POWER-FREQUENCY INTERACTIONS IN AN AC/DC/AC SYSTEM
Date
1976-01
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Degree Level
Masters
Abstract
A study of power-frequency interactions in an AC/DC/AC system is presented in this thesis. The selected system consists of three connected hydro-electric generating stations, which transmit power to a receiving AC system over two HVDC bipolar transmission links. Mathematical models of the DC bipoles, and the sending end and receiving end AC systems are
developed and are amalgamated to provide an equivalent of the composite AC/DC/AC system. The derived linearized model is suitable for representing low frequency power—frequency interactions.
The model of the DC bipole includes representation of the firing angle, master current order and power order controllers. The sending end generators are represented by voltages behind transient reactances and inertial equations. The voltages behind the transient reactances are assumed to vary such that voltages at the high tension buses are maintained constant. To concentrate on interactions between the sending end generators and the DC bipoles, the receiving end system is assumed to be an infinite bus.
The stability of the composite AC/DC/AC system is investigated using root locus studies and real time simulations. The sending end system is unstable when the DC links are operated in the constant power mode. It is shown that modulation of power flow of the DC links stabilizes the system. Lead-lag and double lead-lag modulators are investigated.
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Degree
Master of Science (M.Sc.)
Department
Electrical Engineering