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This paper intends to address the dynamic repair scheduling of electric power transmission systems based on look-ahead strategy approximation. The objective is to minimize system functionality loss during the restoration stage after disruptive events. A series of decisions regarding which damaged component to be repaired has to be made successively considering currently available information of repair time and its uncertainty in the future. To achieve this goal, the dynamic repair scheduling problem is represented as a stochastic Markovian decision process (MDP). To overcome the computational complexity of MDP derived from exponentially growing state space, the cost-to-go function is approximated by a look-ahead strategy based on repair importance ordering. Stage-dependent coefficients are used to balance the approximated functionality loss at different decision stages. The tradeoff between the efficiency and optimality can be achieved by adjusting the look-ahead depth and the updating policy of look-ahead strategy. The IEEE-14 and 118-bus systems were used for performance evaluation of the proposed method and comparison with various approaches. The results show that it can produce decisions close to the best-known solutions within small amount of time. [ABSTRACT FROM AUTHOR]

This paper studies the optimal transmission switching (OTS) problem for power systems, where certain lines are fixed (uncontrollable) and the remaining ones are controllable via on/off switches. The goal is to identify a topology of the power grid that minimizes the cost of the system operation while satisfying the physical and operational constraints. Most of the existing methods for the problem are based on first converting the OTS into a mixed-integer linear program (MILP) or mixed-integer quadratic program (MIQP), and then iteratively solving a series of its convex relaxations. The performance of these methods depends heavily on the strength of the MILP or MIQP formulations. In this paper, it is shown that finding the strongest variable upper and lower bounds to be used in an MILP or MIQP formulation of the OTS based on the big- $M$ or McCormick inequalities is NP-hard. Furthermore, it is proven that unless $P=NP$ , there is no constant-factor approximation algorithm for constructing these variable bounds. Despite the inherent difficulty of obtaining the strongest bounds in general, a simple bound strengthening method is presented to strengthen the convex relaxation of the problem when there exists a connected spanning subnetwork of the system with fixed lines. With the proposed bound strengthening method, remarkable improvements in the runtime of the mixed-integer solvers and the optimality gaps of the solutions are achieved for medium- and large-scale real-world systems. [ABSTRACT FROM AUTHOR]

Independent system operators (ISOs) are responsible for the secure and economic operation of the power systems. Accordingly, ISOs should solve an optimal power flow to minimize the operating cost of a system while meeting the system's security constraints. However, transmission congestion could drastically limit more economical generating units from being dispatched in the power system operation. In this paper, a decentralized transmission switching is introduced in the operation of multi-area power systems to manage the congestion both on regional transmission lines and tie lines while considering credible contingencies. Our proposed methodology relies on a decentralized optimization methodology. Thus, regional control centers in areas would be able to locally manage the congestion within their regional networks as well as tie lines connecting them to their neighboring areas. Several testing systems are studied in this paper to test the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents an online event location estimating process in a wide-area power system using the phasor measurement unit (PMU). For real-world applications of PMU-based event location estimation (ELE), it is necessary to consider the insufficiency of PMU data caused by a lack of PMUs, communication failure, PMU malfunction, etc., because insufficient PMU data cannot guarantee event observability over the entire network. To ensure possible event locations in a real-world system, an estimation method is developed by combining offline zonal analysis and an online ELE algorithm. The K-mean clustering method is utilized for electrical-bus clustering, which enables us to recognize separate electrical zones (EZs). Then, we propose a two-stage ELE algorithm by estimating the event EZ and localizing the specified event section within the estimated EZ. Proposed ELE algorithm is applied to a real-world PMU data collected from southwestern part of the United States. Finally, successful results from a real-world PMU data application are presented at the end of this paper. [ABSTRACT FROM AUTHOR]

This paper extends the dynamic coherency determination (DCD) method by including Type-3 wind power plants (WPPs) models in the coherency evaluation process and quantifies impacts of the high depth of wind power penetration on the coherency phenomena of interconnected power systems. The method is based on frequency-deviation signals, measured at nongenerator buses and terminal buses of WPPs and synchronous generators. Salient features of the presented method are its ability to account for the hybrid nature of enhanced generic models of Type-3 WPPs and expanding notion of the power system coherency beyond the classical definition by including models of Type-3 WPPs. This paper also investigates impacts of the high depth of wind power penetration; i.e., up to 30%, on the coherency structure of the 16-machine/68-bus NPCC equivalent system. The studies are based on time-domain simulations in PSS/E software. The investigations reveal that Type-3 WPPs can introduce new coherent areas, significantly change areas’ boundaries and number of areas, and alter frequencies/dampings of interarea modes. [ABSTRACT FROM AUTHOR]

This paper presents a new method for studying electromechanical transients in power systems using three phase, combined transmission and distribution models (hybrid models). The methodology models individual phases of an electric network and associated unbalance in load and generation. Therefore, the impacts of load unbalance, single phase distributed generation and line impedance unbalance on electromechanical transients can be studied without using electromagnetic transient simulation (EMTP) programs. The implementation of this methodology in software is called the Three Phase Dynamics Analyzer (TPDA). Case studies included in the paper demonstrate the accuracy of TPDA and its ability to simulate electromechanical transients in hybrid models. TPDA has the potential for providing electric utilities and power system planners with more accurate assessment of system stability than traditional dynamic simulation software that assume balanced network topology. [ABSTRACT FROM PUBLISHER]

Total transfer capability (TTC) is an effective indicator to evaluate the transmission limit of the interconnected systems. However, due to the large-scale wind power integration, operation conditions of a power system may change rapidly, yielding time-varying characteristics of the TTC. As a result, the traditional time-consuming transient stability constrained TTC model is unable to assess the online transmission margin. In this paper, we propose an online measurement-based TTC estimator using the nonparametric analytics. It consists of three major components: the probabilistic data generation, the composite feature selection, and the group Lasso regression-based training scheme. Specifically, we present a probabilistic data generation approach to take into account the uncertainties of the day-ahead generation scheduling and to reduce the number of redundant or infeasible data. Then, the composite feature selection is used to reduce the dimension of the generated data and identify the features which are highly correlated with TTC. The features are determined by the maximal information coefficients and nonparametric independence screening approach. Finally, these selected features are trained by the group Lasso regression to learn the correlation between the TTC and the online measurements. Once real-time measurements are available, the TTC can be assessed immediately through the learned correlation relationship. Extensive numerical results carried out on the modified New England 39-bus test system demonstrate the feasibility of the proposed TTC estimator for online applications. [ABSTRACT FROM AUTHOR]

Robust simulation is essential for reliable operation and planning of transmission and distribution power grids. At present, disparate methods exist for steady-state analysis of the transmission (power flow) and distribution power grid (three-phase power flow). Due to the nonlinear nature of the problem, it is difficult for alternating current power flow and three-phase power flow analyses to ensure convergence to the correct physical solution, particularly from arbitrary initial conditions, or when evaluating a change (e.g., contingency) in the grid. In this paper, we describe our equivalent circuit formulation approach with current and voltage variables, which models both the positive sequence network of the transmission grid and three-phase network of the distribution grid without loss of generality. The proposed circuit models and formalism enables the extension and application of circuit simulation techniques to solve for the steady-state solution with excellent robustness of convergence. Examples for positive sequence transmission and three-phase distribution systems, including actual 75k+ nodes Eastern Interconnection transmission test cases and 8k+ nodes taxonomy distribution test cases, are solved from arbitrary initial guesses to demonstrate the efficacy of our approach. [ABSTRACT FROM AUTHOR]

Visualization of electric power transmission systems centers on the one-line diagram, which is a simplified logical depiction of the circuit's connections and elements. Such a graph drawing is useful for supporting the study, analysis, and presentation of power system data. This paper proposes an automated way to generate one-line diagrams, given substation identifiers with geographic tags and the system bus-branch model. Two approaches to drawing the substations are given: a force-directed approach and a greedy approach, which in different ways modify the position and size of substations as drawn. For transmission line routing between substations, a Delaunay-based method is employed, which segments the transmission line drawings to avoid overlapping with substations and other lines. These methods show good visual properties in spacing, geographic context, relatively straight lines, and computational speed. The result is that large power systems, real and synthetic, can be easily and quickly visualized with a diagram that merges geographic context with logical clarity. [ABSTRACT FROM AUTHOR]

This paper studies key aspects of preventive and corrective security strategies to coordinate flexible transmission network infrastructure. To do so, we propose a two-stage stochastic optimization model that can efficiently coordinate available preventive and corrective control actions (pre- and post-contingency) from flexible network technologies, generation, and demand, while explicitly considering the likelihood of postcontingency events and wind/solar uncertainty. This stochastic/probabilistic model constitutes the counterfactual against which current deterministic, preventive operational practices are compared. Flexible network equipment such as HVDC and FACTS devices are efficiently modeled through a tight MILP representation and network losses are also included through a linear representation. Through several case studies, we demonstrate the advantages of probabilistic, corrective security to improve coordination of HVDC and FACTS setpoints and thus reduce network congestion and reserve holding levels, improving the overall efficiency of the system operation. We also quantify the value loss associated with current deterministic, preventive control operational practices when coordinating setpoints of flexible network equipment, demonstrating that adding flexible network technology could even increase system costs under a preventive security approach. [ABSTRACT FROM AUTHOR]

Power system reliability evaluation (PSRE) typically involves with finding the system (or bus) reliability index from known component reliability parameters. In this paper, we consider the case of using the system (or bus) reliability index to obtain the unknown component reliability parameter (UCRP). This problem is called the inverse PSRE problem. Analytical model of the inverse PSRE problem is constructed and formulated as the nonlinear algebraic equations. In particular, analytical models for the composite generation and transmission system and the generating system are developed based on the state enumeration method. Solution method using the interval analysis is developed by transforming the nonlinear algebraic equations into the interval nonlinear equations with UCRPs represented by the interval numbers. A modified Krawczyk-operator algorithm based on interval bisection elimination scheme is developed to overcome the difficulty of selecting the appropriate initial interval in the problem-solving process. The RBTS, IEEE-RTS, and a 91-bus system are used for the case study to verify the effectiveness of the proposed model and the solution method. In addition, an application to power system planning is investigated to examine how the component reliability parameters can be modified quantitatively to achieve the desired system reliability improvement. [ABSTRACT FROM AUTHOR]

As the rapid development of natural-gas fired units (NGUs), power systems begin to rely more on a natural gas system to supply the primary fuel. On the other hand, natural gas system contingency might cause the nonavailability of NGUs and inevitably jeopardize power system security. To address this issue, this paper studies security-constrained joint expansion planning problems for this combined energy system. We develop a computationally efficient mixed-integer linear programming (MILP) approach that simultaneously considers N-1 contingency in both natural gas system and electricity power system. To reduce the combinatorial search space of MILP models, an extension of a reduced disjunctive model is proposed to decrease the numbers of binary and continuous variables as well as constraints. The involving nonlinear terms in N-1 constraints are exactly linearized without sacrificing any optimality. Numerical results on two typical integrated energy systems demonstrate the necessity of extending N-1 criterion to the whole network of a combined energy system. Experimental results also show that compared with the conventional approach, our proposed MILP approach achieves a great computational performance improvement in solving security-constrained co-optimization expansion planning problems. [ABSTRACT FROM AUTHOR]

In this paper, solution operator discretization methods with linear multistep and implicit Runge–Kutta (SOD-LMS/IRK) are presented for efficient eigen-analysis of large delayed cyber-physical power system (DCPPS). First, the time integration-based discretization generates highly structured approximate matrices to the solution operator. Exploitation of the structure ensures low computational burden and high efficiency in solving the matrix-inversion-vector product involved in eigenvalue computation. Second, the implicitly restarted Arnoldi algorithm is employed to compute critical eigenvalue from the solution operator's discretized matrices. SOD-LMS/IRK are endowed with scalability in analyzing very large DCPPS by fully utilizing the inherent sparsity in the augmented system state matrices. The main contribution of the presented SOD-LMS/IRK is the improved efficiency and scalability of existing SOD-PS (pseudo-spectral collocation) and SOD-LMS/IRK. Numerical results on the 16-generator 68-bus test system, a 516-bus, and a 33028-bus real-life large transmission systems validate the effectiveness of the proposed SOD-LMS/IRK. [ABSTRACT FROM AUTHOR]

The power flow is a nonlinear problem that requires a Newton's method to be solved in dc microgrids with constant power terminals. This paper presents sufficient conditions for the quadratic convergence of the Newton's method in this type of grids. The classic Newton's method as well as an approximated Newton's method are analyzed in both master–slave and island operation with droop controls. Requirements for the convergence as well as for the existence and uniqueness of the solution starting from voltages close to 1 pu are presented. Computational results complement this theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper develops an effective model for microgrid optimal scheduling with dynamic network reconfiguration. Network reconfiguration can effectively alter local power flow and thus provide an opportunity to reduce microgrid distribution network losses during grid-connected operation (supporting microgrid economic objectives) and to reduce potential load curtailments during the islanded operation (supporting microgrid reliability objectives). The proposed optimal scheduling model is decomposed into a grid-connected operation master problem and an islanded operation subproblem. A novel and highly accurate dynamic linear power flow model, with the ability of line switching, is developed and included in both problems. The optimal schedule determined in the master problem is assessed to meet the microgrid islanding feasibility in the subproblem. If infeasible, the decision variables are amended using the islanding cuts, which will accordingly revise the network reconfiguration, as well as the schedule of dispatchable units, energy storage, and adjustable loads. The simulation results on a test microgrid demonstrate the effectiveness and satisfying performance of the proposed model. [ABSTRACT FROM AUTHOR]

The risk of cascading blackouts greatly relies on failure probabilities of individual components in power grids. To quantify how component failure probability (CFP) influences blackout risk (BR), this paper proposes a sample-induced semianalytic approach to characterize the relationship between CFP and BR. To this end, we first give a generic component failure probability function (CoFPF) to describe CFP with varying parameters or forms. Then, the exact relationship between BR and CoFPFs is built on the abstract Markov-sequence model of cascading outages. Leveraging a set of samples generated by blackout simulations, we further establish a sample-induced semianalytic mapping between the unbiased estimation of BR and CoFPFs. Finally, we derive an efficient algorithm that can directly calculate the unbiased estimation of BR when the CoFPFs change. Since no additional simulations are required, the algorithm is computationally scalable and efficient. Numerical experiments well confirm the theory and the algorithm. [ABSTRACT FROM AUTHOR]

In conventional contingency analysis (CA), the overloading of transmission lines is identified by the violation of current or power flow rather than the temperature rise. Thus, the transient thermal behavior of transmission lines is usually neglected, which may cause underestimation of power transfer capability and lead to misoperations. In this paper, a new CA method that considers the transient thermal behavior of overhead transmission lines is proposed, where a transient heat balance based power flow (THB-PF) model is established to estimate the temperature dynamics of the lines after contingencies. The THB-PF model is represented by algebraic differential equations, which can be solved as a sequence of extended power flow problems by discretizing the differential equations into difference equations. Moreover, a simplified solution method for the THB-PF is also developed, in which the THB difference equations are linearized and solved separately from the power flow equations. The simplified method can yield an acceptable approximate solution within a considerably shorter time. Numerical simulations verify the effectiveness and efficiency of the proposed methods. [ABSTRACT FROM AUTHOR]

Transmission network expansion planning (TNEP) is expected to cope with the power transmission inadequacy problem resulting from rapid growth of wind generation in power systems. However, due to significant uncertainties on the generation side, TNEP based solely on one snapshot or a limited number of scenarios cannot capture the time-variant characteristics of wind power and may be suboptimal. In this paper, a new heuristic methodology for TNEP based on chronological evaluation is presented. First, to assess the transmission adequacy, the multiperiod DC optimal power flow considering the generators’ ramping limits is employed for a system production simulation covering an entire year. Second, two sensitivity factors derived from Lagrange multipliers, i.e., the sensitivity factors of the branch capacity and the branch admittance, are applied to determine the initial set of the transmission network expansion plan (I-STNEP). Finally, the cost-benefit incremental relationship index and a degressive method are used to identify the best subset of the transmission network expansion plan within the I-STNEP. Simulation results based on a 3000-bus real-world network in northern China validate the effectiveness of the proposed TNEP method. [ABSTRACT FROM AUTHOR]

Electricity companies have been under a great pressure to improve their technical and financial performances in order to survive and thrive in the deregulated environment. Therefore, these companies are seeking for innovative approaches to take the most out of the restricted resources. These approaches inherently concentrate the available budgets to the most critical components. In this regard, prioritizing the system components and identifying the most critical ones play a vital role in the planning and operation of the system. This paper presents a novel approach to prioritize power transmission system components. In the proposed methodology, a criticality factor is defined and implemented to rank the components based on their impacts on the operation of the power system. Furthermore, a complete model of substations including misoperation of circuit breakers and protection systems is, for the first time, taken into account in the critical component identification process. The proposed approach is used to identify the vulnerable parts of the system and assist the decision makers to manage the limited resources. The proposed methodology is, then, applied to the IEEE 24-bus Reliability Test System, and components are prioritized accordingly. [ABSTRACT FROM AUTHOR]

This paper proposes an efficient solution approach based on Benders’ decomposition to solve a network-constrained ac unit commitment problem under uncertainty. The wind power production is the only source of uncertainty considered in this paper, which is modeled through a suitable set of scenarios. The proposed model is formulated as a two-stage stochastic programming problem, whose first-stage refers to the day-ahead market, and whose second-stage represents real-time operation. The proposed Benders’ approach allows decomposing the original problem, which is mixed-integer nonlinear and generally intractable, into a mixed-integer linear master problem and a set of nonlinear, but continuous subproblems, one per scenario. In addition, to temporally decompose the proposed ac unit commitment problem, a heuristic technique is used to relax the inter-temporal ramping constraints of the generating units. Numerical results from a case study based on the IEEE one-area reliability test system (RTS) demonstrate the usefulness of the proposed approach. [ABSTRACT FROM AUTHOR]

Recent years have witnessed significant interest in convex relaxations of the power flows, with several papers showing that the second-order cone relaxation is tight for tree networks under various conditions on loads or voltages. This paper shows that ac-feasibility, i.e., to find whether some generator dispatch can satisfy a given demand, is NP-hard for tree networks. [ABSTRACT FROM AUTHOR]

Oscillations threaten the stability of a power system. Timely detecting oscillations can improve operators' situational awareness of system stability and enable remedial reactions. To detect oscillations during their early stages, this paper proposes a cross-coherence method using multiple-channel phasor measurement unit (PMU) data. Oscillations are related to the peaks in coherence spectra and can be detected by visual inspection and setting up a threshold. Using simulation data, it is shown that the proposed coherence method can detect oscillations even under low signal-to-noise ratios. Three algorithms for estimating coherence spectra are implemented and evaluated. Their performances are compared using Monte Carlo methods. Based on the comparison, this paper makes some recommendations for proper use of the algorithms. [ABSTRACT FROM AUTHOR]

This paper discusses a recent event in the western American power system when a forced oscillation was observed at a frequency that was close to a well-known 0.38-Hz inter-area electromechanical mode frequency of the western system. The event motivates a systematic investigation in this paper on the possibility of resonant interactions between forced oscillations and electromechanical inter-area oscillatory modes in power systems. When the natural oscillatory mode of a power system is poorly damped, and the forced oscillation occurs at a frequency close to system mode frequency at critical locations for the mode, resonance is observed in simulation test cases of the paper. It is shown that the MW oscillations on tie-lines can be as high as 477 MW from a 10-MW forced oscillation in Kundur test system because of resonance. This paper discusses the underlying system conditions and effects as related to resonance in power systems caused by forced oscillations and discusses ways to detect such scenarios using synchrophasors. Simulated data from Kundur two-area test power system as well as measurement data from western American power system are used to study the effect of forced oscillations in power systems. [ABSTRACT FROM AUTHOR]

This paper presents an improved corrective security constrained optimal power flow (CSCOPF) for a meshed AC/DC power transmission network with voltage source converter based multi-terminal HVDC (VSC-MTDC) grids. The security constrains of N-1 contingencies for both AC and DC networks are fully considered in the CSCOPF problem. The corrective actions employed in this paper include not only the traditional long-term rescheduling control actions of the AC system, but also the short term post-contingency fast corrective control of multi-terminal VSC-HVDC. A hybrid method is developed to solve the improved CSCOPF problem and the effectiveness of the proposed method is evaluated and demonstrated in this paper by two example meshed AC/DC power systems. [ABSTRACT FROM AUTHOR]

In this paper we address some shortcomings in existing nonlinear dynamic models of power system experiencing symmetrical and unsymmetrical faults in their transmission/distribution networks. The shortcomings relate to: 1) approximations relating to stator dynamics, internal voltage of the positive sequence network and the dynamics of the negative and zero sequence networks, and 2) existing models are time -variant, which may not be suitable for system studies such as stability and fault detection studies that require time invariant model. The approximations outlined in 1) adversely affect the modeling accuracy, especially that of the system response during the period immediately after the occurrence of faults. We present in this paper a full fault-dependent time-invariant dynamical model of power systems experiencing symmetrical and unsymmetrical faults in their transmission/distribution networks and verify it through simulation studies mimicking real life scenarios. IEEE 30 bus power system is considered as the study case. The simulation results are compared to Matlab's “SimPower” and PSCAD/EMTDC software packages. [ABSTRACT FROM AUTHOR]

The paper addresses the problem of determining the maximum distributed energy resource (DER) capacity that can be connected to low-voltage (LV) networks without creating voltage-rise problems. That maximum capacity depends on the network characteristics and on the candidate sites for DER connection. When sites are multiple and LV networks are poorly characterized, such maximum capacity cannot be determined with power-flow or other admittance-matrix-based approaches. This paper proposes an approach to estimate voltage rise caused by DER under reduced network characterization. Such approach is built upon customary voltage and impedance measurements to be made at the sites of DER injection and gives sufficiently accurate results under most practical situations. The paper validates the accuracy of the proposed approach against exact power-flow results for well-characterized networks and load situations and provides guidelines for DER connection based on maximum capacity nodal allocation. [ABSTRACT FROM PUBLISHER]

The novel cascade-mitigation scheme developed in Part I of this paper is implemented within a receding-horizon model predictive control (MPC) scheme with a linear controller model. This present paper illustrates the MPC strategy with a case-study that is based on the IEEE RTS-96 network, though with energy storage and renewable generation added. It is shown that the MPC strategy alleviates temperature overloads on transmission lines by rescheduling generation, energy storage, and other network elements, while taking into account ramp-rate limits and network limitations. Resilient performance is achieved despite the use of a simplified linear controller model. The MPC scheme is compared against a base-case that seeks to emulate human operator behavior. [ABSTRACT FROM PUBLISHER]

This two-part paper addresses the design of retail electricity tariffs for distribution systems with distributed energy resources such as solar power and storage. In particular, the optimal design of dynamic two-part tariffs for a regulated monopolistic retailer is considered, where the retailer faces exogenous wholesale electricity prices and fixed costs on the one hand and stochastic demands with intertemporal price dependencies on the other. Part I presents a general framework and analysis for revenue adequate retail tariffs with advanced notification, dynamic prices, and uniform connection charges. It is shown that the optimal two-part tariff consists of a dynamic price that may not match the expected wholesale price and a connection charge that distributes uniformly among all customers the retailer's fixed costs and a price-volume risk premium. A sufficient condition for the optimality of the derived two-part tariff among the class of arbitrary ex-ante tariffs is obtained. Numerical simulations quantify the substantial welfare gains that the optimal two-part tariff may bring compared to the optimal linear tariff (without connection charge). Part II focuses on the impact of two-part tariffs on the integration of distributed energy resources. [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]

With the sustainable growth in the number of new power plants and scale of transmission systems, the probability of the current exceeding the short-circuit rating of circuit breakers increases. A fault current limiter (FCL), which can be used to reduce current surges, has attracted considerable attention from utilities. However, the appropriate placement of FCLs in a power system for obtaining the most effective cost-to-benefit solution is crucial. This paper proposes a two-stage placement approach, where Stage I combines the hierarchical fuzzy logic decision (HFLD) method and Hashing-integrated generic algorithm (HIGA). The HFLD method is used for sorting feasible solutions, and the HIGA determines an optimal FCL placement in the reduced search space. Particle swarm optimization is then employed in Stage II for optimizing the FCL parameters. To verify the effectiveness of the proposed approach in solving the optimal FCL placement problem, the method is verified using the IEEE 30-bus system and system of a manufacturing factory in Taiwan. The numerical results show that the proposed method achieves a favorable solution in a short time with fewer placements of FCLs. [ABSTRACT FROM PUBLISHER]

This paper focuses on distribution systems featuring renewable energy sources (RESs) and energy storage systems, and presents an AC optimal power flow (OPF) approach to optimize system-level performance objectives while coping with uncertainty in both RES generation and loads. The proposed method hinges on a chance-constrained AC OPF formulation, where probabilistic constraints are utilized to enforce voltage regulation with prescribed probability. A computationally more affordable convex reformulation is developed by resorting to suitable linear approximations of the AC power-flow equations as well as convex approximations of the chance constraints. The approximate chance constraints provide conservative bounds that hold for arbitrary distributions of the forecasting errors. An adaptive strategy is then obtained by embedding the proposed AC OPF task into a model predictive control framework. Finally, a distributed solver is developed to strategically distribute the solution of the optimization problems across utility and customers. [ABSTRACT FROM PUBLISHER]

Distributed optimization for solving nonconvex optimal power flow (OPF) problems in power systems has attracted considerable attention in the last decade. Most studies are based on the geographical decomposition of the IEEE test systems for verifying the feasibility of the proposed approaches. However, it is not clear if one can extrapolate from these studies that similar approaches can also be applied to very large-scale real-world systems. In this paper, we show, for the first time, that distributed optimization can be effectively applied to a large-scale real transmission network, namely, the Polish 2383-bus system for which no predefined partitions exist, by using a recently developed partitioning technique. More specifically, the problem solved is the ac OPF problem with geographical decomposition of the network using the alternating direction method of multipliers (ADMM) method in conjunction with the partitioning technique. Through extensive simulations and analytical studies, we show that with the presented partitioning technique the convergence performance of the ADMM method can be improved substantially, which enables the application of distributed approaches to very large-scale systems. [ABSTRACT FROM PUBLISHER]

The number and locations of transmission lines that are likely to get simultaneously congested are useful information for analysis of power market. In this paper, we present a study that demonstrates the number of simultaneously congested transmission lines is very limited, as well as an algorithm for identifying a small set of transmission lines that may become simultaneously congested based on the current states of the system and market. To this end, we first investigate the maximum number of simultaneously congested lines. Then, a novel algorithm is developed to identify a smaller set using two scientific criteria – one is concerned with the absolute impact of generation dispatch decisions, and the other, the relative sensitivities of line flows with respect to the changes of generation outputs. The effectiveness of the proposed algorithm is demonstrated through two simulation studies, one based on IEEE 39-bus for illustration of concepts, and the other based on a large-scale, real-world power system for showing the practical application and significance of results. [ABSTRACT FROM AUTHOR]

Optimal power flow (OPF) programs must be able to provide sound operating points for power systems under different conditions while meeting a large number of constraints. These constraints, however, either due to the operating conditions at hand or by construction, can have linearly dependent gradients, thus defining ill-behaved feasible sets. This paper analyzes the use of an alternative set of optimality conditions, derived from the Fritz-John (FJ) conditions, to represent OPF solutions in such critical cases. Results are presented for realistic test systems. [ABSTRACT FROM PUBLISHER]

This paper addresses the problem of a multiyear security constrained hybrid generation-transmission expansion planning. It is assumed that the overall generation requirements of a network are known along the planning horizon, but their allocations are unknown. Moreover the fuel cost throughout the net- work is not uniform. By allocating the overall generation capacity among the grid nodes, and determining the new transmission element additions along the planning horizon, the overall cost of the system is minimized. The problem is formulated as a mixed integer nonlinear programming problem, which for a large-scale system is very difficult to solve. In this paper a new constructive heuristic approach is proposed, so that the problem can be readily solved. To assess the capabilities of the proposed approach, two networks are studied: the Garver test grid as a small grid and the Iranian power grid as a large-scale grid. [ABSTRACT FROM AUTHOR]

This paper proposes a chance constrained formulation to tackle the uncertainties of load and wind turbine generator in transmission network expansion planning. A combined Monte Carlo simulation/analytical probabilistic power flow analysis method is first presented to obtain the probability density function of wind turbine generator output. The paper then shows the development of the chance constrained formulation with the inclusion of the wind turbine generator probability density function and probabilistic power flow in the formulation. The proposed formulation is more computationally efficient and can deal with uncertainties in transmission network expansion planning. The power of the new method is shown through the application of the formulation to two test systems. [ABSTRACT FROM AUTHOR]

The paper applies the well-known red-green-blue (RGB) coloring method to visualize traveling waves initiated by switching events or faults occurring in power systems. The three-phase voltage profile along a given transmission line is obtained first. This profile is then converted into a colored picture by assigning different colors to phase signals according to their intensity. An interesting outcome of repeating this process for each time step is the emergence of the Bewley diagram [1] which is commonly used to illustrate the behavior of traveling waves in space-time. The main contribution of the paper is to show that RGB coloring of phase signals reveals essentially the same profile as the one obtained by using the aerial mode of the signals transformed into the modal domain. Furthermore, it discusses how this result can possibly be useful in applications such as fault location. [ABSTRACT FROM AUTHOR]

Forward contracts play an important role for market power mitigation and risk hedging in electricity markets. In this paper, a two-settlement electricity market including a forward market and a spot market is formulated as a two-stage game. The linear supply function equilibrium (LSFE) model and Cournot model are used to model strategic bidding for the spot market, while the forward market is modeled by Cournot model. A co-evolutionary genetic algorithm (CGA) is employed to determine the market equilibrium. The paper then examines the question whether generation companies (GenCos) would voluntarily enter forward markets due to economic inspiration and studies theoretically and numerically the factors which can affect the bidding behaviors of GenCos. The effectiveness of CGA in determining the market equilibrium is investigated and demonstrated based on two test examples. The studies show that GenCos' decisions on the participation in forward markets depend significantly on the type of competition that they have in the spot market. Moreover, GenCos' bidding behaviors in the forward market can be affected by their cost parameters and the slope of system demand function significantly. [ABSTRACT FROM AUTHOR]

Financial transmission rights (FTRn) are complementary to the locational marginal pricing of energy. The basic aim of the FTR mechanism is to guard forward contracts from uncertain congestion charges. FTRs are also useful to individual generators and loads for selling and buying power, respectively, at the prices of other locations. The concept has evolved, encompassing many features such as a simultaneous feasibility test, various ways to conduct auctions and allocations and secondary trading. FTRs also have a close relation to market power and transmission investment. This paper reviews most of the landmark research papers on the evolution of the FTR concept. It reports a comprehensive assessment of various facets of FTRs and allied issues. Financial transmission rights and flowgate rights (FGRs) are compared. The concept of long-term FTRs is discussed. The paper also touches upon future proposals in this area. [ABSTRACT FROM AUTHOR]

In electricity markets, a pool trading model with a power exchange pool is a typical market organization that attracts much more attention than a bilateral trading model. To date, quite a few papers have focused on bilateral trading models, particularly those under network constraints. This trend is due to the model's complexity in terms of the various trading patterns, reflecting the self-interested behavior of the market participants striving to find potentially profitable transactions. In this paper, we propose a new approach based on complex networks suitable for assessing different aspects of bilateral market. This work strives to analyze the bilateral trading patterns in the electricity markets where physical network constraints need to be considered for the feasible and se- cure operation of the power systems. The goal of the work is to find the stable network structures that can be used to anticipate possible bilateral transactions in the real market place and to provide a novel and applicable approach to studying the bilateral model in electricity markets. The proposed approach has been tested on several test systems in which the transmission network structure of the market that accommodates the transactions is considered. The proposed model is illustrated with examples using a four-bus test system, the IEEE 30-bus, and the IEEE 118-bus test systems. [ABSTRACT FROM AUTHOR]

This paper analyzes the implementability of locational marginal price (LMP) and financial transmission right (FTR) mechanisms in the presence of high voltage dc (HVDC) lines in the regulated (i.e., under the control of system operator) network. The established framework of LMP-FTR mechanism assumes that the system under regulation is fully ac. Unregulated (or private) HVDC lines are taken into account within this framework through proxy-transaction bids from the line owners. However, as the flow over a regulated HVDC line has to be controlled by the system operator himself, the existing LMP-FTR framework becomes insufficient if the system contains or is expanded with regulated HVDC lines. The augmentation that should be made to the existing framework to include regulated HVDC lines is explained in this paper. It is shown that the flow over a regulated HVDC line can be modeled as a non-chargeable bilateral transaction without causing any threat of negative congestion surplus. For this power dispatch model, revenue adequacy of FTRs can be still ensured by means of the conventional simultaneous feasibility test (SFT) model. By utilizing the capacities of dc lines, a more general SFT model is further developed. The modified auction problem is discussed and tested for the non-negativity of net auction collection. The process of revenue adequate issuance of auction revenue rights is explained. Finally, the relative merit of a regulated HVDC line over a private HVDC line is discussed through a case study. [ABSTRACT FROM AUTHOR]

The idea behind the first proposal of the fuzzy power flow (FPF) was to analyze the impact of the uncertainties in load and generation at the power flow level, when no statistical information is available. Further development of the field addressed the optimal power flow problem and the use of fuzzy methodologies to help planners of the composite generation-transmission system. In a market environment, transmission system adequacy may be defined as the ability of the system to meet reasonable demands for the transmission of electricity. The starting point of this paper is that FPF can be used as a tool to quantify this adequacy, without the need of making too many assumptions about load and generation uncertainties. However, some changes in the basic concept of the FPF are needed in order to accomplish this task—part of this paper is devoted to the description of the adequate formulation. We will also show that this formulation can be used both in the normal operation situation and in the reliability evaluation of the transmission system. An illustrative example completes this paper. [ABSTRACT FROM AUTHOR]

Conventional measurement and verification for non-interval metered, direct load control (DLC) programs bidding into wholesale electricity markets usually requires a PURPA-compliant load research study. This requirement con- tributes to high operating costs and has been a factor in recent reductions in the amount of emergency demand response available to regional transmission system operators. This paper describes. a collaborative effort by PJM members to determine whether regional modeling using pooled historical data could satisfy DLC measurement and verification (M&V) requirements without sacrificing estimation accuracy. This paper also describes how PJM incorporated the regional "deemed savings estimates" into its Load Data Systems Manual. This paper concludes that regional approaches to MଦV could yield large cost savings for DLC resource providers around the country. [ABSTRACT FROM AUTHOR]

A hybrid method which combines four different algorithms for low-frequency oscillation parameter estimation using wide-area measurements is presented in this paper. The first algorithm is the discrete Fourier transform which is used to start the low-frequency oscillation estimation process. The second one is the finite-impulse response (FIR) window filter which is employed in filtering unwanted components, and window correction factor is provided to eliminate the side effect of FIR window filter. The third one is the prototype algorithm which is proposed to estimate low-frequency oscillation parameters, and the last one is the least-square error method which is employed to enhance the computational accuracy by varying the window size. This hybrid method has been implemented in wide-area phasor measurements system by Java language and is under test in Taiwan's power system. Matlab/Simulink simulation and field test results are provided in the present paper. [ABSTRACT FROM AUTHOR]

In isolated power systems, frequency stability is traditionally considered to be assured by maintaining sufficient spinning reserve that is usually equal to the largest generation output of all the units in operation. However, the system security depends on the spinning reserve allocation to the units in operation and the provision of adequate emergency or fast reserve that need be available in the first crucial seconds after a loss of generation event. The system emergency reserve is usually much lower than that expected if only the unit droops are taken into account. Also, the generating units can be overloaded for a short time period and this capability can contribute to a faster frequency restoration. This paper presents an improved speed governor model that utilizes the short time overloading capability of the generating units. The efficient computational method described in the paper for the optimal spinning reserve allocation in isolated power systems was developed by taking into account a composite security criterion in the most economic way. Furthermore, a statistical analysis is presented in order to investigate the contribution of spinning reserve to the short-term system security. In the paper the developed method is applied to a typical isolated power system and it demonstrates its advantages. [ABSTRACT FROM AUTHOR]

This paper analyzes the behavior of Hong's point estimate methods to account for uncertainties on the probabilistic power flow problem. This uncertainty may arise from different sources as load demand or generation unit outages. Point estimate methods constitute a remarkable tool to handle stochastic power system problems because good results can be achieved by using the same routines as those corresponding to deterministic problems, while keeping low the computational burden. In previous works related to power systems, only the two-point estimate method has been considered. In this paper, four different Hong's point estimate schemes are presented and tested on the probabilistic power flow problem. Binomial and normal distributions are used to model input random variables. Results for two different case studies, based on the IEEE 14-bus and IEEE 118-bus test systems, respectively, are presented and compared against those obtained from the Monte Carlo simulation. Particularly, this paper shows that the use of the 2m + 1 scheme provides the best performance when a high number of random variables, both continuous and discrete, are considered. [ABSTRACT FROM AUTHOR]

High-temperature low-sag (HTLS) conductors, which can double the ampacity of conventional conductors, are becoming a mature option to uprate thermally limited transmission lines. This paper addresses several issues related to the widespread use of HTLS conductors in existing power systems. The first part of the paper analyzes the influence of higher line resistances on power transfer capability as well as the accuracy of conventional network models, based on constant conductor temperatures. The second part deals with the problem planners are facing when considering existing network reinforcement options versus the new alternative offered by HTLS conductors, intended to replace Alloy Aluminum Conductor Steel Reinforced (ACSR) equipment in situ. This leads to a security-constrained optimization problem involving binary decision variables. The 57-bus system is used throughout the paper to illustrate the main ideas. [ABSTRACT FROM AUTHOR]

Long extra high voltage (EHV) ac lines cannot be loaded to their thermal Limits in order to keep sufficient margin against transient instability. With the scheme proposed in this paper, it is possible to load these lines very close to their thermal limits. The conductors are allowed to carry usual ac along with dc superimposed on it. The added dc power flow does not cause any transient instability. This paper presents the feasibility of converting a double circuit ac line into composite ac-dc power transmission line to get the ad- vantages of parallel ac-dc transmission to improve stability and damping out oscillations. Simulation and experimental studies are carried out for the coordinated control as well as independent control of ac and dc power transmissions. No alterations of conductors, insulator strings, and towers of the original line are needed. Substantial gain in the loadability of the line is obtained. Master current controller senses ac current and regulates the dc current orders for converters online such that conductor current never exceeds its thermal limit. [ABSTRACT FROM AUTHOR]

The creation of competitive electricity markets has increased the complexity of the economics of system operation. Independent system operators (ISOs) perform optimizations based on a market-driven objective function. However, there may be other objectives that the ISO wishes to consider. These objectives are called secondary objectives, as they are dominated by the economic objective. In this paper, a hierarchical multiobjective (HMO) optimization is developed that, through coordinated control of network devices such as phase shifting transformers and series flexible ac transmission systems (FACTS), allows the market objective to be optimized in a global sense, while the secondary objectives are locally optimized. The method is applied to a modified IEEE 30-bus system incorporating a wide-area impact index-minimizing secondary objective. Formulated in this paper, the wide-area impact index accurately measures the effects of parallel flow over multiple lines in a region. Comparisons are made between the HMO's performance with other single and multiple objective optimizations and between the wide-area impact index and traditional parallel flow calculations. [ABSTRACT FROM AUTHOR]

This paper describes very short-term wind prediction for power generation, utilizing a case study from Tasmania, Australia. Windpower presently is the fastest growing power generation sector in the world. However, windpower is intermittent. To be able to trade efficiently, make the best use of transmission line capability, and address concerns with system frequency in a re-regulated system, accurate very short-term forecasts are essential. The research introduces a novel approach—the application of an adaptive neuro-fuzzy inference system to forecasting a wind time series. Over the very short-term forecast interval, both windspeed and wind direction are important parameters. To be able to be gain the most from a forecast on this time scale, the turbines must be directed toward on oncoming wind. For this reason, this paper forecasts wind vectors, rather than windspeed or power output. [ABSTRACT FROM AUTHOR]