• Title/Summary/Keyword: electrical impedance

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On DC-Side Impedance Frequency Characteristics Analysis and DC Voltage Ripple Prediction under Unbalanced Conditions for MMC-HVDC System Based on Maximum Modulation Index

  • Liu, Yiqi;Chen, Qichao;Li, Ningning;Xie, Bing;Wang, Jianze;Ji, Yanchao
    • Journal of Power Electronics
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    • v.16 no.1
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    • pp.319-328
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    • 2016
  • In this study, we first briefly introduce the effect of circulating current control on the modulation signal of a modular multilevel converter (MMC). The maximum modulation index is also theoretically derived. According to the optimal modulation index analysis and the model in the continuous domain, different DC-side output impedance equivalent models of MMC with/without compensating component are derived. The DC-side impedance of MMC inverter station can be regarded as a series xR + yL + zC branch in both cases. The compensating component of the maximum modulation index is also related to the DC equivalent impedance with circulating current control. The frequency characteristic of impedance for MMC, which is observed from its DC side, is analyzed. Finally, this study investigates the prediction of the DC voltage ripple transfer between two-terminal MMC high-voltage direct current systems under unbalanced conditions. The rationality and accuracy of the impedance model are verified through MATLAB/Simulink simulations and experimental results.

A Study on Implementation of Stable Interaction Control System

  • Yongteak Lim;Kim, Seungwoo
    • Proceedings of the IEEK Conference
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    • 2000.07b
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    • pp.608-611
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    • 2000
  • We introduce Adaptive Fuzzy Impedance Controller for position and force control when robot contact with environment. Because Robot and environment was always effected by nonlinear conditions, it need to deal with parameter’s uncertainty. For solving this problem, it induced Fuzzy System in Impedance Control so fuzzy system is impedance’s stiffness gain. We apply adaptive fuzzy impedance controller in One-Link Robot System, it shows the good performance on desired position control and force control about contacting with arbitrarily environment.

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Study on Measurement Technology for Equivalent Series Impedance of High-voltage Pulsed Power Capacitors (펄스파워용 고전압 커패시터 등가직렬 임피던스 측정에 관한 연구)

  • Lee, Byeong-Yoon;Lee, Byung-Ha
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.62 no.7
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    • pp.937-942
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    • 2013
  • Equivalent series impedance of high-voltage pulsed power capacitor is one of the important electrical characteristics both for users and for capacitor manufacturers because it may have serious effects on the performance of pulse forming circuits. In this paper, definition of equivalent series impedance and factors which generate equivalent series impedance are reviewed. Theoretical analysis for the calculation of equivalent series impedance based on differential measurement method is described and calculation program has been developed. In order to acquire data which are necessary to calculate equivalent series impedance from discharging current waveform, charging-dischargig controller has been manufactured. Measurement results of equivalent series impedance for high voltage pulsed power capacitor have been given.

Optimal Electrode Selection for Detection of Human Leg Movement Using Bio-Impedance (생체 임피던스를 이용한 인체 하지운동 출을 위한 최적 전극위치 선정)

  • 송철규;윤대영;이동헌;김승찬;김덕원
    • The Transactions of the Korean Institute of Electrical Engineers D
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    • v.52 no.8
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    • pp.506-509
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    • 2003
  • This paper describes the possibility of analyzing gait pattern from the changes of the lower leg electrical impedance. This impedance was measured by the four-electrode method. Two current electrodes were applied to the thigh, knee, and foot., and two potential electrodes were applied to the lateral, medial, and posterior position of human leg. The correlation coefficients of the joint angle and the impedance change from human leg movement was obtained using a electrogoniometer and 4ch impedance measurement system developed in this study. We found the optimal electrode position for knee and ankle joint movements based on high correlation coefficient, least interference, and maximum magnitude of impedance change. The correlation coefficients of the ankle, knee, and the hip movements were -0.913, 0.984 and 0.823, respectively. From such features of the human leg impedance, it has been made clear that different movement patterns exhibit different impedance patterns and impedance level. This system showed feasibility that lower leg movement could be easily measured by impedance measurement system with a few skin-electrodes.

Setting Characteristic Assessment of Cementitious Materials using Electrical Impedance Spectroscopy (전기 임피던스 분광법을 이용한 시멘트계 재료의 응결 특성 평가)

  • Lee, Jun-Cheol;Park, In-Yong
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.5 no.4
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    • pp.474-480
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    • 2017
  • In this study, the evolution of electrical impedance of electric nodes was investigated to determine the setting time of cement paste using the electrical impedance spectroscopy method. The electric nodes were embedded in fresh cement paste and the electrical impedance signatures were continuously monitored. Vicat needle test and semi-adiabatic calorimetry test were also conducted to validate the electrical impedance spectroscopy method. During hydration period of cement paste, the magnitude of conductance gradually increased, and then started to decrease rapidly at a first certain time. After that, the magnitude of conductance gradually decreased at a second certain time. The times of turning point in the curves of magnitude of conductance seem to be related with the setting time by Vicat needle test. Also, the setting times by the electrical impedance spectroscopy method are well posed within the setting period estimated by the semi-adiabatic calorimetry test. Based on the results, it can be concluded that the setting time of cement paste can be effectively monitored through the electrical impedance spectroscopy method.

An Enhanced Power Sharing Strategy for Islanded Microgrids Considering Impedance Matching for Both Real and Reactive Power

  • Lin, Liaoyuan;Guo, Qian;Bai, Zhihong;Ma, Hao
    • Journal of Power Electronics
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    • v.17 no.1
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    • pp.282-293
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    • 2017
  • There exists a strong coupling between real and reactive power owing to the complex impedances in droop based islanded microgrids (MGs). The existing virtual impedance methods consider improvements of the impedance matching for sharing of the voltage controlled power (VCP) (reactive power for Q-V droop, and real power for P-V droop), which yields a 1-DOF (degree of freedom) tunable virtual impedance. However, a weak impedance matching for sharing of the frequency controlled power (FCP) (real power for $P-{\omega}$ droop, and reactive power for $Q-{\omega}$ droop) may result in FCP overshoots and even oscillations during load transients. This in turn results in VCP oscillations due to the strong coupling. In this paper, a 2-DOF tunable adaptive virtual impedance method considering impedance matching for both real and reactive power (IM-PQ) is proposed to improve the power sharing performance of MGs. The dynamic response is promoted by suppressing the coupled power oscillations and power overshoots while realizing accurate power sharing. In addition, the proposed power sharing controller has a better parametric adaptability. The stability and dynamic performances are analyzed with a small-signal state-space model. Simulation and experimental results are presented to investigate the validity of the proposed scheme.

The Structure of a Powered Knee Prosthesis based on a BLDC Motor and Impedance Control using Torque Estimation on Free Swing (BLDC 모터 기반 동력 의족의 구성과 토크 추정을 활용한 유각기의 임피던스 제어)

  • Gyeong, Gi-Yeong;Kim, Jin-Geol;Lee, Young-Sam
    • Journal of Institute of Control, Robotics and Systems
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    • v.21 no.5
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    • pp.407-412
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    • 2015
  • This paper presents the design of a lab-built powered knee prosthesis based on a BLDC motor, a sensored impedance control using a force sensor, and a sensorless impedance control through torque estimation. Firstly, we describe the structure of the lab-built powered knee prosthesis and its limitations. Secondly, we decompose the gait cycle into five stages and apply the position-based impedance control for the powered knee prosthesis. Thirdly, we perform an experiment for the torque estimation and the sensorless impedance control of the prosthesis. The experimental results show that we can use the torque estimation to control the low impedance during the swing phase, although the estimated torque data has a delay compared with the measured torque by a load cell.

Stability Analysis Using G-Parameters of Converters Constituting DC Microgrid and Stability Enhancement Through Virtual Impedance (G-parameter를 이용한 직류 마이크로그리드의 컨버터 상호 안정도 분석 및 가상 임피던스를 이용한 안정도 향상)

  • Lee, Jae-Suk;Lee, Gi-Young;Kim, Rae-Young
    • The Transactions of the Korean Institute of Power Electronics
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    • v.23 no.5
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    • pp.321-327
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    • 2018
  • DC microgrid system composed of multiple converters has a tendency to make the system unstable due to the interaction of converters. To solve this problem, in this paper, the interaction between cascaded converters with LC input filter is analyzed with impedance modeling using g-parameter. The input impedance and the output impedance of the system can be obtained through this technique. The stability of the system can be determined by applying Middlebrook's stability criterion to the impedance. Virtual impedance is added to the controller to enhance stability. The validity of the analysis is verified by the result of several simulations and experiments.

Development of Impedance Locus Model for Protective Relay Dynamic Test (보호 계전기 동특성 테스트를 위한 임피던스 궤적 모델 개발)

  • Kim, Su-Nam;Lee, Jae-Gyu;Lee, Myeong-Su;Yu, Seok-Gu
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.51 no.9
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    • pp.451-459
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    • 2002
  • This paper presents a method for modelling of the impedance locus in order to test the protective relay with dynamic. This paper has the two parts, the first part is the configuration of impedance locus with voltage magnitude, total impedance magnitude and angle. And the second part is the control of the locus speed with deviation of two frequencies. The proposed method is applied to two machine equivalent system with PSCAD/EMTDC to show its effectiveness.

Effect of input current patterns on dynamic electrical impedance imaging of two-phase flows (이상유동의 동적 전기 임피던스 가시화에 대한 전류패턴의 영향)

  • Chung, Soon-Il;ljaz, U.Z.;Khambampati, A.K.;Kim, Sin;Kim, Kyung-Youn;Kim, Min-Chan
    • 유체기계공업학회:학술대회논문집
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    • 2006.08a
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    • pp.475-478
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    • 2006
  • In electrical impedance tomography (EIT) an array of electrodes is attached on the boundary of an object and small alternating currents are injected through these electrodes, and then the resulting voltages are measured. An estimation for the cross-sectional resistivity distribution in the object is obtained by using these current and voltage data in a nondestructive manner. In this paper, the electrical impedance imaging of two-phase flows undergoing rapid transient is considered with a special emphasis on the effect of the current pattern on the image reconstruction. The trigonometric current pattern, which is commonly used in the conventional static electrical impedance imaging, shows poor performance in case of the dynamic imaging considered in this work. Extensive numerical experiments are conducted with various kinds of current patterns and their effects on the image reconstruction performance are examined.

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