Temperature compensation for improved field weakening accuracy

1. A method for controlling field-weakening accuracy in an integrated permanent magnet (IPM) electric motor, comprising:

generating a phase voltage feed back signal V ph , based in part on pre-defined optimal current commands (I d * and Iq*) received by the IPM;

generating a phase voltage command V phcmd based in part on a temperature (T R ) of a magnetic rotor of the IPM;

generating a phase voltage error V error by subtracting the phase voltage feed back signal V ph from the phase voltage command V phcmd ;

generating a d-axis command current correction values ΔI d and a q-axis command current correction value ΔI q from the phase voltage error V error ; and

adjusting the pre-defined optimal current commands (Id* and Iq*) by the d-axis and the q-axis command current correction values (ΔI d and ΔI q ).

2. The method of claim 1 wherein the phase voltage command V phcmd′ is a product of a speed of the magnetic rotor of the IPM and a rotor flux command ψ phCmd .

3. The method of claim 2 wherein the rotor flux command (ψ phCmd ) is generated from a data structure containing temperature based flux-linkage data that is accessed by a temperature of the magnetic rotor of the IPM, a d-axis adjusted current command (I d **), and a q-axis adjusted current command (I q **).

4. A field weakening control loop for an electric machine including a permanent magnetic rotor, comprising:

a first current regulator configured to convert a d-axis adjusted current command (I d **) and a d-axis current feedback (I d ) to a synchronous voltage command (V d *);

a second current regulator configured to convert an q-axis adjusted current command (I q **) a q-axis current feedback (I q ) to a synchronous voltage command (V q *);

an arithmetic unit configured to generated a phase voltage (V ph ) from the synchronous voltage commands (V d * and V q *);

flux linkage correction module, the flux linkage correction module configured to receive a rotor temperature (T R ) and a rotor speed (ω R ) and configured to produce a phase voltage command (V phcmd ); and

a feed back path configured to subtract the phase voltage (V ph ) from the phase voltage command (V phcmd ) and configured to generate both of a d-axis command current correction value ΔI d and a q-axis command current correction value ΔI q based on the subtraction as inputs to the first current regulator and the second current regulator.

5. The field weakening control loop of claim 4 , wherein the flux linkage correction module comprises a memory device containing flux linkage data stored therein, wherein the flux linkage data relates a synchronous d-axis current (I d ) to a corresponding q-axis current (I q ) at a specific magnetic rotor temperature.

6. The field weakening control loop of claim 5 , wherein the flux linkage data is stored in a look up table that uses a temperature (T R ) of the permanent magnetic rotor, the d-axis adjusted current command (I d **) and the q-axis adjusted current command (I q **) for input values and produces a rotor flux command (ψ phCmd ).

7. The field weakening control loop of claim 6 , wherein the rotor flux command (ψ phCmd ) is multiplied by the rotor speed to generate phase voltage command (V phCmd ).

8. The field weakening control loop of claim 7 , further comprising a proportional integrator configured to convert a difference between the phase voltage command (V phCmd ) and the phase voltage (V ph ) into the d-axis command current correction value (ΔI d ).

9. The field weakening control loop of claim 7 , further comprising an amplifier configured to convert the d-axis command current correction value (ΔI d ) into the d-axis command current correction value.

10. A field weakening control loop for an electric machine with a permanent magnetic rotor and an inverter, comprising:

a first current regulator configured to convert a d-axis adjusted current command (I d **) and a d-axis current feedback (I d ) to a synchronous command voltages (V d *);

a second current regulator configured to convert a q-axis adjusted current command (I q **) and a q-axis current feedback (I q ) to a synchronous command voltages (V q *);

an arithmetic unit configured to generated a phase voltage (V ph ) from the synchronous command voltages (V d * and V q *) adjusted for a voltage drop (V drop ) and a resistance loss (R inv ) across the inverter;

flux linkage correction module, the flux linkage correction module configured to receive a rotor temperature (T R ), a rotor speed (ω R ) and a phase current (I ph ) and configured to produce a phase voltage command (V phCmd ); and

a feed back path configured to subtract the phase voltage (V ph ) from the phase voltage command (V phcmd ) and configured to generate both of a d-axis command current correction value (ΔI d ) and a q-axis command current correction value (ΔI q ) based on the subtraction as inputs to the first current regulator and the second current regulator.

11. The field weakening control loop of claim 10 , wherein the flux linkage correction module comprises a memory device containing flux linkage data stored therein, wherein the flux linkage data relates a stationary d-axis current (I d ) to a corresponding q-axis current (I q ) at a specific magnetic rotor temperature.

12. The field weakening control loop of claim 11 , wherein the flux linkage data is stored in a look up table that uses a temperature of the permanent magnetic rotor, the d-axis adjusted current command (I d **) and the q-axis adjusted current command (I q **) for input values and produces a rotor flux command (ψ phCmd ).

13. The field weakening control loop of claim 12 wherein the rotor flux command (ψ phCmd ) is multiplied by the rotor speed to generate an adjusted phase voltage (V ph *).

14. The field weakening control loop of claim 13 , further comprising a stator resistance look up table.

15. The field weakening control loop of claim 14 , wherein the stator resistance look up table receives the phase current (I ph ), the rotor speed and a temperature of a stator as input values and produces a resistance adjustment value (R′).

16. The field weakening control loop of claim 15 , wherein the phase current (I ph ) is multiplied by the resistance adjustment value (R′) to generate a voltage adjustment (V′).

17. The field weakening control loop of claim 16 wherein the voltage adjustment (V′) is added to the adjusted phase voltage (V ph *) to produce the phase voltage command (V phCmd ).

18. The field weakening control loop of claim 17 , further comprising a proportional integrator configured to convert a difference between the phase voltage command (V phCmd ) and the phase voltage (V ph ) into the d-axis command current correction value (ΔI d ).

19. The field weakening control loop of claim 18 , further comprising an amplifier configured to convert the d-axis command current correction value (ΔI d ) into the d-axis command current correction value.