U.S. patent application number 14/340642 was filed with the patent office on 2016-01-28 for method and apparatus for controlling an electric machine.
The applicant listed for this patent is GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Harry J. Bauer, Daniel J. Berry, George D. Dolan, Steven L. Hayslett, Paul F. Turnbull.
Application Number | 20160023573 14/340642 |
Document ID | / |
Family ID | 55065664 |
Filed Date | 2016-01-28 |
United States Patent
Application |
20160023573 |
Kind Code |
A1 |
Turnbull; Paul F. ; et
al. |
January 28, 2016 |
METHOD AND APPARATUS FOR CONTROLLING AN ELECTRIC MACHINE
Abstract
A method for operating an electric machine of a ground vehicle
includes periodically determining an aging parameter based upon a
temperature of the electric machine and periodically determining a
short-term aging effect based upon the periodically determined
aging parameter. A long-term aging effect is determined based upon
the short-term aging effect. A short-term temperature adjustment is
determined based upon the short-term aging effect and a long-term
temperature adjustment is determined based upon the long-term aging
effect. A temperature-based derated motor torque is determined
based upon the long-term temperature adjustment and the short-term
temperature adjustment. Operation of the electric machine is
controlled responsive to an operator command for torque based upon
the temperature-based derated motor torque.
Inventors: |
Turnbull; Paul F.; (Canton,
MI) ; Hayslett; Steven L.; (Troy, MI) ; Bauer;
Harry J.; (Troy, MI) ; Berry; Daniel J.;
(Macomb Township, MI) ; Dolan; George D.;
(Pontiac, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM GLOBAL TECHNOLOGY OPERATIONS LLC |
DETROIT |
MI |
US |
|
|
Family ID: |
55065664 |
Appl. No.: |
14/340642 |
Filed: |
July 25, 2014 |
Current U.S.
Class: |
701/22 |
Current CPC
Class: |
H02P 29/60 20160201;
B60L 2240/425 20130101; B60L 2240/423 20130101; Y02T 10/72
20130101; B60L 15/20 20130101; H02P 29/68 20160201; Y02T 10/64
20130101 |
International
Class: |
B60L 15/20 20060101
B60L015/20 |
Claims
1. A method for operating a high-voltage electric machine of a
ground vehicle, comprising: periodically determining an aging
parameter based upon a temperature of the electric machine;
periodically determining a short-term aging effect based upon the
periodically determined aging parameter; determining a long-term
aging effect based upon the short-term aging effect; determining a
short-term temperature adjustment based upon the short-term aging
effect; determining a long-term temperature adjustment based upon
the long-term aging effect; determining a temperature-based derated
motor torque based upon the long-term temperature adjustment and
the short-term temperature adjustment; and controlling, by a
controller, operation of the electric machine based upon the
temperature-based derated motor torque.
2. The method of claim 1, wherein periodically determining an aging
parameter based upon the temperature of the electric machine
comprises: empirically developing a temperature-aging relationship
based upon temperature-induced changes in insulative material of
insulated conductive wires of the electric machine; and
periodically determining the aging parameter based upon the
temperature of the electric machine and the empirically developed
temperature-aging relationship.
3. The method of claim 2, wherein empirically developing a
temperature-aging relationship based upon temperature-induced
changes in insulative material of insulated conductive wires of the
electric machine comprises empirically developing the
temperature-aging relationship based upon fatigue of the insulative
material induced by cyclically applied loads related to temperature
of the electric machine.
4. The method of claim 1, wherein periodically determining a
short-term aging effect based upon the periodically determined
aging parameters comprises dynamically integrating the periodically
determined aging parameters during each driving cycle.
5. The method of claim 1, wherein determining a long-term aging
effect based upon the short-term aging effect comprises
accumulating the periodically determined short-term aging effects
and, at the end of a present driving cycle, integrating the
accumulated short-term aging effects with a long-term aging effect
determined during a previous driving cycle.
6. The method of claim 1, wherein determining a short-term
temperature adjustment based upon the short-term aging effect
comprises dynamically determining a short-term adjustment in
temperature based upon a temperature-induced material stress in the
electric machine.
7. The method of claim 6, further comprising resetting the
short-term temperature adjustment to zero at the beginning of each
driving cycle.
8. The method of claim 1, wherein determining a long-term
temperature adjustment based upon the long-term aging effect
comprises determining a long-term adjustment in temperature based
upon temperature-induced material stress in the electric machine,
said long-term temperature adjustment updated once each driving
cycle.
9. The method of claim 1, wherein controlling, by a controller,
operation of the electric machine based upon the temperature-based
derated motor torque comprises dynamically controlling maximum
torque output of the electric machine, said maximum torque output
limited by the temperature-based derated motor torque.
10. A method for operating an electrically-powered torque machine
configured to generate tractive torque in a ground vehicle,
comprising: periodically determining an aging parameter based upon
a temperature of the electric machine; determining a short-term
aging effect based upon an accumulation of the periodically
determined aging parameter; determining a long-term aging effect
based upon an accumulation of the short-term aging effect;
determining a short-term temperature adjustment based upon the
short-term aging effect; determining a long-term temperature
adjustment based upon the long-term aging effect; determining a
temperature-based derated motor torque based upon the long-term
temperature adjustment and the short-term temperature adjustment;
and controlling, by a controller, operation of the electric machine
responsive to an operator command for torque limited based upon the
temperature-based derated motor torque.
11. The method of claim 10, wherein periodically determining an
aging parameter based upon a temperature of the electric machine
comprises: empirically developing a temperature-aging relationship
based upon fatigue of the insulative material induced by cyclically
applied loads related to temperature of the electric machine; and
periodically determining the aging parameter based upon the
temperature of the electric machine and the empirically developed
temperature-aging relationship.
12. The method of claim 10, wherein determining a short-term aging
effect based upon an accumulation of the periodically determined
aging parameters comprises dynamically integrating the periodically
determined aging parameters during each driving cycle.
13. The method of claim 10, wherein determining a long-term aging
effect based upon an accumulation of the short-term aging effect
comprises accumulating the short-term aging effects and, at the end
of a present driving cycle, integrating the accumulated short-term
aging effects with a long-term aging effect determined during a
previous driving cycle.
14. The method of claim 10, wherein determining a short-term
temperature adjustment based upon the short-term aging effect
comprises dynamically determining a short-term adjustment in
temperature based upon a temperature-induced material stress in the
electric machine.
15. The method of claim 14, further comprising resetting the
short-term temperature adjustment to zero at the beginning of each
driving cycle.
16. The method of claim 10, wherein determining a long-term
temperature adjustment based upon the long-term aging effect
comprises determining a long-term adjustment in temperature based
upon temperature-induced material stress in the electric machine,
said long-term temperature adjustment updated once each driving
cycle.
17. The method of claim 10, wherein controlling, by a controller,
operation of the electric machine responsive to an operator command
for torque limited based upon the temperature-based derated motor
torque comprises dynamically controlling operation of the electric
machine responsive to the operator command for torque limited based
upon a maximum torque output of the electric machine, said maximum
torque output limited by the temperature-based derated motor
torque.
Description
TECHNICAL FIELD
[0001] This disclosure relates to an electric machine, and
operational control of the electric machine related to operating
temperature.
BACKGROUND
[0002] The statements in this section merely provide background
information related to the present disclosure and may not
constitute prior art.
[0003] Powertrain systems employing electric machines for tractive
torque derate motor torque based upon a single control parameter,
e.g., motor temperature, with tractive torque effort derated as a
function of the motor temperature to avoid reduced service life of
the electric machine. In one embodiment, torque derating occurs in
a temperature range between a minimum temperature for derating,
e.g., 170.degree. C. and a maximum permissible operating
temperature, e.g., 190.degree. C. This includes permitting maximum
motor torque at motor temperatures below the minimum temperature
for derating, linearly derating the motor torque as motor
temperature increases thereabove, e.g., from 170.degree. C. to
190.degree. C. and permitting zero motor torque output, i.e.,
prohibiting motor torque output when the motor temperature reaches
the maximum permissible operating temperature.
[0004] Under one known severe driving schedule, an electric machine
can spend a majority of its operating time operating at motor
temperatures slightly less than the minimum temperature for
derating, e.g., at approximately 160.degree. C. A motor control
approach employing motor temperature as a single control parameter
permits indefinite operation of an electric machine at motor
temperatures that are slightly below the minimum temperature for
derating, affecting its service life. Furthermore, a motor control
approach employing motor temperature as a single control parameter
prohibits short-duration high temperature excursions even though
such excursions may not affect service life.
SUMMARY
[0005] A method for operating an electric machine of a ground
vehicle is described, and includes periodically determining an
aging parameter based upon a temperature of the electric machine
and periodically determining a short-term aging effect based upon
the periodically determined aging parameter. A long-term aging
effect is determined based upon the short-term aging effect. A
short-term temperature adjustment is determined based upon the
short-term aging effect and a long-term temperature adjustment is
determined based upon the long-term aging effect. A
temperature-based derated motor torque is determined based upon the
long-term temperature adjustment and the short-term temperature
adjustment. Operation of the electric machine is controlled
responsive to an operator command for torque based upon the
temperature-based derated motor torque.
[0006] The above features and advantages, and other features and
advantages, of the present teachings are readily apparent from the
following detailed description of some of the best modes and other
embodiments for carrying out the present teachings, as defined in
the appended claims, when taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] One or more embodiments will now be described, by way of
example, with reference to the accompanying drawings, in which:
[0008] FIG. 1 schematically illustrates an electrically-powered
electric machine coupled to an inverter module that is controlled
by a controller of control system, in accordance with the
disclosure;
[0009] FIG. 2 schematically shows a flowchart of a motor torque
derate routine that is iteratively executed during ongoing
operation to determine a derated motor torque for dynamically
controlling an electric machine based upon a time-integrated
temperature of the electric machine, in accordance with the
disclosure;
[0010] FIG. 3 graphically shows a plurality of aging-based derated
motor torques plotted with torque derating in the form of allowed
percentage of maximum torque in relation to temperature, in
accordance with the disclosure; and
[0011] FIG. 4 graphically shows a thermal aging curve for an
electric machine, including total service life (hours) in relation
to motor temperature (.degree. C.) in accordance with the
disclosure.
DETAILED DESCRIPTION
[0012] Referring now to the drawings, wherein the depictions are
for the purpose of illustrating certain exemplary embodiments only
and not for the purpose of limiting the same, FIG. 1 schematically
illustrates an electrically-powered torque machine (electric
machine) 35 coupled to an inverter module 32 that is controlled by
a controller 11 of a control system. When employed on a ground
vehicle, an output member of the electric machine 35 may rotatably
couple to a vehicle driveline to transmit tractive torque to a
drive wheel, either directly or through a transmission gear system
or a belt-drive assembly. The inverter module 32 and/or the
electric machine 35 may be configured with a cooling system to
transfer heat away therefrom.
[0013] The inverter module 32 includes a motor control processor
(MCP) 16, a gate drive circuit 15 and power switches 13. The power
switches 13 include IGBTs or other suitable power switch devices
that electrically connect between high and low power lines of a
high-voltage DC bus 29. In one embodiment, each power switch 13
includes input pins for monitoring electrical current flow through
the power switch 13. The gate-drive circuit 15 generates and
employs pulsewidth-modulation (PWM) to control the power switches
13 to transfer electric power from the high-voltage DC bus 29
through a multi-phase motor control power bus 31 to the electric
machine 35 for tractive torque generation in either an acceleration
mode or a regenerative braking mode. In operation, the controller
11 generates a motor torque command 102 that is communicated to the
MCP 16, which generates PWM duty cycle control commands 106 that
are communicated to the gate drive 15 in response to the motor
torque command 102. The gate-drive circuit 15 generates a plurality
of PWM control signals 110 to control the power switches 13 to
control electric power flow between the high-voltage DC bus 29 and
the multi-phase motor control power bus 31 to control operation of
the electric machine 35.
[0014] Internal parameters originating in the gate drive circuit 15
and monitored parameters 112 from the power switches 13 that are
communicated to a monitoring circuit 17 are provided as feedback
108 to the MCP 16 for control and analysis. The internal parameters
include electric current flow and others that can be employed to
determine temperature of the electric machine 35. The temperature
of the electric machine 35 can be determined by any suitable
scheme, including by way of example, direct measurement with a
thermistor or another temperature monitoring sensor or estimation
based upon the aforementioned internal parameters and monitored
parameters 112, and coolant flow in a cooling system heat exchange
configuration, if any. In one embodiment, the MCP 16 generates a
temperature signal 104 that is communicated to the controller
11.
[0015] The electric machine 35 can be any suitable multi-phase
electric motor, e.g., an induction motor or a synchronous motor
that converts electrical energy to mechanical power in the form of
torque, and includes a stator and a coaxial rotor. The stator
includes a plurality of windings fabricated from insulated
conductive wires arranged as coils that form magnetic poles when
electrically energized.
[0016] Control module, module, control, controller, control unit,
processor and similar terms mean any one or various combinations of
one or more of Application Specific Integrated Circuit(s) (ASIC),
electronic circuit(s), central processing unit(s) (preferably
microprocessor(s)) and associated memory and storage (read only,
programmable read only, random access, hard drive, etc.) executing
one or more software or firmware programs or routines,
combinational logic circuit(s), input/output circuit(s) and
devices, appropriate signal conditioning and buffer circuitry, and
other components to provide the described functionality. Software,
firmware, programs, instructions, routines, code, algorithms and
similar terms mean any controller executable instruction sets
including calibrations and look-up tables. The control module has a
set of control routines executed to provide the desired functions.
Routines are executed, such as by a central processing unit, and
are operable to monitor inputs from sensing devices and other
networked control modules, and execute control and diagnostic
routines.
[0017] FIG. 2 is a flowchart configured to describe execution of a
motor torque derate routine 200, which is preferably iteratively
executed during operation of an electric machine to determine a
derated motor torque for dynamically controlling the electric
machine based upon a time-integrated temperature of the electric
machine, e.g., the electric machine 35 described with reference to
FIG. 1. Table 1 is provided as a key wherein the numerically
labeled blocks and the corresponding functions are set forth as
follows, corresponding to the motor torque derate routine 200.
TABLE-US-00001 TABLE 1 BLOCK BLOCK CONTENTS 200 Motor torque derate
routine 202 Monitor temperature 204 Determine aging parameter
periodically 210 Determine short-term aging effect based upon
periodically determined aging parameters 212 Determine short-term
temperature adjustment based upon short-term aging effect 220
Determine long-term aging effect based upon the short-term aging
effect 222 Determine long-term temperature adjustment based upon
long-term aging effect 230 Accumulating the long-term temperature
adjustment and the short-term temperature adjustment 240 Determine
derated motor torque 250 Control electric machine based upon
derated motor torque
[0018] Execution of the motor torque derate routine 200 is
described in context of a driving cycle for an electric machine,
wherein a driving cycle is defined as a period of time starting
with a key-on command from an operator and ending with a subsequent
key-off command from the operator when the electric machine is
employed on a vehicle. Dynamic operation and conditions indicate
the ongoing, second-by-second control, operation and monitoring of
the electric machine during each driving cycle. The motor torque
derate routine 200 executes by dynamically monitoring or otherwise
determining motor temperature 201 for the electric machine during
operation (202) at a sampling rate that comprehends thermal time
constants of the various components and systems of the electric
machine. The motor temperature 201 can be determined by any
suitable method and/or device, including, e.g., by direct
measurement of temperature on the electric machine, by inference
from measurement of temperature at a related location, by
estimation based upon monitored parameters related to operation of
the electric machine, or by some combination thereof. In one
embodiment, the motor temperature 201 is determined at a sampling
rate of 1 Hz, although other sampling rates may be employed with
similar effect.
[0019] An aging parameter 209 is periodically determined based upon
the motor temperature 201 using a temperature-aging relationship
207 that has been developed for the subject electric machine (204).
The temperature-aging relationship 207 is graphically shown with
magnitude of the aging parameter on the vertical axis 205 and motor
temperature on the horizontal axis 203. The temperature-aging
relationship 207 is empirically developed and comprehends effects
of changes in the physical and chemical properties of the specific
insulative material employed for the insulated conductive wires of
the stator of the electric machine. The temperature-aging
relationship 207 accounts for the nature and duration of
electrical, mechanical, thermal and environmental stresses applied
to the insulative material that cause fatigue of the insulative
material. Fatigue is the weakening of a material caused by
repeatedly applied stresses resulting in progressive and localized
structural damage due to cyclic loading. The temperature-aging
relationship 207 can be based upon a life-temperature relationship
for the insulative material that is based upon an expectation that
functional life of the insulated conductive wires of the stator and
hence the service life of the electric machine is proportional to
the inverse reaction rate of the process due to temperature, e.g.,
an Arrhenius life-stress relationship. Measurements related to
low-cycle fatigue provide a quantifiable measure of material aging
that accrue over time as a function of cyclically applied loads
related to elevated motor temperature and can be described using
known relationship forms, e.g., a Coffin-Manson relationship.
[0020] A short-term aging effect 211 is determined by ongoingly
accumulating the periodically determined aging parameters 209
(210). Accumulating the periodically determined aging parameters
preferably includes dynamically monitoring and integrating the
periodically determined aging parameters 209, with the short-term
aging effect regularly updated during each vehicle driving cycle.
This preferably includes updating the short-term aging effect 211
after each aging parameter is determined.
[0021] Accumulating the periodically determined aging parameters
209 includes dynamically monitoring and integrating the
periodically determined aging parameters, which can be accomplished
using a suitable cumulative model related to aging and fatigue. In
one embodiment, this can include executing a Miner's rule
calculation that sums ratios of time at temperature and capability
at temperature according to the following:
CumAging = T min T max Time ( Ti ) Capability ( Ti ) [ 1 ]
##EQU00001##
[0022] wherein [0023] CumAging is an index associated with
cumulative aging, [0024] Tmax is a maximum temperature, [0025] Tmin
is a minimum temperature, [0026] Time(Ti) is amount of operating
time at temperature Ti, and [0027] Capability(Ti) is service life
at temperature Ti.
[0028] The service life at temperature Ti, i.e., Capability(Ti) is
determined using a service life calculation that has been
predetermined using a representative model of the motor that has
been developed for the subject electric machine and corresponds to
the temperature-aging relationship 207 previously described. FIG. 4
graphically shows an example of a temperature-based service life
for a representative electric machine, with total service life
(hours) 410 on the vertical axis in relation to motor temperature
(.degree. C.) 420 on the horizontal axis. The scale of the vertical
axis is logarithmic with the total service life (hours) 410. A
relationship 430 between the total service life and the motor
temperature is shown, and indicates a reduction in motor service
life with an increase in accumulated time at an elevated operating
temperature of the electric machine.
[0029] Referring again to FIG. 2, a short-term temperature
adjustment 219 is periodically determined based upon the short-term
aging effect 211 using a short-term temperature-adjustment
relationship 217 that has been developed for the subject electric
machine (212). The short-term temperature-adjustment relationship
217 is graphically shown with temperature adjustment (.degree. C.)
on the vertical axis 215 and short-term aging on the horizontal
axis 213. The short-term temperature-adjustment relationship 217
comprehends a relation between elevated temperatures in the
electric machine and induced material stress and fatigue in the
short-term, which can be empirically developed. Thus, there may be
benefit to a temperature-based derating of torque output of the
electric machine to dynamically reduce output torque capability of
the electric machine to reduce aging and thus improve service life
of the electric machine. By way of example, the short-term
temperature-adjustment relationship 217 is imposed upon a
temperature-based motor torque derating curve, examples of which
are shown with reference to FIG. 3. The short-term
temperature-adjustment relationship 217 provides a temperature
adjustment in the form of a reduction in temperature that ranges
from 0.degree. C. at a low magnitude for the short-term aging
effect 211 to 10.degree. C. at a high magnitude for the short-term
aging effect 211, with the reductions in temperature imposed upon
the temperature-based motor torque derating curve. The short-term
temperature-adjustment relationship 217 is application-specific,
and can be implemented as a lookup table or an executable equation
in a controller. The short-term temperature adjustment 219 resets
to zero at the beginning of each driving cycle.
[0030] A long-term aging effect 221 is determined by accumulating
the periodically determined short-term aging effects 211 and
integrating the accumulated short-term aging effects at the end of
each driving cycle with a long-term aging effect determined during
a previous driving cycle (220). A long-term temperature adjustment
229 is periodically determined based upon the long-term aging
effect 221 using a long-term temperature-adjustment relationship
227 that has been developed for the subject electric machine (222).
The long-term temperature-adjustment relationship 227 is
graphically shown with temperature adjustment (.degree. C.) on the
vertical axis 225 and long-term aging on the horizontal axis 223.
The long-term temperature-adjustment relationship 227 comprehends
that elevated temperatures in the electric machine can induce
material stress and fatigue in the long-term, and can be
empirically developed. Thus, there may be benefit to a
temperature-based derating of torque output of the electric machine
to reduce output torque capability of the electric machine to
reduce aging and thus improve service life of the electric machine.
By way of example, the long-term temperature-adjustment
relationship 227 is imposed upon the temperature-based motor torque
derating curve, examples of which are shown with reference to FIG.
3. By way of example, the long-term temperature-adjustment
relationship 227 ranges from 0.degree. C. at a low magnitude for
the long-term aging effect 221 to 2.degree. C. at a high magnitude
for the long-term aging effect 221, with the reductions in
temperature imposed upon the temperature-based motor torque
derating curve. The long-term temperature-adjustment relationship
227 is application-specific and can be implemented as a lookup
table or an executable equation in a controller.
[0031] The long-term temperature adjustment 229 and the short-term
temperature adjustment 219 are accumulated, e.g., by summing to
determine an aging-based temperature adjustment (230). The
aging-based temperature adjustment 235 is employed to determine an
aging-based derated motor torque for the electric machine (240),
and operation of the electric machine is dynamically controlled
based upon the derated motor torque, including limiting torque
output from the electric machine using the aging-based derated
motor torque (250).
[0032] FIG. 3 graphically shows a plurality of temperature-based
motor torque derating curves plotted with torque derating in the
form of allowed percentage of maximum motor torque on the vertical
axis 304 and motor temperature on the horizontal axis 302. Line 310
depicts a temperature-based motor torque derating curve for a known
electric machine employing a simple temperature-based derating
system, and shows 100% of the maximum torque is allowed up to a
motor temperature of 170.degree. C., with a linear decline to 0% of
the maximum torque allowed at a motor temperature of 190.degree. C.
Line 320 depicts a temperature-based motor torque derating curve
for the same electric machine employing an embodiment of the motor
torque derate routine 200 described with reference to FIG. 2. Line
320 shows 100% of the maximum torque is allowed up to a motor
temperature of 180.degree. C., with a linear decline to 0% of the
maximum torque allowed up at a motor temperature of 200.degree. C.
when the electric machine is in a new condition. Lines 322 and 324
depict temperature-based motor torque derating curves for the same
electric machine employing the motor torque derate routine 200 and
showing decreases in the maximum temperature at which 100% of the
maximum torque is allowed below a motor temperature of 180.degree.
C., with a corresponding linear decline to 0% of the maximum
torque. Such derating may be short-term and reversible when due to
short-term temperature excursions with the electric machine in a
new condition. Such derating may be long-term and irreversible when
due to repeated occurrences of short-term temperature excursions as
the electric machine experiences operational aging.
[0033] Thus, in an operating environment for an electric machine
that experiences few excursions into high loads and high
temperatures, likelihood of motor damage is low and the control
system can operate with a motor torque derating scheme that permits
motor temperatures that are 10.degree. C. higher than a system
employing a simple temperature-based derating system in one
embodiment. Such a configuration enables short excursions to higher
temperatures, for brief periods of time providing full motor torque
capability. When an electric machine operates at elevated motor
temperatures, the motor torque derate routine described herein will
shift the torque derating scheme to the nominal values. The
short-term aging effect immediately and dynamically influences the
derating strategy. The long-term aging effect is purposely weighted
to a much lesser degree, to moderately influence the derating
strategy under dynamic conditions. As such the control system
improves intermittent performance and extends motor life.
[0034] The detailed description and the drawings or figures are
supportive and descriptive of the present teachings, but the scope
of the present teachings is defined solely by the claims. While
some of the best modes and other embodiments for carrying out the
present teachings have been described in detail, various
alternative designs and embodiments exist for practicing the
present teachings defined in the appended claims.
* * * * *