Patent ID: 8664899

Claim:
A motor drive control device having a three-phase full bridge circuit composed of elements having diodes for passing currents in reverse direction provided in parallel to each switching element, for converting a direct-current power supply, or a dummy direct-current power supply obtained by rectifying and smoothing an alternating-current supply, into a dummy three-phase alternating current of arbitrary voltage and arbitrary frequency in the three-phase full bridge circuit, and driving the motor at a desired rotating speed, wherein the dummy three-phase alternating current is a dummy three-phase alternating current cyclically repeating positive direction feeding period, non-feeding period, negative direction feeding period, and non-feeding period in each phase, further comprising: a control circuit for detecting the terminal voltage of the motor in non-feeding period, obtaining the time of change of terminal voltage from positive to negative as the time of change of corresponding phase current from negative to positive, obtaining the time of change of terminal voltage from negative to positive as the time of change of corresponding phase current from positive to negative, and adjusting the phase of applied voltage so that the difference between the current phase based on each obtained current change time and the phase of alternating voltage at the motor terminal generated as a result of the applied voltage has a predetermined value, wherein in the dummy three-phase alternating current, the absolute value of terminal voltage generated from each bridge in feeding period is a constant voltage with respect to a neutral point potential of a direct-current portion, wherein the absolute value of terminal voltage generated from each bridge in the feeding period is adjusted on the basis of the deviation between an actual rotating speed and a desired rotating speed, and wherein when an actual rotating speed is lower than a desired rotating speed and if the absolute value of the terminal voltage is smaller than a maximum possible value, a ratio of non-feeding period is increased, and a feeding start phase is adjusted so that a current polarity is inverted right after coming into non-feeding period.