JPS5838072B

PURPOSE:To continue the operation of a separately-excited inverter, by temporarily advancement angle when the failure in the commutation of the inverter is detected. coupling current-limiting resistors to an inverter DC circuit and increasing the advancement angle when the failure in the commutation of the inverter is detected. CONSTITUTION:When the commutation of the inverter 4 fails at a time to, the inverter suffers from DC short-circuit and its DC voltage E1N drops to zero but the current Id increases. An emergency operation instruction unit 12 detects the failure in the commutation of the inverter to apply an auxiliary input signal to a current regulator 8 and apply a resistor connecting instruction to a controller 11. The controller opens short-circuit switches S1-S3 in accordance with the instruction from the instruction unit 12 to couple the resistors R1-R3 to the inverter DC circuit to limit the current below an allowable level. The inverter is then operated with a controlled advance angle of 90 deg. by the current regulator 8 and put in such a state that the self-restoring capacity of the inverter against the failure in the commutation is raised. When the cause of the failure in the commutation is eleminated, the inverter is restored to normal commutation at a time t4, for example. Therefore, the separately-excited inverter can be restored to normal operation without the useless stoppage of the operation of the inverter.