• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.3
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• pp.36-44
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• 2006

In general, the generated harmonics and noise of the PWM inverter are affected by PWM switching method, switching frequency, dv/dt and di/dt. Since multilevel inverters are often applied to the high power system, and operates with low switching frequency, theyproduce large size of harmonic contents and noise. Thus it is necessary to install output filters in the multilevel inverter. In this paper a filter design approach for the harmonic and noise reduction the three phase induction motor driving system using H-bridge 7-level inverter system is presented. The passive filter that has low cost and simple structure and can effectively reduce harmonics and noise, is designed and applied to the three phase induction motor drive having multilevel inverter system. The designed system is implemented and verified by simulation and experiments.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.3
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• pp.270-278
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• 2013

This paper proposes a control method for high voltage direct current(HVDC) with modular multilevel converter (MMC) under unbalanced voltage conditions considering the submodule(SM)'s current capacity and circulating current. It is aimed to propose a control method in which the current peak value does not exceed the maximum value of HVDC-MMC by considering the current capacity of the SM under unbalance voltage conditions. And it analyzes the effect of the unbalanced voltage on circulating currents in MMC and then proposes a control method considering each component of circulating currents under unbalanced voltages. The effectiveness of the proposed controlling method is verified through simulation results using PSCAD/EMTDC.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1081-1092
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• 2014

Renewable energy is being spotlighted as the electric power generating source for the next generation. Due to an increase in renewable energy systems in the grid system, their impact on the grid has become non-negligible. Thus, many countries in the world, including Europe, present their own grid codes for grid power conversion devices. In order to experiment with these grid codes, grid fault test equipment is required. This paper proposes both equipment and a control method, which are constructed with a 7-level cascaded H-bridge converter, that are capable of generating various grid faults. In addition, the Pulse Width Modulation (PWM) method for multilevel converters is compared and analyzed. The proposed structure, the control method, and the PWM method are verified through simulation and experimental results.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.5
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• pp.359-365
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• 2018

This study introduces a model predictive control method for controlling a cascaded flying capacitor multilevel rectifier used as an AC-DC rectifier of a solid-state transformer for DC distribution systems. The proposed method reduces the number of states that need to be considered in model predictive control by separately controlling input current, output DC link voltage, and flying capacitor voltage. Thus, calculation time is shortened to facilitate the level expansion of the cascaded flying capacitor multilevel rectifier. The selection of weighting factors did not present difficulties because the weighting factors in the cost function of the conventional model predictive control are not used. The effectiveness of the proposed method is verified through computer simulation using powersim and experiment.

• Journal of the Korea Society of Computer and Information
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• v.21 no.5
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• pp.19-29
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• 2016

This paper suggests a method to refine a massive collective intelligence data, and visualize with multilevel sentiment network, in order to understand information in an intuitive and semantic way. For this study, we first calculated a frequency of sentiment words from each movie review. Second, we designed a Heatmap visualization to effectively discover the main emotions on each online movie review. Third, we formed a Sentiment-Movie Network combining the MDS Map and Social Network in order to fix the movie network topology, while creating a network graph to enable the clustering of similar nodes. Finally, we evaluated our progress to verify if it is actually helpful to improve user cognition for multilevel analysis experience compared to the existing network system, thus concluded that our method provides improved user experience in terms of cognition, being appropriate as an alternative method for semantic understanding.

• Proceedings of the KIPE Conference
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• 1998.11a
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• pp.13-17
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• 1998

In recent years H-bridge multievel inverters have been focused on and selected as the power inverter in several high voltage and high power application. This paper proposes an new PWM method for the multievel H-bridge inverter systems. The proposed PWM method is a carrierwave-based space vector PWM method which utilizes the phase voltage redundancies considering both the switch and conduction loss of the devices. We describe the new PWM method in detail and the effectiveness of the new PWM method is verified by the simulation results.

• Proceedings of the KIPE Conference
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• 2013.11a
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• pp.79-80
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• 2013

MMC(Modular Multilevel Converter)는 여러 개의 Power Module을 직렬로 연결하여 정현파에 가까운 고전압의 파형을 얻을 수 있는 토폴로지로 대용량 전력변환 분야의 요구를 만족하면서 전력 품질을 향상시킬 수 있어 근래에 상당히 주목받고 있다. 당사에서는 5Mvar급 STATCOM(STATic synchronous COMpensator)을 MMC 형태로 제작하였다. 제작된 5Mvar급 STATCOM은 한 상당 12대의 Power Module로 구성하여 25-Level로 제작되었다. 제어시스템은 DSP(Digital Signal Processor)를 이용하였으며, 하나의 Main Controller와 다수의 Cell Controller, FPGA 보드 등으로 구성되어 있다. Controller 간의 상호 정보를 교환하기 위해 CAN 통신을 이용하였고, Power Module의 스위칭을 위한 보드는 각각에 연결되어 있으며, Cell Controller보드와는 절연을 위해 광신호로 연결하였다. 본 논문에서는 MMC 시스템의 제어기간 CAN 통신인터페이스와 Power Module의 PWM 동기화에 대해 설명을 하였다.

• The Transactions of the Korea Information Processing Society
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• v.7 no.6
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• pp.1886-1902
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• 2000

RBAC(Role Based Access Control) is an access control method based on the user's roles and it provides more flexibility and applicability on the various computer and network security fields than DAC(Discretionary Access Control) or MAC(Mandator Access Control). In this paper, e newly propose ERBAC\ulcorner(Extended RBAC\ulcorner) model by considering subject's and object's roles and security levels for roles additionally to RBAC\ulcorner model which is firstly proposed by Ravi S. Sandhu as a base model. The proposed ERBAC\ulcorner model provides finer grained access control with multilevel security on he base of subject and object level than RBAC\ulcorner model.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1037-1050
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• 2018

This paper presents a novel reconfigurable selective harmonic elimination technique to control harmonics over a wide range of Modulation Indexes (MI) in Multi-Level Inverter (MLI). In the proposed method, the region of the MI is divided into various sectors and expressions are formulated with different switching patterns for each of the sectors. A memetic BBO-MAS (Biogeography Based Optimization - Mesh Adaptive direct Search) optimization algorithm is proposed for solving the Selective Harmonic Elimination - Pulse Width Modulation (SHE-PWM) technique. An experimental prototype is developed using a Field Programmable Gate Array (FPGA) and their FFT spectrums are analyzed over a wide range of MI using a fluke power logger. Simulation and experimental results have validated the performance of the proposed optimization algorithms and the reconfigurable SHE-PWM technique. Further, the sensitivity of the harmonics has been analyzed considering non-integer variations in the magnitude of the input DC sources.

• Proceedings of the KOR-KST Conference
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• 2007.11a
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• pp.210-218
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• 2007

Road freight transport industry in Korea contains many and complicate problems such as over supply of the vehicle caused by rapid policy changes, illegal multilevel transactions, poor truck drivers working environment, lack of road freight transport related statistics and so on. Korean government has developed various logistics industrial policy trying to solve these problems in various ways. However, the relationship among the problems and action plans has been more and more entangled since the part of suggested policies have made another perverted problems. These complex structure of the toad freight transport industry in Korea makes difficult to identify and to solve the problems. Causal map method helps to give a clean picture to understand the complex industry at a glance. This study contributes for visualization of the causal relationships among the existing problems and related policy issues in the road freight transport industry in Korea by causal map. This study could be helpful to develop the actual road freight transport industrial policies including the illogical multilevel and unfair transaction in Korea.