Impedance model-based stability analysis of grid-connected converters under wide-range operating conditions

Recently, the converter-based renewable power generation systems have caused severe oscillation issues, for instance, the subsynchronous oscillation (SSO). To analyse these oscillations, the impedance model (IM)-based method has been widely used due to its efficiency and accuracy. In existing works, the IM-based analyses are usually carried out under a specific operating condition. However, the IM is affected by the operating condition, which means the IM-based analysis results will be invalid if the operating condition changes. To overcome this defect, this paper proposes an operating-condition-dependent IM of the voltage source converter (VSC) first, and this IM is expressed as a function of the active and reactive power. After that, based on the proposed IM, the stability of a grid-connected VSC system is analysed under wide-range operating conditions. Then, a stable operating region (SOR) is further obtained, beyond which the system will be unstable. Finally, the time-domain simulations are done to validate the accuracy of the proposed method in the stability analysis under wide-range operating conditions.