Variable frequency independent speed motor

Abstract

The present disclosure relates to variable frequency independent speed motors, and in particular, an electric motor device may include a rotor and a stator. The device may include a main field motor stage, the main field motor stage having a set of stator armature windings located on the stator and a set of main field windings located on the rotor, wherein the set of stator armature windings is configured to receive a main multi-phase power signal from an AC power bus, the main multi-phase power signal having a first current that causes a first rotating magnetic flux rotating relative to the stator, wherein the set of main field windings is configured to receive a secondary multi-phase power signal, the secondary multi-phase power signal having a second current that causes a second rotating magnetic flux rotating relative to the rotor, and wherein a combination of the first rotating magnetic flux and the second rotating magnetic flux causes the rotor to rotate at a predetermined reference frequency.

Description

Technical Field

[0001] The present disclosure relates generally to multiphase motors, and more particularly to variable frequency independent speed motors. Background Art

[0002] A typical induction motor includes an active set of multiphase windings connected to the stator and a passive (or reactive) set of multiphase windings connected to the rotor. A multiphase power signal is applied to the multiphase windings of the active set. The current generated by the multiphase power signal in the windings of the active set generates a magnetic field, which induces a reverse current in the multiphase windings of the passive set. The reverse current causes a reverse magnetic field that causes the rotor to rotate. As the rotor rotates, the reverse current in the multiphase windings of the passive set decreases, which reduces the magnetic field. The motor is ultimately at a balanced speed based on the load attached to the motor and the frequency of the multiphase power signal. The balanced speed is typically a frequency slightly less than the frequency of the AC power signal. The difference between the frequency of the AC power signal and the rotational frequency of the rotor is called the difference frequency (or slip angle). In a typical system with a constant load, the rotational frequency and slip angle of the rotor depend on the frequency of the AC power signal.

[0003] To achieve independent rotational frequencies, a typical motor system may rely on a rectifier circuit to perform a full-power AC to DC power conversion, and then rely on an inverter to perform another full-power DC to AC power conversion on a new AC power signal having a desired frequency, amplitude, and phase. The new AC power signal can then be used to drive the induction motor at a corresponding new frequency. This full-scale power conversion may result in significant power losses. Further, the components required to perform the power conversion may add significant weight, which may not be desirable in certain applications (such as within an aircraft). Summary of the invention

[0004] A variable frequency independent speed motor that overcomes at least one of the above-mentioned deficiencies is disclosed. In an embodiment, an electric motor apparatus includes a high frequency transformer stage for sending an excitation signal from a stator to a rotor. The excitation signal can be used to power a set of main field windings located on the rotor. Further, the AC power signal can be directly coupled to a set of main field windings located on the stator. The two sets of main field windings can be powered with most of the effective power applied to a set of main field windings located on the stator without performing a full-scale power transfer. By generating current in a set of main field windings located on the rotor, the balanced speed of the motor can be adjusted to a predetermined speed independent of the frequency of the AC signal.

[0005] In an embodiment, an electric motor device includes a rotor and a stator. The device also includes a high-frequency transformer stage for sending an excitation signal from the stator to the rotor, the high-frequency transformer stage having a first set of transformer windings located on the stator and a second set of transformer windings located on the rotor. The device also includes a main field motor stage, the main field motor stage having a set of stator armature windings located on the stator and a set of main field windings located on the rotor, wherein the set of stator armature windings is configured to receive a main multi-phase power signal from an AC power bus, the main multi-phase power signal having a first current that causes a first rotating magnetic flux rotating relative to the stator, wherein a set of main field windings is configured to receive a secondary multi-phase power signal, the secondary multi-phase power signal having a second current that causes a second rotating magnetic flux rotating relative to the rotor, wherein a combination of the first rotating magnetic flux and the second rotating magnetic flux causes the rotor to rotate at a predetermined reference frequency.

[0006] In some embodiments, the device includes: a rectifier coupled to the rotor and electrically connected to the second set of transformer windings, the rectifier being configured to rectify the excitation signal to generate a DC power signal; and an inverter coupled to the rotor and electrically connected to the rectifier, wherein the inverter is configured to modulate the DC power signal to generate a secondary multiphase power signal. In some embodiments, the device includes: an encoder; and an embedded controller circuit coupled to the rotor, the embedded controller circuit being configured to: generate an electrical phase signal based on the main multiphase power signal; receive the rotor phase signal from the encoder; generate a combined phase signal based on the difference between the electrical phase signal and the rotor phase signal; and generate a pulse width modulation signal based on the combined phase signal to control the inverter so that the secondary multiphase power signal has the following frequency, amplitude and phase, the frequency, amplitude and phase enable the first rotating magnetic flux and the second rotating magnetic flux to combine to rotate the rotor at a predetermined reference frequency.

[0007] In some embodiments, the device includes a control signal connector having a first portion arranged on the stator and a second portion arranged on the rotor, wherein the control signal connector is a non-contact optical connector, and wherein the embedded controller circuit is configured to receive one or more control signals from the controller circuit of the motor control unit via the control signal connector. In some embodiments, the embedded controller is further configured to: receive a reference frequency signal from the motor control unit, the reference frequency signal representing a predetermined reference frequency; generate a Q-axis current signal based on the reference frequency signal and the rotor frequency signal; generate a Q-axis voltage signal based on the Q-axis current signal and the Q-axis feedback current signal; receive a D-axis reference current signal from the motor control unit; generate a D-axis current signal based on the D-axis reference current signal and the D-axis feedback current signal; and use the Q-axis voltage signal and the D-axis current signal as inputs to an inverse Pike transformation, in which the combined phase signal is applied to generate an alpha-beta voltage signal, wherein the pulse width modulation signal is derived from the alpha-beta voltage signal at the pulse width modulation generator circuit.

[0008] In some embodiments, the embedded controller is also configured to: receive a rotor feedback current signal from the set of stator armature windings; use the rotor feedback current signal as an input to a Clarke transform to generate an α-β current feedback signal by applying a Clarke transform; and use the α-β current feedback signal as an input to a Park transform to generate a D-axis feedback current signal and a Q-axis feedback current signal by applying a combined phase signal in a Park transform.

[0009] In some embodiments, the group of stator armature windings is directly connected to the second group of transformer windings and is configured to receive a secondary multiphase power signal from the second group of transformer windings. In some embodiments, the excitation signal includes a high-frequency modulated signal component and a secondary multiphase power component, wherein the inductance at the second group of transformer windings and a group of stator armature windings filters the high-frequency modulated signal component to form a secondary multiphase power signal. In some embodiments, the predetermined reference frequency of the rotor is independent of the frequency of the main multiphase power signal. In some embodiments, the first group of transformer windings, the second group of transformer windings, a group of main field windings, and the group of stator armature windings each include three windings for operating with a 3-phase power signal. In some embodiments, the frequency of the excitation signal is between approximately 1kHz and 1MHz.

[0010] In an embodiment, a system includes a motor control unit and a motor. The motor includes a rotor and a stator. The system includes a high-frequency transformer stage for sending an excitation signal from the stator to the rotor, the high-frequency transformer stage having a first set of transformer windings located on the stator and a second set of transformer windings located on the rotor. The system also includes a main motor stage, the main motor stage having a set of stator armature windings located on the stator and a set of main field windings located on the rotor, wherein a set of main field windings is configured to receive a main multi-phase power signal from an AC power bus, the main multi-phase power signal having a current that causes a first rotating magnetic flux rotating relative to the stator, wherein the set of stator armature windings is configured to receive a secondary multi-phase power signal, the secondary multi-phase power signal having a current that causes a second rotating magnetic flux rotating relative to the rotor, wherein a combination of the first rotating magnetic flux and the second rotating magnetic flux causes the rotor to rotate at a predetermined reference frequency.

[0011] In some embodiments, the motor control unit includes: a rectifier configured to rectify a main multi-phase power signal from an AC power bus to generate a DC power signal; a controller circuit; and a frequency converter including an inverter, wherein the controller circuit is configured to control the frequency converter to modulate the DC power signal to generate an excitation signal. In some embodiments, the controller circuit is configured to further control the inverter so that the excitation signal includes a high-frequency modulated signal component and a secondary multi-phase power component, wherein the inductance at the second group of transformer windings and a group of stator armature windings filters the high-frequency modulated signal component to form the secondary multi-phase power component, and wherein the controller circuit is configured to control the inverter to generate a secondary multi-phase power signal having a frequency, an amplitude, and a phase, wherein the frequency, the amplitude, and the phase cause the combination of the first rotating magnetic flux and the second rotating magnetic flux to rotate the rotor at a predetermined reference frequency.

[0012] In some embodiments, the controller circuit is configured to: generate an electrical phase signal based on a main multi-phase power signal; receive a rotor phase signal from an encoder; generate a combined phase signal based on a difference between the electrical phase signal and the rotor phase signal; and generate a pulse width modulation signal based on the combined phase signal to control the inverter so that the secondary multi-phase power signal has the following frequency, amplitude and phase, which frequency, amplitude and phase enable the first rotating magnetic flux and the second rotating magnetic flux to combine to cause the rotor to rotate at a predetermined reference frequency.

[0013] In some embodiments, the controller circuit is also configured to: receive a reference frequency signal, the reference frequency signal representing a predetermined reference frequency; generate a Q-axis current signal based on the reference frequency signal and the rotor frequency signal; generate a Q-axis voltage signal based on the Q-axis current signal and the Q-axis feedback current signal; receive a D-axis reference current signal; generate a D-axis current signal based on the D-axis reference current signal and the D-axis feedback current signal; and use the Q-axis voltage signal and the D-axis reference signal as inputs to an inverse Parker transformation, in which the combined phase signal is applied to generate an α-β voltage signal, wherein a pulse width modulation signal is derived from the α-β voltage signal.

[0014] In some embodiments, the controller circuit is configured to: filter the excitation signal to extract the rotor feedback current signal; use the rotor feedback current signal as an input to a Clarke transform, apply the Clarke transform to generate an α-β current feedback signal; and use the α-β current feedback signal as an input to a Park transform, apply the combined phase signal in the Park transform to generate a D-axis feedback current signal and a Q-axis feedback current signal.

[0015] In an embodiment, the method includes the following steps: receiving a main multi-phase power signal at a set of main field windings connected to the stator of the motor device, the main multi-phase power signal having a current that causes a first rotating magnetic flux rotating relative to the stator. The method also includes the following steps: receiving a secondary multi-phase power signal at a set of stator armature windings connected to the rotor of the motor device, the secondary multi-phase power signal having a current that causes a second rotating magnetic flux rotating relative to the rotor. The method also includes the following steps: generating an electrical phase signal based on the main multi-phase power signal. The method includes the following steps: receiving a rotor phase signal from an encoder configured to monitor the rotation of the rotor. The method includes the following steps: generating a combined phase signal based on the difference between the electrical phase signal and the rotor phase signal. The method also includes the following steps: generating a pulse width modulation signal based on the combined phase signal to control the inverter so that the secondary multi-phase power signal has the following frequency, amplitude and phase, which frequency, amplitude and phase enable the first rotating magnetic flux and the second rotating magnetic flux to be combined to rotate the rotor at a predetermined reference frequency.

[0016] In some embodiments, the predetermined reference frequency of the rotor is independent of the frequency of the main multi-phase power signal. In some embodiments, the method includes the steps of: transferring an excitation signal from the stator to the rotor using a high frequency transformer stage, the high frequency transformer stage including a first set of transformer windings coupled to the stator and a second set of transformer windings coupled to the rotor; and powering the secondary multi-phase power signal using the excitation signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a block diagram depicting an embodiment of a variable frequency independent speed motor system.

[0018] Figure 2 is a block diagram depicting an embodiment of a control system for a variable frequency independent speed motor system.

[0019] Figure 3 is a block diagram depicting an embodiment of a variable frequency independent speed motor system.

[0020] Figure 4 is a block diagram depicting an embodiment of a control system for a variable frequency independent speed motor system.

[0021] Figure 5 is a diagram depicting an embodiment of a single phase of a pulse width modulated excitation signal having a modulation component and a multi-phase power signal component.

[0022] Figure 6 is a diagram depicting an embodiment of three phases of a low pass filtered pulse width modulated excitation signal.

[0023] Figure 7 is a flow chart depicting an embodiment of a method for a variable frequency independent speed motor system.

[0024] Although the present disclosure is susceptible to various modifications and alternative forms, it has been shown in the drawings by way of example and will be described in detail herein in detail. However, it should be understood that the present disclosure is not intended to be limited to the particular form disclosed. On the contrary, it is intended to cover all modifications, equivalents, and alternatives that fall within the scope of the present disclosure. DETAILED DESCRIPTION

[0025] Reference Figure 1 , depicts an embodiment of a variable frequency independent speed motor system 100. The system 100 may include a rotor 102 and a stator 104. The system may also include a high frequency transformer stage 106 and a main field stage 108.

[0026] The high frequency transformer stage 106 may include a first set of transformer windings 110 and a second set of transformer windings 112. The first set of transformer windings 110 may be coupled to and located on the stator 104, and the second set of transformer windings 112 may be coupled to and located on the rotor 102. The first set of transformer windings 110 and the second set of transformer windings 112 may include 3-phase windings for sending excitation signals from the stator 104 to the rotor 102.

[0027] As used herein, high frequency means that the frequency of the signal is greater than the rotation frequency of the rotor 102. For example, as the frequency of the excitation signal to be sent from the first set of transformer windings 110 to the second set of transformer windings 112 increases, the effect of the rotation of the rotor 102 becomes less significant. This can make it possible to send the excitation signal without significant interference or power loss caused by the rotation of the rotor 102. Further, the high frequency transformer stage 106 can omit the contact power transmission mechanism between the stator 104 and the rotor 102. For example, although a typical power transmission mechanism may include a slip ring or a similar contact power transmission mechanism, the system 100 can omit these contact mechanisms. By eliminating the contact power transmission mechanism between the stator 104 and the rotor 102, performance problems such as arcing, wear, and contact resistance can be avoided. This can lead to greater reliability, lower maintenance costs, less downtime, and reduced power losses. Other advantages may exist.

[0028] The main field stage 108 may include a rectifier 114 and an inverter 116, which are coupled to and located on the rotor 102. The rectifier 114 may be configured to rectify the high frequency excitation signal to generate a DC power signal. For example, the rectifier 114 may be a 3-phase diode rectifier. The inverter 116 may include a plurality of switches for modulating the DC power signal as described herein.

[0029] The main field stage 108 may also include a set of stator armature windings 118 coupled to and located on the stator 104 and a set of main field windings 120 coupled to and located on the rotor 102. The set of stator armature windings 118 may be coupled to the AC power bus 140 and configured to receive a multi-phase power signal 242 from the AC power bus 140. The multi-phase power signal 242 may be a 3-phase power signal. A set of main field windings 120 may be coupled to the output of the inverter 116 and configured to receive a secondary multi-phase power signal 280 from the inverter 116.

[0030] The main field stage 108 may include an embedded controller circuit 122 that is coupled to and at least partially located on the rotor 102. The embedded controller circuit 122 may include logic circuitry to control the inverter 116 to generate a secondary multiphase power signal 280 having a predetermined frequency, amplitude, and phase as described herein. Alternatively or additionally, the embedded controller circuit 122 may include a processor and corresponding memory configured to control the inverter 116 as described herein.

[0031] The system 100 may also include a signal coupling 124 that transmits a control signal, such as a reference frequency signal 202 further described herein, from the stator 104 to the rotor 102 without physical contact. The signal coupling 124 may have a first portion disposed on the stator 104 and a second portion disposed on the rotor 102, and may include an optical link. As can be seen, the signal coupling 124 may be a contactless coupling in order to generate less friction as compared to a contact signal coupling.

[0032] The rotor 102 may include a shaft 128 coupled to the rotor 102 for transferring mechanical power to an external system. For example, the shaft 128 may provide rotational power to a propulsion system of an aircraft or other vehicle. The encoder 126 may monitor the rotation of the shaft 128 and may generate a rotor phase signal 240 representing the position of the shaft 128.

[0033] The system 100 may include a motor control unit 130. The motor control unit 130 may be outside the rotor 102 and the stator 104. Further, the motor control unit 130 may be placed away from other parts of the system 100. The motor control unit 130 may include a rectifier 132, an inverter 134, and a controller circuit 136.

[0034] The rectifier 132 may be coupled to the AC bus 140 and configured to generate a DC power signal for generating an excitation signal by the inverter 134 and to power the controller circuit 136. The controller circuit 136 may be configured to control a plurality of switches within the inverter 134 to generate the excitation signal. For example, the inverter 134 may include a power modulator circuit (not shown).

[0035] The controller circuit 135 may be implemented as a logic circuit to control the frequency converter 134. Alternatively or additionally, the controller circuit 136 may include a processor and a corresponding memory configured to control the frequency converter 134. For example, in some embodiments, the controller circuit 136 may include a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), a peripheral interface controller (PIC), another microprocessor, and / or a combination thereof. The controller circuit 136 may be implemented as an integrated circuit, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a combination of logic gate circuits, other types of digital or analog electrical design components, or a combination thereof.

[0036] During operation, the AC bus 140 may provide a main multi-phase power signal 242 to the set of stator armature windings 118. The AC bus 140 may simultaneously provide the main multi-phase power signal 242 to the rectifier 132 of the motor control unit 130.

[0037] The rectifier 132 may rectify the main multiphase power signal 242 to generate a DC power signal for powering the inverter 134 and the controller circuit 136. The controller circuit 136 may send a signal 150 to the inverter 134 to control the inverter 134 to use the DC power signal to generate a high frequency excitation signal that may be sent to the first set of transformer windings 110. The frequency of the excitation signal may be between approximately 1 kHz and 1 MHz.

[0038] The first set of transformer windings 110 may send a high frequency excitation signal to the second set of transformer windings 112, and the rectifier 114 may convert the high frequency excitation signal into a DC power signal that may be used by the inverter 116. The controller circuit 136 may monitor the phase 242a of the main AC power signal 242 on the AC bus 140. The controller circuit 136 may also send a control signal including a signal representing the electrical phase of the main AC power signal 242, such as the reference frequency signal 202, to control the embedded controller circuit 122 via the signal connector 124. The embedded controller circuit 122 may also receive the rotor phase signal 240 from the encoder 126 and a signal representing the current associated with the secondary multiphase power signal 280 based on the output of the inverter 116.

[0039] Based on the control signal and the feedback signal, the embedded controller circuit 122 may control the inverter 116 using a pulse width modulation signal 222 to generate a secondary multi-phase power signal 280 that may be applied to a set of primary windings 120 .

[0040] By applying the AC power signal from the AC bus 140 to the set of stator armature windings 118 without performing full power conversion, the system 100 can be more efficient than a typical induction motor that relies on rectification and modulation between the power bus and the input of the main stage. Further, by effectively applying the secondary multi-phase power signal 280 to a set of main field windings 120, the rotor can be set to rotate at a predetermined frequency that is independent of the frequency of the multi-phase power signal on the AC bus 140. It can be seen that the system 100 can more efficiently achieve the independent speed of the motor 102 by directly applying a large portion (e.g., 90%) of the effective power of the power signal on the AC bus 140 to the set of stator armature windings 118. The remaining portion (e.g., 10%) of the effective power can be transmitted to the rotor 102, independently converted and applied to a set of main field windings 120 to achieve a rotation frequency that is independent of the frequency of the multi-phase power signal on the AC bus 140. Other advantages of the system 100 may exist.

[0041] Reference Figure 2, depicts a control system 200 for a variable frequency independent speed motor system. Portions of the control system 200 may be located on the stator 104, and other portions may be located on the rotor 102. Further, Figure 2 The functions of the embedded controller circuit 122 are described. The functions may be performed by a logic circuit, a processor, or any combination thereof, the processor being coupled to a memory having instructions for causing the processor to perform the functions. It should be noted that for each signal described herein, a separate signal may be generated for each phase of a multi-phase power system.

[0042] The control system 200 can receive a reference frequency signal 202 via the signal connector 124. In some embodiments, the reference frequency signal 202 can be obtained from Figure 1 Alternatively, the reference frequency signal 202 may be set by a user or may be hard-coded into the controller circuit 136.

[0043] The control system 200 may include a speed proportional integral derivative (PID) 204. The speed PID 204 may receive a reference frequency signal 202 and a rotor frequency signal 206, which are further described herein. Based on the reference frequency signal 202 and the rotor frequency signal 206, the speed PID 204 may generate a quadrature axis (Q axis) current signal 208.

[0044] The control system 200 may also include a torque PID 210. The torque PID 210 may receive a Q-axis current signal 208 and a Q-axis feedback current signal 212, which are further described herein. Based on the Q-axis current signal 208 and the Q-axis feedback current signal 212, the torque PID 210 may generate a Q-axis voltage signal 214.

[0045] The control system 200 may also include an inverse-Park circuit 216. The inverse-Park circuit 216 may receive the Q-axis voltage signal as well as the direct-axis (D-axis) current signal 236 and a combined phase signal 250 (these signals are further described herein). The combined phase signal 250 may be applied in an inverse-Park transformation to transform the Q-axis voltage signal 214 and the D-axis current signal 236 into an alpha-beta voltage signal 218.

[0046] The system 200 may include a pulse width modulation generator 220 that may receive the alpha-beta voltage signal 218 and use it to derive a pulse width modulation signal 222 that drives the inverter 116. The inverter may then generate a secondary multiphase power signal 280 that drives a set of primary windings 120.

[0047] The set of stator armature windings 118 may be driven by a first rotating magnetic field caused by the AC bus 140. A set of main field windings 120 may be driven by a secondary multiphase power signal 280 that is generated at the inverter 116 and causes a second rotating magnetic field. The combination of the first rotating magnetic flux and the second rotating magnetic flux may cause the rotor to rotate at a predetermined reference frequency represented by the reference frequency signal 202. The predetermined reference frequency may be independent of the frequency of the multiphase power signal on the AC bus 140.

[0048] With respect to the rotor frequency signal 206, the encoder 126 may monitor the mechanical rotation of the rotor 102 and generate a rotor phase signal 240. The system 200 may include a speed converter 252 that receives the rotor phase signal 240 and converts it into the rotor frequency signal 206. For example, the speed converter 252 may determine the time required for the rotor phase represented by the rotor phase signal 240 to complete one full rotation (i.e., a period associated with the rotor 102), and determine the frequency of the rotor frequency signal 206 using the time taken for one full rotation.

[0049] Regarding the combined phase signal 250, the system 200 may include an electrical phase angle converter 244. The electrical phase angle converter 244 may monitor the phase 242a of the multiphase power signal 242 on the AC bus 140, and by determining a period associated with the phase of the multiphase power signal, the electrical phase angle converter 244 may generate an electrical phase signal 246.

[0050] The system 200 may include a combining circuit 248. For example, the combining circuit 248 may be a phase add / subtract circuit. Also, the combining circuit 248 may be a processor and memory programmed to perform add and subtract functions, as described herein. The combining circuit 248 may generate a combined phase signal 250 by determining a difference between the rotor phase signal 240 and the electrical phase signal 246.

[0051] Regarding the D-axis current signal 236, the system 200 can receive the D-axis reference current signal 230 via the signal connector 124. The D-axis reference current signal 230 can be obtained from Figure 1 The controller circuit 136 receives and may be set by a user, may be hard-coded into the controller circuit 136 , or may be calculated based on the desired power output of the rotor 102 .

[0052] The system 200 can include a flux PID 232. The flux PID 232 can receive a D-axis reference current signal 230 and a D-axis feedback current signal 234, which are further described herein. The flux PID 232 can generate a D-axis current signal 236 using the D-axis reference current signal 230 and the D-axis feedback current signal 234.

[0053] With respect to the D-axis feedback current signal 234 and the Q-axis feedback current signal 212 , the system 200 may include a Clarke transformation circuit 262 . The current signals 260 for each phase of a set of main field windings 120 may be transformed to generate alpha-beta current signals 264 .

[0054] System 200 may include a Park transform circuit 266 that receives the alpha-beta current signal 264 and the combined phase signal 250. The D-axis feedback current signal 234 and the Q-axis feedback current signal 212 may be generated by applying the combined phase signal 250 to a Park transform with the alpha-beta current signal 264 as input.

[0055] Any of the circuits and / or modules of the system 200 may be combined and may share logic circuits. Further, any of the circuits and / or modules of the system 200 may include a processor or may share a processor to perform the functions described with respect to each circuit and / or module.

[0056] A benefit of the control system 200 is that it can enable the generation of pulse width modulated control signals that control the inverter 116 to generate a secondary multiphase power signal that, when applied to a set of main field windings 120, creates a second rotating magnetic field that, when combined with the first rotating magnetic field generated by the set of stator armature windings 118, causes the rotor 102 to rotate at a predetermined reference frequency represented by the reference frequency signal 202. The predetermined reference frequency can be independent of the frequency of the multiphase power signal on the AC bus 140. Other advantages may be present.

[0057] Reference Figure 3 , depicting an embodiment of a variable frequency independent speed motor system 300. Figure 1 1 , the system 300 may include a rotor 102 and a stator 104 having a high frequency transformer stage 106 and a main field stage 108. The high frequency transformer stage 106 may include a first set of transformer windings 110 and a second set of transformer windings 112. The main field stage 108 may include a set of stator armature windings 118 and a set of main field windings 120. The rotor 102 may be coupled to a rotor shaft 128, and the encoder 126 may be configured to monitor the rotation of the motor shaft 128. The AC power bus 140 may provide a multi-line power signal for powering the system 300.

[0058] System 300 may differ from system 100 in that the second set of transformer windings 112 may be directly coupled to a set of main windings 120. As used herein, the term "direct coupling" means that there is no intervening rectifier circuit or inverter circuit between the second set of transformer windings 112 and a set of main windings 120.

[0059] The system 300 may also include a motor control unit 130. The motor control unit 130 may include a rectifier 132, an inverter 134, and a controller circuit 136. The controller circuit 136 may include a controller module 322 that performs functions for controlling the inverter 134 via control signals 150. The controller module 322 may be implemented as a logic circuit or as a processor and memory programmed to perform the functions described herein.

[0060] During operation, the AC bus 140 can provide a main multi-phase power signal 242 to the first set of main windings 118. The AC bus 140 can simultaneously provide the main multi-phase power signal 242 to the rectifier 132 of the motor control unit 130. The rectifier 132 can rectify the main multi-phase power signal to generate a DC power signal for powering the inverter 134 and the controller circuit 136. The controller circuit 136 can control the inverter 134 to use the DC power signal to generate a high-frequency excitation signal that can be sent to the first set of transformer windings 110.

[0061] The excitation signal may include a high-frequency modulation component and a secondary multiphase power signal component. The secondary multiphase power signal component may be generated based on feedback signals provided to the controller module 322 of the controller circuit 136, such as the phase 242a of the multiphase power signal 242, the rotor phase signal 240, and the feedback high-frequency excitation signal 370. For example, the motor control unit 130 may include a low-pass filter 302. The low-pass filter 302 may be used to filter each phase of the excitation signal to provide a feedback current signal. The feedback current signal may represent the current to be applied to a set of main field windings 120. The controller module 322 may also receive a rotor phase signal from the encoder 126 and a signal representing the electrical phase of the main AC power signal from the AC bus. Based on these feedback signals, the frequency converter 134 may be controlled by the controller circuit 136 to generate a high-frequency excitation signal.

[0062] The first set of transformer windings 1120 can send a high frequency excitation signal to the second set of transformer windings 112. The inductance between the second set of transformer windings 112 and the set of main field windings 120 can filter the high frequency modulation component from the high frequency excitation signal, which results in a remaining secondary multi-phase power signal 280 that can effectively drive the set of main field windings 120.

[0063] As the main multi-phase power signal from the AC bus 140 is applied to the set of stator armature windings 118, a first rotating magnetic flux can be generated at the set of main field windings 118. As the secondary multi-phase power signal 280 is applied to the set of main field windings 120, a second rotating magnetic flux can be generated, which, when combined with the first rotating magnetic flux, causes the rotor 102 to rotate at a predetermined reference frequency. Because the rotational frequency of the rotor 102 is based on the combination of the first rotating magnetic flux and the second rotating magnetic flux, the frequency of the rotor 102 can be independent of the frequency of the main multi-phase power signal on the AC bus 140.

[0064] An advantage of the system 300 is that the rotor 102 can rotate at an independent frequency while also enabling direct power transfer from the AC bus 140 to the set of stator armature windings 118. This can enable the system 300 to be more efficient, as compared to typical AC motors that are configured to operate at a frequency independent of the AC power bus that powers them, and can rely on full-scale power conversion between the primary windings and the AC bus. Further, the system 300 can omit complex circuitry on the rotor 102 by generating a secondary multi-phase power signal within the motor control unit 130 and then sending the secondary multi-phase power signal to the rotor 102 as a component of the high-frequency excitation signal generated by the inverter 134.

[0065] Reference Figure 4 , depicts a control system 400 for a variable frequency independent speed motor system. Much of the control system 400 may be located outside of the rotor 102 and stator 104. For example, portions of the control system 400 may be located within the controller module 22 within the controller circuit 136. Further, the functions described may be performed by a logic circuit, a processor, or any combination thereof, the processor being coupled to a memory having instructions for causing the processor to perform the functions. It should be noted that for each signal described herein, a separate signal may be generated for each phase of a multi-phase power system.

[0066] The control system 400 may receive the reference frequency signal 202. The reference frequency signal 202 may be set by a user, generated by the controller circuit 136, or may be hard-coded into the controller circuit 136.

[0067] The control system 200 may include a speed PID 204. The speed PID may receive a reference frequency signal 202 and a rotor frequency signal 206, which are further described herein. Based on the reference frequency signal 202 and the rotor frequency signal 206, the speed PID 204 may generate a Q-axis current signal 208.

[0068] The control system 400 may also include a torque PID 210. The torque PID 210 may receive a Q-axis current signal 208 and a Q-axis feedback current signal 212, which are further described herein. Based on the Q-axis current signal 208 and the Q-axis feedback current signal 212, the torque PID 210 may generate a Q-axis voltage signal 214.

[0069] The control system 400 may also include an inverse Pike circuit 216. The inverse Pike circuit 216 may receive the Q-axis voltage signal and the D-axis current signal 236 and a combined phase signal 250 (these signals are further described herein). The combined phase signal 250 may be applied in an inverse Pike transformation to transform the Q-axis voltage signal 214 and the D-axis current signal 236 into an alpha-beta voltage signal 218.

[0070] The system 400 may include a pulse width modulation generator 220 that may receive the alpha-beta voltage signal 218 and use it to derive a pulse width modulation signal 222 that drives the inverter 116. The inverter 116 may then generate an excitation signal including a secondary multiphase power signal component that may be transferred from the stator 104 to the rotor 102 via the high frequency transformer windings 110, 112. The extracted secondary multiphase power signal 280 may then drive a set of main field windings 120.

[0071] The set of stator armature windings 118 can be driven by a first rotating magnetic field caused by the AC bus 140. A set of main field windings 120 can be driven by a secondary multi-phase power signal 280, which causes a second rotating magnetic field. The combination of the first rotating magnetic flux and the second rotating magnetic flux can cause the rotor 102 to rotate at a predetermined reference frequency represented by the reference frequency signal 202. The predetermined reference frequency can be independent of the frequency of the multi-phase power signal on the AC bus 140.

[0072] With respect to the rotor frequency signal 206, the encoder 126 may monitor the mechanical rotation of the rotor 102 and generate a rotor phase signal 240. The system 200 may include a speed converter 252 that receives the rotor phase signal 240 and converts it into the rotor frequency signal 206. For example, the speed converter 252 may determine the time required for the rotor phase represented by the rotor phase signal 240 to complete one full rotation (i.e., a period associated with the rotor 102), and determine the frequency of the rotor frequency signal 206 using the time taken for one full rotation.

[0073] Regarding the combined phase signal 250, the system 200 may include an electrical phase angle converter 244. The electrical phase angle converter 244 may monitor the multiphase power signal on the AC bus 140 and by determining a time period associated with a single phase 242a of the multiphase power signal 242, the electrical phase angle converter 244 may generate an electrical phase signal 246.

[0074] The system 400 may include a combining circuit 248. For example, the combining circuit 248 may be a phase add / subtract circuit. Also, the combining circuit 248 may be a processor and memory programmed to perform add and subtract functions, as described herein. The combining circuit 248 may generate a combined phase signal 250 by determining a difference between the rotor phase signal 240 and the electrical phase signal 246.

[0075] Regarding the D-axis current signal 236, the system 200 can receive the D-axis reference current signal 230. The D-axis reference current signal 230 can be obtained from Figure 1 The controller circuit 136 receives and may be set by a user, may be hard-coded into the controller circuit 136 , or may be calculated based on the desired power output of the rotor 102 .

[0076] The system 400 can include a flux PID 232. The flux PID 232 can receive a D-axis reference current signal 230 and a D-axis feedback current signal 234, which are further described herein. The flux PID 232 can generate a D-axis current signal 236 using the D-axis reference current signal 230 and the D-axis feedback current signal 234.

[0077] With respect to the D-axis feedback current signal 234 and the Q-axis feedback current signal 212, the system 200 may include a Clarke transformation circuit 262. The current signal 260 for each phase of a set of main windings 120 may be transformed to generate an alpha-beta current signal 264. To generate the current signal 260, the system 400 may include a low pass filter 302 that extracts the secondary multiphase power signal 280 from the excitation signal 370. This is different from the system 200, which directly measures the secondary multiphase power signal 280 as it is applied to a set of main windings 120.

[0078] The system 400 may include a Park transform circuit 266 that receives the α-β current signal 264 and the combined phase signal 250. The D-axis feedback current signal 234 and the Q-axis feedback current signal 212 may be generated by applying the combined phase signal 250 to the Park transform circuit 266 with the α-β current signal 264 as input.

[0079] Any of the circuits and / or modules of the system 200 may be combined and may share logic circuits. Further, any of the circuits and / or modules of the system 200 may include a processor or may share a processor to perform the functions described with respect to each circuit and / or module.

[0080] A benefit of the control system 400 is that it can enable the generation of pulse width modulated control signals that control the inverter 116 to generate a secondary multiphase power signal 280 that, when applied to a set of main field windings 120, creates a second rotating magnetic field that, when combined with the first rotating magnetic field generated by the set of stator armature windings 118, causes the rotor 102 to rotate at a predetermined reference frequency represented by the reference frequency signal 202. The predetermined reference frequency can be independent of the frequency of the multiphase power signal on the AC bus 140. Other advantages can exist.

[0081] Reference Figure 5 , depicting an implementation of a single phase of a high-frequency excitation signal. As shown, the high-frequency excitation signal may include a high-frequency modulated component consisting of rectangular pulses. The high-frequency excitation signal may also include a sub-modulated power signal that is encoded based on the duration or width of each rectangular pulse. The varying pulse width of the rectangular pulses may provide an average power that forms a sinusoidal signal when the high-frequency excitation signal is filtered using either a low-pass filter or based on an inductance within the circuit. The inductance may be a leakage inductance from a second set of transformer windings 112 and a set of main field windings 120, or it may be a dedicated inductance inserted separately between the windings 112, 120. The energy carried within the excitation signal is determined by Figure 5 The sinusoidal lines depicted are used to represent this.

[0082] Reference Figure 6 , depicts the pulse width modulated excitation signal after it has been filtered through a low pass filter (e.g., Figure 5 As shown in the figure, in the filtering Figure 5 The excitation signal depicted is a high-frequency rectangular pulse that is smoothed into a sinusoidal power phase. Figure 6 The depicted multi-phase signals may be used to drive a set of main field windings 120 to generate a second rotating magnetic flux at the rotor 102 .

[0083] Reference Figure 7 , depicting a method 700. The method 700 may include the following steps: At 702, a main multi-phase power signal having a current causing a first rotating magnetic flux rotating relative to the stator is received at a set of main field windings coupled to a stator of a motor device.

[0084] The method 700 may further include the step of receiving, at 704 , a secondary multi-phase power signal at a set of stator armature windings coupled to a rotor of the motor device, the secondary multi-phase power signal having a current that induces a second rotating magnetic flux that rotates relative to the rotor.

[0085] The method 700 may further include the step of generating, at 706 , an electrical phase signal based on the main multi-phase power signal.

[0086] The method 700 may include the step of, at 708 , receiving a rotor phase signal from an encoder configured to monitor rotation of a rotor.

[0087] The method 700 may further include the step of generating, at 710 , a combined phase signal based on a difference between the electric phase signal and the rotor phase signal.

[0088] Method 700 may also include the following steps: at 712, a pulse width modulation signal is generated based on the combined phase signal to control the inverter so that the secondary multi-phase power signal has a frequency, amplitude and phase, wherein the frequency, amplitude and phase enable the first rotating magnetic flux and the second rotating magnetic flux to be combined to cause the rotor to rotate at a predetermined reference frequency.

[0089] A benefit of method 700 is that the motor can rotate at a speed independent of the frequency of the AC bus used to drive the motor. Further, method 700 can be more efficient than typical induction motor methods that rely on rectification and modulation between the power bus and the input of the primary. Other advantages of method 700 may exist.

[0090] Further, the present disclosure includes examples according to the following clauses:

[0091] Item 1. An electric motor device, the electric motor device comprising: a rotor; a stator; a high-frequency transformer stage, the high-frequency transformer stage being used to send an excitation signal from the stator to the rotor, the high-frequency transformer stage having a first set of transformer windings located on the stator and a second set of transformer windings located on the rotor; and a main field motor stage, the main field motor stage having a set of stator armature windings located on the stator and a set of main field windings located on the rotor, wherein the set of stator armature windings is configured to receive a main multi-phase power signal from an AC power bus, the main multi-phase power signal having a first current that causes a first rotating magnetic flux that rotates relative to the stator, wherein the set of main field windings is configured to receive a secondary multi-phase power signal, the secondary multi-phase power signal having a second current that causes a second rotating magnetic flux that rotates relative to the rotor, wherein a combination of the first rotating magnetic flux and the second rotating magnetic flux causes the rotor to rotate at a predetermined reference frequency.

[0092] Item 2. The device of Item 1 further includes: a rectifier connected to the rotor and electrically connected to the second set of transformer windings, the rectifier being configured to rectify the excitation signal to generate a DC power signal; and an inverter connected to the rotor and electrically connected to the rectifier, wherein the inverter is configured to modulate the DC power signal to generate a secondary multi-phase power signal.

[0093] Item 3. The device of Item 2 also includes: an encoder; and an embedded controller circuit, which is connected to the rotor, and the embedded controller circuit is configured to: generate an electrical phase signal based on the main multi-phase power signal; receive the rotor phase signal from the encoder; generate a combined phase signal based on the difference between the electrical phase signal and the rotor phase signal; and generate a pulse width modulation signal based on the combined phase signal to control the inverter so that the secondary multi-phase power signal has the following frequency, amplitude and phase, which frequency, amplitude and phase enable the first rotating magnetic flux and the second rotating magnetic flux to combine to cause the rotor to rotate at a predetermined reference frequency.

[0094] Item 4. The device of Item 3 further includes: a control signal connector having a first portion arranged on the stator and a second portion arranged on the rotor, wherein the control signal connector is a non-contact optical connector, and wherein the embedded controller circuit is configured to receive one or more control signals from the controller circuit of the motor control unit via the control signal connector.

[0095] Item 5. The device of Item 3, wherein the embedded controller is further configured to: receive a reference frequency signal from a motor control unit, the reference frequency signal representing a predetermined reference frequency; generate a Q-axis current signal based on the reference frequency signal and the rotor frequency signal; generate a Q-axis voltage signal based on the Q-axis current signal and the Q-axis feedback current signal; receive a D-axis reference current signal from the motor control unit; generate a D-axis current signal based on the D-axis reference current signal and the D-axis feedback current signal; and use the Q-axis voltage signal and the D-axis current signal as inputs to an inverse Parker transform, in which a combined phase signal is applied to generate an α-β voltage signal, wherein a pulse width modulation signal is derived from the α-β voltage signal at a pulse width modulation generator circuit.

[0096] Item 6. The device of Item 5, wherein the embedded controller is further configured to: receive a rotor feedback current signal from a set of main field windings; use the rotor feedback current signal as an input to a Clarke transform, apply the Clarke transform to generate an α-β current feedback signal; and use the α-β current feedback signal as an input to a Park transform, apply the combined phase signal in the Park transform to generate a D-axis feedback current signal and a Q-axis feedback current signal.

[0097] Clause 7. The apparatus of clause 1, wherein the set of primary field windings is directly coupled to the second set of transformer windings and is configured to receive the secondary multiphase power signal from the second set of transformer windings.

[0098] Item 8. The apparatus of Item 7, wherein the excitation signal comprises a high-frequency modulated signal component and a secondary multiphase power component, and wherein inductance at a second set of transformer windings and a set of main field windings filters the high-frequency modulated signal component to form a secondary multiphase power signal.

[0099] Clause 9. The apparatus of clause 1, wherein the predetermined reference frequency of the rotor is independent of the frequency of the main multi-phase power signal.

[0100] Clause 10. The apparatus of clause 1, wherein the first set of transformer windings, the second set of transformer windings, the set of main field windings, and the set of stator armature windings each include three windings for operating with a 3-phase power signal.

[0101] Clause 11. The apparatus of clause 1, wherein the excitation signal has a frequency between approximately 1 kHz and 1 MHz.

[0102] Item 12. A system comprising a motor control unit and a motor, the motor comprising: a rotor; a stator; a high-frequency transformer stage for sending an excitation signal from the stator to the rotor, the high-frequency transformer stage having a first set of transformer windings located on the stator and a second set of transformer windings located on the rotor; and a main motor stage having a set of stator armature windings located on the stator and a set of main field windings located on the rotor, wherein a set of stator armature windings is configured to receive a main multi-phase power signal from an AC power bus, the main multi-phase power signal having a current that causes a first rotating magnetic flux to rotate relative to the stator, and wherein a set of main field windings is configured to receive a secondary multi-phase power signal, the secondary multi-phase power signal having a current that causes a second rotating magnetic flux to rotate relative to the rotor, wherein a combination of the first rotating magnetic flux and the second rotating magnetic flux causes the rotor to rotate at a predetermined reference frequency.

[0103] Item 13. The system of Item 12, wherein the motor control unit comprises: a rectifier configured to rectify a main multi-phase power signal from an AC power bus to generate a DC power signal; a controller circuit; and a frequency converter comprising an inverter, wherein the controller circuit is configured to control the frequency converter to modulate the DC power signal to generate an excitation signal.

[0104] Item 14. A system according to Item 13, wherein the controller circuit is configured to also control the inverter so that the excitation signal includes a high-frequency modulated signal component and a secondary multi-phase power component, wherein the inductance between the second set of transformer windings and a set of main field windings filters the high-frequency modulated signal component to form the secondary multi-phase power component, and wherein the controller circuit is configured to control the inverter to generate a secondary multi-phase power signal having a frequency, amplitude, and phase that causes a combination of the first rotating magnetic flux and the second rotating magnetic flux to cause the rotor to rotate at a predetermined reference frequency.

[0105] Item 15. A system of Item 13, wherein the controller circuit is configured to: generate an electrical phase signal based on a main multi-phase power signal; receive a rotor phase signal from an encoder; generate a combined phase signal based on a difference between the electrical phase signal and the rotor phase signal; and generate a pulse width modulation signal based on the combined phase signal to control the inverter so that the secondary multi-phase power signal has a frequency, amplitude, and phase that enable the first rotating magnetic flux and the second rotating magnetic flux to combine to cause the rotor to rotate at a predetermined reference frequency.

[0106] Item 16. The system of Item 15, wherein the controller circuit is further configured to: receive a reference frequency signal, the reference frequency signal representing a predetermined reference frequency; generate a Q-axis current signal based on the reference frequency signal and the rotor frequency signal; generate a Q-axis voltage signal based on the Q-axis current signal and the Q-axis feedback current signal; receive a D-axis reference current signal; generate a D-axis current signal based on the D-axis reference current signal and the D-axis feedback current signal; and use the Q-axis voltage signal and the D-axis reference signal as inputs to an inverse Pike transform, in which a combined phase signal is applied to generate an α-β voltage signal, wherein a pulse width modulation signal is derived from the α-β voltage signal.

[0107] Item 17. The system of Item 16, wherein the controller circuit is further configured to: filter the excitation signal to extract the rotor feedback current signal; use the rotor feedback current signal as an input to a Clarke transform, applying the Clarke transform to generate an α-β current feedback signal; and use the α-β current feedback signal as an input to a Park transform, applying the combined phase signal in the Park transform to generate a D-axis feedback current signal and a Q-axis feedback current signal.

[0108] Item 18. A method, the method comprising the following steps: receiving a main multi-phase power signal at a set of stator armature windings connected to the stator of a motor device, the main multi-phase power signal having a current that causes a first rotating magnetic flux to rotate relative to the stator; receiving a secondary multi-phase power signal at a set of main field windings connected to the rotor of the motor device, the secondary multi-phase power signal having a current that causes a second rotating magnetic flux to rotate relative to the rotor; generating an electrical phase signal based on the main multi-phase power signal; receiving a rotor phase signal from an encoder configured to monitor the rotation of the rotor; generating a combined phase signal based on the difference between the electrical phase signal and the rotor phase signal; and generating a pulse width modulation signal based on the combined phase signal to control an inverter so that the secondary multi-phase power signal has a frequency, amplitude and phase, and the frequency, amplitude and phase enable the first rotating magnetic flux and the second rotating magnetic flux to be combined to cause the rotor to rotate at a predetermined reference frequency.

[0109] Clause 19. The method of clause 18, wherein the predetermined reference frequency of the rotor is independent of the frequency of the main multi-phase power signal.

[0110] Clause 20. The method of clause 18, further comprising the steps of: transferring an excitation signal from the stator to the rotor using a high frequency transformer stage, the high frequency transformer stage comprising a first set of transformer windings connected to the stator and a second set of transformer windings connected to the rotor; and using the excitation signal to power a secondary multiphase power signal.

[0111] While various embodiments have been shown and described, the disclosure is not so limited, and is to be construed to include all such modifications and alterations as would be apparent to those skilled in the art.

Claims

1. An electric motor device, comprising: ROTOR(102); stator (104); A high frequency transformer stage (106) for sending an excitation signal (370) from the stator to the rotor, the high frequency transformer stage having a first set of transformer windings (110) located on the stator and a second set of transformer windings (112) located on the rotor; as well as A main field stage (108) having a set of stator armature windings (118) located on the stator and a set of main field windings (120) located on the rotor, wherein the set of stator armature windings is configured to receive a main multi-phase power signal (242) from an AC power bus (140), the main multi-phase power signal (242) having a first current causing a first rotating magnetic flux rotating relative to the stator, wherein the set of main field windings is configured to receive a secondary multi-phase power signal (280) having a current causing a first rotating magnetic flux rotating relative to the stator. A second current of a second rotating magnetic flux rotating the rotor, wherein a combination of the first rotating magnetic flux and the second rotating magnetic flux causes the rotor to rotate at a predetermined reference frequency, wherein the set of main field windings is directly connected to the second set of transformer windings and is configured to receive the secondary multi-phase power signal from the second set of transformer windings, wherein the excitation signal includes a high-frequency modulated signal component and a secondary multi-phase power component, and wherein the inductance at the second set of transformer windings and the set of main field windings filters the high-frequency modulated signal component to form the secondary multi-phase power signal.

2. The device according to claim 1, further comprising a motor control unit, the motor control unit comprising: A rectifier (114) configured to rectify a main multi-phase power signal from the AC power bus to generate a DC power signal; a controller circuit (136); and A frequency converter (134) includes an inverter (116), wherein the controller circuit is configured to control the frequency converter to modulate the DC power signal to generate the excitation signal.

3. The device according to claim 2, wherein: The controller circuit is configured to also control the inverter, and wherein the controller circuit is configured to control the inverter to generate the secondary multi-phase power signal having a frequency, amplitude, and phase such that a combination of the first rotating magnetic flux and the second rotating magnetic flux rotates the rotor at the predetermined reference frequency.

4. The device according to claim 2, wherein: The controller circuit is configured to perform the following operations: generating an electrical phase signal based on the main multiphase power signal (246); Receive a rotor phase signal (240) from an encoder; generating a combined phase signal based on a difference between the electrical phase signal and the rotor phase signal (250); and A pulse width modulation signal (222) is generated based on the combined phase signal to control the inverter so that the secondary multi-phase power signal has the following frequency, amplitude and phase, which enable the first rotating magnetic flux and the second rotating magnetic flux to combine to rotate the rotor at the predetermined reference frequency.

5. The device according to claim 4, wherein: The controller circuit is also configured to perform the following operations: Receiving a reference frequency signal (202), the reference frequency signal representing the predetermined reference frequency; Generate a Q-axis current signal based on the reference frequency signal and the rotor frequency signal (208); Generate a Q-axis voltage signal based on the Q-axis current signal and the Q-axis feedback current signal (214); Receive a D-axis reference current signal (230); Generate a D-axis current signal based on the D-axis reference current signal and the D-axis feedback current signal (236); as well as The Q-axis voltage signal and the D-axis reference signal are used as inputs to an inverse Pike circuit (216) where the combined phase signal is applied to generate an alpha-beta voltage signal (218), wherein the pulse width modulation signal is derived from the alpha-beta voltage signal.

6. The device according to claim 5, wherein: The controller circuit is also configured to perform the following operations: Filtering the excitation signal to extract a current signal (260); using the current signal as an input to a Clarke transform circuit (262), applying the Clarke transform circuit to generate an alpha-beta current feedback signal (264); and The alpha-beta current feedback signal is used as an input to a Parker transformation circuit (266) where the combined phase signal is applied to generate the D-axis feedback current signal and the Q-axis feedback current signal.

7. The device according to claim 1, wherein: Satisfy at least one of the following: The predetermined reference frequency of the rotor is independent of the frequency of the main multi-phase power signal; The first set of transformer windings, the second set of transformer windings, the set of main field windings, and the set of stator armature windings each include three windings for operating with a 3-phase power signal; and The frequency of the excitation signal is between 1 kHz and 1 MHz.

8. A system comprising a motor control unit (130) and a motor system (100), the motor system (100) comprising: ROTOR(102); stator (104); A high frequency transformer stage (106) for sending an excitation signal (370) from the stator to the rotor, the high frequency transformer stage having a first set of transformer windings (110) located on the stator and a second set of transformer windings (112) located on the rotor; as well as A main field stage (108) having a set of stator armature windings (118) located on the stator and a set of main field windings (120) located on the rotor, wherein the set of stator armature windings is configured to receive a main multi-phase power signal (242) from an AC power bus (140), the main multi-phase power signal (242) having a current that causes a first rotating magnetic flux to rotate relative to the stator, wherein the set of main field windings is configured to receive a secondary multi-phase power signal (280) having a current that causes a first rotating magnetic flux to rotate relative to the stator The rotor rotates a current of a second rotating magnetic flux, wherein the combination of the first rotating magnetic flux and the second rotating magnetic flux causes the rotor to rotate at a predetermined reference frequency, wherein the set of main field windings is directly connected to the second set of transformer windings and is configured to receive the secondary multi-phase power signal from the second set of transformer windings, the excitation signal includes a high-frequency modulated signal component and a secondary multi-phase power component, wherein the inductance between the second set of transformer windings and the set of main field windings filters the high-frequency modulated signal component to form the secondary multi-phase power signal.

9. The system according to claim 8, wherein: The motor control unit comprises: A rectifier (114) configured to rectify a main multi-phase power signal from the AC power bus to generate a DC power signal; a controller circuit (136); and A frequency converter (134) includes an inverter (116), wherein the controller circuit is configured to control the frequency converter to modulate the DC power signal to generate the excitation signal.

10. The system according to claim 9, wherein: The controller circuit is configured to also control the inverter, and wherein the controller circuit is configured to control the inverter to generate the secondary multi-phase power signal having a frequency, amplitude, and phase such that a combination of the first rotating magnetic flux and the second rotating magnetic flux rotates the rotor at the predetermined reference frequency.

11. The system according to claim 9, wherein: The controller circuit is configured to perform the following operations: generating an electrical phase signal based on the main multiphase power signal (246); Receive a rotor phase signal (240) from an encoder; generating a combined phase signal based on a difference between the electrical phase signal and the rotor phase signal (250); and A pulse width modulation signal (222) is generated based on the combined phase signal to control the inverter so that the secondary multi-phase power signal has the following frequency, amplitude and phase, which enable the first rotating magnetic flux and the second rotating magnetic flux to combine to rotate the rotor at the predetermined reference frequency.

12. The system according to claim 11, wherein: The controller circuit is also configured to perform the following operations: Receiving a reference frequency signal (202), the reference frequency signal representing the predetermined reference frequency; Generate a Q-axis current signal based on the reference frequency signal and the rotor frequency signal (208); Generate a Q-axis voltage signal based on the Q-axis current signal and the Q-axis feedback current signal (214); Receive a D-axis reference current signal (230); Generate a D-axis current signal based on the D-axis reference current signal and the D-axis feedback current signal (236); as well as The Q-axis voltage signal and the D-axis reference signal are used as inputs to an inverse Pike circuit (216) where the combined phase signal is applied to generate an alpha-beta voltage signal (218), wherein the pulse width modulation signal is derived from the alpha-beta voltage signal.

13. The system according to claim 12, wherein: The controller circuit is also configured to perform the following operations: Filtering the excitation signal to extract a current signal (260); using the current signal as an input to a Clarke transform circuit (262), applying the Clarke transform circuit to generate an alpha-beta current feedback signal (264); and The alpha-beta current feedback signal is used as an input to a Parker transformation circuit (266) where the combined phase signal is applied to generate the D-axis feedback current signal and the Q-axis feedback current signal.

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