Patent Description:
The present invention relates generally to a system for recharging a power storage device, and more particularly for discharging or supplying power from a power storage device mounted on a vehicle, for example.

Many plug-in hybrid electric vehicles (PHEVs) have two electric motors. One motor may typically be utilized for traction while the other is utilized for power generation. There are also other accessory electric motors in these vehicles (i.e., air conditioning compressor, and power steering pump). These motors are often three-phase permanent magnet motors, which, during operation are powered by an on-board power supply, such as a battery. As the vehicle is operated, the on-board power supply discharges and requires recharging at some point.

The PHEVs have on-board power generation capabilities using a fuel based generator to partially recharge the on-board electrical power supply as needed. However, it may be preferred to recharge the on-board power supply using an external power source when possible.

For opportunistic recharging using an external power source, it is beneficial for the vehicle to have the ability to accept power from any standard electrical outlet and Electric Vehicle Support Equipment (EVSE) and possibly a DC source. Electronics associated with such opportunistic recharging may undesirably add cost and/or weight to the vehicle. Since it may not be practical to plug-in charge and drive the vehicle at the same time, dual purposing the drive magnetics and power electronics and/or the accessory motor systems as part of the battery charger may be utilized.

For example, the battery charger may be integrated into a dual three-phase motor drive train with star connected motor windings by connecting a plug-in power supply to the neutral node of each three-phase motor.

With the neutral node connected configuration, equal currents can be made to flow through the motor windings to avoid creating motor torque. When equal currents are caused to flow through three-phase windings of the motor, however, what can be utilized is only the leakage inductance of the windings. Therefore, there may be problems that the commercial power supply cannot sufficiently be boosted to the battery voltage, or influence of ripple to the input side increases.

Further, when single-phase or dual-phase motor windings are selected and a current is caused to flow therein to utilize the higher magnetic inductance, the motor generates torque which could cause the vehicle to move or oscillate during charging especially as the stator winding current changes direction each AC half line cycle.

Further, these neutral node connected integrated charging systems tend to induce a high common-mode noise, electromagnetic interference (EMI), and unwanted ground currents.

<CIT> relates to a power controller exchanging electric power between a commercial power supply and a power storage device mounted on a vehicle, as well as to a vehicle equipped with the power controller. An electronic control unit (ECU) detects an effective value and phase of a voltage from a commercial power supply, based on a voltage from a voltage sensor. Further, the ECU generates a command current, which is a command value of current caused to flow through power lines and in-phase with the voltage of the commercial power supply, based on the detected effective value and the phase and on a charge/discharge power command value for a power storage device. Then, the ECU controls zero-phase voltage of inverters based on the generated command current.

<CIT> discloses a drive and recharge system including a bidirectional dc power source, two voltage-fed inverters, two induction motors, and a control unit. In the drive mode, power is bidirectionally connected between the dc power source and the motors. In the recharge mode, single-phase power applied to the neutral ports of the two motors is converted with unity power factor to return energy to the dc power source. An alternate scheme is also presented which uses a single motor having two sets of windings.

An integrated bi-directional charge transfer system is disclosed. The integrated bi-directional charge transfer system comprises a plug-in power supply directly and electrically connected between at least one of a first plurality of switch legs of a first inverter and at least one of a second plurality of switch legs of a second inverter, wherein a switch leg is a pair of serially connected switching elements of an inverter; and a controller operatively coupled to the first inverter and the second inverter. The controller is configured to selectively modulates the plurality of switch legs of the first inverter that are not connected to the plug-in power supply and of the plurality of switch legs of the second inverter that are not connected to the plug-in power supply to reduce common mode noise between the plug-in power supply and an on-board vehicle power supply. During a charging operation of the on-board vehicle power supply, the controller is configured to selectively modulate switch legs such that electric current flow alternates between at least one of a first plurality of stator windings of a first motor to charge the on-board vehicle power supply during a first plug-in supply voltage polarity state and at least one of a second plurality of stator windings of a second motor to charge the on-board vehicle power supply during a second plug-in supply voltage polarity state. During a discharging operation of the on-board vehicle power supply, the controller is configured to selectively modulate at least one of the plurality of switch legs of the first inverter and the plurality of switch legs of the second inverter such that electric current flows to the plug-in supply through the at least one of the first plurality of stator windings of the first motor or the at least one of the second plurality of stator windings L4, L5, L6) of the second motor to discharge the on-board vehicle power supply.

It is to be understood that the figures and descriptions of embodiments of a charge transfer system have been simplified to illustrate elements that are relevant for a clear understanding, while eliminating, for the purpose of clarity, many other elements found in typical vehicle systems. Those of ordinary skill in the art may recognize that other elements and/or steps are desirable and/or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein.

The non-limiting embodiments described herein are with respect to a charge transfer system. The charge transfer system may be modified for a variety of applications and uses while remaining within the scope of the claims. The embodiments and variations described herein, and/or shown in the drawings, are presented by way of example only and are not limiting as to the scope. The descriptions herein may be applicable to all embodiments of the charge transfer system including, for example but not limited to, an integrated bi-directional charge transfer system although it may be described with respect to a particular embodiment.

Referring now to the drawings wherein similar reference numerals refer to similar elements across the several views, a charge transfer system is described. The embodiments described herein provide an on-board charging solution for an electric or hybrid electric vehicle by integrating with the on-board drive magnetics and power electronics.

In general and as further described herein below, embodiments of the present invention connect the plug-in supply to at least one switch leg of both inverters. Such a configuration can be used to perform several types of bridgeless power factor correction (PFC) boost/buck conversions within the dual inverter/motor drive system to charge and discharge the vehicle power supply. One of these bridgeless PFC boost/buck conversions creates two distinct and complementary boost/buck converter circuits. Each PFC boost/buck converter circuit utilizing a single motor's windings as its inductive element. Full wave rectification is accomplished by alternating between the two boost/buck circuits each AC half power line cycle. This configuration along with PFC modulation benefits from increased boost inductance, stable zero torque angle within each motor, and reduced noise levels.

<FIG> is a top level diagram of a vehicle charging system <NUM> in accordance with an embodiment. The vehicle charging system <NUM> includes an on-board vehicle motor system <NUM> and a plug-in power supply <NUM>.

On-board vehicle motor system <NUM> includes an on-board power supply <NUM>, a first inverter <NUM> and a second inverter <NUM>, a first permanent magnetic motor <NUM> and a second permanent magnetic motor <NUM>. The first inverter <NUM> includes a plurality of switch legs A, B, C. Each of the plurality of switch legs A, B, C includes a pair of switching elements Q1/Q2, Q3/Q4, and Q5/Q6 respectively. Each switching element QI, Q2, Q3, Q4, Q5, and Q6 includes an associated paralleling diode D1, D2, D3, D4, D5, and D6 respectively for clamping voltage transients experienced when switching inductive loads. Similarly, the second inverter <NUM> includes a plurality of switch legs A', B', C'. Each of the plurality of switch legs A', B', C' includes a pair of switching elements Q7/Q8, Q9/Q10, and Q11/Q12 respectively. Each switching element Q7, Q8, Q9, Q10, Q11, and Q12 includes an associated paralleling diode D7, D8, D9, D10, D11, and D12 respectively for clamping voltage transients experienced when switching inductive loads. The first motor <NUM> includes a plurality of stator windings Li, L2, L3 connected to the plurality of switch legs A, B, C of the first inverter <NUM>. The second motor <NUM> includes a plurality of stator windings L4, L5, L6 connected to the plurality of switch legs A', B', C' of the second inverter <NUM>. The plug-in power supply <NUM> is connected between switch legs A and A' of inverters <NUM> and <NUM>, respectively. Alternatively, the plug-in power supply <NUM> may be connected between one or more of the switch legs A, B and C of inverter <NUM> and one or more of the switch legs A', B' and C', of inverter <NUM>.

In the examples described herein, the plurality of switching elements Q1-Q12 can represent either insulated-gate bipolar transistor (IGBT) or metal-oxide-semiconductor field-effect transistor (MOSFET) devices, by way of non-limiting example only. In an embodiment, with the bidirectional aspect of MOSFET devices one could turn any of the corresponding switching elements to "ON" for each switch where the paralleling diode is conducting to further reduce conduction losses.

Referring now to <FIG>, there is shown a more detailed diagram of an embodiment of the vehicle charging system <NUM> of <FIG>. On-board vehicle motor system <NUM> includes an on-board supply <NUM>, a first inverter <NUM> and a second inverter <NUM>, a controller <NUM>, a first motor <NUM> and a second motor <NUM>. The on-board supply <NUM> may include a battery <NUM> and capacitor Cl. As will be understood by one of ordinary skill in the art, capacitor Cl may be used for absorbing and supplying high frequency currents during pulsed switching. The plug-in supply <NUM> includes a filter <NUM> and a switch K1 for completing a circuit between the plug-in supply <NUM> and the on-board vehicle motor system <NUM>.

As described above, the first inverter <NUM> includes a plurality of switch legs A, B, C. Each of the plurality of switch legs A, B, C includes a pair of switching elements Q1/Q2, Q3/Q4, and Q5/Q6 respectively. Each switching element Q1, Q2, Q3, Q4, Q5, and Q6 includes an associated paralleling diode D1, D2, D3, D4, D5, and D6 respectively for clamping voltage transients experienced when switching inductive loads. Similarly, the second inverter <NUM> includes a plurality of switch legs A', B', C'. Each of the plurality of switch legs A', B', C' includes a pair of switching elements Q7/Q8, Q9/Q10, and Q11/Q12 respectively. Each switching element Q7, Q8, Q9, Q10, Q11, and Q12 includes an associated paralleling diode D7, D8, D9, D10, D11, and D12 respectively for clamping voltage transients experienced when switching inductive loads. The first motor <NUM> includes a plurality of stator windings Li, L2, L3 connected to the plurality of switch legs A, B, C of the first inverter <NUM>. The second motor <NUM> includes a plurality of stator windings L4, L5, L6 connected to the plurality of switch legs A', B', C' of the second inverter <NUM>.

The controller <NUM> includes current inputs II, <NUM>, <NUM>, <NUM> and a voltage input Vdc corresponding to the associated induced currents and respective voltage Vdc in the on-board vehicle motor system <NUM>. The controller <NUM> also includes a second voltage input, Vac, which corresponds to the Vac output from the plug-in supply <NUM>. The controller <NUM> also includes a plurality of outputs <NUM> - <NUM>, and <NUM> - <NUM> for switches QI-Q6, and Q7-Q12, respectively and output <NUM> for KI, for controlling the closing and opening of those respective switches. Accordingly, the controller <NUM> may include software, firmware or the like to perform the operations allocated to it.

The plug-in power supply <NUM> is connected to switch legs A and A' of inverters <NUM> and <NUM>, respectively, and the filter <NUM>, which may be an electromagnetic interference (EMI) filter, which in turn may be connected to an external charge port, (e.g., standard electrical outlet or standard EVSE, DC source, or load). Alternatively, the plug-in power supply <NUM> may be connected between one or more of the switch legs A, B and C of inverter <NUM> and one or more of the switch legs A', B' and C', of inverter <NUM>.

Referring now to <FIG>, there is shown an example of an on-board vehicle power supply charging operation in accordance with the invention. The operations shown in <FIG> is a boost modulation that alternates between motors <NUM> and <NUM> to maintain a sufficiently stable stator flux vector angle in each motor. Alternation between motors <NUM> and <NUM> depends on the polarity of the AC line voltage of the plug-in supply <NUM>. The boost modulation may be performed such that the instantaneous plug-in supply current is proportional to the plug-in supply voltage to achieve a unity power factor, (i.e., PF=<NUM>). Unity power factor may be achieved using power factor correction (PFC).

<FIG> show a high frequency (e.g., <NUM>-<NUM> kilohertz (kHz) modulated first and second switch states when the AC line voltage polarity of the plug-in power supply <NUM> is positive, (i.e., during a positive half line cycle). <FIG> show a high frequency (e.g., <NUM>-<NUM> kilohertz (kHz)) modulated first and second switch states when the AC line voltage polarity of the plug-in power supply <NUM> is negative, (i.e., during a negative half line cycle). The duty cycle ratio between the respective first and second switch states is such that a unity power factor is achieved.

Depending on the polarity of the AC line voltage of the plug-in power supply <NUM>, either the first inverter <NUM> or the second inverter <NUM> is in a non-switching state, (referred herein as the "non-switching state inverter"), while the remaining one of the first inverter <NUM> or the second inverter <NUM> is modulating the switch legs not directly connected to the plug-in supply, (which is for purposes of illustration only shown as switch legs B, C, B' and C' in <FIG>), to keep the line current in phase with the line voltage to maintain a unity power factor load condition (PF=<NUM>). The non-switching state inverter provides a low frequency reference, (which is instrumental in reducing noise levels), between the on-board supply <NUM> and the plug-in supply <NUM> through a low side paralleling diode of the plug-in connected switch leg (switch leg A or switch leg A') during each AC half line cycle (i.e., either a positive or negative half line cycle), where an AC line cycle may be <NUM>, by way of non-limiting example. The frequency of the AC line cycle may be any applicable value for any applicable region.

At zero line power crossings, (i.e., when the polarity of the AC line voltage goes from positive to negative polarity and vice-versa), the non-switching state inverter flips from non-switching state mode to PFC boost modulation or vice versa and then back again alternating with the AC line voltage polarity. In some examples, interleaving or distributing the pulsed switching of the switch legs not connected to the plug-in power supply <NUM> (switch legs B and C or B' and C') can also be used to reduce line ripple and for limited adjustment of the zero torque rotor angle position for first and second motors <NUM> and <NUM>. Additionally the switch leg modulation frequency (e.g., <NUM>-<NUM>) may be adjusted based on the terminal inductance of the motors <NUM> and <NUM> to minimize line distortion, including but not limited to line ripple, in the plug-in power supply <NUM>.

<FIG> and <FIG> depict the high frequency (e.g., <NUM>-<NUM> kilohertz (kHz)) modulated first and second switch states, when the AC line voltage polarity of the plug-in power supply <NUM> is positive. That is, <FIG> and <FIG> depict a positive plug-in polarity boost modulation. <FIG> depicts the first positive switch state. During the first positive switch state, controller <NUM> generates and transmits control signals through outputs <NUM> and <NUM> to switches Q4 and Q6 of the first inverter <NUM>, causing switches Q4 and Q6 to close and current I to flow into motor <NUM> thereby charging the inductance of stator windings Li, L2 and L3 of motor <NUM> as shown. Diode D8 operates to allow current I to flow accordingly.

<FIG> depicts the second positive switch state. During the second positive switch state, controller <NUM> generates and transmits control signals through outputs <NUM> and <NUM> to switches Q4 and Q6 of the first inverter <NUM>, causing switches Q4 and Q6 to open, thereby allowing the charged inductance of stator windings Li, L2 and L3 to discharge and allow the current I to flow from the plug-in supply <NUM> to the on-board supply <NUM>, thereby resulting in the charging of the on-board supply <NUM> for the positive plug-in polarity boost modulation. Diodes D3, D5, and D8 operate to allow current I to flow accordingly.

<FIG> and <FIG> depict the high frequency modulated first and second negative switch states. That is, <FIG> and <FIG> depict a negative plug-in polarity boost modulation. <FIG> depicts the first negative switch state. During the first negative switch state, controller <NUM> generates and transmits control signals through outputs <NUM> and <NUM> to switches Q10 and Q12 of the second inverter <NUM>, causing switches Q10 and Q12 to close and current I to flow into motor <NUM> thereby charging the inductance of stator windings L4, L5 and L6 of motor <NUM> as shown. Diode D2 operates to allow current I to flow accordingly.

<FIG> depicts the second negative switch state. During the second negative switch state, controller <NUM> generates and transmits control signals through outputs <NUM> and <NUM> to switches Q10 and Q12 of the second inverter <NUM>, causing switches Q10 and Q12 to open, thereby allowing the charged inductance of stator windings L4, L5 and L6 to discharge and allow the current I to flow from the plug-in supply <NUM> to the on-board supply <NUM>, thereby resulting in the charging of the on-board supply <NUM> for the negative plug-in polarity boost modulation. Diodes D2, D9, and D <NUM><NUM> operate to allow current I to flow accordingly.

Accordingly, during the positive plug-in polarity boost modulation, charging of the on-board supply <NUM> occurs through motor <NUM>, while during the negative plug-in polarity boost modulation, charging occurs through motor <NUM>. Charging, then, alternates between motors <NUM> and <NUM>. The magnetizing current I is unidirectional within each motor <NUM> and motor <NUM>, respectively, which may result in a stationary zero torque rotor angle.

Referring now to <FIG>, there is shown an example of an on-board vehicle power supply discharging operation in accordance with the invention. That is, the operations shown in <FIG> are a PFC buck modulation that alternates between motor <NUM> and motor <NUM>. <FIG> and <FIG> depict a positive plug-in polarity buck modulation and <FIG> and <FIG> depict a negative plug-in polarity buck modulation.

<FIG> depicts a first positive switch state for positive plug-in polarity buck modulation. During the first positive switch state, controller <NUM> generates and transmits control signals through outputs <NUM>, <NUM> and <NUM> to switches Q1 of first inverter <NUM>, and switches Q10 and Q12 of the second inverter <NUM>, respectively, causing the switches Q1 of first inverter <NUM>, and switches Q10 and Q12 of the second inverter <NUM> to close, and current I to flow from the on-board supply <NUM> out through the plug-in supply <NUM>, and into motor <NUM>, thereby charging the inductance of stator windings L4, L5 and L6 of motor <NUM> as shown.

<FIG> depicts a second positive switch state for the positive plug-in polarity buck modulation. During the second positive switch state, controller <NUM> generates and transmits control signals through outputs <NUM>, <NUM> and <NUM> to switches Q1 of first inverter <NUM>, and switches Q10 and Q12 of the second inverter <NUM>, respectively, causing the switches Q1 of first inverter <NUM> to remain closed and switches Q10 and Q12 of the second inverter <NUM> to open, thereby allowing the charged inductance of stator windings L4, L5 and L6 to discharge thus allowing the current I to continue flowing to the plug-in supply <NUM> to a charge port, (which for example, is shown in <FIG>), resulting in power being supplied out through the plug-in supply <NUM> for the positive plug-in polarity buck modulation. Diodes D9 and DII operate to allow current I to flow accordingly.

<FIG> depicts a first negative switch state for the negative plug-in polarity buck modulation. During the first negative switch state, controller <NUM> generates and transmits control signals through outputs <NUM> and <NUM> and <NUM> to switches Q4 and Q6 of inverter <NUM> and switch Q7 of inverter <NUM>, respectively, causing switches Q4 and Q6 of inverter <NUM> and switch Q7 of inverter <NUM> to close, thereby causing current I to flow from the on-board supply <NUM> out through the plug-in supply <NUM>, and into motor <NUM> , thereby charging the inductance of stator windings Li, L2, and L3 of motor <NUM> as shown.

<FIG> depicts a second negative switch state for the negative plug-in polarity buck modulation. During the second negative switch state, controller <NUM> generates and transmits control signals through outputs <NUM>, <NUM> and <NUM> to switches Q4 and Q6 of inverter <NUM> and switch Q7 of inverter <NUM>, respectively, causing switches Q4 and Q6 of inverter <NUM> to open and switch Q7 of inverter <NUM> to remain closed, thereby allowing charged inductance of stator windings Li, L2 and L3 to discharge thus allowing the current I to continue flowing to the plug-in supply <NUM> to a charge port, (which for example, is shown in <FIG>), resulting in power being supplied out through the plug-in power supply <NUM> for the negative plug-in polarity buck modulation. Diodes D3 and D5 operate to allow current I to flow accordingly.

Accordingly, during the positive plug-in polarity buck modulation, output to the plug-in supply <NUM> occurs through motor <NUM>, while during the negative plug-in polarity buck modulation, output occurs through motor <NUM>. Again, the magnetizing current I is unidirectional within each motor <NUM> and <NUM>, which may result in a stable zero torque rotor angle. The low frequency reference, (which is instrumental in reducing noise levels), between the on-board supply <NUM> and the plug-in supply <NUM> is made through the high side switch Q1 or Q7 of the plug-in power supply <NUM> connected switch leg A or A' during this discharging operation. Similar to the charging operation as shown for example in <FIG>, the plug-in power supply current is made to be proportional to plug-in power supply voltage yet the difference being the plug-in supply current is in the opposite direction relative to the plug-in voltage polarity.

In both the charging or boost, (<FIG>), and discharging or buck, (<FIG>), embodiments, the current through the on-board supply <NUM> is pulsed on/off at high frequency and the current through the plug-in power supply <NUM> is relatively continuous, being smoothed out by the inductance of the stator windings.

The above embodiments may accommodate the range of standard electric supply outlets including special purposed EVSE level <NUM> plug-in supplies, (e.g., 240V, 60A, <NUM> kW by way of non-limiting example). By connecting the two wire single phase power supply between a switch leg of the two inverters rather than the neutral node of the two motor windings as is conventionally done, an inherent low frequency path between the external power source and the high voltage on board battery may be created that results in a reduction of unwanted common mode noise when using the alternating boost and/or buck modulation schemes described above. This low frequency reference between supplies may reduce the capacitive coupled currents in the earth ground and improve plug in safety.

In this example, a significantly higher boost inductance path may be created by incorporating the magnetizing inductance of a motor, such as motors <NUM> or <NUM>, in addition to the stator leakage inductance. This higher inductance may reduce line ripple and harmonic distortion seen at the plug-in supply input.

Furthermore, the resulting flux vector created in each motor, for example motors <NUM> and <NUM>, is unidirectional, and since the magnetizing flux does not change angles, there is no rotor oscillation during charging. However, the rotor may develop torque persuading it to align with the zero torque flux angle position if not already in angular alignment. Once in alignment, the result is effectively an electric brake like behavior on the rotor shaft thus preventing vehicle movement. Furthermore, since the current only flows through each motor, for example, motor <NUM> and <NUM>, half of the total time the associated heat is distributed between them, this may result in higher total power capability of the system.

In the examples described above, the on-board supply <NUM>, (e.g., battery <NUM>), voltage may need to be higher than the peak plug-in supply voltage to avoid unregulated current flow. Accordingly, an intermediate DC to DC converter between the battery <NUM> and inverter bus to satisfy this voltage constraint and also to smooth out the battery current during charging may be utilized.

The embodiments described above may be applied to either AC induction and/or permanent magnet motors and/or switched reluctance motors, for example. The motor windings may also be a variety of configurations including star connected, delta connected, split-phase, or open ended.

The plug-in supply <NUM> can also be connected to a DC source or load such that bi-directional charge transfer is inherent within a single set of boost modulation or buck modulation plug-in polarity switch states, depending on the plug-in supply voltage polarity. The plug-in supply versatility and bidirectional transfer could be applied to a variety of charge transfer operations including vehicle-to-vehicle charge transfer for roadside assistance of discharged vehicles equipped with this invention.

The methods provided, to the extent applicable, may be implemented in a general purpose computer, a processor, or a processor core. Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. Such processors may be manufactured by configuring a manufacturing process using the results of processed hardware description language (HDL) instructions and other intermediary data including netlists (such instructions capable of being stored on a computer readable media). The results of such processing may be maskworks that are then used in a semiconductor manufacturing process to manufacture a processor which implements aspects of the embodiments.

The methods or flow charts provided herein, to the extent applicable, may be implemented in a computer program, software, or firmware incorporated in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magnetooptical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs).

Claim 1:
A charge transfer system (<NUM>), comprising:
a plug-in power supply (<NUM>) directly and electrically connected between at least one of a first plurality of switch legs (A, B, C) of a first inverter (<NUM>) and at least one of a second plurality of switch legs (A', B', C') of a second inverter (<NUM>), wherein a switch leg is a pair of serially connected switching elements of an inverter; and
a controller (<NUM>) operatively coupled to the first inverter (<NUM>) and the second inverter (<NUM>),
wherein the controller (<NUM>) is configured to selectively modulate the plurality of switch legs (A, B, C) of the first inverter (<NUM>) that are not connected to the plug-in power supply (<NUM>) and of the plurality of switch legs (A', B', C') of the second inverter (<NUM>) that are not connected to the plug-in power supply (<NUM>) to reduce common mode noise between the plug-in power supply (<NUM>) and an on-board vehicle power supply (<NUM>), and
wherein, during a charging operation of the on-board vehicle power supply (<NUM>), the controller (<NUM>) is configured to selectively modulate switch legs such that electric current flow alternates between at least one of a first plurality of stator windings (L1, L2, L3) of a first motor (<NUM>) to charge the on-board vehicle power supply (<NUM>) during a first plug-in supply voltage polarity state and at least one of a second plurality of stator windings (L4, L5, L6) of a second motor (<NUM>) to charge the on-board vehicle power supply (<NUM>) during a second plug-in supply voltage polarity state, and
wherein, during a discharging operation of the on-board vehicle power supply (<NUM>), the controller (<NUM>) is configured to selectively modulate at least one of the plurality of switch legs (A, B, C) of the first inverter (<NUM>) and the plurality of switch legs (A', B', C') of the second inverter (<NUM>) such that electric current flows to the plug-in supply through the at least one of the first plurality of stator windings (L1, L2, L3) of the first motor (<NUM>) or the at least one of the second plurality of stator windings L4, L5, L6) of the second motor (<NUM>) to discharge the on-board vehicle power supply (<NUM>).