• Title, Summary, Keyword: Nyquist criterion

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Performance Evaluation Criterion of FTN-Based Transmission System (FTN 기반 전송 시스템의 성능 평가 기준에 관한 연구)

  • Kwak, Sangwoon;Yun, Joungil;Baek, Myungsun;Lim, Hyoungsoo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.41 no.11
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    • pp.1645-1652
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    • 2016
  • FTN(Faster-Than-Nyquist) signaling is a method of transmitting symbols at rates faster than the Nyquist rate in the same bandwidth by overlapping transmission pulses. The transmission power of the FTN signal is greater than that of the Nyquist signal, because the number of symbols in the FTN signal is larger than that in the Nyquist signal for the same time interval. Hence, to evaluate the performance of an FTN-based transmission system properly, the performance evaluation criterion should be carefully set, and conversion formulas among the criteria which are used in Nyquist-based system should also be applied attentively. In this paper, the performance evaluation criteria of the FTN-based transmission system is analyzed and a valid way to set the criteria is proposed.

Generalized Nyquist Criterion for the Stability of Xenon Oscillation (일반화된 Nyquist 요건에 의한 제논진동의 안전성 분석)

  • Park, You-Cho;Park, Goon-Cherl;Chung, Chang-Hyun;Park, Chong-Kyun
    • Nuclear Engineering and Technology
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    • v.22 no.4
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    • pp.371-379
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    • 1990
  • The Xenon spatial oscillation may give rise to operational difficulties in a nuclear power plant. In this study, in order to investigate the Xenon instability for a PWR, the frequency-domain technique is adopted by using Generalized Nyquist Criterion, which is more general and suitable for the multi-input/multi-output system. Also linearized modal fluxes are obtained by a modal expansion. This model has been implemented to test the axial Xenon stability of YGN-1 unit against the changes in plant operating parameters ; power level, control rod position, and core average burnup. The results show that the increase of power level and the deeper insertion of control rod have the destabilizing effect, and that the burnup progress makes the core less stable. Also the results show that the overestimation due to modal interaction was found not to be significant.

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Characteristics of One Step Advanced Discrete Time D-Control with Time Delay in Noncolocated Flexible System (비병치 유연계의 시간지연 이산제어에서 한스텝선행 미분제어기의 특성)

  • Kang, Min-Sig
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.7
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    • pp.1678-1685
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    • 1993
  • This paper considers a time delay control of noncolocated flexible mechanical systems in discrete time domain. A stability criterion suggested in the previous paper is,extended in the consideration of infinite mode property of flexible systems and finite control sampling frequency. Based on the stability criterion, the one step advanced discrete time derivative control is suggested, which can stabilize infinite number of modes of a flexible system. The sensitivity analysis shows the robustness of the one step advanced control to the system parameter uncertainties and time delay errors. Application to a simply supported beam verifies the extended stability criterion and the effectiveness of the one step advanced D-control.

A Study on Relative Stability for Poppet Valve with Drain Orifice (드레인 오리피스를 갖는 포펫 밸브의 상대 안정도에 관한 연구)

  • Yun, S.N.;Jeong, H.H.;Seo, J.K.;Ham, Y.B.
    • 유공압시스템학회:학술대회논문집
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    • pp.12-17
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    • 2010
  • The poppet valve had used every field area due to high quality of leakage property and response characteristic. But this valve still has terrible disadvantage that is self-exited vibration. This problem affects stability of total system and raises noise. The researcher tries to reduce that self-exited vibration when valve was designed. The stability discriminant is the typical study to improve the performance of the poppet valve. This paper concerns about stability discriminant that uses poppet valve with a drain orifice. At the first, the mathematical model is computed from poppet valve. After that, the limitation of stability is calculated that based on Nyquist criterion. At the final, the stability discriminant is selected in each condition and the graph that shows stability in the system is drown by dimensionless quantity.

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Complex Bandpass Sampling for SDR front-end (SDR front-end를 위한 Complex Bandpass Sampling)

  • Wang, Hong-Mei;Kim, Jae-Hyung;Kim, Hyung-Jung
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.15 no.8
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    • pp.1805-1812
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    • 2011
  • Bandpass sampling technique has an advantage that it uses lower sampling frequency than Nyquist criterion. But special care is required in choosing sampling frequency to avoid self-image overlapping in the first Nyquist region. Recently, the second-order BPS techniques which can suppress possible self-image by using an additional ADC and by employing digital signal processing have been proposed. This paper addresses a complex BPS based SDR front-end. Unlike general second-order BPS, it needs simple FIR filter to compensate delay in the second ADC. We show a method to find proper sampling frequencies to down convert RF signals selected by tunable RF filter operating in arbitrary frequency range.

An approach to the coupled dynamics of small lead cooled fast reactors

  • Zarei, M.
    • Nuclear Engineering and Technology
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    • v.51 no.5
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    • pp.1272-1278
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    • 2019
  • A lumped kinetic modeling platform is developed to investigate the coupled nuclear/thermo-fluid features of the closed natural circulation loop in a low power lead cooled fast reactor. This coolant material serves a reliable choice with noticeable thermo-physical safety characteristics in terms of natural convection. Boussienesq approximation is resorted to appropriately reduce the governing partial differential equations (PDEs) for the fluid flow into a set of ordinary differential equations (ODEs). As a main contributing step, the coolant circulation speed is accordingly correlated to the loop operational power and temperature levels. Further temporal analysis and control synthesis activities may thus be carried out within a more consistent state space framework. Nyquist stability criterion is thereafter employed to carry out a sensitivity analysis for the system stability at various power and heat sink temperature levels and results confirm a widely stable natural circulation loop.

Combustion Stability Analysis using Feedback Transfer Function (피드백 전달함수를 이용한 연소 안정성 해석)

  • Kim, Jina;Yoon, Myunggon;Kim, Daesik
    • Journal of the Korean Society of Combustion
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    • v.21 no.3
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    • pp.24-31
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    • 2016
  • In this paper we propose a new approach for an analysis and a prediction of combustion instability of lean premixed gas turbines. Our approach is based on the Nyquist stability criterion in control theory and a transfer function representation of a one-dimensional (1D) thermoacoustic system. A key advantage of the proposed approach is that one can systematically characterize the effects of various parameters of a combustor system on combustion instability. Our analysis method was applied to a real combustion system and the analysis results were consistent with experimental data.

Stability analysis of fuzzy logic controller using the concept of sector bound nonlinearity (제한된 부채꼴에서의 비선형 개념을 이용한 퍼지 논리제어기의 안정성 해석)

  • 김인익;박상배;이균경
    • 제어로봇시스템학회:학술대회논문집
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    • pp.573-578
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    • 1991
  • A stability analysis technique has been proposed for linear SISO system associated with fuzzy logic controller. An analysis technique using the concept of well-known sector bound nonlinearity and its graphical interpretation, i.e., the circle criterion, is presented. Thus the use of classical Nyquist locus and the BODE diagram is brought into the picture. The aim of this present note is to represent a graphical approach based on sector bound nonlinearity and circle criterion for assessing the performance(degree of stability) of the linear SISO system associated with fuzzy logic controller. The degree of stability of the system is defined in terms of its gain and phase margins as defined in Section 3.

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Evaporator Superheat Control of a Multi-type Air-conditioning/Refrigeration System (멀티형 공조/냉동시스템의 증발기 과열도 제어)

  • Kim, Tae-Sub;Hong, Keum-Shik;Sohn, Hyun-Chul
    • Proceedings of the KSME Conference
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    • pp.712-717
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    • 2001
  • This paper investigates the control problem of evaporator superheat, i.e., the difference between the temperature of the refrigerant at the entrance region of an evaporator and that at the exit region, for multi-type air-conditioning/refrigeration systems. Mathematical equations describing the characteristics of compressor, condenser, evaporator, and electronic expansion valve are first derived. Then, the transfer functions from the current input of the electronic expansion valve to wall temperatures of evaporator tube at two-phase region and superheated region, respectively, are derived. The stability and performance of the closed loop system with a PI controller are analyzed by Nyquist stability criterion. Simulation results are provided.

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Evaporator Superheat Control of a Multi-type Air-Conditioning/Refrigeration System (멸티형 공조/냉동시스템의 증발기 과열도 제어)

  • 김태섭;홍금식;손현철
    • Journal of Energy Engineering
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    • v.10 no.3
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    • pp.253-265
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    • 2001
  • This paper investigates a PI control problem for the evaporator superheat, i.e., temperature difference between the two-phase region and the exit region of an evaporator, for multi-type air-conditioning/refrigeration system. Mathematical model describing the characteristics of compressor, condenser, evaporator, and electronic expansion valve are first derived. Then, two transfer function from the current input applied to an electronic expansion valve to the wall-temperatures of an evaporator tube at two-phase region and superheated region, respectively, are derived. The stability of the closed loop system with the PI controller designed it analyzed by using Nyquist stability criterion. Simulation results are provided.

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