The calculation of eddy current losses in foil windings exposed to a 2-D fringing field is a complex task because of the current displacement along the height of the foil. For model-based optimization of magnetic components, loss calculation with 2-D finite element method simulation is not an option because of the high computational effort. The existing alternative calculation methods with low computational effort, rely on approximations applicable only to a certain geometrical arrangement of the windings and the air gap. Therefore, in this study, a new semi-numerical method was developed to overcome these limitations. The method is based on the mirroring method and is applicable to arbitrary air gaps and winding arrangements. The accuracy of the new method was verified by measurements, and the deviation of the model results from the measured losses was found to be below 15%.

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Solar power is not the only attractive energy, but a wind turbine generator is also an attractive energy option from the point of view of reducing double carbon oxide emission. However, to connect the wind turbine generator system to the grid, the independent power producer (IPP) must compensate the power disturbance caused by the wind turbine. Thus, it is necessary to install a power conditioner for stabilizing power disturbance. In this study, the authors have developed a new power conditioner using batteries. The control technique, specifications, circuit configuration, and prototype test results are described.

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We built a new electronic frequency converter (EFC) in the Tokaido Shinkansen to replace the rotary frequency changer. The new EFC is individually operated using a basic feeding pattern; these converters require over-current tolerance in the converters. In this paper, we describe the application of EFC to the Shinkansen railyard, showing the development of the control scheme that can control the over-current. The new EFC has a unique feature in connecting pre-existing power supplies apart from the new EFC, for covering various feeding situations. We also describe the interconnection method.

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A general-purpose inverter controls the output current using information from current sensors for high-performance motor control. However, these sensors outputs, however, have some gain and offset errors that depend on the peripheral components and the characteristics of the current sensor. These errors cause an imbalance in the output current, which causes a torque ripple. The torque ripple leads to many problems. The authors have proposed a periodic disturbance observer (PDO) as a control method for vibration suppression. The current sensor error causes a vibration with a specific frequency; thus, this paper proposes a current sensor error compensation method to apply the PDO for suppressing this specific frequency. This method can suppress the harmonic current in real time, and the current control performance can be improved by error compensation. This paper explains the proposed method and demonstrates the effectiveness of the proposed method through simulation and experimental results. In addition, this paper verifies the follow-ability of sensor error variation.

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Precise output power control and seamless transition of microsource converters (MSCs) between grid-tied and islanding operation modes are of great significance for the stability of voltage and frequency, and for power flow control in a microgrid. The wireless droop control method (WDCM) is an effective method for MSCs to share loads dynamically and automatically and realize the “plug and play” function. However, this method strongly relies on the local sampling signals of MSCs to dynamically control its output power. Therefore, the voltage drop induced by the line impedance will cause errors in the output power control of the MSCs and lead to system instability. To realize accurate power tracking and sharing, two virtual impedances and an on-line estimated power compensation conductance are proposed, which form a unified controller along with the refined droop control method and automatic voltage compensation mechanism. The proposed method enables the microgrid to realize automatic switching of the control objective when the operation mode changes, which ensures seamless transition between the different operation modes of the microgrid. This method is valid for all types of line impedances and loads. In addition, as the required voltage and current signals are sampled at the local output terminals of an MSC, the modularity and reliability of the controller is increased. Finally, the improved control scheme is verified via simulations and experiments.

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A permanent magnet hybrid-type axial magnetically levitated motor is proposed in this paper. The motor consists of a spherical permanent magnet and an axial type bearingless motor with a tilt control function. The rotor has two permanent magnets on one side, and the motor stator has eight poles, which include eight concentrated windings. The operating principle was investigated through numerical analysis. It was verified that the proposed motor can control the translational motion, inclinational motion, and rotational motion independently. A test rig was fabricated to investigate the control performance. The time responses of each controlled axes were quick. In addition, stable levitated rotation was observed in each actively controlled axes up to 2000min^-1.

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This paper investigates the effect of permanent magnet demagnetization on the performance of interior permanent magnet synchronous motors (IPMSMs). In our study, magnetic demagnetization was imitated by decrease in magnet volume. The demagnetization level in our study is less than that in previous research studies, that is, the volume of PMs is reduced in the radial and axial directions by 2.5, 5.0, and 7.5%. Simulation results show that the stator current is useful for fault detection of a PMSM with a demagnetized PM under constant V/f open-loop control. Further, for detecting a demagnetized PM within a PMSM under vector control, stator voltage is useful except in the middle torque range: the stator current is useful in a large torque range. The simulated results are verified through experiments.

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This paper describes a fast analytical model for computing the nonlinear magnetization and static torque characteristics of a switched reluctance machine (SRM). This model is developed using the flux-tube and gage-curve methods. The proposed model is used for computing the magnetization (flux-linkage) and torque characteristics of three and four-phase SRMs. The simulation results obtained using the proposed analytical model are compared to those obtained using magnetostatic finite-element analysis (FEA) for a three-phase 12/8 SRM and for a four-phase 8/6 SRM. Finally, experimental verification of the analytical model is presented for the 12/8 SRM and 8/6 SRM prototypes.

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This paper describes a high-speed protection circuit against a hard-switching fault (HSF) and a fault under load (FUL). The demand for high-speed protection circuits for insulated-gate bipolar transistors (IGBTs) subjected to an HSF increases with increasing power density of power semiconductor devices. The reverse transfer capacitance of an IGBT depends on the collector-emitter voltage, such that it produces a significant effect on the switching behavior under HSF conditions as well as under normal conditions. Accordingly, a significant difference appears in the gate charge characteristics between under HSF conditions and under normal turn-on conditions. Hence, an HSF can be detected by monitoring the gate-emitter voltage and the amount of gate charge. IGBTs can be rapidly protected from destruction because no blanking time is required. An FUL can be also detected by the same protection procedure because a gate charge characteristic under FUL conditions also differs from that under normal turn-on conditions. Simulated and experimental results verify the validity of the novel protection circuit based on a gate charge characteristic.

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Using strings of cascaded submodules for multilevel dc/ac conversion has attracted considerable attention owing to the widespread popularity of the modular multilevel converter (MMC). Recently, it has been shown that such conventional submodule strings can be adapted to achieve single-stage dc/dc conversion. Although the modular string configurations for dc/ac and dc/dc conversion are similar, the underlying power transfer mechanisms employed by each differ significantly. This paper compares the dc/ac and dc/dc energy conversion processes for series-cascaded submodules and highlights their key similarities and differences. In addition, converter operation and control requirements for dc/ac and dc/dc conversion are discussed and compared. A capacitor voltage regulation scheme for dc/dc conversion is proposed, whereby vars generation can be arbitrarily allocated between the converter arms in order to maximize conversion efficiency. It is shown that single-stage dc/dc conversion can reduce converter cost and operating losses by up to 50% as compared to conventional cascaded dc/ac stages, i.e. dc/ac-ac/dc conversion.

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Modular multilevel converter (MMC) is a recently emerged multilevel topology for high-voltage high-power applications. However, in wind power applications, to the best of the authors knowledge, the performance of the MMC has not been extensively investigated. In this paper, the application of the MMC to wind energy systems is studied. The converters used to connect the wind turbine to the grid, which have rated active powers of 2MW and 10MW, are proposed and investigated. The electrical losses and thermal loading of the power devices in the proposed converter solutions are analyzed based on the gird conditions/requirements for wind power. The efficiency of the MMC under different P/Q boundaries defined by grid codes is investigated and compared with two-level (2L) and three-level (3L) neutral point clamped converters. It is concluded that it is possible to use the MMC in wind power applications, and the losses are evenly distributed between the submodules of the MMC. However, inside a submodule, the losses of the power devices are not equal, which may lead to the de-rating of the converter.

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Recently, because of research and development into SiC power devices, power converter circuits such as high-power isolated DC-DC converters (dual active bridge) using medium-frequency (MF) transformers have been proposed. The converter circuit requires the MF transformer and inductors, but these magnetic components dominate the volume of the circuit. To realize a high-power-density isolated DC-DC converter, it is necessary to analyze the losses in the MF transformer and inductors.  In this paper, an iron loss calculation method based on the improved generalized Steinmetz equation (iGSE) is presented. To analyze the iron loss in detail, an analysis method which divides the iron loss into the hysteresis loss and the eddy-current loss is also presented. Further, this paper presents a loss separation procedure for the iron loss in the MF transformer and inductors. In this analysis, the iron loss analysis is performed for different operation modes of the DC-DC converter. Finally, the validity of the separation procedure is confirmed by both analytical and experimental results.

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A novel single-drive bearingless motor with a high passive stiffness and wide gap factor is proposed. The single-drive bearingless motor has only one set of three-phase windings. It independently generates both the torque and axial suspension force with only one three-phase inverter and one displacement sensor. Therefore, the single-drive bearingless motors have the advantages of low cost and small size. Only the axial direction z-axis is actively positioned. The other axes, the radial movements x and y and the tilting movements θ_x and θ_y, are passively stabilized by repulsive passive magnetic bearings. The stator consists of six C-shaped cores and one set of three-phase windings. A novel V-shaped winding structure is proposed to simultaneously generate the torque and active axial force. In this paper, the winding arrangement is presented. In addition, the mathematical calculations are presented in this paper.

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This paper introduces the concept of a discrete control method of class E amplifiers to achieve nominal operation for varying load resistance. In the proposed method, shunt capacitance and output resonant capacitance are varied electronically by setting the status of switches that are connected to the capacitances. The proposed method can maintain nominal operation, i.e., zero-voltage switching and zero-derivative switching (ZVS/ZDS), both when the load resistance is higher and lower than the designed value. Design equations are presented considering the parasitic capacitance of a MOSFET switch. A design example is also provided in the paper. Finally, the operation of the proposed circuit is verified through experiments.

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This paper presents a new two-phase mathematical model of a linear induction motor (LIM). This model is simpler than the conventional model but can correctly calculate both the asymmetric primary current and thrust ripple performances. In addition, an improved DC testing method is proposed to determine all circuit parameters in the model. This method has the advantage of needing only one standstill test to be carried out. Hence, both the no-load steady-state operation and lock tests, which are difficult to perform on built-in LIMs, are not needed to determine the model parameters. The proposed method was implemented on a three-phase, four-pole, and 12-slot single-sided LIM and validated by the experimental and simulation results.

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Two of the most important characteristics of electric vehicle motors are their low cost and high reliability. Unfortunately, armature windings of such motors are difficult to manufacture with automated techniques and are not very reliable. Thus, to obtain a motor at low cost with high reliability, we investigated a transverse-flux motor (TFM) containing a torus coil. In this study, we propose an enhanced TFM and discuss its principles and basic characteristics. The rotor comprises radially magnetized permanent magnets, and the stator comprises torus coils and axial 9-shaped cores. The stator core is alternately arranged in the circumferential direction and has radial and axial air gaps. Results of our analysis confirm that the enhanced TFM produces a high torque per motor volume of 4.72kN·m/m³.

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A single-stage reconfigurable isolated DC/DC converter⁽¹⁾ is proposed for use in hybrid and electric vehicles (EVs and HEVs) to supply a 12V automotive network from the HV battery. The purpose of the proposed topology is to increase the converter efficiency at the higher voltage range of the HV battery. A zero voltage transition (ZVT) phase shift (PS) full bridge (FB) converter is the basis for the reconfigurable topology, which is adapted to operate as a push-pull converter. The ZVT PS FB configuration covers the upper range of input voltages, in which an increased converter efficiency has more effect. It is furthermore reconfigured into the less efficient, hard-switching, push-pull configuration to cover the lower, less significant voltage range. The reconfiguration voltage is chosen to maximize the average efficiency according to the histogram of the HV-battery voltage during a typical driving cycle. Experimental validation of the proposed converter and its efficiency improvement are also presented.

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This paper presents a power IC technology platform based on AlGaAs/InGaAs/AlGaAs pseudomorphic field-effect transistors (pHEMTs) on a GaAs substrate. A quantitative assessment of a foundry-available 11-V GaAs pHEMT process indicates that owing to their superior material properties, the intrinsic figure of merit for pHEMT switching devices exhibits an order of magnitude improvement over state-of-the-art silicon NMOS transistors. The characterization results for GaAs pHEMTs with a breakdown voltage up to 47V are presented and shown to be comparable to GaN-based transistors for power switching applications. An integrated pHEMT DC-DC converter that can switch at frequencies above 100MHz is demonstrated. A 4.2-V pHEMT buck converter designed for envelope tracking applications is able to achieve 88% conversion efficiency at 100MHz.

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In this paper, we present a novel way of induction cooking. Traditionally, an alternating magnetic field is used to induce currents in a ferromagnetic pan to heat foods. We use nonferromagnetic materials and optimize the design for high repulsive forces in order to levitate the pan while simultaneously heating it and its contents. We use a simulation-based approach to study the influence of different parameters and to perform multidimensional analyses for the high force versus the power or loss goals. Finally, an experimental prototype is realized and successfully operated.

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This paper discusses how to improve the efficiency of switched reluctance motors (SRMs) by means of a step-skewed rotor (SSR). The cross-sectional configuration of the tested SRM with SSR, including the size and shape of the salient poles, was nearly identical to that of a conventional SRM. The tested SRM was divided into three stacks, of which only one rotor was skewed. The skewed angle was designed to reduce both the torque ripple and the radial force. Experiments were carried out to confirm the effectiveness of efficiency improvement of the SRM with SSR: a maximum efficiency of more than 90% was achieved. Compared with the efficiency of a conventional SRM, the efficiency of the proposed SRM with SSR was greater by more than 10 percentage points.

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This paper deals with an amplitude-adjusting method for signal injection in position sensorless control of interior permanent magnet synchronous motor (IPMSM) drives. Signal injection is necessary for position estimation at standstill and low speeds. Response signals to the injected signals have position information because of the saliency of the IPMSMs. The position information appears in inductances depending on the rotor positions; therefore, time derivative of motor currents has to be measured directly or indirectly. The position estimation method discussed in this paper is based on an extended electromotive force (EEMF) model. Although the EEMF model is mainly used in middle- and high-speed regions of IPMSM drives, it can be applied to all speed regions by combining it with signal injection methods. We adopt a signal injection method to stabilize the estimation and reduce the effects of disturbances. Then, the amplitude of the signal currents is adjusted to maintain a sufficiently high amplitude of EEMF against disturbances. Signal setting becomes easier because the lower limit of EEMF can be adjusted against the degree of disturbances.

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Many researchers have studied electric vehicles (EVs) for improving their efficiency to increase the driving range. The system design of an electrical power train has significant influence on the total driving range per charge and has been widely researched. A series chopper power train using a buck-boost chopper has been proposed as an electrical power train system. This electrical power train achieves high efficiency due to low and high inverter input voltage in the low and high speed regions, respectively. In previous studies, a high efficiency control optimizing the chopper output voltage was proposed, and a motor test bench with characteristics similar to actual EVs was constructed by using a battery emulation system with voltage variation characteristics, which occur due to the state of charge (SOC) and internal resistance. This paper shows the effects of optimizing the chopper output voltage on the driving range per charge in both efficiency estimation and the motor test bench experiment. This allows the verification of the usefulness of optimizing the chopper output voltage for increasing the efficiency. The results indicate an improvement of 0.9% and 2.7% in the driving range per charge during efficiency estimation and the motor test bench experiment, respectively.

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This paper designs the rotor structure for two types of permanent magnet synchronous motors. The proposed optimization method combines a topology optimization method, which uses a genetic algorithm and a cleaning procedure, and a method considering ease of manufacturing. The designed rotor of a compressor motor for an air conditioner has 32% higher average torque than that of a conventional motor. The designed rotor has a larger torque/current than that of a hybrid vehicle motor at a low output power.

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When an inductive power transfer system is applied to a battery charger for electric vehicles, a diode bridge rectifier with a dc-dc converter, called a secondary-side converter in this paper, is connected to the secondary side of the resonant circuit in order to regulate the current and voltage of the battery. A compensation capacitor is typically used to improve the input power factor in an inductive power transfer system, and a resonant circuit is configured. This paper presents a design method for the primary compensation capacitor in an inductive power transfer system with series compensation on the primary side and parallel compensation on the secondary side (S/P topology) to connect a boost or buck converter via a rectifier circuit on the receiving side. For the S/P topology, the capacitance of the primary-side compensation capacitor influences the duty ratio of the switch used in the secondary-side converter because it affects the input-to-output voltage ratio of the resonant circuit. Further, the duty ratio of the secondary-side converter affects the resonant-circuit efficiency. In addition, the primary compensation capacitance affects the output power factor of the inverter, which is connected to the primary side of the resonant circuit. Therefore, the capacitance of the primary-side compensation capacitor also affects the inverter efficiency and resonant-circuit efficiency. In this paper, a primary-side capacitor design method is examined. The results show that the optimum capacitance using a buck converter differs from that using a boost converter.

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Traction drive-trains of modern locomotives consist of a flexible multi-inertia structure that experiences significant wheelset wear due to wheel-rail contact and ageing of rubber elastic joints during its operational life. For control design, an accurate and suitable reduced model is required. Therefore, a reduced model identification is proposed, taking branched traction drive-trains and parameter adaption in terms of wheelset wear and rubber ageing into consideration. The identification effort is lowered by applying previous knowledge of the flexible structure in order to comply with the limitations imposed by the traction application. For predictive maintenance, the effects of ageing and wheel wear are decoupled, enabling precise estimation of the variable mechanical parameters, namely, the rubber joint stiffness and the wheel disc radius, on the basis of an identified modal three-inertia model. Finally, the proposed scheme is tested with data from a European high-performance locomotive.

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Factors related to interlocking, which is known to affect the core magnetic properties of motors and generators, were analyzed with the aim of achieving greater accuracy in the prediction of core losses. In a ring core sample assembled by V-type interlocking, dowel formation and dowel jointing showed comparable contributions to iron loss increase at low frequencies (e.g., 50Hz), whereas at high frequencies, increases in iron loss due to dowel jointing were greater than those due to dowel formation. It was suggested that dowel formation increased iron loss because of the strains originating from the plastic constraint due to the existence of dowels. Jointing of individual dowels increased eddy current loss at higher frequencies (e.g., 400Hz). Furthermore, eddy current loss increased significantly under the existence of an interlinkage magnetic flux across the line between two adjacent dowels, including the case of staggered dowel arrangements. The increase in iron loss in a motor core owing to interlocking can be estimated by the obtained degradation tendencies of iron losses in ring cores with respect to the density of interlocking dowels.

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Electric trains require high deceleration capability and stable traveling performance. This paper focuses on electric train deceleration under wet railway track conditions. Electric trains typically have electric brakes and air brakes. Under low-adhesion-coefficient conditions, each axle experiences skidding. The driving wheel may then become locked because of the air brake. This causes damage to the wheel tread that can result in what is called a “wheel flat”. Many studies have focused on overcoming this problem. This paper proposes an anti-lock control system for electric train driving wheels using driving wheel speed and acceleration. This anti-lock driving wheel control system is evaluated in this study using numerical simulation.

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This paper presents the duality of PWM (Pulse Width Modulation) strategies for reducing the DC ripples between current and voltage source AC/DC converters. The authors propose a PWM strategy of a voltage source converter for reducing the DC current ripples using the PWM strategy of a current source converter. The validity of the duality of the PWM strategies between current and voltage source converters is verified through experiments.

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