• 제어로봇시스템학회:학술대회논문집
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• 1987.10b
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• pp.214-217
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• 1987

In this paper self tuning control of interconnected systems are dealt in view point of large scale system control. The plant model is given in multiple ARMA process. This process is simplified as independent SISO ARMA process having offset terms. This offset was considered as effects of interconnections. In each decentralized system, self tuning controller with instrumental variable method is adopted. As a result, this algorithm enables the parameter estimation to be unbiased and non-drift. This controller contains a new implicit offset rejection technique. Simulation results considers well with the analysis in case of linear interconnection.

• Proceedings of the KIPE Conference
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• 1996.06a
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• pp.26-30
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• 1996

This paper proposes a novel method to reduce the torque ripple due to the non-ideality of the current sensing parts in vector-controlled inverter-fed PMSM(Permanent Magnet Synchronous Motor) drive systems. The motor output torque equations are derived in terms of their offset voltages and different voltage transducing gains. And the effects of phase current errors on motor torque are analyzed for both salient PMSM and non-salient PMSM. The proposed method can eliminate the torque ripple by nulling the offset voltages and setting the voltage transducing gains to the same value. To verify the proposed method, digital simulations are carried out for non-salient PMSM.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.4
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• pp.365-370
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• 2013

In this paper, we propose robust blind estimators for the frequency offset of orthogonal frequency division multiplexing in non-Gaussian noise environments. We first propose a maximum likelihood (ML) estimator in non-Gaussian noise modeled as a complex isotropic Cauchy process, and then, a simpler estimator based on the ML estimator is proposed. From numerical results, we confirm that the proposed estimators are robust to the non-Gaussian noise and have a better estimation performance over the conventional estimator in non-Gaussian noise environments.

• Journal of Korean Society of Forest Science
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• v.101 no.1
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• pp.83-90
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• 2012

Forests as carbon sinks and sources, play an important role in mitigating global climate change. Nonpermanence problem of forest carbon offset projects should be addressed practically and properly for obtaining credible forest carbon credits. This study aims to analyze major non-permanence approaches and their applicability for Korean forest carbon offset projects. Introduction of the buffer system, one of the most generally used non-permanence approaches, should be considered first for domestic forest carbon offset schemes. From the research survey, experts preferred the buffer system to other approaches such as forest certification, conservation easement, and longer conservation period. Standard development including a buffer system with a risk assessment tool is required to assure project participation and permanence of carbon credits.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.6
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• pp.955-961
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• 2016

Fault location estimation is an important element for rapid recovery of power system when fault occur in transmission line. In order to calculate line impedance, most of fault location algorithm uses by measuring relaying waveform using DFT. So if there is a calculation error due to the influence of phasor by DC offset component, due to large vibration by line impedance computation, abnormal and non-operation of fault locator can be issue. It is very important to implement the robust fault location algorithm that is not affected by DC offset component. This paper describes an enhanced fault location algorithm based on the DC offset elimination filter to minimize the effects of DC offset on a long transmission line. The proposed DC offset elimination filter has not need any erstwhile information. The phase angle delay of the proposed DC offset filter did not occurred and the gain error was not found. The enhanced fault location algorithm uses DFT filter as well as the proposed DC offset filter. The behavior of the proposed fault location algorithm using off-line simulation has been verified by data about several fault conditions generated by the ATP simulation program.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.4A
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• pp.250-258
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• 2005

An initial carrier frequency offset estimation algorithm is proposed for a multi-user frequency bowing orthogonal frequency division modulation-frequency division multiple access (FH-OFDMA) system with a single preamble symbol. To mitigate the effect of the frequency offset, every mobile station needs to accurately and rapidly acquire synchronization. The proposed algorithm uses only one preamble symbol in which two kinds of subcarriers are designed for coarse and fine frequency offset estimation. The non-data aided estimation using the energy spectrum is exploited for fine offset estimation, and maximum likelihood estimation using correlation for coarse offset estimation. By combining the two estimation results, an accurate frequency offset can be estimated with a single symbol. Through simulations, the performance of the proposed algorithm is evaluated by comparing estimation error variance with a conventional method.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.2
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• pp.67-73
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• 2015

Distance relay is widely used for the protection of long transmission line. Most of distance relay used to calculate line impedance by measuring voltage and current using DFT. So if there is a computation error due to the influence of phasor by DC offset component, due to excessive vibration by measuring line impedance, overreach or underreach can be occurs, and then abnormal and non-operation of distance relay can be issue. It is very important to implement the robust distance relaying that is not affected by DC offset component. This paper describes an enhanced distance relaying based on the DC offset elimination filter to minimize the effects of DC offset on a long transmission line. The proposed DC offset elimination filter has not need any prior information. The phase angle delay of the proposed DC offset filter did not occurred and the gain error was not found. The enhanced distance relay uses fault current as well as residual current. The behavior of the proposed distance relaying using off-line simulation has been verified using data about several fault conditions generated by the ATP simulation software.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6C
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• pp.391-397
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• 2011

This paper investigates the frequency offset (PO) estimation scheme for the orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems. In the CR environments, the conventional FO estimation schemes for the OFDM systems experience significant performance degradation due to the effect of the non-Gaussian noise. In this paper, a novel FO estimation scheme based on the maximum likelihood criterion is proposed for the OFDM-based CR systems in non-Gaussian noise environments. The proposed scheme does not require a specific pilot structure and has a better estimation performance compared with that of the conventional scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6C
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• pp.626-633
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• 2009

ISO/IEC/WD 24753 defines new modem specifications for a long-range RFID communications and application protocol for a sensor tag system. According to the standard, the frequency offset of the tag is 4%. In general wireless communications systems, it is known that a coherent receiver is superior to a non-coherent receiver. However, if the frequency offset is large, it is difficult to restore the original data accurately with a coherent receiver, and the performance of a coherent receiver is easily degraded. In this paper, a non-coherent receiver structure is adopted to solve the frequency offset problem of long-range RFID communications. We designed a frequency estimation block to find an optimal frequency from the received signal with 4% frequency offset and proposed a start frame delimiter (SFD) detection algorithm to determine the start position of the payload. The frequency estimation block finds the optimal frequency from the received signal using 9-correlators. And the SFD detection block searches the received signal to find the start position of the payload with dual correlator. We implemented a long-range RFID reader with the proposed methods and evaluated its performance in a wired/wireless test network. The implemented long-range RFID reader showed more superior performance than the commercial RFID reader in terms of recognition range.

• Proceedings of the KSPS conference
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• 2006.05a
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• pp.109-112
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• 2006

This study investigated the acoustical characteristics of phonatory offset-onset mechanisms. And this study shows the comparative results between non-stutterers (N=3) and a stutterer (N=1). Phonatory offset-onset means a laryngeal articulatory in the connected speech. In the phonetic context V_V), pattern 0(there is no changes) appeared in all subjects, and pattern 4(this indicate the trace of glottal fry and closure in spectrogram)was only in a Stutterer. In high vowels(/i/, /u/), pattern 3 and 4 appeared only in a stutterer. Although there is no common pattern among the non-stutterers, individual's preference pattern was founded. This study offers the key to an understanding of physiological movement on a block of stutter.