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With the rapid growth of voltage source converter based high-voltage direct current (VSC-HVdc)-integrated offshore wind farms, wind turbines (WTs), and VSC stations are required to provide frequency regulation to maintain the onshore system frequency stability. However, after a temporary power increase during the initial period of a disturbance, WTs and VSC stations must reduce their output power to restore their own initial operating states. If there is no other power injection to offset the corresponding power shortage, a significant second frequency drop (SFD) may occur. To address this issue, this paper proposes an adaptive frequency regulation method with grid-friendly restoration. Different frequency regulation strategies are designed to adaptively use the releasable kinetic energy in WTs or the electrostatic energy in VSC stations according to their own real-time operating status. In addition, a system-level grid-friendly coordination is proposed to use the persistent energy reserves of WTs with a deloading strategy to increase the instantaneous power injection and avoid a significant SFD while other WTs or VSC stations restore their operating states. The quantitative calculation and switching mechanism of the additional power injections of deloading WTs are highlighted, and the effectiveness of the proposed method is verified in a case study. [ABSTRACT FROM AUTHOR]

System operators are required to serve the load in the most cost-effective way while maintaining the integrity of the system and heeding reliability requirements. In the day-ahead market, operators acquire reserves in an attempt to guarantee N-1 reliability; yet, reserve deliverability is not guaranteed. Prior research has shown that the use of transmission switching, or topology control, may help improve reserve deliverability. In this paper, transmission switching is used as a corrective mechanism to help the system achieve N-1-1 reliability, where not only has the system lost a single element, but also it experiences the loss of a second major element after an adjustment period. In an attempt to preserve N-1-1 reliability, for this paper, a day-ahead unit commitment model that acquires supplementary reserves is solved. The day-ahead market solution is then tested for N-1-1 reliability using contingency analysis models with and without transmission switching. The methodology can be employed at the day-ahead time stage to ensure the system has acquired sufficient supplemental reserves. The results demonstrate that not only can corrective transmission switching be beneficial post-contingency without inhibiting the ability to return to N-1 reliability, but it can also help obtain an N-1-1 reliable solution. [ABSTRACT FROM AUTHOR]

This paper formulates a block-layer method for the reliability assessment of distribution systems. The characteristics of the method include: 1) identifying the impact of distribution component reliability on the system and load points using a block-layer structured assessment; 2) incorporating time-dependent failure parameters; and 3) taking account of the topological, seasonal, and meteorological features of the distribution systems under analysis. The proposed method first identifies the three critical parts of the distribution system: main supply, feeder, and secondary substation. It can also include reserve connections and distributed generation. Second, the method frames these parts into the layered structure, each corresponding to the zone of total load curtailment. To verify this reliability technique, this paper simulates distribution feeders assembled in a number of topologies and compares them with the state sampling technique. Data provided by the local utility company are processed to model the equipment and load for the base year. The results show that the proposed method can provide a wide range of partial and system indices. These values assist in the identification of parts of the distribution system and scenarios with low reliability and to determine possible remedial actions. [ABSTRACT FROM AUTHOR]

This paper summarizes simulation based technical feasibility and cost benefit analyses of a range of off-the-shelf electrical losses reduction intervention solutions in the Isle of Wight (IoW) 11 kV distribution network in the United Kingdom (UK), assessed over a period of 45 years. Based on presented results, the paper provides a brief commentary on the merits, drawbacks, risks and recommendations associated with each considered network intervention. Among considered network interventions, the transformer auto stop-start scheme, where one of the transformers among a pair at a primary substation would be switched depending on the substation's varying load, was found to be the optimal solution, i.e., in reducing technical losses significantly and may also have a reasonable Net Present Value (NPV) with a good rate of Return on Investment (RoI) when fully implemented. [ABSTRACT FROM PUBLISHER]

The calculation of standard reliability indices is critical for assessing quality service and guiding the planning and operation of distribution systems. Traditionally, such calculation has relied on the application of analytical methods based on simulation techniques, which preclude the use of exact methodologies when reliability assessment is incorporated into operation and planning models. This shortcoming has been recently addressed by the development of two optimization-based approaches for the analytical reliability assessment of distribution systems. Unfortunately, both methods are either incomplete or computationally expensive as compared with those based on simulation. In order to overcome these issues, this paper presents a novel and efficient algebraic approach to calculate the standard network-dependent reliability indices of distribution systems. As a distinctive feature over previous non-simulation-based methods, no optimization process is involved. Thus, the proposed approach relies on the solution of a set of linear equations for which effective algorithms are available. Several benchmarks including a real-life 1080-node system have been used to demonstrate the computational superiority of the proposed method. The successful numerical experience supports the suitability of the proposed algebraic model for reliability-constrained distribution system operation and planning. [ABSTRACT FROM AUTHOR]

The new IEEE 1547-2018 standard includes dynamic Volt/VAr control for photovoltaic (PV) smart inverters. While recent research has addressed the problem of optimal inverter dispatch, the interaction between inverters and the classical Volt/VAr control (VVC) regulation system needs further study. This paper proposes an approach that builds on the classical VVC solution with PVs, by computing for each inverter a rule that modulates the smart inverter reactive power in function of its real power. Two approaches are presented for computing the inverter's reactive power equation slope: the first approach is based on the robust minimization of the absolute voltage magnitude deviation via a linear program, whereas the second approach yields closed-form solutions inspired from distributionally robust chance constraints. Numerical results are presented on weakly meshed distribution networks having up to 3146 nodes; they demonstrate that the voltage violations due to intermittent real power variations are significantly reduced by the decision rules as compared to maintaining the last computed VVC set-points, even when the inverters operate at constant power factor or with default Volt/VAr settings proposed in the literature; additionally, the reactive power decision rules maintain a network loss level that is close to the average from a centralized solution. [ABSTRACT FROM AUTHOR]

Distribution service restoration (DSR) is critical for improving the resilience and reliability of modern distribution systems by strategically and sequentially energizing the system components and customer loads. Restoring electricity service to affected customers also requires multiple crews with different skill sets to perform multiple tasks that are procedurally interdependent with safety guaranteed. However, in existing DSR practices, switch operations and crew dispatch are scheduled separately, and their interdependence is not fully considered. As advanced technologies are enabling remote communication, control, and dispatch, utilities now desire an integrated DSR framework to achieve seamless coordination among multiple DSR tasks such as switch operation, crew dispatch, and component repair. In this paper, we introduce a synthetic model that integrates the service restoration model and the crew dispatch model based on a universal routing model. The proposed model can provide the estimated time of restoration for each load, the switching sequence for safely operating remotely/manually operated switches, and dispatch solutions for crews with different skill sets. The proposed synthetic model is formulated as a mixed-integer linear programming model, and its effectiveness is evaluated via the IEEE 123 bus test feeder and several large-scale test feeders (EPRI Ckt5, Ckt7, Ckt24, and IEEE 8500 node test feeder. [ABSTRACT FROM AUTHOR]

The ever-increasing utilization of sensitive loads in the industrial, commercial, and residential areas in distribution networks requires enhanced reliability and quality of supply. This can be achieved, thanks to self-healing features of smart grids that already include the control technologies necessary for the restoration strategy in case of a fault. In this paper, an analytical and global optimization model is proposed for the restoration problem. A novel mathematical formulation is presented for the reconfiguration problem reducing the number of required binary variables while covering more practical scenarios compared to the existing models. The considered self-healing actions besides the network reconfiguration are the nodal load-rejection, the tap setting modification of voltage regulation devices (incl. OLTCs, SVR, and CBs), and the active/reactive power dispatch of DGs. The voltage dependency of loads is also considered. Thus, the proposed optimization problem determines the most efficient restoration plan minimizing the number of de-energized nodes with the minimum number of self-healing actions. The problem is formulated as a Mixed-Integer Second Order Cone Programming (MISOCP) and solved using the Gurobi solver via the MATLAB interface YALMIP. A real 83–node distribution network is used to test and verify the presented methodology. [ABSTRACT FROM AUTHOR]

This paper examines the operation of distribution networks that have large aggregations of thermostatically controlled loads (TCLs) providing frequency regulation to the bulk power system. Specifically, we assess the prevalence of distribution network constraint violations, such as over- or under-voltages and overloading of transformers. Our goal is to determine the set of constraints that are at increased risk of being violated when TCLs provide regulation. We compare network operation in two cases: first, with TCLs operating freely; and second, with TCLs controlled to track a regulation signal. Using GridLAB-D, we run power flow simulations of five real distribution networks. Our results indicate that voltage limits are at increased risk of violation when TCLs provide regulation because of increased voltage variation. Effects on transformer aging are more nuanced and depend on the method used for dispatching TCLs. Overall, we find that, for the networks studied, the set of constraints at risk of violation is a small subset of all network constraints. Therefore, network-protecting load control algorithms may only need to consider a small set of constraints, enhancing their computational efficiency. [ABSTRACT FROM AUTHOR]

To solve the coordinated dispatch and time-space coupling problem in the distribution network with distributed generations (DGs), a novel two-stage (Heuristic search and Variable correction) dynamic reactive power dispatch strategy is proposed in this paper. Meanwhile, according to the analysis of Gauss-type and Z-type membership function, a new objective function is put forward to achieve the balance between network loss and voltage deviation. First, the pre-optimization is made in Niche genetic algorithm to coordinate on-load tap changer (OLTC), capacitor banks (CBs), and DGs. Second, the sequential fuzzy c-means (SFCM) based on artificial bee colony (ABC) algorithm is proposed and then the Heuristic search based on this method is used to formulate the day-ahead plans of OLTC and CBs. Finally, the dispatch plans of OLTC and CBs are applied to recalibrate the day-ahead dispatch plans of DGs. Comparing with existing schemes, strategies and optimization approaches based on diverse evaluation indicators, optimization results on IEEE 33-bus, IEEE 14-bus, and PG&E 69-bus test systems verify the practicality and efficiency of the proposed method. In addition, the effects on the optimization results with different adjustment step and action time of the discrete adjust devices are discussed by the IEEE 33-bus test system. [ABSTRACT FROM AUTHOR]

This paper proposes a new data-driven model-free Volt-Var control (VVC) scheme for the operation of radial power distribution systems. Unlike existing methods, the proposed VVC is neither reliant on model-based computer simulations nor limited to intuition/experience-driven rules for the operation of switchable capacitors and voltage regulators inside a feeder. Despite the model-free feature, the proposed scheme can still give optimal performances by using statistical estimations on measurement data such as the one provided by an advanced metering infrastructure system. Effectiveness and feasibility of the proposed idea is demonstrated by simulation studies on an IEEE 123 nodes test feeder. After few days of initial exploration, the proposed VVC is capable to give satisfactory results near to that of a model-based optimization technique. The promising outcome of this study suggests a novel application for emerging measurement and communication technologies in the operation of modern grids. [ABSTRACT FROM AUTHOR]

Optimal power management of shipboard power system for failure mode (OPMSF) is a significant and challenging problem considering the safety of system and person. Many existing works focused on the transient-time recovery without consideration of the operating cost and the voyage plan. In this paper, the OPMSF problem is formulated considering the mid-time scheduling and the faults at bus and generator. Two-side adjustment methods including the load shedding and the reconfiguration are coordinated for reducing the fault effects. To address the formulated non-convex problem, the travel equality constraint and fractional energy efficiency operation indicator limitation are transformed into the convex forms. Then, considering the infeasibility scenario affected by faults, a further relaxation is adopted to formulate a new problem with feasibility guaranteed. Furthermore, a sufficient condition is derived to ensure that the new problem has the same optimal solution as the original one. Because of the mixed-integer nonlinear feature, an optimal management algorithm based on Benders decomposition (BD) is developed to solve the new one. Due to the slow convergence caused by the time-coupled constraints, a low-complexity near-optimal algorithm based on BD is proposed. The results verify the effectivity of the proposed methods and algorithms. [ABSTRACT FROM AUTHOR]

Smart inverters provide additional control capability to help optimize the operation of distribution systems. This paper proposes a framework for exact optimal active and reactive power dispatch of distributed photovoltaic (PV) generation, switched capacitors, and voltage regulators in large multi-phase unbalanced distribution systems. The objectives of the optimal dispatch are minimization of the energy loss, PV active power curtailment, and operations of capacitors and voltage regulators, in addition to elimination of voltage violations and reverse power flow. The optimization problem is formulated in rectangular coordinates as a nonlinear, nonconvex problem. Effective computational strategies are proposed to allow the application of predictor-corrector primal-dual interior point method to solve optimization problems in real-time with a large number of constraints and variables, including discrete variables corresponding to switched capacitors and voltage regulators. The accuracy of the numerical solution and the ability to implement the proposed framework are validated using the unbalanced multi-phase IEEE 34-bus and EPRI 2,998-bus distribution systems with 15-minute load and PV data. The results show a significant loss reduction and elimination of both voltage violations and reverse power flow. [ABSTRACT FROM AUTHOR]

Inadequate frequency response can arise due to a high penetration of wind turbine generators (WTGs) and requires a frequency support function to be integrated in the WTG. The appropriate design for these controllers to ensure adequate response has not been investigated thoroughly. In this paper, a safety supervisory control (SSC) is proposed to synthesize the supportive modes in WTGs to guarantee performance. The concept, region of safety (ROS), is stated for safe switching synthesis. An optimization formula is proposed to calculate the largest ROS. By assuming a polynomial structure, the problem can be solved by a sum of squares program. A feasible result will generate a polynomial, the zero sublevel set of which represents the ROS and is employed as the safety supervisor. A decentralized communication architecture is proposed for small-scale systems. Moreover, a scheduling loop is suggested so that the supervisor updates its boundary with respect to the renewable penetration level to be robust with respect to variations in system inertia. The proposed controller is first verified on a single-machine three-phase nonlinear microgrid, and then implemented on the IEEE 39-bus system. Both results indicate that the proposed framework and control configuration can guarantee adequate response without excessive conservativeness. [ABSTRACT FROM AUTHOR]

The existing microgrid-based distribution system restoration methods follow traditional restoration criteria, which achieve a maximum coverage of distribution systems. In extreme conditions (e.g., natural disasters and physical and cyber attacks), the traditional restoration plans could pose additional financial and security risks to local utility customers. That is, restored services could be further interrupted by subsequent outages in the extended event. To address such resilience challenges, this paper proposes the formation of adaptive multimicrogrids as part of the critical service restoration strategy. The proposed strategy comprises microgrid formation (MF) and load switching sequence (LSS) steps. The MF forms multiple microgrids with minimum overall scale and radial or looped topologies and includes optimally positioned mobile emergency resources to address potential risks in extreme conditions. The LSS determines a proper load switching sequence for ensuring the system dynamic performance in the restoration process. The effectiveness of the proposed strategy is verified by a case study on the IEEE 132-node test feeder system and the time-domain simulation in MATLAB Simulink. [ABSTRACT FROM AUTHOR]

Individual microgrids have proven their ability to provide uninterrupted power to critical end-use loads during severe events. Building on the performance of individual microgrids during extreme events, there has been an increasing interest in the operations of network microgrids. By networking microgrids during extreme events, it is possible to share resources, increase the duration for which they can operate islanded, improve efficiency, and increase the resiliency of critical end-use loads. While there are benefits to networking the operations of resiliency-based microgrids, the switching operations that they require introduce transients, which can result in a loss of dynamic stability. The issue of dynamic stability is especially acute in microgrids with high penetrations of inverter-connected generation, and correspondingly low system inertia. While the low inertia of these microgrids can be increased by over-sizing the rotating generators, the increased capital and operating costs can become a barrier to deployment. This paper will present a method of augmenting primary frequency controls to support the switching transients necessary for the operation of networked microgrids, without the need to over-size rotating machines. [ABSTRACT FROM AUTHOR]

Direct current (DC) network has been recognized as a promising technique especially for shipboard power systems (SPSs). Fast resilience control is required for an SPS to survive after faults. Towards this end, this paper proposes the indices of survivability and functionality based on which a two-phase resilience control method is derived. The on/off status of loads is determined in the first phase to maximize survivability, while the functionality of supplying loads are maximized in the second phase. Based on a comprehensive model of a DC-SPS, the two-phase method renders two mixed-integer non-convex problems. To make the problems tractable, we develop second-order-cone-based convex relaxations, thus converting the problems into mixed-integer convex problems. Though this approach does not necessarily guarantee feasible, hence global, solutions to the original nonconvex formulations, we provide additional mild assumptions, which ensures that the convex relaxations are exact when the line constraints are not binding. In the case of inexactness, we provide a simple heuristic approach to ensure feasible solutions. Numerical tests empirically confirm the efficacy of the proposed method. [ABSTRACT FROM AUTHOR]

Conventional electromagnetic transient (EMT) and phasor-domain hybrid simulation approaches presently exist for transmission system level studies. Their simulation efficiency is generally constrained by the EMT simulation. With an increasing number of distributed energy resources and nonconventional loads being installed in distribution systems, it is imperative to extend the hybrid simulation application to include distribution systems and integrated transmission and distribution systems. Meanwhile, it is equally important to improve the simulation efficiency as the modeling scope and complexity of the detailed system in the EMT simulation increases. To meet both requirements, this paper introduces an advanced EMT and phasor-domain hybrid simulation approach. This approach has two main features: first, a comprehensive phasor-domain modeling and simulation framework which supports positive-sequence, three-sequence, three-phase, and mixed three-sequence/three-phase representations and second, a robust and flexible simulation mode switching scheme. The developed scheme enables simulation switching from hybrid simulation mode back to pure phasor-domain dynamic simulation mode to achieve significantly improved simulation efficiency. The proposed method has been tested on integrated transmission and distribution systems. The results show that with the developed simulation switching feature, the total computational time is significantly reduced compared to running the hybrid simulation for the whole simulation period while maintaining good simulation accuracy. [ABSTRACT FROM AUTHOR]

During faulty conditions, a sustained and heterogeneous stream of information, coming mainly from field signaling devices and customer calls, arrives at the Distribution Management System. This data should be promptly and systematically processed so that the faulted section can be isolated and service restored to customers as soon as possible. This paper presents a matrix-based framework allowing the status of the distribution grid and associated protection, signaling and switching devices to be compactly modeled and tracked. By means of algebraic expressions, the proposed information management system can infer the existence of a blackout (loss of load) and assist the operator in decision making during the identification and isolation of the affected areas. The proposed framework considers the potential presence of embedded distributed generation. With the help of both a tutorial system and a real-life case study, application examples are discussed to illustrate the potential of the proposed methodology. [ABSTRACT FROM AUTHOR]

A novel method is proposed to locate the source of events in power distribution systems by using distribution-level phasor measurement units, a.k.a., micro-PMUs. An event in this paper is defined rather broadly to include any major change in any component across the distribution feeder. The goal is to enhance situational awareness in distribution grid by keeping track of the operation (or misoperation) of various grid equipment, assets, distribution energy resources, loads, etc. The proposed method is built upon the compensation theorem in circuit theory to generate an equivalent circuit to represent the event by using voltage and current synchrophasors that are captured by micro-PMUs. Importantly, this method makes critical use of not only magnitude but also synchronized phase angle measurements, thus, it justifies the need to use micro-PMUs, as opposed to ordinary RMS-based voltage and current sensors. The proposed method can work with data from as a few as only two micro-PMUs. The effectiveness of the developed method is demonstrated through computer simulations on the IEEE 123-bus test system, and also on micro-PMUs measurements from a real-life 12.47 kV test feeder in Riverside, CA. The results verify that the proposed method is accurate and robust in locating the source of different types of events on power distribution systems. [ABSTRACT FROM AUTHOR]

Geomagnetically induced currents (GICs) can increase the reactive power loss in transformers and potentially cause permanent damage due to overheating. This paper considers line switching as a remedial action to protect transformers from geomagnetic disturbances. The algorithm uses linear sensitivity analysis to find an effective switching strategy, which minimizes the number of opened lines subject to satisfying the transformer thermal limits. To reduce the computational complexity for large-scale power systems, the critical lines are identified through sensitivity analysis and the optimization is performed on the reduced system. Furthermore, the effect of GICs on the ac power flow solution is modeled and heuristic techniques are developed to provide sufficient security measures in terms of both GIC flows and ac analysis. Finally, a multiaction solution with an alternating schedule is developed for severe storms when the losses are significant and a single switching action cannot remove the stress from all transformers at a time. The actions are obtained through a recursive algorithm, which divides the original problem into smaller subproblems with fewer constraints and solves them recursively. The effectiveness of the proposed algorithm is demonstrated through numerical results using a 150-bus and a 2000-bus system. [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]

This paper presents a comprehensive set of steady-state models to be included in power flow simulation studies of dc railway networks. This simulation framework covers all important aspects and features of each element of modern dc railways. The proposed models are simplified to achieve the maximum simulation speed while keeping the required accuracy. Not only nonreversible, controlled, and uncontrolled reversible substations are considered, but also onboard and offboard accumulation systems. The train model can consider the low network receptivity (overvoltage protection for trains equipped with regenerative braking) and overcurrent protection. It is also possible to include in the simulation dc/dc links between nodes of the railway network at the same or different voltage. To date, there is no other work able to conjugate all the mentioned models in a complex multitrain scenario. [ABSTRACT FROM AUTHOR]

Static security constraint management, formulated as security constrained optimal power flow (SCOPF), is one of the critical tasks performed during planning and operation. These constraints at any operating point can be divided into noncritical and critical constraints, where former can be managed with preventive controls, while the latter cannot. The violation of at least one critical constraint indicates that network is overstressed and needs a prompt activation of remedial actions to preserve system integrity. Accordingly, critical constraint violations (CCVs) must be identified by solving related SCOPF problem, as information on their types and locations can help to devise and activate optimal remedial actions. However, when dealing with overstressed systems, conventional SCOPF methods may not be able to identify CCVs due to problem infeasibility and there is no commonly accepted method to find related CCVs. Extending previously developed metaheuristic approach, this paper first identifies the CCVs and then proposes a novel methodology to devise the most effective remedial actions to mitigate overstressed system operating conditions. The practical relevance of the remedial actions is demonstrated using IEEE 30-bus, 39-bus, and 57-bus test networks. [ABSTRACT FROM AUTHOR]

In order to provide the ancillary service for smart grid, this paper proposes a modelling and control protocol design approach for the aggregation of heterogeneous thermostatically controlled loads (TCLs). A 2-D state bin is proposed to model the second-order TCL dynamics in a population model. Detailed procedure of calculating the transition probability in the system matrix is provided. In the controller design, a model predictive control (MPC) scheme is proposed to obtain the optimal control actions along the prediction horizon. In addition, implementation of the control signal for adjusting TCLs' statuses are also investigated with practical situations considered. Simulation results reveal the feasibility and efficacy of the proposed modelling and control approach when applied on a large population of TCLs. Some factors that may affect the service performance are also discussed in this paper. [ABSTRACT FROM AUTHOR]

Copper losses in low voltage distribution circuits are a significant proportion of total energy losses and contribute to higher customer costs and carbon emissions. These losses can be evaluated using network models with customer demand data. This paper considers the under-estimation of copper losses when the spiky characteristics of real customer demands are smoothed by arithmetic mean averaging. This is investigated through simulation and by analysis of measured data. The mean losses in cables and equipment supplying a single dwelling estimated from half-hourly data were found to have significant errors of 40%, compared to calculations using high resolution data. Similar errors were found in estimates of peak thermal loading over a half-hour period, with significant variation between results for each customer. The errors reduce as the demand is aggregated, with mean losses for a group of 22 dwellings under-estimated by 7% using half-hourly data. This paper investigates the relationship between the demand data time resolution and errors in the estimated losses. Recommendations are then provided for the time resolution to be used in future measurements and simulation studies. A linear extrapolation technique is also presented whereby errors due to the use of averaged demand data can be reduced. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel method for topology detection in distribution networks called the Time-series signature verification method for topology detection (TSV-Top). The TSV-Top analyzes data from phasor measurement units (PMU or $\mu$ PMU) installed on power distribution feeders. The TSV-Top relies on the fact that measurement data time series from power systems contain similar trends when network topology changes occur, and basically performs the projection of actual voltage phasorial patterns onto a library of signals associated with possible topology transictions of a given distribution network. The proposed algorithm is validated using a 33-bus testbed and the IEEE 123-bus feeder, and then compared with another state-of-the-art algorithm using the IEEE 37-bus feeder. [ABSTRACT FROM AUTHOR]

In this paper, we model topology control through transmission switching as a recourse action in the day-ahead operation of power systems with large-scale renewable generation resources. We prove that transmission switching could only reduce the linear objective value of direct current optimal power flow when congestion exists. However, we also show, through a simple example, that unit commitment cost could be reduced by transmission switching even in the absence of congestion. To solve the stochastic unit commitment with topology control within reasonable computational time, we proposed a heuristic that first decomposes a practical system into zones and then solves the problem for each zone in parallel. The benefit of topology control recourse is demonstrated on a network representing the Central European System. We compare the costs of the network with different loading and renewable generation conditions. The cost reduction of the test system can reach 3.34% with heavy load and large-scale renewable generation while in a single zone the cost reduction can be above 7%. [ABSTRACT FROM PUBLISHER]

Remote-controlled switches (RCSs) play an important role in prompt service restoration of distribution systems (DSs). However, the cost of RCSs and the vast footprint of DSs limit widespread utilization of RCSs. In this paper, we present a new approach to RCS allocation for improving the performance of restoration and optimizing reliability benefits with reasonable RCS cost. Specifically, the optimal number and locations of to-be-upgraded switches can be determined with different objectives: maximizing the reduction of customer interruption cost; maximizing the reduction of system average interruption duration index; or maximizing the amount of loads that can be restored using the upgraded RCSs. We show that these models can actually be formulated as mixed-integer convex programming problems. We further introduce a novel method to equivalently transform and efficiently solve each of them. The global optimum can thus be computed within a reasonable amount of time. The IEEE 33-node and 123-node test systems are used to demonstrate the proposed models and algorithms. [ABSTRACT FROM PUBLISHER]

This paper proposes a fractional order sliding mode control (FOSMC) strategy for grid-connected doubly fed induction generator (DFIG). The novel approach aims to directly control the active/reactive power output of a DFIG-based wind energy conversion system with FOSMC, which has never been utilized in the control of DFIG. The fractional order sliding mode control with disturbance is introduced and the Caputo derivative is employed in constructing the sliding surface. Meanwhile, an enhanced exponential reaching law is utilized in order to mitigate the chattering phenomenon in the sliding stage and accelerate the reaching progress in the meantime. A comparative study is conducted subsequently to verify the superior performance of the proposed FOSMC control scheme over that of the conventional sliding mode control and the vector control approach. A steady state simulation is first conducted to tune the parameters of the FOSMC. A variable wind condition is subsequently simulated to compare the performance of those methods. After that, simulations with background harmonics of the grid voltage and parameter perturbation are considered. Ultimately, an experimental test is conducted to further validate the proposed method. The superior performance and the effectiveness of the FOSMC are fully validated with the above four comparative tests. [ABSTRACT FROM PUBLISHER]

High congestion costs and new congestion patterns, formed by intermittent renewable generation, demand for more efficient utilization of the transmission system. Transmission switching (TS) and variable-impedance series FACTS devices are two technologies that provide such efficiency gains through controlling the power flows. As the system operators begin to utilize these tools, it is essential to understand the interdependence between them at various stages, such as planning and operation. This paper develops an optimal power flow framework that incorporates both FACTS and TS to study the link between the two power flow control technologies. The simulation results on an RTS 96-bus system suggest that: 1) substantial economic savings can be achieved through utilization of both TS and FACTS, beyond the independent capabilities of each technology; 2) performing TS actions affect the optimal location and set point of FACTS devices; and 3) operation of FACTS devices affect the location and frequency of TS actions. It is, thus, essential to acknowledge the interdependence between the two technologies both at the planning and operation stage. Failure to do so will lead to economic inefficiencies that can be avoided through co-optimization of generation dispatch, TS, and FACTS. [ABSTRACT FROM PUBLISHER]

This paper considers line switching as a remedial action to mitigate the geomagnetically induced currents (GICs) in large-scale power syste-kazerooni-2753840ms. The algorithm uses linear sensitivity analysis to find the best switching strategy which minimizes the GIC-saturated reactive power loss. Furthermore, the coupling between the ac power flow solution and the GIC flows is modeled and heuristic strategies are designed to maintain the system security measures in terms of both GICs and ac power flow. Finally, the computational complexity of the algorithm is analyzed for large-system implementations. To reduce the complexity, the critical lines are identified through the sensitivity analysis and the calculations are performed only on the reduced system. The effectiveness of the proposed algorithm is demonstrated through numerical results using a small 20-bus test case as well as large power systems. [ABSTRACT FROM PUBLISHER]

Transmission grid topology control makes power systems more flexible and efficient. However, a line switching action itself may cause transient instability since a large flow disturbance may be involved. In this paper, a critical switching flow (CSF) concept is developed and an associated preventive stabilizing redispatch scheme is proposed to provide control guidelines for line switching actions to prevent instability and enhance transient stability for the system. The CSF is calculated in the day-ahead stage using a two-stage Monte Carlo algorithm, in which the uncertainties of generations and loads are considered and the worst case in the system is identified statistically. The obtained information is then used in the proposed scheme in the operation stage. Selected generators are dispatched before a switching action to ensure system stability. The IEEE reliability test system, the modified IEEE-118 bus system, and the Texas 2000 system are used to demonstrate the effectiveness and scalability of the proposed algorithm and scheme. [ABSTRACT FROM PUBLISHER]

Microgrid formation is a potential solution in postdisaster electric grid recovery efforts. Recent works propose a distribution level microgrid formation model that applies to radial distribution systems characterized by directed power flows. However, with high renewable penetration levels in future power systems, the flows are expected to be undirected even in distribution grids. In this paper, we develop a model to deal with the restoration process of future power systems, embedding some of the characteristics these systems are likely to have. More specifically, our formulation can deal with radial and meshed topologies, and it requires little preprocessing of the input data. Additionally, we extend the model to allow for possible mobile and fixed distributed generation technologies and distributed energy resources, and explicitly include demand responsive loads with a minimum satisfiability constraint. Thus, this extended formulation can be used as an operation and a short term planning tool for the DG scenario-based location problem. We compare our extended formulation results to those obtained for the radial cases found in the literature. Also, we apply the proposed approach to other instances of the problem based on the IEEE 37-bus, 30-bus, and 118-bus systems. [ABSTRACT FROM PUBLISHER]

The resilience and reliability of modern power systems are threatened by increasingly severe weather events and cyber-physical security events. An effective restoration methodology is desired to optimally integrate emerging smart grid technologies and pave the way for developing self-healing smart grids. In this paper, a sequential service restoration (SSR) framework is proposed to generate restoration solutions for distribution systems and microgrids in the event of large-scale power outages. The restoration solution contains a sequence of control actions that properly coordinate switches, distributed generators, and switchable loads to form multiple isolated microgrids. The SSR can be applied for three-phase unbalanced distribution systems and microgrids and can adapt to various operation conditions. Mathematical models are introduced for three-phase unbalanced power flow, voltage regulators, transformers, and loads. The SSR problem is formulated as a mixed-integer linear programming model, and its effectiveness is evaluated via the modified IEEE 123 node test feeder. [ABSTRACT FROM PUBLISHER]

Estimation-based indirect dc-voltage control in MMCs interacts with circulating current control methods. This paper proposes an estimation-based indirect dc-voltage control method for MMC-HVDC systems and analyzes its performance compared to alternative estimations. The interactions between estimation-based indirect dc-voltage control and circulating current control methods, active/reactive power regulation are also investigated. The proposed method delivers similar performance to measurement-based direct dc-voltage control, regardless of the circulating current control method. Steady-state and transient performance is demonstrated using a benchmark MMC-HVDC transmission system, implemented in a real-time digital simulator. The results verify the theoretical evaluations and illustrate the operation and performance of the proposed indirect dc-voltage control method. [ABSTRACT FROM PUBLISHER]

As one of the featured initiatives in smart grids, demand response is enabling active participation of electricity consumers in the supply/demand balancing process, thereby enhancing the power system's operational flexibility in a cost-effective way. Industrial load plays an important role in demand response because of its intense power consumption, already existing advanced monitoring, and control infrastructure, and its strong economic incentive due to the high energy costs. As typical industrial loads, cement plants are able to quickly adjust their power consumption rate by switching on/off the crushers. However, in the cement plant as well as other industrial loads, switching on/off the loading units only achieves discrete power changes, which restricts the load from offering valuable ancillary services such as regulation and load following, as continuous power changes are required for these services. In this paper, we overcome this restriction of poor granularity by proposing methods that enable these loads to provide regulation or load following with the support of an onsite energy storage system. [ABSTRACT FROM PUBLISHER]

Voltage instability occurs when a power system is unable to meet the reactive power demand, and is typically corrected by switching on additional reactive power devices such as capacitor banks. Real-time monitoring and communication technologies can potentially improve voltage stability by enabling the rapid detection of low voltages and the implementation of corrective actions. These corrective actions, however, will only be effective in restoring stability if they are chosen in a timely, scalable manner. In this paper, we propose a submodular optimization approach for designing a control strategy that prevents voltage instability. Our key insight is that the voltage deviation from the desired level is a supermodular function of the set of reactive power injections that are employed, leading to computationally efficient control algorithms for stabilization with provable optimality guarantees. This submodular control framework is tested on the IEEE 300-bus transmission system. [ABSTRACT FROM PUBLISHER]

This paper presents a methodology for integrated planning of real-life medium-voltage networks based on the utility planning concepts. The research is motivated by the need to develop a methodology that would line-up with utility day-to-day businesses and could be applied in real-life. Its core is a two-stage optimization process, where the first stage solves the static investment optimization and the second stage considers operational problem. A probabilistic decision tree approach is proposed for the solution of the entire problem to consider uncertainties in the planning period. The overall formulation is given first, which is followed by details of the investment model and outlines of the proposed operation planning. The novelty of the investment problem, which determines optimal network reinforcements, is explicit modeling of network security constraints of radially operated networks, whilst considering different operating regimes. Additional novel features include modeling of real-life supply restoration rules through network reconfiguration and optimal placement of new switching devices, as well as consideration of “customer flows” on the network. Connection of new distributed generation and demand centers and construction of circuits on new corridors are also included. Two investment models are formulated as mixed-integer nonlinear optimization problems, tested on several MV networks and compared with established methods. The proposed operational problem is solved in two stages, quality-of-supply and operation cost optimization. Computational aspects are also presented. [ABSTRACT FROM PUBLISHER]

This paper proposes a method for studying the reliability implications of line switching operations in power systems. Two case studies are conducted on RTS and IEEE 118-bus system to illustrate this method. This method is designed to explore previously overlooked areas in reliability evaluation of line switching operations. Line removal test is proposed to obtain simulation data of the system, and then with risk analysis and impact analysis, six reliability indices are used to evaluate reliability performance of each transmission line in the system. Instead of the traditionally used mean value, this method introduces variance into analysis. Weibull distribution is used to reconstruct distributions of reliability indices which provide worst case scenario comparisons in reliability evaluation. Eventually, with results obtained from the proposed reliability evaluation method, categorization for line switching operations is introduced to classify all transmission lines based on their reliability performance. The categories provide reliability implications of line switching operations and can be used for guidance in actual operations. [ABSTRACT FROM PUBLISHER]

As the modern transmission control and relay technologies evolve, transmission line switching has become an important option in power system operators’ toolkits to reduce operational cost and improve system reliability. Most recent research has relied on the DC approximation of the power flow model in the optimal transmission switching problem. However, it is known that DC approximation may lead to inaccurate flow solutions and also overlook stability issues. In this paper, we focus on the optimal transmission switching problem with the full AC power flow model, abbreviated as AC optimal transmission switching (AC OTS). We propose a new exact formulation for AC OTS and its mixed-integer second-order cone programming relaxation. We improve this relaxation via several types of strong valid inequalities inspired by the recent development for the closely related AC optimal power flow problem [Kocuk et al., “Strong SOCP relaxations for the optimal power flow problem,” Oper. Res., vol. 64, no. 6, pp. 1177–1196, 2016]. We also propose a practical algorithm to obtain high-quality feasible solutions for the AC OTS problem. Extensive computational experiments show that the proposed formulation and algorithms efficiently solve IEEE standard and congested instances and lead to significant cost benefits with provably tight bounds. [ABSTRACT FROM PUBLISHER]

Implementing automation system in distribution networks needs a huge investment that usually cannot be funded entirely in a short period of time. So distribution companies (DISCOs) should develop long-term plans to equip their network with automation technologies as far as economically justifiable. Aiming to provide a methodology for development such plans, this paper presents a novel multistage planning model for implementing distribution automation system considering all main hardware and software infrastructures. The proposed method optimally determines the type, location, and time in which an equipment or infrastructure must be added to network considering the network capacity expansion plan. The objective function of the planning problem is to maximize the net present value of the DISCO's profit in the planning time horizon. In this method, the optimization problem is solved using the genetic algorithm approach as a promising technique in solving the mixed integer nonlinear programming problems. The proposed method is evaluated on an illustrative test network and the obtained results are presented and discussed. [ABSTRACT FROM PUBLISHER]

The effect of bus-bar splitting on the static stability limit is studied in this paper. A novel online bus-bar splitting methodology is developed to increase the static stability limit of a look-ahead (i.e., short term, say, 30 minutes ahead) power system. The proposed methodology, designed for online application, is based on a strategy consisting of screening, ranking, and decision stages. A tailored model of bus-bar splitting is developed to accurately model bus-bar splitting scenarios. The effectiveness of the proposed online bus-bar splitting methodology is evaluated on the IEEE 118-bus, 1648-bus, and 3120-bus power systems. Results indicate that significant load margin increases can be achieved by bus-bar splitting. [ABSTRACT FROM PUBLISHER]

This paper describes the rationale for developing and disseminating an entire curriculum dedicated to Electric Energy System (EES) education at undergraduate and graduate levels. It presents the benefits of teaching just a few well thought out fundamentals-based courses in this area at the undergraduate level that allow students to take complementary courses and thus be broadly educated. This allows them flexibility upon graduation to work in industry, to go on to graduate school and Ph.D. research, or to work in a field different than power/energy. It describes the graduate courses being developed with the help of experts in their respective fields. Finally, this paper describes the dissemination of this material to other universities and practicing engineers by establishing a Consortium of Universities for Sustainable Power (CUSP™) that as of now has been joined by over 170 universities. [ABSTRACT FROM PUBLISHER]

This paper presents a new control method, in which a distributed generator (DG) actively participates in steady-state voltage control, together with an under-load tap changer (ULTC) and shunt capacitors (Sh.Cs). In the conventional DG control method, the integration of DGs into a distribution power system increases the number of switching operations of the ULTC and the Sh.Cs. To solve this problem, this paper proposes that the DG output voltage be dispatched cooperatively with the operation of the ULTC and the Sh.Cs, based on load forecasts for one day in advance. The objective of the proposed method is to decrease the number of switching device operations, as well as to reduce the power loss in the distribution lines, while maintaining the grid voltage within the allowed range. The proposed method is designed and implemented with Matlab, using two different dynamic programming algorithms for a dispatchable and a nondispatchable DG, respectively. Simulation studies demonstrate that the objective can be achieved under various grid conditions, determined by factors such as the DG output power characteristics, the location of the DG-connected bus on the feeder, and the load profile of the feeder containing the DG. [ABSTRACT FROM PUBLISHER]

Due to increasing shares of renewable energy sources, more frequency reserves are required to maintain power system stability. In this paper, we present a decentralized control scheme that allows a large aggregation of refrigerators to provide Primary Frequency Control (PFC) reserves to the grid based on local frequency measurements and without communication. The control is based on stochastic switching of refrigerators depending on the frequency deviation. We develop methods to account for typical lockout constraints of compressors and increased power consumption during the startup phase. In addition, we propose a procedure to dynamically reset the thermostat temperature limits in order to provide reliable PFC reserves, as well as a corrective temperature feedback loop to build robustness to biased frequency deviations. Furthermore, we introduce an additional randomization layer in the controller to account for thermostat resolution limitations, and finally, we modify the control design to account for refrigerator door openings. Extensive simulations with actual frequency signal data and with different aggregation sizes, load characteristics, and control parameters, demonstrate that the proposed controller outperforms a relevant state-of-the-art controller. [ABSTRACT FROM AUTHOR]

Transmission switching (TS) has gained significant attention recently. However, barriers still remain and must be overcome before the technology can be adopted by the industry. The state-of-the-art challenges include AC feasibility, computational complexity, the ability to handle large-scale real power systems, and dynamic stability. This paper investigates these challenges by developing an AC corrective TS (CTS) based real-time contingency analysis (RTCA) tool that can handle large-scale systems within a reasonable time. The tool quickly proposes multiple high-quality corrective switching actions for contingencies with potential violations. To reduce the computational complexity, three heuristic algorithms are proposed to generate a small set of candidate switching actions. Parallel computing is implemented to further speed up the solution time. Moreover, time-domain simulations are performed to check for dynamic stability of the proposed CTS solutions. The promising results, tested on the Tennessee Valley Authority (TVA) system and actual energy management system snapshots from the PJM Interconnection (PJM) and the Electric Reliability Council of Texas (ERCOT), show that the tool effectively reduces post-contingency violations. It is concluded that CTS is ripe for industry adoption for RTCA application. [ABSTRACT FROM AUTHOR]

Steady-state models of the hybrid power flow controller (HPFC) for power flow and optimal power flow (OPF) studies are presented in this paper, considering the multiple control modes of the device. A strategy for control mode switching and limit handling in power flow calculations is proposed. The OPF model of the HPFC represents all the device control and physical limits as constraints in the mathematical formulation, so that the HPFC can be optimally dispatched as a part of the transmission system control assets. The power flow model is demonstrated and validated through loadability studies on a two-area benchmark test system, where the OPF model is used to determine the optimal ratings of the device based on a cost-benefit analysis. A study is also presented of the HPFC application to Ontario-Canada's grid, to address particular congestion problems in this network; an HPFC cost analysis is also shown for this system. The presented studies demonstrate the application of the proposed models for planning and operation studies, illustrating the performance, effectiveness, and feasibility of the controller to solve congestion issues in a real grid. [ABSTRACT FROM AUTHOR]

This paper proposes a switching angle controller (SAC) and an automatic generation controller (AGC) for the doubly-fed induction generator (DFIG) to control the frequency of DFIG-based wind power penetrated power systems. The concept of virtual rotor angle of the DFIG is defined. The virtual rotor angle is controlled by the SAC in a bang-bang manner such that the active power of the DFIG is regulated to provide frequency support to the external power grids. The output of the SAC is also used for the control of pitch angle to offer a short-term regulation of the mechanical power input to the DFIG, and the long-term control of the mechanical power input is achieved with the AGC. Small-signal analysis is undertaken to verify the effectiveness of the SAC and the AGC. Simulation studies are carried out in a two-machine power system and a modified Kundur four-machine two-area power system, respectively. The frequency support performance of DFIGs having different control configurations is investigated. Modal analysis is undertaken to evaluate the effect of the SAC and the AGC in providing additional damping to the rotor oscillation modes of the modified Kundur four-machine two-area power system. [ABSTRACT FROM AUTHOR]

A Rectangular Interval Power Flow (RIPF) method is proposed to improve solutions for intervals of power flow problems due to nondeterministic characteristics of demand loads and output of generators. It is based on affine arithmetic which is a self-validated numerical analysis and serves to improve the interval results through optimization method. Since no approximation is presumed, the RIPF method acquires narrower intervals of voltage phase and active power of branches than Polar Interval Power Flow (PIPF), it is an excellent method raised before. However, as RIPF is no better than that of PIPF for estimating intervals of voltage magnitude, because it relaxes restriction of the voltage equations. Therefore, a Mixed Interval Power Flow (MIPF) method is envisaged and developed in the paper to incorporate merits of RIPF for computing the intervals of voltage phase and active power of branches but not giving the advantage of PIPF for evaluating intervals of voltage magnitude. As a validation of our suggested approach, two case studies are carried out, and results conclude that the MIPF method acquires more accurate power flow intervals than the conventional method. [ABSTRACT FROM AUTHOR]