This study proposes angle detection technique to reduce angular errors due to the coupling between the two windings of a split-winding dual resolver. The proposed technique comprises two elements. First, the voltage frequencies of the two excited windings of the split-winding dual resolver differ from each other. Secondly, the sampled voltage of one of the output windings is processed to reduce the interference voltage from one other winding. The experimental results indicate that the proposed technique can reduce the angular errors substantially.

This paper proposes a new gradient driver with a gradational voltage inverter for low power loss and downsized filter circuits. Gradient drivers produce direct current with low ripple amplitudes to achieve high image quality and high slew rates to obtain images rapidly. The proposed gradient driver is characterized by low ripple amplitude of the output current from the inverter composed of SiC-MOSFETs and high output voltage from another inverter composed of IGBTs. This paper discusses both the principle of operation and control method of the new gradient driver. Experimental verification is performed on a full-scale system. The results show the advantages of the proposed gradient driver based on loss analysis by calculations.

To construct a new inspection technique for insulation systems of wind turbine generators, we propose an on-line insulation degradation diagnosis system that monitors the load and capacitive leakage currents. Both currents with different service operation periods in the same wind firm were measured in the field. The SN ratio of the measured currents for a doubly fed generator driven by a power conditioning subsystem could be more than 40 dB using the developed diagnosis system. The difference between the off-line current converted from the capacitance and the on-line leakage current was evaluated. Furthermore, variational correlations between the load current and capacitive leakage currents of the generators were verified, indicating that signs of insulation degradation in the wind turbine generator could be detected using the proposed system.

This paper proposes an automatic design method of typical parameters such as number of phases, number of poles, stack thickness, stator outer diameter, rotor outer diameter, and number of turns of a switched reluctance motor from the requirement of the N-T characteristic. In particular, a specific parameter related to the magnetic saturation is defined in order to arbitrarily determine how much to use the magnetic properties of the iron core material. In the proposed method, the typical motor parameters in order to realize a miniaturized volume which satisfies an input N-T characteristic are obtained by setting the parameter related to magnetic saturation, maximum electrical frequency, maximum current density, maximum copper loss, conductor slot fill factor, magnetic properties of material, and input voltage. The designed motor is analyzed using the Finite Element Method in order to validate the proposed method.

In this study, we propose a novel pulse-width modulation (PWM) method to reduces common-mode noise. The proposed method includes a 120-degree dormant two-phase modulated three-phase inverter that the comparative carrier of one of the two modulation phases. This configuration is easy to implement because it uses a triangular-wave carrier comparison. In an experiment using a three-phase inverter, the common-mode current was reduced by approximately 60%, and in particular, the carrier frequency component was reduced to approximately 1/10 that of the conventional sine-wave comparison PWM.

Dynamic wireless power transfer (DWPT) systems have garnered considerable interest for promoting the sale of battery electric vehicles (BEVs). In DWPT, a receiving coil is attached to the vehicle and power is transmitted during driving. Therefore, depending on the coil mounting location, the gap between coils may vary according to acceleration/deceleration and unevenness of the road surface during driving, which may affect power transmission. In this study, we quantify the amount of variation in the gap between coils depending on the coil mounting location by taking into account the suspension variation and tire deformation due to load changes during actual driving. The coil gap variation effects on power transfer due to the coil mounting location is thus investigated experimentally.

Harmonic magnetic field analysis considering magnetic saturation and a DC bias magnetic field has been developed to rapidly calculate the high-frequency inductance and resistance of a motor during operation and to build its equivalent circuit model to describe the corresponding high-frequency phenomena. This novel analysis method has been found to be faster than the conventional nonlinear transient analysis by 6-7 times (in the 2D case) or 17-20 times (in the 3D case). When the proposed technique is applied to a typical permanent magnet synchronous motor, it is observed that the resistance increases at frequencies above 100Hz, and the inductance decreases at frequencies above 1kHz. It is also noted that the high-frequency inductance and resistance reduce to 1/5 of their original values as the phase current increases, while their variations with the rotor position are no more than 13%.

Triple active bridge (TAB) DC/DC converters have attracted attention in power distribution systems because of their ability to connect multiple DC power sources organically. In previous research, it is reported that the reactive power increase owing to cross-currents between the power sources in operating areas with imbalanced power loads. This paper proposes a control method to suppress such cross-currents by intermittently turning off all the gates of a specific active bridge connected to the power source. Moreover, a power transmission model is derived, and the control parameters are calculated by formulating the power factor optimization problem based on the model. Experiments were conducted to verify the advantages of the proposed control method. The results showed that the proposed control method was useful in about 10% of the total operating area. In addition, it was confirmed that the power conversion efficiency was improved by about 3 percentage points at the operating point where the cross-currents were maximally reduced.

This study proposes a method to estimate the states-of-charge (SoCs) and states-of-temperature (SoTs) of secondary batteries using neural networks and electrochemical impedance spectroscopy. The impedances in the frequency range of 100mHz-10kHz of a general lithium-ion battery were measured for various SoCs and SoTs and used for training a neural network with two hidden layers. The performance was evaluated using the measured impedances that were not used for the training. The mean square errors obtained were 2.094% and 0.511°C for SoC and SoT respectively.

This research group focuses on the control algorithm of motor drive systems. This document introduces our research topics and activities.