Power converter

A power converter apparatus for driving a motor, of the type having a control unit responsive to a torque command and a motor speed, for producing a voltage command vector which is given as a rotating coordinate voltage command value defined by reference to two orthogonal axes in a rotating coordinate system, calculating three phase voltage command values based on said voltage command vector, and producing PWM signals;

• and a converter circuit having a plurality of switching circuits comprising:
• a coordinate transformation means for transforming said voltage command vector defined by reference to the rotating coordinate system to voltage command values defined by reference to orthogonal .alpha. and .beta. axes on a stationary coordinate system;
• a section determination means for determining which of a plurality of sections of the stationary coordinate system contains said voltage command vector;
• a three phase voltage calculation means for selecting at least a formula for calculating said three phase voltage command values based on which section of said coordinate system is determined to contain said voltage command vector, and for calculating said three phase voltage command values utilizing said voltage command values by reference to said .alpha. and .beta. axes;
• a sinusoidal wave phase voltage generation means for causing two phase-to-three phase conversion of said voltage command vector;
• an output judgment means for changing an output mode in response to said torque command and motor speed;
• and
• a voltage switchover means for switching between a voltage command from said sinusoidal wave phase voltage generation means and a voltage command from said three phase voltage generation means.