Studies on the effects of thyristor dynamic extinction angle on HVDC commutation failure

This paper focuses on the key technology of ultra high voltage direct current (UHVDC) converter valve equipment which is resistant to commutation failures. The simulation model is established, which can reflect the whole turn-off process of thyristor. The paper also offers the simulation models of converter valve model and of the double-fed high voltage direct current (HVDC) system. The transient fault and the failure mechanism of commutation failure are studied. The internal and external factors that affect commutation failure are analyzed in depth and the impact of operating conditions on commutation failure is quantified. The calculation method of the thyristor dynamic turn-off time and the related key technical indexes are proposed to optimize the commutation characteristics of the high power thyristor. This paper presents the method of intelligent trigger detection, such as forward voltage monitoring method, turn-off angle direct measurement method and minimum turn-off angle estimation method, together with their application approach in multi-infeed HVDC system (MIDC). The intelligent trigger monitoring device and the converter valve module prototype which is resistant to commutation failure are developed, and then verified by functional test.