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This paper proposes a coordinated voltage control scheme for transmission systems based on linearized power flow functions to determine the set points of local control voltage devices. The scheme considers models and interactions between different devices to attain the appropriate performance (non-optimal or optimal) of the whole power system. The sensitivity analysis is used to formulate a partly linearized model that relates the voltage variations of buses to the reactive power variation of synchronous machines, settings of static VAr compensators (SVCs), shunt capacitors susceptance, and tap position of load tap changers (LTCs) to determine the set of the settings of the voltage control devices. Two formulations are proposed by considering the susceptance of SVCs or the slope and reference voltage of characteristics of SVCs as control variables. The developed formulation based on the linearized power flow functions provides the possibility of the practical implementation of the coordinated voltage control scheme, especially the optimal one, by reducing the model complexity and solving time. The performance of the proposed formulations is investigated by some studies of voltage control and an optimally coordinated problem on the IEEE 30-bus and IEEE 118-bus test systems. • Coordinated voltage control of a wide variety of voltage control devices dispersed on the transmission network. • Formulating a partly linearized model based on a sensitivity analysis of nonlinear power flow functions. • Formulations by considering two different models for SVC. • Applicable to both non-optimal coordinated or optimal coordinated problems. • Considering a complete set of objectives, including operation indices of the network and fast and slow voltage control devices. [ABSTRACT FROM AUTHOR]

• Reactive power management. • Point estimation method. • Hony Badger algorithm. • Two-stage stochastic programming. • Inverter reactive power capability. In order to reduce the Static Var Compensators' (SVCs') initial investment costs and their anticipated yearly running costs, this paper offers a two-layer methodology for the allocation and sizing of the SVCs in radial distribution systems. First, the Power Loss (PLI) is used to choose the best candidate buses for allocating SVCs. A two-stage stochastic programming algorithm is then proposed to solve the sizing problem, with the Point Estimate Method (PEM) being used to account for the uncertainties in the PV and load powers. Analysis is also done on the advantages of combining the SVCs and the PV inverter's ability to provide reactive power. The optimization problem is solved using Honey Badger Algorithm (HBA) and compared to Archimedes Optimization Algorithm (AOA), Beetle antenna based Grey Wolf Optimization (BGWO), Particle Swarm Optimization (PSO) and Genetic Algorithm (GA). The IEEE 33 and 69 radial bus systems have been used to validate the suggested methodology. The findings demonstrate that, HBA models delivered the best outcomes in terms of convergence characteristics and computation time. When considering the PV inverter's capability to provide reactive power, estimated yearly operating costs are reduced by 17.44 % and 36.36 % for compensations of 600 kVAR and 1,000 kVAR, respectively. [ABSTRACT FROM AUTHOR]

In order to effectively compensate negative sequence current (NSC) of the V/v traction system and reduce the capacity and cost of railway power conditioner (RPC), a low-cost hybrid railway power conditioner (HRPC) technology scheme considering regenerative braking energy is proposed in this paper. The proposed HRPC consists of an RPC with a modular multilevel converter structure (MMC-RPC) and a railway static var compensator (RSVC). First, the circuit topology of the proposed scheme and the principle of NSC compensation considering regenerative braking energy are given. Then, the capacity configurations of MMC-RPC and RSVC are presented to reduce the capacity of active equipment and further lower the investment cost of HRPC. On this basis, the HRPC with energy storage units (ESU-HRPC) is studied to recycle the remaining regenerative braking energy, and the difference from the proposed HRPC is further analyzed. Subsequently, the capacities of HRPC and ESU-HRPC are designed based on the measured power data from a heavy-haul railway in China as an example. Besides, the system control strategy is given. Finally, the proposed technical schemes are verified by the hardware in loop (HIL) experiments. [ABSTRACT FROM AUTHOR]

This paper presents an interpolation-based solution that allows the application of traveling wave (TW)-based algorithms even using sampling rates lower than those typically considered as a requirement for classical approaches. Two phasor (PH)-based and one TW-based fault location methods are compared with the proposed technique and applied through Alternative Transients Program (ATP) fault simulations in a 500 kV/60 Hz Brazilian double circuit series-compensated transmission lines with high-voltage direct current lines (HVDCs) and static var compensators (SVCs) in the vicinity. The results show that the proposed interpolation-based technique is reliable and suitable for TW-based fault location using data records with sampling rates lower than those used in commercially available equipment. Moreover, its accuracy is comparable to classical TW-based fault location solutions, revealing its usefulness for practical application when only traditional digital fault recorders (DFRs) are available. • Application of traveling wave (TW)-based algorithms using low sampling rate records. • Interpolation technique combined with TW-based applications. • Application for inferior band of frequency spectrum from fault induced transients. • Use low sampling rate digital fault recorders (DFRs) for (TW)-based applications. [ABSTRACT FROM AUTHOR]

• Real-world HIL setups for hybrid SVC with full-bridge MMC. • Regular and small time-step simulations match exceptionally well. • Regular and small time-step simulation approaches valid in this case. • Small time-step contrivances introduce significant discrepancy from reality. • Small-time step partitioning contrivances must be considered. Hydro-Québec built two static var compensators at the 735-kV La Verendrye substation in 1985. Each has a capacity of +330/-110 Mvar to help regulate system voltage and power system dynamic. They exceeded their useful life, and their operation was becoming challenging due to the aging control technology. Spare part availability and cost were also becoming an issue. A refurbishment project was thus undertaken. Due to design constraints, a hybrid SVC was selected: traditional thyristor-switched capacitors are used, but thyristor-controlled inductors are replaced by full-bridge modular multilevel converters. Throughout the ongoing project, hardware-in-the-loop real-time simulation was used for dynamic performance testing, factory acceptance tests and pre-commissioning studies. Two modeling approaches were used to represent the hybrid SVC: conventional electromagnetic transient simulation and small time-step approach. As this paper demonstrates, both approaches are valid in this case and produce matching results if simulation contrivances are not neglected. [ABSTRACT FROM AUTHOR]

Electric power system is complex interconnected system that is subjected to rapid change in its structure. Addition of new equipment, operation close to stability limits and variation of load in summer and winter are some factors that make power system unstable and introduce electro-mechanical oscillations in the system. These oscillations, though of small magnitude often persist for long periods of time and restrict the power transfer capacity. To stabilize the power system different control strategies are used to damp the oscillations previously but all rely on linearized model of the power system. Synergetic controller based on synergetic control theory, is a non-linear controller that forces the system toward global stability. In this paper, synergetic synthesis of the Static Var compensator (SVC) is proposed for a nonlinear model of the power system. The proposed synergetic controller is implemented in a Single Machine Infinite Bus (SMIB) system with HVDC link and the performance is compared with linear dynamic compensator based on eigen-value assignment technique. The results provided show the effectiveness of the controller for damping system oscillations in the case of variation in load whereas the linear dynamic compensator destabilized the system. [ABSTRACT FROM AUTHOR]

Excessive penetration of renewable energy resources into the distribution grid without additional preventive measures has led to several operational problems. However, most strategies developed to accommodate more renewable energy units suffered from other operational problems. Therefore, further efforts are needed to address the other key vulnerabilities of the grid in addition to maximizing the hosting capacity. In this regard, this study is devoted to a new multi-objective formulation to maximize the hosting capacity and minimize the total energy losses while satisfying the operational constraints and maximizing the energy transferred to off-peak hours. The Multi-Objective Advanced Gray Wolf Optimization (MOAGWO) algorithm is used as a solution tool. The proposed formulation and solution algorithm are tested on IEEE-33-bus and 69-bus medium voltage test systems. The impacts of energy storage systems, voltage regulators, and static var compensators on the hosting capacity and the objective functions are identified using several scenarios. The results showed that the optimal device type and locations depend on the level of DG penetration. Finally, a comparison according to two popular multi-objective performance indices showed that the quality of the Pareto front distribution obtained by MOAGWO was better than the ones obtained with the two other popular heuristic methods. • Maximization of the hosting capacity while minimizing the energy losses. • Maximization of the energy transferred to the off-peak hours through intelligent control. • Multi-Objective Advanced GWO algorithm to determine the Pareto front solutions. • Singular and collaborative impacts of the reinforcement units on the objectives. • High-quality Pareto solutions and high computational efficiency of MOAGWO. [ABSTRACT FROM AUTHOR]

• Large scale wind farm is designed including SCIG and DFIG units in two sites. • Proposed control strategy designs off-grid and grid-tied functionality for sites. • Sites and grid are supported by STATCOM and SVC to deal with voltage imbalance. • Fault ride through capability is enhanced by the proposed control strategy. • Frequency control is designed under grid-tied and off-grid operations. This paper presents a multi-objective control scheme on the interconnected wind farms which are formed by different wind turbines including doubly fed induction generators (DFIG) and squirrel cage induction generators (SCIG). The proposed control system aims to control voltage, frequency, and mechanical power in the wind farms under wind/load alterations, faults, and outages. The voltage stability and fault ride through capability are improved. The proposed model also deals with unbalanced loading and faulty conditions. All the aforementioned points are realized under both off-grid and grid-tied conditions. For voltage stability improvement, each wind farm is integrated with one static VAR compensator (SVC) and the grid-side is integrated with one static synchronous compensator (STATCOM). In the grid-tied, the resilience following events is improved by proper control of STATCOM. In the off-grid, the installed SVC at each site is responsible for increasing resilience. The proposed control systems are modeled and implemented on a typical test grid, and numerical simulations are carried out in MATLAB/SIMULINK software. It is demonstrated that the proposed multi-objective control scheme efficiently controls all individual wind farms, achieves a coordinated management between different wind farms, deals with stability/unbalanced operating condition/faults, increases resilience and improves fault ride through capability. [ABSTRACT FROM AUTHOR]

• Computational modeling to evaluate the LOE protection of synchronous generators connected to a transmission line with static var compensator (SVC). • Comparative of traditional LOE protection of with a proposed LOE protection method based on a multilayer perceptron-type artificial neural network (ANN). • Show the effectiveness of the proposed ANN LOE protection to reach faster actuation time than the traditional LOE protection. Flexible Alternating Current Transmission Systems (FACTS) connected to Transmission Lines (TLs) make systems more flexible, and optimize their operational capacity. Despite improvements in TL operational aspects, added FACTS can modify the amplitude, voltage, and current angles of the system wherein they are inserted and consequently the measured impedance, which can affect synchronous machine protections that are based on this feature. Firstly, this paper presents a set of computational simulations to evaluate possible changes in the synchronous machine protection connected to a TL with Static Var Compensator (SVC). Finally, is this context the traditional loss of excitation (LOE) protection is comparing with a proposed approach based on the use of a multilayer perceptron-type Artificial Neural Network (ANN). The simulation results show the effectiveness and robustness of the proposed ANN LOE protection to reach faster actuation time than the traditional LOE protection. [ABSTRACT FROM AUTHOR]

• An optimal VVC model considering diverse controllable resources including energy storage devices, distributed generators, step voltage regulators, static var compensators, and switchable capacitor banks in the ADN is proposed in this paper, in which the VVC problem is considered in a more complete energy management framework coupling with active power control. • Given that the active distribution network VVC problem is a computation-intensive MINLP problem with high-dimensional variables and strong non-convexity, the Kriging assisted surrogate model is trained to approximate the computationally expensive black-box nonlinear system, reducing the total number of actual time-consuming simulations, and moderating the computational burden without losing precision. • By expected improvement and dynamic updating techniques, the Kriging assisted modified adaptive particle swarm optimization (KA-MAPSO) is ultimately developed to solve the proposed VVC optimization problem, avoids the low convergence in non-convex and nonlinear power flow calculations. And the simulation result shows that the proposed method outperforms other referred algorithm and accelerate the solving process of traditional heuristic calculation. The increasing penetration of distributed energy resources exacerbates the risk of power loss increment and voltage violations in active distribution networks (ADN). The Volt/Var control (VVC) involving multiple controllable resources is widely considered to be an effective means of ensuring the secure and stable operation of ADN. Firstly, considering diverse controllable resources including energy storage devices, distributed generators, step voltage regulators, static var compensators and switchable capacitor banks in the ADN, a comprehensive/novel VVC optimization model is established as a mixed-integer non-linear programming problem with high-dimensional variables. In order to mitigate the computational burden with enormous networks and reduce the dependence on an initial physical model of the distribution network, a Kriging-assisted evolutionary computation method for VVC problem is proposed in this paper. The surrogate model is used to approximate the nonconvex and nonlinear network, reduce the frequency of complex simulations, assist optimization decision-making and avoid the complicated explicit analysis. Furthermore, the surrogate-assisted model enabled heuristic algorithm, owning promising performance in approximating the computationally expensive black-box system, can be obtained via continuous training and dynamic updating. Finally, the numerical results on the modified IEEE 33-bus and PG 69-bus systems verify the effectiveness of the proposed method. The simulation results indicate that the proposed Kriging-assisted evolutionary algorithm outperforms other algorithms in the aspect of calculation efficiency and robustness while accelerating the solving process of traditional evolutionary calculation. [ABSTRACT FROM AUTHOR]

In our recent work [1] , we constructed a reduced-order model of the Western Electricity Coordinating Council (WECC) power system using mathematically derived parameters from real Synchrophasor data. These parameters include inter and intra-area impedances, inertias, and damping factors for aggregate synchronous generators representing five geographical, and yet coherent, areas of WECC. In this paper, we use this reduced-order model as a tool to design a supplementary controller for a Static VAr Compensator (SVC), located at the terminal bus of one of the aggregate generators. Wide-area feedback consisting of phase angle and frequency measurements from Phasor Measurement Units (PMUs) in the other areas is used to design this controller. The objective is to damp the inter-machine oscillation modes of the reduced-order model, which in the full-order system corresponds to inter-area oscillations. The controller input is chosen via statistical variance analysis, and its parameters are tuned to improve the damping factors of the slow modes. The model is implemented in a real-time digital simulator, and validated using a wide range of disturbance scenarios. The closed-loop system is observed to be highly robust to all of these disturbances as well as the choice of operating points. Detailed experimental analyses of the capacity of the SVC to satisfy the damping specifications of supplementary control are also presented via multiple contingencies. The results are promising in aiding damping of inter-area modes in WECC, especially at a time of increasing penetration of wind and other renewable resources. [ABSTRACT FROM AUTHOR]

• The proposed protection strategy enhances the stability and reliability of power systems by. • Precise discrimination between transient and permanent SLG faults. • Fast and precise diagnosis of the successful reclosing time in a case of the transient SLG fault. • Significant reduction in the dead time in a case of the transient SLG fault. • Being efficient even in noise exposure situations and not dependent on the fault location or threshold values. Opportune detection of transient faults and restoration of the faulty phase in the least possible time plays a key role in improving the stability of high voltage transmission lines (HVTLs). This paper presents a novel four-step strategy for the protection of HVTLs so that the stability and reliability of power systems are enhanced. Firstly, the cumulative sum (CUSUM) algorithm is used to quickly detect the transient and determine the faulty phase. In the second step, the settings of the static var compensator (SVC) are changed to reduce the reclosing dead time as much as possible. Afterward, the transient or permanent type of the fault is identified based on the proposed principal component analysis-support vector machine (PCA-SVM) algorithm. In the fourth step, if a transient fault is recognized, the successful single-phase reclosing time is identified by the PCA-SVM and the reclosing command is issued to high voltage circuit breakers (HVCBs). Simulation results obtained by using EMTP-RV and MATLAB for a sample 400 kV power system illustrate that the proposed protection strategy can increase the reliability of the power system via reduction of the dead time, correct detection of transient faults from permanent ones, and accurate detection of the reclosing time. [ABSTRACT FROM AUTHOR]

Highlights: [•] Combination of optimal reclosing of circuit breakers and SVC is proposed for power system transient stability enhancement. [•] The performance of the proposed combination of optimal reclosing and SVC is compared with the combination of conventional reclosing and SVC. [•] The performance of the proposed combination of optimal reclosing and SVC is better than that of the combination of conventional reclosing and SVC. [•] Combined operation of optimal reclosing and SVC can be considered as an effective means for power system transient stability enhancement. [ABSTRACT FROM AUTHOR]

• Static var compensator causes a delay in operation of loss of excitation protection. • Delay also depends on the power dispatch and the severity of the loss of excitation. • Static var compensator causes under-reach of commercial loss of excitation relay. • Presence of static var compensator causes a displacement of impedance trajectory. • Positive offset relay adjustment seems to be more adequate than negative adjustment. The static var compensator (SVC) is one of the devices that has been widely used for reactive compensation to improve the capacity and flexibility of power transfer in the electrical power system. However, the SVC changes the voltages and currents of the power network to which it is connected. Consequently, the measured impedance can be changed and affect protection relays operation based on this characteristic. Several papers have been published about the SVC effects on distance protection applied in transmission lines (TL). However, it is not widely known the impact of SVC on the transient behavior of generators, such as protection against loss of excitation (LOE) in synchronous machines connected to TL with SVC. In this sense, based on the modeling of a test electrical power system in the PSCAD/EMTDC simulation environment, the assessment of the effects of SVC on the behavior of the ANSI 40 protection function for the conditions of the total LOE and partial LOE since these events can cause the synchronous machine to operate in conditions above the rated ones. In addition, this paper presents a testbed that allows performing secondary tests in physical relays when simulated signals are applied to perform protection studies in the presence of SVC in power systems. [ABSTRACT FROM AUTHOR]

• Yet there are few studies for the extremely short-term forecasting of wind power. • Since the proposed approach is nonlinear, it provides more accurate modelling than the ARMA approach. • The proposed approach only uses the EKF algorithm to update the parameters which makes it suitable for online implantation. • It is robust against noisy easements and probabilistic behavior of the wind speed profile. • A proper model for the wind farm to simulate and evaluate the performance of the SVC based on real data is proposed. The inherent time-varying nature of the wind farm power causes undesired voltage flicker in the power network. In order to mitigate the flicker to enhance the performance of the wind power system with very fast dynamics, the static VAr compensator (SVC) is utilized. However, the SVC operates with some delays which negatively affects its performance. This persuades us to predict the reactive power of the wind farm to compensate for the real-world delay. The predicted reactive power is then utilized in the SVC. Therefore, this paper develops a novel fuzzy one-step-ahead prediction approach for the wind farm reactive power. The proposed fuzzy prediction uses a Takagi-Sugeno (TS) fuzzy representation whose unknown parameters are tuned online based on an extended Kalman filter (EKF). The wind farm is modeled as a time-varying current source which its amplitude and phase change every 0.01 s. A large set of the actual data of a wind farm in Manjil, Iran is gathered and directly utilized in the simulation process. Several flicker indices are calculated to evaluate the proposed prediction method. The obtained results show the performance enhancement and flicker mitigation of the suggested power scheme. [ABSTRACT FROM AUTHOR]

Abstract: New insights into the application of One-Machine Infinite Bus (OMIB) equivalents to the analysis and study of the inter-area mode phenomenon in stressed power systems are provided. First, the notion of a time-varying OMIB equivalent is briefly reviewed and details of the adopted analytical model are introduced. On the basis of this representation, a systematic technique is then proposed to extract the underlying dynamics of the process directly from time-domain transient stability simulations. The analysis tool takes into account both, the dynamics of the slow inter-area oscillations and the dynamics of the fast inter-machine oscillations. Criteria to interpret inter-area oscillations in terms of the kinetic energy transfer between the most disturbed machines, and the rest of the system following the onset of a major contingency are given and methods to implement the proposed approach are discussed. A case study on a 5-area dynamic equivalent model of the Mexican interconnected system in which several static VAR compensators are used to support system voltage is presented to illustrate the developed procedures. Studies are conducted to identify and characterize the energy transfer process that accompanies the inter-area mode separation as well as to evaluate the effect of voltage support on system damping. The results show that time-varying OMIB dynamic equivalents can be used to capture the dominant features of the inter-area mode behavior, which are needed in the analysis and control of system dynamic performance. [Copyright &y& Elsevier]

• The proposed method based on support vector multi-regressors, is able to capture the non-linear and chaotic dynamic in an electric arc furnace model. • Estimation of the arc furnace model parameters takes into account the harmonics and sub-harmonics of the voltage waveform generated by the electric arc furnace. • The proposed method can be used to evaluate the accuracy of any parametric model of an electric arc furnace. In the iron and steel industry, electric arc furnaces (EAFs) are used in the melting and refining process of metals. They are known to demand large amounts of reactive power and cause significant power quality (PQ) problems due to their highly non-linear time varying voltage-current characteristic. Several EAF models have been proposed with the purpose to predict the voltage and current waveforms, to assess the performance of different compensating devices such as static var compensator, synchronous static compensator, active power filters, and –still under study– energy storage systems, and also for planning the installation of iron and steel facilities considering existing real data from similar facilities. An important aspect of these models is related to the estimation of their parameters. This paper presents a new method to estimate the parameters of an EAF model. The method utilizes a multiple-input multiple-output regressor based on support vector machine, that maps from voltage characteristics of the electric arc to the values of the model parameters. The multidimensional support vector regressor (M-SVR) is designed in the training phase, using data from several simulations of the EAF model. These simulations are carried out adjusting the parameters of the model within the search space, and considering the real arc current as input to the model. Then, in the validation phase, for the real voltage waveform, the estimated parameters are obtained using each regressor of the M-SVR. The proposed method is validated by the comparison between the waveforms obtained using the EAF model with actual data from a steel plant. Results show that the relative error between the fundamental component of the current and voltage, for real and simulated waveforms, are 2.1 % and 6.3 % respectively. [ABSTRACT FROM AUTHOR]

• A new reintegration-driven ICI framework, called R-ICI, is proposed. • The proposed R-ICI model improves frequency stability of islands using ESSs. • Transient voltage stability of islands is improved using ESSs and SVCs. • The interaction between frequency and voltage is considered by a linear IFR model. • An active/reactive charging and discharging scheme is introduced for ESSs. In this paper, a reintegration-based multi-objective intentional controlled islanding (ICI) model is proposed to enhance resiliency of electrical power systems under catastrophic events. This remedial measure plan relies on a mixed-integer linear programming model with two objective functions including reintegration risk and total load shedding value. While ensuring that each island includes only coherent generators, the proposed multi-objective model solves the controlled islanding problem using lexicographic optimization approach. To ease the islands' reintegration, charging reactive power, reliability, capacity, and power flow disruption of transmission lines are considered in the model. After implementation of controlled islanding, each resulted island may face temporary active/reactive load-generation imbalance, which may put the islands at the risk of frequency instability, transient voltage instability or a combination of both. The proposed model reduces these risks by modeling energy storage systems (ESSs) and static VAR compensators (SVCs) as fast corrective control actions. In addition to modeling voltage dependent loads in the controlled islanding problem, a linear island frequency response (IFR) model is proposed for frequency stability assessment. The test results of the proposed ICI model on the IEEE 39-bus and IEEE 118-bus test systems demonstrate its performance. [ABSTRACT FROM AUTHOR]

• Impacts of non-periodic are similar to harmonic current but more difficult to mitigate. • Time-frequency distortion index is most suitable for non-periodic loads. • Hybrid time-frequency method provides temporally distributed current reference. • Temporal distribution of compensation increases efficiency and reduces overall cost. • Fuzzy algorithm based on non-periodic characteristics decreases bandwidth requirements. This paper presents a new technique for the compensation of non-periodic load current. The method provides control references for three co-located devices, each corresponding to one moving calculation window and one decomposed part of the compensated current. They are slow compensator with high power rating, large calculation window, and low switching frequency; fast compensator with lower power rating, shorter calculation window, and higher switching frequency; and the reactive compensator which is an ordinary static VAR compensator (SVC). A fuzzy based adaptive window is proposed for the slow compensator to find the optimum window for different load characteristics. The technique is evaluated using real-world data and controller hardware-in-the-loop (HIL) implementation. [ABSTRACT FROM AUTHOR]

• Considering a wide variety of controlled and mechanically switched voltage control devices dispersed in transmission network in the coordinated control voltage scheme. • Considering a complete set of adjustable parameters of the voltage control devices as control variables. • Defining a day ahead multi indices decision model including indices of network and control voltage devices performance along with complete set of network and devices constraints. • Investigating the scheme performance and robustness when the transmission buses are encountered major changes at load profiles. • Using an efficient and elective solving method for defined multi-objective optimization problem to simultaneous optimize the control variables and obtain suitable weighting coefficients. Need for sufficient reactive power reserve for fast reaction against large disturbances necessitates developing an integrated and coordinated voltage control scheme including controlled and mechanically switched control devices. This paper proposes a day-ahead optimal voltage control scheme for transmission system considering static var compensators (SVCs), capacitor banks, load tap changers(LTCs) transformers and synchronous machines. The scheme is based on defining an optimization problem which includes two objective functions for reactive power reserve and voltage regulation precision of SVCs, two objective functions related to number of capacitors switching and LTCs tap changing, and two objective functions for improving the network performance. The multi-objective optimization problem is solved subject to a complete set of constraints related to the network and voltage control devices. The solution algorithm of the proposed problem is based on defining a single objective function by applying appropriate weighting coefficients to the normalized indices. Performance of the proposed scheme is investigated on IEEE 30-bus system through various studies. Particularly, the effectiveness of the scheme is demonstrated to realize the objectives for conditions where the load profiles at transmission buses are considerably modified due to structuring changes in the downstream networks. [ABSTRACT FROM AUTHOR]

• Simultaneous tuning of different controllers taking into account several operating scenarios improves the joint dynamic performance of the power electric systems. • Multi-objective optimization allows adjusting controllers in different analysis domains (frequency and time). • Parallel computing techniques applied to coordinated and simultaneous tuning of controllers expands search space and reduces computing time to reach optimal solutions. This work proposes a computational methodology for coordinated tuning of the power system controllers based on Genetic Algorithm which acts maximizing simultaneously two objective functions, representing each of them the damping of electromechanical oscillations and the improvement of the automatic voltage regulator responses, considering at the same time several critical operating conditions. The coordinated tuning procedure was posted as a multi-objective optimization problem, through the weighted sum technique. The controllers considered into the adjusting scheme correspond to the automatic voltage regulators, power system stabilizers and static var compensators to enhance the electromechanical and voltage response for a several critical operating conditions considered. The Genetic Algorithm was adapted for parallel computing in order to achieve both dynamic responses encompassing several critical operating conditions to reduce high computational efforts. Simulation results of the parallel implementation were more significant than the sequential version, and the proposed approach becomes an interesting alternative tool for operation planning and stability studies. [ABSTRACT FROM AUTHOR]

• The main contributions of this work are summarized as follows. • Considering different load types, their outage costs, and their daily load profiles to find the best UFLS scenario with lowest interruption cost. • Performing the PLSA after UFLS by means of reactive power control apparatus. • Checking the adaptive UFLS/PLSA scenarios by transient stability analysis. • Finding the optimal UFLS/PLSA scenarios all day long. • Damping the background voltage and frequency fluctuations. The conventional under frequency load shedding (UFLS) strategies disconnect the preset amount of the load from the power grid in specific steps. These approaches ignore the daily load variations and the total outage costs, leading to a non-optimal solution. This paper proposes an adaptive UFLS scheme that considers the daily profiles of the different load types to minimize the total outage cost. To obtain the exact amount of the load to be shed, the dynamic performance of the load clusters is modeled. Furthermore, a series of post load-shedding corrective actions (PLSA) are implemented after the UFLS to satisfy the voltage constraints, using the installed reactive power control apparatus and static VAR compensators (SVCs). Two static (frequency-domain) and transient (time-domain) indexes are defined to evaluate the feasibility of possible UFLS/PLSA scenarios. The promising solutions are ranked and the most favorable ones are embedded in a number of look-up tables. The proposed UFLS/PLSA approach is applied to the main grid as well as the potential islands. The performance of the proposed adaptive UFLS/PLSA approach is tested on the IEEE 39-bus system via numerous scenarios, and the results show feasibility, fast and optimal performance of the proposed method. [ABSTRACT FROM AUTHOR]