Determination of permanent magnetic flux in an electric machine

Patent metadata

Field	Value
Publication number	US-9755567-B2
Application number	US-201514932603-A
Country	US
Kind code	B2
Filing date	Nov 4, 2015
Priority date	Nov 4, 2015
Publication date	Sep 5, 2017
Grant date	Sep 5, 2017

Abstract

An electric machine assembly has an electric machine having a stator and a rotor. The rotor has a rotor temperature and is configured to rotate at a rotor speed (ω). The stator has stator windings at a stator winding temperature (t S ) and the electric machine defines a number of pole pairs (P). A controller is operatively connected to the electric machine and is configured to receive a torque command (T*). The controller has a processor and tangible, non-transitory memory on which is recorded instructions for executing a method for determining a total permanent magnetic flux (ψ T ) as a function of the rotor temperature. Execution of the instructions by the processor causes the controller to determine a high-speed magnetic flux factor (ψ H ) and a low-speed magnetic flux factor (ψ L ).

First claim

The invention claim is:

1. An electric machine assembly comprising:
an electric machine including a stator and a rotor, the rotor having a rotor temperature and configured to rotate at a rotor speed (ω);
wherein the stator has stator windings at a stator winding temperature (t S ) and the electric machine defines a number of pole pairs (P);
a controller operatively connected to the electric machine and configured to receive a torque command (T*);
wherein the controller has a processor and tangible, non-transitory memory on which is recorded instructions for executing a method for determining a total permanent magnetic flux (ψ T ) as a function of the rotor temperature, execution of the instructions by the processor causing the controller to determine a high-speed magnetic flux factor (ψ H ) and a low-speed magnetic flux factor (ψ L );
wherein the controller is operative to control at least one operating parameter of the electric machine based at least partially on the total permanent magnetic flux (ψ T );
wherein the total permanent magnetic flux (ψ T ) is based at least partially on a weighting factor (k), the high-speed magnetic flux factor (ψ H ) and the low-speed magnetic flux factor (ψ L ), such that: ψ T =[k*ψ H +(1−k)*ψ L ] and 0<k<1;
wherein the weighting factor (k) is one when the rotor speed (ω) is above a predefined high speed threshold; and
wherein the weighting factor (k) is zero when the rotor speed (ω) is below a predefined low speed threshold.

2. The assembly of claim 1 , further comprising:
a first temperature sensor operatively connected to the controller and configured to measure the stator winding temperature (t S ); and
a second temperature sensor operatively connected to the controller and configured to measure a rotor temperature.

3. The assembly of claim 1 , wherein determining the total permanent magnetic flux (ψ T ) includes:
obtaining a first function (F 1 ), via the controller, as a product of a look-up factor and the torque command (T*),wherein the look-up factor is based at least partially on the rotor speed (ω), the stator winding temperature (t S ) and a characterized torque error;
wherein the characterized torque error is defined as a difference between two independent estimates of torque produced by the electric machine; and
wherein the look-up factor is a slope of a portion of a graph of the characterized torque error versus the torque command (T*), the portion being below 80% of a maximum of the torque command (T*).

4. The assembly of claim 3 , wherein determining the total permanent magnetic flux (ψ T ) includes: obtaining a second function (F 2 ), via the controller, as a sum of the first function (F 1 ), a torque achieved (T a ) at the rotor temperature and a predefined first constant (Y) such that: F 2 =(F 1 +T a +Y).

5. The assembly of claim 4 , wherein determining the total permanent magnetic flux (ψ T ) includes:
obtaining the low-speed magnetic flux factor (ψ L ) based at least partially on the second function (F 2 ), the magnetic flux (ψ C ) at the baseline temperature, a torque achieved (T C ) at the baseline temperature, a third function (F 3 ) and a fourth function (F 4 ) such that: ψ L =ψ C −[(2*(T C −F 2 )*F 3 )/(3*F 4 )].

6. The assembly of claim 5 , wherein the third function (F 3 ) is a ratio of the stator winding resistance (r C ) at a baseline temperature and a stator winding resistance (r ts ) at the stator winding temperature (t S ) such that: F 3 =(r C r ts ).

7. The assembly of claim 6 , wherein the fourth function (F 4 ) is a product of the pole pair (P) and a commanded current (i d *) such that: F 4 =[P*i q *].

8. The assembly of claim 4 , wherein determining the total permanent magnetic flux (ψ T ) includes:
obtaining the high-speed magnetic flux factor (ψ H ) based at least partially on the second function (F 2 ), the magnetic flux (ψ C ) at the baseline temperature, a stator winding resistance (r ts ) at the stator winding temperature (t S ), a fifth function (F 5 ) and a sixth function (F 6 ) such that: ψ L =ψ C +{2*[F 5 −(r ts *F 2 )]/(3*F 6 )}.

9. The assembly of claim 8 , wherein the fifth function (F 5 ) is a product of the stator winding resistance (r C ) at a baseline temperature and a torque achieved (T C ) at the baseline temperature, such that: F 5 =(r C *T C ).

10. The assembly of claim 9 , wherein the sixth function (F 6 ) is a product of the pole pair (P), the rotor speed (ω), a commanded current (i d *) and an inductance factor (L d0 ) such that: F 6 =[P*ω*i d **L d0 ].

11. A method for determining magnetic flux in an electric machine assembly, the electric machine assembly including an electric machine with a stator having stator windings, a rotor having a rotor temperature and configured to rotate at a rotor speed (ω), and a controller operatively connected to the electric machine, the controller having a processor and tangible, non-transitory memory, the method comprising:
determining a total permanent magnetic flux (ψ T ) as a function of the rotor temperature, including determining a high-speed magnetic flux factor (ψ H ) and a low-speed magnetic flux factor (ψ L );
wherein the total permanent magnetic flux (ψ T ) is based at least partially on a weighting factor (k), the high-speed magnetic flux factor (ψ H ) and the low-speed magnetic flux factor (ψ L ), such that: ψ T =[k*ψ H +(1−k)*ψ L ] and 0<k<1;
wherein the weighting factor (k) is one when the rotor speed (ω) is above a predefined high speed threshold; and
wherein the weighting factor (k) is zero when the rotor speed (ω) is below a predefined low speed threshold; and
controlling the electric machine based upon the total permanent magnetic flux factor (ψ T ) for efficiency.

12. The method of claim 11 , wherein determining the total permanent magnetic flux (ψ T ) includes:
obtaining a first function (F 1 ), via the controller, as a product of a look-up factor and the torque command (T*), wherein the look-up factor is based at least partially on the rotor speed (ω), the stator winding temperature (t S ) and a characterized torque error;
wherein the characterized torque error is defined as a difference between two independent estimates of torque produced by the electric machine; and
wherein the look-up factor is a slope of a portion of a graph of the characterized torque error versus the torque command (T*), the portion being below 80% of a maximum of the torque command (T*).

13. The method of claim 12 , wherein determining the total permanent magnetic flux (ψ T ) includes:
obtaining a second function (F 2 ), via the controller, as a sum of the first function (F 1 ), a torque achieved at the rotor temperature (T tr ) and a predefined first constant (Y) such that: F 2 =(F 1 +T tr +Y).

14. The method of claim 13 , wherein determining the total permanent magnetic flux (ψ T ) includes:
obtaining the low-speed magnetic flux factor (ψ L ), via the controller, based at least partially on the second function (F 2 ), the magnetic flux (ψ C ) at the baseline temperature, a torque achieved (T C ) at the baseline temperature, a third function (F 3 ) and a fourth function (F 4 ) such that: ψ L =ψ C −[(2*(T C −F 2 )*F 3 )/(3*F 4 )].

15. The method of claim 14 , wherein the third function (F 3 ) is a ratio of the stator winding resistance (r C ) at a baseline temperature and a stator winding resistance (r ts ) at the stator winding temperature (t S ) such that: F 3 =(r C /r ts ).

16. The method of claim 14 , wherein the fourth function (F 4 ) is a product of the pole pair (P) and a commanded current (i d *) such that: F 4 =[P*i q *].

Assignees

• Gm Global Tech Operations Llc

Inventors

• Simili Dwarakanath V
• Jang Jihoon

Classifications

• H02P21/141 Primary

  Flux estimation · CPC title

• H02P29/0066 Primary

  Electricity · mapped topic

• H02P29/0055

  Electricity · mapped topic

• H02P21/148

  Electricity · mapped topic

• H02P2207/05

  Synchronous machines, e.g. with permanent magnets or DC excitation · CPC title