WOUND FIELD FLUX SWITCHING MACHINE WITH SINUSOIDAL BACK ELECTROMOTIVE FORCE

MACHINE A COMMUTATION DE FLUX A CHAMP ENROULE COMPRENANT UNE FORCE CONTRE-ELECTROMOTRICE SINUSOIDALE

English Abstract

A wound field flux switching machine with a sinusoidal back electromotive force features a rotor with teeth and a stator with groups of teeth wherein each group has a field winding and each tooth has a phase winding.

French Abstract

Une machine à commutation de flux à champ enroulé ayant une force contre-électromotrice sinusoïdale comprend un rotor muni de dents et un stator muni de groupes de dents où chaque groupe comporte un enroulement à champ et chaque dent comporte un enroulement à phase.

Claims

CLAIMS
1. A machine comprising:
a rotor with teeth;
a stator with groups of teeth, each group having a field winding,
each tooth having a phase winding; and
rotor and stator teeth in adjacent groups configured to be out of
phase, the rotor and stator teeth configured such that opposite teeth on the
rotor are aligned
with one another and aligned with the teeth of opposite stator teeth field
winding groups and
in an adjacent stator teeth field winding group no rotor tooth is aligned with
said stator
phase.
2. The machine of claim 1 in which the rotor and stator have an even number
of teeth, the stator having more teeth than the rotor.
3. The machine of claim 2 in which the rotor has ten teeth and the stator
has
twelve teeth.
4 The machine of claim 2 in which each stator group has three teeth
with
four said groups.
5. The machine of claim 1 in which the rotor teeth are wider than the
stator
teeth.
9

6. The machine of claim 1 in which the equal spacing between adjacent
stator
teeth in a group is equal and the spacing between adjacent groups is equal but
greater than
the spacing between stator teeth in a group.
7. The machine of claim 1 in which the rotor teeth are skewed.
8. A machine comprising:
a rotor with ten teeth;
a stator with twelve teeth having a 24° pitch arranged in groups,
each group having a field winding, each tooth having a phase winding;
the rotor and stator teeth configured such that in a stator teeth
field winding group a rotor tooth is aligned with a stator phase and in an
adjacent stator
teeth field winding group no rotor tooth is aligned with said stator phase;
and
the pitch between stator teeth in adjacent groups being larger
than 24°.
9. The machine of claim 8 in which each stator group has three teeth with
four said groups.
10. The machine of claim 8 in which the rotor teeth are wider that the
stator
teeth.

11 The machine of claim 8 in which the rotor teeth are skewed.
12. A machine comprising:
a rotor with teeth;
a stator with groups of teeth, each group having a field winding,
each tooth having a phase winding;
the spacing between each group of stator teeth being equal and
being greater than an equal spacing between adjacent stator teeth in a group;
and
the rotor teeth configured for an out of phase relationship between
rotor and stator teeth in adjacent groups, the rotor and stator teeth
configured such that in a
stator teeth field winding group a rotor tooth is aligned with stator phase
and in an adjacent
stator teeth field winding group no portion of a rotor tooth is aligned with
said stator phase.
13. The machine of claim 12 in which the rotor and stator have an even
number of teeth, the stator having more teeth than the rotor.
14. The machine of claim 13 in which the rotor has ten teeth and the stator
has
twelve teeth.
11

15. The machine of claim 12 in which each stator group has three teeth
with
four said groups.
16. The machine of claim 12 in which the rotor teeth are wider that the
stator
teeth.
17. The machine of claim 12 in which the rotor teeth are skewed.
12

Description

CA 02831578 2013-10-29
APPLICATION
FOR
UNITED STATES LETTERS PATENT
Be it known that I David C. Meeker residing at 21 Virginia Road, Natick, MA
01760 and being a citizen of the United States; have invented a certain new
and useful
WOUND FIELD FLUX SWITCHING MACHINE WITH SINUSOIDAL BACK
ELECTROMOTIVE FORCE
of which the following is a specification:
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CA 02831578 2015-07-17
RELATED APPLICATIONS
This application claims benefit of and priority to US, Provisional Application
Serial No, 61/722,282 filed November 5, 2012.
FIELD OF THE INVENTION
This invention relates to motors and generators.
BACKGROUND OF THE MENTION
A present method of generating power on aircraft is through an Auxiliary Power
Unit (A.PU), APUs are used on airliners to provide electricity when the main
engines are
off (e.g. to run the air conditioning while passengers are boarding), These
systems
consist of a small gas turbine engine connected to a wound-field synchronous
generator.
This class of generator is desirable because the output voltage of the
generator can be
regulated by servoing the current in the field winding. So that the generator
does not have
to endure high rotational stress, the generator is typically coupled to the
engine through a
speed-reducing gear box.
However, the power level of most A.PUs is low compared to that required to
operate Directed Energy Weapons (DEWs), To reduce generator weight for DEW
applications, it is desirable to directly couple the generator to the gas
turbine, since power
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CA 02831578 2015-07-17
density of an electric machine goes up roughly linearly with rotational speed,
Wound
field machines have a complicated rotor structure. Most machines have a
windings and a
rectifier bridge located on the rotor, and a separate exciter rotor section is
needed to
induce the DC field winding current on the rotor. It is difficult to make a
wound-field
rotor with the mechanical integrity required to run at high speeds.
Consequently, most high-speed generators disclosed in the literature are of
one of
three types: Surface-mount permanent magnet motor (PM), Induction motor (IM),
and
Switched reluctance motor (SRM). See, A. ArkIcio et al., "Induction and
Permanent-
Magnet Synchronous Machines for High Speed Applications," Proceedings of the
Eighth
International Conference on Electrical Machines and Systems, 29-29 Sept. 2005.
The disclosed machine is in the general class of Doubly Salient or Flux
Switching
machines. Flux switching machines that are superficially similar to the
presently
disclosed machine are described in the literature, See, F, Liang, Y. Liao, and
T. Lipo, "A
new variable reluctance motor utilizing an auxiliary commutation Winding",
IEEE
Transactions on Industrial Applications, 30(2):423-432, MadApr 1994.
See
also, 12., Cao et aL: A Linear Doubly Salient Permanent-Magnet Motor With
Modular and
Complementary Structure", IEEE Transactions on Magnetics, 47(12):4809.4821,
Dec
2011, However, the presently
disclosed machine
has novel design differences that reduce cogging torque and produce better
conditioned
output voltage,
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CA 02831578 2013-10-29
SUMMARY OF THE INVENTION
Featured is a wound field flux switching machine (motor or generator) with a
net
flux linkage for each phase that is symmetric about zero and close to
sinusoidal in shape
resulting in a sinusoidal back electromotive force (BEMF) and an output
voltage that can
be easily regulated.
Featured is a machine comprising a rotor with teeth and a stator with groups
of
teeth, wherein each group has a field winding and each stator tooth has a
phase winding.
The result is a wound field flux switching machine with a sinusoidal back
electromotive
forces. In some embodiments, the rotor and stator teeth in adjacent groups are
configured
to be out of phase.
In one design, the rotor and stator have an even number of teeth, the stator
having
more teeth than the rotor. For example, one rotor has ten teeth and a stator
has twelve
teeth. Here, each stator group has three teeth with four said groups.
Preferably, the rotor
teeth are wider that the stator teeth. Also featured is a machine in which the
spacing
between each stator group of teeth is equal and greater than the equal spacing
between
adjacent stator teeth in a group. Preferably, the rotor teeth are skewed.
Also featured is a machine comprising a rotor with an even number of teeth, a
stator with an even number of teeth arranged in groups, each group having a
field
winding, each tooth having a phase winding, and the stator having more teeth
than the
rotor.
The subject invention, however, in other embodiments, need not achieve all
these
objectives and the claims hereof should not be limited to structures or
methods capable of
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achieving these objectives.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Other objects, features and advantages will occur to those skilled in the art
from
the following description of a preferred embodiment and the accompanying
drawings, in
which:
Fig. 1 is a cross sectional view of a wound field flux switching machine with
sinusoidal BEMF;
Fig. 2 is three dimensional partially cutaway view of the machine shown in
Fig. 1.
Fig. 3 is a three dimensional schematic view of a stator in accordance with an
example of the invention; and
Fig. 4 is a schematic three dimensional front view showing the stator of Fig.
3 as
well as a rotor in accordance with an example of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Aside from the preferred embodiment or embodiments disclosed below, this
invention is capable of other embodiments and of being practiced or being
carried out in
various ways. Thus, it is to be understood that the invention is not limited
in its
application to the details of construction and the arrangements of components
set forth in
the following description or illustrated in the drawings. If only one
embodiment is
described herein, the claims hereof are not to be limited to that embodiment.
Moreover,
the claims hereof are not to be read restrictively unless there is clear and
convincing
evidence manifesting a certain exclusion, restriction,. or disclaimer.
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CA 02831578 2013-10-29
This disclosure concerns, in one example, a wound field flux switching
electric
machine. In one design, see Figs. 1 and 2, the machine employs a 10-toothed
rotor built
out of laminated iron. There are typically no windings on the rotor. The
machine may
have a 12-toothed stator. The stator teeth are segregated in four quadrants.
Each
quadrant has three teeth, each wrapped with a coil from a single phase. All
three teeth in
a quadrant are wrapped by a stationary field winding. A coil from a single
phase is
wound around each tooth and a stationary field coil encircles every three
stator teeth.
This machine gives the advantages of a wound-field generator (i.e., easy-to-
regulate
output voltage, simple power conditioning electronics, sinusoidal output
voltage) with
that of a Switched Reluctance machine (simple, robust construction,
concentrated stator
windings, no brushes or exciter required). The machine may be appropriate for
high-
speed generating applications such as a direct-drive alternator attached to a
gas turbine
engine. The machine also may be appropriate as a motor for electric vehicle
applications
where field weakening is needed at high speeds and simple machines without
rare earth
magnets are needed to obtain low cost.
Unlike typical SRMs, the rotor teeth are wider than the stator teeth. The
rotor
tooth and slot pitch are even, and the rotor tooth with is 3/2 the stator
tooth width (i.e. 36
degree tooth pitch and 18 degree tooth width). The rotor teeth are skewed over
1/3 of the
width of the tooth over the length of the rotor (i.e. 6 degree skew).
The three stator phases may be connected together in a Wye winding
configuration. The rotor teeth are fatter than the stator teeth, the rotor is
skewed, and the
teeth in top and bottom quadrants are out of phase with the left and right
quadrants. This
combination results in a net flux linkage for each phase that is symmetric
about zero and
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CA 02831578 2013-10-29
close to sinusoidal in shape. Consequently, the back-EMF waveform of the line-
to-line
voltage is nearly sinusoidal as well.
rotor teeth, 12 stator teeth grouped into "quadrants" with 24 degree tooth
pitch,
and a skewed rotor allow the machine to retain the advantages of the SRM: a
simple
5 laminated rotor structure and concentrated winding for simplicity and
good heat flow.
The invention also mitigates shortcomings of the SRM design in that the
proposed
design does not require complicated drive electronics to act as a generator.
The
sinusoidal BEMF and output voltage that can be easily regulated via the field
winding
allow a simple/light rectifier bridge to be used as the associated generator
power
10 electronics. Torque ripple is not high. Choice of relative tooth widths
and rotor tooth
skew reduces torque ripple versus SRM/Doubly Salient machines. The power
density of
the machine is about the same as a SRM machine.
Figs. 14 show machine 10 (e.g., a generator or motor) with stator 12 and rotor
14.
Rotor 14, in this example, has ten equal size and equally spaced teeth 16
resulting in a
symmetrical (balanced) rotor. Stator 12 has three teeth 18a, 18b, 18c in each
group
defining phases A, B, and C as shown and four such groups of three teeth or 12
teeth
total. In a group, the stator teeth are equal in size and spaced equally.
Between groups,
the spacing is greater. Each stator tooth has a phase winding 13, and each
group of three
stator teeth has a field winding Fv, better depicted in Figs. 34.
Thus, the rotor teeth and the stator teeth and adjacent groups are configured
to be
out of phase (e.g., the rotor teeth at the top and bottom of the rotor as
shown in Fig. 1 are
aligned with the B phase while the rotor teeth on the right and left sides are
not).
Fig. 2 shows how rotor teeth 16 are preferably skewed. The result is a wound
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CA 02831578 2015-07-17
field flux switching machine with a sinusoidal back electromotive four which
is easily
regulated.
Although specific features of the invention are shown in some drawings and not
in others, this is for convenience only as each feature may be combined with
any or all of
the other features in accordance with the invention, The words "including",
"comprising", "having", and "with" as used herein are lobe interpreted broadly
and
comprehensively and are not limited to any physical interconnection. Moreover,
any
embodiments disclosed in the subject application are not to be taken as the
only possible
embodiments.
In addition, any amendment presented during the prosecution of the patent
application for this patent is not a disclaimer of any claim clement presented
in the
application as filed: those skilled in the art cannot reasonably be expected
to draft a claim
that would literally encompass all possible equivalents, many equivalents will
be
unforeseeable at the time of the amendment and are beyond a fair
interpretation of what
is to be surrendered (if anything), the rationale underlying the amendment may
bear no
more than a tangential relation to many equivalents, and/or there are many
other reasons
the applicant can not be expected to describe certain insubstantial
substitutes for any
claim element amended.
Other embodiments will occur to those skilled in the art and are within the
following claims,
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Representative Drawing