The Extreme Temperature Weather Impact Mechanism Analysis of MMC-HVDC’s Harmonic Impedance and Its Dynamic Stability

In recent years, the small-signal stability of modular multilevel converter (MMC)-based high-voltage direct current (HVDC) systems has garnered significant attention. But little attention has been paid to the impact of extreme temperature weather, although it may change the parameters of outdoor devices and lead to oscillations in a weak system. To explore the impact of environmental temperature on the stability of the MMC-HVDC system, this paper firstly establishes a comprehensive harmonic state space (HSS) model, incorporating the effect of temperature on the impedance of AC and DC transmission lines based on the thermal balance equation. By comparing the theoretical and simulation results, the accuracy of the model is validated. Subsequently, the mechanisms through which extreme temperature conditions affect system stability were analyzed. The results indicate that under extreme high-temperature conditions, the impedance of the MMC is significantly affected, weakening system stability and potentially causing small-signal instability. In contrast, extreme low-temperature conditions show no noticeable impact on system stability.