Modal control of an HV DC system for the damping of subsynchronous oscillations

A novel control scheme is presented for the design of a supplementary subsynchronous damping controller (SSDC) equipped at the rectifier end of an HVDC link that is connected in parallel with an existing resonating AC line. To stabilise the unstable subsynchronous resonance (SSR) modes, an approach based on modal control theory is developed for the design of the SSDC. Since the subsynchronous oscillations resulting from high levels of compensation on the AC line can be effectively damped out, the power transfer capability of the AC line can be enhanced by the proposed SSDC