Synchronous motor control circuit and control method

• US 10,411,629 B2
• Filed: 04/05/2017
• Issued: 09/10/2019
• Est. Priority Date: 10/19/2016
• Status: Active Grant

• Current Assignee: Delta Electronics Incorporated
• Original Assignee: Delta Electronics Incorporated
• Inventors: Lee, Yu-Ling, Chen, Ming-Tsung, Hsieh, Tung-Chin
• Primary Examiner(s): Carrasquillo, Jorge L
• Assistant Examiner(s): Joseph, Devon A
• Application Number:
  US15/479,295
• Publication Number:
  US 20180109217A1
• Time in Patent Office: 888 Days
• Field of Search: 318400
• CPC Class Codes: H02P 21/0089 using field weakening

Abstract

A control method for controlling a synchronous motor includes calculating d-axis and q-axis current commands according to a frequency command and frequency of the synchronous motor by a MTPA control unit; when a feedback output voltage of the synchronous motor is larger than a control level, outputting a flux-weakening current command by a voltage control unit; calculating a flux-weakening current feed-forward value according to the frequency, a target level and the q-axis current command by a feed-forward control unit; when the sum of the flux-weakening current command and the flux-weakening current feed-forward value is smaller than the d-axis current command, adjusting the d-axis current command by the sum of the flux-weakening current command and the flux-weakening current feed-forward value; and outputting d-axis and q-axis voltage commands according to the adjusted d-axis current command and the q-axis current command to control the synchronous motor.

Claims

1. A control method for controlling a synchronous motor, comprising:

calculating, by a MTPA control unit, a first d-axis current command and a q-axis current command according to a frequency command and an electric frequency of the synchronous motor;

outputting, by a voltage control unit, a flux-weakening current command when a feedback output voltage of the synchronous motor is larger than a voltage control level;

calculating, by a feed-forward control unit, a flux-weakening current feed-forward value according to the electric frequency, a voltage target level and the q-axis current command;

adjusting the first d-axis current command by the sum of the flux-weakening current command and the flux-weakening current feed-forward value when the sum of the flux-weakening current command and the flux-weakening current feed-forward value is smaller than the first d-axis current command, in order to output a second d-axis current command; and

outputting, by a voltage command output unit, a d-axis voltage command and a q-axis voltage command according to the second d-axis current command and the q-axis current command respectively to control the synchronous motor;

wherein calculating the flux-weakening current feed-forward value by the feed-forward control unit comprises;

obtaining a reference model according to a flux linkage parameter of the synchronous motor; and

calculating the flux-weakening current feed-forward value according to the electric frequency, the voltage target level and the q-axis current command based on the reference model.

2. The control method of claim 1, further comprising:

calculating, by a voltage saturation adjusting unit, a frequency command correction value according to a d-axis current error value and a q-axis current error value, wherein the d-axis current error value is the difference between the second d-axis current command and a d-axis feedback current, and the q-axis current error value is the difference between the q-axis current command and a q-axis feedback current; and

adjusting, by the voltage saturation adjusting unit, the frequency command according to the frequency command correction value.

3. The control method of claim 1, further comprising:

calculating, by a first calculating unit, the difference between the sum of the flux-weakening current command and the flux-weakening current feed-forward value, and the first d-axis current command, to obtain a flux-weakening current compensating value;

executing, by a limiting unit, a limitation to the flux-weakening current compensating value, wherein when the flux-weakening current compensating value is larger than zero, the flux-weakening current compensating value output by the limiting unit is zero; and

correcting, by a second calculating unit, the first d-axis current command to output the second d-axis current command according to the limited flux-weakening current compensating value.

4. The control method of claim 1, wherein outputting the d-axis voltage command and the q-axis voltage command by the voltage command output unit comprises:

calculating, by a third calculating unit, a d-axis current error value according to the second d-axis current command and a d-axis feedback current of the synchronous motor;

outputting, by a d-axis current controller of the voltage command output unit, the d-axis voltage command according to the d-axis current error value;

calculating, by a fourth calculating unit, a q-axis current error value according to the q-axis current command and a q-axis feedback current of the synchronous motor; and

outputting, by a q-axis current controller of the voltage command output unit, the q-axis voltage command according to the q-axis current error value.

5. The control method of claim 1, further comprising:

receiving, by a first proportional controller in the voltage control unit, a dc bus voltage to output the voltage control level; and

receiving, by a second proportional controller in the feed-forward control unit, the dc bus voltage to output the voltage target level.

6. A synchronous motor control circuit, comprising:

a MTPA control unit, configured to calculate a first d-axis current command and a q-axis current command according to a frequency command and an electric frequency of a synchronous motor;

a voltage control unit, configured to output a flux-weakening current command according to a feedback output voltage of the synchronous motor and a voltage control level;

a feed-forward control unit, configured to calculate a flux-weakening current feed-forward value according to the electric frequency, a voltage target level and the q-axis current command;

a current command compensating unit, electrically coupled to the MTPA control unit, the voltage control unit and the feed-forward control unit, and configured to adjust the first d-axis current command according to the flux-weakening current command and the flux-weakening current feed-forward value, in order to output a second d-axis current command; and

a voltage command output unit, electrically coupled to the current command compensating unit and the MTPA control unit, and configured to output a d-axis voltage command and a q-axis voltage command respectively according to the second d-axis current command and the q-axis current command, to control the synchronous motor;

wherein the feed-forward control unit comprises a reference model obtained according to a flux linkage parameter of the synchronous motor, and the feed-forward control unit calculates the flux-weakening current feed-forward value based on the reference model.

7. The synchronous motor control circuit of claim 6, further comprising:

a voltage saturation adjusting unit, wherein the voltage saturation adjusting unit comprises;

a voltage saturation adjuster configured to calculate a frequency command correction value according to the difference between the second d-axis current command and a d-axis feedback current, and the difference between the q-axis current command and a q-axis feedback current; and

a frequency command calculating unit, configured to adjust the frequency command according to the frequency command correction value.

8. The synchronous motor control circuit of claim 6, wherein the current command compensating unit comprises:

a first calculating unit, configured to calculate the difference between the sum of the flux-weakening current command and the flux-weakening current feed-forward value, and the first d-axis current command, to obtain a flux-weakening current compensating value;

a limiting unit, configured to execute a limitation to the flux-weakening current compensating value, wherein when the flux-weakening current compensating value is larger than zero, the flux-weakening current compensating value output by the limiting unit is zero; and

a second calculating unit, configured to correct the first d-axis current command output by the MTPA control unit according to the flux-weakening current compensating value output by the limiting unit, in order to output the second d-axis current command.