Subsynchronous oscillation controller for Vindhyachal back-to-back HVDC link

The Vindhyachal back-to-back HVDC link interconnects the 400 kV AC networks of the Northern and Western power in India. The phenomena of subsynchronous oscillations due to adverse interaction between turbine generator torsional modes of oscillations and an HVDC system was discovered in 1977. To avoid damage to turbine-generator sets, it is therefore necessary to get a positive damping contribution for frequencies of interest from the HVDC system. The authors present results from such a study performed for the Vindhyachal back-to-back HVDC link on a simulator. It was found that the HVDC system could contribute negative damping to some of the torsional modes of oscillations of turbine generator units on both sides of the link. By modulating the firing angle of the converters with a signal generated from a wideband type of SSO controller, it was found that the oscillatory modes are well damped