Sustainable energy technologies have become promising solutions to global warming and climate change. Operation of the electric power grid has been dominated in the past by synchronous generation, wherein conventional sustainable energy inverters are designed simply to feed maximum real power into the grid. With the increasing penetration of renewable energy, it is undergoing a rapid shift toward the power generation of inverter-based resources (IBRs). As a result, transitioning to a power grid with more IBRs requires introducing advanced inverter technology that can respond to various disturbances in frequency and voltage occurring on the grid. The grid-forming (GFM) inverter equipped with an energy storage system featuring frequency and voltage support functionalities is vital for the stability of the micro power grid system. The GFM inverter also offers PV output smoothing, low voltage ride through, and low frequency ride through. In addition, the GFM inverter functions as a voltage source inverter to supply energy under off-grid state when the main grid is in fault conditions. A SiC-based 30kVA GFM inverter is presented with a 3-phase 3-level neutral-point-clamped (NPC) topology for high-frequency operation to achieve high efficiency and power density. Design challenges in gate driver design, PCB layout, and thermal consideration are addressed. The performances of the designated GFM inverter are measured and tested under on-grid and off-grid operations to verify the functionalities of the advanced inverter, as well.

This paper describes emerging approaches in the design of power electronics aiming to address the twin challenges of miniaturization and efficiency through the use of piezoelectric-based energy storage elements. Piezoelectric components, including piezoelectric resonators and transformers, store energy in mechanical inertia and compliance, with energy storage densities that are orders of magnitude higher than those achievable with magnetics at small scales. Piezoelectrics can potentially enable radical improvements in the achievable size and efficiency of power converters for some applications, but advances in circuits, controls, passive component design, and packaging are required to fully realize these benefits. We present an overview of the opportunities, recent progress, and present challenges in piezoelectric-based power electronics, and provide supporting examples that illustrate their promise.

A prototype bidirectional isolated DC-DC converter with an output of 3.6 kW, using GaN-HEMTs, employing a planar transformer and operating at a maximum frequency of 400kHz, was developed and evaluated. Typical circuits for bidirectional isolated DC-DC converters are the LLC resonant converter and the dual active bridge (DAB), both of which have the disadvantage of low efficiency at light loads. In this paper, GaN-HEMTs were used as a rectifier device to reduce DAB losses with natural commutation under light loads, utilizing their no reverse recovery loss characteristics. Zero-voltage switching was achieved using the transformer excitation current as a lagging phase current on the input side. As a result of the efficiency comparison between the LLC resonant converter and DAB under the same components and input/output conditions, higher efficiency was obtained in DAB under most conditions. The maximum efficiency was 98.6%.

Herein, we propose a control method for a single-phase active filter composed of a universal smart power module (USPM). The USPM is a modularization technology concept that comprises various power conversion systems. Depending on the application, the USPM is a full-bridge inverter with a wideband controller and filter, and the power converter is constructed using several USPMs. In this study, the target system was an active filter composed of modules connected in series or parallel to accommodate arbitrary voltage and current capacitances. The proposed method solves the communication delays between the master and slave controllers owing to the distributed control in wireless communications and the interference problem caused by multiple USPM connections. The experimental results of the steady-state response showed that despite the communication delays, the total harmonic distortion (THD) of the input current was improved by up to 63.0%, and the power factor was 0.997. Moreover, load fluctuation experiments confirmed that the system transitioned to a steady -state and operated stably by updating the command value of the slave controller for the first time after the load fluctuation. The harmonic current elimination can be realized as an active filter, and the effectiveness of the proposed method was confirmed.

Operation delay of DC circuit breakers causes a voltage sag of several milliseconds in high-voltage DC (HVDC) grids. The DC voltage sag can cause an overcurrent in the DC side of the modular multilevel converter (MMC), resulting in halting the MMC. This study investigates a method to facilitate continuous operation of the half-bridge MMC during a DC voltage sag. The proposed method performs feedback control of the DC current during DC voltage sags by decreasing the DC and AC voltages of the half-bridge MMC. When the method is applied to symmetrical monopole HVDC systems, the MMC can maintain both its DC and AC currents within the rated range during the voltage sag caused by pole-to-ground faults. Simulation results obtained by a three-terminal HVDC grid verify the DC fault ride-through capability of the half-bridge MMC.

Many soft switching techniques utilize a resonance between an inductor and parasitic output capacitors of switching devices. However, output capacitance has nonlinear characteristics, which obscures the resonant period for soft switching. In this paper, a new method is proposed to derive the resonant period by considering nonlinear characteristics of the output capacitance. The method can be applied to a bridge-type converter which utilizes resonance for soft switching. Other parasitic capacitances which affect the resonant period, are also considered. To verify the proposed method, simulations and experiments were performed with a 3-kVA prototype half bridge auxiliary resonant commutated pole inverter.

This study estimates the axial magnetic suspension loss and efficiency of a one-axis actively positioned single-drive bearingless motor in the rotational speeds of 1000 to 30 000r/min. Bearingless motors have the advantage of enhanced efficiency owing to the absence of friction loss caused by mechanical ball bearings. In this study, the input powers of a bearingless motor with radial passive magnetic suspension and that of a motor with ball bearings were measured. Moreover, the mechanical ball bearing loss was also measured. Furthermore, the axial magnetic suspension loss in the single-drive bearingless motor was estimated. The efficiencies of both test motors were compared. Additionally, the ratios of the axial magnetic suspension loss and the ball bearing loss with respect to their input powers were evaluated.

There is an increasing interest in powering the subsea loads, such as subsea motor drives, from renewable energy sources, either from the shore or offshore. Due to the long distance from the motor controller to the motor, the use of sensor cables causes electromagnetic interference (EMI) and noise problems in the position information signals. Hence, the sensorless operation of subsea drives becomes important. In addition, variations in system parameters due to changes in operating conditions can result in the deterioration of the performance of drives, and may even lead to unstable operations. In this paper, a closed-loop observer-based method is proposed for estimating the speed and inductances of the equivalent system, which includes a transformer, cable, and motor inductances. The proposed estimation scheme is validated using MATLAB (2020a)/Simulink and Typhoon hardware-in-the-loop for a 500kW, 4.2kV interior permanent magnet synchronous motor (IPMSM).

This paper presents a new simple approach based on a short distance running race in athletics to determine the maximum power peak (MPP) of a photovoltaic (PV) power system to achieve a high speed and searching accuracy. The operating principle of this approach is based on the division of the active area of contestants at the starting line. Each position of the contestant corresponds to a duty ratio value to control the DC boost converter. Based on the proposed athletics running algorithm, the optimal duty ratio value is determined for the load to receive the best electrical power from the PV system. Based on new concepts of regional division and updated positions, the global MPP can be determined precisely with the rapid convergence of the positions to the global maximum power region. Consequently, the proposed method demonstrates excellent tracking ability with high accuracy and zero oscillation amplitude. Simulation results show that the proposed algorithm achieves high efficiency, particularly under partial shading effects.

Interior permanent magnet synchronous motors (IPMSMs) are used for various applications and high efficiency control is required. Maximum torque per ampere (MTPA) control is a method to control IPMSMs with high efficiency. However, since the motor parameters vary with magnetic saturation, MTPA control cannot be easily realized. Here in, we propose a fully online and automatic MTPA control method. To find the MTPA point while driving the motor, it is necessary to predict the entire flux linkage surface. Therefore, the flux linkage surface is approximated by a plane from the sensor information at a specific current condition that considers the effect of magnetic cross-saturation. MTPA control is achieved using the estimated flux linkage plane and the gradient ascent method. The simulation results reveal that the torque maximized in two search periods, which was completed in 0.06s. The proposed method is effective for a wide current range.

Since the 1960's, rotary frequency changers (RFCs) have been used as frequency converters applied to AC power supplies of high-speed railways, and they still play a major role today. On the other hand, electronic frequency converters (EFCs), which have advantages compared to RFCs in terms of maintenance cost and energy saving, have been introduced, and we have been working toward increasing the installation ratio of EFCs. As a result of the progress, we have reached a stage where we need to reduce the number of frequency conversion substations (FC-SSs) that require RFCs in order to further increase the installation ratio of EFCs. Under this situation, we studied a new interconnection control technology to realize the interconnection operation with the existing remote power supply systems to replace all RFCs with EFCs at the Nishisagami FC-SS of the Tokaido Shinkansen. In this paper, we present a new control block diagram for the fixed power factor output method voltage control with reference voltage command value adjustment for EFCs, which can prevent overload of a power supply system placed apart while maintaining stable voltage when EFCs are interconnected to distant power supplies.

This study proposes strategies for improving the accuracy and usefulness of leakage inductance modeling using the Dowell model (DM). As the analytical method of modeling the leakage inductance model considers geometrical factors, it is vital for front-loading transformer design. DM is one such widely used one-dimensional magnetic field-based approach for analytically modeling both AC resistance and leakage inductance. It is more accurate and requires less computational work than other analytical approaches proposed in previous studies. However, some approximations may cause errors and eventually lead to inaccurate results. Therefore, this study aims to ascertain the conditions that result in inaccurate leakage inductance modeling. Additionally, a simple exponential-based model and an artificial neural network are developed to increase the accuracy of inaccurate modeling. The results clarify the conditions that result in a frequency-dependent and bias error. Moreover, the intended findings indicate that the proposed strategies effectively improve modeling accuracy while simultaneously providing some extra advantages for transformer design.

This paper presents a method for measuring the iron loss of ferrite cores under compressive stress. Moreover, a novel methodology is proposed for analyzing the local heat generation of ferrite cores for wireless power transfer by considering an increase in the iron loss because of compressive stress. The effectiveness of the proposed analysis method is experimentally verified.

Wireless transmission of gate control signals is expected to improve insulation performance and design flexibility. This paper proposes high-speed and low-latency transmission by millimeter wave digital wireless system for Si-IGBT/SiC-MOSFET driver control. High-speed and low-latency transmission is realized by continuous transmission using the millimeter wave radio. Solutions for handling errors and reliability are also presented. The effectiveness of the proposed system is demonstrated by evaluating the transmission latency, the effect of wireless errors using a real-time simulator, and its connection to an actual inverter.

Accurate and fast models of the equivalent circuit (EC) elements of gapped multiwinding inductors are essential for the design of galvanically isolated converters, such as Flyback and LLC converters. Typically, the EC elements are acquired from measurements or time-consuming FEM simulations, both of which are disadvantageous for optimizing the design of the magnetic device. This paper proposes a multiwinding magnetic device EC that exclusively uses the impedance matrix elements, i.e., self- and mutual impedances. The advantage of the impedance matrix equivalent circuit (IMEC) is that self- and mutual impedances are directly measurable. Furthermore, the paper presents an analytical 2D magnetic field model to calculate the EC elements. It is quantitatively confirmed that frequency significantly affects the resistances and the inductances of magnetically coupled windings. In particular, eddy currents in windings induced by the fringing field of the air gap play a role besides the well known skin and proximity effect. The proposed model accurately considers all these effects in foil, Litz, and round wire conductors. The model is verified using FEM simulations and measurements.

This study investigated the important elements of emulated inertia control for grid-connected inverter-based power supply sources and identified the issues to be addressed for its integration into the electric power transmission and distribution system. For the first time, we categorized the emulated inertial control algorithms into five types based on three different aspects. Five emulated inertia control algorithms were simulated in order to compare their effectiveness in suppressing frequency fluctuations. In addition, a representative emulated inertia control algorithm based on the voltage-controlled method and another based on the current-controlled method were distinguished. The two emulated inertia control algorithms were implemented and demonstrated using the experimental hardware of a 5[kVA] inverter-based power supply.

A control method for electric vehicle (EV) of a dual inverter system with one battery is proposed. The conventional dual inverter system consists of an open-end winding motor and two inverters, and each inverter is powered by an independent battery. In the case of a battery failure, it can be operated as a multi-level inverter by controlling the voltage of the smoothing capacitor on the failure side to half of the battery voltage, and improvement in system efficiency can be expected. However, it is difficult to maintain the capacitor voltage at half of the battery voltage across the entire operating region of the EV. Therefore, a control method that switches between single inverter operation and dual inverter operation according to the operating conditions, and respond to changes in the capacitor voltage during operation switching is developed. The developed control scheme is demonstrated by hardware in-loop simulation and an experimental vehicle.

This study investigates an active gate driver (AGD) for an SiC-MOSFET. The source current feedback type AGD utilizes the induced voltage of the source wire inductance as a negative feedback signal to regulate the source current di/dt. Recent improvements in the switching performance of the AGD is limited due to the feedback system bandwidth. In this paper, a high bandwidth current feedback type power operational amplifier is applied as the gate drive circuit. Switching characteristics of the conventional resistive gate driver and AGD are experimentally investigated via a double pulse test setup. The switching setup condition is 700V/80A. This paper describes the development of the AGD circuit and experimental results. The over-shoot and ringing of the V_ds and I_s are reduced using the AGD. Moreover, the switching loss is simultaneously reduced.

For the online condition monitoring of IGBTs, a new estimation method of both the junction temperature (T_J) and the load current (I_L) of IGBTs using a momentary high-Z gate driving (MHZGD) from the output voltage (V_OUT) of the gate driver is proposed, which can be integrated into the gate driver ICs. T_J is estimated from V_OUT difference during and after the MHZGD period, and I_L is estimated from V_OUT during MHZGD. In the 110 switching measurements at 11 different T_J's from 25^°C to 125^°C and 10 different I_L's from 12.5A to 80A for each of the three IGBTs,T_J and I_L estimation errors in a low test cost parameter determination method are +4.9^°C/-8.4^°C and +1.1 A/-4.3 A, respectively. In contrast,T_J and I_L estimation errors in a parameter determination method with small error are +4.9^°C/-8.1^°C and +1.0A/-1.8A, respectively.

A capacitively coupled modular DC-DC power electronic transformer (DCPET) has been proposed. The proposed DCPET consists of capacitively coupled unregulated LLC resonant converter modules; these modules are connected in series-parallel combinations. The capacitive coupling topology is considered to be promising to develop highly efficient high-power-density converter modules, and the series-parallel connection of these modules smoothly achieves various voltage ratios of DCPETs. A trial design for a 48V-48V, 450W capacitively coupled LLC converter module using GaN-FETs has been demonstrated, and the potential to achieve 99%, 15W/cm³ has been confirmed. Moreover, the 48V-384V DCPET using eight 98.8%, 15W/cm³ converter modules has been demonstrated, and the feasibility of the proposed topology has been verified. The proposed DCPET overcomes the stagnant relationship between the efficiency and the output power density of isolated converters, and the proposed topology contributes to the prevalence of power electronics equipment for the economical use of electric power.

Permanent magnet synchronous motors (PMSMs) are widely utilized for many purposes owing to their high efficiency. Such frequent applications require less noise and fewer vibrations. This work focuses on multi-three-phase PMSMs that can independently control the current among winding groups to suppress the vibrations caused by air gap imbalances, which must be detected for suppression control. The representative effects of air gap imbalance include static and dynamic eccentricities. Dynamic eccentricity varies the air gap length in time; therefore, the instantaneous detection of the air gap length condition is necessary for suppression control. We propose a method that instantaneously detects dynamic eccentricity using the fundamental and fourth-order harmonic components of no-load line-line voltages, which are easily measurable in practical manufacturing processes. The proposed real-time detection method is applied to a finite element analysis (FEA) model with dynamic eccentricity, and confirm its detection ability is confirmed experimentally.

This paper proposes a novel control method for a dual-active-bridge (DAB) single-phase AC-DC converter with an active energy buffer circuit. The proposed control method realizes continuous-current-mode (CCM) operation of the DAB converter by adjusting the switching frequency according to the phase angle of the single-phase AC-line voltage; thereby improving the power conversion efficiency. Experimental results verify the CCM operation with the proposed control method and demonstrate an improved power conversion efficiency of 92.8% for a 220-V, 5.4-kW output.

The impact on the stability of power systems is also increasing with the rapid spread of distributed power-supply systems. Consequently, the performance requirements for grid-tied inverters are increasing. However, MW-level grid-connected inverters have limited carrier frequency. This paper proposes a disturbance compensation deadbeat control with a 1MHz multi-sampling method that can respond to changes in state variables between carrier intervals by increasing the sampling frequency even at low carrier frequencies. An FPGA-based hardware controller is used to implement all control calculations in the FPGA circuit. In addition, controller hardware-in-the-loop (C-HIL) is used to verify the control performance solving the difficulty of experimental verification in a megawatt-class grid-tied inverter. The control system can be verified using the controller used in an actual system. The effectiveness of the proposed method is demonstrated by verifying the control system with the C-HIL platform, and its superior characteristics are confirmed.

The SUSTIE test facility was completed in 2020, and it facilitates to the development of energy-conservation technologies while contributing to the realization of more comfortable and energy-efficient indoor environments. The facility achieved the top rank of energy performance certification “Building-Housing Energy-efficiency Labeling System (BELS)” and wellness-office certification “Comprehensive Assessment System for Built Environment Efficiency-Wellness Office (CASBEE-WO)” in Japan. To accelerate research and evaluation, we propose an efficient Internet-of-things (IoT) platform called the SUSTIE Core Engine. The platform gathers data in real time, stores both design data and time-series data with coordinates, and act as simulation interface to satisfy three requirements of an IoT platform for smart facilities: an architecture that allows adding/removing functions without stopping operation, data management features for time-series/coordinates data, and common interface for simulations/controls. We implement the platform which covers the requirements to on-site system in the test facility, and evaluate the gateway, spatiotemporal database, and simulation interface. Our platform showed that it satisfies the three functional requirements of IoT platforms. Furthermore, it was shown that the database can obtain sufficient demonstrated for practical use.

We developed a variable-magnetization internal permanent magnet (VM-IPM) motor for electric vehicles (EVs). This motor can vary the magnetization of a permanent magnet (PM) to realize highly efficient operation across a wide range of speed. Optimizing the inverter capacity is crucial for maintaining quality and reliability during the mass production of traction motor systems for EVs. However, the magnetization current should be less than thrice the rated current if the magnetization state of the PM is to be varied without increasing inverter capacity. Our proposed VM-IPM motor can vary even small magnetization currents. Our results confirm that the proposed motors in which variable permanent magnets (V-PMs) and constant permanent magnets (C-PMs) are arranged inside two U-shaped cavities provide excellent operation performance over a wide range of speed and power. In addition, the proposed motors can vary the magnetization state of the PMs by applying demagnetization and remagnetization currents that are twice the rated current. The back-electromotive force of the motor can vary from 56.4% to 97.4% and from 61.2% to 93.4% in the parallel and series models, respectively, because of the varying magnetization state of the V-PMs at a magnetization current that is twice the rated current.

This paper proposes a load test method for high-frequency transformers using two power supplies. In this method, the two power supplies need to supply only the power losses of the transformer because the power is circulated between the primary and secondary sides. Hence, this load test can be performed on high-frequency transformers with capacity higher than that of the power supply without requiring a high-frequency load. The experimental results show that the load test method can be applied to a transformer under a 100kHz sinusoidal voltage/current using two power supplies with a capacity of 50VA/unit, which is much smaller than the rated capacity of the transformer, i.e., 900VA. Furthermore, the load test can be performed at all power factors from 0 to 1. In addition, the experimental results show that using the proposed method, the accuracy of power loss measurement is improved compared with the existing method that obtains the power loss by subtracting the output power from the input power of the transformer.

A new multiple DC-inputs direct electric-power converter (D-EPC) was proposed. It can be applied to motor-drive systems with two direct-current (DC) power sources. The D-EPC can charge a DC power source with motoring by another DC power source. This charging is controlled by the voltage command multiplied by a power distribution ratio of more than 1.0 for the DC power source supplying power to the motor and another DC power source. If charging power is required in the condition of phase voltage saturation, the phase voltage command calculated using the power distribution ratio of more than 1.0 cannot be increased to more than the phase voltage limit. This paper proposes a new charging control for D-EPCs by controlling the switches on the free-wheel current path. The distribution ratio of this proposed control does not exceed 1.0. The simulation results showed that one DC power source can be charged with motoring by another DC power source using the proposed charging control.

As a new space station succeeding the International Space Station (ISS), a lunar orbit manned base, called “Gateway,” is considered and manned lunar surface exploration via the Gateway is also studied. To realize manned lunar surface exploration, new technologies are required to overcome the severe condition of the lunar night. As one of these technologies, applying wireless power transfer (WPT) to a spacecraft, such as a rover, is proposed. The WPT system contributes to the improvement of heat insulation performance and is ideal for reducing the weight of the battery of the spacecraft. In addition, magnetic transmissive multi-layer insulation (MT-MLI) is developed to suppress the generation of eddy currents. In WPT experiments with MT-MLI, the power transmission efficiency between coils is 90% or more. Furthermore, thermal vacuum tests demonstrate that the combination of WPT and MT-MLI reduces thermal leakage.

Investigation of the magnetic flux density and force characteristics is essential to advance the design and development of new motors. This paper proposes a mathematical solution for predicting the flux density distributions in a tubular magnetic geared linear motor capable of generating a high thrust force. The proposed method can calculate both radial and axial components of flux densities while consuming less computing time than the finite element method. The force transmission capacity of the magnetic gear and the thrust of the motor are calculated based on the predicted flux density. In comparing the calculation, finite element analysis, and experimental results the consistency in the results validates the proposed method.

This study investigates the influence of parasitic capacitance on the common mode (CM) noise in a converter. A thermal pad on a switching device is necessary for sufficient heat dissipation. In addition, the thermal pad increases the CM capacitance between the printed circuit board and the ground plane. The parasitic capacitances form CM noise propagation paths. However, which node in the circuit and the corresponding parasitic capacitance influences the CM noise the most and the degree of the parasitic capacitance influence on the CM noise are unclear. In this study, the parasitic capacitance that influences the CM noise in a converter is identified, and the extent to which the parasitic capacitance affects the CM noise is investigated through simulations and experiments.

In this paper we propose a compact magnetic rotation angle sensor which comprises a permanent magnet, Hall-effect sensors, and partial arc-shaped stator located in a large-diameter traction motor to reduce the size and weight of automotive vehicles. The proposed rotation angle sensor removes a specific harmonic component of the leakage flux from the electric motor by converting the signal from three-phase to two-phase using three Hall-effect sensors. The design concept of the rotation angle and its magnetic design results are shown in this study. A prototype of the proposed rotation angle sensor was created and its weight, size, and magnetic performances were measured. The measurement results achieved a 38 and 33% weight and volume reduction, respectively, compared with a conventional variable reluctance resolver. Furthermore, the experimental results demonstrated that the angle position of the motor can be detected in line with the electromagnetic design and target of the angle error.

Parallel resonant permanent-magnet synchronous generator (PMSG) systems, which consist of a diesel engine, PMSG with a resonant parallel capacitor, and diode full-wave rectifier, may potentially be applied to series hybrid vehicle traction systems owing to their high efficiency and low cost. In general, the power generation in series hybrid vehicle traction systems is controlled using a pulse-width modulated (PWM) converter. However, the power generation in a parallel resonant PMSG hybrid traction system cannot be adjusted using a PWM converter and a new power-generation control method is required. An appropriate power generation control method that considers battery deterioration, number of engine-starts, and fuel economy has not been developed yet. Therefore, this study proposes a power generation control method for parallel resonant PMSG systems applied to series hybrid vehicle traction systems.

Lately, permanent magnet synchronous motors (PMSMs) have been widely employed in several fields such as industrial equipment, home appliances, and electric vehicles due to their high efficiency and power density. Previous studies have confirmed that PMSM motor drive system with deadbeat control has a superior response to the current reference. In this paper, a universal smart power module (USPM) controller is used to realize a high-performance motor drive system. Because this controller can achieve 50MHz sampling of the state variables, we proposed a 10MHz multi-sampling deadbeat control that uses fast sampling ability to follow the load disturbance fluctuation even between carriers and to enhance the robustness to parameter variations. The proposed method was verified through simulations and experiments.

Recently, energy storage devices (ESDs) have been introduced to railway vehicles to operate even in an emergency case, such as a power outage. However, there have been no proposals for simultaneous design methods of power capacity and energy capacity of onboard ESD for emergency operation. In this paper, a model for the calculation of power and energy capacity of onboard ESD, which are utilized in an emergency case, is proposed. Furthermore, we propose a method to design the power and energy capacity of onboard ESD by considering the required power for traction and an auxiliary power supply system.

Speed sensorless vector control for induction motors using an adaptive flux observer makes it difficult to output high and stable torque at a standstill condition when the output voltage error mainly due to dead-time of the inverter. This voltage error leads to a speed estimation error. Consequently, axis misalignment occurs, and a torque value that tracks the reference command value cannot be output. A method has been proposed to compensate for this voltage error by using a current command value; however, the compensation accuracy is limited because of the forward voltage drop and nonlinear characteristics of power switching devices. This study applies the conventional dead-time compensation to the model reference adaptive system, and the effect of varying the amount of compensation, instead of investigating the true dead-time length, on the start-up is evaluated using a 2.2kW experimental system and through dynamic analysis.

This paper proposes an innovative integrated inductor technology for hybrid energy source systems (HESS). The proposed inductor utilizes novel variable coupling coefficient integrated inductor (VCCII) technology to integrate two inductors that are required for a dual boost converter for HESS. VCCII has an integrated structure of two inductors, and enables control the coupling coefficient between the two inductors depending on the power distribution ratio of two power sources. In a low-power operation, the coupling coefficient between the two inductors is structurally zero, which enables the VCCII technology to independently control each output of energy sources without interference. In high-power operation, the coupling coefficient of the two windings increases by utilizing the non-linear characteristics of a magnetic core. These coupling effects peak shaving of the inductor current, which contributes to loss reduction and increase the maximum power capability. A prototype result verifies a 50% increase of peak power density and a 15% increase of maximum power capability under 20V/100A and 25V/40A inputs and 42V output HESS. Additionally, the result gives 1.9 point of efficiency improvement in a double boost converter circuit operating at 100-kHz switching, 810W output.

Global warming is a critical and urgent global issue hindering the establishment of a sustainable world for all creatures on the planet. Owing to this issue, an Electric Vehicle (EV) society in the near future is necessary to establish a carbon free society. This study introduces the utilization of V2X (Vehicle to X: from Home=H to Power Grid=G), bidirectional charger/discharger for EVs, and the development of VPP (Virtual Power Plant) utilization in Japan as solutions to the energy crisis induced by global warming. We believe that the application of the V2X system can provide one of the best solutions to the energy crisis.

Condition monitoring helps improve the reliability of power electronic converters including their dc-link capacitors because it can predict converter failure and degradation. In practice, however, condition monitoring usually utilizes current sensors to obtain health condition, which is a constraint with regard to cost. This paper proposes a current-sensor-less condition monitoring method of a dc-link capacitor in a three-phase PWM inverter with a front-end six-pulse diode rectifier and a dc inductor. The proposed method measures both the capacitance and equivalent-series resistance (ESR) of the capacitor without using current sensors. Theoretical analysis reveals that the capacitor current is calculated using the three-phase ac source voltage and the dc inductor. Experimental results obtained from a 200-V laboratory system confirmed that both the ESR and capacitance changes were observed without using current sensors.

In this paper, we propose asymmetric winding structure to achieve a low torque ripple and high slot fill factor. Existing methods developed for this purpose improve the winding factors of harmonics and the slot fill factor by ensuring that the winding arrangement and number of turns for each coil are asymmetric. In contrast, an asymmetric winding structure generally lowers the symmetry of the magnetomotive force of the stator and generates electromagnetic excitation forces with lower spacial order modes, resulting in increased vibration. Therefore, in this study, we aim to improve the winding factor and the slot fill factor by changing the winding arrangement and the number of turns while considering the symmetry of the electromagnetic field. First, the working principle of techniques for improving the characteristics of the proposed winding structure are discussed. Thereafter, the results of magnetic field analysis and the verification of the said improvements to the asymmetric prototype, along with the effects, are presented.