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Gallium-nitride-field-effect transistors (GaN-FETs) are promising switching devices with fast switching capability. However, they commonly have low gate threshold voltage, suffering from susceptibility to the false triggering. Particularly, the oscillatory false triggering, i.e., a self-sustaining repetitive false triggering, can occur after a fast switching, which is a severe obstacle for industrial applications. The purpose of this paper is to elucidate the design instruction for preventing this phenomenon. The oscillatory false triggering is known to be caused by the parasitic oscillator circuit formed of a GaN-FET, its parasitic capacitance and the parasitic inductance of the wiring. This paper analyzed the nonoscillatory condition of this oscillator. The result revealed an appropriate ratio between the gate-drain capacitance and the common-source inductance is a key to prevent the oscillatory false triggering. Experiment successfully verified this analysis result, supporting the effectiveness of the appropriate design of this ratio for preventing the oscillatory false triggering. [ABSTRACT FROM AUTHOR]

Recent progress of widebandgap semiconductor switching devices enabled extremely high-frequency operation of power converters owing to their ultrafast switching capability. Fast switching may cause large switching noise at the common source inductance, which may increase the switching loss and lead to false triggering. Therefore, measurement of the common source inductance is often intensely required in practical design of fast switching power converters. However, measurement of the common source inductance is difficult, because 1) the wiring path hidden beneath the molded package significantly contributes to this inductance, 2) the mutual inductance between the gating circuit and the power circuit also contributes to this inductance, and 3) this inductance cannot be defined as the stray inductance of a loop wiring path. These difficulties are addressed in this paper by proposing a novel measurement method of the common source inductance. The proposed method is applicable to already-mounted power circuits. In addition, the proposed method offers a straightforward measurement procedure with common instruments, such as a signal generator, an oscilloscope, and voltage and current probes. Along with the measurement principle, this paper also presents an experiment to evaluate the proposed method. [ABSTRACT FROM PUBLISHER]

Switched reluctance motors (SRMs) have recently attracted researchers’ attention owing to their robust mechanical construction, high thermal tolerance, and strong cost-effectiveness, which are promising for vehicle propulsion. However, they tend to generate large ripples in the torque and input currents to the inverter; this deteriorates the driving comfort, and damages the battery lifetime. Preceding articles have investigated using the phase currents of SRMs to eliminate these ripples. However, these articles had difficulties in sufficiently eliminating these ripples in operations under magnetic saturation. This article further evolves one of these preceding articles, and proposes a derivation method for the phase-current waveform for improving the elimination of the torque and input-current ripples in operation under magnetic saturation. The proposed method analytically determines the phase-current waveform based on a nonlinear behavior model of the SRM while considering the magnetic saturation. A finite-element-method-based simulation and experiment are performed to evaluate the proposed method. These results reveal the successful reduction of the torque and input-current ripples under the magnetic saturation relative to a preceding study, supporting the appropriateness of the proposed method. [ABSTRACT FROM AUTHOR]

Switched reluctance motor (SRM) is recently emerging as a cost-effective but mechanically and thermally robust motor for vehicle propulsion. However, the conventional driving method of the SRM causes a large input current and torque ripples, both of which are scarcely acceptable for vehicle application. Recently, a promising driving method has been proposed that tunes the phase current to eliminate the input current and torque ripples simultaneously, although this method suffers from large copper loss when applied to the normal SRMs. To solve this problem, this article proposes simultaneous tuning of the rotor shape in combination with the recently proposed driving method, which includes only tuning of the phase current. Tuning of the rotor shape is targeted at minimizing the copper loss. Meanwhile, the stator structure is the same as the normal SRM design. The proposed approach was revealed to reduce the effective value of the phase current by 18% in simulation and by 23% in experiment compared with the recently proposed driving method, without increasing the input current and torque ripples. This result suggests the effectiveness of tuning both the rotor shape and the phase current for applying SRMs to vehicle propulsion. [ABSTRACT FROM AUTHOR]

It is quite often to utilize the transformer leakage inductance in the resonant tank of the LLC resonant converter to allow for a drastic reduction in the converter cost, weight, size, and volume. The effects of the secondary leakage inductance on the operation of the LLC resonant converter are not well discussed in the relevant literature, and it is the purpose of this paper to give an insight into these effects. The contribution of this paper lies in the following: first, highlighting that it is not always an accurate assumption to consider that the values of the primary and secondary leakage inductance are identical, specifically in asymmetric magnetic core structures. Second, it has been disclosed that the well-known coupling factor (k12) cannot properly express the unequalized leakage inductance distribution in the proposed asymmetric transformer. Therefore, the authors bring the primary coupling factor (k1) and secondary coupling factor (k2) into practice to appropriately express the unequalized leakage distribution on the primary and secondary windings, which can be controlled by the allocation of the relevant winding with respect to the air gap, utilizing the noise absorber, and changing the distance between the winding. Several transformer prototypes had been built and experimentally tested to validate these hypotheses. Third, it has been observed that the transformer voltage gain and efficiency can be improved when the transformer leakage inductance is concentrated on the secondary side to avoid the voltage drop inflicted by the relatively large value of the magnetizing current $(i_{m})$ , especially at the light load condition. Fourth, it has been reported that in a transformer structure with a concentrated value of leakage on the secondary side would decrease the resonant tank input impedance, vertically widen the voltage–gain curve of the converter, and eventually increase the frequency control bandwidth with respect to the load variation. Transformer prototypes had been constructed and tested in a 390 V/12 V–220 W LLC resonant converter to evaluate the proposed analysis. [ABSTRACT FROM AUTHOR]