Control apparatus for a synchronous motor

1. 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.

2. The control apparatus for a synchronous motor according to claim 1 ,

wherein, the predetermined threshold has a hysteresis characteristics, and when the speed of the synchronous motor is less than the first set speed, a value obtained by adding the low speed load angle to the detection angle of the position detector is taken as the reference phase angle, and when the speed of the synchronous motor increases and becomes to the second set speed, a value obtained by adding the low-speed load angle to the correction angle is set as the reference phase angle, and when the speed of the synchronous motor is equal to or higher than the second set speed, a value obtained by adding the correction angle to the detection angle of the position detector is used as the reference phase angle, and the detection angle of the position detection means is detected only when the speed of the synchronous motor falls below the first set speed.

3. The control apparatus for a synchronous motor according to claim 1 ,

wherein, the drive controller hold the output of the voltage controller when the synchronous motor decelerates and its speed falls below the predetermined threshold, and uses the held correction angle instead of the low speed load angle.

4. The control apparatus for a synchronous motor according to claim 1 ,

wherein, the drive controller set the initial value of the integral output of the voltage controller to the low speed load angle, when the synchronous motor accelerates and its speed is above the predetermined threshold, and after that, a value obtained by adding the correction angle to the detection angle of the position detector is used as the reference phase angle.

5. The control apparatus for a synchronous motor according to claim 2 ,

wherein, the drive controller hold the output of the voltage controller when the synchronous motor decelerates and its speed falls below the predetermined threshold, and uses the held correction angle instead of the low speed load angle.

6. The control apparatus for a synchronous motor according to claim 2 ,

wherein, the drive controller set the initial value of the integral output of the voltage controller to the low speed load angle, when the synchronous motor accelerates and its speed is above the predetermined threshold, and after that, a value obtained by adding the correction angle to the detection angle of the position detector is used as the reference phase angle.

7. The control apparatus for a synchronous motor according to claim 3 ,

wherein, the drive controller set the initial value of the integral output of the voltage controller to the low speed load angle, when the synchronous motor accelerates and its speed is above the predetermined threshold, and after that, a value obtained by adding the correction angle to the detection angle of the position detector is used as the reference phase angle.

8. The control apparatus for a synchronous motor according to claim 5 ,

wherein, the drive controller set the initial value of the integral output of the voltage controller to the low speed load angle, when the synchronous motor accelerates and its speed is above the predetermined threshold, and after that, a value obtained by adding the correction angle to the detection angle of the position detector is used as the reference phase angle.