Common mode current reduction hybrid drive system

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.

TECHNICAL FIELD

This application is generally related to a common mode current reduction system for a hybrid drive system of an electrified vehicle.

BACKGROUND

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

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.

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.

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.

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.

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.

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.

DETAILED DESCRIPTION

FIG. 1depicts 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 battery2may be coupled to an inverter4. The inverter4may be configured with outputs to drive phase windings6A,6B,6C of an electric machine8. The electric machine8further includes a first secondary winding10A and a second secondary winding10B. The first secondary winding10A may be electrically coupled to a rectifier circuit12. The second secondary winding10B may be coupled to a diagnostic circuit14.

FIG. 2depicts an electrified vehicle112that may be referred to as a plug-in hybrid-electric vehicle (PHEV). A plug-in hybrid-electric vehicle112may comprise one or more electric machines114mechanically coupled to a hybrid transmission116. The electric machines114may be capable of operating as a motor or a generator. In addition, the hybrid transmission116is mechanically coupled to an engine118. The hybrid transmission116is also mechanically coupled to a drive shaft120that is mechanically coupled to the wheels122. The electric machines114can provide propulsion and deceleration capability when the engine118is turned on or off. The electric machines114may 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 machines114may also reduce vehicle emissions by allowing the engine118to operate at more efficient speeds and allowing the hybrid-electric vehicle112to be operated in electric mode with the engine118off under certain conditions. An electrified vehicle112may also be a battery electric vehicle (BEV). In a BEV configuration, the engine118may not be present. In other configurations, the electrified vehicle112may be a full hybrid-electric vehicle (FHEV) without plug-in capability.

A traction battery or battery pack124stores energy that can be used by the electric machines114. The vehicle battery pack124may provide a high-voltage direct current (DC) output. The traction battery124may be electrically coupled to one or more power electronics modules126. One or more contactors142may isolate the traction battery124from other components when opened and connect the traction battery124to other components when closed. The power electronics module126is also electrically coupled to the electric machines114and provides the ability to bi-directionally transfer energy between the traction battery124and the electric machines114. For example, a traction battery124may provide a DC voltage while the electric machines114may operate with a three-phase alternating current (AC) to function. The power electronics module126may convert the DC voltage to a three-phase AC current to operate the electric machines114. In a regenerative mode, the power electronics module126may convert the three-phase AC current from the electric machines114acting as generators to the DC voltage compatible with the traction battery124.

The vehicle112may include a variable-voltage converter (VVC)152electrically coupled between the traction battery124and the power electronics module126. The VVC152may be a DC/DC boost converter configured to increase or boost the voltage provided by the traction battery124. By increasing the voltage, current requirements may be decreased leading to a reduction in wiring size for the power electronics module126and the electric machines114. Further, the electric machines114may be operated with better efficiency and lower losses.

In addition to providing energy for propulsion, the traction battery124may provide energy for other vehicle electrical systems. The vehicle112may include a DC/DC converter module128that converts the high-voltage DC output of the traction battery124to a low voltage DC supply that is compatible with low-voltage vehicle loads. An output of the DC/DC converter module128may be electrically coupled to an auxiliary battery130(e.g., 12V battery) for charging the auxiliary battery130. The low-voltage systems may be electrically coupled to the auxiliary battery130. One or more electrical loads146may be coupled to the high-voltage bus. The electrical loads146may have an associated controller that operates and controls the electrical loads146when appropriate. Examples of electrical loads146may be a fan, an electric heating element and/or an air-conditioning compressor.

The electrified vehicle112may be configured to recharge the traction battery124from an external power source136. The external power source136may be a connection to an electrical outlet. The external power source136may be electrically coupled to a charger or electric vehicle supply equipment (EVSE)138. The external power source136may be an electrical power distribution network or grid as provided by an electric utility company. The EVSE138may provide circuitry and controls to regulate and manage the transfer of energy between the power source136and the vehicle112. The external power source136may provide DC or AC electric power to the EVSE138. The EVSE138may have a charge connector140for plugging into a charge port134of the vehicle112. The charge port134may be any type of port configured to transfer power from the EVSE138to the vehicle112. The charge port134may be electrically coupled to a charger or on-board power conversion module132. The power conversion module132may condition the power supplied from the EVSE138to provide the proper voltage and current levels to the traction battery124. The power conversion module132may interface with the EVSE138to coordinate the delivery of power to the vehicle112. The EVSE connector140may have pins that mate with corresponding recesses of the charge port134. Alternatively, various components described as being electrically coupled or connected may transfer power using a wireless inductive coupling.

One or more wheel brakes144may be provided for decelerating the vehicle112and preventing motion of the vehicle112. The wheel brakes144may be hydraulically actuated, electrically actuated, or some combination thereof. The wheel brakes144may be a part of a brake system150. The brake system150may include other components to operate the wheel brakes144. For simplicity, the figure depicts a single connection between the brake system150and one of the wheel brakes144. A connection between the brake system150and the other wheel brakes144is implied. The brake system150may include a controller to monitor and coordinate the brake system150. The brake system150may monitor the brake components and control the wheel brakes144for vehicle deceleration. The brake system150may respond to driver commands and may also operate autonomously to implement features such as stability control. The controller of the brake system150may implement a method of applying a requested brake force when requested by another controller or sub-function.

Electronic modules in the vehicle112may 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 battery130. 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 inFIG. 2but it may be implied that the vehicle network may connect to any electronic module that is present in the vehicle112. A vehicle system controller (VSC)148may be present to coordinate the operation of the various components.

With reference toFIG. 3, a system300is provided for controlling a power electronics module (PEM)126. The PEM126ofFIG. 3is shown to include a plurality of switches302configured to collectively operate as an inverter with first, second, and third phase legs316,318,320. 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 PEM126may include multiple converters with each inverter in the PEM126including three or more phase legs. For example, the system300may include two or more inverters in the PEM126. The PEM126may 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.

The switches302may 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.

As shown inFIG. 3, the inverter may be a DC-AC converter. In operation, the DC-AC converter receives DC power from a DC power link306through a DC bus304and converts the DC power to AC power. The DC power bus may include a positive bus conductor304A and a return bus conductor304B. 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 machine114, such as a three-phase permanent-magnet synchronous motor (PMSM) as depicted inFIG. 3. In such an example, the DC power link306may be electrically coupled to a DC storage battery (e.g., traction battery124) to provide DC power to the DC bus304. In another example, the inverter may operate as an AC-DC converter that converts AC power from the electric machine114(e.g., operating as a generator) to DC power that the DC bus304can transfer to the DC power link306. Furthermore, the system300may control the PEM126in other power electronic topologies.

With continuing reference toFIG. 3, each of the phase leg outputs316,318,320in the inverter126are coupled to associated power switches302, which may be implemented by various types of controllable switches. In one embodiment, each power switch302may include a diode and a transistor, (e.g., an IGBT). The diodes ofFIG. 3are labeled Da1, Da2, Db1, Db2, Dc1, and Dc2while the IGBTs ofFIG. 3are respectively labeled Sa1, Sa2, Sb1, Sb2, Sc1, and Sc2. The power switches Sa1, Sa2, Da1, and Da2are part of phase leg A of the three-phase inverter126, which is labeled as the first phase leg A316inFIG. 3. Similarly, the power switches Sb1, Sb2, Db1, and Db2are part of phase leg B318and the power switches Sc1, Sc2, Dc1, and Dc2are part of phase leg C320of the three-phase converter. The inverter126may include any number of the power switches302or circuit elements depending on the particular configuration of the inverter126. The diodes (Dxx) are connected in parallel with the IGBTs (Sxx). 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.

As illustrated inFIG. 3, current sensors CSa, CSb, and CScmay be provided to sense current flow in the respective phase legs316,318,320.FIG. 3depicts the current sensors CSa, CSb, and CScas being separate from the PEM126. However, the current sensors CSa, CSb, and CScmay be integrated as part of the PEM126depending on the configuration. Current sensors CSa, CSb, and CScofFIG. 3may be installed in series with each of phase legs A, B and C (i.e., phase legs316,318,320inFIG. 3) and provide respective feedback signals for the phase currents ias, ibs, and ics(also illustrated inFIG. 3) of the system300. The feedback signals ias, ibs, and icsmay be raw current signals processed by logic device (LD)310or may be embedded or encoded with data or information about the current flow through the respective phase legs316,318,320. Also, the power switches302(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 ias, ibs, and ics. 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.

Referring again toFIG. 3, the system300includes a logic device (LD) or controller310. The controller or LD310can be implemented by various types or combinations of electronic devices and/or microprocessor-based computers or controllers. To implement a method of controlling the PEM126, the controller310may execute a computer program or algorithm embedded or encoded with the method and stored in volatile and/or persistent memory312. 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 ofFIG. 3, the controller310receives and processes the feedback signals ias, ibs, and icsto control the phase currents ia, ib, and icsuch that the phase currents ia, ib, and icflow through the phase legs316,318,320and into the respective phase windings of the electric machine114according to various current or voltage patterns. For example, current patterns can include patterns of phase currents ia, ib, and icflowing into and away from the DC-bus304or a DC-bus capacitor308. The DC-bus capacitor308ofFIG. 3is shown separate from the PEM126. However, the DC-bus capacitor308may be integrated as part of the PEM126.

As shown inFIG. 3, a storage medium312(hereinafter “memory”), such as computer-readable memory may store the computer program or algorithm embedded or encoded with the method. In addition, the memory312may store data or information about the various operating conditions or components in the PEM126. The memory312may 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 memory312may store data or information about current flow through the respective phase legs316,318,320. The memory312can be part of the controller310as shown inFIG. 3. However, the memory312may be positioned in any suitable location accessible by the controller310.

As illustrated inFIG. 3, the controller310may transmit at least one control signal322to the power converter system126. The power converter system126may receive the control signal322and control the switching configuration of the inverter126to control the current flow through the respective phase legs316,318, and320. The switching configuration may be a set of switching states of the power switches302in the inverter126. In general, the switching configuration of the inverter126determines how the inverter126converts power between the DC power link306and the electric machine114.

To control the switching configuration of the inverter126, the inverter126changes the switching state of each power switch302in the inverter126to either an ON state or an OFF state based on the control signal322. In the illustrated embodiment, to switch the power switch302to either ON or OFF states, the controller/LD310provides the gate voltage (Vg) to each power switch302and therefore drives the switching state of each power switch302. Gate voltages Vga1, Vga2, Vgb1, Vgb2, Vgc1, and Vgc2(shown inFIG. 3) control the switching state and characteristics of the respective power switches302. While the inverter126is shown as a voltage-driven device inFIG. 3, the inverter126may be a current-driven device or controlled by other strategies that switch the power switches302between ON and OFF states. The controller310may change the gate drive for each of the power switches302based on the rotational speed of the electric machine114, 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.

As also shown inFIG. 3, each phase leg316,318, and320includes two switches302. In general, each phase leg includes a switch coupled between the positive bus conductor304A and the associated phase leg output (upper switch) and a switch coupled between the return bus conductor304B and the associated phase leg output (lower switch). However, only one switch in each of the legs316,318,320may be in the ON state without shorting the DC power link306. 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., Sa1, Sb1, Sc1) or a single IGBT.

Two situations can occur during an active state of the three-phase converter example illustrated inFIG. 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.

The power switches302may 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 LD310may 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.

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.

FIG. 4depicts an electric drive system400having an electric machine that includes one or more secondary windings. The electric drive system400may include an electric machine414that includes three phase windings that are configured to rotate a shaft and rotor when driven by current. In addition, the electric machine414may include a first secondary winding402and the second secondary winding408. The first secondary winding402and the second secondary winding408may be configured to operate as a CMV transformer. For example, the first secondary winding402may be configured to harvest power of the CMV that would cause current to flow through the structure of the electric machine414. The first secondary winding402may provide a low-impedance path for the common-mode current. This may reduce undesired common-mode current flowing through the electric machine414, particularly the bearings. The second secondary winding408may be similarly configured.

The first secondary winding402may be electrically coupled to a rectifier circuit404. The rectifier circuit404may be configured to process an AC voltage from the first secondary winding402so that current only flows in one direction. The rectifier circuit404may include an arrangement of passive circuit elements such as diodes. The rectifier circuit404may include a capacitor to smooth the resulting voltage. The rectifier circuit404may be configured to provide a generally constant DC voltage level at the output.

The output of the rectifier circuit404may be electrically coupled to a gate driver circuit406. The gate driver circuit406may be configured to drive gate inputs of the power switches302. The gate driver circuit406may be powered by the output of the rectifier circuit404. The gate driver circuit406may be alternatively powered by the low-voltage bus when no power is being received from the rectifier circuit404. For example, under conditions in which the electric machine phase windings are not driven, there may be no CMV-induced currents flowing.

The gate driver circuit406may also be controlled by control signals from a controller412. For example, the controller412may provide the gate drive signals as a PWM signal. The gate driver circuit406may filter and process the gate drive signals to provide a physical gate drive voltage with the appropriate characteristics to drive the power switches302in the desired state.

The second secondary winding408may be electrically coupled to diagnostic circuit410that is configured to output a diagnostic signal. The diagnostic signal may be input to a controller412. The diagnostic circuit410may 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 winding408. The controller412may be programmed to monitor the diagnostic signal to determine if the electric machine414and/or the power electronics module126is operating properly. In some configurations, the controller412may utilize the diagnostic signal to control operation of the power switches302. For example, the controller412may operate the power switches302to reduce the CMV below a predetermined level.

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. 5is an exploded perspective view of an electric machine500having a stator504that defines a plurality of stator teeth506along an inner diameter that defines a cavity configured to permit a rotor502to spin freely about a rotational axis510. Each of stator teeth506has 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 stator504includes end windings508that carry a current in windings that travel in the slots in between the stator teeth506to induce a field in the stator teeth506. In this application a current flowing in the end windings508between 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.

FIG. 6is a cross sectional view of a stator core600for an electric machine. Here, a 24-tooth stator is shown. The stator504may be symmetrical around the rotational axis510about which the rotor may be configured to spin. The stator504may be divided into sections by a first plane602A and a second plane602B that intersect along the rotational axis510. 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−.

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 segment606A that is routed in the slot clockwise from A1+ and returns via a conductor segment606B 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 segment608A that is routed in the slot clockwise from B1+ and returns via a conductor segment608B that is routed in the slot clockwise from B1−. The third phase winding may be formed by a conductor segment610A that is routed in the slot clockwise from C1+ and returns via a conductor segment610B that is routed in the slot clockwise from C1−. The second phase winding consisting of B1+ 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.

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.

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 segments604A-F that may be arranged in the slots as shown inFIG. 7.FIG. 6depicts the secondary winding as being inserted closest to the rotational axis510. However, in some configurations, the relative position of the secondary windings (defined by604A-F) and the power windings (defined by606,608, and610) may be swapped. Further, some configurations may include a second secondary winding similar that defined by604A-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.

FIG. 7depicts 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 segment604A 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 segment604B. The conductor may then be routed next to the B+ tooth as represented by a third segment604C. The conductor may then be routed next to the A-tooth as represented by a fourth segment604D. The conductor may then be routed next to the C+ tooth as represented by a fifth segment604E. The conductor may then be routed next to the B− tooth a represented by a sixth segment604F. The pattern may be reproduced to achieve a predetermined number of turns or iterations for the secondary winding604. The terminals of the secondary winding may be the connections to the first segment604A and the sixth segment604F.

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 stator504. As an example, the B1− slot may be coupled to the A2+ slot. The conductor may be routed with the same pattern.

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.

Referring again toFIG. 4, the controller412may be configured to receive the signal indicative of the common mode voltage. The controller412may be configured to adjust the operation of the switches302based on the voltage. For example, the controller412may 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 controller412may change the common mode voltage by altering the switching pattern of the power switches302.

FIG. 8is a cross sectional schematic diagram of power winding connections800for 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 A606, B608, and C610. 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 plane602A (e.g., a reference plane) that intersects with a rotational axis510of the electric machine. The stator may be further divided into quarters by a second plane602B that also intersects with the rotational axis510.

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 output316. 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 output318. 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 output320. 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.

FIG. 9depicts an electrical schematic900of 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 winding902that is magnetically coupled to a first secondary winding904A and a second secondary winding904B. The first secondary winding904A and the second secondary winding904B may be electrically isolated from one another and share a common magnetic core formed by the stator metal structure and a common primary winding902. During operation of the power windings using PWM signals, a CMV is created at the primary winding902. The CMV is induced in the first secondary winding904A and the second secondary winding904B.

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. 10depicts a first system configuration1000in which the secondary windings are configured to be voltage sources. The first secondary winding904A may be electrically coupled to a first rectifier network1002A. The first rectifier network1002A may cause current to flow in one direction at the output of the first rectifier network1002A. For example, the output of the first rectifier network1002A may be electrically coupled to a DC bus to function as a voltage source. A first capacitor1004may be electrically coupled across output terminals of the first rectifier network1002A. The first capacitor1004may smooth and filter the output of the first rectifier network1002A resulting in a DC voltage level.

The second secondary winding904B may be electrically coupled to a second rectifier network1002B. The second rectifier network1002B may cause current to flow in one direction from to the output of the second rectifier network1002B. For example, the output of the second rectifier network1002B may be electrically coupled to a DC bus to function as a voltage source. A second capacitor1006may be electrically coupled across output terminals of the second rectifier network1002B. The second capacitor1006may smooth and filter the output of the second rectifier network1002B resulting in a DC voltage level.

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 network1002may be adjusted by selecting the number of windings for the associated secondary winding904. 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.

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.

The CMV transformer may also be utilized as a diagnostic sensor.FIG. 11depicts a second system configuration1100that includes a voltage source and a diagnostic circuit. The voltage source may include the first secondary winding904A coupled to the first rectifier network1002A and first capacitor1004as described previously. The diagnostic circuit may be coupled to the second secondary winding904B. The diagnostic circuit may include an analog circuit1102and an analog-to-digital (A/D) converter1104. The A/D converter1104may be configured to convert the output of the second secondary winding904B to a digital value for use by the controller (e.g., controller412inFIG. 4). The analog circuit1102may include components to generate an analog signal indicative of the CMV. For example, the analog circuit1102may be configured to output an analog signal indicative of the frequency of the CMV.

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.

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 controller412may be programmed to identify the abnormal operating conditions by monitoring the analog and digital outputs of the diagnostic sensor. The controller412may shut down operation of the inverter responsive to detecting an abnormal operation condition.