• 한국전기전자재료학회논문지
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• 제30권12호
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• pp.817-821
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• 2017

As a ZnO varistor is subjected to electrical and environmental stresses, it degrades gradually, which may result in power interruption by short circuit. This study investigates changes in the electrical characteristics of ZnO varistors due to deterioration owing to energy absorption, and determines the optimal parameters for on-line diagnosis of the varistor. Two types of varistors were used for an accelerated aging experiment involving the application of the $8/20{\mu}s$ standard lightning impulse current. The electrical characteristics in terms of the reference voltage, total leakage current, resistive leakage current, and third-harmonic component of the total leakage current were measured, and their change rates were analyzed. The results revealed that the total leakage current increased slightly with an increase in the varistor absorbed energy, while the resistive leakage current and the third-harmonic component increased apparently. Therefore, the third-harmonic component of the total leakage current was proposed as the optimal parameter for on-line monitoring of ZnO varistor conditions.

• 한국신뢰성학회지:신뢰성응용연구
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• 제7권1호
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• pp.1-11
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• 2007

This paper presents a derating design approach for reliability improvement of a regulator IC. The IC is usually used in SMPS. The main failure mechanism of interest is voltage drop due to the package delamination mainly caused by two stresses, i.e. temperature and current. The lifetime under stresses is modeled as a function of stresses and time using accelerating life testings. Quantitative and qualitative variation in lifetime according to stress variations are investigated using the modeled lifetime. Stress levels would be determined to achieve required reliability levels in the aspect of derating design for reliability.

• Journal of Power Electronics
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• 제15권6호
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• pp.1654-1663
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• 2015

Compared to LC resonance, LCL resonance has distinct advantages such as a large resonant capability, low voltage and current stresses of the power device, constant voltage or current output characteristics, and fault-tolerance capability. Thus, LCL resonant compensation is employed for a movable Inductive Contactless Power Transfer (ICPT) system with a multi-load in this paper, which achieves constant current output characteristics. Peculiarly, the primary side adopts a much larger compensation inductor than the primary leakage inductor to lower the reactive power, reduce the input current ripple, generate a large current in the primary side, and realize soft-switching. Furthermore, this paper proposes an approximate resonant point for large inductor-ratio LCL resonant compensation through fundamental wave analysis. In addition, the PWM control strategy is used for this system to achieve constant current output characteristics. Finally, an experimental platform is built, whose secondary E-Type coils can ride and move on a primary rail. Simulations and experiments are conducted to verify the effectiveness and accuracy of both the theory and the design method.

• Journal of Power Electronics
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• 제16권5호
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• pp.1689-1697
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• 2016

Continuous conduction mode (CCM) boost converters are commonly used in home appliances and various industries because of their simple topology and low input current ripples. However, these converters suffer from several disadvantages, such as hard switching of the active switch and reverse recovery problems of the output diode. These disadvantages increase voltage stresses across the switch and output diode and thus contribute to switching losses and electromagnetic interference. A new topology is presented in this work to improve the switching characteristics of CCM boost converters. Zero-current turn-on and zero-voltage turn-off are achieved for the active switches. The reverse-recovery current is reduced by soft turning-off the output diode. In addition, an input current sensorless control is applied to the proposed topology by pre-calculating the duty cycles of the active switches. Power factor correction is thus achieved with less effort than that required in the traditional method. Simulation and experimental results verify the soft-switching characteristics of the proposed topology and the effectiveness of the proposed input current sensorless control.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.694-700
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• 1998

A novel zero-voltage-transition (ZVT) isolated PWM boost converter for single stage power factor correction (PFC) is presented to improve the performance of the previously presented ZVT converter[8]. A simple auxiliary circuit which includes only one active switch provides zero-voltage-switching (ZVS) condition to all semiconductor devices. (Two active switches are required for the previous ZVT converter) This leads to reduced cost and simplified control circuit comparing to the previous ZVT converter. The ZVS is achieved for wide line and load ranges with minimum device voltage and current stresses. Operation principle, control strategy and features of the proposed converter are presented and verified by the experimental results from a 1.5 kW, 100 KHz laboratory prototype.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.385-387
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• 1996

A novel two stage soft-switching ac-to-dc convener with power factor correction is proposed. The proposed convener provides zero-voltage-switching (ZVS) condition to main switch of boost pre-regulator without auxiliary switch. Comparing to the conventional two stage approach(ZVS-PWM boost rectifier followed by off-line ZVS dc-dc step down converter), the proposed approach is simple and reducing EMI noise problem. A new simple DC-linked energy feedback circuit provides zero-voltage-switching condition to boost pre-regulator without imposing additional voltage and current stresses and loss of PWM capability. Operational principle, analysis, control of the proposed converter together with the simulation results of 1KW prototype are presented.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 연구회 합동 학술발표회 논문집
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• pp.44-48
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• 1998

In the buck-boost DC-DC converter which is used at a certain situation such as in factories where loads often change a lot, the switches in the device make big energy loss in operating at Buck-Boost Mode due to hard switching and are affected by lots of stresses which decrease the efficiency rate of the converter. In order to improve this problem, to decrease the loss of snubber and switching, it has been investigated that zero voltage switching mode and zero current switching mode which make the operation of switches with soft switching. For the more sophisticated and advanced device, this paper is presented the Partial Resonant Soft Switching Mode Power Converter which is adapted the power converter having the partial resonant soft switching mode, that makes switches operate when the resonant current or voltage becomes zero by making the resonant circuit partially at turning on and off of the switches with suitable layout of the resonant elements and switch elements in the converter. Also, this paper includes the analysis and simulation of the Partial Resonant type Buck-Boost Chopper.

• 전자공학회논문지B
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• 제28B권12호
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• pp.38-50
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• 1991

A current-controlled scheme of pulse width modulation voltage source inverter (PWM VSI) has attracted considerable attention due to its fast response with current limit and especially suitable for potentially high performance applications such as AC motor drives and UPS systems. These features yield near-sinusoidal currents in the load with reduced current peaks, lower inverter switching frequency and reduce inverter and load stresses. A high performance current-controlled inverter must have a quick response in transient state and low harmonic current in steady state. This paper compares and shows the controlled-characteristics with hysteresis controller(HC), ramp comparison controller(RCC) and predictive controller(PC) of PWM inverter to control actual current of VSI-IM.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권3호
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• pp.188-194
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• 2000

This paper presents new Zero-Voltage-/Zero-Current-Switching (ZVZCS) PWM DC-DC converters. The proposed soft-switching technique achieves ZVS and ZCS simultaneously at both turn-on and turn-off of the main switch and diode by using only one auxiliary switch. Also, the proposed soft-switching technique is suitable for not only minority but also majority carrier semiconductor devices. The auxiliary circuit of the proposed topology is placed out the main power path and therefore, there are no voltage/current stresses on the main switch and diode. The operating principle of the proposed topology is illustrated by a detailed study with a boost converter as an example. Theoretical analysis, simulation and experimental results are presented to explain the proposed schemes.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.261-263
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• 2006

A new soft switched active snubber circuit is proposed to achieve zero voltage and zero current switching for all the switching devices in PWM DC-DC converters. The unique location of the snubber and inductor ensures low current/voltage stresses and commutation losses. With a saturable reactor, the conduction loss of auxiliary switch could be further minimized. A boost converter adopting this technique is presented as an example, to illuminate its operation principles and derive the design procedures. Simulation and hardware implementation have been made to validate its performance. Some other basic PWM DC-DC topologies using the proposed snubber have also been given.