Synchronous motor and control method of synchronous motor

A method for controlling a synchronous motor including a three-phase inverter for supplying three-phase AC voltages of variable amplitude and frequency and position sensors for detecting the magnetic poles of the synchronous motor, wherein a microcomputer incorporated in the synchronous motor executes said method and said method comprises steps of:

• an input current detection step of converting the detected input current or a value equivalent to the detected input current to the corresponding digital quantity;
• a motor speed calculation step of digitally calculating the speed of the synchronous motor on the basis of the outputs of the position sensors;
• a digital communication reception step of receiving through communication a digital speed command value, a digital input current command value or a digital input power command value from outside the synchronous motor;
• a digital feedback control step of adjusting the amplitudes and frequency of the AC voltages outputted from the three-phase inverter in such a manner that the speed of the synchronous motor, the input current or the input power approaches the speed command value, the input current command value or the input power command value, respectively;
• and
• a digital communication transmission step of transmitting the digital signals representing the motor speed, the input current or the input power to outside the synchronous motor.