• Journal of Power Electronics
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• 제17권6호
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• pp.1469-1479
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• 2017

Primary-side regulation (PSR) scheme is widely applied in low power applications, such as cell phone chargers, network adapters, and LED drivers. However, the efficiency and standby power requirements have been improved to a high standard due to the new trends of DOE (Department Of Energy) Level VI and COC (Code Of Conduct specifications) V5. The major drawbacks of PSR include poor regulation due to inaccurate feedback and difficulty in acquiring acceptable regulation. A novel adaptive blanking strategy for constant current and constant voltage regulation is proposed in this paper. An accurate model for the sample blanking time related to transformer leakage inductance and the metal-oxide-semiconductor field-effect transistor (MOSFET) parasitic capacitance is established. The proposed strategy can achieve accurate detection for ultra-low standby power. In addition, numerous control factors are analyzed in detail to eliminate the influence of leakage inductance on the loop stability. A dedicated controller integrated circuit (IC) with a power MOSFET is fabricated to verify the effectiveness of the proposed control strategy. Experimental results demonstrated that the prototype based on the proposed IC has excellent performance.

• Journal of Electrical Engineering and Technology
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• 제9권2호
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• pp.649-654
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• 2014

In this paper, an analytical model for Surrounding Gate (SG) metal-oxide- semiconductor field effect transistors (MOSFETs) considering quantum effects is presented. To achieve this goal, we have used variational approach for solving the Poission and Schrodinger equations. This model is developed to provide an analytical expression for inversion charge distribution function for all regions of device operation. This expression is used to calculate the other important parameters like inversion charge density, threshold voltage, drain current and gate capacitance. The calculated expressions for the above parameters are simple and accurate. This paper also focuses on the gate tunneling issue associated with high dielectric constant. The validity of this model was checked for the devices with different dimensions and bias voltages. The calculated results are compared with the simulation results and they show good agreement.

• Journal of Power Electronics
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• 제12권1호
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• pp.113-119
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• 2012

This paper describes the design and control of a phase shift full bridge converter with a current doubler, which can be used for the on-board charger for the lead-acid battery of electric forklifts. Unlike the common resistance load, the battery has a large capacitance element and it absorbs the entire converter output ripple current, thereby shortening the battery life and degrading the system efficiency. In this paper a phase shift full bridge converter with a current doubler has been adopted to decrease the output ripple current and the transformer rating of the charger. The charge controller is designed by using the small signal model of the converter, taking into consideration the internal impedance of the battery. The stability and performance of the battery charger is then verified by constant current (CC) and constant voltage (CV) charge experiments using a lead-acid battery bank for an electric forklift.

• 전기학회논문지
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• 제59권5호
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• pp.860-865
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• 2010

When a circuit breaker is opened, a large capacitance around the buses, the circuit breaker and the potential transformer (PT) might cause PT ferroresonance. During PT ferroresonance, the iron core repeats saturation and unsaturation even though the supplied voltage is a rated voltage. This paper describes an analytical analysis of PT ferroresonance in the transient-state. To analyze ferroresonance analytically, the iron core is modelled by a simplified two-segment core model in this paper. Thus, a nonlinear ordinary differential equation (ODE) for the flux linkage is changed into a linear ODE with constant coefficients, which enables an analytical analysis. In this simplified model, each state, which is either saturated or unsaturated state, corresponds to one of the three modes, i.e. overdamping, critical damping and underdamping. The flux linkage and the voltage in each state are obtained analytically by solving the linear ODE with constant coefficients. The proposed transient analysis is effective in the more understanding of ferroresonance and thus can be used to design a ferroresonance prevention or suppression circuit of a PT.

• Journal of Power Electronics
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• 제18권4호
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• pp.1255-1267
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• 2018

Parasitic parameters have a larger influence on Silicon Carbide (SiC) devices with an increase of the switching frequency. This limits full utilization of the performance advantages of the low switching losses in high frequency applications. By combining a theoretical analysis with a experimental parametric study, a mathematic model considering the parasitic inductance and parasitic capacitance is developed for the basic switching circuit of a SiC MOSFET. The main factors affecting the switching characteristics are explored. Moreover, a fast-switching double pulse test platform is built to measure the individual influences of each parasitic parameters on the switching characteristics. In addition, guidelines are revealed through experimental results. Due to the limits of the practical layout in the high-speed switching circuits of SiC devices, the matching relations are developed and an optimized layout design method for the parasitic inductance is proposed under a constant length of the switching loop. The design criteria are concluded based on the impact of the parasitic parameters. This provides guidelines for layout design considerations of SiC-based high-speed switching circuits.

• 한국세라믹학회지
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• 제49권5호
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• pp.475-483
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• 2012

High capacitance X5R MLCCs based on $BaTiO_3$ ceramic dielectric layers exhibit a single broad, asymmetric arc shape impedance and modulus response over the wide frequency range between 1 MHz to 0.01 Hz. Analysis according to the conventional brick-layer model for polycrystalline conductors employing a series connection of multiple RC parallel circuits leads to parameters associated with large errors and of little physical significance. A new parametric impedance model is shown to satisfactorily describe the experimental spectra, which is a parallel network of one resistor R representing the DC conductivity thermally activated by 1.32 eV, one ideal capacitor C exactly representing bulk capacitance, and a constant phase element (CPE) Q with complex capacitance $A(i{\omega})^{{\alpha}-1}$ with ${\alpha}$ close to 2/3 and A thermally activated by 0.45 eV or ca. 1/3 of activation energy of DC conductivity. The feature strongly indicate the CK1 model by J. R. Macdonald, where the CPE with 2/3 power-law exponent represents the polarization effects originating from mobile charge carriers. The CPE term is suggested to be directly related to the trapping of the electronic charge carriers and indirectly related to the ionic defects responsible for the insulation resistance degradation.

• 한국세라믹학회지
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• 제55권3호
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• pp.244-260
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• 2018

Issues in the electrical characterization of semiconducting photoanodes in a photoelectrochemical (PEC) cell, such as the cell geometry dependence, scan rate dependence in DC measurements, and the frequency dependence in AC measurements, are addressed, using the example of a $TiO_2$ photoanode. Contrary to conventional constant phase element (CPE) modeling, the capacitive behavior associated with Mott-Schottky (MS) response was successfully modeled by a Havriliak-Negami (HN) capacitance function-which allowed the determination of frequency-independent Schottky capacitance parameters to be explained by a trapping mechanism. Additional polarization can be successfully described by the parallel connection of a Bisquert transmission line (TL) model for the diffusion-recombination process in the nanostructured $TiO_2$ electrode. Instead of shunt CPEs generally employed for the non-ideal TL feature, TL models with ideal shunt capacitors can describe the experimental data in the presence of an infinite-length Warburg element as internal interfacial impedance - a characteristic suggested to be a generic feature of many electrochemical cells. Fully parametrized impedance spectra finally allow in-depth physicochemical interpretations.

• 한국광물학회지
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• 제17권2호
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• pp.157-168
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• 2004

수용액 내 캐올리나이트와 할로이사이트의 표면화학 특성을 전위차 적정 실험과 FITEQL3.2 프로그램을 이용하여 연구하였다. 표면복합반응 모델 중 일정용량 모델을 적용하였으며, 표면을 사면체 자리와 팔면체 자리로 나누어 설정한 2 sites - 3 $pK_{a/s}$ 모델은 캐올리나이트와 할로이사이트의 표면화학 특성을 설명하는데 적합하였다. 두 점토광물 표면은 pH 4 이상에서 음전하를 띄며 pH가 높아질수록 양성자 표면 전하 밀도는 낮아진다. 산성 및 중성 영역에선 Si 사리(≡$SiO^{-}$ )가, 염기성 영역에선 Al 자리(≡$AlO^{-}$)가 양이온을 흡착하는데 중요한 역할을 할 것으로 예상된다. 모델링 결과 캐올리나이트의 경우 $pK_{a2(si)}$ /$^{int}$, p $K_{al(Al) }$ /$^{int}$ /, $pK_{a2}$ $(Al)^{int}$ /는 각각 4.436. 4.564, 및 8.461이며, 할로이사이트의 경우는 각각 7.852, 3.885, 7.084이다. 캐올리나이트의 총 Si 표면자리 농도와 총 Al 표면자리 농도는 0.215와 0.148 mM이며, 할로이사이트의 경우는 0.357과 0.246 mM이다 두 광물 모두 Si 표면자리 밀도 : Al 표면자리 밀도가 1 : 0.69로 비슷하다. 캐올리나이트의 총 표면자리 밀도는 3.774 sites/$nm^2$로 할로이사이트의 2.292 sites/n $m^2$ 값보다 약 1.6배정도 높다.다.

• 한국전자파학회지:전자파기술
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• 제2권2호
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• pp.30-37
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• 1991

GaAs MESFET의 소신호 등가 모델에서 외부 푀로 성분들을 결정하는 개선된 방법을 제시하였다. 정화간 내부 회로 성분값들을 구하기 위하여 외부 회로 성분들을 제거하는 것이 중요하다. 전송선로를 포함한 기생 인덕터와 커패시터로 이루어지 ㄴ외부 회로를 정립하고, 산란 행렬로부터 이들의 값을 구한 후에 내부 회로 성분을 구하였다. 특히 기생 인덕턴스와 커패시턴스값들은 주파수에 따라 거의 일정한 변화를 보였다.

• 전력전자학회논문지
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• 제4권2호
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• pp.175-183
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• 1999

PWM 컨버터에서 직류출력전압의 빠른 응답을 위해 입력 및 출력의 전력평형개념을 시스템 모델링에 도입하는 것이 바람직하다. 이 경우 시스템은 비선형이 되며 제어기 설계가 용이하지 않다. 본 논문에서는 입출력 궤환선형화 기법을 응용하여 시스템의 비선형성을 제거하였으며 그 결과 빠른 전압응답특성을 얻을 수 있었다. 또한 작은 용량의 전해커패시터를 사용하더라도 부하변동에 대해 직류출력전압을 일정하게 유지하는 것이 가능함을 보였다.