JPS6450792A - Inverter - Google Patents

Abstract

PURPOSE:To enable a motor to be always driven at the highest efficiency point, by comparing a detection power-factor at the time of driving the motor, with a previously stored optimum power-factor value, and by controlling output voltage. CONSTITUTION:From a reference voltage setting unit 12, the output of reference voltage V according to desired frequency f is generated, and from a reference power-factor generator 15, the output of a reference power-factor PF' is generated according to the frequency f. In this case, the V/F pattern and optimum power-factor pattern of the output voltage and frequency are stored on memory. Besides, by a temperature correcting device 14, according to the detection value of a temperature detector 11, the reference power-factor PF' is corrected. In the meantime, by a power-factor detector 10, a power-factor PF at the time of driving a motor is detected. Then, by an output voltage correcting device 13, according to a difference component between the reference power-factor PF' and the detected power-factor PF, the reference voltage V is corrected. By a PWM signal generator 9, according to the set frequency f and voltage V of provided input, a switching element 3 is driven.