Traditional power system stability assessment based on full model computation shows its drawbacks in real-time applications where fast variations are present at both demand side and supply side. This work presents the use of data mining techniques, in particular the Decision Trees (DTs), for fast evaluation of power system oscillatory stability and voltage stability from synchrophasor measurements. A regression tree-based approach is proposed to predict the stability margins. Modal analysis and continuation power flow are the tools used to build the knowledge base for off-line DT training. Corresponding metrics include the damping ratio of critical electromechanical oscillation mode and MW-distance to the voltage instability region. Classification trees are used to group an operating point into predefined stability state based on the value of corresponding stability indicator. A novel methodology for knowledge base creation has been elaborated to assure practical and sufficient training data. Encouraging results are obtained through performance examination. The robustness of the proposed predictor to measurement errors and system topological variations is analyzed. A scheme has been proposed to tackle the problem of when and how to update the data mining tool for seamless online stability monitoring. The optimal placement for the phasor measurement units (PMU) based on the importance of DT variables is suggested. A measurement-based voltage stability index is proposed and evaluated using field PMU measurements. It is later revised to evaluate the impact of wind generation on distribution system voltage stability. Next, a new data mining tool, the Probabilistic Collocation Method (PCM), is presented as a computationally efficient method to conduct the uncertainty analysis. As compared with the traditional Monte Carlo simulation method, the collocation method could provide a quite accurate approximation with fewer simulation runs. Finally, we show how to overcome the disadvantages of mode meters and ringdown analyzers by using DTs to directly map synchrophasor measurements to predefined oscillatory stability states. The proposed measurement-based approach is examined using synthetic data from simulations on IEEE test systems, and PMU measurements collected from field substations. Results indicate that the proposed method complements the traditional model-based approach, enhancing situational awareness of control center operators in real time stability monitoring and control.

In the pursuit of a cleaner and sustainable environment, solar photovoltaic (PV) power has been established as the fastest growing alternative energy source in the world. This extremely fast growth is brought about, mainly, by government policies and support mechanisms world-wide. Solar PV technology that was once limited to specialized applications and considered very expensive, with low efficiency, is becoming more efficient and affordable. Solar PV promises to be a major contributor of the future global energy mix due to its minimal running costs, zero emissions and steadily declining module and inverter costs. With the expanding practice of managing decentralized power systems around the world, the role of private investors is increasing. Thus, the perspective of all stakeholders in the power system, including private investors, has to be considered in the optimal planning of the grid. An abundance of literature is available to address the central planning authority’s perspective; however, optimal planning from an investor’s perspective is not widely available. Therefore, this thesis focuses on private investors’ perspective. An optimization model and techniques to facilitate a prospective investor to arrive at an optimal investment plan in large-scale solar PV generation projects are proposed and discussed in this thesis. The optimal set of decisions includes the location, sizing and time of investment that yields the highest profit. The mathematical model considers various relevant issues associated with PV projects such as location-specific solar radiation levels, detailed investment costs representation, and an approximate representation of the transmission system. A detailed case study considering the investment in large-scale solar PV projects in Ontario, Canada, is presented and discussed, demonstrating the practical application and usefulness of the proposed methodology and tools.

Wind generation has become one of the most popular choices of technology for adding new generation capacity to power systems worldwide. Several factors have contributed to the increased integration of wind generation, including environmental concerns and the continual increase in fossil fuel prices. As well, recent regulations have moved toward limitations on greenhouse gases, especially in the European Union (EU). Similar laws are currently under consideration in the US and other parts of the world. Other factors have also promoted the use of wind energy, such as advances in manufacturing and control technology and the attractiveness of wind as a “green” source of energy. The large-scale integration of wind power into an electricity system introduces planning and operational challenges because of the intermittent nature of wind speed and the difficulty involved in predicting it. For these reasons, wind energy is often considered an unreliable energy source. Additional problems are associated with the integration of large-scale wind farms into an electrical grid, among which wind power fluctuation is the most challenging. To maximize the penetration level of wind energy in a grid, a reliable technology must be developed in order to eliminate or at least decrease wind power fluctuation. The primary goal of this thesis was to develop methods of maximizing the penetration level of wind energy conversion systems (WECSs) into a grid, which requires mitigating wind power fluctuation. A robust control technique has therefore been developed for mitigating wind power fluctuation. This control technique exploits historical environmental data collected over a number of years in order to evaluate the profile of the output power of a variety of wind energy conversion systems (WECSs). The developed control technique was applied to Types A and C WECSs modifying the pitch angle controller of Type A WECS and the back-to-back converter control of Type C WECS. The Attachment of a storage device to the WECSs after the control technique is applied was investigated from both an economic and a technical point of view. The optimum sizing and siting of the wind energy conversion system equipped with the proposed control technique was also studied. This research is expected to contribute to the advancement of WECS technology by presenting a feasible solution to the problems associated with the integration of large-scale WECSs into electrical grids.

Interest in Distributed Generation (DG) in power system networks has been growing rapidly. This increase can be explained by factors such as environmental concerns, the restructuring of electricity businesses, and the development of technologies for small-scale power generation. DG units are typically connected so as to work in parallel with the utility grid; however, with the increased penetration level of these units and the advancements in unit’s control techniques, there is a great possibility for these units to be operated in an autonomous mode known as a microgrid. Integrating DG units into distribution systems can have an impact on different practices such as voltage profile, power flow, power quality, stability, reliability, and protection. The impact of the DG units on stability problem can be further classified into three issues: voltage stability, angle stability, and frequency stability. As both angle and frequency stability are not often seen in distribution systems, voltage stability is considered to be the most significant in such systems. In fact, the distribution system in its typical design doesn’t suffer from any stability problems, given that all its active and reactive supplies are guaranteed through the substation. However, the following facts alter this situation: • With the development of economy, load demands in distribution networks are sharply increasing. Hence, the distribution networks are operating more close to the voltage instability boundaries. • The integration of distributed generation in distribution system introduces possibility of encountering some active/reactive power mismatches resulting in some stability concerns at the distribution level. Motivated by these facts, the target of this thesis is to investigate, analyze and enhance the voltage stability of distribution systems with high penetration of distributed generation. This study is important for the utilities because it can be applied with Connection Impact Assessment (CIA ). The study can be added as a complement assessment to study the impacts of the installation of DG units on voltage stability. In order to accomplish this target, this study is divided into three perspectives: 1) utilize the DG units to improve the voltage stability margin and propose a method to allocate DG units for this purpose, 2) investigate the impact of the DG units on proximity to voltage stability 3) conduct harmonic resonance analysis to visualize the impacts of both parallel and series resonance on the system’s stability. These perspectives will be tackled in Chapter 3, Chapter 4, and Chapter 5, respectively. Chapter 3 tackles placing and sizing of the DG units to improve the voltage stability margin and consider the probabilistic nature of both the renewable energy resources and the load. In fact, placement and sizing of DG units with an objective of improving the voltage stability margin while considering renewable DG generation and load probability might be a complicated problem, due to the complexity of running continuous load flow and at the same time considering the probabilistic nature of the load and the DG unit’s resources. Therefore, this thesis proposes a modified voltage index method to place and size the DG units to improve the voltage stability margin, with conditions of both not exceeding the buses’ voltage, and staying within the feeder current limits. The probability of the load and DG units are modeled and included in the formulation of the sizing and placing of the DG units. Chapter 4 presents a model and analysis to study the impact of the DG units on proximity to voltage instability. Most of the modern DG units are equipped with power electronic converters at their terminals. The power electronic converter plays a vital role to match the characteristics of the DG units with the requirements of the grid connections, such as frequency, voltage, control of active and reactive power, and harmonic minimization. Due to the power electronics interfacing, these DG units have negligible inertia. Thus, they make the system potentially prone to oscillations resulting from the network disturbances. The main goal of this chapter is to model and analyze the impact of distributed generation DG units on the proximity of voltage instability, with high penetration level of DG units. Chapter 5 studies the harmonic resonance due to the integration of DG units in distribution systems. Normally, the harmonic resonance phenomenon is classified as a power quality problem, however, this phenomenon can affect the stability of the system due to the parallel and series resonance. Thus, the main goal of this chapter is to study and analyze the impact of the integration of distributed generation on harmonic resonance by modeling different types of DG units and applying impedance frequency scan method.

Modern power networks are being driven ever closer to both their physical and operational limits. As a result, control systems are being increasingly relied on to assure satisfactory system performance. Power system stabilizers (PSSs) are one example of such controllers. Their purpose is to increase system damping and they are typically designed using a model of the network that is valid during nominal operating conditions. The limitation of this design approach is that during off-nominal operating conditions, such as those triggered by daily load fluctuations, performance of the controller can degrade. The research presented in this report attempts to evaluate the possibility of employing an adaptive PSS as a means of avoiding the performance degradation precipitated by off-nominal operation. Conceptually, an adaptive PSS would be capable of identifying changes in the network and then adjusting its parameters to ensure suitable damping of the identified network. This work begins with a detailed look at the identification algorithm employed followed by a similarly detailed examination of the control algorithm that was used. The results of these two investigations are then combined to allow for a preliminary assessment of the performance that could be expected from an adaptive PSS. The results of this research suggest that an adaptive PSS is a possibility but further work is needed to confirm this finding. Testing using more complex network models must be carried out, details pertaining to control parameter tuning must be resolved and closed-loop time domain simulations using the adaptive PSS design remain to be performed.

ABSTRACT In this thesis, relationship between two most important transient stability indices, critical clearing time and generator rotor angle is examined for one machine-infinite bus system and then extended to the multimachine case and is observed to be linear. By using the linear relationship between critical clearing time and generator rotor angle and utilizing the daily load curve, a new preventive method is proposed. The aim of this method is to make all critical clearing times longer than the relay and circuit breaker combination operation time. In the proposed method, desired critical clearing times are obtained by using on line system data and daily load curves. Then desired values are adjusted by generators output rescheduling and terminals voltage control Visual computer language is used for graphical and numerical solutions. Comprehension of one machine infinite bus system and multimachine system transient stability become easier.

The interdependencies that exist within and between infrastructures can cause unexpected system properties to emerge when their components fail due to large disruptions. As witnessed following emergencies such as Hurricane Katrina, the complexities of these interdependencies make it very difficult to effectively recover infrastructure because of the challenges they create in prioritizing the most critical components for repair. The Joint Infrastructure Interdependencies Research Program was initiated by Public Safety Canada (PSC) and the Natural Sciences and Engineering Research Council of Canada (NSERC) in 2005 to research methods for remedying this problem. As a part of this research, the University of British Columbia (UBC) is developing an infrastructure interdependency simulator, named I2Sim, to simulate disasters and develop strategies for dealing with emergencies. Part of this development is to construct a model of the UBC electrical distribution system and interface it with I2Sim. In this research, a general methodology for such a model is presented, which employs an off-the-shelf powerflow modeling tool. In addition, a model of the UBC information technology infrastructure is developed to provide a second infrastructure model to demonstrate the electrical model's usefulness in multi-infrastructure disaster recovery simulations. Simulations with these models have shown that the recovery of this two-infrastructure system can be carried out more effectively following an earthquake if both infrastructures are considered together in the repair approach, rather than individually. This difference was on the order of thirty percent. To extend this research from electrical distribution systems to electrical bulk systems, an interdependency model of the British Columbia Transmission Corporation bulk power network and its communications system was also developed, along with a post-blackout restoration procedure. Using these, simulations of a post-blackout recovery were carried out to study the level of risk that communications outages may pose to the electrical network's recovery. These simulations revealed a correlation between restoration time and the number of communication points lost. This research also demonstrates there is value in combining the results of such simulations with risk evaluation tools. Together these results provided a clearer indication of where vulnerabilities exist.

Thesis (PhD) -- University of South Australia, 1993

Along with the increasing scale of the power system and stressed operation in the transmission network, the stability margin is reduced considerably. As a traditional solution, the constructions of new transmission lines and generators sometimes are constrained by local environmental and regulatory constraints. Another characteristic of a modern network is the higher number of transmission inter-connections which appear in the large-scale power system. As an economic benefit, inter-connection can reduce the cost of electricity and enhance system reliability [1]. Those inter-connected tie lines are operated normally under heavy flow to maximize the usage benefit. This characteristic contributes to the complexity of operating and controlling the system. In recent years, along with the development of power electronic devices, the Flexible AC Transmission Systems (FACTS) has been used in the system as an alternative solution. It can maximize the usage benefit of the HV transmission line and make the large-scale power system more controllable. By using FACTS devices, the system can survive serious system contingencies with real-time control action, instead of providing a large steady state stability margin. Therefore, the system transfer capacity can be significantly increased. Electromechanical oscillations are observed in today's power system; such oscillations are recognized as a major concern in power system operation. Once begun, the oscillations may continue for a while before being halted by the damping torque from the system, or they may continue to grow (inadequate damping) and eventually cause system instability by losing synchronicity. The traditional and widely applied solution for oscillation damping is the Power System Stabilizer (PSS), which is efficient in damping local mode oscillation and inter-area oscillation in certain conditions. In recent years, research and development of the application of FACTS devices in suppressing system oscillations, especially for inter-area mode oscillation damping, has attracted increasing interest [1]. The primary objective of this thesis is to design robust FACTS controllers for enhancing power system dynamic stability by damping low frequency electromechanical oscillations. Recently, various nonlinear control techniques have been applied in power system control. The performance of nonlinear controllers is influenced by the parameter uncertainty and external disturbance. This thesis will present a novel approach of a robust Variable Structure Control (VSC)-based FACTS controller for damping multi-mode oscillations. Robust performances of the proposed controllers in different power systems are demonstrated by computer simulation.

Bibliography: leaves 238-248 / xxix, 248 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis is concerned with the design and coordination of linear, fixed parameter controllers for the purpose of enhancing the dynamic performance of a multimachine power system. The studies are based on linear control theory and involve state space analysis, modal analysis, eigenanalysis and conventional frequency response techniques. The emphasis is on the small-signal performance of the system / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 1997?