Demand for inverter air conditioners with superior energy conservation properties has recently increased globally. To promote inverter air conditioners, an electrolytic capacitor-less inverter is proposed that can meet the power supply harmonics regulations as a low-cost solution. This study presents motor current optimization technique based on the equations for an IPMSM and an electrolytic capacitor-less inverter, and the reduction of heavy rare earth. As a result, the motor peak current was reduced by 6.7% and the inductance of the AC input inductor was reduced, and the amount of heavy rare earth elements used in permanent magnet synchronous motors was decreased to less than 1/10th of that used in 1996.

This paper focuses on controlling directly the load-side acceleration to suppress the vibration of the industrial robots, which is modeled as a two-inertia system. This paper proposes a load-side acceleration control based on a single inertialization compensator (SIC) and a jerk observer (JOb). A wideband acceleration sensor capable of acquiring the direct current component is installed on the load side of the experimental equipment. Using this acceleration signal, the single inertialization of a two-inertia system is realized and the JOb is designed. The load-side acceleration control suppresses the resonant vibration of the two-inertia system by designing an acceleration controller using JOb. Two load-side acceleration controller designs are proposed. The effectiveness of these designs is verified by theoretical analysis, simulations, and experiments based on one joint of an industrial robot.

Multiport converters can be achieved from the modular multilevel converter (MMC) configuration by integrating generation units or loads at the cell level. This can offer advantages in applications such as photovoltaic panels and battery storage units where the loads or generation units have a modular structure. However, this multiport configuration requires an active power balancing of the cells both between arms (inter-arm balancing) and within the arms (intra-arm balancing). It has been pointed out that the intra-arm balancing controller has a compensation limit for the power unbalance. This paper introduces an evaluation functional for quantifying the compensation capabilities of intra-arm balancing controllers in a multiport converter controlled with phase shifted modulation. Two intra-arm balancing control strategies with extended compensation capabilities are developed by maximizing this proposed evaluation functional. The first strategy uses either the dc or grid-frequency component to modify the cell ac voltage depending on the operating conditions. The second proposed method adds also higher harmonic components to the cell ac voltage to further improve the balancing performance. A theoretical evaluation and numerical analysis indicate that the two proposed controllers offer compensation capabilities superior to those of conventional methods. In addition, experimental results confirm the validity of the proposed controllers.

The objective of this study was to achieve thrust control of a propeller propulsion system with two rotor blades rotated by a motor. Previously reported thrust control methods employ constant thrust coefficients or variable thrust coefficients as functions of the rate of progression. However, these methods resulted in thrust response errors with changes in the propeller angular velocity or wind speed. Therefore, this study established a method wherein the thrust coefficient in the controller is a function of the angular velocity of the propeller and wind speed. The effectiveness of the proposed thrust controller was verified experimentally and through simulation. The results indicated that the proposed method provided relatively better thrust control performance under multiple wind conditions.

This paper proposes a method of achieving both common-mode (CM) noise reduction and a high-voltage utilization ratio for electric compressors in vehicle air conditioners. The voltage output from the non-linear region is effectively utilized by considering both the modulator, which is based on previous studies, and the outer current controller. The proposed method consists of a simple time limiter to achieve remote-state (RS) pulse width modulation (PWM), feedback on the voltage error caused by the limiter, and a rotation direction detector to determine the voltage vector to use. As the current controller is designed using the conventional method, the proposed method is easily introduced. The effectiveness of the proposed method is compared with the conventional methods—continuous PWM (CPWM), discontinuous PWM (DPWM), and RSPWM—through experimental evaluations. The results show that the proposed method reduces CM noise by approximately 10dB in the frequency range of several hundred kHz to several MHz without additional circuits. Moreover, the proposed method has higher speed range than RSPWM and achieves the maximum voltage utilization ratio of DPWM.

Wireless power transfer requires a high operating frequency to ensure an electromotive force owing to the low coupling coefficient caused by a large air gap between coils. Traction inverters and inverters for auxiliary power units in battery-powered railway vehicles, have a switching frequency of 1-5kHz owing to a high-power range. The sampling frequency of the microcontroller is selected based on its switching frequency. As the sampling frequency of a microcontroller is considered feasible if it is several tens of times the switching frequency, this paper proposes a feasible power control method with a low sampling frequency. The proposed control method is a feedback control of the average DC power per operating cycle, which eliminates the influence of single-phase power fluctuations. The controller gain is designed using a Bode diagram. 100-W-class experiments verified its inductance independence and high responsiveness, and full-scale 300-kW-class simulations demonstrated the effectiveness of the proposed power control.

In bi-directional wireless or contactless power transfer, stable synchronization of switching between primary and secondary is essential. This paper presents a bi-directional contactless connector based on inductive power transfer and near-field electromagnetic coupling communication (NFEMC) to solve the switching synchronization problem. We developed a new cross-coupler of NFEMC with two redundant channels to realize high noise immunity and safety variable distance operation for practical application. Moreover, the proposed system detects the distance by using the error correction code of NFEMC to realize safe connection and disconnection. The prototype achieved 94.5% efficiency for a power transfer of ±10kW at a distance of 0-4mm. The prototype maintained power fluctuation within ±2.8% even when subjected to ±1mm vibration. We expect that the proposed system contribute to the safe and efficient application of contactless power transfer systems with synchronized switching.

In this study, a design method is proposed for forming notches on the rotor surface to reduce the cogging torque of interior permanent magnet synchronous motors (IPMSMs) with double-layered magnets. The proposed method is predominantly based on theoretical equations and can be applied to general double-layered IPMSMs, regardless of the magnet arrangement. First, the waveform of the square of the air-gap flux density (B_g²) for the reference model is approximated using a two-step trapezoidal waveform. Using the approximation, the harmonic components of B_g² are formulated when notches are fabricated on the rotor surface. Additionally, we derive a B_g² waveform that minimizes the main harmonic components of the cogging torque. The position and width of the notches are determined based on the derived waveform, and only the notch depth is adjusted by finite element analysis. The finite element analysis reveals that the cogging torque for the model with the optimized notch placement is significantly reduced. Furthermore, prototypes were manufactured and their cogging torque waveforms were measured. The measurements confirm that the amplitude and major components of the cogging torque are reduced.

This paper proposes wireless power transfer (WPT) system with Halbach coils to reduce leakage magnetic flux. The transmission coil using the Halbach coils generates magnetic flux in the vertical direction and coils that generate a magnetic flux in the horizontal direction. The WPT systems with Halbach and spiral coils are developed and experimentally tested to verify the effect of reducing the leakage magnetic flux density. The experimental results show that the magnetic flux density decreases by 35.6% at maximum.

In this study, we propose a method for acquiring a spatial high-resolution thermal distribution from a low-resolution infrared thermal camera while correcting the temperature based on emissivity. Thermal images depend on the color and material of the measurement target. Therefore, temperature cannot directly be measured accurately by infrared thermal camera. This is a serious problem for measuring the temperature of an electrical terminal carrying a large current in electrical equipment monitoring. In this study, we improved the temperature profile of targets by example-based super-resolution, in other words, by creating a dictionary comprising pairs of low-resolution and high-resolution thermal images corrected by emissivity. We experimentally proved that temperature profiles were improved, that is, the temperature profiles were close to the measurements obtained by thermocouples and high-resolution infrared thermal camera.

Boost converters are key components of DC power conversion used for electric mobility and renewable energy applications. In addition to constant voltage control of the output, variable voltage control has been attracting attention in recent years for high-efficiency drive of loads. However, the dynamic characteristics of boost converters exhibit nonlinear and nonminimum phase characteristics. Therefore, the inverse model for feedforward control is unstable, making high-precision voltage trajectory tracking control challenging. This study aims to present a noncausal and nonlinear feedforward controller to compensate for the nonlinear and nonminimum phase characteristics of the boost converter and to achieve perfect tracking control with respect to the output voltage trajectory. This study also establishes a method for identifying circuit parameters and deriving the time length of noncausal control input for practical implementation. The effectiveness of this control method is demonstrated by experiments using a boost converter.

This study aims to verify the application of amorphous metals to high-speed drive motors. We propose a new high-speed motor that applies amorphous metal to ultra-high-speed motors used in home appliances. The proposed motor can reduce both the iron loss and copper loss compared to conventional vacuum cleaner motors. We performed characteristic analysis and prototype evaluation through magnetic field analysis of the proposed motor. The analysis results at the same operating point, confirm that the efficiency improvement effect was approximately 1% compared to the highest grade electrorical steel sheet machine. The prototype evaluation results of the new high-speed motor, confirm that various characteristics obtained by the analysis could be reproduced. As a result of evaluating prototypes composed of different materials, the effect of improving motor efficiency by applying amorphous metal is confirmed quantitatively.

In this study, a direct drive in-wheel system is proposed as a high power density system for reducing the intermediate parts, such as a speed reducer by increasing the torque. We propose a design strategy to show that multipolarization and the improvement of the gap magnetic flux density can effectively increase the power density. A Halbach array magnet rotor that combines the main electrode magnets and spoke magnets with the core is adopted as a technique for improving the gap magnetic flux density. We compare the Halbach array type rotor to the conventional SPM type rotor by using both of magnetic circuit calculation and FEM analysis. Moreover, the actual sized in-wheel motor prototype with the developed Halbach array magnet rotor is fabricated and measures the no-load induced back EMF. The measured no-load induced back EMF agrees well with the analyzed waveform.