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Analysis of Stability Regions Load Frequency Control with Time Delay Systems Considering Rotor Speed Control
(Institute of Electrical and Electronics Engineers Inc., 2024) Gul, Kübra Nur; Şönmez, Şahin In; Ayasun, Saffet
This paper presents the stability regions of the time-delayed load frequency control (LFC) system enhanced by dynamic participation of wind turbine (WT). Although the integration of WT into LFC enhances the dynamic stability of the system, the complexities of the system increase. Therefore, it is crucial to determine the stability regions and boundaries of the Proportional-Integral (PI) controller in the parameter space for the LFC system including WT dynamics. In this study, the stability regions of the system in the controller parameter space are determined using the stability boundary locus method. The obtained stability regions are verified by time-domain simulations in MATLAB/Simulink. The obtained findings show that the integration of WT including inertia control and deloading control loops into LFC system improves the stability regions. © 2025 Elsevier B.V., All rights reserved.
Damping Based Relative Stability Regions in Load Frequency Control System with Plug-in Electric Vehicles and Communication Delays
(IEEE (Institute of Electrical and Electronics Engineers), 2020) Naveed, Ausnain; Sönmez, Şahin; Ayasun, Saffet
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.
Determination of stability delay margins for multi-area load frequency control systems with incommensurate time delays through eigenvalue tracing method
(Elsevier Ltd, 2022) Aydın, Ömer; Sönmez, Şahin; Ayasun, Saffet
This work presents delay-dependent stability analysis using eigenvalue tracing method for multi-area load frequency control (LFC) systems with incommensurate time delays. LFC systems face inevitable communication delays that adversely affect the frequency stability. Time delays exceeding the allowable limit lead to system instabilities. In this study, stability delay margins of a time-delayed LFC system are computed by a simple yet effective frequency-domain method for computing critical eigenvalues and the corresponding delay margins without using the characteristic equation of the system. By tracing eigenvalue loci of a transformation matrix, the method easily determines the critical eigenvalues on the imaginary axis and obtains stability delay margins. Both stability delay margins and the effectiveness of stability regions in the time delay space are confirmed by time-domain simulations and the quasi-polynomial mapping-based root finder (QPmR) algorithm. Results indicate that more accurate delay margin values are obtained as compared to ones with Lyapunov stability theory based algorithms.
Determination Of Stability Margins In Single Area Load Frequency Control System Having Incommensurate Communication Delays Due To Plug-In Electric Vehicles
(Nigde Omer Halisdemir University, 2020) Navee, Ausnain; Sönmez, Şahin; Ayasun, Saffet
This work investigates the impact of time delays on the stability of a single-area load frequency control (LFC) system that includes plug-in multiple electric vehicles (EVs) aggregators to regulate the system frequency. Communication delays are caused by open communication networks used to transceive control signals. These delays can degrade the performance of the controller leading to undesired system frequency oscillations and may even cause instability if they exceed an upper bound limit known as stability margin. These delays can be commensurate or incommensurate depending upon the nature of the communication network. Hence, it is important to determine stability margins of the single-area LFC system with plug-in EVs aggregators to ensure the stable operation under both types of delays. This study determines the stability margins for extensive proportional-integral (PI) controller gains of the single-area LFC system with plug-in EVs by implementing a simulation approach. The knowledge of stability delay margins makes it possible to appropriately tune the PI controller gains that ensure a stable operation of the LFC system even in the presence of inevitable communication delays.
Dinamik talep cevabı içeren zaman gecikmeli iki bölgeli yük frekans kontrol sistemlerinin kararlılık bölgelerinin hesaplanması
(2024) KATİPOĞLU, Deniz; sonmez, sahin; Ayasun, Saffet
Bu çalışmada, dinamik talep cevabı (DTC) ve haberleşme zaman gecikmesi içeren iki bölgeli yük frekans kontrol (YFK-DTC) sisteminin kararlılık sınır eğrisi yöntemi kullanılarak denetleyici parametre düzleminde kararlılık bölgeleri hesaplanmıştır. DTC kontrol, kontrol edilebilir yük gruplarını frekans kontrol servisine dahil ederek, üretim ve puant yük talebi arasında dengenin daha kısa sürede sağlanması ve yenilenebilir enerji kaynaklarında güç dengesizlikleri problemlerine karşı önemli bir çözüm sunmaktadır. DTC kontrol mekanizmasının yük frekans kontrol sistemlerinde kullanımı, sistemin güvenliği ve güvenilirliğini sağlamasına rağmen, haberleşme ağlarından kaynaklanan zaman gecikmeleri, denetleyici performansını ve sistemin kararlılığını olumsuz etkileyebilmektedir. Dolayısıyla, bu çalışma zaman gecikmesi içeren iki bölgeli YFK-DTC sisteminin kararlılığını garanti edecek tüm oransal-integral (PI) denetleyici kazanç değerlerini elde etmektedir. Bu amaçla, zaman gecikmeli YFK-DTC sisteminin denetleyici parametre düzleminde kararlılık bölgelerini oluşturan kompleks kök sınır (Complex Root Boundary, CRB) eğrisini ve reel kök sınır (Real Root Boundary, RRB) eğrisini bulmak için kararlılık sınır eğrsi yöntemi kullanılmıştır. Elde edilen teorik sonuçların doğruluğu, quasi-polynomial mapping root (QPmR) algoritması ve zaman düzleminde yapılan benzetim çalışmaları ile gösterilmiştir. Sonuçlar, DTC kontrol çevriminin katkısı ile zaman gecikmeli YFK sisteminin kararlılık bölgelerinin ve kararlılık payının arttığını göstermektedir.
Dinamik talep cevabı ve elektrikli araç grupları içeren iki bölgeli yük frekans kontrol sisteminin zaman gecikmesine bağlı kararlılık analizi
(IEEE (Institute of Electrical and Electronics Engineers), 2020) Tek, Bilal; Sönmez, Şahin; Ayasun, Saffet
Bu çalışmada, elektrikli araç (EA) ve dinamik talep cevabı (DTC) ile geliştirilen iki bölgeli yük frekans kontrol (YFK) sisteminin kararlılığı üzerinde zaman gecikmesinin etkisi incelenmiştir. EA bataryası gibi enerji depolama cihazları ve DTC kontrol çevriminin çeşitli yükleri kontrol edebilmesi, sistemin kararlılığının arttırılması bakımından önemli gelişmelerdir. Ancak, güç sistemlerinde kontrol merkezi ve üretim birimleri arasında kontrol sinyallerinin iletilmesi sırasında yaşanan zaman gecikmeleri sistem frekansında istenmeyen salınımlara yol açmaktadır. Dolayısıyla, EA grupları ve DTC kontrol çevrimi içeren iki bölgeli YFK sisteminin kararlı çalışması için sistemin sınırda kararlı olabileceği maksimum zaman gecikme değerlerinin bilinmesi önemlidir. Bu çalışmada, zaman düzleminde yapılan benzetim çalışmaları yardımıyla, oransal-integral (PI) denetleyici kazançlarının bir seti için sistemin maksimum zaman gecikme değerleri belirlenmiştir
The effect of demand response control on stability delay margins of load frequency control systems with communication time-delays
(TÜBİTAK, 2021) Katipoğlu, Deniz; Sönmez, Şahin; Ayasun, Saffet; Naveed, Ausnain
ThIs paper studIes the effect of dynamIc demand response (DR) control on stabIlIty delay margIns of load frequency control (LFC) systems IncludIng communIcatIon tIme-delays. A DR control loop Is Included In each control area, called as LFC-DR system and RekasIus substItutIon Is utIlIzed to IdentIfy stabIlIty margIns for varIous proportIonalIntegral (PI) gaIns and partIcIpatIon ratIos of the secondary and DR control loops. The purpose of RekasIus substItutIon technIque Is to obtaIn purely complex roots on the ImagInary axIs of the tIme-delayed LFC-DR system. ThIs substItutIon fIrst converts the characterIstIc equatIon of the LFC-DR system IncludIng delay-dependent exponentIal terms Into an ordInary polynomIal. Then the well-known Routh-HurwItz stabIlIty method Is applIed to fInd those ImagInary roots and the correspondIng stabIlIty delay margIn known as maxImal tIme-delay. Delay margIn results IndIcate that the InclusIon of DR control loop sIgnIfIcantly Increases stabIlIty delay margIn and Improves the frequency dynamIc behavIor of the LFC system IncludIng tIme-delays. TheoretIcal stabIlIty margIns are confIrmed by a proven algorIthm, quasI-polynomIal mappIng-based root fInder (QPmR) algorIthm and tIme-domaIn sImulatIons. © 2021 Turkiye Klinikleri. All rights reserved.
Enhancement of stability delay margins by virtual inertia control for microgrids with time delay
(2022) Hasen, Suud Ademnur; sonmez, sahin; Ayasun, Saffet
Large-scale deployment of renewable energy sources (RESs) contributes to fluctuations in the system frequency due to their inherent reduced inertia feature. Time delays have emerged as a major source of concern in microgrids (MGs) as a result of the broad adoption of open communication networks since significant delays inevitably reduce the controller’s performance and even cause instabilities. In this article, a frequency-domain direct method is used to evaluate the impact of the virtual inertia (VI) control on the stability delay margins of MG with communication delays. By avoiding approximation, the approach first removes transcendental terms from characteristic equations and turns the transcendental characteristic equations into regular polynomials. With this method, roots of the original characteristic equation on the imaginary axis correspond to exactly the positive real roots of the new regular polynomial not including any exponential term. This new polynomial can be used to find out whether the system stability is delay- dependent or not and enables us to compute stability delay margin for the delay-dependent stability case. The proposed analytical method is utilized for evaluating stability delay margins with regard to system parameters for various values of proportional-integral (PI) gains where the MG is marginally stable. Moreover, quantitative effect of virtual inertia and damping gains is comprehensively investigated. Based on the results, it is concluded that incorporating VI control enhances stability delay margins and enhances the MG’s stability performance. Theoretical delay margin results are verified using time-domain simulations and quasipolynomial mapping-based root finder (QPmR) algorithm.
Identification of gain and phase margins based robust stability regions for a time-delayed micro-grid system including fractional-order controller in presence of renewable power generation
(2022) GÜNDÜZ, Hakan; sonmez, sahin; Ayasun, Saffet
This study examines the gain and phase margins (GPMs) based robust stability margins in the parameter\rspace of fractional order proportional-integral (FOPI) controller for a micro-grid (MG) system with communication\rtime delays. Fluctuations in renewable energy sources (RESs), uncertainties in parameters of system components and\rcommunication delays could adversely affect the dynamical analysis and frequency stability of the MG system. Such a\rMG system has an interval characteristic due to the parametric variations and the interval transfer functions defined\rby Kharitonov’s theorem, which presents a solution for checking of robust stability. Therefore, this study addresses the\rrobust stability regions containing a set of robust FOPI controller gains for all possible transfer functions of the MG system\rby a simple graphical method working in controller parameter space. In this way, the impact of fractional order degree of\rintegral controller on the robust stability regions is exhaustively examined by the graphical method. Additionally, robust\rperformance of the interval MG system in terms of design specifications including GPMs is analyzed, and the effect of\rGPMs on the robust regions is investigated by the graphical method. Results indicate that GPM parameters provide\rthe desirable performances for the MG and fractional order of integral controller considerably increases the robustness\rof the stability margin of the MG when compared with the integer order PI controller.
Impact of electric vehicles aggregators with communication delays on stability delay margins of two-area load frequency control system
(SAGE Publications, 2021) Naveed, Ausnain; Sönmez, Şahin; Ayasun, Saffet
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 stability delay margins is thoroughly analysed and the results are verified by time domain simulations and quasi-polynomial mapping-based root finder (QPmR) algorithm.
Impact of load sharing schemes on the stability delay margins computed by Rekasius substitution method in load frequency control system with electric vehicles aggregator
(2020) Naveed, Ausnain; Sönmez, Şahin; Ayasun, Saffet
The impact of load sharing between the electric vehicles (EVs) aggregator and theconventional generator on stability delay margins in a two-area load frequencycontrol (LFC) system is investigated in this work. A frequency-domain Rekasiussubstitution method is used to compute stability delay margins for different valuesof proportional-integral (PI) controller gains. The proposed method computes com-plex roots on the imaginary axis of the quasi-characteristic equation. The substitu-tion first converts the quasi-characteristic equation of the LFC with EVsaggregator (LFC-EVs) system including delay-dependent exponential terms intoan ordinary polynomial. Then, the Routh–Hurwitz stability method is applied tofind those imaginary roots and the corresponding stability delay margins. Thequalitative impact of different sharing schemes between the conventional genera-tor and EVs aggregator and the impact of EVs gains on stability delay margins arethoroughly analyzed, and the results are validated by time domain simulationsand quasi-polynomial mapping-based root finder algorithm. It is observed that forany given PI controller gains, stability delay margins decrease when the participa-tion of EVs into the frequency regulation increases.
Stability regions in time delayed two-area LFC system enhanced by EVs
(TÜBİTAK / Türkiye Bilimsel ve Teknik Araştırma Kurumu / Scientific and Technical research Council of Turkey, 2022) Naveed, Ausnain; Sönmez, Şahin; Ayasun, Saffet
With the extensive usage of open communication networks, time delays have become a great concern in load frequency control (LFC) systems since such inevitable large delays weaken the controller performance and even may lead to instabilities. Electric vehicles (EVs) have a potential tool in the frequency regulation. The integration of a large number of EVs via an aggregator amplifies the adverse effects of time delays on the stability and controller design of LFC systems. This paper investigates the impacts of the EVs aggregator with communication time delay on the stability. Primarily, a graphical method characterizing stability boundary locus is implemented. The approach is based on the stability boundary locus that can be easily determined by equating the real and the imaginary parts of the characteristic equation to zero. 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.The effects of communication delay and participation factor of EVs aggregator on the obtained stability regions is thoroughly examined. Results clearly illustrate that stability regions become smaller as the time delay and participation factor of EVs increase. Finally, the accuracy of region boundaries known as real root boundary and complex root boundary is confirmed by time-domain simulations along with an independent algorithm, quasipolynomial mapping-based root finder (QPmR) algorithm.
Tuning of Controller Parameters for Time-Delayed Micro-Grid System including Electric Vehicle
(IEEE (Institute of Electrical and Electronics Engineers), 2020) Gündüz, Hakan; Sönmez, Şahin; Ayasun, Saffet
This paper presents the design of proportional-integral (PI) controller parameters of a communication time-delayed micro-grid (MG) system with electric vehicle (EV) via a simple analytical approach known as Weighted Geometrical Center (WGC). This method aims to calculate the WGC point of the stability regions obtained by stability boundary locus method in PI controller parameters space. The WGC points of the stability regions for the time-delayed MG ensure a good dynamic performance. Therefore, the study investigates the system frequency responses for WGC points of computed stability regions for different participation factors of EVs and time delay values. The performance of designed controller parameters by WGC method is compared with Ziegler-Nichols (Z-N) based controller parameters.
Yük frekans kontrol sistemlerinde gürbüz kararlılık zaman gecikmesi paylarının belirlenmesi
(2024) GÜL, Kübra Nur; sonmez, sahin; Ayasun, Saffet
Bu çalışma, zaman gecikmesi içeren Yük Frekans Kontrol (YFK) sistemlerinde parametrik belirsizliklerin olması durumunda sistemin gürbüz kararlılık gecikme payı değerlerini hesaplamayı amaçlamaktadır. YFK sistemlerinde frekans kararlılığının sürdürülmesi bakımından çeşitli elektrik verilerinin ölçülerek kontrol merkezine iletilmesi ve kontrol merkezinden frekans kontrol servisine katılım sağlayan santrallere kontrol sinyallerinin iletilmesi gerekmektedir. Bu süreçte, haberleşme ağlarında veri iletimi nedeniyle, zaman gecikmeleri kaçınılmaz hale gelmektedir ve sistemin dinamik performansı ve kararlılığı olumsuz etkilenmektedir. Ayrıca, YFK sisteminin modellenmesinden kaynaklı ve güç sisteminde oluşabilecek belirsizlikler nedeniyle sistem parametrelerinin belirsizlikleri dikkate alınarak haberleşme ağı tabanlı gözlemlenebilecek gecikme değerleri üzerinde böylesi belirsizliklerin etkisi incelenmelidir. Bu amaçla, YFK sisteminde üstel terimin yok edilmesi yöntemi ile Kharitonov Teoremi birlikte kullanılarak sistemin gürbüz kararlılığını sağlayabilen gürbüz zaman gecikme payı değerlerinin teorik olarak hesaplanması sağlanmıştır. Aynı zamanda Matlab/Simulink programı ve QPmR (Quasi Poliynomial Mapping Root Finder) algoritması kullanılarak elde edilen teorik sonuçların doğruluğu kanıtlanmıştır.
Zaman Gecikmeli Elektrik Güç Sistemlerinin Gecikmeye Bağlı Kararlılık Bölgelerinin Hesaplanması
(Gazi Üniversitesi, 2021) Sönmez, Şahin; Ayasun, Saffet
Bu çalışma, bir özdeğer izleme yöntemi kullanarak güç sistem dengeleyici (GSD) ve otomatik gerilim regülatörü (OGR) içeren zaman gecikmeli jeneratör uyarma kontrol sisteminin zaman gecikmeleri düzleminde kararlılık bölgesini elde etmeyi ve zaman gecikmesine bağlı kararlılık analizini incelemektedir. Elektrik güç sistemlerinde gerilim ve frekans kararlılığının sürdürülmesi bakımından haberleşme alt yapısına ve ölçme sistemlerine ihtiyaç duyulmaktadır. Ancak, haberleşme alt yapısı ve ölçme sistemlerinden dolayı sistemin dinamik davranışını ve kararlılığını olumsuz etkileyen zaman gecikmeleri meydana gelmektedir. Bu çalışmada, jeneratör uyarma kontrol sisteminin durum denklem modellerini kullanarak özdeğerlerini ve bu özdeğerlere karşılık gelen zaman gecikmesi değerlerini belirleyen bir yöntem kullanılmıştır. Ayrıca, bu gecikme değerleri kullanılarak gecikmeye bağlı bir kararlılık bölgesi elde edilmiştir. Kararlılık analizleri için, GSD ve OGR içeren tek makineli sonsuz baralı (TMSB) bir güç sistemi seçilmiştir. Gecikmeye bağlı kararlılık bölgelerinin doğruluğu, zaman düzleminde gerçekleştirilen benzetim çalışmaları ve zaman gecikmeli sistemlerin köklerini kompleks düzlemde hesaplayan QPmR (the quasi-polynomial mapping-based root finder) algoritması ile gösterilmiştir.

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