PURPOSE: To improve the power performance by setting an increase rate to the rotational speed of a motor of a field current command determining the intensity of field weakening at a value smaller than that of the field current command at the time of partial load operation.
CONSTITUTION: The revolution of a rotor is converted into a binary signal by an interface 52, and changed into the angle of rotation θ on the basis of conversion display stored in a ROM 54. The binary signal is converted into voltage V proportional to rotational speed by an F/V converter 56. Two phase currents iu, iw in the three-phase armature windings of a motor 12 are inputted to a three-phase two-phase converter 60 through an A/D converter 58. The three-phase two-phase converter 60 feeds back flux currents id and torque currents iq to a current amplifier 62. The current amplifier 62 obtains a d-axis voltage command Vd* and a q-axis voltage command Vq* on the basis of a torque command iq* and a field current command id*. Fueld-weakening control characteristics weak ening the grade of the field current command id* for determining the intensity of field-weakening control with the reduction of load are stored in a field command generating circuit 74.
MURATA KAZUHIRO
TAKANO TADASHI
