• Title/Summary/Keyword: Line Current

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A Decentralized Optimal Load Current Sharing Method for Power Line Loss Minimization in MT-HVDC Systems

  • Liu, Yiqi;Song, Wenlong;Li, Ningning;Bai, Linquan;Ji, Yanchao
    • Journal of Power Electronics
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    • v.16 no.6
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    • pp.2315-2326
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    • 2016
  • This paper discusses the elimination of DC voltage deviation and the enhancement of load current sharing accuracy in multi-terminal high voltage direct current (MT-HVDC) systems. In order to minimize the power line losses in different parallel network topologies and to insure the stable operation of systems, a decentralized control method based on a modified droop control is presented in this paper. Averaging the DC output voltage and averaging the output current of two neighboring converters are employed to reduce the congestion of the communication network in a control system, and the decentralized control method is implemented. By minimizing the power loss of the cable, the optimal load current sharing proportion is derived in order to achieve rational current sharing among different converters. The validity of the proposed method using a low bandwidth communication (LBC) network for different topologies is verified. The influence of the parameters of the power cable on the control system stability is analyzed in detail. Finally, transient response simulations and experiments are performed to demonstrate the feasibility of the proposed control strategy for a MT-HVDC system.

Droop Control Method for Circulating Current Reduction in Parallel Operation of BESS (BESS의 병렬운전 시 발생되는 순환 전류 저감을 위한 드룹 제어 기법)

  • Sin, Eun-Suk;Kim, Hyun-Jun;Yang, Won-Mo;Han, Byung-Moon
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.64 no.5
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    • pp.708-717
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    • 2015
  • This paper proposes a new reduction scheme of circulating current when two units of BESS (Battery Energy Storage System) are operated in parallel with conventional droop control. In case of using conventional droop, the terminal voltage of each BESS are not equal due to the unequal line impedance, which causes the circulating current. The operation performance of BESS is critically dependant on the circulating current because it increases system losses which causes the increasement of required system rating. This paper introduces a new reduction scheme of circulating current in which the terminal voltage difference of each BESS is compensated by adding feed-forward path of line voltage drop to the droop control. The feasibility of proposed scheme was first verified by computer simulations with PSCAD/EMTDC software. After then a hardware prototype with 5kW rating was built in the lab and many experiments were carried out. The experimental results were compared with the simulation results to confirm the feasibility of proposed scheme. Two parallel operating BESS with proposed scheme shows more accurate performance to suppress the circulating current than those with the conventional droop control.

Analysis of induced voltage of CCPU with unbalanced current from Distribution Line on Underground Transmission Cable System (지중송전계통에서 배전선 불평형전류 유입에 따른 영향 검토)

  • Kang, J.W.;Jang, T.I.;Hong, D.S.;Jung, C.K.;Yoon, D.S.;Yoon, J.K.;Kim, H.H.
    • Proceedings of the KIEE Conference
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    • 2005.07a
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    • pp.459-461
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    • 2005
  • This paper analyses the induced voltage characteristic of CCPU with unbalanced current from distribution line on underground transmission power cable systems. In switching surge strokes, in order to obtain the data of induced voltage/current on CCPU, the actual proof test carried out. This paper is expected to contribute the establishment of proper protection methods of CCPU against the unbalanced current from distribution line on underground transmission power cable systems.

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Frequency analysis based fault detection and isolation of induction motors (주파수 해석을 이용한 유도전동기의 고장 검출 및 분류)

  • 신필재;이인수;전기준
    • 제어로봇시스템학회:학술대회논문집
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    • 1996.10b
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    • pp.702-705
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    • 1996
  • Recently, induction motors are used more widely because of their low cost and simple structure. Therefore, the importance of fault detection and isolation of induction motors significantly increases. In most case the line current is used for fault detection and isolation. But in case that an induction motor has an inverter for control, it distorts the information of faulty state included in the line current. This paper proposes a new method for fault detection and isolation of induction motors that is speed controlled by the inverter using frequency analysis of the reference current instead of the line current for fault detection and isolation.

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A Study on Parallel Operation Between Inverter System and Utility Line (인버터 시스템과 상용 전력 계통과의 병렬 운전에 관한 연구)

  • 천희영;박귀태;유지윤;안호균
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.41 no.4
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    • pp.369-378
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    • 1992
  • This paper proposes a utility parallel processing inverter system, which consists of a voltage source PWM inverter, isolation transformer and a reactor linking the inverter to utility line. This system realizes following functions : (1) voltage phase frequency and amplitude synchronization between inverter and utility line at stand-alone mode. (2) current phase synchronization between inverter and load at parallel mode. Therefore, despite sudden increase in load current over setting point at stand-alone mode, inverter system can be transferred into parallel mode immediately without transient current. Furthermore, high frequency(18KHz) PWM control and sinusoidal filtering improve the inverter output waveform by eliminating high order harmonic components as well as low order. As a switching device, IGBT is used for high frequency switching and large current capacity.

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An EMTDC Analysis for Ground Faults with a Superconducting Fault Current Limiter (초전도 한류기를 포함한 계통의 지락사고에 대한 EMTDC 해석)

  • Choe, Hyo-Sang;Hyeon, Ok-Bae;Go, Tae-Guk
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.48 no.4
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    • pp.161-166
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    • 1999
  • We have performed an EMTDC simulation for the current limiting effects of a superconducting fault current limiter (SFCL). The fault currents in the 154 kV transmission line between the arbitrary S1 and S2 substations increased up to 39 kA during the single and double line-to-ground faults, respectively. The SFCL in the transmission line is sufficient.

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Calculation of the Induced Voltage and Current for a Human and an Object Close to 765kV AC Double Circuit Transmission Line (765kV 교류 2회선 송전선 인근의 생체 및 물체 유도 전압, 전류 계산)

  • Min, Suk-Wen;Kim, Eung-Sik;Myeong, Sung-Mo;Lee, Byeong-Yoon;Park, Jong-Keun
    • Proceedings of the KIEE Conference
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    • 1994.07b
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    • pp.1509-1511
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    • 1994
  • This paper calculates the induced voltage and current for a human and a car under 765 kV AC double circuit transmission line. A human and a car is simulated as two dimension by the use of charge simulation method and as three dimension by using surface charge method. The phase arrangement of transmission line is varied to calculate the induced voltage and current. In two cases a human and a car is grounded or floated, the induced voltage and current is also compared.

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A Low Power SDRAM Output Buffer with Minimized Power Line Noise and Feedthrough Current (최소화된 Power line noise와 Feedthrough current를 갖는 저 전력 SDRAM Output Buffer)

  • Ryu, Jae-Hui
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.39 no.8
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    • pp.42-45
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    • 2002
  • A low power SDRAM output buffer with reduced power line noise and feedthrough current is presented. In multi I/O SDRAM output buffer, feedthrough current as well as the corresponding power dissipation are reduced utilizing proposed undershoot protection circuits. Ground bounce is minimized by the pull down driver using intelligent feedback scheme. Ground bounce noise is reduced by 66.3% and instantaneous and average power are reduced by 27.5% and 11.4%, respectively.

ELF Electric and Magnetic Fields under the Transmission Line Including Electric Power System States (계통상태를 고려한 송전선의 ELF 전자계)

  • 김두현;김상철
    • Journal of the Korean Society of Safety
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    • v.11 no.3
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    • pp.89-96
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    • 1996
  • This paper presents a study on the analysis and evaluation for ELF( Extremely Low Frequency) electric and magnetic fields under the transmission line according to the power system states. The power system states are classified into two types, normal state resulting from normal operation and alert state from outages. The current in a system is changed continually owing to the load fluctuations even in a normal operation. To calculate the current of the concerned line in a normal state, the system load level is devided into light, base and heavy load level. In case of contingency, an efficient algorithm based on matrix inversion lemma is developed to figure out the current changes. In order to analyze the variations of ELF field caused by the current fluctuations the electrostatic field approach which is far simpler than the electromagnetic field one based on Maxwell equation is introduced in this paper. The suggested method is applied to the IEEE 14 bus system to demonstrate the usefulness.

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Analysis on the Protective Coordination on Neutral Line of Main Transformer in Power Distribution Substation with Superconducting Fault Current Limiter (MTR 중성점 접지에 초전도 전류제한기 적용시 지락과전류계전기 동작 분석)

  • Kim, Jin-Seok;Lim, Sung-Hun;Moon, Jong-Fil;Kim, Jae-Chul;Hyun, Ok-Bae
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.58 no.11
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    • pp.2089-2094
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    • 2009
  • The fault current has increased due to growth of distributed generations for the large power demand in power distribution system. To solve some problem such as excess of the circuit breaker's cut-off ratings, the superconducting fault current limiter(SFCL) has been progressed. However, the operational characteristics of the relay is changed by SFCL. Therefore, the proper impedance for the SFCL should be selected to keep protective coordination with the SFCL when SFCL is introduced on the neutral line of main transformer in distribution system. In this paper, the proper normal conducting resistance was suggested to solve the problem in case of the protection coordination with SFCL.