<p>The growing energy demand has caused the interconnected power systems to operate close to their stability limit. As a consequence, poorly damped low-frequency oscillations are becoming a common phenomenon. Such oscillations weaken the system security and if not effectively damped can lead to widespread blackouts. A contemporary solution is the addition of Power System Stabilizers (PSSs) to generators. A relatively recent solution based on the advancements in high-power semiconductors is the Flexible AC Transmission System (FACTS) technology meant for transmission locations. FACTS technology comprises of a multitude of FACTS devices among which the <i>Unified Power Flow Controller (UPFC)</i> possesses a unique capability of providing both power flow and voltage control. Particularly, with a suitable transient control system the UPFC can satisfactorily mitigate power system oscillations.</p>
<p>This thesis proposes an adaptive control scheme that supplements an existing Proportional-Integral (PI) UPFC control system in damping power system oscillations. PI control is a well-established theory and a commonly used industrial controller. However, its application in a power system that experiences continuously changing system conditions demands its frequent re-tuning. On the other hand, the proposed scheme is a Self Tuning (ST) controller that automatically adapts to the system changes and thereby provides an optimal control for a wide range of operating scenarios. The proposition of assisting the primary PI control action is unique in its approach since it retains the functionality of the existing PI controllers and also enhances the overall damping performance through an add-on ST control loop.</p>
<p>The proposed novel ST scheme consists of a Constrained Recursive Least Squares (CRLS) identifier that tracks system parameters recursively and a self-tuning Pole Shift (PS) controller that works on the identified system model to generate a robust control output. Also, to effectively smoothen out the rapid variations of identified system parameters and consequent ringing of control output during large disturbances, the thesis specifies the replacement of the standard-RLS identifier with a "constrained" RLS (CRLS) identifier. The damping enhancement achieved by the proposed controller has been verified through time-domain simulations. The test results clearly depict that the proposed add-on scheme not only enhances the overall damping but is also robust with respect to power flow level, fault type and location. Its inherent flexibility and the positive test results suggest that with little modification, it can be easily applied to other FACTS devices currently incorporated in transmission networks.</p>
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-04182011-152519 |
| Date | 30 May 2011 |
| Creators | Malhotra, Urvi |
| Contributors | Gokaraju, Ramakrishna, Wu, Fang Xiang, Billinton, Roy, Nguyen, Ha |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-04182011-152519/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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