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The paper proposes a WADC approach using CART technique to dampen inter-area oscillations (IAOs) in bulk power systems. In this case, PMU data are filtered to estimate inter-area dynamics in which using pade approximation, a pole-zero IAO compensation block is designed. An online random decrement technique is also developed to identify the coherent groups and damping ratios to activate the WADC for oscillation damping. An offline process is provided to identify 200 critical IAO contingencies and tunes WADC gains using PSO for training CARTs via a set of 200 input inter-area signals and assigning output controlling gains pre-trained data and evaluating the CART estimations through online operation. The WADC approach is validated for oscillation damping on a 39-bus system and a realistic 561-generator Iranian grid. Simulations show 98 % accuracy in achieving sufficient damping ratios (>0.6) across various operating conditions. • A new approach based on WADC is proposed for damping inter-area oscillations. • A new scheme based on individual WADC for each generator is proposed. • CART technique is used for estimating optimal gains of individual WADC controller. • A combination index is proposed to find the most effective individual WADCs. [ABSTRACT FROM AUTHOR]

This paper introduces a reinforcement learningbased controller, utilising the deep deterministic policy gradient (DDPG) method, to mitigate low-frequency disturbances in electrical grids with renewable energy sources. It features a novel reward function inversely related to the control error and employs a state vector comprising absolute and integral errors to enhance error reduction. The controller, tested on a dualregion system with solar power, utilises phasor measurement unit (PMU) data for global inputs. Its performance is validated through time-domain simulations, pole-zero mapping, modal analysis, frequency response, and participation factor mapping, using a custom MATLAB and Simulink toolkit. The design accounts for communication delays and adapts to variable conditions, which proves to be effective in reducing oscillations and improving system stability. [ABSTRACT FROM AUTHOR]

This article aims at designing a robust wide-area damping controller (WADC) to address the problems associated with communication failures. The proposed controller is a state feedback-based controller, which uses generators' states as the controller inputs. The structure of the proposed controller's feedback gain matrix is a combination of two feedback gain matrices to achieve adequate robust performance over different disturbances and communication losses. These two feedback gain matrices are; full-scale feedback gain matrix and decentralized scale feedback gain matrix. Both models are designed by considering all generators' states are available at the controller input side. However, both matrices' structures are different from each other. The conventional LQR state feedback control technique is used to design the full-scale matrix. On the other hand, the decentralized scale matrix is computed using a structurally constrained H 2 -norm optimization technique to acquire the required structure. The full-scale model gives robust performance under different faults. Whereas, the decentralized scale matrix will result robust performance against communication failures. Therefore, to achieve superior performance under all conditions, the proposed controller can be used. To show the efficacy of the proposed controller, it is compared with different existing controllers and the results are illustrated. Simulation studies are conducted on well-known IEEE 39-bus and 68-bus test systems to validate the robustness of the proposed controller considering different faults and communication failures. [ABSTRACT FROM AUTHOR]

This paper presents a new scheme of controlling inter-area oscillation consisting of a wide-area controller and critical inter-area angle index as controlled islanding criteria. For this purpose, based on the wide area measuring system, the correlation factor between all Synchronous Generator (SG) pairs is calculated and the coherent synchronous generators are determined. In this case, by identifying two oscillating areas, the inter-area oscillation is evaluated in the center of inertia frame which is used as the global inter-area signal through the proposed Wide Area Controller (WAC) scheme. Also, for estimating the inter-area damping ratio, a random decrement technique is proposed which by evaluating Global Inter-Area Signal (GIS) signals through consecutive time windows, the Inter-area Damping Ratio (IDR) signals are evaluated. In the case of identifying an unstable IDR, by evaluating the GIS signal and identifying the GIS zero crossing points as the Critical Inter-area Angle (CIA) tripping index, the corresponding emergency action (islanding/damping) is determined. The proposed approach is an online and non-model-based scheme in which by evaluating GIS signals through consecutive time windows, the system’s dynamic securities and emergency actions are provided. The effectiveness of the proposed scheme is evaluated on the IEEE 39-bus system indicating positive effects through damping the inter-area oscillation.

In interconnected modern power systems, renewable energy sources, HVDC transmission lines, and energy storage devices are growing after being installed globally with development in power electronics and communication technology. Low-frequency inter-area oscillations (0.2–0.8 Hz) have a severe influence on the operation of an interconnected power system due to the numerous generators. This paper provides a comprehensive literature review of the wide-area measurement system-based wide-area damping control systems with operational uncertainties, including signal communication effects, such as time delay, packet loss, noise, and disorder, , on damping control performance. Different wide-area damping control techniques are investigated, emphasizing their advantages inadequacies and categorized according to vital features. In recent years, the resilience of wide-area damping control systems to cyber-physical attacks has recently been brought back to the researcher's consideration because of the opportunities produced by information-communication technologies and the renewed interest in installing renewable energy sources. This paper provides recent developments in methods of damping performance enhancement that deserve further study in cyber-physical power systems. Overall, the present study is helpful for academicians and researchers to identify the objectives in the area of cyber-physical power systems to enhance the wide-area damping performance. [ABSTRACT FROM AUTHOR]

Abstract This paper examines how the combined use of hydro governors and a wide‐area damping controller (WADC) can improve the damping of inter‐area oscillations in power systems. Such oscillations can endanger the stability of power grids, thus damping them is a high priority for transmission system operators (TSO). To ensure that low‐frequency oscillations decay as fast as possible, a modal linear quadratic Gaussian (LQG) is proposed as a wide‐area controller approach. Using the 10‐machine New England Test System, the combined application of the WADC in hydropower plants via generator excitation as well as via the hydro governor is examined for their effectiveness in terms of damping capability. In order to minimize the number of essential PMUs in power systems for the model‐based WADC, the residue‐based input/output signal selection method is applied. To increase the robustness against large disturbance faults, the generator voltage as additional signal is utilized for the WADC. For controller performance and robustness, the verification has been done under various operating points, tie‐line failures as well as different PMU delays. The successful damping of the inter‐area oscillation by means of wide‐area controlled hydropower plants has been also demonstrated through a nonlinear time domain simulation.

Abstract This paper presents an online protective scheme of estimating critical inter‐area angle for controlling the inter‐area oscillations based on evaluating the rate of changes of rotor angle oscillations as an adaptive tripping index (ATI)‐based protective zone. For this purpose, by using wide area measuring system technology, oscillatory signals Δδ and Δω are measured which based on correlation coefficients criteria, coherent groups are identified which based on evaluating oscillating areas, inter‐area signals ΔδCOI‐AB and ΔωCOI‐AB are provided. In the case of evaluating an inter‐area oscillation, the proposed ATI scheme is activated which the first zero crossing point (ZCP0) of δCOI‐AB is determined as the critical criteria for estimating unstable situation. The proposed ATI approach consists of two adaptive protective zones ATI1 and ATI2 to estimate inter‐area oscillatory and inter‐area transient instabilities, respectively. The proposed ATI is an online and non‐model‐based scheme which evaluates the system dynamic stability through two straight and sinusoidal‐based adaptive zones. The effectiveness of the proposed ATI approach is evaluated on three different test systems IEEE 39‐bus, modified IEEE 39‐bus with converter‐based low inertia sources and a practical Iran nation power grid with presenting positive effects of damping inter‐area oscillations through different operational and topological conditions.

In the last decades, various events have shown that electromechanical oscillations are a major concern for large interconnected Alternative Current (AC) power systems. DC segmentation - a method that consists in turning large AC grids into a set of asynchronous AC clusters linked by Direct Current (DC) links - is a promising solution to mitigate this and other issues. However, no systematic segmentation procedure for a given AC power system exists so far. This paper aims at filling this gap and proposes an algorithm for DC segmentation for a given AC power system to mitigate electromechanical oscillations. In this proposal, DC segmentation is implemented with High Voltage Direct Current links based on Voltage Source Converters (VSC-HVDC). The algorithm uses small-signal stability techniques and the concept of dominant inter-area oscillation paths to eliminate the main inter-area mode of the power system. The algorithm will be explained using a six-generator test system and will then be used on the Nordic 44 test system. The proposed algorithm for DC segmentation has been validated by means of non-linear time-domain simulation and small-signal stability analysis (SSSA).

This paper presents an online scheme of intelligent wide area damping controller based on decision tree (DT) technique using wide area measuring system. In this case, a central damping controller is developed which uses the speed and angle deviations of the oscillating areas as global signals. For this issue, the proposed DT scheme plays as an online gain estimator estimates the controlling gains for direct presentation to exciter systems. The proposed intelligent controller is a non-model and online scheme which plays as global power system stabilizer through real-time environment. In the case of optimizing global controlling signals, considering a set of unstable inter-area oscillations, the proposed DTs are trained off-line which by using inter-area signals in working mode, online controlling gains are estimated. The effectiveness of the proposed control scheme is carried out in the modified IEEE 39-bus test system with indicating positive effects for damping inter-area oscillations.

Communication failures and transmission delays are two major issues associated with Wide-Area Damping Controllers (WADCs). While transmission delays have been extensively studied and various solutions have been proposed, little research has been done on communication failures and most of the proposed methods are based on preventive controls. However, in today’s liberalized electricity markets, preventive controls are no longer acceptable and the trend is to use emergency controls instead. This paper proposes a novel emergency control scheme to counteract the loss of remote signals related to the input and to the output of the WADC (i.e., sensor and actuator failures). The proposed scheme is based on a simple criterion, which overcomes the complexity of the previous methods. Modal analysis and time domain simulations are performed to verify the performance of the proposed method. The simulation results show that the proposed method performs well in handling communication failures and can maintain good damping performance. This research work is particularly important in view of the trend towards the wide-scale adoption of wide-area measurement technologies, while the vulnerability to cyber-attacks is increasing.

This paper examines how the combined use of hydro governors and a wide‐area damping controller (WADC) can improve the damping of inter‐area oscillations in power systems. Such oscillations can endanger the stability of power grids, thus damping them is a high priority for transmission system operators (TSO). To ensure that low‐frequency oscillations decay as fast as possible, a modal linear quadratic Gaussian (LQG) is proposed as a wide‐area controller approach. Using the 10‐machine New England Test System, the combined application of the WADC in hydropower plants via generator excitation as well as via the hydro governor is examined for their effectiveness in terms of damping capability. In order to minimize the number of essential PMUs in power systems for the model‐based WADC, the residue‐based input/output signal selection method is applied. To increase the robustness against large disturbance faults, the generator voltage as additional signal is utilized for the WADC. For controller performance and robustness, the verification has been done under various operating points, tie‐line failures as well as different PMU delays. The successful damping of the inter‐area oscillation by means of wide‐area controlled hydropower plants has been also demonstrated through a nonlinear time domain simulation. [ABSTRACT FROM AUTHOR]

This paper presents an online protective scheme of estimating critical inter‐area angle for controlling the inter‐area oscillations based on evaluating the rate of changes of rotor angle oscillations as an adaptive tripping index (ATI)‐based protective zone. For this purpose, by using wide area measuring system technology, oscillatory signals Δδ and Δω are measured which based on correlation coefficients criteria, coherent groups are identified which based on evaluating oscillating areas, inter‐area signals ΔδCOI‐AB and ΔωCOI‐AB are provided. In the case of evaluating an inter‐area oscillation, the proposed ATI scheme is activated which the first zero crossing point (ZCP0) of δCOI‐AB is determined as the critical criteria for estimating unstable situation. The proposed ATI approach consists of two adaptive protective zones ATI1 and ATI2 to estimate inter‐area oscillatory and inter‐area transient instabilities, respectively. The proposed ATI is an online and non‐model‐based scheme which evaluates the system dynamic stability through two straight and sinusoidal‐based adaptive zones. The effectiveness of the proposed ATI approach is evaluated on three different test systems IEEE 39‐bus, modified IEEE 39‐bus with converter‐based low inertia sources and a practical Iran nation power grid with presenting positive effects of damping inter‐area oscillations through different operational and topological conditions. [ABSTRACT FROM AUTHOR]

This manuscript reports the first step towards building a robust and efficient model reduction methodology to capture transient dynamics in a transmission level electric power system. Such dynamics is normally modeled on seconds-to-tens-of-seconds time scales by the so-called swing equations, which are ordinary differential equations defined on a spatially discrete model of the power grid. Following Seymlyen (1974) and Thorpe, Seyler, and Phadke (1999), we suggest to map the swing equations onto a linear, inhomogeneous Partial Differential Equation (PDE) of parabolic type in two space and one time dimensions with time-independent coefficients and properly defined boundary conditions. We illustrate our method on the synchronous transmission grid of continental Europe. We show that, when properly coarse-grained, i.e., with the PDE coefficients and source terms extracted from a spatial convolution procedure of the respective discrete coefficients in the swing equations, the resulting PDE reproduces faithfully and efficiently the original swing dynamics. We finally discuss future extensions of this work, where the presented PDE-based modeling will initialize a physics-informed machine learning approach for real-time modeling, $n-1$ feasibility assessment and transient stability analysis of power systems.

We investigate coherent oscillations in large scale transmission power grids, where large groups of generators respond in unison to a distant disturbance. Such long wavelength coherent phenomena are known as inter-area oscillations. Their existence in networks of weakly connected areas is well captured by singular perturbation theory. However, they are also observed in strongly connected networks without time-scale separation, where applying singular perturbation theory is not justified. We show that the occurrence of these oscillations is actually generic. Applying matrix perturbation theory, we show that, because these modes have the lowest oscillation frequencies of the system, they are only moderately sensitive to increased network connectivity between well chosen, initially weakly connected areas, and that their general structure remains the same, regardless of the strength of the inter-area coupling. This is qualitatively understood by bringing together the standard singular perturbation theory and Courant’s nodal domain theorem.

This paper presents an adaptive wide-area control strategy based on energy function. The proposed method enhances the post-fault oscillation damping capability of Static Var Compensators (SVC) by incorporating load dynamics in the wide-area controller design that adapts to load variations. The load dynamics are obtained using Phasor Measurement Units (PMU) through load power and voltage data measurements, which are used to estimate a Moving Average (MA) dynamic load model. The obtained load model is then integrated into the wide-area controller to obtain the required SVC supplementary control action which modulates the load power in response to a disturbance based on inter-area dynamics obtained by employing a nonlinear Kalman filter and PMU measurements. The performance of the proposed strategy is evaluated on the simplified 14 generator model of the southeast Australian power system by using composite load models comprised of induction motor loads of various sizes and combinations. The obtained results show significant improvements in the system stability when the proposed control strategy is applied.

Modern power systems are witnessing a noticeable increase in the integration of low-inertia renewable sources which require robust control schemes to damp out low-frequency oscillations emerged by this expansion. This paper proposes a reinforcement learning (RL)-based controller using a deep deterministic policy gradient (DDPG) algorithm to damp inter-area oscillations. The learning process of the controller is enhanced using a discrete reward-function which is selected to be a reciprocal function of the input error. To allow the agent to drive the total error lower and lower, both the absolute error and integral of error are included in the observation state vector. A two-area system with a solar plant integrated is used as the test system. The controller obtains its global input signal from PMU devices in wide-area measurement systems using frequency information. A comprehensive analysis is presented using several analytical control tools including time-domain simulation, pole-zero plot, mode shape, frequency response, and participation factor map. Furthermore, a package of programs has been developed for this study using MATLAB and Simulink. The communication latency is also included in the design of the controller considering constant and variable practical values of latency. The proposed controller demonstrates its effectiveness in damping inter-area oscillation and improving the system stability. [ABSTRACT FROM AUTHOR]

Improving the stability of power systems using FACT devices is an important and effective method. This paper uses a static synchronous series compensator (SSSC) installed in a power system to smooth out inter-area oscillations. A meta-heuristic optimization method is proposed to design the supplementary damping controller and its installation control channel within the SSSC. In this method, two control channels, phase and magnitude have been investigated for installing a damping controller to improve maximum stability and resistance in different operating conditions. An effective control channel has been selected. The objective function considered in this optimization method is multi-objective, using the sum of weighted coefficients method. The first function aims to minimize the control gain of the damping controller to the reduction of control cost, and the second objective function moves the critical modes to improve stability. It is defined as the minimum phase within the design constraints of the controller. A hybrid of two well-known meta-heuristic methods, the genetic algorithm (GA) and grey wolf optimizer (GWO) algorithm have been used to design this controller. The proposed method in this paper has been applied to develop a robust damping controller with an optimal control channel based on SSSC for two standard test systems of 4 and 50 IEEE machines. The results obtained from the analysis of eigenvalues and nonlinear simulation of the power system study show the improvement in the stability of the power system as well as the robust performance of the damping in the phase control channel. [ABSTRACT FROM AUTHOR]

Being the primary cause of inter-area oscillations and due to the fact that they limit the generation's output, Low-Frequency Electromechanical Oscillations (LFEOs) represent a real threat to power system networks. Mitigating their effects is therefore crucial as it may lead to system collapse if not properly damped. As rotor angle instability is the primary cause of LFEOs, this paper presents a novel Model-Reference Adaptive Control (MRAC) scheme that enhances its stability. The proposed scheme is tested using the Single-Machine Infinite Bus (SMIB) network. The results obtained validate the proposed decentralized control architecture. The robustness of this oscillation damping controller is verified through simulations in MATLAB/SIMULINK. With Gaussian noise added to the structure of the generator to emulate small load variations responsible for the rotor angle instability, the results of the simulations show that the rotor angle remains stable. Furthermore, when subjected to faults, the recovery time is less than 500 ms. [ABSTRACT FROM AUTHOR]

It is vital that the synchronous generator rotor angle be kept stable to avoid disastrous consequences such as the loss of synchronism amongst generators within a power system network. Once it is unstable, the time that is taken to remedy this is advised to be 5–10 s for smaller power systems and 15–20 s for larger ones. The instability that is caused by poorly damped Low-Frequency Electromechanical Oscillations (LFEOs) may result in inter-area oscillations, where a group of generators in one area oscillates against those in another area, thus affecting the stability of the entire network. This paper explores two control architectures, namely, a nonlinear Lyapunov-based trajectory tracking controller and a Model Reference Adaptive Controller (MRAC) as options to enhance the stability of the rotor angle. The performance of each of these controllers was assessed under steady-state conditions, and then, the synchronous generator was subjected to Gaussian noise and an impulse. While the first one is aimed at emulating small variations in the system loads that are responsible for inter-area oscillations, the latter one is an attempt to explore their performance for transient stability. [ABSTRACT FROM AUTHOR]

The increasing deployment of new technologies to contribute to the decarbonization of power systems is imposing new challenges in terms of system dynamics and stability. To deal with different operating and control issues in this sense, and support actual needs, advanced tools and solutions are required. Therefore, this paper presents a digital twin of a dynamic hardware emulator that can be used for controller hardware in the loop (CHIL) testing and is based on a small-scale laboratory system. To build the simulation model, the parameters of involved synchronous machines, excitation systems, prime movers and transmission lines have been identified and then compared to laboratory measurements to assess the accuracy of the digital twin. Static and dynamic accuracy have been investigated and an overall good accuracy can be shown with the help of quantification of errors. Furthermore, a case study is presented where the digital twin was used to design a controller to damp inter-area oscillations with the help of wide area measurements. This controller was then implemented and tested within the dynamic hardware emulator in the laboratory. [ABSTRACT FROM AUTHOR]

This article presents a perturbation observer–based robust nonlinear damping control (RNDC) scheme for a doubly fed induction generator (DFIG)–based wind farm to damp the inter-area oscillations of multi-area power systems. In the RNDC scheme, the perturbation term is introduced to describe the combined effects of nonlinearities, uncertainties, and disturbances of multi-area power systems with wind farms. The feedback linearization control is realized for reactive power control loops of the DFIG based on state estimation and perturbation estimation derived from a perturbation observer, thus achieving the damping control of the DFIG. The proposed RNDC scheme only needs one measurement signal, and it does not require any model parameters of the power grid and wind farm. Simulation studies are carried out on a two-area power system model connected with the wind farm to validate the control performance of the RNDC scheme under the conditions of three-phase-to-ground faults, parameter variations, and time delays.

Abstract Inter-area oscillations are, by far, the most detrimental oscillation category to the integrity of synchronously interconnected power systems. Inter-area oscillations are characterized by the inherent weak damping. The inherent poor damping associated with the inter-area oscillations leaves open wide probabilities for irrevocable widespread blackouts with the consequent eventual devastating outcomes measured in terms of the huge economic casualties and the possible human fatalities. The main purpose of this work is to mitigate inter-area power oscillations. This article explores the effectiveness of dual thyristor controlled braking resistor units with Interval Type-2 fuzzy-based centralized architecture for neutralizing the jeopardy of inter-area power oscillations in Kundur’s two-area test system using MATLAB™/Simulink environment. The effectiveness of the proposed scheme is examined by considering four case studies with different degrees of severity. The simulation results show that the proposed scheme is simple yet effective in treating the inter-area oscillations appropriately under the considered case studies.

Forced Oscillations can occur even for a power system with good damping performance. With increasing high penetration of renewable energy generation towards 100% renewable generation in the power grid, exploitation of future control potential from wind turbines becomes inevitable. This paper develops an isolation and suppression method of Forced Oscillations by using wind farms (WFs) under both grid-following and grid-forming control principles. The proposed method controls a WF to absorb or release active and reactive power in a timely manner and as a result Forced Oscillations are prevented from spreading to the rest of the power grid and hence they are isolated. The Forced Oscillations of the disturbed area, which is bounded by the location of WF installation, are also reduced and suppressed. The proposed method is easy to implement and economically effective as there is no requirement of extra energy storage and power electronic devices, and a prior knowledge of the frequency of Forced Oscillations is not required. With the proposed control method, the loss of wind power capture is negligible. Furthermore, the control method is also able to damp natural oscillations. Simulations of both doubly fed induction generator (DFIG)-, and permanent magnetic synchronous generator (PMSG)-based WFs under either grid-following or grid-forming control principle, with constant or varying wind speeds and different WF locations with respect to the source of Forced Oscillations, on the modified two-area and IEEE 39-bus power systems, using Real-time Digital Simulator (RTDS) and Dymola, are used to verify the effectiveness of the proposed method.

In power systems, identification and damping of low-frequency oscillations(LFO) is very crucial to maintain the small signal stability. Hence the computation of eigenvalues, eigenmode shapes, participation factors, and coherency of generators are essential parameters of critical LFO modes. The existing data-driven approaches explore either one or two aspects of modal parameters from the dynamic pattern of the measurement data. In the present work, two approaches i) Iterative Approach(IA) ii) Non-Iterative Subspace(SS) method of data-driven techniques are used to estimate the state-space model of the system under study from the measurement data in a holistic framework. Based on the estimated system model, the eigenvalues of LFO, eigenmode shapes, participation factor, and coherency of associated generators participating in electromechanical oscillations are computed. Finally, from the estimated participation factors for the Inter-area oscillation mode (IAM), the Static Synchronous Compensator (STATCOM) damping controller is designed and placed at the generator with the highest participation factor for damping of inter-area oscillation. The enhancement of damping ratio of inter area mode with STATCOM damping controller is estimated and verified using IA & SS data driven approaches for the first time. In this work, IA uses prediction-error minimization algorithm (PEM) & Parallel computing techniques and SS method uses Multivariable Output Error State Space (MOESP) algorithm for the estimation of Hankel matrix from the measured data. The effectiveness of data-driven approaches are demonstrated by the simulation of a IEEE 4-machine,10-bus power system using MATLAB/Simulink. IA & SS methods incorporating wavelet based denoising techniques are very effective in identifying the LFO modes even with noisy measurement. The efficacy of the denoising to suppress the effect of noise is demonstrated by comparing with noiseless environment. The results of data-driven approaches indicate their high degree of accuracy and efficiency in being consistent with Eigenvalue analysis (EA) performed on the system.

This paper suggests an inter‐area oscillation suppressor based on second‐order sliding mode controller (SOSMC) for doubly fed induction generator (DFIG) to suppress the inter‐area power system oscillations. SOSMC‐based suppressor targets at improving the reactive power control capability of DFIG to retrieve the stability of affected power system caused by fault occurrence into the stable condition. This controller has been initially designed for two‐area power system, after that it has been extended for multi‐area power systems. SOSMC‐based suppressor has no sensitivity to the uncertainty and variation of the parameter in all system operation conditions as compared with the conventional suppressors. Due to exploration and exploitation capability of chaotic whale optimization algorithm (CWOA), it is applied as main optimizer to optimally tune the suppressor's parameters and merge with the dynamic stability scheme. This optimization algorithm is beneficial for complex dynamic stability problem, because during the iterative procedure, it can enhance the exploration capability to find the best solution. The optimization scheme based on CWOA has been compared with the conventional whale optimization algorithm (WOA) and particle swarm optimization (PSO). The suppressor damping capability has been evaluated with consideration of some possible disturbance scenarios. Furthermore, the objective function has been carried out based on the prominent dynamic performance criteria such as integral of time multiplied absolute error (ITAE), integral of absolute error (IAE), integral of squared error (ISE), and integral of time multiplied squared error (ITSE). Considering the various operating points, the SOSMC‐based suppressor ameliorates the system robustness as compared to the conventional suppressor. At last, the simulation results extracted from both interconnected power systems confirm the enhancement of power system operability and performance in suppression of the inter‐area oscillations, and also validate the robustness of the suggested control strategy against the model uncertainties and unmodeled dynamics. [ABSTRACT FROM AUTHOR]

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The wide-area controller (WAC) is used to damp out inter-area oscillations in the power system. Conventionally, to implement WAC in the power system, efficient wide-area communication channels are essential. The performance of the WAC can get degraded with under-performing communication channels. Although, the communication are begin made efficient and redundant, data integrity may pose another threat to the performance of the WAC. In order to subside the dependency on wide-area communication channel, this paper proposes a communication free wide-area controller (CF-WAC) to damp out inter-area oscillations even in the worst scenarios (in terms of communication channels). The CF-WAC is designed based on the state feedback principle and with limited states. The chosen design path can be achieved by using structurally constrained $H_{2}$ -norm optimization. The proposed CF-WAC is designed in a centralized manner and implemented in a decentralized way and yet retain the near conventional WAC performance. The performance of the proposed CF-WAC is compared with full-scale WAC (FS-WAC i.e., conventional WAC), sparsity-promoting WAC (SP-WAC), and reduced-scale WAC (RS-WAC). Simulation studies are carried out on the IEEE 68-bus test system to evaluate the potential of the CF-WAC in damping inter-area low-frequency oscillations by considering different disturbances and communication channel losses.

This paper introduces the concept of adaptive coordination of damping controllers for enhancing power system stability. The coordination uses phasor measurement units (PMUs) to adapt to different disturbances by selecting the switching status (on/off) of damping controllers that minimizes an energy-based dynamic performance measure. This dynamic performance measure, referred to as total action (TA), uses a physical interpretation of excited modes rather than fixed targeted modes as in the traditional damping control design. The coordination is formulated as a binary integer programming problem, which is solved by using the total action sensitivity (TAS). The concept of oscillation energy and the implementation of the adaptive coordination scheme is tested in the western North America power system (wNAPS). The results show that the proposed adaptive control scheme can improve oscillation damping for different short-circuit locations even in the presence of large communication delays.

It is vital that the synchronous generator rotor angle be kept stable to avoid disastrous consequences such as the loss of synchronism amongst generators within a power system network. Once it is unstable, the time that is taken to remedy this is advised to be 5–10 s for smaller power systems and 15–20 s for larger ones. The instability that is caused by poorly damped Low-Frequency Electromechanical Oscillations (LFEOs) may result in inter-area oscillations, where a group of generators in one area oscillates against those in another area, thus affecting the stability of the entire network. This paper explores two control architectures, namely, a nonlinear Lyapunov-based trajectory tracking controller and a Model Reference Adaptive Controller (MRAC) as options to enhance the stability of the rotor angle. The performance of each of these controllers was assessed under steady-state conditions, and then, the synchronous generator was subjected to Gaussian noise and an impulse. While the first one is aimed at emulating small variations in the system loads that are responsible for inter-area oscillations, the latter one is an attempt to explore their performance for transient stability.

Improving the stability of power systems using FACT devices is an important and effective method. This paper uses a static synchronous series compensator (SSSC) installed in a power system to smooth out inter-area oscillations. A meta-heuristic optimization method is proposed to design the supplementary damping controller and its installation control channel within the SSSC. In this method, two control channels, phase and magnitude have been investigated for installing a damping controller to improve maximum stability and resistance in different operating conditions. An effective control channel has been selected. The objective function considered in this optimization method is multi-objective, using the sum of weighted coefficients method. The first function aims to minimize the control gain of the damping controller to the reduction of control cost, and the second objective function moves the critical modes to improve stability. It is defined as the minimum phase within the design constraints of the controller. A hybrid of two well-known meta-heuristic methods, the genetic algorithm (GA) and grey wolf optimizer (GWO) algorithm have been used to design this controller. The proposed method in this paper has been applied to develop a robust damping controller with an optimal control channel based on SSSC for two standard test systems of 4 and 50 IEEE machines. The results obtained from the analysis of eigenvalues and nonlinear simulation of the power system study show the improvement in the stability of the power system as well as the robust performance of the damping in the phase control channel.

Being the primary cause of inter-area oscillations and due to the fact that they limit the generation’s output, Low-Frequency Electromechanical Oscillations (LFEOs) represent a real threat to power system networks. Mitigating their effects is therefore crucial as it may lead to system collapse if not properly damped. As rotor angle instability is the primary cause of LFEOs, this paper presents a novel Model-Reference Adaptive Control (MRAC) scheme that enhances its stability. The proposed scheme is tested using the Single-Machine Infinite Bus (SMIB) network. The results obtained validate the proposed decentralized control architecture. The robustness of this oscillation damping controller is verified through simulations in MATLAB/SIMULINK. With Gaussian noise added to the structure of the generator to emulate small load variations responsible for the rotor angle instability, the results of the simulations show that the rotor angle remains stable. Furthermore, when subjected to faults, the recovery time is less than 500 ms.

The new surge of interest towards mass integration of Electric Vehicles (EVs) in distribution smart grids can expose the high-voltage grid to instability conditions, for instance, through cyber threats initiated from the residential or public EV Supply Equipment (EVSE). This paper (i) investigates the impact of switching attacks on EV charging infrastructure and their impacts on the inter-area stability of the transmission grid, and (ii) proposes a two-stage detection and mitigation technique for those attacks. Initially, we demonstrate that leveraging the existing vulnerabilities in charging stations’ cyberspace and the topology of the grid, an adversary can switch the injected or absorbed power of EVs with inter-area frequency and cause a blackout by destabilizing the angular speed of the grid’s generators. Then, a Back Propagation Neural Network (BPNN) scheme is designed and hosted at the central management system (CMS) of a public EVSE network. Using this BPNN scheme, the switching attacks are accurately detected by analyzing the features of charging/discharging requests. Moreover, the detected attacks are mitigated by delaying or discarding the request execution. Finally, to cope with the conditions where the residential chargers are under-attack, or when the BPNN fails to provide accurate detection, a wide area $\text{H}^{\infty }$ controller is designed to keep the angular speed of the synchronous generators within the acceptable limits. The effectiveness of the proposed techniques is evaluated using two-area Kundur and 5-area Australian grids. [ABSTRACT FROM AUTHOR]

With the ever-growing complexity of a modern power system, decentralized control is becoming a more advantageous framework for maintaining its stable operation. Recently, some research work has been done on decentralized control for mitigating inter-area oscillations based on dynamic state estimation. This paper illustrates that in the decentralized control scheme, the use of dynamic state estimation can compromise controller performance and decrease the damping of inter-area oscillations. To address this problem, this paper proposes a cooperative-based supplementary excitation control strategy for damping inter-area oscillations using dynamic state information. By eigenvalue analysis, this paper reveals the relationship between the estimator's parameter and inter-area modes. Furthermore, communication is utilized in the proposed controller to neutralize the adverse impact of using dynamic state estimation on damping performance. The connection between the communication structure and inter-area modes is also analytically given. Finally, the well-known New England test system with 10 generators and 39 buses is employed to demonstrate the analytical results.

Wide-area damping controllers (WADCs) are effective means of improving the damping of inter-area oscillations and thereby ensuring a secure operation of modern highly stressed interconnected power systems; however, their implementation costs are high. Therefore, the controller must be well configured and designed to ensure its cost-effectiveness. Several techniques have been proposed in the literature to design effective controllers and good results have been achieved. However, some important practical aspects that could potentially impact the performance of the designed controller have not been addressed or studied in sufficient detail in these previous works. One such aspect is assessing the performance of the designed controllers under major system upsets resulting in large deviations in the frequency and fluctuations in the power. These may lead to controller saturation which could negatively impact its damping performance or even cause instability. In this paper, the impact of such large upsets is investigated on several test systems via extensive small- and large-signal analyses and it is shown that, during severe transients, controller saturation may occur and persist over a long period of time, posing a potential threat to the power system stability. This paper presents a very effective solution to alleviate this problem and help design more robust WADCs. The simulation results show that the proposed solution works well and leads to improved power system stabilisers performance during transient upsets. [ABSTRACT FROM AUTHOR]

The increasing deployment of new technologies to contribute to the decarbonization of power systems is imposing new challenges in terms of system dynamics and stability. To deal with different operating and control issues in this sense, and support actual needs, advanced tools and solutions are required. Therefore, this paper presents a digital twin of a dynamic hardware emulator that can be used for controller hardware in the loop (CHIL) testing and is based on a small-scale laboratory system. To build the simulation model, the parameters of involved synchronous machines, excitation systems, prime movers and transmission lines have been identified and then compared to laboratory measurements to assess the accuracy of the digital twin. Static and dynamic accuracy have been investigated and an overall good accuracy can be shown with the help of quantification of errors. Furthermore, a case study is presented where the digital twin was used to design a controller to damp inter-area oscillations with the help of wide area measurements. This controller was then implemented and tested within the dynamic hardware emulator in the laboratory.

The conception of electromechanical oscillations initiates in the power network when there is an installation of the generator in parallel with the existent one. Further, the interconnection of multiple areas, extension in transmission, capricious load characteristics, etc. causes low-frequency oscillations in the consolidated power network. This paper proposes variants of a booming population-based grey wolf optimization (GWO) algorithm in the tuning of power system stabilizer parameters of a multi-machine system in damping low-frequency oscillations. The parameters have been tuned by framing an objective function considering the improving damping ratios for the system states with lesser damping ratios and shifting the system eigenvalues towards the left-hand side of s-plane for the improved settling characteristics for the oscillations in the system. The requisites of stabilizer strategy are mapped with the hallmarks of prevalent algorithms and designed hybrid versions of GWO for the enhancement of the multi-machine power system stability. Four variants of GWO technique are nominated based on the competent stabilizer performance namely, modified grey wolf optimization (MGWO), hybrid MGWO particle swarm optimization (MGWOPSO), hybrid MGWO sine cosine algorithm (MGWOSCA) and hybrid MGWO crow search algorithm (MGWOCSA) for the designed multi-machine power network. The proposed methods have been realized with the statistical analysis on the 23 benchmark functions. Nonparametric statistical tests, namely, Feidman test, Anova test and Quade tests, have been performed on the test system, further analysed in detail. A detailed comparative analysis under the self-clearing fault is presented to illustrate the suitability of the proposed techniques. For the analysis purpose, the location of system eigenvalues has been observed along with their oscillating frequencies and corresponding damping ratios. Further, the damping nature offered with considered system uncertainty for the system states also presented with the PSS parameters obtained by the proposed algorithms. • Amendments were made by hybridizing GWO with PSO, SCA and CSA and recommended for the electrical power system stability enhancement. • Realization of these amended algorithms was done on 23 benchmark functions. • Algorithms mentioned above were utilized to tune traditional power system stabilizer considering system uncertainties. • Eigenvalue analysis and damping characteristics of system states have been presented under system uncertainties. • Non-parametric statistical analysis was performed for the amended GWO algorithms. [ABSTRACT FROM AUTHOR]

Out‐of‐step or out‐of‐synchronism is the loss of magnetic coupling between the rotor and the stator of a synchronous generator. Recent research has shown that loss of synchronism condition of a synchronous generator due to the local and inter‐area oscillations can cause severe damage to the machine and power system. In other words, if these oscillations do not damp, the power system will become unstable. It is worth highlighting that, along with the growth of grid interconnections, the stability has been a significant concern in the operation of the power systems, and the generators play a substantial role in this issue. Consequently, to reduce these oscillations and failures, the instability tolerant synchronous generator (ITSG), presented in this study, applied in the critical points of the network. The proposed generator is designed in such a way that it has a higher specific magnetic loading to stabilise the power system much more. The simulation tests demonstrate that the applied generator is effective in stabilising the network and improving the transient stability of the system in response to oscillations. [ABSTRACT FROM AUTHOR]

The object of this paper is to demonstrate the performance of a Ramp-Rejecting electric Power Prefilter (RRPP), which is a modification of the Conventional electric Power Prefilter (CPP) for a speed-PSS. The RRPP can markedly reduce the undesirable swings in generator voltage and reactive power output due to ramping of turbine power. Like the Dual Input Prefilter (DIP) of the integral-of-accelerating-power (IAP) PSS the RRPP (i) significantly attenuates the torsional modes; and (ii) enhances modal damping. Significantly, the RRPP does not require an externally-estimated rotor-speed input signal - which is an important requirement of the DIP. For example, using generator terminal variables for the DIP it is difficult to accurately estimate a rotor-speed input that covers a wide range of operating conditions and modal frequencies. [ABSTRACT FROM AUTHOR]

The strong nonlinearity, time-varying structure, and complex operating conditions in interconnected power systems with the wind farm deteriorate the control performance of wide-area damping control (WADC) designed by conventional model-based methods. In this paper, an improved model-free adaptive control (MFAC), which employs the pseudo-partial derivative (PPD) to linearize the nonlinear power system dynamically, considering WADC requirements and system disturbances is proposed to damp out the inter-area oscillation for wind farm. In addition, to compensate for communication delays in a wide-area measurement system (WAMS), an adaptive delay compensator (ADC) is employed to reimbursed both constant and variable delays. The proposed controller depends only on online I/O data, which avoids the complicated system modeling process and can adapt to variations of system operating conditions and delay scenarios. Moreover, compared to existing MFAC damping approaches, the proposed approach provides additional advantages for wind farm on managing initial values and the stability region of PPD. The communication delays are compensated, which is not considered in other MFAC-based methods. Finally, case studies with various uncertainties and disturbances are conducted to validate the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hybrid technique called enhanced grey wolf optimization‐sine cosine algorithm‐cuckoo search (EGWO‐SCA‐CS) algorithm to improve the electrical power system stability. The proposed method comprises of a popular grey wolf optimization (GWO) in an enhanced and hybrid form. It embraces the well‐balanced exploration and exploitation using the cuckoo search (CS) algorithm and enhanced search capability through the sine cosine algorithm (SCA) to elude the stuck to the local optima. The proposed technique is validated with the 23 benchmark functions and compared with state‐of‐the‐art methods. The benchmark functions consist of unimodal, multimodal function from which the best suitability of the proposed technique can be identified. The robustness analysis also presented with the proposed method through boxplot, and a detailed statistical analysis is performed for a set of 30 individual runs. From the inferences gathered from the benchmark functions, the proposed technique is applied to the stability problem of a power system, which is heavily stressed with the nonlinear variation of the load and thereby operating conditions. The dynamics of power system components have been considered for the mathematical model of a multimachine system, and multiobjective function has been framed in tuning the optimal controller parameters. The effectiveness of the proposed algorithm has been assessed by considering two case studies, namely, (i) the optimal controller parameter tuning, and (ii) the coordination of oscillation damping devices in the power system stability enhancement. In the first case study, the power system stabilizer (PSS) is considered as a controller, and a self‐clearing three‐phase fault is considered as the system uncertainty. In contrast, static synchronous compensator (STATCOM) and PSS are considered as controllers to be coordinated, and perturbation in the system states as uncertainty in the second case study. [ABSTRACT FROM AUTHOR]

Generally, the mathematical formulation of the dynamics governing multi‐area power systems with Unified Power Flow Controller (UPFC) is a challenging task owing to the presence of both differential and algebraic sub‐systems. The proposed research work attempts to integrate the two subsystems by replacing the algebraic subsystem with a differential approximant that leads to a non‐linear system of differential equations. Solution of the proposed model with a properly chosen Lyapunov function produce a nonlinear control signal which damps inter‐area oscillations effectively. The non‐linear control signal is realised using the backstepping method. Moreover, the new formulation enables utilisation of the law for uncertain parameters using the standard parametric feedback form, such that the advantage of such a controller is unaffected by these parameters. In addition to this major contribution, full utilisation of UPFC, by using a lone multi‐variable PI controller which eliminates negative interaction between the controllers, is also achieved. Empirical verification of the proposed approach is done by simulating various scenarios with varying degrees of complexity – from dual area power networks to 39 buses New England system. The results of the experiments indicate the efficacy of the method. [ABSTRACT FROM AUTHOR]

During grid fault, transmission lines reach its thermal limit and lose its capability to transfer. If this fault current enters generator terminals, it will lead to dip in stator voltage and consequently produces torque and real power oscillations. This further affects in the form of internal heat in rotor windings and finally damages the generator. A new control strategy is proposed to limit fault current using dual STATCOM, which will damp power oscillations and mitigate the voltage dip due to a severe symmetrical fault. It is achieved by diverting the fault current to the capacitor using the dual-STATCOM controller. It is best suitable to maintain power system stability with uninterrupted power supply, effective power transfer capability and rapid reactive power support and to damp inter-area oscillations. The effectiveness of SG and DFIG due to the transmission line short circuit symmetrical fault was studied.

The overview of Russian-Chinese Workshop “Mathematical Modeling of Renewable and Isolated Hybrid Power Systems” is given. This workshop hosted by Melent’ev Energy Systems Institute of Siberian Branch of Russian Academy of Sciences was held from 2nd till 6th of August 2017 in Irkutsk city.