Efficient restoration of the electric grid from significant disruptions – both natural and manmade – that lead to the grid entering a failed state is essential to maintaining resilience under a wide range of threats. Restoration follows a set of black start plans, allowing operators to select among these plans to meet the constraints imposed on the system by the disruption. Restoration objectives aim to restore power to a maximum number of customers in the shortest time. Current state-of-the-art for restoration modeling breaks the problem into multiple parts, assuming a known network state and full observability and control by grid operators. These assumptions are not guaranteed under some threats. This paper focuses on a novel integration of modeling and analysis capabilities to aid operators during restoration activities. A power flow-informed restoration framework, comprised of a restoration mixed-integer program informed by power flow models to identify restoration alternatives, interacts with a dynamic representation of the grid through a cognitive model of operator decision-making, to identify and prove an optimal restoration path. Application of this integrated approach is illustrated on exemplar systems. Validation of the restoration is performed for one of these exemplars using commercial solvers, and comparison is made between the steps and time involved in the commercial solver, and that required by the restoration optimization in and of itself, and by the operator model in acting on the restoration optimization output. Publications and proposals developed under this work, along with a path forward for additional expansion of the work, and summary of what was achieved, are also documented.
Pumped Storage Hydropower (PSH) is one of the most popular energy storage technologies in the world. It uses an upper reservoir to store water which can be later used during high-demand. In the United States, most of the energy storage capability actually corresponds to PSH. Moreover, PSH also brings multiple benefits to grid operation. This report presents the Simulink models of three common PSH technologies: Fixed-Speed (FS), Variable-Speed (VS), and Ternary (T)-PSH. These models are available to the general public on this GitHub repository, which contains the MATLAB model initialization files, the Simulink model files, and supplementary MATLAB code used to obtain the figures in this work. For each PSH model, an introductory description of the model components and other relevant functionalities are provided. For further information regarding the models and the initialization parameters, the reader is referred to the shared files in the repository. This report also presents the dynamic behavior of each model. The response of such models to a load event is analyzed and matched with each model's features. A custom IEEE 39 bus case is employed for the FS and T-PSH simulations, while the VS-PSH is simulated on a simplified three-bus test system due to the computational complexity of the model. For the T-PSH, the steady-state and the switching between several operating modes are also studied in this work.
This is the final Technical Report for DOE-SETO Project Award # DE-EE0036461. The goal of this project is to advance the understanding of the grid impact of high penetration of photovoltaic (PV) generation by developing novel numerical methods to solve the differential algebraic equations (DAEs) that define power systems. This will overcome the limitations of current software packages – namely that they only consider fast dynamics over brief time periods. The work presented in this final project report covers results over the entire period of the project. This includes results on model development, code development for the PST repository, datasets in the PST repository, algorithm development and results from variable time-step simulations, development and results from multirate simulations, and sensitivity analysis of key parameter in variable time-step methods. In addition, this report discusses project outreach activities to stakeholders, and a summary of project products. Also covered in this final report is the writing of two conference papers (one of which has already been accepted) and a journal paper. In addition, the updating of two inverter models (both grid forming and grid following) to be compatible with the latest version of PST software is discussed.
This paper presents a visualization technique for incorporating eigenvector estimates with geospatial data to create inter-area mode shape maps. For each point of measurement, the method specifies the radius, color, and angular orientation of a circular map marker. These characteristics are determined by the elements of the right eigenvector corresponding to the mode of interest. The markers are then overlaid on a map of the system to create a physically intuitive visualization of the mode shape. This technique serves as a valuable tool for differentiating oscillatory modes that have similar frequencies but different shapes. This work was conducted within the Western Interconnection Modes Review Group (WIMRG) in the Western Electric Coordinating Council (WECC). For testing, we employ the WECC 2021 Heavy Summer base case, which features a high-fidelity, industry standard dynamic model of the North American Western Interconnection. Mode estimates are produced via eigen-decomposition of a reduced-order state matrix identified from simulated ringdown data. The results provide improved physical intuition about the spatial characteristics of the inter-area modes. In addition to offline applications, this visualization technique could also enhance situational awareness for system operators when paired with online mode shape estimates.
This paper presents a preliminary investigation on controlling the existing high voltage dc (HVDC) links connecting the North American western interconnection (WI) to the other interconnections, to provide damping to inter-area oscillations. The control scheme is meant to damp inter-area modes of oscillation in the WI by using wide area synchrophasor feedback. A custom model is developed in General Electric's PSLF software for the wide area damping control scheme, and simulations are analyzed on a validated full 22,000 bus WI model. Results indicate that implementing the proposed control technique to the existing HVDC links in the WI can significantly improve the damping of the inter-area modes of the system.
A methodology for the design of control systems for wide-area power systems using solid-state transformers (SSTs) as actuators is presented. Due to their ability to isolate the primary side from the secondary side, an SST can limit the propagation of disturbances, such as frequency and voltage deviations, from one side to the other. This paper studies a control strategy based on SSTs deployed in the transmission grid to improve the resilience of power grids to disturbances. The control design is based on an empirical model of an SST that is appropriate for control design in grid level applications. A simulation example illustrating the improvement provided by an SST in a large-scale power system via a reduction in load shedding due to severe disturbances are presented.
Forced oscillations in power systems are of particular interest when they interact and reinforce inter-area oscillations. This paper determines how a previously proposed inter-area damping controller mitigates forced oscillations. The damping controller modulates active power on the Pacific DC Intertie (PDCI) based on phasor measurement units (PMU) frequency measurements. The primary goal of the controller is to improve the small signal stability of the north south B mode in the North American Western Interconnection (WI). The paper presents small signal stability analysis in a reduced order system, time-domain simulations of a detailed representation of the WI and actual system test results to demonstrate that the PDCI damping controller provides effective damping to forced oscillations in the frequency range below 1 Hz.
This paper describes the design and implementation of a proof-of-concept Pacific dc Intertie (PDCI) wide area damping controller and includes system test results on the North American Western Interconnection (WI). To damp inter-area oscillations, the controller modulates the power transfer of the PDCI, a ±500 kV dc transmission line in the WI. The control system utilizes real-time phasor measurement unit (PMU) feedback to construct a commanded power signal which is added to the scheduled power flow for the PDCI. After years of design, simulations, and development, this controller has been implemented in hardware and successfully tested in both open and closed-loop operation. The most important design specifications were safe, reliable performance, no degradation of any system modes in any circumstances, and improve damping to the controllable modes in the WI. The main finding is that the controller adds significant damping to the modes of the WI and does not adversely affect the system response in any of the test cases. The primary contribution of this paper, to the state of the art research, is the design methods and test results of the first North American real-time control system that uses wide area PMU feedback.
The Energy Surety Design Methodology (ESDM) provides a systematic approach for engineers and researchers to create a preliminary electric grid design, thus establishing a means to preserve and quickly restore customer-specified critical loads. Over a decade ago, Sandia National Laboratories (Sandia) defined Energy Surety for applications with energy systems to include elements of reliability, security, safety, cost, and environmental impact. Since then, Sandia has employed design concepts of energy surety for over 20 military installations and their interaction with utility systems, including the Smart Power Infrastructure Demonstration for Energy Reliability and Security (SPIDERS) Joint Capability Technology Demonstration (JCTD) project. In recent years, resilience has also been added as a key element of energy surety. This methodology document includes both process recommendations and technical guidance, with references to useful tools and analytic approaches at each step of the process.
Battery energy storage systems (BESS) are a critical technology for integrating high penetration renewable power on an intelligent electrical grid. As limited energy restricts the steady-state operational state-of-charge (SoC) of storage systems, SoC forecasting models are used to determine feasible charge and discharge schedules that supply grid services. Smart grid controllers use SoC forecasts to optimize BESS schedules to make grid operation more efficient and resilient. This paper presents three advances in BESS SoC forecasting. First, two forecasting models are reformulated to be conducive to parameter optimization. Second, a new method for selecting optimal parameter values based on operational data is presented. Last, a new framework for quantifying model accuracy is developed that enables a comparison between models, systems, and parameter selection methods. The accuracies achieved by both models, on two example battery systems, with each method of parameter selection are then compared in detail. The results of this analysis suggest variation in the suitability of these models for different battery types and applications. The proposed model formulations, optimization methods, and accuracy assessment framework can be used to improve the accuracy of SoC forecasts enabling better control over BESS charge/discharge schedules.
Power system inter-area oscillations can be damped using distributed control of multiple power injections within the interconnection. This type of control traditionally requires system-wide measurements which are transmitted from dispersed, sometimes remote, locations and are subject to delays. This paper evaluates the effect that delayed feedback signals have on the stability of a two-area power system and presents delay-dependent criteria for stability using two different implementations of a damping controller. The controllers are based on a uniform proportional control action and use two feedback signals one from each area of the two-area power system. Each of these signals is subject to an independent delay. Using a Lyapunov-based approach, sufficient conditions for stability that depend on each time delay are found for a range of proportional control gains. Numerical results show that the regions of time delays for which the system is stable are reduced as the proportional gain increases. Time domain simulations validate these stability regions and show the varying responses for the two control implementations and different values of the proportional gain.
This study describes the implementation of a tool to estimate latencies and data dropouts in communication networks transferring synchrophasor data defined by the C37.118 standard. The tool assigns a time tag to synchrophasor packets at the time it receives them according to a global positioning system clock and with this information is able to determine the time those packets took to reach the tool. The tool is able to connect simultaneously to multiple phasor measurement units (PMUs) sending packets at different reporting rates with different transport protocols such as user datagram protocol or transmission control protocol. The tool is capable of redistributing every packet it receives to a different device while recording the exact time this information is re-sent into the network. The results of measuring delays from a PMU using this tool are presented and compared with those of a conventional network analyzer. The results show that the tool presented in this paper measures delays more accurately and precisely than the conventional network analyzer.
This report serves as the executive summary to the comprehensive document that describes the software, control logic, and operational functions of the Pacific DC Intertie (PDCI) Oscillation Damping Controller. The purpose of the damping controller (DCON) is to mitigate inter-area oscillations in the Western Interconnection (WI) by active improvement of oscillatory mode damping using phasor measurement unit (PMU) feedback to modulate power flow in the PDCI. This report provides the high level descriptions, diagrams, and charts to receive a basic understanding of the organization and structure of the DCON software. This report complements the much longer comprehensive software document, and it does not include any proprietary information as the more comprehensive report does. The level of detail provided by the comprehensive report on the software documentation is intended to assist with the process needed to obtain compliance for North American Electric Reliability Corporation Critical Infrastructure Protection (NERC-CIP) as a Bulk energy system Cyber Asset (BCA) device. That report organizes, summarizes, and presents the charts, figures, and flow diagrams that detail the organization and function of the damping controller software. The PDCI Wide-Area Damping Controller is the result of a collaboration between Sandia National Laboratories (SNL), Bonneville Power Administration (BPA), Montana Tech University (MTU), and the Department of Energy (DOE).
Inter-area oscillations are present in all power systems dispersed over large areas and can have detrimental effects limiting transmission capacity or even causing blackouts. The availability of wide-area measurements in power systems has enabled damping of inter-area oscillations using distributed control methods and system components, such as energy storage devices. We investigate the performance of damping control enabled by energy storage devices distributed throughout an example two-area power system assuming the availability of wide-area measurements of generator machine speeds. The energy storage devices are capable of injecting active power into the system in order to damp inter-area oscillations that occur after a fault in the system. An analysis of the linearized system and several simulations of the nonlinear system with multiple combinations of controlled power injections from energy storage devices are performed. From the results, we quantify and discuss how damping performance depends on the sizes and locations of injections.
Synchrophasor data, now prevalent in power systems around the world, is enabling the development of applications such as wide area control systems (WACS). Because synchrophasor data is transmitted from dispersed locations it is only available to WACS after a certain delay and at irregular time intervals. This paper initially shows that these non-uniformities in the availability of the data cause the WACS output command to be non-smooth potentially affecting the actuator. Next, paper also shows how delays in the WACS input signal are translated into erroneous and inverted WACS output commands. Finally, the paper proposes exact time-synchronization of the data as a solution of the above problems to ensure that the control action is not compromised.
A wide-area controller to damp inter-area oscillations in the North American Western Interconnection (WI) by modulating power transfers in a HVDC link is used in this paper to investigate the effects that latencies in its feedback signals have on its performance. This controller uses two feedback measurements to perform its control action. The analysis show that the stabilizing effect of the controller in transient stability and small signal stability is compromised as the feedback measurements experience higher delays. The results show that one of the feedback signals can tolerate more delay than the other. The analysis was performed with Bode plots and time domain simulations on a reduced order model of the WI from which a linear version was obtained.
This paper explores the controllability of power system oscillation modes by multiple high voltage DC (HVDC) transmission lines. The controllability exploration is performed in a reduced model of the Western Electricity Coordination Council (WECC) system, with added HVDC lines according to previously proposed lines. The exploration shows that various oscillation modes, across several system areas, can be simultaneously controlled by coordinating three or more HVDC lines. The degree of damping in each oscillation mode can be selected by designing a multi-input multi-output control system on the HVDC lines.
This report documents the use of wind turbine inertial energy for the supply of two specific electric power grid services; system balancing and real power modulation to improve grid stability. Each service is developed to require zero net energy consumption. Grid stability was accomplished by modulating the real power output of the wind turbine at a frequency and phase associated with wide-area modes. System balancing was conducted using a grid frequency signal that was high-pass filtered to ensure zero net energy. Both services used Phasor Measurement Units (PMUs) as their primary source of system data in a feedforward control (for system balancing) and feedback control (for system stability).
This paper presents simulation results of a control scheme for damping inter-area oscillations using high-voltage DC (HVDC) power modulation. The control system utilizes realtime synchrophasor feedback to construct a supplemental commanded power signal for the Pacific DC Intertie (PDCI) in the North American Western Interconnection (WI). A prototype of this controller has been implemented in hardware and, after multiple years of development, successfully tested in both open and closed-loop operation. This paper presents simulation results of the WI during multiple severe contingencies with the damping controller in both open and closed-loop. The primary results are that the controller adds significant damping to the controllable modes of the WI and that it does not adversely affect the system response in any of the simulated cases. Furthermore, the simulations show that a feedback signal composed of the frequency difference between points of measurement near the Washington-Oregon border and the California-Oregon border can be employed with similar results to a feedback signal constructed from measurements taken near the Washington-Oregon border and southern California. This is an important consideration because it allowed the control system to be designed without relying upon cross-system measurements, which would have introduced significant additional delay.
Distributed control compensation based on local and remote sensor feedback can improve small-signal stability in large distributed systems, such as electric power systems. Long distance remote measurements, however, are potentially subject to relatively long and uncertain network latencies. In this work, the issue of asymmetrical network latencies is considered for an active damping application in a two-area electric power system. The combined effects of latency and gain are evaluated in time domain simulation and in analysis using root-locus and the maximum singular value of the input sensitivity function. The results aid in quantifying the effects of network latencies and gain on system stability and disturbance rejection.
Lightly damped electromechanical oscillations are a source of concern in the western interconnect. Recent development of a reliable real-time wide-area measurement system (WaMS) has enabled the potential for large-scale damping control approaches for stabilizing critical oscillation modes. a recent research project has focused on the development of a prototype feedback modulation controller for the Pacific DC Intertie (PDCI) aimed at stabilizing such modes. The damping controller utilizes real-time WaMS signals to form a modulation command for the DC power on the PDCI. This paper summarizes results from the first actual-system closed-loop tests. Results demonstrate desirable performance and improved modal damping consistent with previous model studies.
Inter-area oscillation is one of the main concerns in power system small signal stability. It involves wide area in power system, therefore identifying the causes and damping these oscillations are challenging. Undamped inter-area oscillations may cause severe problems in power systems including large-scale blackouts. Designing a proper controller for power systems also is a challenging problem due to the complexity of the system. Moreover, for a large-scale system it is impractical to collect all system information in one location to design a centralized controller. Decentralized controller will be more desirable for large scale systems to minimize the inter area oscillations by using local information. In this paper, we consider a large-scale power system consisting of three areas. After decomposing the system into three subsystems, each subsystem is modeled with a lower order system. Finally, a decentralized controller is designed for each subsystem to maintain the large-scale system frequency at the desired level even in the presence of disturbances.
Power systems can be stabilized using distributed control methods with wide-area measurements for feedback. However, wide-area measurements are subject to time delays in communication, which can have undesirable effects on system performance. We present time-domain analysis results regarding the small-signal stability of a two-area power system with damping control subjected to asymmetric time delays in the feedback measurements. We consider two wide-area damping control implementations. The first is implemented with a High Voltage DC transmission line, and the second uses distributed Energy Storage devices. Numerical results show regions of stability for the closed-loop systems that depend on the time delays and the choice of the control gain. These results show that increasing the control gains cause the systems to be less robust to time delays, and, under certain conditions, increasing the time delays can have a stabilizing effect. Furthermore, we provide analysis of time simulations and eigenvalue plots that verify these stability regions and show how stability is affected as time delays increase.
This paper describes the initial open-loop operation of a prototype control system aimed at mitigating inter-area oscillations through active DC power modulation. The control system uses real-time synchrophasor feedback to construct a commanded power signal added to the scheduled power on the Pacific DC Intertie (PDCI) within the western North American power system (wNAPS). The control strategy is based upon nearly a decade of simulation, linear analysis, and actual system tests. The control system must add damping to all modes which are controllable and 'do no harm' to the AC grid. Tests were conducted in which the damping controller injected live probing signals into the PDCI controls to change the power flow on the PDCI by up to ±125 MW. While the probing tests are taking place, the damping controller recorded what it would have done if it were providing active damping. The tests demonstrate that the dynamic response of the DC system is highly desirable with a response time of 11 ms which is well within the desired range. The tests also verify that the overall transfer functions are consistent with past studies and tests. Finally, the tests show that the prototype controller behaves as expected and will improve damping in closed-loop operation.
This paper describes the design strategy and testing results of a control system to improve damping of inter-area oscillations in the western North American Power System (wNAPS) in order to maintain dynamic stability of the grid. Extensive simulation studies and actual test results on the wNAPS demonstrate significant improvements in damping of inter-area oscillations of most concern without reducing damping of peripheral oscillations. The design strategy of the control system features three novel attributes: (1) The feedback law for the control system is constructed using real-time measurements acquired from Phasor Measurement Units (PMUs) located throughout the power grid. (2) Control actuation is delivered by the modulation of real power flow through a High Voltage Direct Current (HVDC) transmission line. (3) A supervisory system, integrated into the control system is in charge of determining damping effectiveness, maintaining failsafe operation, and ensuring that no harm is done to the grid.
To demonstrate and validate the performance of the wide-are a damping control system, the project plans to conduct closed-loop tests on the PDCI in summer/fall 2016. A test plan details the open and closed loop tests to be conducted on the P DCI using the wide-area damping control system. To ensure the appropriate level of preparedness, simulations were performed in order to predict and evaluate any possible unsafe operations before hardware experiments are attempted. This report contains the result s from these simulations using the power system dynamics software PSLF (Power System Load Flow, trademark of GE). The simulations use the WECC (Western Electricity Coordinating Council) 2016 light summer and heavy summer base cases.
This paper describes a control scheme to mitigate inter-area oscillations through active damping. The control system uses real-time phasor measurement unit (PMU) feedback to construct a commanded power signal to modulate the flow of real power over the Pacific DC Intertie (PDCI) located in the western North American Power System (wNAPS). A hardware prototype was constructed to implement the control scheme. To ensure safe and reliable performance, the project integrates a supervisory system to ensure the controller is operating as expected at all times. A suite of supervisory functions are implemented across three hardware platforms. If any controller mal-function is detected, the supervisory system promptly disables the controller through a bumpless transfer method. This paper presents a detailed description of the control scheme, simulation results, the bumpless transfer method, and a redundancy and diversity method in the selection of PMU signals for feedback. This paper also describes in detail the supervisory system implemented to ensure safe and reliable damping performance of the real-time wide area damping controller.
With increasing renewable penetrations and advancements in power electronics associated with smart grid technologies, distributed control of the power grid is quickly becoming a necessity. Once communications are introduced into a control system, the impacts of latency and unreliable communications quickly become a priority. Vector Lyapunov techniques are well suited for the analysis of control systems with structured perturbations. These perturbations can be employed to model uncertainty in communications as well as parameter uncertainty. In this paper, we present results for small signal stability of a simplified two area power system model for several scenarios: bandwidth limited local communications and tie line uncertainty; local communications and bandwidth limited global communications combined with tie line uncertainty; and uncertainty in global communications. These results are intended to be a starting point for the analysis of the impact of communications uncertainty on the stability of power systems.
This report supplements the document, "Protocol for Uniformly Measuring and Expressing the Performance of Energy Storage Systems," issued in a revised version in April 2016 (see [4]), which will include the photovoltaic (PV) smoothing application for an energy storage system (ESS). This report provides the background and documentation associated with the determination of a duty cycle for an ESS operated in a PV smoothing application for the purpose of measuring and expressing ESS performance in accordance with the ESS performance protocol. ACKNOWLEDGEMENTS The authors gratefully acknowledge the support of Dr. Imre Gyuk, program manager for the DOE Energy Storage Systems Program. The authors would also like to express their appreciation to all the stakeholders who participated as members of the PV Smoothing Subgroup. Without their thoughtful input and recommendations, the definitions, metrics, and duty cycle provided in this report would not have been possible. A complete listing of members of the PV Smoothing Subgroup appears in the first chapter of this report. Special recognition should go to the staffs at Pacific Northwest National Laboratory (PNNL) and Sandia National Laboratories (SNL) in collaborating on this effort. In particular, Mr. David Conover and Dr. Vish Viswanathan of PNNL and Dr. Summer Ferreira of SNL were especially helpful in their suggestions for the determination of a duty cycle for the PV Smoothing application.
Schoenwald, David A.; Schoenwald, David A.; Eto, Joseph H.; Eto, Joseph H.; Stewart, Emma M.; Stewart, Emma M.; Kirkham, Harold K.; Kirkham, Harold K.; Tuffner, Francis T.; Tuffner, Francis T.; Smith, Travis S.; Buckner, Mark B.
This report addresses the potential use of phasor measurement units (PMUs) within electricity distribution systems, and was written to assess whether or not PMUs could provide significant benefit, at the national level. We analyze examples of present and emerging distribution-system issues related to reliability, integration of distributed energy resources, and the changing electrical characteristics of load. We find that PMUs offer important and irreplaceable advantages over present approaches. However, we also find that additional research and development for standards, testing and calibration, demonstration projects, and information sharing is needed to help industry capture these benefits.
This report supplements the document, “Protocol for Uniformly Measuring and Expressing the Performance of Energy Storage Systems,” issued in a revised version in April 2016, which will include the renewables (solar) firming application for an energy storage system (ESS). This report provides the background and documentation associated with the determination of a duty cycle for an ESS operated in a renewables (solar) firming application for the purpose of measuring and expressing ESS performance in accordance with the ESS performance protocol.
Electromechanical oscillations often limit transmission capacity in the western North American Power System (termed the wNAPS). Recent research and development has focused on employing large-scale damping controls via wide-area feedback. Such an approach is made possible by the recent installation of a wide-area real-time measurement system based upon Phasor Measurement Unit (PMU) technology. One potential large-scale damping approach is based on energy storage devices. Such an approach has considerable promise for damping oscillations. This paper considers the placement of such devices within the wNAPS system. We explore combining energy storage devices with HVDC modulation of the Pacific DC Intertie (PDCI). We include eigenanalysis of a reduced-order wNAPS system, detailed analysis of a basic two-area dynamic system, and full-order transient simulations. We conclude that the optimal energy storage location is in the area with the lower inertia.
The purpose of this study is to characterize the technical performance of the PNM Prosperity electricity storage project, and to identify lessons learned that can be used to improve similar projects in the future. The PNM Prosperity electricity storage project consists of a 500 kW/350 kWh advanced lead-acid battery with integrated supercapacitor (for energy smoothing) and a 250 kW/1 MWh advanced lead-acid battery (for energy shifting), and is co-located with a 500 kW solar photovoltaic (PV) resource. The project received American Reinvestment and Recovery Act (ARRA) funding. The smoothing system is e ective in smoothing intermittent PV output. The shifting system exhibits good round-trip efficiencies, though the AC-to-AC annual average efficiency is lower than one might hope. Given the current utilization of the smoothing system, there is an opportunity to incorporate additional control algorithms in order to increase the value of the energy storage system.
The U.S. Department of Energys Energy Storage Systems (ESS) Program, through the support of Pacific Northwest National Laboratory (PNNL) and Sandia National Laboratories (SNL), facilitated the development of the protocol provided in this report. The focus of the protocol is to provide a uniform way of measuring, quantifying, and reporting the performance of ESSs in various applications; something that does not exist today and, as such, is hampering the consideration and use of this technology in the market. The availability of an application-specific protocol for use in measuring and expressing performance-related metrics of ESSs will allow technology developers, power-grid operators and other end-users to evaluate the performance of energy storage technologies on a uniform and comparable basis. This will help differentiate technologies and products for specific application(s) and provide transparency in how performance is measured. It also will assist utilities and other consumers of ESSs to make more informed decisions as they consider the potential application and use of ESSs, as well as form the basis for documentation that might be required to justify utility investment in such technologies.
The goal of this study was to evaluate the small signal and transient stability of the Western Electric- ity Coordinating Council (WECC) under high penetrations of renewable energy, and to identify control technologies that would improve the system performance. The WECC is the regional entity responsible for coordinating and promoting bulk electric system reliability in the Western Interconnection. Transient stability is the ability of the power system to maintain synchronism after a large disturbance while small signal stability is the ability of the power system to maintain synchronism after a small disturbance. Tran- sient stability analysis usually focuses on the relative rotor angle between synchronous machines compared to some stability margin. For this study we employed generator speed relative to system speed as a metric for assessing transient stability. In addition, we evaluated the system transient response using the system frequency nadir, which provides an assessment of the adequacy of the primary frequency control reserves. Small signal stability analysis typically identi es the eigenvalues or modes of the system in response to a disturbance. For this study we developed mode shape maps for the di erent scenarios. Prony analysis was applied to generator speed after a 1.4 GW, 0.5 second, brake insertion at various locations. Six di erent WECC base cases were analyzed, including the 2022 light spring case which meets the renewable portfolio standards. Because of the di culty in identifying the cause and e ect relationship in large power system models with di erent scenarios, several simulations were run on a 7-bus, 5-generator system to isolate the e ects of di erent con gurations. Based on the results of the study, for a large power system like the WECC, incorporating frequency droop into wind/solar systems provides a larger bene t to system transient response than replacing the lost inertia with synthetic inertia. From a small signal stability perspective, the increase in renewable penetration results in subtle changes to the system modes. In gen- eral, mode frequencies increase slightly, and mode shapes remain similar. The system frequency nadir for the 2022 light spring case was slightly lower than the other cases, largely because of the reduced system inertia. However, the nadir is still well above the minimum load shedding frequency of 59.5 Hz. Finally, several discrepancies were identi ed between actual and reported wind penetration, and additional work on wind/solar modeling is required to increase the delity of the WECC models.
This report describes an algorithm, implemented in Matlab/Simulink, designed to reduce the variability of photovoltaic (PV) power output by using a battery. The purpose of the battery is to add power to the PV output (or subtract) to smooth out the high frequency components of the PV power that that occur during periods with transient cloud shadows on the PV array. The control system is challenged with the task of reducing short-term PV output variability while avoiding overworking the battery both in terms of capacity and ramp capability. The algorithm proposed by Sandia is purposely very simple to facilitate implementation in a real-time controller. The control structure has two additional inputs to which the battery can respond. For example, the battery could respond to PV variability, load variability or area control error (ACE) or a combination of the three.
Article 690.11 in the 2011 National Electrical Code{reg_sign} (NEC{reg_sign}) requires new photovoltaic (PV) systems on or penetrating a building to include a listed arc fault protection device. Currently there is little experimental or empirical research into the behavior of the arcing frequencies through PV components despite the potential for modules and other PV components to filter or attenuate arcing signatures that could render the arc detector ineffective. To model AC arcing signal propagation along PV strings, the well-studied DC diode models were found to inadequately capture the behavior of high frequency arcing signals. Instead dynamic equivalent circuit models of PV modules were required to describe the impedance for alternating currents in modules. The nonlinearities present in PV cells resulting from irradiance, temperature, frequency, and bias voltage variations make modeling these systems challenging. Linearized dynamic equivalent circuits were created for multiple PV module manufacturers and module technologies. The equivalent resistances and capacitances for the modules were determined using impedance spectroscopy with no bias voltage and no irradiance. The equivalent circuit model was employed to evaluate modules having irradiance conditions that could not be measured directly with the instrumentation. Although there was a wide range of circuit component values, the complex impedance model does not predict filtering of arc fault frequencies in PV strings for any irradiance level. Experimental results with no irradiance agree with the model and show nearly no attenuation for 1 Hz to 100 kHz input frequencies.
Design and operation of the electric power grid (EPG) relies heavily on computational models. High-fidelity, full-order models are used to study transient phenomena on only a small part of the network. Reduced-order dynamic and power flow models are used when analysis involving thousands of nodes are required due to the computational demands when simulating large numbers of nodes. The level of complexity of the future EPG will dramatically increase due to large-scale deployment of variable renewable generation, active load and distributed generation resources, adaptive protection and control systems, and price-responsive demand. High-fidelity modeling of this future grid will require significant advances in coupled, multi-scale tools and their use on high performance computing (HPC) platforms. This LDRD report demonstrates SNL's capability to apply HPC resources to these 3 tasks: (1) High-fidelity, large-scale modeling of power system dynamics; (2) Statistical assessment of grid security via Monte-Carlo simulations of cyber attacks; and (3) Development of models to predict variability of solar resources at locations where little or no ground-based measurements are available.
A multi-laboratory ontology construction effort during the summer and fall of 2009 prototyped an ontology for counterfeit semiconductor manufacturing. This effort included an ontology development team and an ontology validation methods team. Here the third team of the Ontology Project, the Data Analysis (DA) team reports on their approaches, the tools they used, and results for mining literature for terminology pertinent to counterfeit semiconductor manufacturing. A discussion of the value of ontology-based analysis is presented, with insights drawn from other ontology-based methods regularly used in the analysis of genomic experiments. Finally, suggestions for future work are offered.
This is the final report for a LDRD effort to address human behavior in decision support systems. One sister LDRD effort reports the extension of this work to include actual human choices and additional simulation analyses. Another provides the background for this effort and the programmatic directions for future work. This specific effort considered the feasibility of five aspects of model development required for analysis viability. To avoid the use of classified information, healthcare decisions and the system embedding them became the illustrative example for assessment.
As part of DARPA Information Processing Technology Office (IPTO) Software for Distributed Robotics (SDR) Program, Sandia National Laboratories has developed analysis and control software for coordinating tens to thousands of autonomous cooperative robotic agents (primarily unmanned ground vehicles) performing military operations such as reconnaissance, surveillance and target acquisition; countermine and explosive ordnance disposal; force protection and physical security; and logistics support. Due to the nature of these applications, the control techniques must be distributed, and they must not rely on high bandwidth communication between agents. At the same time, a single soldier must easily direct these large-scale systems. Finally, the control techniques must be provably convergent so as not to cause undo harm to civilians. In this project, provably convergent, moderate communication bandwidth, distributed control algorithms have been developed that can be regulated by a single soldier. We have simulated in great detail the control of low numbers of vehicles (up to 20) navigating throughout a building, and we have simulated in lesser detail the control of larger numbers of vehicles (up to 1000) trying to locate several targets in a large outdoor facility. Finally, we have experimentally validated the resulting control algorithms on smaller numbers of autonomous vehicles.
CommAspen is a new agent-based model for simulating the interdependent effects of market decisions and disruptions in the telecommunications infrastructure on other critical infrastructures in the U.S. economy such as banking and finance, and electric power. CommAspen extends and modifies the capabilities of Aspen-EE, an agent-based model previously developed by Sandia National Laboratories to analyze the interdependencies between the electric power system and other critical infrastructures. CommAspen has been tested on a series of scenarios in which the communications network has been disrupted, due to congestion and outages. Analysis of the scenario results indicates that communications networks simulated by the model behave as their counterparts do in the real world. Results also show that the model could be used to analyze the economic impact of communications congestion and outages.
This report documents work undertaken to endow the cognitive framework currently under development at Sandia National Laboratories with a human-like memory for specific life episodes. Capabilities have been demonstrated within the context of three separate problem areas. The first year of the project developed a capability whereby simulated robots were able to utilize a record of shared experience to perform surveillance of a building to detect a source of smoke. The second year focused on simulations of social interactions providing a queriable record of interactions such that a time series of events could be constructed and reconstructed. The third year addressed tools to promote desktop productivity, creating a capability to query episodic logs in real time allowing the model of a user to build on itself based on observations of the user's behavior.
This report describes the features of Aspen-EE (Electricity Enhancement), a new model for simulating the interdependent effects of market decisions and disruptions in the electric power system on other critical infrastructures in the US economy. Aspen-EE extends and modifies the capabilities of Aspen, an agent-based model previously developed by Sandia National Laboratories. Aspen-EE was tested on a series of scenarios in which the rules governing electric power trades were changed. Analysis of the scenario results indicates that the power generation company agents will adjust the quantity of power bid into each market as a function of the market rules. Results indicate that when two power markets are faced with identical economic circumstances, the traditionally higher-priced market sees its market clearing price decline, while the traditionally lower-priced market sees a relative increase in market clearing price. These results indicate that Aspen-EE is predicting power market trends that are consistent with expected economic behavior.