U.S. patent application number 09/766127 was filed with the patent office on 2002-07-25 for method and apparatus for controlling an induction machine.
Invention is credited to Degner, Michael W., Gale, Allan Roy, Liang, Feng.
Application Number | 20020097025 09/766127 |
Document ID | / |
Family ID | 25075483 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020097025 |
Kind Code |
A1 |
Gale, Allan Roy ; et
al. |
July 25, 2002 |
METHOD AND APPARATUS FOR CONTROLLING AN INDUCTION MACHINE
Abstract
An electrical machine (10) suitable for use as a
starter/alternator for an automotive vehicle, has an inverter
circuit (12), a rectifier circuit (14), and a stator circuit (16)
that couples the inverter circuit (12) to the rectifier circuit
(14). In addition, a switch circuit (18) having a first switch,
switch A, and a second switch, switch B, is used to couple inverter
circuit (12) to rectifier circuit (14). By controlling the
operation of switch circuit (18) so that in a start up mode the
switches are closed and in a generating mode the switches are open,
a high output torque may be obtained from the electrical machine
while a wide operating speed range may be also achieved.
Inventors: |
Gale, Allan Roy; (Livonia,
MI) ; Liang, Feng; (Canton, MI) ; Degner,
Michael W.; (Farmington Hills, MI) |
Correspondence
Address: |
Kevin G. Mierzwa
Artz & Artz PLC
Suite 250
28333 Telegraph Road
Southfield
MI
48034
US
|
Family ID: |
25075483 |
Appl. No.: |
09/766127 |
Filed: |
January 20, 2001 |
Current U.S.
Class: |
322/28 ; 322/37;
322/8 |
Current CPC
Class: |
H02P 9/08 20130101 |
Class at
Publication: |
322/28 ; 322/37;
322/8 |
International
Class: |
H02P 009/00 |
Claims
What is claimed is:
1. An electric machine having a power supply comprising: an
inverter circuit; a rectifier circuit; a stator circuit coupling
said inverter circuit to said rectifier circuit; a pair of switches
selectively coupling said inverter circuit to said power supply so
that in a starting mode said switches are closed and in a
generating mode said switches are open.
2. An electrical machine as recited in claim 1 wherein said stator
circuit comprises a plurality of windings having a respective
tapped phase lead.
3. An electrical machine as recited in claim 1 wherein said
plurality of windings are coupled in a wye.
4. An electrical machine as recited in claim 1 wherein said stator
circuit comprises a dual winding configuration wherein a first
winding portion is electrically separated from, co-located with and
magnetically coupled to a second winding.
5. An electrical machine as recited in claim 1 wherein said
electric machine comprises a starter alternator.
6. An electrical machine as recited in claim 1 wherein said pair of
switches are incorporated into said rectifier circuit.
7. An electrical machine as recited in claim 6 further comprising a
pair of diodes coupled between a respective switch and said
inverter circuit.
8. An electrical machine as recited in claim 1 wherein said
rectifier circuit comprises a full wave rectifier.
9. An electric machine having a power supply comprising: an
inverter circuit; a rectifier circuit; a stator circuit coupling
said inverter circuit to said rectifier circuit, said stator
circuit having a first winding, a second winding, and a third
winding coupled in a wye configuration; each winding having a phase
lead coupled to said inverter circuit and tapped phase lead coupled
to said rectifier circuit; and, a pair of switches selectively
coupling said inverter circuit to said power supply so that in a
starting mode said switches are closed and in a generating mode
said switches are open.
10. An electrical machine as recited in claim 9 wherein said tapped
lead having an effective winding turn count less than its
respective winding
11. An electrical machine as recited in claim 9 wherein said
electric machine comprises a starter alternator.
12. An electrical machine as recited in claim 9 wherein said pair
of switches are incorporated into said rectifier circuit.
13. An electrical machine as recited in claim 9 further comprising
a pair of diodes coupled between a respective switch and said
inverter circuit.
14. An electrical machine as recited in claim 9 wherein said
rectifier circuit comprises a full wave rectifier.
15. A method of operating an electrical machine having a power
supply, stator winding circuit, an inverter circuit and a rectifier
circuit comprises the steps of: in a starting mode of operation,
directly coupling the power supply to the inverter circuit though a
pair of switches; in a generating mode of operation, opening the
pair of switches to decouple the inverter circuit from the power
supply.
16. A method as recited in claim 15 wherein said diode bridge
comprises a plurality of diodes, wherein said step of directly
coupling comprises controlling the operation of said plurality of
diodes to be non-conducting.
17. An electrical machine as recited in claim 15 wherein the step
of opening comprises the steps of controlling the operation of said
plurality of diodes to be conducting.
18. An electrical machine as recited in claim 15 wherein the step
of directly coupling comprises controlling the operation of said
plurality of diodes to be non-conducting.
19. An electrical machine as recited in claim 15 wherein the step
of inducing a magnetic field in the stator windings so that power
is supplied to the power supply.
20. An electrical machine as recited in claim 15 further comprising
a capacitor coupled to the inverter circuit, wherein the step of
opening comprises the step of maintaining or increasing the voltage
level across the capacitor as a speed of the electrical machine
increases.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to internal
combustion engines for automotive vehicles, and more specifically,
to an automotive vehicle having a starter/alternator coupled to the
engine.
BACKGROUND
[0002] Automotive vehicles with internal combustion engines are
typically provided with both a starter motor and alternator. In
recent years, a combined alternator and starter motor has been
proposed. During initial startup of the vehicle, the
starter/alternator functions as a starter. While functioning as a
starter, the starter/alternator provides a sufficient amount of
torque to rotate the crankshaft of the engine before the cylinders
are fired.
[0003] After the engine is started, the starter/alternator is used
as a generator to provide electric power to the electrical system
of the vehicle and/or for driveline damping.
[0004] In foreseeable automotive applications, the engine may be
shut down during stops (e.g., red lights). When the accelerator is
depressed the engine will resume firing. Thus, many startups would
occur over the course of a trip. Acceleration in such systems is
inherently low absent intervention since torque levels from the
engine upon startup are low. Thus, starter/alternators may be used
to provide boost torque to help accelerate the vehicle as well.
[0005] As shown in FIG. 1, there are two distinct features that
characterize the torque versus speed requirement of
starter/alternators. The first is the high torque required to
provide cold engine starts. The second distinct feature is the high
generating power requirement in a wide speed range. To meet both
the starting torque and generating power requirements
simultaneously, the stator windings of a starter/alternator are
typically designed with a low number of series turns to allow for a
wider generating speed range. In order to simultaneously meet the
starting torque requirement with a low number of series turns a
high current level is needed, resulting in the starter/alternator
having a relatively high peak current rating which often exceeds
700 amps for a 42-volt electrical system. The high peak current
increases the current rating for the power devices, cabling and
connectors. Also, cost, thermal requirements, electromagnetic
interference and compatibility issues are also raised.
[0006] It would therefore be desirable to provide a
starter/alternator capable of operating with a decreased peak
current requirement during starting and which operates with an
extended speed range for generating.
[0007] Known methods for accomplishing these goals include
reconfiguring the stator windings from series to parallel or by
changing them from a wye to a delta winding configuration. These
types of configurations allow the stator winding to have a greater
number of series turns during starting than during generating.
Typically, however, such systems are very complex and costly due to
the mechanical switches needed to provide the reconfiguration.
[0008] Another known method for achieving these goals is to provide
a DC to DC boost converter to supply the inverter and the machine
with an increased voltage during the generating mode over that of
the nominal battery power provided in the vehicle. This allows the
number of series turns in the stator windings to be increased,
which decreases the amount of current needed to achieve the same
starting torque. The cost associated with such a DC to DC converter
is typically prohibitive.
[0009] It would therefore also be desirable to avoid the
above-mentioned problems of reconfiguring the stator windings or
adding a DC to DC converter to allow high starting torque and a
wide speed range.
SUMMARY OF THE INVENTION
[0010] It is therefore one object of the invention to provide an
improved integrated starter/alternator system suitable for use as a
starter motor that allows high torque to be achieved during
starting while providing a high generating power requirement over a
wide range of speeds.
[0011] In one aspect of the invention, the system comprises an
inverter circuit, a rectifier circuit and an electric machine,
which has a stator circuit coupling to the inverter circuit and the
rectifier circuit. A pair of switches selectively couples the
rectifier circuit to the inverter circuit so that in a startup mode
the switches are closed and in a generator mode the switches are
open.
[0012] In a further aspect of the invention, a method of operating
a system having a power supply, an electric machine with a stator
winding circuit, an inverter circuit and a rectifier circuit
comprises the steps of:
[0013] in a starting mode of operation, directly coupling the power
supply to the inverter circuit though a pair of switches;
[0014] in a generating mode of operation, opening the pair of
switches to decouple the inverter circuit from the power
supply.
[0015] One advantage of the invention is that the current capacity
required for the wiring and connectors is substantially reduced.
This is true even though a higher voltage requirement exists for
such configurations.
[0016] Another advantage of the invention is that the relatively
large number of series turns connected to the inverter portion of
the controller is such that the amount of magnetizing current is
lower when compared with a lower turn number machine design. This
reduces the inverter switching and conduction losses. Yet another
advantage of the invention is that the turns ratio between the two
stator coil groups may be changed depending on the particular
system requirements.
[0017] Other objects and features of the present invention will
become apparent when viewed in light of the detailed description of
the preferred embodiment when taken in conjunction with the
attached drawings and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a plot of torque versus speed requirement of a
starter/alternator for an automotive vehicle.
[0019] FIG. 2 is a schematic view of an electric machine formed
according to the present invention.
[0020] FIG. 3 is a partial schematic view of an alternative stator
circuit according to the present invention.
[0021] FIG. 4 is a plot of torque versus speed for various
operating modes of a starter/alternator according to the present
invention.
[0022] FIG. 5 is a schematic view of an alternative electric
machine circuit according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] In the following figures, the same reference numerals will
be used to identify the same components in the various views. The
present invention is described with respect to a starter/alternator
for an automotive vehicle. However, those skilled in the art will
recognize other applications for the electrical machine that
require a high starting torque and a generator that operates in a
wide speed range.
[0024] Referring now to FIG. 2, a schematic view of an electrical
machine system 10 that is suitable for use as a starter/alternator
in an automotive vehicle, is illustrated. Electrical machine system
10 has an inverter circuit 12 and a rectifier circuit 14. A stator
circuit 16 of the electrical machine is coupled between inverter
circuit 12 and rectifier circuit 14. A switch circuit 18
selectively couples inverter circuit 12 to rectifier circuit 14 in
addition to stator circuit 16. Switch circuit 18 comprises a first
switch, switch A, and a second switch, switch B. As illustrated,
switches A and B are illustrated as mechanical type switches.
However, those skilled in the art will recognize that various types
of switches including electrical switches may be incorporated as
long as they are capable of functioning as described below.
Preferably, switches A and B operate simultaneously.
[0025] Inverter circuit 12 includes a plurality of switching
element 20A-20F and a capacitor 22. switching element may include
transistors and diode as is commonly known in the art. Inverter
circuit 12 is used to control the operation of stator circuit 16 as
will be further described below. In addition to the elements shown,
the inverter 12 includes control circuitry for controlling the
switching elements 20A-20F in a desirable manner.
[0026] Inverter circuit 12 is coupled to a feed bus 24 and a return
bus 26 of electrical machine 10. Each switching element is coupled
to either feed bus 24 or return bus 26. In the present
configuration, switching elements 20A, 20C, and 20E are coupled to
feed bus 24. Switching elements 20B, 20D, and 20F are coupled to
return bus 26. Switching elements 20A and 20B have a common node N1
therebetween. Switching elements 20C and 20D have a common node N2
therebetween. Switching elements 20E and 20F have a common node N3
therebetween.
[0027] Rectifier circuit 14 is preferably a full wave rectifier
having diodes D1-D6. Diodes D1, D3, and D5 are coupled to feed bus
24. As pictured, diodes D1, D3, and D5 have the cathode coupled to
feed bus 24. Diodes D2, D4, and D6 are coupled to return bus 26.
That is, diodes D2, D4, and D6 have anodes 26 coupled to return bus
26. Diodes D5 and D6 have a common node N4 therebetween. Diodes D3
and D4 have a common node N5 therebetween. Diodes D1 and D2 have a
common node N6 therebetween.
[0028] Each of the diodes pairs D1 and D2, D3 and D4, and D5 and D6
have a respective anode coupled to a respective cathode. Stator
circuit 16 generally comprises three windings configured in a
predetermined manner. As will be further described below,
alternative phase winding configurations may be used without
varying from the true scope of the invention. In this embodiment,
three windings 28A, 28B, and 28C each have a respective phase lead
30A, 30B, and 30C coupled to nodes N3, N2, and N1 respectively of
inverter circuit 12. Windings 28A, 28B, and 28C have a common node
N7 therebetween representing the common node of a wye
configuration. Each of the windings has a phase lead 32A, 32B, and
32C coupled to nodes N6, N7, and N8 respectively of rectifier
circuit 14 . Phase leads 32A, 32B, and 32C are coupled to windings
28A, 28B, and 28C as a tapped phase lead.
[0029] A power supply 34 such as a battery is coupled to feed bus
24 and return bus 26 so that the positive lead of the power supply
34 is coupled to feed bus 24 and the neutral side of the battery is
coupled to return bus 26.
[0030] Referring now to FIG. 3, an alternative embodiment of stator
circuit 16' is illustrated having a dual winding configuration.
Rather than using a tapped winding as shown in FIG. 2, stator
circuit 16' has a first winding 40A, 40B, and 40C coupled in a wye
configuration and a co-located second winding 42A, 42B, and 42C
having respective phase leads 44A, 44B, and 44C coupled to
rectifier circuit 14. The winding count of the first winding is
preferably more than the second winding count. Windings 40A, 40B,
and 40C are connected to the inverter circuit.
[0031] Those skilled in the art will recognize that additional
stator winding configurations exist that may be used with the
present invention. An example is a tapped stator winding. In this
configuration the inner portion of the stator winding, which is
connected to the rectifier circuit, could be connected in either a
wye or a delta configuration. Other examples include a dual stator
winding configuration where either or both sets of stator windings
could be connected in a delta arrangement instead of a wye
arrangement.
[0032] The operation of the circuits shown in FIGS. 2 and 3 is
similar and therefore will be discussed simultaneously below.
[0033] In operation, two distinct modes of operation are present, a
starting mode and a generating mode. Switches A and B are
preferably simultaneously controlled. In starting mode, switches A
and B are closed and inverter circuit 12 is operated in a manner to
achieve the desired starting torque. In starting mode, operation is
at a relatively low speed relative to the peak speed of electrical
machine 10. Therefore, the back EMF in the machine is relatively
low and diodes D1-D6 in the rectifier circuit 14 do not conduct.
When electrically viewed from the inverter terminals, electrical
machine 10 appears to have a relatively large number of series
turns in starting mode.
[0034] In generating mode, switches A and B are opened to
disconnect battery 34 from inverter 12. Inverter circuit 12 is
operated so that the windings connected to nodes N1, N2, and N3 are
excited with the necessary magnetizing field needed by the machine.
The magnetic field created by this excitation induces a voltage in
the stator windings that are connected to the diodes of rectifier
circuit 14. The induced voltage in the stator windings causes the
diodes to conduct and therefore power is generated back into the
battery and the electrical system of the vehicle. The amounts of
power generated can be controlled by varying the level of
magnetization excitation supply from inverter circuit 12.
[0035] Referring now to FIG. 4, a torque versus speed plot of the
electrical machine shown in FIG. 2 is illustrated. The torque
versus speed plot is dependent on the number of turns chosen for
the coil groups in each of the stator phase windings for a given
phase current of the electric machine. The number of turns in the
two coil groups may be chosen independently. This is in contrast to
the switch configuration described in the background in which only
a fixed ratio may be used.
[0036] As represented in FIG. 5, several modes of operation are
illustrated. Essentially, four modes of operation are illustrated
in FIG. 5. The first two modes of operation are when the inverter
circuit 12 is coupled directly to the power supply 34. If the
electrical machine 10 is properly controlled in this mode of
operation, diodes D1-D6 will not conduct and the capability of
electrical machine 10 is equivalent to that of a machine with the
same total series turn in the stator winding operated using an
inverter at the voltage level of power supply 34.
[0037] In a second mode of operation, the generating capability of
the machine and the rectifier circuit 14 is illustrated. In this
mode, inverter circuit 12 is operated to provide the necessary
excitation to the machine so that diodes D1-D6 of rectifier circuit
14 conduct. The generating capability is shown for the same current
rating in the inverter and diode rectifier portion. It should be
noted, however, that the same current rating is not a
requirement.
[0038] The final two capabilities shown in the figure are for the
mode of operation where inverter circuit 12 is disconnected from
the power supply 34 and operate to produce transient motoring or
generating torque. These are illustrated as dashed lines in FIG. 5.
Because of these configurations, all of the energy required to
produce the transient torque or generated by the transient torque
must either come from or be stored in capacitor 22. Because the
capacitor has a size limit and voltage rating, only a limited
operating capability in this region is possible and therefore the
transient label is given thereto. The extended constant torque
region for the transient mode of operation is a result of the
increased voltage required in the inverter portion of the
controller in order to supply the required magnetization excitation
as the speed of the electrical machine 10 increases.
[0039] In the specific operation of the circuit, when inverter
circuit 12 is disconnected from power supply 34, the charge in
capacitor 22 connected thereacross needs to be maintained at a
level so that there is a sufficient voltage to supply the required
magnetic field. Therefore, inverter circuit 12 is controlled to
produce not only the magnetization current but also a small
torque-producing component of current. The required magnitude of
this torque-producing current is such that it offsets the losses
associated with providing the magnetization excitation to the
machine, thereby maintaining the desired voltage in the capacitor.
As the speed of the electrical machine 10 increases, the voltage
needed to supply the required magnetization excitation will
increase. Due to the relatively large number of series turns
connected to the inverter portion of the controller, this voltage
will eventually increase until it is greater than that of power
supply 34, with its peak value being roughly equal to the power
supply voltage times the ratio of the total series stator turns
connected to the inverter circuit to the number of series turns
connected to the rectifier circuit 14. The increased voltage in the
inverter portion of the controller requires switching elements 20
in inverter circuit 12 to have a higher voltage rating than the
diodes D1-D6 in rectifier circuit 14. The increased voltage rating
of the device is offset by the reduced current rating compared to
such configurations described in the background in which a single
set of phase leads and inverter circuit are always connected to the
power supply. Advantageously, the reduced current rating thus
requires reduced current capacity for the wiring and the connectors
associated therewith. Another advantage of the system is that the
higher voltage portion is isolated from other portions in a
vehicle. Also, the short duration of the starting events and
relatively low magnetization current required in the windings
connected to inverter circuit 12 allows the winding wires to be
formed of a higher gauge and thus more room is available in the
slots for the windings connected to rectifier circuit 14 and thus
lowers their resistance and consequently reduces losses.
[0040] There are numerous ways in which the generating load needed
to supply the electrical losses could be controlled. The first
would be to run it continuously with its levels closely matched to
that of the electrical losses. In this method the voltage of the
capacitor across the inverter circuit would stay roughly constant
(with the necessary increase in voltage as the speed increases). A
second method would be to operate the generating load in a pulsed
fashion so that the voltage of the capacitor across inverter
circuit would increase to a higher level while the generating load
was present and then decay to a lower level when the generating
load was removed. The application and removal of the generating
load is determined by the allowable variation in the voltage level
(calibratable). It should be noted that the amount of generating
required on average preferably compensates for electrical losses
associated with the power supply.
[0041] Referring now to FIG. 5, the same reference numerals are
used to identify the same components from FIG. 2. In this circuit,
however, switch A' and switch B' have been moved within rectifier
circuit 14. A pair of diodes D7 and D8 are used to separate
rectifier circuit 14' from inverter circuit 12. In operation of
this circuit during starting mode, switches A and B are opened and
inverter circuit 12 are operated identically to that described
above. The switches A' and B' when used in conjunction with diodes
D7 and D8 prevent circulating current from flowing between
rectifier circuit 14 and inverter 12 during starting mode. The
diodes D7 and D8 clamp the voltage in inverter circuit 12 so it
will not fall below that of power supply 34. Diodes D7 and D8 may
allow the inverter circuit to be at a voltage level higher than
that of the power supply 34 during the starting mode. This
situation would occur if the capacitor across the inverter circuit
were charged to a higher voltage level as may occur during the
generating mode of operation. The presence of a higher voltage
level allows for more energetic starts which would be useful,
especially for a stop/start mode of operation in an automotive
vehicle.
[0042] Another alternative embodiment eliminates switches A' and
switch B' from that shown in FIG. 5. The operation of such is
similar to that described above.
[0043] While particular embodiments of the invention have been
shown and described, numerous variations and alternate embodiments
will occur to those skilled in the art. Accordingly, it is intended
that the invention be limited only in terms of the appended
claims.
* * * * *