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Wide-area time-synchronized measurements have recently revealed troublesome forced oscillations (FOs) within modern synchronized power grids. In some cases, these FOs represent a dangerous hazard to the system. Recent research has focused on locating the source of FOs to provide operators with knowledge for mitigating their impact locally. This paper presents a complementary mitigation strategy, which is to purposely induce a second oscillation into the grid which cancels the impact of the FO. Such a strategy is complementary in that it may provide valuable time to operators attempting to locate the FOs source and to determine how to rectify it. This paper presents a suppression control strategy which modulates controllable devices to automatically cancel the impact of the FO without the need for locating the source of the original FO. The strategy is based upon tuned feedback control. The approach is demonstrated on a simulation system via modulation of inverter-based generation. [ABSTRACT FROM AUTHOR]

The paper proposes a new adaptive approach to power system model reduction for fast and accurate time-domain simulation. This new approach is a compromise between linear model reduction for faster simulation and nonlinear model reduction for better accuracy. During the simulation period, the approach adaptively switches among detailed and linearly or nonlinearly reduced models based on variations of the system state: it employs unreduced models for the fault-on period, uses weighted column norms of the admittance matrix to decide which functions to be linearized in power system differential-algebraic equations for large changes of the state, and adopts a linearly reduced model for small changes of the state. Two versions of the adaptive model reduction approach are introduced. The first version uses traditional power system partitioning where the model reduction is applied to a defined large external area in a power system and the other area defined as the study area keeps full detailed models. The second version applies the adaptive model reduction to the whole system. The paper also conducts comprehensive case studies comparing simulation results using the proposed adaptively reduced models with the linearly reduced model and coherency-based reduced model on the Northeast Power Coordinating Council 140-bus 48-machine system. [ABSTRACT FROM AUTHOR]

Integrated energy systems (IESs) are composed of multiple heterogeneous subsystems, i.e., electrical power system, natural gas system, and district heating system (DHS), which endow the whole system with excellent performance in overall efficiency and renewable energy utilization. The paper aims to offer a concise and analytical model for the thermal dynamic characteristics (i.e., thermal inertia) of the district heating network (DHN) and buildings to facilitate the analysis, planning, and operation of IESs. Firstly, an equivalent start network is introduced for modeling the radial DHN, and a synchronous response model is proposed for buildings to approximate the optimal response of heat load. Secondly, the thermal inertia aggregation model (TIAM) is proposed, which offers an accurate DHN and buildings model for the planning and operation of IESs. Finally, some properties of the TIAM are derived to reveal its potential in general applications such as analysis and evaluation. Simulation results of different scale systems demonstrate the performance of the proposed model and reveal its advantages in the computational efficiency and sensitive information protection of DHN. [ABSTRACT FROM AUTHOR]

In this paper, we formulate and solve the ac optimal power flow (AC-OPF) as an equivalent circuit problem in terms of current, voltage, and admittance state variables. The generator models are represented using conductance and susceptance state variables, and the operational and network constraints are translated to corresponding current/voltage constraints without loss of accuracy or generality. To understand the physics behind the optimality conditions of the optimization problem, we extend the linear adjoint circuit theory to translate them to equivalent circuit domain. It is shown that the operating point that defines the equivalent circuit solution precisely represents an AC-OPF solution. We then further exploit the equivalent circuit representation to use power flow simulation techniques to robustly solve the optimization problem. The efficiency of our approach is demonstrated for several AC-OPF benchmark test cases (up to 70 k buses) under nominal and congested operating conditions, and the runtime and scalability properties are presented. [ABSTRACT FROM AUTHOR]

Combined transmission and distribution systems (CoTDS) simulation for power systems requires development of algorithms and software that are numerically stable and at the same time accurately simulate dynamic events that can occur in practical systems. The time scales of simulation can be orders of magnitude apart making the combined simulation extremely challenging. This has led to increased research in applying co-simulation techniques for integrated simulation of the two systems. In this paper, two methods for dynamic co-simulation of CoTDS are proposed using parallel and series computation of the transmission system and distribution systems. The convergence of numerical methods in co-simulation is addressed from a fundamental mathematical perspective and the impact of the integration time-step is studied on proposed CoTDS dynamic co-simulation methods. Both these co-simulation methods are validated against total system simulation in a single time-domain simulation environment. The proposed CoTDS co-simulation method is also validated against commercial EMTP dynamic simulation. CoTDS dynamic co-simulation is further demonstrated on a New England 39-bus transmission system with ten load buses replaced by distribution systems including a 5780-node distribution system on one load bus for a detailed fault-induced delayed voltage recovery simulation study. [ABSTRACT FROM AUTHOR]

The objective of this paper is to determine an optimal plan for expanding the capacity of a power grid in order to minimize the likelihood of a large cascading blackout. Capacity-expansion decisions considered in this paper include the addition of new transmission lines and the addition of capacity to existing lines. We embody these interacting considerations in a simulation optimization model, where the objective is to minimize the probability of a large blackout subject to a budget constraint. The probability of a large-scale blackout is estimated via Monte Carlo simulation of a probabilistic cascading blackout model. Because the events of interest are rare, standard simulation is often intractable from a computational perspective. We apply a variance-reduction technique within the simulation to provide results in a reasonable time frame. Numerical results are given for some small test networks including an IEEE 14-bus test network. A key conclusion is that the different expansion strategies lead to different shapes of the tails of the blackout distributions. In other words, there is a tradeoff between reducing the frequency of small-scale blackouts versus reducing the frequency of large-scale blackouts. [ABSTRACT FROM PUBLISHER]

This paper studies the techniques for modeling modular multilevel converter (MMC) based multi-terminal HVDC (MTDC) systems in the electromechanical transient mode. Firstly, the mathematical model of the MMC and its corresponding equivalent circuit are established, which are similar to those of the two level converters. Then, a power flow calculation method for AC/DC systems containing MMC-MTDC systems is developed. Two dynamic models for MMC-MTDC systems are developed in the paper. One is the detailed model, taking into account of the AC side circuit, the inner controllers, the modulation strategies, the outer controllers and the MTDC circuit. The other is the simplified model, which only reserves the outer controllers and partial dynamics of the MTDC circuit based on a quantitative analysis of the detailed model's dynamic processes, and it can be used in electromechanical transient simulation with a larger step size. Both the detailed and the simplified models are implemented on PSS/E and compared with the accurate electromagnetic transient models on PSCAD in a four terminal MMC-MTDC system; the result proves the validity of the developed models. Lastly, a stability study of a modified New England 39-bus system is executed, and the result shows that the AC fault can be isolated well in an MMC-MTDC asynchronously connected AC grid. [ABSTRACT FROM PUBLISHER]

Simulation scheme constructed by transient models is widely used for interconnected power system studies. However, it has shortcomings when used in automatic generation control (AGC) and AGC relevant fields. In this paper, a novel simulation scheme designed for AGC and its relevant studies is presented. The scheme uses dynamic energy balancing equation and a single central frequency as core algorithm. Moreover, models described by algebraic equations are adopted instead of transient models described by differential equations. The simplified models reduce computational power requirement to about 3% of transient models and require fewer parameters. By ignoring transient dynamics and inter-area oscillations which are insignificant in AGC timescale, the presented scheme achieves high computational efficiency and acceptable accuracy making it acceptable for up to year-long simulation. At the end of the paper, comparative tests are performed to provide differences, validity and accuracy of proposed scheme. [ABSTRACT FROM PUBLISHER]

In a cascading power transmission outage, component outages propagate nonlocally; after one component outages, the next failure may be very distant, both topologically and geographically. As a result, simple models of topological contagion do not accurately represent the propagation of cascades in power systems. However, cascading power outages do follow patterns, some of which are useful in understanding and reducing blackout risk. This paper describes a method by which the data from many cascading failure simulations can be transformed into a graph-based model of influences that provides actionable information about the many ways that cascades propagate in a particular system. The resulting “influence graph” model is Markovian, in that component outage probabilities depend only on the outages that occurred in the prior generation. To validate the model, we compare the distribution of cascade sizes resulting from $n-2$ contingencies in a 2896 branch test case to cascade sizes in the influence graph. The two distributions are remarkably similar. In addition, we derive an equation with which one can quickly identify modifications to the proposed system that will substantially reduce cascade propagation. With this equation, one can quickly identify critical components that can be improved to substantially reduce the risk of large cascading blackouts. [ABSTRACT FROM AUTHOR]

This paper presents a novel perturbation observer-based multiloop control method for the integrated control of the doubly-fed induction generator-based wind turbine (DFIG-WT) in a multimachine power system. The DFIG-WT is decoupled into four independent subsystems in accordance with four outputs. A perturbation state is introduced into each subsystem, and the optimal output feedback control of each subsystem is achieved with the estimate of perturbation obtained by a sliding-mode perturbation observer. Thus a four-loop perturbation observer-based control (POC) scheme is adopted to achieve the integrated control of the DFIG-WT. The design of the four-loop POC does not require any accurate system model, and it is robust to external disturbances and parameter variations. Meanwhile, the four-loop POC presents a fast tracking rate and shows the capability of damping the oscillations of output variables. Moreover, interactions between two DFIG-WT-based wind farms and their influence to the stability of power system are also investigated. Simulation studies reveal that superior integrated control of DFIG-WT can be achieved by the four-loop POC under various conditions compared with the conventional vector control scheme. [ABSTRACT FROM AUTHOR]

Measurement-based load modeling is a promising approach to reliably represent load behavior in dynamic simulations of large power systems. This paper presents a methodology that starts with the acquisition of voltages and currents from power quality monitoring systems and highlights the issues associated with selecting, processing and resampling the data to estimate the relationship between the power deviations as a function of the voltage deviations. The load model mathematical structure chosen is a second-order transfer function, whose parameters are estimated using a genetic algorithm (GA) as the optimization technique that minimizes the error between the real data that are measured and the data that are simulated with the proposed models. Some insights were achieved regarding the appropriate search space choice. [ABSTRACT FROM PUBLISHER]

The increasing penetration of distributed generation (DG) power plants into distribution networks (DNs) causes various issues concerning, e.g., stability, protection equipment, and voltage regulation. Thus, the necessity to develop proper control techniques to allow power delivery to customers in compliance with power quality and reliability standards (PQR) has become a relevant issue in recent years. This paper proposes an optimized distributed control approach based on DN sensitivity analysis and on decentralized reactive/active power regulation capable of maintaining voltage levels within regulatory limits and to offer ancillary services to the DN, such as voltage regulation. At the same time, it tries to minimize DN active power losses and the reactive power exchanged with the DN by the DG units. The validation of the proposed control technique has been conducted through a several number of simulations on a real MV Italian distribution system. [ABSTRACT FROM PUBLISHER]

Numerical methods play an important role in improving efficiency for power system time-domain simulation. Motivated by the need to perform high-speed extended-term time-domain simulation (HSET-TDS) for online purposes, this paper presents design principles for numerical solvers of differential algebraic systems associated with power system time-domain simulation, focusing on DAE construction strategies, integration methods, nonlinear solvers, and linear solvers. We have implemented a design appropriate for HSET-TDS, and we have compared the proposed integration method, Hammer-Hollingsworth 4 (HH4), with Trapezoidal rule in terms of computational efficiency and accuracy, using the New England 39-bus system, an expanded 8775-bus system, and PJM 13 029-bus system. [ABSTRACT FROM PUBLISHER]

This paper proposes a dynamic time simulation model for long-term generation capacity investment decisions in the presence of either perfect or imperfect electricity market. The model is based on system dynamics concept in which the dynamics of capacity construction is traced using the forecast of electricity price cleared in the short-term electricity market. Both the perfect and oligopolistic competitions are considered and a market power index is defined to evaluate the competition level of the electricity market. The short-term and long-term dynamic analysis are used to represent the generation firms' behavior in bidding strategy and capacity investment, respectively. Both possibilities of using forward bilateral contracts and application of wind power generation have been assessed individually in the proposed model in order to mitigate the market power. The time simulation results derived from a case study demonstrate the effectiveness of the model in illustrating the oligopoly in electricity marketplace and also the alternative decisions to attenuate it. Such a decision tool enables both the generation firms and the regulators to gain perfect insight into the oligopoly and its consequences in the long-term capacity investment in the electricity market. [ABSTRACT FROM PUBLISHER]

Many probabilistic maintenance models developed for maintenance scheduling and optimization are based on state diagrams. Classical maintenance models based on state diagrams provide inaccurate results when inspection rates are nonperiodic. An attempt has been made to rectify some modeling properties through the use of an alternative graph; however, it requires Monte Carlo simulation to accurately calculate reliability. This paper highlights an idealistic property of classical state diagrams and proposes new state diagrams to correct it. The accuracy of Markov models based on proposed state diagrams is verified through a theoretical discussion. Significant differences between the results given by classical and proposed maintenance models are shown through a numerical example for imperfect maintenance. The behavior of mean time between failures is also analyzed to validate the proposed models. With the proposed model, reliability analysis of different maintenance activities can be calculated analytically without the use of Monte Carlo simulation. [ABSTRACT FROM PUBLISHER]

The recently proposed power-synchronization control for grid-connected voltage-source converters (VSCs) has been shown to be a feasible solution for high-voltage direct-current (HVDC) transmission connected to high-impedance weak ac systems. In this paper, power-synchronization control is investigated for VSC-HVDC links connected to another type of weak ac system, i.e., low-inertia or island systems. As an example, a linear model of a typical island system feeding by a VSC-HVDC link, including a synchronous generator, an induction motor, and some passive loads, is developed for tuning the control parameters of the VSC-HVDC link. Time simulations in PSCAD/EMTDC demonstrate that VSC-HVDC systems using power-synchronization control are flexible for various network conditions, such as large-ac-system connection, island systems, or passive networks. The time simulations also show that power-synchronization control can seamlessly handle transitions between operation modes, as well as ride through ac-system faults in all network conditions. [ABSTRACT FROM PUBLISHER]

This paper proposes an optimized transmission line modeling (TLM) method for the real-time transient simulation of systems with multiple nonlinearities. The proposed method allows the simulation to be carried out with larger time-steps while maintaining the accuracy. A detailed case study of a nonlinear bridge circuit is presented to illustrate the advantages of the optimized TLM method in comparison with other methods. The new formulation is then implemented in real-time for the transient simulation of the nonlinear bridge. Real-time simulation results are validated by comparing them with experimental measurements. A second case study includes a power system with several surge arresters which is also simulated in real-time by the aid of the optimized TLM method and verified using offline simulation. [ABSTRACT FROM PUBLISHER]

In this paper, the power system with an excitation controller is represented as a class of large-scale, uncertain, interconnected nonlinear continuous-time system in strict-feedback form. Subsequently, dynamic surface control (DSC)-based adaptive neural network (NN) controller is designed to overcome the repeated differentiation of the control input that is observed in the conventional backstepping approach. The NNs are utilized to approximate the unknown subsystem and the interconnection dynamics. By using novel online NN weight update laws with quadratic error terms, the closed-loop signals are shown to be locally asymptotically stable via Lyapunov stability analysis, even in the presence of NN approximation errors in contrast with other NN techniques where a bounded stability is normally assured. Simulation results on the IEEE 14-bus power system with generator excitation control are provided to show the effectiveness of the approach in damping oscillations that occur after disturbances are removed. The end result is a nonlinear decentralized adaptive state-feedback excitation controller for damping power systems oscillations in the presence of uncertain interconnection terms. [ABSTRACT FROM PUBLISHER]

This paper proposes a three-stage offline approach to detect, identify, and correct series and shunt branch parameter errors. In Stage 1 the branches suspected of having parameter errors are identified through an Identification Index (II). The II of a branch is the ratio between the number of measurements adjacent to that branch, whose normalized residuals are higher than a specified threshold value, and the total number of measurements adjacent to that branch. Using several measurement snapshots, in Stage 2 the suspicious parameters are estimated, in a simultaneous multiple-state-and-parameter estimation, via an augmented state and parameter estimator which increases the V-\theta state vector for the inclusion of suspicious parameters. Stage 3 enables the validation of the estimation obtained in Stage 2, and is performed via a conventional weighted least squares estimator. Several simulation results (with IEEE bus systems) have demonstrated the reliability of the proposed approach to deal with single and multiple parameter errors in adjacent and non-adjacent branches, as well as in parallel transmission lines with series compensation. Finally the proposed approach is confirmed on tests performed on the Hydro-Québec TransÉnergie network. [ABSTRACT FROM PUBLISHER]

Matpower is an open-source Matlab-based power system simulation package that provides a high-level set of power flow, optimal power flow (OPF), and other tools targeted toward researchers, educators, and students. The OPF architecture is designed to be extensible, making it easy to add user-defined variables, costs, and constraints to the standard OPF problem. This paper presents the details of the network modeling and problem formulations used by Matpower, including its extensible OPF architecture. This structure is used internally to implement several extensions to the standard OPF problem, including piece-wise linear cost functions, dispatchable loads, generator capability curves, and branch angle difference limits. Simulation results are presented for a number of test cases comparing the performance of several available OPF solvers and demonstrating Matpower's ability to solve large-scale AC and DC OPF problems. [ABSTRACT FROM AUTHOR]