ANALYSIS OF TORSIONAL INTERACTIONS IN MTDC SYSTEMS

A detailed study of the subsynchronous frequency torsional interaction s in a multi-terminal DC (MTDC) system is presented based on small sig nal stability analysis. The torsional intel actions result in negative damping of torsional modes, with the converter controls particular ly when the turbine-generator is located close to a converter terminal. The linearized mathematical model of the system is derived from detail ed models of the components such as the turbine-generator, AC and DC n etworks, converters and their controllers. The effects of the selectio n of voltage setting terminal (VST), the controller gains and the loca tion of the generator are presented through the eigenvalue analysis of a two and a three terminal system.