Abstract: A control for an inverter operable for converting direct voltage and current to alternating voltage and current. The inverter includes a plurality of electrical valves each operable to conduct current in a single direction upon the application of a positive voltage in the forward direction and the receipt of a trigger pulse. The control provides successive trigger pulses for commutating the current between successive valves at predetermined electrical firing angles and includes a voltage-time area calculating circuit for calculating the maximum permissible firing angle which will permit successful commutation. An inverter commutation failure prevention circuit is coupled to the alternating current network for detecting abnormal voltage conditions and for producing a control signal functionally related to any deviation in the alternating voltage from the expected voltage condition. The control is responsive to the control signal for reducing the electrical angles of the trigger pulses provided to the valves.