U.S. patent application number 16/398486 was filed with the patent office on 2020-11-05 for system and method for reducing power losses for magnetics integrated in a printed circuit board.
The applicant listed for this patent is Rockwell Automation Technologies, Inc.. Invention is credited to Gennadi Sizov, Gary L. Skibinski, Zoran Vrankovic.
Application Number | 20200350111 16/398486 |
Document ID | / |
Family ID | 1000004084278 |
Filed Date | 2020-11-05 |
United States Patent
Application |
20200350111 |
Kind Code |
A1 |
Sizov; Gennadi ; et
al. |
November 5, 2020 |
System and Method for Reducing Power Losses for Magnetics
Integrated in a Printed Circuit Board
Abstract
A system and method for integrating a magnetic component within
a power converter includes a coil integrated on a PCB. The PCB
includes multiple layers and traces on each layer to form a single
coil or to form multiple coils on the magnetic component. The PCB
further includes at least one opening in the PCB through which a
core component may pass, such that the magnetic component is
defined by the coils and the core material. To reduce eddy currents
built up within the traces, the dimensions of traces on a layer are
varied and the position of traces between layers of the PCB are
varied. The widths and locations of individual traces are selected
to reduce coupling of the trace to leakage fluxes within the
magnetic component. A floating conductive layer may also be
provided to still further reduce the magnitude of eddy currents
induced within the coil.
Inventors: |
Sizov; Gennadi; (Shorewood,
WI) ; Vrankovic; Zoran; (Greenfield, WI) ;
Skibinski; Gary L.; (Milwaukee, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rockwell Automation Technologies, Inc. |
Mayfield Heights |
OH |
US |
|
|
Family ID: |
1000004084278 |
Appl. No.: |
16/398486 |
Filed: |
April 30, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01F 27/2885 20130101;
H01F 27/2804 20130101; H05K 1/181 20130101; H05K 2201/0792
20130101; H02M 1/12 20130101; H01F 2027/2809 20130101; H01F 27/346
20130101; H05K 2201/08 20130101 |
International
Class: |
H01F 27/28 20060101
H01F027/28; H01F 27/34 20060101 H01F027/34; H05K 1/18 20060101
H05K001/18; H02M 1/12 20060101 H02M001/12 |
Claims
1. A magnetic component, comprising: a circuit board having a
plurality of layers and an opening extending through the circuit
board; and a coil defined by a plurality of traces, wherein: the
plurality of traces includes at least one trace on each of the
plurality of layers of the circuit board, the at least one trace on
each layer extends around the opening extending through the circuit
board to define a plurality of loops on the respective layer, the
plurality of loops on one layer define an inner trace proximate the
opening through the circuit board, an outer trace distal from the
opening through the circuit board, and at least one intermediate
trace located between the inner trace and the outer trace, a first
width of the inner trace is less than a second width of the at
least one intermediate trace, and a second width of the at least
one intermediate trace is less than a third width of the outer
trace.
2. The magnetic component of claim 1 wherein: the circuit board
includes a top layer and a bottom layer, the top layer is selected
from the plurality of layers and is the layer closest to a first
surface of the circuit board, the bottom layer is selected from the
plurality of layers and is the layer closest to a second surface of
the circuit board, the second surface of the circuit board is
opposite the first surface of the circuit board, and the magnetic
component further comprises a first shield located on one of the
plurality of layers between the top layer and the coil to induce
eddy currents in the first shield and, thereby, reduce eddy
currents induced in the coil.
3. The magnetic component of claim 2 further comprising a second
shield located on one of the plurality of layers between the bottom
layer and the coil to induce eddy currents in the second shield
and, thereby, reduce eddy currents induced in the coil.
4. The magnetic component of claim 1 wherein: the inner trace on
each layer has a first axis, the at least one intermediate trace on
each layer has a second axis, the outer trace on each layer has a
third axis, at least one of the first axis, the second axis, and
the third axis on one layer is offset from the corresponding axis
on another layer.
5. The magnetic component of claim 4 wherein: the plurality of
layers includes a top layer, a bottom layer, and at least one
intermediate layer, the first axis, the second axis, and the third
axis on the at least one intermediate layer are each offset from
the respective axis on the bottom layer, and the first axis, the
second axis, and the third axis on the top layer are each offset
from the respective axis on the at least one intermediate
layer.
6. The magnetic component of claim 1 wherein: a plane of symmetry
extends through the circuit board parallel with the plurality of
layers, the first axis, the second axis, and the third axis on a
first side of the plane of symmetry are offset from the
corresponding axis on adjacent layers in a first pattern, and the
first axis, the second axis, and the third axis on a second side
second side of the plane of symmetry are offset from the
corresponding axis on adjacent layers in a second pattern
symmetrical to the first pattern.
7. The magnetic component of claim 1 further comprising: a core
material, wherein: the core material extends over the opening
through the circuit board and laterally over at least a portion of
the circuit board, a portion of the core material extends through
the opening in the circuit board, a first portion of the coil
located on the circuit board between the opening and a first side
of the circuit board is under the core material, a second portion
of the coil located on the circuit board between the opening and a
second side of the circuit board is under the core material, a
third portion of the coil located on the circuit board proximate a
first end of the circuit board defines a first end turn of the coil
and is beyond a first end of the core material, and a fourth
portion of the coil located on the circuit board proximate a second
end of the circuit board defines a second end turn of the coil and
is beyond a second end of the core material.
8. The magnetic component of claim 7 wherein each trace on one
layer of the circuit board has a first sectional profile in the
first portion of the coil and a second sectional profile in the
second portion of the coil.
9. A magnetic component, comprising: a circuit board having a
plurality of layers and an opening extending through the circuit
board; and a coil defined by a plurality of traces, wherein: the
plurality of traces includes at least one trace on each of the
plurality of layers of the circuit board, the at least one trace on
each layer extends around the opening through the circuit board to
define a plurality of loops on the respective layer, the plurality
of loops on one layer define an inner trace proximate the opening
through the circuit board, an outer trace distal from the opening
through the circuit board, and at least one intermediate trace
located between the inner trace and the outer trace, the inner
trace on each layer has a first axis, the at least one intermediate
trace on each layer has a second axis, the outer trace on each
layer has a third axis, at least one of the first axis, second
axis, and third axis on one layer is offset from the corresponding
axis on another layer.
10. The magnetic component of claim 9 wherein: the plurality of
layers includes a top layer, a bottom layer, and at least one
intermediate layer, the first axis, the second axis, and the third
axis on the at least one intermediate layer are each offset from
the respective axis on the bottom layer, and the first axis, the
second axis, and the third axis on the top layer are each offset
from the respective axis on the at least one intermediate
layer.
11. The magnetic component of claim 9 wherein: the circuit board
includes a top layer and a bottom layer, the top layer is selected
from the plurality of layers and is the layer closest to a first
surface of the circuit board, the bottom layer is selected from the
plurality of layers and is the layer closest to a second surface of
the circuit board, the second surface of the circuit board is
opposite the first surface of the circuit board, and the magnetic
component further comprises a first shield located on one of the
plurality of layers between the top layer and the coil to induce
eddy currents in the first shield and, thereby, reduce eddy
currents induced in the coil.
12. The magnetic component of claim 11 further comprising a second
shield located on one of the plurality of layers between the bottom
layer and the coil to induce eddy currents in the second shield
and, thereby, reduce eddy currents induced in the coil.
13. The magnetic component of claim 9 wherein: a first width of the
inner trace is less than a second width of the at least one
intermediate trace, and a second width of the at least one
intermediate trace is less than a third width of the outer
trace.
14. The magnetic component of claim 9 wherein: a plane of symmetry
extends through the circuit board parallel with the plurality of
layers, the first axis, the second axis, and the third axis on a
first side of the plane of symmetry are offset from the
corresponding axis on adjacent layers in a first pattern, and the
first axis, the second axis, and the third axis on a second side
second side of the plane of symmetry are offset from the
corresponding axis on adjacent layers in a second pattern
symmetrical to the first pattern.
15. The magnetic component of claim 9 further comprising: a core
material, wherein: the core material extends over the opening
through the circuit board and laterally over at least a portion of
the circuit board, a portion of the core material extends through
the opening in the circuit board, a first portion of the coil
located on the circuit board between the opening and a first side
of the circuit board is under the core material, a second portion
of the coil located on the circuit board between the opening and a
second side of the circuit board is under the core material, a
third portion of the coil located on the circuit board proximate a
first end of the circuit board defines a first end turn of the coil
and is located beyond a first end of the core material, and a
fourth portion of the coil located on the circuit board proximate a
second end of the circuit board defines a second end turn of the
coil and is located beyond a second end of the core material.
16. The magnetic component of claim 15 wherein each trace on one
layer of the circuit board has a first sectional profile in the
first portion of the coil and a second sectional profile in the
second portion of the coil.
17. A method of integrating a magnetic component in a circuit
board, the method comprising the steps of: defining a plurality of
traces for a circuit board, the circuit board including a plurality
of layers and an opening extending therethrough, wherein: the
plurality of traces includes at least one trace on each of the
plurality of layers of the circuit board, the at least one trace on
each layer extends around the opening through the circuit board to
define a plurality of loops on the respective layer, the plurality
of loops on one layer define an inner trace proximate the opening
through the circuit board, an outer trace distal from the opening
extending the circuit board, and at least one intermediate trace
located between the inner trace and the outer trace, a first width
of the inner trace is less than a second width of the at least one
intermediate trace, and a second width of the at least one
intermediate trace is less than a third width of the outer trace,
and mounting a core to the circuit board, wherein a portion of the
core is inserted through the opening and the core extends laterally
over at least a portion of the plurality of traces.
18. The method of claim 17, wherein: the inner trace on each layer
has a first axis, the at least one intermediate trace on each layer
has a second axis, the outer trace on each layer has a third axis,
at least one of the first axis, the second axis, and the third axis
on one layer is offset from the corresponding axis on another
layer.
19. The method of claim 18, wherein: the plurality of layers
includes a top layer, a bottom layer, and at least one intermediate
layer, the first axis, the second axis, and the third axis on the
at least one intermediate layer are each offset from the respective
axis on the bottom layer, and the first axis, the second axis, and
the third axis on the top layer are each offset from the respective
axis on the at least one intermediate layer.
20. The method of claim 17 wherein: the circuit board includes a
top layer and a bottom layer, the top layer is selected from the
plurality of layers and is the layer closest to a first surface of
the circuit board, the bottom layer is selected from the plurality
of layers and is the layer closest to a second surface of the
circuit board, and the second surface of the circuit board is
opposite the first surface of the circuit board, the method further
comprising the step of defining a shield on one of the plurality of
layers between the top layer and the coil to induce eddy currents
in the shield and, thereby, reduce eddy currents induced in the
coil.
Description
BACKGROUND INFORMATION
[0001] The subject matter disclosed herein relates generally to
reducing power losses in magnetic devices for use in power
conversion devices and, more specifically, to a system for reducing
power losses in a magnetic device integrated in a printed circuit
board (PCB) for use in the power conversion device.
[0002] As is known to those skilled in the art, power conversion
devices receive power in a first form at an input to the device and
provide power in a second form at an output from the device. The
power may be received or delivered as either alternating current
(AC) or direct current (DC) at varying amplitudes of voltage and/or
current. Common power conversion devices include an AC-to-DC
converter, a DC-to-AC converter, a boost converter, a buck
converter, a multi-level converter, a voltage regulator, and the
like. When the power conversion device uses a switching element to
perform the power conversion, it may also be referred to as a
switched-mode power converter (SMPC) or a switched-mode power
supply (SMPS). The switching element in a SMPC is typically a
solid-state device having a sufficient power rating to handle the
power conversion, such as an insulated-gate bipolar transistor
(IGBT), metal-oxide semiconductor field-effect transistor (MOSFET),
or other power electronic switching device. The switching element
is controlled to alternately turn off and on, thereby alternately
opening or closing a conduction path that is used either singly or
in combination with other power electronic switching devices to
convert the power from the first form at the input to the second
form at the output.
[0003] As is also known, the power conversion device may utilize a
modulation routine, such as pulse width modulation, to control
turning the power electronic switching devices on and off. The
modulation may occur at frequencies ranging from the hundreds of
hertz to tens of kilohertz. The frequency at which modulation
occurs is commonly referred to as the switching frequency, and the
length of time for one switching cycle is commonly referred to as
the switching period. Each electronic switching device is either
turned on or off for a percentage of the switching period. The
length of time within a switching period and the number of cycles
for which a particular electronic switching device is turned on
will help define the amplitude of the voltage output from the power
conversion device. Additional components, such as inductors and/or
capacitors within the power conversion device may be used to
increase or decrease the amplitude of voltage and/or current or to
smooth the waveform of the output voltage or current from the power
conversion device.
[0004] While the modulation routine controls the switching devices
to convert the power from the first form to the second form, it
also generates electrical signals at undesired frequencies. If, for
example, the output power is an AC voltage, the modulation routine
will generate an output voltage with a fundamental frequency at the
desired frequency of the AC output voltage. The modulation routine,
however, also generates high frequency signals at the switching
frequency and multiples, or harmonics, thereof. The high frequency
signals may result in undesired radiated and/or conducted emissions
at the output of the power converter.
[0005] Historically, it has been known to provide a choke at the
output of the power converter to reduce the undesired high
frequency content from the power converter. The choke is a high
frequency filter that allows DC or low frequency AC components to
pass while attenuating or eliminating high frequency AC components.
The choke may be configured to filter the harmonic content
generated by modulation of the switching device and to allow the
desired fundamental AC component to pass. The choke is typically
constructed of a core material and one or more windings of
conductors wrapped around the core material. The choke acts, in
large part, as an inductor, representing high impedance to
high-frequency AC components. The energy in these high-frequency
components is, therefore, dissipated in the choke in the form of
heat. As the power rating of the power conversion device increases,
the current rating of the conductors and, therefore, the size of
the wires increases. Similarly, the size of the core around which
the wires are to be wrapped increases. The amount of heat lost in
the choke as a result of filtering the high frequency content also
increases. While an increase in the size of the core may provide
some capacity for increased heat dissipation by the core, the
additional energy dissipated in the core from increased high
frequency content may demand further cooling of the choke, such as
a heat sink, air cooling, or liquid cooling. The size and heat
dissipation requirements of the choke typically result in a bulky
filter component requiring substantial space in a control cabinet
and may also require a fan or fluid pumps and hydraulic components
to implement air or liquid cooling.
[0006] More recently, efforts have been made to incorporate a
magnetic component within the power converter. However, such
efforts are subject to the same drawbacks as external chokes.
Introduction of the magnetic component within the power converter
moves the power losses and heat generation caused by the magnetic
component within the power conversion device. The heat generation
limits the application of magnetic components within the power
converter to low power devices. Alternately, the heat generation
may require addition of heat sinks, forced air cooling, or liquid
cooling increasing the size and cost of the power converter.
[0007] Thus, it would be desirable to provide a system and method
for integrating a magnetic component within a power converter that
minimizes the power losses within the magnetic component. It is a
further aspect of the invention, that the magnetic component is
scalable to power converters of greater power ratings as a result
of the reduced power losses within the magnetic component.
BRIEF DESCRIPTION
[0008] The subject matter disclosed herein describes a system and
method for integrating a magnetic component within a power
converter that minimizes the power losses within the magnetic
component. The magnetic component includes a coil integrated on a
printed circuit board (PCB) within the power converter. The PCB
includes multiple layers and traces on each layer are joined
together to form a single coil or to form multiple coils on the
magnetic component. The PCB further includes at least one opening
in the PCB through which a core component may pass. The traces
forming the coils may be laid out to encircle the opening and the
core material, such that the magnetic component is defined by the
coils and the core material. According to a first aspect of the
invention, the dimensions of traces on a layer are varied within
the coil to reduce eddy currents within the traces resulting from
air-gap fringing flux. The air-gap fringing flux is greatest
proximate the opening in the PCB and at the air-gap in the core
component. By making the width of individual traces that are
closest to the opening within the coil narrower than traces that
are further from the opening, the conductive material of the coil
located within the region of high air-gap fringing flux is reduced.
As a result, the eddy currents induced within the coil due to the
air-gap fringing flux is reduced. According to another aspect of
the invention, the position of traces between layers of the PCB are
varied. The locations of individual traces are selected such that a
higher percentage of traces are located in a region having a lower
magnetic field component and, therefore, reducing coupling to
leakage fluxes within the magnetic component. According to still
another aspect of the invention, a floating conductive layer is
positioned between the coil and the core material. The floating
conductive layer may be a conductive sheet or series of traces
located on one layer of the PCB where the conductive layer is not
connected to the coil. The conductive layer is preferably located
near a surface of the PCB such that eddy currents and the resulting
heat induced within the conductive layer are more readily
dissipated out of the PCB. As a result of the various features to
reduce the power losses and increase the efficiency within the
magnetic component, the magnetic component is scalable to power
converters having greater power ratings than a magnetic component
of traditional construction.
[0009] According to one embodiment of the invention, a magnetic
component includes a circuit board and a coil defined by multiple
traces located on the circuit board. The circuit board has multiple
layers and an opening extending through the circuit board. The
traces include at least one trace on each of the of layers of the
circuit board, where at least one trace on each layer extends
around the opening through the circuit board to define multiple
loops on the respective layer. The loops on one layer define an
inner trace proximate the opening through the circuit board, an
outer trace distal from the opening through the circuit board, and
at least one intermediate trace located between the inner trace and
the outer trace. A first width of the inner trace is less than a
second width of the at least one intermediate trace, and a second
width of the at least one intermediate trace is less than a third
width of the outer trace.
[0010] According to another embodiment of the invention, a magnetic
component includes a circuit board, having multiple layers and an
opening extending through the circuit board, and a coil defined by
multiple traces. The traces include at least one trace on each
layer of the circuit board, and the trace on each layer extends
around the opening through the circuit board to define multiple
loops on the respective layer. The plurality of loops on one layer
define an inner trace proximate the opening through the circuit
board, an outer trace distal from the opening through the circuit
board, and at least one intermediate trace located between the
inner trace and the outer trace. The inner trace on each layer has
a first axis, the at least one intermediate trace on each layer has
a second axis, and the outer trace on each layer has a third axis.
At least one of the first axis, second axis, and third axis on one
layer is offset from the corresponding axis on another layer.
[0011] According to still another embodiment of the invention, a
method of integrating a magnetic component in a circuit board is
disclosed. Multiple traces are defined for a circuit board, where
the circuit board includes multiple layers and an opening extending
therethrough. The traces include at least one trace on each of the
layers of the circuit board, and the trace on each layer extends
around the opening through the circuit board to define multiple
loops on the respective layer. The loops on one layer define an
inner trace proximate the opening extending the circuit board, an
outer trace distal from the opening through the circuit board, and
at least one intermediate trace located between the inner trace and
the outer trace. A first width of the inner trace is less than a
second width of the at least one intermediate trace, and a second
width of the at least one intermediate trace is less than a third
width of the outer trace. A core is mounted to the circuit board,
where a portion of the core is inserted through the opening and the
core extends laterally over at least a portion of the plurality of
traces.
[0012] These and other advantages and features of the invention
will become apparent to those skilled in the art from the detailed
description and the accompanying drawings. It should be understood,
however, that the detailed description and accompanying drawings,
while indicating preferred embodiments of the present invention,
are given by way of illustration and not of limitation. Many
changes and modifications may be made within the scope of the
present invention without departing from the spirit thereof, and
the invention includes all such modifications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Various exemplary embodiments of the subject matter
disclosed herein are illustrated in the accompanying drawings in
which like reference numerals represent like parts throughout, and
in which:
[0014] FIG. 1 is a top view of a magnetic component integrated into
a PCB according to one embodiment of the invention;
[0015] FIG. 2 is a top plan view of the PCB for the magnetic
component of FIG. 1;
[0016] FIG. 3 is an exploded view of a magnetic component
integrated into a PCB according to another embodiment of the
invention;
[0017] FIG. 4 is a top plan view of one layer of the PCB of FIG.
3;
[0018] FIG. 5 is a partial sectional view of one embodiment of a
magnetic component integrated into a PCB illustrating a core
material and a baseline layout of traces on each layer of a PCB
enclosed within the core material;
[0019] FIG. 6 is a partial sectional view of the magnetic component
of FIG. 5 taken at 6-6 illustrating air-gap fringing flux;
[0020] FIG. 7 is a partial sectional view of the magnetic component
of FIG. 5 taken at 7-7 illustrating slot window leakage flux;
[0021] FIG. 8 is a top plan view of the magnetic component of FIG.
5;
[0022] FIG. 9 is a partial sectional view of the magnetic component
of FIG. 8 taken at 9-9;
[0023] FIG. 10 is a partial sectional view of a magnetic component
according to one embodiment of the invention illustrating a trace
configuration in which the widths of the traces are varied;
[0024] FIG. 11 is a partial sectional view of a magnetic component
according to one embodiment of the invention illustrating a trace
configuration in which the positions of the traces are varied;
[0025] FIG. 12 is a partial sectional view of a magnetic component
according to one embodiment of the invention illustrating a trace
configuration in which both the widths and the positions of the
traces are varied;
[0026] FIG. 13 a partial sectional view of another embodiment of a
magnetic component integrated into a PCB illustrating a core
material with a distributed air gap and a baseline layout of traces
on each layer of a PCB enclosed within the core material;
[0027] FIG. 14 is a partial sectional view of a magnetic component
incorporated into the core material with the distributed air gap
shown in FIG. 13 illustrating a trace configuration in which both
the widths and the positions of the traces are varied;
[0028] FIG. 15 is a partial sectional view of a magnetic component
incorporated into the core material with the distributed air gap
shown in FIG. 13 illustrating a trace configuration in which both
the widths and the positions of the traces are varied and in which
a floating shield layer is included;
[0029] FIG. 16 is a partial sectional view of a magnetic component
incorporated into the core material with the distributed air gap
shown in FIG. 13 illustrating a trace configuration for end-turns
in which both the widths and the positions of the traces are
varied; and
[0030] FIG. 17 is a partial sectional view of a magnetic component
incorporated into the core material with the distributed air gap
shown in FIG. 13 illustrating a trace configuration for end-turns
in which both the widths and the positions of the traces are varied
and in which floating shield layers are included.
[0031] In describing the various embodiments of the invention which
are illustrated in the drawings, specific terminology will be
resorted to for the sake of clarity. However, it is not intended
that the invention be limited to the specific terms so selected and
it is understood that each specific term includes all technical
equivalents which operate in a similar manner to accomplish a
similar purpose. For example, the word "connected," "attached," or
terms similar thereto are often used. They are not limited to
direct connection but include connection through other elements
where such connection is recognized as being equivalent by those
skilled in the art.
DETAILED DESCRIPTION
[0032] The various features and advantageous details of the subject
matter disclosed herein are explained more fully with reference to
the non-limiting embodiments described in detail in the following
description.
[0033] As previously discussed, the subject matter disclosed herein
describes a system and method for integrating a magnetic component
within a power converter that minimizes the power losses within the
magnetic component. One such power conversion device is a motor
drive. Although the magnetic component disclosed herein may be used
in a number of different power converters or SMPSs, application
within a motor drive will be considered for purposed of
explanation. Motor drives are utilized to control operation of a
motor by regulating the magnitude and frequency of the output
voltage provided to the motor to achieve, for example, a desired
operating speed of the motor or a desired torque produced within
the motor. According to one common configuration, a motor drive
includes a DC bus having a DC voltage of suitable magnitude from
which an AC voltage may be generated and provided to the motor. The
DC voltage may be provided as an input to the motor drive or,
alternately, the motor drive may include a rectifier section which
converts an AC voltage input to the DC voltage present on the DC
bus. The motor drive includes power electronic switching devices,
such as insulated gate bipolar transistors (IGBTs), field-effect
transistors (FETs), metal-oxide semiconductor FETs (MOSFETs),
thyristors, or silicon-controlled rectifiers (SCRs). The motor
drive further includes a reverse conduction power electronic
device, such as a free-wheeling diode, connected in parallel across
the power electronic switching device. The reverse conduction power
electronic device is configured to conduct during time intervals in
which the power electronic switching device is not conducting. A
controller, such as a microprocessor or dedicated motor controller,
generates switching signals to selectively turn on or off each
power electronic switching device to generate a desired DC voltage
on the DC bus or a desired motor voltage.
[0034] The controller for the motor drive typically utilizes a
modulation routine, such as pulse width modulation, to generate the
switching signals to control the power electronic switching devices
that alternately connect and disconnect the DC bus to one phase of
the output to the motor. The modulation routine determines a
percentage, or duty cycle, of the duration of one modulation period
for which the DC bus is connected to the output. Ideally, when the
output is connected to the DC bus, the voltage level on the DC bus
is present at the output, and when the output is disconnected from
the DC bus, there is zero volts present at the output. Multiplying
the voltage level on the DC bus by the duty cycle yields an average
value of voltage present at the output during each modulation
period. By controlling the duty cycle, the modulation routine
controls the average value of voltage present at the output. In
addition, if the modulation period is small (i.e., the switching
frequency is high) the average value may be controlled to
approximate an AC output voltage.
[0035] Although the modulation routine converts a DC voltage into
an AC voltage, it also generates electrical signals at frequencies
other than the desired fundamental frequency of the AC output
voltage. The modulation routine generates high frequency square
waves having variable duty cycles. While the square wave includes a
fundamental component having an amplitude and frequency
corresponding to the desired operation of the motor, the square
wave also includes harmonic content at various frequencies that are
multiples of the switching frequency. Further, the amplitude of the
voltage and current conducted through the switching devices may be
sizable in comparison, for example, to control signals within the
drive or other electronic devices. The motor may require
fundamental output voltages having magnitudes, for example, of 230
or 460 V at currents having magnitudes in the amps to hundreds of
amps. Although, the magnitude of the harmonic content is a
percentage of the fundamental output to the motor, the magnitude of
the high frequency signals may still be significant and generate
undesirable radiated emissions from the motor drive.
[0036] In one embodiment of the motor drive, switching devices
suitable for more rapid switching may be selected. The switching
device may be, for example, field-effect transistors (FETs) made of
silicon carbide (SiC MOSFETs) or gallium nitride (GaN FETs) where
the switching frequencies may increase to tens or hundreds of
kilohertz (e.g., 30 kHz-500 kHz) in contrast to traditional FETs
which are typically limited to upper switching frequencies in the
range of 10 kHz-20 kHz. The greater the frequency at which the
power switching devices are able to be modulated, the lower the
amplitude of the harmonic content present on the output of the
motor drive. Thus, including switching devices suitable for
switching in the tens to lower hundreds of kilohertz range reduces
the magnitude of the harmonic content that requires filtering and
similarly reduces the physical size of the magnetic component.
[0037] It is desirable to eliminate the harmonic content and to
deliver a sinusoidal output from the motor drive rather than a
modulated square wave to control operation of the motor.
Integration of a magnetic device as a filter at the output of the
motor drive may attenuate or eliminate the harmonic content of the
output voltage while allowing the desired fundamental component to
be provided to the motor. It is further contemplated that three
separate magnetic components may be incorporated into the motor
drive, where each magnetic component is connected in series with
one phase of a three-phase output to a motor to deliver a
three-phase sinusoidal output voltage to the motor.
[0038] Turning initially to FIG. 1, a first embodiment of a
magnetic component 10 integrated into a circuit board 20 is
illustrated. The PCB 20 is a multi-layer board where a coil 50 is
defined by multiple loops of circuit traces on the PCB. With
reference also to FIG. 2, a first opening 24 extends through the
PCB 20 which is configured to receive a center portion of a core
80. A pair of side openings 29 also extend through the PCB 20 with
a first side opening 29 positioned to one side of the first opening
24 and a second side opening 29 positioned on the opposite side of
the first opening 24. An "E-shaped" member 84 of the core 80 may be
inserted into the openings with a central portion 81 of the core 80
extending through the first opening 24 and a pair of side members
83 of the core 80 extending through the side openings 29. Although
not visible in FIG. 1, a second member of the core, such as an
"I-shaped" member 82 of the core 80 may be positioned on the
reverse side of the PCB 20. Clips 27 extending up through the side
openings 29 secure the two members of the core 80 together and
positively retain the core 80 to the PCB 20. Optionally, an
adhesive material may be applied between contacting surfaces of the
"E-shaped" and "I-shaped" members to secure the core members
together.
[0039] With reference also to FIG. 5, an exemplary sectional view
of such an E-I core configuration is illustrated. The E-shaped
member 84 is illustrated on the lower surface and the I-shaped
member 82 is illustrated on the upper surface. It is understood
that terms such as upper and lower, left and right, front and back,
and the like are intended to be relational with respect to a figure
and are not intended to be limiting. The illustrated magnetic
component 10 may be rotated around a vertical axis, horizontal
axis, or about any other axis of rotation for installation within a
power converter and the associated components will similarly be
rotated. It is further contemplated that various other
configurations of the core 80 may be utilized without deviating
from the scope of the invention. For example, other shapes
including, but not limited to, U-shaped members, C-shaped members,
R-shaped members, T-shaped members, D-shaped members, F-shaped
members, and the like may be utilized according to the application
requirements. Suitable openings may be cut through the PCB 20 and a
suitable arrangement of traces on each layer 30 of the PCB 20 may
be implemented to complement the corresponding members of the core
80. For ease of illustration and discussion herein, the E-I
configuration of the core 80 will be discussed.
[0040] With reference also to FIGS. 3 and 4, the circuit traces 52
are distributed on the PCB 20 such that they loop around the
opening 24. Multiple loops may be formed on each layer 30 of the
PCB 20 where an inner trace 54 is closest to the opening 24 and
outer trace 58 is furthest from the opening 24. Various numbers of
intermediate traces 56 may be defined between the inner trace 54
and the outer trace 58. Vias extending between layers of the PCB 20
may join coils on different layers to form a single coil spanning
multiple layers 30. The embodiment illustrated in FIGS. 3 and 4
includes 4 loops on a layer for ease of illustration. It is
contemplated that various other numbers of loops may be utilized
according to the application requirements. Similarly, the
illustrated embodiment includes eight layers on the PCB. A top
layer 26 and a bottom layer 28 each include solder pads to which
wires or other electrical conductors may be connected. Six
intermediate layers 30a-30f are illustrated between the top and
bottom layers, where each of the intermediate layers 30a-30f
includes four loops. It is contemplated that the PCB 20 may include
various other numbers of layers 30 according to the length of the
traces and number of loops desired. In one embodiment of the
invention, the PCB 20 may include 20 layers. The number, length,
and cross-section of the traces defining loops on a layer 30 and
further the number of layers 30 on which loops are present define
an inductance for the magnetic component. The layout and selection
of the number of loops and number of layers, therefore, are
selected according to the filtering requirements of the application
in which the magnetic component is integrated.
[0041] Turning next to FIG. 5, a baseline arrangement of a magnetic
component 10 includes a core having an E-I configuration. The
sectional view is taken at a point through the core 80. The
E-shaped member 84 is illustrated on the bottom with a circuit
board 20 positioned on top of the E-shaped member 84. The central
portion 81 of the core extends upward through the center opening 24
in the PCB 20 and each side member 83 extends upward through a side
opening 29 in the PCB 20. For ease of illustration, however, the
PCB 20 is only shown within the core between the two side members
83. The I-shaped member 82 spans across the two side members 83 and
an air gap 85 exists between the end of the central portion 81 of
the core 80 and the surface of the I-shaped member 82. The
sectional view of the PCB 20 is shown as a solid block without
illustrating individual layers 30 of the PCB 20 for ease of
illustration. The sectional view of each trace 52 is shown, where
it is understood that each trace 52 in a row is on the same layer
30 of the PCB 20. The baseline arrangement includes traces 52 of
uniform width arranged in uniform rows and columns. Segments of the
magnetic component 10 from FIG. 5 are illustrated in more detail in
FIGS. 6 and 7 along with a graphical representation of flux
linkages that, at least in part, induce eddy currents and generate
losses within the traces 52 of the magnetic component.
[0042] Turning first to FIG. 6, flux lines 91 are shown extending
through the core 80. The air gap 85 is designed to create a region
of high magnetic reluctance through which the flux 91 is forced to
traverse. Air has a relatively low magnetic permeability compared
to the magnetic core material. Because of the high magnetic
reluctance at the air gap 85 region, a portion of the flux 93
fringes outward from the air gap 85. If the air gap 85 existed only
directly between two core materials (e.g., a gap in a bar), the air
gap fringe flux 93 would be generally arc-shaped as it exited the
core 80 on one side of the air gap 85 and entered the core 80 on
the other side of the air gap 85. However, because the I-shaped
member 82 extends laterally beyond the air gap 85 a portion of the
fringing flux 93 extends outward from the end of the central
portion of the E-shaped member 84 and reenters the I-shaped member
82 laterally beyond the periphery of the central portion 81 of the
E-shaped member, passing through the PCB 20. Conductive members,
such as traces 52, located within the path of the air gap fringing
flux 93 have eddy currents induced within the traces 52 as a result
of the flux passing through the traces. The eddy currents, in turn,
cause localized heating in those traces within the path of the air
gap fringing flux 93.
[0043] Turning then to FIG. 7, magnetic flux lines 91 are again
shown extending through the core 80. In addition, leakage flux
lines 95 are shown illustrating slot window leakage fluxes passing
through a portion of the traces 52 on the PCB 20. As shown, the
slot window leakage fluxes are small or non-existent toward the
outer edge of the core 80. Moving from right-to-left in FIG. 7, the
number of turns of the coil increases closer to the air gap 85 in
the core 80, thereby increasing the magnetomotive force (MMF)
present in the magnetic circuit. The increasing MMF, in turn,
causes a portion of the flux in the magnetic circuit to travel
between the I-shaped member 82 and the E-shaped member 84 at a
location other than the air gap. These flux lines 95 are referred
to as slot window leakage fluxes and increase in density as the MMF
increases closer to the air gap in the core 80. The slot window
leakage fluxes 95 induce eddy currents within the traces 52 present
along the path of the flux lines 95 causing localized heating in
those traces.
[0044] With reference next to FIGS. 8 and 9, still another source
of eddy currents in the magnetic component 10 is illustrated. FIG.
9 is a sectional view of the magnetic component 10 looking through
the PCB 20 at a point where the coil 50 is outside of the core 80.
The upper and lower portions of the coil 50 are also referred to as
end turns 51, where each end turn 51 joins the portions of the coil
under the core 80 on either side of the central opening 24. When
the coil 50 is not located under the core 80, the magnetic flux
produced from currents flowing through the traces 52 result in
end-turn leakage flux 97. Without the presence of the core 80, the
magnetic flux exits the PCB 20 travels through air and returns to
the PCB 20. Similar flux paths are established in the absence of a
core material 80, also referred to as an air-core magnetic
component. The density of the end-turn leakage flux 97 is greater
along the inner periphery of the coil 50 as the MMF is similarly
greater along the inner periphery of the coil 50 and decreases
toward the outer periphery of the coil 50. The end-turn leakage
fluxes 97 induce eddy currents within the traces 52 present along
the path of the flux lines 97 causing localized heating in those
traces.
[0045] As discussed above, magnetic flux that is established
outside of the core material 80 and that passes through traces 52
creates eddy currents within those traces 52 present along the path
of the flux lines 97. The eddy currents result in power losses and
localized heating within the magnetic component 10. Various
embodiments of the present invention utilize one or more techniques
to reduce the interaction between the leakage fluxes and the traces
52 on the PCB 20.
[0046] Turning next to FIG. 10, a first embodiment of the magnetic
component 10 varies the width of traces 52 in the PCB 20. For ease
of illustration, the PCB 20 is not shown. FIG. 10 includes only
sectional views of the E-shaped member 84 and I-shaped member 82 of
the core 80 as well as sectional views of traces 52 on the PCB 20.
However, traces 52 illustrated in the same row in FIG. 10 are on a
single layer of the PCB 20. The inner trace 54 on each layer has a
first width 62. According to the illustrated embodiment, the first
width 62 is the same for the inner trace 54 on each layer. Each
intermediate trace 56 has a second width 64. As shown in FIG. 10,
the coil includes twelve columns of intermediate traces 56. Each
column is defined by its own width 64A-64L. As illustrated, the
intermediate widths 64A-64L of the traces 52 in each column is the
same for each layer of the PCB 20. The outer trace 58 on each layer
has a third width 66. According to one embodiment of the invention,
the width of the traces 52 are continuously varying between the
inner trace 54 and the outer trace 58 such that each width (62,
64A-64L, 66) is different. Optionally, a portion of the widths may
vary. According to the illustrated embodiment, the first width 62
of the inner trace 54 is less than the first intermediate width 64A
of the intermediate trace 56 adjacent to the inner trace 54. The
width of the intermediate traces 56 varies between the first
intermediate trace and the sixth intermediate trace. Thus, the
intermediate widths 64A-64F incrementally increase for each
intermediate trace 56 located further from the inner trace 54.
Between the sixth intermediate trace and the outer trace 58, the
remaining widths (64F-64L, 66) of the traces are the same. As
previously discussed, the fringing flux 93 and the slot window
leakage flux 95 both increase in concentration closer to air gap
and, therefore, also closer to the inner trace 54 of the coil. The
interaction of these fluxes with the traces 52 on the PCB 20 result
in eddy currents being induced in the traces. The proposed
embodiment of FIG. 10 reduces the sectional area of traces 52
present in the region proximate the air gap 85 and, therefore,
reduces the magnitude of the resultant eddy currents induced in the
traces 52. Reducing the magnitude of the eddy currents induced in
the traces 52 along the inner loops of the coil reduces the
localized heating in the PCB and increases the efficiency of the
magnetic component 10. As another aspect of the invention, the
inner trace 54 may be spaced apart from the central portion 81 of
the E-shaped member 84 by an inner spacing 68 to eliminate any
traces 52 from the region of the magnetic component 10 in which the
greatest concentration of leakage fluxes is present.
[0047] With reference next to FIG. 11, a second embodiment of the
magnetic component 10 varies the position of traces 52 in the PCB
20. Once again, for ease of illustration, the PCB 20 is not shown.
FIG. 11 includes only sectional views of the E-shaped member 84 and
I-shaped member 82 of the core 80 as well as sectional views of
traces 52 on the PCB 20. However, traces 52 illustrated in the same
row in FIG. 11 are on a single layer of the PCB 20. Each of the
traces 52 has a uniform width and an axis 70 defined extending
vertically through a midpoint of the trace 52. The traces 52 on the
lowest layer have a first axis 70A, and the traces 52 on each
subsequent layer extending upward through the PCB have a
corresponding axis (70B-70K) defined. The axes are illustrated only
in the column of inner traces 54, however, it is understood that
each column of traces has a unique set of axes. The second axis
70B, defined in the trace 52 immediately above the trace having the
first axis 70A, is offset from the first axis 70A in a direction
further away from the central portion 81 of the E-shaped member 84.
The third axis 70C, defined in the trace 52 immediately above the
trace having the second axis 70B, is again offset from the second
axis 70B an additional distance away from the central portion 81 of
the E-shaped member 84. As may be seen in FIG. 11, each subsequent
trace 52 transitioning from the lowest layer to the highest layer
is offset from the trace in the adjacent layer such that the inner
trace 54 on the highest layer is spaced the furthest distance from
the central portion 81 of the E-shaped member 84 compared to each
of the other inner traces 54. With reference again to FIG. 6, the
arrangement of traces 52 shown in FIG. 11 shifts the traces nearest
the air gap 85 away from the air gap, thereby reducing the amount
of fringing flux 93 interacting with the traces 52 and reducing the
magnitude of the resultant eddy currents induced in the traces 52.
Reducing the magnitude of the eddy currents induced in the traces
52 reduces the localized heating in the PCB and increases the
efficiency of the magnetic component 10.
[0048] Turning then to FIG. 12, a third embodiment of the magnetic
component 10 varies both the width and the position of traces 52 in
the PCB 20. Once again, for ease of illustration, the PCB 20 is not
shown. FIG. 12 includes only sectional views of the E-shaped member
84 and I-shaped member 82 of the core 80 as well as sectional views
of traces 52 on the PCB 20. However, traces 52 illustrated in the
same row in FIG. 12 are on a single layer of the PCB 20. Each
column of traces 52 includes a gradual offset of the axes between
traces 52 in adjacent layers such that the trace 52 in the upper
most layer of each column is offset away from the central portion
81 of the E-shaped member 84 further than the trace 52 in the
lowest layer of the respective column in a manner similar to that
discussed above with respect to FIG. 11. Additionally, the widths
of the traces 52 are varied to reduce the cross-sectional area of
traces present near the air gap 85. The widths of traces 52 in a
column nearest the central portion 81 of the E-shaped member 84'
are narrowest with incremental increases in the width of traces in
adjacent columns moving away from the central portion 81 of the
E-shaped member 84. In addition, the widths of traces 52 are
further varied within individual columns. A trace 52 at the lowest
layer has a width greater than the trace 52 at the next layer of
the PCB 20 above the lowest trace. As traces 52 are laid out in
each layer 30, the trace 52 on a layer adjacent to and immediately
above another layer has a width that is less than the trace 52 on
the layer below. As a result, the width of the traces 52 become
incrementally narrower in sequence moving from the lowest layer to
the uppermost layer. The combination of varying the width and the
position of the traces 52 reduces the cross-sectional area of
traces 52 in regions of higher fringing and leakage fluxes 93, 95
thereby reducing the localized heating in the PCB resulting from
eddy currents induced in traces in those regions and increasing the
efficiency of the magnetic component 10.
[0049] The various embodiments of the invention have thus far been
discussed with respect to a single air gap 85 located in the center
of the core 80. It is further contemplated that the invention may
be incorporated into a core 80' with a distributed air gap as shown
in FIG. 13. The distributed air gap includes a first air gap 85
between the central portion 81' of the E-shaped member 84' and the
I-shaped member 82' and side air gaps 87 that are located between
the side members 83' of the E-shaped member 84' and the I-shaped
member 82'. With an air gap 85, 87 located on either side of the
coil, the fringing flux 93 and leakage flux 95 effects previously
discussed with respect to FIGS. 6 and 7 occur on either side of the
coil. Consequently, it would be desirable to vary the position
and/or width of the traces 52 on either side of the coil.
[0050] Turning next to FIG. 14, an exemplary embodiment of the
magnetic component 10 varies both the width and the position of the
traces 52 on both sides of the coil in the PCB 20. In accordance
with prior illustrations, FIG. 14 includes only sectional views of
the E-shaped member 84' and I-shaped member 82' of the core 80'
with a distributed air gap as well as sectional views of traces 52
on the PCB 20. However, traces 52 illustrated in the same row in
FIG. 14 are on a single layer of the PCB 20. Each column of traces
52 includes a gradual offset of the axes between traces 52 in
adjacent layers such that the trace 52 in the upper most layer of
each column is offset toward the center of the coil 50 further than
the trace 52 in the lowest layer of the respective column in a
manner similar to that discussed above with respect to FIG. 11.
However, in addition to offsetting the columns away from the
central portion 81' of the E-shaped member 84' the columns closer
to the outer periphery of the coil 50 are offset from the side
members 83' of the E-shaped member 84' toward the center of the
coil. Additionally, the widths of traces 52 are varied to reduce
the cross-sectional area of traces present near either air gap 85,
87. The widths of traces 52 in a column nearest the central portion
81' or the side member 83' of the E-shaped member 84' are narrowest
with incremental increases in the width of traces in adjacent
columns moving toward the center of the coil 50. In addition, the
widths of traces 52 are further varied within individual columns. A
trace 52 at the lowest layer has a width greater than the trace 52
at the next layer of the PCB 20 above the lowest trace. As traces
52 are laid out in each layer 30, the trace 52 on a layer adjacent
to and immediately above another layer has a width that is less
than the trace 52 on the layer below. As a result, the width of the
traces 52 become incrementally narrower in sequence moving from the
lowest layer to the uppermost layer. The combination of varying the
width and the position of the traces 52 reduces the cross-sectional
area of traces 52 in regions of higher fringing and leakage fluxes
93, 95 thereby reducing the localized heating resulting from eddy
currents induced in traces in those regions and increasing the
efficiency of the magnetic component 10.
[0051] Turning next to FIG. 15, still another embodiment of the
invention may include a shield 60 located between the I-shaped
member 82' and the rest of the coil 50. One layer of the PCB 20 at
or near the top layer, may include a trace defining the shield 60.
It is contemplated that the shield may be a planar conductive
surface extending over a majority of the layer. Optionally, a trace
may be routed in a coil, in a back-and-forth pattern, or any
combination thereof to provide a conductive layer overlaying a
majority of the coil 50. Unlike the different layers within the
coil, which may be joined together by vias to form a single, or
multiple, conductive coils, the shield layer 60 is electrically
isolated from, or not connected to, the other traces 52 in the coil
50. The fringing flux 93 and the slot window leakage flux 95 enter
the shield 60 layer and induce eddy currents in this layer. By
causing the leakage fluxes to enter the shield layer 60, the
localized heating and undesirable eddy currents are primarily
contained within the shield layer 60. Because the shield 60 is
located near the upper surface of the PCB 20, removal and
management of heat induced within the shield 60 is improved than if
the heat is induced in traces 52 more centrally located within the
PCB.
[0052] The embodiments discussed previously have focused on layout
of traces 52 on the PCB 20 in regions covered by the core 80. As
discussed above, with respect to FIGS. 8 and 9, end turn regions 51
or coreless PCBs exhibit leakage flux 97 in a somewhat different
pattern. Because there is no influence of the core material, the
flux 97 established around the coil 50 in open air radiates further
and in a more symmetrical pattern around the coil. Because the coil
illustrated in FIG. 9 has traces 52 arranged in a generally
rectangular shape, having a greater width than height, the end-turn
flux 97 resulting from current conducted in the traces is generally
radiated around the coil in an oval shape where the oval is more
elongated with respect to the width than the height. A greater
concentration of flux 97 is present along the inner trace 54 due to
an increased MMF as well as the proximity of the other half of the
coil positioned on the other side of the opening 24. Nevertheless,
the flux 97 generated is generally symmetric about a horizontal
axis extending through the middle of the layers on which traces are
present. As a result, the traces 52 may be arranged on the PCB 20
to reduce coupling with the end-turn flux 97.
[0053] With reference then to FIGS. 16 and 17, two exemplary
patterns of traces 52 for the PCB 20 are illustrated. A plane of
symmetry 55 extends horizontally through the PCB 20 such that an
equal number of layers with traces 52 are included above and below
the plane of symmetry 55. The traces 52 on FIGS. 16 and 17
extending upward from the plane of symmetry 55 are configured in a
manner similar to that discussed above with respect to FIG. 14 or
15, respectively. Both the width and the position of the traces 52
are varied in both FIGS. 16 and 17 to reduce the presence of traces
52 within regions of higher concentration of end-turn flux 97 and a
shield 60A is included in FIG. 17 to absorb the end-turn flux 97
and induce eddy currents within the shield 60a. The traces 52 on
FIGS. 16 and 17 that extend downward from the plane of symmetry 55
are a mirror image of the traces extending upward. Thus, the traces
in both the upper and lower halves of the PCB 20 are arranged to
reduce the cross-sectional area of traces 52 in regions of higher
end-turn flux 97 and to reduce the localized heating resulting from
eddy currents induced in traces in those regions.
[0054] According to still another aspect of the invention, it is
contemplated that the traces 52 located on the PCB 20 in the
end-turns 51, or otherwise in regions not located under or between
core material, may have a first sectional profile and the traces 52
located on the PCB 20 in regions located under or between core
material may have a second section profile such that the sectional
area of the traces 52 in each region are optimized for the
different flux distributions experienced in each region. A
transitional region located between the two sectional profiles may
establish an electrical connection between traces in each region,
ensuring a continuous coil 50 is defined on the PCB 20.
[0055] It should be understood that the invention is not limited in
its application to the details of construction and arrangements of
the components set forth herein. The invention is capable of other
embodiments and of being practiced or carried out in various ways.
Variations and modifications of the foregoing are within the scope
of the present invention. It also being understood that the
invention disclosed and defined herein extends to all alternative
combinations of two or more of the individual features mentioned or
evident from the text and/or drawings. All of these different
combinations constitute various alternative aspects of the present
invention. The embodiments described herein explain the best modes
known for practicing the invention and will enable others skilled
in the art to utilize the invention.
* * * * *