Abstract: A method and apparatus are disclosed for controlling a pulse width modulated (PWM) inverter controlled for ignition by a (PWM) pulse produced with a carrier wave and a modulation wave. The method comprises sampling an amplitude of the modulation wave at a cycle rate related to the frequency of the carrier wave. The modulation wave and the carrier wave are synchronized when the sample modulation wave amplitude has a peak value greater than an amplitude of the carrier wave. The modulation wave and the carrier wave are asynchronized when the sampled modulation wave has a peak value less than the amplitude of the carrier wave.

Abstract: A control system for controlling a PWM inverter so that the inverter drives an induction motor at a variable voltage and a variable frequency while keeping constant a ratio of the output voltage of the inverter to the output frequency thereof, is disclosed which includes current component detecting means for detecting an effective current corresponding to a load, from the input current of the induction motor, frequency setting means for setting the output frequency of the PWM inverter, flux setting means for setting the amount of magnetic flux generated in the induction motor, correcting-frequency calculating means for calculating a frequency correcting quantity proportional to the effective current, and correcting-flux calculating means for calculating a flux correcting quantity proportional to the effective current.

Abstract: When an abnormality is detected during driving of an inverter, the output of the inverter is interrupted for a period of several milliseconds and then operated again. At this time, if no abnormality is detected, driving is continued, while if an abnormality is again detected, driving is stopped.

Abstract: A PWM inverter system for converting DC power to AC power comprises an output voltage setting circuit for generating a pattern of output voltage value corresponding to a speed command value, an oscillator for generating a pulse train having a frequency proportional to the speed command value, a frequency division circuit for dividing the frequency of the pulse train produced by the oscillator to produce interrupt pulses, a pulse interval measuring circuit for measuring a pulse interval between predetermined ones of the interrupt pulses supplied from the frequency division circuit, an arithmetic unit responding to the input of the interrupt pulses from the frequency division circuit to produce a timing signal corresponding to the timing at which said interrupt pulse is inputted and update data associated with current operating phase relative to a fundamental wave, to thereby produce pulse width data corresponding to the result of multiplication of a value associated with the output voltage value supplied from