U.S. patent application number 16/464975 was filed with the patent office on 2019-10-17 for capacitor component for an electric motor or generator.
The applicant listed for this patent is PROTEAN ELECTRIC LIMITED. Invention is credited to Geoffrey Owen, Gareth Roberts.
Application Number | 20190318878 16/464975 |
Document ID | / |
Family ID | 58073368 |
Filed Date | 2019-10-17 |
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United States Patent
Application |
20190318878 |
Kind Code |
A1 |
Owen; Geoffrey ; et
al. |
October 17, 2019 |
CAPACITOR COMPONENT FOR AN ELECTRIC MOTOR OR GENERATOR
Abstract
A capacitor component comprising a first busbar, a second
busbar, one or more capacitor elements and a housing, the housing
having a first portion and a second portion, where-in the first
portion and the second portion are arranged to extend around an
aperture, the first portion includes a section for housing the one
or more capacitor elements, with the second portion extending
between a first end and a second end of the first portion. The
first busbar and the second busbar are arranged to extend around
the first portion and the second portion of the housing. A first
power supply terminal is formed at the first end of the first
portion and is coupled to the first busbar, and a second power
supply terminal is formed at the second end of the first portion
and is coupled to the second busbar.
Inventors: |
Owen; Geoffrey; (Farnham
Surrey, GB) ; Roberts; Gareth; (Farnham Surrey,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PROTEAN ELECTRIC LIMITED |
Farnham Surrey |
|
GB |
|
|
Family ID: |
58073368 |
Appl. No.: |
16/464975 |
Filed: |
November 22, 2017 |
PCT Filed: |
November 22, 2017 |
PCT NO: |
PCT/GB2017/053503 |
371 Date: |
May 29, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02K 3/522 20130101;
H01L 2224/49111 20130101; H02K 11/33 20160101; H02K 2203/09
20130101; Y02T 10/7022 20130101; H01G 2/08 20130101; H01G 2/04
20130101; H01G 4/248 20130101; H01G 2/106 20130101; H01G 4/38
20130101; H01G 4/40 20130101; H05K 7/1432 20130101; H01G 4/224
20130101; H02K 11/0094 20130101 |
International
Class: |
H01G 4/40 20060101
H01G004/40; H01G 2/04 20060101 H01G002/04; H01G 2/10 20060101
H01G002/10; H01G 4/38 20060101 H01G004/38; H02K 11/00 20060101
H02K011/00; H02K 11/33 20060101 H02K011/33; H05K 7/14 20060101
H05K007/14; H01G 4/224 20060101 H01G004/224 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2016 |
GB |
1620270.7 |
Claims
1. A capacitor component comprising a first busbar, a second
busbar, one or more capacitor elements, and a housing, the housing
having a first portion and a second portion, wherein the first
portion and the second portion are arranged to extend around an
aperture, the first portion includes a section for housing the one
or more capacitor elements, with the second portion extending
between a first end and a second end of the first portion, wherein
the first busbar and the second busbar are arranged to extend
around the first portion and the second portion of the housing, a
first power supply terminal is formed at the first end of the first
portion and a second power supply terminal is formed at the second
end of the first portion, wherein the first power supply terminal
is coupled to the first busbar and the second power supply terminal
is coupled to the second busbar, wherein a first conductive layer
of the one or more capacitor elements is coupled to the first
busbar and a second conductive layer of the one or more capacitor
elements is coupled to the second busbar.
2. A capacitor component according to claim 1, wherein the first
busbar has a first section arranged to extend around the first
portion of the housing and a second section arranged to extend
around the second portion of the housing.
3. A capacitor component according to claim 1, wherein the second
busbar has a first section arranged to extend around the first
portion of the housing and a second section arranged to extend
around the second portion of the housing.
4. A capacitor component according to claim 2, wherein the first
busbar and/or the second busbar includes a gap in the first section
of the first busbar and/or the second busbar.
5. A capacitor component according to claim 1, wherein the first
busbar and the second busbar are separated by an insulating
film.
6. A capacitor component according to claim 1, wherein a first
subset of the plurality of capacitor elements corresponds to a
first capacitor and a second subset of the plurality of capacitor
elements corresponds to a Y capacitor, wherein the Y capacitor is
arranged in series and in parallel to the first capacitor.
7. An electric motor or generator comprising: a stator having two
coil sets arranged to produce a magnetic field for generating a
drive torque; two control devices; and a capacitor component
comprising: a first busbar; a second busbar; one or more capacitor
elements; and a housing having a first portion and a second
portion, wherein the first portion and the second portion are
arranged to extend around an aperture, the first portion includes a
section for housing the one or more capacitor elements, with the
second portion extending between a first end and a second end of
the first portion; wherein the first busbar and the second busbar
are arranged to extend around the first portion and the second
portion of the housing, a first power supply terminal is formed at
the first end of the first portion and a second power supply
terminal is formed at the second end of the first portion; wherein
the first power supply terminal is coupled to the first busbar and
the second power supply terminal is coupled to the second busbar;
wherein a first conductive layer of the one or more capacitor
elements is coupled to the first busbar and a second conductive
layer of the one or more capacitor elements is coupled to the
second busbar; wherein the capacitor component is arranged to be
coupled to a power source for providing current to the two control
devices; wherein the first control device is coupled to a first
coil set and the capacitor component and the second control device
is coupled to a second coil set and the capacitor component; and
wherein each control device is arranged to control current in the
respective coil set to generate a magnetic field in the respective
coil set.
8. An electric motor or generator according to claim 7, wherein
each coil set includes a plurality of coil sub-sets, wherein the
first control device is coupled to the plurality of coil sub-sets
for the first coil set and the second control device is coupled to
the plurality of coil sub-sets for the second coil set and each
control device is arranged to control current in the respective
plurality of coil sub-sets to generate a magnetic field in each
coil sub-set to have a substantially different magnetic phase to
the other one or more coil sub-set in the respective coil set.
9. An electric motor or generator according to claim 7, wherein the
first control device, the second control device and the capacitor
component are mounted adjacent to the stator.
10. An electric motor or generator according to claim 7, wherein
the stator includes an annular recess for housing the capacitor
component.
11. An electric motor or generator according to claim 10, wherein
the first control device and the second control device are mounted
on the stator adjacent to the annular recess.
12. An electric motor or generator according to claim 10, wherein
the first control device and the second control device are mounted
on the stator between the outer radial edge of the stator and the
annular recess.
13. An electric motor or generator according to claim 7, wherein
the first control device includes a first inverter for controlling
current flow in the first coil set and the second control device
includes a second inverter for controlling current flow in the
second coil set, wherein each inverter is coupled to the first
capacitor.
14. An electric motor or generator according to claim 13, wherein
the first inverter and the second inverter are mounted at
substantially the same distance radially from the capacitor
component.
15. An electric motor or generator according to claim 13, wherein
the first inverter and second inverter are coupled to the first
electrical busbar and the second electrical busbar.
16. An electric motor or generator according to claim 7, wherein
the first portion of the housing forms a section of an annular ring
and the second portion of the housing is arranged to extend around
cooling conduits entering the electric motor or generator and/or
cabling entering the electric motor or generator.
17. An electric motor or generator according to claim 7, wherein
the first portion of the housing forms a section of an annular ring
and the second portion of the housing is substantially straight.
Description
[0001] The present invention relates to a capacitor component, in
particular a capacitor component for an electric motor or
generator.
[0002] Electric motor systems typically include an electric motor
and a control unit arranged to control the power of the electric
motor. Examples of known types of electric motor include the
induction motor, synchronous brushless permanent magnet motor,
switched reluctance motor and linear motor. In the commercial arena
three phase electric motors are the most common kind of electric
motor available.
[0003] A three phase electric motor typically includes three coil
sets, where each coil set is arranged to generate a magnetic field
associated with one of the three phases of an alternating
voltage.
[0004] To increase the number of magnetic poles formed within an
electric motor, each coil set will typically have a number of coil
sub-sets that are distributed around the periphery of the electric
motor, which are driven to produce a rotating magnetic field.
[0005] By way of illustration, FIG. 1 shows a typical three phase
electric motor 10 having three coil sets 14, 16, 18. Each coil set
consists of four coil sub-sets that are connected in series, where
for a given coil set the magnetic field generated by the respective
coil sub-sets will have a common phase.
[0006] The three coil sets of a three phase electric motor are
typically configured in either a delta or wye configuration.
[0007] A control unit for a three phase electric motor having a DC
power supply will typically include a three phase bridge inverter
that generates a three phase voltage supply for driving the
electric motor. Each of the respective voltage phases is applied to
a respective coil set of the electric motor.
[0008] A three phase bridge inverter includes a number of switching
devices, for example power electronic switches such as Insulated
Gate Bipolar Transistor (IGBT) switches, which are used to generate
an alternating voltage from a DC voltage supply.
[0009] To reduce the effects of inductance on inverters when
switching current, capacitors are used as a local voltage source
for electric motor inverters. By placing a capacitor close to an
inverter the inductance associated with the voltage source is
minimised. Accordingly, for an electric motor having multiple
inverters an annular capacitor ring is desirable to minimise the
distance between the capacitor element and the inverters.
[0010] A capacitor needs to have a busbar to allow charge to flow
to and from the capacitor plates.
[0011] However, an optimum busbar configuration may be inconsistent
with the design needs for the capacitor and/or an electric motor or
generator.
[0012] It is desirable to improve this situation
[0013] In accordance with an aspect of the present invention there
is provided a capacitor component according to the accompanying
claims.
[0014] The present invention provides the advantage of optimising
current flow within a capacitor busbar while reducing inductance
and optimising capacitor placement within an electric motor with
improved space envelope utilisation.
[0015] The present invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
[0016] FIG. 1 illustrates a prior art three phase electric
motor;
[0017] FIG. 2 illustrates an exploded view of a motor embodying the
present invention;
[0018] FIG. 3 illustrates an exploded view of the electric motor
shown in FIG. 1 from an alternative angle;
[0019] FIG. 4 illustrates an electric motor according to an
embodiment of the present invention;
[0020] FIG. 5 illustrates control modules for an electric motor
according to an embodiment of the present invention;
[0021] FIG. 6 illustrates a partial view for an electric motor
according to an embodiment of the present invention;
[0022] FIG. 7 illustrates a control module for an electric motor
according to an embodiment of the present invention;
[0023] FIG. 8 illustrates a cross sectional view of a stator
according to an embodiment of the present invention;
[0024] FIG. 9 illustrates a capacitor component according to an
embodiment of the present invention;
[0025] FIG. 10 illustrates a capacitor component according to an
embodiment of the present invention;
[0026] FIG. 11 illustrates a schematic diagram for a capacitor
component according to an embodiment of the present invention;
[0027] FIG. 12 illustrates a partial view of a control module
housing according to an embodiment of the present invention.
[0028] The embodiment of the invention described is for an electric
motor having a capacitor component, where the electric motor is for
use in a wheel of a vehicle. However the electric motor may be
located anywhere within the vehicle. The motor is of the type
having a set of coils being part of the stator for attachment to a
vehicle, radially surrounded by a rotor carrying a set of magnets
for attachment to a wheel. For the avoidance of doubt, the various
aspects of the invention are equally applicable to an electric
generator having the same arrangement. As such, the definition of
electric motor is intended to include electric generator. In
addition, some of the aspects of the invention are applicable to an
arrangement having the rotor centrally mounted within radially
surrounding coils. As would be appreciated by a person skilled in
the art, the present invention is applicable for use with other
types of electric motors.
[0029] For the purposes of the present embodiment, as illustrated
in FIG. 2 and FIG. 3, the in-wheel electric motor includes a stator
252 comprising a heat sink 253, multiple coils (not shown), two
control modules 400 mounted on the heat sink 253 on a rear portion
of the stator for driving the coils, and a capacitor component 257
mounted on the stator within a recess 255 formed on the rear
portion of the heat sink 253. In a preferred embodiment the
capacitor component is substantially annular in shape. The coils
are formed on stator tooth laminations to form coil windings, where
the stator tooth laminations are mounted on the heat sink 253. The
heat sink 253 includes at least one cooling channel for allowing a
coolant to flow within the heat sink 253 for providing cooling,
thereby allowing the heat sink 253 to extract heat from components
attached to the heat sink 253, for example the coil windings, the
capacitor component 257 and the control modules 400. A stator cover
256 is mounted on the rear portion of the stator 252, enclosing the
control modules 400 to form the stator 252, which may then be fixed
to a vehicle and does not rotate relative to the vehicle during
use.
[0030] Each control module 400 includes two inverters 410 and
control logic 420, which in the present embodiment includes a
processor, for controlling the operation of the inverters 410,
which is schematically represented in FIG. 5.
[0031] The capacitor component 257 is coupled across the inverters
410, as described below, for distributing the DC power supply to
the inverters 410 and for reducing voltage ripple on the electric
motor's power supply line, otherwise known as the DC busbar, during
operation of the electric motor. For reduced inductance the
capacitor component 257 is mounted adjacent to the control modules
400. Although the capacitor component 257 within the electric motor
of the present embodiment is substantially annular in shape, the
capacitor element may take other forms.
[0032] As described below, the capacitor component 257 includes a
section 260 that can be shaped to accommodate conduits, cables and
other external features that need to be coupled to the electric
motor without increasing the inductance of the capacitor
component/electric motor configuration. Examples of conduits and
cables include conduits 261 for providing cooling to the electric
motor and/or electrical cabling that can include both cabling for
providing a power supply to the electric motor and communications
between the electric motor and an external controller.
[0033] A rotor 240 comprises a front portion 220 and a cylindrical
portion 221 forming a cover, which substantially surrounds the
stator 252. The rotor includes a plurality of permanent magnets 242
arranged around the inside of the cylindrical portion 221. For the
purposes of the present embodiment 32 magnet pairs are mounted on
the inside of the cylindrical portion 221. However, any number of
magnet pairs may be used.
[0034] The magnets are in close proximity to the coil windings on
the stator 252 so that magnetic fields generated by the coils
interact with the magnets 242 arranged around the inside of the
cylindrical portion 221 of the rotor 240 to cause the rotor 240 to
rotate. As the permanent magnets 242 are utilized to generate a
drive torque for driving the electric motor, the permanent magnets
are typically called drive magnets.
[0035] The rotor 240 is attached to the stator 252 by a bearing
block 223. The bearing block 223 can be a standard bearing block as
would be used in a vehicle to which this motor assembly is to be
fitted. The bearing block comprises two parts, a first part fixed
to the stator and a second part fixed to the rotor. The bearing
block is fixed to a central portion of the wall of the stator 252
and also to a central portion 225 of the housing wall 220 of the
rotor 240. The rotor 240 is thus rotationally fixed to the vehicle
with which it is to be used via the bearing block 223 at the
central portion 225 of the rotor 240. This has an advantage in that
a wheel rim and tyre can then be fixed to the rotor 240 at the
central portion 225 using the normal wheel bolts to fix the wheel
rim to the central portion of the rotor and consequently firmly
onto the rotatable side of the bearing block 223. The wheel bolts
may be fitted through the central portion 225 of the rotor through
into the bearing block itself. With both the rotor 240 and the
wheel being mounted to the bearing block 223 there is a one to one
correspondence between the angle of rotation of the rotor and the
wheel.
[0036] FIG. 3 shows an exploded view of the same motor assembly
illustrated in FIG. 2 from the opposite side. The rotor 240
comprises the outer rotor wall 220 and circumferential wall 221
within which magnets 242 are circumferentially arranged. As
previously described, the stator 252 is connected to the rotor 240
via the bearing block at the central portions of the rotor and
stator walls.
[0037] The rotor also includes a set of magnets 227 for position
sensing, otherwise known as commutation magnets, which in
conjunction with sensors mounted on the stator allows for a rotor
flux angle to be estimated. The rotor flux angle defines the
positional relationship of the drive magnets to the coil windings.
Alternatively, in place of a set of separate magnets the rotor may
include a ring of magnetic material that has multiple poles that
act as a set of separate magnets.
[0038] To allow the commutation magnets to be used to calculate a
rotor flux angle, preferably each drive magnet has an associated
commutation magnet, where the rotor flux angle is derived from the
flux angle associated with the set of commutation magnets by
calibrating the measured commutation magnet flux angle. To simplify
the correlation between the commutation magnet flux angle and the
rotor flux angle, preferably the set of commutation magnets has the
same number of magnets or magnet pole pairs as the set of drive
magnet pairs, where the commutation magnets and associated drive
magnets are approximately radially aligned with each other.
Accordingly, for the purposes of the present embodiment the set of
commutation magnets has 32 magnet pairs, where each magnet pair is
approximately radially aligned with a respective drive magnet
pair.
[0039] A sensor, which in this embodiment is a Hall sensor, is
mounted on the stator. The sensor is positioned so that as the
rotor rotates each of the commutation magnets that form the
commutation magnet ring respectively rotates past the sensor.
[0040] As the rotor rotates relative to the stator the commutation
magnets correspondingly rotate past the sensor with the Hall sensor
outputting an AC voltage signal, where the sensor outputs a
complete voltage cycle of 360 electrical degrees for each magnet
pair that passes the sensor.
[0041] For improved position detection, preferably the sensor
includes an associated second sensor placed 90 electrical degrees
displaced from the first sensor.
[0042] As illustrated in FIG. 4, in the present embodiment the
electric motor includes four coil sets 60 with each coil set 60
having three coil sub-sets 61, 62, 63 that are coupled in a wye
configuration to form a three phase sub-motor, resulting in the
motor having four three phase sub-motors. The operation of the
respective sub-motors is controlled via one of two control
devices/control modules 400, as described below. However, although
the present embodiment describes an electric motor having four coil
sets 60 (i.e. four sub motors) the motor may equally have one or
more coil sets with associated control devices. In a preferred
embodiment the motor 40 includes eight coil sets 60 with each coil
set 60 having three coil sub-sets 61, 62, 63 that are coupled in a
wye configuration to form a three phase sub-motor, resulting in the
motor having eight three phase sub-motors. Similarly, each coil set
may have any number of coil sub-sets, thereby allowing each
sub-motor to have two or more phases.
[0043] FIG. 5 illustrates the connections between the respective
coil sets 60 and the control modules 400, where a respective coil
set 60 is connected to a respective three phase inverter 410
included in a control module 400. As is well known to a person
skilled in the art, a three phase inverter contains six switches,
where a three phase alternating voltage may be generated by the
controlled operation of the six switches. However, the number of
switches will depend upon the number of voltage phases to be
applied to the respective sub motors, where the sub motors can be
constructed to have any number of phases.
[0044] The respective coils of the four coil sets are wound on
individual stator teeth, which form part of the stator. The end
portions 501 of the coil windings protrude through the planar rear
portion 502 of the stator heat sink, as illustrated in FIG. 6. FIG.
6 illustrates a partial perspective view of the stator, where the
end portions 501 of the coil windings for two of the four coil sets
60 extend away from the planar portion of the stator heat sink
253.
[0045] The control modules 400 are positioned adjacent to the
planar portion of the stator heat sink 253, for mounting to the
planar portion of the stator heat sink 253. For illustration
purposes, a view of a single control module 400 separated from the
stator heat sink 253 is shown in FIG. 6. As stated above, an
annular recess 255 is formed in the planar portion of the heat sink
253 for housing the capacitor component.
[0046] For the purposes of the present embodiment, the planar
portion of the heat sink 253 is located on the side of the stator
that is intended to be mounted to a vehicle.
[0047] Preferably, to facilitate the mounting of the respective
control modules 400 to the stator heat sink 253, the end sections
501 of the coil windings for the respective coil sets are arranged
to extend away from the heat sink portion of the stator in a
substantially perpendicular direction relative to the surface of
the heat sink portion of the stator.
[0048] FIG. 7 illustrates a modular construction of the control
module 400 with an exploded view of a preferred embodiment of a
control module 400, where each control module 400, otherwise known
as a power module, includes a power printed circuit board 500 in
which are mounted two power substrate assemblies 510, a control
printed circuit board 520, four power source busbars (not shown)
for connecting to the capacitor component, six phase winding
busbars (not shown) for connecting to respective coil windings, two
insert modules 560 and six current sensors. Each current sensor
includes a Hall sensor and a section of soft ferromagnetic material
530 arranged to be mounted adjacent to the Hall sensor, where
preferably each Hall sensor is arranged to be mounted in a cutout
section of a piece of soft ferromagnetic material fashioned in a
toroid shape.
[0049] Each of the control module components are mounted within a
control module housing 550 with the four power source busbars and
the six phase winding busbars being mounted, via the respective
insert modules, on the power printed circuit board 500 on opposite
sides of the control device housing 550.
[0050] Each power substrate 510 is arranged to be mounted in a
respective aperture formed in the power printed circuit board 500,
where each of the power substrates 510 has a 3mm copper base plate
600 upon which is formed a three phase inverter 410. A
corresponding aperture 511 is also formed in the control module
housing 550 to allow the copper base plate for each of the power
substrates 510 is placed in direct contact with the stator heat
sink 253 when the control device housing 550 is mounted to the
stator, thereby allowing for cooling to be applied directly to the
base of each of the power substrates 510.
[0051] Mounted on the underside of the power printed circuit board
500, adjacent to the copper base plate of the power substrate
assemblies 510, are the six Hall sensors (not shown) for measuring
the current in the respective coil windings associated with two of
the four coil sets. The Hall sensor readings are provided to the
control printed circuit board 520.
[0052] The power printed circuit board 500 includes a variety of
other components that include drivers for the inverter switches
formed on the power substrate assemblies 510, where the drivers are
used to convert control signals from the control printed circuit
board 520 into a suitable form for operating switches mounted on
the power printed circuit board 500, however these components will
not be discussed in any further detail.
[0053] The insert modules 560 are arranged to be mounted over the
power printed circuit board 500 when the power printed circuit
board 500 is mounted in the control module housing 550.
[0054] Each insert module 560 is arranged to be mounted over a
respective power substrate assembly 510 mounted on the power
printed circuit board 500, with each insert module 560 having an
aperture arranged to extend around inverter switches formed on a
respective power substrate assembly 510.
[0055] Each insert module 560 is arranged to carry two power source
busbars and three phase windings busbars for coupling the inverter
formed on the power substrate assembly 510, over which the insert
module 560 is mounted, to the capacitor component and to the phase
windings of a coil set, respectively.
[0056] The insert module 560 also acts as a spacer for separating
the control printed circuit board 520 from the power printed
circuit board 500 when both the power printed circuit board 500 and
the control printed circuit board 520 are mounted in the control
module housing 550.
[0057] A first pair of the power source busbars mounted on one of
the insert modules 560 is for providing a voltage source to a first
inverter 410 formed on one of the power substrates assemblies 510.
A second pair of the power source busbars mounted on a second
insert module 560 is for providing a voltage source to a second
inverter 410 formed on the other power substrate assembly 510.
[0058] For each pair of power source busbars, one of the power
source busbars is located in a first plane formed above the plane
of the power circuit board 500. The other power source busbar is
located in a second plane above the first plane. Preferably, each
pair of power source busbars are arranged to be substantially
co-planar.
[0059] Located in the control module housing 550 on the opposite
side of the respective power substrate assemblies 510 to the power
source busbars are the six phase winding busbars. A phase winding
busbar is coupled to each inverter leg for coupling to a respective
coil winding, as is well known to a person skilled in the art (i.e.
a phase winding busbar is coupled to each leg of the three phase
inverter formed on one of the power substrate assemblies 510 and a
phase winding busbar is coupled to each leg of the three phase
inverter formed on the other power substrate assembly 510).
[0060] The control printed circuit board 520 is arranged to be
mounted in the control module housing 550 above the power printed
circuit board 500.
[0061] The control printed circuit board 520 includes a processor
420 for controlling the operation of the respective inverter
switches to allow each of the electric motor coil sets 60 to be
supplied with a three phase voltage supply using PWM voltage
control across the respective coil sub-sets 61, 62, 63. For a given
torque requirement, the three phase voltage applied across the
respective coil sets is determined using field oriented control
FOC, which is performed by the processor on the control printed
circuit board using the current sensors mounted within the control
module housing 550 for measuring the generated current. PWM control
works by using the motor inductance to average out an applied pulse
voltage to drive the required current into the motor coils. Using
PWM control an applied voltage is switched across the motor
windings. During the period when voltage is switched across the
motor coils, the current rises in the motor coils at a rate
dictated by their inductance and the applied voltage. The PWM
voltage control is switched off before the current has increased
beyond a required value, thereby allowing precise control of the
current to be achieved.
[0062] The inverter switches can include semiconductor devices such
as MOSFETs or IGBTs. In the present example, the switches comprise
IGBTs. However, any suitable known switching circuit can be
employed for controlling the current. One well known example of
such a switching circuit is the three phase bridge circuit having
six switches configured to drive a three phase electric motor. The
six switches are configured as three parallel sets of two switches,
where each pair of switches is placed in series and form a leg of
the three phase bridge circuit. A DC power source is coupled across
the legs of the inverter, with the respective coil windings of an
electric motor being coupled between a respective pair of switches,
as is well known to a person skilled in the art. A single phase
inverter will have two pairs of switches arranged in series to form
two legs of an inverter.
[0063] The three phase voltage supply results in the generation of
current flow in the respective coil sub-sets and a corresponding
rotating magnetic field for providing a required torque by the
respective sub-motors.
[0064] Additionally, each control printed circuit board 520
includes an interface arrangement to allow communication between
the respective control modules 400 via a communication bus with one
control module 400 being arranged to communicate with a vehicle
controller mounted external to the electric motor, where the
externally mounted controller will typically provide a required
torque value to the control module 400. The processor 420 on each
control modules 400 is arranged to handle communication over the
interface arrangement.
[0065] As stated above, although the present embodiment describes
each coil set 60 as having three coil sub-sets 61, 62, 63, the
present invention is not limited by this and it would be
appreciated that each coil set 60 may have one or more coil
sub-sets.
[0066] FIG. 8 illustrates a cross sectional view of a section of
the stator with the capacitor component 800 being housed within a
recess 255 formed in the planar portion of the heat sink 253.
[0067] The capacitor component 800 includes a first busbar, where
the first busbar is coupled to a first internal capacitor electrode
via a first external electrode. A second busbar mounted adjacent to
the first busbar is coupled to a second internal capacitor
electrode via a second external electrode, as described below. The
first busbar allows charge to flow to and from the first internal
capacitor electrode. The second busbar allows charge to flow to and
from the second internal capacitor electrode. The first internal
capacitor electrode and the second internal capacitor electrode
correspond to the capacitor plates.
[0068] FIG. 9 illustrates an exploded view of the capacitor
component 800 with FIG. 10 illustrating a perspective view of the
capacitor component 800. As illustrated in FIG. 9 both the first
busbar 900 and the second busbar 910 are mounted around the outer
surface of a plurality of capacitor elements 920 with the first
busbar 900 and the second busbar 910 being separated by a first
insulating film 930.
[0069] The first busbar 900, the second busbar 910, the plurality
of capacitor elements 920, and the first insulating film 930 are
arranged within a recess 990 formed within a housing 940, as
described below.
[0070] The housing 940 has a first portion 980 that is arranged to
house the first busbar 900, the second busbar 910, the plurality of
capacitor elements 920, and the first insulating film 930. The
first portion 980 of the housing 940 is configured as a section of
an annular ring having a recessed section 990 for housing the first
busbar 900, the second busbar 910, the plurality of capacitor
elements 920, and the first insulating film 930.
[0071] The first portion of the housing has a first end section 981
and a second end section 982, where the first circumferential end
section 981 and the second circumferential end section 982 are
connected via a second portion 983 of the housing 940 that acts as
a link between the respect end sections 981, 982 of the first
portion 980.
[0072] The first busbar 900 includes a first busbar coupling
element 905 that is mounted within the second portion 983 of the
housing 940 to allow an electrical connection to be maintained
between the regions of the first busbar 900 located at the first
end section 981 and the second end section 982 of the housing
940.
[0073] Similarly, the second busbar 910 includes a second busbar
coupling element 915 that is mounted within the second portion 983
of the housing 940 to allow an electrical connection to be
maintained between the regions of the second busbar 910 located at
the first end section 981 and the second end section 982 of the
housing 940.
[0074] Having concentric busbars 900, 910 formed around the
capacitor elements 920, where the busbars 900, 910 are separated by
a thin insulation layer 930, rather than being placed on separate
sides of the respective capacitor elements 920, minimises the
inductance, thereby reducing losses in the inverter.
[0075] As no capacitor elements 920 are formed or mounted within
the second portion 983 of the housing 940, the second portion 983
of the housing 940 can be designed to follow a different shape
and/or configuration to the first portion 980 of the housing 940,
thereby providing greater freedom for allowing the ingress of
interface elements such as cabling and/or conduits into the
electric motor without effecting the inductance of the electric
motor/capacitor configuration while also allowing a more even
distribution of current around the first busbar 900 and the second
busbar 910, as described below.
[0076] For example, the second portion 983 of the housing 940,
which as stated above corresponds to a section of the housing 940
encapsulating a section of the first busbar 900 and the second
busbar 910 without capacitor elements, can be configured to extend
around cooling conduits 261 and/or electrical cabling entering the
motor, as illustrated in FIG. 2. Additionally, the second portion
983 can also be configured to avoid contact with other features of
the electric motor, for example the bearing 223 that is mounted
within the stator cavity. The second portion 983 of the housing 940
can be configured to have any suitable shape.
[0077] The first busbar 900 includes a first electrical coupling
element 950 formed towards the first end section 981 region of the
first portion of the housing. The first electrical coupling element
950 is used for coupling the first busbar 900 to a first terminal
of a DC power source, for example a battery located within the
vehicle housing the in-wheel electric motor. Similarly, the second
busbar 910 includes a second electrical coupling element 960 formed
towards the second end section 982 region of the first portion of
the housing. The second electrical coupling element 950 is used for
coupling the second busbar to a second terminal of the DC power
source, thereby allowing the annular capacitor element to be
coupled in parallel between the DC power source and the respective
inverters mounted in the in-wheel electric motor.
[0078] Accordingly, the first electrical coupling element 905 and
the second electrical coupling element 915 are coupled to the
respective busbars 900, 910 on opposite sides of the second portion
983 of the housing 940.
[0079] Additionally, the first busbar 900 and the second busbar 910
include coupling members 970 for coupling to the respective
inverter power source busbars mounted in the control modules 400 to
allow the capacitor component 920 to act as a voltage source to
each of the corresponding inverters, thereby allowing a single
capacitor component to be used to support a plurality of
inverters.
[0080] Maintaining an electrical connection on the first busbar 900
in the second portion 983 of the housing 940 allows an even
distribution of current to flow from the first electrical coupling
element 950 to the respective inverters coupled to the first busbar
900. By way of illustration, substantially half the current flow
from/to the DC power source will flow in an anticlockwise direction
on the first busbar 900 for providing current to the two inverters
coupled to the first busbar 900 in the anticlockwise direction and
half the current flow will flow through the first busbar coupling
element 905 to the two inverters coupled to the first busbar 900 in
the clockwise direction.
[0081] Similarly, maintaining an electrical connection on the
second busbar 910 in the second portion 983 of the housing 940
allows an even distribution of current to flow from the second
electrical coupling element 960 to the respective inverters coupled
to the second busbar 910. By way of illustration, substantially
half the current flow from/to the DC power source will flow in an
clockwise direction on the second busbar 910 for providing current
to the two inverters coupled to the second busbar 910 in the
clockwise direction and half the current flow will flow through the
second busbar coupling element 915 to the two inverters coupled to
the second busbar 910 in the anticlockwise direction.
[0082] For example, if the current requirements for each of the
inverters coupled to the first busbar 900 and the second busbar 910
is 100 Amps, in the above described configuration only 200 Amps
needs to flow in the respective busbars in both a clockwise and an
anticlockwise direction. In contrast, without the first busbar 900
having a first busbar coupling element 905 and the second busbar
910 having a second busbar coupling element 915 it would be
necessary for 400 Amps to flow from the first coupling element 950
on the first busbar 900 in an anticlockwise direction with 400 Amps
flowing from the second coupling element 960 in the second busbar
910 in a clockwise direction. Inductance can be calculated using
the equation:
L=R.mu..sub.o[ln 8R/.alpha.-2]
[0083] where a corresponds to the wire radius, R corresponds to the
current loop radius, .mu. corresponds to the magnetic permeability.
Accordingly, if the current flow around the first busbar and the
second busbar is in opposite directions the value for R will
correspond to the radius of the first busbar and the second busbar.
In contrast, if the current flow around the first busbar and the
second busbar is in the same direction the value for R will
correspond to the gap between the first busbar and the second
busbar.
[0084] In one embodiment, the first busbar 900 and the second
busbar 910 may be prefabricated annular sections that are push fit
onto the recess portion of the first housing so that the busbars
900, 910 are concentric. However, to minimise the dimensional
tolerances of the busbars 900, 910 and the risk of damage to the
capacitor assembly that could result from thermal expansion,
preferably at least one of the busbars 900, 910 are manufactured to
have a section removed approximately opposite to the second portion
283 of the housing 940, where a section of each of the busbars 900,
910 is removed to allow for variations in the diameter of the
annular capacitor component 920 resulting from manufacture and/or
thermal expansion. Similarly, having a gap in the first busbar 900
and the second busbar 910 allows the busbars to expand/contract
without causing stress to the surrounding components. The gap that
is formed in the first busbar 900 and the second busbar 910 to form
the C shaped busbars may be of any suitable size, however
preferably the size of the gap will calculated using the
coefficient of thermal expansion values of the materials used for
the busbars and engineering manufacturing tolerances and component
size to determine a gap size that will avoid the ends of the
busbars coming into contact over the thermal envelope of the
electric motor.
[0085] Preferably a first set of the plurality of capacitor
elements 920 are arranged to perform a first capacitor function and
a second set of the plurality of capacitor elements 920 are
arranged to perform a second capacitor function.
[0086] The first set of capacitor elements are arranged to couple
the DC voltage source to the respective inverters mounted in the
control modules 400 on the electric motor, where the first set of
capacitor elements are arranged to inhibit voltage transients
generated across the inverter switches, which could cause losses
and electrical stress on the switching devices and provide high
pulse current loads from the inverter. This has the effect of
reducing inductance on the inverters during current switching. The
first capacitor element is coupled in parallel between the DC
voltage source and the respective inverters.
[0087] To reduce electro-magnetic noise generated by the inverters,
the second set of capacitor act as Y capacitor elements and are
coupled in series with each other and in parallel with the first
set of capacitor elements.
[0088] Y capacitors act as part of an EMC solution within an
electric motor system, where Y capacitors are used in combination
with a local DC link capacitor (i.e. the first capacitor) to
reduce/control electromagnetic emissions by providing a path for
common mode EMC currents to flow back to the DC link, thereby
reducing the EMC currents flowing out of the motor.
[0089] For an electric motor having a plurality of sub-motors with
associated inverters, typically two Y capacitors are required for
each inverter. For a multi-inverter configuration this can have an
adverse impact on packaging, cost and reliability of an electric
motor system. However, the present invention allows a single Y
capacitor configuration to support multiple inverters, thereby
reducing packaging requirements and simplifying the manufacturing
process.
[0090] FIG. 11 illustrates an equivalent circuit for the integrated
capacitor component 800 with the first capacitor 1010 being coupled
between the positive and negative power rails of the DC voltage
source with the second capacitor 1020 being coupled between the
positive power rail and a reference potential, for example the
vehicle chassis, and the third capacitor 1030 being coupled between
the negative power rail and the reference potential. As stated
above, the respective inverters are coupled across the positive and
negative power rails of the DC voltage source.
[0091] By placing a set of capacitor elements in close proximity to
the plurality of separate inverters this has the effect of reducing
inductive effects and removing the need for snubber capacitors.
[0092] To allow the respective coil windings for two of the four
coil sets 60 to be coupled to a respective phase winding busbar
within a control module housing 550, the control module housing 550
is arranged to have six apertures 610, see FIG. 12.
[0093] The six apertures 610 are formed on an outer edge of the
control module housing 550 on the side of the housing 550 that is
to be mounted adjacent to the planar portion of the stator heat
sink 253.
[0094] The size and position of the six apertures 610 formed in the
control module housing 550 are arranged to match the positions and
diameters of the end portions of the coil windings that extend from
the planar portion of the stator heat sink 253, thereby allowing
the respective end portions of the coil windings to extend through
the apertures 610 when the control housing module 550 is mounted on
to the planar portion of the stator heat sink 253.
[0095] A partial perspective view of the control module housing 550
is illustrated in FIG. 16. A recess 710 is formed around each of
the six apertures 610 formed in the control module housing 550,
where each recess 710 is sized to allow a partial toroid made of
soft ferromagnetic material 530, for example a ferrite element, to
be located in the recess 710. The top of the partial toroid is
arranged to be substantially level with the bottom section of the
control module housing 550 when the partial toroid 530 is mounted
in a recess 710. The partial toroid of ferromagnetic material 530
has a section missing from the toroid that substantially
corresponds to the size of the Hall sensor mounted on the power
printed circuit board 500. To facilitate the guiding of the coil
windings as they pass through the aperture 610, the control module
housing 550 is arranged to have a conduit section formed around
each aperture 610. The conduit sections formed around each of the
respective apertures also prevent an elastomer placed in the
control module housing 550 from escaping through the apertures
during the curing process for the elastomer.
[0096] Preferably the recesses 710 formed in the base of the
control module housing 550 are keyed to ensure that the partial
toroids of soft ferromagnetic material 530 can only be oriented
within a recess 710 in a position where the missing section of the
toroid is aligned with the position of the Hall sensor mounted on
the power printed circuit board 500 when the power printed circuit
board 500 is mounted within the control module housing 550.
[0097] Once the partial toroids of soft ferromagnetic material 530
have been mounted in the respective recesses 710 formed in the base
of the control module housing 550, the power printed circuit board
500 is lowered into position in the control module housing. Upon
the power printed circuit board 500 being lowered into position in
the control module housing 550, as a result of the alignment of the
partial toroids of soft ferromagnetic material 530 and the Hall
sensors mounted on the power printed circuit board 500, the Hall
sensors mounted on the power printed circuit board 500 are inserted
into the missing sections of the respective partial toroids 530
mounted in the control module housing 550.
[0098] Once the power printed circuit board 500 has been lowered
into position in the control module housing the insert modules are
positioned over a respective power substrate assembly with the
respective inverter formed on the power substrates being coupled to
the respective power source busbars and phase winding busbars.
[0099] Each of the phase winding busbars formed on the respective
insert modules are arranged to include a coupling section for
coupling the phase winding busbar to a phase winding of one of the
coil sets. The coupling section for each phase winding busbar is
arranged to extend around a respective aperture 610 formed in the
base of the control module housing 550.
[0100] The control printed circuit board 520 is then mounted in the
control module housing 550 above the power printed circuit board
500, with the control printed circuit board 520 being electrically
coupled to the power printed circuit board 500 to allow the control
printed circuit board 520 to control the operation of the switches
on the inverters formed on the power substrate assemblies 510.
[0101] To mount the control module 400 to the stator, the
respective end sections of the coil windings form two coil sets 60
that extend away from the planar surface of the stator heat sink
253 (i.e. six coil winding end sections) are aligned with the
respective apertures 610 formed in the base of the control module
housing 550. The control module 400 is then pushed flush with the
surface of the stator so that the respective end sections of the
coil windings for two coil sets 60 that extend away from the planar
surface of the stator heat sink 253 (i.e. six coil winding end
sections) extend through the respective apertures 610 formed in the
base of the control module housing 550 with each of the current
sensors mounted in the control module 400 being mounted adjacent to
a respective end section of a coil winding.
[0102] The control module may be mounted to the stator by any
suitable means, for example one or more bolts that extend through
the control module into the surface of the stator heat sink.
[0103] Once the control module has been mounted to the stator, the
respective coupling sections of the phase winding busbars mounted
on the power printed circuit board 500 are coupled to a respective
end section of a coil winding, where any suitable means may be used
to couple the coupling section of the phase winding busbar to a
respective end section of a coil winding, for example crimping or
welding. Similarly, the respective power source busbars housed in
the control modules are coupled to respective coupling members on
the first busbar and the second busbar using any suitable means,
for example crimping or welding.
[0104] The inverter 410 formed on one power assembly 510, which is
coupled via the respective phase winding busbars to a first coil
set 60, is arranged to control current in the first coil set. The
other inverter 410 formed on the other power assembly 510 in the
control module 400 is arranged to control current in a second coil
set 60, where the current measurements made by the respective
current sensors are used by the processor on the control printed
circuit board 520 to control current in the respective coil sets
60.
[0105] Similarly, the second control module 400 is arranged to
control current in a third and fourth coil set 60.
* * * * *