Operating point determination in an electric motor system
Systems and methods are disclosed for determining an operating point for controlling an electric motor. An exemplary system may include a voltage monitor configured to determine a voltage applied to the electric motor. The system may also include a controller configured to determine the operating point based on the voltage. The controller may include a comparator configured to determine a difference between the voltage and a reference voltage. The controller may also include a regulator configured to generate a correction signal for reducing the difference. The controller may be configured to determine the operating point when the difference is below a predetermined threshold.
1. A system for determining an operating point for controlling an electric motor, the system comprising:
a voltage monitor configured to determine a voltage applied to the electric motor; and
a controller configured to determine the operating point based on the voltage, the controller including:
a comparator configured to determine a difference between the voltage and a reference voltage;
a regulator configured to generate a correction signal for reducing the difference by holding a field flux linkage component of a current command constant and adjusting a torque component of the current command constant and limit the rate of change in the torque component; and
a limiter configured to nullify the correction signal when the correction signal indicates that the electric motor operates in a non-field weakening mode;
wherein the controller is configured to determine the operating point when the difference is below a predetermined threshold; and
wherein the limiter is omitted during a calibration process.
2. The system of claim 1 , wherein the operating point includes a maximum torque per ampere (MTPA) point in a field weakening region.
3. The system of claim 1 , wherein the operating point includes a current command, the current command including:
a magnitude and an angle of a current vector; or
direct and quadrature components of the current vector in a reference frame.
4. The system of claim 1 , wherein:
the electric motor is driven by an inverter configured to convert a direct current (DC) voltage to an alternating current (AC) voltage applied to a stator of the electric motor; and
the reference voltage is a maximum AC voltage that can be produced by the inverter by converting the DC voltage.
5. The system of claim 1 , wherein the voltage monitor is configured to:
sample direct and quadrature components of a voltage command output by a current regulator; and
determine the voltage applied to the electric motor based on the direct and quadrature components of the voltage command.
6. The system of claim 1 , wherein:
the controller includes a normalizer configured to normalize the difference determined by the comparator based on an electrical speed; and
the regulator is configured to generate the correction signal based on the normalized difference.
7. The system of claim 1 , wherein the regulator is configured to limit the correction signal within a predetermined range.
8. The system of claim 1 , wherein the controller is configured to determine the operating point during real time operation of the electric motor.
9. The system of claim 1 , wherein the controller is configured to determine the operating point during calibration of the electric motor.
10. The system of claim 1 , wherein the controller is configured to:
determine whether the electric motor operates in a regeneration mode; and
modify the correction signal when it is determined that the electric motor operates in the regeneration mode.
11. A method for determining an operating point for controlling an electric motor, the method comprising:
determining, by a voltage monitor, a voltage applied to the electric motor; and
determining, by a controller, the operating point based on the voltage, including:
determining, by a comparator, a difference between the voltage and a reference voltage;
generating, by a regulator, a correction signal for reducing the difference by holding a field flux linkage component of a current command constant and adjusting a torque component of the current command constant and limit the rate of change in the toque component;
nullifying, by a limiter, the correction signal when the correction signal indicates that the electric motor operates in a non-field weakening mode; and
determining the operating point when the difference is below a predetermined threshold; and
omitting the limiter during a calibration process.
12. The method of claim 11 , wherein the operating point includes a maximum torque per ampere (MTPA) point in a field weakening region.
13. The method of claim 11 , wherein the operating point includes a current command, the current command including:
a magnitude and an angle of a current vector; or
direct and quadrature components of the current vector in a reference frame.
14. The method of claim 11 , comprising:
converting, by an inverter, a direct current (DC) voltage to an alternating current (AC) voltage to drive the electric motor, wherein the reference voltage is a maximum AC voltage that can be produced by the inverter by converting the DC voltage.
15. The method of claim 11 , comprising:
sampling, by the voltage monitor, direct and quadrature components of a voltage command output by a current regulator; and
determining, by the voltage monitor, the voltage applied to the electric motor based on the direct and quadrature components of the voltage command.
16. The method of claim 11 , comprising:
normalizing the difference between the voltage and the reference voltage based on an electrical speed; and
generating the correction signal based on the normalized difference.
17. The method of claim 11 , comprising: limiting, by the regulator, the correction signal within a predetermined range.
18. The method of claim 11 , comprising: determining the operating point during real time operation of the electric motor.
19. The method of claim 11 , comprising: determining the operating point during simulated operation of the electric motor.
20. The method of claim 11 , comprising:
determining whether the electric motor operates in a regeneration mode; and
modifying the correction signal when it is determined that the electric motor operates in the regeneration mode.
21. A motor system, comprising:
an electric motor including a rotor and a stator; and
a motor control system configured to control the electric motor, the motor control system including:
a voltage monitor configured to determine a voltage applied to the stator of the electric motor; and
a controller configured to determine an operating point based on the voltage, the controller including:
a comparator configured to determine a difference between the voltage and a reference voltage;
a regulator configured to generate a correction signal for reducing the difference by holding a field flux linkage component of a current command constant and adjusting a torque component of the current command constant and limit the rate of change in the toque component; and
a limiter configured to nullify the correction signal when the correction signal indicates that the electric motor operates in a non-field weakening mode;
wherein the controller is configured to determine the operating point when the difference is below a predetermined threshold; and
wherein the limiter is omitted during a calibration process.
22. The motor system of claim 21 , wherein the electric motor includes a synchronous electric motor.
23. The motor system of claim 22 , wherein the electric motor includes an interior permanent magnet (IPM) motor.