Coordinated damping control through multiple HVDC systems: A decentralized approach

The role of multiple HVDC links - both CSC and VSC - in improving the AC system dynamic performance is presented here. An Australian equivalent system with three critical inter-area modes is considered through case studies performed in DIgSILENT PowerFactory. Subspace-based multi-input-multi-output (MIMO) system identification is used to estimate and validate linearized state-space models through injecting pseudo random binary sequence (PRBS) probing signals at the HVDC controller inputs. Choice of appropriate input-output combinations is done through modal residue analysis taking note of not only the magnitudes but also the phase angles. The decentralized control design is posed as an optimization problem and solved using an evolutionary technique. The results are validated through linear analysis and non linear simulation in DIgSILENT for two extreme (light and heavy loading) operating conditions.