Load Characteristic Influence on Power Oscillation Damping : Case Study on HVDC-interconnected AC-Grids

Sammanfattning: The increasing share of renewables in the electric grid may have a negative impact on the systemstability to which conventional control methods are insucient. The report focuses on the stabilityof low frequency inter-area modes. Along the development of renewables, power electronics aremore frequently used between the actual load and the grid. Hence the characteristics of the loadsis undergoing a change as well. This report investigates how dierent load characteristics inuencethe damping in the grids. The investigation is performed by a simulation experiment where a modelconsisting of two AC-grids interconnected via an HVDC-link is implemented in two simulation softwareprograms, PSCAD and Simulink. The HVDC-link has an implemented active power oscillationdamping control to improve the damping of the overall system. The report also review which softwarethat is most suitable for the given investigation. It is shown that active power loads contributesto the damping best if they are modelled as constant impedance loads and less for constant powerloads. Reactive loads with inductive behaviour contributes to the damping best if they are modelledas constant power loads and contributes least if they are constant impedance loads. The evidencesuggest that the damping provided by the loads is uncorrelated with the damping provided by theHVDC-link. The simulation software that suited the author's preference best was Simulink. Theseresults contribute to the understanding of how loads inuence the system damping and can be usedin future studies, where it is interesting to know if the load damping is over or underestimated.