Driving apparatus for electric motor

A driving apparatus for an electric motor, comprising:

• an inverter;
• a current detector configured to detect an output current of the inverter;
• and
• a vector controller configured to transform the output current, detected by the current detector, into a torque current and a magnetization current, and to control the torque current and the magnetization current,
• wherein the vector controller comprises:
• a three-to-two phase transformation section configured to transform three-phase currents, detected by the current detector, into two-phase currents;
• a stationary-to-rotational coordinate transformation section configured to transform the two-phase currents on a stationary coordinate system, which have been transformed by the three-to-two phase transformation section, into a torque current and a magnetization current on a rotating coordinate system;
• a torque-voltage control section configured to determine a torque-voltage command value based on a deviation between a torque-current command value and the torque current;
• a magnetization-voltage output section configured to output 0 as a magnetization-voltage command value;
• a rotational-to-stationary coordinate transformation section configured to transform the torque-voltage command value and the magnetization-voltage command value on a rotating coordinate system into a torque-voltage command value and a magnetization-voltage command value on a stationary coordinate system;
• a two-to-three phase transformation section configured to transform the torque-voltage command value and the magnetization-voltage command value, which have been transformed by the rotational-to-stationary coordinate transformation section, into three-phase voltage command values;
• a velocity calculator configured to calculate an angular velocity of a rotor of the electric motor from the magnetization current, a magnetization-current command value, and the torque-voltage command value;
• a target-torque-current determination section configured to determine the torque-current command value based on a deviation between the angular velocity and an angular-velocity command value;
• a target-output-voltage determination section configured to determine a target-output-voltage value from the angular velocity of the rotor;
• and
• a target-magnetization-current determination section configured to determine the magnetization-current command value based on a deviation between the torque-voltage command value and the target-output-voltage value.