1,433 research outputs found
Wide-area monitoring and control of future smart grids
Application of wide-area monitoring and control for future smart grids with substantial
wind penetration and advanced network control options through FACTS and HVDC
(both point-to-point and multi-terminal) is the subject matter of this thesis.
For wide-area monitoring, a novel technique is proposed to characterize the system dynamic
response in near real-time in terms of not only damping and frequency but also
mode-shape, the latter being critical for corrective control action. Real-time simulation
in Opal-RT is carried out to illustrate the effectiveness and practical feasibility of the proposed
approach. Potential problem with wide-area closed-loop continuous control using
FACTS devices due to continuously time-varying latency is addressed through the proposed
modification of the traditional phasor POD concept introduced by ABB. Adverse
impact of limited bandwidth availability due to networked communication is established
and a solution using an observer at the PMU location has been demonstrated.
Impact of wind penetration on the system dynamic performance has been analyzed along
with effectiveness of damping control through proper coordination of wind farms and
HVDC links. For multi-terminal HVDC (MTDC) grids the critical issue of autonomous
power sharing among the converter stations following a contingency (e.g. converter outage)
is addressed. Use of a power-voltage droop in the DC link voltage control loops
using remote voltage feedback is shown to yield proper distribution of power mismatch
according to the converter ratings while use of local voltages turns out to be unsatisfactory.
A novel scheme for adapting the droop coefficients to share the burden according
to the available headroom of each converter station is also studied.
The effectiveness of the proposed approaches is illustrated through detailed frequency
domain analysis and extensive time-domain simulation results on different test systems
Comparing Kalman Filters and Observers for Power System Dynamic State Estimation with Model Uncertainty and Malicious Cyber Attacks
Kalman filters and observers are two main classes of dynamic state estimation
(DSE) routines. Power system DSE has been implemented by various Kalman
filters, such as the extended Kalman filter (EKF) and the unscented Kalman
filter (UKF). In this paper, we discuss two challenges for an effective power
system DSE: (a) model uncertainty and (b) potential cyber attacks. To address
this, the cubature Kalman filter (CKF) and a nonlinear observer are introduced
and implemented. Various Kalman filters and the observer are then tested on the
16-machine, 68-bus system given realistic scenarios under model uncertainty and
different types of cyber attacks against synchrophasor measurements. It is
shown that CKF and the observer are more robust to model uncertainty and cyber
attacks than their counterparts. Based on the tests, a thorough qualitative
comparison is also performed for Kalman filter routines and observers.Comment: arXiv admin note: text overlap with arXiv:1508.0725
Wide-Area Control Schemes to Improve Small Signal Stability in Power Systems
One of the main concerns for the secure and reliable operation of power systems is the small signal stability problem. In the complex and highly interconnected structure of future power systems, relying solely on operator responses and conventional controls cannot assure reliability. Therefore, there is a need for advanced Wide-Area Control Schemes (WACS) that can automatically respond to degradation of reliability in the system.
The main objective of this dissertation is to address two key challenges regarding the design and implementation of wide-area control schemes for damping inter-area oscillations. First is the high communication cost associated with optimal centralized control approaches. As power networks are large-scale systems, both the synthesis and the implementation of centralized controllers suggested by most of the previous studies are often impossible in practice. Second is the difficulty of obtaining accurate system-wide dynamic models for initiating and updating the control design.
In this research, we introduced wide-area damping control strategies that not only ensure the small signal stability with the desired performance but also consider communication and model information limitations in the design. A state feedback formulation is proposed that aims to simultaneously optimize a standard Linear Quadratic Regulator (LQR) cost criterion and induce a pre-defined communication structure. We solved the proposed problem with three different objectives to target a specific wide-area damping control design challenge in each setting. First, the communication structure is enforced as a constraint in the optimization and solved for a large idealized power network with information symmetry. Second, to make the method suitable for systems with arbitrary structures and information patterns, we proposed a group-sparse regularization to be added to the optimization cost function. Applications of the method for inducing the desired communication network and finding effective measurement and control signal combinations were also investigated. Third, we paired the proposed optimal control with a real-time model identification approach, to create a wide-area control framework that is capable of dealing with model information limitations and inaccuracies in online implementation. The performances of the proposed wide-area damping control architectures are validated through nonlinear simulations on different test systems
Voltage Stability Indices Based on Active Power Transfer Using Synchronized Phasor Measurements
In recent years and in the foreseeable future, power demands generally around the world and particularly in North America will experience rapid increases due to the increase of customers\u27 requirements, while the development of transmission systems in North America is rather slow. Voltage stability assessment becomes one of the highest priorities to power utilities in North America. Voltage stability index is a feature for solving voltage stability problems. It is generated from the basic power flow equations and/or energy functions. The mathematical expression of a VSI is often written as a polynomial containing the systems real-time measurements such as voltage magnitudes, phase angles, bus injected power and branch power flow values, etc. In this thesis, the principle and derivation process of two voltage stability indices are presented. Relevant simulations are analyzed to demonstrate the VSIs\u27 functions as illustrating the system\u27s stability condition, estimating the systems operating states, determining system sensitive buses; and generator-sensitive buses and to help system apply voltage stability protection strategy. The thesis also discussed the application of VSIs with synchronized phasor measurement units, a precise system phasor measuring device using global positioning signal to obtain wide-area system measurements simultaneously. The effect of measurements errors on the computation of the VSI is studied and examined. Finally, a discussion of the future development of synchrophasors and VSI methods is given
Data-Driven Diagnostics of Mechanism and Source of Sustained Oscillations
Sustained oscillations observed in power systems can damage equipment,
degrade the power quality and increase the risks of cascading blackouts. There
are several mechanisms that can give rise to oscillations, each requiring
different countermeasure to suppress or eliminate the oscillation. This work
develops mathematical framework for analysis of sustained oscillations and
identifies statistical signatures of each mechanism, based on which a novel
oscillation diagnosis method is developed via real-time processing of phasor
measurement units (PMUs) data. Case studies show that the proposed method can
accurately identify the exact mechanism for sustained oscillation, and
meanwhile provide insightful information to locate the oscillation sources.Comment: The paper has been accepted by IEEE Transactions on Power System
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An Assessment of PIER Electric Grid Research 2003-2014 White Paper
This white paper describes the circumstances in California around the turn of the 21st century that led the California Energy Commission (CEC) to direct additional Public Interest Energy Research funds to address critical electric grid issues, especially those arising from integrating high penetrations of variable renewable generation with the electric grid. It contains an assessment of the beneficial science and technology advances of the resultant portfolio of electric grid research projects administered under the direction of the CEC by a competitively selected contractor, the University of California’s California Institute for Energy and the Environment, from 2003-2014
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