Comparing Research On HVDC Transmission Systems With The Capacitor Commutated Converters

The system performance of a HVDC link applying CCC technology is studied.The mathematical model representing the CCC-HVDC system's steady-state characteristics is derived,which is composed of 15 basic equations.Then the steady-state mathematical model is analyzed by means of numerical computation method,some important advantages of CCC-HVDC systems are revealed vis-a-vis that of LCC based on HVDC system.Moreover,several recommendations on the selection of commutated capacitor's size were presented considering the technological and commercial factors.Then the conventional converter system and the CCC-HVDC system are both modeled on the electromagnetic transient simulation software PSCAD/EMTDC based on Hei-He back to back HVDC bi-polar transmission project.The operation characteristics and recovery performance are analyzed when several faults are applied in the inverter ac-network including close-in AC faults and converters faults.The comparison shows that the CCC converter have a higher operational stability during AC system disturbances,and are able to increase the power transfer capability when connecting to weak AC networks.