• Journal of Power Electronics
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• v.19 no.4
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• pp.907-921
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• 2019

This paper presents two advanced hybrid pulse-width modulation (PWM) strategies for multilevel inverters (MLIs) that provide both common-mode voltage (CMV) elimination and current ripple reduction. The first PWM utilizes sequences that apply one switching state at the double ends of a half-carrier cycle. The second PWM combines the advantages of the former and an existing four-state PWM. Analyses of the harmonic characteristics of the two groups of switching sequences based on a general switching voltage model are carried out, and algorithms to optimize the current ripple are proposed. These methods are simple and can be implemented online for general n-level inverters. Using a three-level NPC inverter and a five-level CHB inverter, good performances in terms of the root mean square current ripple are obtained with the proposed PWM schemes as indicated through improved harmonic distortion factors when compared to existing schemes in almost the entire region of the modulation index. This also leads to a significant reduction in the current total harmonic distortion. Simulation and experimental results are provided to verify the effectiveness of the proposed PWM methods.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.291.1-291.1
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• 2016

Graphene by one of the two-dimensional (2D) materials has been focused on electronic applications due to its ultrahigh carrier mobility, outstanding thermal conductivity and superior optical properties. Although graphene has many remarkable properties, graphene devices have low on/off current ratio due to its zero bandgap. Despite considerable efforts to open its bandgap, it's hard to obtain appropriate improvements. To solve this problem, heterojunction barristor was proposed based on graphene. Mostly, this heterojunction barristor is made by transition metal dichalcogenides (TMDs), such as molybdenum disulfide ($MoS_2$) and tungsten diselenide ($WSe_2$), which have extremely thickness scalability of TMDs. The heterojunction barristor has the advantage of controlling graphene's Fermi level by applying gate bias, resulting in barrier height modulation between graphene interface and semiconductor. However, charged impurities between graphene and $SiO_2$ cause unexpected p-type doping of graphene. The graphene's Fermi level modulation is expected to be reduced due to this p-doping effect. Charged impurities make carrier mobility in graphene reduced and modulation of graphene's Fermi level limited. In this paper, we investigated theoretically and experimentally a relevance between graphene's Fermi level and p-type doping. Theoretically, when Fermi level is placed at the Dirac point, larger graphene's Fermi level modulation was calculated between -20 V and +20 V of $V_{GS}$. On the contrary, graphene's Fermi level modulation was 0.11 eV when Fermi level is far away from the Dirac point in the same range. Then, we produced two types heterojunction barristors which made by p-type doped graphene and graphene treated 2.4% APTES, respectively. On/off current ratio (32-fold) of graphene treated 2.4% APTES was improved in comparison with p-type doped graphene.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5A
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• pp.402-406
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• 2005

A multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) system using low-density parity-check (LDPC) code and iterative decoding is presented. The iterative decoding is performed by combining the zero-forcing technique and LDPC decoding through the use of the 'turbo principle.' The proposed system is shown to be effective with high order modulation and outperforms the space frequency block code (SFBC) method with iterative decoding.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.4
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• pp.330-336
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• 2012

In this paper, novel zero-voltage-transition(ZVT) synchronous buck converter of pulse-width-modulation(PWM) method is proposed to utilize auxiliary circuit. In this proposed scheme, designed to operate low output voltage for portable system and applied synchronous scheme to improve efficiency. Also proposed circuit is designed to do soft-switching operation in every switch. In this paper, the circuit operation is explained and analysed, and design guidelines are presented. To verify the availability of the proposed circuit, experiment and simulation is carried out.

• Journal of Satellite, Information and Communications
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• v.10 no.2
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• pp.60-69
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• 2015

A new and effective Doppler effects compensation method based on constellation estimation as well as an average power saving strategy by modified modulation scheme utilizing zero point constellation are presented with theoretical analysis and relevant simulations. The suggested schemes are proved to be very effective for satellite OFDM signals relayed by power limiting transponder for the mobile terminal on high speed vehicles.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.7
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• pp.28-36
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• 2008

This paper presents a novel prototype of zero current switching pulse frequency modulation (ZCS-PFM )high frequency series resonant inverter using IGBT power module for electromagnetic induction eddy current heated roller in copy and printing machines. The operating principle and unique features of this voltage-fed half bridge inverter with two additional soft commutation inductor snubber are presented including the transformer modeling of induction heated rolling drum. This soft switching inverter can achieve stable zero current soft commutation under a discontinuous and continuous resonant load current for a widely specified power regulation processing. The experimental results and computer-aided analysis of this inverter are discussed from a practical point of view.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.323-326
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• 1999

For decrease the harmonic current components of the power source, a first method is insert the choke coil that used the choke input type rectifier, the booster chopper circuit and buck chopper circuit. And the several method are studying like as the PWM(Pulse Width Modulation) converter and the active filter type which is used the high frequency switching and the sinusoidal wave formed input current. In this type, there are many problem as a low efficiency, increased the noise, the high leakage current and cost up by the high frequency switching. For improve this problems, the partial resonan method is used on the booster inducter and lossles snubber condenser. This method decreased the distortion factor has lower harmonic components than the hard switching and there is no switching loss by the ZCS(Zero Current Switching) at switch turn-on and the ZVS(Zero Voltage Swithcing) at switch turn-off

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.7
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• pp.59-69
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• 2012

There are two types of inverters that are generally used in induction heating systems: voltage type inverters and high-frequency half-bridge inverters. This paper proposes a new resonant inverter for induction heating systems using the current type full-bridge method. The proposed method can remove capacitors at the input end, and enables unity power factor operation by preventing phase differences of voltage and current. Furthermore, Zero Voltage Switching (ZVS) which is in tune with current type inverter can be adopted and continuous power adjustment is possible through duty ratio changes and frequency modulation in switching operation. Simulations and experiments showed that the proposed current type full-bridge resonant inverter could be used for unity power factor control and ZVS operation in induction heating systems.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.7
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• pp.20-28
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• 2009

This paper presents the design of zero current switching ZCS pulse frequency modulation type DC-DC converter for magnetron power supply. A magnetron serving as the microwave source in a microwave oven is driven by a switch mode power supply (SMPS). SMPSs have the advantages of improved efficiency, reduced size and weight, regulation and the ability to operate directly from the converter DC bus. The demands of the load system and the design of the power supply required to produce constant power at 4[kV]. A magnetron power supply requires the ability to limit the load current under short circuit conditions. The current source series resonant converter is a circuit configuration which can achieve this. The main features of the proposed converter are an inherent protection against a short circuit at the output, a high voltage gain and zero current switching over a large range of output power. These characteristics make it a viable choice for the implementation of a high voltage magnetron power supply.

• Proceedings of the KIPE Conference
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• 2003.07b
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• pp.648-653
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• 2003

영벡터로 V(000)이 적용된 종전의 2상 RCD-PWM(Random Centered Distribution PWM)은 변조지수 M이 1에 가까울수록, 모터 전압 및 전류 스펙트럼의 광대역화 효과가 증가되지 않는 단점이 있다. 본 연구에서는 M에 따라서 영벡터를 선택하는 2상 MZRCD(Multi-Zero Vectors RCD)기법을 제안하였다. 2상 MZRCD기법은 M이 0.7보다 크게되면 영벡터로 V(111)을 선택하고, 작은 경우에는 V(000)을 선택하여, M의 전 영역에 걸쳐서 스펙트럼의 광대역화를 이룰 수 있는 방법이다. 본 연구의 타당성을 입증하기 위하여 Matlab simulink에 의하여 시뮬레이션을 수행하였다. M의 변화에 따른 모터 전압 및 전류의 스펙트럼을 검토하였으며, M과 무관하게 모터 전압 및 전류 스펙트럼이 광대역으로 선형화된 분포를 얻을 수 있었다.