U.S. patent application number 13/795594 was filed with the patent office on 2014-09-18 for system and method for temperature estimation in an integrated motor drive.
This patent application is currently assigned to Rockwell Automation Technologies, Inc.. The applicant listed for this patent is ROCKWELL AUTOMATION TECHNOLOGIES, INC.. Invention is credited to David M. Brod, Mark Cooper, Rongjun Huang, Zoran Vrankovic.
Application Number | 20140265741 13/795594 |
Document ID | / |
Family ID | 51455200 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140265741 |
Kind Code |
A1 |
Vrankovic; Zoran ; et
al. |
September 18, 2014 |
System and Method for Temperature Estimation in an Integrated Motor
Drive
Abstract
A system to monitor the temperature of power electronic devices
in a motor drive includes a base plate defining a planar surface on
which the electronic devices and/or circuit boards within the motor
drive may be mounted. The power electronic devices are mounted to
the base plate through the direct bond copper (DBC). A circuit
board is mounted to the base plate which includes a temperature
sensor mounted on the circuit board proximate to the power
electronic devices. The temperature sensor generates a digital
signal corresponding to the temperature measured by the sensor. A
copper pad is included between each layer of the circuit board and
between the first layer of the circuit board and the sensor. The
circuit board also includes vias extending through each layer of
the board. The copper pads and vias establish a thermally
conductive path between the temperature sensor and the base
plate.
Inventors: |
Vrankovic; Zoran;
(Greenfield, WI) ; Huang; Rongjun; (Fox Point,
WI) ; Cooper; Mark; (Eden Prairie, MN) ; Brod;
David M.; (Bloomington, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ROCKWELL AUTOMATION TECHNOLOGIES, INC. |
Mayfield |
OH |
US |
|
|
Assignee: |
Rockwell Automation Technologies,
Inc.
Mayfield
OH
|
Family ID: |
51455200 |
Appl. No.: |
13/795594 |
Filed: |
March 12, 2013 |
Current U.S.
Class: |
310/68C ;
318/490 |
Current CPC
Class: |
H02K 11/33 20160101;
H02K 11/0094 20130101; H02K 11/25 20160101 |
Class at
Publication: |
310/68.C ;
318/490 |
International
Class: |
H02K 11/00 20060101
H02K011/00 |
Claims
1. A temperature detection system for estimating a junction
temperature of power electronic devices in a motor drive, the
system comprising: a base plate; a plurality of power electronic
devices, each power electronic device mounted to the base plate and
mounted proximate to each other within the integrated motor drive;
a sensor generating a digital signal corresponding to a measured
temperature within the integrated motor drive; a circuit board
having a front surface and a rear surface, wherein the rear surface
is mounted to the base plate and the front surface is configured to
receive the sensor and wherein the sensor is located on the circuit
board proximate to the power electronic devices; and a copper pad
on the front surface of the circuit board defining a thermally
conductive path between the circuit board and the sensor.
2. The temperature detection system of claim 1 wherein the circuit
board includes a plurality of layers and a plurality of copper pads
between each of the layers and aligned with the copper pad on the
front surface.
3. The temperature detection system of claim 1 wherein the circuit
board includes a plurality of layers and a plurality of vias
extending through at least a portion of the layers between the base
plate and the sensor.
4. The temperature detection system of claim 3 wherein the circuit
board further includes a plurality of additional copper pads
between each of the layers and aligned with the copper pad on the
front surface.
5. The temperature detection system of claim 4 wherein, the copper
pad, each of the additional copper pads, and each of the vias
between the sensor and the base plate are isolated from
electrically conductive traces on the circuit board.
6. The temperature detection system of claim 1 further comprising:
a memory device configured to store a series of instructions and at
least one thermal model; and a processor configured to receive the
digital signal from the sensor and configured to execute the series
of instructions to determine a temperature as a function of the
thermal model and of the digital signal.
7. The temperature detection system of claim 6 wherein the thermal
model is a function of at least one of an average power loss in the
power electronic devices during operation and a frequency of a
voltage output to a motor connected to the integrated motor
drive.
8. The temperature detection system of claim 1 wherein the sensor
is located less than 1.5 cm from the power electronic devices.
9. A power converter for controlling operation of a motor, the
power converter configured to be mounted to the motor, the power
converter comprising: a housing configured to be mounted to a
surface of the motor; an input connection mounted in the housing
and configured to receive an input voltage; at least one output
configured to be electrically connected to the motor, each output
extending between an opening in the housing and an opening in the
surface of the motor to which the housing is mounted; a DC bus
electrically connected between the input connection and an inverter
section, wherein the inverter section includes at least one power
switching device, each power switching device configured to
selectively connect the DC bus to one of the outputs; a base plate
at least partially enclosed within the housing, wherein each of the
power switching devices is mounted to the base plate; a circuit
board mounted to the base plate; a sensor generating a digital
signal corresponding to a measured temperature, wherein the sensor
is mounted to the circuit board proximate to one of the power
switching devices; and a processor configured to receive the
digital signal from the sensor.
10. The power converter of claim 9 further comprising a first
copper pad on the circuit board defining a thermally conductive
path between the circuit board and the sensor.
11. The power converter of claim 10 wherein the circuit board
includes a plurality of layers and a plurality of additional copper
pads, each additional copper pad mounted on one of the layers and
aligned with the first copper pad.
12. The power converter of claim 9 wherein the circuit board
includes a plurality of layers and a plurality of vias extending
through at least a portion of the layers between the base plate and
the sensor.
13. The power converter of claim 12 wherein the circuit board
further includes a plurality of additional copper pads, each
additional copper pad mounted on one of the layers and aligned with
each of the other additional copper pads between the sensor and the
base plate.
14. The power converter of claim 9 further comprising a memory
device configured to store a series of instructions and at least
one thermal model and wherein the processor is further configured
to execute the series of instructions to determine a temperature as
a function of the thermal model and of the digital signal.
15. The power converter of claim 14 wherein the thermal model is a
function of at least one of an average power loss in the power
switching devices during operation and a speed of rotation of the
motor connected to the integrated motor drive.
16. The power converter of claim 9 wherein the sensor is located
less than 1.5 cm from the power switching devices.
17. A method of determining a junction temperature of a power
electronic device in an integrated motor drive, wherein the power
electronic device is mounted to a base plate within the integrated
motor drive, the method comprising the steps of: mounting a circuit
board on the base plate, wherein at least a portion of the circuit
board is proximate to the power electronic device; mounting a
sensor on the portion of the circuit board proximate to the power
electronic device, wherein the circuit board includes a thermally
conductive pad between the sensor and a front surface of a first
layer of the circuit board; generating a digital signal from the
sensor corresponding to a temperature measured by the sensor;
receiving the digital signal with a processor; obtaining a thermal
model of heat transfer between the power electronic device and the
sensor from a memory device in communication with the processor;
and determining the junction temperature of the power electronic
device by the processor as a function of the thermal model and of
the digital signal from the sensor.
18. The method of claim 17 further comprising the step of
determining an average power loss of the power electronic device
during operation of the integrated motor drive, wherein the
junction temperature is determined as a function of the thermal
model, the digital signal, and the average power loss.
19. The method of claim 17 further comprising the step of
determining a frequency of a voltage output to a motor connected to
the integrated motor drive, wherein the junction temperature is
determined as a function of the thermal model, the digital signal,
and the frequency of the voltage output to the motor.
20. The method of claim 17 further comprising the steps of:
determining an average power loss of the power electronic device
during operation of the integrated motor drive; and determining a
frequency of a voltage output to a motor connected to the
integrated motor drive, wherein the junction temperature is
determined as a function of the thermal model, the digital signal,
the average power loss, and the frequency of the voltage output to
the motor.
Description
BACKGROUND OF THE INVENTION
[0001] The subject matter disclosed herein relates generally to
temperature estimation in a motor drive and, more specifically, to
an improved system for monitoring the temperature of power
electronic devices in an integrated motor drive.
[0002] As is known to those skilled in the art, motor drives are
utilized to control operation of a motor. The motor drive is
configured to control the magnitude and frequency of the output
voltage provided to the motor to achieve, for example, a desired
operating speed or torque. 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), thyristors, or silicon controlled rectifiers (SCRs). The
power electronic switching device 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 switching device to
generate a desired DC voltage on the DC bus or a desired motor
voltage.
[0003] It is also known that each of the power electronic devices
has certain inherent power losses, such as conduction losses and
switching losses. Thus, as each of the power electronic devices
conducts current or as it is turned on and off, power is dissipated
as heat within the device. In order to prevent device failure, it
is desirable to monitor the junction temperature of the power
electronic devices.
[0004] Historically, motor drives have been mounted in control
cabinets at a location separated from the motor which it is
controlling. The motor drives typically utilize power modules which
contain the power electronic devices. A power module may include,
for example, six IGBTs and their respective free-wheeling diodes
(FWDs). The IGBTs and FWDs are enclosed within a plastic housing
and terminals are provided to establish an electrical connection
between each power electronic device and the DC bus and/or the
motor. Also enclosed within each module may be a thermistor to
monitor the temperature of module.
[0005] However, developments in the power electronic devices used
to control the motor have reduced the size of the components. This
reduction in size of the power electronic devices along with a
desire to reduce the size of the control enclosures have led to
placing at least a portion of the motor controller electronics on
the motor itself as an integrated motor drive. Specifically, the
inverter section, which converts the DC voltage on the DC bus to
the AC voltage supplied to the motor, is mounted on the motor.
Because the motors are typically located on a machine or within an
industrial process line, it is desirable to use an enclosure for
the integrated motor drive which has a footprint equal to or less
than the area of the surface on the motor to which it is mounted
and which has a low profile, and conventional power modules may not
fit within the desired enclosure.
[0006] As a result, motor controllers have been developed in which
individual power electronic devices are mounted within the housing
to form an inverter section. The individual power electronic
devices may be mounted in a smaller area than traditional power
modules. However, by eliminating the traditional power module, the
thermistor is no longer present. Providing a separate thermistor
within the integrated motor drive has its drawbacks. The thermistor
generates an analog signal that is susceptible to interference from
modulation of the power electronic devices. Further, the analog
signal requires conversion of the signal to a digital signal prior
to being input to a controller and isolation of the signal from the
controller. Finally, the signal generated is non-linear and
requires calibration and compensation within the controller.
[0007] Thus, it would be desirable to provide an improved system
and method for monitoring the temperature of power electronic
devices in an integrated motor drive.
BRIEF DESCRIPTION OF THE INVENTION
[0008] The subject matter disclosed herein describes a system to
monitor the temperature of power electronic devices in a motor
drive and, more specifically, the junction temperature of power
electronic devices utilized in an integrated motor drive. The motor
drive includes a base plate, typically a copper base plate,
defining a planar surface on which the electronic devices and/or
circuit boards within the motor drive may be mounted. The power
electronic devices are mounted to the base plate through the direct
bond copper (DBC). A circuit board is mounted proximate to the
power electronic devices and includes solder pads configured to
establish electrical connections between the power electronic
devices and the control and power circuits in the integrated motor
drive. These electrical connections conduct, for example, the
switching signals to control operation of the power electronic
devices as well as the DC voltage from the DC bus through the power
electronic device to the motor. A temperature sensor is mounted on
the circuit board proximate to these solder pads and, therefore,
proximate to the power electronic devices. The temperature sensor
generates a digital signal corresponding to the temperature
measured by the sensor. The circuit board may be single layer, but
is more commonly a multi-layer board. A copper pad is included
between each layer of the circuit board and between the first layer
of the circuit board and the sensor. The circuit board also
includes multiple vias extending through each layer of the board
between temperature sensor and the base plate. Each via includes a
thermally conductive material such as copper lining its inner
periphery. Optionally, each via may be filled with a thermally
conductive material, such as solder. The copper pads and vias
establish a thermally conductive path between the temperature
sensor and the base plate having known or controlled thermal
characteristics.
[0009] According to one embodiment of the invention, a temperature
detection system for estimating a junction temperature of power
electronic devices in a motor drive includes a base plate, a
plurality of power electronic devices, and a sensor. Each power
electronic device is mounted to the base plate and mounted
proximate to each other within the integrated motor drive, and the
sensor generates a digital signal corresponding to a measured
temperature within the integrated motor drive. The temperature
detection system also includes a circuit board, having a front
surface and a rear surface, where the rear surface is mounted to
the base plate, the front surface is configured to receive the
sensor, and the sensor is located on the circuit board proximate to
the power electronic devices. A copper pad is mounted on the front
surface of the circuit board defining a thermally conductive path
between the circuit board and the sensor.
[0010] According to another embodiment of the invention, a power
converter for controlling operation of a motor and configured to be
mounted to the motor includes a housing configured to be mounted to
a surface of the motor. The power converter includes an input
connection and at least one output connection. The input connection
is mounted in the housing and configured to receive a DC voltage
greater than 50 volts, and at least one output is configured to be
electrically connected to the motor. Each output extends between an
opening in the housing and an opening in the surface of the motor
to which the housing is mounted. A DC bus is electrically connected
between the input connection and an inverter section. The inverter
section includes at least one power switching device, configured to
selectively connect the DC bus to one of the outputs. The power
converter further includes a base plate at least partially enclosed
within the housing and a circuit board mounted to the base plate.
Each of the power switching devices is mounted to the base plate. A
sensor generates a digital signal corresponding to a measured
temperature, where the sensor is mounted to the circuit board
proximate to one of the power switching devices, and a processor is
mounted on the circuit board and configured to receive the digital
signal from the sensor.
[0011] According to yet another embodiment of the invention, a
method of determining a junction temperature of a power electronic
device in an integrated motor drive is disclosed. The power
electronic device is mounted to a base plate within the integrated
motor drive. The method includes the steps of mounting a circuit
board on the base plate and mounting a sensor on the portion of the
circuit board proximate to the power electronic device. At least a
portion of the circuit board is proximate to the power electronic
device, and the circuit board includes a thermally conductive pad
between the sensor and a top surface of a first layer of the
circuit board. A digital signal is generated from the sensor,
corresponding to a temperature measured by the sensor. The digital
signal is received by a processor, and the processor uses a thermal
model of heat transfer between the power electronic device and the
sensor to determine an estimate of the junction temperature of the
power electronic device as a function of the thermal model and of
the digital signal from the sensor.
[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 an exemplary motor control system illustrating a
pair of integrated motor drives incorporating the present
invention;
[0015] FIG. 2 is a schematic representation of the motor control
system of FIG. 1;
[0016] FIG. 3 is a schematic representation of an inverter section
of FIG. 2.
[0017] FIG. 4 is a block diagram representation of a portion of one
of the integrated motor drives of FIG. 1; and
[0018] FIG. 5 is a partial cross-sectional view of one of the
integrated motor drives of FIG. 1.
[0019] 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 OF THE PREFERRED EMBODIMENTS
[0020] Turning initially to FIG. 1, an exemplary embodiment of a
distributed motor control system 10 includes a power interface
module 12, a pair of motors 14, and a pair of integrated motor
drives 30. Each integrated motor drive 30 includes a housing 32
configured to mount the integrated motor drive 30 to one of the
motors 14. It is contemplated that the distributed control system
10 may include various other numbers of motors 14 and integrated
motor drives 30. A first communication cable 16 is connected
between the power interface module 12 and a first communication
connector 17 on the first integrated motor drive 30. A second
communication cable 18 connects a second communication connector 19
from the first integrated motor drive 30 to the first communication
connector 17 on the second integrated motor drive 30. Similarly,
additional second communication cables 18 may be provided to
connect additional integrated motor drives 30, if provided, in the
distributed motor control system 10. A communications terminating
connector 20 is provided on the second communication connector 19
of the final integrated motor drive 30 in the distributed motor
control system 10. A first power cable 22 is connected between the
power interface module 12 and a first power connector 23 on the
first integrated motor drive 30. A second power cable 24 connects a
second power connector 25 from the first integrated motor drive 30
to the first power connector 23 on the second integrated motor
drive 30. Similarly, additional second power cables 24 may be
provided to connect additional integrated motor drives 30, if
provided, in the distributed motor control system 10. A power
terminating connector 26 is provided on the second power connector
25 of the final integrated motor drive 30 in the distributed motor
control system 10. According to various embodiments of the
invention, it is contemplated that the first and second
communication connectors, 17 and 19 respectively, may be identical
connectors, the first and second communications cables, 16 and 18
respectively, may be identical cables of the same or of varying
length, the first and second power connectors, 23 and 25
respectively, may be identical connectors, and the first and second
power cables, 22 and 24 respectively, may be identical cables of
the same or of varying length.
[0021] Referring next to FIG. 2, the power interface module 12
includes a rectifier section 40, connected in series between the
input voltage 13 and a DC bus 42, and a DC bus capacitor 48
connected across the DC bus 42. It is understood that the DC bus
capacitor 48 may be a single capacitor or multiple capacitors
connected in parallel, in series, or a combination thereof. The
rectifier section 40 may be either passive or active, where a
passive rectifier utilizes electronic devices such as diodes, which
require no control signals, and an active rectifier utilizes
electronic devices, including but not limited to transistors,
thyristors, and silicon controlled rectifiers, which receive
switching signals to turn on and off. The power interface module 12
also includes a processor 50 and a memory device 52. It is
contemplated that the processor 50 and memory device 52 may each be
a single electronic device or formed from multiple devices.
Optionally, the processor 50 and/or the memory device 52 may be
integrated on a field programmable array (FPGA) or an application
specific integrated circuit (ASIC). The processor 50 may send
and/or receive signals to the rectifier section 40 as required by
the application requirements. The processor 50 is also configured
to communicate with external devices via an industrial network 15,
including but not limited to, DeviceNet, ControlNet, or Ethernet/IP
and its respective protocol. The processor 50 further communicates
with other devices within the motor control system 10 via any
suitable communications medium, such as a backplane connection or
an industrial network, which may further include appropriate
network cabling and routing devices.
[0022] The DC bus 42 includes a first voltage rail 44 and a second
voltage rail 46. Each of the voltage rails, 44 or 46, are
configured to conduct a DC voltage having a desired potential,
according to application requirements. According to one embodiment
of the invention, the first voltage rail 44 may have a DC voltage
at a positive potential and the second voltage rail 46 may have a
DC voltage at ground potential. Optionally, the first voltage rail
44 may have a DC voltage at ground potential and the second voltage
rail 46 may have a DC voltage at a negative potential. According to
still another embodiment of the invention, the first voltage rail
44 may have a first DC voltage at a positive potential with respect
to the ground potential and the second voltage rail 46 may have a
second DC voltage at a negative potential with respect to the
ground potential. The resulting DC voltage potential between the
two voltage rails, 44 and 46, is the difference between the
potential present on the first voltage rail 44 and the second
voltage rail 46.
[0023] According to one embodiment of the invention, the DC bus 42
of the power interface module 12 is connected in series with the DC
bus 42 of each of integrated motor drives 30. Electrical
connections are established between the respective DC buses 42 via
the power cable 22, 24 to transfer the DC bus voltage between
devices. Each integrated motor drive 30 further includes a
processor 54 and a memory device 56. It is contemplated that the
processor 54 and memory device 56 may each be a single electronic
device or formed from multiple devices. Optionally, the processor
54 and/or the memory device 56 may be integrated on a field
programmable array (FPGA) or an application specific integrated
circuit (ASIC).
[0024] The DC voltage on the DC bus 42 is converted to an AC
voltage by an inverter section, 60. According to one embodiment of
the invention, each inverter section 60 converts the DC voltage to
a three-phase output voltage available at an output 66 connected to
the respective motor 14. The inverter section 60 includes multiple
switches 61 which selectively connect one of the output phases to
either the first voltage rail 44 or the second voltage rail 46.
Referring also to FIG. 3, each switch 61 may include a transistor
62 and a diode 64 connected in parallel to the transistor 62. Each
transistor 62 receives a switching signal 68 to enable or disable
conduction through the transistor 62 to selectively connect each
phase of the output 66 to either the first voltage rail 44 or the
second voltage rail 46 of the DC bus 42.
[0025] Referring next to FIG. 4, each integrated motor drive 30
includes a base plate 80 mounted within the housing 32. The base
plate 80 is constructed of a thermally conductive material such as
a metal. According to one embodiment of the invention, the base
plate 80 is made from copper. As illustrated, a circuit board 70 is
mounted over the base plate 80 and has an outer periphery 73 that
is equal to or greater than the outer periphery of the base plate
80. Optionally, the outer periphery of the base plate 80 may be
greater than the outer periphery 73 of the circuit board 70. It is
contemplated that the circuit board 70 may be a single circuit
board or multiple circuit boards mounted to and covering various
portions of the base plate 80. Optionally, the circuit board 70 may
further include multiple boards, mounted one over the other or in
various other configurations without deviating from the scope of
the invention. The base plate 80 is exposed through an opening 72
in the circuit board 70. Each of the power electronic devices
(e.g., the IGBT 62 and the FWD 64) are mounted to the base plate
80, also referred to as direct bonded copper (DBC) devices. A
temperature sensor 58 is mounted to the circuit board 70 proximate
to the opening 72 and, therefore, proximate to the power electronic
devices 62, 64. According to one embodiment of the invention, the
temperature sensor 58 is located within 5.0 cm, preferably within
1.5 cm, and more preferably about 0.6 cm from the power electronic
devices. The temperature sensor 58 generates a digital signal 55
corresponding to the measured temperature which may be provided to
the processor 54. The processor 54, executing a program stored in
the memory device 56, may be configured to monitor the digital
signal 55 from the temperature sensor 58 and generate alerts and/or
shut down operation of the integrated motor drive 30 as a function
of the measured temperature.
[0026] Referring next to FIG. 5, each of the power electronic
devices includes a bare die power electronic device 82, such as an
IGBT or FWD, mounted to a first copper layer 86 via solder 84. A
ceramic layer 90 separates the first copper layer 86 from a second
copper layer 88, and the second copper layer 88 is, in turn,
mounted to the base plate 80 via solder 92. The first copper layer
86 may be etched to form conductive paths, or traces, between
multiple power electronic devices 82 mounted to the first copper
layer 86. The ceramic layer 90 provides an electrically insulating
layer between the first and second copper layers, 86 and 88
respectively. The second copper layer 88 may be, for example, a
ground plane.
[0027] According to the illustrated embodiment, the circuit board
70 is a multi-layer board and, more specifically, includes four
layers 74. Optionally, the circuit board 70 may include six, or any
other suitable number of layers 74 according to the application
requirements. The circuit board 70 is secured to the copper base
plate by glue or by any other suitable fastener, for example, via
mounting screws. A layer of glue and dielectric grease 71 may be
included between the circuit board 70 and the base plate 80 to
secure the circuit board 70 and to provide a thermally conductive
layer between the circuit board 70 and the base plate 80. The
temperature sensor 58 includes a body 53 from which leads 57
extend. The leads 57 are secured to the first layer 74 of the
circuit board 70 by solder joints 59 according to methods
understood in the art. A first copper pad 78 is located on the
first layer 74 of the circuit board 70 between the front side of
the first layer 74 and the rear side of the temperature sensor 58.
Additional copper pads 76 are located between each of the layers 74
of the circuit board 70 positioned between the temperature sensor
58 and the base plate 80. Multiple vias 77 are also located between
the temperature sensor 58 and the base plate 80. The vias 77 extend
through one or more layers 74 of the circuit board 70 and,
preferably, extend through each layer 74 of the circuit board 70
except the layer 74 secured to the base plate 80. The first copper
pad 78, additional copper pads 76, and vias 77 are, preferably,
electrically isolated from circuit components mounted on the
circuit board 70.
[0028] In operation, the power interface module 12 receives an AC
input voltage 13 and converts it to a DC voltage with the rectifier
section 40. The AC input voltage 13 may be either a three phase or
a single phase AC voltage. If the rectifier section 40 is an active
rectifier, the processor 50 will receive signals from the active
rectifier corresponding to, for example, amplitudes of the voltage
and current on the AC input and/or the DC output. The processor 50
then executes a program stored in memory 52 to generate switching
signals to activate and/or deactivate the switches in the active
rectifier, where the program includes a series of instructions
executable on the processor 50. In addition, the switching signals
may be generated such that power may be transferred in either
direction between the AC input and the DC output. Whether there is
a passive rectifier or an active rectifier, the DC bus capacitor 48
connected across the DC bus 42 reduces the ripple resulting from
the voltage conversion. The DC voltage is then provided via the DC
bus 42 between the power interface module 12 and subsequent
integrated motor drives 30. The level of DC voltage transferred via
the DC bus 42 is typically greater than 50 volts and may be, for
example, at least 325 VDC if the AC input voltage 13 is 230 VAC or
at least 650 VDC if the AC input voltage 13 is 460 VAC.
[0029] The processor 50 of the power interface module 12 may
further be configured to communicate with other external devices
via the industrial network 15. The processor 50 may receive command
signals from a user interface or from a control program executing,
for example, on an industrial controller. The command signals may
include, but are not limited to, speed, torque, or position
commands used to control the rotation of each motor 14 in the
distributed motor control system 10. The processor 50 may either
pass the commands directly or execute a stored program to interpret
the commands and subsequently transmit the commands to each
integrated motor drives 30. The processor 50 communicates with the
processors 54 of the integrated motor drives 30 either directly or
via a daisy chain topology and suitable network cables 16, 18.
Further, the processor 50 may either communicate using the same
network protocol with which it received the commands via the
industrial network 15 or convert the commands to a second protocol
for transmission to the integrated motor drives 30.
[0030] Each integrated motor drive 30 converts the DC voltage from
the DC bus 42 to an AC voltage suitable to control operation of the
motor 14 on which it is mounted. The processor 54 executes a
program stored on a memory device 56. The processor 54 receives a
reference signal via the communications medium 16 or 18 identifying
the desired operation of the motor 14. The program includes a
control module configured to control the motor 14 responsive to the
reference signal and responsive to feedback signals such as voltage
sensors, current sensors, and/or the angular position sensors
mounted to the motor 14. The control module generates a desired
voltage reference signal and provides the desired voltage reference
signal to a switching module. The switching module uses, for
example, pulse width modulation (PWM) to generate the switching
signals 68 to control the switches 61 responsive to the desired
voltage reference signal.
[0031] In order to protect the switches 61 in the inverter section
60, the processor 54 monitors the temperature signal 55 generated
by the temperature sensor 58. The processor 54 then determines an
estimate of the temperature of the switches as a function of the
temperature signal 55 and of a thermal model of the heat transfer
path between the temperature sensor 58 and the switches 61. It is
contemplated that a single thermal model may be determined to
generate a single temperature estimate. Optionally, separate
thermal models may be determined to generate temperature estimates
for each of the power electronic devices. According to still
another embodiment of the invention, a first thermal model may be
determined to generate an estimated junction temperature of the
IGBTs 62 and a second thermal model may be determined to generate
an estimated junction temperature of the FWDs 64.
[0032] Each thermal model includes three primary thermal
impedances. A first thermal impedance is determined for the
transfer of heat between the bare die power electronic device 82
and the base plate 80. A second thermal impedance is determined for
the transfer of heat between the base plate 80 and the temperature
sensor 58. Inclusion of the first copper pad 78, additional copper
pads 76, and vias 77 improves the thermal conductance between the
base plate 80 and the temperature sensor 58 or, conversely, reduces
the thermal impedance between the base plate 80 and the temperature
sensor 58. The third thermal impedance exists inside the base plate
80 from the location below the IGBTs 62 or the FWDs 64 and the
location below the temperature sensor 58. Because the temperature
sensor 58 is placed proximate to the IGBTs 62 and the FWDs 64 and
because the base plate 80 has a high thermal conductance, the third
thermal impedance is much less than first and the second thermal
impedance.
[0033] Each thermal model is also a function of the power
dissipated in the corresponding power electronic device. The power
electronic devices incur both switching losses and conduction
losses which are primarily dissipated within the device as heat.
The magnitude of the switching loss and conduction loss are
additionally a function of the current conducted through the
device. The processor 54 monitors at least one feedback signal
corresponding to the current output to the motor 14 and may
determine an average power loss in each of the IGBTs 62 and/or the
FWDs 64. In addition, distribution of power losses among the power
electronic devices may vary at varying frequency of output voltage
to the motor 14. According to one embodiment of the invention, the
processor 54 monitors at least one of a speed command or a speed
feedback signal to determine the speed of the motor 14 and may
further utilize the speed information in each of the first and
second thermal models. According to another embodiment of the
invention, the processor 54 may monitor a commanded frequency of
the output voltage to the motor 14 and determine the speed of the
motor. According to still another embodiment of the invention,
BF.sub.--I(f) and BF.sub.--D(f) may be determined as frequency
dependent compensation factors and the commanded output frequency
may be utilized directly by each thermal model. The processor 54
then determines the temperature of the IGBTs 62 as a function of
the first thermal model and determines the temperature of the FWDs
64 as a function of the second thermal model.
[0034] 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
* * * * *