Research Of Coordinated Control Strategy On VSC-HVDC And LCC-HVDC Hybrid-HVDC System

The hybrid-HVDC topology, which consists LCC and VSC, is the research object of this thesis. It combines their advantages and has extensive application prospects. Hybrid-HVDC can control the active power and reactive power flexible, so it can supply to the weak power grid even passive network. The rectifier and inverter don’t need rapid communication. Comparing to the VSC-HVDC it can reduce the loss and costs. In this thesis, the Hybrid-HVDC system mathematical model was presented, the LCC and VSC control strategy were analyzed, at the same time, a few improvement measures for control strategy of VSC was presented. Using adaptive current limiter to improve the recover ability of ac voltage when the hybrid-HVDC connected ac system occur a serious fault. This thesis analyzed using effective short-circuit ratio (ESCR) to quantitatively evaluate Hybrid-HVDC access ac system voltage stability. The VSC converter valve over-current protection measure was put forward and triggering angle oscillation damping measures was presented. Making an analysis of the control strategy of Hybrid-HVDC when the rectifier side ac system occur a fault.The simulation model of Hybrid-HVDC was built in the PSCAD/EMTDC, The model including a power model and control model of the system. Based on a hybrid-HVDC control system simulation model and the principle of improvement measures, a improved control system simulation model is established. Transient and steady state changes of hybrid-HVDC system were made to test the accuracy of hybrid-HVDC Primary system and control system simulation models built in this thesis.It is proved that hybrid-HVDC primary system simulation model is consistent to real operating system, the VSC converter valve over-current protection control and triggering angle oscillation damping control can effectively improve the system performance. Adaptive current limiter enhances the system voltage recovery ability after the system fault, and increase the value of ESCR, Coordinated control measures of the rectifier and inverter are more conducive to play the role of VSC enhance system stability.