Asynchronous rotor control for a switch bridge of a wound field rotor

Abstract

Systems and methods are provided for controlling the application of current to stator and rotor windings of a motor. An electric machine includes a stator including stator windings. A stator controller is configured to control current through the stator winding to generate a wireless power signal. A rotor includes a rotor winding and a rotor circuit. The rotor circuit includes a switch bridge coupled to the rotor winding and a capacitor coupled across the switch bridge. The rotor winding receives the wireless power signal from a stator winding of the stator windings. A rotor controller determines a capacitor voltage, a reference current based on the capacitor voltage, and a rotor current through the rotor winding. The rotor controller controls the switch bridge of the rotor circuit to change a switching state based on the reference current and the rotor current.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63 / 615,211, filed on December 27, 2023, titled “ASYNCHRONOUS ROTOR CONTROL FOR A SWITCH BRIDGE OF A WOUND FIELD ROTOR,” which is hereby incorporated by reference in its entirety. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] N / A BACKGROUND

[0003] Electric motors of various types have been produced and used in many industries and contexts. A synchronous motor is an alternating current (AC) motor having a stator that is driven by AC supply signals (e.g., one signal for each phase of the stator) to cause rotation of a rotor. More particularly, the AC supply signals in stator windings of the stator generate magnetic fields that interact with a magnetic field or fields of the rotor to cause rotation of the rotor. The rotation of the rotor is generally synchronous with the frequency of the AC supply current. The rotor may be a permanent magnet rotor or a wound field rotor. In the case of a wound field rotor, current is supplied to one or more field windings of the rotor to generate the magnetic field or fields of the rotor through a DC power source. For example, a wound field synchronous motor may receive DC power from a DC power source (e.g., a battery or a rectifier fed by an AC grid), where the DC power source is mechanically coupled to the rotor through a slip ring, which provides DC power to the field winding(s) of the rotor. SUMMARY OF THE DISCLOSURE

[0004] The present disclosure provides, in some examples, systems, methods, instructions on computer readable media, and / or hardware-based implementations of control algorithms related to a wound field rotor of a wound field synchronous (WFS) machine and control thereof. For example, the wound field rotor may include one or more rotor windings, a rotor capacitor, a rotor controller that is electrically isolated from a power source of the stator, and a dual function switch bridge that (i) during startup, without active control of switches making up the switch bridge, directs power received from a stator by the rotor winding(s) to charge the rotor capacitor to enable powering and booting of the rotor controller, and (ii) upon bootup of the rotor controller, is actively controlled by the rotor controller to capture power transmitted by the stator to continue to charge the rotor capacitor and to energize the rotor winding(s) of the wound field rotor to generate magnetic fields to create torque to rotate the wound field rotor. Additionally, in some examples, after bootup, the rotor controller controls the switch bridge to cycle between switch states to enable continued creation of torque to rotate the rotor. For example, the rotor controller may control the switch bridge to cycle between states based on rotor state variables and, in some examples, a present switching state of a rotor switch bridge. This control may be performed by the rotor controller without explicit or shared information or commands from the stator and without a phase-locked loop.

[0005] In some aspects, the disclosure provides an electric machine. The electric machine includes a stator including stator windings; a stator controller configured to control current through the stator winding to generate a wireless power signal; a rotor including a rotor winding, a rotor circuit, and a rotor controller; and a rotor controller. The rotor circuit includes a switch bridge coupled to the rotor winding and a capacitor coupled across the switch bridge, the rotor winding configured to receive the wireless power signal from a stator winding of the stator windings. The rotor controller is configured to: determine a capacitor voltage, the capacitor voltage indicating a voltage across the capacitor; determine a reference current based on the capacitor voltage; determine a rotor current through the rotor winding; and control the switch bridge of the rotor circuit to change a switching state based on the reference current and the rotor current.

[0006] In some aspects, the present disclosure provides a method of controlling a motor. The method includes receiving, by a rotor winding of a rotor, a first power signal wirelessly from a stator winding of a stator; determining, by a rotor controller, a capacitor voltage, the capacitor voltage indicating a voltage across a capacitor of a rotor circuit coupled to the rotor winding; determining, by the rotor controller, a reference current based on the capacitor voltage; determining, by the rotor controller, a rotor current through the rotor winding; and controlling, by the rotor controller, a switch bridge of the rotor circuit to change a switching state based on the reference current and the rotor current.

[0007] In some aspects, the present disclosure provides a nontransitory computer readable medium storing instructions that, when executed by one or more electronic processors of a motor system, cause the motor system to: receive, by a rotor winding of a rotor, a first power signal wirelessly from a stator winding of a stator; determine, by a rotor controller, a capacitor voltage, the capacitor voltage indicating a voltage across a capacitor of a rotor circuit coupled to the rotor winding; determine, by the rotor controller, a reference current based on the capacitor voltage; determine, by the rotor controller, a rotor current through the rotor winding; and control, by the rotor controller, a switch bridge of the rotor circuit to change a switching state based on the reference current and the rotor current.

[0008] In some aspects, the present disclosure provides a rotor chipset assembly for an electric machine comprising: a rotor circuit including a switch bridge configured to be coupled to a rotor winding and a capacitor coupled across the switch bridge, the rotor winding configured to receive a wireless power signal from a stator winding, and a rotor controller configured to: determine a capacitor voltage, the capacitor voltage indicating a voltage across the capacitor, determine a reference current based on the capacitor voltage, determine a rotor current through the rotor winding, and control the switch bridge of the rotor circuit to change a switching state based on the reference current and the rotor current.

[0009] In some aspects, the present disclosure provides an electric machine comprising: a stator including stator windings; a stator controller configured to control current through the stator winding to generate a wireless power signal; and a rotor including a rotor winding, a rotor circuit, and a rotor controller, the rotor circuit including a switch bridge coupled to the rotor winding and a capacitor coupled across the switch bridge, the rotor configured to implement a boot-up sequence wherein: the rotor circuit is configured to passively convert the wireless power signal to charge the capacitor to increase a capacitor voltage across the capacitor, and the rotor controller is configured to: boot in response to the capacitor voltage exceeding a boot-up threshold, in response to the rotor controller completing booting, control the switch bridge to cycle a switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding, determine that at least one of a rotor current or the capacitor voltage has exceeded a minimum threshold, and control, by the rotor controller, the switch bridge according to a steady state operation.

[0010] In some aspects, the present disclosure provides a method of controlling a motor, the method comprising: passively converting, by a rotor circuit of a rotor, a wireless power signal received by a rotor winding from a stator winding to charge a capacitor of the rotor circuit to increase a capacitor voltage across the capacitor; in response to the capacitor voltage exceeding a boot-up threshold, booting a rotor controller of the rotor; in response to the rotor controller completing booting, controlling, by the rotor controller, a switch bridge of the rotor circuit to cycle a switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding; determining that at least one of a rotor current or the capacitor voltage has exceeded a minimum threshold; and controlling, by the rotor controller, the switch bridge according to a steady state operation.

[0011] In some aspects, the present disclosure provides a nontransitory computer readable medium storing instructions that, when executed by one or more electronic processors of a motor system, cause the motor system to: passively convert, by a rotor circuit of a rotor, a wireless power signal received by a rotor winding from a stator winding to charge a capacitor of the rotor circuit to increase a capacitor voltage across the capacitor; in response to the capacitor voltage exceeding a boot-up threshold, boot a rotor controller of the rotor; in response to the rotor controller completing booting, control, by the rotor controller, a switch bridge of the rotor circuit to cycle a switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding; determine that at least one of a rotor current or the capacitor voltage has exceeded a minimum threshold; and control, by the rotor controller, the switch bridge according to a steady state operation.

[0012] In some aspects, the present disclosure provides a rotor chipset assembly for an electric machine comprising: a rotor circuit including a switch bridge configured to be coupled to a rotor winding and a capacitor coupled across the switch bridge, the rotor circuit configured to passively convert a wireless power signal received by the rotor winding from a stator winding to charge the capacitor to increase a capacitor voltage across the capacitor; and a rotor controller configured to: boot in response to the capacitor voltage exceeding a boot-up threshold, in response to the rotor controller completing booting, control the switch bridge to cycle a switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding, determine that at least one of a rotor current or the capacitor voltage has exceeded a minimum threshold, and control, by the rotor controller, the switch bridge according to a steady state operation.

[0013] The foregoing and other aspects and advantages of the present disclosure will appear from the following description. In the description, reference is made to the accompanying drawings that form a part hereof, and in which there is shown by way of illustration one or more embodiments. These embodiments do not necessarily represent the full scope of the invention(s), however, and reference is therefore made to the claims and herein for interpreting the scope of the invention(s). Like reference numerals will be used to refer to like parts from Figure to Figure in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 illustrates a motor system for a wound field synchronous (WFS) motor according to some embodiments.

[0015] FIG. 2 illustrates a diagram for the rotor assembly of FIG. 1 according to some embodiments.

[0016] FIGS. 3 A and 3B illustrate a perspective view and a section view of an example electric machine for the motor system of FIG. 1 according to some embodiments.

[0017] FIG. 4 illustrates a diagram for the motor system of FIG. 1 according to some embodiments.

[0018] FIG. 5 illustrates a rotor control process 500 for controlling a switch bridge of a wound field rotor according to some embodiments.

[0019] FIG. 6 illustrates a graph of rotor phase reference current versus the average rotor capacitor voltage.

[0020] FIG. 7 illustrates a boot-up sequence process for starting operation of a motor according to some embodiments.

[0021] FIGS. 8A and 8B illustrate wave diagrams of rotor current and voltage versus time during the boot-up sequence process of FIG. 7. DETAILED DESCRIPTION

[0022] One or more embodiments are described and illustrated in the following description and accompanying drawings. These embodiments are not limited to the specific details provided herein and may be modified in various ways. Furthermore, other embodiments may exist that are not described herein. Also, functions performed by multiple components may be consolidated and performed by a single component. Similarly, the functions described herein as being performed by one component may be performed by multiple components in a distributed manner. Additionally, a component described as performing particular functionality may also perform additional functionality not described herein. For example, a device or structure that is “configured” in a certain way is configured in at least that way but may also be configured in ways that are not listed.

[0023] As used in the present application, "non-transitory computer-readable medium” comprises all computer-readable media but does not consist of a transitory, propagating signal. Accordingly, non-transitory computer-readable medium may include, for example, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a RAM (Random Access Memory), register memory, a processor cache, or any combination thereof.

[0024] In addition, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. For example, the use of “comprising,” “including,” “containing,” “having,” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Additionally, the terms “connected” and “coupled” are used broadly and encompass both direct and indirect connecting and coupling, and may refer to physical or electrical connections or couplings. Furthermore, the phase "and / or" used with two or more items is intended to cover the items individually and the items together. For example, “a and / or b" is intended to cover: a without b; b without a; and both a and b.

[0025] Controlling the application of current to the stator windings and rotor windings at the particular time and amplitude to efficiently drive a wound field synchronous (WFS) motor can be challenging. For example, a motor controller may control an inverter to provide an AC signal to each phase of the motor based on current rotor position and other characteristics of the motor. The physics of the magnetic fields of each stator winding interacting with the rotating rotor can lead to complex mathematics problems that are challenging to create and solve to address factors that lead to efficient driving of the motor.

[0026] In some sy stems, motor controllers operate using a rotating reference frame to simplify the motor control. For example, motor characteristics (in a stationary reference frame) may be measured and transformed into a direct-quadrature-Null (DQN) space, or DQN + rotor (R) space or reference frame (also referred to as the DQNR, RDQNull, and RDQ0 reference frame), using a transform based on the Clarke and Park transforms. In other words, the motor characteristics (e.g., stator currents, rotor currents, and rotor position) can be transformed into a D-axis value, a Q-axis value, an N-axis (or 0-axis) value, and an R (rotor field) value. By using a rotating reference frame where the stator rotates at the frequency of the AC signals, the AC signals can be treated as direct current signals (i.e., the D, Q, N, and R values), which can simplify the calculations used to determine control signals. Desired DQN and R values may be calculated based on the determined DQN and R values, and then transformed back into stator and rotor control values in the stationary reference frame to control the motor.

[0027] Relative to permanent magnet (PM) synchronous motors, in RDQN control schemes for WFS motors, the rotor provides an extra state cross-coupling between the (stator) D-axis and R (rotor field), in addition to a state of coupling between the (stator) D-axis and Q-axis that may exist in both PM synchronous and WFS motors. In other words, for both PM synchronous and WFS motors, changes to the D-axis impact the Q-axis and changes to the Q- axis impact the D-axis. However, for WFS motors, an additional control complexity is present in that changes to the D-axis impact R, and changes to R impact the D-axis. This cross-coupling between the D-axis and R components stems, at least in some cases, from the inherent air gap between the stator and rotor, which leads to non-negligible leakage current and an effective rotor-stator turns ratio that is different than intended. These cross-couplings increase the complexity and present challenges to designing motors and motor controllers for high performance applications of WFS motors.

[0028] In some WFS motors, to provide current through rotor windings of the rotor, the rotor includes brushes or a slip ring to make electrical contact with stationary contacts or terminals as the rotor rotates. The stationary contacts may be mechanically and / or electrically coupled to a power source and, accordingly, power is transferred to the rotor through direct or wired connections as the rotor rotates. This power may then be used to provide current through the rotor windings. In other WFS motors, the rotor may receive power wirelessly from the stator, which the rotor then uses to apply a current through the rotor windings. The wireless power transfer may occur through an inductive coupling between stator windings and rotor windings. The wireless power may be received by the rotor winding as an alternating current (AC) wireless power signal. The rotor may convert the wireless power signal to power components of a rotor circuit.

[0029] To convert the wireless power signal, the rotor may include a passive or active converter. A passive converter is less complex than an active converter, but may be less effective than an active converter (e.g., less efficient), can lead to damaging temperatures of semiconductor and / or circuit elements due to the lower efficiency, may be physically large, may lead to a damaging overvoltage condition on rotor elements system when uncontrolled, and, when implemented as an H-bridge, cannot provide a non-zero average phase current (e.g., cannot provide a phase current that does not return to zero) leading to large torque ripple and / or noise, vibration, and harshness (NVH) in operation. As an example, a passive converter signal may have a ripple current larger than an average current (e.g., 5 ampere (A) average, but ripple with amplitude greater than 5 A), whereas an active converter signal may have an average current that is greater than the current ripple (e.g., a 10 A average with a 5 A ripple). An active converter, on the other hand, may involve a more complex control strategy and additional control hardware to control switches of the active converter. If the control hardware is positioned on the rotor where the rotor does not have direct or wired connections to a power source, an additional consideration may be a scheme to provide power to the control hardware, particularly at start-up. Additionally, once in operation, the control software to control switching of the active converter can be complex. For example, it can be challenging to properly trigger control signals to the switches of the active converter. For example, some systems can rely on a rotor controller that controls the active converter to have either explicit or shared information as to frequency, phase, and magnitudes of the wireless power signal from the stator, or to have an online estimation of the frequency and phase, for example, using a phase-locked loop.

[0030] The present disclosure provides systems, methods, instructions on computer readable media, and hardware-based implementations of control algorithms that address these and other issues related to WFS motors or other coupled inductor systems where an active converter system is electrically isolated and is initialized, or booted, to perform active switching and / or control of its electrically isolated components. For example, the present disclosure provides asynchronous rotor control for a switch bridge of a wound field rotor. The rotor control may act asynchronously (e.g., during startup periods) or synchronously as an active controller for a synchronous motor controller (e.g., during motoring or generating). In either case, the rotor control can be implemented based on rotor state variables and, in some examples, present switching state of a rotor switch bridge, and without explicit or shared information from the stator and without a phase-locked loop. Further, as mentioned, the asynchronous rotor control may be used as part of a boot-up sequence for starting operation of the WFS rotor (e.g., for “dark start-up”). Such approaches can significantly reduce the signal processing and computational burden for wireless power transfer to the rotor, can enable changing power transfer frequency without prior communication between the rotor and the stator (or other off-rotor components), and / or can allow multiplexing of multiple power transfer frequencies with no additional signal processing or computational burden.

[0031] FIG. 1 illustrates a motor system 100, according to some embodiments. The motor system 100 includes a power supply 105, a stator control system 110, and a motor assembly 115. The power supply 105 provides direct current (DC) power to the stator control system 110. In some embodiments, the power supply 105 includes a DC power source 120 that provides the DC power to the stator control system 110. The DC power source 120 may be, for example, one or more batteries, photovoltaic cells, or the like. In some embodiments, the power supply 105 includes an AC / DC converter 125 that receives alternative current (AC) power from an AC power source 130, which may be a utility grid or external generator. In these embodiments, the AC / DC converter 125 outputs the DC power to the stator control system 110. In some embodiments, the AC power source 130 is part of the power supply 105 (e.g., in the case of an on-site wind turbine or generator). In some embodiments, the power supply 105 includes both the DC power source 120 and the AC / DC converter 125, and the DC power from the power supply 105 to the stator control system 110 is provided from one or both sources.

[0032] The stator control system 110 is configured to control the application of power from the power supply 105 to the motor assembly 115 to drive rotation of a rotor of the motor assembly 115. More particularly, the stator control system 110 includes a stator controller 135, a stator drive circuit 150, and motor sensors 155. Generally, the stator controller 135 monitors characteristics of the motor assembly 115 based on signals received from the motor sensors 155 and, based on these characteristics, provides control signals to the stator drive circuit 150 to control the application of power from the power supply 105 to the motor assembly 115 to drive rotation of the motor assembly 115.

[0033] The stator controller 135 may include an electronic processor. The electronic processor may be configured to, among other things, receive instructions and data from a memory of the stator controller 135 and execute the instructions to, for example, carry out the functionality of the stator controller 135 described herein. For example, the memory may include control software. In some embodiments, instead of or in addition to executing software from the memory to carry out the functionality of the stator controller 135 described herein, the electronic processor includes one or more hardware circuit elements configured to perform some or all of this functionality. For example, the electronic processor may be made up of some analog circuitry or entirely of analog circuitry to perform some or all of the functionality of the stator controller 135 described herein. Additionally, or alternatively, in some examples, the electronic processor is implemented as a field programmable gate array (FPGA), an application specific integrated circuit, or a combination thereof to carry out some or all of the functionality of the rotor controller 220 described herein. Additionally, although a particular controller, electronic processor, and memory may be referred to as a respective, single unit herein, in some embodiments, one or more of these components is a distributed component. For example, in some embodiments, an electronic processor includes one or more microprocessors and / or hardware circuit elements.

[0034] The motor sensors 155 include one or more current sensors 165 for sensing current, one or more voltage sensors 167 for sensing voltage, and one or more position sensors 170 for determining a rotor position of a rotor assembly 185 (also referred to as rotor 185) of the motor assembly 115 (also referred to as motor 115). In some embodiments, additional or fewer motor sensors are included in the motor sensors 155. For example, the motor sensors 155 may also include one or more vibration sensors, temperature sensors, and the like. In some embodiments, current and / or voltage sensors are provided for each stator phase and / or each rotor phase of the motor assembly 115. In some examples, the stator controller 135 infers a first motor characteristic (e.g.. current or voltage), rather than directly sensing the motor characteristic. Accordingly, in some embodiments, for example, one or more of the current sensors 165 is / are not included in the motor system 100. For example, the stator controller 135 may be configured to determine rotor current or a state of the motor assembly 115 via the voltage sensors 167 on the stator assembly 180 (e.g., by sensing back electromotive force (back emf)). In another example, the stator controller 135 is configured to infer incremental inductance via sensing voltage and / or current, and changes thereto, with respect to time.

[0035] In some examples, the position sensor 170 includes a Hall effect sensor configured to sense and output an indication of a magnetic field of a rotating rotor of the rotor assembly 185 passing nearby the Hall effect sensor, which is indicative of the rotor position of the motor assembly 115. In some examples, the position sensor 170 is a rotary encoder (e.g., optical or mechanical), that provides an output indicative of the rotation position of the rotor of the rotor assembly 185. Additionally, in some examples, the stator controller 135 implements "sensorless" control that derives rotor position through monitoring of current and / or voltage of the motor assembly 115, such that a separate position sensor 170 may not be included in the motor sensors 155. The stator controller 135 may determine the position or rotational speed of the rotor through back emf estimation (e.g., based on voltage changes in stator windings), or through high frequency signal injection or perturbation. For example, the stator controller 135 may inject a perturbation into the motor assembly 115 to prevent the motor assembly 115 from operating at steady-state over meaningful periods of time. Such a signal can be used to prevent unobservable conditions, e.g., unidentifiable position, or force energy exchange between the stator and rotor. Typically, a perturbation is chosen with a frequency that is at least 1-2, 2-5, or 5-10 times higher than a fundamental frequency of the motor assembly 115 to prevent an interaction with torque generation resulting in, for example, torque ripple. Such perturbations can be injected at certain phase angles to minimize their interaction with torque production.

[0036] The motor assembly 115 includes a stator assembly 180 and a rotor assembly 185. The stator assembly 180 includes a stator core 182 and a plurality of stator windings 184 on the stator core that are selectively driven with current to induce magnetic fields that rotate the rotor assembly 185. The stator core 182 may be, for example, a lamination stack formed by a plurality of laminations. The lamination stack may include a generally annular profile with teeth extending radially inward (in the case of an outer stator) or radially outward (in the case of an inner stator). The stator windings 184 may be wrapped around the teeth or may include conductors that otherwise fill the slots between teeth. The stator may be wound as a concentrated winding, with windings around single stator teeth. This may be done concentrically around the pole tooth, or toroidally around the back iron of the machine. Alternatively, the stator windings may be distributed, spanning multiple stator teeth and overlapping the area of other windings. Distributed windings may be used with a synchronous machine to increase the operational speed, limit harmonics, and reduce NVH despite presenting electromagnetic and control challenges in some embodiments for the modulation of power transfer and torque production.

[0037] The rotor assembly 185 includes a rotor core, a rotor circuit, and at least one rotor winding. Generally, as current is driven through the rotor winding, a magnetic field is generated that interacts with the magnetic fields generated by current through the stator windings to generate torque to rotate the rotor of the rotor assembly 185. An example of the rotor assembly 185 is described in further detail below with respect to FIG. 2.

[0038] Further, as is well known, an electric machine serving as an electric motor that outputs mechanical power from input electric power may also operate in reverse and serve as an electric generator that outputs electric power from input mechanical power. Accordingly, for ease of description, the electric machines described herein will generally be referred to as motors (e.g., the motor assembly 115), but are meant to also encompass electric generators and devices that may operate as both an electric motor and an electric generator.

[0039] FIG. 2 illustrates a block diagram of an example of the rotor assembly 185 of the motor system 100, according to some embodiments, with certain aspects illustrated in further detail. For example, FIG. 2 illustrates a rotor assembly 185 including one or more rotor windings 205, a rotor core 210, a rotor controller 220, a rotor circuit 225, and rotor sensors 230.

[0040] As explained in further detail below, the rotor windings 205 may be selectively driven with current or voltage, as controlled by the rotor controller 220, to induce magnetic fields that interact with the magnetic fields of the stator assembly 180 to rotate the rotor.

[0041] In some examples, the rotor core 210 includes a lamination stack formed by a plurality of laminations. The lamination stack may include a generally annular profile with teeth extending radially inward (in the case of an outer rotor) or radially outward (in the case of an inner rotor). The rotor windings 205 may be wrapped around the teeth or may include conductors that otherwise fill the slots between teeth. In some embodiments, the rotor assembly 185 includes a combination of permanent magnets and field windings (i.e., a hybrid permanent magnet-would field rotor) secured to the rotor core 210.

[0042] The rotor controller 220 may include an electronic processor. The electronic processor may be configured to, among other things, receive instructions and data from a memory of the rotor controller 220 and execute the instructions to, for example, carry out the functionality of the rotor controller 220 described herein. For example, the memory may include control software. In some embodiments, instead of or in addition to executing software from the memory to carry out the functionality of the rotor controller 220 described herein, the electronic processor includes one or more hardware circuit elements configured to perform some or all of this functionality. For example, the electronic processor may be made up of some analog circuitry or entirely of analog circuitry to perform some or all of the functionality of the rotor controller 220 described herein. Additionally, or alternatively, in some examples, the electronic processor is implemented as a field programmable gate array (FPGA), an application specific integrated circuit, or a combination thereof to carry out some or all of the functionality of the rotor controller 220 described herein. Additionally, although a particular controller, electronic processor, and memory may be referred to as a respective, single unit herein, in some embodiments, one or more of these components is a distributed component. For example, in some embodiments, an electronic processor includes one or more microprocessors and / or hardware circuit elements.

[0043] In some examples, the rotor circuit 225 includes a rotor capacitor 240 and a switch bridge 245. The switch bridge 245 includes, for example, a plurality of power switching elements connected in a bridge-type configuration. The power switching elements can include semiconductor switching devices such as, for example, field effect transistors (FETs) (e.g., a metal-oxide-semiconductor field effect transistors (MOSFETs)), which can include wide bandgap devices (e.g., silicon-carbide-semiconductor field effect transistors (SiC FETs) or gallium-nitride-semiconductor field effect transistors (GaN FETs), bipolar junction transistors (BJTs), or insulated gate bipolar transistors (IGBTs). In some examples, the rotor capacitor 240 may be coupled across the switch bridge 245. The rotor capacitor 240 and the switch bridge 245 may be coupled to the one or more rotor windings 205. The components of the rotor assembly 185, including the rotor circuit 225, the rotor controller 220, and the rotor windings 205, may be electrically isolated from a power source of the stator assembly 180 (e.g., the DC power supply 105 of FIG. 1).

[0044] The rotor controller 220 is configured to control the rotor circuit 225 to selectively apply power to the one or more rotor windings 205. For example, and as explained further below, the rotor controller 220 may control the switch bridge 245 (i) to actively convert the power received from the stator windings 184 (see FIG. 1) to charge the rotor capacitor 240 with the power received, and (ii) to discharge the rotor capacitor 240 to provide current through the one or more rotor windings 205 to generate a magnetic field to create torque.

[0045] In some examples, the rotor capacitor 240 may further be coupled to the rotor controller 220 to provide power to the rotor controller 220 to perform processing operations, as described further below.

[0046] In some examples, the switch bridge 245 (also referred to as an active switch bridge 245) may passively convert power received from the stator windings 184 (for example, at startup). The passive conversion may charge the rotor capacitor 240. Once the rotor capacitor 240 reaches a level sufficient to power the rotor controller 220, the rotor controller 220 may be booted. The boot may occur automatically wherein the rotor controller 220 will assert its active control on the system. The booted rotor controller 220 may then begin controlling the switch bridge 245 to perform active conversion to charge the rotor capacitor and controlling the switch bridge 245 to discharge the rotor capacitor 240, as described above. Thus, the switch bridge 245 may be dual function circuit that, in some time periods, performs passive conversion (e.g., passive rectification) and, in other time periods, performs active conversion (e.g., active rectification). The passive conversion may occur to provide power to boot-up the rotor controller. The active conversion may occur to provide power to energize the rotor windings 205 to generate a magnetic field (e.g., rotor pole(s)) to create torque. The booted rotor controller 220 may then also begin controlling the switch bridge 245 to perform motor control functions on the rotor to interact with the stator for the purposes of mechanical power or electrical generation.

[0047] The rotor sensors 230 may include one or more current sensors 255 and / or one or more voltage sensors 260. The rotor sensors 230 may measure one or more rotor electrical characteristics (e.g., current and / or voltage) and provide sensor data indicative of the measured characteristic(s) to the rotor controller 220. The rotor controller 220 may control operations (e.g., control the switch bridge 245) based on the sensor data, as described further below.

[0048] FIG. 3A and 3B illustrate an example electric motor 300 in accordance with various aspects of the present disclosure. More particularly, FIG. 3B illustrates a cross-section of the motor 300 illustrated in FIG. 3A. The motor 300 is an example of the motor assembly 115 of FIG. 1. As shown in FIG. 3B, the electric motor 300 includes a motor casing 305 that houses a stator assembly 310, and a rotor assembly 320 that rotates within the stator assembly 310, and a rotor chipset assembly 330 disposed within the rotor assembly 320. The motor casing 305 is not illustrated in FIG. 3A. The stator assembly 310 includes a stator core 332 and stator windings 334. The rotor assembly 320 includes the rotor chipset assembly 330 and a rotor core 342. The rotor core 342 may include laminations, around which rotor windings 344 may be wrapped, and a rotor shaft 345 extending through the laminations. The rotor core 342 may support the rotor chipset assembly 330. For example, the rotor chipset assembly 330 may be positioned within and secured to the rotor shaft, as illustrated in FIG. 3B. The rotor chipset assembly 330 may include, for example, a rotor controller (e.g., the rotor controller 220), a rotor circuit (e.g., the rotor circuit 225), and one or more rotor sensors (e.g., the rotor sensors 230). The rotor chipset may be electrically isolated from a power source of the stator assembly 310 or motor 300 (e.g., the DC power supply 105 of FIG. 1). The electric motor 300 illustrated in FIGS. 3A and 3B is merely an example of a motor that may incorporate aspects of the disclosure; in other examples, another motor may incorporate aspects of the disclosure.

[0049] During operation of the motor 300, the rotor assembly 320 defines multiple rotor poles based on energizing the rotor windings 344 (e.g., by selectively actuating and controlling current through the rotor windings 344) and the stator assembly 310 defines multiple stator poles energizing the stator windings 334 (e.g., by selectively controlling current through the stator windings 334). A motor ‘‘pole” (e.g., a stator pole or a rotor pole) may be described as a topological section on either a stator or rotor that emits a single polarity of magnetic flux across an air gap at a given point in time. Poles can be characterized by high field regions. Moreover, poles can result from permanent magnets or from electromagnetic fields. While the number of poles on a stator or rotor are often fixed during manufacturing, in some implementations, the number of poles for the rotor, stator, or both, can be changed during operation. During operation of the motor, one or more of the rotor poles may interact with one or more of the stator poles to produce relative force between the rotor assembly 320 and the stator assembly 310. The relative force can generate a torque that rotates the rotor assembly 320 with respect to the stator assembly 310.

[0050] FIG. 4 illustrates an example diagram 400 of the system in accordance with various aspects of the present disclosure. The diagram 400 includes a stator drive circuit 410, a motor circuit 420, and a rotor circuit 430. The stator drive circuit 410 is an example of the stator drive circuit 150 of FIG. 1 and the rotor circuit 430 is an example of the rotor circuit 225 of FIG. 2. Accordingly, the diagram 400 may represent a circuit of the motor assembly 115 of FIG. 1 and / or the motor 300 of FIG. 3.

[0051] The motor circuit 420 may be an equivalent circuit representing a motor (e.g., the motor assembly 115 and / or the motor 300). The equivalent circuit represents the stator and rotor windings of the motor with three inductors: Ldd, Ln, and Lrd, where “d” represents the d-axis in a rotational reference frame, and “r” represents the rotor axis in the rotational reference frame.

[0052] The stator drive circuit 402 can include four or more power switching elements 412a-d in an inverter bridge arrangement. Each of the power switching elements 412a-d is enabled or disabled by a respective control signal, using, for example, the methodology described below. The stator drive circuit 410 can include two connection points or nodes 414 connecting to the motor circuit 420. The nodes 414 may be coupled to the motor circuit 420 such that the stator drive circuit 410 can control current through, and a voltage across, one or more stator windings of the motor circuit 420. For example, in the case of a three-phase motor, the stator drive circuit 410 may be controlled to provide current through, and a voltage across, any two phases of the three-phase windings of the motor circuit 420 at a given time. The two phases receiving current and the direction of current through the winding phases may be selectively controlled by controlling the power switching elements 412a-d (e.g., by the stator controller 135).

[0053] The rotor circuit 430 can also include four or more power switching elements 432a-d in an inverter bridge arrangement, collectively referred to as a switch bridge 432. Each of the power switching elements 432a-d are enabled or disabled by a respective rotor control signal. The rotor control signals are provided, for example, based on the methodology described below. The rotor control signals may be provided by the rotor controller 220 (FIG. 2). The rotor circuit 430 can include two connection points or nodes 440 connecting to the motor circuit 420. The nodes 440 may be coupled to the motor circuit 420 such that the rotor circuit 430 can control current through, and a voltage across, one or more rotor windings of the motor circuit 420.

[0054] The rotor circuit 430 may further including a diodes 433a-d arranged as a diode bridge 433. As described further below with respect to FIG. 7, the diodes 433a-d may be arranged and coupled to the nodes 440 to perform passive conversion (e.g., when the switches are in an open state as illustrated) of a wireless power signal received from the stator windings (see stator windings 184 of FIG. 1). The passively converted signal may charge the rotor capacitor 434.

[0055] The switch bridge 432 and diode bridge 433 together are an example of the switch bridge 245 of FIG. 2. Although the diodes 433a-d and the power switching elements 432a-d are illustrated as separate components, each diode-switch pair may be part of a single FET. For example, the power switching element 432a and the diode 433a may be a FET, where the diode 433a is a body diode of the FET. Accordingly, the switch bridge 435 may include four FETs to provide the switch bridge 432 and the diode bridge 433. Thus, the switch bridge 435 may be a dual function bridge that includes active components (e.g., FETs) that perform both passive conversion (e.g., to capture power from the stator to boot the rotor circuit) and active conversion (e.g., to both continue to capture power from the stator to power the rotor circuit to enable control of the switch bridge and to energize the rotor windings to generate torque).

[0056] In some example, the rotor circuit 430 further includes a battery or the like (e.g., coupled in parallel or series with the rotor capacitor 434) that may store charge for longer periods of time than the rotor capacitor 434 (e.g., during extended periods when the motor is not in operation) and, thus, may be used to power the rotor controller 220 at startup. In such examples, the battery may be charged in a similar way as the rotor capacitor 434 is charged, as described herein. However, in other examples, the rotor circuit 430 does not include such a separate battery (e.g., as illustrated in FIG. 4).

[0057] In FIG. 5, a rotor control process 500 for controlling a switch bridge of a wound field rotor is provided. The process 500 is described as being carried out by the rotor controller 220 implemented in rotor assembly 185 of FIG. 2, which may be a part of the motor system 100 of FIG. 1 and / or implemented in the motor 300 of FIG. 3. However, in some embodiments, the process 500 may be implemented by another rotor control system. Additionally, although the blocks of process 500 are illustrated in a particular order, in some embodiments, one or more of the blocks may be excluded partially or entirely in parallel, may be executed in a different order than illustrated in FIG. 5, or may be bypassed.

[0058] In block 510, a rotor winding of a rotor receives, wirelessly, a first power signal from a stator winding of a stator. For example, with reference to FIGS. 1 and 2, the stator controller 135 can control the stator drive circuit 15 0 to drive one or more of the stator windings 184. For example, the stator controller 135 can control the stator drive circuit 150 to drive one or more of the stator windings 184 with a power transfer signal to cause the wireless transmission of the power signal (which may be modulated in frequency and amplitude) from the one or more of the stator windings 184 to the rotor assembly 185 (see FIG. 1) or, more particularly, to one or more of the rotor windings 205 of the rotor assembly 185 (see FIG. 2) as the wound rotor with rotor circuit 225 acts as a coupled inductor to the stator. The rotor windings 205 may be coupled to the rotor circuit 225 and, accordingly, the first power signal may also be received by the rotor circuit 225. For example, with reference to FIG. 4, the rotor circuit 430, which is an example of the rotor circuit 225 of FIG. 2, may receive the power signal at nodes 440 from one or more rotor windings of the motor circuit 420.

[0059] In general, the stator windings may be driven with three types of signals: torque control signals, power transfer signals, and data signals. Torque control signals generate a magnetic field in the stator winding(s) that receive the torque control signals, which interact with the magnetic field of the rotor winding(s) to drive movement of the rotor with respect to the stator. Power transfer signals are modulations or modulated signals (e.g., modulated in amplitude or frequency) that transfer power wirelessly (or, inductively) from the stator to the rotor, which may ultimately be used, e.g., to energize rotor windings to generate a magnetic field for magnetomotive coupling and to power circuit(s) on the rotor. Data signals are modulations that transfer data (e.g., encoded control information) wirelessly (or, inductively) from the stator to the rotor. In some examples, a stator winding is driven with a signal that may be classified as more than one of the types of stator signals (e.g., a multi-purpose signal). For example, a stator winding may be driven with a signal that may be classified as both a torque control signal and a power transfer signal in that the signal generates a magnetic field in the stator winding to drive movement of the rotor with respect to the stator, and also transfers power inductively from the stator to the rotor. In some examples, a stator winding may be driven by one or more of these stator signals simultaneously such that the signal through the stator winding is a composite of the one or more of these stator signals. As noted, in block 510, a stator winding of stator windings 184 may be driven with a power transfer signal (e.g., alone or with another signal) by the stator controller 135, causing a rotor winding of rotor windings 205 to receive, wirelessly, a first power signal from the stator winding.

[0060] In block 520, a rotor controller of the rotor determines a capacitor voltage, where the capacitor voltage indicates a voltage across a capacitor of a rotor circuit coupled to the rotor winding. For example, with reference to FIG. 2, the capacitor may be rotor capacitor 240 of the rotor circuit 225. Additionally, with reference to the rotor circuit 430 of FIG. 4, which is a more detailed example of the rotor circuit 225, the capacitor voltage can be vCr across rotor capacitor 434. Further, as illustrated, the rotor capacitor 434 of the rotor circuit 430 is coupled to the rotor windings.

[0061] In block 530, the rotor controller determines a reference current (iR re^) based on the capacitor voltage. For example, the rotor controller 220 may use a function that maps capacitor voltages to reference currents (a current-voltage map). In some examples, the rotor controller 220 uses the function by evaluating or solving the function in real time to calculate the reference current. In some examples, the rotor controller 220 uses the function by accessing a look-up table, defined by the function, that maps capacitor voltages to reference currents. The look-up table and / or function may be stored on the rotor controller 220.

[0062] FIG. 6 illustrates a plot 600 of an example function that maps capacitor voltages to reference currents, which the rotor controller 220 may use in implementing block 530 to determine the reference current iRref based on the capacitor voltage. The plot 600 is a piecewise function having three sections: a first section in which capacitor voltages below a threshold map to a minimum reference current value; a second section in which a relationship between the capacitor voltage and the reference current is linear with a positive slope; and a third section in which the capacitor voltage reaches a high or maximum voltage level and reference current increases to prevent capacitor voltage from increasing above the threshold. In the example plot 600, each section of the piecewise function is linear and, accordingly, the plot 600 may be referred to as a piecewise linear function. In other examples, the rotor controller 220 uses a different function defining the relationship between capacitor voltages and reference currents to determine the reference current. For example, the function may be a non-linear function, the function may be piecewise with non-linear sections, and / or the function may be a piecewise function with fewer or more sections. The function defining the relationship between the capacitor voltage and reference current may be customized and / or unique to a particular motor system.

[0063] In block 540, the rotor controller determines a rotor current iRfbk through the rotor winding. For example, with reference to FIG. 2, the rotor controller 220 determines the rotor current iRfbk using the current sensor 255 in rotor assembly 185. With reference to FIG. 4, the current sensor 255 may be configured to sense rotor current iRfbk by sensing current passing through node 440 and / or the rotor capacitor 434. The current sensor 255 may output a signal indicative of the sensed or measured current to the rotor controller 220. For example, the magnitude of the signal may vary according to the amount of current sensed.

[0064] In block 550, the rotor controller controls a switch bridge of the rotor circuit to change the switching state based on the reference current and the rotor current. For example, with reference to FIG. 2, the rotor controller 220 may control the switch bridge 245 of the rotor circuit 225. Further, with reference to the rotor circuit 430 of FIG. 4, which is an example of the rotor circuit 225, the rotor controller 220 may control the switching of the power switching elements 432a-d. The switching of the power switching elements 432a-d can control whether the voltage is being imposed on, or connected across, the rotor capacitor 434 is positive, zero, or negative, thereby charging or discharging the rotor capacitor 434. Additionally, by controlling the power switching elements 432a-d as described herein, the rotor controller 220 may control the rotor circuit 225 to actively convert the power signal received wirelessly from the stator winding (e.g., to charge the rotor capacitor 434). Further, by controlling the power switching elements 432a-d as described herein, with reference to FIG. 2, the rotor controller 220 may control energization of the rotor windings 205 of the rotor assembly 185 to generate rotor poles. With reference to FIG. 1, the rotor poles generated by the rotor assembly 185 may interact with stator poles of the stator assembly 180 to generate torque (e.g., to rotate the rotor assembly 185).

[0065] In some examples, in block 550, the rotor controller 220 controls the switch bridge 245,432 of the rotor circuit 225,430 to change the switching state thereof, based on the reference current and the rotor current, according to a hysteresis control technique. The hysteresis control technique may synchronous or asynchronous on the rotor of the synchronous machine. The hysteresis control technique defines state transitions, controlled by the rotor controller 220, for the switch bridge 245,432 and, thereby, for the rotor circuit 225, 430 based on state variables of the rotor circuit 225, 430 and, in some cases, a present switching state of the switch bridge 245, 432 (and, thereby, of the rotor circuit 225, 430). In some examples, the state variables of the rotor circuit 225,430 (also referred to as rotor state variables) may include capacitor voltage (as determined in block 520, and used to determine reference current in block 530) and rotor current (as determined in block 540). In some examples, the switching state of the rotor circuit 225,430 may be one of three options: state 0V (a net zero voltage state), state +VDC (a positive voltage state), or state -VDC (a negative voltage state), where these options each correspond to a voltage being imposed across the rotor capacitor 434. For example, with reference to FIG. 4: a. In state 0V, the (high-side) power switching elements 432a-b d are open (disabled) and the (low-side) power switching elements 432c-d are closed (enabled), or vice versa; the rotor phase current does not flow through the capacitor 434 b. in state +VDC, the power switching elements 432b and 432c are closed (enabled) and power switching elements 432a and 432d are open (disabled), accordingly, a positive voltage is applied to the rotor winding, resulting in a negative (discharging) current through the capacitor 434; and c. in state -VDC, the power switching elements 432b and 432c are open (disabled) and power switching elements 432a and 432d are closed (enabled), accordingly, a negative voltage is applied to the rotor winding, which causes a positive (charging) current into the capacitor 434.

[0066] In some examples, the hysteresis control technique defines the state transition based on state variables of the rotor circuit 225, 430 and a present switching of the rotor circuit 225, 430 (Technique A). In other examples, the hysteresis control technique defines the state transition based on state variables of the rotor circuit 225, 430 and without regard for a present switching state of the rotor circuit 225, 430 (Technique B). Each of these control techniques is described further below.

[0067] Technique A. For examples of the hysteresis control technique that define state transitions based on rotor state variables and the present switching state, the rotor controller 220 may determine the present switching state of the rotor circuit 225,430. As described above, the present switching state of the rotor circuit 225, 430 corresponds to the switching state of the power switching elements 432a-d of the switch bridge 432. Accordingly, the rotor controller 220 may determine the present switching state may determining which power switching elements the rotor controller 220 has enabled and which power switching elements the rotor controller 220 has disabled. The rotor circuit 225, 430 may default to the state 0V (e.g., at start up). Depending on the present switching state, the rotor controller 220 applies different criteria for determining the next switching state. State another way, the rotor controller 220 select state transition criteria to apply based on the present switching state. To apply the state transition criteria, the rotor controller 220 may determine whether a difference between the reference current (determined in block 530) and the rotor current (determined in block 540) is greater than or less than one or more thresholds. Based on this determination, the rotor controller 220 may determine the next switching state of the rotor circuit 225, 430.

[0068] An example of the state transition criteria, for each present switching state, that the rotor controller 220 may apply to determine a next switching state is as follows: a. When the present switching state is state 0V If iRfbk - iRref > icrit_on, then next state = state -VDC If iRfbk - ^Rref < -icritjm, then next state = state +VDC Else: remain in state 0V b. When the present switching state is state +VDC If iRfbk - iRref > icritjm, then next state = state -VDC If iRfbk ~ iRref > icrit_of^ then next state = state 0V Else: remain in state +VDC c. When the present switching state is state -VDC If iRfbk - iRref < -icritjm, then next state = state +VDC If ^ / bk ~      < ~icrit_off ', then next State = State 0V Else: remain in state -VDC

[0069] As one example of applying the transition criteria, the rotor controller 220 may determine that the rotor circuit 225, 430 is in the state +VDC. The rotor controller 220 may then determine a difference between the reference current (determined in block 530) and the rotor current (determined in block 540) by subtracting the reference current from the rotor current. The rotor controller 220 may then compare this difference to a first current threshold (hrit on) 1° determine whether the difference is greater than the first current threshold. When the rotor controller 220 determines that the difference is greater than the first current threshold, the rotor controller 220 controls the switch bridge 245, 432, and thereby the rotor circuit 225, 430, to switch to the state -VDC. When the difference is less than the first current threshold, the rotor controller 220 may then compare this difference to a second current threshold (Crit off) to determine whether the difference is greater than the second current threshold. When the rotor controller 220 determines that the difference is greater than the second current threshold, the rotor controller 220 controls the switch bridge 245, 432, and thereby the rotor circuit 225, 430, to switch to the state 0V. When the difference is less than the first current threshold and less than the second current threshold, the rotor controller 220 may remain in the state +VDC. In some examples, the comparisons may happen in parallel or in a different order. Using similar principles, the rotor controller 220 may similarly apply the corresponding transition criteria for state 0V when the rotor controller 220 determines the rotor circuit 225, 430 is in the state 0V and may similarly apply the corresponding transition criteria for state -VDC when the rotor controller 220 determines the rotor circuit 225, 430 is in the state -VDC.

[0070] Technique B. For examples of the hysteresis control technique that define state transitions based on rotor state variables and without regard for the present switching state, the rotor controller 220 may, without regard for the present switching state, apply state transition criteria for determining the next switching state. That is, regardless of the present switching state, the rotor controller 220 may apply the same state transition criteria. To apply the state transition criteria, the rotor controller 220 may determine whether a difference between the reference current (determined in block 530) and the rotor current (determined in block 540) is greater than or less than one or more thresholds. Based on this determination, the rotor controller 220 may determine the next switching state of the rotor circuit 225, 430.

[0071] An example of the state transition criteria that the rotor controller 220 may apply to determine a next switching state is as follows: If iRfbk -     < -icrit on, then next state =state +VDC If iRfbk - iRref > icrit_on, then next state = state -VDC Else: next state = state OV

[0072] As one example of applying the transition criteria, the rotor controller 220 may determine a difference between the reference current (determined in block 530) and the rotor current (determined in block 540) by subtracting the reference current from the rotor current. The rotor controller 220 may then compare this difference to a first current threshold (-icrit_on) to determine whether the difference is less than the first current threshold. When the rotor controller 220 determines that the difference is less than the first current threshold, the rotor controller 220 controls the switch bridge 245, 432, and thereby the rotor circuit 225, 430, to switch to (or remain in) the state +VDC. When the difference is greater than the first current threshold, the rotor controller 220 may then compare this difference to a second current threshold (icrit on) to determine whether the difference is greater than the second current threshold. When the rotor controller 220 determines that the difference is greater than the second current threshold, the rotor controller 220 controls the switch bridge 245, 432, and thereby the rotor circuit 225, 430, to switch to (or remain in) the state -VDC. When the difference is greater than the first current threshold and less than the second current threshold, the rotor controller 220 controls the switch bridge 245, 432, and thereby the rotor circuit 225, 430, to switch to (or remain in) the state 0V. In some examples, the comparisons may happen in parallel or in a different order. Relative to Technique A, Technique B simplifies the switching logic and uses less information to make a determination of the next state.

[0073] Accordingly, by applying one of the hysteresis control techniques, in block 550 of FIG. 5, the rotor controller 220 controls the switch bridge 245,432 of the rotor circuit 225, 430 to change the switching state thereof, based on the reference current and the rotor current.

[0074] In some examples, the process 500 may continuously loop during operation of the motor (e.g., the motor assembly 115 and / or the motor 300), returning from block 550 to 510 and proceeding again through blocks 520, 530,540 and 550. By looping, the rotor winding can continue to receive a power signal wirelessly from the stator and the rotor controller can continue to determine capacitor voltage, reference current, rotor current, and control the switch bridge based on the reference current and rotor current. Accordingly, by looping, the rotor controller 220 may control the switch bridge of the rotor circuit to cycle the switching state among the available switching states (e.g., state 0V, state +VDC, and state -VDC) based on the reference current and the rotor current. By executing this method, the rotor controller 220 can implement an asynchronous or synchronous control of the rotor circuit 225, 430 to control the switch bridge 245, 432 (i) to actively convert the power received wirelessly from the stator windings 184 (see FIG. 1) to charge the rotor capacitor 240 with the power received, and (ii) to discharge the rotor capacitor 240 to provide current through the one or more rotor windings 205 to generate a magnetic field to create torque.

[0075] In the process 500, the measurements of voltage, current and the updated switching state can be performed asynchronous to the injection of power from the stator drive circuit 410 of the synchronous machine. Further, by implementing the process 500, the rotor controller 220 can control the rotor circuit 225, 430 independently, without receiving instructions or communications from the stator controller (e.g., to synchronize operation of the rotor assembly 185 and the stator assembly 180). The performance of the control techniques can improve by increasing a sampling rate of the rotor sensors 230 and by increasing an update rate performed by the rotor controller 220. In some examples, the rotor controller 220 can be entirely in asynchronous analog and digital circuitry, as opposed to a microcontroller or logic controller running at a fixed clock rate, which can increase the overall efficiency of the motor system.

[0076] The control techniques described herein take advantage of an asymmetry in control authority between a primary (stator D-axis) and a secondary (rotor) of a coupled inductor system of the motor system 100. In some examples, the ratio of control authority is around 25:1, but could be effective at ratios of 5:1, of 1:1, or of another ratio. This ratio can be a designed variable by selecting a turn ratio between the primary and secondary. As the stator assembly 180 observes a rotating field of the rotor assembly 185, a majority of the voltage authority contributes to counteracting the back-electromotive force (BEMF), which can arise from the DQ axes rotating with respect to the physical conductors. Therefore, in some examples, the turn count and can be low, and the voltage authority can be high, based on volts-per-tum, allowing the stator power or voltage command to dominate the high-frequency response of the coupled system between the stator and the rotor. In some aspects, the asymmetry can simplify valid actions available to the rotor controller 220 to perform the duties of low frequency phase current control and high-frequency voltage synchronization for power transfer.

[0077] During steady state operation of the motor system 100 (e.g., while looping through the process 500 of FIG. 5), the charge of the rotor capacitor 434 can be equal to the time-based integration of the capacitor current. For example, the capacitor current can be positive when the switching state is -VDC (icr = +iRc), negative when the switching state is +VDC (icr = -iRc), and zero when the switching state is OV (icr = 0). When the average rotor current is equal to zero, a charge can be accumulated by the capacitor 434, as negative phase currents are directed to be positive capacitor current. Likewise, positive phase currents can be directed to be positive capacitor currents. Accordingly, in some embodiments, for example, the current is increased as a function of capacitor voltage, which increases the proportion of time in the +VDC, raising the average rotor current to be greater than zero, and decreases the rate of charge accumulation until the rate reaches zero. This control strategy can place the rotor phase voltage in quadrature to the stator power injection (i.e., lagging by 90°), which can be the desired phase shift for maximum power transfer for a given voltage amplitude of the primary and secondary n the coupled system.

[0078] Although blocks 520, 530, and 540 refer to determinations by the rotor controller 220, as noted with respect to FIG. 2, the rotor controller 220 may be implemented as an analog circuit or otherwise as a control device that does not retrieve and execute instructions to perform the functionality described herein. Accordingly, in such examples, the analog circuitry the rotor controller 220 may "‘determine” a current or voltage by, for example, including circuitry that receives a signal indicative of such current or voltage (e.g., from a sensor) and may “determine” a reference current by including a circuit designed to translate an input signal (e.g., indicative of the capacitor voltage) to an output signal (e.g., representative of the reference current). For example, an amplifier circuit may perform the translation. In other examples, the analog circuitry of the rotor controller 220 may “determine” values or reference values using other techniques.

[0079] In FIG. 7, a boot-up sequence process 700 is provided for starting operation of a motor with rotor controller on a wound field rotor where the rotor controller may be electrically isolated. The process 700 is described as being carried out by the rotor controller 220 implemented in rotor assembly 185 of FIG. 2, which may be a part of the motor system 100 of FIG. 1 and / or implemented in the motor 300 of FIG. 3. However, in some embodiments, the process 700 may be implemented by another rotor control system. Additionally, although the blocks of process 700 are illustrated in a particular order, in some embodiments, one or more of the blocks may be excluded partially or entirely in parallel, may be executed in a different order than illustrated in FIG. 7, or may be bypassed.

[0080] In block 710, a rotor circuit may use or passively convert a power signal received, wirelessly, from a stator winding of a stator to capture energy. The converted power signal may charge a rotor capacitor to increase a capacitor voltage thereof (e.g., for the purpose of turning on the rotor controller 220). For example, with reference to FIGS. 1 and 2, the stator controller 135 can control the stator drive circuit 15 0 to drive one or more of the stator windings 184. For example, as described with respect to block 510 of FIG. 5, the stator controller 135 can control the stator drive circuit 150 to drive one or more of the stator windings 184 with a power transfer signal to cause the wireless transmission of the power signal from the one or more of the stator windings 184 to the rotor assembly 185 (see FIG. 1) or, more particularly, to one or more of the rotor windings 205 of the rotor assembly 185 (see FIG. 2). The rotor windings 205 may be coupled to the rotor circuit 225 and, accordingly, the first power signal may also be received by the rotor circuit 225. For example, with reference to FIG. 4, the rotor circuit 430, which is an example of the rotor circuit 225 of FIG. 2, may receive the power signal at nodes 440 from one or more rotor windings of the motor circuit 420.

[0081] At this point during start-up, the rotor controller 220 is not yet powered on or enabled (e.g., because sufficient power is not provided to a power input (Vcc) of the rotor controller 220 and the rotor controller 220 is electrically isolated from the power source 105). Accordingly, the rotor controller 220 may be unable to control switching of the switch bridge 245. In this case, the received power signal, which may be an alternating signal, is passively converted by the switch bridge 245. More particularly, with reference to FIG. 4, the diodes 433a-d of the switch bridge 245 provide passive conversion or rectification of the (alternating) power signal to provide a DC voltage output to charge the rotor capacitor 434 to increase the capacitor voltage (vCr) of the rotor capacitor 434. During this stage, the power switching elements 432a-d of the switch bridge 245 may be in a default open state. That is, the power switching elements 432a-d may be in a default start-up state and not actively controlled (e.g., their switching state of open may be static or maintained) during this stage where the rotor controller 220 is not yet powered on or enabled, and this default start-up state causes the switch bridge 245 to direct or shunt the power to charge the rotor capacitor 434.

[0082] In block 720, in response to the capacitor voltage of the rotor capacitor exceeding a boot-up threshold, a rotor controller is booted. For example, when the capacitor voltage (yCr) of the rotor capacitor 434 exceeds a boot-up threshold of 3.3V, 5V, or another value, the rotor controller 220 may boot-up. Boot-up may include executing a power-on routine, for example, by retrieving boot instructions from a memory of the rotor controller 220 and executing the boot instructions, or otherwise initializing the rotor controller 220 for operation. During boot-up, the rotor controller 220 may control the switch bridge 245, 432 to state 0V (e.g., power switching elements 432a-b enabled, 432c-d disabled, or vice versa).

[0083] In block 730, in response to completing the booting of the rotor controller, the rotor controller controls the switch bridge of the rotor circuit to cycle the switching state among switching states. By cycling the switching state among switching states, the rotor controller may actively convert the power signal received wirelessly from the stator winding and to control current through a rotor winding. For example, to implement the controlling of the switch bridge in block 730, the rotor controller 220 may control the switch bridge 245 according to an asynchronous hysteresis control technique, such as, for example, described with respect to the process 500 of FIG. 5. Accordingly, in block 730, the rotor circuit ceases passive conversion used for boot-up of the rotor controller 220 and transitions to active conversion and control of the wirelessly received power signal from the stator windings. This transition is desirable, for example, because passive conversion may be less efficient than active conversion and may prohibit the operation of the motor beyond the boot-up of the rotor controller 220; the lower efficiency can lead to increased or damaging temperatures of the conversion elements or damaging overvoltage condition on the rotor assembly 185 (particularly because the voltage of the primary (stator winding) is amplified on the secondary (rotor winding) by the turns ratio of secondary to primary, which may be greater than 10:1; and because passive conversion through an H-bridge cannot provide a non-zero average phase current.

[0084] In some examples, for example, where the rotor controller 220 is an analog circuit, a separate booting step or initialization routine may not be implemented. Rather, block 720 and 730 of the process 700 may be combined such that, in response to the capacitor voltage of the rotor capacitor exceeding a boot-up threshold (as described with respect to block 720), the rotor controller 220 proceeds to control the switch bridge of the rotor circuit to cycle the switching state among switching states (as described with respect to block 730).

[0085] The rotor controller 220 may continue to control the switch bridge according to the asynchronous hysteresis control technique until one or both of the capacitor voltage exceeds a minimum voltage threshold and / or the rotor current exceeds a minimum current threshold. The rotor controller 220 may determine that the capacitor voltage exceeds the minimum voltage threshold by sensing the capacitor voltage with the voltage sensor 260 and comparing the capacitor voltage to the minimum voltage threshold. The rotor controller 220 may determine that the rotor current exceeds the minimum current threshold by sensing the rotor current with the current sensor 255 and comparing the rotor current to the minimum current threshold.

[0086] In block 740, in response to one or both of the minimum current and voltage thresholds being exceeded, the rotor controller may control the rotor circuit according to a steady state operation control technique. For example, the rotor controller 220 may control the switch bridge 245 according to a synchronous technique based on communications from the stator controller 135. The stator controller 135 may convey the communications via a wireless signal transmitted via the stator winding(s) 184, received by the rotor winding(s) 205, and sensed by the rotor controller 220 via one of the rotor sensors 230. In other examples, the wireless communication can occur through signal generated via a photodiode, a Bluetooth® protocol, a real-time WiFi® protocol, or the like, where both the stator and the rotor have a respective transceiver coupled to their respective controllers (e.g., for communicating and processing). In other examples, in steady state operation in block 740, the rotor controller 220 may control the switch bridge 245 using a different asynchronous hysteresis control technique than used in block 730. For example, the rotor controller 220 may switch from Technique A to Technique B, or from Technique B to Technique A, described above with respect to the process 500 of FIG. 5. In other examples, in steady state operation in block 740, the rotor controller 220 may continue to control the switch bridge 245 using the same asynchronous hysteresis control technique used in block 730. In some examples, in block 740, the stator controller 135 is able to detect rotor current or rotor state using back electromotive force (back EMF) techniques. In some examples, the stator controller 135 may, upon detecting rotor current or rotor state, transition from a start-up sequence to a steady state operation mode. In steady state operation mode, the stator controller 135 may control current through the stator windings 184 to meet a given operating point, be that circuit operating state (phase currents and capacitor voltage commands) or mechanical operating state (torque, speed, position, etc.).

[0087] FIG. 8A is a waveform diagram 800 that illustrates an example of rotor electrical characteristics over time during execution of the process 700 (e.g., with the motor system 100). The waveform diagram 800 plots rotor voltage 805, rotor capacitor voltage 810, rotor winding current 815, and stator current 820. With reference to FIG. 4, the rotor voltage 805 may be the voltage across nodes 440, the rotor capacitor voltage 810 may be the capacitor voltage across capacitor 434, the rotor winding current 815 may be the rotor current ir of a rotor winding of the motor circuit 420 and circulating through nodes 440, and stator current 820 may be the current through the nodes 414 to / from the motor circuit 420.

[0088] In FIG. 8A, the waveform diagram 800 illustrates phases of a motor system during the process 700, which will be described with respect to the motor system 100 and FIGS. 1-4. In phase 830, the motor system 100 is idle. In phase 832, the stator controller 135 drives current through the stator windings, indicated by the waveform of the stator current 820. In this phase 832, rotor current is induced in the rotor winding(s), as indicated by the waveform of the rotor winding current 815 and the waveform of the rotor voltage 805. In other words, the stator winding transfers a power signal, wirelessly, to the rotor winding(s). During this phase 832, the switch bridge 245 (e.g., the diode bridge 433 of FIG. 4) passively converts the received power signal. The converted power signal charges the rotor capacitor 434, as indicated by the rising rotor capacitor volage 810. Phase 832 may correspond to block 710 of FIG.7.

[0089] At phase 834, the rotor capacitor volage 810 exceeds a boot-up threshold and the rotor controller 220 is booted. Phase 834 may correspond to block 720 of FIG.7. At phase 836, the booted rotor controller 220 begins controlling the switch bridge 245, 432 of the rotor circuit 225, 430, actively converting the received power signal. Phase 834 may correspond to block 730 of FIG.7. In some examples, phase 834 may also correspond to block 740 of FIG. 7.

[0090] FIG. 8B is a waveform diagram 850. The waveform diagram 850 is an enlarged view of a time slice 840 of the waveform diagram 800 of FIG. 8A.

[0091] Although the present application is primarily described above with respect to a rotary electric machines, the disclosed concepts similarly apply to linear electric machines, where the stator and rotor (or primary and secondary coils) may translate with respect to one another, rather than rotate. Additionally, in some examples, the independently powered coil or windings (also referred to as the primary coil) could be on the stationary component (stator) of the electric machine and the secondary coil may be on the rotating or translating component of the electric machine (as described above). However, in other examples, the independently powered primary coil can be positioned on the moving component (rotor / translator) of the electric machine and transfer power to the stationary secondary coil. For example, a fuel source and generator may drive a locomotive on an unpowered track, or some other energy' input can be harvested by the moving portion and then transferred to the stationary' portion in order to achieve force / torque and motion.

[0092] Performance of the various techniques and operations described herein may be facilitated by an electronic controller (e.g., a processor-based computing device), such as the stator controller 135, the rotor controller 220, or the like as described herein. Such an electronic controller may include a processor-based device such as a computing device, and so forth, that may include a central processor unit (CPU) or a processing core. In addition to the CPU or processing core, the system includes main memory, cache memory, and bus interface circuits. The electronic controller may include a memory storage device, such as a hard drive (solid state hard drive, or other types of hard drive), or flash drive associated with the computer system. The electronic controller may further include a keyboard, or keypad, or some other user input interface, and a monitor, e.g., an LCD (liquid crystal display) monitor, that may be placed where a user can access them.

[0093] A memory storage device of the electronic controller may include a computer program product that when executed on the electronic controller (which, as noted, may be a processor-based device) causes the processor-based device to perform operations to facilitate the implementation of procedures and operations described herein. The electronic controller may further include peripheral devices to enable input / output functionality. Such peripheral devices may include, for example, flash drive (e.g., a removable flash drive), or a network connection (e.g., implemented using a USB port and / or a wireless transceiver), for downloading related content to the connected system. Such peripheral devices may also be used for downloading software containing computer instructions to enable general operation of the respective system / device. Alternatively, and / or additionally, in some embodiments, special purpose logic circuitry, e.g., an FPGA (field programmable gate array), an ASIC (application-specific integrated circuit), a DSP processor, a graphics processing unit (GPU), application processing unit (APU), etc., may be used in the implementations of the electronic controller. Other modules that may be included with the electronic controller may include a user interface to provide or receive input and output data. The electronic controller may include an operating system.

[0094] Computer programs (also known as programs, software, software applications or code) include machine instructions for a programmable processor, and may be implemented in a high-level procedural and / or object-oriented programming language, and / or in assembly / machine language. As used herein, the term “machine-readable medium” refers to any non-transitory computer program product, apparatus and / or device (e.g., magnetic discs, optical disks, memory, Programmable Logic Devices (PLDs)) used to provide machine instructions and / or data to a programmable processor, including a non-transitory machine-readable medium that receives machine instructions as a machine-readable signal.

[0095] In some embodiments, any suitable computer readable media can be used for storing instructions for performing the processes / operations / procedures described herein. For example, in some embodiments computer readable media can be transitory or non-transitory. For example, non-transitory computer readable media can include media such as magnetic media (such as hard disks, floppy disks, etc.), optical media (such as compact discs, digital video discs, Blu-ray discs, etc.), semiconductor media (such as flash memory, electrically programmable read only memory (EPROM), electrically erasable programmable read only Memory (EEPROM), etc.), any suitable media that is not fleeting or not devoid of any semblance of permanence during transmission, and / or any suitable tangible media. As another example, transitory computer readable media can include signals on netw orks, in wires, conductors, optical fibers, circuits, any suitable media that is fleeting and devoid of any semblance of permanence during transmission, and / or any suitable intangible media.

[0096] Although particular embodiments have been disclosed herein in detail, this has been done by way of example for purposes of illustration only, and is not intended to be limiting with respect to the scope of the appended claims, which follow. Features of the disclosed embodiments can be combined, rearranged, etc., within the scope of the application to produce more embodiments. Some other aspects, advantages, and modifications are considered to be within the scope of the claims provided below. The claims presented are representative of at least some of the embodiments and features disclosed herein. Other unclaimed embodiments and features are also contemplated. FURTHER EXAMPLES

[0097] Example 1: A method, apparatus, and / or non-transitory computer-readable medium storing processor-executable instructions for an electric machine comprising: a stator including stator windings; a stator controller configured to control current through the stator winding to generate a wireless power signal; and a rotor including a rotor winding, a rotor circuit, and a rotor controller, the rotor circuit including a switch bridge coupled to the rotor winding and a capacitor coupled across the switch bridge, the rotor winding configured to receive the wireless power signal from a stator winding of the stator windings, and the rotor controller configured to: determine a capacitor voltage, the capacitor voltage indicating a voltage across the capacitor; determine a reference current based on the capacitor voltage, determine a rotor current through the rotor winding, and control the switch bridge of the rotor circuit to change a switching state based on the reference current and the rotor current.

[0098] Example 2: The method, apparatus, and / or non-transitory computer readable medium any of Examples 1, wherein the rotor controller is further configured to: control the switch bridge of the rotor circuit to cycle the switching state among switching states based on the reference current and the rotor current.

[0099] Example 3: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 2, wherein, to determine the reference current based on the capacitor voltage, the rotor controller is configured to apply the capacitor voltage as an input to a current-voltage map, the current-voltage map defining a relationship between voltage values and current values using a piecewise linear function.

[00100] Example 4: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 3, wherein, to control the switch bridge to change the switching state is based on a difference between the rotor current to the reference current, the rotor controller is further configured to: control the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold, control the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, and control the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

[00101] Example 5: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 4, wherein, to control the switch bridge to change the switching state is based on a difference between the rotor current to the reference current, the rotor controller is further configured to: control the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold, control the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, and control the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

[00102] Example 6: The method, apparatus, and / or non-transitory computer readable medium of Example 5, wherein, to control the switch bridge to enter the positive voltage state, the negative voltage state, or the net zero voltage state based on the difference and the present switching state, the rotor controller is configured to: when the present switching state is the net zero voltage state, control the switch bridge to enter the positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a first negative current threshold, control the switch bridge to enter the negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a first positive current threshold; when the present switching state is the positive voltage state, control the switch bridge to enter the net zero voltage state when the difference is greater than a second positive current threshold, control the switch bridge to enter the negative voltage state to apply the negative voltage to the capacitor to discharge the capacitor when the difference is greater than the first positive current threshold; and when the present switching state is the negative voltage state, control the switch bridge to enter the positive voltage state to apply the positive voltage to the capacitor to charge the capacitor when the difference is less than the first negative current threshold, control the switch bridge to enter the net zero voltage state when the difference is less than a second negative current threshold.

[00103] Example 7: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 6, wherein the switching state defines operational states of switches of the switch bridge to cause at least one of a positive DC capacitor voltage, a negative DC capacitor voltage, or a net zero capacitor voltage.

[00104] Example 8: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 7, wherein, to implement a boot-up sequence: the rotor circuit is configured to passively convert the wireless power signal to charge the capacitor to increase the capacitor voltage; and the rotor controller is configured to: boot in response to the capacitor voltage exceeding a boot-up threshold; and in response to the rotor controller completing booting, control the switch bridge to cycle the switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding.

[00105] Example 9: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 7, wherein, to implement a boot-up sequence: the rotor circuit is configured to passively convert the wireless power signal to charge the capacitor to increase the capacitor voltage; and the rotor controller is configured to: in response to the capacitor voltage exceeding a boot-up threshold, control the switch bridge to cycle the switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding.

[00106] Example 10: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 8 to 9, wherein the rotor controller is further configured to: determine that at least one of the rotor current or the capacitor voltage has exceeded a minimum threshold; and control the switch bridge according to a steady state operation.

[00107] Example 11: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 10, wherein the stator controller is further configured to energize the stator windings to define stator poles, and wherein the rotor controller is further configured to energize the rotor winding to define a rotor pole that interacts with the stator poles to produce relative force between the rotor and the stator.

[00108] Example 12: A method, apparatus, and / or non-transitory computer-readable medium storing processor-executable instructions for a rotor chipset assembly of an electric machine comprising: a rotor circuit including a switch bridge configured to be coupled to a rotor winding and a capacitor coupled across the switch bridge, the rotor winding configured to receive a wireless power signal from a stator winding, and a rotor controller configured to: determine a capacitor voltage, the capacitor voltage indicating a voltage across the capacitor, determine a reference current based on the capacitor voltage, determine a rotor current through the rotor winding, and control the switch bridge of the rotor circuit to change a switching state based on the reference current and the rotor current.

[00109] Example 13: The method, apparatus, and / or non-transitory computer readable medium of Examples 12, wherein the rotor controller and the rotor circuit are supported by a rotor core including a rotor shaft and rotor laminations.

[00110] Example 14: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 12 to 13, further comprising: at least one rotor sensor selected from a group of a current sensor and a voltage sensor.

[00111] Example 15: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 12 to 14, wherein the rotor controller is implemented as analog circuitry, a field programmable gate array, an application specific integrated circuit, a microprocessor, or a combination thereof.

[00112] Example 16: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 12 to 15, wherein, to implement a boot-up sequence: the rotor circuit is configured to passively convert the wireless power signal to charge the capacitor to increase the capacitor voltage; and the rotor controller is configured to: boot in response to the capacitor voltage exceeding a boot-up threshold; and in response to the rotor controller completing booting, control the switch bridge to cycle the switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding.

[00113] Example 17: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 12 to 15, wherein, to implement a boot-up sequence: the rotor circuit is configured to passively convert the wireless power signal to charge the capacitor to increase the capacitor voltage; and the rotor controller is configured to: in response to the capacitor voltage exceeding a boot-up threshold, control the switch bndge to cycle the switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding.

[00114] Example 18: The method, apparatus, and / or non-transitory computer readable medium any of Examples 12 to 17, wherein the rotor controller is further configured to: control the switch bridge of the rotor circuit to cycle the switching state among switching states based on the reference current and the rotor current.

[00115] Example 19: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 12 to 18, wherein, to determine the reference current based on the capacitor voltage, the rotor controller is configured to apply the capacitor voltage as an input to a current-voltage map, the current-voltage map defining a relationship between voltage values and current values using a piecewise linear function.

[00116] Example 20: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 12 to 19, wherein, to control the switch bridge to change the switching state is based on a difference between the rotor current to the reference current, the rotor controller is further configured to: control the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold, control the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, and control the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

[00117] Example 21: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 12 to 20, wherein, to control the switch bridge to change the switching state is based on a difference between the rotor current to the reference current, the rotor controller is further configured to: control the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold, control the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, and control the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

[00118] Example 22: The method, apparatus, and / or non-transitory computer readable medium of Example 21, wherein, to control the switch bridge to enter the positive voltage state, the negative voltage state, or the net zero voltage state based on the difference and the present switching state, the rotor controller is configured to: when the present switching state is the net zero voltage state, control the switch bridge to enter the positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a first negative current threshold, control the switch bridge to enter the negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a first positive current threshold; when the present switching state is the positive voltage state, control the switch bridge to enter the net zero voltage state when the difference is greater than a second positive current threshold, control the switch bridge to enter the negative voltage state to apply the negative voltage to the capacitor to discharge the capacitor when the difference is greater than the first positive current threshold; and when the present switching state is the negative voltage state, control the switch bridge to enter the positive voltage state to apply the positive voltage to the capacitor to charge the capacitor when the difference is less than the first negative current threshold, control the switch bridge to enter the net zero voltage state when the difference is less than a second negative current threshold.

[00119] Example 23: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 12 to 22, wherein the switching state defines operational states of switches of the switch bridge to cause at least one of a positive DC capacitor voltage, a negative DC capacitor voltage, or a net zero capacitor voltage.

[00120] Example 24: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 16 to 17, wherein the rotor controller is further configured to: determine that at least one of the rotor current or the capacitor voltage has exceeded a minimum threshold; and control the switch bridge according to a steady state operation.

[00121] Example 25: A method, apparatus, and / or non-transitory computer-readable medium storing processor-executable instructions for an electric machine comprising: a stator including stator windings; a stator controller configured to control current through the stator winding to generate a wireless power signal; and a rotor including a rotor winding, a rotor circuit, and a rotor controller, the rotor circuit including a switch bridge coupled to the rotor winding and a capacitor coupled across the switch bridge, the rotor configured to implement a boot-up sequence wherein: the rotor circuit is configured to passively convert the wireless power signal to charge the capacitor to increase a capacitor voltage across the capacitor, and the rotor controller is configured to: boot in response to the capacitor voltage exceeding a bootup threshold, in response to the rotor controller completing booting, control the switch bridge to cycle a switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding, determine that at least one of a rotor current or the capacitor voltage has exceeded a minimum threshold, and control, by the rotor controller, the switch bridge according to a steady state operation.

[00122] Example 26: The method, apparatus, and / or non-transitory computer readable medium of Example 25, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to: determine the capacitor voltage, determine a reference current based on the capacitor voltage, determine the rotor current through the rotor winding, and control the switch bridge of the rotor circuit to cycle the switching state based on a difference between the reference current and the rotor current.

[00123] Example 27: The method, apparatus, and / or non-transitory computer readable medium of Example 26, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to: control the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold, control the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, and control the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

[00124] Example 28: The method, apparatus, and / or non-transitory computer readable medium of Example 26, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to: control the switch bridge to enter a positive voltage state, a negative voltage state, or a net zero voltage state based on the difference and on a present switching state.

[00125] Example 29: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 25 to 28, wherein the switching state defines operational states of switches of the switch bridge to cause at least one of a positive DC capacitor voltage, a negative DC capacitor voltage, or a net zero capacitor voltage.

[00126] Example 30: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 25 to 29, wherein the stator controller is further configured to energize the stator windings to define stator poles, and wherein the rotor controller is further configured to energize the rotor winding to define a rotor pole that interacts with the stator poles to produce relative force between the rotor and the stator.

[00127] Example 31: A method, apparatus, and / or non-transitory computer-readable medium storing processor-executable instructions for a rotor chipset assembly of an electric machine comprising: a rotor circuit including a switch bridge configured to be coupled to a rotor winding and a capacitor coupled across the switch bridge, the rotor circuit configured to passively convert a wireless power signal received by the rotor winding from a stator winding to charge the capacitor to increase a capacitor voltage across the capacitor; and a rotor controller configured to: boot in response to the capacitor voltage exceeding a boot-up threshold, in response to the rotor controller completing booting, control the switch bridge to cycle a switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding, determine that at least one of a rotor current or the capacitor voltage has exceeded a minimum threshold, and control, by the rotor controller, the switch bridge according to a steady state operation.

[00128] Example 32: The method, apparatus, and / or non-transitory computer readable medium of Example 31, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to: determine the capacitor voltage, determine a reference current based on the capacitor voltage, determine the rotor current through the rotor winding, and control the switch bridge of the rotor circuit to cycle the switching state based on a difference between the reference current and the rotor current.

[00129] Example 33: The method, apparatus, and / or non-transitory computer readable medium of Example 32, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to: control the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold, control the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, and control the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

[00130] Example 34: The method, apparatus, and / or non-transitory computer readable medium of Example 32, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to: control the switch bridge to enter a positive voltage state, a negative voltage state, or a net zero voltage state based on the difference and on a present switching state.

[00131] Example 34: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 31 to 34, wherein the rotor controller is configured to: energize the rotor winding to define a rotor pole that interacts with a stator pole to produce relative force between the rotor and a stator.

[00132] Example 35: A method, apparatus, and / or non-transitory computer-readable medium storing processor-executable instructions for a rotor chipset assembly of an electric machine comprising: a stator including stator windings; a stator controller configured to control current through the stator winding to generate a wireless power signal; and a rotor including a rotor winding and the rotor chipset assembly of any of Examples 31 to 34.

[00133] Example 36: A method, apparatus, and / or non-transitory computer-readable medium storing processor-executable instructions for a rotor chipset assembly of an electric machine comprising: a stator including stator windings; a stator controller configured to control current through the stator winding to generate a wireless power signal; and a rotor including a rotor winding and the rotor chipset assembly of any of Examples 12 to 24.

Claims

1. An electric machine comprising:a stator including stator windings;a stator controller configured to control current through the stator winding to generate a wireless power signal; anda rotor including a rotor winding, a rotor circuit, and a rotor controller, the rotor circuit including a switch bridge coupled to the rotor winding and a capacitor coupled across the switch bridge,the rotor winding configured to receive the wireless power signal from a stator winding of the stator windings, andthe rotor controller configured to:determine a capacitor voltage, the capacitor voltage indicating a voltage across the capacitor,determine a reference current based on the capacitor voltage, determine a rotor current through the rotor winding, and control the switch bridge of the rotor circuit to change a switching state based on the reference current and the rotor current.

2. The electric machine of claim 1, wherein the rotor controller is further configured to: control the switch bridge of the rotor circuit to cycle the switching state among switching states based on the reference current and the rotor current.

3. The electric machine of claim 1, wherein, to determine the reference current based on the capacitor voltage, the rotor controller is configured to apply the capacitor voltage as an input to a current-voltage map, the current-voltage map defining a relationship between voltage values and current values using a piecewise linear function.

4. The electric machine of claim 1, wherein, to control the switch bridge to change the switching state is based on a difference between the rotor current to the reference current, and wherein the rotor controller is further configured to:control the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold,control the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, andcontrol the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

5. The electric machine of claim 1, wherein, to control the switch bridge to change the switching state is based on a difference between the rotor current to the reference current, and wherein the rotor controller is further configured to:control the switch bridge to enter a positive voltage state, a negative voltage state, or a net zero voltage state based on the difference and a present switching state.

6. The electric machine of claim 5, wherein, to control the switch bridge to enter the positive voltage state, the negative voltage state, or the net zero voltage state based on the difference and the present switching state, the rotor controller is configured to:when the present switching state is the net zero voltage state,control the switch bridge to enter the positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a first negative current threshold,control the switch bridge to enter the negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a first positive current threshold;when the present switching state is the positive voltage state,control the switch bridge to enter the net zero voltage state when thedifference is greater than a second positive current threshold,control the switch bridge to enter the negative voltage state to apply the negative voltage to the capacitor to discharge the capacitor when the difference is greater than the first positive current threshold; andwhen the present switching state is the negative voltage state,control the switch bridge to enter the positive voltage state to apply the positive voltage to the capacitor to charge the capacitor when the difference is less than the first negative current threshold,control the switch bridge to enter the net zero voltage state when the difference is less than a second negative current threshold.

7. The electric machine of claim 1, wherein the switching state defines operational states of switches of the switch bridge to cause at least one of a positive DC capacitor voltage, a negative DC capacitor voltage, or a net zero capacitor voltage.

8. The electric machine of claim 1, wherein, to implement a boot-up sequence:the rotor circuit is configured to passively convert the wireless power signal to charge the capacitor to increase the capacitor voltage; andthe rotor controller is configured to:boot in response to the capacitor voltage exceeding a boot-up threshold; andin response to the rotor controller completing booting, control the switch bridge to cycle the switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding.

9. The electric machine of claim 1, wherein, to implement a boot-up sequence:the rotor circuit is configured to passively convert the wireless power signal to charge the capacitor to increase the capacitor voltage; andthe rotor controller is configured to:in response to the capacitor voltage exceeding a boot-up threshold, control the switch bridge to cycle the switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding.

10. The electric machine of one of claim 8 or claim 9, wherein the rotor controller is further configured to:determine that at least one of the rotor current or the capacitor voltage has exceeded a minimum threshold; andcontrol the switch bridge according to a steady state operation.

11. The electric machine of claim 1,wherein the stator controller is further configured to energize the stator windings to define stator poles, andwherein the rotor controller is further configured to energize the rotor winding to define a rotor pole that interacts with the stator poles to produce relative force between the rotor and the stator.

12. A method of controlling a motor, the method comprising:receiving, by a rotor winding of a rotor, a first power signal wirelessly from a stator winding of a stator;determining, by a rotor controller, a capacitor voltage, the capacitor voltage indicating a voltage across a capacitor of a rotor circuit coupled to the rotor winding;determining, by the rotor controller, a reference current based on the capacitor voltage;determining, by the rotor controller, a rotor current through the rotor winding; and controlling, by the rotor controller, a switch bridge of the rotor circuit to change a switching state based on the reference current and the rotor current.

13. The method of claim 12, further comprising:controlling, by the rotor controller, the switch bridge of the rotor circuit to cycle the switching state among switching states based on the reference current and the rotor current.

14. The method of claim 12, wherein, to determine the reference current based on the capacitor voltage, the rotor controller is configured to apply the capacitor voltage as an input to a current-voltage map, the current-voltage map defining a relationship between voltage values and current values using a piecewise linear function.

15. The method of claim 12, wherein controlling, by the rotor controller, the switch bridge to change the switching state is based on a difference between the rotor current to the reference current, the method further comprising:controlling the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold,controlling the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, andcontrolling the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

16. The method of claim 12, wherein controlling, by the rotor controller, the switch bridge to change the switching state is based on a difference between the rotor current to the reference current and further based on a present switching state of the switch bridge, the method further comprising:controlling the switch bridge to enter a positive voltage state, a negative voltage state, or a net zero voltage state based on the difference and the present switching state.

17. The method of claim 16, wherein controlling the switch bridge to enter the positive voltage state, the negative voltage state, or the net zero voltage state based on the difference and the present switching state comprises:when the present switching state is the net zero voltage state, controlling the switch bridge to enter the positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a first negative current threshold,controlling the switch bridge to enter the negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a first positive current threshold;when the present switching state is the positive voltage state,controlling the switch bridge to enter the net zero voltage state when the difference is greater than a second positive current threshold,controlling the switch bridge to enter the negative voltage state to apply the negative voltage to the capacitor to discharge the capacitor when the difference is greater than the first positive current threshold; andwhen the present switching state is the negative voltage state,controlling the switch bridge to enter the positive voltage state to apply the positive voltage to the capacitor to charge the capacitor when the difference is less than the first negative current threshold,controlling the switch bridge to enter the net zero voltage state when the difference is less than a second negative current threshold.

18. The method of claim 12, wherein the switching state defines operational states of switches of the switch bridge to cause at least one of a positive DC capacitor voltage, a negative DC capacitor voltage, or a net zero capacitor voltage.

19. The method of claim 12, further including a boot-up sequence comprising:passively converting the first power signal to charge the capacitor to increase the capacitor voltage;in response to the capacitor voltage exceeding a boot-up threshold, booting the rotor controller; andin response to the rotor controller completing booting, controlling, by the rotor controller, the switch bridge to cycle the switching state among switching states to actively convert the first power signal and to control current through the rotor winding.

20. The method of claim 19, further including:determining that at least one of the rotor current or the capacitor voltage has exceeded a minimum threshold; andcontrolling, by the rotor controller, the switch bridge according to a steady state operation.

21. The method of claim 12,wherein the stator includes stator windings including the stator winding,wherein a stator controller is further configured to energize the stator windings to define stator poles, andwherein the rotor controller is further configured to energize the rotor winding to define a rotor pole that interacts with the stator poles to produce relative force between the rotor and the stator.

22. A nontransitory computer readable medium comprising instructions that, when executed by one or more electronic processors of a motor system, cause the motor system to:receive, by a rotor winding of a rotor, a first power signal wirelessly from a stator winding of a stator;determine, by a rotor controller, a capacitor voltage, the capacitor voltage indicating a voltage across a capacitor of a rotor circuit coupled to the rotor winding;determine, by the rotor controller, a reference current based on the capacitor voltage;determine, by the rotor controller, a rotor current through the rotor winding; and control, by the rotor controller, a switch bridge of the rotor circuit to change a switching state based on the reference current and the rotor current.

23. The nontransitory computer readable medium of claim 22, comprising further instructions that, when executed by the one or more electronic processors of the motor system, cause the motor system to:control the switch bridge of the rotor circuit to cycle the switching state among switching states based on the reference current and the rotor current.

24. The nontransitory computer readable medium of claim 22, comprising further instructions that, when executed by the one or more electronic processors of the motor system, cause the motor system to control the switch bridge to change the switching state based on a difference between the rotor current to the reference current by:controlling the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold,controlling the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, andcontrolling the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

25. The nontransitory computer readable medium of claim 22, comprising further instructions that, when executed by the one or more electronic processors of the motor system, cause the motor system to control the switch bridge to change the switching state based on a difference between the rotor current to the reference current by:controlling the switch bridge to enter a positive voltage state, a negative voltage state, or a net zero voltage state based on the difference and a present switching state of the switch bridge.

26. The nontransitory computer readable medium of claim 22, comprising further instructions that, when executed by the one or more electronic processors of the motor system, cause the motor system to implement a boot-up sequence comprising:passively converting the first power signal to charge the capacitor to increase the capacitor voltage;in response to the capacitor voltage exceeding a boot-up threshold, booting the rotor controller; andin response to the rotor controller completing booting, controlling, by the rotor controller, the switch bridge to cycle the switching state among switching states to actively convert the first power signal and to control current through the rotor winding.

27. The nontransitory computer readable medium of claim 26, comprising further instructions that, when executed by the one or more electronic processors of the motor system, cause the motor system to:determine that at least one of the rotor current or the capacitor voltage has exceeded a minimum threshold; andcontrol, by the rotor controller, the switch bridge according to a steady state operation.

28. A rotor chipset assembly for an electric machine comprising:a rotor circuit including a switch bridge configured to be coupled to a rotor winding and a capacitor coupled across the switch bridge, the rotor winding configured to receive a wireless power signal from a stator winding, anda rotor controller configured to:determine a capacitor voltage, the capacitor voltage indicating a voltage across the capacitor,determine a reference current based on the capacitor voltage, determine a rotor current through the rotor winding, andcontrol the switch bridge of the rotor circuit to change a switching state based on the reference current and the rotor current.

29. The rotor chipset assembly of claim 28, wherein the rotor controller and the rotor circuit are supported by a rotor core including a rotor shaft and rotor laminations.

30. The rotor chipset assembly of claim 28, further comprising: at least one rotor sensor selected from a group of a current sensor and a voltage sensor.

31. The rotor chipset assembly of claim 28, wherein the rotor controller is implemented as analog circuitry, a field programmable gate array, an application specific integrated circuit, a microprocessor, or a combination thereof.

32. The rotor chipset assembly of claim 28, wherein, to implement a boot-up sequence:the rotor circuit is configured to passively convert the wireless power signal to charge the capacitor to increase the capacitor voltage; andthe rotor controller is configured to:boot in response to the capacitor voltage exceeding a boot-up threshold; andin response to the rotor controller completing booting, control the switch bridge to cycle the switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding.

33. The rotor chipset assembly of claim 28, wherein, to implement a boot-up sequence:the rotor circuit is configured to passively convert the wireless power signal to charge the capacitor to increase the capacitor voltage; andthe rotor controller is configured to:in response to the capacitor voltage exceeding a boot-up threshold, control the switch bridge to cycle the switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding.

34. An electric machine comprising:a stator including stator windings;a stator controller configured to control current through the stator winding to generate a wireless power signal; anda rotor including a rotor winding, a rotor circuit, and a rotor controller, the rotor circuit including a switch bridge coupled to the rotor winding and a capacitor coupled across the switch bridge, the rotor configured to implement a boot-up sequence wherein:the rotor circuit is configured to passively convert the wireless power signal to charge the capacitor to increase a capacitor voltage across the capacitor, andthe rotor controller is configured to:boot in response to the capacitor voltage exceeding a boot-up threshold,in response to the rotor controller completing booting, control the switch bridge to cycle a switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding,determine that at least one of a rotor current or the capacitor voltage has exceeded a minimum threshold, andcontrol, by the rotor controller, the switch bridge according to a steady state operation.

35. The electric machine of claim 34, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to:determine the capacitor voltage,determine a reference current based on the capacitor voltage,determine the rotor current through the rotor winding, andcontrol the switch bridge of the rotor circuit to cycle the switching state based on a difference between the reference current and the rotor current.

36. The electric machine of claim 35, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to:control the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold,control the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, andcontrol the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

37. The electric machine of claim 35, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to:control the switch bridge to enter a positive voltage state, a negative voltage state, or a net zero voltage state based on the difference and on a present switching state.

38. The electric machine of claim 34, wherein the switching state defines operational states of switches of the switch bridge to cause at least one of a positive DC capacitor voltage, a negative DC capacitor voltage, or a net zero capacitor voltage.

39. The electric machine of claim 34,wherein the stator controller is further configured to energize the stator windings to define stator poles, andwherein the rotor controller is further configured to energize the rotor winding to define a rotor pole that interacts with the stator poles to produce relative force between the rotor and the stator.

40. A method of controlling a motor, the method comprising:passively converting, by a rotor circuit of a rotor, a wireless power signal received by a rotor winding from a stator winding to charge a capacitor of the rotor circuit to increase a capacitor voltage across the capacitor;in response to the capacitor voltage exceeding a boot-up threshold, booting a rotor controller of the rotor;in response to the rotor controller completing booting, controlling, by the rotor controller, a switch bridge of the rotor circuit to cycle a switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding;determining that at least one of a rotor current or the capacitor voltage has exceeded a minimum threshold; andcontrolling, by the rotor controller, the switch bridge according to a steady state operation.

41. The method of claim 40, wherein controlling the switch bridge to cycle the switching state among switching states comprises:determining the capacitor voltage,determining a reference current based on the capacitor voltage,determining the rotor current through the rotor winding, andcontrolling the switch bridge of the rotor circuit to cycle the switching state based on a difference between the reference current and the rotor current.

42. The method of claim 41, wherein controlling the switch bridge to cycle the switching state among switching states comprises:controlling the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold,controlling the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, andcontrolling the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

43. The method of claim 41, wherein controlling the switch bridge to cycle the switching state among switching states comprises:controlling the switch bridge to enter a positive voltage state, a negative voltage state, or a net zero voltage state based on the difference and on a present switching state.

44. The method of claim 40, further comprising:energizing the stator winding to define a stator pole, andenergizing the rotor winding to define a rotor pole that interacts with the stator pole to produce relative force between the rotor and the stator.

45. A nontransitory computer readable medium storing instructions that, when executed by one or more electronic processors of a motor system, cause the motor system to:passively convert, by a rotor circuit of a rotor, a wireless power signal received by a rotor winding from a stator winding to charge a capacitor of the rotor circuit to increase a capacitor voltage across the capacitor;in response to the capacitor voltage exceeding a boot-up threshold, boot a rotor controller of the rotor;in response to the rotor controller completing booting, control, by the rotor controller, a switch bridge of the rotor circuit to cycle a switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding;determine that at least one of a rotor current or the capacitor voltage has exceeded a minimum threshold; andcontrol, by the rotor controller, the switch bridge according to a steady state operation.

46. The nontransitory computer readable medium of claim 45, wherein, to control the switch bridge to cycle the switching state among switching states, the nontransitory computerreadable medium comprises further instructions that, when executed by the one or more electronic processors of the motor system, cause the motor system to:determine the capacitor voltage,determine a reference current based on the capacitor voltage, determine the rotor current through the rotor winding, and control the switch bridge of the rotor circuit to cycle the switching state based on a difference between the reference current and the rotor current.

47. The nontransitory computer readable medium of claim 46, wherein, to control the switch bridge to cycle the switching state among switching states, the nontransitory computer readable medium comprises further instructions that, when executed by the one or more electronic processors of the motor system, cause the motor system to:control the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold,control the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, andcontrol the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

48. The nontransitory computer readable medium of claim 46, wherein, to control the switch bridge to cycle the switching state among switching states, the nontransitory computer readable medium comprises further instructions that, when executed by the one or more electronic processors of the motor system, cause the motor system to:control the switch bridge to enter a positive voltage state, a negative voltage state, or a net zero voltage state based on the difference and on a present switching state.

49. The nontransitory computer readable medium of claim 45, comprising further instructions that, when executed by the one or more electronic processors of the motor system, cause the motor system to:energize the stator winding to define a stator pole, andenergize the rotor winding to define a rotor pole that interacts with the stator pole to produce relative force between the rotor and the stator.

50. A rotor chipset assembly for an electric machine comprising:a rotor circuit including a switch bndge configured to be coupled to a rotor winding and a capacitor coupled across the switch bridge, the rotor circuit configured to passively convert a wireless power signal received by the rotor winding from a stator winding to charge the capacitor to increase a capacitor voltage across the capacitor; anda rotor controller configured to:boot in response to the capacitor voltage exceeding a boot-up threshold,in response to the rotor controller completing booting, control the switch bridge to cycle a switching state among switching states to actively convert the wireless power signal and to control current through the rotor winding,determine that at least one of a rotor current or the capacitor voltage hasexceeded a minimum threshold, andcontrol, by the rotor controller, the switch bridge according to a steady state operation.

51. The rotor chipset assembly of claim 50, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to:determine the capacitor voltage,determine a reference current based on the capacitor voltage,determine the rotor current through the rotor winding, andcontrol the switch bridge of the rotor circuit to cycle the switching state based on a difference between the reference current and the rotor current.

52. The rotor chipset assembly of claim 51, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to:control the switch bridge to enter a positive voltage state to apply a positive voltage to the capacitor to charge the capacitor when the difference is less than a negative current threshold,control the switch bridge to enter a negative voltage state to apply a negative voltage to the capacitor to discharge the capacitor when the difference is greater than a positive current threshold, andcontrol the switch bridge to enter a net zero voltage state when the difference is between the negative current threshold and the positive current threshold.

53. The rotor chipset assembly of claim 51, wherein, to control the switch bridge to cycle the switching state among switching states, the rotor controller is configured to:control the switch bridge to enter a positive voltage state, a negative voltage state, or a net zero voltage state based on the difference and on a present switching state.

54. The rotor chipset assembly of claim 50, wherein the rotor controller is configured to: energize the rotor winding to define a rotor pole that interacts with a stator pole to produce relative force between the rotor and a stator.

55. An electric machine comprising:a stator including stator windings;a stator controller configured to control current through the stator winding to generate a wireless power signal; anda rotor including a rotor winding and the rotor chipset assembly of any of claims 2833.

56. An electric machine comprising:a stator including stator windings;a stator controller configured to control current through the stator winding to generate a wireless power signal; anda rotor including a rotor winding and the rotor chipset assembly of any of claims 5054.

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