Control of high voltage direct current links with overall large-scale grid objectives

Abstract

When a high voltage direct current (HVDC) link connects two distinct power systems, the latter are usually modelled by two infinite buses. However, in some context of use, the HVDC links are no longer separating two systems but they are embedded into meshed AC systems in parallel with other AC lines and interact with other elements of the power system. This led us to enhance the control objectives by considering stability requirements. In this context, the previous modeling assumption presents serious limitations. Instead, a more efficient control model is used. It is developed such that the concerned dynamics of the system are taken into account during the synthesis. It is shown how the controllers of the HVDC converters can be synthesised using the control model mentioned above such that global grid performances are ensured, in addition to the local objectives like power and DC voltage control. In order to avoid remote measures, an output feedback control which uses only local measures is developed. The new controller is tested in comparison with the standard vector control and a non-linear feedback linearisation control via simulation tests. The tests showed that the controller synthesised using the new control model contributes to a better coordination of the control actions and thus improve grid performances. In particular, the transient stability of the neighbour zone is a priori taken into account at the synthesis level.