U.S. patent application number 12/241851 was filed with the patent office on 2010-04-01 for power electronic module with an improved choke and methods of making same.
This patent application is currently assigned to Rockwell Automation Technologies, Inc.. Invention is credited to Peter John Halpin, Paul Thomas Krause, Robert Allen Savatski.
Application Number | 20100079228 12/241851 |
Document ID | / |
Family ID | 41510666 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100079228 |
Kind Code |
A1 |
Halpin; Peter John ; et
al. |
April 1, 2010 |
POWER ELECTRONIC MODULE WITH AN IMPROVED CHOKE AND METHODS OF
MAKING SAME
Abstract
An improved choke assembly for a power electronics device is
provided. More specifically, a choke assembly with improved
protection from environmental conditions such as dirt and water is
provided. An improved choke assembly may include a double layer of
protection around an inductor coil of a choke that seals the
inductor coil from the outside environment. Another embodiment may
include a choke with a projection that seals the cabinet from the
cooling channel while allowing the choke leads to pass into the
cabinet.
Inventors: |
Halpin; Peter John; (Mequon,
WI) ; Savatski; Robert Allen; (Port Washington,
WI) ; Krause; Paul Thomas; (Fredonia, WI) |
Correspondence
Address: |
Susan M. Donahue;Rockwell Automation, Inc./FY
1201 South Second Street, E-7F19
Milwaukee
WI
53204
US
|
Assignee: |
Rockwell Automation Technologies,
Inc.
Mayfield Heights
OH
|
Family ID: |
41510666 |
Appl. No.: |
12/241851 |
Filed: |
September 30, 2008 |
Current U.S.
Class: |
336/96 ;
29/602.1; 318/558 |
Current CPC
Class: |
H01F 27/04 20130101;
H01F 37/00 20130101; H02M 1/126 20130101; Y10T 29/4902 20150115;
H01F 41/127 20130101 |
Class at
Publication: |
336/96 ; 318/558;
29/602.1 |
International
Class: |
H01F 27/32 20060101
H01F027/32; H02P 29/00 20060101 H02P029/00; H01F 7/128 20060101
H01F007/128 |
Claims
1. A motor drive comprising: rectifier circuitry coupled to an AC
power source and configured to provide power to a DC bus; inverter
circuitry coupled to the DC bus and configured to generate drive
signals for driving a motor; a cooling channel disposed adjacent to
the rectifier circuitry and the inverter circuitry and configured
to draw heat from the rectifier circuitry and the inverter
circuitry; and a choke assembly disposed in the cooling channel
comprising: an inductor coil comprising an insulated conductor
wound around a central axis; a potting disposed about the inductor
coil, the potting configured to encase the inductor coil in a
ring-shaped housing with an opening for receiving a magnetic core;
and a magnetic core disposed within the opening, coaxially with the
inductor coil, wherein the inductor coil comprises inductor leads
coupled to the ends of the insulated conductor and wherein the
potting comprises a projection that insulates a portion of the
inductor leads inside the cooling channel and mates with an opening
in a barrier separating the cooling channel from at least the
rectifier circuitry and the inverter circuitry.
2. (canceled)
3. The motor drive of claim 1, wherein the inductor leads are
flexible and pass through the barrier via the opening at the
interface of the projection and the opening.
4. The motor drive of claim 1, wherein the inductor leads comprise
thin, laminated, metal straps.
5. The motor drive of claim 1, comprising a gasket disposed between
the projection and the opening in the barrier, the gasket forming a
water tight seal around the opening.
6. The motor drive of claim 1, wherein the insulated conductor
comprises a conductive sheet disposed adjacent to an electrically
insulative sheet.
7. The motor drive of claim 1, comprising a layer of varnish
surrounding the choke assembly and filling a void between the
magnetic core and the potting.
8. The motor drive of claim 1, wherein the choke assembly comprises
at least two inductor coils, at least one of the conductor coils
coupled to a high side of the DC bus, and at least one of the
conductor coils coupled to a low side of the DC bus.
9. The motor drive of claim 8, wherein the magnetic core comprises
an E-shaped magnetic material comprising a center projection and
two side projections, and wherein two of the at least two inductor
coils are disposed around the two side projections.
10. A choke assembly, comprising: an inductor coil comprising an
insulated conductor wound around a central axis, wherein the
inductor coil further comprises electrical leads coupled to the
ends of the insulated conductor and configured to be coupled to an
electrical bus; a potting material surrounding the inductor coil,
the potting configured to encase the inductor coil in a ring-shaped
housing with an opening for receiving a magnetic core, and to seal
the inductor coil from the outside environment; and a magnetic core
disposed within the opening, coaxially with the inductor coil,
wherein the potting material comprises a projection that insulates
a portion of the electrical leads inside a cooling channel, the
projection configured to mate with an opening in a barrier
separating a cooling channel from at least a rectifier circuitry
and an inverter circuitry.
11. (canceled)
12. (canceled)
13. The choke assembly of claim 10, wherein the projection includes
a raised surface configured to mate with the opening in the
barrier.
14. The choke assembly of claim 10, wherein the magnetic core
comprises an E-shaped ferromagnet.
15. The choke assembly of claim 10, wherein the electrical leads
are flexible to allow a size of the opening to be reduced while
still permitting the electrical leads to pass through the
opening.
16. A method of fabricating a choke, comprising: coupling at least
two electrical leads to an inductor coil comprising an insulated
conductor, wherein the electrical leads are coupled to the ends of
the insulated conductor; winding the insulated conductor around a
central axis to form a coil; placing the coil into a ring-shaped
mold with an opening for receiving a magnetic core; filling the
mold with potting material and allowing the potting material to
harden to form a potted coil comprising a main body configured to
surround the coil, wherein the potting material comprises a
projection configured to surround a portion of the at least two
electrical leads inside a cooling channel, the projection
configured to mate with an opening in a barrier separating a
cooling channel from at least a rectifier circuitry and an inverter
circuitry: and inserting a magnetic core into the opening,
coaxially with the inductor coil.
17. The method of claim 16, wherein the insulated conductor
comprises a conductive sheet disposed adjacent to an insulative
sheet, and wherein the insulative sheet is interposed between the
layers of the conductive sheet during the formation of the
coil.
18. The method of claim 16, wherein the magnetic core includes two
pieces, a first piece being inserted through the opening, and a
second piece being magnetically coupled to the first piece after
insertion of the first piece through the opening.
19. The method of claim 16, wherein the at least two electrical
leads include a lamination of a plurality of thin, flexible, metal
straps.
20. (canceled)
Description
BACKGROUND
[0001] The invention relates generally to the field of power
electronic devices such as those used in power conversion and for
applying power to motors and similar loads. More particularly, the
invention relates to a motor drive with an improved choke that
provides improved protection from the environment.
[0002] In the field of power electronic devices, a wide range of
circuitry is known and currently available for converting,
producing and applying power to loads. Depending upon the
application, such circuitry may convert incoming power from one
form to another as needed by the load. In a typical arrangement,
for example, constant (or varying) frequency alternating current
power (such as from a utility grid or generator) is converted to
controlled frequency alternating current power to drive motors, and
other loads. In this type of application, the frequency of the
output power can be regulated to control the speed of the motor or
other device. Many other applications exist, however, for power
electronic circuits that convert alternating current power to
direct current power, or vice versa, or that otherwise manipulate,
filter, or modify electric signals for powering a load. Circuits of
this type generally include rectifiers (converters), inverters, and
power conditioning circuits. For example, a motor drive will
typically include a rectifier that converts AC power to DC.
Inverter circuitry then converts the DC signal into an AC signal of
a particular frequency desired for driving a motor at a particular
speed. Often, power conditioning circuits, such as a choke and/or a
capacitor bus are used to remove unwanted voltage ripple on the
internal DC bus. Depending on the power load, the power
conditioning circuits, such as the choke, may conduct high levels
of current and generate significant levels of heat.
[0003] The housing that holds most of the circuitry described above
may be referred to as a cabinet. To dissipate the heat generated by
the circuitry inside the cabinet, a motor drive unit will typically
include a cooling channel adjacent to the cabinet that conducts
cooling air through a heatsink thermally coupled to the circuits.
To make efficient use of the space within the motor drive unit and
keep heat generated by the choke out of the cabinet and away from
other circuit components, the choke is usually deployed within the
cooling channel rather than the cabinet. Furthermore, the motor
drive may be deployed such that the cooling channel is exposed to
the outdoors. Thus the choke may be subject to harsh environmental
conditions due to weather, dust, and cleaning.
[0004] Therefore, it may be advantageous to provide a motor drive
unit with an improved choke that enables increased protection from
the environment. In particular, it may be advantageous to provide a
choke that enables improved protection from water, dust, and
salt.
BRIEF DESCRIPTION
[0005] The present invention relates generally to a choke
configuration that addresses such needs. One embodiment of the
present invention employs a double layer of protection around an
inductor coil of a choke that seals the inductor coil from the
outside environment. Another embodiment includes a choke with a
projection that seals the cabinet from the cooling channel while
allowing the choke leads to pass into the cabinet. Although the
present invention is described, for convenience, in relation to a
motor drive application, it will be appreciated that chokes
fabricated in accordance with present techniques may be used in any
choke related application, such as electrical power transmission
and telecommunications, for example.
DRAWINGS
[0006] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0007] FIG. 1 is a diagrammatical representation of an exemplary
motor drive circuit employing an improved choke in accordance with
one embodiment of the present invention;
[0008] FIG. 2 is a perspective exploded view of a partial motor
drive unit depicting an improved choke in accordance with one
embodiment of the present invention;
[0009] FIG. 3 is a perspective view of the improved choke shown in
FIG. 2;
[0010] FIG. 4 is a perspective view of an inductor coil shown in
FIG. 2 with portions of the structure cut away to show additional
details of the internal construction;
[0011] FIG. 5 is a cross section of an exemplary inductor coil
shown in FIG. 4 providing additional details regarding the
construction of the choke;
[0012] FIG. 6 is an enlarged view of one of the inductor leads
shown in FIG. 5; and
[0013] FIG. 7 is a flow chart of an exemplary method of fabricating
the improved choke.
DETAILED DESCRIPTION
[0014] FIG. 1 is a diagrammatical representation of an exemplary
motor drive circuit 10 employing an improved choke configuration in
accordance with present embodiments. The motor drive circuit 10
includes a three phase power source electrically coupled to a set
of input terminals 12, 14 and 16 that provides three phase AC power
of constant frequency to a rectifier circuitry 18. In the rectifier
circuitry 18, a set of six silicon-controlled rectifiers (SCRs) 34
provide full wave rectification of the three phase voltage
waveform. Each input terminal entering the rectifier circuitry 18
is coupled between two SCRs 34 arranged in series, anode to
cathode, which span from the high side 38 of the DC bus 36 to the
low side 40 of the DC bus 36. Also coupled to the DC bus 36 is a
choke 20 that has improved protection from the environment as will
be explained further below. The choke 20 may include inductors 42
that are coupled to either the high side 38 or the low side 40 of
the DC bus 36 and serve to smooth the rectified DC voltage
waveform. Capacitors 44 link the high side 38 of the DC bus 36 with
the low side 40 of the DC bus 36 and are also configured to smooth
the rectified DC voltage waveform. Together, the inductors 42 and
capacitors 44 serve to remove most of the AC ripple presented by
the rectifier circuitry 18 so that the DC bus 36 carries a waveform
closely approximating a true DC voltage. It should be noted that
the three-phase implementation described herein is not intended to
be limiting, and the invention may be employed on single-phase
circuitry, as well as on circuitry designed for applications other
than motor drives. Furthermore, the choke 20 may also be used in
applications that include more than two inductors 42. For example,
in some embodiments, the choke 20 may be coupled to a three phase
power source and include three inductors, one for each phase.
[0015] An inverter 24 is coupled to the DC bus 36 and generates a
three phase output waveform at a desired frequency for driving a
motor 32 connected to the output terminals 26, 28 and 30. Within
the inverter 24, two switches 46 are coupled in series, collector
to emitter, between the high side 38 and low side 40 of the DC bus
36. Three of these switch pairs are then coupled in parallel to the
DC bus 36, for a total of six switches 46. Each switch 46 is paired
with a flyback diode 48 such that the collector is coupled to the
anode and the emitter is coupled to the cathode. Each of the output
terminals 26, 28 and 30 is coupled to one of the switch outputs
between one of the pairs of switches 46. The driver circuitry 50
signals the switches 46 to rapidly close and open, resulting in a
three phase waveform output across output terminals 26, 28 and 30.
The driver circuitry 50 is controlled by the control circuitry 52,
which responds to the remote control and monitoring circuitry 54
through the network 56.
[0016] Turning to FIG. 2, a perspective view of an exemplary motor
drive unit 58 employing an improved choke configuration in
accordance with one embodiment is shown. Many of the circuit
components described above, including the choke 20, will typically
generate significant amounts of heat, which can lead to component
failure due to overheating. Therefore, the motor control circuit 10
may be packaged within a unit that includes a system for enhancing
the heat dissipating properties of the motor control circuit 10.
Accordingly, the motor drive unit 58 may include a frame 60 that
defines a cooling channel 62. The cooling channel may include a
heatsink 68 that is thermally coupled to the electrical components
described above. The motor drive unit 58 may also include a set of
fans 64 to provide a flow of cooling air through the cooling
channel 62 and the heatsink 68, drawing heat from the motor drive
circuitry.
[0017] In some embodiments, the cooling channel may be subject to
harsh environmental conditions. For example, the motor drive unit
58 may be mounted to an exterior wall, such that the front side of
the motor drive unit 58 (i.e. the cabinet) faces the interior of
the building to provide access to the controls and electrical
inputs and outputs of the drive unit 58, while the backside of the
motor drive unit (i.e. the cooling channel 62) faces the outdoors.
In this case, although the circuitry on the front side of the motor
drive unit is protected from the outside environment by the barrier
66, the cooling channel 62 is exposed to the outside environment.
Therefore, the cooling channel may be sealed off from the cabinet
to prevent exposing sensitive electronics to water, dust and
salt.
[0018] The switches 46, SCRs 34, capacitors 44, driver circuitry 50
and controller circuitry 52 may be situated adjacent to the cooling
channel 58 on top of the heatsink 64 and the barrier 66. Thus, the
barrier 66 and the top surface of the heatsink 64 form the base of
the cabinet within which most of the motor drive circuitry will be
contained. The barrier 66 separates the cabinet from the cooling
channel, protecting the motor drive circuitry in the cabinet from
exposure to harmful environmental conditions while the heatsink 64
allows heat from the circuitry to pass through into the cooling
channel. To form a water tight seal between the cabinet and the
cooling channel 62, a gasket 70 is situated between the heatsink 68
and the barrier 66.
[0019] As mentioned above, the choke 20 may be situated within the
cooling channel 62 to make efficient use of the space within the
motor drive 58 and keep heat generated by the choke 20 out of the
cabinet. Therefore, the choke 20 may be exposed to the outside
environment. The choke 20 is coupled to the DC bus 36 by the
inductor leads 72, which extend into the cabinet. To prevent dust,
water or salt from entering the cabinet, the interface between the
choke and the cabinet may be sealed. For example, in the depicted
embodiment, the choke is covered by a protective plate 74 that
extends through and fastens to the barrier 66. The plate 74
includes openings 76 that allow the inductor leads 72 to extend
into the cabinet from the cooling channel 62. Additionally, a
gasket 78 is positioned between the barrier 66 and the plate 74 to
form a seal around the interface between the barrier 66 and the
protective plate 74. Two gaskets 80 are also positioned between the
plate 74 and the choke 20 around the openings 76. To ensure a tight
seal between the plate 74 and the choke 20, the choke 20 is shaped
to interface with the plate 74 and the gaskets 80, as will be
described further below. Furthermore, to prevent electrical failure
of the choke 20, the choke 20 itself may also be sealed in
accordance with embodiments discussed herein to protect against
dust, water, and salt.
[0020] Turning to FIG. 3, an exemplary choke 20 that provides
improved protection from the environment is shown. The choke 20 may
include an E-shaped core element 82 coupled to an I-shaped core
element 84 with brackets 86. Both the E-shaped core element 82 and
the I-shaped core element 84 may include any form of magnetic
material, such a ferromagnetic material. The two inductor coils 42
are mounted to the outside arms of the E-shaped core element 82.
The I-shaped core element 84 is positioned over the inductor coil
42 and coupled to the E-shaped core element 82 via the brackets 86,
completing the magnetic circuit between the two inductor coils 42
and providing a desired level of mutual inductance between the
inductors 42. The mutual inductance may be adjusted by controlling
the air gap between the E-shaped core element 82 and the I-shaped
core element 84. The air gap is controlled by the dimensions of the
bracket 86. Additionally, the brackets 86 may also include mounting
holes 88 for attaching the choke 20 to the motor drive unit 58.
[0021] The choke 20 may also include the inductor leads 72, which
couple each respective inductor 42 to the high-side 38, or the
low-side 40 of the DC bus 36. As will be described further below
with respect to FIGS. 4 and 5, the inductor coils 42 may be sealed
inside a potting 90 that includes a main body 92 and a projection
94. The main body 92 seals the inductor coils 42 from the magnetic
core and the outside environment, while the projection 94 surrounds
a portion of the inductor coil leads 72 and enables a water tight
seal to be made between the cooling channel 62 and the cabinet.
[0022] Turning now to FIG. 4, a perspective view of an inductor
coil 42 is shown in accordance with embodiments. As can be more
easily seen in FIG. 4, the main body 92 of the potting 90 forms a
ring-like shape with an opening 96 that may receive a magnetic
core. The inductor coil 42 may be formed with any suitable
conductor, such as aluminum or copper sheets or wire. The height of
the conductor as well as the number of windings of the conductor
will, in part, determine the inductance of the choke. The gauge or
thickness of the sheet will, in part, determine the power handling.
The inductor coil 42 is wrapped around the opening 94 and is
completely surrounded by the potting 90. The potting 90 may form a
unitary piece and may be made of any suitable potting material,
such as an epoxy or other resin. In certain embodiments, the
potting material may include PD6 Elantis 300 LV, or Dolphon
CB-1109. Furthermore, in certain embodiments, the potting 90 may be
injection molded.
[0023] Within the potting 90 and surrounding the inductor coil 42
are several layers of an insulator. Specifically, a winding
insulator 98 separates the layers of the inductor coil 42 and
surrounds the inside and outside of the inductor coil. The winding
insulator 98 may be a single sheet of insulative material that is
wound together with the inductor coil 42. To ensure an effective
barrier between the layers of the inductor coil 42, the winding
insulator 98 may have a greater height compared to inductor coil
42. To cover both the inside and outside surfaces of the inductor
coil 42, the winding insulator may fold over one end of the
inductor coil 42. Additionally, a top insulator 100 covers the top
of the inductor coil 42, and a bottom insulator 102 covers the
bottom of the inductor coil 42. In this way, two layers of
electrical insulator surround the inductor coil 42, the insulators
98, 100 and 102, and the potting 90. The insulators 98, 100 and 102
may be made of any suitable electrically insulative material, such
as Nomex.RTM., for example. In other embodiments, the conductor may
be wire and the winding insulator may be a thin insulative layer
that surrounds the wire, in which case the top insulator 100 and
the bottom insulator 102 may be eliminated.
[0024] As mentioned above, the potting 90 is made out of two
sections, the main body, 92, which contains the inductor coil 42,
and the projection, which contains the inductor leads 72. The
inductor leads extend from the choke 20 through openings 76 in the
plate 74 and into the cabinet. The projection 94 is shaped to
insulate the inductor leads 72 from each other and from the outside
environment. Further, the height of the projection is sized so that
the projection insulates that segment of each inductor lead 72 that
sits within the cooling channel. In other words, the inductor leads
72 only emerge from the projection inside the cabinet, with no part
of the inductor leads 72 being exposed inside the cooling channel
62. Additionally, the projection 94 also includes a raised surface
104 that fits through the openings 76 and the gasket 80 described
above in relation to FIG. 2. The raised surface 104, enables proper
alignment between the choke 20 and the openings 76, and helps to
ensure a water tight seal between the cooling channel 62 and the
cabinet. In some embodiments, a water proofing may be applied
around the opening 76 in addition to, or in place of, the gaskets
80.
[0025] Turning now to FIG. 5, a cross-section of the assembled
inductor coil 42 of FIG. 4 is shown. In FIG. 5 it can be seen that
the windings of the inductor coil 42 are separated and surround by
the winding insulator 98 and that the top insulator 100 and bottom
insulator 102 further insulate the inductor coil 42, forming a
complete insulative layer around the inductor coil 42 within the
potting 90 as explained above in relation to FIG. 4. As an
additional layer of protection, another insulator 110 may be laid
flat over a portion of the top of the main body 92 of the potting
90. The insulator 110 provides an additional layer of electrical
separation between the inductor coil 42 and the I-shaped core
element 84. The insulator 110 may be any suitable insulator, such
as Nomex.RTM., for example.
[0026] FIG. 5 also depicts the coupling between the inductor coil
42 and the inductor leads 72. Specifically, the inductor leads 72
may lie flat against a surface of the inductor coil 42 at opposite
ends of the inductor coil 42. The inductor leads 72 may be
electrically coupled to the inductor coil 42 via soldering.
Additionally, the winding insulator 98 may wrap around the inductor
leads 72 where they couple to the inductor coil 42.
[0027] The inductor leads 72 extend through the projection 94. As
seen in FIG. 5, the inside edge of the projection 94 is flush with
the side of the opening 96. This allows the I-shaped core element
to sit flush over the portion of the E-shaped core element that
extends through the opening 96. At the outer edge, however,
projection 94 hangs over the outer edge of the main body 92. This
provides more substantial potting material around the inductor
leads 94. Furthermore, the inductor leads 72 curve toward the outer
edge in order to be centered within the projection 94. Inside the
projection 94, a spacer 106 is situated between the inductor leads
72 and a strap is situated around the inductor leads 72. Together,
the spacer 106 and the strap 108 ensure the proper spacing between
the inductor leads 72 during the process of molding the potting 90
around the inductor coil 42. Additionally, in some embodiments, the
ends of one or both leads 72 that emerge from the projection 94 may
be surrounded by an insulator 112 that butts against the raised
surface 104. The insulator 112 may be shrink tubing, for example.
Line 6-6 shows the location of a close-up view of the inductor lead
72 illustrated in FIG. 6.
[0028] In some embodiments, the inductor leads 72 may be flexible.
Making the inductor leads 72 flexible allows the manufacturing
tolerances of the choke 20 to be relaxed while still mating the
inductor leads 72 to the DC bus 36 at the appropriate position
within the cabinet. Furthermore, the flexibility of the inductor
leads 72 enables the openings 76 to be relatively small, due to the
fact that, during installation of the choke, the leads 72 may be
straightened out for passing the leads 72 through the openings 76
and then bent into place for coupling to the power source. Reducing
the size of the openings 76 reduces the size of the area to be
sealed and enables the projection 94 to more reliably and
conveniently mate with the openings 76.
[0029] To achieve flexibility of the inductor leads 72, the
inductor leads 72 may be a laminate of several thin metal layers
114, as shown in FIG. 6. In one embodiment, the inductor leads 72
are made of seven layers of 0.01 inch thick copper strap. To
provide rigidity inside the main body 92 of the potting 90 and
ensure a reliable electrical contact to the inductor coil 42, the
metal layers 114 may be soldered together over a portion of their
length.
[0030] Turning now to FIG. 7, a method of fabricating the choke
assembly illustrated in FIGS. 4 and 5 is illustrated. Process 116
begins at step 118, in which the inductor leads 72 are coupled to
the conductor that will make up the inductor coil. For example, the
inductor leads 72 may be soldered to the conductor. In embodiments
in which the inductor lead includes several metal layers 114, as
shown in FIG. 6, the metal layers 114 may also be soldered to one
another during step 118.
[0031] Next, at step 120, the conductor and an adjacent winding
insulator 98 are wound around a bobbin to form the inductor coil
42. The winding insulator 98 may be folded over the conductor at
one end so that the internal and external surfaces of the winding
are covered by the insulator. The winding insulator 98 may be
fastened at one end with tape, an adhesive or other suitable
fastener, to prevent the insulator from being pushed away from the
inductor coil during the molding step. In some embodiments, the
bobbin may be removed after the inductor coil is formed.
[0032] Next, at step 122, insulators 100 and 102 are placed over
the top and bottom of the inductor coil 42. In embodiments, the
insulators 100 and 102 may be held in place by tape, an adhesive,
or any other suitable fastening mechanism. Additionally, the
inductor leads 72 may be shaped so that they will pass through the
projection 94 at the desired position and orientation. In the
embodiment shown in FIG. 5, the inductor leads 72 emerge from the
top of the projection 94 at approximately the middle of the
projection 94, thus helping to ensure substantial insulation on all
sides of the inductor leads 72. To hold the inductor leads in the
proper position, the spacer 106 may be positioned between the
inductor leads 106, and the strap 108 may be placed around the
inductor leads.
[0033] Next, at step 124, the inductor coil is placed in the mold.
The mold may be a two piece mold with a parting line at the top of
the main body 92 of the potting 90. To facilitate the removal of
the potting 90 from the mold, both pieces of the mold may be
tapered. After the inductor coil is positioned within the mold, the
mold may filled with potting material, which is allowed to
harden.
[0034] Next, at step 126, the potted inductor coil 42 is removed
from the mold and placed over the magnetic core. In embodiments,
the magnetic core may include an E-shaped core element 82, in which
case, two inductor coils 42 may be installed over the side
projections of the E-shaped core element 82 and the brackets 86. At
this time, the insulator(s) 112 may be applied to the portion of
the inductor lead that extends from the potting 90. In embodiments,
the insulator 112 may be a shrink tubing that is heated to conform
to the shape of the inductor lead 72. Additionally, the insulator
110 may also be placed over the inductor coil 42 coil. The
insulator 110 may be held in place by an adhesive, tape or other
fastener, or may be held in place by the pressure of the I-shaped
core element 84.
[0035] Next, at step 128, the I-shaped core element 84 may be
attached to the E-shaped core element 82. The spacing between the
I-shaped core element 84 and the E-shaped core element 82 may be
predetermined according to known inductive characteristics of such
chokes. Finally, at step 130 the assembled choke 20 may, in some
embodiments, be covered with a layer of varnish. The varnish may
provide an additional level of protection against dust, water and
salt, protection against corrosion, and may also serve to securely
fasten the inductor coil 42 to the core element 70, thereby
minimizing vibrations. The choke 20 may then be installed within
the motor drive unit 58.
[0036] With the choke arrangement described above, significant
protection from environmental conditions may be realized. The
techniques described provide two layers of protection around the
inductor coil 42. The insulators 98, 100, and 102 surround the
inductor winding and forming a first layer of protection, while the
potting 82 provides a second layer of protection and forms a hard
shell around the inductor coil. Furthermore, the molded projection
94 insulates the inductor leads 72 while also providing a surface
that mates with the cabinet, allowing a water tight seal between
the cooling channel 62 and the cabinet. By providing a choke with
significant protection against outside environmental conditions,
the motor drive unit 58 may be mounted such that the cooling
channel 62 is projected through an exterior wall of a building and
exposed to the outdoor environment.
[0037] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *