Mechanism Analysis of HVDC Commutation Failure Influence on AC Power Network Relay Protection

In the AC/DC interconnection system,the DC commutation failure caused by AC power network fault can lead to maloperation of AC power network protection.In this paper,under the commutation failure condition,a switching function model of inverters and a transient change model of DC current were established.According to modulation theory and convolution theorem,the dynamic phasor model of DC system equivalent current of power-frequency component variation was deduced.The analysis shows that the variation characteristics of the equivalent current of power-frequency component variation are different from those of pure AC system,which may lead to maloperation of AC power network protection under the DC commutation failure caused by AC power network fault.At last,combining the two specific AC power network protection,the mechanism for maloperation of AC power network protection caused by DC commutation failure was analyzed,which provided a theoretical basis for research on protection strategy of AC/DC interconnection system.