• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.457-458
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• 2011

본 논문에서는 2KW급 LLC 컨버터를 적용한 전원장치의 병렬운전 및 Load Sharing 기법을 제안한다. 각 모듈의 제어기로는 TI사의 TMS320F28035를 사용하였으며 모듈 각각의 독립적인 전압제어를 담당한다. 그리고 Load Share 모드에서는 CAN통신을 사용하여 각 전원장치의 전류제어 및 전압제어를 수행한다. 각 모듈에 전체전류의 1/N의 균일한 전류를 흐르게 하여 각 모듈에 임피던스 불균형으로 인한 스트레스를 줄일 수 있다. 기존방식은 마스터(Master) 모듈의 지령치에 따라 슬레이브(Slave)모듈에서 부한 분담을 수행하는 반면, 제안된 Load Share 알고리즘은 멀티 마스터(Multi-Master: MM) 방식으로써 각 모듈의 평균전류를 레퍼런스로 갖는 구조로 정확한 부하분담을 수행한다.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.1
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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.

• Journal of Korean Institute of Industrial Engineers
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• v.23 no.4
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• pp.817-824
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• 1997

This paper is concerned with a parallel system that sustains a time-independent load and consists of n components with exponential lifetimes. It is assumed that the total load is shared by the functioning components and the failures of components induce higher failure rates in the surviving components according to the relationship between the load and the failure rates. The power rule model among several load-failure rate relationships is considered. Firstly, the reliability function is obtained. Secondly, the optimization problem in this load-sharing parallel system is considered. The optimal redundant units and inspection interval are obtained. Some numerical examples are studied.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.3
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• pp.106-112
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• 2000

Since the oil crisis, we have been concerned about the energy saving techniques of electric generating systems. As a part of the effort to save energy, automatic electric load sharing device was developed. Usually, ship's electric generating system consists of two or three sets of generator. And, electric generating system is operated as single or parallel operation mode according to the demanded electric power. Therefore, it is important to investigate generators operating mode for the supply of required electric power in the ship in order to decrease the operating cost. So, this paper suggests the method to solve the optimal electric load distribution problem by dynamic programming. And, this thesis indicates that the proposed method is superior to the lagrange multiplier's method in obtaining optimal load distribution solution in the ship's electric generating system.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.4
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• pp.341-349
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• 2004

A parallel operation of Uninterruptible Power Supply(UPS) systems is used to increase power capacity of the system or to secure higher reliability at critical loads. In the conventional parallel operation, the load-sharing control to maintain the current balance is the most important, since the load-sharing is very sensitive to discord between components of each module, amplitude/phase difference, line impedance, output LC filter, and so on. To solve these problems various control algorithms are researching. However, these methods cannot apply to the different ratings of UPS. In the case, master and slave control algorithm for parallel operation is adequate. However, if the UPS ratings are different, the value of passive filters L, C is different, and it affects the sharing of current. This paper presents general problems of conventional parallel operation systems, and control strategy for parallel operation with different ratings. The validity of the proposed control strategy is investigated through simulation and experiment in the parallel operation system with two 3-phase UPS systems.

• Journal of Power Electronics
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• v.19 no.1
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• pp.234-243
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• 2019

Studying the control strategy of a microgrid under the load unbalanced state helps to improve the stability of the system. The magnitude of the power fluctuation, which occurs between the power supply and the load, is generated in a microgrid under the load unbalanced state is called negative sequence reactive power $Q^-$. Traditional power distribution methods such as P-f, Q-E droop control can only distribute power with positive sequence current information. However, they have no effect on $Q^-$ with negative sequence current information. In this paper, a stationary-frame control method for power sharing and voltage unbalance compensation in islanded microgrids is proposed. This method is based on the proper output impedance control of distributed generation unit (DG unit) interface converters. The control system of a DG unit mainly consists of an active-power-frequency and reactive-power-voltage droop controller, an output impedance controller, and voltage and current controllers. The proposed method allows for the sharing of imbalance current among the DG unit and it can compensate voltage unbalance at the same time. The design approach of the control system is discussed in detail. Simulation and experimental results are presented. These results demonstrate that the proposed method is effective in the compensation of voltage unbalance and the power distribution.

• Proceedings of the KIPE Conference
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• 1996.06a
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• pp.71-75
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• 1996

As the Three-level ZVS PWM DC-DC converter operates likewise full-bridge ZVS PWM DC-DC converter and the blocking voltage of each switching device is a half of the DC-link voltage, it is suitable for the high imput voltage applications. However, it has some problems as follows; The blocking voltage of each devices is unbalanced and it causes the power losses of the inner switching devices to be increased. Also, it has narrow load range so that the switching losses and the efficiency are reduced as it goes to the light load. This paper presents an nove Three-level ZVS PWM DC-DC converter, which can reduce the overvoltage of the outer switches, eliminate the unbalance of the voltage sharing between the switches at turn-off due to the stray inductances, and operate from no load to full load. The characteristics and the performances of the proposed Three-level ZVS PWM DC-DC converter are verified by simulation and experimental results

• Geomechanics and Engineering
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• v.1 no.1
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• pp.97-112
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• 2009

The interactions between a granular pile and raft placed on top are investigated using the continuum approach. The compatibility of vertical and radial displacements along the pile - soil interface and of the vertical displacements along the raft - top of ground interfaces are satisfied. Results show that consideration of radial displacement compatibility does not influence the settlement response of or sharing of the applied load between the granular pile and the raft. The percentage load carried by the granular pile (GP) increases with the increase of its stiffness and decreases with the increase of the relative size of raft. The normal stresses at the raft - soil interface decrease with the increase of stiffness of GP and/or relative length of GP. The influences of GP stiffness and relative length of GP are found to be more for relatively large size of raft. The percentage of load transferred to the base of GP increases with the increase of relative size of raft.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.3
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• pp.177-185
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• 2017

In this paper, we proposed a concept of interference load to analyze the performance of spectrum sharing technologies in unlicensed frequency bands. The interference load can quantitatively compare the technical properties of various spectrum sharing technologies, such as frequency hopping(FH), duty cycle(DC), listen-before-talk(LBT). Therefore, it can help to evaluate whether a local regulation about spectrum sharing is reasonably established or not. In order to verify the suggested concept, we applied it to 2.4 GHz frequency bands. Also, we demonstrated a real-time test-bed. Two bit error rate(BER) curves for FH with 10 random channels and DC of 10 %, show such good agreement that our proposed concept is expected to be widely used to assess various spectrum sharing technologies.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.3
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• pp.188-194
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• 2020

This paper presents a high-efficiency Switch Mode Line Transformer (SMLT) composed of load-shared dual modules, which is based on the AC/AC LLC resonant converter. Given that the conventional adaptor is usually composed of two power stages, namely, the PFC and DC/DC converters, its system size can be increased according to the output power. However, given that the proposed SMLT can separate the PFC converter from the adaptor, the size reduction of the system can be achieved. Meanwhile, the SMLT with a single module has the limit of the size reduction because of a high resonant current. Thus, it can be configured with dual or multiple modules to reduce the resonant current. Then, their load sharing can be guaranteed by only the proposed transformer structure without an extra current controller. The validity of the proposed converter is proven through a 850-W prototype.