Abstract: In a power conversion device according to the present invention, an AC power source voltage signal Vac which is the instantaneous value of AC power source 1 detected by a power source voltage detection circuit comprising a transformer 5, rectifier 6 and A/D converter 7 is averaged by an averaging circuit 9 and an average AC power source voltage signal Vave is output. This average AC power source voltage signal Vave and AC power source voltage signal Vac are compared in comparator 8 and, if their deviation is more than a prescribed value, a power source voltage drop detection signal PSF_S is output. Spurious detection of power source voltage drop resulting from the effect of power source fluctuations can thereby be prevented.

Abstract: In a power conversion device according to the present invention, an AC power source voltage signal Vac which is the instantaneous value of AC power source 1 detected by a power source voltage detection circuit comprising a transformer 5, rectifier 6 and A/D converter 7 is averaged by an averaging circuit 9 and an average AC power source voltage signal Vave is output. This average AC power source voltage signal Vave and AC power source voltage signal Vac are compared in comparator 8 and, if their deviation is more than a prescribed value, a power source voltage drop detection signal PSF_S is output. Spurious detection of power source voltage drop resulting from the effect of power source fluctuations can thereby be prevented.

Abstract: According to this invention, there is provided a motor control apparatus comprising a field weakening device for converting a velocity feedback signal obtained from the rotational speed of a motor into a secondary magnetic flux reference signal by using a field pattern, a field pattern selector for comparing a predetermined signal with a q-axis torque current reference signal obtained on the basis of the secondary magnetic flux reference signal converted by the field weakening device, the velocity feedback signal, a velocity reference signal, and a torque reference signal, and outputting, on the basis of the comparison result, a control signal for switching the field pattern, and a field pattern storage section for switching, on the basis of the control signal output from said field pattern selector, the field pattern to be used in the field weakening device. Since the selector can switch the field pattern, an accurate torque output can be realized.