Research On DC Transmission Control Strategy For Power System Restoration

As the mainstream topology of HVDC transmission,MMC-HVDC has the advantages of large dynamic capacity,high security and stability,high controllability and so on.It has been widely applied in HVDC transmission,high-power converter and other occasions.This thesis discusses the feasibility of MMC-HVDC as the starting power of black start,and analyzes the working principle,control strategy,the ability of load recovery.In this thesis,the circuit topology,control strategy and mathematical model of MMC-HVDC are introduced,and the basic principle of MMC-HVDC is analyzed.Secondly,the formation mechanism of frequency overvoltage caused by capacitive effect on charging long no-load lines and the formation mechanism of switching overvoltage caused by switching on no-load lines is analyzed,and the corresponding control strategy of MMC-HVDC suppressing overvoltage is designed.Aiming at the problem of frequency and voltage fluctuation when starting the non-black-start unit,a control strategy based on voltage and frequency feedback regulation is designed.Finally,according to the principle of black start,a complete grid restoration scheme based on MMC-HVDC as a black start power is designed,and the whole process of black start is simulated by PSCAD/EMTDC.The results of simulation show that during the process of black start restoration,the voltage and frequency of the system are in the required range of stability,which validates the feasibility of MMC-HVDC as a black start power source for power grid restoration.