Adaptive Dual Droop Control Strategy of VSC-HVDC for Supporting Frequency Stability of Sending-End System with Renewable Energy

[Objective] The increasing penetration rate of renewable energy has decreased the inertia of power systems. The traditional fixed-parameter frequency control strategy makes it difficult to effectively support system frequency stability requirements. Frequency stability faces severe challenges， especially in renewable energy sending systems. [Methods] To enhance the frequency support performance of VSC-HVDC for sending-end systems with renewable energy， an adaptive dual droop control strategy based on changes in system frequency and DC voltage is proposed. First， a model of renewable energy transmitted by a VSC-HVDC system was established. For frequency droop control， a frequency-adaptive coefficient was designed based on the logistic function of frequency deviation to enable the system to dynamically adjust the droop coefficient and respond flexibly to frequency changes. For the DC voltage droop control， via the coupling relationship between DC voltage and active power using virtual inertia technology， the DC adaptive coefficient was designed as the adaptive virtual inertia coefficient based on the frequency deviation and the rate of change of frequency to enhance the system’s ability to suppress frequency fluctuations. Finally， a simulation model based on the PSCAD/EMTDC platform was established， and a comparison study with the traditional method in different scenarios was performed. [Results] The results show that the proposed strategy reduces the maximum frequency deviation by more than 10% in various scenarios while increasing the maximum utilization of the VSC-HVDC system by over 10%. [Conclusions] Compared with traditional methods， the proposed strategy can significantly reduce the maximum frequency deviation and effectively improve the frequency support performance of VSC-HVDC systems.