Analytically Evaluating the Impact of Voltage Stability on Commutation Failure in Multi-Infeed LCC-HVDC Systems

Both the local and concurrent commutation failures (LCF and CCF) are concerned threats to the secure operation of multi-infeed LCC-HVDC (MIDC) systems, which will be largely impacted by the voltage stability. However, this impact has not been clearly revealed yet by earlier works due to the lack of the related analytical evaluation method. Thus in this paper, the analytical evaluation method related to the LCF and CCF with the voltage stability in MIDC systems is firstly proposed considering the complicated inter-inverter interactions. This is realized by deriving the analytical expressions of the LCF and CCF immunity indices (LCFII and CCFII) as the functions of the voltage stability factor (VSF) based on the system quasi-steady-state models. Moreover, the proposed method is used to clearly evaluate the impact of the voltage stability on the LCF and CCF by comprehensively conducting the parametric dependence analysis of the LCFII, CCFII, and VSF versus various system parameters and operation variables. The analysis results indicate that in some certain situations, increasing the voltage stability of MIDC systems however imposes an unexpected negative impact on the LCF and CCF. Finally, the simulation results of the PSCAD/EMTDC program based on a tri-infeed LCC-HVDC system validate the theoretical developments.