Note: Descriptions are shown in the official language in which they were submitted.
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SELF-EXCITED ASYNCHRONOUS ALTERNATING CURRENT
GENERATOR WITH PARAMUTUAL INDUCTIVE COUPLING
. The present invention relates to an alternating current induction
generator/motor and more particularly to an asynchronous single-phase
alternator.
BACKGROUND OF THE INVENTION
For simplicity and ease of construction, the typical alternating current
generator, or alternator, includes a stationary armature winding composed of a
large
number of individual conductors assembled in slots formed in the inner surface
of a
hollow cylindrical iron stator, and a revolving field structure, or rotor,
which has
plurality of individual field windings and is mounted for rotation within the
stator
When the armature winding is installed, the conductors are connected in pairs
to form
coils which are so positioned in the stator that the two conductors of each
coil overlie
field windings of opposite polarity. The coils are in turn connected in a
group or
groups, one such group for each phase of the alternator. Since the relative
movement
between a magnetic field and a sequence of conductors is necessary for
production
of electricity, the field windings of an alternator must be energized or
excited. Most
generators are synchronous machines that are designed to enable them to supply
their
own magnetic requirements. TI11S IS aCCOnIpIIShed by applying DC power through
brushes and slip rings or, in a brushless synchronous unit, by an inductive
coupling
to a secondary (DC) generator on the same shaft.
A less expensive alternative is to use a standard induction motor and drive it
with another power source, i.e., a combustion engine, to generate electricity.
Such
units have to rely on a host utility to create the magnetic field. if that
power source
is cut off, the induction generator will cease production of electricity.
Thus, all
conventional induction machines are dependent upon an outside power source for
their magnetic requirements.
A basic requirement for an induction alternator is that a revolving magnetic
field must be produced in the air gap between the rotor and the stator. In a
two
phase or any polyphase induction alternator, the fact that the currents
flowing in the
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different phase windings are at 90 electrical degrees to each other produces a
sinusoidally distributed magnetic field which revolves in synchronism with the
magnetized rotor field. In the most common types of conventional alternators,
the
magnetic field has typically been energized by current supplied from a source
which
is external of the alternator itself. This is particularly true in the case of
single-phase
asynchronous alternators wherein the pulsating stator field produced is non-
directional and does not create a revolving field. Without the influence of an
out-of
phase or reactive current, the magnetic field created in the gap between the
armature
winding and the rotating field windings in a single phase asynchronous
alternator will
alternately expand and collapse. However, since there is no movement of the
magnetic field between field windings, the current thus generated is non-
directional.
In the most commonly used single phase asynchronous generators, i.e., split
capacitor
alternators, a large energy winding is directly connected to the power supply
line and
an out-of phase current is supplied by a small auxiliary winding and a
serially
connected capacitor which are connected to the energy winding and across the
power
lint.
Even the split capacitor alternators are efFcient only when the magnetic field
in the large energy winding is balanced with that of the auxiliary winding and
their
respective currents are displaced by 90 electrical degrees. Since the 90
degree
displacement exists only at design loan, a disproportionate distribution of
magnetic
flux occurs at other load points, with consequent negative sequence currents
in the
rotor and stator, space harmonics in the air gap, and high leakage reactance.
Furthermore, the energy produced by the collapse of the magnetic field is
returned
to the system as VARS, which adversely affects power factor and efficiency.
Accordingly, asynchronous single-phase alternators have achieved only limited
acceptance in industry due to the fact that they typically operate with
efficiencies of
40-GO% and power factors of 10-60%. In addition, because the LC circuit is
tied
directly to the power line, whenever a split capacitor alternator is connected
to a non
linear load there is the risk of drawing high current to the resonant winding
to the
point of failure of the alternator.
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SUMMARY OF THE INVENTION
An object of this invention is to make possible,
through auto-controlled self-excitation, the independent and
efficient operation of a single-phase asynchronous
alternator. The present invention overcomes the
inadequacies and limitations of the prior known alternators
by provision of an asynchronous single-phase alternator
which achieves improved energy transfer across the air gap
from rotor to stator thus permitting operational
efficiencies of 75-90% and power factors of 95-97%. These
results are obtained by excitation of the magnetic field
with internally-generated alternating current, the frequency
of which corresponds to the frequency of rotation of the
magnetic field. This is accomplished by providing in the
armature winding a reflux coil which is positioned at 90
electrical degrees to the energy coils and which is
paramutually inductively coupled to the energy coil through
the rotor.
A broad aspect of the invention provides a single
phase, self-excited, asynchronous alternator which includes
a cylindrical rotor having a plurality of field poles spaced
about its periphery , a toroid-shaped armature, said rotor
being mounted for rotation within the armature, an energy
coil mounted on said armature in close proximity to the
rotor, and AC generating means mounted on said armature to
energize said field poles with alternating current which
corresponds in frequency with the speed of rotation of the
rotor, said AC generating means being electrically and
inductively isolated from the energy coil and paramutually
inductively coupled therewith.
Another broad aspect of the invention provides an
asynchronous alternator/motor which includes a rotor having
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a plurality of conductors spaced about a circumference, an
armature, said rotor being mounted for rotation relative to
said armature, a winding mounted on said armature in close
proximity to said conductors, said winding including an
energy coil and a reflux coil which are electrically and
inductively isolated from each other and paramutually
inductively coupled through the rotor, said reflux coil
being positioned at 90 electrical degrees to the energy coil
and tuned to minimize the inductive reactance of the
alternator/motor.
A further broad aspect of the invention provides
an asynchronous alternator/motor which includes a
cylindrical rotor having a plurality of conductors spaced
about its periphery, a toroid-shaped armature, said rotor
being mounted for rotation within said armature, a winding
mounted on said armature in close proximity to said
conductors, said winding including energy coils interspersed
with reflux coils to create a rotating magnetomotive force
field between the rotor and the armature, the reflux coils
being electrically and inductively isolated from the energy
coils with each reflux coil positioned at 90 electrical
degrees from an energy coil, said reflux coils being
paramutually inductively coupled with the energy coils
through the rotor.
BRIEF DESCRIPTION OF THE DRAWINGS
The best mode presently contemplated of carrying
out the invention will be understood from the detailed
description of the preferred embodiments illustrated in the
accompanying drawing in which:
FIG. 1 is a schematic view in elevation of an
alternator/motor according to the present invention, which
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illustrates the armature winding as including an energy coil
and a tuned reflux coil; and
FIG. 2 is a schematic view in elevation of a two-
pole, single-phase alternator according to the present
invention; and
FIG. 3 is a schematic view in elevation showing
the present invention as applied to a two-pole, two-phase
alternator/motor.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring more particularly to FIG. 1, the
armature winding for each pole of the present alternator
includes an energy coil 11. A variable AC capacitance 13 is
connected in series with the refulx coil 12 to form a tuned
tank circuit which is connected through a resistor, or metal
oxide varistor, 10 to neutral or electrical ground L2. A
cylindrical rotor 14 is mounted for rotation about its
longitudinal axis
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on a shaft 15. A number of field windings 15-19 are evenly spaced around the
circumference of the rotor in proximity to the coils 11 and 12. The resistor
10 is
sized to bleed off any electro-static potential which may build up on the
reflux coil.
The reflux coil is electrically and inductively isolated from the energy coil.
Since both
coils are inductively connected to the rotor, but not to each other, this
inductive
coupling through the rotor is referred to as a paramutual or transitional
coupling.
In the two-pole single phase alternator illustrated in FIG. 2, energy coils 21
and 22 are disposed on diametrically opposite sides of a rotor 23. The energy
coils
are connected in series with each other and across the AC supply line L1, L2.
Reflux
coils 24 and 25 are disposed on diametrically opposite sides of the rotor 23
at 90
electrical degrees to, and midway between, the energy coils. The reflux coils
are
connected in series with each other and with a variable AC capacitance 2G to
form
a tuned tank circuit which is connected through a resistor 20 to neutral or
electrical
ground L2. The rotor 23 is a cylindrical structure which is mounted for
rotation
about its longitudinal axis. The AC capacitance is adjusted to bring the
capacitive
reactance into balance with the inductive reactance of the generator and the
designed
load. The number of turns in each reflux coil is chosen to minimize the amount
of
capacitance necessary to produce the required alternating VARS. A series of
parallel,
elongated conductors 27-30 are spaced about and imbedded in the periphery of
the
cylindrical structure in close proximity to the energy and reflux coils and
are
circumferentia(ly short-circuited at both ends by conducting rings to form
what is
known as a squirrel cage rotor. This is the preferred rotor construction for
small and
medium size alternators wherein the parallel conductors serve as field poles
or
windings. However, it is understood that an alternative rotor structure may be
employed, particularly for use with large alternators, wherein individual
wound coils
on the peripheral surface of the cylindrical structure form the field poles.
In the operation of the present two-pole, single phase alternator of FIG. 2,
as
the rotor structure rotates, the conductors 27-30 are individually and
sequentially
moved past the energy coils 21 and 22. If the conductors are energized,
current is
then induced onto line LI as the lines of magnetic flux emanating from the
conductors
27-30 are cut by the energy coils. While much of the energy carried by the
individual
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conductors is dissipated as they pass the energy coils, there is substantial
residual
energry remaining in each of the conductors as they are carried away from the
energy
coils and toward the reflux coils 24 and 25. As the residual flux lines from
the
conductors are cut by the reflux coils, current flows from the reflux coils to
the AC
capacitance 26 where it is stored as the capacitor is charged. The AC
capacitor then
discharges before the conductors pass clear of the reflux coils. The
alternating
current discharged from the capacitor flows back through the reflux coils and
across
the air gap to energize or excite the conductors. Since the capacitor 26 is
continually
charged and then discharged, the conductors are continually energized by the
reflux
coils. Thus, as the rotor structure rotates, the electrical charge on the
conductors is
alternately inductively transferred to the energy coils and then renewed by
the tank
circuit which includes the re(lux coils.
While the present invention is primarily directed to single phase alternators,
it is, in many instances, also applicable to polyphase alternators.
Accordingly, a two-
I S phase alternator according to the present invention is illustrated in FIG.
3, wherein
two pairs of series-connected energy coils 31, 32 and 33, 34 are each
connected
across the AC supply line LI, L2, L3. The energy coils of each pair are
oppositely
wound and are arranged on opposite sides of a rotor 35 such that the four
coils are
evenly spaced about the circumference of the rotor. Two pairs of reflux coils
36, 37
and 38, 39 arc each connected in series with a variable AC capacitance 40, 41
to form
two tuned tank circuits, each of which is connected through a resistor 50 to
neutral
or electrical ground L2. A separate tank circuit is required for each phase of
the
alternator. Similar to the rotor 23 of FIG. 2, the rotor 35 is a cylindrical
structure
mounted for rotation about its longitudinal axis. A series of parallel,
elongated
conductors 42-49 is evenly spaced about the periphery of the rotor and
circumferentially short circuited at both ends to form a squirrel cage
construction.
The energy coils 3 I-34 and the reflux coils 36-39 are positioned in close
proximity
to the conductors 42-49 and are evenly spaced from each other. The energy
coils are
evenly spaced, in this case at 90 mechanical degrees, from the adjacent energy
coils,
while the reflux coils are positioned at 90 electrical degrees from, or midway
between, the adjacent energy coils. The two-phase alternator of FIG. 3
operates in
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a similar manner to the single phase alternator of FIG. 2, in that, as the
individual
conductors 42-49 are moved past the energy coils and the reflux coils in
sequence,
energy is generated in the energy coils and transferred to the supply line and
the
conductors are then re-energized by alternating current produced by the reflux
coils
S and tank circuits. Because a constant rotating field is created in a
polyphase machine,
such as shown in FIG. 3, the polyphase machine will fiznction both as a
generator and
as a motor. When the usage of the machine is determined to be as a generator,
the
values ofthe AC capacitances are so adjusted as to instantaneously produce a
reflux
field strength of sufficient intensity to allow the machine to provide the
necessary
magnetizing current for the connected load. However, when usage is determined
to
be as a motor, the AC capacitive reactances are set to a pre-determined
magnitude
suElicient only to offset the internal magnetizing requirements of the
machine.
It is usually necessary to provide a method for automatically and quickly
adjusting the field current of the alternator to meet the excitation needs for
varying
loads. Variation of the alternator field current to maintain a steady voltage
can be
accomplished by varying the rellux or excitor voltage. The circuitry is tuned
so that
energy transfer from the reflux coils to the rotating field poles or windings
and then
to the energy coils occurs with the highest efficiency when the field poles or
windings
are rotating in synchronism with the quasi-rotating field which is formed in
the gap
between the field poles and the armature winding. The efficiency of energy
transfer
varies with the impedance of the field poles which, in turn, varies inversely
with the
rotational speed of the field poles or windings.
The present invention requires that the tuned tank circuit be energized during
start up in order for the alternator to be self excited. The tank circuit
becomes
activated when an initial charge is placed on the AC capacitance from some
suitable
external or internal power source. This can be accomplished in a number of
ways,
such as: from a small permanent magnet imbedded in the rotor, or by a small
battery
( I .5 volts) connected through an inverter to the primary of a step-up
transformer, the
secondary of which is connected, through suitable switches, to the
capacitance.
While the invention has been described with reference to specifically
illustrated preferred embodiments, it should be understood that various
changes may
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be made without departing from the disclosed inventive subject matter
particularly
pointed out and claimed here below.
