Patent US 4,151,586

Upon a stop command, the current conducting state of the main valves and the recovery valves of an inverter with bridged valves is monitored. A change of the firing pulses for the main valves is blocked if the valves connected to one d-c bus of the inverter conduct current simultaneously. After a predetermined time has passed or upon the arrival of a monitoring signal that the current in the inverter is extinguished, the transmission of the firing pulses to the controlled main valves of the inverter is then blocked.