• Smart Structures and Systems
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• v.25 no.3
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• pp.385-391
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• 2020

In this paper, a new passive lossless snubber circuit with energy transfer capability is proposed. The proposed lossless snubber circuit provides Zero-Current Switching (ZCS) condition for turn-on instants and Zero-Voltage Switching (ZVS) condition for turn-off instants. In addition, its diodes operate under soft switching condition. Therefore, no significant switching losses occur in the converter. Since the energy of the snubber circuit is transferred to the output, there are no significant conduction losses. The proposed snubber circuit can be applied on isolated and non-isolated converters. To verify the operation of the snubber circuit, a boost converter using the proposed snubber is implemented at 70W. Also, the measured conducted Efficiency Electromagnetic Interference (EMI) of the proposed boost converter and conventional ones are presented which show the effects of proposed snubber on EMI reduction. The experimental results confirm the presented theoretical analysis.

• Smart Structures and Systems
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• v.26 no.4
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• pp.521-531
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• 2020

In this paper, a new interleaved high step-up converter with low voltage stress on the switches is proposed. In the proposed converter, soft switching is provided for all switches by just one auxiliary switch, which decreases the conduction loss of auxiliary circuit. Also, the auxiliary circuit is expanded on the converter with more input branches. In the converter all main switches operate under zero voltage switching condition and auxiliary switch operate under zero current switching condition. Because of the interleaved structure, the reliability of converter increases and input current ripples decreases. The clamp capacitor in the converter not only absorb the voltage spikes across the switch due to leakage inductance, but also improve voltage gain. The proposed converter is fully analyzed and to verify the theoretical analysis, a 100 W prototype was implemented. Also, to show the effectiveness of auxiliary circuit on conduction EMI, EMI of the proposed converter comprised with hard switching counterpart.

• Journal of Power Electronics
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• v.13 no.1
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• pp.1-8
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• 2013

This paper presents a resonant non-inverting buck-boost converter in which all switches operate under ZCS conditions. In a symmetric configuration, a CLL resonant tank along with an inverter arm and a rectifying diode are employed. The diode is turned off at ZCS and hence the problem of its reverse recovery is obviated also. As a result switching losses and EMI are reduced and switching frequency can be increased. The converter can work at DCM and CCM depend on the switching frequency and the load-current. Experimental results from a 200W/200KHz laboratory prototype verify operation of the proposed converter and the presented theoretical analysis.

• Structural Engineering and Mechanics
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• v.11 no.2
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• pp.199-210
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• 2001

Axially compressed circular cylinders repeat symmetry-breaking bifurcation in the postbuckling region. There exist stable equilibria with all symmetry broken in the buckled configuration, and the minimum postbuckling strength is attained at the deep bottom of closely spaced equilibrium branches. The load level corresponding to such postbuckling stable solutions is usually much lower than the initial buckling load and may serve as a strength limit in shell stability design. The primary concern in the present paper is to compute these possible postbuckling stable solutions at the deep bottom of the postbuckling region. Two computational approaches are used for this purpose. One is the application of individual procedures in computational bifurcation theory. Path-tracing, pinpointing bifurcation points and (local) branch-switching are all applied to follow carefully the postbuckling branches with the decreasing load in order to attain the target at the bottom of the postbuckling region. The buckled shell configuration loses its symmetry stepwise after each (local) branch-switching procedure. The other is to introduce the idea of path jumping (namely, generalized global branch-switching) with static imperfection. The static response of the cylinder under two-parameter loading is computed to enable a direct access to postbuckling equilibria from the prebuckling state. In the numerical example of an elastic perfect circular cylinder, stable postbuckling solutions are computed in these two approaches. It is demonstrated that a direct path jump from the undeformed state to postbuckling stable equilibria is possible for an appropriate choice of static perturbations.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1669-1677
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• 2016

A new auxiliary circuit for boost, buck, buck-boost, Cuk, SEPIC, and zeta converters is introduced to provide soft switching for pulse-width modulation converters. In the aforementioned family of DC-DC converters, the main and auxiliary switches turn on under zero current transition (ZCT) and turn off with zero voltage and current transition (ZVZCT). All diodes commutate under soft switching conditions. On the basis of the proposed converter family, the boost topology is analyzed, and its operating modes are presented. The validity of the theoretical analysis is justified by the experimental results of a 100W, 100 kHz prototype. The conducted electromagnetic emissions of the proposed boost converter are measured and found to be lower than those of another ZCT boost converter.

• Journal of Power Electronics
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• v.15 no.3
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• pp.602-609
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• 2015

In this paper, a zero current transition (ZCT) double-ended flyback converter is proposed. All of the switching elements act under soft switching conditions and the voltage stress of the main switches is limited to the input voltage due to the innate behavior of the double-ended flyback converter. Providing soft switching conditions and clamping the voltage stress improves the efficiency and electromagnetic compatibility (EMC). The Proposed converter is analyzed in detail and its operating modes are discussed in detail. Experimental results are presented to verify the theoretical predictions. Moreover, the conducted electromagnetic emissions of the proposed ZCT double-ended flyback converter are measured to show another merit of the proposed converter in addition to providing soft switching conditions. The measured electromagnetic interference (EMI) of the proposed converter demonstrates that its EMI is lower than the conventional double-ended flyback converter. Furthermore, two simple and cost effective EMI reduction methods are applied to satisfy the EMC standard.

• Journal of Power Electronics
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• v.17 no.5
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• pp.1127-1136
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• 2017

This paper proposes a new soft switching dual input converter for renewable energy systems. Multi-input converters are produced by combining discrete converters. These converters reduce the number of circuit elements, cost, volume and weight of the converter and provide a constant output power in different weather conditions. Furthermore, soft switching techniques can be applied to increase efficiency. In this paper, a Zero Voltage Transition (ZVT) dual input boost converter is presented. Only one auxiliary circuit is used to provide the soft switching condition for all of the semiconductor elements. The proposed converter, which is simulated by ORCAD software, is theoretically analyzed. To confirm the validity of the theoretical analysis, a prototype of proposed converter was constructed. Simulation and experimental results confirm the theoretical analysis. An efficiency comparison shows a one percent improvement at nominal loads.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.197-204
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• 2014

In this paper an Improved Zero Voltage Zero Current Pulse Width Modulation Forward converter which employs a simple resonance snubber circuit is introduced. A simple snubber circuit consists of a capacitor, an inductor and two diodes. In proposed converter, switch Q1 operates at ZCS turn-on, and ZVS turn-off conditions and all-passive semiconductor devices operate at ZVZCS turn-on and turn-off state. The proposed converter is analyzed and various operating modes of the ZVZCS-PWM forward converter are discussed. Analysis and design considerations are presented and the prototype experimental results of a 100w (40 V/2.5A) proposed converter operating at 30 KHz switching frequency confirm the validity of theoretical analysis.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.6
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• pp.57-63
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• 2000

A multi-branch thermo-optic switch has a problem that driving powers in the switching states are different from each other; the power consumption for the inner output port is more than twice as large as that form the outer output port. In this pater, to solve this problem unequal width heaters and the waveguide structure with a thin overcladding layer are proposed in a four-branch thermo-optic switch. The proposed structure is fabricated with the polymer materials with high index difference, Teflon and polyimides. The fabricated device was measured at the wavelength of 1550 nm. The measured characteristics exhibit the smaller difference in the power consumption between the switching states and the driving power les than the previous four-branch thermo-optic switch with equal width heaters. As for the device performance, the crosstalk is better than - 16 dB at about 310 ~ 390 mW, the insertion loss is 4.7 dB, and the switching time is less than 1 ms.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.8
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• pp.96-103
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• 2008

In this paper, a new algorithm based on sensitivity method for alleviating overloads in power networks is presented to find the switching branches effectively. By applying the new sensitivity of the line flow with respect to the change of the branch impedance, both on and off switchings for alleviating overloads in power networks are performed systematically at once and an effective scheme for drawing up a plan to alleviate overloads of the lines is presented through screening a large number of line switching cases easily. The ranking of switching branches is calculated according to the new switching algorithm based on sensitivity method and the switching of the ranked branches is performed in the order of ranking until overloads are eliminated. In order to show the effects of this algorithm, it is applied to a small scale power system of IEEE 39-bus test system.