• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 F
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• pp.2546-2548
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• 1999

This paper describes characteristics of independent load sharing of parallel UPS systems and proposes a method of control which does not require control interconnections at each UPS system and compensates for line impedance. Simulation results of a two-module UPS system with different power latins and line impedance have demonstrated the feasibility of the proposed control scheme in load sharing.

• 정보처리학회논문지A
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• 제8A권4호
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• pp.455-460
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• 2001

어떤 응용프로그램에서는 계산구조가 프로그램의 수행도중 동적으로 변한다. 이런 경우 정적으로 태스크를 분할하고 할당하는 것은 병렬컴퓨터에서 높은 성능을 얻는데 충분하지 못하다. 이 논문에서는 동적으로 변하는 트리구조를 가진 계산을 프로세서들에 효율적으로 분배하는 부하분산 알고리즘을 소개한다. 이 알고리즘의 메쉬구조상에서의 구현기법이 소개되고 복잡도가 분석된다. 실험을 통하여 이 알고리즘이 좋은 성능을 나타내는 것을 보인다.

• Composites Research
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• 제21권1호
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• pp.30-39
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• 2008

본 논문에서는 기존의 유전자 알고리즘을 대신하여 병렬 마이크로 유전자 알고리즘을 사용한 복합재료 적층 구조물의 최적설계를 수행하였다. 마이크로 유전자 알고리즘은 한 세대 당 보통 5개의 개체로 해를 탐색한다 비록 세대를 구성하는 인구수는 적지만 공칭수렴 판단과 재초기화 과정을 통해 다양성을 제공하기 때문에 최적해 탐색이 가능하다. 2가지의 복합재 구조물의 최적화 문제를 가정하고 이를 마이크로 유전자 알고리즘을 사용하여 해를 구하였다. 효율성 판단을 위해서 기존의 유전자 알고리즘과 결과를 비교하였다. 두 문제 모두 마이크로 유전자 알고리즘이 비슷한 결과를 도출하면서도 약 70%의 계산량 감소를 보였다. 마이크로 유전자 알고리즘을 사용하여 일정 범위 내에서 변하는 하중을 받고 있는 복합재 적층 구조물의 최적설계를 수행하였다. 계산 결과 고정된 하중상태 하에서 얻은 최적해보다 하중 변화에 덜 민감한 설계변수를 얻을 수 있었다. 이상의 문제를 통해 다양한 설계변수를 갖는 복합재 적층 구조물의 최적설계의 한 방법으로서 마이크로 유전자 알고리즘이 효율적임을 확인하였다.

• Journal of Power Electronics
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• 제15권3호
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• pp.741-752
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• 2015

This study proposes a new solution for the parallel operation of microgrid inverters in terms of circuit topology and control structure. A combined three-phase four-wire inverter composed of three single-phase full-bridge circuits is adopted. Moreover, the control structure is based on adaptive three-order sliding-mode control and wireless load-sharing control. The significant contributions are as follows. 1) Adaptive sliding-mode control performance in inner voltage loop can effectively reject both voltage and load disturbances. 2) Virtual resistive-output-impedance loop is applied in intermediate loop to achieve excellent power-sharing accuracy, and load power can be shared proportionally to the power rating of the inverter when loads are unbalanced or nonlinear. 3) Transient droop terms are added to the conventional power outer loop to improve dynamic response and disturbance rejection performance. Finally, theoretical analysis and test results are presented to validate the effectiveness of the proposed control scheme.

• 전력전자학회논문지
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• 제26권1호
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• pp.53-58
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• 2021

Operation of the interleaved Boost PFC converter in Critical Conduction Mode (CrM) shows the advantages of high efficiency and good EMI characteristics owing to the valley switching of FET. However, when it is designed for a highly pulsating load, operation at a relatively high frequency is inevitable at non-pulsating typical load condition, resulting in efficiency degradation. Moreover, the physical size of the inductor becomes problematic because of the nature of the CrM operation, where the inductor peak current is about two times the inductor average current, thereby requiring high DC-bias characteristics, which is worse when the output power is high. In this study, a new parallel driving method of two sets of interleaved boost PFC converters for highly pulsating high-power application is proposed. The proposed method does not require any additional load-sharing controller, resulting in high efficiency and smaller inductor size.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(3)
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• pp.97-100
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• 2000

As network resources have become faster and demands for multimedia service through network have increased, the demand for Media server system has increased. These kinds of media server solve their bottle neck problem of internal storage device by using parallel system which takes advantage of fast network resource. Many vendors have suggested each of their media server system to solve these problem radically, but most of them require major modification of infra component and additional drawback has added. For example, storage mechanism for specific media requires new file system which is totally different from traditional one, and algorithm for enhancing performance may not suit for traditional operating system environment. In this paper, we designed a parallel media server based on web interface of traditional system and implemented a program for media server. Implemented server system performs parallel processing through web interface without any modification of traditional system, and controls which is related to merging load by distributed data is charged only to client and control server and consequently load of storage server can be minimized. And also, data transfer protocol for streaming media includes Retransfer algorithm and client Admission control policy relevant to performance of whole system.

• 한국컴퓨터정보학회논문지
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• 제18권7호
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• pp.1-10
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• 2013

본 논문에서는 Thumb-2 명령어 집합 구조의 성능을 개선하기 위하여 분기 명령어와 사용 빈도가 높은 명령어를 동시에 실행하는 병렬 분기 명령어 집합을 제시한다. 제시된 기법에서는 16비트 분기 명령어와 사용 빈도가 높은 16비트 LOAD, ADD, MOV, STORE, SUB 명령어를 각각 결합하는 새로운 32비트 명령어를 도입한다. 새로운 명령어의 인코딩 공간을 제공하기 위해 사용 빈도가 낮은 기존 명령어의 레지스터 필드에 사용되는 비트 수를 줄이고 이를 통해 절약된 비트들을 이용하여 병렬 분기 명령어를 인코딩한다. 실험 결과, 제시된 방법은 코드 크기를 증가시키지 않고 전통적인 방식과 비교하여 평균 8.0%의 성능을 향상시킨다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권12호
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• pp.725-731
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• 2004

In this study, the three type hybrid interrupters according to the arrangement of the thermal expansion chamber and the puffer cylinder(they are called 'serial type', 'parallel/exchanged type', and 'parallel/separated type' respectively in this work) were designed and manufactured. This paper presents the tested results of the thermal recovery characteristics on the interrupters using a simplified synthetic test facility. The 'serial type' hybrid interrupter which is to obtain more easily the pressure rise for the thermal recovery compared with the others has the best capability in the thermal recovery characteristics. In order to investigate the stress on the operating mechanism, the distortion of the stroke wave in on-load test was examined to the stroke curve in no-load test. The biggest distortion was occurred in the 'parallel/exchanged type' hybrid interrupter. Finally, the small interruption capability on the three type interrupters was estimated by a theoretical form and the 'parallel/separated type' hybrid interrupter has the advantage of the others in the view of structure.

• Journal of Power Electronics
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• 제11권4호
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• pp.533-541
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• 2011

The redundant operation of a parallel AC to DC converter via a serial communication bus is presented. The proposed system consists of three isolated CUK power factor correction modules. The controller for each converter is a dsPIC30F6010 microcontroller while a RS485 communication bus and the clock signal are used for synchronizing the data communication. The control strategy of the redundant operation relies on the communication of information among each of the modules, which communicate via a RS485 serial bus. This information is received from the communication checks of the converter module connected to the system to share the load current. Performance evaluations were conducted through experimentation on a three-module parallel-connected prototype, with a 578W load and a -48V dc output voltage. The proposed system has achieved the following: the current sharing is quite good, both the transient response and the steady state. The converter modules can perform the current sharing immediately, when a fault is found in another converter module. In addition, the transient response occurs in the system, and the output voltages are at their minimum overshoot and undershoot. Finally, the proposed system has a relatively simple implementation for the redundant operation.

• Tribology and Lubricants
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• 제32권5호
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• pp.147-153
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• 2016

Friction reduction between machine components is important for improving their efficiency and lifespan. In recent years, surface texturing has received considerable attention as a viable means to enhance the efficiency and tribological performance of highly sliding mechanical components such as parallel thrust bearings, mechanical face seals, and piston rings. In this study, we perform lubrication analysis to investigate the effect of dimple shapes and orientations on the lubrication characteristics of a surface textured parallel thrust bearing. Numerical analysis involves solving the continuity and Navier-Stokes equations using a commercial computational fluid dynamics (CFD) code, FLUENT. We use dimples consisting of hemispherical and different semiellipsoidal orientations for simulation. We compare pressure and streamline distributions, load capacity, friction force, and leakage flowrate for different numbers of dimples and orientations. We find that the dimple shapes, orientations, and their numbers starting from an inlet influence the lubrication characteristics. The results show that partial texturing of the bearing inlet region, and the ellipsoidal dimples with the major axis aligned along the lubricant flow direction exhibit the best lubrication characteristics in terms of higher load capacity and lower friction. The results can be used in the design of optimum dimple characteristics for parallel thrust bearings, for which further research is required.