Bruce F. Wollenberg

Toward a smart grid: power delivery for the 21st century

In this article, we present the security, agility, and robustness/survivability of a large-scale power delivery infrastructure that faces new threats and unanticipated conditions. By way of background, we present a brief overview of the past work on the challenges faced in online parameter estimation and real-time adaptive control of a damaged F-15 aircraft. This work, in part, provided the inspiration and laid the foundation in the 1990s for the flight testing of a fast parameter estimation/modeling and reconfigurable aircraft control system that allowed the F-15 to become self-healing in the face of damaged equipment.

Transmission management in the deregulated environment

Three very different methods of accomplishing the same task-managing the operation of the transmission system in the deregulated power system operating environment-have been implemented as deregulated market structures have been created around the world. They are first, the optimal power flow (OPF) model found in various implementations in the United Kingdom, parts of the United States, and in Australia and New Zealand. Second, the point tariff, price area congestion control model used in the Nordpool market area in Norway and Sweden. Third, the US transaction-based model. All are pragmatic solutions implemented in advance of complete theoretical understanding. Each has strengths and flaws, and there are some surprising inter-relationships. Each maintains power system security but differs in its impact on the economics of the energy market. No clearly superior method has so far emerged. In the future, methods of combining decentralized market solutions with operational use of optimal power flow may provide better solutions to existing and emerging problems.

On-line power system security analysis

A broad overview of on-line power system security analysis is provided, with the intent of identifying areas needing additional research and development. Current approaches to state estimation are reviewed and areas needing improvement, such as external system modeling, are discussed. On-line contingency selection has become practical, particularly for static security. Additional work is necessary to identify better indices of power system stress to be used in on-line screening filters for both static and dynamic security analysis. Use of optimal power flow schemes to recommend optimal preventive and corrective strategies is presented on a conceptual level. Techniques must be further developed to provide more practical contingency action plans, which include real-world operating considerations and use a reasonably small number of control actions. Techniques must be developed for costing operating variables which are not easily quantified in dollars. Soft or flexible constraints and time variables must be included in the preventive and corrective strategy formulation. Finally, the area of on-line transient and dynamic security analysis is presented. >

Monitoring and Optimization for Power Grids: A Signal Processing Perspective

Although the North American power grid has been recognized as the most important engineering achievement of the 20th century, the modern power grid faces major challenges [87]. Increasingly complex interconnections even at the continent size render prevention of the rare yet catastrophic cascade failures a strenuous concern. Environmental incentives require carefully revisiting how electrical power is generated, transmitted, and consumed, with particular emphasis on the integration of renewable energy resources. Pervasive use of digital technology in grid operation demands resiliency against physical and cyberattacks on the power infrastructure. Enhancing grid efficiency without compromising stability and quality in the face of deregulation is imperative. Soliciting consumer participation and exploring new business opportunities facilitated by the intelligent grid infrastructure hold a great economic potential.

Feasibility Study for an Energy Management System Intelligent Alarm Processor

Alarm processing has been a traditional feature of energy management systems and has not changed significantly over several generations of EMS design. Problems are obvious, however, and operations personnel have often voiced a desire for a better way to monitor a power system than provided by existing alarm processing software and hardware. The thesis of this paper and the experiments reported show promise of a truly different methodology for handling alarms. This is realized through the application of a realtime expert system dedicated to continuous analysis and reporting of system conditions rather than simply printing numerous specific alarm messages. Results show the ability of the expert system to present operators with concise alarm information extracted from a standard set of alarm messages.

Intelligent alarm processing in power systems

Concerns about the effectiveness of conventional alarm processing systems have prompted the development of expert systems designed to present a clearer description of disturbances to the power system operator. The features of the various intelligent alarm processors which are described in the technical literature are discussed in order to highlight the issues which must be addressed and the design decisions which must be made in the development of these systems. A number of systems described in the technical literature under the name intelligent alarm processor are in fact fault diagnosis systems. The authors attempt to clarify the criteria which separate these two types of systems. >

Optimal Placement of Phasor Measurement Units via Convex Relaxation

Instrumenting power networks with phasor measurement units (PMUs) facilitates several tasks including optimum power flow, system control, contingency analysis, visualization, and integration of renewable resources, thus enabling situational awareness-one of the key steps toward realizing the smart grid vision. The installation cost of PMUs currently prohibits their deployment on every bus, which in turn motivates their strategic placement across the power grid. As state estimation is at the core of grid monitoring, PMU deployment is optimized here based on estimation-theoretic criteria. Considering both voltage and incident current readings per PMU-instrumented bus and incorporating conventionally derived state estimates under the Bayesian framework, PMU placement is formulated as an optimal experimental design task. To bypass the combinatorial search involved, a convex relaxation is developed to obtain solutions with numerical optimality guarantees. In the tests performed on standard IEEE 14-, 30-, and 118-bus benchmarks, the proposed relaxation approaches and oftentimes attains the optimum PMU placement.

Risk assessment of generators bidding in day-ahead market

Competition in power markets exposes companies which participate in physical and financial uncertainties. Generator companies, bidding to supply power in day-ahead markets may face forced outages after bids are accepted by the system operator. When this happens they have to buy power from the real-time hourly spot market and sell to the ISO at the set day-ahead market clearing price. This paper shows simulations of random forced outages for generators and the resulting risk profiles of generators. Value at Risk (VaR) is calculated at 98% confidence level as a measure of financial risk. The risk profiles and the VaR of the generators are changed with changes in bidding functions. The simulations do not consider transmission limits or demand side bidding.

Survey on Excessive Alarms

In recent years a great deal of attention has been paid to the design of alarm processing hardware and software to guarantee that no alarms are lost when an event triggers a large number of alarms within a short period of time. The resulting systems are capable of filling alarm message displays much faster than human operators can read and comprehend them. The main objective behind conducting this survey was an attempt to answer the following questions: 1) Is there a problem with excessive alarms in modern power control centers? 2) If yes, what is the nature of the problem and what is the best way to cope with the problem? The idea for the project came as a result of a discussion in 1985 within the Joint Working Group on Power System Control Centers. An opinion was expressed that a problem existed with alarm processing in power system control centers and that perhaps the remedy for this situation ought to be studied. This opinion met with immediate agreement by some members and was disputed by others. The working group then decided to conduct a survey of control center operators to determine if problems existed with alarm processing. The survey contained many questions which required a simple yes, no or numerical response. In addition, the survey contained many questions which asked the respondent to express an opinion.

Application of mechanism design to electric power markets

As competition is introduced across the electric power industry around the world, market design for the industry is urgently needed to shape its future structure and performance. When generator companies compete with one another in a deregulated market, they may not be willing to share the information needed to perform an economic dispatch of the generation. Using game theory, this paper designs a new mechanism that achieves efficiency (economic dispatch) in spite of this information problem. In this mechanism, when each company acts in the best of its own interests, the outcome is efficient. The paper demonstrates the merits of the mechanism by simulations including the IEEE 14-bus case.