Optimal Rotational Load Shedding via Bilinear Integer Programming

This paper addresses the problem of managing rotational load shedding schedules for a power distribution network with multiple load zones. An integer optimization problem is formulated to find the optimal number and duration of planned power outages. Various types of damage costs are proposed to capture the heterogeneous load shedding preferences of different zones. The McCormick relaxation along with an effective procedure feasibility recovery is developed to solve the resulting bilinear integer program, which yields a high-quality suboptimal solution. Extensive simulation results corroborate the merit of the proposed approach, which has a substantial edge over existing load shedding schemes.Comment: 6 pages, 11 figures. To appear at the conference of APSIPA ASC 201

MODEL UPDATING AND STRUCTURAL HEALTH MONITORING OF HORIZONTAL AXIS WIND TURBINES VIA ADVANCED SPINNING FINITE ELEMENTS AND STOCHASTIC SUBSPACE IDENTIFICATION METHODS

Wind energy has been one of the most growing sectors of the nation’s renewable energy portfolio for the past decade, and the same tendency is being projected for the upcoming years given the aggressive governmental policies for the reduction of fossil fuel dependency. Great technological expectation and outstanding commercial penetration has shown the so called Horizontal Axis Wind Turbines (HAWT) technologies. Given its great acceptance, size evolution of wind turbines over time has increased exponentially. However, safety and economical concerns have emerged as a result of the newly design tendencies for massive scale wind turbine structures presenting high slenderness ratios and complex shapes, typically located in remote areas (e.g. offshore wind farms). In this regard, safety operation requires not only having first-hand information regarding actual structural dynamic conditions under aerodynamic action, but also a deep understanding of the environmental factors in which these multibody rotating structures operate. Given the cyclo-stochastic patterns of the wind loading exerting pressure on a HAWT, a probabilistic framework is appropriate to characterize the risk of failure in terms of resistance and serviceability conditions, at any given time. Furthermore, sources of uncertainty such as material imperfections, buffeting and flutter, aeroelastic damping, gyroscopic effects, turbulence, among others, have pleaded for the use of a more sophisticated mathematical framework that could properly handle all these sources of indetermination. The attainable modeling complexity that arises as a result of these characterizations demands a data-driven experimental validation methodology to calibrate and corroborate the model. For this aim, System Identification (SI) techniques offer a spectrum of well-established numerical methods appropriated for stationary, deterministic, and data-driven numerical schemes, capable of predicting actual dynamic states (eigenrealizations) of traditional time-invariant dynamic systems. As a consequence, it is proposed a modified data-driven SI metric based on the so called Subspace Realization Theory, now adapted for stochastic non-stationary and timevarying systems, as is the case of HAWT’s complex aerodynamics. Simultaneously, this investigation explores the characterization of the turbine loading and response envelopes for critical failure modes of the structural components the wind turbine is made of. In the long run, both aerodynamic framework (theoretical model) and system identification (experimental model) will be merged in a numerical engine formulated as a search algorithm for model updating, also known as Adaptive Simulated Annealing (ASA) process. This iterative engine is based on a set of function minimizations computed by a metric called Modal Assurance Criterion (MAC). In summary, the Thesis is composed of four major parts: (1) development of an analytical aerodynamic framework that predicts interacted wind-structure stochastic loads on wind turbine components; (2) development of a novel tapered-swept-corved Spinning Finite Element (SFE) that includes dampedgyroscopic effects and axial-flexural-torsional coupling; (3) a novel data-driven structural health monitoring (SHM) algorithm via stochastic subspace identification methods; and (4) a numerical search (optimization) engine based on ASA and MAC capable of updating the SFE aerodynamic model

Smart Senja electrical network expansion modeling

The addition of variable renewable energy sources into the electrical energy systems of the world has been increasing in recent years. This form of distributed energy production with high production volatility can introduce massive challenges in operating a lower voltage distribution network. One of these affected networks is on the island of Senja in northern Norway, with an eldering radial electrical network with a single connection to the national transmission grid. In this study, prescriptive analysis of the network through mathematical optimization is implemented to investigate if there are more effective solutions to this problem other than building more electrical lines. In selected parts of the island, the electrical network experiences electrical faults of different magnitude and concern affecting 1500 hours a year. In this thesis, the model GenX is presented which prescribes solutions reducing these faults to zero while also cutting costs compared to the baseline scenario of today’s system. Results from the model indicate that simple installments of distributed power generation in conjunction with electrical energy storage drastically improve network capacity and industrial expansion opportunities. Also investigated is the feasibility of operating the electrical network on the island without any connection to the external grid. Meant as a proof of concept for the application of mathematical optimization on electrical grids in other more remote parts of the world. The model proves that investments in local electricity production positively impact the system at a fraction of the cost of building new regional distribution infrastructure. Finally, some drawbacks of the chosen analytical tool used to construct the mathematical optimization model are presented alongside selected methods applicable to apprehend or circumvent these limitations

Towards optimal operation of power systems with high IBR penetration: a stability-constrained optimization approach

Renewable Energy Sources (RES) have been massively integrated into the modern electric power system in the past few decades due to the environmental and sustainability concerns throughout the world. As a result, the power electronic converters are anticipated to acquire a steadily increasing role as they are the key element for the interface between RES and the grid. However, owing to the intermittency of the RES and the distinguished features of the Inverter-Based Resources (IBRs). The main focus of this thesis is to develop optimal system operation strategies to maintain the security and stability of the grid while considering the fast and accurate control of the IBR units. To achieve this, we investigate challenges in different areas. Regarding system frequency and low inertia issues, the main challenges are the incorporation of differential equation-based frequency dynamics into algebraic equation-based optimization problem as well as the optimal utilization of the frequency support from different sources. We first target on the optimal system scheduling on a transmission system level to achieve system operation cost minimization while maintaining the frequency security. In addition, the frequency stability problem in microgrids after unintentional islanding events is also studied. We consider the frequency support from WTs, PV and storage systems as well as noncritical load shedding to ensure the microgrid frequency security after unintentional islanding events. Furthermore, a SCC-constrained Unit Commitment (UC) model is developed, maintaining a minimum SCC level at different locations in the system such that enough reactive current could be supplied during the fault to trigger the protection devices and maintain the post-fault voltages. Moreover, the static voltage stability in systems with high IBR penetration is also investigated considering the interactions among the IBR units and their reactive power support capability within rating limits.Open Acces

New Approaches in Automation and Robotics

The book New Approaches in Automation and Robotics offers in 22 chapters a collection of recent developments in automation, robotics as well as control theory. It is dedicated to researchers in science and industry, students, and practicing engineers, who wish to update and enhance their knowledge on modern methods and innovative applications. The authors and editor of this book wish to motivate people, especially under-graduate students, to get involved with the interesting field of robotics and mechatronics. We hope that the ideas and concepts presented in this book are useful for your own work and could contribute to problem solving in similar applications as well. It is clear, however, that the wide area of automation and robotics can only be highlighted at several spots but not completely covered by a single book

Stability, control, and optimization of nonlinear dynamical systems with applications in electric power networks

Electric power systems in recent years have witnessed an increasing adoption of renewable energy sources as well as restructuring of distribution systems into multiple microgrids. These trends, together with an ever-growing electricity demand, are making power networks operate closer to their stability margins, thereby raising numerous challenges for power system operators. In this thesis, we focus on two major challenges: How to efficiently assess and certify the stability of power systems; and how to optimize the operation of multiple microgrids while maintaining their stability. In the first part of the thesis, we focus on the first question, and study one of the most fundamental models of power systems, namely the swing equation model. We develop sufficient conditions under which the equilibrium points of swing equations are asymptotically stable. We also discuss the connection between the stability of equilibrium points and the network structure. This for example reveals an analog of Braess’s Paradox in power system stability, showing that adding power lines to the system may decrease the stability margin. Based on the developed theories, we also introduce several distributed control schemes for maintaining the stability of the system. Since swing equations belong to a more general class of second-order ordinary differential equations (ODEs) which are the cornerstone of studying many other physical and engineering systems, a considerable part of this thesis is devoted to the study of this general class of ODEs, where we investigate the impact of damping as a system parameter on the stability, hyperbolicity, and bifurcation in such systems. In the second part of the thesis, we address the second question and provide a computationally efficient method for optimizing multi-microgrid operation while ensuring its stability. Our goal is to maintain the frequency stability of multi-microgrid networks under an islanding event and to achieve optimal load shedding and network topology control with AC power flow constraints. Attaining this goal requires solving a challenging optimization problem with stability constraints. To cope with this challenge, we develop a strong mixed-integer second-order cone programming (MISOCP)-based reformulation and a cutting plane algorithm for scalable computation of the problem. The optimization frameworks and stability certificates developed in this thesis can be used as powerful decision support tools for power system operators.Ph.D

Operation of Microgrids with Conventional and Virtual Energy Storage Systems

Distribution systems are now increasingly becoming more active due to the sustainable integration of Distributed Energy Resources (DER). While this has enabled a cleaner and more efficient generation, it has also resulted in new challenges for the operation of modern power systems. In this context, the operation of isolated microgrids is particularly challenging, as these systems are characterized by a low inertia and significant renewable integration, and must be capable of an autonomous operation without the support of other electrical grids. Thus, the present thesis focuses on the design of an Energy Management System (EMS) for the reliable and economic operation of modern isolated microgrids. Isolated microgrid operation requires considering additional aspects typically omitted in the operation of robust bulk power systems. In particular, as demonstrated in this thesis, second-to-second renewable power fluctuations need to be considered in the microgrid EMS, since these fluctuations can have a large impact on the system’s frequency regulation due to its low inertia. Furthermore, to ensure an economic yet reliable operation, modern flexible technologies capable of counterbalancing these short-term fluctuations, such as Battery Energy Storage Systems (BESS) and Demand Response (DR), need to be integrated in the microgrid EMS. Hence, the present thesis focuses on designing a microgrid EMS model that integrates short-term renewable power fluctuations, their impact on frequency regulation, and the role that BESS and DR can play for their management. In the first part of the thesis, models are presented to characterize short-term renewable power fluctuations and their impact on microgrid operations, including the role that BESS can play to manage power fluctuations and the battery degradation resulting from providing this service. These models are then used to develop a practical EMS considering short-term renewable fluctuations and BESS flexibility, which is validated through exhaustive simulations on two realistic test microgrids, showing the operational benefits of the proposed EMS and highlighting the need to properly model short-term fluctuations and battery degradation in EMS for isolated microgrids. In the second part of the thesis, the above EMS model is extended to also incorporate the impact of short-term power fluctuations on the microgrid’s frequency regulation performance. For this purpose, accurate linear equations describing the frequency deviation and Rate-of-Change-of-Frequency (RoCoF) resulting from these fluctuations are developed, which are then used to build a frequency-constrained EMS model capable of guaranteeing an adequate frequency regulation performance in line with current DER operating standards. Exhaustive transient simulations on a realistic test microgrid considering detailed frequency dynamic and control models are presented, demonstrating the accuracy of the proposed frequency-constrained EMS and the operational benefits resulting from its implementation. Finally, the integration of DR techniques for an enhanced microgrid operation is discussed. In particular, the smart control of Thermostatically Controlled Loads (TCL) is studied, as these type of loads comprise a significant share of the total residential demand, and have the capability of managing second-to-second power imbalances without significantly affecting customer comfort. Since computational limitations prevent the direct integration of TCLs within operational models, alternative computationally efficient aggregate models representing TCL flexibility and frequency dynamics are proposed, which are referred to as Virtual Energy Storage Systems (VESS) due to their close resemblance to Conventional Energy Storage Systems (CESS) such as batteries. The proposed aggregate VESS models are then used to design a practical EMS integrating TCL flexibility, and study the impact of TCL integration on microgrid operation and frequency control. Computational experiments using detailed frequency transient and thermal dynamic models are presented, demonstrating the accuracy of the proposed aggregate VESS models, as well as the economic and reliability benefits resulting from using these aggregate models to integrate TCLs in microgrid operation

Transmission expansion planning and unit commitment with large-scale integration of wind power

The large-scale integration of wind generation into the power system brings great challenges to transmission expansion planning (TEP) and unit commitment (UC). The intermittence nature of wind generation needs to be fully considered in these two problems, which stimulates the research of this thesis. The selection of candidate lines is the prerequisite for the TEP problem. Considering the limitations of manual selection approach, a method to select candidate lines automatically is proposed, which consists of five stages to reinforce existing corridors and new corridors. Results of the two test systems illustrate that the locational marginal price difference is neither sufficient nor necessary condition for candidate lines. The uncertainty of load demand and wind power is studied both in the TEP and UC problems. In the term of TEP, a two-stage stochastic formulation of TEP is proposed. The stochastic dual dynamic programming (SDDP) approach is applied to consider the uncertainty, and the whole model is solved by Benders decomposition (BD) technique. In the term of UC, the chance-constrained two-stage programming formulation is proposed for the day-ahead UC problem. The chance-constrained stochastic programming formulation is converted into an equivalent deterministic formulation by a sequence of approximation and verification

WINDERFUL Wind and INfrastructures

WINDERFUL (an acronym for Wind and INfrastructures: Dominating Eolian Risk For Utilities and Lifelines) is the title of a research project carried out by eight Italian Universities from the end of 2001 to the end of 2003. The project was centred on how "to keep a city running and ensuring quality services during and after major windstorms", avoiding "major failures" of engineering facilities and main infrastructures. The book reports the main results obtained in the project, and for each typology the tool for assessing its reliability are discussed, together with the criteria for its improvement