U.S. patent application number 16/012136 was filed with the patent office on 2019-12-19 for common mode current reduction hybrid drive system.
The applicant listed for this patent is FORD GLOBAL TECHNOLOGIES, LLC. Invention is credited to Silong LI, Jiyao WANG, Wei XU, Yinghan XU.
Application Number | 20190381890 16/012136 |
Document ID | / |
Family ID | 68724919 |
Filed Date | 2019-12-19 |
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United States Patent
Application |
20190381890 |
Kind Code |
A1 |
WANG; Jiyao ; et
al. |
December 19, 2019 |
COMMON MODE CURRENT REDUCTION HYBRID DRIVE SYSTEM
Abstract
An electric drive system for a vehicle includes an electric
machine having first conductors arranged in slots of a stator to
form phase windings and a second conductor arranged in the slots to
form a secondary winding that produces a voltage indicative of a
common mode voltage caused by voltages applied to the phase
windings. The voltage can be used to supply power to electronic
components and for diagnosis and control of the electric machine
and an associated inverter.
Inventors: |
WANG; Jiyao; (Canton,
MI) ; XU; Wei; (Canton, MI) ; XU; Yinghan;
(San Jose, CA) ; LI; Silong; (Canton, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FORD GLOBAL TECHNOLOGIES, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
68724919 |
Appl. No.: |
16/012136 |
Filed: |
June 19, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60L 1/00 20130101; B60L
50/51 20190201; B60L 2210/30 20130101; B60L 3/0061 20130101; B60L
2210/42 20130101; B60L 2220/54 20130101; B60L 15/007 20130101; B60L
50/60 20190201; B60L 3/003 20130101; B60L 2240/429 20130101; B60L
2220/58 20130101; B60L 53/22 20190201; B60L 53/14 20190201; B60L
2240/427 20130101; B60L 2210/46 20130101 |
International
Class: |
B60L 11/18 20060101
B60L011/18; B60L 15/00 20060101 B60L015/00 |
Claims
1. An electric machine comprising: a rotor; a stator defining a
plurality of teeth separated by slots; first conductors arranged in
the slots to form phase windings for driving the rotor; and a
second conductor arranged in the slots to form a secondary winding
configured to produce a voltage indicative of a common mode voltage
caused by phase voltages applied to the phase windings, wherein the
second conductor passes through some of the slots that include the
first conductors such that the voltage includes an induced voltage
component from each of the phase windings.
2. (canceled)
3. The electric machine of claim 1 wherein a cross-sectional area
of the second conductor is less than a cross-sectional area of the
first conductors.
4. The electric machine of claim 1 wherein the second conductor is
arranged in some of the slots that define more than one pole-pair
of the electric machine.
5. The electric machine of claim 1 wherein the second conductor is
configured to have an impedance that is lower than an impedance
associated with an impedance path through a bearing of the electric
machine.
6. An electric drive system comprising: an electric machine
including first conductors arranged in slots of a stator to form
phase windings and a second conductor arranged in the slots to from
a secondary winding that produces a voltage indicative of a common
mode voltage caused by phase voltages applied to the phase
windings; and a circuit configured to receive the voltage and power
an electronic device, wherein the circuit includes a rectifier and
a capacitor that are configured to convert the voltage to a
generally constant voltage level.
7. The electric drive system of claim 6 wherein the second
conductor passes through some of the slots that include the first
conductors such that the voltage includes an induced component from
each of the phase windings.
8. (canceled)
9. The electric drive system of claim 6 wherein the electronic
device includes a gate driver of an inverter that is configured to
drive switching devices.
10. The electric drive system of claim 6 wherein the electric
machine further includes a third conductor arranged in some of the
slots to form a second secondary winding that produces a second
voltage indicative of the common mode voltage.
11. The electric drive system of claim 10 wherein the third
conductor is arranged in the slots that the second conductor is
arranged in.
12. The electric drive system of claim 10 further comprising a
second circuit that is configured to receive the second voltage and
output a diagnostic signal.
13. The electric drive system of claim 12 wherein the second
circuit includes an analog to digital converter configured to
convert the diagnostic signal to a digital value.
14. A vehicle comprising: an electric machine including first
conductors arranged in slots of a stator to form phase windings and
a second conductor arranged in the slots to form a secondary
winding that produces a voltage indicative of a common mode voltage
caused by voltages applied to the phase windings; and a controller
configured to operate an inverter according to the voltage to
reduce a common mode current in the electric machine and to control
a switching frequency of switching devices based on the
voltage.
15. The vehicle of claim 14 wherein the second conductor passes
through some of the slots that include the first conductors such
that the voltage includes an induced component from each of the
phase windings.
16. (canceled)
17. The vehicle of claim 14 wherein the electric machine further
includes a third conductor arranged in the slots to form a second
secondary winding that produces a second voltage indicative of the
common mode voltage.
18. The vehicle of claim 17 further comprising a circuit configured
to receive the second voltage and power an electronic device.
19. The vehicle of claim 18 wherein the circuit includes a
rectifier and a capacitor that are configured to convert the second
voltage to a generally constant voltage level.
20. The vehicle of claim 14 wherein the second conductor is
configured to have an impedance that is lower than an impedance
associated with an impedance path through a bearing of the electric
machine.
Description
TECHNICAL FIELD
[0001] This application is generally related to a common mode
current reduction system for a hybrid drive system of an
electrified vehicle.
BACKGROUND
[0002] Electrified vehicles including hybrid-electric vehicles
(HEVs) and battery electric vehicles (BEVs) rely on a traction
battery to provide power to a traction motor for propulsion and a
power inverter therebetween to convert direct current (DC) power to
alternating current (AC) power. The typical AC traction motor is a
three-phase motor that may be powered by three sinusoidal signals
each driven with 120 degrees phase separation. Modern power
inverters output a pulse-width modulated voltage to each of the
phases and the traction motor impedance results in generally
sinusoidal currents. The pulse width modulated voltage causes a
common-mode voltage within the traction motor that results in a
common-mode current flowing through parts of the traction
motor.
SUMMARY
[0003] An electric machine includes a rotor and a stator defining a
plurality of teeth separated by slots. The electric machine
includes first conductors arranged in the slots to form phase
windings for driving the rotor. The electric machine further
includes a second conductor arranged in the slots to form a
secondary winding configured to produce a voltage indicative of a
common mode voltage caused by phase voltages applied to the phase
windings.
[0004] The second conductor may pass through some of the slots that
include the first conductors such that the voltage includes an
induced voltage component from each of the phase windings. A
cross-sectional area of the second conductor may be less than a
cross-sectional area of the first conductors. The second conductor
may be arranged in some of the slots that define more than one
pole-pair of the electric machine. The second conductor may be
configured to have an impedance that is lower than an impedance
associated with an impedance path through a bearing of the electric
machine.
[0005] An electric drive system includes an electric machine
including first conductors arranged in slots of a stator to form
phase windings and a second conductor arranged in the slots to form
a secondary winding that produces a voltage indicative of a common
mode voltage caused by phase voltages applied to the phase
windings. The electric drive system further includes a circuit
configured to receive the voltage and power an electronic
device.
[0006] The second conductor may pass through some of the slots that
include the first conductors such that the voltage includes an
induced component from each of the phase windings. The circuit may
include a rectifier and a capacitor that are configured to convert
the voltage to a generally constant voltage level. The electronic
device may include a gate driver of an inverter that is configured
to drive switching devices. The electric machine may further
include a third conductor arranged in the slots to form a second
secondary winding that produces a second voltage indicative of the
common mode voltage. The third conductor may be arranged in the
slots that the second conductor is arranged in. The electric drive
system may further include a second circuit that is configured to
receive the second voltage and output a diagnostic signal. The
second circuit may include an analog to digital converter
configured to convert the diagnostic signal to a digital value.
[0007] A vehicle includes an electric machine including first
conductors arranged in slots of a stator to form phase windings and
a second conductor arranged in the slots to form a secondary
winding that produces a voltage indicative of a common mode voltage
caused by voltages applied to the phase windings. The vehicle
further includes a controller configured to operate an inverter
according to the voltage to reduce a common mode current in the
electric machine.
[0008] The second conductor may pass through some of the slots that
include the first conductors such that the voltage includes an
induced component from each of the phase windings. The controller
may be configured to control a switching frequency of switching
devices based on the voltage. The electric machine may further
include a third conductor arranged in the slots to form a second
secondary winding that produces a second voltage indicative of the
common mode voltage. The circuit may be configured to receive the
second voltage and power an electronic device. The circuit may
include a rectifier and a capacitor that are configured to convert
the second voltage to a generally constant voltage level. The
second conductor may be configured to have an impedance that is
lower than an impedance associated with an impedance path through a
bearing of the electric machine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a diagram of an electrified vehicle including an
electric machine with secondary windings.
[0010] FIG. 2 is a diagram of an electrified vehicle illustrating
typical electric drivetrain and energy storage components including
an inverter.
[0011] FIG. 3 is a schematic diagram of a power electronics module
coupled to an electric machine.
[0012] FIG. 4 is a schematic diagram of a power inverter and
electric machine with a common mode current reduction circuit.
[0013] FIG. 5 is an exploded view of an electric machine
illustrating stator teeth and a rotor.
[0014] FIG. 6 is a cross sectional view of a stator core for an
electric machine illustrating power windings and common mode
voltage windings to form a common mode transformer.
[0015] FIG. 7 is a wiring diagram of a common mode voltage winding
for a stator core.
[0016] FIG. 8 is a cross sectional diagram of a configuration of
stator windings.
[0017] FIG. 9 is a schematic diagram of a common mode voltage
transformer.
[0018] FIG. 10 is a schematic diagram of a common mode voltage
transformer isolation circuit.
[0019] FIG. 11 is a schematic diagram of a common mode voltage
transformer isolation circuit configured as a digital and analog
diagnostic sensor.
DETAILED DESCRIPTION
[0020] Embodiments of the present disclosure are described herein.
It is to be understood, however, that the disclosed embodiments are
merely examples and other embodiments can take various and
alternative forms. The figures are not necessarily to scale; some
features could 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
skilled 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 can 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.
Various combinations and modifications of the features consistent
with the teachings of this disclosure, however, could be desired
for particular applications or implementations.
[0021] FIG. 1 depicts a hybrid electric vehicle illustrating
internal electric powertrain components configured to implement
secondary windings in an electric machine to form a common-mode
voltage (CMV) transformer. A battery 2 may be coupled to an
inverter 4. The inverter 4 may be configured with outputs to drive
phase windings 6A, 6B, 6C of an electric machine 8. The electric
machine 8 further includes a first secondary winding 10A and a
second secondary winding 10B. The first secondary winding 10A may
be electrically coupled to a rectifier circuit 12. The second
secondary winding 10B may be coupled to a diagnostic circuit
14.
[0022] FIG. 2 depicts an electrified vehicle 112 that may be
referred to as a plug-in hybrid-electric vehicle (PHEV). A plug-in
hybrid-electric vehicle 112 may comprise one or more electric
machines 114 mechanically coupled to a hybrid transmission 116. The
electric machines 114 may be capable of operating as a motor or a
generator. In addition, the hybrid transmission 116 is mechanically
coupled to an engine 118. The hybrid transmission 116 is also
mechanically coupled to a drive shaft 120 that is mechanically
coupled to the wheels 122. The electric machines 114 can provide
propulsion and deceleration capability when the engine 118 is
turned on or off. The electric machines 114 may also act as
generators and can provide fuel economy benefits by recovering
energy that would normally be lost as heat in a friction braking
system. The electric machines 114 may also reduce vehicle emissions
by allowing the engine 118 to operate at more efficient speeds and
allowing the hybrid-electric vehicle 112 to be operated in electric
mode with the engine 118 off under certain conditions. An
electrified vehicle 112 may also be a battery electric vehicle
(BEV). In a BEV configuration, the engine 118 may not be present.
In other configurations, the electrified vehicle 112 may be a full
hybrid-electric vehicle (FHEV) without plug-in capability.
[0023] A traction battery or battery pack 124 stores energy that
can be used by the electric machines 114. The vehicle battery pack
124 may provide a high-voltage direct current (DC) output. The
traction battery 124 may be electrically coupled to one or more
power electronics modules 126. One or more contactors 142 may
isolate the traction battery 124 from other components when opened
and connect the traction battery 124 to other components when
closed. The power electronics module 126 is also electrically
coupled to the electric machines 114 and provides the ability to
bi-directionally transfer energy between the traction battery 124
and the electric machines 114. For example, a traction battery 124
may provide a DC voltage while the electric machines 114 may
operate with a three-phase alternating current (AC) to function.
The power electronics module 126 may convert the DC voltage to a
three-phase AC current to operate the electric machines 114. In a
regenerative mode, the power electronics module 126 may convert the
three-phase AC current from the electric machines 114 acting as
generators to the DC voltage compatible with the traction battery
124.
[0024] The vehicle 112 may include a variable-voltage converter
(VVC) 152 electrically coupled between the traction battery 124 and
the power electronics module 126. The VVC 152 may be a DC/DC boost
converter configured to increase or boost the voltage provided by
the traction battery 124. By increasing the voltage, current
requirements may be decreased leading to a reduction in wiring size
for the power electronics module 126 and the electric machines 114.
Further, the electric machines 114 may be operated with better
efficiency and lower losses.
[0025] In addition to providing energy for propulsion, the traction
battery 124 may provide energy for other vehicle electrical
systems. The vehicle 112 may include a DC/DC converter module 128
that converts the high-voltage DC output of the traction battery
124 to a low voltage DC supply that is compatible with low-voltage
vehicle loads. An output of the DC/DC converter module 128 may be
electrically coupled to an auxiliary battery 130 (e.g., 12V
battery) for charging the auxiliary battery 130. The low-voltage
systems may be electrically coupled to the auxiliary battery 130.
One or more electrical loads 146 may be coupled to the high-voltage
bus. The electrical loads 146 may have an associated controller
that operates and controls the electrical loads 146 when
appropriate. Examples of electrical loads 146 may be a fan, an
electric heating element and/or an air-conditioning compressor.
[0026] The electrified vehicle 112 may be configured to recharge
the traction battery 124 from an external power source 136. The
external power source 136 may be a connection to an electrical
outlet. The external power source 136 may be electrically coupled
to a charger or electric vehicle supply equipment (EVSE) 138. The
external power source 136 may be an electrical power distribution
network or grid as provided by an electric utility company. The
EVSE 138 may provide circuitry and controls to regulate and manage
the transfer of energy between the power source 136 and the vehicle
112. The external power source 136 may provide DC or AC electric
power to the EVSE 138. The EVSE 138 may have a charge connector 140
for plugging into a charge port 134 of the vehicle 112. The charge
port 134 may be any type of port configured to transfer power from
the EVSE 138 to the vehicle 112. The charge port 134 may be
electrically coupled to a charger or on-board power conversion
module 132. The power conversion module 132 may condition the power
supplied from the EVSE 138 to provide the proper voltage and
current levels to the traction battery 124. The power conversion
module 132 may interface with the EVSE 138 to coordinate the
delivery of power to the vehicle 112. The EVSE connector 140 may
have pins that mate with corresponding recesses of the charge port
134. Alternatively, various components described as being
electrically coupled or connected may transfer power using a
wireless inductive coupling.
[0027] One or more wheel brakes 144 may be provided for
decelerating the vehicle 112 and preventing motion of the vehicle
112. The wheel brakes 144 may be hydraulically actuated,
electrically actuated, or some combination thereof. The wheel
brakes 144 may be a part of a brake system 150. The brake system
150 may include other components to operate the wheel brakes 144.
For simplicity, the figure depicts a single connection between the
brake system 150 and one of the wheel brakes 144. A connection
between the brake system 150 and the other wheel brakes 144 is
implied. The brake system 150 may include a controller to monitor
and coordinate the brake system 150. The brake system 150 may
monitor the brake components and control the wheel brakes 144 for
vehicle deceleration. The brake system 150 may respond to driver
commands and may also operate autonomously to implement features
such as stability control. The controller of the brake system 150
may implement a method of applying a requested brake force when
requested by another controller or sub-function.
[0028] Electronic modules in the vehicle 112 may communicate via
one or more vehicle networks. The vehicle network may include a
plurality of channels for communication. One channel of the vehicle
network may be a serial bus such as a Controller Area Network
(CAN). One of the channels of the vehicle network may include an
Ethernet network defined by Institute of Electrical and Electronics
Engineers (IEEE) 802 family of standards. Additional channels of
the vehicle network may include discrete connections between
modules and may include power signals from the auxiliary battery
130. Different signals may be transferred over different channels
of the vehicle network. For example, video signals may be
transferred over a high-speed channel (e.g., Ethernet) while
control signals may be transferred over CAN or discrete signals.
The vehicle network may include any hardware and software
components that aid in transferring signals and data between
modules. The vehicle network is not shown in FIG. 2 but it may be
implied that the vehicle network may connect to any electronic
module that is present in the vehicle 112. A vehicle system
controller (VSC) 148 may be present to coordinate the operation of
the various components.
[0029] With reference to FIG. 3, a system 300 is provided for
controlling a power electronics module (PEM) 126. The PEM 126 of
FIG. 3 is shown to include a plurality of switches 302 configured
to collectively operate as an inverter with first, second, and
third phase legs 316, 318, 320. While the inverter is shown as a
three-phase power converter, the inverter may include additional
phase legs. For example, the inverter may be a four-phase power
converter, a five-phase power converter, a six-phase power
converter, etc. In addition, the PEM 126 may include multiple
converters with each inverter in the PEM 126 including three or
more phase legs. For example, the system 300 may include two or
more inverters in the PEM 126. The PEM 126 may further include a
DC-DC converter having high-power switches (e.g., IGBTs) to convert
a power electronics module input voltage to a power electronics
module output voltage via boost, buck or a combination thereof.
[0030] The switches 302 may be solid state devices (SSD) such as
Insulated Gate Bipolar Junction Transistors (IGBTs), Metal Oxide
Semiconductor Field Effect Transistors (MOSFETs), or Bipolar
Junction Transistors (BJTs). Operation of an IGBT and a MOSFET is
voltage controlled, in which the operation is based on a voltage
applied to a gate of the IGBT or MOSFET, while operation of a BJT
is current controlled, in which the operation is based on a current
applied to a base of the BJT. Here, the use of SSDs or high-power
relays may be used to control, alter, or modulate a current between
a battery and an electric machine of a vehicle.
[0031] As shown in FIG. 3, the inverter may be a DC-AC converter.
In operation, the DC-AC converter receives DC power from a DC power
link 306 through a DC bus 304 and converts the DC power to AC
power. The DC power bus may include a positive bus conductor 304A
and a return bus conductor 304B. The AC power may be transmitted
via the phase currents ia, ib, and ic to drive an AC machine also
referred to as the electric machine 114, such as a three-phase
permanent-magnet synchronous motor (PMSM) as depicted in FIG. 3. In
such an example, the DC power link 306 may be electrically coupled
to a DC storage battery (e.g., traction battery 124) to provide DC
power to the DC bus 304. In another example, the inverter may
operate as an AC-DC converter that converts AC power from the
electric machine 114 (e.g., operating as a generator) to DC power
that the DC bus 304 can transfer to the DC power link 306.
Furthermore, the system 300 may control the PEM 126 in other power
electronic topologies.
[0032] With continuing reference to FIG. 3, each of the phase leg
outputs 316, 318, 320 in the inverter 126 are coupled to associated
power switches 302, which may be implemented by various types of
controllable switches. In one embodiment, each power switch 302 may
include a diode and a transistor, (e.g., an IGBT). The diodes of
FIG. 3 are labeled D.sub.a1, D.sub.a2, D.sub.b1, D.sub.b2,
D.sub.c1, and D.sub.c2 while the IGBTs of FIG. 3 are respectively
labeled S.sub.a1, S.sub.a2, S.sub.b1, S.sub.b2, S.sub.c1, and
S.sub.c2. The power switches S.sub.a1, S.sub.a2, D.sub.a1, and
D.sub.a2 are part of phase leg A of the three-phase inverter 126,
which is labeled as the first phase leg A 316 in FIG. 3. Similarly,
the power switches S.sub.b1, S.sub.b2, D.sub.b1, and D.sub.b2 are
part of phase leg B 318 and the power switches S.sub.c1, S.sub.c2,
D.sub.c1, and D.sub.c2 are part of phase leg C 320 of the
three-phase converter. The inverter 126 may include any number of
the power switches 302 or circuit elements depending on the
particular configuration of the inverter 126. The diodes (D.sub.xx)
are connected in parallel with the IGBTs (S.sub.xx). However, as
the polarities are reversed for proper operation, this
configuration is often referred to as being connected
anti-parallel. A diode in this anti-parallel configuration is also
called a freewheeling diode.
[0033] As illustrated in FIG. 3, current sensors CS.sub.a,
CS.sub.b, and CS.sub.c may be provided to sense current flow in the
respective phase legs 316, 318, 320. FIG. 3 depicts the current
sensors CS.sub.a, CS.sub.b, and CS.sub.c as being separate from the
PEM 126. However, the current sensors CS.sub.a, CS.sub.b, and
CS.sub.c may be integrated as part of the PEM 126 depending on the
configuration. Current sensors CS.sub.a, CS.sub.b, and CS.sub.c of
FIG. 3 may be installed in series with each of phase legs A, B and
C (i.e., phase legs 316, 318, 320 in FIG. 3) and provide respective
feedback signals for the phase currents i.sub.as, i.sub.bs, and
i.sub.cs (also illustrated in FIG. 3) of the system 300. The
feedback signals i.sub.as, i.sub.bs, and i.sub.cs may be raw
current signals processed by logic device (LD) 310 or may be
embedded or encoded with data or information about the current flow
through the respective phase legs 316, 318, 320. Also, the power
switches 302 (e.g., IGBTs) may include current sensing capability.
The current sensing capability may include being configured with a
current mirror output, which may provide data/signals
representative of i.sub.as, i.sub.bs, and i.sub.cs. The
data/signals may indicate a direction of current flow, a magnitude
of current flow, or both the direction and magnitude of current
flow through the respective phase legs A, B, and C.
[0034] Referring again to FIG. 3, the system 300 includes a logic
device (LD) or controller 310. The controller or LD 310 can be
implemented by various types or combinations of electronic devices
and/or microprocessor-based computers or controllers. To implement
a method of controlling the PEM 126, the controller 310 may execute
a computer program or algorithm embedded or encoded with the method
and stored in volatile and/or persistent memory 312. Alternatively,
logic may be encoded in discrete logic, a microprocessor, a
microcontroller, or a logic or gate array stored on one or more
integrated circuit chips. As shown in the embodiment of FIG. 3, the
controller 310 receives and processes the feedback signals
i.sub.as, i.sub.bs, and i.sub.cs to control the phase currents
i.sub.a, i.sub.b, and i.sub.c such that the phase currents i.sub.a,
i.sub.b, and i.sub.c flow through the phase legs 316, 318, 320 and
into the respective phase windings of the electric machine 114
according to various current or voltage patterns. For example,
current patterns can include patterns of phase currents i.sub.a,
i.sub.b, and i.sub.c flowing into and away from the DC-bus 304 or a
DC-bus capacitor 308. The DC-bus capacitor 308 of FIG. 3 is shown
separate from the PEM 126. However, the DC-bus capacitor 308 may be
integrated as part of the PEM 126.
[0035] As shown in FIG. 3, a storage medium 312 (hereinafter
"memory"), such as computer-readable memory may store the computer
program or algorithm embedded or encoded with the method. In
addition, the memory 312 may store data or information about the
various operating conditions or components in the PEM 126. The
memory 312 may include both persistent and non-persistent memory
devices. For example, persistent memory may include read-only
memory (ROM), FLASH memory, and magnetic storage. Non-persistent
memory may include random access memory (RAM). The memory 312 may
store data or information about current flow through the respective
phase legs 316, 318, 320. The memory 312 can be part of the
controller 310 as shown in FIG. 3. However, the memory 312 may be
positioned in any suitable location accessible by the controller
310.
[0036] As illustrated in FIG. 3, the controller 310 may transmit at
least one control signal 322 to the power converter system 126. The
power converter system 126 may receive the control signal 322 and
control the switching configuration of the inverter 126 to control
the current flow through the respective phase legs 316, 318, and
320. The switching configuration may be a set of switching states
of the power switches 302 in the inverter 126. In general, the
switching configuration of the inverter 126 determines how the
inverter 126 converts power between the DC power link 306 and the
electric machine 114.
[0037] To control the switching configuration of the inverter 126,
the inverter 126 changes the switching state of each power switch
302 in the inverter 126 to either an ON state or an OFF state based
on the control signal 322. In the illustrated embodiment, to switch
the power switch 302 to either ON or OFF states, the controller/LD
310 provides the gate voltage (Vg) to each power switch 302 and
therefore drives the switching state of each power switch 302. Gate
voltages Vg.sub.a1, Vg.sub.a2, Vg.sub.b1, Vg.sub.b2, Vg.sub.c1, and
Vg.sub.c2 (shown in FIG. 3) control the switching state and
characteristics of the respective power switches 302. While the
inverter 126 is shown as a voltage-driven device in FIG. 3, the
inverter 126 may be a current-driven device or controlled by other
strategies that switch the power switches 302 between ON and OFF
states. The controller 310 may change the gate drive for each of
the power switches 302 based on the rotational speed of the
electric machine 114, the mirror current, or a temperature of the
power switch. The change in gate drive may be selected from a
plurality of gate drive currents in which the change gate drive
current is proportional to a change in switching speed of the power
switches.
[0038] As also shown in FIG. 3, each phase leg 316, 318, and 320
includes two switches 302. In general, each phase leg includes a
switch coupled between the positive bus conductor 304A and the
associated phase leg output (upper switch) and a switch coupled
between the return bus conductor 304B and the associated phase leg
output (lower switch). However, only one switch in each of the legs
316, 318, 320 may be in the ON state without shorting the DC power
link 306. Thus, in each phase leg, the switching state of the lower
switch is typically opposite the switching state of the
corresponding upper switch. The upper switches may be referred to
as high-side switches (i.e., 302A, 302B, 302C) and the lower
switches may be referred to as low-side switches (i.e., 302D, 302E,
302F). Consequently, a HIGH state of a phase leg refers to the
upper switch in the leg in the ON state with the lower switch in
the OFF state. Likewise, a LOW state of the phase leg refers to the
upper switch in the leg in the OFF state with the lower switch in
the ON state. IGBTs with current mirror capability may be on all
IGBTs, a subset of IGBTs (e.g., S.sub.a1, S.sub.b1, S.sub.c1) or a
single IGBT.
[0039] Two situations can occur during an active state of the
three-phase converter example illustrated in FIG. 3: (1) two of the
phase legs may be in the HIGH state while the third phase leg is in
the LOW state, or (2) one phase leg may be in the HIGH state while
the other two of the phase legs are in the LOW state. Thus, one
phase leg in the three-phase converter, which may be defined as the
"reference" phase for a specific active state of the inverter, is
in a state opposite to the other two of the phase legs, or
"non-reference" phases, that have the same state. Consequently, the
non-reference phases are either both in the HIGH state or both in
the LOW state during an active state of the inverter.
[0040] The power switches 302 may be controlled with a Pulse-Width
Modulated (PWM) gate control signal. The gate control signal may be
further characterized with a switching frequency. The switching
frequency may define a fastest rate at which a duty cycle of the
PWM gate signal may be changed. By controlling the duty cycle of
the gate control signals, a sinusoidal current output for each
phase leg may be achieved. The voltage at the phase leg output may
achieve two levels depending upon the switching state. The two
levels are the positive bus voltage and the return bus voltage. The
LD 310 may be programmed to vary the duty cycle of the gate control
signals to achieve a sinusoidal current through the phase windings.
However, because the voltages are not sinusoidal waveforms, a
common mode voltage exists. Note that in a balanced three-phase
system, the voltages would sum to zero. In a PWM system, the
voltages cannot sum to zero. This results in the presence of a
common mode voltage (CMV). The CMV may have a value that is the
average voltage of the phase legs. In a three-phase example, the
CMV may be (Va+Vb+Vc)/3, where Vx are the phase voltages of each
phase winding.
[0041] The CMV is a by-product of the PWM mode of operation and may
have negative effects on the system. The CMV may cause current in
the stator of the electric machine causing additional heating. The
CMV may cause current flow through bearings which can lead to
degradation of the bearings. As such, reducing the CMV can have
beneficial effects for the electric machine.
[0042] FIG. 4 depicts an electric drive system 400 having an
electric machine that includes one or more secondary windings. The
electric drive system 400 may include an electric machine 414 that
includes three phase windings that are configured to rotate a shaft
and rotor when driven by current. In addition, the electric machine
414 may include a first secondary winding 402 and the second
secondary winding 408. The first secondary winding 402 and the
second secondary winding 408 may be configured to operate as a CMV
transformer. For example, the first secondary winding 402 may be
configured to harvest power of the CMV that would cause current to
flow through the structure of the electric machine 414. The first
secondary winding 402 may provide a low-impedance path for the
common-mode current. This may reduce undesired common-mode current
flowing through the electric machine 414, particularly the
bearings. The second secondary winding 408 may be similarly
configured.
[0043] The first secondary winding 402 may be electrically coupled
to a rectifier circuit 404. The rectifier circuit 404 may be
configured to process an AC voltage from the first secondary
winding 402 so that current only flows in one direction. The
rectifier circuit 404 may include an arrangement of passive circuit
elements such as diodes. The rectifier circuit 404 may include a
capacitor to smooth the resulting voltage. The rectifier circuit
404 may be configured to provide a generally constant DC voltage
level at the output.
[0044] The output of the rectifier circuit 404 may be electrically
coupled to a gate driver circuit 406. The gate driver circuit 406
may be configured to drive gate inputs of the power switches 302.
The gate driver circuit 406 may be powered by the output of the
rectifier circuit 404. The gate driver circuit 406 may be
alternatively powered by the low-voltage bus when no power is being
received from the rectifier circuit 404. For example, under
conditions in which the electric machine phase windings are not
driven, there may be no CMV-induced currents flowing.
[0045] The gate driver circuit 406 may also be controlled by
control signals from a controller 412. For example, the controller
412 may provide the gate drive signals as a PWM signal. The gate
driver circuit 406 may filter and process the gate drive signals to
provide a physical gate drive voltage with the appropriate
characteristics to drive the power switches 302 in the desired
state.
[0046] The second secondary winding 408 may be electrically coupled
to diagnostic circuit 410 that is configured to output a diagnostic
signal. The diagnostic signal may be input to a controller 412. The
diagnostic circuit 410 may be an analog circuit and may include an
analog-to-digital converter. The analog circuit may include
elements for filtering the voltage received from the second
secondary winding 408. The controller 412 may be programmed to
monitor the diagnostic signal to determine if the electric machine
414 and/or the power electronics module 126 is operating properly.
In some configurations, the controller 412 may utilize the
diagnostic signal to control operation of the power switches 302.
For example, the controller 412 may operate the power switches 302
to reduce the CMV below a predetermined level.
[0047] The electric machine may include a rotor and a stator
defining a plurality of teeth separated by slots. The electric
machine may further include a first set of conductors arranged in
the slots to form phase windings for driving the rotor. FIG. 5 is
an exploded perspective view of an electric machine 500 having a
stator 504 that defines a plurality of stator teeth 506 along an
inner diameter that defines a cavity configured to permit a rotor
502 to spin freely about a rotational axis 510. Each of stator
teeth 506 has a winding around it to induce a field channeled by
the tooth upon which the winding is wound. In this example, the
stator has 48 stator teeth. Also, the stator 504 includes end
windings 508 that carry a current in windings that travel in the
slots in between the stator teeth 506 to induce a field in the
stator teeth 506. In this application a current flowing in the end
windings 508 between a connection point and a slot is assumed to be
insufficient to induce a field in a stator tooth, while the current
when flowing in a winding located in a slot is sufficient to induce
a field in a stator tooth.
[0048] FIG. 6 is a cross sectional view of a stator core 600 for an
electric machine. Here, a 24-tooth stator is shown. The stator 504
may be symmetrical around the rotational axis 510 about which the
rotor may be configured to spin. The stator 504 may be divided into
sections by a first plane 602A and a second plane 602B that
intersect along the rotational axis 510. In this example
configuration, the phase windings may be defined by windings
associated with the teeth. For example, teeth associated with the
first phase winding may be labeled as Ax+ and Ax-. Teeth associated
with the second phase winding may be labeled as Bx+ an Bx-. Teeth
associated with the third phase winding may be labeled as Cx+ and
Cx-.
[0049] The teeth may define slots into which wiring may be inserted
to form the phase windings. Each winding may enter the slot
clockwise to the positive label and exit in the slot clockwise to
the negative label thus inducing a field in three stator teeth
therebetween. For example, the first phase winding may be formed by
a conductor segment 606A that is routed in the slot clockwise from
A1+ and returns via a conductor segment 606B that is routed in the
slot clockwise from A1-. The first phase winding consisting of A1+
and A1- may induce a field in the teeth numbered 1, 2, and 3. The
second phase winding may be formed by a conductor segment 608A that
is routed in the slot clockwise from B1+ and returns via a
conductor segment 608B that is routed in the slot clockwise from
B1-. The third phase winding may be formed by a conductor segment
610A that is routed in the slot clockwise from C1+ and returns via
a conductor segment 610B that is routed in the slot clockwise from
C1-. The second phase winding consisting of B+ and B1- may induce a
field in the teeth numbered 3, 4, and 5, and the third phase
winding consisting of C1+ and C1- may induce a field in the teeth
numbered 2, 3, and 4. Further, each lead may occupy any number of
slots thus, each winding can occupy 2, 4, 6, 8, etc. slots.
[0050] The phase windings may include a plurality of wiring
segments. The pattern depicted may be repeated a number of times
such that each of the phase windings may be comprised of a number
of wiring loops arranged about the teeth in the pattern shown. Note
that other wiring patterns are possible and the secondary windings
described herein may be applied to these other wiring patterns.
[0051] The above describes how the phase windings for driving the
electric machine may be configured. Also, depicted is the secondary
winding configuration. The electric machine may include a
conductive element arranged in the slots to form one or more
secondary windings configured to produce a voltage indicative of a
common mode voltage caused by phase voltages applied to the phase
windings. The secondary winding may include conductor segments
604A-F that may be arranged in the slots as shown in FIG. 7. FIG. 6
depicts the secondary winding as being inserted closest to the
rotational axis 510. However, in some configurations, the relative
position of the secondary windings (defined by 604A-F) and the
power windings (defined by 606, 608, and 610) may be swapped.
Further, some configurations may include a second secondary winding
similar that defined by 604A-F. In such configurations, the power
windings may be wrapped between the secondary windings. The
placement of the windings within the slots may be chosen to
optimize the CMV properties.
[0052] FIG. 7 depicts a possible winding diagram for the secondary
windings. The secondary windings may be configured to pass through
all of the machine phases to cover the CMV path. The secondary
windings may be configured such that a voltage is induced by each
of the power phase windings. By forming a loop that includes all of
the phase voltages, the CMV may induce a current in the secondary
windings. As an example, a first segment 604A represents that
portion of the secondary winding that is routed next to the A+
tooth. The conductor may then be routed next to the C- tooth as
represented by a second segment 604B. The conductor may then be
routed next to the B+ tooth as represented by a third segment 604C.
The conductor may then be routed next to the A- tooth as
represented by a fourth segment 604D. The conductor may then be
routed next to the C+ tooth as represented by a fifth segment 604E.
The conductor may then be routed next to the B- tooth a represented
by a sixth segment 604F. The pattern may be reproduced to achieve a
predetermined number of turns or iterations for the secondary
winding 604. The terminals of the secondary winding may be the
connections to the first segment 604A and the sixth segment
604F.
[0053] The example depicted shows the secondary winding formed in
one of the pole-pairs of the electric machine. The secondary
winding may cover multiple pole-pairs or all pole pairs of the
electric machine. Further, the secondary winding may extend to
other sections of the stator 504. As an example, the B1- slot may
be coupled to the A2+ slot. The conductor may be routed with the
same pattern.
[0054] The conductive element may pass through slots that include
conductors from the conductors that make up the phase windings such
that the voltage includes an induced voltage component from each of
the phase windings. The cross-sectional area of the conductive
element making up the secondary windings may be less than a
cross-sectional area of conductors forming the phase windings. The
conductive element for the secondary windings may be arranged in
slots that define more than one pole-pair of the electric machine.
The conductive element for the secondary windings may be configured
to have an impedance that is lower than an impedance associated
with an impedance path through a bearing of the electric
machine.
[0055] Referring again to FIG. 4, the controller 412 may be
configured to receive the signal indicative of the common mode
voltage. The controller 412 may be configured to adjust the
operation of the switches 302 based on the voltage. For example,
the controller 412 may be configured to adjust the switching
frequency to reduce the common mode voltage to a desired level. For
example, reducing the switching frequency may reduce the common
mode voltage. In some configuration, the controller 412 may change
the common mode voltage by altering the switching pattern of the
power switches 302.
[0056] FIG. 8 is a cross sectional schematic diagram of power
winding connections 800 for a stator of an electric machine. Here,
twelve windings are shown associated with a 24-tooth stator. In
each section of the stator are the 3-phase leads A 606, B 608, and
C 610. In one embodiment, each lead in this diagram may be
associated with one stator tooth when the stator has 24 teeth,
however if this was a 48-tooth stator, each lead may be associated
with two stator teeth. However, in other configurations, each lead
in this diagram may be associated with more than one stator tooth,
such as 3 stator teeth or 6 stator teeth. Also, each winding shown
here with two leads (e.g., A1+ and A1-) may occupy any number of
slots. So, each winding can occupy 2, 4, 6, 8, etc. slots. A slot
is the open area between two stator teeth wherein copper windings
may be placed inside the slots. The number of slots is equal to the
number of teeth. Further, the stator may be divided in half along a
first plane 602A (e.g., a reference plane) that intersects with a
rotational axis 510 of the electric machine. The stator may be
further divided into quarters by a second plane 602B that also
intersects with the rotational axis 510.
[0057] In a single-inverter configuration, the associated phase
windings may be coupled in series such that three-phase leads are
defined. In this example, the connection labeled A1- may be
electrically connected to A2+. A2- may be electrically coupled to
A3+. A3- may be electrically coupled to A4+. A4- may be
electrically coupled to a neutral conductor. The connection labeled
A1+ may be electrically coupled to the first phase leg output 316.
Similarly, the second phase winding may be defined by electrically
coupling B1- to B2+, B2- to B3+, B3- to B4+, and B4- to the neutral
conductor. The connection labeled B1+ may be electrically coupled
to the second phase leg output 318. Similarly, the third phase
winding may be defined by electrically coupling C1- to C2+, C2- to
C3+, C3- to C4+, and C4- to the neutral conductor. The connection
labeled C1+ may be electrically coupled to the third phase leg
output 320. The phase windings may be continuous wires that are
routed through the slots as described above. The electrical
connections between the slots may form end windings of the
stator.
[0058] FIG. 9 depicts an electrical schematic 900 of the resulting
CMV transformer that may be formed by including two secondary
windings within the stator slots. The CMV transformer may be
modeled as a primary winding 902 that is magnetically coupled to a
first secondary winding 904A and a second secondary winding 904B.
The first secondary winding 904A and the second secondary winding
904B may be electrically isolated from one another and share a
common magnetic core formed by the stator metal structure and a
common primary winding 902. During operation of the power windings
using PWM signals, a CMV is created at the primary winding 902. The
CMV is induced in the first secondary winding 904A and the second
secondary winding 904B.
[0059] The voltage induced in the secondary windings may depend
upon the number of turns in the corresponding secondary winding. By
using a different number of turns in each secondary winding,
different voltage levels may be created. FIG. 10 depicts a first
system configuration 1000 in which the secondary windings are
configured to be voltage sources. The first secondary winding 904A
may be electrically coupled to a first rectifier network 1002A. The
first rectifier network 1002A may cause current to flow in one
direction at the output of the first rectifier network 1002A. For
example, the output of the first rectifier network 1002A may be
electrically coupled to a DC bus to function as a voltage source. A
first capacitor 1004 may be electrically coupled across output
terminals of the first rectifier network 1002A. The first capacitor
1004 may smooth and filter the output of the first rectifier
network 1002A resulting in a DC voltage level.
[0060] The second secondary winding 904B may be electrically
coupled to a second rectifier network 1002B. The second rectifier
network 1002B may cause current to flow in one direction from to
the output of the second rectifier network 1002B. For example, the
output of the second rectifier network 1002B may be electrically
coupled to a DC bus to function as a voltage source. A second
capacitor 1006 may be electrically coupled across output terminals
of the second rectifier network 1002B. The second capacitor 1006
may smooth and filter the output of the second rectifier network
1002B resulting in a DC voltage level.
[0061] The frequency of the CMV does not depend on the frequency of
the current through the power windings. The frequency of the CMV
may be equal to the switching frequency of the inverter which may
be in the range of 1-20 KHz. The switching frequency may be that
frequency at which the gate drive signals of the power switches are
changed. As a result, the capacitance value of the capacitor at the
output of the rectifier network may be a value that is sufficient
to filter the PWM frequency. The resulting CMV transformer may not
pass the DC component of the CMV. The output voltage of each
rectifier network 1002 may be adjusted by selecting the number of
windings for the associated secondary winding 904. The CMV
transformer may be used to supply different voltage levels that are
galvanically isolated from one another. If a secondary winding
becomes short-circuited, the secondary winding may drop to zero
voltage. The magnetic coupling between the secondary windings may
cause all voltage sources to drop to zero voltage as well.
[0062] The CMV transformer may be used to serve as a power source
for the inverter gate drive circuitry. Since one failed voltage
source may drive the others to zero, this may cause all gate
drivers to shut down. By stopping the gate drive circuitry, the CMV
voltage is also stopped and the switching devices are no longer
being switched. This may provide an additional mechanism for
stopping the gate drive circuit.
[0063] The CMV transformer may also be utilized as a diagnostic
sensor. FIG. 11 depicts a second system configuration 1100 that
includes a voltage source and a diagnostic circuit. The voltage
source may include the first secondary winding 904A coupled to the
first rectifier network 1002A and first capacitor 1004 as described
previously. The diagnostic circuit may be coupled to the second
secondary winding 904B. The diagnostic circuit may include an
analog circuit 1102 and an analog-to-digital (A/D) converter 1104.
The A/D converter 1104 may be configured to convert the output of
the second secondary winding 904B to a digital value for use by the
controller (e.g., controller 412 in FIG. 4). The analog circuit
1102 may include components to generate an analog signal indicative
of the CMV. For example, the analog circuit 1102 may be configured
to output an analog signal indicative of the frequency of the
CMV.
[0064] The diagnostic sensor may provide information on system
operation. The diagnostic sensor may be configured to detect that
the electric machine cables are connected properly. For example, if
a phase winding is not connected to the associated phase leg of the
inverter, a distinct analog signal may be generated. The diagnostic
sensor may also be configured to detect if one or more of the
switching devices are functioning.
[0065] The diagnostic sensor may also be configured to detect the
level of CM current that may be flowing through the bearings. The
diagnostic sensor may also be configured to detect proper operation
of the inverter such as reconstructing the PWM ratios and detecting
rising/falling edges of the inverter switches. Proper operation may
be determined by monitoring the analog and digital outputs of the
diagnostic circuit during normal operating conditions. The analog
and digital outputs may also be monitored during abnormal operating
conditions. Differences in the signals may be observed between
normal and abnormal operating conditions. The controller 412 may be
programmed to identify the abnormal operating conditions by
monitoring the analog and digital outputs of the diagnostic sensor.
The controller 412 may shut down operation of the inverter
responsive to detecting an abnormal operation condition.
[0066] Control logic or functions performed by controller may be
represented by flow charts or similar diagrams in one or more
figures. These figures provide representative control strategies
and/or logic that may be implemented using one or more processing
strategies such as event-driven, interrupt-driven, multi-tasking,
multi-threading, and the like. As such, various steps or functions
illustrated may be performed in the sequence illustrated, in
parallel, or in some cases omitted. Although not always explicitly
illustrated, one of ordinary skill in the art will recognize that
one or more of the illustrated steps or functions may be repeatedly
performed depending upon the particular processing strategy being
used. Similarly, the order of processing is not necessarily
required to achieve the features and advantages described herein,
but are provided for ease of illustration and description. The
control logic may be implemented primarily in software executed by
a microprocessor-based vehicle, engine, and/or powertrain
controller, such as controller. Of course, the control logic may be
implemented in software, hardware, or a combination of software and
hardware in one or more controllers depending upon the particular
application. When implemented in software, the control logic may be
provided in one or more computer-readable storage devices or media
having stored data representing code or instructions executed by a
computer to control the vehicle or its subsystems. The
computer-readable storage devices or media may include one or more
of a number of known physical devices which utilize electric,
magnetic, and/or optical storage to keep executable instructions
and associated calibration information, operating variables, and
the like.
[0067] The processes, methods, or algorithms disclosed herein can
be deliverable to/implemented by a processing device, controller,
or computer, which can include any existing programmable electronic
control unit or dedicated electronic control unit. Similarly, the
processes, methods, or algorithms can be stored as data and
instructions executable by a controller or computer in many forms
including, but not limited to, information permanently stored on
non-writable storage media such as Read Only Memory (ROM) devices
and information alterably stored on writeable storage media such as
floppy disks, magnetic tapes, Compact Discs (CDs), Random Access
Memory (RAM) devices, and other magnetic and optical media. The
processes, methods, or algorithms can also be implemented in a
software executable object. Alternatively, the processes, methods,
or algorithms can 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.
[0068] While exemplary embodiments are described above, it is not
intended that these embodiments describe all possible forms
encompassed by the claims. The words used in the specification are
words of description rather than limitation, and it is understood
that various changes can be made without departing from the spirit
and scope of the disclosure. As previously described, the features
of various embodiments can be combined to form further embodiments
of the invention that may not be explicitly described or
illustrated. While various embodiments could 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 can be compromised to
achieve desired overall system attributes, which depend on the
specific application and implementation. These attributes may
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 can be desirable for particular applications.
* * * * *