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A major priority for practicing engineers in an electric power system is preserving the stability of frequency and voltage levels. Any change in these two factors will impact the efficiency and lifespan of the machines connected to the power supply. Therefore, this paper provides a control approach utilizing the Interval Type-2 Fuzzy Sets- Proportional Integral Derivative (IT2FSs-PID) controller and Advanced Thyristor Controlled Series Capacitor (ATCSC) with a combined Load Frequency Control-Automatic Voltage Regulator (LFC-AVR). Several inspections were implemented to demonstrate the controller's strength, including various disturbances in the power system. The LFC-AVR was studied using two different dynamic models, referred to as open and closed loops on the Generation Rate Constraint (GRC) forms. A comparison was made using different techniques from the literature using the same model. Before using the approach, the frequency deviation of area-1 had a very large settling time value, which was caused by system instability. However, after implementing the approach, this value decreased to 4.9236 s. Finally, an additional ATCSC was added to the proposed model to observe its effect on the power system. The simulation was implemented using MATLAB/SIMULINK tools. [ABSTRACT FROM AUTHOR]

Meta-heuristic algorithms (MHAs) have gained popularity in recent years due to their successful results in solving a wide variety of scientific problems. They offer ease of use, fast implementation, and effective convergence toward the optimal solution. Although MHAs have been extensively tested in solving well-known mathematical benchmark problems with one or more dimensions as well as civil and mechanical engineering problems in their initial demonstrations, controller design problems are not typically considered. Furthermore, the literature lacks a standardized optimization process for controller design problems using MHAs. Due to variations in iteration numbers, population sizes, number of trials, objective functions, and insufficient analysis presented in research papers, it becomes challenging to compare and evaluate the controller design performance of MHAs in a successful and fair manner. This work aims to establish a standardized approach for evaluating the performance of MHAs in controller design by proposing a consistent function evaluation metric. To achieve this goal, we present the most comprehensive and comparative study of MHAs' performance in controller design conducted to date. In this paper, we utilize two commonly used objective functions in controller design: Zwe Lee Gaing and Integral Time Absolute Error. Additionally, we employ a total of twenty algorithms, consisting of ten classical algorithms and ten recently popular algorithms. We evaluate the performance of these algorithms on the "automatic voltage regulation" electric power system problem, which serves as a widely used benchmark for meta-heuristically optimized controllers. We consider three different controllers with three (PID), five (FOPID), and seven (FOPIDD) parameters. The performance results of the selected algorithms are thoroughly discussed, considering various analysis techniques such as box plot analysis, convergence curves, and transient response performances, as well as statistical tests like Wilcoxon and Friedman tests. As a result, symbiotic organisms search, teaching–learning based optimization, chaos game optimization, supply–demand based optimization, and jellyfish search algorithms generally emerge as the best-performing algorithms across all optimization processes for the three types of controllers. Researchers interested in conducting further analysis and comparing the improved algorithms can access all the models,parameters, and codes used in this study from the provided link (https://www.mathworks.com/matlabcentral/fileexchange/161336-fractional-order-controller-optimization-for-avr). [ABSTRACT FROM AUTHOR]

Frequency, tie-line power, and the terminal voltages of synchronized generators must all be kept within prescribed limits to ensure the stability of an interconnected power grid through combined automatic generation control (AGC) and automatic voltage regulator (AVR) loops. Thermal power plants, electric vehicles, and renewable energy sources—including solar and wind, geothermal, and solar thermal power plants—form the two-area integrated power system in present research. A new cascade controller named the cascaded proportional integral derivative (PID) and fractional-order PID (CPID-FOPID) controller is proposed for the first time, whose performance is compared with the PID and FOPID controller. The results show that the proposed cascade controller outperforms PID and FOPID in delivering superior dynamic characteristics, including short settling times and low oscillation amplitudes. A new metaheuristic algorithm named the coot algorithm was applied to optimize the parameters of these controllers. The suggested controller outperforms FOPID in the combined AGC and AVR problem under uncertain conditions (random load disturbance, variable input of solar irradiation, and wind power). Robustness of the controller is tested with significant variation in the turbine time constant of the thermal and geothermal power plant. In this study, authors also investigated the best possible coordination between the superconducting magnetic energy storage (SMES) and gate-controlled series capacitor (GCSC) devices to control both voltage and frequency simultaneously. The effect of communication time to the power system is analyzed in this study. Additionally, the obtained results are satisfactorily validated using OPAL-RT real-time digital simulator. [ABSTRACT FROM AUTHOR]

The need for better-performing algorithms to solve real-world power systems engineering problems has always been a challenging topic. Due to their stochastic nature, metaheuristic algorithms can provide better results. Thus, they have a rising trend in terms of investigation. This paper is a further attempt to offer a better optimizing structure, therefore, aims to provide a better-performing algorithm both for designing an appropriate proportional–integral–derivative (PID) controller to effectively operate an automatic voltage regulator (AVR) system and extracting the optimum parameters of a power system stabilizer (PSS) employed in a single-machine infinite-bus (SMIB) power system. Therefore, the paper discusses the development of the Lévy flight-based reptile search algorithm with local search capability and evaluates its potential against challenging power systems engineering optimization problems. The Lévy flight concept is used for better exploration capability in the proposed algorithm, whereas the Nelder–Mead simplex search algorithm is integrated for further exploitation. The latter case is confirmed through 23 benchmark functions with different features using statistical and nonparametric tests. The superiority of the proposed Lévy flight-based reptile search and Nelder–Mead (L-RSANM) algorithm-based PID controller for the AVR system is demonstrated comparatively using convergence, statistical and nonparametric tests along with transient and frequency responses. Besides, it is also assessed against previously reported and different methods, showing further superiority for AVR system control. Furthermore, the extraordinary ability of the L-RSANM algorithm to design an efficient PSS employed in the SMIB power system is demonstrated, as well. In conclusion, the proposed L-RSANM algorithm is shown to be more capable to solve the challenging power systems engineering design problems. [ABSTRACT FROM AUTHOR]

Conservation through voltage reduction (CVR) aims to reduce the peak load and energy savings in electric power systems and is being deployed at various utilities. The effectiveness of the CVR program depends on the load characteristics, i.e., the sensitivity of the load to voltage variation, and voltage regulation device settings. In the current literature, there is a lack of discussion on the CVR factor calculation using different measurements, and there is a lack of method for active power loss estimation using substation measurements. This paper provides insights into CVR factor calculation based on the measurements captured at the substation and those at the load location. This paper also proposes a new method based on curve fitting and artificial neural network to estimate the active power loss using input active power, input reactive power and input voltage at the substation. The CVR comparison study conducted in this paper helps in understanding the factors affecting CVR factor and may provide guidance in CVR implementation and impact assessment. The proposed loss estimation method sheds light on the impacts of CVR in terms of load and loss reduction. The results based on simulation studies using the IEEE 13-bus and 34-bus systems are reported in this paper, noting that the proposed methods are applicable to larger systems, as long as the required measurements at the substation are available. Future research includes testing and refining the methods using large IEEE and utility distribution systems and considering the stochastic nature of the CVR factor with changing load and voltage regulator control schemes. [ABSTRACT FROM AUTHOR]

The penetration of renewable-based converter-interfaced generation and flexible alternating current transmission systems significantly changes properties and dynamic characteristics of modern electric power systems, which leads to the need to take measures to ensure security of their operation. These measures may consist in using the capabilities of new penetrated units or in adapting conventional means. Such adaptation consists in reconfiguration of control systems, development of new systems or approaches to settings determination, which include tuning of automatic voltage regulators with power system stabilizers of conventional synchronous generation. This paper proposes a new approach to tuning of automatic voltage regulators, based on the use of the most complete and reliable information about processes in modern power systems. This approach allows to get settings that are most adequate to practical conditions of operation as part of power systems. For this purpose, the hybrid real-time power system simulator and concept of hybrid modeling are used, and within this paper, and the hybrid modeling tools necessary for the tuning process have been developed. The result of the study is a comprehensive assessment of the reliability of the simulation results obtained using the developed tools, which allows to conclude about the possibility of their application. [ABSTRACT FROM AUTHOR]

This paper presents an entirely new subject to prevent SSR in thermal power plants. The SSR phenomenon is firstly analyzed by using the frequency scanning method in the frequency domain under considering other operating conditions for operating grid-configurations, and then the SSR due to the self-excitation and the transient phenomenon is analyzed to provide the inputs for working out an effective solution. Three devices, namely the thyristor controlled series capacitor (TCSC), static synchronous compensator (STATCOM), and blocking filter (BL) are considered as a proposed choice, and the control strategy for each mentioned device is developed to mitigate the SSR. For TCSC, the control strategy is designed based on two PI controllers for the voltage and current regulator, respectively; besides, the auxiliary subsynchronous damping controller is proposed to provide a supplementary signal of dynamic current on the input signal that is chosen the generator rotor speed deviation. For STATCOM, two PI controllers, using for the DC and connected point voltage regulator, proposed; besides, the auxiliary sub-synchronous damping controller is proposed to provide a supplementary signal of dynamic current on the input signal that is chosen the generator rotor speed deviation. For BL, the natural torsional vibration frequency of models to ensure that SSR due to torsional interaction (TI), torque amplification (TA), and induction generator effect (IEG) are prevented. The effectiveness of this study is verified via a time-domain simulation of the Vietnam Quang-Tri electric power system connected to the 500/220 kV transmission system using EMTP-RV and PSS/E programs. The obtained results show that the frequency scanning method is chosen as a useful method to analyze SSR and the effective solution can be applied to immediately solve the difficulties encountering in the Vietnamese power system to be BL. [ABSTRACT FROM AUTHOR]

Electric power systems are allowing higher penetration levels of renewable energy resources, mainly due to their environmental benefits. The majority of electrical energy generated by renewable energy resources is contributed by wind farms. However, the stochastic nature of these resources does not allow the installed generation capacities to be entirely utilized. In this context, this paper attempts to improve the performance of fixed-speed wind turbines. Turbines of this type have been already installed in some classical wind farms and it is not feasible to replace them with variable-speed ones before their lifetime ends. A fixed-speed turbine is typically connected to the electric grid with a Static VAR Compensator (SVC) across its terminal. For a better dynamic voltage response, the controller gains of a Proportional-Integral (PI) voltage regulator within the SVC will be tuned using a variety of optimization techniques to minimize the integrated square of error for the wind farm terminal voltage. Similarly, the controller gains of the turbine's pitch angle may be tuned to enhance its dynamic output power performance. Simulation results, in this paper, show that the pitch angle controller causes a significant minimization in the integrated square of error for the wind farm output power. Finally, an advanced Proportional-Integral-Acceleration (PIA) voltage regulator controller has been proposed for the SVC. When the PIA control gains are optimized, they result in a better performance than the classical PI controller. [ABSTRACT FROM AUTHOR]

Curtailable loads (CLs) are regarded as one of the last lines of defence to maintain the security and stability of power systems. Nevertheless, if organised carefully, they can also be exploited as preventive security procurement measures for power systems. This is especially true for heavily loaded power systems in which the normal control schemes are already exhausted. In this study, a new power market approach is proposed to utilise CLs' potential in ensuring voltage stability margin (VSM) for heavily-loaded power systems. The proposed method aims to provide a mechanism to engage CLs as active players in the power market, and hence, minimise the disruptive effect of the load curtailment. Next, CLs participation in the power market is utilised to minimise the cost of achieving a desired level of VSM, at normal and N - 1 contingency conditions, in a preventive manner. The most efficient load curtailment and power generation pattern are determined, using a modified particle swarm optimisation algorithm, to minimise the system's total cost, while meeting grid's VSM requirements. The simulation results verify that the desired level of VSM can be effectively obtained using the proposed approach, with much less operational cost compared to the established methods. [ABSTRACT FROM AUTHOR]

Abstract During recent decades with the power system restructuring process, centralized energy sources are being replaced with decentralized ones. This phenomenon has resulted in a novel concept in electric power systems, particularly in distribution systems, known as Distributed Generation (DG). On one hand, utilizing DG is important for secure power generation and reducing power losses. On the other hand, widespread use of such technologies introduces new challenges to power systems such as their optimal location, protection devices' settings, voltage regulation, and Power Quality (PQ) issues. Another key point which needs to be considered relates to specific DG technologies based on Renewable Energy Sources (RESs), such as wind and solar, due to their uncertain power generation. In this regard, this paper provides a comprehensive review of different types of DG and investigates the newly emerging challenges arising in the presence of DG in electrical grids. Highlights • Proposing a comprehensive review on Distributed Generations (DGs). • Investigating the impact of DGs on the protection of distribution systems. • Reviewing the voltage regulation methods in the presence of DGs. [ABSTRACT FROM AUTHOR]

Load characteristics have substantial influence on the voltage stability of power systems. The self-restorative characteristic and stalling of induction motor loads can deteriorate the voltage stability, so it is necessary to develop accurate and efficient dynamic analysis methods for voltage stability analysis of systems with induction motor loads. In this paper, a set of methods based on holomorphic embedding is proposed, which is able to solve steady states and dynamics of a power system with induction motors. The paper is the first work that applies holomorphic embedding to dynamic problems of power systems. The test cases on the IEEE 14-bus system, the NPCC 140-bus system, and the Polish 2383-bus system verify both accuracy and efficiency of the proposed methods. [ABSTRACT FROM AUTHOR]

Highlights • Multi PSS multi-objective optimal design is developed. • Combined stability and nonlinearity indices objective function. • The nonlinearity index is derived from the 2th order participation factor. • The new design strongly preserves under stress systems performances. • Employed a newly developed HSS optimization algorithm. Abstract Design of power system stabilizer (PSS) withstanding critical situations is a challenging task. In this paper, an effective method for the design of a coordinated multiple PSS in power systems are offered and weaknesses of the existing methods are disclosed. The setup includes the nonlinear model of the system, a specific multi-objective function and a newly developed meta-heuristic Hyper-Spherical Search (HSS) optimization algorithm. The objective function includes both eigenvalue stability index (SI) and nonlinearity index (NI). The employed new NI is the second order modal interaction of the lightly damped electromechanical modes. The performance of the proposed Stability-Nonlinearity index (SN) based PSS design by HSS (SNPSS-HSS) is compared with SNPSS-GA, SI based PSS (SPSS) and the conventional design method (CPSS) under various operating conditions and disturbances. The investigations are conducted over both a single lead PSS and PSS2B. The performance is detailed using time domain simulations, SI and NI analysis. A four-machine two-area system and the IEEE 39-bus system are utilized for test purpose. The results of extensive simulations indicate the superiority of SNPSS-HSS design with respect to the others. The obtained relative stability is higher and the nonlinearity index is lower than the product of the other designs. Besides, as it is expected, using a high degree of freedom PSS2B improves the performance of the aforementioned algorithms. [ABSTRACT FROM AUTHOR]

In this paper, an online adaptive optimal controller is firstly designed to optimize the performance of an automatic voltage regulator (AVR). Towards this end, an optimal quadratic tracking problem is defined based on the error between the synchronous generator’s terminal voltage and its desired value. Then, this optimal control problem is solved using an adaptive dynamic programming (ADP) method, called the policy iteration technique. Using this technique, the optimal performance is achieved without knowledge of the AVR parameters. To eliminate the steady state error between the AVR output and its desired value, a modification is made in the original policy iteration technique base on the integral action control and another adaptive optimal controller is designed. In addition, an approach is proposed to represent a large-scale power system through several Single-Machine Infinite-Bus (SMIB) systems. The equivalent SMIB system then may be linearized through modal analysis to be employed by the proposed control scheme. Simulation results show that the designed adaptive optimal controllers are so effective and can be used in practical power systems. [ABSTRACT FROM AUTHOR]

Oscillatory instability in modern power system has increased due to increasing complexity and integration of dynamic loads. Stability analysis of such interconnected power system is very prominent in the presence of uncertain load/generation. In this paper, a power system stabilizer (PSS) design approach, which aims at enhancing the oscillatory stability of the multi-machine power system over the specified uncertainty range in forecasted load/generation, is presented. With non-statistical uncertainty, problem of selecting design parameters of the PSS is formulated as an optimization problem with minimization of eigenvalues and damping ratios based multi-objective function. In order to account the non-statistical uncertainties, a boundary active power loss (BAPL) based objective function is proposed. This non-linear BAPL objective function is minimized for determining the optimal setting of the generators voltage and taps of the online tap changing transformers (OLTC) under various power system constraints. In this paper, both the objective functions are solved by a new metaheuristic technique known as gray wolf optimization (GWO). Boundary value-based approach is used to minimize the repeated load flows under uncertain load/generation scenarios. Improved small-signal stability (SSS) is achieved with optimal active power loss of uncertain power system. Eigenvalue and time domain analysis for New England system are carried out under wide range of disturbances to demonstrate the potential of the proposed approach. [ABSTRACT FROM AUTHOR]

In this study, a multi-stage long-term expansion planning model for an active distribution network (ADN) is presented, with the aim of minimising the investment and operation cost in a coordinated manner over an established horizon. The planning model optimises the following alternatives: upgrading the capacities of substations, reinforcing and/or constructing cable circuits, placing voltage regulators (VRs) and/or static VAR generators, and determining the connection points for distributed generators (DGs). The investment decisions are optimised over the entire planning horizon which can be further divided into multiple periods, and the operation strategies, e.g. active management of DG as well as ADN topology reconfiguration, are determined according to the profiles of representative scenarios. To relieve the computational burden, the original model is properly simplified as a mixed-integer quadratic constrained programming problem through linearisation and approximation techniques, and the solution optimality is guaranteed after invoking the off-the-shell solver. A 24-node test system is employed to validate the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

This paper investigates the artificial bee colony (ABC)- and gray wolf optimization (GWO)-based robust controllers in an isolated winddiesel hybrid power system (IWDHPS). The IWDHPS comprises a wind energy conversion system (WECS) and a diesel engine set. A permanent-magnet induction generator and a synchronous generator are used for power generation with WECS and diesel engine set, respectively. The voltage fluctuations at the generator terminal occur because of the mismatch between generated and consumed reactive power in the system, which further causes a reduction in the quality and stability of the power supply. An automatic voltage regulator (AVR) and a static synchronous compensator (STATCOM) are utilized to suppress these voltage fluctuations in the considered system. Both AVR and STATCOM are equipped with proportional integral (PI) controllers with a single input. The performance and robustness conditions of the control system are expressed as the optimization problem based on the H loop shaping. The ABC and GWO algorithms are applied to solve the optimization problem and to achieve the values of PI controllers for AVR and STATCOM simultaneously. The proposed controller performance is compared with the performance of the bacterial foraging optimization algorithm, particle swarm optimization algorithm, genetic algorithm, and conventional based controller, for the same IWDHPS. [ABSTRACT FROM AUTHOR]

In this paper, the application of the fuzzy logic based power systems stabilizer (FLPSS) to damp power system oscillation is presented. Various types of fuzzy logic controller are used to replace the conventional power system stabilizer (CPSS). The classic fuzzy logic controller based PSS (FLCPSS), the polar FLC (PFLCPSS) and the interval type-2 fuzzy logic controller based PSS (IT2FLCPSS) are applied to the New England - New York interconnected power system and the obtained results are compared. For coordination purposes, genetic algorithm (GA) is used to tune the FLCPSS's gains. The non-linear simulation in the presence of noise confirms the robustness and the superiority of the IT2FLCPSS. [ABSTRACT FROM AUTHOR]

This paper presents a detailed review of the indices found in the literature for voltage stability monitoring. These indices quantify the condition of stability through a scalar magnitude, which can be monitored by network operators, and take measures to avoid a voltage collapse. Unlike other bibliographic reviews, this paper presents the mathematical formulation of each index and an exhaustive classification is carried out considering the following aspects: if the indices use different types of load, if they are based on phasor measurement units - PMU, if they can be calculated in real time, if they consider the operational constraints that arise in a power electrical system, the test systems in which they have been implemented, and if they have been applied in large power systems. Finally, as a result, an analysis that allows to identify work areas, which have been little explored in this topic, specifically those offered by wide area measurement systems WAMS through PMUs, is presented. [ABSTRACT FROM AUTHOR]

This study presents a two area combined Automatic Load Frequency Control (ALFC) and Automatic Voltage Regulator (AVR) system having reheat thermal and wind as Generating Companies (GENCOs) of area1 while reheat thermal and diesel as GENCOs of area2 in a deregulated environment. The thermal plant is considered with system nonlinearities. A proportional-integral and fractional order derivative having a filter controller is introduced for the combined ALFC-AVR system. A lightning search algorithm is employed for finding the best values of controller parameters. The comparative performance of the proposed controllers with some classical controllers proves the superiority of the proposed controller to others. The significance of the Interline Power Flow Controller (IPFC) and IPFC in combination with Superconducting Magnetic Energy Storage (SMES) in the considered system is investigated under bilateral transaction. The analysis reflects that addition of IPFC improves the dynamic responses. The combination of both IPFC and SMES enhances the system dynamics further. The sensitivity analysis against different Distribution Companies Participation Matrix and variation of the contact violation amount gives the robust performance of the introduced controller parameters. [ABSTRACT FROM AUTHOR]

Voltage sags triggered by a thunder-strike and a short-circuit fault could result in false tripping of ac contactor, a type of highly sensitive electrical equipment applied extensively. Serious consequences, such as unintended shutdown in consecutive industrial manufacturing, would be caused subsequently. Thus, an uninterrupted switching topology for ac contactor from mains supply to backup power supply is proposed in this paper, based on the reverse external voltage turn-off characteristic of the silicon-controlled rectifier. Accordingly, the exciting current is continuous, which ensures the engagement of the contactor under voltage sag and even short interruption. Simulations and experiments are conducted simultaneously. Selected emulational and experimental results are reported to validate the correctness and feasibility of the proposed topology and its control strategy. [ABSTRACT FROM AUTHOR]

Growing electricity demand and scarcity of energy sources are the driving force of exploration of renewable energy sources. However, uncertain energy production of these sources creates difficulties in their control and operation with or without a grid utility connection. This paper proposes a novel power control strategy which employs a voltage band in the DC-link voltage to maintain voltage stability and thereby improve the power quality during temporary disturbances in a network. It is applied to act as an inverter’s inertia and obtain maximum benefit from the storage system, based on the features of a DC busbar to avoid a voltage limit violation. It also proposes a demand dispatch strategy based on a client’s terminal voltage, which avoids the complexity of communication lines, to balance the network power during power shortages. The developed control algorithm is tested on an IEEE 16 bus test feeder with multiple DG units and from the results it is found that the proposed control methods provide effective control of the voltage and power quality during transient conditions and scarce power generation. [ABSTRACT FROM AUTHOR]

Automatic voltage regulators and power system stabilizers have been employed successfully to deal with fast dynamics associated to local oscillations phenomena. Whereas, inter-area oscillations damping in large power systems requires remote feedback controllers fed by Wide Area Monitoring Systems (WAMS). Although these improvements in the inter-area oscillations behavior have been effective, a new challenge emerges: reaching stability with a closed loop control despite latencies due to measurements taken far away from the control centre. The research was motivated by the need for modernization of power systems capable of dealing with control difficulties in centralised WAMS for damping inter-area oscillations in power systems caused by delays in the communication system. Herein, time delay and control problems are addressed separately. The time delay problem is solved by a database based time compensation solution relying on the most updated available state of the system. The control problem is solved by a Model Predictive Control (MPC) with terminal cost and constraint set to handle complexities due to nonlinearities of the power system, the large scale of the problem and the parametric variations. Both solutions work in a coordinated way with local controllers to implement a decentralised coordinated strategy that manages slow global dynamics and fast local dynamics as well. The integrated proposed approach is called Time-Delay-Tolerant Model Predictive Control (TDT-MPC). Coordinated and coherent performance of the two TDT-MPC components (Kalman compensator and MPC) is achieved thanks to unifying power system reference models for both strategies. The approach has been tested on the IEEE 39 system and validated with time domain nonlinear simulations, obtaining post-fault damped oscillations and a good tracking of new power references when tripping tie lines. [ABSTRACT FROM AUTHOR]

This paper addresses an optimal model reference adaptive system (MRAS) to design power system stabilizer (PSS) in multi-machine electric power systems. Weighting factors of the proposed MRAS are adjusted by particle swarm optimization (PSO) as well as its input signal is limited by a normalization technique to assure network stability. The proposed modified-optimal MRAS-PSS is evaluated against conventional PSS to demonstrate its advantages. In order to investigate the performance of the proposed MRAS-PSS under parametric uncertainties, three operating conditions are defined and simulated. Several nonlinear and time-domain simulations are carried out to validate the viability and effectiveness of the proposed MRAS-PSS under network uncertainties. [ABSTRACT FROM AUTHOR]

For large power systems with huge proportions of industrial loads, dynamic var sources (DVSs) such as STATCOMs and generators provide significant protection against short-term voltage instability. Simultaneously optimizing the locations and capacities of STATCOMs and the settings for adjustment coefficients of generator excitation systems is a goal of this paper; thus, we formulate a multi-objective, mixed-integer dynamic optimization (MOMIDO) model subject to short-term voltage security and rotor-angle stability under multiple contingencies. We also present a reduced convex relaxation (RCR) method to handle STATCOM locations (which are integer variables) and to avoid their combinatorial explosion, and convert the MOMIDO model into a multi-objective nonlinear programming problem via Radau collocation. To obtain complete Pareto optimal solutions for the MOMIDO model, we propose a reduced wide normalized normal constraint (RWNNC) method by enlarging the Utopia plane so that the Pareto optimal solutions are covered completely by its vertical projection, while pruning redundant sections on the Utopia plane to reduce the amount of calculations. Moreover, the simulation results on an IEEE standard 39-bus system and a real provincial power system demonstrate that the proposed method can handle integer variables effectively and obtain complete Pareto optimal solutions. [ABSTRACT FROM PUBLISHER]

Higher transistor density in modern processors leads to an increase in computing power, which results in higher power consumption. To combat this, system-level power saving features like dynamic voltage transitions (DVTs) are introduced where the voltage required by the processor is varied according to computational load. In commercially available systems, the slew rate of the voltage transition is limited, which has the negative effect of increasing computational latency to ensure safe operation of the switch mode power converter. This study addresses the limitations of the existing techniques by introducing an adaptive DVT, which enables finer granularity of the operating voltage levels and promotes greater power savings. The switching surface-based analysis is performed to derive the conditions for (near) optimal voltage transitions constrained by inductor saturation limits. The results of an experimental prototype achieving the fastest safe transition response are shown to correlate well with the analysis across a wide range of DVT conditions. [ABSTRACT FROM AUTHOR]

In emerging distribution systems with a proliferation of distributed energy resources (DERs) and flexible demand assets, operation characters of the unbalance network and voltage regulation devices need to be accurately addressed for ensuring the secure and economic operation. This paper focuses on the modeling and solution approach of AC optimal power flow (ACOPF) for unbalanced distribution systems with DERs and voltage regulation transformers (VRT). The ACOPF problem is formulated as a chordal relaxation based semidefinite programming (SDP) model, and a tighter convexification model of VRTs is proposed for mitigating solution inexactness. Analytical conditions are presented and proved to determine whether global optimal solution to the original ACOPF problem can be retrieved from solutions of the chordal relaxation based SDP model. Numerical studies on modified IEEE 34-bus and 8500-node systems show that the proposed approach presents a better computational performance as compared to rank relaxation based SDP approaches and general nonlinear solvers. [ABSTRACT FROM PUBLISHER]

Summary: The operational conditions of power systems change constantly as a result of load variations. Most conventional power system stabilizers do not tolerate the variations of operational conditions. Also, a power system containing flexible AC transmission system devices like static synchronous compensator (STATCOM) requires more accurate modeling and stabilizing methods. In this paper, the problem of designing a power system stabilizer by Takagi‐Sugeno (T‐S) fuzzy method for power systems including STATCOM and random load changes is investigated. Load variations are modeled as a continuous‐time finite‐state Markovian chain. The suggested T‐S fuzzy stabilizer contains 2 levels: a surface explaining the Markov jump stochastic processes and a fuzzy surface dealing with the nonlinear power system dynamics. The sufficient conditions for the stochastic stability of the power system are expressed as linear matrix inequalities (LMIs), and the stabilizer gains are obtained via solving LMIs. The proposed stabilizer is tested on both single and multiple machine power systems including stochastic load variations and STATCOM. Simulation results show the efficiency of the proposed stabilizer in comparison with the conventional stabilizers. [ABSTRACT FROM AUTHOR]

This paper presents an optimal coordinated voltage control scheme for preserving long-term voltage stability of power systems. Linear quadratic integral (LQI) controller is employed to construct this scheme. Also, this paper considers the detailed dynamic model of doubly-fed induction generator (DFIG) wind turbine, synchronous generators, over excitation limiter (OEL) and under-load tap changer (ULTC) system, which are important elements influencing voltage stability of power systems. The proposed approach at each time instance involves following two major steps: First, the power system nonlinear equations are linearized and optimal controllers are obtained by LQI technique. Then, in the second step the system dynamic behavior is investigated via time-domain simulations by applying the attained optimal control signals at the first step. The impact of the proposed coordinated voltage control scheme is evaluated by time domain simulations on a well-known test system, under variable wind speed and fault conditions. [ABSTRACT FROM AUTHOR]

The extensive existence of governor deadband has a significant influence on the minimum frequency of power system after a disturbance. However, the strong non-linearity of deadband makes it difficult to quantify its impact on the frequency response. For this end, the backlash non-linearity is adopted to represent for the governor with deadband. The non-linear characteristics of governor with deadband are thus well approximated. The describing function method is applied to linearise the backlash non-linearity. Then a first-order model of governor system is derived to consider the deadband effect quantitatively. Minimum frequency estimation algorithm is proposed based on the first-order model. The proposed algorithm is effective to reflect the effects of various widths of deadbannd on the minimum value of frequency. Case study is conducted to prove its adequate performance in minimum frequency estimation with a practical power grid in China. [ABSTRACT FROM AUTHOR]

A variable inductor consists of a magnetic core, primary dc windings, and secondary ac windings. The effective inductance of the secondary ac winding can be controlled by the primary dc current because of its nonlinear magnetic characteristic. Hence, variable inductors can be applied as a reactive power compensator for voltage stabilization in electric power systems, and have desirable features such as a simple and robust structure, low cost, and high reliability. In a previous paper, a concentric-winding-type three-phase variable inductor with a 2-D structure has been proposed. It was demonstrated that the 2-D variable inductor has good controllability and a low distortion current. To further increase productivity and reduce costs, this paper presents a novel concentric-winding-type three-phase variable inductor with a 3-D structure. It is demonstrated that the leakage flux of the proposed 3-D variable inductor is reduced by more than 30%. Furthermore, a 6.6 kV–100 kVA 3-D variable inductor is designed and compared to its 2-D counterpart. It is proved that eddy current loss, which is induced within an oil-immersed self-cooled tank because of leakage flux from the variable inductor, can be reduced to one-third of that of the 2-D variable inductor. [ABSTRACT FROM AUTHOR]

This paper studies the impact of leveraging both static synchronous compensator (STATCOM) and power system stabilizer (PSS) on multi-machine power systems. Considering a standard IEEE 9-bus test power network, classic and intelligent controllers are applied to achieve the desirable system performance. Simulated tests show the usefulness of STATCOM on network power quality in terms of voltage profile. In addition, it is shown that it can significantly improve the damping oscillations of synchronous generator under normal and abnormal network conditions. As shown, the PSS also contributes to improving the synchronous generator parameters. It is also observed that using intelligent controllers with STATCOM and PSS leads to a better performance relative to the classic controllers. [ABSTRACT FROM AUTHOR]

To guarantee the secure and reliable operations of power systems through the rapid damping of low-frequency electromechanical oscillations (LFEOs) is the ultimate objective of this study. This paper presents a coordination of a flexible AC transmission system (FACTS) device and power system stabilizer (PSS) to meet this objective, and deals with the design of a damping controller based on a thyristorcontrolled phase shifter (TCPS) and a PSS. The proposed design is incorporated in the framework of a single-machine infinite-bus (SMIB) power system. The effectiveness of the proposed design in damping power system oscillations is explored through eigenvalue analysis, time-domain simulations and damping torque contribution. A comparative study on different control schemes, such as with an SMIB including a PSS and an SMIB including a TCPS-based damping controller is also carried out. The obtained results prove the superior performance of the proposed design in improving the stability of the given power system. All the digital simulations are performed using MATLAB/ SIMULINK. [ABSTRACT FROM AUTHOR]

This paper presents a survey on optimization techniques used to tune the controller parameters on Automatic Voltage Regulator (AVR) system. AVR is a device used to adjust the terminal voltage of synchronous generator. Since output voltage has slow response and instability, a Controller is used to improve stability and to get better response by minimizing maximum overshoot, reducing rise time, reducing settling time and improving steady state error. Proportional-Integral- Derivative (PID), Fraction Order PID (FOPID) and fuzzy logic are some examples of controllers which are used. Optimization techniques are used to tune the Controller due to nonlinear loads, time delays, variable operating points and others. There are different types of optimization techniques as Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Artificial Bee Colony (ABC), Harmony Search Algorithm (HSA), Local Unimodal Sampling (LUS), Teaching Learned Based Optimization (TLBO), and others. Researches are performed on different optimization techniques to improve terminal voltage response and stability. [ABSTRACT FROM AUTHOR]

Power delivery networks with distributed on-chip voltage regulators (VRs) serve as an effective way for fast localized voltage regulation within modern microprocessors. Without careful consideration of the interactions among the distributed VRs and the power grid, unbalanced current sharing (CS) among those regulators may, however, lead to efficiency degradations, stability, and reliability issues, and even malfunctions of the regulators. This paper is a first attempt to investigate the efficiency, stability, and reliability implications of unbalanced CS among distributed on-chip VRs. Benefits of balanced CS are demonstrated with concrete examples, showing the necessity of an appropriate current balancing scheme. An adaptive reference voltage control method and the corresponding control algorithms specifically for distributed on-chip VRs are proposed to balance the CS among regulators at different locations. The proposed techniques successfully balance the CS among distributed VRs and can be applied to different regulator types. Simulation results based on practical microprocessor setups confirm the efficiency, stability, and reliability implications. [ABSTRACT FROM AUTHOR]

Multiple operating conditions in power systems including wind power sources significantly affect the damping of low frequency oscillation modes due to diverse generating and loading conditions, random wind speeds, line outage contingencies, etc. To cope with multiple operating conditions, this paper proposes the new parameter optimization technique of the power system stabilizer (PSS) and the doubly-fed induction generator (DFIG) wind turbine with the power oscillation damper (POD) based on the probability method. Different operating conditions are randomly generated by Monte Carlo simulation. Under the generated operating points, the particle swarm optimization of PSS and POD parameters is carried out to achieve the highest probability that the damping ratios of all oscillation modes are greater than the desired damping ratio for all operating points. Study results in the IEEE New England 39-bus system indicate that under the occurrence of faults, the PSS and POD optimized by the proposed method yield better stabilizing performance than the conventional PSS and POD over a wide range of operating points. [ABSTRACT FROM AUTHOR]

An iterative method is presented to determine the most probable voltage stability limit by identifying the closest saddle node bifurcation in a probability-loading space starting at the expected initial system state. The iterative method is applied to the probability space to identify the closest saddle node bifurcation by means of the Mahalanobis distance. Further the method provides an ellipsoidal load subspace corresponding to the most probable bifurcation. This ellipsoid is a lower bound for the probability of bifurcation. To verify the proposed methodology examples are given and the minimum Mahalanobis distance, for dependent and independent load patterns, is compared with the minimum Euclidian distance. [ABSTRACT FROM AUTHOR]

Power system forced oscillations are low-frequency oscillations caused by external fluctuating power disturbances. They could still happen even when power system stabilizers (PSSs) are installed, jeopardizing the safety and stability of power grid seriously. The reason for the unsatisfying suppression performance of PSS on forced oscillations is investigated in this paper. The result reveals that limited by the critical stability gain, conventional PSS is hard to mitigate forced oscillations effectively while maintaining the stability of power system. Then, aiming at suppressing forced oscillations, a novel PSS with proportional-resonant controller is proposed. By leveraging proportional-resonant controller, the amplification factor of the disturbance at the oscillation frequency is reduced significantly without approaching the critical stability gain. Hence, the stability of the system is not influenced. The simulation results in 16-machine and 68-bus system demonstrate that, compared with conventional PSS, the proposed method has better performance on suppressing forced oscillations of both single mode and multimode caused by various types of disturbances. [ABSTRACT FROM AUTHOR]

Despite recognition from a vast number of publications that contemplate performance studies of so called saturated reactors aimed at voltage regulation, the subject, when weighed against the benefits, such as new material based technologies and application perspectives, still presents various challenging topics. In fact, investigations made concerning the physical principles governing its constructive design, the retrieval of representative electric and magnetic parameters, the development of computational models, enabling means for evaluating the effectiveness of the processes for restoring the busbar voltage, among other aspects, are still deserving of research, development and modeling. Given this setting, the present paper considers aspects that guide the physical design concepts and parameterization of these devices, computational strategies aimed at the computational modeling and evaluation of such equipment in voltage regulation and other correlated phenomena. Theoretical results are compared to corresponding experimental performances intent on defining the established models' degree of adhesion. [ABSTRACT FROM AUTHOR]

In this paper, fuzzy logic-based power system stabilizer (FPSS) is designed to have effective damping. As to achieve impressive performance of a controlled plant, the rule base/fuzzy rule matrix (FRM) of a fuzzy logic controller (FLC) is designed by trial–error method, which is a time-consuming process. In this paper, a systematic procedure is given to design FRM for effective damping of single-machine infinite-bus (SMIB) and two-area four-machine ten-bus power system. To design the novel FRM, the existing rule tables, proposed by different researchers, are tested with SMIB system, and empirical relationships have been drawn. The response validity and rule justification is carried out using linguistic phase-plane trajectory method. Finally, the contribution to design FRM is made to get effective damping for SMIB as well as a multi-machine system. The effectiveness of the FPSS based on the proposed FRM over a wide range of operating conditions on SMIB system and the comparison of system response without PSS, with Conventional PSS, and with FPSS is carried out. Similarly, the multimachine power system is considered without PSS and with FPSS, and performance comparison is carried out. The response of FPSS with proposed FRM enables to show the effective damping of system oscillations. [ABSTRACT FROM AUTHOR]

Two main topics regarding the energy function approach for voltage stability analysis are addressed in this paper. First, the problem of the critical low voltage solution identification is discussed. For this sake, the ability of the tangent vector method to correctly identify the low voltage solution that ultimately coalesce with the power system operating solution is investigated. It is shown that the methodology is consistent with the mechanism of the low voltage solutions. Second, the definition of the group of buses related to the weak area of a system is addressed. It is shown that the combined use of the low voltage solution methodology and the tangent vector technique yields good results. Tests were carried out in the IEEE-30, IEEE-57 and IEEE-118 bus test systems. [ABSTRACT FROM AUTHOR]

Computer simulations involving electric power systems need to be implemented upon structures that execute actions and which are able to reach specific proposals for switching and control. This very question is incorporated into the underlying proposal of this paper, which is shown through the presentation of an analysis performed using the software Alternative Transients Program, where the two main resources: MODELS language simulation and Transients Analysis of Control Systems were used in order to simulate the performance of the distributed generator controllers under different modes of operation and analyze their influence on the stability of an industrial plant. In those simulated cases, where disturbances were encountered, causing the opening and closing of switching commands, the regulators output signals are modified, thus controlling the behavior of the electrical and mechanical magnitudes associated with the generators. The obtained results show the performance of distributed generator controllers as adequate, in that they guarantee the stability of the industrial system, when responding to alterations in its operating conditions. [ABSTRACT FROM AUTHOR]

This paper proposes an improved voltage regulation method in a multisource-based dc electrical power system in the more electric aircraft. The proposed approach, which can be used in terrestrial dc microgrids as well, effectively improves the load sharing accuracy under high droop gain circumstance with consideration of cable impedance. Since no extra communication line and controllers are required, it is easily implemented and also increases the system modularity and reliability. By using the proposed approach, the dc transmission losses can be reduced and the system stability is not deteriorated for normal and fault scenarios. In this paper, optimal droop gain settings are investigated and the selection of individual droop gains as well as the proportional power sharing ratio has been described. Simulation and experimental results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Power systems are subject to undesirable small oscillations that might grow to cause system shutdown and consequently great loss of national economy. The present manuscript proposes two designs for observer-based robust power system stabilizer (PSS) using Linear Matrix Inequality (LMI) approach to damp such oscillations. A model to describe power system dynamics for different loads is derived in the norm-bounded form. The first controller design is based on the derived model to achieve robust stability against load variation. The design is based on a new Bilinear matrix inequality (BMI) condition. The BMI optimization is solved interatively in terms of Linear Matrix Inequality (LMI) framework. The condition contains a symmetric positive definite full matrix to be obtained, rather than the commonly used block diagonal form. The difficulty in finding a feasible solution is thus alleviated. The resulting LMI is of small size, easy to solve. The second PSS design shifts the closed loop poles in a desired region so as to achieve a favorite settling time and damping ratio via a non-iterative solution to a set of LMIs. The approach provides a systematic way to design a robust output feedback PSS which guarantees good dynamic performance for different loads. Simulation results based on single-machine and multimachine power system models verify the ability of the proposed PSS to satisfy control objectives for a wide range of load conditions. [ABSTRACT FROM AUTHOR]

The development of optimization techniques in power system is to determine the sizing of Flexible AC Transmission System (FACTS) devices such as Unified Power Flow Series Compensator (UPFC) controller in improving the voltage stability and bus voltage margin. An attempt is made to modify the Particle Swarm Optimization (PSO) and Artificial Bee Colony (ABC) with Hybrid-Genetic Algorithm (H-GA) for determination of sizing of the device. Fast Voltage Stability Index (FVSI) is used to identify the location of the device to be connected. The proposed methods are implemented in IEEE 30 Bus system and its results are tabulated for each technique. [ABSTRACT FROM AUTHOR]

With the development of power system interconnection, low-frequency oscillation is becoming more and more prominent, and may cause instability of power systems. In this paper, two sources of uncertainty are modelled: plant and controller uncertainties. The non-linear dynamics of power systems under wide load variations are represented by a linear model with uncertainty in the form of a norm-bounded structure. The controller uncertainty resulting from resistor tolerance used in practical implementation is also represented by a norm-bounded model. This paper presents the design of resilient power system stabilizers (PSSs). The proposed PSS keeps stability against plant uncertainty and controller gain errors in the form of a linear matrix inequality (LMI)-sufficient condition. In addition to robust stability, the PSS design achieves regional pole placement to control the settling time and damping ratio, and consequently achieves good dynamic performance. The simulation shows that the proposed PSS design is efficient using the power system model and can drastically improve the dynamic performance of a single machine and a multi-machine power system. [ABSTRACT FROM AUTHOR]