Estimating human stiffness is crucial for achieving precise robotic manipulation through variable impedance control. For in order to enable a robot to replicate human-like stiffness, it is essential to have a comprehensive understanding of the stiffness characteristics exhibited by humans during different tasks. Consequently, the development of an estimation method becomes imperative. One significant challenge in estimating human stiffness is to accurately assess arm stiffness when it is in contact with a highly rigid environment. Therefore, this study aimed to devise a method to estimate the stiffness of the human arm during contact with such environments. The proposed approach involves an equation for estimating arm stiffness using force information obtained from the human hand.

Magnetic-geared motors have many advantages over mechanical gearboxes, such as reduced maintenance and overload protection. However, the limited life of the mechanical bearings, which hold a high-speed rotor, is problematic in terms of durability. In this paper, a magnetic-geared motor with an integrated bearingless high-speed rotor having a novel structure is proposed to solve this problem. The proposed magnetic-geared motor has an additional three-phase winding to achieve magnetic suspension for the high-speed rotor. In addition, the proposed structure has a consequent-pole high-speed rotor for simplified suspension control, and it can reduce the number of sensors. This paper presents the principles of magnetic suspension and torque generation. In addition, a comparison of the magnetic suspension characteristics and torque capabilities of different motor topologies determined by finite element analysis is discussed.

Power electronics technologies play important roles in energy conservation and low-carbon goals, whereby power devices, such as silicon IGBTs and SiC-MOSFETs, are key components that support the efficient use of energy by power electronics and are indispensable for power supply and control. This paper provides an overview of market trends for power semiconductor devices, and introduces and focuses on state-of-the-art SiC power devices, such as SiC-MOSFET and SiC-SBD. This paper also reports on the requirements and applications of power electronics equipment that utilizes SiC power devices.

Automatic detection of defects in a substrate is important in the manufacturing process. Defect detection in metal-ceramic substrates relies on manual assembly lines, which are laborious and time consuming. This study develops a novel defect detection method that automatically localizes the substrate area without a background and enhances the defect area by combining images acquired using a platform with different illumination patterns. In this study, we use a defect image dataset to train convolutional neural networks (CNNs) for defect discrimination. Seven evaluation metrics, i.e., accuracy, F1-score, area under the curve, and prediction time of all the patch images in the test set, are comprehensively considered to select the optimal parameter configuration. A developed ResNet-50-based model achieves the highest defect discrimination accuracy of 99.8%. Based on extensive experiments and their results, this study provides clear guidance for devising a feature extraction method based on multidirection filter processing and optimization of CNNs for classification tasks. Finally, a framework for defect detection in a metal-ceramic substrate for practical use in the power device industry is developed.

The feedback of load-side acceleration is an effective method in the control of a two-inertia system. The load-side acceleration is generally obtained using an acceleration sensor. However, the bias drift of the sensor poses problems. Under an acceleration sensor bias, the velocity response experiences drift phenomena caused by sensor bias. In this paper, an observer that estimates the bias of the load-side acceleration sensor is designed. The proposed observer is evaluated using proportional velocity control. As an application, the proposed observer was applied to the load-side acceleration control, and it compensated for the effect of the acceleration sensor bias. Its effectiveness was verified through simulations and experiments.

Maximum torque per ampere (MTPA) control is a typical control method for achieving a high-efficiency operation for interior permanent magnet synchronous motors (IPMSMs). However, inductances of IPMSMs with magnetic saturation, vary depending on the current; thus, obtaining the MTPA condition is difficult. This study developed an online MTPA angle search method for IPMSMs with cross-saturation. In the proposed method, a flux-linkage plane is modeled and the model parameters are identified using the recursive least squares (RLS) method. The proposed method searches for the optimum current phase angle (MTPA angle) achieving MTPA control based on the gradient ascent method using the parameters identified for the flux-linkage plane model. This study conducted various experiments to evaluate the performance of the proposed online MTPA angle search method. The effectiveness of the method was demonstrated.

This paper presents the disturbance response and sensor-less force control of a magnetic lead screw actuator (MLSA) that generates linear motion; it is composed of a magnetic lead screw and a rotary motor. This MLSA exhibits elasticity owing to magnetic spring properties, and it can respond flexibly against disturbances. The implemented magnetic lead screw has a spiral structure composed of arc shape permanent magnets and soft iron teeth instead of a spiral shape permanent magnet. This design advantageously reduces the number of parts and simplifies assembly. In the experiment, both the MLSA and a ball screw actuator undergo forced oscillation induced by a load actuator. Each actuator is controlled to maintain the zero contact force. The root mean squared error of the MLSA was found to be smaller than that of the ball screw actuator, demonstrating superior disturbance response of the MLSA. In addition, the effectiveness of the sensor-less force control method focused on a magnetic phase difference was verified through modeling of thrust and friction characteristics in the experimental results. Control experiments indicate that the MLSA can regulate force without the need for a force sensor.

A dual current source inverter for an induction motor drive is presented in this paper. The dual inverter consists of two inverters connected in parallel and has single a dc power source. The inverters are operated using the same pulse width modulation (PWM) pattern, with one of the patterns being phase-shifted to the other. Each inverter supplies the torque current and the exciting current to the motor, respectively. The control strategies for constant voltage, constant exciting current, and slip frequency are demonstrated for the motor drives. The experimental results of the dual inverter are compared with those of the conventional single inverter in the steady-state and transient operation. The experiments show that, in the steady-state, the dual inverter system has the same motor characteristics as the single inverter system. The dual inverter can regulate not only the amplitude but also the phase of the output current, depending on the motor condition. The results from the transient operation demonstrate that the motor driven by the dual inverter can rapidly produce the desired torque and has good performance with fast response.

This paper is a re-evaluation of a completed project (High Efficiency Demonstration Grant Using High Voltage SiC Device) from the perspective of accurate efficiency measurement; additionally, this paper discusses on device dv/dt estimation. A topology called the high-efficiency energy conversion system (HEECS), which is one variety of partial boost circuit topologies, is introduced to achieve efficiency over 99.5%. The topology exhibits a very high efficiency for applications in which the output voltage variation is within a certain ratio of the rated output voltage. This paper summarizes the basic features of the topology and theoretically derives the principle of high-efficiency realization. The high efficiency is measured by the back-to-back (BTB) connection of two converters, and the efficiency and accuracy on this method are theoretically derived and confirmed using the measured data of 3.3kV output voltage at 100kW output. The theoretical estimation of dv/dt for a 3.3kV SiC device to reduce dual-active-bridge (DAB) soft-switching loss is discussed. Furthermore, a trend of DC-DC conversion efficiency is shown, and we show that the partial boost topology is a promising approach for achieving high efficiency dc-dc conversion.

High-switching frequency power converters are used in wireless power transmission and material processing. Soft-switching technique is crucial to reduce switching loss in high-frequency operation, e. g. ISM (Industrial Scientific and Medical) bands such as 13.56MHz and 27.12MHz. Recently, GaN power devices are expected to realize high-frequency operation of a power converter. The voltage dependency of the output capacitance in GaN power device exhibits highly nonlinear characteristics, making the analysis and design of the power converter difficult. This paper proposes to apply the sigmoid function to model the voltage dependency of the output capacitance in a GaN power device. The design of the class-E amplifier using the proposed model is presented. Circuit simulations with device model and experiments demonstrate class-E switching operation.

This paper presents a novel rotor structure for spoke-type interior permanent magnet motors. In the proposed motor, the rotor is fastened to the shaft using a resin unit. Thus, the inner-side core, which is the leakage path for the magnetic flux, can be eliminated. As a result, the torque density of the proposed motor can be improved compared with that of conventional motors without increasing the magnet volume. A numerical verification was performed using the finite element method to validate the effectiveness of the proposed structure. Moreover, the proposed structure was experimentally verified using a prototype motor. The results of numerical and experimental verifications indicate that the proposed structure could improve the torque density without increasing the magnet volume.

This study developed a two-dimensional heat path topology optimization method that minimizes the peak temperature inside motor slots. By representing the coil and varnish as a homogenized material, the problem was simplified to a two-phase topology optimization of the homogenized material and heat conductor. The motor performance was represented as a constraint on the magnetomotive force, which is related to the heating rate of the windings. Because the heating rate depends on the winding occupancy, we developed a new formulation for the sensitivity of the objective function. The heat path geometry was optimized without volume limitation under the trade-off relationship between the heat transfer efficiency and heat generation rate. The results indicated an 8.84% reduction in the peak temperature of a motor slot compared to that of a conventional simple aluminum plate.

This paper proposes a phase-synchronization method for double-sided LCC wireless power transfer systems with active rectifiers, achieved by using a current detector. The detector can be constructed inexpensively by simply adding a winding to the compensation inductor. Furthermore, the detector provides voltage step-down and isolation functions. Experimental results confirmed that the proposed method successfully synchronizes the primary and secondary systems across a wide range of coupling states for the transmission coils, with a coupling factor k ranging from 0.05 to 0.3.

In high-speed surface permanent-magnet motors, eddy current loss in the rotor caused by magnetic flux harmonics is a significant problem. Although copper sleeves can reduce the eddy current loss of the rotor, the reduction effect on each eddy current harmonic component is not clear. In this paper, we calculate the eddy current loss in the rotor using finite element analysis, divide the losses into each harmonic magnetic flux component, and analyze the influence of copper sleeve on each harmonic component. Based on the knowledge obtained in the analysis, we propose the use of copper sleeve with holes as a method for reducing rotor loss further. The effect of the proposed method is verified using electromagnetic simulation.

This paper proposes a zero-voltage switching (ZVS) scheme for a dual active bridge (DAB) converter in the full load range. The switching state of the DAB converter with a phase-shift control becomes a hard switching state under an input and output voltage imbalance or light load. Thus, the proposed method regulates the phase-shift angle, output voltage angle of full-bridge circuits, and switching frequency to achieve ZVS for the DAB converter. The DAB converter implementing the proposed ZVS scheme is applied to vehicle-to-home (V2H) systems. Experimental results reveal that a V2H unit using the DAB converter achieves an efficiency 97.2% with the proposed ZVS scheme.