Abstract: A pulse width modulation inverter is controlled by the use of the fundamental wave voltage E.sub.1 of the inverter output as a feedback quantity, the fundamental wave voltage E.sub.1 being obtained as the product of a function g(K.sub.H) which is determined by the amplitude ratio K.sub.H of a carrier wave and a modulated wave, and a d.c. voltage E.sub.D input of the inverter.

Abstract: Disclosed is a method and apparatus for operating an induction motor by an inverter of the pulse-width modulation (PWM) type, wherein the slip frequency is calculated from the speed command and the actual motor speed so as to produce the phase compensation signal, and the frequency command for the inverter is produced by adding the phase compensation signal, the slip frequency signal and the motor speed signal. The primary current command is calculated from the slip frequency, the amplitude ratio of pulse-width modulation is calculated basing on the primary current command and the actual primary current, and the inverter is controlled in accordance with the amplitude ratio so as to control the primary current of the induction motor.

Abstract: An amplitude ratio K.sub.H of a specific level of a modulating wave and a crest value of a carrier wave is introduced into control of a pulse width modulated inverter, and a desired pulse width modulating signal is calculated by a microcomputer, using the amplitude ratio K.sub.H as a control variable.

Abstract: A pulse width modulation inverter in which a staircase wave signal is used as the modulating wave. The number M of the stair steps of the staircase wave signal is set at a given integer in a range defined by 2.ltoreq.M.ltoreq.(N-3)/2 where N represents the number of the carrier waves appearing during a half period of the staircase wave and an odd integer not smaller than 7.

Abstract: When a power conversion apparatus such as inverter or chopper comprises gate turn-off thyristors (GTO's), current limiting reactors are connected to cathodes of the GTO's and opposite ends of each of the reactors are connected to positive and negative terminals, respectively, of a gate power supply which supplies a turn-on current and a turn-off current to the respective GTO. With this arrangement, an energy stored in each of the reactors at the turn-off of the GTO is absorbed by the gate power supply.

Abstract: A control device for a pulse-width modulated inverter comprises means for generating as a carrier wave a triangular wave synchronizing with an AC output from the inverter, means for generating as a modulating wave a train of rectangular wave pulses which synchronize with the triangular wave and have a width corresponding to a section effective for a modulating operation and a predetermined amplitude, voltage level setting means for setting the amplitude of the train of rectangular wave pulses, and means for modulating the triangular wave with the train of rectangular wave pulses and generating a control pulse for the AC output.