Browsing by Author "Kotian, S.M."

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A Novel Method for Calculating Steady-State Operating Conditions for DFIG-Based Wind Turbines
(Institute of Electrical and Electronics Engineers Inc., 2024) Lazar, A.; Navaneeth, K.; Kotian, S.M.
This paper utilizes a modified Newton-Raphson (MNR) iterative technique for steady-state initialization of doubly fed induction generator (DFIG)-based wind turbine (WT) connected to the grid. The MNR technique discussed in this paper is based on the Adomian decomposition method. The steady-state values obtained using the MNR method are compared with those obtained using the conventional Newton-Raphson (NR) method to check the accuracy of the MNR method. Further, the number of iterations taken for both methods to converge was compared. From the case studies, it is noted that the MNR method results in steady-state values, which are identical to those obtained using the NR method with lesser number of iterations. The steady-state values calculated using the MNR method are utilized to carry out the eigenvalue analysis and time-domain simulations of a DFIG-based WT power system. Â© 2024 IEEE.
A simulation-based analysis of subsynchronous resonance with TCSC
(Universitatea Politehnica din Timisoara blucretiu@yahoo.com, 2013) Batchu, S.; Kotian, S.M.; Shubhanga, K.N.
In this paper a time-domain simulation-based SSR analysis has been carried out in PSCAD/EMTDC employing the IEEE first-benchmark system with thyristor-controlled series capacitor (TCSC). Though torsionalmode detuning behavior of a TCSC is well known its tuning performance for certain firing angles is demonstrated employing modal-speed evaluations. An attempt has been made to understand this nature of TCSC by obtaining its frequency response characteristics using frequency scanning technique. From the results it is inferred that the equivalent impedance of TCSC offers fictitious resistive component leading to mode-detuning. However, it is observed that at higher values of firing angle the resistive behavior diminishes thus resulting in mode-tuning.
A toy model to understand subsynchronous resonance and real-time simulation of the model using RTAI-Linux
(Institute of Electrical and Electronics Engineers Inc., 2016) Kotian, S.M.; Latha, A.H.; Shubhanga, K.N.
This paper presents a toy- model to demonstrate the concepts of torsional interactions that occur during the subsynchronous resonance (SSR) problem in power systems.The content of the paper evolves as a tutorial and motivates a novice to take up SSR studies on relatively complex systems such as the IEEE first and second benchmark systems which contain many intricate modal interactions. To show the utility of the model and to impart a realistic touch in the lab environment the complete system is simulated in real-time using real-time application interface (RTAI)-enabled Linux platform. Using a peripheral component interconnect (PCI) card, the real-time simulation results are captured on an oscilloscope and are validated using off-line MATLAB simulations. Â© 2015 IEEE.
An Accurate Method for Steady State Initialization of Doubly Fed Induction Generator
(Institute of Electrical and Electronics Engineers Inc., 2022) Karthik, D.R.; Kotian, S.M.; Manjarekar, N.S.
In this paper, an accurate method for calculation of steady-state values of a doubly fed induction generator (DFIG) is proposed. The assumption of active power (P) and reactive power (Q) or terminal voltage (Vt) as constant variables at DFIG bus may not yield accurate results as wind speed is variable in nature. So, an initialization strategy considering input wind speed (Vw) as known variable, is employed in the present work, which is an accurate way to start with initialization. The approach followed in this paper also considers grid side filter losses, and non-zero reactive power flow through grid side converter (GSC). The steady-state values obtained from the approach followed in this paper is dynamically tested on SMIB system by conducting modal studies and time domain simulations. Â© 2022 IEEE
Analysis of Inter-area Oscillations-based Switching Attack in Large Power Systems
(Institute of Electrical and Electronics Engineers Inc., 2022) Bhatnagar, N.; Kotian, S.M.
Inter-area oscillations-based switching attack is the new class of cyber-physical attack on power systems. In this type of attack, the adversary first obtains the inter-area mode details through a measurement-based approach. Then the adversary perturbs the load(s) at inter-area frequencies. In this work, inter-area-based switching attack characteristics and their effects on large power systems are analyzed. The Prony method is employed to estimate the inter-area oscillation mode frequencies and damping factor. Inter-area switching attacks are analyzed in the 4-machine 2-area, 10-machine 3-area and 16-machine 5-area power systems. It is observed that the system is driven to instability faster when switching attack is applied on the loads that are in the vicinity of the generators which are participating in the least-damped inter-area modes. Â© 2022 IEEE.
Analytical design of static VAR compensator-based subsynchronous damping controller
(2018) Kotian, S.M.; Shubhanga, K.N.
In this paper, using a dynamic phasor model of static VAR compensator (SVC) a method to determine the phase response of a system analytically is presented. Then using the phase compensation method a subsynchronous damping controller (SSDC) for SVC is designed to mitigate subsynchronous resonance (SSR) in series capacitor compensated power systems. The designed SSDC is validated using detailed time-domain simulations in PSCAD/EMTDC. The case studies are carried out on the IEEE first benchmark system. � 2018 IEEE.
Analytical design of static VAR compensator-based subsynchronous damping controller
(Institute of Electrical and Electronics Engineers Inc., 2018) Kotian, S.M.; Shubhanga, K.N.
In this paper, using a dynamic phasor model of static VAR compensator (SVC) a method to determine the phase response of a system analytically is presented. Then using the phase compensation method a subsynchronous damping controller (SSDC) for SVC is designed to mitigate subsynchronous resonance (SSR) in series capacitor compensated power systems. The designed SSDC is validated using detailed time-domain simulations in PSCAD/EMTDC. The case studies are carried out on the IEEE first benchmark system. Â© 2018 IEEE.
Application of Wide-Area Power System Stabilizer for Damping of Inter-area Oscillations
(Springer Science and Business Media Deutschland GmbH, 2025) Navaneeth, K.; Kotian, S.M.
Inter-area oscillations (IAO) are a main concern for the stability of power systems. Conventional controllers used for IAO damping depend on local signals. Damping provided by such controllers is sometimes insufficient, as the controller does not have enough information of the inter-area modes from local signals. With extensive research and development in the field of wide-area measurement system (WAMS), signals from remote points of the system can be obtained and utilized along with local signals, thereby providing better damping for the inter-area modes. This brings with it its own set of challenges, from choosing the appropriate remote signal to be utilized to time delays due to measurement and transmission delays of the communication network. In this paper, a summary of the various works that have been carried out by researchers, pertaining to development of wide-area control (WAC) for various power system devices, mainly wide-area power system stabilizer (PSS) for synchronous generators is discussed. The wide-area PSS is used in a two-area, four-machine power system, and itâ€™s effectiveness in damping out IAO is demonstrated. Eigenvalue analysis is carried out. Time-domain simulations are used to validate the eigen-inferences. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Computation of steady-state operating conditions of a DFIG-based wind energy conversion system considering losses
(Springer Science and Business Media Deutschland GmbH, 2023) Karthik, D.R.; Manjarekar, N.S.; Kotian, S.M.
In this paper, steady-state operating conditions of a doubly fed induction generator (DFIG) are computed considering losses of grid-side (GS) filter. Two different cases are studied for steady-state initialization of the DFIG-based wind turbine systems (WTS). In the first case, active power (P) and reactive power (Q) at DFIG terminals are assumed to be known. In the other case wind speed (Vw), Q is assumed to be known. Apart from considering losses of the DFIG and GS filter, both the cases also consider the non-unity power factor operation of the grid side converter (GSC). For the first case, steady-state operating conditions are calculated by iterative method as well as by non-iterative method. For the second case, iterative method is used to calculate steady-state operating conditions. Calculation of steady-state values of other subsystems of DFIG-based WTS like drive train, controller and network is also shown. The initial values calculated are validated and compared by performing modal analysis and time-domain simulations. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Design of a subsynchronous damping controller using a dynamic phasor-based model of TCSC
(2016) Kotian, S.M.; Shubhanga, K.N.
In this paper, a dynamic phasor-based continuous-time model of thyristor-controlled series capacitor (TCSC) has been used to obtain the phase-response characteristic of a system, analytically. This in-turn enables the usage of the well-known phase compensation technique to design a supplementary subsynchronous damping controller (SSDC). It is found that at higher series compensation levels, the design depends on the quiescent firing angles of the TCSC. Through case studies it is shown that the method offers a reliable and systematic approach to design SSDC with ease. All results are validated using detailed time-domain simulations in PSCAD/EMTDC. � 2016 IEEE.
Design of a subsynchronous damping controller using a dynamic phasor-based model of TCSC
(Institute of Electrical and Electronics Engineers Inc., 2016) Kotian, S.M.; Shubhanga, K.N.
In this paper, a dynamic phasor-based continuous-time model of thyristor-controlled series capacitor (TCSC) has been used to obtain the phase-response characteristic of a system, analytically. This in-turn enables the usage of the well-known phase compensation technique to design a supplementary subsynchronous damping controller (SSDC). It is found that at higher series compensation levels, the design depends on the quiescent firing angles of the TCSC. Through case studies it is shown that the method offers a reliable and systematic approach to design SSDC with ease. All results are validated using detailed time-domain simulations in PSCAD/EMTDC. Â© 2016 IEEE.
Design of Wide Area Controllers for Synchronous Generators
(Institute of Electrical and Electronics Engineers Inc., 2024) Navaneeth, K.; Kotian, S.M.
Inter-area oscillations (IAO) affect power system stability and power transfer capability. In order to damp out these oscillations, damping controllers such as power system stabilizers and other such controllers are used. However, conventional controllers rely on local signals of the device on which they are mounted in order to provide control action. These local signal based controllers may not be effective in damping out such oscillations. Therefore, wide area controllers were proposed. This has been made possible due to the research and development that has taken place in the area of wide area measurement systems (WAMS).These controllers, which utilise remote signals, have the necessary observability of the inter-area modes in order to dampen out those modes effectively. The use of remote signals, however, introduces non-negligible time delays. This may lead to getting undesirable and even counter-productive effects from the controller. Therefore, during the design of wide area controllers, care must be taken in order to properly compensate for time delays. In this paper, the design process of a wide area controller for synchronous generator is presented. The wide area controller designed is used in a two area, four machine power system and it's effectiveness in damping out IAO is demonstrated. The effect of time delays on the controller performance is explored. Additional compensation for time delay effects are discussed. Eigenvalue analysis is carried out and time-domain simulations are used to validate the eigen-inferences. Â© 2024 IEEE.
Dynamic phasor modelling and simulation
(2016) Kotian, S.M.; Shubhanga, K.N.
In this paper, the basics of dynamic phasor (DP) modelling has been introduced by employing a simple RL-series circuit. In the example, the actual time-domain simulation and the DP-based simulation are presented in addition to the eigenvalue analysis of the RL-circuit in the DP-domain. With this introduction, following a systematic procedure, the DP-model of a static VAr compensator (SVC) which involves periodic switchings, is derived. To verify this model, a case study with an SVC in the IEEE first benchmark system for subsynchronous resonance (SSR) study has been simulated. The simulation results are also compared with those obtained using a susceptance model for SVC. A PSCAD/EMTDC-based detailed simulation demonstrated that the DP-model offers good-enough accuracy with much less computational effort. � 2015 IEEE.
Dynamic phasor modelling and simulation
(Institute of Electrical and Electronics Engineers Inc., 2016) Kotian, S.M.; Shubhanga, K.N.
In this paper, the basics of dynamic phasor (DP) modelling has been introduced by employing a simple RL-series circuit. In the example, the actual time-domain simulation and the DP-based simulation are presented in addition to the eigenvalue analysis of the RL-circuit in the DP-domain. With this introduction, following a systematic procedure, the DP-model of a static VAr compensator (SVC) which involves periodic switchings, is derived. To verify this model, a case study with an SVC in the IEEE first benchmark system for subsynchronous resonance (SSR) study has been simulated. The simulation results are also compared with those obtained using a susceptance model for SVC. A PSCAD/EMTDC-based detailed simulation demonstrated that the DP-model offers good-enough accuracy with much less computational effort. Â© 2015 IEEE.
Large-Signal Performance of Synchronous Machine Models in Power Systems
(2017) Kotian, S.M.; Shubhanga, K.N.
In this paper, the IEEE-specified generator models such as the equivalent circuit (EC) models and the operational inductance (OI) models are compared to analyze the influence of the differences in the standard transfer functions among these models on the large-disturbance rotor-angle stability (or transient stability) of the power system. The large disturbances such as unsymmetrical and symmetrical short-circuit faults are considered. Critical clearing time (CCT) corresponding to first swing stability is evaluated for each of the models and compared. Such a study is of major importance when comparing results obtained using different commercial grade packages. � 2016 IEEE.
Large-Signal Performance of Synchronous Machine Models in Power Systems
(Institute of Electrical and Electronics Engineers Inc., 2017) Kotian, S.M.; Shubhanga, K.N.
In this paper, the IEEE-specified generator models such as the equivalent circuit (EC) models and the operational inductance (OI) models are compared to analyze the influence of the differences in the standard transfer functions among these models on the large-disturbance rotor-angle stability (or transient stability) of the power system. The large disturbances such as unsymmetrical and symmetrical short-circuit faults are considered. Critical clearing time (CCT) corresponding to first swing stability is evaluated for each of the models and compared. Such a study is of major importance when comparing results obtained using different commercial grade packages. Â© 2016 IEEE.
Performance of synchronous machine models in a series-capacitor compensated system
(Institute of Electrical and Electronics Engineers Inc., 2014) Kotian, S.M.; Shubhanga, K.N.
This paper compares the IEEE-specified generator models such as the equivalent circuit (EC) models and the operational inductance (OI) models to understand their damping performances in the IEEE first-benchmark system for subsynchronous resonance study. These models are found to differ from one another only to an extent they accurately represent the standard transfer functions. By carrying out different case studies an effort is made to analyze the influence of these differences among the models on the damping performance of swing-mode and torsional modes. Through a detailed eigenvalue analysis and time-domain simulations, it is demonstrated that these models offer differing results with respect to swing-mode, thereby strongly influencing the power system stabilizer (PSS) performances, especially when the system is series compensated. Even the torsional mode interactions are found to exhibit dependency on the models employed for the generators. Such a study is expected to provide better insight into the behavior of generator models and controller design/tuning in system analysis. © 1969-2012 IEEE.
Stability Analysis of a Grid-Connected DFIG Operating in Sub-synchronous and Super-synchronous Conditions
(Institute of Electrical and Electronics Engineers Inc., 2022) Lazar, A.; Kotian, S.M.
This paper examines the impact of power grid strength, power level, rotor side converter (RSC) controller parameters, and shaft parameters on the small-signal stability of a doubly fed induction generator (DFIG)-integrated power system. In each of the parametric variations, both sub-and super-synchronous operating conditions of DFIG are considered. Using the eigenvalue technique the effects of parameter are analyzed and these eigen-inferences are further validated using time-domain simulations. From the analysis it is observed that the in sub-synchronous operating point, weak-grid conditions and RSC controller parameters may result in small-signal instability. Â© 2022 IEEE.
Steady-state Initialization of Doubly Fed Induction Generator Based Wind Turbine Considering Grid Side Filter
(IEEE Computer Society, 2021) Karthik, D.R.; Kotian, S.M.; Manjarekar, N.S.
In this paper, a steady-state initialization method for a doubly fed induction generator (DFIG) based wind turbines including grid side (GS) filter equations is discussed. The approach employed considers factors like non-zero grid side converter (GSC) reactive power and GS filter losses. As per the recent grid code requirements, DFIG should be able to participate in reactive power support to maintain voltage stability during faults. Also GSC acts as STATCOM by its structure and supports in damping inter-area oscillations. Above conditions mandates to consider the non-unity power factor operation of GSC. The approach employed also considers GS filter losses, by which an accurate initial values can be obtained. Dynamic evaluation of the steady-state values obtained are performed using eigenvalues and time-domain simulations. The studies are performed on a single-machine-infinite-bus (SMIB) system and the results are compared with dynamic results with a case wherein GS currents are considered as dummy states. Â© 2021 IEEE.
A toy model to understand subsynchronous resonance and real-time simulation of the model using RTAI-Linux
(2016) Kotian, S.M.; Latha, A.H.; Shubhanga, K.N.
This paper presents a toy- model to demonstrate the concepts of torsional interactions that occur during the subsynchronous resonance (SSR) problem in power systems.The content of the paper evolves as a tutorial and motivates a novice to take up SSR studies on relatively complex systems such as the IEEE first and second benchmark systems which contain many intricate modal interactions. To show the utility of the model and to impart a realistic touch in the lab environment the complete system is simulated in real-time using real-time application interface (RTAI)-enabled Linux platform. Using a peripheral component interconnect (PCI) card, the real-time simulation results are captured on an oscilloscope and are validated using off-line MATLAB simulations. � 2015 IEEE.