Selective phase control of an electric machine
Methods, controllers and electric machine systems are described for selective phase control of electric machines (e.g. electric motors and generators).
1. An electric machine, comprising:
a stator having a multiplicity of spaced-apart individual stator windings; and
a rotor in proximity to the stator, the rotor being rotationally responsive to current delivered to the individual stator windings;
a controller, the controller being electrically coupled to the stator so as to independently provide delivery of current to the individual stator windings, the controller configured to;
deliver current to the individual stator windings in a plurality of sequential phases to drive motion of the rotor; and
selectively skip one or more of the plurality of sequential phases or a portion of one or more of the plurality of sequential phases in response to an input demand to the electric machine.
2. The electric machine as recited in claim 1 , wherein each phase of the plurality of sequential phases corresponds to a delivery of current to one or more respective stator windings; and
wherein selectively skipping one or more of the plurality of sequential phases comprises restricting or limiting delivery of current the one or more respective stator windings corresponding to a skipped phase.
3. The electric machine as recited in claim 1 , wherein the controller is further configured to modify one or more of a magnitude and timing of one or more of the plurality of sequential phases that are not selected to be skipped.
4. The electric machine as recited in claim 3 , wherein the one or more of the magnitude and timing are selected to modify an output of the electric machine to correspond to the input demand.
5. The electric machine as recited in claim 4 , wherein modifying the timing of a non-skipped phase comprises modifying one or more commutation angles of the non-skipped phase.
6. The electric machine as recited in claim 1 , wherein the controller is further configured to determine a skip fraction corresponding to the input demand, the skip fraction corresponding to a ratio of the number of skipped phases to phase activation opportunities.
7. The electric machine as recited in claim 6 , wherein the skip fraction is calculated as a function of the input demand and a given machine speed.
8. The electric machine as recited in claim 6 , wherein the controller is further configured to select a phase timing sequence as a function of the skip fraction, the phase timing sequence comprising selection of which phases are skipped from the plurality of sequential phases.
9. The electric machine as recited in claim 8 , wherein the controller comprises a sigma-delta controller configured to calculate the phase timing sequence.
10. The electric machine as recited in claim 1 , wherein the electric machine comprises a switch reluctance motor.
11. A method of controlling operation of an electric machine, the method comprising:
providing a rotor in proximity to a stator, the stator comprising a multiplicity of spaced-apart individual stator windings and the rotor being rotationally responsive to current delivered to the individual stator windings;
delivering current to the individual stator windings in a plurality of sequential phases to drive motion of the rotor; and
selectively skipping one or more of the plurality of sequential phases or a portion of one or more of the plurality of sequential phases in response to an input demand to the electric machine.
12. The method as recited in claim 11 , wherein each phase of the plurality of sequential phases corresponds to a delivery of current to one or more respective stator windings; and
wherein selectively skipping one or more of the plurality of sequential phases comprises restricting or limiting delivery of current the one or more respective stator windings corresponding to a skipped phase.
13. The method as recited in claim 11 , further comprising:
modifying one or more of a magnitude and timing of one or more of the plurality of sequential phases that are not selected to be skipped.
14. The method as recited in claim 13 , wherein the one or more of the magnitude and timing are selected to modify an output of the electric machine to correspond to the input demand.
15. The method as recited in claim 14 , wherein modifying the timing of a non-skipped phase comprises modifying one or more commutation angles of the non-skipped phase.
16. The method as recited in claim 11 , further comprising:
determining a skip fraction corresponding to the input demand, the skip fraction corresponding to a ratio of the number of skipped phases to phase activation opportunities.
17. The method as recited in claim 16 , wherein the skip fraction is calculated as a function of the input demand and a given machine speed.
18. The method as recited in claim 16 , further comprising:
calculating a phase timing sequence as a function of the skip fraction, the phase timing sequence comprising selection of which phases are skipped from the plurality of sequential phases.
19. The method as recited in claim 18 , wherein a sigma-delta controller is used to calculate the phase timing sequence.
20. The method as recited in claim 11 , wherein the electric machine comprises a switch reluctance motor.