Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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POWER CONVERSION SYSTEMS
UTILIZING WIRE CORE INDUCTIVE DEVICES
Field of the Invention
The present invention relates to the field of power conversion
systems, and more particularly to power supplies, inverters, and ballasts
utilizing wire core inductive devices.
Background of the Invention
The overwhelming majority of electronic circuits require
constant voltages to ensure appropriate operation. For example, many
microcomputers require 5 volt and 12 volt sources capable of providing a
current of 10 to 100 A. Other signal processing systems in which the
currents produced vary with load conditions are required to maintain supply
voltages at nearly constant levels (e.g., 5, 12, and 15 volts). In addition,
many motor drives and control systems require dc supplies whose voltage
levels are dynamically adjusted to meet desired operating conditions.
For portable systems, batteries may be used. More frequently,
however, electronic circuits are energized by a circuit, or a power supply,
which converts the alternating current waveform received from power lines
(e.g., a 110 volt to 220 volt rms, 60-Hz sinusoid in the United States) to
direct voltage of constant amplitude utilizing at least one transformer or
inductive device. Often these systems power the device and charge the
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battery as well.
It is common and universal for low frequency application
transformers and other inductive devices to be made up of a magnetic core
comprising a plurality of sheets of steel, the sheets being die cut and
stacked to create the desired thickness of a core. Individual sheets of
selected thickness are oxide-coated, varnished or otherwise electrically
insulated from one another in order to reduce/minimize eddy currents in the
magnetic core. For many years the thickness (thus number of necessary
pieces) of the stampings has been determined by a strict set of
constraints-magnitude of eddy currents versus number of necessary pieces.
The magnetic core of a transformer or the like generally
passes through the center of the electric winding, and closes on itself to
provide a closed magnetic circuit. Since the magnetic core then supports
the electric windings, it is natural that the core has also been used as the
support for the transformer. That is to say, one attaches the magnetic core
to a container or baseboard in order to support the transformer.
When a stack of metal sheets is used as the magnetic core for
an inductive device, it is usual to provide a shape, such as an E with the
electric windings on the center leg of the E. After the windings are in
place, an additional stack of sheets usually in an I configuration is applied
to connect the ends of the E, thereby completing the magnetic circuit.
Using such a technique, it will be understood that the windings are
necessarily wound separately, and subsequently placed on the magnetic
core. The windings must therefore be large enough to slip onto the
magnetic core.
Also, the shape of the windings is necessarily rectangular
rather than circular which detracts from optimal operation. Such
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construction contributes to the inherent noisiness of an inductive device and
necessarily the power conversion device, because the electric windings
must be somewhat loose on the core. As a result, when an alternating
voltage is applied to the electric windings, the sheets making up the core
tend to vibrate with the alternating magnetic field or in sympathy in a
subharmonic. Any resulting gaps and spaces between the electrical
components and the magnetic components also reduce coupling and
efficiency of action.
Transformers and other inductive devices inherently generate
electromagnetic fields. Such fields external to the device lessen efficiency,
as well as pose interferences to the immediately surrounding environment.
Although the strength of these electromagnetic fields decreases with
distance from the transformer, shielding of either the electromagnetic field
source or the affected components is often required. As components in
today's electronics are made more sensitive and their packaging more
dense, susceptibility to electromagnetic interaction increases dramatically.
To assure optimum performance of these components, stray
electromagnetic fields must be minimized often at a substantial cost. As
noted above, one manner in which these fields may be minimized is to
provide shielding around the source in order to contain the electromagnetic
fields and to prevent interference from external sources.
Thus, a need exists for an improved power conversion system
which may be manufactured in an efficient and cost effective manner and
which utilizes transformers or other inductive devices which provide a high
level of efficiency and superior shielding capabilities.
Summary of the Invention
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Accordingly, it is a primary object of the present invention to
provide a novel and improved power conversion system and related method
that are particularly adapted to be manufactured in an efficient and cost
effective manner, and which overcome the limitations of the prior art.
Another object of the present invention is to provide a power
conversion system that is particularly adapted to utilize an inductive device
having a magnetic core formed from a plurality of wires.
Yet another object of the present invention is to provide a
power conversion system which provides superior shielding capabilities.
Still another object of the present invention is to provide a
power conversion system which houses all of its components within a
magnetic core of an inductive device.
It is another object of the present invention to provide a
method of making a power conversion system utilizing a plurality of wires
to form a magnetic core.
Additional objects, advantages and other novel features of the
invention will be set forth in part in the description that follows and in
part
will become apparent to those skilled in the art upon examination of the
following or may be learned with the practice of the invention. The objects
and advantages of the invention may be realized and obtained by means of
the instrumentalities and combinations particularly pointed out in the
appended claims.
To achieve the foregoing and other objects, and in accordance
with the purposes of the present invention as described herein, there is
provided an improved power conversion system which utilizes an inductive
device having a magnetic core comprising a plurality of wires. The power
conversion system can be any circuit that provides power with
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characteristics required by a load from an external power source with
characteristics incompatible with the load, i.e., it makes the load compatible
with the available external power source. Accordingly, the power
conversion system may be any type of power supply, including but not
5 limited to an analog power supply or a switch mode power supply, an
inverter, a ballast, or the like.
An electric winding, or windings dependent upon the
inductive device, is wound directly onto the plurality of wires forming the
magnetic core. The ends of the wires forming the magnetic core are spread
and formed over the electric windings, the two ends of the wires meeting to
form a complete magnetic circuit. A band or other connector means holds
the ends of the wires together. Advantageously, the wires formed in this
manner envelop the electric windings and magnetic core to provide a shield
substantially containing the electromagnetic fields emanating from the
system and reducing the intrusion of electromagnetic fields from external
sources. Additional shielding may be provided by binding at least a portion
of the wires forming the shield with a transversely wound wire in place of
the band.
In accordance with an important aspect of the present
invention, the magnetic core of the inductive device may form a housing
for some, or preferably all, of the remaining components of the power
conversion system. For example, a typical analog power supply may
include additional components such as a fuse, an on/off switch, a rectifier, a
filter, and/or a regulator. In accordance with the present invention, these
components would be housed within the housing formed by the magnetic
core. In this manner, the inductive device, as well as the components of the
power conversion system are physically protected and shielded against the
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intrusion of electromagnetic or radio frequency interferences from external
sources. Further shielding can be accomplished by enclosing the interior of
the transformer and the electronic components with shield plates.
The inductive device may include a mounting post bound within the
plurality of wires forming the magnetic core and extending therefrom for
supportably mounting the power conversion device. The mounting post
may extend from either side or both sides of the magnetic core as desired.
Also, the make-up of the magnetic core may be otherwise varied
considerably. Wire of various diameters may be used to achieve greater
density of the core; a few large wires may be spaced around the core to
provide rigidity; and, one or more tubes may be incorporated into the core,
the tubes carrying air or a fluid for cooling the inductive device and the
power conversion device. The cooling tubes are preferably constructed of
non-magnetic and non-electrical-conducting material.
In a further aspect of the invention, in accordance with its
objects and purposes, a method of making a power conversion system
includes the steps of forming the magnetic core of a plurality of wires,
placing at least one electric winding along the length of the magnetic core,
connecting the electric winding to the remaining components of the power
conversion system, and shielding the inductive device by forming the wires
of the magnetic core over the at least one electric winding to envelop the
winding and form a complete magnetic circuit.
Still other objects of the present invention will become
apparent to those skilled in this art from the following description wherein
there is shown and described the preferred embodiments of this invention,
simply by way of illustration of some of the modes best suited to carry out
the invention. As it will be realized, the invention is capable of other
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different embodiments and its several details are capable of modification in
various, obvious aspects all without departing from the invention.
Accordingly, the drawings and descriptions will be regarded as illustrative
in nature and not as restrictive.
Brief Description of the Drawings
The accompanying drawings incorporated in and forming a
part of the specification, illustrates several aspects of the present
invention,
and together with the description serves to explain the principles of the
invention. In the drawings:
Figure 1 is a block schematic diagram of a typical power
conversion system;
Figure 2 is a perspective view of an inductive device,
specifically a transformer, made in accordance with the present invention
for use in a power conversion system;
Figure 3 is a cross-sectional view of an inductive device for
use in a power conversion system showing electric windings formed on a
magnetic core of wires, the wires enveloping the electric windings and the
core in accordance with the present invention;
Figure 4 is a cross-sectional view of an alternate embodiment
of an induction device showing electric windings formed beside one
another on a magnetic core of wires;
Figure 5 is a perspective view of an inductive device for use
in a power conversion system showing the housing formed by the magnetic
core;
Figure 6 is a cross-sectional view of an inductive device for
use in a power conversion system showing the housing formed by the
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magnetic core and the electric windings, the wires enveloping the electric
windings and the core in accordance with the present invention;
Figure 7a is an illustration showing the step of forming a
magnetic core by gathering a plurality of wires pulled from a creel to form a
bundle, securing the wires with bands, and severing the bundled wires;
Figure 7b is an illustration showing the step of forming an
electric winding directly on the magnetic core;
Figures 7c and 7d are illustrations showing. an alternate
method for forming a magnetic core by winding one or a plurality of wires
on a spindle, and severing the wound wires to form the core; and
Figure 7e is an illustration showing the step of shielding a
transformer by forming a plurality of wires of the magnetic core over
electric windings to envelop the windings and form a complete magnetic
circuit.
Reference will now be made in detail to the present preferred
embodiment of the invention, an example of which is illustrated in the
accompanying drawings.
Detailed Description of the Preferred Embodiment
For purposes of illustration and description of the present
invention, reference is now made to Figure 1 showing the present preferred
embodiment of a power conversion system 10. The preferred power
conversion system 10 includes a conversion means 11, a rectifier 12, a
capacitor filter 13, and a regulator 14. However, in accordance with the
broadest teachings of the present invention, the power conversion system
10 can be any circuit generally known in the field of power conversion
systems that provides power with characteristics required by a load L from
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an external power source S with characteristics incompatible with the load
L, and wherein the conversion means 11 is any type of inductive device
(e.g. a transformer, an inverter, a ballast) having a magnetic core 23 formed
of a plurality of wires 24.
As shown in Figure 2, for example, the conversion means 11
of the present preferred embodiment is a transformer 20 having leads 21 for
connecting a power source P (not shown) to the primary winding of the
transformer 20, and leads 22 for connecting the secondary winding to a
load L (not shown). Those skilled in the art will realize that designation of
primary and secondary windings is somewhat arbitrary, and that one may
use the leads 22 for connection to the power source P, and the leads 21 for
connection to the load L. The designations of "primary" and "secondary"
are therefore used herein as a convenience, and it should understood that
the windings are reversible.
As best shown in Figure 3, a magnetic core 23 of the
transformer 20 is made up of a plurality of wires 24 rather than the
conventional sheets of steel. As is usual, however, the electric windings 25
and 26 are received on the magnetic core 23. The plurality of wires 24
utilized to form the magnetic core 23 extend outwardly therefrom and are
further formed around and envelop the electric windings 25 and 26. The
ends of the plurality of wires 24 meet, and are held together by a band 27
forming a complete magnetic circuit. The leads 21 and 22 pass between the
plurality of wires 24 to connect to the electric windings 25 and 26,
respectively.
Importantly, the use of finer core wires 24 and the very small
but distributed gaps brought about by the ends of the wires meeting, allow
the transformer 20 of the present preferred embodiment or other conversion
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means 11 to operate at higher frequencies than typical sheet-type magnetic
core devices. Advantageously, the transformers 20 or other conversion
means 11 may be utilized in switchmode power supplies and other devices
requiring higher frequencies. For example, the conversion means 11 may
5 include a switching means (not shown) for controlling the phase and
frequency of an output from extremely low frequencies of below three
kilohertz up to and including low frequencies of between 30 to 100
kilohertz or more.
In accordance with another important aspect of the present
10 invention, the wires 24 form a shield 28 substantially containing
electromagnetic fields emanating from the transformer 20 and reducing the
intrusion of electromagnetic fields including electromagnetic interference
and/or magnetic flux from external sources. Additional shielding may be
provided as shown in Figure 4 by binding at least a portion of the wires
forming the shield 28 with a transversely wrapped wire 29. Preferably, the
wire 29 is a fine iron or steel wire for binding the ends of the wires 23 or
at
least a portion of the shield 28, and thus replacing the band 27.
Referring back to Figure 3, a mounting post 30, preferably
threaded, may be extended from the bottom of the transformer 20 providing
a convenient mounting means for the transformer 20. Centrally of the
magnetic core 23, the mounting post 30 is held in place simply by being
embedded within the plurality of wires 24 forming the magnetic core 23.
Of course, the mounting post 30 may support the transformer 20 from
below, as illustrated in Figures 2 and 3, or alternatively may extend from
the top of a transformer 32 with the transformer 32 depending from the
mounting post 30 (not shown).
As shown in Figure 4, an alternate embodiment of a
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transformer 32 for use in the power conversion system 10 in accordance
with the present invention is similar to the transformer 20, but electrical
windings 33 and 34 are positioned beside one another on magnetic core 35
instead of one upon the other as in the transformer 20. In addition, the
mounting post 36 extends from both the top and bottom of the transformer
32. Necessarily, the transformer 32 may be mounted from either top or
bottom, or from both.
While the use of a mounting post provides a readily
convenient manner by which to mount a transformer, one may wish to
utilize the transformer of the present invention in a conventional setting,
wherein the mounting post is not convenient. Conventional transformers
are typically supported by their magnetic core structure. Since the magnetic
core of the transformer 20 of the preferred embodiment of the present
invention is not adapted to provide similar support, one might utilize the
mounting posts 30 or 36 to fix the transformer to a bracket that can be
mounted as a conventional transformer. Alternatively, the magnetic core
area may have no stud, but be filled solely with core wires with mounting
secured by other means, such as external strapping.
In accordance with another important aspect of the present
invention, the magnetic core 23 of the inductive device 20 may form a
housing 40 to house some, or preferably all, of the remaining components
of the power conversion system 10 (see Figure 5). For example, a typical
analog power supply may include additional components (not shown) such
as a fuse, an on/off switch, a rectifier, a capacitor filter, and/or a
regulator.
In accordance with the present invention, these components or at least some
of these components are housed within the housing 40 formed by the
magnetic core 23. In this manner, the inductive device 20, as well as the
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remaining components which comprise the power conversion system 10 are
physically protected and shielded against the intrusion of electromagnetic
interference and magnetic flux from external sources.
In accordance with the broadest possible teachings of the
present invention, the housing 40 can generally be formed in any size and
shape. For purposes of illustration and description, the present preferred
housing 40 is a generally cylindrical housing open at both ends to an
ambient environment. As shown in Figure 6, plates 41, 42 may be secured
over the openings to provide additional physical protection and shielding
against the intrusion of electromagnetic interference and magnetic flux
from external sources.
As indicated above, the remaining components of the power
conversion system 10 shown in Figure 1 include the rectifier 12, the
capacitor filter 13, and the regulator 14. Each of these components are well
known in the art and may be utilized in accordance with the teachings of
the present invention in any known form or combination dependent upon
the required design parameters of the power conversion system 10. For
example, the rectifier 12 can be a half-wave rectifier utilizing a single
diode
to convert the sinusoidal input waveform into a unidirectional though not
constant waveform, or a full-wave rectifier which comprises two half-wave
rectifiers. Similarly, the capacitor filter 13 can be a simple capacitor
shunted across the load L in order to decrease the ripple voltage, or a more
efficient capacitor-input filter or choke-input filter wherein more than one
passive element is utilized. The regulator 14 can be a Zener diode, a
combination of discrete components including a differential amplifier and
pass transistor, a monolithic regulator such as the Motorola MC7800C
series of fixed-voltage regulators, for example, or one of many different
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switching regulators. These examples are presented only to illustrate a few
of the numerous types of rectifiers, filters and regulators which may be
combined with an inductive device in accordance with the teachings of the
present invention to form the novel power conversion system and are not
meant to be an exhaustive list.
In a further aspect of the invention, a method of making a
power conversion system includes the steps of forming a magnetic core of a
plurality of wires, placing at least one electric winding along the length of
the magnetic core, connecting the electric winding to an external power
source and at least one passive element, and connecting the passive element
to an external load.
In accordance with that method, Figure 7a shows the step of
forming a magnetic core 50 by gathering a plurality of wires 51 pulled from
a creel (not shown) to form a bundle 52, and severing the bundle at a
predetermined length with a knife K or the like. The resulting magnetic
core 50 is held together by bands 53 or the like. It will be recognized that
the plurality of wires 51 pulled from the creel may all be the same diameter
or may be a combination of different diameters. As noted above, the use of
different diameter wires allows for a more dense packing of the magnetic
core 50, thereby improving its magnetic characteristics.
In accordance with the present preferred method, at least one
electric winding 54 is next placed on the magnetic core 50. The electric
winding may be formed by winding a coil of wire on a spindle, in
accordance with the prior art, for slipping over a magnetic core. In
accordance with an important aspect of the present preferred invention,
however, the electric winding 54 is wound directly on the magnetic core 50,
as shown by action arrow A in Figure 7b. Advantageously, this direct
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placement of the electric winding 54 onto the magnetic core 50 in a circular
manner provides a more efficient, and thus more economical method of
manufacturing by eliminating steps in the prior art manufacturing methods.
Another advantage is that, by winding the electric winding 54
directly on the magnetic core 50, the electric winding 54 assists in binding
the wires which form the core tightly together, thereby offering several
mechanical and electrical advantages. These advantages include tighter
magneto-electric coupling, greater efficiency, and reduced vibrational noise
from the core 50.
Figure 7c illustrates an alternate method for forming a
magnetic core in accordance with the present invention. In the alternate
method, a magnetic core 55 is formed by feeding one wire or a plurality of
wires 56 to a winder W. Since a winder W of this type may be very high
speed, it is practicable to use thin wires to form the magnetic core 55.
However, one may also use a variety of wires having different diameters,
the wires being geometrically sized and arranged to be densely packed and
drawn onto the form at the same time. The plurality of wires 56 are
removed from the winder W, severed at a predetermined length, and
straightened as shown in Figure 7d. By appropriately deforming the wound
wires before severing, the ends will be substantially square or the winding
skein can have several straight sides essentially forming a triangular cross-
section. As in the preferred method shown in Figure 4a, bands 53 or the
like hold the plurality of wires 56 together thus forming the magnetic core
55.
With the electric winding 54 in place on the preferred
magnetic core 50, the next step in the preferred method is to shield the
inductive device by forming the plurality of wires 51 extending from the
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magnetic core 50 around the electric winding 54 to envelop the winding
and form a complete magnetic circuit. Figure 7e illustrates one manner of
forming the plurality of wires 51, for example, by using a pair of cones C to
spread the wires generally radially. Alternatively, finer wires can be spread
5 by centrifugal force. Conventional means may then be used to form the
wires 51 completely around the electric windings 54 to form a shield
generally as shown in Figure 2.
Those skilled in the art will recognize that the magnetic core
of an inductive device preferably forms a complete magnetic circuit. As
10 best shown in Figures 2 and 3, the forming of the plurality of wires 24
extending from the magnetic core 23 around the electric windings 25, 26
causes the ends of the wires to meet. In accordance with the inventive
method, the wires 24 are preferably prepared by having their ends cleaned;
then, when the ends of the wires meet, they are held together by the band
15 27. Alternatively, the band 27 may be used in conjunction with or be
replaced by a fine iron or steel wire 29 wrapped transversely around the
device 20 or augmented by a magnetic metal bearing epoxy or glue.
In addition to providing the desired complete magnetic
circuit, it will be seen that the entire inductive device, e.g., transformer
20,
is thus covered by the wires 24 forming shield 28. The device made in
accordance with the method of the present invention may therefore be used
in electrically noisy environments without adversely affecting or being
adversely affected by surrounding components.
It will therefore be understood that the present invention
provides a highly efficient method for making a power conversion system
10 having a conversion means 20 having a magnetic core 23 formed of a
plurality of wires 24. It should be noted that the core wires 24 of the
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conversion means 20 of the present invention may be made of substantially
the same silicon and other steel that is used for conventional cores.
Furthermore, the process of drawing the wire produces the same desirable
grain structure, and in the proper direction, as is found in the present
stamped sheets where it is desirable to use grain oriented silicon steel, for
example. The wires of the present invention will be coated to be
electrically insulated from one another to reduce eddy currents, and the
diameter of the wires will be selected to reduce eddy currents.
The foregoing description of a preferred embodiment of the
invention has been presented for purposes of illustration and description. It
is not intended to be exhaustive or to limit the invention to the precise form
disclosed. Obvious modifications or variations are possible in light of the
above teachings. The preferred embodiment was chosen and described to
provide the best illustration of the principles of the invention and its
practical application to thereby enable one of ordinary skill in the art to
utilize the invention in various embodiments and with various
modifications as are suited to the particular use contemplated. All such
modifications and variations are within the scope of the invention as
determined by the appended claims when interpreted in accordance with the
breadth to which they are fairly, legally and equitably entitled.
