The rotational speed of the induction motor estimation apparatus and method for estimating

摘要

PPROBLEM TO BE SOLVED: To reduce an estimation error in the rotating speed of an induction motor even when there is a voltage difference in the output of a PWM inverter. PSOLUTION: An estimator for the number of revolutions of an induction motor is so configured that the following is implemented: an induction motor 1 is controlled through a PWM inverter 2 according to a voltage command; an alternating-current voltage oscillator 6 produces a single-phase alternating-current voltage with a swept frequency; a primary current obtained when the alternating-current voltage is applied to an idling induction motor is detected with a three-phase/two-phase converter 4; and the number of revolutions of the induction motor is estimated from the ratio of minor axis/major axis of an ellipse drawn by the resulting current Lissajous figure. An amplitude computing unit 9A determines a current amplitude from αβ axis components of the current Lissajous figure with resect to each sweep of the frequency of the single-phase alternating-current voltage. A frequency adjuster 9B reduces the carrier frequency of the PWM inverter until the maximum value of current amplitude becomes equal to or higher than a reference value. After an estimation of the number of revolutions carried out when the maximum value of current amplitude becomes equal to or higher than the reference value, the frequency adjuster returns the carrier frequency to the original frequency. PCOPYRIGHT: (C)2011,JPO&INPIT