Control apparatus for a synchronous motor

A control apparatus for a synchronous motor having

• an inverter that converts power supplied from an AC power supply into a desired output voltage and frequency to drive a synchronous motor;
• a current detector for detecting the output current of the inverter;
• a voltage detector for detecting an output voltage of the inverter;
• a. position detector for detecting the rotation angle of the synchronous motor;
• a drive controller that controls an output of the inverter,
• the drive controller comprising:
• a speed controller for controlling the speed feedback obtained by differentiating the output of the position detector to be a predetermined speed reference and outputting a Q-axis current reference;
• first 3-phase/DQ converter for obtaining a Q-axis feedback current and a D-axis feedback current by converting the detected current of the current detector into 3-phase/DQ converter;
• a Q-axis current controller for controlling the deviation between the Q-axis current reference and the Q-axis feedback current to be zero and outputting a Q-axis voltage reference;
• a D-axis current controller for controlling the D-axis feedback current to be zero and outputting a D-axis voltage reference;
• a DQ/3-phase converter for DQ to 3-phase conversion of the Q-axis voltage reference and the D-axis voltage reference to obtain voltage reference of each phase of the three-phase output of the inverter;
• a PWM controller for PWM controlling the voltage reference of each phase and outputting a gate signal to switching elements constituting the inverter;
• second 3-phase/DQ converter for obtaining a Q-axis feedback voltage and a D-axis feedback voltage by converting the detection voltage of the voltage detector into 3-phase/DQ converter;
• a voltage controller for PI control so that the D-axis feedback voltage becomes zero and outputting a correction angle;
• wherein, when the speed of the synchronous motor is equal to or higher than a predetermined threshold value, a value obtained by adding the correction angle to the detection angle of the position detector is taken as a reference phase angle of the first 3-phase/DQ converter, the second 3-phase/DQ converter and the DQ/3-phase converter, when the speed of the synchronous motor is less than a predetermined threshold value, a value obtained by adding a low-speed load angle preset to the detection angle of the position detector is used as the reference phase angle.