Subsynchronous Torsional Interaction Behaviour of Wind Turbine-Generator Unit Connected to an HVDC System

Utilisation of wind energy to generate electricity has attracted considerable attention worldwide, and is rapidly-growing. The integration of large wind farms with high voltage direct current (HVDC) transmission network could be one of the preferred options for supplying bulk power over a long distance. Since HVDC rectifier stations with constant current control may introduce negative damping on the nearby generating units, it is important to identify the torsional interaction characteristics between turbine-generator units and the HVDC systems over a frequency range of interest. However, very little related information exists in regard to wind turbine-generators. This paper presents the electromagnetic transient time domain analysis to investigate the possible subsynchronous torsional interaction (SSTI) phenomenon of fixed-speed (induction machine based) wind turbine-generator (WTG) unit interconnected to a CIGRE first HVDC benchmark system. Electrical disturbances, such as three-phase short circuit fault at the inverter station and DC power flow change are simulated to examine the possible dynamic interactions of the WTG unit. Simulation studies are conducted using PSCAD(R)/EMTDC(C).