CONTROL SYSTEM FOR BEARINGLESS MOTOR-GENERATOR

• US 20090058335A1
• Filed: 10/30/2008
• Published: 03/05/2009
• Est. Priority Date: 12/17/2004
• Status: Active Grant

• Current Assignee: University of Toledo
• Original Assignee: University of Toledo
• Inventors: Kascak, Peter E., Jansen, Ralph H., Dever, Timothy P.
• Granted Patent: US 7,667,418 B2
• Time in Patent Office: Days
• US Class Current: 318/400.20
• CPC Class Codes: F16C 32/0446 Determination of the actual position of the moving member, e.g. details of sensors
• CPC Class Codes: F16C 32/0493 integrated in an electrodynamic machine, e.g. self-bearing motor
• CPC Class Codes: H02K 7/09 with magnetic bearings
• CPC Class Codes: H02P 21/0003 Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control
• CPC Class Codes: H02P 25/16 characterised by the circuit arrangement or by the kind of wiring

Abstract

A control system for an electromagnetic rotary drive for bearingless motor-generators comprises a winding configuration comprising a plurality of individual pole pairs through which phase current flows, each phase current producing both a lateral force and a torque. A motor-generator comprises a stator, a rotor supported for movement relative to the stator, and a control system. The motor-generator comprises a winding configuration supported by the stator. The winding configuration comprises at least three pole pairs through which phase current flows resulting in three three-phase systems. Each phase system has a first rotor reference frame axis current that produces a levitating force with no average torque and a second rotor reference frame axis current that produces torque.

Claims

1. A motor drive system comprising:

an electrical motor having

i) a stator with a core;

ii) a rotor supported for movement relative to the stator, and

iii) polyphase windings wound on the core, each polyphase winding being spatially separated by 360 electrical degrees;

a polyphase power supply for each of the polyphase stator windings, each polyphase power supply comprising a pole pair;

an inner loop controller configured for controlling the polyphase power supply for each of the polyphase windings, the inner loop controller having a pole pair configured for controlling a rotor reference frame q-axis current and

a rotor reference frame d-axis current; and

an outer loop controller configured for;

i) determining torque and force requirements necessary for motoring and levitation (rotor lateral position control); and

ii) converting the torque and force requirements to appropriate commands for the rotor reference frame q-axis currents and the rotor reference frame d-axis currents for each of the polyphase systems,

whereby the rotor reference frame d-axis current commands and the rotor reference frame q-axis currents commands are sent to the inner loop control.

2. The motor drive system of claim 1, wherein the 360 electrical degrees span exactly one of the motor pole pairs.

3. The motor drive system of claim 1, wherein the rotor has the same number of poles as the stator.

4. The motor drive system of claim 1, wherein each polyphase winding is separated by 360 electrical degrees, whereby each winding is configured to interact with exactly one of the motor pole pairs.

5. The motor drive system of claim 1, wherein each polyphase winding which spans one pole pair has one terminal per phase by which power can be applied.

6. The motor drive system of claim 5 wherein the polyphase windings have “

n”

phases, where “

n”

is an integer greater than 1.

7. The motor drive system of claim 6, wherein, when “

n”

is equal to two, each phase in every two-phase winding is exactly the same but spatially separated by 90 electrical degrees.

8. The motor drive system of claim 6, wherein, when “

n”

is greater than two, each phase in the polyphase windings is exactly the same but spatially separated by 360/n electrical degrees.

9. The motor drive system of claim 6, wherein the “

n”

phase stationary reference frame is transformed to a two-phase rotating reference frame.

10. The motor drive system of claim 6, wherein, when the “

n”

polyphase currents are transformed into a two-phase rotating reference frame, a first phase is aligned with rotor flux, which is the rotor reference frame d-axis current; and

a second phase is aligned 90 electrical degrees to the rotor reference frame d-axis current, which is the rotor reference frame q-axis current.

11. The motor drive system of claim 1, wherein each pole pair has an independent rotor reference frame q-axis current and an independent rotor reference frame d-axis current, whereby different a rotor reference frame q-axis flux and a different rotor reference frame d-axis flux are created for each polyphase system.

12. The motor drive system of claim 1, wherein an imbalance of d-axis flux creates a lateral force on the rotor.

13. The motor drive system of claim 1, wherein a d-axis flux requirement is imposed on all pole pairs for motoring, and d-axis flux is added or subtracted to each polyphase pole pair system to create a desired lateral force on the rotor.

14. The motor drive system of claim 1, wherein the sum of all the q-axis flux creates a torque on the rotor.

15. The motor drive system of claim 1, wherein the rotor reference frame q-axis current and the rotor reference frame d-axis current are not directly controlled, such that the q-axis current and the d-axis current do not have an explicit control loop, but are indirectly controlled, since the motor torque and stator flux are directly controlled;

wherein constant motor torque and stator flux produce constant rotor reference frame q and d axis currents.

16. The motor drive system of claim 1, wherein, when energy is converted from electrical energy to mechanical energy, the motor drive system is motoring.

17. The motor drive of claim 1, wherein, when energy is converted from mechanical energy to electrical energy, the motor drive system is generating.

18. The motor drive system of claim 1, wherein the lateral force is a levitating force which is directed in the radial direction for a radial motor, in the axial direction for an axial motor, and in both the radial and axial directions for a conical motor.

19. The motor drive system of claim 1, wherein the lateral force is a levitating force which has components in both the radial and axial directions.

20. The motor drive system of claim 1, wherein the outer loop controller is configured to control radial position.

21. The motor drive system of claim 1, wherein the rotor radial position is determined and subtracted from a desired position to determine position error, wherein a controller determines the force necessary to force this error to zero, and wherein the force is translated to current commands for the inner loop.

23. The motor drive system of claim 1, wherein the rotor has permanent magnets which create the same number of poles as the stator.

24. The motor drive system of claim 1, wherein the rotor is an induction motor type, wherein magnetic flux, induced by the difference of frequency of the stator current and the rotor current, has the same number of poles as the stator.

25. The motor drive system of claim 1, wherein a magnetic circuit of a pole pair and the rotor has periodic varying magnetic reluctance.

26. The motor drive system of claim 1, wherein the rotor has wound coils with the same number of poles as the stator.

27. The motor drive of claim 1, wherein the stator windings are concentrated, one coil per phase.

28. The motor drive of claim 1, wherein the stator windings are distributed, having multiple coils per phase.

29. The motor drive of claim 1, wherein the stator is wound with six poles and the rotor has a six pole structure.

30. The motor drive system of claim 1, wherein the outer loop controller uses six force vectors which are generated by applying rotor reference frame d-axis current to the three pole pairs in a positive or negative manner, to generate a desired arbitrary force.

35. The motor drive system of claim 1, wherein the desired force includes an axial component, and wherein the axial force is created by adding an equal amount of rotor reference frame d-axis current to each of the three phase pole pair systems.

36. The motor drive system of claim 1, wherein the power supply is a plurality three-phase inverters comprised of a plurality of switches for controlling the flow of phase current.

37. The motor drive system of claim 1, wherein the power supply is three three-phase inverters comprised of eighteen switches.

22. The motor drive system of claim 22, wherein the position error is forced to zero with PID control.

31. The motor drive system of claim 31, wherein the angle of the radial component of each of the available six vectors is calculated.

32. The motor drive system of claim 32, wherein two of the available vectors are used to create a force on the rotor.

33. The motor drive of system claim 33, wherein a desired arbitrary force is converted from the vector basis to two rotor reference frame d-axis currents.

34. The motor drive system of claim 34, wherein the desired arbitrary force is given by its x and y components and converted to two rotor reference frame d-axis currents.

38. A five axis suspended bearingless motor drive system comprising:

a plurality of motor drives that share a common rotor structure;

an integrated position controller controlling five position quantities; and

an integrated motoring controller.

39. The motor drive system of claim 38, wherein two motors of conical shape, which produce axial force in opposite directions, are placed on a common rotor structure.

40. The motor drive system of claim 38, wherein a desired net force in the axial direction is achieved by having a different sum of rotor reference frame d-axis currents on each motor.

41. The motor drive system of claim 38, wherein the five axes are defined as the rotor center for a plane intersecting the first motor, in x1 and y1 Cartesian coordinates, and a rotor center at a plane intersecting the second motor, in x2 and y2 Cartesian coordinates, and a distance that the rotor is moved off center axially, defined as z.

42. The motor drive system of claim 38, wherein the five axes are the x and y positions of the center of mass, the two tilt angles about the axes perpendicular to the axis or rotation running through the center of mass, and the displacement of the rotor in the axial direction.