Research on the Wide-Band Oscillation in the Flexible HVDC Transmission Systems

This research comprehensively investigates the broadband oscillation issues associated with the integration of wind energy into Flexible High Voltage Direct Current (Flexible HVDC) transmission systems. The research employs the impedance scanning method to identify critical regions of system instability, including capacitive and inductive impedance, zerocrossing points, and negative resistance. Detailed analysis of oscillation attributes reveals the impact of converter and grid parameters, as well as environmental conditions, on frequency, damping, and stability. The research identifies sub/supersynchronous and medium to high-frequency oscillations, attributing them to control parameter misalignments and AC line length. Specifically, the research highlights the role of excessive proportional control gains in HVDC systems and DFIG wind turbine grid-side converters' PLL in inducing oscillations. The findings offer critical insights for the optimization of control strategies, aiming to mitigate oscillation risks and ensure the stable and secure transmission of renewable energy, thereby advancing the theoretical understanding and technical application of HVDC systems in the context of renewable energy integration.