Method and apparatus for controlling operation of a permanent magnet rotary electric machine

1. A method for controlling a permanent magnet rotary electric machine including a stator and a rotor, wherein the rotor includes a plurality of permanent magnets, the method comprising:

determining a first reactive power term associated with the electric machine based upon voltage;

determining a second reactive power term associated with the electric machine based upon flux, wherein the flux is determined based upon a temperature of the permanent magnets;

determining a first motor temperature associated with the electric machine based upon the first and second reactive power terms; and

controlling power output from the permanent magnet electric machine based upon the first motor temperature.

2. The method of claim 1 , wherein determining the first reactive power term associated with the electric machine based upon voltage comprises:

determining a voltage, a current, a rotational speed, and a torque command associated with operation of the electric machine;

determining a flux term based upon the torque command;

determining a first stator voltage term based upon the rotational speed, the current and the flux term;

determining a second stator voltage term based upon the rotational speed, the current and the flux term; and

determining the first reactive power term based upon the first and second stator voltage terms.

3. The method of claim 1 , wherein determining the second reactive power term associated with the electric machine based upon flux comprises:

determining a current and a rotational speed;

determining the temperature of the permanent magnets of the electric machine;

determining a first flux term based upon the current and the temperature of the electric machine;

determining a second flux term based upon the current and the temperature of the permanent magnets of the electric machine; and

determining the second reactive power term based upon the rotational speed and the first and second flux terms.

4. The method of claim 3 , wherein determining the second reactive power term based upon the rotational speed and the first and second flux terms comprises determining the second reactive power term based upon the rotational speed and a difference between the first and second flux terms.

5. The method of claim 3 , wherein the temperature of the permanent magnets of the electric machine comprises an estimated temperature of the permanent magnets.

6. The method of claim 1 , wherein determining the first motor temperature associated with the electric machine based upon the first and second reactive power terms comprises determining a temperature of a rotor magnet of the electric machine.

7. The method of claim 1 , further comprising:

determining, via a thermal model, a second motor temperature;

comparing the first motor temperature and the second motor temperature; and

controlling power output from the permanent magnet electric machine based upon the comparing of the first motor temperature and the second motor temperature.

8. The method of claim 7 , wherein controlling the power output from the permanent magnet electric machine based upon the comparing of the first motor temperature and the second motor temperature comprises derating the power output from the permanent magnet electric machine when a difference between the first motor temperature and the second motor temperature is greater than a threshold.

9. The method of claim 7 , wherein controlling the power output from the permanent magnet electric machine based upon the comparing of the first motor temperature and the second motor temperature comprises maximizing the power output from the permanent magnet electric machine when a difference between the first motor temperature and the second motor temperature is less than a threshold.

10. A system, including:

a permanent magnet rotary electric machine including a stator and a rotor, wherein the rotor includes a plurality of permanent magnets;

an inverter;

a controller, operatively coupled to the inverter and in communication with current, voltage and speed sensors that are disposed to monitor the rotary electric machine, the controller including an instruction set, the instruction set executable to:

determine a first reactive power term associated with the electric machine based upon voltage;

determine a second reactive power term associated with the electric machine based upon flux, wherein the flux is determined based upon a temperature of the permanent magnets;

determine a first motor temperature associated with the electric machine based upon the first and second reactive power terms; and

control, via the inverter, power output from the permanent magnet electric machine based upon the first motor temperature.

11. The system of claim 10 , wherein the instruction set executable to determine the first reactive power term associated with the electric machine based upon voltage comprises the instruction set executable to:

determine a voltage, a current, a rotational speed, and a torque command associated with operation of the electric machine;

determine a flux term based upon the torque command;

determine a first stator voltage term based upon the rotational speed, the current and the flux term;

determine a second stator voltage term based upon the rotational speed, the current and the flux term; and

determine the first reactive power term based upon the first and second stator voltage terms.

12. The system of claim 10 , wherein the instruction set executable to determine the second reactive power term associated with the electric machine based upon flux comprises the instruction set executable to:

determine a current and a rotational speed;

determine the temperature of the permanent magnets of the electric machine;

determine a first flux term based upon the current and the temperature of the electric machine;

determine a second flux term based upon the current and the temperature of the permanent magnets of the electric machine; and

determine the second reactive power term based upon the rotational speed and the first and second flux terms.

13. The system of claim 12 , wherein the instruction set executable to determine the second reactive power term based upon the rotational speed and the first and second flux terms comprises the instruction set executable to determine the second reactive power term based upon the rotational speed and a difference between the first and second flux terms.

14. The system of claim 12 , wherein the temperature of the permanent magnets of the electric machine comprises an estimated temperature of the permanent magnets.

15. The system of claim 10 , wherein the instruction set executable to determine the first motor temperature associated with the electric machine based upon the first and second reactive power terms comprises the instruction set executable to determine a temperature of a rotor magnet of the electric machine.

16. The system of claim 10 , wherein the instruction set is further executable to:

determine, via a thermal model, a second motor temperature;

compare the first motor temperature and the second motor temperature; and

control power output from the permanent magnet electric machine based upon the comparing of the first motor temperature and the second motor temperature.

17. The system of claim 16 , wherein the instruction set executable to control the power output from the permanent magnet electric machine based upon the comparing of the first motor temperature and the second motor temperature comprises the instruction set executable to derate the power output from the permanent magnet electric machine when a difference between the first motor temperature and the second motor temperature is greater than a threshold.

18. The system of claim 16 , wherein the instruction set executable to control the power output from the permanent magnet electric machine based upon the comparing of the first motor temperature and the second motor temperature comprises the instruction set executable to maximize the power output from the permanent magnet electric machine when a difference between the first motor temperature and the second motor temperature is less than a threshold.