• Title/Summary/Keyword: Constant power loads

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Direct Calculation of A Matrix in Multimachine Electric Power Systems (다수 발전기 계통의 A행렬 직접계산법)

  • Kwon, Sae-Hyuk
    • Proceedings of the KIEE Conference
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    • 1989.07a
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    • pp.221-225
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    • 1989
  • Direct calculation algorithm for the elements of A matrix in multimachine power systems with constant impedance loads has been suggested. Generator's rotor parameters need not be determined from the manufacturer's data. We can identify the elements of A matrix into two categories: One is related to only generator parameters, and the other is related to generator parameters, initial values, and $Z_{Bus}$ matrix.

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The Influence of Inductive Loads on Power System Voltage Stabilization (유도부하가 전력 계통의 전압안정화에 미치는 영향)

  • Chung, Jai-Kil;Park, Sung-Dae;Cho, Yang-Haeng;Oh, Chang-Keun
    • Proceedings of the KIEE Conference
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    • 1993.11a
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    • pp.35-37
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    • 1993
  • This paper shows that the presence of constant impedance loads and induction motors in power system's loading contents can lead to transient voltage instabilities during normal system manipulations such as switchings. The abnormal induction motor characteristics during system transients which initiate the voltage instabilities are illustrated. The influence of motor and network parameters, such as motor inertia mechanical load quantity and nature on the severity of the voltage instability are studied.

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A study on the optimal load shedding scheme considering the voltage stability improvement (전압안정도 개선을 고려한 적정 부하차단 기법)

  • 이상중;김건중;김원겸;김용배
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.44 no.3
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    • pp.270-273
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    • 1995
  • This paper proposes an optimal load shedding algorithm by which the system loss can be minimized when the load shedding is unavoidable in case of severe contingency such as the outage of key generators or lines. Shedding load .DELTA.S = .DELTA.P + J.DELTA.Q(MVA) is performed on the weakest bus (on the view of voltage stability), step by step, by the priority of the I.DELTA. = SQRT(.lambda.$\_$P/$\^$2/ + .lambda.$\_$Q/$\^$2/) index given for each load bus, where .lambda.$\_$P/ and .lambda.$\_$Q/ are the sensitivity indices representing the system loss variation versus active and reactive power change of the bus load bus. All loads are assumed to be constant power loads for convenience. A 5 bus sample system proves the effectiveness of the algorithm proposed.

A study on the modelling of power transformer winding vibration (변압기 권선진동의 모형화 연구)

  • Lee, Sung-Ho;Kang, Chang-Gu;Kim, Jae-Chul;Chung, Chan-Soo;Kwak, Hee-Ro;Joo, Byung-Soo;Yoon, Jin-Yeol;Chung, Sang-Jin
    • Proceedings of the KIEE Conference
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    • 1994.07a
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    • pp.216-218
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    • 1994
  • This paper established on vibration model of transformer winding caused, mainly, by load current. We considered the rotations between loads and vibration amplitudes by changing load current in constant temperature and voltage, to get the modeling of transformer winding vibration. Equation between loads and vibration signal's amplitudes using LS approximation mode it possible to predict a vibration signal's amplitude at any load. With this equation, we arc willing to establish the basis data for power transformer diagnosis.

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Numerical Studies of Cell Temperature Distribution in MCFC Stack According to Electrical Loads (전기 부하에 따른 용융탄산염 연료전지 스택 온도 분포에 관한 수치 해석 연구)

  • Kim, Do-Hyung;Kim, Beom-Joo;Lee, Jung-Hyun;Kang, Seung-Won;Lim, Hee-Chun
    • Journal of Hydrogen and New Energy
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    • v.21 no.4
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    • pp.258-263
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    • 2010
  • A numerical stack model has been developed to predict the temperature at a constant-load operation of molten carbonate fuel cell stacks. For the validity of the model, the simulated results with several boundary conditions were compared in the cell temperature data obtained from 75 kW class MCFC stack operation. It was shown that the simulated results with the existing boundary condition, which the stack outlet temperature was fixed at $650^{\circ}C$, didn't match well with the measured data. On the other hand, the stack model with the outlet temperature modified by the outlet manifold temperature measured from the stack under several electric loads was found to explain the measured cell temperature distribution well. The results show that the model can be used to predict the cell temperature distribution in the stacks by the measurement of the manifold outlet temperature.

Free vibration and buckling analyses of functionally graded annular thin sector plate in-plane loads using GDQM

  • Mohammadimehr, Mehdi;Afshari, Hasan;Salemi, M.;Torabi, K.;Mehrabi, Mojtaba
    • Structural Engineering and Mechanics
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    • v.71 no.5
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    • pp.525-544
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    • 2019
  • In the present study, buckling and free vibration analyses of annular thin sector plate made of functionally graded materials (FGMs) resting on visco-elastic Pasternak foundation, subjected to external radial, circumferential and shear in-plane loads is investigated. Material properties are assumed to vary along the thickness according to an power law with Poisson's ratio held constant. First, based on the classical plate theory (CPT), the governing equation of motion is derived using Hamilton's principle and then is solved using the generalized differential quadrature method (GDQM). Numerical results are compared to those available in the literature to validate the convergence and accuracy of the present approach. Finally, the effects of power-law exponent, ratio of radii, thickness of the plate, sector angle, and coefficients of foundation on the fundamental and higher natural frequencies of transverse vibration and critical buckling loads are considered for various boundary conditions. Also, vibration and buckling mode shapes of functionally graded (FG) sector plate have been shown in this research. One of the important obtained results from this work show that ratio of the frequency of FG annular sector plate to the corresponding values of homogeneous plate are independent from boundary conditions and frequency number.

Harmonics Control of Electric Propulsion System using Direct Torque Control (직접벡터제어방식을 사용하는 전기추진시스템의 고조파 제어)

  • Kim, Jong-Su;Oh, Sae-Gin
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.13 no.12
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    • pp.2618-2624
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    • 2009
  • Harmonics (or distortion in wave form) has always existed in electrical power systems. It is harmless as long as its level is not substantial. However, with the recent rapid advancement of power electronics technology, so-called nonlinear loads, such as variable frequency drives for motor power/speed control, are increasingly finding their way to shipboard or offshore applications. In this paper a new approach to direct torque control (DTC) of induction motor drive is presented. In comparison with the conventional DTC methods the inverter switching frequency is constant and is dramatically increased, requiring neither any increase of the sampling frequency, nor any high frequency dither signal. The well-developed space vector modulation technique is applied to inverter control in the proposed DTC-based induction motor drive system, thereby dramatically reducing the current harmonics. As compared to the existing DTC approach with constant inverter switching frequency, the presented new approach does not invoke any concept of deadbeat control, thereby dramatically reducing the computations.

Primary Current Generation for a Contactless Power Transfer System Using Free Oscillation and Energy Injection Control

  • Li, Hao Leo;Hu, Aiguo Patrick;Covic, Grant Anthony
    • Journal of Power Electronics
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    • v.11 no.3
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    • pp.256-263
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    • 2011
  • This paper utilizes free oscillation and energy injection principles to generate and control the high frequency current in the primary track of a contactless power transfer system. Here the primary power inverter maintains natural resonance while ensuring near constant current magnitude in the primary track as required for multiple independent loads. Such energy injection controllers exhibit low switching frequency and achieve ZCS (Zero Current Switching) by detecting the high frequency current, thus the switching stress, power losses and EMI of the inverter are low. An example full bridge topology is investigated for a contactless power transfer system with multiple pickups. Theoretical analysis, simulation and experimental results show that the proposed system has a fast and smooth start-up transient response. The output track current is fully controllable with a sufficiently good waveform for contactless power transfer applications.

Individual DC Voltage Balancing Method at Zero Current Mode for Cascaded H-bridge Based Static Synchronous Compensator

  • Yang, Zezhou;Sun, Jianjun;Li, Shangsheng;Liao, Zhiqiang;Zha, Xiaoming
    • Journal of Electrical Engineering and Technology
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    • v.13 no.1
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    • pp.240-249
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    • 2018
  • Individual DC voltage balance problem is an inherent issue for cascaded H-bridge (CHB) based converter. When the CHB-based static synchronous compensator (STATCOM) is operating at zero current mode, the software-based individual DC voltage balancing control techniques may not work because of the infinitesimal output current. However, the different power losses of each cell would lead to the individual DC voltages unbalance. The uneven power losses on the local supplied cell-controllers (including the control circuit and drive circuit) would especially cause the divergence of individual DC voltages, due to their characteristic as constant power loads. To solve this problem, this paper proposes an adaptive voltage balancing module which is designed in the cell-controller board with small size and low cost circuits. It is controlled to make the power loss of the cell a constant resistance load, thus the DC voltages are balanced in zero current mode. Field test in a 10kV STATCOM confirms the performance of the proposed method.

A Study on a Substation Static Load Model Including the Mobility of a Railway Load (철도 부하의 이동성을 반영한 변전소 정태부하모델링 수립에 대한 연구)

  • Chang, Sang-Hoon;Youn, Seok-Min;Kim, Jung-Hoon
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.64 no.2
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    • pp.315-323
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    • 2015
  • Nowadays, it is expected that mobility loads such as electric railways and electric vehicles will be penetrated gradually and affect on the power system stability by their load characteristics. Various researches have been carried out about electric vehicles for the recent decade though the load of electric railway could be forecasted because of the specified path and timetable, is a field with a long historic background. Some precise 5th polynomial equations are required to analyze the power system stability considering mobility load to be increased in the immediate future while the electric railway dispatching simulator uses load models with constant power and constant impedance for the system analysis. In this paper, seasonal urban railway load models are established as the form of 5th polynomial equations and substation load modeling methods are proposed merging railway station load models and general load models. Additionally, load management effects by the load modeling are confirmed through the case studies, in which seasonal load models are developed for Seoul Subway Line No. 2, Gyeongui Line and Airport Railroad and the substation load change is analyzed according to the railway load change.