Control device for alternating-current motor

A control device for an alternating-current motor including a rotor and a stator,

• the control device comprising:
• a fundamental wave current control circuit which obtains a current control output which controls a fundamental wave component of a motor current in an axis coordinate system which rotates in synchronization with the rotor with respect to a d axis current which is mainly an exciting current component of a phase current of the alternating-current motor and a q axis current which is mainly a torque current component of the same;
• a higher harmonic current control circuit which controls an e axis current and an f axis current, the e axis current and the f axis current having a frequency which is an integer multiple of a frequency of the fundamental wave component of the alternating motor, the higher harmonic current control circuit realizing the e and f axes current controls on the d axis current control and the q axis current control;
• an addition circuit which adds an output from the fundamental wave current control circuit and an output from the higher harmonic current control circuit;
• and
• an inverter circuit which receives an output from the addition circuit and outputs a motor driving current,
• wherein PI control in the higher harmonic current control circuit is also executed as current control on the d and q axes.

A current control circuit which separates an α phase current and a β phase current as current components of axes which are fixed to a stator and orthogonal to each other with respect to an alternating-current motor including a rotor and the stator, and controls the respective phase currents based on an α phase current error and a β phase current error which are errors from command values of motor currents of the α phase current and the β phase current,

• the current control circuit comprising:
• an α phase proportional unit which multiplies the α phase current error by a predetermined proportional coefficient to obtain an α phase proportional control component;
• an α phase integrator which integrates a difference value between the α phase current error and a coefficient multiple based on a rotational frequency of the rotor as an output from a β phase integrator;
• a β phase integrator which integrates an added value of the β phase current error and a coefficient multiple based on a rotational frequency as an output from the α phase integrator;
• an α phase voltage command unit which adds an α phase integration control component obtained by multiplying an output from the α phase integrator by a predetermined proportional coefficient and an α phase proportional control component as an output from the α phase proportional unit, and outputs an α phase voltage command;
• a β phase voltage command unit which adds a β phase integration control component obtained by multiplying an output from the β phase integrator by a predetermined proportional coefficient and a β phase proportional control component as an output from the β phase proportional unit, and outputs a β phase voltage command;
• and
• an inverter circuit which drives the alternating-current motor based on the α phase voltage command and the β phase voltage command from the α phase voltage command unit and the β phase voltage command unit.