Power distribution in electrical machine

Abstract

To provide a technique for wirelessly transferring electric power within an electric machine.SOLUTION: An electric machine includes: a stator; and a rotor that can be excited by a magnetic field generated by the stator upon receiving a stator current to generate a relative motion between the rotor and the stator. A controller is configured to send a stator current through the stator at a certain current angle measured from the closest one of the magnetic poles of the rotor, to determine a desired operation output of the electric machine, and to determine a desired rotor motion corresponding to the desired operation output of the electric machine. The controller is further configured to calculate a vector control modulation to be applied to the stator for causing the desired rotor motion, and adjust the current angle of the stator current based on the vector control modulation to cause the rotor to perform the desired rotor motion, thus achieving the desired operation output of the electric machine.SELECTED DRAWING: Figure 3B

Description

[Technical Field]

[0001] Priority claims

[0001] This application claims the benefit of priority under 35 U.S.C. §119(e) of U.S. patent application Ser. No. 63 / 059929, filed July 31, 2020, the entire contents of which are incorporated herein by reference.

[0002] Technical Field

[0002] The present invention relates to electric motors and generators. [Background technology]

[0003] background

[0003] Electric motors generally comprise a fixed component, often referred to as a stator, and a rotating component, often referred to as a rotor. An electric current is converted into an electromagnetic field, which generates a mechanical force, or torque, between the stator and rotor. The mechanical force, or torque, can be used to perform work. A generator operates on a similar principle, but by converting mechanical force into an electric current. The principles described herein are primarily described with respect to rotational force, or torque, but are also applicable to linear motors. In the case of a linear motor, in some implementations, the rotor acts as the fixed component and the stator acts as the component that is translated. Summary of the Invention [Problem to be solved by the invention]

[0004] overview

[0004] This disclosure describes techniques related to wirelessly transferring power within an electric machine. [Means for solving the problem]

[0005]

[0005] An exemplary implementation of the subject matter described in this disclosure is an electric machine having the following features: A stator defines a plurality of stator poles by associated stator windings; A rotor defines a plurality of rotor poles fixed by associated rotor windings; The rotor defines a magnetic field that can be excited by a magnetic field generated by the stator windings to generate relative motion between the rotor and the stator; The rotor is maintained synchronized with the magnetic field generated by the stator during operation; A controller is configured to send current through the stator windings at a current angle measured from the nearest one of the rotor poles; The controller is configured to adjust the magnitude of the sent current depending on operating conditions; The controller is configured to adjust the current depending on operating conditions.

[0006]

[0006] In some implementations, the stator windings include concentrated windings.

[0007]

[0007] In some implementations, the stator windings include distributed windings.

[0008]

[0008] In some implementations, the stator windings include salient pole windings.

[0009]

[0009] In some implementations, the rotor windings include concentrated windings.

[0010]

[0010] In some implementations, the rotor windings include salient pole windings.

[0011]

[0011] In some implementations, the rotor windings comprise non-lap windings.

[0012] In some implementations, the rotor includes permanent magnets, hi some implementations, the permanent magnets are substantially aligned with the rotor poles.

[0013]

[0013] In some implementations, the controller is further configured to excite the stator windings. In some implementations, the controller is further configured to generate a stator magnetic field in the stator via the excited stator windings. In some implementations, the controller is further configured to generate a corresponding rotor magnetic field in a ferromagnetic material in the rotor via the stator magnetic field. In some implementations, the controller is further configured to generate a rotor tangential force via a shift in the stator magnetic field. In some implementations, the controller is further configured to move the rotor via the generated tangential force. In some implementations, the controller is further configured to maintain a magnetic flux in the rotor via a current in the rotor coil responsive to the magnetic field shift. The stator magnetic field and the rotor are maintained synchronized with each other during operation.

[0014] An exemplary implementation of the subject matter described in this disclosure is a method of controlling an electric machine. A stator winding on a stator is energized to generate a stator magnetic field in the stator. The stator magnetic field modifies a corresponding rotor magnetic field in a ferromagnetic material in the rotor. The shift in the stator magnetic field generates a tangential force on the rotor. The generated tangential force causes the rotor to move. The stator magnetic field and rotor are maintained synchronized with each other during operation. Decay of magnetic flux in the rotor is resisted by current in the rotor coils in response to the magnetic field shift. Current is sent through the stator winding at a current angle measured from the nearest one of the rotor poles. The magnitude of the sent current is adjusted according to operating conditions. The current angle is adjusted according to operating conditions.

[0015]

[0015] An exemplary implementation of the subject matter described in this disclosure is a wound field rotor synchronous machine having the following features: A stator defines a plurality of stator poles with associated stator windings; A rotor defines a plurality of rotor poles; The rotor is configured to rotate synchronously with the stator; The rotor includes a rotor winding associated with each of the rotor poles; The rotor windings are configured to be excited by a magnetic field generated by the stator windings; The excited rotor windings generate a rotor magnetic field; Permanent magnets are embedded within the rotor; A controller is configured to excite the stator windings; The controller is configured to generate a stator magnetic field in the stator by sending a control signal to the stator winding by sending a current through the stator winding at a current measured relative to the nearest one of the rotor poles; The controller is configured to adjust the magnitude of the sent current depending on operating conditions; The controller is configured to adjust a current angle depending on operating conditions.

[0016]

[0016] In some implementations, the permanent magnets are not aligned with the rotor poles.

[0017]

[0017] In some implementations, the stator windings include concentrated windings.

[0018]

[0018] In some implementations, the stator windings include distributed windings.

[0019]

[0019] In some implementations, the stator windings include salient pole windings.

[0020]

[0020] In some implementations, the rotor windings include concentrated windings.

[0021]

[0021] In some implementations, the rotor windings include salient pole windings.

[0022]

[0022] In some implementations, the rotor windings include non-lap windings.

[0023]

[0023] The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, drawings, and claims. [Brief explanation of the drawings]

[0024] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] FIG. 1 is a schematic diagram of an example of an electric drive system. [Figure 2]

[0025] FIG. 2 is a schematic diagram of an exemplary power switch for an electrical winding. [Figure 3A]

[0026] 1 is a perspective view of an exemplary electric machine. [Figure 3B] FIG. 1 is a side view of an exemplary electric machine. [Figure 3C]

[0027] 1 is a perspective view of an exemplary electric machine. [Figure 3D] FIG. 1 is a side view of an exemplary electric machine. [Figure 4]

[0028] FIG. 1 is a side view of an exemplary electric machine. [Figure 5A]

[0029] FIG. 2 is a front view of an exemplary rotor coil. [Figure 5B]

[0030] FIG. 5B is a perspective view of the rotor coil of FIG. 5A. [Figure 5C]

[0031] FIG. 5C is a side view of the rotor coil of FIGS. 5A and 5B. [Figure 6]

[0032] FIG. 1 is a schematic diagram of an electric motor configured for control in accordance with the present disclosure. [Figure 7]

[0033] FIG. 1 is a block diagram of an exemplary controller that may be used in aspects of the present disclosure. [Figure 8]

[0034] 1 is a flowchart of a method that may be used in aspects of the present disclosure. [Figure 9A]

[0035] 1 is a flowchart of a method for responding to a torque increase request, according to an aspect of the present disclosure. [Figure 9B]

[0036] 10 is another flowchart of a method for responding to a torque increase request in accordance with an aspect of the present disclosure. [Figure 9C]

[0037] 1 is a flowchart of a method for starting an electric motor according to an aspect of the present disclosure. [Figure 9D]

[0038] 1 is a flowchart of a method for responding to a torque increase request, according to an aspect of the present disclosure. [Figure 10]

[0039] 1 is a graph of average magnetic field strength for various machine configurations. DETAILED DESCRIPTION OF THE INVENTION

[0025]

[0040] Like reference numbers and designations in the various drawings refer to like elements.

[0026] Detailed Description

[0041] The present disclosure relates to a wound-field synchronous motor with a rotor and stator that are directly electromagnetically coupled. The rotor's rotor poles are topologically and electrically fixed to the rotor surface. The rotor is substantially energetically isolated from stator components other than the stator windings. That is, the rotor field is configured to be excited by the field generated by the stator windings. The stator field and rotor are maintained synchronized with each other during operation. During operation, a controller is configured to send current through the stator and actively adjust the magnitude and angle of the current in response to current or changing operating conditions. Such a motor can operate with the efficiency of a synchronous machine without requiring expensive rare-earth magnets or separate brushes or excitation circuits to excite the windings in the rotor.

[0027]

[0042] The electric machines described herein feature shorted concentrated windings that define the rotor poles. While shorted damper bars within the rotor have been proposed for transient damping, such damper bars tend to have limited frequency response. In contrast, shorted concentrated windings can provide effective transient damping over a wide range of frequencies during operation. Additionally, various electric machines described within this disclosure can take advantage of the inherent nonlinearities and asymmetries that occur during saturation of the rotor back iron, resulting in asymmetric inductance within the coils and resulting net torque.

[0028]

[0043] Thus, the present disclosure provides subject matter for controlling electric machines or motors to achieve a variety of different goals, for example, to achieve desired operating goals without or with reduced reliance on rare earth elements or wear elements such as brushes or excitation circuits, or to improve other operating aspects of the system, such as generating a net torque designed to control undesirable torque ripple.

[0029]

[0044] 1 shows an electric drive system 100 including an electric motor 102 and an electric motor controller 104 coupled to the electric motor 102. The electric motor controller 104 is configured to operate the electric motor 102 to drive a load 110. The load 110 may be an additional gear train, such as a gear set, vehicle wheels, a pump, a compressor, or other electric motors that may be coupled together to operate in parallel.

[0030]

[0045] The motor 102 has an output shaft 107 that is rotatable relative to a motor housing 105, which serves as a datum for rotation and other motion of the motor components. In use, the output shaft 107 may be coupled to a load 110 to which the motor 102 may impart a rotational force when electrically activated by appropriate power and signals from a motor controller 104. The output shaft 107 extends through the motor and may be exposed at both ends, meaning that rotational force may be transmitted at both ends of the motor. The motor housing 105 may be rotationally symmetric about the axis of rotation of the output shaft 107, but may also be of any external shape and may generally include means for securing the housing to another structure to prevent housing rotation during motor operation.

[0031]

[0046] The electric motor 102 comprises an active magnetic component 106, such as a stator, and a passive magnetic component 108, such as a rotor. For purposes of explanation, the stator will be used as a representative example of an active magnetic component, and the rotor will be used as a representative example of a passive magnetic component.

[0032]

[0047] The rotor 108 is associated with the stator 106 and may be disposed within the stator 106 (e.g., in an internal rotor radial gap motor) or parallel to the stator (e.g., in an axial gap motor or linear motor). As described in more detail below, appropriately controlled electrical activity in the stator 106 drives the motion of the rotor 108. The rotor 108 is rotationally coupled to the output shaft 107 such that any rotational component of the resulting rotor motion is transferred to and rotates the output shaft 107. The stator 106 is fixed to the motor 102 so that the rotor 108 moves about or parallel to the stator 106 during operation.

[0033]

[0048] Current flowing through a loop of wire creates a substantially uniform magnetomotive force (MMF), resulting in a motor pole within the wound or enclosed area. In a typical electric motor, such a loop has a diameter sufficient to carry the desired current load, but is thin enough that the skin depth at the driving frequency penetrates the loop completely. To increase the pole field strength, multiple turns, i.e., overlapping loops of wire, may be used. This topology is generally referred to as a wound-field pole. A collection of such overlapping loops is referred to as a coil. For purposes of this disclosure, multiple coils acting together within a stator or rotor are referred to as a winding. In some instances, the coils may overlap and surround multiple teeth on either the rotor or stator. Such lap-wound coils may be referred to as an armature or distributed winding. The magnetic pole is the magnetic center of the distributed winding, and therefore, the magnetic pole can move relative to the individual coils within such a distributed winding in response to the driving current passing through the winding.

[0034]

[0049] As examples described in more detail throughout this disclosure, the stator 106 defines a plurality of stator poles with associated electrical windings, and the rotor 108 includes a plurality of rotor poles. As examples described in more detail throughout this disclosure, the rotor 108, together with the stator 106, defines a nominal air gap between the stator poles and the rotor poles. The rotor 108 is movable relative to the stator 106 along the direction of motion.

[0035]

[0050] 2 shows another exemplary power switch 200 for an individual electrical winding 132. The power switch 200 may have an H-bridge circuit with four switching elements 202a, 202b, 202c, and 202d in an H-shaped configuration centered around the electrical winding 132. The switching elements 202a, 202b, 202c, and 202d may be bipolar or FET transistors. Each switching element 202a, 202b, 202c, and 202d may be coupled to a corresponding diode D1, D2, D3, and D4. The diodes are called catch diodes and may be of the Schottky type. The top end of the bridge is connected to a power source, e.g., a battery V batand the lower end is grounded. The gates of the switching elements 202a, 202b, 202c, and 202d may be coupled to a controller operable to send a corresponding control voltage signal to each switching element 202a, 202b, 202c, and 202d. The control voltage signal may be a DC voltage signal or an AC (alternating current) voltage signal.

[0036]

[0051] Switching elements 202a, 202b, 202c, and 202d can be individually controlled by motor controller 104 and can be turned on / off independently. In some cases, when switching elements 202a and 202d are turned on, the left stator lead is connected to a power source and the right stator lead is connected to ground. Current begins to flow through the stator, energizing electrical winding 132 in a forward direction. In some cases, when switching elements 202b and 202c are turned on, the right stator lead is connected to a power source and the left stator lead is connected to ground. Current begins to flow through the stator, energizing electrical winding 132 in the opposite, reverse forward direction. That is, by controlling the switching elements, electrical winding 132 can be energized / actuated in either of two directions. While primarily shown and described using a single-phase H-bridge configuration, a typical six-switch inverter system can be used with a polyphase machine without departing from this disclosure.

[0037]

[0052] The motor controller 104 may be configured to sequentially operate the switches 134 or 200 for corresponding pole excitation duty cycles to generate magnetic flux across the air gap between the stator poles and the rotor poles. The switches may be controlled to sequentially energize the stator poles to generate local attractive forces that pull the rotor. Such sequential excitation (or actuation) may cause the rotor 108, output shaft 107, and load 110 to rotate.

[0038]

[0053] The components and controls of an electric motor may be discussed relative to the D-axis 312 (illustrated in FIGS. 3A and 3B) and Q-axis of the motor's rotor and / or stator. The direct axis, or D-axis 312, in an electric motor may be defined as the pole centerline perpendicular to the air gap 314 and may apply to either the stator poles 411 (see FIG. 4) or the rotor poles 408. The rotor may be characterized by the D-axis 312 at each pole when viewed in a synchronous reference frame. In a wound rotor, the D-axis 312 is the center point of the resulting magnetic center of the coil or field winding, whether the field winding is concentrated in a single large slot or spans multiple small slots. The stator poles may be similarly characterized.

[0039]

[0054] The Q axis is perpendicular to the D axis (i.e., 90 degrees electrically) in the magnetic reference frame. In general, forces along the Q axis generate electromotive forces, such as torque. Topologically, the Q axis of a rotor or stator is generally located directly between two magnetic poles.

[0040]

[0055] In systems where the control signal can be converted into DQ axis components, a third z-axis component also exists, which can be described as a signal or magnetic quantity that does not map directly to the D or Q axes, for example, a component orthogonal to the plane in which the Q and D components can be determined.

[0041]

[0056] The current phase shifter angle 318 is the relative angle of the rotor pole D-axis with respect to the stator magnetic center (as illustrated in FIGS. 3A-3D). A positive current phase shifter angle indicates that the stator magnetic center leads the rotor poles in the direction of motion. This situation results in the stator magnetic center "pulling" the rotor poles toward the stator magnetic center. Similarly, a negative current angle indicates that the stator magnetic center lags the rotor poles. This situation "pulls" the rotor poles in the opposite direction. Such a negative current phase shifter angle 318 may be used in braking situations. In some implementations, a current phase shifter angle 318 greater than 90° may be used. Such a large phase shifter current angle 318 can "push" adjacent poles in the direction of motion. Similarly, a current phase shifter angle 318 less than -90° may be used to "push" adjacent poles in the opposite direction, such as during braking operations. The conversion of the current phase shifter angle 318 between the fixed and synchronous reference frames can be done using the following equation: θ e =(P / 2)θ m (1) θ e is the current phase shifter angle in the synchronous reference frame, P is the number of stator poles, and θ m is the current phase shifter angle in a fixed reference frame. Regardless of the current phase shifter angle, it can be separated into a D-axis component and a Q-axis component. Generally, in the motors and generators described herein, the D-axis component acts to "charge" or modulate the magnetic field in the rotor poles, and the Q-axis component acts to apply a force or torque to the rotor poles. Adjusting both the current phase shifter angle 318 and the current amplitude based on operating conditions is described in detail throughout this disclosure.

[0042]

[0057] For example, the current angle, duty cycle, and D-axis to Q-axis current injection can all be varied. In some examples, an increase in instantaneous D-axis current relative to the Q-axis current can be achieved by at least 5%, 10%, 20%, or 30% during the D-axis injection period. In some examples, the resulting decrease in current angle during the injection cycle can be achieved by, for example, 5 to 60 degrees, 10 to 50 degrees, 15 to 45 degrees, or 22.5 to 67.5 degrees. In some examples, an injection pulse width of 2 to 70 ms, 5 to 50 ms, or 10 to 25 ms can be used. In some examples, a charge duty cycle of 5%, 10%, 15%, or 25% of the total operating time can be used. In some examples, the transition time from D-axis injection to normal operation, determined by the rotor current decreasing to zero, can be 500 μs to 15 ms, 2 ms to 12 ms, or 4 ms to 10 ms. In some examples, the current angle is changed by less than 15 degrees, less than 10 degrees, or less than 5 degrees. In some examples, the D-axis and Q-axis magnitudes are simultaneously changed by at least 5%, 10%, 20%, or 30% during the D-axis injection period. The system may be operated as a current control or a voltage control. For example, regardless of the specific operating parameters, the signal may be injected through a current source inverter with the variance of the current injection ripple magnitude controlled to be within a desired tolerance.

[0043]

[0058] As described throughout this disclosure, the coil structure on the rotor receives power / signals from the stator via inductive coupling that includes at least one loop centered on a rotor pole. In some implementations, the rotor coil for the conductive loop forms a capacitance, and in some implementations, the capacitance is formed, inserted, or defined by a specific portion of the rotor coil or conductive loop. In some implementations, the rotor coil or conductive loop includes a resonant frequency. In some implementations, the resonant frequency of the rotor coil is within the permeability range of the magnetic pole or rotor coil material.

[0044]

[0059] During operation, the rotor poles can be flux-injected via the stator D-axis signal, and the coil structure resists the flux change and conducts current. The rotor Q-axis signal generates torque in the flux-injected machine. In some topologies, such as salient-pole winding synchronous machines, maximum torque per ampere (MTPA) occurs at a current angle between 60 and 90 degrees. For a given operating condition (e.g., torque and speed), the controller establishes the MTPA (e.g., through a lookup table or model-based estimator), which includes combining the D-axis and Q-axis currents (the main control portion) to establish the current phase shifter angle. This current phase shifter angle may be modulated or oscillated to periodically maintain a desired level of rotor flux and may be monitored by an observer or estimator or established by a model-based approach. When the D-axis is modulated to increase the rotor flux, the magnitude of the Q-axis current may be modulated proportionally to limit torque ripple and suppress the adverse effects of changes in the current phase shifter angle, or may limit changes in the current phase shifter angle.

[0045]

[0060] 3A and 3B are perspective and side views of an exemplary electric machine 300. The electric machine 300 includes a stator 302 that defines multiple stator poles with associated stator windings 304. A "motor pole" may be described as a topological section of either the stator or rotor that emits magnetic flux of a single polarity across the air gap at a given time. When determining the number or location of motor poles, the magnetic flux carried by the stator or rotor back iron is considered. Magnetic poles are generally characterized by regions of high magnetic field that can exceed 5,000 gauss. Magnetic poles may originate from permanent magnets or electromagnetic fields. While the number of stator or rotor poles is often fixed at the time of manufacture, in some implementations described herein, the number of poles on the rotor, stator, or both can be changed during operation.

[0046]

[0061] Although the stator 302 illustrated herein is shown as having distributed stator windings 304, salient, concentrated, and / or non-lapped stators may likewise be used without departing from this disclosure.

[0047]

[0062] The rotor 306 defines a plurality of rotor poles 308 with associated rotor coils 310. The rotor poles 308 are topologically and electrically fixed to the rotor surface. A fixed-pole rotor is one whose poles are topologically and electromagnetically fixed or held stationary relative to a synchronous reference frame; for example, the rotor 306 is a fixed-pole rotor. That is, the rotor 306 always rotates at substantially the same speed as, or synchronous with, the drive frequency provided by the stator (allowing for an inherent level of torque ripple). The synchronous reference frame is the same as the magnetic reference frame. For this reason, fixed-pole motors are often referred to as "synchronous" motors. Wound-field rotors, surface permanent magnet rotors, reluctance motors, and interior permanent magnet rotors are all examples of fixed-pole rotors. Fixed-pole rotor designs maximize the use of ferromagnetic material in the rotor's D-axis 312 region (the center of the rotor poles) and, in the case of wound-field rotors, ensure that the effective magnetic center coincides with the D-axis 312. As a result, fixed-pole rotors are considered more efficient than moving-pole rotors for a given size and power rating; however, fixed-pole rotors are difficult to control in that it is difficult to maintain a constant current phase shifter angle under dynamic load conditions and dynamic operating speeds. For example, accelerating or maintaining speed of an electric motor during load changes involves actively adjusting the current phase shifter angle 318, current magnitude, and / or drive frequency based on input from a position sensor 316. The concepts described herein are primarily applicable to synchronous machines, where the stator field and rotor, e.g., rotor 306, remain synchronized with each other during operation.

[0048]

[0063] In contrast, the magnetic poles of a moving-pole rotor are not topologically or electromagnetically fixed and move relative to a fixed reference frame during operation. This means that the rotor constantly "slips," lagging behind the drive frequency provided by the stator, or out of synchronization. For this reason, these motors are often referred to as "asynchronous" motors. Examples of moving-pole rotors include wound squirrel-cage induction rotors, armature-wound rotors, brush motors, and other similar motors. While moving-pole rotors can self-adjust the current phase shifter angle 318 during operation, a design compromise must be made between the D-axis ferromagnetic material and the Q-axis field winding to allow the magnetic poles to move uniformly across the rotor surface. As a result, for a given size and power rating of a moving-pole rotor, such a motor will have higher electrical resistance, require more starting current, and produce a lower magnetic field strength.

[0049]

[0064] The magnetic field of the rotor 306 is configured to be excited by the magnetic field generated by the stator windings 304. The rotor 306 and the stator 302 are configured to move relative to each other in response to the excited rotor magnetic field. The rotor 306 is substantially energetically isolated from components of the stator 302 other than the stator windings 304.

[0050]

[0065] In an electric machine, the stator and rotor may be coupled to enable power transfer, signal transmission, and / or electromagnetic field modulation during operation. Coupling may be classified as direct or indirect coupling. Direct coupling occurs between the stator 302 and rotor 306 along a primary working air gap, such as air gap 314. Indirect coupling occurs along a secondary interface away from the primary working air gap.

[0051]

[0066] Direct coupling is generally characterized as inductive coupling; for example, a squirrel-cage induction rotor is considered to be directly coupled to the stator. While direct coupling is common and easily controlled in asynchronous machines, direct coupling in synchronous machines is difficult to control for reasons explained throughout this disclosure. For example, rotor position often needs to be known to ensure that proper current magnitude and / or frequency are maintained.

[0052]

[0067] Indirect coupling operates along secondary couplings, which may be radially or axially oriented, and may communicate via electrical contacts, inductive coupling along separate air gaps, capacitive coupling, or optical coupling. Secondary couplings may be used for a variety of functions to improve the efficiency and / or overall controllability of electric machines, but often require additional components that can increase the weight, complexity, frequency of failure, and cost (both operational and capital) of machines utilizing such systems.

[0053]

[0068] Coupling may be further classified as power coupling or signal coupling. Power coupling transfers electrical power from the stator to the rotor, which is used to directly drive a magnetomotive force along the primary working air gap, thereby generating torque. Signal coupling transfers signals between the stator and rotor that can be used to individually regulate electrical circuits in the rotor or monitor rotor conditions, such as temperature or position relative to a fixed reference frame. Signal coupling transmits at very low power levels relative to the motor's rated power, e.g., less than 5% of the motor's rated power. In some implementations or under some operating parameters, it may be desirable for signal coupling to transmit power at levels relative to the motor's rated power, e.g., 7.5%, 5%, 3%, or 2.5%.

[0054]

[0069] Energetically isolated motors and generators such as those described throughout this disclosure primarily use direct coupling (within the limits of standard electromagnetic shielding) to transfer power and signals between the stator and rotor, without indirect or secondary coupling. The electric machines described herein include direct coupling for both power and signal coupling between the rotor 306 and the stator 302.

[0055]

[0070] In some implementations, the wound rotor needs to be, or can benefit from being, charged when it is at position D, as shown in FIG. 3B , or when it transitions from position D to position Q through modulation of the current phase shifter angles. Charging may mean generating current in one or more rotor windings, or transferring, increasing, or storing magnetic flux in the rotor, each of which may involve some power transfer from the stator to the rotor. Such a task may be accomplished in various ways, for example, by forward modulating the stator excitation current phase shifter angles (e.g., advancing or retarding the stator excitation current angles as appropriate), increasing the frequency of change in the stator excitation current phase shifter angles, increasing the magnitude of the excitation current in the stator (or any of the resulting signal components), or any combination thereof. In some examples, the rotor field may need to be weakened (e.g., reduce the level of current or magnetic flux present in the rotor and / or rotor field windings), for example, by operating at or near position D′ (e.g., by transitioning from position Q to position D′ or from position D′ to Q′). Such a task may be accomplished in various ways, such as by modulating the current phase shifter angle (e.g., advancing or retarding the stator excitation current angle as appropriate), lowering the frequency of change of the stator excitation current phase shifter angle, reducing the magnitude of the excitation current (or any of the resulting signal components) in the stator, or any combination thereof. Alternatively or additionally, field weakening may be achieved through passive loss of rotor field winding current due to ohmic losses. During operation, in some implementations, frequency and harmonic independence may be observed between the signal emitted by the stator and the fundamental operating frequency that determines rotor speed. As will be described below, this disclosure recognizes that control of the motor may be accomplished in a manner that goes beyond simply moving the rotor and prioritizes additional goals, such as increasing system efficiency, controlling losses in the system, or mitigating the likelihood of operating conditions that may impair or reduce the effectiveness of the system. Further details regarding such systems are provided throughout this disclosure, for example, in FIG. 6 and the associated discussion.

[0056]

[0071] 3C and 3D are perspective and side views of an exemplary electric machine 350. Electric machine 350 is substantially similar to electric machine 300, except for the differences described herein. Rotor 356 includes six rotor poles 358. Stator 352 includes distributed windings 354. Electric machine 350 has six rotor teeth (pole 358) and 36 stator teeth 370, resulting in a rotor tooth to stator tooth ratio of 1:6. This differs from electric machine 300, which has four rotor teeth (pole 308) and 12 stator teeth 320, resulting in a rotor tooth to stator tooth ratio of 1:3. Other rotor tooth to stator tooth ratios, such as a 1:2 or 1:4 ratio, may be used without departing from this disclosure. Other ratios of rotor teeth to stator teeth can be used without departing from this disclosure, whether salient concentrated or distributed stator windings are used.

[0057]

[0072] FIG. 4 is a side view of an exemplary electric machine 400. The electric machine 400 is substantially similar to the electric machine 300 described above, except for the differences described herein. The rotor 406 is the outer rotor, and the stator 402 is the inner stator. In other words, the rotor 406 surrounds the stator 402 and rotates around the stationary stator 402. The stator 402 defines stator poles 411 with salient, non-lapped, concentrated stator windings 404. The rotor 406 includes permanent magnetic material 416 embedded within the rotor 406. As shown, each rotor pole 408 includes four channels of permanent magnetic material 416 arranged in a generally "M" shape in a "W" configuration, although other arrangements may be used without departing from this disclosure. The permanent magnetic material 416 may include various materials, including ferrite, SmFeN, N35, and N45. Typically, a low magnetic strength permanent magnetic material is used, although less powerful magnetic material can be used without departing from this disclosure. The permanent magnetic material 416 can extend the entire longitudinal length of each rotor pole 408 or can extend partially across each rotor pole 408. In some implementations, the permanent magnetic material 416 can be configured in multiple layers or laminations.

[0058]

[0073] As shown, the permanent magnetic material 416 provides a net magnetic force that is substantially aligned with each rotor pole 408. In some implementations, the permanent magnetic material may be positioned such that the net magnetic force from the permanent magnetic material 416 is not aligned with the rotor pole 408. Generally, the placement of the permanent magnetic material depends on the desired cross-sectional magnetic flux density of the magnetic material within the rotor. In implementations in which the permanent magnetic material 416 is positioned within the rotor coils 310, the magnetic flux in each set of permanent magnetic material 416 can be individually adjusted and / or modulated by adjusting the charge of the surrounding rotor coils 310. Such implementations also protect the magnets from demagnetization that may be caused by a strong stator magnetic field. In implementations in which the permanent magnetic material 416 is not surrounded by the rotor coils, adjustments to the magnetic flux caused by the stator magnetic field may affect multiple sets of permanent magnetic material 416 within the rotor 406.

[0059]

[0074] 5A-5C show front, side, and perspective views of an exemplary rotor coil 310. As shown in FIGS. 3A, 3B, and 4, each rotor coil 310 functions as its own winding, with a single coil around each pole, such as rotor pole 308 or 408. As such, the rotor may be described as including concentrated, salient, and / or non-lap windings. In some implementations, the winding direction of each coil may alternate with each adjacent rotor pole 308 or 408. For example, implementations using a stator with salient, concentrated, and / or non-lap windings may use such an arrangement. In some implementations, the winding direction need not alternate between adjacent rotor poles. For example, implementations using a stator with distributed windings may use such an arrangement. Although coil 310 is shown as a single coil shorted to itself, other geometries may be used as long as each coil is shorted to itself and does not overlap adjacent coils. In general, rotor coils are often configured so that the current skin depth at power transfer frequencies completely penetrates the coil's conductor. In the context of this disclosure, "current skin depth" refers to the depth from the conductor surface through which current, particularly eddy currents induced from a changing magnetic field at a given frequency, primarily flows. For a given material, the skin depth may be calculated as follows: δ≒1 / √πfμσ (2) "f" is the magnetic switching frequency, μ is the magnetic permeability of the material (in H / mm), and σ is the electrical conductivity of the material. Achieving full skin-depth penetration within the rotor coil 310 allows for uniform inductance within the rotor coil 310. In some implementations, the drive frequency may range from 0 Hz to 20 Hz. In some implementations, the drive frequency may range from 100 Hz to 2000 Hz. Generally, the rotor coil is configured such that decay of magnetic flux within the rotor is resisted by current flow in the rotor coil in response to magnetic field shifts from the stator.

[0060]

[0075] Traditionally, synchronous motors lack a magnetizing current to magnetize the material, so the magnets must be magnetized in the factory or before installation. Therefore, if the magnetic material demagnetizes during operation (e.g., due to an overloaded stator), the magnets may be damaged or the motor may not operate at all. The rotor coil 310 helps protect the permanent magnets from the potential demagnetization effects of the stator. When operating between the Q axis (90°) and the D axis (0°), a high level of charge is generated with substantial inductive damping (e.g., maintaining the magnetic field). Damping can be observed due to current passing through the rotor coils (310, 410) to resist changes in magnetic flux. Under such a control scheme (in combination with coils 310 or 410), the rotor magnetic field can be modulated based on the current phase shifter angle, which can result in a wider operating range. Operation from the D axis to the Q axis, in some instances, allows for a shielding effect to protect the magnetic material, which allows for reduced magnetic material, low-coercivity materials, or both. Alternatively or additionally, the field weakening due to D-axis injection is not constant compared to that of permanent magnet machines. Similarly, the rotor field can be modulated by passing a current magnitude through the stator. In many cases, both the current magnitude and the current phase shifter angle can be adjusted simultaneously to achieve the desired rotor field modulation.

[0061]

[0076] FIG. 6 shows a schematic diagram of an electric motor 600 along with the alignment between the rotor 602 and stator 604. Position D is defined as the alignment of opposing stator 604 and rotor 602 poles (i.e., NS and SN). Positions Q and Q' are defined as being electrically orthogonal to D and D' due to misaligned poles (i.e., approaching like poles and approaching opposite poles, respectively) or alignment of like stator 604 and rotor 602 poles (i.e., NN and SS). In some implementations, particularly with highly salient rotors, peak torque occurs between positions D and Q in the synchronous reference frame (e.g., due to its reluctance component). In other implementations, such as cylindrical rotors (e.g., machines with low saliency), peak torque occurs between positions Q and D'. In instances where permanent magnet motors are used, peak torque operation may require demagnetization at high loads and weakening of the field at high speeds, which may compromise size / weight and / or torque production if weaker magnets are used.

[0062]

[0077] In some embodiments, permanent magnets may be used. To increase magnetic current capability without the risk of demagnetization, rotor windings as described herein are used. At low torques, rotor winding currents can be reduced, lowering cogging (resistive) torque and eliminating the need for stronger permanent magnet active flux weakening. Using modulation of the current phase shifter angle herein, the wound rotor can be flux weakened or flux strengthened through a control mechanism (e.g., reducing or increasing current in the rotor field winding, reducing or increasing magnetic flux in the rotor pole body). As a non-limiting example, the current phase shifter angle of the synchronous excitation from the stator can be modulated. In at least some configurations, a secondary control system or additional commutation hardware, such as in a wound rotor synchronous motor, to control the stator field is not required.

[0063]

[0078] As described herein, wound rotor configurations according to the present disclosure do not require additional stator-to-rotor coupling elements. Rather, signals are transmitted using the stator and rotor windings along with the rotor laminations. This reduces costs and components, improves performance (e.g., eliminates brush ohmic losses), eliminates or controls physical contacts and wear components, reduces package size, and provides control flexibility compared to schemes that incorporate special detectors, sensors, wired or wireless connections, or brushes to transmit signals from the stator to the rotor.

[0064]

[0079] As described throughout this specification, in systems where control signals may be converted to DQ axis components, such as that shown in Figure 6, a third z-axis component also exists, which may be described as a signal or magnetic quantity that does not map directly to the D or Q axes, for example, a component orthogonal to the plane that may define the Q and D components as shown.

[0065]

[0080] In operation, field-oriented control, or vector control, involving specific modulations (e.g., modulation of signals or signal parameters) can be used to control various aspects of the rotor magnetic field. These modulations can be used to adjust the signal excitation coupling between the stator and rotor and to control the stator excitation waves (e.g., relative position and magnitude) relative to the rotor. Thus, the rotor response, i.e., the direct correlation of the currents induced in the rotor windings, can be effectively "engineered" by the stator and inverter. In other words, such control can shape the dynamic behavior of the machine in response to the currents in the D-axis and Q-axis magnetic fields, as coordinated by a controller such as controller 104 or controller 700 (FIG. 7). Among other strategies (e.g., torque generation), vector modulation can be used to help define the modulation of the current phase shifter angles.

[0066]

[0081] This disclosure recognizes that vector control modulation can be used to directly influence rotor response through a given stator signal. Furthermore, these rotor responses may be modulated on either the D-axis or Q-axis, and may be achieved using current phase shifter angle modulation. The relative effectiveness of the current phase shifter angle modulation may be proportional to both the magnitude of the modulation and the rate of change (e.g., over time). The rate at which the current phase shifter angle is adjusted may be varied by the controller and selected for the intended effect on the rotor material or rotor response. In some cases, the frequency may be selected based on the machine speed, while in other cases, a fixed modulation may be selected. The frequency of the modulation may be selected based on various considerations. For example, in some configurations, the frequency may be at least 2-4 times higher than the fundamental frequency of the machine. In other situations, the modulation may be 5-10 times higher than the fundamental frequency of the machine. In yet further configurations, the frequency may be 10-30 times higher than the fundamental frequency of the machine. For example, in some configurations, the frequency may be selected to prevent interaction with torque generation (e.g., to reduce torque ripple). The current phase shifter angle can be controlled using vector component control, which involves controlling the fundamental frequency current expressed in the DQ reference frame shown in Figure 6 by i d , i q , and i z (e.g., the main control component including the current phase shifter angle). These signals may be directly modulated, or an independent excitation modulation may be added to either the D / Q axis that is added to the fundamental current to give the total stator current: i dtotal =i d +i dmodulation (3) i qtotal =i q +i qmoduation (4) i ztotal =i z +i zmodulation (5) where i d , i q , and i zare the normal excitation currents along each axis, and i dexcitation , i qexcitation , and i zexcitation is an independent modulation signal that can be selected and controlled by a motor controller or other controller as described in more detail below. The modulation can be selected to be sinusoidal or can take any form, for example, such modulation can be further described as: i dexcitation =m d cos(w d t) (6) i qexcitation =m q sin(w q t) (7) i zexcitation =m z sin(w z t) (8) The modulation magnitude and frequency can be selected independently for each component and vector sum to vary the current phase shifter angle, or the current phase shifter angle (γ) can be directly controlled to vary the main component as follows: i dtotal =i d *cos(γ) (9) i qtotal =i q *sin(γ) (10) i ztotal =i z *sin(γ) (11) Similarly, the following modulation can be performed with respect to the set current phase shifter angle: i dtotal =i d *cos(γ+γ moduation ) (12) i qtotal =i q *sin(γ+γ moduation ) (13) i ztotal =i z *sin(γ+γ moduation ) (14) where γ modulation can be described, for example, as a sinusoidal oscillation about a fixed current angle. gamma dmoduation =md cos(w d t) (15) gamma qmodulation =m q sin(w q t) (16) gamma zmodulation =m z sin(w z t) (17)

[0067]

[0082] In each case, modulation may be applied to a single axis, leaving the other two axes unmodulated, and used to generate rotor response. Alternatively or additionally, D-axis current modulation can be used, and varied in parallel with Q-axis current modulation, with the goal of controlling or minimizing torque ripple. If D-axis modulation is insufficient, Q-axis modulation can be used. In some implementations, Q-axis modulation is used in combination with D-axis modulation to create rotating vector injection. Z-axis modulation does not inherently affect torque ripple and does not require knowledge of the DQ reference frame. However, Z-axis modulation often has limited effect on the rotor, but can be used to couple the stator to the rotor for either power or side-information coupling (e.g., speed and / or position).

[0068]

[0083] The frequency of current modulation, i.e., the current phase shifter oscillation, can be described by a duty cycle. This duty cycle can be divided into two main components: flux injection (e.g., D-axis) and torque generation (e.g., Q-axis). In starting conditions, before the split operation between D-axis and Q-axis for torque generation, the duty cycle on D-axis for the strong rotor flux injection may be 100%, or 75-100%, or 40-100%. In split operation, it may be a 50%-50% split, 30%-70%, 20-80%, or 10-90% split (D-axis:Q-axis). This may also manifest as oscillations around the current phase shifter angle during steady-state or quasi-steady-state operation, with the current phase shifter angle and resulting magnetic field varying by 5, 10, 20, or even 30-45 degrees around that angle. In some implementations, the frequency of the vibration or amplitude modulation can be varied to both elicit rotor response and / or limit torque ripple during operation.

[0069]

[0084] Additionally, the control strategy may utilize higher frequency operation, i.e., pulsing, to limit the amount of magnetic flux decaying over time in the rotor coils. That is, by shortening the time step of the rotor MMF cycle (which decays over time), it is possible to reduce the dispersion of magnetic flux across the rotor coils, making the flux stiffer and reducing negative torque moments or associated torque ripple. Additional signal modulation, such as skewed signal, trapezoidal, or pulse-width modulation (PWM) techniques, may be used to aid in flux injection into the rotor, limit torque ripple, and smooth transitions between current phase shifter angles during operation.

[0070]

[0085] Because stator-side currents may correspond to stator-side voltages, schemes involving signals embedded in currents may correspond to equivalent schemes involving signals embedded in voltages. Implementations described throughout this disclosure with respect to stator-side voltage signals may be equivalent to stator-side current signals, and vice versa, and may be similarly described.

[0071]

[0086] As described above, control of the rotor magnetic field can be manipulated by a controller through the stator windings using modulation of the current phase shifter angle. This modulation can be defined by magnitude and frequency and can be observed by the machine's magnetic field, stator excitation, and primary control components. Current phase shifter angle modulation can be used to transfer power to AC coils, with the current angle oscillation defined with respect to a set operating point of the current angle defined by a DQ reference frame (e.g., the current angle can be modulated to achieve a target torque per ampere, or MTPA). Current phase shifter angle modulation perturbations can be defined by the oscillation, magnitude, and frequency of the excitation magnetic field. Modulation of the current magnitude at a given current phase shifter angle can be used to transfer power to the rotor or induce a response within the rotor, with the largest response being seen at the current angle (in the DQ reference frame of a given pole) that is most coupled to the rotor. For example, for a wound rotor aligned with the D axis relative to the axes of the synchronous reference frame, maximum power transfer occurs when the current phase shifter angle is 0° electrical (where 0° electrical is defined as the D axis of the synchronous reference frame).

[0072]

[0087] FIG. 7 is a block diagram of an example controller 700 that may be used in embodiments of the present disclosure. The controller 700 may be used in addition to or instead of the electric motor controller 104 described above. In the former example, the controller 700 and the electric motor controller 104 may be combined into a single integrated controller, or the controller 700 and the electric motor controller 104 may be separate, individual controllers. The controller 700 may, among other things, monitor parameters of the electric machines (300, 400) and send signals to actuate and / or adjust various operating parameters of the electric machines (300, 400). As shown in FIG. 7 , the controller 700, in certain examples, includes a processor 750 (e.g., implemented as a single processor or multiple processors) and a memory 752 (e.g., implemented as a single memory or multiple memories) that includes instructions that cause the processor 750 to perform the operations described herein. The processor 750 is coupled to an input / output (I / O) interface 754 for sending and receiving communications with components within the electric machines (300, 400), including, for example, rotor position sensors or current sensors. In certain examples, the controller 700 may additionally communicate status and send actuation and / or control signals (including power or drive signals to the stator) to one or more of the various electromechanical components of the electric machines (300, 400) (such as power or drive signals to the stator) and other sensors (e.g., temperature sensors, vibration sensors, and other types of sensors) provided on the electric machines (300, 400). Communications may be wired, wireless, or a combination of wired and wireless. In some implementations, the controller 700 may be a distributed controller with various parts located in different locations, for example, in different parts of a vehicle. Additional controllers may be used in combination with the controller 700, either as standalone controllers or networked controllers, without departing from this disclosure.

[0073]

[0088] The controller 700 may have various levels of autonomy for controlling the electric machine (300, 400). For example, the controller 700 may begin detecting a change in load and / or speed, and an operator adjusts the power frequency, current magnitude, and / or current angle. Alternatively, the controller 700 may begin detecting a change in load and / or speed, receive additional input from an operator, and adjust the frequency, current magnitude, and / or current angle without other input from the operator. Alternatively, the controller 700 may begin detecting a change in load and / or speed, and adjust the frequency, current magnitude, and / or current angle without other input from the operator. In general, the controller 700 may receive a signal indicative of a desired operating point, may receive a signal indicative of a current operating point, and may then adjust the frequency, current magnitude, and / or current angle accordingly to converge the current operating point to the desired operating point.

[0074]

[0089] For example, in operation, the controller may be configured to send control signals to the stator windings to excite them and generate a stator magnetic field within the stator. The controller may be configured to generate the stator magnetic field by sending current through the stator at a current angle and magnitude and actively adjusting the current angle and magnitude depending on the operating conditions of the electric machine (300, 400). In some implementations, the current phase shifter angle 318 increases ahead of the rotor poles (308, 408) in the direction of movement during high torque conditions. That is, an increase in the current phase shifter angle 318 may be necessary when more current per unit torque is required. Generally, a larger current phase shifter angle 318 activates more of the rotor coils (310, 410) (more current flows through the coils) due to a smaller D-axis component 312. In other words, the larger the current phase shifter angle 318, the faster the magnetic field of each rotor winding decays. Although increased activity in the coils may lead to increased unmitigated torque ripple, the increased current amplitude during the increased D-axis component experienced by each pole can counteract the potential negative torque generated by increasing the current angle 318. Alternatively or additionally, the current phase shifter angle 318 is reduced during high speed, low torque operation. Alternatively or additionally, the current angle can become negative during braking operation. Regardless of the operating mode used, the controller 700 can adjust the current angle and / or current amplitude to meet the current demands of the electric machine (300, 400) in a given situation.

[0075]

[0090] In particular, the current phase shifter angles or current amplitudes of the machine's major components can be adjusted during operation to generate torque. In some instances, for example, if the rotor has sufficient field strength, no (or less) magnetizing current may be applied compared to previous time steps. In other instances, such as high-speed operation, it may be possible to lower the rotor field to reduce back electromotive force (EMF) and provide voltage headroom, reduce cogging torque, limit torque ripple, and avoid active field-weakening operation.

[0076]

[0091] The controller can communicate with the rotor through the stator at a wide range of frequencies, for example, from 50 to 1000 Hertz (Hz). In some implementations, communication occurs at 100 to 1000 Hz. In either case, the system can transmit changes faster than conventional systems. For example, conventional squirrel-cage induction machines communicate at essentially 7 Hz. The high-frequency transmission capability allows the controller 700 to actively reduce torque ripple regardless of operating conditions and quickly respond to changing operating conditions.

[0077]

[0092] FIG. 8 is a flowchart of a method 800 that can be used in embodiments of the present disclosure. All or a portion of method 800 can be performed by controller 700 and / or controller 104. At 802, the stator coils are energized. At 804, the stator magnetic field changes a corresponding rotor magnetic field in a ferromagnetic material in the rotor. At 806, the shift in the stator magnetic field generates a tangential force on the rotor. At 808, the generated tangential force moves the rotor. The stator magnetic field and rotor are maintained synchronized with each other during operation. At 810, decay of magnetic flux in the rotor is resisted by current in the rotor coils in response to the magnetic field shift. At 812, current is sent through the stator at a current angle. Typically, the current angle leads the rotor poles in the direction of movement. In some examples, at 814, the magnitude of the current is adjusted depending on operating conditions. In some examples, the current angle relative to the rotor poles (D-axis) is adjusted in response to operating conditions at 816. Notably, steps 814 and 816 are shown dotted because both steps are not required, nor are they required to be in that order; that is, the current magnitude and current angle may be adjusted separately and independently of each other.

[0078]

[0093] The current electric machine operating power is then compared to the desired electric machine operating power. If the current electric machine operating power is at the desired electric machine operating power, the machine continues to operate using the most recently adjusted parameters of the stator current. If not, the process repeats, returning to adjusting at least one of the stator current magnitude or current angle until the current electric machine operating power is at the desired electric machine operating power.

[0079]

[0094] Referring now to FIG. 9A, a non-limiting example of process control according to the present disclosure is provided. In particular, FIG. 9A provides an exemplary flowchart for controlling an electric motor system to achieve increased torque 900 according to the present disclosure. Process 900 begins with a request for increased torque at 902. According to the present disclosure, fulfilling this request can be conceptualized as performing two parallel workflows. However, in practice, the controller need not be programmed or designed to operate in independent, parallel, or other different flows. To fulfill the request for increased torque 902, the controller determines that achieving the increased torque can be done by increasing the rotor flux at 904. To do this, the controller determines the rotor flux at 906. d This increases the rotor flux at 908. This continues until the desired rotor torque is achieved, after which I d However, while attempting to increase the rotor flux, the controller recognizes that Q-axis current modulation can also be used and varied in parallel with D-axis current modulation with the goal of controlling or minimizing torque ripple. Thus, the controller also works to maintain torque performance at 912. To this end, the controller also reduces I at 914. q , thereby obtaining the desired torque increase at 916, but without the adverse effects of unstable torque performance as can be caused by torque ripple.

[0080]

[0095] 9B, another non-limiting example of a control process 918 for responding to a request for increased torque at 920 is provided. In response to the request at 920, the controller determines that achieving increased torque can be achieved by requesting an increase in rotor flux at 922. To accomplish this, the controller attempts to modulate the current angle toward the D-axis at 924, as this readily increases the rotor flux at 924, and the rotor field is further controlled by modulating the current angle toward the Q-axis at 928. In parallel, the controller modulates the I-axis as described above. q This acts to maintain torque performance at 930 by modulating the torque, thus resulting in the requested torque increase at 934.

[0081]

[0096] 9C, another non-limiting example of a control process for reaching a desired torque profile is provided at 936. At start-up, the rotor is locked at 938. To begin rotation, the current angle is modulated toward the D-axis at 940, and rotor flux is established or increased as the rotor moves toward the D-axis at 942. The current angle is modulated toward the Q-axis at 944, and this process continues until the desired torque is generated at 946.

[0082]

[0097] 9D provides yet another non-limiting example of a control process for reaching a desired torque at 948. In this case, the process begins with the motor already running at high speed 950. The duty cycle of the current angle modulation is reduced at 952, and the amplitude of the current modulation is reduced at 954. As a result, the rotor flux decreases at 956. The back EMF decreases at 958, and the reduced rotor flux at 960 reduces the cogging torque. This control ultimately results in an increase in torque at 962, given the high speed of the motor at 950.

[0083]

[0098] Thus, the described system and method has been found to lead to a net increase in torque through sinusoidal excitation due to asymmetric flux vector control of the rotor field lines along the stator D-axis, resulting in a net rotor field D-axis current injection. As a result, net D-axis current injection is possible in conventional circuits with analog circuitry. Machines with rotor coil configurations experience less saturation and provide a net advantage over shorted coils in terms of average torque generation. Net D-axis current injection allows for greater sheet current density under equivalent stator excitation due to rotor coil reactive current.

[0084]

[0099] As shown in Figure 10, a graph of the average magnetic field strength is provided for three different interior permanent magnet machines. The first machine does not include a coil. In the second, the machine includes a shorted coil. As can be clearly seen from Figure 10, the magnetic field strength increases in the machine with the coil structure compared to the machine without a coil.

[0085]

[0100] Thus, particular implementations of the inventive subject matter have been described. Other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results.

Claims

1. a stator defining a plurality of stator poles with associated stator windings configured to receive a stator current; a rotor defining a plurality of rotor poles fixed by associated rotor windings, the rotor defining a magnetic field that can be excited by a magnetic field generated by the stator windings in response to the stator current being received by the stator windings to produce relative motion between the rotor and the stator, the rotor being maintained in synchronization with the magnetic field generated by the stator during operation of the electric machine; a controller, directing the stator current through the stator winding at a current angle measured from the nearest one of the rotor poles; determining a desired operational output of the electric machine; determining a desired rotor motion corresponding to the desired operational output of the electric machine; calculating a vector control modulation to be applied to the stator to produce the desired rotor motion; adjusting the current angle of the stator current based on the vector control modulation to cause the rotor to perform the desired rotor motion and achieve the desired operating output of the electric machine; With a controller configured as An electric machine comprising:

2. The electric machine of claim 1 , wherein the controller is further configured to modulate at least one of a magnitude or a frequency of the stator current based on the vector control modulation.

3. The electric machine of claim 1 , wherein the controller is configured to adjust the current angle in only one axis of the electric machine.

4. The electric machine of claim 3 , wherein the one axis is one of a D-axis or a Q-axis of the electric machine.

5. The controller: modulating the D-axis current to control rotor torque ripple while the rotor achieves the desired rotor motion; Achieving the desired operating output of the electric machine The electric machine of claim 4 , configured as follows:

6. The controller: adjusting at least one of the frequency or amplitude of the stator current to cause the rotor to achieve the desired rotor motion; Achieving the desired operating output of the electric machine, or controlling rotor torque ripple when the rotor is performing the desired rotor motion and achieving the desired operating output of the electric machine. The electric machine of claim 1 further configured as follows:

7. 2. The electric machine of claim 1, wherein the controller is configured to increase the current angle of the stator current along the stator windings to lead the rotor poles to deliver increased torque to achieve the desired operating output of the electric machine.

8. The electric machine of claim 7 , wherein the controller is configured to increase the magnitude of the stator current while simultaneously increasing the current angle of the stator current to control rotor torque ripple.

9. 2. The electric machine of claim 1, wherein the controller is configured to decrease the stator current angle and deliver reduced torque at an increased rotor speed to achieve the desired operating output of the electric machine.

10. The electric machine of claim 1 , wherein the controller is configured to cause the stator current angle to become negative to provide a braking function for the rotor to achieve the desired operating output of the electric machine.

11. The stator winding includes a distributed winding, and the rotor includes: concentrated winding, Salient pole winding, Non-lap winding, or Permanent magnet The electric machine of claim 1 , comprising:

12. The electric machine of claim 11 , wherein the rotor includes permanent magnets, the permanent magnets being substantially aligned with the rotor poles.

13. The controller: using the stator current to excite the stator windings; a stator magnetic field is generated within the stator by the excited stator windings; the stator magnetic field generating a corresponding rotor magnetic field in a ferromagnetic material within the rotor; a magnetic field shift of the stator to generate a tangential force on the rotor; The generated tangential force moves the rotor; maintaining magnetic flux in the rotor by current in rotor coils responsive to the magnetic field shift; The stator field and the rotor are maintained in synchronization with each other during operation. The electric machine of claim 1 further configured as follows:

14. 1. A method for controlling an electric machine, the method comprising: exciting a stator winding of a stator with a stator current to generate a stator magnetic field within the stator; the stator magnetic field causing a corresponding rotor magnetic field to change within a ferromagnetic material within a rotor, the rotor defining a plurality of rotor poles; generating a tangential force on the rotor due to the shift of the stator magnetic field; moving the rotor with the generated tangential force, wherein the stator field and the rotor are maintained in synchronization with one another during operation; resisting decay of magnetic flux in the rotor with current in a rotor coil in response to the magnetic field shift; adjusting a current angle of the stator current measured from a nearest one of the rotor poles based on a desired operating output of the electric machine; adjusting a magnitude of the stator current independently of the current angle of the stator current based on the desired operating output of the electric machine; A method comprising:

15. The method of claim 14 further comprising modulating a frequency of the stator current based on the desired operating output of the electric machine.

16. The method of claim 14 , wherein adjusting the current angle comprises adjusting the current angle only in one axis of the electric machine.

17. 15. The method of claim 14, further comprising selecting an adjustment to at least one of the current angle or the current magnitude to control rotor torque ripple while achieving the desired operating output of the electric machine.

18. 1. A wound field rotor synchronous machine, comprising: a stator defining a plurality of stator poles with associated stator windings; a rotor defining a plurality of rotor poles, the rotor configured to rotate synchronously with the stator, the rotor including a rotor winding associated with each of the rotor poles, the rotor windings configured to be excited by a magnetic field generated by the stator winding, the excited rotor windings generating a rotor magnetic field; a controller, exciting the stator winding with a stator current having a magnitude and phase angle measured relative to a nearest one of the rotor poles; Achieving the desired operating output of said wound field rotor synchronous machine by: determining rotor performance to achieve the desired operating output of the wound field rotor synchronous machine; adjusting one of the phase angle or the magnitude of the stator current to achieve the desired operating output of the wound field rotor synchronous machine; receiving a signal indicative of a present operating output of the wound field rotor synchronous machine; comparing the current operating output of the wound field rotor synchronous machine to the desired operating output of the wound field rotor synchronous machine; adjusting the other of the phase angle or the magnitude of the stator current to achieve the desired operating output of the wound field rotor synchronous machine; thereby achieving the desired operating output of the wound field rotor synchronous machine. With a controller configured as A wound field rotor synchronous machine comprising:

19. 20. The wound field rotor synchronous machine of claim 18, wherein the controller is further configured to modulate a frequency of the stator current in response to the desired operating output of the wound field rotor synchronous electric machine.

20. 20. The wound field rotor synchronous machine of claim 18, wherein to adjust the current angle, the controller is further configured to adjust the current angle only in only one axis of the wound field rotor synchronous electric machine.

21. 20. The wound field rotor synchronous machine of claim 18, wherein the controller is further configured to select adjustments to at least one of the current angle or the current magnitude to control rotor torque ripple while achieving the desired operating output of the wound field rotor synchronous electric machine.

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