Frequency Characteristic Analysis of the VSC-HVDC DC Oscillating Power under AC Sub-Synchronous Disturbances

The DC-side response characteristics of the VSC-HVDC transmission system under AC-side sub-synchronous disturbances may lead to the propagation of AC/DC oscillations, and then there may be non-fundamental frequency oscillation on the DC-side. To clarify the interactive influence mechanism and propagation evolution law of the AC and DC side sub-synchronous oscillations in the VSC-HVDC transmission system, the frequency characteristics of the DC-side oscillation power are investigated by considering the effect of converter control links. First, the AC-side voltage and current frequency responses under single/multiple SSO components are analyzed. Secondly, the frequency characteristics of the DC-side power after the injection of single/multiple SSO components are investigated. Meanwhile, the effect of system control parameters on the sub-synchronous responses of the DC-side power is investigated. Finally, the theoretical analysis is verified with PSCAD/EMTDC simulations. The results show that under the influence of the AC-side SSO components, the DC-side of VSC-HVDC faces the risk of multi-frequency oscillations; when there are multiple SSO components on the AC-side, there is a coupling between the components, and the system control parameters affect the amplitude of the DC-side oscillation power.