• Journal of Power Electronics
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• 제11권4호
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• pp.599-605
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• 2011

This paper proposes a gain scheduling method that improves the stability of grid-connected systems employing an LCL-filter. The method adjusts the current controller gain through an estimation of the grid impedance in order to reduce the resonance that occurs when using an LCL-filter to reduce switching harmonics. An LCL-filter typically has a frequency spectrum with a resonance peak. A change of the grid-impedance results in a change to the resonant frequency. Therefore an LCL-filter needs a damping method that is applicable when changing the grid impedance for stable system control. The proposed method instantaneously estimates the grid impedance and observes the resonant frequency at the same time. Consequently, the proposed method adjusts the current controller gain using a gain scheduling method in order to guarantee current controller stability when a change in the resonant frequency occurs. The effectiveness of the proposed method has been verified by simulations and experimental results.

• 한국정밀공학회지
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• 제16권10호
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• pp.132-140
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• 1999

This paper treats the estimation of human impedance and their application to human-robot collaboration work. Initially, we perform an experiment at which the human becomes a slave and the robot behaves like a master having F/T sensor on its end. The human impedance expressed in terms of mass, damping, and stiffness properties are estimated based on the force data measured by F/T sensor and the commanded position data of the robot. To show the effectiveness of the estimated human impedance, we perform the second experiment at which the roles of the human and the robot are reversed. It is shown that the robot using the estimated human impedance follows the trajectory commanded by human very smoothly.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2010년도 정기 학술대회
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• pp.783-786
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• 2010

This paper presents a finite element analysis on impedance parameters of anchor plates of structural cables under the change in cable forces. To achieve the objective, four approaches are implemented as follows: Firstly, theoretical background of electro-mechanical impedance is described. Secondly, anchor plates of structural cables are selected to experimentally examine the relationship between impedance parameters and cable force changes. Thirdly, finite element analysis is performed to verify the experimental results. Fourthly, a comparison between the experimental and numerical analysis on impedance parameters of anchor plate of structural cables under cable force changes is carried out.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 B
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• pp.940-942
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• 2003

This paper describes the possibility of analyzing gait pattern from the variation of the lower leg electrical impedance. This impedance is measured by the four-electrode method. Two current electrodes are applied to the thigh and foot, and two potential electrodes are applied to the lateral aspect, medial aspect, and posterior position of lower leg. 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. From such features of the lower leg impedance, it has been made clear that different movement patterns exhibit different impedance patterns and impedance level.

• Journal of Mechanical Science and Technology
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• 제18권7호
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• pp.1131-1139
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• 2004

A new impedance controller is proposed for bilateral teleoperation under a time delay. The proposed controller does not need to measure or estimate the time delay in the communication channel using the force loop-back. In designing a stable impedance controller, absolute stability is used as a stability analysis tool, which results in a less conservative controller than the passivity concept. Moreover, in order to remove the conservatism associated with the assumption of infinite port impedances, the boundaries of human and environment impedance are set to finite values. Based on this, this paper proposes a parameter design procedure for stable impedance controllers. The validity of the proposed control scheme is demonstrated by experiments with a 1-dof master/slave system.

• 대한의용생체공학회:의공학회지
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• 제31권5호
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• pp.375-384
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• 2010

The purpose of this study is to determine whether there is a correlation between the segmental bio-impedance measurement with the frequency modulations and the life-style disease of obesity. An obesity is not simply the factor for estimating the life-style disease of obesity, but also the risk factor occurring. There are many methods (BMI, WHR, Waist, CT, DEXA, BIA, etc.) for measuring a degree of obesity; the bio-impedance measurement is more economic and more effective than others. The physical examination, the blood test, the medical imaging diagnosis and the bio-impedancemeasurementswithmultiple frequencies for each body parts have been conducted for 77 people. The estimated value has been calculated through a segmental bio-impedance model based on multi-frequency that was created to reflect the highest correlation by analyzing correlation with linear regression analysis method for the measured bio-impedance and the risk factors. Then we compared with the clinical diagnosis. In case of high level cholesterol, low HDL-C and high LDL-C for life-style disease, the sensitivity is 80~100%and the specificity is 83~100%. This study has shown conclusively that bio-impedance can be a possible predictor to analyze the disease risk rate of population and individual health maintenance. And also the multi-frequency segmental bio-impedance can be used as early predictor to estimate the life-style disease of obesity.

• 대한교통학회지
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• 제27권5호
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• pp.189-194
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• 2009

환승은 대중교통의 대표적인 취약점으로 꼽히는 불편함으로, 대중교통의 경쟁력을 약화시키는 요소이다. 이에 환승으로 인한 불편함 중 개선가능한 요소들을 체계적이고 효과적으로 개선하기 위하여 환승시설 및 환승체계의 물리적 요소들에 대한 보행자 편의성을 계량화하여 환승역사의 환승 편의성에 대한 객관적 평가기준을 마련하고자 한다. 본 연구는 특히 KTX 역사 및 철도 역사를 대상으로 지역간 통행에 있어서 환승역사의 물리적 특성이 환승수단의 선택에 미치는 영향을 파악하고 그 과정에서 환승저항 모형을 구축하였다. 또한 이를 바탕으로 국내 주요 KTX역사 및 철도역사 환승시설을 대상으로 환승저항값을 산정하여 비교하였다. KTX 역사와 철도역사의 물리적 요소들 중 환승 의사결정에 유의하게 영향을 미치는 요소는 환승패스의 외부보행거리, 환승패스의 내부보행거리, 계단 수, 에스컬레이터 수로 동일하게 나타났으나 환승저항 요소의 상대적 크기에 있어서는 차이가 있는 것으로 분석되었다. 에스컬레이터 1대는 약 1~3분의 체감시간 절감 효과를 가지는 것으로 나타났다. 산출된 환승저항 모형은 환승역사별 시설여건을 비교하고 시설개선의 우선순위를 판단하는 데에 객관적 지표로 활용될 수 있을 것이라 기대된다.

• 조명전기설비학회논문지
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• 제26권2호
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• pp.99-105
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• 2012

This paper deals with the experimental results of the frequency-dependent resultant ground impedance of vertical ground electrodes installed with a regular n-polygon. In order to propose an effective method of installing the vertically-driven multiple ground electrodes used to obtain the low ground impedance, the resultant ground impedance of ground electrodes installed with a regular n-polygon were measured as functions of the number of ground electrodes and the frequency of test currents and the results were discussed based on the potential interferences among ground electrodes. As a consequence, the effect of potential interference on the resultant ground impedance of vertical ground electrodes is frequency-dependent and it is significant in the low frequency of a few hundreds [Hz]. The resultant ground impedance of multiple vertical ground electrodes is not decreased in linearly proportion to the number of ground electrodes due to the overlapped potential interferences. Also the distributed-parameter circuit model considering the potential interference, the frequency-dependent relative permittivity and resistivity of soil was proposed. The simulated results of the frequency-dependent resultant ground impedance of multiple vertical ground electrodes are in good agreement with the measured data.

• Journal of Power Electronics
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• 제17권1호
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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.

• 전력전자학회논문지
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• 제20권6호
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• pp.526-533
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• 2015

A new algorithm is proposed for the estimation of equivalent grid impedance at the point of common coupling of a grid-tie inverter output. The estimated impedance parameter can be used for the improvement of the performance and the stability of the distributed generation system. The estimation error is inevitable in the conventional estimation method because of the axis rotation due to PLL. In the conventional estimation error, the d-q voltage and current are used for the calculation of the impedance with active and reactive current injections. Conversely, in the proposed algorithm, the negative sequence current is injected, and then the negative sequence voltage is measured for the impedance estimation. As the positive and negative sequence current controller is independent and the PLL is based on the positive sequence component only, the estimation of the equivalent impedance can be achieved with high accuracy. Simulation and experimental results are compared to validate the proposed algorithm.