U.S. patent application number 17/487334 was filed with the patent office on 2022-01-13 for parallel magnetic circuit motor.
This patent application is currently assigned to QM Power, Inc.. The applicant listed for this patent is QM Power, Inc.. Invention is credited to Charles J. Flynn.
Application Number | 20220014080 17/487334 |
Document ID | / |
Family ID | |
Filed Date | 2022-01-13 |
United States Patent
Application |
20220014080 |
Kind Code |
A1 |
Flynn; Charles J. |
January 13, 2022 |
Parallel Magnetic Circuit Motor
Abstract
A parallel magnetic circuit motor includes a rotor without
magnets and a stator with magnets. The stator has stator poles with
windings. The windings are energized on a first plurality of stator
poles with current in a same first direction and the windings are
energized on a second plurality of stator poles with current in a
same second direction opposite the same first direction.
Inventors: |
Flynn; Charles J.;
(Greenwood, MO) |
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Applicant: |
Name |
City |
State |
Country |
Type |
QM Power, Inc. |
Kansas City |
MO |
US |
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|
Assignee: |
QM Power, Inc.
Kansas City
MO
|
Appl. No.: |
17/487334 |
Filed: |
September 28, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16459503 |
Jul 1, 2019 |
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17487334 |
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12907858 |
Oct 19, 2010 |
10340778 |
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16459503 |
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61253018 |
Oct 19, 2009 |
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International
Class: |
H02K 21/44 20060101
H02K021/44; H02K 1/17 20060101 H02K001/17 |
Claims
1. A method comprising: in a machine comprising a rotor without
magnets and a stator comprising a plurality of phase sections, each
phase section corresponding to one of a plurality of electrically
independent phases of the machine and each phase section having
pairs of pole faces of permanent magnets arranged with same facing
magnetic poles in which a magnetic pole of a permanent magnet faces
a same magnetic pole of another permanent magnet, a plurality of
stator poles between the same facing permanent magnet pole faces,
and a winding on each of the stator poles, energizing windings on
two stator poles of each phase section in a same first direction
and energizing windings on two other stator poles of each phase
section in a same second direction opposite the same first
direction
2. The method of claim 1 wherein: each winding has a side facing
one of the permanent magnets and another side facing the rotor; and
the method further comprises energizing first windings between two
north same facing permanent magnet pole faces to cause each first
winding to have a south magnetic pole on the permanent magnet side
and a north magnetic pole on the rotor side.
3. The method of claim 1 wherein: the two stator poles comprise
first and second stator poles; the other two stator poles comprise
third and fourth stator poles; the first stator pole has a first
winding wound about the first stator pole, the second stator pole
has a second winding wound about the second stator pole, the third
stator pole has a third winding wound about the third stator pole,
and the fourth stator pole has a fourth winding wound about the
fourth stator pole; the first and third windings are wound in a
winding same first direction; the second and fourth windings are
wound in a winding same second direction; and the method further
comprises: energizing the first and third windings with a first
current in the same first direction; and energizing the second and
fourth windings with a second current in the same second direction
opposite the same first direction.
4. The method of claim 3 further comprising: energizing the first
and third windings with the first current in the same first
direction while not energizing the second and fourth windings; and
energizing the second and fourth windings with the second current
in the same second direction opposite the same first direction
while not energizing the first and third windings.
5. The method of claim 3 further comprising energizing the first
and third windings with a first magnitude of current and energizing
the second and fourth windings with a second magnitude of current,
wherein the first magnitude of current is different than the second
magnitude of current.
6. The method of claim 5 further comprising energizing the first
and third windings with a first unidirectional current having a
first magnitude of current and energizing the second and fourth
windings with a second unidirectional current having a second
magnitude of current, wherein: the second unidirectional current
flows in a direction opposite of the first unidirectional current;
the first magnitude of current energizes at least one of the first
and third windings to produce a flux linkage between the rotor and
the stator; and the second magnitude of current energizes at least
one of the second and fourth windings to prevent the flux linkage
between the rotor and the stator.
7. The method of claim 3 further comprising dissipating energy
stored in the first and third windings prior to a rotor pole and
one of the stator poles coming into full alignment.
8. The method of claim 3 further comprising dissipating energy
stored in the first and third windings prior to a rotor pole and
one of the stator poles coming into full alignment and cause the
dissipating energy to flow into the second and fourth windings and
maintain flux through the first and second windings as the rotor
pole and the one of the stator poles move into full alignment.
9. The method of claim 3 wherein the first current enters a first
start turn of the first winding and exits a second start turn of
the third winding, and the second current enters a third start turn
of the second winding and exits a fourth start turn of the fourth
winding.
10. The method of claim 9 wherein the first current causes magnetic
flux from north same facing permanent magnet pole faces to traverse
from the first winding through the rotor and through the third
winding to south same facing permanent magnet pole faces.
11. The method of claim 9 wherein the second current causes
magnetic flux from south same facing permanent magnet pole faces to
traverse from the fourth winding through the rotor and through the
second winding to north same facing permanent magnet pole
faces.
12. The method of claim 1 further comprising changing direction of
rotation of the rotor by changing a sequence of energizing the
windings.
13. The method of claim 1 further comprising controlling torque by
altering a voltage used for energizing the windings.
14. The method of claim 1 further comprising controlling speed by
altering a voltage used for energizing the windings.
15. The method of claim 1 further comprising selecting the machine
as at least one of a two phase machine, a three phase machine, and
a six phase machine.
16. The method of claim 1 further comprising selecting the machine
as at least one of a two phase motor, a three phase motor, and a
six phase motor.
17. The method of claim 1 wherein the machine produces
unidirectional torque.
18. A method comprising: in a machine comprising a rotor without
magnets and a stator comprising a plurality of phase sections, each
phase section corresponding to one of a plurality of electrically
independent phases of the machine and each phase section having
pairs of pole faces of permanent magnets arranged with same facing
magnetic poles in which a magnetic pole of a permanent magnet faces
a same magnetic pole of another permanent magnet, an even number of
stator poles between the same facing permanent magnet pole faces,
and a winding on each of the stator poles, energizing windings on
two stator poles of each phase section in a same first direction
and energizing windings on two other stator poles of each phase
section in a same second direction opposite the same first
direction
19. The method of claim 18 wherein: each winding has a side facing
one of the permanent magnets and another side facing the rotor; and
the method further comprises energizing first windings between two
north same facing permanent magnet pole faces to cause each first
winding to have a south magnetic pole on the permanent magnet side
and a north magnetic pole on the rotor side.
20. The method of claim 18 further comprising changing direction of
rotation of the rotor by changing a sequence of energizing the
windings.
21. The method of claim 18 further comprising controlling torque by
altering a voltage used for energizing the windings.
22. The method of claim 18 further comprising controlling speed by
altering a voltage used for energizing the windings.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/459,503, filed Jul. 1, 2019, entitled
Parallel Magnetic Circuit Motor, which is a continuation of U.S.
patent application Ser. No. 12/907,858, filed Oct. 19, 2010,
entitled Parallel Magnetic Circuit Motor (now U.S. Pat. No.
10,340,778 issued Jul. 2, 2019), which claims priority to U.S.
Provisional Patent Application No. 61/253,018, filed Oct. 19, 2009,
entitled Parallel Magnetic Circuit Motor, the entire contents of
which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates generally to motors. More
particularly, this invention is directed toward a parallel magnetic
circuit motor.
BACKGROUND
[0003] It is desirable to optimize the magnetic circuit used in
permanent magnet [PM] machines to obtain the highest power density
and efficiency possible. Since PM machines typically have a
relatively narrow high efficiency region on their fixed commutation
(uncontrolled) torque vs. speed curve, many rotating machine
technologists focus on increasing the motor size to power out ratio
and the motor controller to enhance the overall performance of PM
machines.
[0004] The focus on the controller to enhance the performance of PM
machines is predicated on the belief that PM machines already
operate at shear stress levels fairly close to their component
materials' physical limits. This statement is misleading, however,
since the true limiting factors are actually the permanent magnets
and the geometry of the machine in which they are used, not the
magnetically soft core materials as implied.
[0005] Wound field machines such as series wound, switched or
variable reluctance machines can operate at shear stress levels at
the material limits. Since these machines use field coils, rather
than permanent magnets to produce the static magnetic field, the
only limitation to the magnitude of the static field is the current
carrying capacity of the copper wire. Such machines can reach the
physical limits of the magnetically soft core material and produce
high gap flux densities, but also result in increased I.sup.2R
losses in the wound field coils and an increase in weight due to
the field coils.
[0006] Permanent magnets are used in rotating machines to replace
the field coils that produce static magnetic fields to provide
three primary benefits: [0007] 1) A reduction in the size of the
machine since the magnets are physically smaller than the coils
they replace; [0008] 2) A reduction in the weight of the machine
since the magnets are physically lighter than the coils they
replace; and [0009] 3) The elimination of the I.sup.2R losses
attributed to the field coils, thus reducing heat losses and
therefore improving the overall machine efficiency.
[0010] However, replacing a rotating machine's field coils with
permanent magnets has the following trade-offs/limitations: [0011]
1) The energy product of a permanent magnet is fixed, thereby
limiting the controllability of the static magnetic field; [0012]
2) State of the art permanent magnets cannot achieve the gap flux
densities that can be achieved with wound field coils; [0013] 3)
Permanent magnets do not make good structural components and can
create bonding issues when placed on a machine's rotor; [0014] 4)
Permanent magnets are more sensitive to temperature; and [0015] 5)
The gap flux density is determined by the energy product of the
permanent magnet and will always be less than B.sub.r or
approximately 1.25 Tesla for neodymium magnets with a typical gap
flux density of 0.8.about.1 Tesla with no power in the phase coils.
The field intensity [H] of the phase coils will drive the gap
density higher but cannot exceed .about.Br of the permanent
magnets. If the flux in the air gap coupling a permanent magnet and
a phase coil exceeds B.sub.r, the amount greater than B.sub.r will
be primarily uncontrolled fringing flux. The permanent magnet's
domains between B.sub.r and B.sub.max require a greater amount of
energy to bring them into temporary magnetic alignment.
[0016] This is not meant to diminish the importance of the motor
controller for improving performance but rather to state that
mathematically, analytically and empirically it can be shown that
the current and commonly accepted PM machine geometries cannot
achieve the shear stress levels of wound field machines. The
typical PM geometry is based on the concept of simply replacing a
wound field coil with a PM without fully realizing or accepting the
limitations and consequences of such a simplistic approach.
Therefore, it would be desirable to provide an improved PM circuit
motor.
SUMMARY
[0017] A parallel magnetic circuit motor has a rotor without
magnets and a stator with magnets. Stator segments have windings.
The rotor, stator and windings are configured to produce
unidirectional current and torque with electrically independent
phases.
[0018] The disclosed Parallel Magnetic Circuit [PMC] or Parallel
Path Magnetic Technology [PPMT] geometry provides solutions for
many of the limitations imposed by merely replacing a machine's
wound field coils with permanent magnets. Improvements include:
[0019] Increased power density by producing gap flux densities
equal to those of a field wound motor; [0020] Increased efficiency
by maintaining the I.sup.2R loss reduction and weight benefits for
using permanent magnets rather than wound field coils; [0021]
Increased efficiency and reliability from the ability to redirect
the static field of a permanent magnet without applying a
destructive opposing field; and [0022] Increased reliability from
negating issues associated with attaching or bonding permanent
magnets to a rotating machine's rotor.
[0023] Notable improved performance attributes include intrinsic
higher efficiency over a wider operating range, a rectangular power
output curve, higher air gap flux densities which result in higher
power density and no rotor attached components. These performance
characteristics make a PMC machine a vastly superior solution
compared to several incumbent PM machine designs. However, in order
for a PMC PM machine to successfully compete with a greater share
of incumbent solutions, multiphase machine geometries need to be
identified that could apply the PMC theory of operation.
[0024] In one aspect, a machine has a rotor without magnets and a
stator comprising a plurality of phase sections, each phase section
corresponding to one of a plurality of electrically independent
phases of the machine and each phase section having pairs of pole
faces of permanent magnets arranged with same facing magnetic poles
in which a magnetic pole of a permanent magnet faces a same
magnetic pole of another permanent magnet, a plurality of stator
poles between the same facing permanent magnet pole faces, and a
winding on each of the stator poles.
[0025] In another aspect, a method comprises providing a machine
comprising a rotor without magnets and a stator comprising a
plurality of phase sections, each phase section corresponding to
one of a plurality of electrically independent phases of the
machine and each phase section having pairs of pole faces of
permanent magnets arranged with same facing magnetic poles in which
a magnetic pole of a permanent magnet faces a same magnetic pole of
another permanent magnet, a plurality of stator poles between the
same facing permanent magnet pole faces, and a winding on each of
the stator poles.
[0026] In another aspect, a machine has a rotor without magnets and
a stator comprising a plurality of phase sections, each phase
section corresponding to one of a plurality of electrically
independent phases of the machine and each phase section having
pairs of pole faces of permanent magnets arranged with same facing
magnetic poles in which a magnetic pole of a permanent magnet faces
a same magnetic pole of another permanent magnet, an even number of
stator poles between the same facing permanent magnet pole faces,
and a winding on each of the stator poles.
[0027] In another aspect, a machine has a rotor without magnets and
a stator comprising a plurality of phase sections, each phase
section corresponding to one of a plurality of electrically
independent phases of the machine and each phase section having a
plurality of north permanent magnet pole faces arranged with north
same facing magnetic poles, a plurality of south permanent magnet
pole faces arranged with south same facing magnetic poles, a first
plurality of stator poles between the north permanent magnet pole
faces, a second plurality of stator poles between the south
permanent magnet pole faces, and a winding on each of the stator
poles, wherein same facing magnetic poles are a magnetic pole of a
permanent magnet facing a same magnetic pole of another permanent
magnet.
[0028] In another aspect, a method comprises providing a rotor
without magnets for a machine and providing a stator for the
machine, the stator comprising a plurality of phase sections, each
phase section corresponding to one of a plurality of electrically
independent phases of the machine and each phase section having
pairs of pole faces of permanent magnets arranged with same facing
magnetic poles in which a magnetic pole of a permanent magnet faces
a same magnetic pole of another permanent magnet, an even number of
stator poles between the same facing permanent magnet pole faces,
and a winding on each of the stator poles.
[0029] In another aspect, a method includes providing a rotor
without magnets for a machine and providing a stator for the
machine, the stator comprising a plurality of phase sections, each
phase section corresponding to one of a plurality of electrically
independent phases of the machine and each phase section having a
plurality of north permanent magnet pole faces arranged with north
same facing magnetic poles, a plurality of south permanent magnet
pole faces arranged with south same facing magnetic poles, a first
plurality of stator poles between the north permanent magnet pole
faces, a second plurality of stator poles between the south
permanent magnet pole faces, and a winding on each of the first
plurality of stator poles and second plurality of stator poles,
wherein same facing magnetic poles are a magnetic pole of a
permanent magnet facing a same magnetic pole of another permanent
magnet.
[0030] In another aspect, a method comprises in a machine
comprising a rotor without magnets and a stator comprising a
plurality of phase sections, each phase section corresponding to
one of a plurality of electrically independent phases of the
machine and each phase section having pairs of pole faces of
permanent magnets arranged with same facing magnetic poles in which
a magnetic pole of a permanent magnet faces a same magnetic pole of
another permanent magnet, the pairs of pole faces comprising two
north same facing permanent magnet pole faces and two south same
facing permanent magnet pole faces, the stator further comprising
two stator poles between the two north same facing permanent magnet
pole faces and two other stator poles between the two south same
facing permanent magnet pole faces, and a winding on each of the
stator poles, energizing the windings on the two stator poles with
current in a same first direction and energizing the windings on
the two other stator poles with current in a same second direction
opposite the same first direction.
[0031] In another aspect, a method comprises in a machine
comprising a rotor without magnets and a stator comprising a
plurality of phase sections, each phase section corresponding to
one of a plurality of electrically independent phases of the
machine and each phase section having a plurality of north
permanent magnet pole faces arranged with north same facing
magnetic poles, a plurality of south permanent magnet pole faces
arranged with south same facing magnetic poles, a first plurality
of stator poles between the north permanent magnet pole faces, a
second plurality of stator poles between the south permanent magnet
pole faces, and a winding on each of the stator poles, wherein same
facing magnetic poles are a magnetic pole of a permanent magnet
facing a same magnetic pole of another permanent magnet, energizing
the windings on the first plurality of stator poles with current in
a same first direction and energizing the windings on the second
plurality of stator poles with current in a same second direction
opposite the same first direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The invention is more fully appreciated in connection with
the following detailed description taken in conjunction with the
accompanying drawings, in which:
[0033] FIG. 1 shows a simple magnetic circuit.
[0034] FIG. 2 shows graph of the attractive force between the poles
and the permanent magnet versus the phase coil current.
[0035] FIG. 3 shows flux from the permanent magnet, with no current
in the phase coils, already permeates the magnetically soft core
which creates an attracting force.
[0036] FIG. 4 shows a graph of the attracting and repelling force
between the poles and the permanent magnet versus the phase coil
current.
[0037] FIG. 5 illustrates a three phase PM machine in accordance
with an embodiment of the invention.
[0038] FIG. 6 illustrates flux densities for the machine of FIG.
8.
[0039] FIG. 7 shows the flux density in the air gap over 360
degrees.
[0040] FIG. 8 shows the flux densities as a rotor permanent magnet
aligns with each of the three phases.
[0041] FIG. 9 illustrates a phase one pole with phase 2 and 3
winding slots removed.
[0042] FIG. 10 shows the flux density for phase 1 if the winding
slots for phases two and three are removed.
[0043] FIG. 11 shows the flux density in the air gap over 360
degrees for phase one with the winding slots for phases two and
three removed and the same applied current as was used to create
FIG. 7.
[0044] FIG. 12 illustrates a design with higher air gap flux
densities.
[0045] FIG. 13 illustrates rise time for phase coils as a function
of attracting and repelling a permanent magnet.
[0046] FIG. 14 shows a model for one phase of a motor as a series
resistor, inductor and voltage source.
[0047] FIG. 15 shows a section of the rotor and stator that
comprise a phase section.
[0048] FIG. 16 shows a case where no phase coils are energized.
[0049] FIG. 17 shows how the flux from the permanent magnets adds
and is directed through a given set of stator poles by selectively
energizing phase coils.
[0050] FIG. 18 illustrates magnetic polarities utilized in
accordance with an embodiment of the invention.
[0051] FIG. 19 illustrates permanent magnet pole face adjustments
utilized in accordance with an embodiment of the invention.
[0052] FIG. 20 shows two uses of bidirectional current in a phase
coil.
[0053] FIG. 21 illustrates stored energy dissipation in accordance
with an embodiment of the invention.
[0054] FIG. 22 shows a PMC two phase machine geometry.
[0055] FIG. 23 contains the timing table for a PMC two phase
machine by phase and pole designators.
[0056] FIG. 24 shows a three phase PMC machine.
[0057] FIG. 25 shows the timing sequence of a three phase PMC
machine.
[0058] FIG. 26 shows a six phase PMC machine.
[0059] FIG. 27 shows the timing sequence of a six phase PMC
machine.
[0060] FIG. 28 shows a typical uncontrolled (left) and controlled
(right) PM motor curve.
[0061] FIG. 29 shows performance comparison versus market
alternatives.
[0062] FIG. 30 is a speed vs. torque & watts out curve speed
vs. torque curve for a fixed commutation 6 phase 1 HP machine PMC
geometry.
[0063] FIG. 31 shows the speed vs. torque curve for a fixed
commutation 6 phase 1 HP machine with PMC geometry.
[0064] FIG. 32 illustrates performance advantages achieved over
conventional motors in accordance with an embodiment of the
invention.
[0065] FIG. 33 shows a speed vs. torque and power out for a 10 KW
motor.
[0066] FIG. 34 shows speed vs. torque and efficiency in accordance
with an embodiment of the invention.
DETAILED DESCRIPTION
[0067] In order to understand the problems solved by the magnetic
circuits or geometries used in accordance with the invention
(occasionally referred to as a QM Power PMC machine), the
limitations associated with commonly used PM machine geometries
first needs to be examined. This section addresses the principles
(and shortcomings) of the commonly used magnetic circuit within
non-PMC brush and brushless three Phase PM motors.
[0068] Brushless three Phase PM motors use overlapped phase
windings wound on a magnetically soft iron stator or rotor. During
motor operation, these phase windings produce magnetic fields that
attract or repel permanent magnets mounted on the rotor [brushless]
or that comprise the stator [brush]. The overlapped phase windings
also reduce the magnetically soft iron forming a pole for a phase,
since winding slots must be present in that pole to accommodate the
other phases.
[0069] A first limitation of commonly used PM machine geometries
relates to attracting and repelling forces. In particular, the
Maxwell stress integral in the air gaps for the same amount of
applied phase coil current is different for an electromagnetic
field that is repelling a permanent magnet than one attracting a
permanent magnet.
[0070] The simple magnetic circuit of FIG. 1, is used to prove this
statement. FIG. 1 illustrates permanent magnets, back iron, air
gaps, poles and coils. When a phase coil is energized in a manner
to attract a permanent magnet, the magnetic fields of the phase
coil and permanent magnet couple and the attractive force
immediately begins to increase with the magnitude of the current in
the phase coil. A graph of the attractive force between the poles
and the permanent magnet versus the phase coil current is in shown
in FIG. 2.
[0071] Since flux from the permanent magnet, with no current in the
phase coils, already permeates the magnetically soft core, the
attracting force does not begin at zero.
[0072] When a phase coil is energized in a manner to repel a
permanent magnet, the magnetic fields of the phase coil and
permanent magnet oppose. Flux from the permanent magnet, with no
current in the phase coils, already permeates the magnetically soft
core which creates an attracting force as shown in FIG. 3.
[0073] When current flows in the phase coil, the flux produced by
the coil must first oppose and displace the flux from the permanent
magnets. As the magnitude of the phase coil current increases,
producing a flux [L*i] that opposes the preexisting permanent
magnet flux, the attracting force is reduced but no repelling force
is present until the preexisting permanent magnet flux is first
displaced.
[0074] A graph of the attracting and repelling force between the
poles and the permanent magnet versus the phase coil current is
shown in FIG. 4. The graph begins at a nonzero attracting force for
both cases, however repelling forces are not present until the
point where the force curve passes through zero and produces
negative values.
[0075] As can be seen in the graphs in FIGS. 2 and 4, at the
maximum applied phase coil current, a repelling force of just 36
lbs is created as opposed to 312 lbs for an attracting force at the
same applied current.
[0076] The equations for calculating Maxwell stress are quadratic
and imply that for the same applied phase current, the attracting
and repelling magnetic forces will remain at the same ratio no
matter what size magnets are used. The phase coil turns could be
increased resulting in increased resistance. This increased
resistance requires a higher input voltage with a lower current
[I=V/R] but the power [P=VI] remains the same.
[0077] The above magnetic circuit is used to illustrate that the
attracting and repelling forces are not the same when identical
current is applied to the phase coils due to the fact that the
permanent magnets produce a flux through the magnetically soft core
material without current in the coils. It further illustrates that
when a phase coil is energized to repel a permanent magnet, the
majority of the current is used to displace the opposing permanent
magnet flux rather than producing a repelling force or `pushing`
torque to move the rotor to the next pole.
[0078] FIG. 5 illustrates these principles when reduced to practice
in an actual three phase PM machine.
[0079] Considering PH1, if the rotor is turning in a clockwise (CW)
direction, with a permanent magnet aligned with the PH1 poles as
shown, pole(s) A would be applying an attracting force on a rotor
magnet producing a major contribution to torque, pole(s) C would be
applying a repelling force on a rotor magnet with a minor
contribution to torque, and pole(s) B would have negligible or no
contribution to torque. (Note that phase 1 poles A, B, and C
combine to form a single phase 1 pole since this machine utilizes
overlapped phases and winding slots for the other phases, which
must also be present in the phase 1 pole. Therefore, phase 1 has 12
poles with each pole consisting of sub-poles A, B, and C.)
[0080] The three overlapped phases maintain this relationship as
the rotor turns where a `leading` pole is always attracting a rotor
permanent magnet and a `trailing` pole is always repelling a rotor
permanent magnet, independent of rotational direction, and the
central pole will have little to no contribution to torque. For the
other phases [PH1 pole A=PH2 pole B=PH3 pole C], [PHI pole B=PH2
pole C=PH3 pole A] and [PH1 pole C=PH2 pole A=PH3 pole B].
[0081] If phase 1 is energized to V.sub.peak the flux densities for
the machine in FIG. 5 are as shown in FIG. 6.
[0082] The maximum gap density at the pole tips for this machine
geometry would be approximately equal to B.sub.r of the permanent
magnet, with the integral values for the entire PH1 pole
significantly lower than B.sub.r. The `trailing` or repelling poles
cannot reach B.sub.r, as shown in FIG. 6.
[0083] FIG. 7 shows the flux density in the air gap over 360
degrees. The 12 attracting phase one poles can clearly be seen and,
as suggested by the simple magnetic circuit analysis in the first
part of this section, the significant torque contribution is
produced by the attracting fields; the repelling fields contribute
very little when compared to the total torque. If one looks more
closely at FIG. 6, it can be seen that the attracting field on the
`leading` end of a permanent magnet raises the load line to B.sub.r
at the pole tips while the repelling fields on the trailing end of
the same permanent magnet are driven below 1/2 B.sub.r. While
strong opposing fields can be present using neodymium magnets owing
to their high coercive force, a PM machine that uses ceramic
magnets to the phase current levels shown in FIG. 6 would
eventually demagnetize those ceramic magnets and render the system
inoperable. That is why most PM machines that use ceramic magnets
give a current rating that cannot be exceeded so as to prevent
destructive opposing fields from being applied to the permanent
magnets. Further, at any given angular position only about 30% of
the area of the rotor to stator gap interface contribute
significantly to the production of torque.
[0084] The gap flux densities shown in FIG. 7 are flux densities
for phase one (of the three phases) when a permanent magnet is
aligned with that phase. FIG. 8 shows the flux densities as a rotor
permanent magnet aligns with each of the three phases.
[0085] In summary, the torque delivered to the shaft will always be
the sum of the repelling and attracting forces in a PM machine's
air gap. The attracting forces will always be dominant and the
repelling forces will always have a higher loss when compared to
their current versus the force produced.
[0086] Unless high coercive force permanent magnets are used, the
phase currents must be limited to prevent demagnetization of the
permanent magnets.
[0087] It follows that only about 30% of the area of the rotor to
stator air gap interface is utilized to produce the majority of the
torque; specifically, the poles producing an attracting force for a
three phase PM machine like the one shown in FIG. 5.
[0088] Another limitation associated with traditional PM machine
geometries relates to flux saturation. In particular, due to
overlapped phase winding slots, the magnetically soft phase poles
will saturate before the air gap can have a mean flux density equal
to B.sub.r of the permanent magnets.
[0089] That is due to the reduced pole area remaining after
sacrificing some to accommodate the overlapped winding slots to
form the three phases. FIG. 6, shows a flux density of .about.2.1
Tesla in the phase pole that is energized to couple with a PM in an
attracting manner. The air gap peak flux density between the rotor
PM and the energized phase poles at their tips is .about.1.35 Tesla
peak flux density, as shown in FIG. 7. The integral of the flux
density across a pole would be much less than B.sub.r for the
permanent magnet.
[0090] For example in the machine shown in FIG. 5, phase one has
slots to accommodate the phase two and three windings, segmenting
what would be a phase one pole into 3 poles. If we look at only the
phase one poles in the machine in FIG. 5 with the winding slots for
phases 2 and 3 removed, a phase one pole would be as shown in FIG.
9.
[0091] FIG. 10 illustrates magnetic flux for this device. FIG. 11
shows the flux density in the air gap over 360 degrees for phase
one with the winding slots for phases two and three removed and the
same applied current as was used to create FIG. 7. Again, the 12
attracting phase one poles can clearly be seen, and with the flux
clearly at or around B.sub.r over a much greater portion of the
area of the pole face. The torque produced by the geometry used in
FIG. 11 was 36 N-m compared to the 24 N-m produced in FIG. 7, an
increase of about 33%.
[0092] The above is not to suggest that the geometry shown in FIG.
9 represents a preferred PM machine geometry but rather to
demonstrate that the loss of core material to winding slots for
overlapped phases has a significant effect on the amount of torque
produced for the same applied current (i.e., the geometry in FIG. 9
could be implemented but it probably would not be optimal). The
conclusion that should be drawn from this is that a multiphase PM
machine geometry that does not have overlapping phase windings
would result in a higher power density machine.
[0093] Another limitation of traditional PM machine geometries
relates to gap flux density. When the machine's phase coils are not
energized, the gap density for aligned poles will be .about.1/2 the
B.sub.r of the permanent magnet if the phase coils are in series
with the permanent magnets; when energized they would add to the
field intensity [H] to increase the flux density across the gap.
The maximum possible gap flux density, since the pole face of the
magnet is essentially the same area as the poles comprising a
machine phase and both are in series with one another (for aligned
poles), will be equal to B.sub.r of the permanent magnet, or
1.2-.about.1.3 Tesla with neodymium magnets when the phase coil has
current flowing through it adding to [H].
[0094] Competitive attempts to increase the gap flux densities in
permanent magnet machines have been implemented that increase the
pole face area of the rotor permanent magnet to be greater than the
pole area, thus allowing for higher air gap flux densities (areas
A1+A2>A3 by 2:1, as shown in FIG. 12). This is done by placing
more than one magnet in slots in the rotor or alternately by
shaping one magnet into a `U` shape (not shown) directed toward a
stator pole.
[0095] Such a solution for increasing the air gap flux density
entails problems. The rotor would require a greater depth, thus
adding weight, and would be more complicated since the magnets
would need to be placed in the magnetically soft rotor iron. Thin
structural metal at the ends of the permanent magnets to keep the
poles of the permanent magnets from shorting would result in a
fragile rotor design. A PMC magnetic circuit provides a solution
for increasing the gap flux densities while mitigating the problems
associated with the above solution.
[0096] Notwithstanding the heavier, fragile and more complicated
rotor, it still does not address the loss of power density due to
repelling fields and the small flux area on a stator pole due to
overlapped phases. Therefore, even if this were a good solution for
increasing the air gap flux density it does not provide a complete
solution for overcoming some of the other limitations of the widely
used three phase permanent magnet motor geometry.
[0097] Another limitation associated with traditional PM machine
geometries relates to current rise times. In particular, the
exponential rise time for the phase coils to obtain I.sub.max is
different when a phase coil is energized to attract a permanent
magnet than when repelling a permanent magnet (as shown in the
graph in FIG. 13). The data in this graph was captured using both
an FEA analysis and from empirical data.
[0098] When energy is applied to a phase coil the expanding
magnetic field is aided when the flux from the permanent magnet is
in the same direction [attracting] as the expanding magnetic field
of the phase coils and opposed when the flux from the permanent
magnet opposes the expanding field of the phase coils [repelling].
Therefore when the permanent magnet flux is in the same direction
as the expanding phase coil field, the current rise time is faster
and when the permanent magnet flux is in the opposite direction the
current rise time is slower.
[0099] Torque versus speed in a rotating PM machine is a function
of the current through the Back Electromotive Force [BEMF]. The
instantaneous current is a function of the phase coil's resistance,
inductance and the applied voltage and BEMF over a given time
interval or:
i = ( Ea - E ocmf R coil ) - ( 1 - .xi. - i R coil L coil )
Equation .times. .times. 1 ##EQU00001##
[0100] The time interval is the time it takes for a rotor pole to
sweep past a stator pole. Torque is a function of the integration
of [i] over this time interval. Therefore, a faster current rise
time has an impact on the speed at which the rotating machine
develops maximum power out. The [L] term is modified by the PM
field orientation relative to the direction the current is flowing
in a phase coil. In the machine shown in FIG. 5, the phase coil's
magnetic field orientation with respect to the permanent magnet's
field is equally distributed between opposing and aiding over
time.
[0101] Therefore, the notion that a PM machine geometry containing
only attracting (or aiding) fields would have superior performance
in both power density and efficiency could easily be proved
mathematically.
1. PMC Formulas & Principles
[0102] The voltage formula for one phase in a PMC machine is:
V in = R I + d .function. ( .lamda. .function. ( .theta. , i ) ) dt
Equation .times. .times. 2 ##EQU00002##
Lambda in the above equates to:
.lamda.(.theta.,1)=L(.theta.)*i+K.sub.pm(.theta.) Equation 3
[0103] The K term, PM flux linkage, gives rise to the dominant
torque in a PMC machine, and also its speed voltage. L is constant
within 2% over Theta in a PMC machine and is therefore independent
of Theta. The torque that corresponds to the above is given in
equation 4. Note that although L is considered to be independent of
Theta, implying that the inductance term could be stated simply as
Li, for mathematical correctness dL(Theta,i) is used so as to
account for any potential variation in L, no matter how small it
may be.
Torque = 1 2 i 2 dL .function. ( .theta. , i ) d .times. .times.
.theta. + i .times. d .times. .times. .kappa. m .function. (
.theta. ) d .times. .times. .theta. + Torque cog .function. (
.theta. ) Equation .times. .times. 4 ##EQU00003##
[0104] The model for one phase of the motor proper is a series
resistor, inductor and voltage source, as depicted in FIG. 14.
[0105] Electrical energy that enters the machine can go to one of
three places (in the absence of core losses). First, it can be lost
as heat in the windings; the winding resistance accounts for this.
Second, it can be stored in the magnetic fields in the machine; the
inductance accounts for this. Finally, it can be converted to
mechanical energy and sent out via the shaft. It is the job of the
BEMF voltage to account for this; the BEMF voltage times the
current through it is the instantaneous electrical power that is
converted to instantaneous mechanical power and sent out via the
shaft. The electrical equation of motion for a PMC machine is:
V = Ri + L di dt + u Equation .times. .times. 5 ##EQU00004##
[0106] Where v and i are the terminal voltage and current,
respectively, u is the BEMF, R is the winding resistance and L is
the winding inductance. Multiplying the equation above by the
current i results in:
Vi = Ri 2 + d dt - 1 2 ( Li 2 ) + ui Equation .times. .times. 6
##EQU00005##
[0107] This is an energy conservation experiment that states that
the power in (vi) goes either to heat (RP), stored magnetic energy
(d/dt( . . . )), or into the BEMF, which represents the mechanical
side of the machine. Thus ui is torque times speed, or mechanical
power out. Finally, going back to equation 1, note that if i=0,
i.e., if the machine is open circuit, then v=u, and so the measured
terminal voltage at a speed that represents the operational speed
equals the BEMF for that particular speed.
[0108] Since a PMC machine contains multiple phases, with multiple
voltages, currents and flux linkages, one set for each phase must
be considered. This is accomplished by creating appropriate vectors
(V, I, Lambda, K) and matrices (R, L), and then by using the
equations above. So, V, I and Lambda become column vectors of the
voltage across, the current through, and the flux linked by each
phase. K then becomes a column vector of the flux linkage
components due to the magnets, which is a function of rotor
position. R becomes a resistance matrix with resistances along the
diagonal, and zeros off the diagonals. Finally, L becomes an
inductance matrix with self inductances down the diagonal, and
mutual inductances on the off diagonals. Note that L will be a
symmetric matrix since the mutual inductance from one phase to
another is the same as the reverse mutual inductance, or, put
mathematically, Lm,n=Ln,m.
[0109] FIG. 15 shows a section of the rotor and stator that
comprise a `phase section.` A `phase section` is the building block
for a PMC machine. The components that comprise a `phase section`
consist of at least two stator poles on a stator segment placed
adjacent and between two north permanent magnet pole faces and a
second stator segment with an equal number of poles placed adjacent
and between two south permanent magnet pole faces. A coil is placed
on each of the stator poles. A `single phase section` can be
repeated more than once in a PMC design as will be apparent when
looking at the geometries for two, three and six phase PMC
machines.
[0110] Both phase coils on the poles between two permanent magnet
north poles will always be energized with current in the same
direction. The coils on the poles between two permanent magnet
south poles will always be energized with current in the opposite
direction to the coils on the poles between permanent magnet north
poles. For example in the six phase version in FIG. 16 if coils `A
and `C` are energized and assuming the coils are wound in the same
direction about the poles, current will enter the start turn of
coil `A` and exit the start turn of coil `C.` Therefore, a
unidirectional current is applied to all of the coils and its
direction is determined by whether the coil resides between either
a north or south permanent magnet pole. The direction the
unidirectional current flows through a coil is determined by the
left hand rule and would be where the coil's magnetic pole located
on the magnet side forms a couple with the magnet. For example if a
coil is located between the North permanent magnet poles the coil's
magnetic pole facing the permanent magnet would be energized to
produce a South magnetic pole on the magnet side and a North
magnetic pole on the rotor side. The `A` and `C` coils are `on`
when the `B` and `D` coils are off or vice versa or alternately
energized. This would mean that only one of the two poles between
permanent magnet North poles and only one of the two poles between
permanent magnet South poles would be energized at any given time
but allowing for some overlap in the coil's `turn on` and `turn off
timing. Some exceptions to the unidirectional current might be
implemented as shown in the example of FIG. 16, there is a first
unidirectional current in the coils `A" and `C` and a second
unidirectional current in coils `B` and `D`, where the second
unidirectional current flows in the opposite direction of the first
unidirectional current. In this case both coils between `like`
permanent magnet poles are energized in opposite directions but
with different magnitudes of current where one coil is energized to
produce a flux linkage between the rotor and stator (normal current
direction) and the other coil is energized only to the point to
prevent a flux linkage or couple between the rotor and stator
(opposite to the normal current direction). Cases exist where
bidirectional current can be used; such cases are shown in FIGS. 20
& 21.
[0111] FIG. 16 shows a case where no phase coils are energized. The
flux from the permanent magnets' north poles would traverse though
the lowest reluctance path, through pole `B,` through the rotor and
then return to the permanent magnets' south poles through pole `D,`
where the flux is illustrated as the blue region.
[0112] FIG. 17 shows how the flux from the permanent magnets adds
and is directed through a given set of stator poles by selectively
energizing phase coils. Coils `A` and `C` are energized to produce
the shown magnetic polarities. The flux from the two permanent
magnet north poles combine and traverse pole `A` through the rotor
and returns through pole `C` to the permanent magnets' south
poles.
[0113] Since rotor poles are not aligned with poles `A` and C,' a
torque is produced on the rotor that will act to align rotor poles
with stator poles `A` and `C.` It would be obvious that if viewed
as a `single phase section` (as in FIG. 17) the rotor direction
would not be predictable. This unpredictability is mitigated when
placed in a phased relationship with other like `single phase
sections.`
[0114] If the rotor is in an angular position where rotor poles are
not in alignment with poles `B` and `D` and if the pole coils for
poles `B` and `D` were energized to have the magnetic polarities
(as shown in FIG. 18), a torque would be produced to bring the
rotor poles in alignment with stator poles `B` and `D.`
[0115] By adjusting the length of the permanent magnet pole faces
`L1` and L2' in FIG. 19, the flux across a stator pole of length
`L3` can be adjusted to be equal to the air gap flux densities
achievable in a field wound machine. The PMC machine geometry is
superior because it makes that possible without adding the copper
weight and suffering additional I2R losses, as would be the case in
a field wound machine.
[0116] In FIG. 20-A, phase coils `B` and `D` are energized only to
the point that the flux through poles `B` and `D` is opposed and
redirected to poles `A` and `C.` That would have a similar effect
as shown in FIG. 17. The current flowing in the phase coils when
opposing the permanent magnet's flux would need to be controlled to
prevent the production of an opposing flux greater than the amount
needed to be displaced. In theory, phase coils `A` and `C` could be
eliminated and coils `B` and `D` could be fed a bidirectional
current that either opposes or redirects the permanent magnets'
flux to the proper poles. In FIG. 20-B, all of the phase coils are
energized both to oppose and displace (`B` and `D`) or to aid and
redirect (`A` and `C`) the flux from the permanent magnets.
[0117] The most compelling reason for using a bidirectional current
in a phase coil within a PMC machine is to dissipate any stored
energy in a phase coil at a `switch off event. The dissipation of
the stored energy is the major source of noise in a switched
reluctance [SR] machine since a brief opposing torque is created
when current is snubbed off just as a rotor and stator pole come
into alignment.
[0118] In a PMC machine, just prior to a rotor and stator pole
coming into full alignment (FIG. 21), the stored energy in phase
coils `A` and `C` is dissipated in phase coils `B` and `D.` The
returned stored energy flowing into coils `B` and `D` is in the
same direction as the supply and opposes the flux from the
permanent magnets, which acts to maintain the flux through poles
`A` and `C` as the rotor moves into alignment. This allows the
returned energy to be dissipated in a manner that supports
rotation, thereby reducing the need for complex energy recovery
circuits as used in SR machines and allowing for quieter
operation.
[0119] A PMC rotating machine can contain a wide variety of phases.
QM Power is presently focusing on two, three and six phase machines
where a two phase machine provides a lower cost solution and a
premium six phase machine provides higher power density with
extremely low torque ripple. The three phase PMC machine will serve
the majority of market applications. These three offering types
will allow a PMC machine to be cost competitive with superior
performance in a cost driven market or provide superior performance
in a performance driven market.
[0120] A PMC two phase machine geometry is shown in FIG. 22 and, as
can be seen, it is made up of `phase sections` as depicted in FIGS.
15 through 18. In the PMC two phase machine every other `phase
section` is offset by 90 electrical degrees. PH1 and PH1' can be
thought of as mirror images of each other because as PH1 poles `A`
and `B` leave alignment, poles `C` and `D` approach alignment; as
that happens in PH1, the opposite is happening with PH1' because
poles `A` and `B` would be approaching alignment while PH1' poles
`C` and `D` would be leaving alignment. This same relationship
exists between the poles of PH2 and PH2'. Four `phase sections`
make up phase 1 and its complement phase and four `phase sections`
make up phase 2 and phase 2'. A timing sequence is shown in FIG.
23. A three phase PMC machine is shown in FIG. 24 along with its
timing sequence in FIG. 25. A six phase PMC machine is shown in
FIG. 26 along with its timing sequence in Figure.
[0121] As with an SR machine, a PMC machine does not have a
steady-state equivalent circuit as compared to AC and DC machines
as a result of the non-linear characteristics as suggested by
equation 3. A PMC machine has the following features: [0122] 1) A
PMC machine has unidirectional current producing unidirectional
torque as opposed to AC machines and all DC machines, except those
in the SR motor class. Since only one switch is required to control
current in a phase this reduces the number of power converter
switches and makes the drive more economical. There is no shoot
through failure mode since a phase switch only faces one side of
the power source. [0123] 2) The torque constant is given by the
slope of the PM flux vs. rotor position and L (Theta,i) making it
non-linear and thus impossible to derive a simple equivalent
circuit. [0124] 3) A PMC motor has high starting torque like a
series DC motor, the workhorse for traction applications. A PMC
motor, however, would be lighter and more efficient than a series
motor given that the field wound coils are replaced with permanent
magnets. [0125] 4) Permanent magnet flux varies with rotor position
and thereby allows for comparably higher performance generating
action, another attractive characteristic for automotive
applications. [0126] 5) The direction of rotation is easily
controlled by changing the phase excitation sequence. [0127] 6)
Features 1, 4 and 5 make the use of a four quadrant controller
possible. [0128] 7) Torque and speed are controlled by altering the
phase excitation voltage. [0129] 8) Current PMC designs do not
operate directly from a three phase line supply without a power
converter. In order to be cost competitive with lower cost fixed
speed induction motors, a synchronous squirrel cage PMC motor is
being developed. [0130] 9) Due to the reduction of power switches
in the converter and simplified rotor design, a PMC machine will
provide superior performance over other PM motors at a lower cost.
[0131] 10) Since rotor position can be accurately controlled a PMC
machine is also suitable for precision high performance servo-motor
applications. [0132] 11) All of the phases in a PMC machine are
`electrically independent` therefore a fault in one phase has no
effect on the other operational phases. A fault in a single phase
in almost all other phased motors types, with the exception of an
SR motor, has catastrophic implications. This feature is especially
beneficial for machines used in `high risk` applications such as
motors, generators and actuators used for aerospace, defense,
medical, nuclear, traction and electric vehicles, chemical
handling, etc. [0133] 12) The performance due to the loss of a
phase, in a multiphase machine, is diminished as a function of the
number of machine phases. As the number of phases increases the
impact on performance from the loss of any one phase is reduced. A
PMC machine can be easily configured to virtually any number of
phases for both motors and generators. [0134] 13) No repelling
fields are used, thus negating the associated losses and power
density reduction associated with their use; it also allows for
faster current rise times for producing higher torque at higher
speeds. [0135] 14) With a PMC geometry, where the magnets are
placed on the stator, the ratios of the total magnet length to the
length of a pole face is such that high gap densities can be
achieved in a light weight and low loss PM configuration. The high
gap flux densities increase the PMC machine's power density when
operating as a motor or as a generator. [0136] 15) A PMC machine
does not use cross rotor flux linkages, nor does the rotor serve as
PM `back iron` as with other PM machines. The resulting significant
reduction in the rotor and overall machine weight is a beneficial
feature for many applications and can be particularly important for
improving the performance of larger machines, including wind
turbine generators. [0137] 16) A PMC machine has no attached
components on the rotor, i.e., permanent magnets. This feature
allows for holding a smaller and more consistent air gap length,
increases reliability and allows the machine to operate at much
higher rotational speeds when operated as a motor or generator.
[0138] 17) The PMC geometry is equally applicable to non-rotary
applications such as actuators, linear motors, linear generators,
high power latches, etc. [0139] 18) A PMC machine's phases are
geometrically independent and do not rely upon overlapped phase
poles. This feature not only increases the effective pole areas, it
additionally isolates the phases from mutual inductance.
[0140] Finding reliable and complete competitive variable speed
motor data is challenging, particularly for smaller scale devices,
where efficiency tends to be lower. Most motor manufacturers only
publish what they want a prospective customer to see or only the
highest performance range on a particular motor's operating
curve.
[0141] One of the most common misconceptions in the scientific and
engineering community is that `motors already operate in the 90
plus percent efficiency range` when in fact motors have a wide
range of efficiencies not just one efficiency. Efficiency is
determined by many factors, including what RPM output level the
motor is operating at within its capacity range, by the controlling
methods employed, by the power density (weight) of the motor, and
whether or not any active cooling is used; a full understanding of
these factors is required to evaluate the intrinsic technical value
proposition of the machine. Since few of these metrics, other than
individual peak efficiencies and weights are typically provided in
manufacturers' product specifications, it is often difficult to
determine which option represents the best choice for an
application. The analysis below focuses on the physics that define
a particular motor geometry and examines the relationship between
motor size, output level and efficiency.
[0142] To begin, it is important to understand that efficiency
normally improves as a rotating electrical machine increases in
diameter since the flux path length tends to scale linearly with
size. So, for a given flux density, and hence shear stress, the
amp-turns must scale linearly too. At the same time the winding
cross section is increasing quadratically, and so the Ohmic loss is
unchanged. On the other hand, the torque out (and power for a fixed
speed) is growing quadratically at constant rotational speed, or at
least linearly with constant tip speed. Thus, efficiency improves
because output goes up while losses stay the same, all at a
constant flux density.
[0143] All motors will have both high and low efficiencies over
their full operating range and at `no-load` and `stall` efficiency
will even be zero. If a competitive motor curve only shows high
efficiencies they are either not showing the entire operating range
of the underlying motor or they are using controlling methods on an
oversized motor, so that the device can run at a lower power than
the machine is capable of, but at a higher point on its intrinsic
efficiency curve.
[0144] The left side of FIG. 28 illustrates the uncontrolled
speed-torque and efficiency curves for conventional PM motors which
have an intrinsically linear speed-torque relationship. Since `peak
power` and `peak efficiency` do not occur at the same point on the
uncontrolled operating curve for the most widely used PM motor
geometries, the challenge for motor designers was to find a way to
obtain the high efficiency found near it's no load speed (i.e., at
the maximum point of its efficiency curve) at a power output level
that commercial applications require. While a fixed commutation
(i.e., uncontrolled) PM motor is shown in the left graph of FIG.
28, the right side shows the same motor using controllers to limit
`power in` and `power out.` FIG. 30 illustrates torque and power
output as a function of RPMs. FIG. 31 illustrates torque as a
function of RPMs.
[0145] The conventional solution has been to use a motor that is
large enough to operate at the targeted application's power
specifications without exceeding the higher intrinsic high
efficiency range, and then using electronic control to limit the
power output to operate in that range. However, as can be seen in
the right side of FIG. 28, in order to achieve such high
operational efficiency, the motor would have to have a peak power
capacity between 30-50% greater than the actual range it is
designed to be run at in the particular application. To obtain such
a higher peak power, the motor has to be larger (oversized), thus
increasing the weight of the machine. Since the cost of a motor is
typically dominated by the steel and copper raw materials (i.e.,
the weight) and the control electronics (if needed) the costs of
fabricating such conventional PM motors are necessarily higher than
they would be for a motor with intrinsically higher efficiency over
a wider range of uncontrolled operating speeds; such a motor would
not need to be oversized since its peak output power would be near
its peak efficiency. Again, a motor with those attributes would not
need to be oversized, and would potentially eliminate (or at least
minimize) the controller components, and would, therefore, lead to
lighter and cheaper to build (and sell) alternatives offering the
same power.
[0146] The design of the invention is the first commercially
available motor that doesn't need to be oversized to meet the
efficiencies demanded by the motor marketplace. The invention
obtains its cost advantages by having an intrinsic hyperbolic
uncontrolled speed-torque curve, which leads to an almost
rectangular efficiency curve. For the disclosed motor, the no load
and stall efficiencies are still zero but they quickly climb above
90% and hold across the operating range of speeds of the device
(see FIG. 32 below)--an especially important quality for variable
speed applications. The disclosed motor allows one to obtain peak
power at or near the machine's intrinsic peak efficiency. While the
weight of a motor is not linear to the power output, the intrinsic
peak efficiency of the linear speed torque curve of an uncontrolled
conventional PM motor occurs at a point that is approximately 27%
lower than that of its peak power.
[0147] FIG. 29 is a comparison of the expected power density,
efficiency and speed benefits of the QM Power alternative compared
to market leading alternatives for variable speed automotive
applications.
[0148] Importantly, there are no known manufacturing or materials
limitations with a PMC Machine that prevent rapid
commercialization. Aside from the automotive market, the prospect
of a motor with smaller size and lower weight, but with the same or
higher efficiencies and output speeds, is a significant value
proposition for a variety of applications.
[0149] FIG. 31 is the speed vs. torque curve for a fixed
commutation 6 phase 1 HP machine with PMC geometry. Efficiency
remained above 90% for over 50% of the range. Due to their linear
speed torque curve, incumbent 1 HP machine alternatives that
produce 1 HP at values above 90% efficiency with fixed commutation
will only remain above 90% efficient for .about.15% of their
operating range, as illustrated in the left hand graph of FIG. 32.
Efficiencies above 90% occur in this graph only from where the
efficiency curve crosses the torque curve on the left side of the
graph to the first dotted vertical line on the left side of the
graph.
[0150] As suggested by the PMC motor equations presented earlier,
speed and torque scale proportionally for a PMC motor based upon
input voltage. The input voltage was held constant during the
testing, therefore constant power was produced at 1 HP for the
above graphs. The Opera-RM analysis results of a 10 KW PMC motor
are shown in FIGS. 33 and 34. FIG. 33 shows a speed vs. torque and
power out for a 10 KW motor and FIG. 34 shows speed vs. torque and
efficiency. Using curve fitting on the speed vs. torque for 1 KW,
10 KW and 50 KW motors we found that torque is a function of speed
to the power of -0.98 for all cases, indicating that scaling is
indeed quadratic. An Opera RM FEA analysis of the disclosed
technology suggested that a continuous 50 KW motor with a peak
torque of 200 N-m could be developed with a proposed motor diameter
of 250 mm, a length of 150 mm with a weight of approximately 32
Kg--all within the given acceptable parameters.
[0151] The foregoing description, for purposes of explanation, used
specific nomenclature to provide a thorough understanding of the
invention. However, it will be apparent to one skilled in the art
that specific details are not required in order to practice the
invention. Thus, the foregoing descriptions of specific embodiments
of the invention are presented for purposes of illustration and
description. They are not intended to be exhaustive or to limit the
invention to the precise forms disclosed; obviously, many
modifications and variations are possible in view of the above
teachings. The embodiments were chosen and described in order to
best explain the principles of the invention and its practical
applications, they thereby enable others skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated. It
is intended that the following claims and their equivalents define
the scope of the invention.
* * * * *