This invention relates in general to electric machines and, more particularly, to short-flux path motors/generators.
Electric machines using rotor/stator configurations (e.g., switched reluctance motors (SRM) and permanent magnet motors (PMM)) generally include components constructed from magnetic materials such as iron, nickel, or cobalt. In an SRM, a pair of opposing coils in the SRM may become electronically energized. The inner magnetic material is attracted to the energized coil causing an inner assembly to rotate while producing torque. Once alignment is achieved, the pair of opposing coils is de-energized and a next pair of opposing coils is energized. In a PMM, the inner assembly may include permanent magnets, which may provide both push and pull forces relative to the energized coils (as opposed to only pulling forces in an SRM).
According to certain embodiment of the present disclosure, an electric machine includes a stator and a rotor. The stator includes a stator pole including a first leg and a second leg, and a gap defined between the first and second legs. The rotor includes a rotor pole. The rotor is configured to rotate relative to the stator such that the rotor pole rotates through the gap defined between the first and second legs of the stator pole. The stator pole includes a laminar stator pole structure including multiple lamination layers.
According to other embodiments of the present disclosure, an electric machine includes a housing, a stator having a stator pole including a first leg and a second leg, and a rotor including a rotor pole. The rotor is configured to rotate relative to the stator. At least one of the stator and the rotor is adjustably coupled to the housing to allow a distance between the stator pole and the rotor pole to be adjusted.
According to other embodiments of the present disclosure, an electric machine includes a first stator, a first rotor, a second stator, and a second rotor. The first stator has a first perimeter and a plurality of first stator poles arranged around the first perimeter, each first stator pole including a first leg and a second leg. The first rotor is configured to rotate relative to the first stator around a first axis. The second stator has a second perimeter and a plurality of second stator poles arranged around the second perimeter, each second stator pole including a first leg and a second leg. The second rotor is configured to rotate relative to the second stator around the first axis. The second stator is rotationally offset from the first stator about the first axis such that the second stator poles are offset from the first stator poles.
According to other embodiments of the present disclosure, an electric machine includes a stator and a rotor. The stator has a plurality of stator pairs arranged around a stator perimeter, each stator pair including two legs. The rotor has a plurality of rotor blades arranged around a rotor perimeter, each rotor blade including two legs. The rotor rotates relative to the stator. At least three stator pairs are energized simultaneously to generate magnetic circuits with at least three corresponding rotor blades.
According to other embodiments of the present disclosure, an electric machine includes a stator and a rotor. The stator has a plurality of stator pairs arranged around a stator perimeter, each stator pair including two legs. The rotor has a plurality of rotor blades arranged around a rotor perimeter, each rotor blade including two legs. All of the plurality of stator pairs are energized simultaneously and de-energized simultaneously, in an repeating manner, in order to cause the rotor to rotate relative to the stator.
According to other embodiments of the present disclosure, an electric machine includes a stator and a rotor. The stator includes a plurality of stator pairs, each stator pair including two legs defining a gap between the two legs. The rotor includes a plurality of rotor blades including a permanent magnet. The rotor is configured to rotate relative to the stator such that the rotor blade rotate through the gaps between the two legs of each stator pair.
According to other embodiments of the present disclosure, an electric machine includes a stator including a stator pole, a rotor including a rotor pole and configured to rotate relative to the stator, and a housing configured to house a fluid for cooling the stator. A first portion of the stator pole projects through a wall in the housing.
According to other embodiments of the present disclosure, an electric machine includes a stator having a stator pole, a rotor including a rotor pole and configured to rotate relative to the stator, and a plurality of slots formed in the stator or the rotor, the plurality of slots configured to reduce eddy currents during operation of the electric machine.
Certain embodiments of the invention may provide numerous technical advantages. For example, a technical advantage of some embodiments may include the capability to produce very high torque and power densities in motors and generators. Other technical advantages of other embodiments may include the capability to balance forces in short-flux path motor/generators to reduce cogging, vibration, and/or noise. Other technical advantages of other embodiments may include the capability to efficiently remove waste heat from electrical and magnetic circuits by evaporating or boiling a volatile fluid. Yet other technical advantages of other embodiments may include methods for laminating stators and rotors for increased magnetic flux and reduced eddy currents. Yet other technical advantages of other embodiments may include methods for increasing the area of overlap between a stator core and a rotor blade, which may increase torque for a given magnetomotive force Ni. Yet other technical advantages of other embodiments may include methods for interrelating U-shaped stators and U-shaped rotors to increase torque. Yet other technical advantages of other embodiments may include methods for adjusting the stator poles and/or rotor poles in an axial direction in order to adjust the area of overlap between the stator poles and rotor poles, which may be used to control the torque output for a given magnetomotive force Ni. Yet other technical advantages of other embodiments may include methods for configuring and controlling a permanent-magnet flat-blade rotor/U-shaped stator design. Yet other technical advantages of other embodiments may include methods for staggering stator sets to overcome noise, vibration, and/or “cogging” effects. Yet other technical advantages of other embodiments may include methods for cooling the electrical machine. Yet other technical advantages of other embodiments may include methods for penetrating a sealed housing wall with a magnetic circuit. Yet other technical advantages of other embodiments may include methods for reducing eddy currents in non-laminar metal, e.g., using slots. Yet other technical advantages of other embodiments may include methods for linking “magnetic legs” to reduce space, noise, vibration, and/or cogging effects.
Various embodiments according to the present disclosure may include none, any one, or any combination of technical advantages discussed above, and/or various other technical advantages not discussed above.
To provide a more complete understanding of the embodiments of the invention and features and advantages thereof, reference is made to the following description, taken in conjunction with the accompanying FIGURES, wherein like reference numerals represent like parts, in which:
in the U-shaped blade/U-shaped core configuration of
with a denominator of 8 for the 6/4 configuration, 16 for a 12/8 configuration, and 32 for a 24/16 configuration;
It should be understood at the outset that although example implementations of embodiments of the invention are illustrated below, embodiments of the present invention may be implemented using any number of techniques, whether currently known or in existence. The present invention should in no way be limited to the example implementations, drawings, and techniques illustrated below. Additionally, the drawings are not necessarily drawn to scale.
Various electric machines such as motors and generators and type variations associated with such motors and generators may benefit from one or more of the embodiments described herein. Example type variations include, but are not limited to, switched reluctance motors (SRM), permanent magnet AC motors, brushless DC (BLDC) motors, switched reluctance generators (SRG), permanent magnet AC generators, and brushless dc generators (BLDCG). Although particular embodiments are described with reference to one or more type variations of motor and/or generators, it should be expressly understood that such embodiments may be utilized with other type variations of motors or generators. Accordingly, the description provided with certain embodiments described herein are intended only as illustrating examples type variations that may avail benefits of embodiments of the invention. For example, teachings of some embodiment of the invention increase the torque, power densities, and efficiency of electric motors, particularly switched reluctance motors (SRM) and permanent magnet AC motors (PMM). Such embodiments may also be used with brushless DC (BLDC) motors, for example. Some of same advantages described with reference to these embodiments may be realized by switched reluctance generators (SRG), permanent magnet AC generators, and brushless dc generators (BLDCG).
In conventional radial and axial SRMs, the magnetic flux flows through a long path through the whole body of a stator and rotor. Due to the saturation of iron, conventional. SRMs have a large drop in the magneto motive force (MMF) because the flux path is so large. One way to reduce the loss of MMF is to design thicker stators and rotors, which reduces the flux density. However, this approach increases the weight, cost, and size of the machine. Accordingly, teachings of embodiment of the invention recognize that a more desirable approach to reduce these losses is to minimize the flux path, which is a function of geometry and type of machine.
Teachings of some embodiments additionally introduce a new family of stator/pole interactions and configurations for SRMs and PMMs. In this family, stator poles have been changed from a conventional cylindrical shape to U-shaped pole pairs. This configuration allows for a shorter magnetic flux path, which in particular embodiments may improve the efficiency, torque, and power density of the machine.
To take full advantage of the isolated rotor/stator structures of this invention, sensorless SRM, PMM, and BLDC control methods may be utilized, according to particular embodiments.
The switched reluctance motor (SRM) has salient poles on both the stator and rotor. It has concentrated windings on the stator and no winding on the rotor. This structure is inexpensive and rugged, which helps SRMs to operate with high efficiency over a wide speed range. Further, its converter is fault tolerant. SRMs can operate very well in harsh environments, so they can be integrated with mechanical machines (e.g., compressors, expanders, engines, and pumps). However, due to the switching nature of their operation, SRMs need power switches and controllers. The recent availability of inexpensive power semiconductors and digital controllers has allowed SRMs to become a serious competitor to conventional electric drives.
There are several SRM configurations depending on the number and size of the rotor and stator poles. Also, as with conventional electric machines, SRMs can be built as linear-, rotary-, and axial-flux machines. In these configurations, the flux flows 180 electrical degrees through the iron. Due to saturation of iron, this long path can produce a large drop in MMF, which decreases torque density, power, and efficiency of the machines. Increasing the size of the stator and rotor back iron can avoid this MMF drop, but unfortunately, it increases the motor size, weight, and cost. Using bipolar excitation of phases can shorten the flux path, but they need a complex converter. Also, they are not applicable when there is no overlapping in conduction of phases.
In addition, many of the issues discussed above regarding switched reluctance motor (SRM) apply also to permanent magnet motors (PMM).
As an example of MMF drop,
The SRM 200 of
The switched reluctance motor 200 in
In particular embodiments, adding more symmetry will further increase torque. For example, six-fold symmetry would increase the torque by three times compared to a conventional switched reluctance motor. In particular embodiments, increased symmetry may be achieved by making the rotor as blade-like projections that rotate within a U-shaped stator, for example, as described below with reference to the embodiments of
As used herein, the term “U-shaped” may refer to any shape defining a pair of legs or elongated portions, or any curved or non-linear shape defining a pair or ends generally extending in the same direction, including, for example, generally U-shaped, V-shaped, or C-shaped, or multi-pronged. “U-shaped” may also be referred to as “C-shaped” or “V-shaped.”
In the rotor/state configuration 300 of
In particular embodiments, a rotor/stator configuration (e.g., the rotor/stator configuration 300 of
In this embodiment, there are eight outer rotor lobes 411 with eight blades 412 in each radial array 413 of rotor poles. In particular embodiments, such symmetry may be necessary to minimize centrifugal stress/deformation. In this configuration, ferromagnetic materials utilized for the operation of the rotor/stator configuration 450 may only be placed in the blades 412 of the radial array 413.
Details of operation of the inner rotor assembly 430 with respect to the outer rotor assembly 400, according to certain embodiments of the invention, as well as with other configuration variations are described in further detail in one or more of the following United States Patents and/or Patent Application Publications: Publication No. 2003/0228237; Publication No. 2003/0215345; Publication No. 2003/0106301; U.S. Pat. No. 6,336,317; and U.S. Pat. No. 6,530,211.
In certain embodiments, during operation, the rotor may expand due to centrifugal and thermal effects. To prevent contact between the rotor poles and stator poles, a large air gap is typically used. However, it is known that the torque is strongly affected by the air gap: a smaller gap results in more torque. Accordingly, there are advantages to reducing the gap as small as possible. Teachings of some embodiments recognize configurations for maintaining small gap during thermal and centrifugal expansion of a rotor.
The rotor/stator configuration 800 of
The magnetic reluctance of each phase changes with position of the rotor 840. As shown in
The configuration of
For a phase coil with current i linking flux, the co-energy W′can be found from the definite integral:
The torque produced by one phase coil at any rotor position is given by:
The output torque of an SRM is the summation of torque of all phases:
If the saturation effect is neglected, the instantaneous torque can be given as:
From Equation 4, it can be seen that to produce positive torque (motoring torque) in SRM, the phase has to be excited when the phase bulk inductance increases, which is the time that the rotor moves towards the stator pole. Then it should be unexcited when it is in aligned position. This cycle can be shown as a loop in flux linkage (λ)—phase current (iph) plane, which is called energy conversion loop as shown in
where, Np, Nr, Nph, ω are the number of stator pole pairs per phase, number of rotor poles, number of stator phases, and rotor speed, respectively.
By changing the number of phases, stator pole pitch, and stator phase-to-phase distance angle, different types of short-flux-path SRMs can be designed.
In this embodiment and other embodiments, there may be no need for a magnetic back-iron in the stator. Further, in this embodiment and other embodiments, the rotor may not carry any magnetic source. Yet further, in particular embodiments, the back iron of the rotor may not need to be made of ferromagnetic material, thereby creating flexibility design of the interface to the mechanical load.
In this embodiment and other embodiments, configuration may offer higher levels of power density, a better participation of stator and the rotor in force generation process and lower iron losses, thereby offering a good solution for high frequency applications. In various embodiments described herein, the number of stator and rotor poles can be selected to tailor a desired torque versus speed characteristics. In particular embodiments, cooling of the stator may be very easy. Further, the modular structure of certain embodiments may offer a survivable performance in the event of failure in one or more phases.
For an optimal operation, the tangential component of the force needs to be optimized while the normal component of the force has to be kept at a minimal level or possibly eliminated. This, however, is not the case in conventional electromechanical converters. To the contrary, the normal force forms the dominant product of the electromechanical energy conversion process. The main reason for this can be explained by the continuity theorem given below. As the flux lines enter from air into a ferromagnetic material with high relative permeability the tangential and normal components of the flux density will vary according to the following equations:
The above equations suggest that the flux lines in the air gap will enter the iron almost perpendicularly and then immediately change direction once enter the iron. This in turn suggests that in a SRM and on the surface of the rotor we only have radial forces.
To enhance the migration of flux lines towards the fringing area, one embodiment of the invention uses a composite rotor surface. In the composite rotor surface, the top most part of the of the rotor is formed by a material that goes to saturation easier and at a lower flux density, thereby reinforcing the fringing at an earlier stage of the electromechanical energy conversion process. In particular embodiments, the shape of the flux barrier or the shape of the composite can be optimized to take full advantage of the magnetic configuration. In another embodiment, flux barriers can be introduced in the rotor to discriminate against radial fluxes entering the rotor normally and push more flux lines towards the fringing area.
Various different rotor/stator configurations are disclosed herein. One type of rotor/stator configuration disclosed herein may be referred to at “U-shaped core/flat blade” rotor/stator configurations. Some examples of the U-shaped core/flat blade configuration are shown and discussed above with reference to
Another type of rotor/stator configuration disclosed herein may be referred to as “U-shaped blade/U-shaped core” rotor/stator configurations. Some examples of the U-shaped blade/U-shaped core configuration are shown and discussed above with reference to
Presented below are methods for calculating the theoretical torque and other performance characteristics provided by various rotor/stator configurations. In particular,
F=Ni=F
c
+F
g
+F
b (9)
where
F=Ni=H
c
l
c
+H
g2g+Hbw (10)
where
B=μH (11)
where
All or portions of blade 1700 and core 1702 may be formed from any suitable materials. In certain applications, metals with high magnetic permeability may be preferred. As an example only, blade 1700 and/or core 1702 may be formed from 0.012-inch-thick M-5 grain-oriented electrical steel.
Various example dimensions are shown in
where
The magnetic flux φ is the same everywhere in the circuit and follows:
φBcAc=BgAg=BbAb (13)
where
If the flat blade width w is small, the magnetic field lines do not have enough space to spread out so the magnetic flux density of the air gap and flat blade 1700 are about the same, thus allowing the following approximation to be made:
Ab≈Ag (14)
Using this relationship, the magnetic flux density can be calculated in each portion of the magnetic circuit.
Substituting the relationships in Equations 15 into Equation 12 gives the following:
The terms in the brackets are the reluctance R (A·turn/Wb) of each portion of the magnetic circuit.
F=Ni=φ+(Rc+Rg+Rb) (17)
where
The work required to supply the energy to a magnetic field is:
where
Substituting the expressions in Equations 18 gives:
The areas may be expressed relative to the core area Ac as follows:
Using the approximation shown in Equation 14, the following equation results:
The instantaneous air gap Ag, which is the instantaneous area of overlap between blade 1700 and core 1702 as blade 1700 moves through the gap between legs 1708 and 1710, is:
where
Equation 25 may be substituted into Equation 19 to give the work required to build the magnetic field:
The following definitions
may be substituted into Equation 26 to provide:
The force f acting on the flat blade as the magnetic flux increases follows:
Taking the derivative of Equation 28 gives
If the core and flat blade are not saturated (where saturated=maximum magnetic flux through the circuit) then Equation 30 simplifies to:
Equation 31 indicates that as long as core 1702 is not saturated, the force acting on flat blade 1700 will be constant and independent of the position x of flat blade 1700. Further, for a given core area Ac and magnetomotive force Ni, the force increases with a smaller gap g, increases with larger close air gap area Ago, and decreases with greater flat blade width b.
Using the following procedure, the equations above allow the calculation of the force in a flat blade, allowing for saturation of the core:
1. Specify the following: Ac, Ago/Ac, b, lc, w, g, Ni, x.
2. Guess φ.
3. Calculate Bc, Bg, and Bb (Equations 15).
4. Calculate μc and μb (e.g., see
5. Calculate φ (Equation 16).
6. Iterate Steps 2 to 5 until convergence.
7. Calculate A, B, and C (Equations 27).
8. Calculate f ((Equation 30).
As shown in
The graphs shown in
In some embodiments, for a torque-dense electric motor, the core should saturate (i.e., maximum B) just as the air gap is fully closed by the blade (i.e., when x/b=1). This strategy may take maximum advantage of the flux carrying capacity of the core. As shown in
To maximize the torque from an electric motor, the core should saturate near x/b=1 (full closure of the air gap between the blade and core). For the condition of saturation at closure (x/b=1):
φmax=Bc,maxAc (32)
The maximum magnetic flux occurs with the maximum allowable magnetomotive force (Ni)max. From Equation 16 for a flat blade:
where Ag=Ab=Ago@x/b=1. Substituting Equation 32 into Equation 33 gives:
The following example shows example parameter values, some of which are taken from
In this example, the reluctance of the blade is small, the reluctance of the air gap is large, and the reluctance of the core is significant. It should be understood that these values are examples only, and that any other suitable values may be used.
Equation 34 may be reformulated as:
where p for the example above is:
Substituting Equation 35 into Equation 31 gives:
The power density of a motor is determined by its average torque and speed. The analysis presented above describes the torque ability of a motor. The volumetric torque density can be calculated as follows:
where
L*=length of unit cell (m)
The number of turns in a wire bundle is:
An individual wire of cross-sectional area Ai has a maximum current capacity imax, which is determined by the electrical conductivity, the heat transfer coefficient, and the allowable temperature rise.
For 10-gauge copper wire (as an example only), standard tables recommend the following:
Multiplying Equation 41 by Equation 42 gives:
Comparison of Equation 43 with Equation 35 shows that the wire bundle cross-sectional area Aw is:
Various example dimensions are shown in
Various example dimensions are shown in
The analysis of the geometries shown in
As a consequence of this increased flux path distance in the configurations of
Ac=Ago=Ab (45)
The inductance of the magnetic circuit in such configurations is as follows:
where
which may be substituted into Equation 46:
The work required to build the magnetic field follows:
The following definitions:
may be substituted into Equation 49:
The force f acting on the blade as the magnetic flux increases follows:
Taking the derivative of Equation 51 gives:
If the core and blade are not saturated then Equation 53 simplifies to:
In certain embodiments, to maximize the torque from an electric motor, the core should saturate near x/c=1 (full closure of the air gap between the blade and the core). For the condition of saturation at closure (x/c=1):
φmax=Bc,maxAc (55)
The maximum magnetic flux occurs with the maximum allowable magnetomotive force (Ni)max.
Assume μb=μc at x/c=1 (i.e., the core and blade materials are the same). Substituting Equation 55 into Equation 56 gives:
Equation 57 may be reformulated as
where p is:
Substituting Equation 58 into Equation 54 gives:
The volumetric torque density can be calculated as follows:
Laminations of Stator and/or Rotor Components
In some embodiments, all or certain portions of the stator and/or rotor may be formed in a laminar manner, which may act to channel the magnetic flux in the direction of the laminar layers, thus reducing undesirable eddy currents.
In this example, flat blade 1950 has a laminar structure in which the layers are generally formed in planes perpendicular to a plane about which rotor 1952 rotates (i.e., a plane defined by a pattern traced by a point on flat blade 1950 as rotor 1952 rotates). Also, U-shaped core 1954 has a laminar structure that generally bends around the U-shaped length of the core. In this example, the laminar structure turns inward toward the end portion of each stator leg. Thus, with such configuration, the lamination layers of flat blade 1950 are aligned generally parallel with the lamination layers exposed at the ends of the two stator legs when flat blade 1950 passes between the stator legs. Thus, the magnetic flux may be channeled through flat blade 1950 from one stator leg to the other, and eddy currents may be reduced.
In this example, flat blade 1950 and U-shaped core 1954 each include five lamination layers. Again, it should be understood that any suitable number of layers may be used.
FIGS. 39 and 40A-40C illustrate an example technique for forming and utilizing a laminar U-shaped stator 1960 having an area ratio Ago/Ac>1, according to certain embodiments.
The laminar material 1970 may be wrapped around mandrel 1972 any desired number of times to form any desired number of lamination layers. For example, as shown in
In alternative embodiments, the position of rotor blade 1990 may be axially adjusted toward or away from stator pair 1960 (e.g., toward or away from a center point about which the rotor rotates) in order to adjust a distance between a point on stator pair 1960 and a point on rotor blade 1990. In such embodiments, rotor blade 1990 may be adjusted in any suitable manner, e.g., using a screw connected to a rotor yoke or support structure, or any other suitable adjustment mechanism.
In other embodiments, the positions of both stator pair 1960 and rotor blade 1990 may be independently adjusted.
Various rotor/stator configuration options are analyzed and compared below. In particular, the torque density and power density generated by various rotor/stator configuration options are calculated and compared as described below.
For 12/10 and 24/22 switched reluctance motors, the denominators are 24 and 48, respectively (instead of 12).
As shown in
The area of the core Ac relative to the surface area of the rotor Ar at radius r follows:
The core area Ac can be calculated as:
where
For this geometry, r=rf
where p is:
r
o
=r+d+0.5c (67)
From Equation 44, an expression for d follows:
The length of a unit cell is the same as the overall length of the motor:
L*=L (69)
e=L*−2(0.5c) (70)
The core area Ac can be calculated as:
where
For this geometry, r=rf (where rf is the effective radius at which the torque is applied)
where p is:
As shown in the unit cell (
r
0
=r+d+c (76)
From Equation 44, an expression for d follows:
The parameter e depends upon the length and the number of stator sets provided along the axis indicated by arrow A.
As discussed above,
In the example configuration shown in
L*=½L (78)
As shown in the unit cell (
e=L*−2(0.5c) (79)
Rotor/Stator Configuration Option B2: U-Shaped Blade/U-Shaped Core with Double Number of Rotors and Stators
In the example embodiment shown in
Opposite stator pairs 1-12 are energized sequentially (currently energized stators are indicated with dark shading) and the relevant U-shaped blades 2408 complete the magnetic circuits. The configuration of
Because the geometry of Option B2 is similar to that of Option B1 (but with double the number of rotors and stators), the rotor and stator width c for Option B2 may be defined with reference to
If the number of stator pairs is halved to six, then the denominator is 12. If number of stator pairs is doubled to 24, then the denominator is 48.
As shown in
L*=L (81)
The other formulas are identical to Option B1.
Rotor/Stator Configuration Option B3: U-Shaped Blade/U-Shaped Core with All Stators Energized/De-Energized Simultaneously
Referring back to the 12/12 configuration shown in
If the number of stator pairs is halved to six, then the denominator is 12. If number of stator pairs is doubled to 24, then the denominator is 48. If number of stator pairs is 16 (e.g., the configuration shown in
As shown in
L*=½L (83)
The other formulas are identical to Option B1.
with a denominator of 8. The denominator for b is 16 for a 12/8 configuration (see
Neglecting edge effects, the area of the core Ar relative to the surface area of the rotor Ac at radius r follows:
The core area Ac can be calculated as:
where
This equation allows the independent specification of Ago/Ac and a/b, where p is
The value for a is
a=(a/b)b (88)
From the unit cell (
L*=2a+0.3333b (89)
The radius where the force is applied, rf, is:
and ro is:
r
o
=r+d+a (91)
From Equation 44, an expression for d follows:
Rotor/Stator Configuration Option C2: Flat Blade/U-Shaped. Core with Reduced Core Width
The ratio j shown in
with a denominator of 8 for the 6/4 configuration, 16 for a 12/8 configuration, and 32 for a 24/16 configuration. (Note: this is the same as Option C1.)
The width of the wire bundle (coil) is m:
Neglecting edge effects, the area of the core Ac relative to the surface area of the rotor Ar at radius r follows:
The core area Ac can be calculated as:
where
This equation allows the independent specification of j, Ago/Ac and a/b where p is:
The value for a is:
a=(a/b)b (99)
From the unit cell (
L*=2a+2m (100)
The radius where the force is applied is:
The relationship for ro is:
r
0
=r+d+a (102)
From Equation 44, an expression for d follows:
Rotor/Stator Configuration Option D: Flat Blade/U-Shaped Core with Permanent Magnet Blades
In the example embodiment shown in
As shown in
In some embodiments, the blade magnets need not be particularly strong because an area ratio Ago/Ac greater than 1 may be used, which concentrates the flux density in the core. For example, as shown in
With configuration Option D, an equal number of stators and blades can be employed. For example,
with a denominator of 8 for the 6/6 configuration, 16 for a 16/16 configuration, and 32 for a 32/32 configuration.
Because the stators are adjacent to each other, if multiple stator sets are used in a particular machine, they may be configured as shown in
The width of the wire bundle is in:
Neglecting edge effects, the area of the core Ac relative to the surface area of the rotor Ar at radius r follows:
The core area Ac can be calculated as:
where
This equation allows the independent specification of, j, Ago/Ac and a/b. The relationship for p is identical to Option C2. The value for a is
a=(a/b)b (110)
From the unit cell (
L*=2a+2m (111)
The radius where the force is applied is:
and ro is:
r
0
=r+d+a (113)
From Equation 44, an expression for d follows:
Provided below are sample calculations for determining the torque density and power density generated by various configuration options discussed above, including configuration Options A, B1, B2, B3, C1, C2, and D. The calculations are based on the “unit cell” methodology explained above such that the different configurations can be fairly compared to each other, generally on a torque-per-physical-volume basis or a power-per-physical-volume basis. In addition, the calculations are based on example dimensions and other physical parameter values. It should be understood that these dimensions and other values are examples only and in no way limit the scope of any embodiments to such dimensions or values.
Option B2: U-Shaped Blade/U-Shaped Core Rotor/Stator Configuration with Double Number of Rotors and Stators
Option B3: U-Shaped. Blade/U-Shaped Core Rotor/Stator Configuration with All Stators Energized/De-energized Simultaneously
Option C2: Flat Blade/U-Shaped Core Rotor/Stator Configuration with Reduced Core Width
Option D: Flat Blade/U-Shaped Core Rotor/Stator Configuration with Permanent Magnet Blades
Tables 1 and 2 summarize the torque density and power density, respectively, resulting from the parametric evaluation of the seven different configurations options. By examining Tables 1 and 2, the following conclusions may be made:
The above description has focused on applying this technology to an electric motor in which electrical energy is converted to rotating shaft power. The concepts may be equally well applied to generators in which rotating shaft power is converted to electrical energy.
A housing 3010 may be provided for housing a cooling fluid. An end portion of each stator pole leg (or stator pole for conventional SRM configurations) 3004 may extend or pierce through a housing wall 3014 of housing 3010. The interface between each stator pole 3004 and housing wall 3014 may be sealed in any suitable manner to prevent cooling fluid 3012 from escaping housing 3010.
Housing wall 3014 may serve to isolate gases, indicated at 3020, that may have a composition and/or pressure different than the surrounding atmosphere. For example, housing wall 3014 may be used to contain gases that are being compressed or expanded using a gerotor compressor/expander, e.g., as described in any of the following United States Patents and Patent Application Publications: Publication No. 2003/0228237; Publication No. 2003/0215345; Publication No. 2003/0106301; U.S. Pat. No. 6,336,317; and U.S. Pat. No. 6,530,211.
Because thermal energy is typically generated from electrical resistance in the wire bundles, and hysteresis losses in the core, stator 3002 may become overheated. To prevent this possibility, stator poles 3004 may be immersed in a cooling fluid 3012 (e.g., gas and/or liquid), as shown in
The thermal energy produced by operation of the device may cause the volatile fluid 3012 to change phase from a liquid to a vapor, which phase change removes thermal energy in the form of latent heat. Because the liquid is boiling, the heat transfer coefficients may be very high, and may thus prevent overheating of stator 3002. In some embodiments, the vapors can be condensed in a heat exchanger 3026, which converts the vapors back into a liquid. In essence, the system is a heat pipe, which is one of the most efficient means for removing heat from systems.
In addition, the laminar and non-laminar portions of stator pole 3004 may be intimately joined together in any suitable manner to eliminate air gaps that would resist the magnetic flux between the two stator pole components. For example, the two stator pole components may be mechanically joined, e.g., using a dovetail joint 3040 shown in
In addition, in some embodiments, as shown in
In this configuration, a flat blade 3070 passes between stator legs 3062 and 3064, as discussed above regarding
The short-flux-path configurations described with reference to the various embodiments herein may be implemented for various SRM motors and/or generators applications by changing the number of stator and rotor poles, sizes, and geometries. Similar configuration may also be utilized for axial-field and linear motors. Several embodiments described herein (e.g., configuration Option D discussed above) may additionally be used for permanent magnet AC machines where the rotor contains alternating permanent magnet poles. Additionally, the embodiments described above may be turned inside out and used as an interior stator SRM or BLDC machines, with the rotor on the outside. These in turn can be used as motor, generators, or both.
Numerous other changes, substitutions, variations, alterations, and modifications may be ascertained to one skilled in the art and it is intended that the present invention encompass all such changes, substitutions, variations, alterations, and modifications as falling within the scope of the appended claims.
This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/952,339, filed. Jul. 27, 2007, The contents of that application are incorporated herein in their entirety by this reference.
Number | Date | Country | |
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60952339 | Jul 2007 | US |
Number | Date | Country | |
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Parent | 12180090 | Jul 2008 | US |
Child | 13300394 | US |