U.S. patent application number 16/386017 was filed with the patent office on 2020-10-22 for constant duty ratio high frequency voltage injection-based resolver offset detection.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Silong Li, Jiyao Wang, Wei Xu.
Application Number | 20200336051 16/386017 |
Document ID | / |
Family ID | 1000004054459 |
Filed Date | 2020-10-22 |
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United States Patent
Application |
20200336051 |
Kind Code |
A1 |
Li; Silong ; et al. |
October 22, 2020 |
CONSTANT DUTY RATIO HIGH FREQUENCY VOLTAGE INJECTION-BASED RESOLVER
OFFSET DETECTION
Abstract
A vehicle power system includes an electric machine, an inverter
electrically connected with the electric machine, and a controller.
The controller, while injecting AC voltage output by the inverter
into the electric machine as a DC voltage input to the inverter
changes, drives a duty ratio of the inverter toward a constant
value to obtain resolver offset information associated with the
electric machine from a current response of the electric machine to
the AC voltage.
Inventors: |
Li; Silong; (Canton, MI)
; Wang; Jiyao; (Canton, MI) ; Xu; Wei;
(Canton, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
1000004054459 |
Appl. No.: |
16/386017 |
Filed: |
April 16, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02P 21/34 20160201;
H02K 15/0006 20130101; H02P 6/183 20130101 |
International
Class: |
H02K 15/00 20060101
H02K015/00; H02P 6/18 20060101 H02P006/18; H02P 21/34 20060101
H02P021/34 |
Claims
1. A vehicle power system comprising: a DC bus; an electric
machine; an inverter electrically between the DC bus and electric
machine; and a controller programmed to command the inverter to
inject AC voltage into the electric machine, and responsive to
changes in DC voltage of the DC bus, alter a magnitude of the AC
voltage to drive a ratio of the DC voltage to the magnitude toward
a constant value as the DC voltage changes.
2. The vehicle power system of claim 1, wherein the controller is
further configured to operate the electric machine according to
resolver offset information derived from a current response of the
electric machine to the AC voltage.
3. The vehicle power system of claim 2, wherein the resolver offset
information is further derived from data contained in a look-up
table.
4. The vehicle power system of claim 1, wherein a ratio of
switching frequency of the inverter and injection frequency of the
AC voltage is between ten and twenty.
5. The vehicle power system of claim 1, wherein the controller is
further configured to inject the AC voltage with constant duty
ratio.
6. The vehicle power system of claim 1 further comprising a
traction battery, wherein the DC bus is electrically between the
traction battery and inverter.
7. A vehicle power system comprising: an electric machine; an
inverter; and a controller programmed to, while injecting AC
voltage output by the inverter into the electric machine as a DC
voltage input to the inverter changes, drive a duty ratio of the
inverter toward a constant value to obtain resolver offset
information associated with the electric machine from a current
response of the electric machine to the AC voltage, wherein the
controller is further programmed to drive the duty ratio toward the
constant value such that a ratio of the DC voltage to a magnitude
of the AC voltage remains constant during the injecting.
8. (canceled)
9. The vehicle power system of claim 7, wherein a ratio of
switching frequency of the inverter and injection frequency of the
AC voltage is between ten and twenty.
10. The vehicle power system of claim 7, wherein the controller is
further configured to command the electric machine to output a
specified torque or speed according to the resolver offset
information.
11. The vehicle power system of claim 10, wherein the resolver
offset information is further derived from data contained in a
look-up table.
12. The vehicle power system of claim 7 further comprising a
traction battery or DC bus configured to provide the DC
voltage.
13. A method for controlling a vehicle power system, comprising:
injecting by a controller AC voltage into an electric machine via
an inverter; and responsive to changes in DC voltage input to the
inverter during the injecting, altering by the controller a
magnitude of the AC voltage to drive a ratio of the DC voltage to
the magnitude toward a constant value to obtain resolver offset
information about the electric machine.
14. The method of claim 13, wherein a ratio of switching frequency
of the inverter and a frequency of the injecting is between ten and
twenty.
15. The method of claim 13, wherein the injecting is associated
with constant duty ratio output.
16. The method of claim 13 further comprising commanding the
electric machine to output a specified torque or speed according to
the resolver offset information.
17. The method of claim 13, wherein the changes in DC voltage are
associated with a traction battery or DC bus.
Description
TECHNICAL FIELD
[0001] This disclosure relates to electric machine operation.
BACKGROUND
[0002] Resolver offset detection operations detect resolver offset
of an electric machine regardless of the influence of inverter
deadtime. If the estimated resolver offset is incorrect, the torque
accuracy of the electric machine and its control algorithms can be
degraded. Moreover, if the resolver offset error is large, it can
result in torque reversal.
[0003] Some high frequency voltage injection-based resolver offset
detection methods detect resolver offset using a fixed injected
voltage amplitude. The accuracy of these techniques, however, is
influenced by inverter deadtime/inverter nonlinearity, which cannot
be avoided. The accuracy is also not consistent under different
DC-bus voltages or battery voltages, since deadtime voltages are
influenced by the DC-bus voltage or battery voltage.
SUMMARY
[0004] A vehicle power system includes a DC bus, an electric
machine, and an inverter electrically between the DC bus and
electric machine. The vehicle power system also includes a
controller that injects AC voltage into the electric machine via
the inverter, and responsive to changes in DC voltage of the DC
bus, alters a magnitude of the AC voltage to drive a ratio of the
DC voltage to the magnitude toward a constant value as the DC
voltage changes.
[0005] A vehicle power system includes an electric machine, an
inverter, and a controller. The controller, while injecting AC
voltage output by the inverter into the electric machine as a DC
voltage input to the inverter changes, drives a duty ratio of the
inverter toward a constant value to obtain resolver offset
information associated with the electric machine from a current
response of the electric machine to the AC voltage.
[0006] A method for controlling a vehicle power system includes
injecting by a controller AC voltage into an electric machine via
an inverter, and responsive to changes in DC voltage input to the
inverter during the injecting, altering by the controller a
magnitude of the AC voltage to drive a ratio of the DC voltage to
the magnitude toward a constant value to obtain resolver offset
information about the electric machine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a d-axis/q-axis plot of deadtime voltage as a
function of angular position for a given DC-bus voltage.
[0008] FIG. 2 is a plot of an example look-up table for resolver
offset detection.
[0009] FIG. 3 is an example of repeated resolver offset detection
results under various rotor positions and DC-bus voltages.
[0010] FIG. 4 is a flow chart of an injection routine
[0011] FIG. 5 is a flow chart of a detection routine.
[0012] FIG. 6 is a block diagram of a vehicle.
DETAILED DESCRIPTION
[0013] Various embodiments of the present disclosure are described
herein. However, the disclosed embodiments are merely exemplary and
other embodiments may take various and alternative forms that are
not explicitly illustrated or described. The figures are not
necessarily to scale; some features may be exaggerated or minimized
to show details of particular components. Therefore, specific
structural and functional details disclosed herein are not to be
interpreted as limiting, but merely as a representative basis for
teaching one of ordinary skill in the art to variously employ the
present invention. As those of ordinary skill in the art will
understand, various features illustrated and described with
reference to any one of the figures may be combined with features
illustrated in one or more other figures to produce embodiments
that are not explicitly illustrated or described. The combinations
of features illustrated provide representative embodiments for
typical applications. However, various combinations and
modifications of the features consistent with the teachings of this
disclosure may be desired for particular applications or
implementations.
[0014] This disclosure proposes constant duty ratio high frequency
voltage injection-based resolver offset detection methods to
mitigate inverter deadtime effects. The amplitude of injected high
frequency voltage is no longer a fixed value. Rather, it varies
with the DC-bus voltage or battery voltage to maintain a relatively
constant controller duty ratio output, which can improve resolver
offset detection accuracy under all DC-bus voltage conditions and
promote detection consistency.
[0015] Resolver offset detection is implemented by introducing a
high frequency voltage signal into the electric machine. For this
high frequency voltage signal and with reference to Eq. (1), a
persistent rotating high frequency voltage vector, V.sub.dqs.sup.s,
in the stationary reference frame is injected into the electric
machine:
V.sub.dqs.sup.s=V.sub.ce.sup.j.omega..sup.c.sup.t (1)
where V.sub.c represents the amplitude of the rotating voltage
vector, and .omega..sub.c represents the frequency of the rotating
voltage vector. The three-phase currents from the electric machine
response are then observed and post-processed for rotor position
detection. The detected rotor position is then compared with a
resolver reading to determine the resolver offset value
accordingly.
[0016] The injection frequency is chosen based on the inverter
switching frequency. A ratio of approximately 10 to 20 between the
switching frequency and injection frequency are example optimized
values. The selection of amplitude V.sub.c is described later.
[0017] The high frequency current response, I.sub.dqs.sup.s, has
the saliency information embedded therein and can be represented by
Eq. (2):
I.sub.dqs.sup.s=I.sub.cpe.sup.j(.omega..sup.c.sup.t+.phi..sup.cp.sup.)+I-
.sub.cne.sup.j(-.omega..sup.c.sup.t+.phi..sup.cn.sup.) (2)
where I.sub.cp and I.sub.cn represent the magnitude of the positive
and negative sequence current response respectively, and
.phi..sub.cp and .phi..sub.ca represent the phase of the positive
and negative sequence current response respectively.
[0018] The phase the of negative sequence current response,
.phi..sub.cn, is represented by Eq. (3):
.PHI. c n = 2 .theta. e - .pi. 2 ( 3 ) ##EQU00001##
where .theta..sub.c is the rotor position in electric degrees. It
includes the electric machine rotor position information, and as
consequence can be used for rotor position and resolver offset
detection.
[0019] With reference to Eq. (4), the phase of the negative
sequence current response, X.sub.k, can be estimated by applying
the discrete Fourier transform (DFT) to the three-phase
current:
X.sub.k=X.sub.k=.SIGMA..sub.n=0.sup.N-1x.sub.ne.sup.-j2.pi.f.sup.c.sup.T-
.sup.s (4)
where N is the number of samples of the discrete Fourier transform
(the more samples taken, the more accurate the DFT results; more
samples, however, require more calculation time that can delay the
detection), x.sub.n is the sampled high frequency current complex
vector, I.sub.qds, and f.sub.c is the frequency of the injected
signal (for the positive sequence, the sign is positive; for the
negative sequence, the sign is negative).
[0020] In real applications, deadtime and nonlinearity exist in
inverter systems. Inverter deadtime, V.sub.dead, will lead to
errors in actual output voltage of the inverter. As a consequence,
the injected high frequency voltage signal is not as expected and
will lead to resolver offset detection error. The inverter
nonlinearity effect is shown in Eqs. (5) and (6):
V dead = T dead + T on - T off T S ( V dc - V sat + V d ) + V sat +
V d 2 ( 5 ) ##EQU00002##
where T.sub.dead, T.sub.on, T.sub.off, and T.sub.s represent the
deadtime, turn-on delay time, turn-off delay time, and pulse width
modulation period, respectively, V.sub.dc is the DC-bus voltage,
V.sub.sat is the on-state voltage drop of the switch, and V.sub.d
is the forward voltage drop of the diode.
[ V d , dead e V q , dead e ] = V dead 2 3 [ cos ( .theta. e ) cos
( .theta. e - 2 .pi. 3 ) cos ( .theta. e + 2 .pi. 3 ) sin ( .theta.
e ) sin ( .theta. e - 2 .pi. 3 ) sin ( .theta. e + 2 .pi. 3 ) ] [
sign ( i a ) sign ( i b ) sign ( i c ) ] ( 6 ) ##EQU00003##
where V.sub.d,dead.sup.e and V.sub.q,dead.sup.e respectively
represent the d-axis and q-axis deadtime voltage in the synchronous
reference frame, and i.sub.a, i.sub.b, and i.sub.c respectively
represent the phase-A, phase-B, and phase-C current. Among all
factors, the inverter deadtime is typically the dominant
factor.
[0021] FIG. 1 shows the deadtime voltage on the d-axis and q-axis
of the synchronous reference frame as a function of angular
position at one particular DC-bus voltage. The inverter deadtime
has different influence on the d-axis as compared with the q-axis,
and shows a six order pattern in one electric cycle.
[0022] To compensate for the influence of the inverter deadtime and
improve resolver offset detection accuracy, a look-up table can be
utilized to compensate for the error. FIG. 2 shows an example of
such look-up table resolver offset detection. Using the look-up
table, the accuracy of the resolver offset detection is achieved
for one particular DC-bus or battery voltage. The deadtime voltage,
however, is also a function of the DC-bus voltage, so additional
action is needed to improve resolver offset detection accuracy at
various DC-bus voltages.
[0023] To achieve this, it is proposed to use a constant duty
ratio. When the DC-bus voltage changes from V.sub.dc1 to V.sub.dc2,
the algorithm also changes the magnitude of the injected high
frequency voltage signal from V.sub.c1 to V.sub.c2 to keep the duty
ratio constant, as shown in Eq. (7):
V dc 1 V c 1 = V dc 2 V c 2 ( 7 ) ##EQU00004##
In such a manner, the phase lag of actual high frequency voltage
output signals is fixed regardless of DC-bus voltage variation, and
the look-up table mentioned above is able to compensate for the
inverter deadtime effect under varying DC-bus voltage
conditions.
[0024] FIG. 3 shows an example of repeated resolver offset
detection results under various rotor positions and DC-bus voltages
(200V variation). All results show small resolver offset detection
error.
[0025] FIG. 4 shows an algorithm 10 for an injection routine
associated with the techniques proposed herein. At operation 14, it
is determined whether constant duty ratio high frequency voltage
injection-based resolver offset detection is enabled. If no, the
injection frequency, .omega..sub.c, and magnitude V.sub.c, are set
to zero at operation 14. The algorithm 10 then ends. If yes, the
adjusted injection magnitude, V.sub.e2, is determined according to
the relation shown (see also Eq. (7)). At operation 18, the
injection angle .THETA..sub.c is updated according to the relation
shown, where T.sub.s is the sampling period. The injection voltage,
V.sub.ds.sup.s, V.sub.qs.sup.s, is then calculated at operation 20
according to the relation shown. At operation 22, the two-phase
stator reference frame is transformed to the three-phase stator
reference frame using standard techniques. And at operation 24, it
is determined whether the injection is finished. If no, the
algorithm 10 returns to operation 18. If yes, the algorithm 10
ends.
[0026] FIG. 5 shows an algorithm 26 for a detection routine
associated with the techniques proposed herein. At operation 28,
the three-phase currents are obtained. The three-phase stator
reference frame is transformed to the two-phase stator reference
frame using standard techniques at operation 30. Rotor position
.THETA..sub.e is then estimated from Eqs. (3) and (4) at operation
32. At operation 34, the look-up table described above is used to
compensate for the inverter deadtime error and obtain compensated
rotor position, .THETA..sub.c_comp. At operation 36, the
compensated rotor position is compared with the resolver position
reading, and the resolver offset is set according to the
difference. The algorithm then ends.
[0027] FIG. 6 is a simplified block diagram of a vehicle 38 that
includes, among other things, a traction battery 40, a DC bus 42,
an inverter 44, an electric machine 46, and a controller 48. Power
from the traction battery 40 can be provided to the electric
machine 46 via the DC bus 42 and inverter 44 as known in the art.
Power can also flow in the other direction. The controller 48 may
implement the techniques contemplated herein to exercise control
over the traction battery 40, inverter 44, and electric machine 46.
The controller 48, for example, may operate the electric machine 46
(e.g., provide it commands to produce a specified torque or speed)
based on resolver offset information derived from a current
response of the electric machine 46 to AC voltage applied thereto
according to the techniques contemplated herein.
[0028] Certain existing high frequency voltage injection-based
resolver offset detection methods detect the resolver offset using
a fixed injected voltage amplitude. The accuracy of these methods
is low due to the inverter deadtime effect, and is inconsistent
under different DC-bus or battery voltages. The use of a constant
duty ratio high frequency voltage injection-based resolver offset
detection method to mitigate inverter deadtime effects is proposed
here. The magnitude of the injected high frequency voltage signal
will vary with DC-bus voltage or battery voltage to maintain
constant controller duty ratio output, which can achieve accurate
resolver offset detection under various DC-bus voltage conditions
with greater consistency, regardless of the inverter
deadtime/nonlinearity effects.
[0029] The algorithms, processes, methods, logic, or strategies
disclosed may be deliverable to and/or implemented by a processing
device, controller, or computer, which may include any existing
programmable electronic control unit or dedicated electronic
control unit. Similarly, the algorithms, processes, methods, logic,
or strategies may be stored as data and instructions executable by
a controller or computer in many forms including, but not limited
to, information permanently stored on various types of articles of
manufacture that may include persistent non-writable storage media
such as ROM devices, as well as information alterably stored on
writeable storage media such as floppy disks, magnetic tapes, CDs,
RAM devices, and other magnetic and optical media. The algorithms,
processes, methods, logic, or strategies may also be implemented in
a software executable object. Alternatively, they may be embodied
in whole or in part using suitable hardware components, such as
Application Specific Integrated Circuits (ASICs),
Field-Programmable Gate Arrays (FPGAs), state machines, controllers
or other hardware components or devices, or a combination of
hardware, software and firmware components.
[0030] The words used in the specification are words of description
rather than limitation, and it is understood that various changes
may be made without departing from the spirit and scope of the
disclosure and claims. As previously described, the features of
various embodiments may be combined to form further embodiments
that may not be explicitly described or illustrated. While various
embodiments may have been described as providing advantages or
being preferred over other embodiments or prior art implementations
with respect to one or more desired characteristics, those of
ordinary skill in the art recognize that one or more features or
characteristics may be compromised to achieve desired overall
system attributes, which depend on the specific application and
implementation. These attributes include, but are not limited to
cost, strength, durability, life cycle cost, marketability,
appearance, packaging, size, serviceability, weight,
manufacturability, ease of assembly, etc. As such, embodiments
described as less desirable than other embodiments or prior art
implementations with respect to one or more characteristics are not
outside the scope of the disclosure and may be desirable for
particular applications.
* * * * *