Simultaneous inter-area decoupling and local area damping by voltage source HVDC

The voltage-source converter (VSC) has 2 independent control degrees of freedom over P and Q (or P and V). Thus a high voltage DC (HVDC) transmission link based on VSCs (VSC HVDC) has 4 steady-state control freedoms. Of these, 2 are devoted to specifying and to coordinating the real power P through the DC link. This leaves one control freedom at each converter station to control the reactive power Q. Dynamically, the VSC-HVDC link has again 4 control freedoms based on the perturbation variables ΔP and ΔQ (or ΔP and ΔV). Through digital simulations, this paper shows that the two ΔPs can de-couple the inter-area modes and each ΔV (or ΔQ) can simultaneously damp local modes within the area in which the converter station is situated. A mathematical proof for these capabilities is given in an appendix