Method of operating a synchronous motor in a flux weakening mode and a controller therefor

1. A method of controlling operation of a synchronous motor using a closed loop controller, the method comprising:

during constant power or constant speed motor operation, determining a value of a stator voltage (v s 2 ) for an orthogonal rotating reference frame of the motor;

comparing the value of the determined stator voltage (v s 2 ) to a threshold voltage (v s 2 _max1 ) in the orthogonal rotating reference frame, said threshold voltage (v s 2 _max1 ) having a predetermined, selected, or calculated value between a value of a maximum stator voltage (v s 2 _max0 ) in the orthogonal rotating reference frame for a basic speed mode of operation of the motor and a value of a maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller;

wherein, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the threshold voltage (v s 2 _max1 ), then controlling operation of the motor in a flux weakening mode of operation to cause a value of a current component (i d −Δi d ) in a d-axis of the orthogonal rotating reference frame to reduce below a value of the current component (i d ) in said d-axis for the basic speed mode of operation of the motor until the value of the current component (i d −Δi d ) reaches a maximum negative value (−i dmax ), or until the value of the stator voltage (v s 2 ) is less than the value of the threshold voltage (v s 2 _max1 ); and

wherein, if the determined value of the stator voltage (v s 2 ) becomes greater than or equal to the value of the maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller, then controlling operation of the motor to cause a value (v g ′) of a voltage component in a q-axis of the orthogonal rotating reference frame to have a value derived from a difference between the value of the maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller and a value (v d 2 ) of a voltage component in the d-axis of the orthogonal rotating reference frame.

2. The method of claim 1 , wherein the method includes determining values of stator voltage components (v d 2 , v q 2 ) in both the d-axis and the q-axis of the orthogonal rotating reference frame when determining the value of said stator voltage (v s 2 ) where v s 2 =v d 2 +v d 2 .

3. The method of claim 1 , wherein, if the determined value of the stator voltage (v s 2 ) becomes less than the value of the maximum stator voltage (v s 2 _max0 ) for the basic speed mode of operation of the motor, then stopping the flux weakening mode of operation and controlling operation of the motor to cause a value of the current component (i d +Δi d ) in the d-axis to increase until it reaches the value of the current component (i d ) in the d-axis for the basic speed mode of operation of the motor.

4. The method of claim 1 , wherein the value of the voltage component (v q ′) in the q-axis is determined from:

v q ′=√{square root over ( Vs 2 _max2− v d 2 )}.

5. A method of controlling operation of a synchronous motor using a closed loop controller, the method comprising:

during constant power motor operation, determining a value of a stator voltage (v s 2 ) for an orthogonal rotating reference frame of the motor;

comparing the value of the determined stator voltage (v s 2 ) to a threshold voltage (v s 2 _max1 ) in the orthogonal rotating reference frame, said threshold voltage (v s 2 _max1 ) having a predetermined, selected, or calculated value between a value of a maximum stator voltage (v s 2 _max0 ) in the orthogonal rotating reference frame for a basic speed mode of operation of the motor and a value of a maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller;

wherein, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the threshold voltage (V s 2 _max1 ), then controlling operation of the motor in a flux weakening mode of operation until a value of a current component (Target_i d ) in a d-axis of the orthogonal rotating reference frame reaches a maximum negative value (−i dmax ) of the current component in the d-axis,

or, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the threshold voltage (v s 2 _max1 ) and if a target value of the stator current (Target_i s ) less a value of a current component (i q 2 ) in a q-axis is less than a maximum value (i dmax ) of the current component in the d-axis, then controlling operation of the motor in a flux weakening mode of operation by reducing a value of the current component (Target_i d ) in the d-axis based on the target value of the stator current (Target_i s ) less the value of the current component (i q 2 ) in the q-axis; and

wherein the method includes determining values of the target stator current (Target_i s ) based on the equation:

Target_ is 2 =i s 2 =i q 2 +i d 2 ≤i s max 2 .

6. The method of claim 5 , wherein, in the flux weakening mode of operation, the value of the current component (Target_i d ) in the d-axis is reduced according to the equation:

Target_ id =−√{square root over (Target_ is 2 −ipf ( i q ) 2 )}.

7. The method of claim 5 , wherein the method includes determining values of stator voltage components (v d 2 , v q 2 ) in both the d-axis and a q-axis of the orthogonal rotating reference frame when determining the value of said stator voltage (v s 2 ) where v s 2 =v d 2 +v q 2 .

8. The method of claim 5 , wherein, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller, then controlling operation of the motor to cause a value (v q ′) of a voltage component in the q-axis of the orthogonal rotating reference frame to have a value derived from a difference between the value of the maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller and a value (v d 2 ) of a voltage component in the d-axis of the orthogonal rotating reference frame.

9. The method of claim 8 , wherein the value of the voltage component (v q ′) in the q-axis is determined from:

v q ′=√{square root over ( Vs 2 _max2− v d 2 )}.

10. The method of claim 5 , wherein, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller, then controlling operation of the motor to cause a value (v q ′) of a voltage component in the q-axis of the orthogonal rotating reference frame to have a value equal to a value of the voltage component (v q ) in the q-axis for the basic speed mode of operation of the motor.

11. A method of controlling operation of a synchronous motor using a closed loop controller, the method comprising:

during a flux weakening mode of operation of the motor, controlling a value of a stator current component (Target_i d ) in a d-axis of an orthogonal rotating reference frame of the motor by selecting a target value of the stator current component (Target_i d ) in the d-axis from a look-up table by reference to motor speed (Fw_speed) values, wherein the look-up table values are obtained by measuring motor speed and corresponding values of the stator current component in the d-axis for a plurality of motor voltage supply values;

wherein the method includes linear approximation of a selected pair of motor speed (Fw_speed) value and stator current component (Target_i d ) value.

12. The method of claim 11 , wherein the method includes determining a value of a stator voltage (v s 2 ) for the orthogonal rotating reference frame of the motor and, if the determined value of the stator voltage (v s 2 ) is greater than or equal to a value of the maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller, then controlling operation of the motor to cause a value (v q ′) of a voltage component in a q-axis of the orthogonal rotating reference frame to have a value derived from a difference between the value of the maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller and a value (v d 2 ) of a voltage component in the d-axis of the orthogonal rotating reference frame.

13. The method of claim 12 , wherein the value of the voltage component (v q ′) in the q-axis is determined from:

v q ′=√{square root over ( Vs 2 _max2− v d 2 )}.

14. The method of claim 11 , wherein the method includes determining a value of a stator voltage (v s 2 ) for the orthogonal rotating reference frame of the motor and, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller, then controlling operation of the motor to cause a value (v q ′) of a voltage component in the q-axis of the orthogonal rotating reference frame to have a value equal to a value of the voltage component (v q ) in the q-axis for the basic speed mode of operation of the motor.

15. The method of claim 11 , wherein the method includes determining values of stator voltage components (v d 2 , v q 2 ) in both the d-axis and a q-axis of the orthogonal rotating reference frame when determining the value of said stator voltage (v s 2 ) where v s 2 =v d 2 +v d 2 .

16. A method of controlling operation of a synchronous motor using a closed loop controller, the method comprising:

during constant power or constant speed motor operation, determining a value of a stator voltage (v s 2 ) for an orthogonal rotating reference frame of the motor;

comparing the value of the determined stator voltage (v s 2 ) to a threshold voltage (v s 2 _max1 ) in the orthogonal rotating reference frame, said threshold voltage (v s 2 _max1 ) having a predetermined, selected, or calculated value between a value of a maximum stator voltage (v s 2 _max0 ) in the orthogonal rotating reference frame for a basic speed mode of operation of the motor and a value of a maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller;

wherein, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the threshold voltage (v s 2 _max1 ), then controlling operation of the motor in a flux weakening mode of operation until a value of a current component (i d −Δi d ) in a d-axis of the orthogonal rotating reference frame reaches a maximum negative value (−i dmax ), or until the value of the stator voltage (v s 2 ) is less than the value of the threshold voltage (v s 2 _max1 ); and

wherein, if the determined value of the stator voltage (v s 2 ) becomes greater than or equal to the value of the maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller, then controlling operation of the motor to cause a value (v d ′) of a voltage component in a q-axis of the orthogonal rotating reference frame to have a value equal to a value of the voltage component (v q ) in the q-axis for the basic speed mode of operation of the motor.

17. A method of controlling operation of a synchronous motor using a closed loop controller, the method comprising:

during constant power or constant speed motor operation, determining a value of a stator voltage (v s 2 ) for an orthogonal rotating reference frame of the motor;

comparing the value of the determined stator voltage (v s 2 ) to a threshold voltage (v s 2 _max1 ) in the orthogonal rotating reference frame, said threshold voltage (v s 2 _max1 ) having a predetermined, selected, or calculated value between a value of a maximum stator voltage (v s 2 _max0 ) in the orthogonal rotating reference frame for a basic speed mode of operation of the motor and a value of a maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller;

wherein, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the threshold voltage (v s 2 _max1 ), then controlling operation of the motor in a flux weakening mode of operation to cause a value of a current component (i d −Δi d ) in a d-axis of the orthogonal rotating reference frame to reduce below a value of the current component (i d ) in said d-axis for the basic speed mode of operation of the motor until the value of the current component (i d −Δi d ) reaches a maximum negative value (−i dmax ), or until the value of the stator voltage (v s 2 ) is less than the value of the threshold voltage (v s 2 _max1 ); and

wherein, if the determined value of the stator voltage (v s 2 ) becomes less than the value of the maximum stator voltage (v s 2 _max0 ) for the basic speed mode of operation of the motor, then stopping the flux weakening mode of operation and controlling operation of the motor to cause a value of the current component (i d +Δi d ) in the d-axis to increase until it reaches the value of the current component (i d ) in the d-axis for the basic speed mode of operation of the motor.

18. A method of controlling operation of a synchronous motor using a closed loop controller, the method comprising:

during constant power motor operation, determining a value of a stator voltage (v s 2 ) for an orthogonal rotating reference frame of the motor;

comparing the value of the determined stator voltage (v s 2 ) to a threshold voltage (v s 2 _max1 ) in the orthogonal rotating reference frame, said threshold voltage (v s 2 _max1 ) having a predetermined, selected, or calculated value between a value of a maximum stator voltage (v s 2 _max0 ) in the orthogonal rotating reference frame for a basic speed mode of operation of the motor and a value of a maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller;

wherein, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the threshold voltage (v s 2 _max1 ), then controlling operation of the motor in a flux weakening mode of operation until a value of a current component (Target_i d ) in a d-axis of the orthogonal rotating reference frame reaches a maximum negative value (−i dmax ) of the current component in the d-axis,

or, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the threshold voltage (v s 2 _max1 ) and if a target value of the stator current (Target_i s ) less a value of a current component (i q 2 ) in a q-axis is less than a maximum value (i dmax ) of the current component in the d-axis, then controlling operation of the motor in a flux weakening mode of operation by reducing a value of the current component (Target_i d ) in the d-axis based on the target value of the stator current (Target_i s ) less the value of the current component (i q 2 ) in the q-axis; and

wherein, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the maximum stator voltage (V s 2 _max2 ) of the motor closed loop controller, then controlling operation of the motor to cause a value (v q ′) of a voltage component in the q-axis of the orthogonal rotating reference frame to have a value equal to a value of the voltage component (v q ) in the q-axis for the basic speed mode of operation of the motor.

19. A method of controlling operation of a synchronous motor using a closed loop controller, the method comprising:

during a flux weakening mode of operation of the motor, controlling a value of a stator current component (Target_i d ) in a d-axis of an orthogonal rotating reference frame of the motor by selecting a target value of the stator current component (Target_i d ) in the d-axis from a look-up table by reference to motor speed (Fw_speed) values, wherein the look-up table values are obtained by measuring motor speed and corresponding values of the stator current component in the d-axis for a plurality of motor voltage supply values;

wherein the method includes determining a value of a stator voltage (v s 2 ) for the orthogonal rotating reference frame of the motor and, if the determined value of the stator voltage (v s 2 ) is greater than or equal to the value of the maximum stator voltage (v s 2 _max2 ) of the motor closed loop controller, then controlling operation of the motor to cause a value (v q ′) of a voltage component in the q-axis of the orthogonal rotating reference frame to have a value equal to a value of the voltage component (v q ) in the q-axis for the basic speed mode of operation of the motor.