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By strategically curtailing active power and providing reactive power support, photovoltaic (PV) systems with advanced inverters can mitigate voltage and thermal violations in distribution networks. Quasi-static time-series (QSTS) simulations are increasingly being utilized to study the implementation of these inverter functions as alternatives to traditional circuit upgrades. However, QSTS analyses can yield significantly different results based on the availability and resolution of input data and other modeling considerations. In this paper, we quantified the uncertainty of QSTS-based curtailment evaluations for two different grid-support functions (autonomous Volt-Var and centralized PV curtailment for preventing reverse power conditions) through extensive sensitivity analyses and hardware testing. We found that Volt-Var curtailment evaluations were most sensitive to poor inverter convergence (−56.4%), PV time-series data (−18.4% to +16.5%), QSTS resolution (−15.7%), and inverter modeling uncertainty (+14.7%), while the centralized control case was most sensitive to load modeling (−26.5% to +21.4%) and PV time-series data (−6.0% to +12.4%). These findings provide valuable insights for improving the reliability and accuracy of QSTS analyses for evaluating curtailment and other PV impact studies.

Global sensitivity analysis (GSA) of voltage to uncertain power injection variations plays an important role for appropriate Volt-VAR optimization. This paper proposes a data-driven GSA method for large-scale distribution systems with a large number of uncertain sources. Specifically, the deep Gaussian process is used to identify the mapping relationship between uncertain power injections and voltages. This allows resorting to the analysis of variance framework to calculate the Sobol indices for GSA. Unlike the existing polynomial chaos expansion and Gaussian process-based approaches, our proposed method has much better scalability. Test results on the EPRI 1747-node K1 circuit with different numbers of uncertain sources with various uncertain levels and different PV distributions demonstrate that the proposed method can achieve accurate GSA. [ABSTRACT FROM AUTHOR]

Global sensitivity analysis (GSA) of distribution system with respect to stochastic PV and load variations plays an important role in designing optimal voltage control schemes. This paper proposes a data-driven framework for GSA of distribution system. In particular, two representative surrogate modeling-based approaches are developed, including the traditional Gaussian process-based and the analysis of variance (ANOVA) kernel ones. The key idea is to develop a surrogate model that captures the hidden global relationship between voltage and real and reactive power injections from the historical data. With the surrogate model, the Sobol indices can be conveniently calculated through either the sampling-based method or the analytical method to assess the global sensitivity of voltage to variations of load and PV power injections. The sampling-based method estimates the Sobol indices using Monte Carlo simulations while the analytical method calculates them by resorting to the ANOVA expansion framework. Comparison results with other model-based GSA methods on the unbalanced three-phase IEEE 37-bus and 123-bus distribution systems show that the proposed framework can achieve much higher computational efficiency with negligible loss of accuracy. The results on a real 240-bus distribution system using actual smart meter data further validate the feasibility and scalability of the proposed framework. [ABSTRACT FROM AUTHOR]

Power system operation and planning studies face many challenges with increasing of renewable energy sources (RESs) penetration. These challenges revolve around the RESs uncertainty and its applications on probabilistic forecasting, power system operation optimization and power system planning. This paper proposes a novel and effective criterion for uncertainties modeling of the RESs as well as system loads. Four sorting stages are applied for the proposed uncertainty cases reduction. Added to that, it proposes three different uncertainty reduction strategies for obtaining different accuracy and speed options. The proposed reduction strategies are tested on medium and large scale distribution systems; IEEE 69-bus and 118-bus systems. The obtained results verify the effectiveness of the proposed criterion in uncertainties modeling in distribution systems with acceptable level of accuracy.

Modern electric power distribution systems are data rich and include growing numbers of distributed energy resources and distribution automation. To take advantage of distribution automation and manage growing penetrations of distributed energy resources, distribution utilities need applications for planning and operations that use all available data and may incorporate distributed approaches to operate and control. The industry would benefit from distribution management applications based on a common platform that makes systems of each type interchangeable. This paper describes an approach to enabling cost-effective development and deployment of advanced applications for distribution system planning and operations based on development of an open-source, standards-based platform for application development called GridAPPS-D, which leverages data abstractions for application development based on standards, such as the distribution system common information model.

There currently exists a mature literature on modeling the aggregate load of a distribution feeder by making use of measurements at its feeder-head at substation. The primary application of such feeder-aggregated load models is in sub-transmission or transmission system analysis. However, there is a growing need in practice also to model each individual load across the feeder. If available, such individual load models have applications in power distribution system analysis, e.g., to better integrate distributed energy resources or to improve power quality and reliability. Motivated by this observation, in this paper, we propose a new method for individual load modeling in power distribution systems. It works by using the measurements only at the feeder-head. It takes an innovative approach to analyzing the load switching events across the distribution feeder itself, instead of or in addition to relying on upstream voltage events that are commonly used in feeder-aggregated load modeling. By tracking the downstream load switching events, the proposed method can make a robust estimation of the ZIP load model parameters for all individual loads. The proposed method is examined on small illustrative test-feeders as well as the IEEE 33-bus test system under various operating scenarios. The adverse impact of errors in measurements and system parameters are also investigated on the performance of the developed load modeling method. [ABSTRACT FROM AUTHOR]

Many applications of Distribution Management Systems (DMSs) are based on power flow solutions. Fast and robust power flow methods capable of accommodating systems of general topologies and the most common models of Distributed Energy Resources (DERs) are, therefore, becoming indispensable. In this context, this paper proposes contributions for the symmetrical component‐based three‐phase power flow methods for distribution system analysis. The introduction of symmetrical components in the three‐phase power flow problem allows it to be decomposed into three single‐phase problems, which can be solved iteratively. Such decomposition significantly expedites the power flow solution problem, simplifies implementation complexity, and makes way for parallel computing techniques. The accuracy and validity of the proposed method were tested on distribution test feeders of different sizes and topologies and the results of several case studies were compared with those obtained by the Sequence Newton–Raphson method, and by the OpenDSS. Contributions of the paper include: (i) A new formulation of the Sequence‐Decoupling Compensation method in terms of real‐valued matrices; (ii) a novel modelling for PV buses; (iii) a simple procedure to tackle convergence issues related to delta and ungrounded‐wye connected transformers; and (iv) a modelling for wye, closed‐ and open‐delta connected step‐voltage regulators in the sequence frame of reference. [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]

Changes in economic, technological, and environmental policies are resulting in a re-evaluation of the dependence on large central generation facilities and their associated transmission networks. Emerging concepts of smart communities/cities are examining the potential to leverage cleaner sources of generation, as well as integrating electricity generation with other municipal functions. When grid connected, these generation assets can supplement the existing interconnections with the bulk transmission system, and in the event of an extreme event, they can provide power via a collection of microgrids. To achieve the highest level of resiliency, it may be necessary to conduct switching operations to interconnect individual microgrids. While the interconnection of multiple microgrids can increase the resiliency of the system, the associated switching operations can cause large transients in low inertia microgrids. The combination of low system inertia and IEEE 1547 and 1547a-compliant inverters can prevent multiple microgrids from being interconnected during extreme weather events. This paper will present a method of using end-use loads equipped with grid friendly appliance controllers to facilitate the switching operations between multiple microgrids; operations that are necessary for optimal operations when islanded for resiliency. [ABSTRACT FROM AUTHOR]

For nearly 20 years, the Test Feeder Working Group of the Distribution System Analysis Subcommittee has been developing openly available distribution test feeders for use by researchers. The purpose of these test feeders is to provide models of distribution systems that reflect the wide diversity in design and their various analytic challenges. Because of their utility and accessibility, the test feeders have been used for a wide range of research, some of which has been outside the original scope of intended uses. This paper provides an overview of the existing distribution feeder models and clarifies the specific analytic challenges that they were originally designed to examine. Additionally, this paper will provide guidance on which feeders are best suited for various types of analysis. The purpose of this paper is to provide the original intent of the Working Group and to provide the information necessary so that researchers may make an informed decision on which of the test feeders are most appropriate for their work. [ABSTRACT FROM PUBLISHER]

This work has two main contributions; First, the development of a general, exact and standardized Step Voltage Regulator model considering all possible configurations and second, the proposal of a 4-Node Test System for testing and evaluation of three-phase Step Voltage Regulator connections. Although the 4-Node Test Feeder for testing three phase transformer configurations is already available in the literature, there is not such model for the inclusion, testing and validation of Step Voltage Regulators in a test feeder. With the work presented in this paper, a new test system will be available to evaluate and benchmark programs or algorithms that attempt to include different configurations of Step Voltage Regulators. The formulation is stated for all three phase Step Voltage Regulators; i.e. wye, close-delta and open-delta connections, both type A and B regulators, in raise or lower positions. Then, all these models are included in a 4-Node Test Feeder to obtain several power flow solutions. All obtained results will be available for power flow software developers on-line. [ABSTRACT FROM AUTHOR]

The increasing complexity of distribution systems requires general, efficient, and large-scale capable methods. This paper proposes a new technique to find the tap positions of step voltage regulators in multiphase load flow solvers in a direct and efficient manner. This is achieved by applying Newton method to the system of equations obtained by using the concept of augmented matrix formulation and adding the constraint equations. This approach allows employing the regulator equations directly. The regulators are modeled by taking into account the line drop compensator circuit with its settings, i.e., the desired voltage level, bandwidth, and R′ and X′ settings, which represent the scaled impedance parameters of the distribution feeder between the regulator and the load center at which the voltage is controlled. The limits of the regulators such as minimum and maximum tap positions are also accounted for. The proposed technique represents a voltage regulator with transformer equations using an augmented matrix formulation. The mismatch equations are developed using the desired voltage setting in constraint equations with transformation ratio of the transformer being the unknown variable. The Jacobian matrix, which is constructed using the augmented matrix formulation, is expanded to hold the constraint equations of voltage regulators. The proposed new method is tested on a variety of test circuits including the large-scale IEEE 8500 Node Test Feeder, and the minimum number of iterations reported in the literature is achieved as presented in this paper. [ABSTRACT FROM AUTHOR]

Storage is being proposed to solve many issues on the electric power grid, especially those issues related to renewable generation such as wind and solar generation. Some North American state and provincial regulators are requiring large amounts of storage to be installed to support anticipated needs of the power grid. Much of that new storage is expected to be connected to distribution feeders. Distribution planners lack tools and methods to assess storage impact on distribution system capacity, reliability, and power quality. Planners are accustomed to static power flow calculations, but accurate analysis of storage requires sequential-time simulation. This paper describes modeling storage for various types of simulations on distribution systems for different time frames typically involved. The basic impact on capacity and voltage regulation can generally be evaluated in simulations with 15-min to 1-h intervals. Evaluations of smoothing of renewable generation variations may require simulations with time step sizes of 1 min or less. Evaluations of such things as frequency control of microgrids and performance during transient disturbances will require dynamics analysis in intervals ranging from seconds down to microseconds. This paper is a summary of recent Electric Power Research Institute research in modeling energy storage for planning studies. [ABSTRACT FROM PUBLISHER]

Regulated electricity utilities are required to provide safe and reliable service to their customers at a reasonable cost. To balance the objectives of reliable service and reasonable cost, utilities build and operate their systems to operate under typical historic conditions. As a result, when abnormal events such as major storms or disasters occur, it is not uncommon to have extensive interruptions in service to the end-use customers. Because it is not cost effective to make the existing electrical infrastructure 100% reliable, society has come to expect disruptions during abnormal events. However, with the increasing number of abnormal weather events, the public is becoming less tolerant of these disruptions. One possible solution is to deploy microgrids as part of a coordinated resiliency plan to minimize the interruption of power to essential loads. This paper evaluates the feasibility of using microgrids as a resiliency resource, including their possible benefits and the associated technical challenges. A use-case of an operational microgrid is included. [ABSTRACT FROM PUBLISHER]

In the past, electric distribution systems have lacked measurement points, and equipment is often operated to its failure point, resulting in customer outages. The widespread deployment of sensors improves distribution level observability. This paper presents an off-line parameter tracking procedure that leverages the increased deployment of distribution level measurement devices to estimate changes in impedance parameters over time. Parameter tracking enables the discovery of non-diurnal and non-seasonal changes, which can be flagged for investigation. The presented method uses an unbalanced distribution-system state-estimator and a measurement-residual based parameter-estimation procedure. Measurement residuals from multiple measurement snapshots are combined to increase effective local redundancy and improve robustness to measurement noise. The input data used in the experiments consists of data from devices on the primary distribution system and from customer meters, via an AMI system. Results of simulations on the IEEE 13-Node Test Feeder with 307 measurements and 246 parameters are presented to illustrate the proposed approach applied to changes in series impedance parameters. The proposed approach can detect a 5% change in series resistance elements with 2% measurement error using less than 1 day of measurement snapshots for a single estimate. [ABSTRACT FROM AUTHOR]

Distribution system states have become more dynamic due to the integration of intermittent distributed generation/load and bi-directional power flows. The availability of close to real-time distribution system models will help the controls and customer participations in the active distribution networks. A framework using on-line and off-line computing power and data in existing distribution management system to work together and build distribution feeder models for operation purposes is proposed. Simulations and evaluation results of the synergy of big heterogeneous topological and measurement data from systems that have different data formats, polling cycles, and accuracy to establish immediate past and future feeder models are presented. Archived customer meter interval and supervisory control and data acquisition (SCADA) data with the same time stamp are used to build quasi dynamic models off-line, and to forecast the states and measurements at the feeder buses. The results are then used in the on-line quasi dynamic state estimations (DySEs). The state tracking capability of two DySE techniques in conjunction with a static state estimator under various data accuracy assumptions is evaluated. Numerical results demonstrate the benefit of data synergy in the improvement of system operation models and network efficiency. [ABSTRACT FROM PUBLISHER]

Quantifying the impact of new technologies on a single distribution feeder is a tractable analysis problem. But the analysis of a single distribution feeder does not provide insight into the complexities and variations of a system-wide deployment. The inability to extrapolate system-wide impacts hinders the deployment of many promising new technologies. This paper presents a three-stage method of extrapolating technological impacts, either simulated or from a field demonstration, from a limited number of distribution feeders to the entire system. The size of the system can vary from the service territory of a single utility, to a region, or to an entire country. The paper will include an example analysis using the United States Department of Energy funded Smart Grid Investment Grant projects, extrapolating their benefits to a national level, and an example of a regionalized deployment of Volt-VAR optimization for peak demand reduction. Both of the example analyses utilize the presented three-stage extrapolation method. [ABSTRACT FROM PUBLISHER]

In a regulated business environment, a utility must be able to validate that deployed technologies provide quantifiable benefits to the end-use customers. While there are well established procedures for determining the benefits derived from the deployment of traditional technologies, the same procedures do not exist for many emerging technologies. Volt-VAR Optimization is an example of an emerging technology that is being deployed across the nation without a standardized method for determining system performance and benefits. This paper will present a method for the evaluation, and quantification of benefits, for field deployments of Volt-VAR Optimization technologies. In addition to presenting the methodology, the paper will present a summary of results, and observations, from two separate Volt-VAR Optimization field evaluations using the presented method. [ABSTRACT FROM PUBLISHER]

This paper presents a methodology for assessing the performance of alternative design strategies for multivoltage-level distribution networks. The key feature of the proposed methodology is its ability to reproduce realistic network topologies and lengths, as calibrated against real distribution networks. Through year-round power flow analysis and optimization processes, the proposed approach allows comprehensive network studies to be carried out for the decision makers to investigate the sensitivity to different parameters and to draw more robust conclusions than those reached through a specific network study. The output metrics used for comparison of network performance are overall network cost, network losses, and reliability, which represent the three most crucial network performance indicators in network design. The validity of the developed models was demonstrated through the investigation of alternative distribution network design for a real medium voltage (MV) network in the U.K. This investigation includes quantitative performance evaluation and comparison between a four-voltage-levels design (e.g., 132 kV/33 kV/11 kV or 6.6 kV/0.4 kV) with three-voltage-levels network arrangements (e.g., 132 kV/11 kV/0.4 kV or 132 kV/20 kV/0.4 kV) and comparison between the peak demand-driven network design versus the optimal loss inclusive network design. [ABSTRACT FROM PUBLISHER]

This study investigates the optimal power flow (OPF) problem for distribution networks with the integration of distributed generation (DG). By considering the objectives of minimal line loss, minimal voltage deviation and maximum DG active power output, the proposed OPF formulation is a multi‐object optimisation problem. Through normalisation of each objective function, the multi‐objective optimisation is transformed to single‐objective optimisation. To solve such a non‐convex problem, the trust‐region sequential quadratic programming (TRSQP) method is proposed, which iteratively approximates the OPF by a quadratic programming with the trust‐region guidance. The TRSQP utilises the sensitivity analysis to approximate all the constraints with linear ones, which will reduce the optimisation scale. Active set method is utilised in TRSQP to solve quadratic programming sub‐problem. Numerical tests on IEEE 33‐, PG&E 69‐ and actual 292‐, 588‐, 1180‐bus systems show the applicability of the proposed method, and comparisons with the primal–dual interior point method and sequential linear programming method are provided. The initialisation and convergence condition of the proposed method are also discussed. The computational result indicates that the proposed algorithm for DG control optimisation in distribution system is feasible and effective. [ABSTRACT FROM AUTHOR]

Recent work in the field of distribution system analysis has shown that the traditional method of peak load analysis is not adequate for the evaluation of emerging distribution system technologies. Voltage optimization, demand response, electric vehicle charging, and energy storage are examples of technologies with characteristics having daily, seasonal, and/or annual variations. In addition to the seasonal variations, emerging technologies such as demand response and plug-in electric vehicle charging have the potential to receive control signals that affects their energy consumption. To support time-series analysis over different time frames and to incorporate potential control signal inputs, detailed end-use load models that accurately represent loads under various conditions, and not just during the peak load period, are necessary. This paper will build on previous end-use load modeling work and outline the methods of general multi-state load models for distribution system analysis. [ABSTRACT FROM PUBLISHER]

Abstract: This paper presents a statistical approach for assessing general LV distribution network design strategies based on a large set of realistic test networks and optimal economic circuit design. The test networks are generated using a fractal-based algorithm that allows creation of generic networks with various topological features (e.g., typical of rural/urban/mixed areas) and characterised by different numbers of substations, numbers of customers, load densities, and so forth. In comparison to standards derived from a traditional approach, that is, case studies on a small number of specific real or test networks, the proposed approach facilitates the derivation of more robust conclusions on optimal network design policies and can thus be used as a valuable tool for decision support. The methodology is exemplified through numerical applications for both urban and rural areas. [Copyright &y& Elsevier]

This paper focuses on representing the state space model of a microgrid in which power regulated (PQ ) and voltage/frequency regulated (Vf) generation units share a distribution system. The generation units considered in this paper are inverter interfaced. This introduces some interesting modeling problems which are treated in the paper, such as the decoupled cascaded control schemes or the non-negligible grid dynamics. A modeling approach is proposed based on four defined complex vectors. These vectors allow for complex-valued system matrices to be formed in a quite automated way. Moreover, a convenient partition of the system matrices is proposed, which in turn allows fast and easy modifications. Additionally, a multivariable methodology is proposed to simultaneously find the control system gains in an optimal sense. A 69-bus radial system, supplied by 20 generation units, is used to demonstrate how the proposal is of easy implementation to conduct small-signal stability analyses. [ABSTRACT FROM AUTHOR]

• A novel MI-QCQP for optimizing reactive power from domestic-scale DERs is proposed • The approach considers both inverter and network losses, and load-voltage sensitivity • Unbalanced European and North American networks are studied, with and without taps • Total demand reduction, of up to 0.5%, depends strongly on inverter loss coefficients • Control with reduced communication requirements can realize 98% of potential benefits This paper proposes a method for studying the potential benefits of reactive power control by domestic-scale inverters, considering network losses, inverter losses, and load-voltage sensitivity. The model is developed as a mixed-integer quadratically constrained quadratic program (MI-QCQP), using a linearization of the unbalanced distribution load flow equations. Networks both with and without on-load tap changers are studied, with the test cases covering both European and North American-style circuits. The use of domestic inverter control is shown to increase benefits compared to conventional tap control by 20%, reducing the total feeder power draw by as much as 0.5% of the feeder load. In contrast, the minimization of either load or losses in isolation is shown to increase the amount of power that a feeder draws in five of the seven circuits. To reduce the communications overhead of the approach, a control scheme is proposed that specifies the reactive power of all inverters on each phase identically; this approach is shown to realise up to 98% of the potential benefits of inverter reactive power control. [ABSTRACT FROM AUTHOR]