Abstract: In a separate excitation type inverter device in which an A.C. power source is used as a commutating source, the inverter device is controlled so as to maintain a certain predetermined amplitude of the commutating voltage when the voltage of the A.C. power source is dropped or becomes unbalanced.

Abstract: In an inverter device comprising an inverter bridge connected across a DC source, an auxiliary thyristor bridge connected to AC terminals of the inverter bridge, a condenser connected across cathode and anode electrodes of the auxiliary thyristor bridge which acts as a first switching circuit for charging and discharging the condenser and a second switching circuit including choppers for connecting anode and cathode electrodes of the auxiliary thyristor bridge across the DC source, there is provided a control method which comprises the steps of comparing voltage of the condenser with a reference voltage, controlling respective switching circuits so as to effect commutation of the inverter bridge in a direction to charge the condenser when the voltage thereof is lower than the respective voltage, controlling respective switching circuits so as to effect commutation of the inverter bridge in a direction to discharge the condenser when the voltage thereof is higher than the reference voltage thereby controlling

Abstract: In a system for controlling field of an induction machine such that the torque of the induction machine is reduced in proportion to a running speed thereof a frequency-voltage converter converts the frequency of a pulse signal (f.sub.N or f) given from or to the induction machine into a voltage. A function generator varies the voltage into an output (V.sub.FG) of a predetermined variation characteristic. A multiplier multiplies the output with a reference value (I.sub.2) indicative of a desired torque. And a voltage-frequency converter converts the product into a frequency (f.sub.S) used for the control of the induction machine.

Abstract: In a method and apparatus for controlling an AC power supply from a power source to a load having a considerably large inductance through electric valve means, the ignition phase angle of the valve means is limited to a value greater than the angle of the power factor. The limiting value is calculated for each cycle based on the power source voltage and a turn-off period of the valve means in the cycle immediately preceding the aforementioned cycle.According to this invention, it is possible to automatically control the ignition of the electric valves over the entire cycle.

Abstract: A pair of switching elements are provided between a source of direct current and a bridge type inverter for commutating together. A commutating circuit having a capacitor is connected in parallel with the bridge type inverter to rapidly commutate the bridge type inverter. The commutating circuit operates so as to apply a voltage of inverse polarity to the thyristor of the inverter when a switching element operates.

Abstract: A crane motor control is disclosed which includes a variable D.C. voltage supply in a Ward-Leonard set which is controlled by a load torque signal obtained by sensing the armature current of a motor, magnetic flux in the motor field winding and the rate of change of motor speed. The torque signal controls the variable D.C. voltage supply to keep the motor armature current or the motor field current at a preset constant value upon completion of motor acceleration.