Several types of electrified vehicles have been developed and launched as a solution for low carbon transportation. Toyota launched the first massproduced hybrid electric vehicle, the Prius, in 1997. With the evolution of electric components in Toyota Hybrid System, 15 million Toyota hybrid electric vehicles have been sold, and reducing 120 million tons of CO₂ in the real world. These electric components have some compatibility with electric vehicles and fuel cell electric vehicles.

The switching frequency of power converters is continuing to increase with the demand for their increased power density. Therefore, the frequency band of the electromagnetic interference (EMI) generated by power converters ranges from several kilohertz to 100MHz or more, thereby increasing the importance of EMI countermeasures in power converters. In addition, with the practical applications of smart grids and microgrids and the introduction of 5G technology, cases wherein power converters and information communication devices are placed in close proximity are continuing to increase. Thus, in societies wherein power converters and information communication devices are highly integrated, it is necessary to ensure electromagnetic compatibility based on a different concept. This paper presents a review on modeling and suppression techniques for the EMI generated by power converters and discusses future prospects in this field.

Oscillatory actuators (OAs) are used in various fields, such as industrial equipment and home appliances. For example, they are applied in active vibration isolation tables, vibration test devices, and haptic interfaces. They have a multiple-degree-of-freedom (DOF) mechanism with short-stroke. Such conventional mechanisms consist of some actuators and links, therefore, the vibration center is shifted and the size and weight increase. To solve these problems, various types of multiple-DOF OAs have been developed. However, a five-DOF OA has been not proposed. To further realize the functionality by increasing the DOF, we propose a five-DOF OA. Its basic structure and operating principle are described. The thrust and torque characteristics are investigated by a magnetic field analysis using a three-dimensional finite element method. The analysis results indicate that the proposed actuator can drive five-DOF without interference between other axes.

Dual three-phase permanent magnet synchronous motors have the characteristics of multi-phase and permanent magnet synchronous motors, whose double- and decoupled-winding models based on the vector space decomposition have been reported. High-frequency signal injection methods enable position sensorless control, parameter identification, and the search for maximum torque per ampere operating points. However, the current control system with high-frequency signal injection for a dual three-phase permanent magnet synchronous motor has not yet been sufficiently discussed. This study compares the double- and decoupled-winding models for the current control system with the high-frequency signal injection and proposes a current control system with high-frequency signal injection. Furthermore, this study proposes a position sensorless control method at low speed based on the high-frequency voltage injection as an application of the proposed current control system with the high-frequency signal injection. Experiments verify the effectiveness of the proposed current control system with the high-frequency signal injection and the proposed position sensorless control method.

A novel magnetic structure for use in LLC resonant converters is proposed in this paper. It is known as a Path-core type Resonant Inductance Adjustable (PRIA) transformer, which is a type of transformer with adjustable resonant inductance. In the proposed transformer, the resonant inductance and magnetizing inductance can be designed separately; therefore, it becomes less challenging to realize the required resonant frequency. Moreover, the magnetizing inductance is not affected by any variation in the resonant inductance. The proposed PRIA transformer is found to improve the efficiency of the LLC converters. In this paper, the design of a resonant inductance of a PRIA transformer is presented. In addition, the application of PRIA transformers to a 1-MHz LLC resonant converter and 1kW 1.4-MHz LLC resonant converter is presented.

An interior permanent magnet synchronous motor (IPMSM) is characterized by high efficiency in a wide range of applications. However, when operating at high speeds, torque ripple and rotor loss occur because of the spatial harmonics generated by fluctuations in the airgap permeance. This study demonstrates the suppression of torque ripple and harmonic loss by magnetic wedges using finite element analysis (FEA). First, the authors examined the torque and loss characteristics by varying the slot opening width and relative permeability of the magnetic wedge. Results indicate that the torque ripple can be suppressed even if the opening width is widened to half the slot pitch. However, this improvement effect saturates when the relative permeability of the magnetic wedge becomes larger than µ_r = 10. Furthermore, the authors confirmed the effect of the magnetic wedge by visualizing the harmonic components of the eddy current loss. The findings reveal that the eddy current loss represents a trade-off between the stator and rotor when using the magnetic wedge.

In this study, parity-time symmetry (PTS) was applied to a wireless power transfer (WPT) system in the low-frequency range of 30-40kHz. A series-parallel topology was analyzed using the coupled mode theory. It was demonstrated that PTS can be preserved over a long transmission distance even at low frequencies by reducing the self-inductance of the receiver coil. The receiver solenoid coil (dimensions: 71 × 30 × 7.4mm, mass: 45.6g, self-inductance: 119µH) was able to maintain a transmission power of 23±1W and an efficiency of 83±1% within a distance of 12-40mm. In addition, the suitable coil orientation range was significantly increased from ±5° to ±65°. The power conversion efficiency of a switching-mode amplifier based on a class-D inverter reached 97% at low frequency. These results are expected to contribute to the expansion of PTS-WPT applications.

Tracked vehicles generally involve slippage owing to the interaction between the road and track surfaces, which renders accurate motion control difficult. This paper proposes a velocity estimation method for a tracked vehicle with slippage, and its application to driving force control. In this method, the disturbance estimated by a disturbance observer was used as information related to slippage, and a neural network was constructed for velocity estimation. In addition, a driving force observer was designed using the estimated velocity. The driving control of the tracked vehicle to suppress slippage was achieved by using the feedback of the estimated driving force. The proposed method was evaluated experimentally through the velocity estimation performance and slip suppression performance tests.

In this paper, we propose a design method for a novel motor using magnetic resonance coupling (MRC) to enable the practical use of electric aircraft. The proposed motor can transfer electrical energy between a stator and a rotor via MRC, which does not require magnetic cores, thus realizing an ultralightweight design. Moreover, we detail the operating characteristics of the proposed motor and its equivalent circuit, analysis, and experiments. From the analysis, we clarify that the proposed MRC motor has a sufficient strength at an ultrahigh speed, and we describe its essential characteristics and the usefulness of its equivalent circuit. Further, our analytical and experimental results confirm that the proposed MRC motor can transfer electrical energy between a stator and a rotor, thereby generating torque.

The development of maximum power point tracking in solar photovoltaic system is important for obtaining the maximum power, which works satisfactorily when subjected to steady, undisturbed irradiation. Under real-time conditions, the solar panel does not always receive uniform irradiation owing to partial shading, thereby reducing the gross power output from the panel. The presence of partial shading is directly recognized by an occurrence of multiple local peaks in the performance characteristics of the solar panel. During partial shading, conventional maximum power point tracking algorithms fail to detect the global maximum power point, thus operating the panel at a much lower efficiency than desired. This study aimed to accurately detect the occurrence of partial shading condition in the solar Photovoltaic (PV) systems under different irradiation conditions and shading patterns. A partial shading detection mechanism is proposed based on power loss generated from a solar PV array without any sensors incorporated in the real-time platform. The proposed method is cost effective and accurate even under different seasonal and weather conditions, without any empirical constant and sensors. The proposed method is tested experimentally in real-time setup and the results are validated. The method provides a much higher accuracy than the current approximation and power loss method, and it does so by using the minimum number of variables. The proposed detection mechanism is compared with other existing methods in the Maximum Power Point Tracking (MPPT) algorithm, which proves the powerfulness of the algorithm. To test the performance of the proposed method, a real-time PV system with data acquisition using National Instruments LabVIEW is developed. Virtual Bench-8012 is used for data acquisition with a high precision along with intrinsic signal conditioning, and compact RIO-9081with a Field-Programmable Gate Array (FPGA) Virtex-5 LX150 is used for the MPPT algorithm implementation. The experimental results are also verified under different shading patterns and irradiation conditions for detecting the shading of the panel. Hence, it is shown that the detection algorithm has an efficiency of 97% in detecting the shading conditions of the panel.

Inductive power transfer (IPT) systems suffer from power loss caused by reactive currents that circulate in the system during soft-switching operation. To address this problem, this paper proposes a novel soft-switching active-bridge (SAB) converter. The SAB converter comprises a full-bridge active (FBA) converter and an LC circuit connected to the one-side leg. This composition suppresses the reactive current circulating between the resonant network and the switching devices. The experiment conducted to compare the proposed converter with a conventional one shows that the efficiency of the IPT system with the SAB converters could be maintained high over a wide operation range. Furthermore, an efficiency improvement by 1.3 pt to the general IPT system could be achieved at 3.3kW-output.

This study presents a design method for the continuous switching test circuits of power devices. Depending on the relationship between the rated voltage of a DC voltage source and device under test (DUT), two types of test circuits are proposed. These test circuits comprise a cascaded buck-boost (or boost-buck) converter to achieve power regeneration. Based on analysis of the test circuits, a design method is proposed to ensure that any failure does not spread to the test circuit even when the DUT fails during the continuous switching tests. A test circuit is designed according to the proposed method, and its experimental results demonstrate the validity of the proposed design.

This study reveals the characteristics of switched reluctance motors (SRMs) made by blanking (a) 20HX1300 of high grade low-iron-loss silicon steel (0.20mm thickness) and (b) 2605SA1 of amorphous alloy (0.025mm thickness). The blanking of the amorphous alloy is an innovative technology for the mass production of the high efficiency amorphous-alloy-motor. The impact of the processing methods on the magnetic properties are evaluated using the ring cores processed by the following methods: the wire cutting and the blanking. On the other hand, the experiment with the SRMs processed by the blanking evaluates the characteristics depending on the material. As first prototype, 70W-SRM (40mm thickness) is manufactured by blanking 1600 sheets of the amorphous alloy and adhesively laminating them. In the experiment, the motor efficiency of the amorphous-alloy-SRM is improved by 6.9p. t. compared with that of silicon-steel-SRM. In addition, the iron loss of amorphous-alloy-SRM is reduced by 78.7% compared with that of silicon-steel-SRM.

In this study, a three-dimensional static magnetic field analysis was conducted on a narrow-gap stepping motor for driving the hands of a wristwatch. The purpose of this analysis was to design a stepping motor with a low power consumption, by calculating the holding and detent torques and rotor shaft attraction force in two cases, namely a rotor with no eccentricity and a rotor with 5µm eccentricity. We analyzed why existing stepping motors are constrained to a gap width of 300µm. We further confirmed that the rotor shaft attraction force, which is derived from the rotor eccentricity, increases rapidly with the decrease in gap width, which in turn has a negative impact on the stepping motor. In the future, we intend to study the movement of a wristwatch comprising a metal wheel bearing, to design a stepping motor with a narrow gap, and subsequently reduce the power consumption.

We propose a novel digital current control method for half-wave rectified brushless synchronous motors (HWRB-SM) with a pulse width modulation (PWM) at a fixed switching frequency. For HWRB-SMs, the field magnetic flux must be excited by high-frequency stator currents. Due to the nonlinear dynamics of the diode short-circuiting the field winding, an appropriate mathematical model is required for controlling the high-frequency excitation current. In this study, we developed equivalent models for both the excitation current control and the fundamental one. The proposed method employs a synchronous PWM and resonant controllers to realize high-frequency excitation current control that is robust against the nonlinearity of the diode. The proposed method was validated using an experimental synchronous motor and a digital control system.

In this study, an effective combination of methods to estimate the magnet operating points in a permanent magnet synchronous motor (PMSM) is proposed. First, the magnet temperature estimation is compensated with the initial temperature and magnet loss based on the error between the estimated temperature obtained using the thermal equivalent circuit and the estimated temperature obtained using the flux observer. In addition, stator loss is compensated based on the error between the measured temperature and estimated temperature obtained using the thermal equivalent circuit. Then, the flux linkage observer is compensated with the d/q inductance value using the magnetic equivalent circuit. A method of estimating the magnetic flux density of a permanent magnet is designed to estimate the magnetic flux density of the motor using a magnetic equivalent circuit reflecting the value of the measured magnet temperature and magnetic flux density in the permanent magnet's B-H curve. Unlike the rotor temperature, the stator temperature can be easily measured, and the magnet operating point estimation can be designed as a more accurate and error-resistant estimation method. Furthermore, simulation and experimental verification demonstrate the effectiveness of the proposed method.

Electro-thermal co-design of power modules is required to maximize the capabilities of promising power semiconductor devices. The chip layout on the substrate, which is restricted by the size of the power module substrate, determines the electrical and thermal characteristics of the power module. This paper proposes a chip layout optimization strategy for power modules based on a multiobjective electro-thermal design algorithm. The parasitic inductance and thermal resistance of the SiC power module are evaluated using the unified simulation model based on the multiphysics solver of the finite element method. The proposed multiobjective optimal design approach uses non-dominated sorting genetic algorithm II (NSGA-II) and the developed simulation model to obtain a Pareto front for the parasitic inductance and thermal resistance of the power module. Module samples with the obtained Pareto front parameters are experimentally characterized and validated with numerical simulation results.

This study aims to reduce the voltage harmonics, caused by pulse width modulation (PWM) in a dual inverter with a floating capacitor topology in the partial-load condition. This work provides an analysis strategy for the output voltage harmonics, which depend on the fundamental voltage, power factor angle, and PWM strategies. Herein, sinusoidal PWM (SPWM), third harmonic injection PWM (THIPWM), and discontinuous PWM (DPWM) are used as the conventional carrier-based modulation techniques, and space vector PWM (SVPWM) and near-state PWM (NSPWM) with reduced number of commutations are used as the proposed modulation methods. The validity of the theoretical analysis is then confirmed by experiments using an open-end winding induction motor. The voltage total harmonic distortion (THD) is reduced by maximizing the modulation indices of both inverters in each modulation method; the experimental results show that voltage THD reductions of 10.9% with NSPWM and 17.3% with SVPWM can be obtained compared with that of SPWM. The total efficiency, including the inverter and motor efficiencies, is improved by up to 2.6% in the low load region (at a torque of 0.5Nm and fundamental frequency of 10Hz) when using the SVPWM.

In this study, a virtual transformer-based loss measurement method is proposed for inverter power conversion efficiency measurements, and the accuracy of this method is theoretically analyzed. This concept is further extended to a practical measurement procedure, wherein asynchronous loss measurements are conducted for powering and regenerating operations using a single set of measurement instruments. The average efficiency can be obtained with a very high accuracy after calibration of the measurement instruments. A high-efficiency system inverter was selected as the converter under test, and its efficiency and accuracy were experimentally measured and validated. An efficiency of 99.75% ± 0.006% was obtained at an output of 1600W.

Methods based on linear analysis have been studied for stable control of permanent magnet synchronous motors; however, they are difficult to apply in the operating regions and under control conditions that cannot be linearized. In such instances, trial and error tuning is required to obtain the desired characteristics. In this study, we investigate a method of learning for an artificial neural network using a large amount of adjusted PMSM parameter data and derive the control parameters to stably drive the PMSM.

In this letter, a turn on/off delay time control for current balancing in parallel connected IGBTs, without increasing a switching loss, that uses a dynamically adjustable gate resistance (R_g) is presented. By dynamically adjusting the gate resistance within a switching period, the turn-on/off delay time can be controlled without affecting dI_C/dt and dV_CE/dt. Therefore, the reduction in dI_C/dt and dV_CE/dt due to the increase in the gate resistance is suppressed. This leads to the successful correction of the current imbalance during the switching transient among IGBTs in the module, without increasing the switching loss.

This letter proposes a control method to reduce the high-order harmonics caused by pulse-width modulation (PWM) in the DC-link current in a dual inverter with a floating capacitor topology, which has the same voltage ratings in two inverters. The proposed control method reduces the high-order harmonic current through a six-step operation at the primary inverter. The secondary inverter supplies a sinusoidal voltage to the motor using a low-rated voltage. The validity of the proposed control method is confirmed through an experiment using an open-end winding induction motor. Furthermore, the floating capacitor voltage dependencies of the input current harmonics are analyzed.

In the characteristic evaluations of large rotating machines, such as turbine generators, modeling of complex structures, small-sized parts, or local physical behaviors may lead to ill-conditioned and/or a large number of elements. In this study, analysis modeling for evaluation of the electromagnetic behaviors using the nonconforming mesh connection technique is developed by improving the sliding method to simulate movements and the developed method is applied to model the coil end part of a turbine generator. The analysis results are verified by measurements and with the results of a model without the nonconforming mesh connection. Then, the merits and important points regarding the application of the nonconforming mesh connection technique are described.

This study presents a new method to reduce current and voltage distortions for matrix converters in the overmodulation range. Analytical overmodulation conditions for input currents and output voltages are derived. Then, a carrier-based overmodulation method is proposed to reduce distortions by appropriately adjusting reference voltages. Simulation results confirm that the distortions of input currents and output voltages can be reduced using the proposed method.

A unique approximation function for the d- and q-axes inductances for a synchronous reluctance motor (SynRM) is shown. This inductance approximation function has excellent features, such as continuous and differentiable over the entire current range when taking into account cross-magnetic saturation and satisfactory reciprocity relation of the mutual inductance. It is also possible to derive an equivalent inverse inductance function that can estimate the d- and q-axes currents from d- and q-axes stator flux linkages. Using the proposed inductance approximation function, the authors derive two mathematical models. The first is a strict model in which the state and input variables are the respectively load current and stator voltage. The second is a simple model in which the state and input variables are respectively the flux linkage and stator voltage, which are derived using the equivalent inverse inductance function. These models are applied to simulate the transient performances considering the iron loss and cross-magnetic saturation. The experimental and simulated results with a flux-barrier SynRM validate the proposed method.

This study proposes a modular multilevel converter by applying a balancing circuit with a resistor for a low-voltage grid converter. The proposed balancing circuit, which is controlled by the same gate signal as that of the main switch, can reduce the loss of the additional balancing circuit and the current rating of the balance switch without the need for additional the cell capacitors. Only one voltage sensor per converter arm is required to automatically balance the cell capacitor voltages. The experimental results indicate that the cell capacitor voltages are well balanced during a rated operation of 10kW and a high efficiency of up to 99.2% is achieved, which is almost the same as that without a balancing circuit.

This study presents a magnetic polarity detection method of an initial rotor position estimation for permanent magnet synchronous motor drives without a position sensor. The magnetic polarity detection method utilizes stator core magnetic saturation caused by the rotor magnet and uses current responses when a high frequency or impulse voltage is applied to the motor. Recently, capacity enlargement, miniaturization, and cost reduction of the motor have been steadily progressing and motors with complicated magnetic saturation characteristics are available. The authors have developed a new magnetic polarity detection method for initial rotor position estimation that is suitable for many motors having common or complicated magnetic saturation characteristics. In the proposed method, high-frequency voltage waves with different amplitudes are applied to the motor. The proposed method measures the motor current ripple components and can estimate the magnetic polarity by using the amount of d-axis inductance variation caused by magnetic saturation. The basic idea, computer simulation, and experimental results are discussed in this paper.