Evaluation of HVDC transmission capability for hydro-wind-solar hybrid power bases considering frequency and voltage support strength

Large-scale hydro-wind-solar integrated power bases exhibit the fundamental characteristics of multi-energy sources, weak grid structure, and limited local loads. Thus the transmission export capability of its large-scale clean energy through HVDC connection is severely subject to system security and stability. With regards to the issue of frequency/voltage support capabilities weakened by high penetration of renewable energy, this paper develops an HVDC transmission capability evaluation model incorporating frequency and voltage support strength. Firstly, a coordinated assessment framework is established based on the analysis of the constraints limiting HVDC transmission capabilities. Next, by integrating spatio-temporal hydraulic-electric constraints of river basin cascade hydropower generation and considering complementary operation of hydro-wind-PV energy resources, a transmission capacity optimization model with the objective of maximizing delivery power is formulated via mixed-integer second-order cone programming method. Finally, security constraint frameworks covering frequency/voltage support requirements are constructed by quantifying system frequency response capability and short-circuit ratios of multiple renewable plants. Furthermore, by taking advantage of second-order cone reconstruction techniques to efficiently process nonlinear frequency constraints, a transmission capacity evaluation methodology is then formulated which balances the multi-energy complementarity and system security requirements. Case studies on modified IEEE benchmark systems are conducted to validate the model's effectiveness through multi-scenario simulations.