Electric motors
An electric motor has a stator defining multiple stator poles with associated electrical windings, and a rotor having multiple rotor poles. The rotor has flux barriers between adjacent rotor poles, the flux barriers each having a material with an electrical conductivity higher than the rotor pole material. The flux barriers are electrically isolated from one another external to the ferromagnetic material. Eddy currents are induced in the flux barrier to cause destructive interference of an impending magnetic field, such that the flux barrier effectively acts to inhibit magnetic flux during motor operation, which in some cases will result in a repulsive force that will act to increase an induced motive force on the rotor poles.
1. An electric motor, comprising:
a stator defining multiple stator poles with associated electrical windings; and
a rotor having multiple rotor poles, the rotor movable with respect to the stator and defining, together with the stator, a nominal gap between the stator poles and the rotor poles, the rotor poles being of a stack of layers of ferromagnetic material separated from one another, at least at a surface of the rotor, by interfaces less electrically conductive than the ferromagnetic material,
wherein the nominal gap is an axial gap perpendicular to a rotational axis of the rotor,
wherein the rotor comprises flux barriers between adjacent rotor poles, the flux barriers each comprising a material having an electrical conductivity higher than the ferromagnetic material, and
wherein the flux barriers are electrically isolated from one another external to the ferromagnetic material.
2. The electric motor of claim 1 , wherein the axial gap is between an end surface of the rotor and an end surface of the stator that are spaced apart along the rotational axis of the rotor.
3. The electric motor of claim 1 , wherein at least one of the flux barriers comprises an electrically conductive material forming a loop about a core of a core material more magnetically permeable than the electrically conductive material.
4. The electric motor of claim 3 , wherein the core material is ferromagnetic.
5. The electric motor of claim 3 , wherein cores and the rotor poles comprise portions of a contiguous piece of ferromagnetic material.
6. The electric motor of claim 3 , wherein the loop forms a portion of an outer surface of the rotor bounding the nominal gap.
7. The electric motor of claim 6 , wherein the core forms a portion of the outer surface of the rotor surrounded by the loop.
8. The electric motor of claim 3 , wherein the loop is disposed beneath a surface of the rotor bounding the nominal gap and comprising edges of the layers of ferromagnetic material.
9. The electric motor of claim 3 , wherein the loop defines a capacitance.
10. The electric motor of claim 9 , wherein the capacitance is formed at a discrete location along the loop.
11. The electric motor of claim 3 , wherein the loop has a resonant frequency in a transmissible range of the ferromagnetic material.
12. The electric motor of claim 3 , wherein an end surface of the rotor comprises pole surface regions forming the rotor poles and inter-pole surface regions formed by the flux barriers between the pole surface regions.
13. The electric motor of claim 12 , wherein cores and the rotor poles form a continuous whole rotor body, and the electrically conductive material of the flux barriers is cast into the cores.
14. The electric motor of claim 12 , wherein the loop comprises loop portions comprising:
a first loop portion forming a portion of the end surface of the rotor,
a second loop portion extending along a first direction parallel to the rotational axis of the rotor to an extent with a first depth and forming a portion of an outer radial surface of the rotor, the end surface being perpendicular to the outer radial surface, and
a third loop portion extending along a second direction parallel to the rotational axis to an extent with a second depth and forming a portion of an inner radial surface of the rotor, the first depth of the second loop portion being identical to the second depth of the third loop portion.
15. The electric motor of claim 14 , wherein the loop portions further comprise:
fourth and fifth loop portions extending along a radial direction from the inner radial surface of the rotor to the outer radial surface of the rotor to form shielding walls between adjacent rotor poles and the core, wherein the fourth and fifth loop portions extend into a rotor body of the rotor to an extent with a third depth identical to the first depth of the second loop portion and the second depth of the third loop portion.
16. The electric motor of claim 15 , wherein each of the loop portions has a consistent and identical thickness that is greater than an electric current skin depth of the electrically conductive material of the loop at a particular operational frequency.
17. An electric motor comprising:
an active magnetic component having a first surface defining multiple active poles with associated electrical windings; and
a passive magnetic component having a second surface movable with respect to the first surface and spaced from the first surface to define a gap, the second surface having a series of spaced-apart pole surface regions of a first material, separated by inter-pole surface regions of the second surface,
wherein the passive magnetic component comprises magnetically permeable material defining internal paths connecting respective adjacent pairs of the pole surface regions on opposite sides of respective inter-pole surface regions,
wherein the inter-pole surface regions comprise an electrically conductive, low energy product second material and are each electrically isolated from one another external to the magnetically permeable material, and
wherein the passive magnetic component comprises a rotor and the active magnetic component comprises a stator, and wherein the inter-pole surface regions and pole surface regions together form an end surface of the rotor, and wherein the gap is an axial gap between the rotor and stator perpendicular to an axis of rotation of the rotor.
18. The electric motor of claim 17 , wherein the end surface of the rotor is perpendicular to the axis of rotation of the rotor, and wherein the end surface of the rotor is spaced apart from an end surface of the stator along the axis of rotation of the rotor.
19. An electric drive system comprising:
a reluctance motor comprising:
an active magnetic component having a first surface defining multiple active poles with associated electrical windings; and
a passive magnetic component having a second surface movable with respect to the first surface and spaced from the first surface to define a gap, the second surface having a series of spaced-apart pole surface regions of a first material, separated by inter-pole surface regions of the second surface,
wherein the passive magnetic component comprises magnetically permeable material defining internal paths connecting respective adjacent pairs of the pole surface regions on opposite sides of respective inter-pole surface regions, and wherein the inter-pole surface regions comprise an electrically conductive, low energy product second material and are each electrically isolated from one another external to the magnetically permeable material, and
wherein the passive magnetic component comprises a rotor and the active magnetic component comprises a stator, and the inter-pole surface regions and pole surface regions together form an end surface of the rotor, and wherein the gap is an axial gap between the rotor and stator perpendicular to an axis of rotation of the rotor; and
a motor controller comprising multiple switches coupled to respective electrical windings or sets of windings of the active magnetic component.
20. The electric drive system of claim 19 , wherein the motor controller is configured to:
sequentially operate the switches for respective pole energization duty cycles to generate magnetic flux across the nominal gap between the active poles and passive poles; and
during an energization duty cycle of each active pole, to pulse current through the winding of the active pole, including a sequence of at least 3 pulses during which sequence windings of adjacent active poles are not energized,
wherein the electrical windings of the motor are configured such that a ratio of maximum and minimum current through the winding of an energized active pole during current pulsing is at least 4:1.