Integration of Utility-Scale Variable Generation into Resistive Networks.

Wind and solar power account for half of newly installed electricity generation capacity worldwide. Due to falling technology costs, this trend is expected to continue despite the global economic turmoil and uncertainty over policy incentives for these fledgling sectors. A sizable portion of this capacity is connected to sub-transmission networks that typically have mesh configurations and are characterized by resistive lines (i.e. lines with X=R 4). The resistivity of subtransmission networks creates a strong coupling between power flows and voltage magnitudes that is atypical in high-voltage transmission systems. In the presence of generation variability, this can lead to extreme voltages, unacceptable voltage fluctuations, unusual (active and reactive) power flow patterns throughout the network, line congestions and increased losses. This can also cause excessive tap-changing operation of transformers with On-Load Tap Changers (OLTCs). These issues can be substantially mitigated with flexible methods of network operation and control. This dissertation examines the impact of variable embedded generation on the voltage profile, structural stability and the OLTC operation of the DTE/ITC network serving Eastern Michigan. It introduces a number of tools and methods to analyze the impact of variable generation in meshed resistive networks. It investigates how network resistivity transforms the impact of the reactive compensation, associated with variable generation, on the structural stability of the system. Finally an optimal voltage control scheme is presented to better coordinate the voltage regulation of variable generation with OLTCs, reduce network losses and enhance the structural stability of the system. The scheme is a model predictive control with an equivalent mixed integer formulation which models the hybrid dynamics of OLTC tap operations.PhDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113584/1/sinasb_1.pd

Risk-based security assessment for operating electric power systems

The power system is a widespread and complex network whose complete behavior, at present, still remains partially characterized. Power systems have operated in most cases reliably, but conservatively with the help of many deterministic techniques that rely heavily on the modeling of system components and the associated dynamics. Now, with increasing competition and growing demand, the power system, however, has been shifting from a deterministically regulated system to a competitive and uncertain market environment. Power utilities are required to have a comprehensive knowledge of the risks as well as benefits in their transmission operations. Our interest is motivated by this need of the industry to provide a method to quantify the risk of operating a power system with consideration to the probabilistic nature of system behaviors. The objective of this dissertation is to develop a foundation of risk-based bulk power system security assessment that leads to the definition, calculation, and application of the risk in operating electric power systems. The work includes three parts of risk assessments: transmission line thermal overload, voltage insecurity, and composite risk assessments. Both the probability of insecurity problems and their cost consequences are measured such that an expected monetary impact is given as the measurement of risk. This quantitative measurement of thermal, voltage, and composite risk is helpful for the operator to trade off the benefits and costs in the competitive utility environment. For making this economic tradeoff, several decision criteria, including both deterministic and probabilistic strategies, from conservative to greedy preference, are introduced to aid the operator to make operating decisions. This research establishes a bridge between power system security and economics by the index of risk that is compatible with the economic results of market-based electricity trading. Both the method to quantify the risk and the ways to apply it in decision-making make contributions to the power industry

A review of dynamic models and stability analysis for a hydro-turbine governing system

Industrial Ecolog

Statistical Analysis of High Sample Rate Time-series Data for Power System Stability Assessment

The motivation for this research is to leverage the increasing deployment of the phasor measurement unit (PMU) technology by electric utilities in order to improve situational awareness in power systems. PMUs provide unprecedentedly fast and synchronized voltage and current measurements across the system. Analyzing the big data provided by PMUs may prove helpful in reducing the risk of blackouts, such as the Northeast blackout in August 2003, which have resulted in huge costs in past decades. In order to provide deeper insight into early warning signs (EWS) of catastrophic events in power systems, this dissertation studies changes in statistical properties of high-resolution measurements as a power system approaches a critical transition. The EWS under study are increases in variance and autocorrelation of state variables, which are generic signs of a phenomenon known as critical slowing down (CSD). Critical slowing down is the result of slower recovery of a dynamical system from perturbations when the system approaches a critical transition. CSD has been observed in many stochastic nonlinear dynamical systems such as ecosystem, human body and power system. Although CSD signs can be useful as indicators of proximity to critical transitions, their characteristics vary for different systems and different variables within a system. The dissertation provides evidence for the occurrence of CSD in power systems using a comprehensive analytical and numerical study of this phenomenon in several power system test cases. Together, the results show that it is possible extract information regarding not only the proximity of a power system to critical transitions but also the location of the stress in the system from autocorrelation and variance of measurements. Also, a semi-analytical method for fast computation of expected variance and autocorrelation of state variables in large power systems is presented, which allows one to quickly identify locations and variables that are reliable indicators of proximity to instability

Mathematical and Numerical Aspects of Dynamical System Analysis

From Preface: This is the fourteenth time when the conference “Dynamical Systems: Theory and Applications” gathers a numerous group of outstanding scientists and engineers, who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without a great effort of the staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our invitation has been accepted by recording in the history of our conference number of people, including good colleagues and friends as well as a large group of researchers and scientists, who decided to participate in the conference for the first time. With proud and satisfaction we welcomed over 180 persons from 31 countries all over the world. They decided to share the results of their research and many years experiences in a discipline of dynamical systems by submitting many very interesting papers. This year, the DSTA Conference Proceedings were split into three volumes entitled “Dynamical Systems” with respective subtitles: Vibration, Control and Stability of Dynamical Systems; Mathematical and Numerical Aspects of Dynamical System Analysis and Engineering Dynamics and Life Sciences. Additionally, there will be also published two volumes of Springer Proceedings in Mathematics and Statistics entitled “Dynamical Systems in Theoretical Perspective” and “Dynamical Systems in Applications”

Static Voltage Stability Analysis for Islanded Microgrids

The ongoing development of renewable energy and microgrid technologies has gradually transformed the conventional energy infrastructure into a modernized system with more distributed generation and localized energy storage options. Compared with power grids utilizing synchronous generation, inverter-based networks cannot physically provide large amounts of inertia. Therefore, more advanced, and extensive studies regarding stability considerations are required for such systems. Appropriate analytical methods are needed for the voltage stability analysis of renewable-dominated power systems, which incorporate many inverters and distributed energy sources. Microgrid voltage stability is being challenged as the power output of renewable energy generation is not as stable as the traditional generation used in the main grid. Therefore, the choice of voltage stability analysis techniques plays an important role in the stable operation of the microgrid. This thesis comprehensively studies static voltage stability analyses of islanded microgrids with high levels of renewable energy penetration. Firstly, a series of generalized evaluation schemes and improvement methods relating to the voltage stability of power systems integrated with various distributed energy resources are discussed. This study presents guidelines for voltage stability analysis and instability mitigation methods for modern renewable-rich power systems. Then, four dominant VSI techniques for microgrids are studied and compared in this paper. An islanded microgrid system is modelled based on the IEEE-14-bus system in PSCAD. The model evaluates the stability results analyzed by different voltage stability indices (VSIs). Four simulation scenarios are applied in this thesis, including changing the output power of distributed generations (DGs) and the connection position of the DGs. The advantages and disadvantages of each technique are discussed based on the simulation results. A ranking of bus voltage stability is obtained based on the simulation and the VSI calculation. Finally, a novel static voltage stability analysis technique is proposed

Voltage Stability Assessment and Enhancement in Power Systems

Voltage stability is a long standing issue in power systems and also is critical in the power system. This thesis aims to address the voltage stability problems. When wind generators reach maximum reactive power output, the bus voltage will operate near its steady-state stability limit. In order to avoid voltage instability, a dynamic L-index minimization approach is proposed by incorporating both wind generators and other reactive power resources. It then verifies the proposed voltage stability enhancement method using real data from load and wind generation in the IEEE 14 bus system. Additionally, power system is not necessary to always operate at the most voltage stable point as it requires high control efforts. Thus, we propose a novel L-index sensitivity based control algorithm using full Phasor measurement unit measurements for voltage stability enhancement. The proposed method uses both outputs of wind generators and additional reactive power compensators as control variables. The L-index sensitivity with respect to control variables is introduced. Based on these sensitivities, the control algorithm can minimise all the control efforts, while satisfying the predetermined L-index value. Additionally, a subsection control scheme is applied where both normal condition and weak condition are taken into account. It consists of the proposed L-index sensitivities based control algorithm and an overall L-index minimisation method. Threshold selection for the subsection control scheme is discussed and extreme learning machine is introduced for status fast classification to choose the method which has less power cost on the transmission line. Due to the high cost of PMUs, a voltage stability assessment method using partial Phasor measurement unit (PMU) measurements is proposed. Firstly, a new optimisation formulation is proposed that minimizes the number of PMUs considering the most sensitive buses. Then, extreme learning machine (ELM) is used for fast voltage estimation. In this way, the voltages at buses without PMUs can be rapidly obtained based on the PMUs measurements. Finally, voltage stability can be assessed by using L-index

ON-LINE TRANSIENT STABILITY STUDIES INCORPORATING WIND POWER

Transient stability is a major concern in power system security and reliability because it is the most common type of instability and its impacts can cause greatest economic losses. For enhancing the energy security, it requires the power system operation to be evaluated during both the planning and the operation stage. Many online/offline transient stability assessment techniques have already been developed for this purpose. However, due to the increase in energy demand, the modern power system has grown to a very sophisticated and large system for which extent transient stability assessment methods may not be able to handle. In addition, the new published regulation rules and new concepts such as the smart grid have also pushed the requirement for transient stability assessment to a higher level. Thus, this dissertation is intended to study large scale power system transient stability. It starts from establishing an analytical approach for power system transient stability assessment. Based on the results, the disadvantages of traditional concepts used in transient stability assessment have been discussed. In order to overcome the difficulties encountered by classical approaches, a new technique for estimating the generator rotor angle difference in multi-machine power system is developed. It is more practical and has been applied to study the impact of wind power generation on power system transient stability afterwards. Since recently there is a significant increase in the importance of renewable energy and its related optimizations in power systems, the final goal of this dissertation focuses on the power system optimal power flow technique with wind power penetration and transient stability constrains. For making results more convincible, the South Carolina offshore wind speed data is used as the availability of wind power. An approach for maintaining the power system economic operation within the security range has been given at the end of this dissertation