Papers by Alexandra Von Meier
This white paper describes the circumstances in California around the turn of the 21 st century t... more This white paper describes the circumstances in California around the turn of the 21 st century that led the California Energy Commission (CEC) to direct additional Public Interest Energy Research funds to address critical electric grid issues, especially those arising from integrating high penetrations of variable renewable generation with the electric grid. It contains an assessment of the beneficial science and technology advances of the resultant portfolio of electric grid research projects administered under the direction of the CEC by a competitively selected contractor,
arXiv (Cornell University), Aug 3, 2020
We present a method for joint phase identification and topology recovery in unbalanced three phas... more We present a method for joint phase identification and topology recovery in unbalanced three phase radial networks using only voltage measurements. By recovering phases and topology jointly, we utilize all three phase voltage measurements and can handle networks where some buses have a subset of three phases. Our method is theoretically justified by a novel linearized formulation of unbalanced three phase power flow and makes precisely defined and reasonable assumptions on line impedances and load statistics. We validate our method on three IEEE test networks simulated under realistic conditions in OpenDSS, comparing our performance to the state of the art. In addition to providing a new method for phase and topology recovery, our intuitively structured linearized model will provide a foundation for future work in this and other applications.
The role of smart grids for the renewable energy transition
This chapter focuses on technological innovations in electric power infrastructure and their enab... more This chapter focuses on technological innovations in electric power infrastructure and their enabling potential for the integration of variable generation resources, electric vehicles (EVs), and microgrids. Many of the innovations described in this chapter were driven by evolving technical and economic constraints that long predated renewable grids: factors other than clean energy have dominated problem solving and investment in new electric power hardware, software, and design strategies over the past several decades. In the context of the renewable energy transition, however, some of these rather esoteric niche technologies take on a new relevance and interest for a broader community of researchers and practitioners.
This report was prepared as the result of work sponsored by the California Energy Commission. It ... more This report was prepared as the result of work sponsored by the California Energy Commission. It does not necessarily represent the views of the Energy Commission, its employees or the State of California. The Energy Commission, the State of California, its employees, contractors and subcontractors make no warrant, express or implied, and assume no legal liability for the information in this report; nor does any party represent that the uses of this information will not infringe upon privately owned rights. This report has not been approved or disapproved by the California Energy Commission nor has the California Energy Commission passed upon the accuracy or adequacy of the information in this report. For more information about the PIER Program, please visit the Energy Commission's website at www.energy.ca.gov/research/ or contact the Energy Commission at 916-654-4878.
Annual Review of Energy and The Environment, Nov 1, 1994
Adaptive Islanding and Self-Sufficiency of Block-Scale Microgrids
This paper discusses adaptive islanding via city-block-scale microgrids as a new paradigm in elec... more This paper discusses adaptive islanding via city-block-scale microgrids as a new paradigm in electric grid operations, which has the potential to vastly improve flexibility and resilience of the grid and facilitate renewable energy integration. We summarize advantages and challenges of adaptive islanding in general and the block scale in particular. We also present an approach to analyze microgrid self-sufficiency probabilistically using time-series simulations, and demonstrate the benefits of the block scale in an example with real household electric data.
Electric Distribution System Simulation and Analysis Tools: Status and Research Gaps for Integration of Renewables and Electric Vehicles
The push to automate and digitize the electric grid has led to widespread installation of Phasor ... more The push to automate and digitize the electric grid has led to widespread installation of Phasor Measurement Units (PMUs) for improved real-time wide-area system monitoring and control. Nevertheless, transforming large volumes of highresolution PMU measurements into actionable insights remains challenging. A central challenge is creating flexible and scalable online anomaly detection in PMU data streams. PMU data can hold multiple types of anomalies arising in the physical system or the cyber system (measurements and communication networks). Increasing the grid situational awareness for noisy measurement data and Bad Data (BD) anomalies has become more and more significant. Number of machine learning, data analytics and physics based algorithms have been developed for anomaly detection, but need to be validated with realistic synchophasor data. Access to field data is very challenging due to confidentiality and security reasons. This paper presents a method for generating realistic synchrophasor data for the given synthetic network as well as event and bad data detection and classification algorithms. The developed algorithms include Bayesian and change-point techniques to identify anomalies, a statistical approach for event localization and multi-step clustering approach for event classification. Developed algorithms have been validated with satisfactory results for multiple examples of power system events including faults and load/generator/capacitor variations/switching for an IEEE test system. Set of synchrophasor data will be available publicly for other researchers.
IEEE Transactions on Instrumentation and Measurement, Sep 1, 2020
In this paper, throughput improvement of device-to-device (D2D)-aided underlaying cellular networ... more In this paper, throughput improvement of device-to-device (D2D)-aided underlaying cellular networks is analyzed. The D2D devices are assumed to be capable of operating at the full duplex (FD) mode to enable the concurrent transmission and reception with a single frequency band. We analyze the impact of activating D2D users on the throughput of FD-based D2D (FD-D2D) aided underlaying network by considering non-ideal self-interference cancellation at the FD devices. Despite of an extra interference imposed on the cellular users (CUs) by the active D2D links, which may erode the signal-to-interference ratio of the former significantly, the FD-D2D mode is still shown to exhibit its superiority in terms of the throughput improvement. Furthermore, in order to avoid a severe FD-D2D-induced interference imposed on the CUs, a new mechanism called ''dynamic cellular link protection (DCLP),'' which prohibits the transmissions of FD-D2D users when they are located inside the pre-set guard areas, is proposed. Numerical results show that the proposed DCLP mechanism is capable of substantially improving the throughput of the underlaying cellular networks without seriously eroding the capacity of the conventional cellular links.
Handling Instrument Transformers and PMU Errors for the Estimation of Line Parameters in Distribution Grids
The knowledge of line parameters is fundamental for building a network model that can become the ... more The knowledge of line parameters is fundamental for building a network model that can become the basis for all the monitoring and management applications. Network line impedances are employed, for instance, for the state estimation or for protection applications in relay setting. The Phasor Measurement Units (PMUs), thanks to the synchronized voltage and current phasor measurements, provide the accurate information that can be used to evaluate the network parameters of the monitored branches. Nevertheless, the impact of instrument transformers (ITs) makes the parameter estimation a hard task. For this reason, in this paper an estimation paradigm is proposed that includes the estimation of both systematic errors (mainly due to ITs) and line parameters. The proposed method, particularly focused on distribution systems, is designed to perform simultaneous estimations across different branches of the network, aiming at exploiting the links between the involved parameters, due to topology and operating conditions. The estimation is based on a sound and detailed model of the uncertainty sources.
arXiv (Cornell University), Jul 23, 2021
Continuous monitoring of voltages ranging from tens to hundreds of kV over environmental conditio... more Continuous monitoring of voltages ranging from tens to hundreds of kV over environmental conditions, such as temperature, is of great interest in power grid applications. This is typically done via instrument transformers. These transformers, although accurate and robust to environmental conditions, are bulky and expensive, limiting their use in microgrids and distributed sensing applications. Here, we present a millimeter-sized optical voltage sensor based on piezoelectric aluminum nitride (AlN) thin film for continuous measurements of AC voltages <350 (via capacitive division) that avoids the drawbacks of existing voltage-sensing transformers. This sensor operated with 110 incident optical power from a low-cost LED achieved a resolution of 170 in a 5kHz bandwidth, a measurement inaccuracy of 0.04% due to sensor nonlinearity, and a gain deviation of +/-0.2% over the temperature range of~20-60 •. The sensor has a breakdown voltage of 100V, and its lifetime can meet or exceed that of instrument transformers when operated at voltages <42. We believe that our sensor has the potential to reduce the cost of grid monitoring, providing a path towards more distributed sensing and control of the grid.
Reachability Analysis for Controlling DERs to Mitigate Disturbances in Distribution Grids
IEEE Transactions on Instrumentation and Measurement, Apr 1, 2019
Effective monitoring and management applications on modern distribution networks require a sound ... more Effective monitoring and management applications on modern distribution networks require a sound network model and the knowledge of line parameters. Network line impedances are used, among other things, for state estimation and protection relay setting. Phasor Measurement Units (PMUs) give synchronized voltage and current phasor measurements, referred to a common time reference (coordinated universal time). All synchrophasor measurements can thus be temporally aligned and coordinated across the network. This feature, along with high accuracy and reporting rates, could make PMUs useful for the evaluation of network parameters. However, instrument transformer behavior strongly affects parameter estimation accuracy. In this paper, a new PMU-based iterative line parameter estimation algorithm for distribution networks, which includes in the estimation model systematic measurement errors, is presented. This method exploits the simultaneous measurements given by PMUs on different nodes and branches of the network. A complete analysis of uncertainty sources is also performed, allowing the evaluation of estimation uncertainty. Issues related to operating conditions, topology and measurement uncertainty are thoroughly discussed and referenced to a realistic model of a distribution network to show how a full network estimator is possible.
The distribution grid is changing to become an active resource with complex modeling needs. The n... more The distribution grid is changing to become an active resource with complex modeling needs. The new active distribution grid will, within the next ten years, contain a complex mix of load, generation, storage and automated resources all operating with different objectives on different time scales from each other and requiring detailed analysis. Electrical analysis tools that are used to perform capacity and stability studies have been used for transmission system planning for many years. In these tools, the distribution grid was considered a load and its details and physical components were not modeled. The increase in measured data sources can be utilized for better modeling, but also control of distributed energy resources (DER). The utilization of these sources and advanced modeling tools will require data management, and knowledgeable users. Each of these measurement and modeling devices have accuracy constraints, which will ultimately define their future ability to be planned and controlled. This paper discusses the importance of measured data accuracy for inverter control, interconnection and planning tools and proposes ranges of control accuracy needed to satisfy all concerns based on the present grid infrastructure.
Elsevier eBooks, 2017
Historically, power distribution systems did not require elaborate monitoring schemes. With radia... more Historically, power distribution systems did not require elaborate monitoring schemes. With radial topology and one-way power flow, it was only necessary to evaluate the envelope of design conditions (i.e., peak loads or fault currents), rather than continually observe the operating state. But the growth of distributed energy resources, such as renewable generation, electric vehicles, and demand response programs, introduces more short-term and unpredicted fluctuations and disturbances [1]. This suggests a need for more refined measurement, given both the challenge of managing increased variability and uncertainty and the opportunity of recruiting diverse resources for services in a more flexible grid. This chapter addresses how the direct measurement of voltage-phase angle might enable new strategies for managing distribution networks with diverse, active components. Specifically, it discusses high-precision micro-synchrophasors, or phasor measurement units (mPMUs), that are tailored to the particular requirements of power distribution to support a range of diagnostic and control applications, from solving known problems to opening as yet unexplored possibilities. 2. Variability, uncertainty, and flexibility in distribution networks Electric transmission and distribution systems are formally distinguished by voltage level, but harbor profound differences in design and operation. These differences explain the diverse sets of challenges encountered in the context of renewables integration, as well as the historical lag of distribution behind transmission systems in terms of observability and sophistication of measurement. Broadly speaking, distribution systems tend to be low-tech, aging, and due for upgrades [2-4]. Architecture: For economy and simplicity of protection, distribution systems are generally laid out radially, with legacy equipment, such as protective relays and voltage regulation devices, designed on the assumption of one-directional power flow from the substation toward loads. Although easier to operate in principle, radial design also presents liabilities: When distributed generation introduces reverse power flow, some older controls may malfunction. In addition, radial design makes the mathematical estimation of the operating state more difficult, by removing the redundancy afforded by Kirchhoff's laws: in other words, the estimate for voltages and currents at one node cannot be corroborated by those at neighboring nodes. Distribution systems also have many more nodes or CHAPTER Renewable Energy Integration.
Cultural factors in technology adoption : a case study of electric utilities and distribution automation
UMI Dissertation Services eBooks, 1995
GridSweep: An Early Report on Active Measurements of Electric Distribution Grids
2022 IEEE Power & Energy Society General Meeting (PESGM), Jul 17, 2022
This project demonstrated that solar PV can be recruited to stabilize the grid, smooth out distur... more This project demonstrated that solar PV can be recruited to stabilize the grid, smooth out disturbances, manage power flows, and assist circuit switching operations. It developed a radically new, layered control framework for Distributed Energy Resources (DER) to act in response to real-time, measured conditions on their local distribution circuit, rather than waiting for a price signal to indicate preferred behavior. By enabling resources to act as good citizens on the electric grid, Phasor-Based Control (PBC) facilitates arbitrarily high solar penetration levels. PBC expresses objectives in terms of voltage phasors, which include information about both the magnitude and the precise timing of grid voltage at each specific location. A supervisory (S-PBC) controller sets voltage phasor targets at different nodes in the transmission or distribution network, and local (L-PBC) controllers recruit real and reactive power from resources such as solar inverters, batteries or loads to track phasor targets. The technology makes use of ultraprecise measurements from micro-phasor measurement units (µPMUs). Phasor-based control prioritizes stabilizing the grid locally, toward operating states known to be safe in accordance with physical operating constraints, while buying time for economic reoptimization after major changes or contingencies. In doing so, it advances grid reliability and resilience. The framework supports many diverse use cases that specify desired voltage phasors at certain nodes. It applies to distribution as well as transmission systems, although this project focused primarily on distribution applications and simulation. Sample use cases tested in this project include power flow control, voltage management, phase balancing, and support for switching operations.
Plausible Futures for Electric Grid Architecture - A Scenario Planning Exercise
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Papers by Alexandra Von Meier