In the power conversion system of electric vehicles, the inverter is shut down when the system fails owing to a drastic load change or other protection reasons. However, when the inverter is shut down in regeneration mode, the DC link capacitor voltage increases dramatically, which will potentially destroy the switching devices. In this paper, the authors propose a halt method to overcome the overvoltage and overcurrent problems if a system failure occurs during the regeneration. In addition, the command voltage vector in Phase 1 is considered from the temporal transition of energy in the drive system in order to suppress the current amplitude. The experimental results demonstrate that the DC link capacitor voltage is 80% lower as compared with that in the conventional method.

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In the analysis of switched reluctance motors (SRMs), the analytical error of 2D FEA caused by the magnetic flux change in the direction of the axis, which is not considered in 2D FEA, is a serious problem. In this paper, a novel method for making a 2D-FEA model of an SRM, which can equivalently consider the influence of the three-dimensional effect, is proposed. A 2D-FEA model of an SRM can be easily made by adjusting only the shape of two regions in a rotor by employing the proposed method. The optimum values of two parameters, defined in this paper for adjusting the shapes of the rotor with the proposed method, are easily extrapolated. A comparison of the experimental results with 2D FEA using the proposed method confirms that the proposed method is effective in considering the three-dimensional effect.

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The Iron loss at higher carrier frequencies up to 190kHz is measured by a single-phase GaN FET inverter because sinusoidal-like waveform is expected to be obtained by new material devices such as those based on SiC or GaN. The measured data show that iron loss excited by PWM inverter does not converge to the iron loss by sinusoidal excitation because the fluctuation in the magnetic field does not converge to zero, even when carrier frequency is 190kHz. Moreover, the iron loss even increases at some carrier frequency for a long dead time. Because of the properties of the GaN FET device, the ON voltage of the GaN FET during the dead time period becomes large, and the minor loop shape in the magnetic hysteresis curve becomes large. These phenomena are observed for a constant applied DC voltage and also for a constant modulation factor constant condition. The properties of the power semiconductor and the dead time of the inverter seriously influence the increase in the iron loss.

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The authors have developed a wireless power transfer (WPT) system for an in-wheel motor (IWM). It is called a wireless in-wheel motor (W-IWM). This paper presents a method that enhances the WPT efficiency in this system. Some methods that maximize the power transfer efficiency by power converter control have been proposed in past WPT research. In this research, a DC-DC converter is inserted on the receiver side to vary the load state. However, the space on the receiver side is very small for the W-IWM; therefore it is preferable to make the secondary circuit small. Therefore, a full bridge converter is used instead of a DC-DC converter in the W-IWM. In this paper, the authors propose a theoretical formula ofor the transfer efficiency of the W-IWM. From an analysis of this formula, there is a combination of a primary voltage and load voltage that maximizes the efficiency. The feasibility is validated by an experiment using a motor bench set.

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This paper proposes a new structural dual rotor SPMSM (Surface Permanent Magnet Synchronous Motor) using ferrite magnets having high torque density, small size, and low noise. In addition, the advantages of having a toroidally winding and adual rotor are examined through analysis, and it is confirmed that the torque density of the proposed motor is competitive to the rare-earth IPMSM (Interior Permanent Magnet Synchronous Motor).

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Recently, constructions of obstruction-warning signals and emergency buttons have been urgently needed at level crossings. However, the construction of these wayside facilities involves considerable inefficiency because it requires a joint survey or instruction to check these visibility from the train cab. Therefore, we have developed a simulator that overlays wayside facilities’ image on video sequences by estimating a three-dimensional position using our rail extraction method. In this paper, we present the concept of the simulator, details of the method, and an accuracy verification based on actual video sequences.

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Compared with Si-IGBT, a silicon carbide (SiC) -MOSFET is expected to reduce the switching loss and conduction loss of the low-current region, and also remove external freewheeling diode. However, because the SiC-MOSFET body diode has high forward voltage, the diode conduction loss increases during dead time, and therefore, its loss reduction effect decreases. This work proposes a novel dead time control circuit using a current sensing transistor integrated with SiC-MOSFET. The proposed circuit has a high responsiveness and high robustness against switching noise, and the dead time can be shortened to within 0.1µs without using external components. In addition, it has not only the dead time control but also the short-circuit current detection, which is the radical function of a current sensor. In the experimental result of using a 10kW boost converter with SiC-MOSFET, the efficiency of the proposed circuit was 1% higher than that without it.

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A multicell dc-dc transformer (DCX) with an efficiency of 98.0% is developed for a next generation dc distribution system. Input Series Output Parallel (ISOP) and Input Parallel Output Series (IPOS) connection topologies of highly efficient dc-dc cell converters have been applied to realize DCXs that have arbitrary I/O voltages and a high transfer factor. The behavior of a DCX based on multicell topology using nonregulated dc-dc converters is analyzed, and the voltage stress in each cell converter is discussed quantitatively considering the variation in converter circuit parameters. Further, the availability of the applied topology and the validity of the analysis are confirmed by fabricating a prototype of a 384V-12V 2,400W DCX. The multicell topology contributes to realizing a low-carbon society pushing the promotion of highly efficient, space-saving and low cost dc power supplies with standardized, highly efficient cell converter modules.

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A sensitive device, for example, a giant magnetoresistive head contained in an electronic equipment, often malfunctions because of the induced voltage of less than 10V when a charged human body is present near the equipment. Such accidents due to electrostatic induction occur when the charged body moves. The author focuses on the induced voltage of opposite polarity generated on the metal box when the charged body moves away from the box. In experiments, metal boxes of different heights are used to change the facing area between the charged body and the box. In addition, the position of the metal box is changed so that the induced voltages of the box can be compared. The results show that the induced voltages and the electric charges increase as the facing area between the metal box and the charged body increases. The induced voltage of the metal box indicates the value of approximately -370% of the charged body when the facing area between the metal box and the charged body increases. Further, the induced voltages and the charges are slightly dependent of the position of the metal box. The results will be useful for the design of electronic equipment from the standpoint of preventing malfunction and failure of the equipment.

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In this paper, a synchronous motor is described in which space harmonic power is utilized for field magnetization instead of permanent magnets. The stator has a concentrated winding structure, and the rotor has two different types of winding, i.e., an induction pole (I-pole) winding that primarily retrieves the second space harmonic and an excitation pole (E-pole) winding for the field magnetization. The two coils are connected via a center-tapped full-bridge diode rectifying circuit. The effects of the rotor electromangetomotive force distribution on the d- and q-axis are theoretically discussed. Then, the effect of the auxiliary poles is experimentally verified using a prototype motor in terms of the adjustable speed drive characteristics and the efficiency map. In addition, it is experimentally clarified that the rotor self-inductance and the rotor winding resistance significantly affect the conduction period of the rotor induced current.

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Motor torque ripples generally produce a problem of noise and vibration. The torque ripple could be caused by an offset in the current sensor output. This paper presents that a current sensor offset leads to the 1^st order harmonic component of the torque ripple to the electric angle. Moreover, the current sensor offset canceller is proposed as a countermeasure against the 1^st order harmonic component. In the offset canceller, the offset value is evaluated from the 1^st order harmonic components of the ripples of d, q axes currents through Fourier series integration. Then, the remote monitoring system for the current sensors can use the proposed offset canceller. The experimental and simulational results prove the efficiency of the offset canceller.

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In recent years, inductive power transfer systems with resonance have been studied. However, additional DC-DC converters are required on the primary and secondary sides of such inductive power transfer systems. The roles of these DC-DC converters are controlling the output power and maintaining the transmission efficiency because the transmission efficiency strongly depends on the load. Moreover, high-accuracy capacitances for resonance with a high-voltage rating are required. These features prevent cost reduction and improvement in the system efficiency. In this paper, a non-resonant inductive power transfer system based on the principle of a dual active bridge converter is proposed in order to overcome above problems. The proposed system has two full bridge inverters on the primary and secondary sides of the non-resonant inductive power transfer system. This configuration reduces the primary current at a rated power in comparison with a conventional non-resonant inductive power transfer system. The output power is controlled by the phase difference between the primary and secondary voltages of the transmitting coils. The phase difference is determined using a hill-climb method by a secondary controller. An experimental verification showed that the proposed system achieves a maximum efficiency of 94.1% with an output power of 0.84kW.

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Our research mission is to develop new insights into the principles that govern the interaction between the Cybernetic world and Power Electronic Systems in the context of modern power grids. Based on the understanding of these principles, we combine analysis and experimental techniques to develop a general system-level methodology and tools that can predict potential instability in power electronics systems in the field.

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