A SELF COMMUTATED POWER CONVERTER FOR STABILIZING TORSIONAL INTERACTIONS (RESONANCE, TRANSMISSION CURRENT FEEDBACK, SUBSYNCHRONOUS)
Abstract
In the Western United States, where large coal power plants may be separated from the load centers by several hundred miles, series compensation of transmission lines with capacitors is often used to increase the amount of power that can be transmitted over the long transmission lines. However, series compensation has been known to cause unstable interactions between the transmission system and the torsional modes of steam turbo-generators. This type of unstable interaction falls into the general category of subsynchronous resonance (SSR). In this research, a new method of counteracting SSR, referred to as transmission current feedback, is investigated. This method involves the measurement of the transmission system currents from which the subsynchronous components that produce torsional interactions are extracted using reference frame theory. Once extracted, these currents are suitably amplified by a power converter and injected into the generator bus of the affected steam turbine so as to cancel the original subsynchronous components that would otherwise produce torsional interactions. A practical realization of a multimegawatt power converter, with a response bandwidth that includes the complete range of subsynchronous frequencies, is set forth. The realization consists of a voltage fed, self commutated power converter which allows independent control of the injected real and reactive power. An analytic model relating the fundamental component of the converter output currents to its controlling variables is derived and a suitable control strategy is formulated. A detailed hybrid computer simulation of the converter, which incorporates the effects of the converter switching transients, is used to verify the accuracy of the analytic representation of the converter and the effectiveness of the control strategy. The generalized Nyquist stability criterion is used to characterize the stability of the IEEE first benchmark power system incorporating the use of transmission current feedback. Finally, the time domain behavior of the IEEE first benchmark power system incorporating the use of transmission current feedback is thoroughly investigated using computer simulations.
Degree
Ph.D.
Subject Area
Electrical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.