Publications

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Cyber-secure, resilient energy is paramount to the prosperity of the United States. As the experience and sophistication of cyber adversaries grow, so too must the US power system’s defenses, situational awareness, and response and recovery strategies. Traditionally, power systems were operated with dedicated communication channels to large generators and utility-owned assets but now there is greater reliance on photovoltaic (PV) systems to provide power generation. PV systems often communicate to utilities, aggregators, and other grid operators over the public internet so the power system attack surface has significantly expanded. At the same time, solar energy systems are equipped with a range of grid-support functions, that—if controlled or programmed improperly—present a risk of power system disturbances. This document is a five-year roadmap intended to chart a path for improving cyber security for communication-enabled PV systems with clear roles and responsibilities for government, standards development organizations, PV vendors, and grid operators.

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For three years, Sandia National Laboratories, Georgia Institute of Technology, and University of Illinois at Urbana-Champaign investigated a smart grid vision in which renewable-centric Virtual Power Plants (VPPs) provided ancillary services with interoperable distributed energy resources (DER). This team researched, designed, built, and evaluated real-time VPP designs incorporating DER forecasting, stochastic optimization, controls, and cyber security to construct a system capable of delivering reliable ancillary services, which have been traditionally provided by large power plants or other dedicated equipment. VPPs have become possible through an evolving landscape of state and national interconnection standards, which now require DER to include grid-support functionality and communications capabilities. This makes it possible for third party aggregators to provide a range of critical grid services such as voltage regulation, frequency regulation, and contingency reserves to grid operators. This paradigm (a) enables renewable energy, demand response, and energy storage to participate in grid operations and provide grid services, (b) improves grid reliability by providing additional operating reserves for utilities, independent system operators (ISOs), and regional transmission organization (RTOs), and (c) removes renewable energy high-penetration barriers by providing services with photovoltaics and wind resources that traditionally were the jobs of thermal generators. Therefore, it is believed VPP deployment will have far-reaching positive consequences for grid operations and may provide a robust pathway to high penetrations of renewables on US power systems. In this report, we design VPPs to provide a range of grid-support services and demonstrate one VPP which simultaneously provides bulk-system energy and ancillary reserves.

This report presents an object-oriented implementation of full state feedback control for virtual power plants (VPP). The components of the VPP full state feedback control are (1) objectoriented high-fidelity modeling for all devices in the VPP; (2) Distribution System Distributed Quasi-Dynamic State Estimation (DS-DQSE) that enables full observability of the VPP by augmenting actual measurements with virtual, derived and pseudo measurements and performing the Quasi-Dynamic State Estimation (QSE) in a distributed manner, and (3) automated formulation of the Optimal Power Flow (OPF) in real time using the output of the DS-DQSE, and solving the distributed OPF to provide the optimal control commands to the DERs of the VPP.

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When renewable energy resources are installed in electricity grids, they typically increase generation variability and displace thermal generator control action and inertia. Grid operators combat these emerging challenges with advanced distributed energy resource (DER) functions to support frequency, and provide voltage regulation and protection mechanisms. This paper focuses on providing frequency reserves using autonomous IEC TR 61850-90-7 pointwise frequency-watt (FW) functions that adjust DER active power as a function of measured grid frequency. The importance of incorporating FW functions into a fleet of photovoltaic (PV) systems is demonstrated in simulation. Effects of FW curve design, including curtailment, deadband, and droop, were analyzed against performance metrics using Latin Hypercube Sampling (LHS) for 20%, 70%, and 120% PV penetration scenarios on the Hawaiian island of Lanai. Finally, to understand the financial implications of FW functions to utilities, a performance function was defined based on monetary costs attributable to curtailed photovoltaic production, load shedding, and generator wear. An optimization wrapper was then created to find the best FW function curve for each penetration level. It was found that in all cases, the utility would save money by implementing appropriate FW functions.

While arc-faults are rare in electrical installations, many documented events have led to fires that resulted in significant damage to energy-generation, commercial and residential systems, as well as surrounding structures, in both the United States and abroad. Arc-plasma discharges arise over time due to a variety of reliability issues related to cable material degradation, electrical and mechanical stresses or acute conductive wiring dislocations. These may lead to discontinuity between energized conductors, facilitating arcing events and fires. Arc-flash events rapidly release significant energy in a localized volume, where the electric arc experiences a reduction in resistance. This facilitates a reduction in electrical resistance as the arc temperature and pressure can increase rapidly. Strong pressure waves, electromagnetic interference (EMI), and intense light from an arc pose a threat to electrical worker safety and system equipment. This arc-fault primer provides basic fundamental insight into arc-fault plasma discharges, and an overview of direct current (DC) and alternating current (AC) arc-fault phenomena. This primer also covers pressure waves and EMI arc-fault hazard analyses related to incident energy prediction and potential damage analysis. Mitigation strategies are also discussed related to engineering design and employment of protective devices including arc-fault circuit interrupters (AFCIs). Best practices related to worker safety are also covered, especially as they pertain to electrical codes and standards, particularly Institute of Electrical and Electronics Engineers (IEEE) 1584 and National Fire Protection Agency (NFPA) 70E. Throughout the primer various modelling and test capabilities at Sandia National Laboratories are also covered, especially as they relate to novel methods of arc-fault/arc-flash characterization and mitigation approaches. Herein, this work describes methods for producing and characterizing controlled, sustained arcs at atmospheric pressures as well as methods for mitigation with novel materials.

With the rapidly changing landscape of grid codes and interconnection standards, manufacturers of DER components are under increasing pressure to reliably update and validate the interoperability and performance of their equipment for different regional requirements and grid conditions. To help vendors meet these standards, AIT and Sandia have teamed up and introduced an approach for the rapid, concurrent development of controls and application software through a controller hardware-in-the-loop (CHIL) testbed integrated with an automated testing platform.

Photovoltaic (PV) distributed energy resources (DER) have reached approximately 27 GW in the U.S., and the solar penetration rate continues to increase. This growth is expected to continue, causing challenges for grid operators who must maintain grid stability, reliability, and resiliency. To minimize adverse effects on the performance of electrical power system (EPS) with increasing levels of variable renewable generation, photovoltaic inverters must implement grid-support capabilities, allowing the DER to actively participate in grid support operations and remain connected during short-term voltage and frequency anomalies. These functions include voltage and frequency regulation features that adjust DER active and reactive power at the point of common coupling. To evaluate the risk of these functions conflicting with traditional distribution system voltage regulation equipment, researchers used several methods to quantify EPS-support function response times for autonomous voltage regulation functions (volt-var function). Based on this study, no adverse interactions between PV inverters with volt-var functions and load tap changing transformers or capacitor banks were discovered.

When renewable energy resources are installed in electricity grids, they typically increase generation variability and displace thermal generator control action and inertia. Grid operators combat these emerging challenges with advanced distributed energy resource (DER) functions to support frequency and provide voltage regulation and protection mechanisms. This paper focuses on providing frequency reserves using autonomous IEC TR 61850-90-7 pointwise frequency-watt (FW) functions that adjust DER active power as a function of measured grid frequency. The importance of incorporating FW functions into a fleet of photovoltaic (PV) systems is demonstrated in simulation. Effects of FW curve design, including curtailment, deadband, and droop, were analyzed against performance metrics using Latin hypercube sampling for 20%, 70%, and 120% PV penetration scenarios on the Hawaiian island of Lanai. Finally, to understand the financial implications of FW functions to utilities, a performance function was defined based on monetary costs attributable to curtailed PV production, load shedding, and generator wear. An optimization wrapper was then created to find the best FW function curve for each penetration level. It was found that in all cases, the utility would save money by implementing appropriate FW functions.