The paper proposes a driving technique that combines a gate pulse time adjustment method with an AC core method to suppress circulating and resonant currents in parallel inverters. The time adjustment method introduces controlled delays in the PWM signals output from the motor controller, while the AC core method connects the inverter output lines through oppositely wound cores, of each inverter, thereby contributing to system miniaturization. Experimental results show that, under operating conditions of 850V and 760Arms, the proposed approach reduces circulating current by 59% and Y-capacitor current by 63% compared with a conventional system without the proposed methods. These results indicate that the proposed technique effectively enhances the power density of parallel inverter systems.

In large-scale factories and power plants, clogging in metal pipes poses a significant risk for serious accidents, making regular inspections essential. Traditionally, non-destructive inspection methods such as endoscopy and radiographic techniques have been commonly used, but the operational challenges incur significant time and effort. Inspection methods using electromagnetic waves, as proposed in previous studies, offer the advantage of rapid defect detection regardless of pipe length. However, inspection methods using electromagnetic waves often rely on experience-based threshold settings, which limits detection accuracy improvements. In this study, we propose a defect detection method that uses machine learning to analyzes the large datasets obtained from electromagnetic field simulators. Specifically, converting the propagation characteristics derived from S-parameters into statistical values significantly improved the accuracy of the predictive model. This advancement enabled the detection of small defects as tiny as 2mm, which were previously difficult to identify using conventional methods, thereby increasing the accuracy and efficiency of defect detection. Through this research, we demonstrate the effectiveness of machine learning-based defect detection, which was not thoroughly explored in previous studies.

This paper presents a current energization method for suppressing torque ripple in permanent magnet synchronous motors. The proposed approach superimposes a cancellation current onto the current reference of the feedback current controller to reduce torque ripple. To ensure accurate injection of the cancellation current at frequencies exceeding the bandwidth of the feedback current controller, a compensation voltage is additionally applied. Experimental results demonstrate the effectiveness of the proposed method.

In this paper, an active power decoupling method using a Dual Active Bridge (DAB) converter is proposed for isolated single-phase AC-DC converter applications. The single-phase power ripple at twice the grid frequency increases the volume of energy buffer as the electrolytic capacitor. Moreover, the electrolytic capacitor may limit the system reliability of the single-phase converter. The active power decoupling technique is a solution to this problem. However, the additional component that provides power decoupling capability decreases power density and efficiency. This paper proposes an active power decoupling method without additional components. The validity of the proposed method is demonstrated by the experimental result. As an experimental result, it was confirmed that the second harmonic component in DC voltage was reduced by 98.5%.

This research marks the first public road experiment of dynamic wireless power transfer (DWPT) to a moving electric vehicle (EV) in Japan. In the experiments, the prototype DWPT system succeeded in transmitting approximately 10kW of power to an actual automobile, recharging 63.3% of the power consumed in driving to the EV by the DWPT system, thereby suppressing the decline in the remaining battery energy. After 18 months of testing, the parameters of the transmission coil buried under the public road were stable against environmental changes without any undesirable behaviors such as false detection or false transmission to other general vehicles. Therefore, the prototype DWPT system can be effectively operated on public roads for a long period of time, and its usefulness was confirmed in an actual automobile on the public road.

This paper presents a pulse design method for synchronous PWM that considers motor current control. Several existing design methods that account for the fundamental and harmonics components of the inverter output voltage have been reported. However, our research reveals that these conventional methods can lead to an unexpected increase in current harmonics. This paper clarifies that this issue arises from the voltage transfer characteristics between the voltage reference and the inverter output. Based on this analysis, we propose new design guidelines for Synchronous PWM. The propose method fully satisfies these guidelines, and its effectiveness is verified through simulation and experimental results.

This paper proposes a method that uses motor leakage inductance to reduce the capacitance in voltage doubler partial switching power factor correction (PFC) converters by utilizing the leakage inductance of a motor. The proposed circuit connects the neutral point of the capacitor leg in the voltage doubler partial switching converter to the neutral point of the motor. This method reduces the capacitance of the capacitor leg by controlling the neutral-point voltage through the zero sequence of a three-phase inverter and the leakage inductance of the motor. Furthermore, the proposed approach incorporates balancing control for the neutral-point voltage of the capacitor leg. An IS-P control strategy is implemented within the voltage control system to enhance the performance of the balancing control because the unbalanced component is primarily influenced by the double-frequency component of the power supply. The validity of the proposed method was confirmed through a prototype. The results showed that capacitance was reduced by 99.6%. In addition, the DC offset in the input current is reduced by 76% by applying voltage balance control.

Simple and cost-effective methods for cavitation detection are essential for stable operation of water pump systems. This paper reviews the characteristics of motor current signals under cavitation conditions and propose a cavitation detection technique for inverter-driven pumps based on these signals. Experimental observations show that the spectral “foot” around the fundamental harmonic in the power spectral density (PSD) of the motor current signals increases during cavitation. Based on this observation, we define an evaluation value metric that quantifies this feature for cavitation detection.

This paper proposes a new method for configuring and designing an adaptive vector control system for permanent-magnet synchronous motors (PMSMs). The adaptive vector control system based on the proposed method adaptively identifies all four parameters of a PMSM simultaneously, and exhibits the following performance. Over the range of 1% to 100% rated speed, the steady-state relative torque error between the command and response is maintained below 0.2% under ideal conditions. Even when the four parameters vary simultaneously and discontinuously, adaptive identification is completed approximately 0.2s after the change, and the desired performance is achieved. Even when the motor speed varies at an acceleration rate of 250rad/s², the desired performance is achieved without being affected by the speed change. The proposed method can be applied to both salient-pole and non-salient-pole PMSMs without any modification.

This paper presents a common-mode (CM) noise model for solid-state transformers (SSTs) with input-series output-parallel (ISOP) connection. A gradational modulation technique that combines PWM and square-wave output cells is proposed for noise reduction. The proposed CM equivalent circuit is validated through experimental measurements on an actual SST prototype. Experimental results demonstrate that the gradational modulation effectively reduces CM noise, confirming the effectiveness of the proposed approach.

In this study, we propose a DC active filter (DCAF) designed to compensate for ripple current in the input to a dual active bridge (DAB) converter. The DCAF is connected in series between a DC source and a DAB converter via a matching transformer. The proposed filter functions as a resistor to dissipate ripple current in the input to the DAB converter. The DC magnetic flux caused by the DC offset of the reference output voltage of the proposed DCAF can be suppressed by applying a control method to prevent DC magnetization. Experimental results demonstrate that the ripple current in the input to the DAB converter was reduced to 75.2% of its original value using the proposed method.

Our research focuses on power electronics, electric machines, and high voltage engineering, especially, ac motor drives, matrix converters, high-performance power sources, voltage sag and swell compensators, wind power generation systems with induction machine. The outline of our research is presented in this paper.