Analysis of Transient Voltage-Frequency Dynamic Coupling Mechanism of High-Proportion Renewable Energy Sending End System Under Commutation Failure Faults

[Objective] Aiming at the new challenge of unclear transient voltage and system frequency operation risks faced by sending-end power systems with a high proportion of renewable energy after commutation failure， this paper reveals the dynamic coupling mechanism between transient voltage and frequency at the sending end. This study provides a theoretical foundation for the stable operation of sending-end systems with high-penetration renewable energy. [Methods] A simulation model of a sending-end system with a high proportion of renewable energy is established based on DIgSILENT/PowerFactory. First， the dynamic coupling law of active power transmission and reactive power consumption of the rectifier during commutation failure is analyzed. Based thereon， the impact of renewable energy fault ride-through characteristics on the imbalanced power of the sending-end system is investigated. Second， considering the influence of the changing renewable energy grid-connected proportion on the system inertia constant and node short-circuit capacity， the dynamic coupling law of transient voltage-frequency， with transient voltage as the conduction path， is revealed. [Results] As the system strength gradually decreases with the increase of renewable energy output， the fault coupling characteristics of “low voltage-high frequency” and “high voltage-high frequency” at the sending end after commutation failure become increasingly severe. It is verified that low-voltage ride-through of renewable energy helps suppress frequency rise， although the recovery process of low-voltage ride-through is unfavorable for the frequency to recover from high frequency to power frequency， while high-voltage ride-through is beneficial for frequency recovery. [Conclusions] This paper reveals the voltage-frequency fault coupling characteristics of sending-end systems with a high proportion of renewable energy， where transient voltage acts as the conduction path after commutation failure. Furthermore， an outlook and analysis on suppression technologies for transient voltage-frequency operation risks in such systems are provided.