saffet ayasun | NIGDE UNIVERSITY (original) (raw)

Papers by saffet ayasun

Research paper thumbnail of Switching Based MIMO Robust Autopilot Design: A Munition Example

2022 IEEE 13th International Conference on Mechanical and Intelligent Manufacturing Technologies (ICMIMT)

Research paper thumbnail of Stability analysis of time-delayed DC motor speed control system

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, the stability of time-delayed DC motor speed control systems is analyzed. The meas... more In this paper, the stability of time-delayed DC motor speed control systems is analyzed. The measurement devices and communication links used by networked control systems, cause a significant amount of time delays. The stability boundary of the system in terms of the time delay is theoretically determined and an expression is obtained to compute the delay margin in terms of system parameters. The delay margin is defined as the maximum amount of time delay for which the DC motor speed control system is marginally stable. The results indicate that the system becomes unstable if the time delay exceeds the delay margin at a given set of parameters. Theoretical delay margin results are verified using the time-domain simulations of MATLAB/Simulink.

Research paper thumbnail of Online Parameter Identification of a Simplified Composite Load Model by Voltage Sag Events

Turkish Journal of Electrical Power and Energy Systems

Research paper thumbnail of Impact of electric vehicles aggregators with communication delays on stability delay margins of two-area load frequency control system

Transactions of the Institute of Measurement and Control, 2021

This paper investigates the impact of electric vehicles (EVs) aggregator with communication time ... more This paper investigates the impact of electric vehicles (EVs) aggregator with communication time delay on stability delay margin of a two-area load frequency control (LFC) system. A frequency-domain exact method is used to calculate stability delay margins for various values of proportional-integral (PI) controller gains. The proposed method first eliminates the transcendental terms in the characteristic equation without using any approximation and then transforms the transcendental characteristic equation into a regular polynomial using a recursive approach. The key result of the elimination process is that real roots of the new polynomial correspond to imaginary roots of the transcendental characteristic equation. With the help of new polynomial, delay-dependent system stability and root tendency with respect to the time delay is determined. An analytical formula is then developed to compute delay margins in terms of system parameters. The qualitative impact of EVs aggregator on s...

Research paper thumbnail of The Impact of Electric Vehicles Aggregator on the Stability Region of Micro-Grid System with Communication Time Delay

2019 IEEE Milan PowerTech, 2019

This paper investigates the impact of Electric Vehicles (EVs) on the stability region of micro-gr... more This paper investigates the impact of Electric Vehicles (EVs) on the stability region of micro-grid (MG) system with constant communication delays. A simple and efficient graphical method based on extracting the boundaries of stability regions is used to compute all stabilizing values in proportional-integral (PI) parameters space for a specified time delay. Verification of theoretical stability region boundaries is shown by time-domain simulations for test points selected from stability regions. Results show that the size of stability regions gets larger with the integration of EVs into the MG system, indicating that the stability of the MG system is improved.

Research paper thumbnail of Damping Based Relative Stability Regions in Load Frequency Control System with Plug-in Electric Vehicles and Communication Delays

2020 2nd Global Power, Energy and Communication Conference (GPECOM), 2020

This paper presents a damping based stability analysis of a time delayed single-area load frequen... more This paper presents a damping based stability analysis of a time delayed single-area load frequency control (LFC) system with plug-in Electric Vehicles (EVs) Aggregator by employing a graphical method. The proposed technique computes all the stabilizing gain values of Proportional Integral (PI) controller of the LFC with plug-in EVs (LFC-EVs) system. The proposed method relies on identifying stability region and the stability boundary locus in the PI controller parameter plane having user defined relative stability. These damping based stability regions are obtained and the accuracy of their Complex Root Boundary (CRB) and Real Root Boundary (RRB) is validated by an independent algorithm and time-domain simulations. Moreover, a simple and effective analytical approach known as Weighted Geometrical Center (WGC) is used for tuning the stabilizing controller parameters to achieve better system performance.

Research paper thumbnail of Probability of small-signal stability of power systems in the presence of communication delays

2009 International Conference on Electrical and Electronics Engineering - ELECO 2009, 2009

This paper presents a probabilistic approach to evaluate the small-signal stability of power syst... more This paper presents a probabilistic approach to evaluate the small-signal stability of power systems in the presence of communication delays. An exact method is first proposed to determine the relationship between delay margin and system parameters such as the system load. The delay margin is then modeled as a random variable and the probability density function (PDF) of the delay margin is determined based on the PDF of the load using a Monte Carlo simulation approach. The communication delays are assumed to be uniformly distributed in a practical range and the probability of system being small-signal stable for a given time delay is determined using the estimated PDF of the delay margin. The proposed method is applied to a single-machine-infinite bus (SMIB) power system with an exciter.

Research paper thumbnail of Impact of load sharing schemes on the stability delay margins computed by Rekasius substitution method in load frequency control system with electric vehicles aggregator

International Transactions on Electrical Energy Systems, 2021

Research paper thumbnail of Evaluation of Time Delay Margin for Added Damping of SDOF Systems in Real-Time Dynamic Hybrid Testing ( RTDHT ) under Seismic Excitation

Time delay is known to be an important issue in structural control systems which aim at better dy... more Time delay is known to be an important issue in structural control systems which aim at better dynamic performance of structures during an earthquake. Time delay, which adversely affects the stability and performance of the actively controlled structures, builds up in the system mainly due to sensors, and actuation and communication delays. This paper presents a practical, simple and exact method to compute the delay margin of SDOF systems in Real-Time Dynamic Hybrid Testing (RTDHT) under seismic excitation. Firstly, the transcendental characteristic equation of delayed system is converted into a polynomial without the transcendentality such that its real roots coincide with the imaginary roots of the characteristic equation exactly. A simple criterion to determine the delay-dependency of the system stability is developed using the polynomial without the transcendentality. Afterwards, an expression in terms of system parameters such as mass, m, damping, c and stiffness, k is derived...

Research paper thumbnail of An Exact Method to Compute Time Delay Margin for Stability of Time- Delayed Generator Excitation Control System

This paper investigates the effect of time delays on the stability of a generator excitation cont... more This paper investigates the effect of time delays on the stability of a generator excitation control system compensated with a stabilizing transformer known as rate feedback stabilizer to damp out oscillations. The time delays are due to the use of measurement devices and communication links for data transfer. A direct and exact method based on Rekasius substitution is proposed to determine the maximum amount of time delay known as delay margin that the system can tolerate without loosing its stability. The proposed method starts with the determination of all possible purely imaginary characteristic roots for any positive time delay. To achieve this, Rekasius substitution is first used to convert the transcendental characteristic equation into a polynomial. Then, Routh stability criterion is applied to determine the critical root, the corresponding oscillation frequency and the delay margin for stability. It is found that the excitation control system becomes unstable when the time delay crosses certain critical values. Theoretical delay margins are computed for a wide range of controller gains and their accuracy are verified by using Matlab/Simulink. Results also indicate that the addition of a stabilizing transformer to the excitation system increases the delay margin and improves the system damping significantly.

Research paper thumbnail of Computation of Time Delay Margins for Stability of a Single-Area Load Frequency Control System with Communication Delays

Time delays have become unavoidable in power systems since communication links are extensively us... more Time delays have become unavoidable in power systems since communication links are extensively used for sending and receiving control signals. This paper investigates the effect of time delays on the stability of a single-area load Frequency Control (LFC) system. A direct and exact method to compute delay margins is presented. The delay margin is the maximum amount of the time delay that the system can tolerate before it becomes unstable for a given operating point.The proposed method starts with the determination of all possible purely imaginary characteristic roots for any positive time delay. To achieve this, Rekasius substitution is first used to convert the transcendental characteristic equation of the LFC system into a polynomial. Then, Routh stability criterion is applied to determine the critical root, the corresponding oscillation frequency and the delay margin for stability. For a wide range of controller gains, delay margins of LFC system are determined to find out the qu...

Research paper thumbnail of Stability of a two-area automatic generation control system with communication delays

2009 International Conference on Electrical and Electronics Engineering - ELECO 2009, 2009

This paper investigates the effect of time delays on the stability of a two-area automatic genera... more This paper investigates the effect of time delays on the stability of a two-area automatic generation control (AGC) system. The time delays are due to the use of measurement devices and communication links for sending and receiving control signals. The maximum amount of time delay known as the delay margin that the system can tolerate without becoming unstable is determined using Matlab/Simulink. The effect of integral controller gain on delay margin is analyzed.

Research paper thumbnail of Ağ Üzerinden Kontrol Edilen Yükselten DA-DA Dönüştürücünün Zaman Gecikmesine Bağlı Kararlılık Analizi

Yukselten dogru Akim (DA)-dogru Akim (DA) donusturuculerin ag uzerinden kapali cevrim kontrol edi... more Yukselten dogru Akim (DA)-dogru Akim (DA) donusturuculerin ag uzerinden kapali cevrim kontrol edilmesi durumunda, kullanilan haberlesme aginin yapisina ve veri iletimine bagli olarak sistemin dinamik performansini olumsuz etkileyecek haberlesme zaman gecikmeleri gozlemlenmektedir. S istemin sinirda kararli olacagi maksimum haberlesme zaman gecikmesinin hesaplanmasi, sistemin guvenilir ve kararli bir bicimde kontrolunun yapabilmesi icin onemlidir. Bu calismada, ag uzerinden kontrol edilen yukselten DA-DA donusturucunun zaman gecikmesine bagli kararlilik analizi yapilmistir. Bu amacla, ilk olarak yukselten DA-DA donusturucunun denge noktasi etrafinda gecerli olan dogrusal zaman gecikmeli durum uzay denklem modeli elde edilmistir. Daha sonra, oransal-integral (PI) denetleyicinin farkli degerleri icin Kronecker carpim ve temel donusum metodu uygulanarak sistemin sinirda kararli olacagi maksimum zaman gecikmesi degerleri analitik olarak hesaplanmistir. Son olarak, bulunan teorik maksimum...

Research paper thumbnail of Identification of Stability Delay Margin for Load Frequency Control System with Electric Vehicles Aggregator using Rekasius Substitution

2019 IEEE Milan PowerTech, 2019

This paper implements a frequency-domain exact method, Rekasius substitution to determine the sta... more This paper implements a frequency-domain exact method, Rekasius substitution to determine the stability delay margin of a single-area load frequency control system (LFC) with electric vehicles (EVs) aggregator having constant communication delay. The method aims to compute all possible, purely complex roots of the characteristic equation for a finite positive time delay. The approach first transforms the characteristic polynomial of the LFC system with transcendental terms into a regular polynomial. Routh-Hurwitz Stability Criterion is then implemented to compute the purely imaginary roots with the crossing frequency and stability delay margin. For a wide range of proportional-integral (PI) controller gains, time delay values at which the LFC system with EVs aggregator is marginally stable are computed. The accuracy of stability delay margin results is verified by the time-domain simulations and by using an independent algorithm, the quasi-polynomial mapping-based root finder (QPmR).

Research paper thumbnail of Impact of Electric Vehicle Aggregator with Communication Time Delay on Stability Regions and Stability Delay Margins in Load Frequency Control System

Journal of Modern Power Systems and Clean Energy, 2021

This paper investigates the impact of electric vehicle (EV) aggregator with communication time de... more This paper investigates the impact of electric vehicle (EV) aggregator with communication time delay on stability regions and stability delay margins of a single-area load frequency control (LFC) system. Primarily, a graphical method characterizing stability boundary locus is implemented. For a given time delay, the method computes all the stabilizing proportional-integral (PI) controller gains, which constitutes a stability region in the parameter space of PI controller. Secondly, in order to complement the stability regions, a frequency-domain exact method is used to calculate stability delay margins for various values of PI controller gains. The qualitative impact of EV aggregator on both stability regions and stability delay margins is thoroughly analyzed and the results are authenticated by time-domain simulations and quasi-polynomial mappingbased root finder (QPmR) algorithm.

Research paper thumbnail of Melez Güç Sistemlerinde Zaman Gecikmesinin Kararlılık Analizi

Journal of Polytechnic, 2019

 Yerel melez enerji üretim sisteminin LFC'sinin gecikmeye bağlı kararlılık analizi gerçekleştiri... more  Yerel melez enerji üretim sisteminin LFC'sinin gecikmeye bağlı kararlılık analizi gerçekleştirildi / Delay-dependent stability of the LFC of hybrid power generation subsystem is analyzed.  Kurgulanan melez güç sisteminin matematiksel modeli ve simülasyonu yapıldı. / Mathematical model and simulation of the proposed hybrid power system is obtained.

Research paper thumbnail of Gain-phase margins-based delay-dependent stability analysis of pitch control system of large wind turbines

Transactions of the Institute of Measurement and Control, 2019

This paper investigates the effect of gain and phase margins (GPMs) on the delay-dependent stabil... more This paper investigates the effect of gain and phase margins (GPMs) on the delay-dependent stability analysis of the pitch control system (PCS) of large wind turbines (LWTs) with time delays. A frequency-domain based exact method that takes into account both GPMs is utilized to determine stability delay margins in terms of system and controller parameters. A gain-phase margin tester (GPMT) is introduced to the PCS to take into GPMs in delay margin computation. For a wide range of proportional–integral controller gains, time delay values at which the PCS is both stable and have desired stability margin measured by GPMs are computed. The accuracy of stability delay margins is verified by an independent algorithm, Quasi-Polynomial Mapping Based Rootfinder (QPmR) and time-domain simulations. The time-domain simulation studies also indicate that delay margins must be determined considering GPMs to have a better dynamic performance in term of fast damping of oscillations, less overshoot a...

Research paper thumbnail of Rekasius Yöntemi̇ Kullanilarak Zaman Geci̇kmeli̇ Jeneratör Uyarma Kontrol Si̇stemi̇ni̇n Maksi̇mum Zaman Geci̇kmesi̇ni̇n Hesaplanmasi

Ömer Halisdemir Üniversitesi Mühendislik Bilimleri Dergisi, 2019

Bu çalışma, otomatik gerilim regülatörü (OGR) ve güç sistem dengeleyici (GSD) içeren zaman gecikm... more Bu çalışma, otomatik gerilim regülatörü (OGR) ve güç sistem dengeleyici (GSD) içeren zaman gecikmeli jeneratör uyarma kontrol sisteminin Rekasius yerine koyma yöntemi kullanılarak zaman gecikmesine bağlı kararlılığını incelemektedir. Sistemin kararlılığını kaybetmeden çalışabileceği zaman gecikmesi üst sınırının hesaplanması için Rekasius yönteminin farklı bir prosedürü kullanılmıştır. Önerilen yöntem, ilk olarak uyarma kontrol sisteminin karakteristik denkleminde bulunan üstel terimi herhangi bir yaklaşık içermeyen bir eşitlik yardımıyla elimine etmekte ve karakteristik denklemi sıradan bir polinoma dönüştürmekte ve daha sonra, sistemin sanal eksen üzerindeki köklerine karşılık gelen maksimum zaman gecikmesi değerlerini hesaplamaktadır. Jeneratör uyarma kontrol sisteminin kararlılık analizi için tek makineli sonsuz baralı (TMSB) bir güç sistemi seçilmiş ve GSD kazanç değerleri için sistemin zaman gecikmesi değerleri hesaplanmıştır. Elde edilen sonuçların doğruluğu, üstel terim içeren polinomların köklerini hesaplamak için geliştirilen QPmR (the quasi-polynomial mapping-based root finder) algoritması ve zaman düzleminde gerçekleştirilen benzetim çalışmaları ile gösterilmiştir.

Research paper thumbnail of Zaman gecikmeli mikro-şebeke sistemlerin Rekasius yerine koyma yöntemiyle kazanç ve faz payı tabanlı kararlılık analizi

Gazi Üniversitesi Mühendislik-Mimarlık Fakültesi Dergisi, 2018

 Gain and phase margins based delay-dependent stability analysis of time delayed micro-grids  A... more  Gain and phase margins based delay-dependent stability analysis of time delayed micro-grids  Application Rekasius substitution method into the stability analysis of micro-grids  Verification of theoretical results using QPMR algorithm Figure A. Cyber physical model of micro-grid Purpose: The purpose of this paper is to investigate the delay-dependent stability of a micro-grid system with constant communication delay considering not only stability but also gain-phase margins (GPMs) and to compute stability delay margins. Theory and Methods: A gain-phase margin tester is introduced to the micro-grid system as to take into GPMs in delay margin computation. A frequency domain analytical method, Rekasius substitution, is utilized to compute the GPMs based stability delay margins. The method aims to calculate all possible purely complex roots of the characteristic equation for a finite positive time delay. The approach first transforms the characteristic polynomial of the micro-grid system with transcendental terms into a regular polynomial. Routh-Hurwitz stability criterion is then implemented to compute the purely imaginary roots with the crossing frequency and stability delay margins. Results: For a wide range of proportional-integral controller gains and GPMs, time delay values for which the microgrid system is both stable and has desired stability margin measured by GPMs are computed. The accuracy of complex roots and delay margins are verified by using an independent algorithm, QPMR algorithm and timedomain simulations, respectively. Results indicate that delay margins based on only the stability causes poor dynamic performance with undesirable oscillations in the frequency and stability delay margins decrease as gain and/or phase margins increase. Conclusion: Simulation studies indicate that delay margins must be determined by considering GPMs to have a better dynamic performance in term of fast damping of oscillations, less overshoot and shorter settling time.

Research paper thumbnail of Computation of PI Controllers Ensuring Desired Gain and Phase Margins for Two-Area Load Frequency Control System with Communication Time Delays

Electric Power Components and Systems, 2018

This article deals with computation of all proportionalintegral (PI) controllers which achieve th... more This article deals with computation of all proportionalintegral (PI) controllers which achieve the desired frequencydomain specifications namely, gain and phase margins (GPMs) of a traditional two-area load frequency control (LFC) system with constant communication delays. An efficient graphical method based on extracting the boundaries of stability regions in PI controller parameter space having user defined GPMs is proposed to obtain GPMs based stability regions. Regions are determined for a wide range of GPMs and time delay. The theoretical region boundaries are validated using a powerful numerical method known as the quasi-polynomial mapping-based root finder (QPmR) and time-domain simulations. Results indicate that the proposed scheme gives faster disturbance rejection and desired frequency response as compared to the recently developed scheme for LFC systems with communication delays. the performance of controllers and adversely affect system dynamics and stability [2]-[5]. Time delays are experienced in LFC systems because of an open and distributed communication network used to transmit measured data from power plant to central controller or vice versa. With the use of open communication infrastructure, large amount of communication delays in the range of 5-15 s are generally observed in LFC systems [5]. The LFC systems are designed to regulate the frequency and to keep the scheduled power exchange in an

Research paper thumbnail of Switching Based MIMO Robust Autopilot Design: A Munition Example

2022 IEEE 13th International Conference on Mechanical and Intelligent Manufacturing Technologies (ICMIMT)

Research paper thumbnail of Stability analysis of time-delayed DC motor speed control system

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, the stability of time-delayed DC motor speed control systems is analyzed. The meas... more In this paper, the stability of time-delayed DC motor speed control systems is analyzed. The measurement devices and communication links used by networked control systems, cause a significant amount of time delays. The stability boundary of the system in terms of the time delay is theoretically determined and an expression is obtained to compute the delay margin in terms of system parameters. The delay margin is defined as the maximum amount of time delay for which the DC motor speed control system is marginally stable. The results indicate that the system becomes unstable if the time delay exceeds the delay margin at a given set of parameters. Theoretical delay margin results are verified using the time-domain simulations of MATLAB/Simulink.

Research paper thumbnail of Online Parameter Identification of a Simplified Composite Load Model by Voltage Sag Events

Turkish Journal of Electrical Power and Energy Systems

Research paper thumbnail of Impact of electric vehicles aggregators with communication delays on stability delay margins of two-area load frequency control system

Transactions of the Institute of Measurement and Control, 2021

This paper investigates the impact of electric vehicles (EVs) aggregator with communication time ... more This paper investigates the impact of electric vehicles (EVs) aggregator with communication time delay on stability delay margin of a two-area load frequency control (LFC) system. A frequency-domain exact method is used to calculate stability delay margins for various values of proportional-integral (PI) controller gains. The proposed method first eliminates the transcendental terms in the characteristic equation without using any approximation and then transforms the transcendental characteristic equation into a regular polynomial using a recursive approach. The key result of the elimination process is that real roots of the new polynomial correspond to imaginary roots of the transcendental characteristic equation. With the help of new polynomial, delay-dependent system stability and root tendency with respect to the time delay is determined. An analytical formula is then developed to compute delay margins in terms of system parameters. The qualitative impact of EVs aggregator on s...

Research paper thumbnail of The Impact of Electric Vehicles Aggregator on the Stability Region of Micro-Grid System with Communication Time Delay

2019 IEEE Milan PowerTech, 2019

This paper investigates the impact of Electric Vehicles (EVs) on the stability region of micro-gr... more This paper investigates the impact of Electric Vehicles (EVs) on the stability region of micro-grid (MG) system with constant communication delays. A simple and efficient graphical method based on extracting the boundaries of stability regions is used to compute all stabilizing values in proportional-integral (PI) parameters space for a specified time delay. Verification of theoretical stability region boundaries is shown by time-domain simulations for test points selected from stability regions. Results show that the size of stability regions gets larger with the integration of EVs into the MG system, indicating that the stability of the MG system is improved.

Research paper thumbnail of Damping Based Relative Stability Regions in Load Frequency Control System with Plug-in Electric Vehicles and Communication Delays

2020 2nd Global Power, Energy and Communication Conference (GPECOM), 2020

This paper presents a damping based stability analysis of a time delayed single-area load frequen... more This paper presents a damping based stability analysis of a time delayed single-area load frequency control (LFC) system with plug-in Electric Vehicles (EVs) Aggregator by employing a graphical method. The proposed technique computes all the stabilizing gain values of Proportional Integral (PI) controller of the LFC with plug-in EVs (LFC-EVs) system. The proposed method relies on identifying stability region and the stability boundary locus in the PI controller parameter plane having user defined relative stability. These damping based stability regions are obtained and the accuracy of their Complex Root Boundary (CRB) and Real Root Boundary (RRB) is validated by an independent algorithm and time-domain simulations. Moreover, a simple and effective analytical approach known as Weighted Geometrical Center (WGC) is used for tuning the stabilizing controller parameters to achieve better system performance.

Research paper thumbnail of Probability of small-signal stability of power systems in the presence of communication delays

2009 International Conference on Electrical and Electronics Engineering - ELECO 2009, 2009

This paper presents a probabilistic approach to evaluate the small-signal stability of power syst... more This paper presents a probabilistic approach to evaluate the small-signal stability of power systems in the presence of communication delays. An exact method is first proposed to determine the relationship between delay margin and system parameters such as the system load. The delay margin is then modeled as a random variable and the probability density function (PDF) of the delay margin is determined based on the PDF of the load using a Monte Carlo simulation approach. The communication delays are assumed to be uniformly distributed in a practical range and the probability of system being small-signal stable for a given time delay is determined using the estimated PDF of the delay margin. The proposed method is applied to a single-machine-infinite bus (SMIB) power system with an exciter.

Research paper thumbnail of Impact of load sharing schemes on the stability delay margins computed by Rekasius substitution method in load frequency control system with electric vehicles aggregator

International Transactions on Electrical Energy Systems, 2021

Research paper thumbnail of Evaluation of Time Delay Margin for Added Damping of SDOF Systems in Real-Time Dynamic Hybrid Testing ( RTDHT ) under Seismic Excitation

Time delay is known to be an important issue in structural control systems which aim at better dy... more Time delay is known to be an important issue in structural control systems which aim at better dynamic performance of structures during an earthquake. Time delay, which adversely affects the stability and performance of the actively controlled structures, builds up in the system mainly due to sensors, and actuation and communication delays. This paper presents a practical, simple and exact method to compute the delay margin of SDOF systems in Real-Time Dynamic Hybrid Testing (RTDHT) under seismic excitation. Firstly, the transcendental characteristic equation of delayed system is converted into a polynomial without the transcendentality such that its real roots coincide with the imaginary roots of the characteristic equation exactly. A simple criterion to determine the delay-dependency of the system stability is developed using the polynomial without the transcendentality. Afterwards, an expression in terms of system parameters such as mass, m, damping, c and stiffness, k is derived...

Research paper thumbnail of An Exact Method to Compute Time Delay Margin for Stability of Time- Delayed Generator Excitation Control System

This paper investigates the effect of time delays on the stability of a generator excitation cont... more This paper investigates the effect of time delays on the stability of a generator excitation control system compensated with a stabilizing transformer known as rate feedback stabilizer to damp out oscillations. The time delays are due to the use of measurement devices and communication links for data transfer. A direct and exact method based on Rekasius substitution is proposed to determine the maximum amount of time delay known as delay margin that the system can tolerate without loosing its stability. The proposed method starts with the determination of all possible purely imaginary characteristic roots for any positive time delay. To achieve this, Rekasius substitution is first used to convert the transcendental characteristic equation into a polynomial. Then, Routh stability criterion is applied to determine the critical root, the corresponding oscillation frequency and the delay margin for stability. It is found that the excitation control system becomes unstable when the time delay crosses certain critical values. Theoretical delay margins are computed for a wide range of controller gains and their accuracy are verified by using Matlab/Simulink. Results also indicate that the addition of a stabilizing transformer to the excitation system increases the delay margin and improves the system damping significantly.

Research paper thumbnail of Computation of Time Delay Margins for Stability of a Single-Area Load Frequency Control System with Communication Delays

Time delays have become unavoidable in power systems since communication links are extensively us... more Time delays have become unavoidable in power systems since communication links are extensively used for sending and receiving control signals. This paper investigates the effect of time delays on the stability of a single-area load Frequency Control (LFC) system. A direct and exact method to compute delay margins is presented. The delay margin is the maximum amount of the time delay that the system can tolerate before it becomes unstable for a given operating point.The proposed method starts with the determination of all possible purely imaginary characteristic roots for any positive time delay. To achieve this, Rekasius substitution is first used to convert the transcendental characteristic equation of the LFC system into a polynomial. Then, Routh stability criterion is applied to determine the critical root, the corresponding oscillation frequency and the delay margin for stability. For a wide range of controller gains, delay margins of LFC system are determined to find out the qu...

Research paper thumbnail of Stability of a two-area automatic generation control system with communication delays

2009 International Conference on Electrical and Electronics Engineering - ELECO 2009, 2009

This paper investigates the effect of time delays on the stability of a two-area automatic genera... more This paper investigates the effect of time delays on the stability of a two-area automatic generation control (AGC) system. The time delays are due to the use of measurement devices and communication links for sending and receiving control signals. The maximum amount of time delay known as the delay margin that the system can tolerate without becoming unstable is determined using Matlab/Simulink. The effect of integral controller gain on delay margin is analyzed.

Research paper thumbnail of Ağ Üzerinden Kontrol Edilen Yükselten DA-DA Dönüştürücünün Zaman Gecikmesine Bağlı Kararlılık Analizi

Yukselten dogru Akim (DA)-dogru Akim (DA) donusturuculerin ag uzerinden kapali cevrim kontrol edi... more Yukselten dogru Akim (DA)-dogru Akim (DA) donusturuculerin ag uzerinden kapali cevrim kontrol edilmesi durumunda, kullanilan haberlesme aginin yapisina ve veri iletimine bagli olarak sistemin dinamik performansini olumsuz etkileyecek haberlesme zaman gecikmeleri gozlemlenmektedir. S istemin sinirda kararli olacagi maksimum haberlesme zaman gecikmesinin hesaplanmasi, sistemin guvenilir ve kararli bir bicimde kontrolunun yapabilmesi icin onemlidir. Bu calismada, ag uzerinden kontrol edilen yukselten DA-DA donusturucunun zaman gecikmesine bagli kararlilik analizi yapilmistir. Bu amacla, ilk olarak yukselten DA-DA donusturucunun denge noktasi etrafinda gecerli olan dogrusal zaman gecikmeli durum uzay denklem modeli elde edilmistir. Daha sonra, oransal-integral (PI) denetleyicinin farkli degerleri icin Kronecker carpim ve temel donusum metodu uygulanarak sistemin sinirda kararli olacagi maksimum zaman gecikmesi degerleri analitik olarak hesaplanmistir. Son olarak, bulunan teorik maksimum...

Research paper thumbnail of Identification of Stability Delay Margin for Load Frequency Control System with Electric Vehicles Aggregator using Rekasius Substitution

2019 IEEE Milan PowerTech, 2019

This paper implements a frequency-domain exact method, Rekasius substitution to determine the sta... more This paper implements a frequency-domain exact method, Rekasius substitution to determine the stability delay margin of a single-area load frequency control system (LFC) with electric vehicles (EVs) aggregator having constant communication delay. The method aims to compute all possible, purely complex roots of the characteristic equation for a finite positive time delay. The approach first transforms the characteristic polynomial of the LFC system with transcendental terms into a regular polynomial. Routh-Hurwitz Stability Criterion is then implemented to compute the purely imaginary roots with the crossing frequency and stability delay margin. For a wide range of proportional-integral (PI) controller gains, time delay values at which the LFC system with EVs aggregator is marginally stable are computed. The accuracy of stability delay margin results is verified by the time-domain simulations and by using an independent algorithm, the quasi-polynomial mapping-based root finder (QPmR).

Research paper thumbnail of Impact of Electric Vehicle Aggregator with Communication Time Delay on Stability Regions and Stability Delay Margins in Load Frequency Control System

Journal of Modern Power Systems and Clean Energy, 2021

This paper investigates the impact of electric vehicle (EV) aggregator with communication time de... more This paper investigates the impact of electric vehicle (EV) aggregator with communication time delay on stability regions and stability delay margins of a single-area load frequency control (LFC) system. Primarily, a graphical method characterizing stability boundary locus is implemented. For a given time delay, the method computes all the stabilizing proportional-integral (PI) controller gains, which constitutes a stability region in the parameter space of PI controller. Secondly, in order to complement the stability regions, a frequency-domain exact method is used to calculate stability delay margins for various values of PI controller gains. The qualitative impact of EV aggregator on both stability regions and stability delay margins is thoroughly analyzed and the results are authenticated by time-domain simulations and quasi-polynomial mappingbased root finder (QPmR) algorithm.

Research paper thumbnail of Melez Güç Sistemlerinde Zaman Gecikmesinin Kararlılık Analizi

Journal of Polytechnic, 2019

 Yerel melez enerji üretim sisteminin LFC'sinin gecikmeye bağlı kararlılık analizi gerçekleştiri... more  Yerel melez enerji üretim sisteminin LFC'sinin gecikmeye bağlı kararlılık analizi gerçekleştirildi / Delay-dependent stability of the LFC of hybrid power generation subsystem is analyzed.  Kurgulanan melez güç sisteminin matematiksel modeli ve simülasyonu yapıldı. / Mathematical model and simulation of the proposed hybrid power system is obtained.

Research paper thumbnail of Gain-phase margins-based delay-dependent stability analysis of pitch control system of large wind turbines

Transactions of the Institute of Measurement and Control, 2019

This paper investigates the effect of gain and phase margins (GPMs) on the delay-dependent stabil... more This paper investigates the effect of gain and phase margins (GPMs) on the delay-dependent stability analysis of the pitch control system (PCS) of large wind turbines (LWTs) with time delays. A frequency-domain based exact method that takes into account both GPMs is utilized to determine stability delay margins in terms of system and controller parameters. A gain-phase margin tester (GPMT) is introduced to the PCS to take into GPMs in delay margin computation. For a wide range of proportional–integral controller gains, time delay values at which the PCS is both stable and have desired stability margin measured by GPMs are computed. The accuracy of stability delay margins is verified by an independent algorithm, Quasi-Polynomial Mapping Based Rootfinder (QPmR) and time-domain simulations. The time-domain simulation studies also indicate that delay margins must be determined considering GPMs to have a better dynamic performance in term of fast damping of oscillations, less overshoot a...

Research paper thumbnail of Rekasius Yöntemi̇ Kullanilarak Zaman Geci̇kmeli̇ Jeneratör Uyarma Kontrol Si̇stemi̇ni̇n Maksi̇mum Zaman Geci̇kmesi̇ni̇n Hesaplanmasi

Ömer Halisdemir Üniversitesi Mühendislik Bilimleri Dergisi, 2019

Bu çalışma, otomatik gerilim regülatörü (OGR) ve güç sistem dengeleyici (GSD) içeren zaman gecikm... more Bu çalışma, otomatik gerilim regülatörü (OGR) ve güç sistem dengeleyici (GSD) içeren zaman gecikmeli jeneratör uyarma kontrol sisteminin Rekasius yerine koyma yöntemi kullanılarak zaman gecikmesine bağlı kararlılığını incelemektedir. Sistemin kararlılığını kaybetmeden çalışabileceği zaman gecikmesi üst sınırının hesaplanması için Rekasius yönteminin farklı bir prosedürü kullanılmıştır. Önerilen yöntem, ilk olarak uyarma kontrol sisteminin karakteristik denkleminde bulunan üstel terimi herhangi bir yaklaşık içermeyen bir eşitlik yardımıyla elimine etmekte ve karakteristik denklemi sıradan bir polinoma dönüştürmekte ve daha sonra, sistemin sanal eksen üzerindeki köklerine karşılık gelen maksimum zaman gecikmesi değerlerini hesaplamaktadır. Jeneratör uyarma kontrol sisteminin kararlılık analizi için tek makineli sonsuz baralı (TMSB) bir güç sistemi seçilmiş ve GSD kazanç değerleri için sistemin zaman gecikmesi değerleri hesaplanmıştır. Elde edilen sonuçların doğruluğu, üstel terim içeren polinomların köklerini hesaplamak için geliştirilen QPmR (the quasi-polynomial mapping-based root finder) algoritması ve zaman düzleminde gerçekleştirilen benzetim çalışmaları ile gösterilmiştir.

Research paper thumbnail of Zaman gecikmeli mikro-şebeke sistemlerin Rekasius yerine koyma yöntemiyle kazanç ve faz payı tabanlı kararlılık analizi

Gazi Üniversitesi Mühendislik-Mimarlık Fakültesi Dergisi, 2018

 Gain and phase margins based delay-dependent stability analysis of time delayed micro-grids  A... more  Gain and phase margins based delay-dependent stability analysis of time delayed micro-grids  Application Rekasius substitution method into the stability analysis of micro-grids  Verification of theoretical results using QPMR algorithm Figure A. Cyber physical model of micro-grid Purpose: The purpose of this paper is to investigate the delay-dependent stability of a micro-grid system with constant communication delay considering not only stability but also gain-phase margins (GPMs) and to compute stability delay margins. Theory and Methods: A gain-phase margin tester is introduced to the micro-grid system as to take into GPMs in delay margin computation. A frequency domain analytical method, Rekasius substitution, is utilized to compute the GPMs based stability delay margins. The method aims to calculate all possible purely complex roots of the characteristic equation for a finite positive time delay. The approach first transforms the characteristic polynomial of the micro-grid system with transcendental terms into a regular polynomial. Routh-Hurwitz stability criterion is then implemented to compute the purely imaginary roots with the crossing frequency and stability delay margins. Results: For a wide range of proportional-integral controller gains and GPMs, time delay values for which the microgrid system is both stable and has desired stability margin measured by GPMs are computed. The accuracy of complex roots and delay margins are verified by using an independent algorithm, QPMR algorithm and timedomain simulations, respectively. Results indicate that delay margins based on only the stability causes poor dynamic performance with undesirable oscillations in the frequency and stability delay margins decrease as gain and/or phase margins increase. Conclusion: Simulation studies indicate that delay margins must be determined by considering GPMs to have a better dynamic performance in term of fast damping of oscillations, less overshoot and shorter settling time.

Research paper thumbnail of Computation of PI Controllers Ensuring Desired Gain and Phase Margins for Two-Area Load Frequency Control System with Communication Time Delays

Electric Power Components and Systems, 2018

This article deals with computation of all proportionalintegral (PI) controllers which achieve th... more This article deals with computation of all proportionalintegral (PI) controllers which achieve the desired frequencydomain specifications namely, gain and phase margins (GPMs) of a traditional two-area load frequency control (LFC) system with constant communication delays. An efficient graphical method based on extracting the boundaries of stability regions in PI controller parameter space having user defined GPMs is proposed to obtain GPMs based stability regions. Regions are determined for a wide range of GPMs and time delay. The theoretical region boundaries are validated using a powerful numerical method known as the quasi-polynomial mapping-based root finder (QPmR) and time-domain simulations. Results indicate that the proposed scheme gives faster disturbance rejection and desired frequency response as compared to the recently developed scheme for LFC systems with communication delays. the performance of controllers and adversely affect system dynamics and stability [2]-[5]. Time delays are experienced in LFC systems because of an open and distributed communication network used to transmit measured data from power plant to central controller or vice versa. With the use of open communication infrastructure, large amount of communication delays in the range of 5-15 s are generally observed in LFC systems [5]. The LFC systems are designed to regulate the frequency and to keep the scheduled power exchange in an