Note: Descriptions are shown in the official language in which they were submitted.
CA 02510646 2006-03-08
MULTIPHASE MOTOR VOLTAGE CONTROL FOR PHASE
WINDINGS OF DIFFERENT WIRE GAUGES AND WINDING
TURNS
Related Applications
This application contains subject matter related to U.S. Patent No.
6,492,756 of Boris Maslov et al., issued on December 10, 2002, copending U.S.
publication number US 2003-0193263 of Boris Maslov et al., published on
October 16, 2003, and International PCT publication number WO 2004/001953
of Boris Maslov et al., published on December 31, 2003, all commonly assigned
with the present application.
Field of the Invention
The present invention relates to the control of a multiphase motor, more
particularly to the application of different voltages to individual phase
windings
of differing winding and wire gauge topologies through a succession of motor
operating speed ranges.
Background
The progressive improvement of electronic systems, such as
microcontroller and microprocessor based applications for the control of
motors,
as well as the availability of improved portable power sources, has made the
development of efficient electric motor drives for vehicles, as a viable
alternative to combustion engines, a compelling challenge. Electronically
controlled pulsed energization of windings of motors offers the prospect of
more
flexible management of motor characteristics. By control of pulse width, duty
cycle, and switched application of a battery source to appropriate stator
windings, functional versatility that is virtually indistinguishable from
alternating current synchronous motor operation can be achieved.
The above-identified U.S. Patent No. 6,492,756 of Maslov et al.,
identifies and addresses the need for an improved motor amenable to simplified
manufacture and capable of
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efficient and flexible operating characteristics. In a vehicle drive
environment, it
is highly desirable to attain smooth operation over a wide speed range, while
maintaining a high torque output capability at miniunum power consumption.
U.S. Patent No. 6,492,756 describes electromagnetic poles as
isolated magnetically permeable structures configured as segments in an
annular ring, relatively thin in the radial direction, to provide advantageous
effects. With this arrangement, flux can be concentrated, with virtually no
loss
or deleterious transformer interference effects in the electromagnet cores, as
compared with prior art embodiments.
The Maslov et al. applications recognize that isolation of the
electromagnet segments permits individual concentration of flux in each
magnetic core segment, with virtually no flux loss or deleterious transformer
interference effects from flux interaction with other core segments.
Operational advantages can be gained by configuring a single pole pair as an
autonomous electromagnet. Magnetic path isolation of the individual pole pair
from other pole pairs eliminates a flux transformer effect on an adjacent
group
when the energization of the pole pair windings is switched.
The above-identified International PCT publication number WO
2004/001953 is directed to a control system for a multiphase motor having
these
structural features. A control strategy is described that compensates for
individual phase circuit characteristics and offers a higher degree of
precision
controllability since each phase control loop is closely matched with its
corresponding winding and structure. Control parameters are specifically
matched with characteristics of each respective stator phase. Successive
switched energization of each phase winding is governed by a controller that
generates signals in accordance with the parameters associated with the stator
phase component for the phase winding energized.
While the motors described in the above-identified applications
provide operational advantages, these motors and prior art motors do not
exhibit uniformly high efficiency at all speeds of a wide operating speed
range,
even with non-variable loads. For a fixed motor topology, the available
magnetomotive force (NI1ViF) is dependent upon the number of winding turns
and energization current. The term "motor topology" is used herein to refer to
physical motor characteristics, such as dimensions and magnetic properties of
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stator cores, the number of coils of stator windings and wire diameter
(gauge),
etc. The available magnetomotive force dictates a variable, generally inverse,
relationship between torque and speed over an operating range. An applied
energization current may drive the motor to a nominal operating speed. As the
motor accelerates toward that speed, the torque decreases, the current drawn
to
drive the motor decreases accordingly, and thus efficiency increases to a
maximum level. As speed increases beyond the level of peak efficiency,
additional driving current is required, thereby sacrificing efficiency
thereafter.
Thus, efficiency is variable throughout the speed range and approaches a peak
at a speed well below maximum speed.
Motors with different topologies obtain peak efficiencies at different
speeds, as illustrated in Fig. 1. This figure is a plot of motor efficiency
versus
operating speed over a wide speed range for motors having different
topologies. The topologies represented in this figure differ solely in the
number of stator winding turns. Each efficiency curve approaches a peak
value as the speed increases from zero to a particular speed and then
decreases
toward zero efficiency. Curve A, which represents the motor with the greatest
number of winding turns, exhibits the steepest slope to reach peak efficiency
at
the earliest speed V2. Beyond this speed, however, the curve exhibits a
similarly steep negative slope. Thus, the operating range for this motor is
limited. The speed range window at which this motor operates at or above an
acceptable level of efficiency, indicated as X% in Figure 1, is relatively
narrow.
Curves B through E represent motors with successively fewer winding
turns. As the number of winding turns decreases, the motor operating speed
for maximum efficiency increases. Curve B attains peak efficiency at speed
V3, Curve C at V4, Curve D at V5 and Curve E at V6. Each motor has pealc
efficiency at a different motor operating speed, and none has acceptable
efficiency over the entire range of motor operating speeds.
In motor applications in which the motor is to be driven over a wide
speed range, such as in a vehicle drive environment, Fig. 1 indicates that
there
is no ideal single motor topology that will provide uniformly high operating
efficiency over the entire speed range. For example, at speeds above V6
curves A and B indicate zero efficiency. At the lower end of the speed range,
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for example up to V2, curves C through E indicate significantly lower
efficiency than curves A and B.
In motor vehicle drives, operation efficiency is particularly important
as it is desirable to extend battery life and thus the time period beyond
which it
becomes necessary to recharge or replace an on-board battery. The need thus
exists for motors that can operate with more uniformly high efficiency over a
wider speed range than those presently in use.
The approach taken therein is to change, on
a dynamic basis, the number of active coils of each stator winding for each of
a
plurality of speed ranges between startup and a maximuin speed at which a
motor can be expected to operate. The speed ranges are identified in a manner
similar to that illustrated in Fig. 1 and a different number of the motor
stator
winding coils that are to be energized are designated for each speed range to
obtain maximum efficiency for each of a plurality of operating speed ranges.
The number of energized coils is changed when the speed crosses a threshold
between adjacent speed ranges. Each winding comprises a plurality of
individual, serially connected, coil sets separated by tap connections. Each
respective tap is connected by a switch to a source of energization during a
single corresponding speed range. The windings thus have a different number
of energized coils for each speed range.
While this arrangement expands the speed range in which high
efficiency may be obtained, the inductive characteristics of the motor
windings
require precisely timed connection and disconnection of the taps to and from
the power source. A significant amount of electronic power circuitry and
control circuitry therefor must be provided to obtain accurate functionality.
Structural constraints in particular motor configurations may limit the number
of taps, and thus coil sets, that are available from individual stator
windings.
The need thus remains for alternative ways in which high efficiency
motor operation can be obtained over extended speed ranges. Described in
the art is motor structure in which each stator phase winding is configured
with a topology different from the topology of each of the other phase
windings. Winding topology is characterized by the total number of coil
turns in each phase winding and the wire gauge of the coil
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in each phase winding. Each phase winding differs from each of the other
phase windings by the total nuinber of coil turns or by wire gauge, preferably
in both respects. With the gauge sizes and total number of coil turns of the
phase windings being in inverse relationship with respect to each other, all
of
the phase windings are provided with substantially the same total coil mass.
Phase winding energization can be tailored to obtain maximum efficiency in
each of several operating speed ranges from startup to the maximum speed at
which a motor can be expected to operate.
The need exists to provide the optimal voltage to be applied to each
phase winding at each operating speed range. For a machine structure that
accommodates a large number of phases, it is necessary to predefine for each
speed range which phase windings are to have no voltage applied as well as to
identify what predefined voltage magnitude is to be applied to each of the
remaining phase windings. The number of, and identity of, the phase windings
that are to be energized, as well as the magnitude of the individually applied
predefined voltages, may differ for each speed range. The predefined optimal
voltages should be applied on a dynamic basis in accordance with the sensed
speed of the motor.
While the predefined voltages for the phase windings can be derived to
provide optimal efficiency over the entire motor operating speed range for a
given torque, many motor applications exist which require control for variable
motor speed, such as in motor vehicles. Motor output torque should be
adjusted in accordance with a user's input command related to desired speed.
The further need thus exists for developing applied phase winding voltages
that optimize efficiency throughout the operating speed range at variable
torque output in accordance with user command.
Disclosure of the Tnvention
The present invention fulfills the above-described needs for controlling,
through a plurality of operating speed ranges, a multiphase motor having a
plurality of ferromagnetically isolated stator electromagnets distributed
about
an axis of rotation, each electromagnet having a phase winding formed on a
ferromagnetic core. Successive ranges of speed during which the motor can be
expected to operate are defined. A specific subset of the electromagnets is
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associated for each speed range, each specific subset comprising a different
combination of electromagnets. Respective voltage inagnitudes to be applied
to each phase winding for each defined speed range are predefined. The motor
speed is sensed throughout motor operation. In each defined speed range, only
the electromagnets of the associated subset are energized, each of the
energized electromagnets having applied thereto a different predefined voltage
magnitude.
The present invention is particularly advantageous in that the different
phase winding topologies of the electromagnets, wherein each phase winding
has a different total number of coil turns and a different wire gauge from
each
of the other phase windings, permits division of the entire operating speed
range into many narrow ranges in which fine adjustment for efficiency can be
obtained. During operation in each defined speed range at least one of the
total number of electromagnet phase windings may be deenergized.
Phase windings that are energized with specified predefined voltages
during one speed range may also be energized, with different predefined
voltages, during another defined speed range. The number and identity of
phase windings energized during one defined speed range may be different
from the number and identity of phase windings energized during another
defined speed range.
A further advantage of the present invention is that the predefined
voltage magnitudes for all speed ranges can be set for maximum motor torque
output. Adjustment of the predefined voltage magnitudes can be made in
accordance with a user torque input command to obtain optimal motor drive
efficiency at other torque outputs. The user torque input command can vary
through a range between zero torque and maximum torque. By relating the
range of the user input to a fractional value that is variable between zero
and
one, the control system can multiply the predefined maximum torque voltage
magnitudes for all speed ranges by the fractional value corresponding to the
user input to obtain optimal motor drive efficiency at all torque outputs.
Additional advantages of the present invention will become readily
apparent to those skilled in this art from the following detailed description,
wherein only the preferred embodiment of the invention is shown and described,
simply by way of illustration of the best mode contemplated of carrying out
the
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invention. As will be realized, the invention is capable of other and
different
embodiments, and its several details are capable of modifications in various
obvious respects, all without departing from the invention. Accordingly, the
drawings and description are to be regarded as ill.ustrative in nature, and
not as
restrictive.
Rrief Descrintion of DrawingS
The present invention is illustrated by way of example, and not by way
of limitation, in the figures of the accompanying drawing and in which like
reference numerals refer to similar elements and in which:
Fig.1 is a plot of motor efficiency versus motor operating speed over a
wide speed range for different conventional motors having different numbers
of winding tums.
Fig. 2 is an exemplary configuration of rotor and stator elements that
may be employed in the present invention.
Fig. 3 is a chart exhibiting wire gauges and total number of winding
turns for each phase of a multiphase motor exemplifying the present invention.
Fig. 4 is a partial block diagram of a voltage supply circuit for the
motor of Fig. 2.
Fig. 5 is an exemplary plot of voltage applied to each phase winding of
the motor of Fig. 2 over the operating speed range.
Fig. 6 is a plot of motor efficiency versus motor operating speed for
voltages applied in accordance with Fig. 5.
Detailed ne.c ription of the Tnvention
Fig. 2 is an exemplary configuration of rotor and stator elements that
may be employed in the present invention. Reference is made to the above
identified copending Maslov et al. publication US 2003-0193263 for a more
detail description of the motor exemplified herein. Rotor member 20 is an
annular ring structure having permanent magnets 21 spaced from each other
and substantially evenly distributed along cylindrical back plate 25. The
permanent magnets are rotor poles that alternate in magnetic polarity along
the
inner periphery of the annular ring. The rotor surrounds a stator member 30,
the rotor. and stator members being separated by an annular radial air gap.
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Stator 30 comprises a plurality of electromagnet core segments of uniform
construction that are evenly distributed along the air gap.
The stator comprises seven core segments, each core segment formed
in a generally u-shaped magnetic structure 36 with two poles having surfaces
32 facing the air gap. The legs of the pole pairs are wound with windings 38,
although the core segment may be constructed to accommodate a single
winding formed on a portion linking the pole pair. Each stator electromagnet
core structure is separate, and magnetically isolated, from adjacent stator
core
elements. Each of the core segments can be considered to represent a phase,
the phase windings identified successively along the air gap by labels 38a-
38g.
The stator elements 36 are secured to a non-magnetically permeable support
structure, thereby forming an annular ring configuration. This configuration
eliminates emanation of stray transformer flux effects from adjacent stator
pole groups. Appropriate stator support structure, which has not been
illustrated herein so that the active motor elements are more clearly visible,
can be seen in the aforementioned patent application.
Windings 38a-38g differ from each other in winding topology with
respect to wire gauges and total number of winding coil turns. While it is
preferable in this embodiment that each phase winding has a unique nuinber of
total winding turns and a unique wire gauge, two or more phase windings may
have similar wire gauges or number of turns. Other embodiments may
comprise a greater number of isolated core segment pole pairs. It may be
preferable in such embodiments that some phase windings have the same
winding topology.
Fig. 3 is a chart exeinplifying phase winding topologies for a seven
phase motor illustrated in Fig. 2. Each phase winding has a unique number of
coil turns and is constructed of a unique wire gauge. The total copper mass of
each of the phase windings is the same.
Fig. 4 is a partial block 'diagram of a voltage supply circuit for the
motor of Fig. 2. Phase windings 38a-38g are connected to d-c power supply
via a series connection, respectively, with voltage converters 42a-42g. A
control terminal of each voltage converter is coupled to controller 44,
wliicli is
also connected across power supply 40. The controller and voltage converters
are conventional devices as described more fully in the copending Maslov et
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al. publication WO 2004/001953. The controller 44, which may comprise a
microprocessor and associated storage means, may have one or more user
inputs and a plurality of inputs for motor conditions sensed during operation.
For clarity of explanation of the present invention, a motor speed input is
the
only motor condition feedback input shown. The speed input signal may be
generated by any conventional motor speed sensor. Stored in the controller is
a table that identifies a voltage level to be applied to each phase winding
for
each of a plurality of speed ranges over the operating range. Voltage values
that have been found to provide maximum operating efficiency at maximum
motor torque output for each of the phase windings 38a-38g in various speed
ranges are identified in the table below. The efficiency. of operation for
each
range is also set forth in the table.
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Table
Voltage 7oltage Voltage Voltage Voltage Voltage Voltage
Mfor phas for phas for phas for phas for phas for phas for phase fficienc
inding inding inding inding inding inding inding y
8a 38c 38e 8 8b 18d 38f
0 4.0 16.3 10.8 6.8 0.0 0.0 0.0 0.0
4.0 16.4 10.9 6.9 0.0 0.0 0.0 13.3
24.0 16.7 11.2 7.2 0.0 0.0 0.0 26.1
24.0 17.1 11.7 7.6 0.0 0.0 0.0 38.1
10 24.0 17.8 12.4 8.1 0.0 0.0 0.0 9.1
50 24.0 18.6 13.3 8.9 0.0 0.0 0.0 59.0
60 24.0 19.6 14.4 9.8 0.0 0.0 0.0 67.6
70 24.0 20.8 15.7 10.8 0.0 0.0 0.0 74.6
80 24.0 22.2 17.2 12.1 0.0 0.0 0.0 79.3
90 24.0 23.8 18.9 13.5 0.0 0.0 0.0 80.9
100 0.0 24.0 20.8 15.0 0.0 0.0 0.0 83.5
110 0.0 24.0 22.9 16.7 0.0 0.0 0.0 83.2
120 0.0 0.0 24.0 18.6 12.7 0.0 0.0 84.1
130 0.0 0.0 24.0 20.7 14.1 0.0 0.0 86.2
140 0.0 0.0 24.0 22.9 15.8 0.0 0.0 84.3
150 0.0 0.0 0.0 24.0 17.5 0.0 0.0 84.5
160 0.0 0.0 0.0 24.0 19.3 0.0 0.0 86.8
170 0.0 0.0 0.0 24.0 21.3 14.0 0.0 85.6
180 0.0 0.0 0.0 24.0 23.4 15.5 0.0 82.8
190 0.0 0.0 0.0 0.0 24.0 17.0 0.0 85.0
200 0.0 0.0 0.0 0.0 24.0 18.6 0.0 87.7
210 0.0 0.0 0.0 0.0 24.0 20.3 0.0 87.4
20 0.0 0.0 0.0 0.0 24.0 22.1 0.0 84.4
230 0.0 0.0 0.0 0.0 24.0 23.9 15.3 80.5
240 0.0 0.0 0.0 0.0 0.0 24.0 16.6 84.9
250 0.0 0.0 0.0 0.0 0.0 24.0 18.0 87.9
260 0.0 0.0 0.0 0.0 0.0 24.0 19.4 88.6
270 0.0 0.0 0.0 0.0 0.0 24.0 20.8 87.2
280 0.0 0.0 0.0 0.0 0.0 24.0 22.3 84.0
290 0.0 0.0 0.0 0.0 0.0 24.0 23.9 79.7
300 0.0 0.0 0.0 0.0 0.0 0.0 24.0 81.9
310 0.0 0.0 0.0 0.0 0.0 0.0 24.0 84.6
320 0.0 0.0 0.0 0.0 0.0 0.0 24.0 87.4
330 0.0 0.0 0.0 0.0 0.0 0.0 24.0 90.1
340 0.0 0.0 0.0 0.0 0.0 0.0 24.0 92.8
350 0.0 0.0 0.0 0.0 0.0 0.0 24.0
360 0.0 0.0 0.0 0.0 0.0 0.0 24.0
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In operation, the controller 44 accesses data from the table to determine
which phase windings are to be energized at startup and the level of voltage
to
be applied to each phase winding. The controller outputs the appropriate
control voltages for these values to the respective voltage converters
connected
to the phase windings. As the motor accelerates, motor speed is repetitively
sampled and fed as a signal input to the controller. In response to the
received
speed input signal, the controller accesses the stored table to receive
voltage
data for each phase winding at the speed range in which the sensed speed is
located. New control signals, corresponding to the accessed data, are output
to
the voltage converters to change, if appropriate, the voltages applied to the
phase windings. As motor load varies, the motor speed may vary accordingly.
The controller, in turn, will adjust its output control voltages for these
changes
as provided by the table thereby to maintain optimum operation efficiency over
the entire operating speed range.
The table represents a speed operating range of 360 rpm that is very
finely divided for application of precisely adjusted voltage levels. This
information is provided in graphic form in Fig. 5, each curve representing
voltages applied to a respective phase winding throughout the range. Curve 1
represents voltages applied to phase winding 38a; curve 2 represents voltages
applied to phase winding 38c; curve 3 represents voltages applied to phase
winding 38e; curve 4 represents voltages applied to phase winding 38g; curve
5 represents voltages applied to phase winding 38b; curve 6 represents
voltages applied to phase winding 38d; and curve 7 represents voltages applied
to phase winding 38f.
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During different portions of the operational speed range, different
combinations of phase windings will be energized. At no time are all seven
phase windings energized. As evident from the table and Fig. 5, at starting,
four phase windings are energized with changing voltage levels as shown up to
speed of 100 rpm. For speeds between 100 and 140 rpm, three phase windings
are energized with voltage levels as shown; between 140 and 160 rpm. two
phase windings are energized; between 160 and 180 rpm. three phase windings
are energized; between 180 and 220 rpm. two phase windings are energized;
between 220 to 230 three windings are energized; between 230 and 290 two
phase windings are energized; and at speeds greater than 290 only a single
winding is energized. For each of these ranges, different combinations of
energized phase windings are identified and are to be supplied with different
energization voltages.
Motor efficiency for operation in accordance with the table over the
entire speed range is illustrated graphically in Fig. 6. Comparison of this
curve
with the efficiency curves of conventionally operated motors, shown in Fig. 1,
illustrates the improved operating efficiency of the present invention. The
stator winding configuration of the present invention, when energized in
accordance with the voltages indicated in the table over the motor operating
range, provides a motor operating efficiency in excess of eighty per cent over
approximately three quarters of the speed range.
The controller user input illustrated in Fig. 4 represents a torque
command signal, such as described in the above-identified PCT publication
WO 2004/001953. A vehicle drive application example is
described therein, the user input representing desired torque indicated by the
user's throttle command. The user may vary the throttle between zero and a
maximum level. An increase in throttle is indicative of a command to increase
speed, which is realized by an increase in torque. Description of to this
point
of the motor operation has focussed on control at maximum motor torque
output, for which the corresponding user input represents maximum throttle.
The variable user torque input command range is related to a fractional
value that is variable between zero for a zero torque input command and one
for maximum torque input command. Motor speed is repetitively sampled and
fed as a signal input to the controller. The controller, in response to the
sensed
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speed signal input will access stored data stored representing the voltage
inagnitude values in the table and multiply these voltage magnitude values by
the fractional value that corresponds to the user torque input command
setting.
As speed signals for different speed ranges are received, the appropriate
voltage magnitude values are obtained from the table and new control signals,
which are products of these voltage magnitudes and the fractional value for
the
user input command are produced. For the set user input command, optimal
motor drive efficiency is achieved for all speed ranges. Maximum operational
efficiency is similarly obtained for all set user torque inputs for all speed
ranges.
In this disclosure there are shown and described only preferred
embodiments of the invention and but a few examples of its versatility. It is
to
be understood that the invention is capable of use in various other
combinations
and environments and is capable of changes or modifications within the scope
of
the inventive concept as expressed herein. For example, as can be appreciated,
motor topologies can vary significantly for different numbers of poles, pole
dimensions and configurations, pole compositions, etc. Different numbers of
coil sets and speed range subsets can be chosen to suit particular topologies.
Instead of winding each stator core segment with wires of different gauges,
the
number of turns on each stator core segment can be varied with all wire being
of
the same gauge. The configuration of the coil sections may be varied to meet
optimum efficiency curves for different topologies. Threshold levels may be
adjusted to increase and/or decrease one or more speed ranges, thus setting a
more even or uneven speed range subset distribution.
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