CONTINUOUS-TIME STATE-SPACE MODEL OF VSC-HVDC AND ITS CONTROL STRATEGY

The paper presents an equivalent continuous-time state-space model of VSC-HVDC in the synchronous dq reference frame.The d-and q-axis of voltage source converter(VSC) model are decoupled using the feed forward compensation method.Therefore,independent control of active and reactive power,DC voltage and reactive power is achieved.Cascade control scheme to be applied to develop power and voltage control.Based on the model,control strategies for VSC-HVDC have been proposed respectively for the cases of connecting active systems and supplying passive systems.The concept of space vector is utilized for the case of supplying passive systems.The simulation results performed on PSCAD/EMTDC verify the validity of the mathematical model and the feasibility of the control strategies effectively.