Device and method for generating an initial controller lookup table for an IPM machine

1. A method for generating initial operating points for controlling an interior peg magnet (IPM) machine, the method comprising:

loading an inductance lookup table, the inductance lookup table including sets of a direct axis inductance (L d ) value and a quadrature axis inductance (L q ) value, each set corresponding to a current peak magnitude and a current control angle, the current control angle indicating amounts of the current peak magnitude appearing as direct axis current (I d ) and quadrature axis current (I q );

first calculating a maximum torque per Ampere (MTPA) trajectory for a first threshold speed based on machine parameters of the IPM machine, the machine parameters including the inductance lookup table;

second calculating a truncated voltage limit ellipse with monotonically increasing torque for a first speed based on the machine parameters, if the first speed is higher than the first threshold speed;

determining an operating trajectory at the first speed based on at least one of the calculated MTPA trajectory and the calculated truncated voltage limit ellipse; and

generating an I d ,I q map that maps an I d value and an I q value to each torque command of a plurality of torque commands for the first speed based on the determined operating trajectory.

2. The method of claim 1 , wherein the first threshold speed is a base speed, the base speed being a maximum shaft speed at which maximum constant output torque of the IPM machine is achieved.

3. The method of claim 1 , wherein the determining step includes:

if the first speed is lower than a second threshold speed and higher than the first threshold speed, the determining step determines the operating trajectory based on a comparison of the calculated MTPA trajectory and the calculated truncated voltage limit ellipse;

if the first speed is the second threshold speed or higher than the second threshold speed, the determining step determines the operating trajectory based on the calculated truncated voltage limit ellipse with monotonically increasing torque only; and

if the first speed is the first threshold speed or lower than the first threshold speed, the determining step determines the operating trajectory based on the calculated MTPA trajectory.

4. The method of claim 3 , wherein the second threshold speed is a critical speed, the critical speed being a speed at which uncontrolled generation (UCG) voltage from a back-electromotive force (backemf) of the IPM machine is equal to a direct current (DC) bus voltage.

5. The method of claim 3 , wherein if the first speed is lower than the second threshold speed and higher than the first threshold speed, the determining step includes:

selecting lesser of an I q value of the calculated MTPA trajectory and an I q value of the calculated truncated voltage limit ellipse for each I d value, wherein the operating trajectory includes the selected I q values.

6. The method of claim 1 , wherein the first calculating step includes:

determining an initial table, the initial table including I d ,I q combinations having values covering all possible values for a preset current limit;

calculating the current peak magnitude, the current control angle, and the L d and L q values for each I d ,I q combination of the initial table;

calculating torque for each I d ,I q combination of the initial table based on the machine parameters;

setting a torque range for each of the plurality of torque commands;

determining a subset of I d ,I q combinations for each torque command based on the calculated torque and the set torque range;

selecting an I d ,I q combination from each subset that has a calculated current peak magnitude less than other I d ,I q combinations of the subset; and

calculating the MTPA trajectory based on the selected sets of I d ,I q combinations.

7. The method of claim 6 , wherein the calculated torque for each of the I d ,I q combinations in the determined subset falls within the set torque range encompassing a respective torque command.

8. The method of claim 1 , wherein the second calculating step includes:

determining an I d vertex value for the voltage limit ellipse right vertex at a set shaft speed based on the machine parameters;

calculating maximum allowable I q values corresponding to a range of I d values, the range of I d values being from the determined I d vertex value to a preset minimum I d limit; and

calculating the voltage limit ellipse for the first speed based on the calculated maximum allowable I q values.

9. The method of claim 8 , wherein the I d vertex value is forced to zero if the determined I d vertex value is greater than zero.

10. The method of claim 8 , wherein the second calculating step further includes:

calculating torque along points of the calculated voltage limit ellipse at the first speed; and

truncating the calculated voltage limit ellipse by disregarding monotonically decreasing torque.

11. The method of claim 1 , further comprising:

obtaining the L d values and the L q values using finite element analysis based simulation; and

generating the inductance look-up table based on the obtained inductance parameters.

12. The method of claim 1 , further comprising:

generating a different I d ,I q map for a plurality of speeds by repeating the second calculating step, the determining step, and the generating step for each speed; and

constructing an integrated I d ,I q map based on the plurality of I d ,I q maps.

13. The IPM machine including a machine controller having the I d ,I q map generated in claim 1 .

14. A method for generating initial operating points for controlling an interior permanent magnet (IPM) machine, the method comprising:

first calculating a maximum torque per Ampere (MTPA) trajectory for a first threshold speed based on machine parameters of the IPM machine;

second calculating a truncated voltage limit ellipse with monotonically increasing torque for a first speed based on the machine parameters, if the first speed is higher than the first threshold speed;

determining an operating trajectory at the first speed based on at least one of the calculated MTPA trajectory and the calculated truncated voltage limit ellipse, the determining step including,

determining the operating trajectory based on a comparison of the calculated MTPA trajectory and the calculated truncated voltage limit ellipse if the first speed is lower than a second threshold speed and higher than the first threshold speed; and

generating an I d ,I q map that maps a direct axis current (I d ) value and a quadrature axis current (I i ) value to each torque command of a plurality of torque commands for the first speed based on the determined operating trajectory.

15. The method of claim 14 , wherein

the first threshold speed is a base speed, the base speed being a maximum shaft speed at which maximum constant output torque of the IPM machine is achieved,

the second threshold speed is a critical speed, the critical speed being a speed at which uncontrolled generation (UCG) voltage from a back-electromotive force (backemf) of the IPM machine is equal to a direct current (DC) bus voltage.

16. The method of claim 14 , wherein the machine parameters include an inductance lookup table, the inductance lookup table including sets of a direct axis inductance (L d ) value and a quadrature axis inductance (L q ) value, each set corresponding to a current peak magnitude and a current control angle, the current control angle indicating amounts of the current peak magnitude appearing as I d and I q .

17. The method of claim 14 , wherein the determining step further includes:

if the first speed is the second threshold speed or higher than the second threshold speed, the determining step determines the operating trajectory based on the calculated truncated voltage limit ellipse with monotonically increasing torque only; and

if the first speed is the first threshold speed or lower than the first threshold speed, the determining step determines the operating trajectory based on the calculated MTPA trajectory.

18. The method of claim 14 , wherein the determining step further includes:

selecting lesser of an I q value of the calculated MTPA trajectory and an I q value of the calculated truncated voltage limit ellipse for each I d value, wherein the operating trajectory includes the selected I q values.

19. The method of claim 14 , wherein the first calculating step includes:

determining an initial table, the initial table including I d ,I q combinations having values covering all possible values for a preset current limit;

calculating the current peak magnitude, the current control angle, and the L d and L q values for each I d ,I q combination of the initial table;

calculating torque for each I d ,I q combination of the initial table based on the machine parameters;

setting a torque range for each of the plurality of torque commands;

determining a subset of I d ,I q combinations for each torque command based on the calculated torque and the set torque range;

selecting an I d ,I q combination from each subset that has a calculated current peak magnitude less than other I d ,I q combinations of the subset; and

calculating the MTPA trajectory based on the selected sets of I d ,I q combinations.

20. The method of claim 19 , wherein the calculated torque for each of the I d ,I q combinations in the determined subset falls within the set torque range encompassing a respective torque command.

21. The method of claim 14 , wherein the second calculating step includes:

determining an I d vertex value at the voltage limit ellipse right vertex point at a set shaft speed based on the machine parameters;

calculating maximum allowable I q values corresponding to a range of I d values, the range of I d values being from the determined I d vertex value to a preset minimum I d limit; and

calculating the voltage limit ellipse for the first speed based on the calculated maximum allowable I q values.

22. The method of claim 21 , wherein the I d vertex value is forced to zero if the determined I d vertex value is greater than zero.

23. The method of claim 21 , wherein the second calculating step further includes:

calculating torque along points of the calculated voltage limit ellipse at the first speed; and

truncating the calculated voltage limit ellipse by disregarding monotonically decreasing torque.

24. The method of claim 14 , further comprising:

generating a different I d ,I q map for a plurality of speeds by repeating the second calculating step, the determining step, and the generating step for each speed; and

constructing an integrated I d ,I q map based on the plurality of I d ,I q maps.

25. The IPM machine including a machine controller having the I d ,I q map generated in claim 14 .

26. A computer processing unit for generating initial operating points for controlling an interior permanent magnet (IPM) machine, the computer processing unit comprising:

a memory configured to store machine parameters, the machine parameters including an inductance lookup table, the inductance lookup table including sets of a direct axis inductance (L d ) value and a quadrature axis inductance (L q ) value, each set corresponding to a current peak magnitude and a current control angle, the current control angle indicating amounts of the current peak magnitude appearing as direct axis current (I d ) and quadrature axis current (I q ); and

a processor configured to first calculate a maximum torque per Ampere (MTPA) trajectory for a first threshold speed based on the machine parameters,

the processor configured to second calculate a truncated voltage limit ellipse with monotonically increasing torque for a first speed based on the machine parameters, if the first speed is higher than the first threshold speed,

the processor configured to determine an operating trajectory at the first speed based on at least one of the calculated MTPA trajectory and the calculated truncated voltage limit ellipse,

the processor configured to generate an I d ,I q map that maps an I d value and an I q value to each torque command of a plurality of torque commands for the first speed based on the determined operating trajectory.

27. The computer processing unit of claim 26 , wherein the first threshold speed is a base speed, the base speed being a maximum shaft speed at which maximum constant output torque of the IPM machine is achieved.

28. The computer processing unit of claim 26 , wherein

if the first speed is lower than a second threshold speed and higher than the first threshold speed, the processor is configured to determine the operating trajectory based on a comparison of the calculated MTPA trajectory and the calculated truncated voltage limit ellipse;

if the first speed is the second threshold speed or higher than the second threshold speed, the processor is configured to determine the operating trajectory based on the calculated truncated voltage limit ellipse with monotonically increasing torque only; and

if the first speed is the first threshold speed or lower than the first threshold speed, the processor is configured to determine the operating trajectory based on the calculated MTPA trajectory.

29. The computer processing unit of claim 28 , wherein the second threshold speed is a critical speed, the critical speed being a speed at which uncontrolled generation (UCG) voltage from a back-electromotive force (backemf) of the IPM machine is equal to a direct current (DC) bus voltage.

30. The computer processing unit of claim 28 , wherein if the first speed is lower than the second threshold speed and higher than the first threshold speed, the processor is configured to select lesser of an I q value of the calculated MTPA trajectory and an I q value of the calculated truncated voltage limit ellipse for each I d value, wherein the operating trajectory includes the selected I q values.

31. The computer processing unit of claim 26 , wherein

the processor is configured to determine an initial table, the initial table including I d ,I q combinations having values covering all possible values for a preset current limit;

the processor is configured to calculate the current peak magnitude, the current control angle, and the La and L q values for each I d ,I q combination of the initial table;

the processor is configured to calculate torque for each I d ,I q combination of the initial table based on the machine parameters;

the processor is configured to set a torque range for each of the plurality of torque commands;

the processor is configured to determine a subset of I d ,I q combinations for each torque command based on the calculated torque and the set torque range;

the processor is configured to select an I d ,I q combination from each subset that has a calculated current peak magnitude less than other I d ,I q combinations of the subset; and

the processor is configured to calculate the MTPA trajectory based on the selected sets of I d ,I q combinations.

32. The computer processing unit of claim 31 , wherein the calculated torque for each of the I d ,I q combinations in the determined subset falls within the set torque range encompassing a respective torque command.

33. The computer processing unit of claim 26 , wherein

the processor is configured to determine an I d vertex value for the voltage limit ellipse right vertex at a set shaft speed based on the machine parameters;

the processor is configured to calculate maximum allowable I q values corresponding to a range of I d values, the range of I d values being from the determined I d vertex value to a preset minimum I d limit; and

the processor is configured to calculate the voltage limit ellipse for the first speed based on the calculated maximum allowable I q values.

34. The computer processing unit of claim 33 , wherein the I d vertex value is forced to zero if the determined I d vertex value is greater than zero.

35. The computer processing unit of claim 33 , wherein

the processor is configured to calculate torque along points of the calculated voltage limit ellipse at the first speed;

the processor is configured to truncate the calculated voltage limit ellipse by disregarding monotonically decreasing torque.

36. The computer processing unit of claim 26 , wherein

the processor is configured to generate a different I d ,I q map for a plurality of speeds by repeating the second calculating step, the determining step, and the generating step for each speed; and

the processor is configured to construct an integrated I d ,I q map based on the plurality of I d ,I q maps.