• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 추계학술대회 논문집
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• pp.182-183
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• 2016

계통 연계형 인버터에서는 고조파 전류를 저감하기 위하여 필터가 필요하다. 이러한 고조파 저감을 위하여 LCL 필터나 LCL 필터의 커패시터 단에 직렬로 L을 추가한 직렬 공진을 이용한 LLCL 필터가 있다. 이러한 필터들은 특정 주파수 대역의 고조파를 효과적으로 제거할 수 있으며 기존의 L 필터보다 용량이 줄어든다. 본 논문에서는 단상 멀티 레벨 컨버터의 PWM 주파수 성분의 고조파 저감 효과를 갖는 L, LLCL 필터를 설계하고 비교한다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2010년도 추계학술대회
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• pp.244-245
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• 2010

본 논문은 1kW급 가정용 연료전지의 계통연계 및 고효율 전력변환 시스템 개발에 관한 것이다. 본 시스템에서 구현된 전력변환장치는 일반적인 연료전지용 PCS와 마찬가지로 DC/DC 컨버터부와 DC/AC 인버터부로 구성되며, 전체 시스템의 동작은, DC/DC 컨버터부에서는 고효율화를 위하여 공진형으로 동작되며, DC/AC 인버터부에서는 출력전력 제어와 계통연계를 수행한다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2019년도 전력전자학술대회
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• pp.293-294
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• 2019

본 논문은 입출력 전력품질이 우수하고 전압별 시리즈화가 용이한 고전압 대용량 전동기 구동용 H-브릿지 멀티레벨 컨버터의 직류 전압 변동 억제를 위한 전압변조 방법에 관하여 기술하였다. H-브릿지 멀티레벨 컨버터의 Phase-shifted PWM에 의해서 전동기 무부하 구동 조건에서 유효전력이 Negative로 전이해서 전력이 전동기에서 컨버터로 유입되어 특정 파워 셀 직류 전압이 상승하는 현상이 발생한다. 따라서, 개발 파워 셀 위상 전이량을 일정 주기마다 변경하여 회생된 에너지를 H-브릿지 멀티레벨 컨버터의 모든 파워 셀에 분산시켜 파워 셀 직류 전압 상승을 억제하였다. 제안된 방법의 타당성과 실용성은 실용량 제품의 현장 적용 시험을 통하여 입증하였다.

• Journal of Power Electronics
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• 제15권5호
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• pp.1380-1391
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• 2015

This paper provides a loss analysis and comparison of high power semiconductor devices in 5MW Permanent Magnet Synchronous Generator (PMSG) Medium Voltage (MV) Wind Turbine Systems (WTSs). High power semiconductor devices of the press-pack type IGCT, module type IGBT, press-pack type IGBT, and press-pack type IEGT of both 4.5kV and 6.5kV are considered in this paper. Benchmarking is performed based on the back-to-back type 3-level Neutral Point Clamped Voltage Source Converters (3L-NPC VSCs) supplied from a grid voltage of 4160V. The feasible number of semiconductor devices in parallel is designed through a loss analysis considering both the conduction and switching losses under the operating conditions of 5MW PMSG wind turbines, particularly for application in offshore wind farms. This paper investigates the loss analysis and thermal performance of 5MW 3L-NPC wind power inverters under the operating conditions of various power factors. The loss analysis and thermal analysis are confirmed through PLECS Blockset simulations with Matlab Simulink. The comparison results show that the press-pack type IGCT has the highest efficiency including the snubber loss factor.

• Journal of Electrical Engineering and Technology
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• 제3권3호
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• pp.391-400
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• 2008

Multi-pulse topology of converters using elementary six-pulse GTO - VSC (gate turn off based voltage source converter) operated under fundamental frequency switching (FFS) control is widely adopted in high power rating static synchronous compensators (STATCOM). Practically, a 48-pulse ($6{\times}8$ pulse) configuration is used with the phase angle control algorithm employing proportional and integral (PI) control methodology. These kinds of controllers, for example the ${\pm}80MVAR$ compensator at Inuyama switching station, KEPCO, Japan, employs two stages of magnetics viz. intermediate transformers (as many as VSCs) and a main coupling transformer to minimize harmonics distortion in the line and to achieve a desired operational efficiency. The magnetic circuit needs altogether nine transformers of which eight are phase shifting transformers (PST) used in the intermediate stage, each rating equal to or more than one eighth of the compensator rating, and the other one is the main coupling transformer having a power rating equal to that of the compensator. In this paper, a two-level 48-pulse ${\pm}100MVAR$ STATCOM is proposed where eight, six-pulse GTO-VSC are employed and magnetics is simplified to single-stage using four transformers of which three are PSTs and the other is a normal transformer. Thus, it reduces the magnetics to half of the value needed in the commercially available compensator. By adopting the simple PI-controllers, the model is simulated in a MATLAB environment by SimPowerSystems toolbox for voltage regulation in the transmission system. The simulation results show that the THD levels in line voltage and current are well below the limiting values specified in the IEEE Std 519-1992 for harmonic control in electrical power systems. The controller performance is observed reasonably well during capacitive and inductive modes of operation.

• Journal of Power Electronics
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• 제18권2호
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• pp.558-572
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• 2018

In addition to its modular nature, a Hybrid Modular Multilevel Converter (HMMC) assembled from half-bridge and full-bridge sub-modules, is able to block DC faults with a minimum number of switching devices, which makes it attractive for high power applications. This paper introduces a control strategy based on the Root-Least Square (RLS) algorithm to estimate the capacitor voltages instead of using direct measurements. This action eliminates the need for voltage transducers in the HMMC sub-modules and the associated communication link with the central controller. In addition to capacitor voltage balancing and suppression of circulating currents, a fault tolerant control unit (FTCU) is integrated into the proposed strategy to modify the parameters of the HMMC controller. On advantage of the proposed FTCU is that it does not need extra components. Furthermore, a fault detection unit is adapted by utilizing a hybrid estimation scheme to detect sub-module faults. The behavior of the suggested technique is assessed using PSCAD offline simulations. In addition, it is validated using a real-time digital simulator connected to a real time controller under various normal and fault conditions. The proposed strategy shows robust performance in terms of accuracy and time response since it succeeds in stabilizing the HMMC under faults.

• 에너지공학
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• 제14권1호
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• pp.37-45
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• 2005

연료 전지 시스템은 아주 유용한 에너지원 중의 하나이다. 시스템은 재사용이 가능하고 환경 친화적인 에너지원이라는 장점을 갖는다. 연료 전지로부터 교류 성분을 얻기 위해서는 인버터가 필요하다. 멀티 레벨 컨버터는 고 전력 연료 전지 시스템에 대한 인버터로서 사용된다. 고조파 분석을 통하여 멀티 레벨컨버터에서 연료 전지의 전압 강하가 증가할 때 기본파 성분은 감소하는 반면 고조파 성분과 왜형률이 증가하는 것을 알 수 있다. 전압 강하 문제를 해결하기 위해서 연료 전지 출력단에 부스트 컨버터 사용, 펄스폭 제어, 울트라커패시터 사용 등 세 가지 서로 다른 해결 방법을 이 논문에서 제안하였다. 제안된 세 가지 해결 방법을 분석하였고 시뮬레이션 결과를 사용하여 비교 분석하였다.

• 치과방사선
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• 제22권2호
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• pp.273-282
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• 1992

The purpose of this study was to propose the utility which was evaluated the digital image processing and clinical application of the videodensitomery. The experiments were performed with IBM-PC/16bit-AT compatible, video camera(CCdtr55, Sony Co., Japan), an color monitor(MultiSync 3D, NEC, Japan) providing the resolution of 512×480 and 64 levels of gray. Sylvia Image Capture Board for the ADC(analog to digital converter) was used, composed of digitized image from digital signal and the radiographic density was measured by 256 level of gray. The periapical radiograph(Ektaspeed EP-21, Kodak Co., U. S. A) which was radiographed dried human mandible by exposure condition of 70 kVp and 48 impulses, was used for primary X-ray detector. And them evaluated for digitzed image by low and high pass filtering, correlations between aluminum equivalent values and the thickness of aluminum step wedge, aluminum equivalent values of sound enamel, dentin, and alveolar bone, the range of diffuse density for gray level ranging from 0 to 255. The obtained results were as follows: 1. The edge between aluminum steps of digitized image were somewhat blurred by low pass filtering, but edge enhancement could be resulted by high pass filtering. Expecially, edge enhancement between distal root of lower left 2nd molar and alveolar lamina dura was observed. 2. The correlation between aluminum equivalent values and the thickness of aluminum step wedge was intimated, yielding the coefficient of correlation r=0.9997(p<0.00l), the regression line was described by Y=0.9699X+0.456, and coefficient of variation amounting to 1.5%. 3. The aluminum equivalent values of sound enamel, dentin, and alvolar bone were 15.41㎜, 12.48㎜, 10.35㎜, respectively. 4. The range of diffuse density for gray level ranging from 0 to 255 was wider enough than that of photodenstiometer to be within the range of 1-4.9.

• 전력전자학회논문지
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• 제14권3호
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• pp.243-250
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• 2009

본 논문은 조명용 LED 구동 장치를 위한 새로운 방식의 Two-stage LED 구동 회로를 제안한다. 제안된 회로는 PFC flyback 회로의 다중 출력을 이용하여 LED 양단에 전압을 인가하여 LED 구동 회로의 출력 전압을 획기적으로 낮출 수 있어 LED 구동 회로에 사용되는 반도체 소자의 전압 스트레스를 크게 줄일 수 있다. 제안된 회로는Universal input에서 25 [W] 이상 조명 장치에 적용되는 IEC 61000-3-2 class C 규제를 만족하고, PWM 디밍을 사용하여 넓은 범위의 휘도 조절이 가능하다. 본 논문에서는 제안 회로의 동작 원리를 설명하고, 시뮬레이션 및 LED에 실제 적용 실험하여 제안 회로의 유용성을 입증하였다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 전력전자학술대회 논문집
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• pp.323-324
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• 2013

This paper presents a simple and cost-effective stand-alone rapid battery charging system of 30kW for electric vehicles. The proposed system mainly consists of active front-end rectifier of neutral point clamped 3-level type and non-isolated bi-directional dc-dc converter of multi-phase interleaved half-bridge topology. The charging system is designed to operate for both lithium-polymer and lithium-ion batteries. The complete charging sequence is made up of three sub-interval operating modes; pre-charge mode, constant-current mode, and constant-voltage mode. The pre-charge mode employs the stair-case shaped current profile to accomplish shorter charging time while maintaining the reliable operation of the battery. The proposed system is specified to reach the full-charge state within less than 16min for the battery capacity of 8kWh by supplying the charging current of 78A. Owing to the simple and compact power conversion scheme, the proposed solution has superior module-friendly mechanical structure which is absolutely required to realize flexible power expansion capability in a very high-current rapid charging system.