Gregary C. Zweigle

Smart Generation and Transmission With Coherent, Real-Time Data

In recent years, much of the discussion involving “smart grids” has implicitly involved only the distribution side, notably advanced metering. However, todays electric systems have many challenges that also involve the rest of the system. An enabling technology for improving the power system, which has emerged in recent years, is the ability to measure coherent, real-time data. In this paper, we describe major challenges facing electrical generation and transmission today that availability of these measurements can help address. We overview applications using coherent, real-time measurements that are in use today or proposed by researchers. Specifically, we describe, normalize, and then quantitatively compare key factors for these power applications that influence how the delivery system should be planned, implemented, and managed. These factors include whether a person or computer is in the loop and (for both inputs and outputs) latency, rate, criticality, quantity, and geographic scope. From this, we abstract the baseline communications requirements of a data delivery system supporting these applications and suggest implementation guidelines to achieve them. Finally, we overview the state of the art in the supporting computer science areas of overlay networking and distributed computing (including middleware) and analyze gaps in commercial middleware products, utility standards, and issues that limit low-level network protocols from meeting these requirements when used in isolation.

Wide-Area Optimal Control of Electric Power Systems With Application to Transient Stability for Higher Order Contingencies

A real-time stabilizing control method for responding to N-K contingencies, with large K, is developed utilizing network and machine time-synchronized measurements. The controls follow an optimality principle in driving rotor-angles to an acceptable equilibrium point, at minimum cost, by predicting state response trajectory to a collection of stepped structural changes, from an admissible set, according to a defined model. A cost metric suitable for mitigating rotor-angle instability is developed. Non-idealities in modeling, measurement latency, control availability, and actuation success are investigated. It is shown how control over system structure in a feedback formulation increases the capability to handle higher order contingencies. As an experimental example, a set of simultaneous N-3 transient stability related contingencies are stabilized for the IEEE 39-bus system. Furthermore, the response after control actuation failure is investigated and it is shown that the system remains driven to a valid stable equilibrium point.

A statistically-based method of control of distributed photovoltaics using synchrophasors

Despite many years of effort in the distributed energy resources (DER) industry, there remains a need for an islanding detection method that a) facilitates, rather than conflicts with, DER participation in grid support functions; b) does not degrade power quality; and c) reliably detects a loss of mains without nuisance trips. This paper describes a method that can meet this challenge. The method is a communications-based method that uses statistical analysis on synchrophasor data measured in two locations, an upstream reference point and at the DER bus. Simulation results, and laboratory and field test results are presented for one very simple implementation of the method. It is shown that the method works very well, even in its simplest form.

A wide-area, wide-spectrum big data system

Power system data undergo significant signal filtering and downsampling at measuring devices before being communicated to wide-area visualization and analysis applications. For these applications, such processing acts in part to reduce network bandwidth requirements while maintaining essential characteristics of the original signal. However, modern communications systems are advancing in their capacity, and the price of data storage continues to drop. The constraints under which existing systems were built are being mitigated. Meanwhile, the need for higher-resolution data across larger areas continues to increase. This paper discusses the design and implementation of a system that delivers wide-spectral bandwidth data with precise time stamps over a wide area. Processing steps, such as converting to phasor representation, are moved to receivers. The system architecture allows a broader utilization of power system data. Several applications are described. Construction of a test system, operating between several cities, is described, and performance results are shown.

Transient Instability Mitigation for Complex Contingencies With Computationally Constrained Cost-Based Control

Transient stability controller design based on an optimality principle is an emerging approach for resolving high order contingencies that can otherwise lead to rotor angle instability. It is difficult to design for high order contingencies due to their complexity. A challenging issue is the nonlinearity of the system, which limits the selection approaches available and results in a potentially large search space to find a suitable control action. Because rotor angle instability evolves rapidly, a fast control response is required. This paper develops a cost-based controller under the constraint of bounded computation. A method to downsize the admissible control search space is developed in a manner that retains controls most likely to provide the best cost. Subsequently, a further reduction in computation is designed through model elimination. A set of common cost metrics is applied for all controllers. Tradeoffs between the model-based and model-free approaches are demonstrated. The effect of computational constraints on the competing goals of control cost and control timeliness for complex contingencies is tested with the New England 39-bus system.

Towards Grid Resilience: A Proposal for a Progressive Control Strategy

This white paper describes preliminary research on the use of progressive control strategies to improve the advanced electric power grids resilience to major grid disturbances. The proposed approach calls to leverage real-time wide-area monitoring and control capabilities to provide globally coordinated distributed control actions under stressed conditions. To that end, the paper illustrates the proposed concept using case studies drawn from major North American blackouts, discusses design challenges, and proposes the design of a Grid Integrity Management System (GIMS) to manage the required communication and computation to meet these challenges.