Control and Protection of Hybrid LCC-VSC HVDC Transmission System based on VDCOL Strategy

The combination of line combined converter LCC and voltage source converter VSC technology provides the benefits of both techniques by constituting a hybrid LCC-VSC HVDC system. In this paper to discover the potential and the performances of this system a control design is adopted for both converter considering the protection by using Voltage dependent current order limiter (VDCOL). This technique used to decrease the current reference of LCC HVDC converter station when the voltage at that station is depressed during disturbances. Different case studies are proposed starting with normal operation, DC current variation, reactive power variation, and finally system operation under AC and DC faults. The responses of the system during faults demonstrate the tracking performance and also its ability to protect the stations and limit the references during AC and DC faults. The control strategy is examined by simulations using Matlab/Simulink software.