High Frequency Oscillation Analysis of Flexible DC Transmission System Based on Modular Multilevel Converter

High Voltage Direct Current Transmission based on modular multilevel converter (MMC-HVDC) may have a wide frequency range of oscillation risks. In order to reproduce the high frequency oscillation of the MMC-HVDC system and analyze its oscillation characteristics, a Four-machine Two-area MMC-HVDC system with wind turbine was built based on MATLAB/Simulink, realized the power transmission between the two areas through MMC-HVDC system. The influence of the outer loop controller, inner loop controller parameters and delay link time constant changes on the characteristics of high frequency oscillations of the MMC-HVDC transmission system of the modular multilevel converter is studied on the built system. The results show that the outer loop controller parameters has little effect on the high frequency oscillation, while the current inner loop controller parameters can significantly affect the high frequency oscillation of the MMC-HVDC system. The delay link also has a significant impact on the high frequency oscillation of the system, and the risk of high frequency oscillation of the system increases with the increase of the long link delay parameter.