book reviews
integrating power the smart grid and wind energy
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two books are reviewed, and both receive accolades from their reviewers. The first book, the reviewer says, is “an excellent set of chapters that cover a spectrum of topics pertaining to the future electric system.” The second book, according to the reviewer, is “a very nice and concise treatment of wind energy systems . . . in the context of large integration into the bulk electric power system.”
Control and Optimization Methods for Electric Smart Grids Aranya Chakrabortty and Marija Ilic, editors Authors Aranya Chakrabortty and Marija Ilic have compiled an excellent set of chapters covering topics pertaining to the future electric system, or the smart grid. The book is divided into three areas: architectures and integration, modeling and analysis, and control and communication. Each chapter covers a different topic, introducing material pertinent to the rapidly changing nature of the electric power grid. Most chapters introduce topics pertaining to the smart grid including markets, renewable resources, communication processes, and demand response. Other chapters analyze the use of phasor measurement units (PMUs) and other approaches for large-scale power system stability and analysis. Prof. Ilic begins the book with her essay on frequency regulation in the Digital Object Identifier 10.1109/MPE.2012.2232772 Date of publication: 20 February 2013
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future grid. She and her coauthor Qixing Liu provide overview the convention frequency regulation through the use of area control error and automatic generation control (AGC). They then propose a new frequency regulation framework, an “enhanced AGC,” that will operate effectively in a system with hard-to-predict supply and demand variations. Relying on PMU information, the authors propose the institution of smart balancing authorities that would coordinate frequency regulation across existing geospacial and temporal boundaries. The approach requires only limited communication between areas but can realize a cost-effective regulation system. The second chapter by Wang and coauthors describes an approach to dynamic competitive electricity markets. The authors develop an approach to modeling the dynamics of electricity markets and propose that the power system network (via the ISO) be included as a player in the competitive market. Through their analyses, the authors provide an explanation for the extreme volatility in prices that have been observed in several instances in the past. Chapter 3 is a short treatise on optimal demand response, especially with respect to rapidly fluctuating renewable sources. The authors, Chen, Li, Jiang, and Low, advocate expanding the communication network and establishing protocols to better use real-time information to better accomplish energy management. They propose a model that captures renewable source variability
and uncertainty, supply and consumption decisions, and day-ahead and realtime availability. The authors show that their model can produce a solution that coordinates the decisions of different appliances in a decentralized manner, reduces peak aggregate demand, and flattens the daily profile to improve the load factor. They also show that the use of energy storage amplified the benefits of demand response. The impact of communication time delays on the stability of the energy market is the subject of Chapter 4. Authors Kiani and Annaswamy introduce a discrete-time framework to develop the economic model to estimate how large a time delay is allowable for the wholesale market to remain stable, with results showing that the wholesale market is most sensitive to the price signal of the GenCos. New communication topologies are proposed that can bypass such problems. The authors of Chapter 5 use multirate model predictive control to coordinate frequency regulation and demand response. Hindi, Greene, and Laventall propose multirate model predictive control to coordinate actions between the slow and fast time scales exhibited by the system dynamics. Regulation has a relatively slow response due to the dynamics of the large generation equipment whereas demand response is an “on-off” control that can drop an unwanted load rapidly. The authors show that, under certain conditions, the fast nature of demand response can enhance the performance of the slower frequency response to better minimize march/april 2013
the demand-supply imbalance. In addition to the model predictive control, the authors also propose a much simpler heuristic controller that provides reasonably good performance. The final chapter in the architectures and integration section provides an overview of “smart vehicles.” Bayram and coauthors specifically promote a general vehicle-to-grid architecture using control, demand response, and communication to meet the quality standards of grid stability. The authors propose an architecture for a plug-in vehicle charging station that incorporates energy storage to reduce the unpredictability of power demand while maintaining a sufficient level of quality service to the customers. This is accomplished through introducing a stochastic model to quantify the probability that new arrivals to the charging station will be denied service. The section on modeling and analysis opens with a chapter by Dominguez-Garcia on models for integrated systems of generators and wind turbines. This model is used to analyze the area control error in the presence of wind. An approach to automatic generation control is also presented. The proposed models can be used for understanding fundamental limits on the amount of wind penetration into a system without violating frequency performance metrics. The chapter by Pan and Venkatasubramanian focuses on eliminating power system low-frequency oscillations by exploiting information obtained from ambient data through the use of PMUs through frequency domain optimization. This approach provides real-time information regarding the shift of system modes in response to changes in generation, load, or network topology. This method has been successfully implemented in practice for real-time oscillation monitoring. Cascading failures are the topic of the next chapter. Authors Susuki, Mezic, and Hikihara use the traditional concept of coherent dynamics to study the newly identified problem of coherent swing instability, an emergent and undesirable dynamic in which a coherent group of generators lose synchronism with the grid in response to local disturbances. This instability propagates across the power system, resulting in eventual system wide failure. The authors illustrate that this phenomenon is nonlinear in nature and cannot be readily understood through traditional linear methods. In the chapter “Toward a Highly Available Modern Grid,” authors Wu and Ruschmann return to the topic of PMUs used to improve system stability. They propose a Markov model to determine the level of PMU redundancy in the system to maintain a prescribed level of data availability. This level of redundancy provides the power system with a series of states from which to operate at reduced functionality while providing a more rapid path to normal state restoration. Parolini, Sinopoli, and Krough discuss the challenges and possibilities offered by introducing a data center as a standalone node of a smart grid. The authors propose a novel approach whereby a data center participates in two servicelevel agreements, one agreement related to quality of service and the other related to cost of electricity, due to the wide range of time scales associated with data centers enables dynamic march/april 2013
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responses from milliseconds to tens of minutes. By organizing the control actions into a hierarchy, a continuous range of response can be achieved. The next chapter explores graph theory as a tool for prioritizing power grid buses and lines for intervention. Authors Wang, Scaglione, and Thomas propose a centrality measure specific to the power grid incorporating electrical impedance characteristics in addition to the network topology. Centrality measures are used to study network properties and identify the most important elements. These critical portions of the network can then be hardened to lessen vulnerability to attack and enhance system robustness. The final section of the book contains chapters on communications and control. The chapter by Ma, Callaway, and Hiskens develops strategies to coordinate plug-in electric vehicle charging. Centralized and decentralized approaches are presented to optimize charging costs. The centralized approach is used to show that the valley filling charging approach is globally optimal. These problems are formulated as large-population games on a finite charging interval. The authors note that the traditional game theory Nash equilibrium is difficult to achieve if electricity price is the sole optimization objective. The section on communications and control would not be complete if it did not include an analysis of cyberattacks on the power grid. Srikhar, Govindarasu, and Liu describe attack scenarios in which the security of the power grid could be severely compromised. The authors assess the risk associated with brute-force and intelligent attacks, both isolated and coordinated. They introduce a probability of successful cybernetwork intrusion and impact on the power system. Their results indicate the significant factors that impact attack severity are network topology, location of attack targets, and the criticality of the component. The chapter by Haughton and Heydt describes the process by which synchronous measurements are obtained and how they can be used to improve the state-estimation process. By using a time march/april 2013
stamp of a GPS, it is possible to obtain a least squared error fit of a phasor to a sinusoidal waveform, yielding positive, negative, and zero sequence voltage and current components. By using synchronous measurements, the state estimation process can be simplified since the complex (phasor) formulation is linear. State estimation at the distribution level can lead to better control, fault management, and energy management. The effect of communication time delays is again discussed in the chapter by Zhang and Chow but with respect to a decentralized adaptation of the economic dispatch problem. Of particular interest is the use of consensus algorithms to coordinate the actions of distributed controllers. Without time delays, controllers can coordinate their actions by comparing their known system states, and discrepancies can be rapidly identified. In the situation of time delays, the system states are seldom consistent, and this adds additional complexity to the control problem of achieving consensus of the system state. This extra complexity potentially adds additional time delays since the controllers may take longer to converge to a consensus. The chapter by Chow and Ghiocel presents an adaptive wide-area interarea mode damping controller using PMU synchrophasor data. The authors show that the additional data provided by the PMUs increase the observability of the system, rendering greater controllability. They also note that the communication delay and computational burdens may add data latency that degrades control performance. The authors propose an adaptive control scheme to counter this variable PMU data latency by adaptively varying the amount of phase-lead compensation in the network. The book is rounded out by the final chapter by Prof. Chakrabortty on interarea modal damping using synchronized phasor measurements. He proposes three steps: model reduction, control aggregation, and control inversion whereby the aggregate control action is divided and distributed to local decentralized controllers. The model reduction step is aided by using the
PMU data to identify oscillation clusters about which the equivalent models can be aggregated. Feedback control is applied to this reduced model to obtain an aggregate control signal, which is then deconstructed to provide individual control signals. This approach provides a scalable approach to using PMU data for control. —Mariesa Crow
Grid Integration and Dynamic Impact of Wind Energy By V. Vittal and R. Ayyanar Perhaps the most significant avenue of endeavor in the power and energy industry today is the pursuit of sustainability of energy sources and the continuous drive for greater energy efficiency both in its utilization and conversion. Nowhere is this more apparent than in the application, research, and development of wind and solar energy systems. On the political scene, state government legislation in many regions has put into place renewable portfolio standards, which continue to push for increased utilization of renewable resources. This is a major factor that has meant a tremendous rise in the integration of wind power plants, and more recently photovoltaic energy systems, throughout North America. The trend, needless to say, is a global one. With these factors, it is clear that both the practicing electrical engineer and the student must have a working knowledge of the application, modeling, and dynamic performance of wind energy systems. As such, congratulations are in order for the authors on what is a welcome addition to the body of literature in this field. The book constitutes a very nice and concise treatment of wind energy systems and their dynamic behavior in the context of large integration into the bulk electric power system. It is quite an easy read and yet quite comprehensive in its treatment of some of the basic and fundamental theory behind the design and control of power electronic based wind energy systems. Digital Object Identifier 10.1109/MPE.2012.2232774 Date of publication: 20 February 2013
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