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Active and reactive power tracing can play an important role in achieving a fair electricity market because system operating, usage, and service costs are appropriately apportioned. However, the presence of power flows around a closed circular trajectory causes the application of commonly used tracing algorithms to fail, leaving power tracing an open question. To overcome this drawback, a novel methodology for tracing the active and reactive power considering the existence of circulating power flows (CPFs) is presented in this paper. The strategy consists of identifying branches possibly involved in this kind of flow and merging the involved buses into a supernode allowing the tracing algorithm to perform normally. Furthermore, the approach properly classifies transmission lines according to their behavior to accurately trace the reactive power flow. The methodology is tested using two power systems presenting diverse operating scenarios. The results demonstrate that the proposed tracing methodology appropriately handles CPFs, representing an advantage over previously proposed approaches. [ABSTRACT FROM AUTHOR]

The paper presents the model of a voltage source converter--high voltage direct current (VSC-HVDC) suitable for optimal power flow (OPF) solutions using Newton's algorithm. The VSC-HVDC's ability to provide independent control of the converters ac voltage magnitudes and phase angles relative to the system voltage, which allows the use of separate active and reactive power control loops for system regulation, is well represented by the model. In this new development in Newton OPF, the VSC-HVDC system equations are incorporated directly into the matrix 14z for a unified optimal solution in a single frame-of-reference. The multipliers method is used to handle all inequality constraints of variables, leading to highly efficient OPF solutions of constrained power networks. The solution approach does not require structural changes in the linearised system of equations during the iterative process using Newton's method. The effectiveness of the VSC-HVDC model and its proposed implementation in Newton OPF is demonstrated by means of two sample systems. Index Terms--Newton method, optimal power flow, voltage-source converter (VSC), VSC-HVDC system.

This contribution deals with the stability analysis of the alternating current arc furnace dynamic operation connected to a supply system using bifurcations theory. The analysis is carried-out in the time domain through the computation of the system eigenvalues and a careful study of the bifurcation diagrams and stability at the equilibrium points. The effect of the bifurcation parameter variation on the arc furnace dynamic behavior is analyzed. The method allows an appropriate assessment of nonlinear oscillations produced by of alternating current Electric Arc Furnace. Index Terms--Alternating current electric arc furnaces, bifurcations, dynamic behavior, eigenvalues, nonlinear oscillations, stability.

A new approach for identifying multiple line outages in electric power systems by using data obtained from synchrophasor measurements is proposed in this paper. A novelty of the proposal is the application of the sensitivity theory to the system's alternating current power flow model to determine the most likely contingency scenario, with not previous knowledge of the number of line outages. Since the proposal considers both voltage and current synchrophasor measurements, a set of observable lines is defined such that their outages are identified directly from those measurements. In this context, the more observed transmission lines there are, the smaller the search space for identifying potential outages in unobserved transmission lines. On the other hand, the detection problem of multiple-line outages is decomposed into the sequential uncovering of different single-line outages by using the concept of total derivative. The reduction of the search space and the decomposition of the multiple-line outages problem significantly reduce the computational burden of the proposed approach. Finally, numerical results demonstrate that the proposal presents a very satisfactory percentage of success for identifying the correct set of line outages, even when a limited number of PMUs is embedded in the system. [ABSTRACT FROM AUTHOR]

Interarea power oscillation damping enhancement in large interconnected power systems is often accomplished using supplementary controls at the synchronous machines involved and with the use of flexible ac transmission system devices. The power system literature has demonstrated that wide area signals could be more effective than the local signals for these controllers. In some cases where phasor measurement units are used, all the required control signals may not be available. To alleviate these cases, control signals are obtained using estimated signals from a “dynamic state estimator,” and a robust supplementary controller is deployed. In this paper, the cited strategy is illustrated using a static var compensator. The feasibility of the proposed method has been demonstrated on the IEEE 50-generator test system. [ABSTRACT FROM AUTHOR]

This paper proposes a novel tracking state estimator to process both fast-rate synchronized phasor and slow-rate supervisory control and data acquisition (SCADA) measurements. The former are assumed to be in limited number. The latter are exploited as and when they arrive to the control center. In order to restore observability, after each execution of the tracking state estimator, forecast SCADA measurements are used as pseudo-measurements in the next estimation. An event detection analysis allows assessing if the system is in quasi-steady-state. If so, an innovation analysis is performed to identify and eliminate erroneous SCADA measurements. The system state is computed by Hachtel’s augmented matrix method. The option of exploiting time-tagged SCADA measurements is also considered. The method is illustrated through detailed dynamic simulations of a test system evolving toward voltage collapse, with and without emergency control. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel active power redispatch sequential approach to solve the transient stability-constrained optimal power flow (TSC-OPF) problem for the preventive control of transient stability. Based on an independent transient stability assessment of the power system for a given contingency scenario, two proposed power redispatch constraints are formulated and embedded into a conventional OPF formulation. Since these two new constraints only depend on steady-state variables, the dimension of the resulting TSC-OPF model is similar to that of a conventional OPF model and can be solved by standard optimization methods to perform a nonheuristic active power redispatch. The stabilization process is performed by sequentially solving the optimization and the transient stability problems until a suitable generation dispatch that provides a transiently stable equilibrium point is assessed. The validity and the effectiveness of the proposed method are numerically demonstrated in the WSCC three-machine, nine-bus system and an equivalent model of the Mexican power system. [ABSTRACT FROM PUBLISHER]

As power generation plants which use wind energy are increasingly integrated into existing electric power systems, it becomes important to evaluate how the wind power uncertainties affect the power system's operation as well as its interdependency with those infrastructures utilized to transport the various forms of primary energy that is converted into electric energy. This paper proposes a robust optimization model for analyzing the interdependency between natural gas, coal and electricity infrastructures considering their operation constraints and wind power uncertainties. The optimization model obtains an uncertainty-immunized solution in a unified framework based on the balance of nodal energy flows, which remains feasible and nearly optimal for all values of uncertain data. Case studies are presented to verify the effectiveness of the proposed solution for a multi-energy system composed by the IEEE-118 test system coupled to a 15-nodes natural gas network and a 4-nodes coal distribution system as well as for the real life Belgian natural gas and electricity infrastructures. [ABSTRACT FROM PUBLISHER]

This paper introduces an advanced model of the STATCOM suitable for steady-state and dynamic simulations of large-scale power systems. It allows for a comprehensive representation of the STATCOM's AC and DC circuits—this is in contrast to current practice where the STATCOM is represented using an equivalent variable voltage source which is not amenable to a proper representation of its DC circuit. The new STATCOM model comprises a voltage source converter (VSC) in series with an LTC transformer. The former is represented by a complex tap-changing transformer whose primary and secondary windings would correspond, in a notional sense, to the VSC's AC and DC buses, respectively. The magnitude and phase angle of the complex tap changer correspond to the amplitude modulation index and the phase shift that would exist in a PWM inverter to enable either reactive power generation or absorption purely by electronic processing of the voltage and current waveforms within the VSC. The numerical technique employed to solve the STATCOM model is the Newton-Raphson method for both operating regimes, the steady-state and the dynamic-state. The latter involves discretization of the STATCOMs and synchronous generators differential equations so that the nonlinear algebraic equations and the discretized differential equations are linearized around a base operating point and assembled together in a unified frame-of-reference for robust iterative solutions. [ABSTRACT FROM PUBLISHER]

This paper proposes the integration of steady-state models of several types of wind generators into a power flow algorithm with automatic load-frequency control. Since the system frequency deviation is considered a state variable to be computed by the power flow solution, this formulation helps identify the operating point of wind generators after the action of the primary frequency control when power imbalances have occurred. The mathematical formulation of fixed-speed wind generators is presented based on the steady-state representation of the induction generator. Furthermore, as variable-speed wind generators keep gaining prominence in power systems, their potential contribution to frequency support is also analyzed herein. These models are formulated within the power flow approach by using a unified single frame of reference and the Newton-Raphson algorithm. The proposed approach is then applied to the analysis of a three-machine, eight-bus system and the IEEE-14 bus test system. [ABSTRACT FROM PUBLISHER]

The restructuring of energy markets has increased the concern about the existing interdependency between the primary energy supply and electricity networks, which are analyzed traditionally as independent systems. The aim of this paper is focused on an integrated formulation for the steady-state analysis of electricity and natural gas coupled systems considering the effect of temperature in the natural gas system operation and a distributed slack node technique in the electricity network. A general approach is described to execute a single gas and power flow analysis in a unified framework based on the Newton–Raphson formulation. The applicability of the proposed approach is demonstrated by analyzing the Belgian gas network combined with the IEEE-14 test system and a 15-node natural gas network integrated with the IEEE-118 test system. [ABSTRACT FROM PUBLISHER]

This article presents an enhanced model of a two-terminal voltage source converter based high-voltage DC system suitable for optimal power flow analysis in electric power systems. Both the back-to-back and the point-to-point voltage source converter and high-voltage DC schemes are addressed. Unlike to other proposals, the new model considers the operational constraints associated with the MVA ratings of the converters. The proposed model is implemented in a Newton-based optimal power flow approach and tested on the Baja California North 160-bus realistic power system. Simulation results show that a practically feasible optimal power flow solution can be obtained by considering the MVA converters' limits. [ABSTRACT FROM PUBLISHER]

An electrical power system's feasibility region is defined by all operating points that can be reached by continuous variation of its parameters without leading the system to instability. The information about the size of this region and its boundary is important for utilities to guarantee the secure operation of power systems. In this paper a new approach is proposed to determine the feasibility region without applying the principle of continuation. For this purpose, a particle swarm optimization is developed to transform the problem of finding one equilibrium point for a given system's conditions into a problem of computing several (all in most cases) equilibrium points for the same operating conditions. Determining several equilibrium points for all possible operating conditions, then joining all results, allow us to assemble a complete bifurcation diagram of the system under analysis. A benchmark power system is used to numerically illustrate the effectiveness of the proposed approach, whose results are compared with those obtained by the application of a continuation method. [ABSTRACT FROM AUTHOR]

This paper presents a new, significantly improved, approach to formulate a global transient stability-constrained optimal power flow (TSC-OPF), where the sets of dynamic and transient stability constraints to be considered in the optimization process are reduced to one single stability constraint. This constraint is derived from dynamic information provided by the SIngle Machine Equivalent (SIME) method and is only expressed in terms of steady-state variables, which allows us to diminish the length of the time-domain simulation to be included into the global TSC-OPF to a single (initial) time step. In this way, the size of the resulting optimization problem is reduced to one very similar to that of a conventional OPF, overcoming the main drawback of global TSC-OPF techniques (its huge dimension) while maintaining its accuracy and improving its practical application to real power networks. Effectiveness of the proposal is demonstrated by numerical examples on the WSCC three-machine, nine-bus system and the Mexican 46-machine, 190-bus system. [ABSTRACT FROM PUBLISHER]

This paper proposes a new approach to model stability and security constraints in optimal power flow (OPF) problems based on a neural network (NN) representation of the system security boundary (SB). The novelty of this proposal is that a closed form, differentiable function derived from the system's SB is used to represent security constraints in an OPF model. The procedure involves two main steps: First, an NN representation of the SB is obtained based on back-propagation neural network (BPNN) training. Second, a differentiable mapping function extracted from the BPNN is used to directly incorporate this function as a constraint in the OPF model. This approach ensures that the operating points resulting from the OPF solution process are within a feasible and secure region, whose limits are better represented using the proposed technique compared to typical security-constrained OPF models. The effectiveness and feasibility of the proposed approach is demonstrated through the implementation, as well as testing and comparison using the IEEE two-area and 118-bus benchmark systems, of an optimal dispatch technique that guarantees system security in the context of competitive electricity markets. [ABSTRACT FROM AUTHOR]

Abstract: Determining suitable locations of series-connected controllers is a practical problem when it is necessary to install them in modern power systems. The aim of this paper is to find the best location of series controllers in order to reduce the proximity to instability of a current operating point of a power system, from a transient stability viewpoint. In order to achieve this goal, a general approach has been developed based on an index of proximity to instability and trajectory sensitivity analysis. An efficient way to carry out multi-parameter sensitivities is formulated analytically and solved simultaneously with the set of differential-algebraic equations representing power system''s dynamics within a single-frame of reference. Simulations are performed on 9-bus and 39-bus benchmark power systems for illustration purposes. Results show that the proposed approach provides the most effective location of series-connected controllers to improve the power system''s transient behavior. [Copyright &y& Elsevier]

This paper presents a new approach to transient stability control using global transient stability-constrained optimal power flow (TSC-OPF) methods. Its novelty consists in using the single machine equivalent (SIME) method to perform (and improve) two main important functions of global TSC-OPF approaches: first, SIME is used to efficiently perform the power system transient stability analysis; second, SIME determines a stable one machine infinite bus equivalent rotor angular trajectory that is used as the reference stability constraint, at one specific integration step. In this way, the stability constraint is adjusted by SIME, at each iteration of the TSC-OPF method, in order to accurately reflect power system dynamic behavior. The prowess and main characteristics of the proposed approach are shown by numerical examples. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) power units, which produce electrical energy from salinity gradient sources located at coastlines, are a technology still in the process of maturation; however, there is an expectation that this technology will need to be integrated into electrical distribution networks. Such integration will drive changes in the electric response of the distribution systems which may lead to harmful operating conditions. Power flow analysis is a tool used to reveal the steady-state operating condition of distribution systems and which could be extended to study and address the integration of PRO power units. To the best of the authors' knowledge, such extension of power flow analysis has not yet been addressed in the literature. Accordingly, this paper comprehensively provides a model to evaluate the electric current and complex power produced by PRO power units. This model is directly embedded in the forward-backward sweep (FBS) method, extending the power flow analysis of electric distribution systems in this way so as to consider the integration of PRO power units. The resulting approach permits revealing of the steady-state operating response of distribution systems and the effects that may be driven by the integration of PRO power units, as corroborated through numerical results on a 14-node test distribution system. [ABSTRACT FROM AUTHOR]

Load forecasting provides essential information for engineers and operators of an electric system. Using the forecast information, an electric utility company's engineers make informed decisions in critical scenarios. The deregulation of energy industries makes load forecasting even more critical. In this article, the work we present, called Nearest Neighbors Load Forecasting (NNLF), was applied to very short-term load forecasting of electricity consumption at the national level in Mexico. The Energy Control National Center (CENACE—Spanish acronym) manages the National Interconnected System, working in a Real-Time Market system. The forecasting methodology we propose provides the information needed to solve the problem known as Economic Dispatch with Security Constraints for Multiple Intervals (MISCED). NNLF produces forecasts with a 15-min horizon to support decisions in the following four electric dispatch intervals. The hyperparameters used by Nearest Neighbors are tuned using Differential Evolution (DE), and the forecaster model inputs are determined using phase-space reconstruction. The developed models also use exogenous variables; we append a timestamp to each input (i.e., delay vector). The article presents a comparison between NNLF and other Machine Learning techniques: Artificial Neural Networks and Support Vector Regressors. NNLF outperformed those other techniques and the forecasting system they currently use. [ABSTRACT FROM AUTHOR]

This letter proposes a new area interchange control model within the context of Newton-based power flow studies, which considers the violation of the maximum amount of power that can be transferred through tie-lines. The validity and the effectiveness of the proposed approach are numerically demonstrated. [ABSTRACT FROM AUTHOR]

In this contribution, a method for harmonic state estimation (HSE) of electrical systems using the discrete exponential expansion (DEE), singular value decomposition (SVD) and a variable measurement model is presented. Variable harmonics, interharmonics, and subharmonics can be estimated using this DEE-SVD time-domain methodology, depending on the number of state variables in the system model and the measurements related through a variable measurement equation, which is proposed as a function of a variable number of measurements and their derivatives to define over, normal and under-determined conditions, respectively. The observability analysis can be verified using the SVD and the resulting null-space vectors, if the electrical system is not completely observable; this analysis can define observable system areas. The HSE regularly receives a limited number of measurements from the system, performs the state estimation and evaluates the global state of the actual harmonic condition. The discrete exponential expansion Newton method determines the periodic steady-state under a particular harmonic condition, obtains a convenient initial steady-state condition to apply the SVD and performs the HSE with a small state estimation error. Noisy measurements adversely affect the state estimation and may increase the state estimation error. The time-domain DEE-HSE can be used to enhance the operation and control of electrical systems under harmonic distortion conditions, e.g., to control active and passive harmonic filters. The state estimation results have been validated through direct comparison against the response obtained with the PSCAD/EMTDC® simulator. • A methodology based on SVD and discrete exponential expansions for harmonic state estimation is proposed. • Variable harmonics and interharmonics are estimated, with over, normal and under-determined conditions. • The observability analysis has been verified using the SVD. Noisy measurement effects are considered. • The HSE received partial measurements from the system and performs the estimation of the state variables. • HSE results have been successfully validated against PSCAD/EMTDC®. [ABSTRACT FROM AUTHOR]