Robust control of a VSC HVDC terminal attached to a weak AC system

In this paper a robust controller for a voltage source converter high voltage direct current (VSC HVDC) transmission system is designed. The dynamic behaviour of the power controlling terminal of VSC HVDC transmission varies with the impedance of the attached AC system and the power flow across the DC link. A single controller is sought to provide the performance across a range of operating conditions. First, a linear fractional transformation (LFT) uncertainty model is constructed from a set of linearised models using a technique based on the singular value decomposition. The controller is then designed using a new iterative algorithm which has low conservatism. The controller is obtained by solving a linear matrix inequality (LMI) problem for which efficient solvers are available. The method produces a successful design: numerical simulation confirms the achievement of realistic control objectives for the nominal model, and an acceptable robust performance for all operating conditions.