Independent real time control of output frequency and voltage of pwm

Abstract

An inverter for driving a motor, when a command frequency is given, the output voltage is increased as output current is increased as to optimize motor efficiency under varying load conditions. The inverter is comprised of a converter to convert an input ac voltage to a dc voltage, a current sensor to measure an output current for determining a load level of the motor, a voltage setting means to calculate a command voltage as a function of a command frequency and the measured current, an encoding means to issue on a real time basis bit patterns containing information on the command frequency and the command voltage, a decoding means to decode the bit patterns into a pulse width modulated (PWM) signal, a clock means to provide a timing signal for the encoding means and the decoding means, and an inverter to modulate the dc voltage by the PWM signal, thereby applying the motor input voltage to the motor.