments using reinforcement learning. Our previous study reduced the learning period by pre-training on a virtual building and simulated the dynamic power characteristics of air-conditioners and room temperature. However, advantages of decreasing the learning period diminish when the difference between the virtual and actual buildings is significant. Therefore, our proposed method first performs pre-training on multiple virtual buildings with different environments. Subsequently, it selects the one whose environment is closest to that of the actual building based on the difference in average rewards.

This paper proposes methodology and gate drive circuit that can immediately detect short-circuit (SC) of multi-paralleled SiC-MOSFETs even under current imbalance condition. Proposed method detects SC current using an integration circuit that can sense di/dt. The detection level of SC current can be adjusted to a desired value regardless of the number of SiC-MOSFETs connected in parallel. The effectiveness of the proposed approach was experimentally validated for four-paralleled SiC-MOSFETs under extreme current imbalance in SC condition. SC was detected within 0.5µs and all SiC-MOSFETs were protected without destruction at most 2.2µs after the onset of SC, for all types of SC 1, 2 and 3.

Joint gap measurement is an important inspection to prevent buckling of railways. However, this measurement is labor intensive and time consuming because the tracks are too long for manual inspections. Therefore, we have developed a rail joint gap measurement method using train frontal images recorded by a handy video camcorder. In this paper, we describe details pertaining to the proposed method and discuss the measurement results obtained based on an experiment involving a commercial train.

This paper presents a novel control method for reducing the torque ripple in permanent magnet synchronous motors. Conventional motor control methods for reducing torque ripple require advance preparation of ripple data, which is time-consuming and resource intensive, making such methods unsuitable for practical use. The proposed motor control scheme utilizes the M-axis current, which includes the information of magnet flux fluctuation, and does not require any torque ripple data. Simulation and experimental results confirm the torque ripple reduction effect of the proposed motor control.

Position detection sensors for railway vehicles can detect railway vehicle locations by detecting multiple metal markers placed along the tracks. However, the effect of the railway body on the sensitivity of the sensor and the reduction in this effect are yet to be investigated. Therefore, the effect of the railway body on the detection sensitivity was evaluated, and the use of magnetic shielding on the sensor was considered. Consequently, the use of a magnetic shield plate on the sensor reduced the effect of the material and structure of the railway body on the sensitivity of the sensor to 37%.

An interior permanent magnet synchronous motor (IPMSM) is characterized by its high efficiency. However, torque ripple and loss occur because of the spatial harmonics generated by air-gap permeance fluctuations. This study clarified that slot harmonic components can be suppressed by inserting magnetic wedges made of a magnetic composite material in the slot opening of an IPMSM. First, the authors examined the torque and loss characteristics by varying relative permeability and saturation magnetic flux density of magnetic wedges using finite element analysis (FEA). Results indicated that the torque ripple and loss could be suppressed when relative permeability of the magnetic wedge was μ_r = 10 to 22 and the saturation magnetic flux density was B_s = 0.5 to 0.75T. Furthermore, the authors produced magnetic composite materials made of various soft magnetic material powders and examined their magnetic properties and viscosities. Results showed that a magnetic composite material with optimal magnetic properties and injectable viscosity could be manufactured using Fe-Si-Al with a low volume fraction.

As electric vehicle (EV) battery voltages are increasing from 400V to 600-800V, an on-board boost converter with 1.5X step-up conversion ratio is required to utilize existing 500V chargers. This paper proposes a zero-voltage switching (ZVS) resonant flying switched capacitor converter with 1.5X fixed step-up conversion ratio. The theoretical model of efficiency and circuit volume reveals that, in comparison with a conventional zero-current switching topology, the proposed ZVS converter achieves higher efficiency and reduced circuit volume by eliminating fixed losses of semiconductor devices. The experimental results of a 1-kW prototype agreed well in terms of efficiency and circuit volume, verifying the theoretical model.