Research Of Operation And Control Of The VSC-MTDC

VSC-HVDC, shorting for VSC-based high voltage DC transmission,is a new DC transmission technology based on full-controlled power semi-conductor-VSC.There are two kinds of VSC-HVDC system,two terminals and multi-terminals system.The number of VSC of the later system should be more than three.This dissertation focuses on the operation and control of the VSC-based multi-terminal HVDC system.Firstly,a static model of VSC in dqO coordinate system is developed. After that, controllers for rectifier and inverter are studied.double-loop controller and instant AC voltage controller are also designed respectively.In order to confirm the effectiveness of those controllers,a simulation in Matlab/Simulink is necessary.Several operating modes for the VSC-MTDC system are analyzed and controllers are designed for the VSC converters operating under every mode in the next chapter. There are two kinds of operating strategy, voltage-droop strategy and master/slaver control strategy presenting in this dissertation.Based on that.an improved mutil-terminal DC-voltage control strategy is developed.This stragety can’t only improve the DC voltage’s quality,but also can increase the utilization of VSCs.At the end of this dissertation, normal master controller for multi-terminals is introduced firstly. Then the influence of master controller to the VSC is studied on the base of three-terminals VSC-MTDC.The result of simulation shows that the master controller can change state of the VSCs by adjusting the power distribution.