Rotor power transfer circuit for electric machine

Abstract

A rotor power transfer circuit for an electric machine. The rotor power transfer circuit may include a multi-lobed direct current (DC) to DC (DC-DC) converter having a plurality of branches connected in parallel to a DC power source. The branch may include a plurality of switches operable to selectively control DC power transfer therethrough in accordance with a plurality of rotor winding excitation modes. The rotor power transfer circuit may include an electrical interface configured to electrically connect each leg with one of one or more rotor windings wound around a plurality of circumferentially spaced apart rotor protrusions of the electric machine.

Description

Technical Field

[0001] The present disclosure relates to rotor power transfer circuits, such as, but not necessarily limited to, rotor power transfer circuits operable to energize rotor windings of an electric machine. Background Art

[0002] The rotor of an electric machine, such as a separately excited electric machine (SEM), may include brushes and slip rings for conductively transferring power to a plurality of rotor windings. The resulting excitation of the rotor windings may generate a magnetic field that may operate with the electric field generated by the stator to produce an output torque. The physics and electrical dynamics of the brushes and slip rings may limit switching frequencies, cause tracking difficulties, and otherwise create other constraints on exciting the rotor windings. Summary of the invention

[0003] One non-limiting aspect of the present disclosure relates to a rotor power transfer circuit operable to improve constraints and other limitations on rotor winding excitation caused by the physics and / or electrodynamics of brushes and slip rings or other electrical connections used to facilitate power transfer to the rotor windings of an electric machine. The rotor power transfer circuit may be operable to provide rotor field excitation via two independent brush loops, optionally at a relatively low frequency, such that the sum of the two excitation signals may cause the rotor windings to experience a beneficial and optionally better switching effect. The rotor power transfer circuit may be operable such that the current received at each brush may be reduced, resulting in a lower current density for each brush, which may allow a wider variety of brushes to be selected. Each positive and negative slip ring may receive one or both of a non-time-shifted waveform and a time-shifted waveform to allow the currents to be summed or added accordingly without requiring rewinding of the rotor windings. This superposition effect may result in lower current ripple, improved tracking, and further reductions in electromagnetic interference (EMI) performance.

[0004] One non-limiting aspect of the present disclosure relates to a rotor power transfer circuit for an electric machine. The circuit may include: a multi-leaf direct current (DC) to DC (DC-DC) converter having a plurality of branches connected in parallel with a DC power source, each branch including a plurality of switches operable to selectively control the transfer of DC power therethrough. The circuit may further include: an electrical interface configured to electrically connect each branch to one of one or more rotor windings wound around a plurality of circumferentially spaced rotor protrusions of the electric machine; and a controller operable to control the switches according to a plurality of rotor winding excitation patterns.

[0005] The rotor winding excitation mode may include a powered excitation mode for transferring DC power from a source to one or more of the rotor windings.

[0006] The rotor winding may include a first rotor winding, the plurality of branches may include a first branch and a second branch, and the power excitation mode may include simultaneously delivering DC power to the first rotor winding through the first branch and the second branch.

[0007] The powered mode may include delivering DC power through the first branch that is out of phase with respect to DC power delivered through the second branch.

[0008] The rotor winding includes a first rotor winding and a second rotor winding, the multiple branches may include a first branch and a second branch, and the power excitation mode may include simultaneously transmitting DC power through the first branch and the second branch, optionally, wherein the first branch transmits DC power to the first rotor winding and the second branch transmits DC power to the second rotor winding.

[0009] The rotor winding excitation mode may include a decay excitation mode for transferring DC power from one or more of the rotor windings to the source.

[0010] The rotor winding excitation mode may include a freewheeling excitation mode for providing a source bypass connection for one or more of the rotor windings. The source bypass connection may bypass the source to independently connect together the positive and negative terminals of the rotor winding associated therewith.

[0011] The rotor winding excitation mode may include a decaying excitation mode for providing a reverse connection for one or more of the rotor windings. The reverse connection may connect the rotor winding with which it is associated to the source with reverse polarity.

[0012] The rotor power transfer circuit may include a DC link capacitor connected in parallel between the source and the multi-leaf DC-DC converter.

[0013] One non-limiting aspect of the present disclosure relates to a rotor power transfer circuit for an electric motor operable to propel a vehicle. The circuit may include: a multi-leaf direct current (DC) to DC (DC-DC) converter having a first branch and a second branch connected in parallel to a DC power source, optionally wherein the first branch includes a plurality of first switches operable to selectively control DC power transfer therethrough, and the second branch includes a plurality of second switches operable to selectively control DC power transfer therethrough. The circuit may further include: an electrical interface configured to electrically connect the first branch and the second branch to a plurality of rotor windings of the electric motor; and a controller operable to control the first switch and the second switch according to a plurality of rotor winding excitation patterns.

[0014] The rotor winding excitation mode may include a power excitation mode for simultaneously transferring DC power from the source to the rotor winding through the first branch and the second branch.

[0015] The powered mode may include delivering DC power through the first branch that is phase shifted relative to DC power delivered through the second branch.

[0016] The first branch may include a first inner branch and a first outer branch connected in parallel across the source, wherein the first inner branch includes a first upper switch of the first switch connected in series with a first lower diode, and the first outer branch includes a first lower switch of the first switch connected in series with the first upper diode.

[0017] The second branch may include a second inner branch and a second outer branch connected in parallel across the source, wherein the second inner branch includes a second upper switch of the second switch connected in series with a second lower diode, and the second outer branch includes a second lower switch of the second switch connected in series with a second upper diode.

[0018] The electrical interface may connect the positive terminal of the rotor winding to a first internal branch between the first upper switch and the first lower diode and a second internal branch between the second upper switch and the second lower diode. The electrical interface may further connect the negative terminal of the rotor winding to a first external branch between the first lower switch and the first upper diode and a second external branch between the second lower switch and the second upper diode.

[0019] One non-limiting aspect of the present disclosure relates to a rotor power transfer circuit for an electric motor for a vehicle, the electric motor having a plurality of rotor winding sets wound around each of a plurality of circumferentially spaced rotor poles. The circuit may include: a multi-leaf direct current (DC) to DC (DC-DC) converter having a first branch and a second branch connected in parallel to a DC power source, wherein the first branch includes a plurality of first switches operable to selectively control DC power transfer therethrough, and the second branch includes a plurality of second switches operable to selectively control DC power transfer therethrough. The circuit may further include: an electrical interface having a first interface configured to electrically connect the first branch to a first set of windings in the rotor winding set and a second interface configured to electrically connect the second branch to a second set of windings in the rotor winding set; and a controller operable to control the first switch and the second switch according to a plurality of rotor winding excitation modes.

[0020] The rotor winding excitation mode may include a dual power excitation mode for simultaneously delivering DC power from a source to the first set of rotor windings and the second set of rotor windings through the first branch and the second branch, respectively.

[0021] The rotor winding excitation mode may include a power freewheeling excitation mode for transferring DC power from a source to a first winding set through a first branch and providing a source bypass connection for a second rotor winding set, the source bypass connection bypassing the source to independently connect the positive and negative terminals of the second rotor winding set together.

[0022] The rotor winding excitation mode may include a decaying excitation mode for providing a reverse connection for the first set of rotor windings and / or the second set of rotor windings, wherein the reverse connection electrically connects the rotor winding associated therewith to the source with reversed polarity.

[0023] The first branch may include a first inner branch and a first outer branch connected in parallel across the source, wherein the first inner branch includes a first upper switch of the first switch connected in series with a first lower diode, and the first outer branch includes a first lower switch of the first switch connected in series with the first upper diode.

[0024] The second branch may include a second inner branch and a second outer branch connected in parallel across the source, wherein the second inner branch includes a second upper switch of the second switch connected in series with a second lower diode, and the second outer branch includes a second lower switch of the second switch connected in series with a second upper diode.

[0025] The electrical interface can connect the first positive terminal of the first rotor winding set to the first internal branch between the first upper switch and the first lower diode; connect the first negative terminal of the first rotor winding set to the first external branch between the first lower switch and the first upper diode; connect the second positive terminal of the second rotor winding set to the second internal branch between the second upper switch; and connect the second negative terminal of the second rotor winding set to the second external branch between the second lower switch and the second upper diode.

[0026] The present disclosure provides the following embodiments.

[0027] 1. A rotor power transfer circuit for an electric motor, comprising: a multi-leaf direct current (DC) to DC (DC-DC) converter having a plurality of branches connected in parallel with a DC power source, each branch including a plurality of switches operable to selectively control the transfer of DC power therethrough; an electrical interface configured to electrically connect each branch to one of one or more rotor windings wound around a plurality of circumferentially spaced rotor protrusions of the electric machine; and A controller is operable to control the switches according to a plurality of rotor winding excitation modes.

[0028] 2. The rotor power transfer circuit of embodiment 1, wherein: The rotor winding excitation mode comprises a power excitation mode which delivers DC power from the source to one or more of the rotor windings.

[0029] 3. The rotor power transfer circuit of embodiment 2, wherein: The rotor winding comprises a first rotor winding; The plurality of branches include a first branch and a second branch; and The power excitation mode delivers DC power to the first rotor winding through the first branch and the second branch simultaneously.

[0030] 4. The rotor power transfer circuit of embodiment 3, wherein: The powered mode delivers DC power through the first branch that is out of phase with respect to the DC power delivered through the second branch.

[0031] 5. The rotor power transfer circuit of embodiment 2, wherein: The rotor winding comprises a first rotor winding and a second rotor winding; The plurality of branches include a first branch and a second branch; and The power excitation mode delivers DC power through the first branch and the second branch simultaneously, wherein the first branch delivers DC power to the first rotor winding and the second branch delivers DC power to the second rotor winding.

[0032] 6. The rotor power transfer circuit of embodiment 1, wherein: The rotor winding excitation mode includes a decay excitation mode that transfers DC power from one or more of the rotor windings to the source.

[0033] 7. The rotor power transfer circuit of embodiment 1, wherein: The rotor winding excitation modes include a freewheeling excitation mode that provides a source bypass connection for one or more of the rotor windings that bypasses the source to independently connect together the positive and negative terminals of the rotor windings associated therewith.

[0034] 8. The rotor power transfer circuit of embodiment 1, wherein: The rotor winding excitation mode includes a decay excitation mode that provides a reverse connection for one or more of the rotor windings that electrically connects the associated rotor winding to the source with reverse polarity.

[0035] 9. The rotor power transfer circuit according to embodiment 1, further comprising: A DC link capacitor is connected in parallel between the source and the multi-leaf DC-DC converter.

[0036] 10. A rotor power transfer circuit for an electric motor operable to propel a vehicle, comprising: a multi-leaf direct current (DC) to DC (DC-DC) converter having a first branch and a second branch connected in parallel to a DC power source, the first branch comprising a plurality of first switches operable to selectively control DC power transfer therethrough, the second branch comprising a plurality of second switches operable to selectively control DC power transfer therethrough; an electrical interface configured to electrically connect the first branch and the second branch to a plurality of rotor windings of the motor; and a controller operable to control the first switch and the second switch according to the plurality of rotor winding excitation modes.

[0037] 11. The rotor power transfer circuit of embodiment 10, wherein: The rotor winding excitation mode includes a power excitation mode that simultaneously transfers DC power from the source to the rotor winding through the first branch and the second branch.

[0038] 12. The rotor power transfer circuit of embodiment 11, wherein: The power excitation mode delivers DC power through the first branch that is phase shifted relative to the DC power delivered through the second branch.

[0039] 13. The rotor power transfer circuit of embodiment 12, wherein: the first branch comprising a first inner branch and a first outer branch connected in parallel across the source, the first inner branch comprising a first upper switch of the first switches connected in series with a first lower diode, the first outer branch comprising a first lower switch of the first switches connected in series with the first upper diode; and The second branch includes a second inner branch including a second upper one of the second switches connected in series with a second lower diode and a second outer branch including a second lower one of the second switches connected in series with a second upper diode connected in parallel across the source.

[0040] 14. The rotor power transfer circuit of embodiment 13, wherein: The electrical interface connects the positive terminal of the rotor winding to a first internal branch between a first upper switch and a first lower diode and to a second internal branch between a second upper switch and a second lower diode; and The electrical interface connects the negative terminal of the rotor winding to a first external branch between a first lower switch and a first upper diode and to a second external branch between a second lower switch and a second upper diode.

[0041] 15. A rotor power transfer circuit for an electric motor for a vehicle, the electric motor having a plurality of rotor winding sets wound around each of a plurality of circumferentially spaced rotor poles, comprising: a multi-leaf direct current (DC) to DC (DC-DC) converter having a first branch and a second branch connected in parallel to a DC power source, the first branch including a plurality of first switches operable to selectively control DC power transfer therethrough, the second branch including a plurality of second switches operable to selectively control DC power transfer therethrough; an electrical interface having a first interface configured to electrically connect a first branch to a first winding set of the rotor winding sets and a second interface configured to electrically connect a second branch to a second winding set of the rotor winding sets; and A controller is operable to control the first switch and the second switch according to a plurality of rotor winding excitation modes.

[0042] 16. The rotor power transfer circuit of embodiment 15, wherein: The rotor winding excitation mode includes a dual power excitation mode that simultaneously transfers DC power from the source to the first and second rotor winding sets through the first and second branches, respectively.

[0043] 17. The rotor power transfer circuit of embodiment 15, wherein: The rotor winding excitation mode includes a power continuous flow excitation mode, which transfers DC power from the source to the first winding set through a first branch and provides a source bypass connection for the second rotor winding set, wherein the source bypass connection bypasses the source to independently connect the positive terminal and the negative terminal of the second rotor winding set together.

[0044] 18. The rotor power transfer circuit of embodiment 15, wherein: The rotor winding excitation mode includes a decay excitation mode that provides a reverse connection for the first rotor winding set and / or the second rotor winding set, the reverse connection electrically connecting the rotor winding associated therewith to the source with reverse polarity.

[0045] 19. The rotor power transfer circuit of embodiment 15, wherein: the first branch comprising a first inner branch and a first outer branch connected in parallel across the source, the first inner branch comprising a first upper switch of the first switches connected in series with a first lower diode, the first outer branch comprising a first lower switch of the first switches connected in series with the first upper diode; and The second branch includes a second inner branch including a second upper one of the second switches connected in series with a second lower diode and a second outer branch including a second lower one of the second switches connected in series with a second upper diode connected in parallel across the source.

[0046] 20. The rotor power transfer circuit of embodiment 19, wherein: The electrical interface connects a first positive terminal of the first rotor winding set to a first internal branch between a first upper switch and a first lower diode; The electrical interface connects a first negative terminal of the first rotor winding set to a first external branch between the first lower switch and the first upper diode; The electrical interface connects a second positive terminal of the second rotor winding set to a second internal branch between the second upper switches; and The electrical interface connects a second negative terminal of the second rotor winding set to a second external branch between the second lower switch and the second upper diode.

[0047] These features and advantages, together with other features and advantages of the present teachings, may become apparent from the following detailed description of the mode for carrying out the present teachings when considered in conjunction with the accompanying drawings. It should be understood that even though the following drawings and embodiments may be described separately, their individual features may also be combined into additional embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings, which may be incorporated in and constitute a part of this specification, illustrate implementations of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0049] Figure 1 A schematic diagram of an electric machine according to one non-limiting aspect of the present disclosure is illustrated.

[0050] Figure 2 A schematic diagram of a vehicle having an electric machine according to one non-limiting aspect of the present disclosure is illustrated.

[0051] Figure 3 A schematic diagram of a rotor transfer circuit operable with a rotor having a single rotor winding set in accordance with one non-limiting aspect of the present disclosure is illustrated.

[0052] Figure 4 A schematic diagram illustrating a power excitation mode according to one non-limiting aspect of the present disclosure is illustrated.

[0053] Figure 5 A dual power graph of a dual power excitation mode is illustrated in accordance with one non-limiting aspect of the present disclosure.

[0054] Figure 6 Illustrated is a schematic diagram illustrating a decaying excitation pattern according to one non-limiting aspect of the present disclosure.

[0055] Figure 7 A schematic diagram illustrating a freewheeling excitation mode according to one non-limiting aspect of the present disclosure is illustrated.

[0056] Figure 8 A schematic diagram of a rotor transfer circuit operable with a rotor having multiple rotor winding sets in accordance with one non-limiting aspect of the present disclosure is illustrated. DETAILED DESCRIPTION

[0057] As desired, detailed embodiments of the present disclosure may be disclosed herein; however, it is understood that the disclosed embodiments may be merely examples of the present disclosure that may be embodied in various and alternative forms. The drawings may not necessarily be drawn to scale; some features may be exaggerated or minimized to illustrate details of particular components. Therefore, the specific structural details and functional details disclosed herein may not need to be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art to adopt the present disclosure in various ways.

[0058] Figure 1 A schematic diagram of an electric machine 10 according to one non-limiting aspect of the present disclosure is illustrated. The electric machine 10 may be of a type that employs a rotor 12 for applying mechanical force to a load in proportion to its electrical excitation and / or generating electrical energy in response to its rotation. At least in the illustrated configuration, the electric machine 10 may be referred to as an electric motor 10 that is operable for propulsion of a vehicle and / or regenerative braking. Figure 2 A schematic diagram of a vehicle 14 having an electric motor 10 is illustrated in accordance with one non-limiting aspect of the present disclosure. The electric motor 10 may be employed within the vehicle 14 to facilitate applying mechanical force to a propulsion system, powertrain, or drivetrain 16 operable to propel or otherwise drive the vehicle 14. The vehicle 14 is illustrated as a hybrid type because the powertrain 12 optionally includes an internal combustion engine (ICE) 18. The powertrain 16 may include a transmission, a drive shaft, a differential, an axle, and / or other componentry to facilitate transferring rotational force from the rotor 10 (see FIG. 1 ). Figure 1 ) coupled to a rotor shaft 30 to transmit power to wheels 20, 22, 24, 26. For non-limiting purposes, vehicle 14 is shown as including powertrain 12 operable with front wheels 20, 24, as the present disclosure fully contemplates its use and application in the context of four-wheel drive automobiles and other non-automotive types of vehicles.

[0059] return Figure 1, the motor 10 may include a housing 32 configured to support a rear end (not shown) of the rotor shaft 30 while permitting the rotor 10 to rotate relative to a stator 36 within an airgap 34. The stator 36 may be annularly disposed about the rotor 10 for the purpose of generating a rotating magnetic field (RMF), which, as will be appreciated by those skilled in the art, may be used to apply a rotational torque sufficient to rotate the rotor 10. Although not shown in detail, the stator 36 may include stator windings or other features that are capable of being electrically energized for the purpose of controlling the RMF and the resulting rotation of the rotor 10. The rotor 10 may include a plurality of rotor windings 38 wound about a plurality of circumferentially spaced rotor protrusions 42, which, when energized, may be used to rotate the rotor 10 at a corresponding plurality of stator poles 44 (see Figure 3 ) to induce a rotor magnetic field within the rotor shaft. The rotor magnetic field can interact with the RMF to facilitate rotating the rotor shaft 30 to propel the vehicle 14 and / or for regenerative braking in response to the rotation of the rotor shaft. The rotor 10 can be formed in a generally annular shape, optionally formed of a plurality of laminations stacked axially along a rotational access A in a side-by-side facing relationship. Although in Figure 1 As generally shown in FIG. 1 and described in more detail below, the present disclosure contemplates a rotor 12 having a rotor protrusion 42 that is wound or otherwise configured with one or more individually energizable rotor windings 38 , i.e., the rotor protrusion 42 is wound with a different and independently energizable set of rotor windings 38 .

[0060] Figure 3A schematic diagram of a rotor transfer circuit 50 operable with a single rotor winding set 52 according to one non-limiting aspect of the present disclosure is illustrated. The single rotor winding set 52 may correspond to a rotor winding 38 wound around a rotor protrusion 42, which is electrically connected to a rotor winding circuit 54, which is illustrated as being in series, but may be otherwise. The rotor winding circuit 54 is illustrated with respect to connecting the rotor winding 38 so that the polarity or directionality (illustrated by arrows) of each rotor pole 44 is opposite or different from the adjacent rotor pole 44, which is done for exemplary purposes, as the present disclosure fully contemplates rotor winding circuits 54 having other configurations, including those whereby one or more adjacent rotor poles 44 may have the same or different polarity. The configuration of the rotor winding circuit 54 may be a design parameter that may vary depending on operational considerations of the motor 10. The rotor transfer circuit 50 described herein may advantageously be operable to provide excitation of the rotor winding 38 for a variety of rotor winding circuit 54 configurations. More specifically, the rotor transfer circuit 50 may be configured to provide DC excitation of the rotor winding 38 via direct current (DC) power delivered through an input terminal (eg, positive terminal) 56 and an output terminal (eg, negative terminal) 58 of the rotor winding circuit 54 .

[0061] The rotor transfer circuit 50 may include a DC to DC (DC-DC) converter 60 operable to control DC power transfer to and from the rotor winding 38, such as controlling DC power transfer between the rotor winding 38 and a DC power source 62. The source 62 may optionally correspond to a rechargeable energy storage system (RESS) operable to store and supply DC power. A DC link capacitor 64 may be connected across a positive terminal 66 and a negative terminal 68 of the source 62 to facilitate filtering and smoothing the DC power. The DC-DC converter 60 may be configured as a multi-leaf DC-DC converter 60 having a plurality of branches 70, 72 connected in parallel to the source 62. Figure 3The illustrated configuration is shown with a first branch 70 and a second branch 72 connected in parallel to the source 62. The first branch 70 may include a plurality of first switches S1, S2, and the second branch 72 may similarly include a plurality of second switches S3, S4. The switches S1, S2 may be semiconductor switches, transistors, etc. that can be selectively controlled between an open state and a closed state. More specifically, the first branch 70 may include a first inner branch 76 having a first upper switch S1 connected in series with a first lower diode D2 and a first outer branch 78 having a first lower switch S2 connected in series with the first upper diode D1. The second branch 72 may similarly include a second inner branch 80 having a second upper switch S2 connected in series with a second lower diode D4 and a second outer branch 82 having a second lower switch S4 connected in series with a second upper diode D3. A controller 90 may be included to facilitate controlling the DC-DC converter 60 according to a plurality of excitation modes, which may include selectively controlling the switches S1, S2, S3, S4 to control the excitation of the rotor winding 38.

[0062] The rotor transfer circuit 50 may include an electrical interface 94 configured to electrically connect each branch 70 , 72 with the rotor winding 38 . Figure 3 The illustrated electrical interface 94 may be characterized as a brush-slip ring configuration, whereby brushes and slip rings may be used to commute electrical power between the DC-DC converter 60 and the winding circuit 54. For example, the electrical interface 94 may include brushes 96, 98, 100, 102 operable to commute electrical power with slip rings 104, 106, wherein a first positive brush 96 and a first negative brush 98 are connected to the first branch 70, and a second positive brush 102 and a second negative brush 100 are connected to the second branch 72. The first and second positive and negative brushes 96, 98, 100, 102 may be correspondingly positioned to physically contact a positive slip ring 104 and a negative slip ring 106 attached to the rotor 12, wherein the physical contact is operable to facilitate the interchange of electrical power therebetween when the rotor 12 is stationary and rotating. The present disclosure fully contemplates electrical interfaces 94 having other configurations suitable for providing electrical energy to and / or receiving electrical energy from the rotor windings 38, such as via capacitive and / or inductive type couplings, whereby physical contact between the DC-DC converter 60 and the rotor winding circuit 54 may not be necessary.

[0063] Figure 4A schematic diagram illustrating control of the rotor transfer circuit 50 according to a power excitation mode in accordance with one non-limiting aspect of the present disclosure is illustrated. For simplicity of presentation, the figure illustrates an equivalent circuit 110 for the rotor winding 38, which may be generally referred to as an inductor Lf and a resistor Rf as can be appreciated by those skilled in the art. The power excitation mode may correspond to the controller 90 controlling the switches S1, S2, S3, S4 to transfer DC power from the source 62 to one or more of the rotor windings 38. The power excitation mode is illustrated with respect to a first branch 70 providing a first DC current 112 and a second branch 72 providing a second DC current 114, wherein the first DC current 112 and the second DC current 114 are summed at the input terminal 56 of the rotor winding circuit 54. This may be referred to as a dual power excitation mode, whereby the rotor winding 38 may be excited with the first DC current 112 and the second DC current 114 simultaneously. The dual power excitation mode may correspond to the controller 90 controlling the first upper switch S1 and the second upper switch S3 and the first lower switch and the second lower switch to a closed or on position. The controller 90 may similarly be operable to provide a single power excitation mode, whereby one of the first DC current 112 or the second DC current 114 may be provided to the rotor winding 38, i.e., instead of both the first branch 70 and the second branch 72 providing current to the rotor winding 38, one of the branches 70, 72 may be prevented from providing current to the rotor winding 38. In the case where it may be desirable to provide only the first current 112, the first upper switch S1 and the first lower switch S2 may be closed, while the second upper switch and the second lower switch are opened. Similarly, in the case where it is desirable to provide only the second current 114, the second upper switch S3 and the second lower switch S4 may be closed, while the first upper switch S1 and the first lower switch S2 are opened.

[0064] The ability of the rotor transfer circuit 50 to simultaneously provide excitation currents 112 , 114 from different branches 70 , 72 may be advantageous in ameliorating constraints and other limitations on rotor winding excitation caused by the physics and / or electrical dynamics of brushes and slip rings or other electrical connections. Figure 5A dual power graph 120 of the dual power excitation mode is illustrated, which graph 120 may include a vertical axis 122 representing current, a horizontal axis 124 representing time, a first current graph 126 representing the first current 112 provided via the first branch 70, a second current graph 128 representing the second current 114 provided via the second branch 72, and a sum graph 130 representing the sum of the first current 112 and the second current 114 at the terminal 56. The rotor power transfer circuit 50 may be operable to provide rotor field excitation, i.e., the first DC current 112 and the second DC current 114, via two independent brush loops, optionally at a relatively low frequency, such that the sum thereof may result in the rotor winding 38 experiencing a beneficial and optionally better switching effect. The rotor power transfer circuit 50 may be operable such that the current 112, 114 received at each brush may be reduced, resulting in a lower current density at each brush, which may allow a wider variety of brushes to be selected. Although illustrated with the first current 112 time-shifted or out-of-phase with respect to the second current 116, each of the positive and negative slip rings 104 and 106 may receive one or both of the non-time-shifted waveform and the time-shifted waveform (i.e., the first current 112 and the second current 114) to allow the currents 112, 114 to be summed or added, respectively, without requiring rewinding of the rotor winding 38. This superposition effect may result in lower current ripple, improved tracking, and further reductions in electromagnetic interference (EMI) performance.

[0065] Figure 6A schematic diagram illustrating control of the rotor transfer circuit 50 according to a decaying excitation mode according to one non-limiting aspect of the present disclosure is illustrated. The decaying excitation mode may correspond to connecting the rotor winding 38 to the source 62 via the first branch 70 and / or the second branch 72 with reverse polarity, i.e., corresponding to a reverse connection for electrically connecting the rotor winding associated therewith to the source 62 with reverse polarity. In other words, the decaying excitation mode may correspond to reversing the directionality of the connection provided between the source 62 and the rotor winding 38 via the DC-DC converter 60 so that the electrical power residing in the rotor winding 38 can be dispersed to the source 62. The decaying excitation mode may correspond to the controller 90 controlling the first upper switch S1 and the second upper switch S2 and the first lower switch S3 and the second lower switch S4 to the disconnected position. The controller 90 may similarly be operable to provide a single decaying excitation mode, whereby one of the first branch 70 or the second branch 72 may be connected with reverse polarity while the other branch is disconnected. In the event that it is desired to provide reverse polarity only via the first branch 70, the first upper switch S1 and the first lower switch S2 may be opened, while the second upper switch S3 is closed and the second lower switch S4 is opened. Similarly, in the event that it is desired to provide reverse polarity only via the second branch 72, the second upper switch S3 and the second lower switch S4 may be opened, while the first upper switch S1 is closed and the first lower switch S2 is opened.

[0066] Figure 7 A schematic diagram illustrating control of the rotor transfer circuit 50 according to a freewheeling excitation mode according to one non-limiting aspect of the present disclosure is illustrated. The freewheeling excitation mode may correspond to connecting the rotor winding 38 via the first branch 70 and / or the second branch 72 with a source bypass connection, wherein the source bypass connection bypasses the source 62 to independently connect the positive terminal 56 and the negative terminal 58 of the rotor winding together via the DC-DC converter 60. In other words, the freewheeling excitation mode may correspond to the first branch 70 and the second branch 72 acting as a controller effectively shorting out the rotor winding 38 so that any residual power therein can be parasitically dissipated. The ability to dissipate electrical power from the rotor winding 38 without draining to the source 62 can be beneficial to maximizing the life of the source 62. The freewheeling excitation mode may correspond to the controller 90 controlling the first upper switch S1 and the second upper switch S3 to a closed position and the first lower switch S2 and the second lower switch S4 to an open position.

[0067] Figure 8A schematic diagram of a rotor transfer circuit 50 operable with multiple rotor winding sets 52A, 52B in accordance with one non-limiting aspect of the present disclosure is illustrated. Although additional rotor winding sets 52A, 52B are contemplated, the rotor 12 is shown as including a first rotor winding set 52A and a second rotor winding set 52B, which may be considered a dual winding implementation, which is shown based on a conductive coupling with the rotor transfer circuit 50, however, this topology may also be adapted for use with inductive and / or capacitive couplings. The multiple winding sets 52A, 52B may correspond to a different rotor winding 38A, 38B wound around each of the rotor protrusions 42, such that each of the corresponding rotor poles 44 includes two separate sets of rotor windings 38A, 38B. The electrical interface 94 and rotor winding circuit 54 described above may be modified so that the positive brush 96 and the negative brush 98 may be connected to the first rotor winding circuit 54A and associated with the first rotor winding set 52A, and the positive brush 102 and the negative brush 104 may be connected to the second rotor winding circuit 54B and associated with the second rotor winding set 52B. In particular, the first positive terminal 140 of the first rotor winding set 52A may be connected to the first internal branch 76 between the first upper switch S1 and the first lower diode D2, the first negative terminal 142 of the first rotor winding set 52A may be connected to the first external branch 78 between the first lower switch S2 and the first upper diode D1, the second positive terminal 102 of the second rotor winding set 52B may be connected to the second internal branch 80 between the second upper switch S3 and the second lower diode D4, and the second negative terminal 104 of the second rotor winding set 52B may be connected to the second external branch 82 between the second lower switch S4 and the second upper diode D3.

[0068] The controller 90 may be configured to utilize the rotor transfer circuit 50 so as to control the excitation of the first rotor winding set 52A and the second rotor winding set 52B according to similar excitation modes. The rotor winding excitation modes may include a dual power excitation mode for simultaneously transferring DC power from the source 62 to the first rotor winding 52A and the second rotor winding 52B, respectively, through the first branch 70 and the second branch 72, i.e., by providing the first current 112 to the first rotor winding set 52A separately from the second current 114 provided to the second rotor winding set 52B. The rotor winding excitation mode may include a power freewheeling excitation mode for transferring DC power from the source 62 to the first winding set 52A or the second winding set 52B through the first branch 70 while simultaneously providing a source 62 bypass connection for the other of the first rotor winding set 52A or the second rotor winding set 52B. The rotor winding excitation mode includes a decaying excitation mode for providing a reverse connection for the first rotor winding 52A and / or the second rotor winding 52B, wherein the reverse connection electrically connects the associated rotor winding set 52A, 52B to the source 62 with reverse polarity. The controller 90 may include a plurality of non-transitory instructions stored on a computer-readable storage medium, which when executed with one or more associated processors may be operable to provide the control method described herein, i.e., to implement the selective opening and closing of the switches S1, S2, S3, S4 included as part of the DC-DC converter 60.

[0069] The terms "comprises", "includes" and "having" are inclusive and thus specify the presence of stated features, steps, operations, elements or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements or components. The order of steps, processes and operations may be changed where possible, and additional or alternative steps may be adopted. As used in this specification, the term "or" includes any and all combinations of the associated listed items. The term "any of..." is understood to include any possible combination of the referenced items, including "any of" the referenced items. "A", "an", "the", "at least one" and "one or more" are used interchangeably to refer to "about" refers to the presence of at least one of the items. There may be multiple such terms unless the context clearly indicates otherwise. Unless otherwise clearly or clearly indicated in view of the context (including the appended claims), all values ​​of parameters (such as values ​​of quantities or conditions) should be understood as being modified by the term "about" in all instances, regardless of whether "about" actually appears before the value. A component that is "configured to" perform a specified function is able to perform the specified function without modification, not just having the potential to perform the specified function after further modification. In other words, when explicitly configured to perform a specified function, the described hardware is specifically selected, created, implemented, utilized, programmed and / or designed for the purpose of performing the specified function.

[0070] Although various embodiments have been described, this description is intended to be exemplary rather than restrictive, and it will be apparent to those of ordinary skill in the art that many more embodiments and implementations within the scope of the embodiments are possible. Any feature of any embodiment may be used in combination with any other feature or element in any other embodiment or replace any other feature or element in any other embodiment, unless specifically limited. Therefore, the embodiments are not limited except in view of the appended claims and their equivalents. Moreover, various modifications and changes may be made within the scope of the appended claims. Although several modes for performing many aspects of this teaching have been described in detail, those skilled in the art who are familiar with the fields to which these teachings relate will recognize various alternative aspects within the scope of the appended claims for practicing this teaching. All content contained in the above description or shown in the accompanying drawings should be intended to be interpreted as an illustration and example of the entire range of alternative embodiments (such as those implied by the included content, equivalent to the included content in structure and / or function, or otherwise apparent based on the included content) that will be recognized by ordinary skill in the art, and not limited only to those embodiments that are explicitly depicted and / or described.

Claims

1. A rotor power transfer circuit for an electric motor, comprising: a multi-leaf direct current (DC) to DC (DC-DC) converter having a plurality of branches connected in parallel with a DC power source, each branch including a plurality of switches operable to selectively control the transfer of DC power therethrough; an electrical interface configured to electrically connect each branch to one of one or more rotor windings wound around a plurality of circumferentially spaced rotor protrusions of the electric machine; as well as A controller is operable to control the switches according to a plurality of rotor winding excitation modes.

2. The rotor power transfer circuit according to claim 1, wherein: The rotor winding excitation mode comprises a power excitation mode which delivers DC power from the source to one or more of the rotor windings.

3. The rotor power transfer circuit of claim 2, wherein: The rotor winding comprises a first rotor winding; The plurality of branches include a first branch and a second branch; and The power excitation mode delivers DC power to the first rotor winding through the first branch and the second branch simultaneously.

4. The rotor power transfer circuit of claim 3, wherein: The powered mode delivers DC power through the first branch that is out of phase with respect to the DC power delivered through the second branch.

5. The rotor power transfer circuit of claim 2, wherein: The rotor winding comprises a first rotor winding and a second rotor winding; The plurality of branches include a first branch and a second branch; as well as The power excitation mode delivers DC power through the first branch and the second branch simultaneously, wherein the first branch delivers DC power to the first rotor winding and the second branch delivers DC power to the second rotor winding.

6. The rotor power transfer circuit of claim 1, wherein: The rotor winding excitation mode includes a decay excitation mode that transfers DC power from one or more of the rotor windings to the source.

7. The rotor power transfer circuit of claim 1, wherein: The rotor winding excitation modes include a freewheeling excitation mode that provides a source bypass connection for one or more of the rotor windings that bypasses the source to independently connect together the positive and negative terminals of the rotor windings associated therewith.

8. The rotor power transfer circuit of claim 1, wherein: The rotor winding excitation mode includes a decay excitation mode that provides a reverse connection for one or more of the rotor windings that electrically connects the associated rotor winding to the source with reverse polarity.

9. The rotor power transfer circuit of claim 1 , further comprising: A DC link capacitor is connected in parallel between the source and the multi-leaf DC-DC converter.

10. A rotor power transfer circuit for an electric motor operable to propel a vehicle, comprising: a multi-leaf direct current (DC) to DC (DC-DC) converter having a first branch connected in parallel to a DC power source and a second branch, the first branch including a plurality of first switches operable to selectively control DC power transfer therethrough, the second branch including a plurality of second switches operable to selectively control DC power transfer therethrough; an electrical interface configured to electrically connect the first branch and the second branch to a plurality of rotor windings of the electric motor; as well as A controller is operable to control the first switch and the second switch according to a plurality of rotor winding excitation modes.

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