Successive commutation failure mechanism analysis and prevention of multi-infeed HVDC system considering reactive power and harmonic interaction

This paper studies the successive commutation failure (SCF) mechanism considering the reactive power and harmonic interaction of multi-infeed high voltage direct current (MIDC) system. It is found that the increase of reactive power exchanged on tie line leads to the decrease of AC voltage amplitude of healthy line during the SCF development stage, so the probability of SCF increases due to the reactive power interaction. Besides, the voltage distortion components in AC voltage of healthy line caused by harmonic interaction plays a negative role on commutation process, which may lead to SCF. Also, there is nonlinear coupling between the effects of reactive power and harmonics on SCF. Thus, the reactive power impact index (RPII) and the voltage distortion index (VDI) are proposed to assess the reactive power impact degree and voltage distortion degree of DC line, respectively. Furthermore, the SCF prevention strategy of MIDC system is proposed, which is realized by reducing the advance angle of faulty line based on RPII and triggering the healthy line earlier based on VDI. Finally, the simulation models of MIDC CIGRE benchmark system and Henan multi-infeed UHVDC system are built, and the effectiveness of the proposed SCF prevention strategy is verified under different fault types.