Research on Spurious Triggering Characteristics during Reverse Recovery for Thyristors

The high power thyristor in HVDC thyristor valve easily suffers a transient voltage with a high rise rate du/dt, especially during reverse recovery, which may cause commutation failure or device damage. The du/dt triggering mechanism during thyristor reverse recovery process is analyzed theoretically based on semiconductor physics and the essential structure of the thyristor. The relationship between initial condition of du/dt triggering and the time point of an impulse voltage applied on a thyristor during reverse recovery is derived by methods of stored charge analysis, which shows that the du/dt threshold of spurious triggering increases exponentially with the increase of the delay of the moment of impulse voltage applied. Meanwhile, experiments are carried out to validate the theoretical analysis, which consider the effects of forward current, impulse voltage and the applied time of impulse voltage. Thereafter, the influence of du/dt triggering characteristics during reverse recovery on the protection design of thyristor valve is discussed. This work wm be beneficial to the protection design of thyristor control unit in HVDC thyristor valve.