Harmonics Interaction Mechanism and Impact on Extinction Angles in Multi-Infeed HVDC Systems

Harmonics interaction is an important factor in causing concurrent commutation failures (CCF) of multiple converter stations in multi-infeed HVDC (MI-HVDC) systems, but it was not studied sufficiently in existing literature. In this paper, the mechanism analysis and quantitative calculation of harmonic interaction are investigated. Firstly, the generation and interaction process of harmonic during AC fault events in the MI-HVDC systems with single-terminal connection and hierarchical connection on the receiving-end are illustrated, respectively. Then, the common characteristics of harmonic interaction in generalized MI-HVDC systems are concluded. Moreover, to evaluate the impact of harmonic interaction on the commutation process quantitatively, an equivalent circuit model of harmonic transfer in MI-HVDC systems is established. Based on this equivalent model, the harmonic voltage transfer coefficient is deduced, and the extinction angle of inverters considering harmonic interaction in MI-HVDC systems can be calculated. Finally, the calculation accuracy based on equivalent model is verified via the electromagnetic transient simulation of MI-HVDC systems. Simulation results show that harmonic interaction will eventually cause the formation of harmonic sources in each converter station of MI-HVDC systems. These harmonic components will change the extinction angle of remote inverters to increase the risk of CCFs.