Commutation failure of DC motor drives from voltage sags during regeneration

DC motor drives are susceptible to nuisance tripping and faults during voltage sags. DC drives incorporating regenerative bridges are particularly vulnerable, and will often fault during a short-duration voltage sag. These faults can result in blown fuses or damaged power electronic components, and cause extended downtime for the end-user. During a voltage sag, thyristors can fail to commutate properly, leading to a ldquoshoot-throughrdquo fault or short circuit in the power electronic circuits. Commutation failure occurs chiefly because the thyristors are line commutated, and voltage sag can lead to insufficient voltage to commutate - causing a fault when a subsequent thyristor is fired. There are several possible scenarios that can cause commutation failure. This paper explores voltage sag situations that can cause commutation failure, simulations of DC drives operating in these situations, and experimental results that demonstrate commutation failure and faults in regenerative DC drives.