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    An Exact Method for Computing Delay Margin for Stability of Load Frequency Control Systems With Constant Communication Delays
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2016) Sonmez, Sahin; Ayasun, Saffet; Nwankpa, Chika O.
    The extensive usage of open communication networks in power system control causes inevitable time delays. This paper studies impacts of such delays on the stability of one-area and two-area load frequency control (LFC) systems and proposes an analytical method to determine delay margins, the upper bound on the delay for stability. The proposed method first eliminates transcendental terms in characteristic equation of LFC systems without making any approximation and transforms the transcendental characteristic equation into a regular polynomial. 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, it is also possible to determine the delay-dependency of system stability and root tendency with respect to the time delay. An analytical formula is then developed to compute delay margins in terms of system parameters. For a large set of controller gains, delay margins of LFC systems are computed to investigate the qualitative effect of controller gains on the delay margin. Finally, simulations studies are carried out to verify the effectiveness of the proposed method.
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    Computation of Robust PI-Based Pitch Controller Parameters for Large Wind Turbines
    (IEEE Canada, 2020) Turksoy, Omer; Ayasun, Saffet; Hames, Yakup; Sonmez, Sahin
    This paper deals with the computation of all proportional-integral (PI)-based pitch controllers which achieve the desired frequency-domain specifications, namely, gain and phase margins (GPMs) of a large wind turbine (LWT) with communication delays. An efficient graphical method based on extracting the boundaries of stability regions in PI controller parameter space having user-defined GPMs has been employed to determine GPM-based stability regions for a wide range of time delays. The theoretical region boundaries are validated by 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 an improved dynamic response compared to the recently developed scheme based on stability only for the pitch control of LWTs with communication delays.
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    Computation of Stability Delay Margin of Time-Delayed Generator Excitation Control System with a Stabilizing Transformer
    (HINDAWI PUBLISHING CORPORATION, 2014) Ayasun, Saffet; Eminoglu, Ulas; Sonmez, Sahin
    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. An analytical method is presented to compute the delay margin for stability. The delay margin is the maximum amount of time delay that the system can tolerate before it becomes unstable. First, without using any approximation, the transcendental characteristic equation is converted into a polynomial without the transcendentality such that its real roots coincide with the imaginary roots of the characteristic equation exactly. The resulting polynomial also enables us to easily determine the delay dependency of the system stability and the sensitivities of crossing roots with respect to the time delay. Then, an expression in terms of system parameters and imaginary root of the characteristic equation is derived for computing the delay margin. Theoretical delay margins are computed for a wide range of controller gains and their accuracy is verified by performing simulation studies. Results indicate that the addition of a stabilizing transformer to the excitation system increases the delay margin and improves the system damping significantly.
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    Computation of stability regions for load frequency control systems including incommensurate time delays
    (Tubitak Scientific & Technological Research Council Turkey, 2019) Sonmez, Sahin
    This article studies the impact of incommensurate communication time delays on stability regions defined in proportional-integral (PI) controller parameter space for a two-area load frequency control (LFC) system. Distributed power generations and large power plants increase the complexity and control issues of interconnected power systems. In interconnected power systems, LFC systems need to have complex communication networks to exchange data between control center and geographically dispersed generations. The receiving/transmitting of remote measuring data through communication infrastructures causes inevitable time delays, which adversely affect controller performance and stability of the LFC system. Time delays introducing feedback control loops of a multiarea LFC system could exhibit incommensurate characteristics. In this study, a simple graphical method based on extracting a stability boundary locus is implemented to get PI controller parameters responsible for stabilizing the LFC system having incommensurate delay values. The boundaries of the stability regions in the PI controller parameter space are confirmed by time-domain simulations and a numerical algorithm known as the quasipolynomial mapping-based root finder algorithm. Results illustrate that incommensurate delays have remarkable effects on the stability region.
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    Damping Based Relative Stability Regions in Load Frequency Control System with Plug-in Electric Vehicles and Communication Delays
    (IEEE, 2020) Naveed, Ausnain; Sonmez, Sahin; 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.
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    Delay - Dependent Stability Analysis of Load Frequency Control Systems Considering Wind Power Participation
    (IEEE, 2024) Gul, Kubra Nur; Sonmez, Sahin; Ayasun, Saffet
    This study presents the delay-dependent stability analysis of the load frequency control (LFC) system enhanced by dynamic participation of wind turbine (WT). The development of the energy conversion technologies in the variable speed WTs provides the inertia support based on rotational kinetic energy and primary frequency reserve for the grid. However, the extensive utilization of communication networks to exchange data for managing and control of generation units causes the network-induced delays which negatively affect the frequency stability of the system. In addition, the LFC-WT systems face with the parametric uncertainty issue due to increasing the complexity of the LFC system and uncertainties in the WT. In this regards, the study aims to obtain the stability delay margins of the LFC system with WT deloading operation by time-domain simulation and Kharitonov theorem. The obtained stability delay margins are verified by Quasi-Polynomial mapping Root (QPmR) finder algorithm. The obtained findings show that the integration of WT including inertia control and deloading control loops into LFC system improves the delay margins and robustness of the system.
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    Delay-Dependent Stability Analysis of Multi-Area LFC-EVs System
    (IEEE-Inst Electrical Electronics Engineers Inc, 2023) Sari, Alperen; Sonmez, Sahin; Ayasun, Saffet; Kabalci, Yasin
    In this study, the delay-dependent stability of a multi-area Load Frequency Control (LFC) system with Electric Vehicle (EV) aggregators is investigated with the help of the Advanced Clustering with Frequency Sweeping (ACFS) method for incommensurate time delays. Both Integer-Order (IO) and Fractional-Order Proportional Integral (FOPI) controllers are utilized as a controller. The communication infrastructure used in LFC systems induces time delays resulting in deteriorations in the system stability. Even if the maximum allowable delay margin limits are not exceeded, these inevitable time delays could cause undesired frequency deviations and tie-line power fluctuations. The ACFS method is employed in this study to investigate impacts of time delays and to ensure better controller performance objectives taking into account the effects of time delays. Firstly, 2-dimensional (2D) stability delay maps are obtained for various LFC-EVs system parameters. The stability regions are then verified by the Quasi-Polynomial Mapping Root (QPmR) finder algorithm and MATLAB/Simulink-based time-domain simulations. The results clearly show that the participation of the EV aggregators in traditional LFC systems improves the frequency regulation and tie-line power-sharing in the system. Finally, it is concluded that the stability regions are enhanced as the fractional order of the FOPI decreases.
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    Gain and phase margin based stability analysis of time delayed single area load frequency control system with fractional order PI controller
    (Gazi Univ, Fac Engineering Architecture, 2019) Sonmez, Sahin; Ayasun, Saffet
    The study investigates gain-phase margin (GPM) based stability analysis for a time-delayed single-area load frequency control (LFC) system with fractional order proportional-integral (FOPI) controller. The extensive usage of open communication networks in power system control causes inevitable time delays. To compute such delays, an analytical direct method determined the imaginary axis crossing of roots of the characteristic equation is proposed for desired gain and phase margins (GPMs) and a large set of FOPI controller. Finally, for time-delayed single area LFC system with FOPI controller, results obtained are verified by using the time-domain simulation studies in Matlab/Simulink and the quasi-polynomial mapping-based root finder (QPMR) algorithm which locates quasi-polynomial roots in time delay systems.
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    Gain and Phase Margins Based Delay- Dependent Stability Analysis of Two-Area LFC System with Communication Delays
    (IEEE, 2017) Sonmez, Sahin; Ayasun, Saffet
    This paper investigates the effect gain and phase margins (GPM) on delay-dependent stability analysis of a two-area load frequency control (LFC) system with communication delays. An frequency-domain based exact method that takes into account both gain and phase margins is utilized to determine stability delay margins in terms of system and controller parameters. A gain-phase margin tester (GPMT) is introduced to the LFC system as to take into gain and phase margins in delay margin computation. For a wide range of proportional - integral (PI) controller gains, time delay values at which LFC system is both stable and have desired stability margin measured by gain and phase margins are computed. The time-domain simulation studies indicate that delay margins must be determined considering gain and phase margins to have a better dynamic performance in term of fast damping of oscillations, less overshoot and settling time.
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    Gain and phase margins based delay-dependent stability analysis of single-area load frequency control system with constant communication time delay
    (SAGE PUBLICATIONS LTD, 2018) Sonmez, Sahin; Ayasun, Saffet
    This paper presents a comprehensive stability analysis of a single-area load frequency control (LFC) system with constant communication delays. First, an exact method that takes into account both gain and phase margins is proposed to determine stability delay margins in terms of system and controller parameters. The method implements an elimination procedure to transform transcendental characteristic equation into a standard polynomial of the crossing frequency. The real roots of this new standard polynomial exactly match with the purely imaginary roots (crossing frequencies) of the original characteristic equation with transcendental terms. Secondly, an effective and simple graphical method is implemented to compute all stabilizing Proportional Integral (PI) controller gains for a given time delay. The approach is based on extracting stability region and the stability boundary locus in the PI controller parameter space having user defined gain and phase margins, and relative stability. The time-domain simulation studies indicate that the proposed scheme improves dynamic performance gain and phase margins are included in delay-dependent stability analysis of single-area LFC with communication delays.
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    Gain and phase margins-based delay margin computation of load frequency control systems using Rekasius substitution
    (Sage Publications Ltd, 2019) Sonmez, Sahin; Ayasun, Saffet
    This paper investigates the effect of gain and phase margins (GPMs) on stability delay margin of a two-area load frequency control (LFC) system with constant communication delay. A gain-phase margin tester (GPMT) is introduced to the LFC system as to take into GPMs in delay margin computation. A frequency domain exact method, Rekasius substitution, is proposed 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 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 controller gains and GPMs, time delay values at which LFC 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, the quasi-polynomial mapping-based root finder and time-domain simulations. Simulation studies indicate that delay margins must be determined considering GPMs to have a better dynamic performance in term of fast damping of oscillations, less overshoot and settling time.
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    Gain-phase margins-based delay-dependent stability analysis of pitch control system of large wind turbines
    (Sage Publications Ltd, 2019) Turksoy, Omer; Ayasun, Saffet; Hames, Yakup; Sonmez, Sahin
    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 and settling time.
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    Impact of Electric Vehicle Aggregator with Communication Time Delay on Stability Regions and Stability Delay Margins in Load Frequency Control System
    (IEEE-Inst Electrical Electronics Engineers Inc, 2021) Naveed, Ausnain; Sonmez, Sahin; Ayasun, Saffet
    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 pro-portional-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 mapping-based root finder (QPmR) algorithm.
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    Impact of electric vehicles aggregators with communication delays on stability delay margins of two-area load frequency control system
    (Sage Publications Ltd, 2021) Naveed, Ausnain; Sonmez, Sahin; 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.
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    Impact of load sharing schemes on the stability delay margins computed by Rekasius substitution method in load frequency control system with electric vehicles aggregator
    (Wiley, 2021) Naveed, Ausnain; Sonmez, Sahin; Ayasun, Saffet
    The impact of load sharing between the electric vehicles (EVs) aggregator and the conventional generator on stability delay margins in a two-area load frequency control (LFC) system is investigated in this work. A frequency-domain Rekasius substitution method is used to compute stability delay margins for different values of proportional-integral (PI) controller gains. The proposed method computes complex roots on the imaginary axis of the quasi-characteristic equation. The substitution first converts the quasi-characteristic equation of the LFC with EVs aggregator (LFC-EVs) system including delay-dependent exponential terms into an ordinary polynomial. Then, the Routh-Hurwitz stability method is applied to find those imaginary roots and the corresponding stability delay margins. The qualitative impact of different sharing schemes between the conventional generator and EVs aggregator and the impact of EVs gains on stability delay margins are thoroughly analyzed, and the results are validated by time domain simulations and quasi-polynomial mapping-based root finder algorithm. It is observed that for any given PI controller gains, stability delay margins decrease when the participation of EVs into the frequency regulation increases.
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    Optimization of PI Controller Gains using Genetic Algorithm for Time-Delayed Load Frequency Control Systems with Electric Vehicles Aggregator
    (IEEE, 2019) Naveed, Ausnain; Zerdali, Emrah; Sonmez, Sahin; Ayasun, Saffet
    This paper presents a genetic algorithm (GA) based approach to optimize controller gains for a single-area load frequency control system that includes an electric vehicles (EVs) aggregator and incommensurate communication time delays. Firstly, a stability boundary locus method is implemented to determine all stabilizing proportional integral (PI) controller gain that constitutes a stability region in the controller parameter space. A GA based optimization approach is then utilized to obtain an optimum set of controller gain that minimizes the mean square error of the deviation in the system frequency response. The effectiveness of the controller in retaining the desired frequency response is validated by time domain-simulation.
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    Stability Delay Margin Computation of Load Frequency Control System with Demand Response
    (IEEE, 2019) Katipoglu, Deniz; Sonmez, Sahin; Ayasun, Saffet
    This paper investigates the impact of dynamic demand response (DR) loop including a communication time delay on the stability delay margin of a single-area load frequency control (LFC) system considering both gain and phase margins (GPMs). A gain-phase margin tester (GPMT) is added to the DR loop of the LFC system as to include GPMs in the calculation of stability delay margins. A direct method in the frequency-domain is employed to compute stability delay margins in terms of system and controller parameters. For a large range of proportional - integral (PI) controller parameters, time delays for which LFC system with DR loop is both stable and has required stability margin quantified by GPMs are determined. Simulation results that delay margins should be computed by taking into account of both gain and phase margins to achieve faster damping of oscillations, less overshoot and settling time.
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    Stability Region in the Parameter Space of PI Controller for a Single-Area Load Frequency Control System With Time Delay
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2016) Sonmez, Sahin; Ayasun, Saffet
    This letter proposes a graphical method to compute the stabilizing values of proportional-integral (PI) controller parameters for a single-area load frequency control (LFC) system with time delay. The method is based on the stability boundary locus. The stability region is displayed in controller parameter space and time-domain simulation studies are carried to verify the accuracy and effectiveness of the proposed method.
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    Stability Regions in the Parameter Space of PI Controller for LFC System with EVs Aggregator and Incommensurate Time Delays
    (IEEE, 2019) Naveed, Ausnain; Sonmez, Sahin; Ayasun, Saffet
    This paper presents a graphical method to compute all stabilizing Proportional Integral (PI) controller gains of a single-area Load Frequency Control (LFC) system with Electric Vehicles (EVs) Aggregator and multiple incommensurate communication time delays. The proposed approach is based on extracting stability region and the stability boundary locus in the PI controller parameter space. For various values of communication time delays, stability regions are obtained and the accuracy of Complex Root Boundary (CRB) and Real Root Boundary (RRB) are verified by means of quasi-polynomial mapping-based root finder (QPmR) algorithm and time-domain simulations.
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    The effect of demand response control on stability delay margins of load frequency control systems with communication time-delays
    (Tubitak Scientific & Technological Research Council Turkey, 2021) Katipoglu, Deniz; Sonmez, Sahin; 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 proportional integral (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.