MEDIUM-/HIGH-SPEED VARIABLE FREQUENCY GOES OPERATIONAL.

The first operational installation of variable voltage, variable frequency control system configuration is introduced with control components consisting of converters, an inverter and a digital regulator and a drive component made up with a helical gear reducer and an ac induction motor. A three-phase ac source is converted into dc voltage through a thyristor converter. This is then turned into three-phase variable voltage and variable frequency ac through a transistor inverter and supplied to the ac induction motor. Rotating speed of the induction motor is directly proportional to the frequency of the input power source when the magnetic flux of the motor is maintained at a specified value by controlling the input voltage. Pulse Width Modulation (PWM) is utilized to regulate the frequency output and the voltage of the inverter. dc voltage output from the converter is treated by high-frequency chopping to modulate its pulse width and produce ac voltage. Voltage is regulated by modulating the size of the pulse width, and frequency, by modulating the cycle of pulse width. Thus, the voltage and frequency can be varied most appropriately in order to respond to speed-command signals.