MODELING OF LCC-HVDC SYSTEMS USING DYNAMIC PHASORS

Abstract

High-Voltage-Direct-Current (H.V.D.C.) Transmission has earned a significant place in the modern power system throughout the world. The conventional use of H.V.D.C. systems for integrating systems of different frequencies or for their role in power sector, especially in the field of transmission via long-distance-transmission lines has now been expanded and is being widely used for evacuation and integration of generation plants operating on renewable energy sources. This report attempts to develop a line-commutated-converter (L.C.C.) based high-voltage-direct current (H.V.D.C.) transmission system model using Dynamic Phasors. The mathematical equations and concept of Dynamic Phasors as illustrated in the report are used to model the AC as well as DC-side of the L.C.C. based H.V.D.C. system, also they are used for modeling the control architecture of 12-pulse Thyristor-Bridge which is used as the basic component of such a system. In order to develop the model of a line-commutated-converter(L.C.C.) using dynamic phasor techniques, the concept of switching functions is used. The developed model includes low frequency dynamics of the systems, i.e., fundamental frequency component (50 Hz) at the ac side and dc component at the dc-side. The developed model has been used to simulate the system during operations which leads to instability/abnormality; such as imbalance voltage operation due to fault at the AC side.