| Summary: | 博士 === 國立清華大學 === 電機工程學系 === 102 === As the power system becomes more stressed and the penetration of renewable energies increases, voltage stability assessment (VSA) becomes a key issue for monitoring and controlling the security of modern bulk power grids. For security considerations, system operators require powerful tools to analyze voltage security of the bulk power system in real-time environments. Traditionally, the VSA is accomplished based on model-based approaches. Although various analytical approaches have been proposed along this direction, their computational complexities may impede their real-time applications. In recent years, with advances of wide-area synchrophasor measurements and distributed computation techniques, these new technologies have opened new perspectives for developing real-time tools for VSA. To this end, this dissertation aims to develop new methodologies for enhancing the real-time voltage stability by using wide-area synchrophasor measurements and distributed computation techniques.
First, based on real-time PMU measurements of individual load bus, a modified coupled single-port model will be proposed for measurement-based VSA. This model will improve underestimations of existing coupled single-port models since the reactive power response extracted from the extended Ward-type equivalent is explored to compensate the reactive power mismatch in the existing coupled single-port model. Then, a mitigation factor based on this reactive power response will be defined to provide a direction for adjusting circuit parameters of the current model, and modified models can be constructed accordingly. In addition, based on this modified coupled single-port model, several voltage stability indicators are developed for real-time VSA.
Second, the phenomenon of the short-term voltage instability of induction generators will be investigated. This phenomenon will lead to over-accelerations of induction generators such that the induction generators with the high slip may not return to the pre-fault equilibrium point. In order to identify this short-term voltage instability of induction generators in real-time manners, a synchrophasor-based short-term voltage stability indicator will be developed by incorporating induction generator equivalent models into modified coupled single-port models.
Third, multi-area Available Transfer Capability (ATC) assessments will be investigated in the distributed computation environments. Three distributed schemes, including (i) Predictor-Corrector Proximal Multiplier Method, (ii) Auxiliary Problem Principle Method, and (iii) Alternative Direction Multiplier Method, will be applied to distributed ATC assessments. System partition with non-overlapping and boundary sub-systems will be employed to a distributed system for implementing proposed iterative distributed algorithms in a distributed manner.
Finally, probabilistic load margin predictions under large-scale penetration of wind generations will be studied. Under wind speed variations, a new computational framework will be proposed to conduct probabilistic load margin estimations. A distributed bi-directional sweep method will be employed in multiple wind generators connected to the main grid for power flow computations. A modified direct method will be presented such that conventional 2N + 1 non-linear equations can be replaced by N + 1 equations for load margin calculations. Accordingly, corresponding probabilistic estimations can be calculated by integrating both modified direct method and Gram-Charlier expansions. Simulations on several IEEE test systems have been used to validate the feasibility and the accuracy of our proposed techniques.
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