Variable-FLUX-intensifying electric machines using iron nitride permanent magnets

Abstract

A rotor for an electric machine has a plurality of pairs of magnets disposed in the rotor near an outer portion of the rotor. The magnets have a coercivity (Hci) of 2,000 Oe to 4,000 Oe, are positioned such that magnetic poles are in line with a rotational axis of the rotor, and are affixed to the rotor by a high-permeable material. Each magnet pair has like magnetic poles facing each other, and each magnet has a longitudinal axis that aligns with a d-axis of the rotor. The rotor includes first nonmagnetic and nonconductive components with a longitudinal axis that aligns with a q-axis of the rotor, and second nonmagnetic and nonconductive components with a curved region that is concave with respect to a surface of the rotor. The magnets are centered relative to the second nonmagnetic and nonconductive components to be disposed in the curved region.

Description

VARIABLE-FLUX-INTENSIFYING ELECTRIC MACHINES USING IRON NITRIDEPERMANENT MAGNETSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. Provisional Application No. 63 / 555,842, filed on February 20, 2024, and U.S. Provisional Application No. 63 / 676,107, filed on July 26, 2024, the disclosures of which are incorporated herein by reference in their entireties for all purposes.FIELD

[0002] The present disclosure relates generally to electric machines, and more specifically to electric machines implementing permanent magnets.BACKGROUND

[0003] Electric machines, such as electric motors and generators, typically use neodymium (NdFeB) magnets and other permanent magnet materials, many with rare earth elements such as samarium cobalt (SmCo) and samarium iron nitride (SmFeN) magnets and other strategic / critical minerals (such as cobalt in AINiCo) whose supply may be limited and / or subject to disruption. Specifically, rare earth magnets are preferred because the extent to which rare-earth permanent magnet synchronous motors (PMSMs) can be flux-weakened is limited due to the high coercive force or intrinsic coercivity (Hci) of the rare earth magnets.

[0004] Externally excited electric machines, such as induction motors and direct- current (DC) brush motors, are able to achieve very high speeds, such as by reducing the external excitation, but the efficiencies of such machines are significantly lower than those of PMSMs. Known electric machine designs that use AINiCo, which are low-coercive- force (LCF) magnet, are also susceptible to demagnetization with high stator currents. When the motor control electronics or the winding of such electric machine designs experience a short-circuit failure condition, permanent magnet machines, especially generators, that implement such designs may become serious and potentially fatal safety issues. For example, when there is a continued generation of voltage, it causes anunconstrained flow of current through the machine due to: (i) overheating of the machine due to the flow of eddy currents caused by the magnetic field of the spinning rotor, (ii) overheating of the machine due to unconstrained current flow in the coil windings, and / or (iii) high voltage on the motor housing, which should be at ground, due to the eddy currents caused by the magnetic field of the spinning rotor.

[0005] As such, there is a need for motors that do not use any rare earth metals or strategic / critical minerals, as well as a system that effectively controls operation of such motors to reduce the risk of failure caused by demagnetization as commonly found in known permanent magnet machines that do not use such rare earth metals or strategic / critical minerals.SUMMARY

[0006] Disclosed herein are examples of variable-flux-intensifying electric machines using permanent magnets with low coercive force, such as iron nitride magnets.

[0007] According to one example (“Example 1”), the rotor includes a plurality of pairs of magnets disposed in the rotor near an outer portion of the rotor. The magnets have a coercivity (Hci) of 2,000 Oe to 4,000 Oe; the magnets are positioned such that magnetic poles are in line with a rotational axis of the rotor; the magnets are affixed to the rotor by a high-permeable material; each pair of the magnets has like magnetic poles facing each other; and each of the magnets has a longitudinal axis that aligns with a d- axis of the rotor. A plurality of first nonmagnetic and nonconductive components are disposed in the rotor. Each of the first nonmagnetic and nonconductive components has a longitudinal axis that aligns with a q-axis of the rotor. A plurality of second nonmagnetic and nonconductive components are disposed in the rotor near the outer portion of the rotor. Each of the second nonmagnetic and nonconductive components has a curved region that is concave with respect to a surface of the rotor, and an end portion near the surface of the rotor. The magnets are centered relative to the second nonmagnetic and nonconductive components such that each of the magnets is disposed in the curved region.

[0008] According to another example (“Example 2”) further to Example 1 , the second nonmagnetic and nonconductive components include smaller-radius componentsand larger-radius components having greater radius than the smaller-radius components. The smaller-radius components are disposed closer to the surface of the rotor than the larger-radius components.

[0009] According to another example (“Example 3”) further to Example 1 or 2, the surface of the rotor has a plurality of indented portions in proximity to the magnets.

[0010] According to another example (“Example 4”) further to any one of Examples 1 to 3, the magnets are disposed adjacent to each other along the rotational axis of the rotor.

[0011] According to another example (“Example 5”) further to any one of Examples 1 to 4, each of the magnets has a volume-to-weight ratio of greater than 0.1 .

[0012] According to another example (“Example 6”) further to any one of Examples 1 to 5, each of the magnets has a permeability of from 1 .8 to 2.0.

[0013] According to another example (“Example 7”) further to any one of Examples 1 to 6, the magnets include iron nitride (FeN) magnets.

[0014] According to another example (“Example 8”) further to any one of Examples 1 to 7, a pair of the plurality of pairs of magnets includes a first magnet and a second magnet such that a first N pole of the first magnet faces a second N pole of the second magnet.

[0015] According to another example (“Example 9”) further to any one of Examples 1 to 7, a pair of the plurality of pairs of magnets includes a first magnet and a second magnet such that a first N pole of the first magnet faces a second N pole of the second magnet.

[0016] According to another example (“Example 10”) further to any one of Examples 1 to 9, the each of the first nonmagnetic and nonconductive components has a transverse distance that is measured perpendicular to the longitudinal axis of the first nonmagnetic and nonconductive component, and the transverse distance measured along the longitudinal axis of the first nonmagnetic and nonconductive component is consistent.

[0017] According to another example (“Example 11”) further to any one of Examples 1 to 9, the each of the first nonmagnetic and nonconductive components has a transverse distance that is measured perpendicular to the longitudinal axis of the firstnonmagnetic and nonconductive component, and the transverse distance varies along the longitudinal axis of the first nonmagnetic and nonconductive component such that the transverse distance measured near the outer portion of the rotor is longer than the transverse distance measured near an inner portion of the rotor.

[0018] According to another example (“Example 12”) further to any one of Examples 1 to 9, the each of the first nonmagnetic and nonconductive components has a transverse distance that is measured perpendicular to the longitudinal axis of the first nonmagnetic and nonconductive component, and the transverse distance varies along the longitudinal axis of the first nonmagnetic and nonconductive component such that the transverse distance measured near the outer portion of the rotor is shorter than the transverse distance measured near an inner portion of the rotor.

[0019] According to another example (“Example 13”) further to any one of Examples 1 to 12, one or more of the first nonmagnetic and nonconductive components and the second nonmagnetic and nonconductive components are made of plastic or resin.

[0020] According to another example (“Example 14”) further to any one of Examples 1 to 13, the magnets and the first nonmagnetic and nonconductive components are disposed in an interspersed configuration in which each of the first nonmagnetic and nonconductive components is disposed between two neighboring magnets of the plurality of pairs of magnets.

[0021] According to another example (“Example 15”), an electric machine includes a stator and the rotor of any one of Examples 1 to 14, and the rotor is disposed in the stator.

[0022] According to one example (“Example 16”), a method of operating an electric machine with the rotor according to any one of Examples 1 to 14 includes: receiving, by a controller operatively coupled with the rotor, a torque command; and performing, by the controller based on the torque command, flux-intensifying operation by operating the rotor to develop a positive reluctance torque and align a current distribution of the stator with a positive d-axis of the rotor such that an overall torque reaches a maximum value at a negative current angle in a field intensifying operation range of the rotor, where inductance is greater in the d-axis of the rotor than in a q-axis of the rotor.

[0023] According to one example (“Example 17”), a method of operating a rotor includes: receiving, by a controller operatively coupled with the rotor, a torque command and a speed command; determining, by the controller based on the torque command and the speed command, an operation type for the rotor; and operating the rotor by applying electric current to the rotor according to the operation type as determined. The operation type is selected from one of the following: (a) a high-torque / low-speed operation in which the rotor operates in a flux-intensified region of electric current angle, (b) a mid-range torque / speed operation in which the rotor operates in a zero-magnetized region of electric current angle, and (c) a low-torque / high-speed operation in which the rotor operates in a flux-weakened region of electric current angle. The rotor includes a plurality of pairs of magnets disposed therein near an outer portion of the rotor. The magnets have a coercivity (Hci) of 2,000 Oe to 4,000 Oe, the magnets are positioned such that magnetic poles are in line with a rotational axis of the rotor, each pair of the magnets has like magnetic poles facing each other, and each of the magnets has a longitudinal axis that aligns with a d-axis of the rotor.

[0024] According to another example (“Example 18”) further to Example 17, in the high-torque / low-speed operation, the rotor is operated to provide torque that is at least 60% of a maximum torque of the rotor and speed that is no greater than 30% of a maximum speed of the rotor.

[0025] According to another example (“Example 19”) further to Example 17, in the mid-range torque / speed operation, the rotor is operated to provide torque that is between 30% and 60% of a maximum torque of the rotor and speed that is between 30% and 60% of a maximum speed of the rotor.

[0026] According to another example (“Example 20”) further to Example 17, in the low-torque / high-speed operation, the rotor is operated to provide torque that is no greater than 30% of a maximum torque of the rotor and speed that is at least 60% of a maximum speed of the rotor.

[0027] According to one example (“Example 21”), a method of making a rotor of an electric machine includes: providing a rotor body comprising a plurality of laminations in a stacked configuration, the rotor body having a plurality of first slots, a plurality of second slots, and a plurality of third slots; disposing a plurality of pairs of magnets in the first slotsof the rotor body near an outer portion of the rotor body, wherein the magnets have a coercivity (Hci) of 2,000 Oe to 4,000 Oe, the magnets are positioned such that magnetic poles are in line with a rotational axis of the rotor, the magnets are affixed to the rotor body by a high-permeable material, each pair of the magnets has like magnetic poles facing each other, and each of the magnets has a longitudinal axis that aligns with a d- axis of the rotor; disposing a plurality of first nonmagnetic and nonconductive components in the second slots of the rotor body, each of the first nonmagnetic and nonconductive components having a longitudinal axis that aligns with a q-axis of the rotor; and disposing a plurality of second nonmagnetic and nonconductive components in the third slots of the rotor body near the outer portion of the rotor body, wherein each of the second nonmagnetic and nonconductive components has a curved region that is concave with respect to a surface of the rotor body, and an end portion near the surface of the rotor body, and the magnets are centered relative to the second nonmagnetic and nonconductive components such that each of the magnets is disposed in the curved region.

[0028] According to another example (“Example 22”) further to Example 21 , disposing the second nonmagnetic and nonconductive components comprises disposing a plurality of smaller-radius components and a plurality of larger-radius components having greater radius than the smaller-radius components, wherein the smaller-radius components are disposed closer to the surface of the rotor than the larger-radius components.

[0029] According to another example (“Example 23”) further to Example 21 or 22, disposing the magnets comprises disposing the magnets adjacent to each other along the rotational axis of the rotor.

[0030] According to another example (“Example 24”) further to any one of Examples 21 to 23, a pair of the plurality of pairs of magnets includes a first magnet and a second magnet such that a first N pole of the first magnet faces a second N pole of the second magnet.

[0031] According to another example (“Example 25”) further to any one of Examples 21 to 23, a pair of the plurality of pairs of magnets includes a first magnet anda second magnet such that a first S pole of the first magnet faces a second S pole of the second magnet.

[0032] According to another example (“Example 26”) further to any one of Examples 21 to 25, the magnets and the first nonmagnetic and nonconductive components are disposed in an interspersed configuration in which each of the first nonmagnetic and nonconductive components is disposed between two neighboring magnets of the plurality of pairs of magnets.BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments, and together with the description serve to explain the principles of the disclosure.

[0034] FIG. 1 is a schematic diagram of a system or electric machine system as disclosed herein.

[0035] FIGs. 2A through 2C show cross-sectional views of a rotor in different configurations as explained herein.

[0036] FIGs. 3A through 3C show diagrams illustrating the current vectors for maximum torque-per-ampere (MTPA) condition in the examples of FIGs. 2A through 2C, respectively.

[0037] FIGs. 4A and 4B are graphs comparing current angles and torque values for field weakening and field intensifying interior permanent magnet synchronous motors.

[0038] FIGs. 5A and 5B are graphs showing magnetic flux density (B) / magnetic field intensity (H) curves with different operating points and magnetization states as disclosed herein.

[0039] FIG. 6 shows a graphical representation of the relationship between magnetic flux linkage and torque for a range of current vectors.

[0040] FIG. 7 shows a partial view of a cross-section of an electric machine according to embodiments disclosed herein.

[0041] FIG. 8 is a graph showing a B / H curves with different load lines and recoil lines for various magnetization states as disclosed herein.

[0042] FIGs. 9A and 9B show graphical representations of efficiency / torque-speed profiles for two different motors as disclosed herein.

[0043] FIG. 10A is a graphical representation of a process of changing permanent magnet flux linkage in various speeds as disclosed herein.

[0044] FIG. 10B is a graphical representation of a difference in loss reduction between a variable flux machine as disclosed herein and a non-variable flux permanent magnet machine.

[0045] FIG. 11 A shows an optimum efficiency map for a variable flux machine as disclosed herein.

[0046] FIG. 11 B shows a magnetization state distribution map that corresponds to the optimum efficiency map of FIG. 11 A.

[0047] FIG. 12 shows a partial view of a cross-section of an electric machine according to embodiments disclosed herein.

[0048] FIG. 13 shows a magnet operating point according to embodiments disclosed herein.

[0049] FIG. 14 shows an input electrical signals to each phase without VF adjustments according to embodiments disclosed herein.

[0050] FIG. 15 shows an input electrical signals to each phase with timing of VF pulses according to embodiments disclosed herein.

[0051] FIG. 16 shows an ideal output torque of each phase according to embodiments disclosed herein.

[0052] FIG. 17 shows an ideal total motor output torque according to embodiments disclosed herein.

[0053] FIG. 18A shows a 4-pole 6-slot winding diagram for an electric machine according to embodiments disclosed herein.

[0054] FIG. 18B shows a 6-pole 9-slot winding diagram for an electric machine according to embodiments disclosed herein.

[0055] FIG. 18C shows a 8-pole 9-slot winding diagram for an electric machine according to embodiments disclosed herein.

[0056] FIG. 18D shows a 8-pole 12-slot winding diagram for an electric machine according to embodiments disclosed herein.

[0057] FIG. 19 shows a BH curve for an iron nitride permanent magnet according to embodiments disclosed herein.

[0058] FIG. 20 shows a flowchart for a process or method of operating an electric machine according to embodiments disclosed herein.

[0059] FIG. 21 shows a flowchart for a process or method of operating an electric machine according to embodiments disclosed herein.

[0060] FIG. 22 shows a flowchart for a process or method of making or manufacturing a rotor of an electric machine according to embodiments disclosed herein.DETAILED DESCRIPTION

[0061] The present disclosure is generally directed to electric machines that in their permanent magnets, do not use any rare earth metals, strategic / critical minerals, nonlanthanide series, nor non-cobalt based materials. In various implementations, the nonlanthanide, non-cobalt materials form at least 85% of the mass of the magnet component material. Various concepts also relate to a system or controller configured to improve the functionality of such electric machines.

[0062] Explanations of the terms usedLCF: low coercive force (Hci)HCF: high coercive force (Hci)PMSM: permanent magnet synchronous motorLd: direct axis stator inductanceLq: quadrature axis stator inductanceFlux intensification (Fl): the condition where Ld > Lq, also referred to as inverse saliency (configuration) or negative saliency (configuration) Flux weakening (FW): the condition where Lq > LdField weakening interior PMSM (FW-IPMSM): the PMSM configuration where Lq > LdPositive reluctance torque: a “cogging” torque that works in favor of the generated torque, occurring during flux intensificationNegative reluctance torque: a “cogging” torque that works against the generated torque, occurring during flux weakeningRecoil permeability (pr): the slope of the B vs. H curve in the working region

[0063] The positioning of the magnets within the rotor, as well as the design of ribs and bridges in the steel rotor structure, determines whether a motor design is flux intensifying (Fl) or flux weakening (FW). In some examples, the magnets may be a series of magnets laminated together. A PMSM motor design is considered FW if the directaxis inductance (Ld) is less than the quadrature-axis inductance (Lq), or Ld < Lq. A PMSM motor design is considered Fl if the direct-axis inductance (Ld) is greater than the quadrature-axis inductance (Lq), or Ld > Lq. Flux intensification, where Ld > Lq, is also called inverse saliency or negative saliency.

[0064] FIG. 1 is a schematic diagram of a system or electric machine system 100 as disclosed herein. The system includes an electric machine 102, such as a motor or generator, for example, that comprises a rotor 104 and a stator 106, as well as one or more sensors 108 coupled therewith to measure parameters associated with the rotor and / or stator, such as the speed of rotation or temperature of the motor, etc. Although it is understood that the rotor 104 may be disposed around the stator 106, in the exemplified system, the rotor 104 is disposed in the stator 106 (or the stator 106 is disposed around the rotor 104), in the preferred embodiment. The system 100 also includes a controller 110 operatively coupled with the electric machine 102 that is capable of controlling operation of the electric machine. The controller 110 may include a processing unit 112 such as a computer processor and a memory unit 114 coupled therewith. The memory unit 114 may be a non-transitory computer-readable medium storing thereon computer readable instructions, which when executed by the processing unit 112, causes the processing unit to execute any one or more of the processes or algorithm as further disclosed herein. The processes and / or algorithm may control the operation of the electric machine based on inputs such as the sensor readings.

[0065] FIGs. 2A through 2C show different examples of how magnets may be arranged in a rotor of the electric machine (rotor topology), such as in a permanent magnet synchronous motor (PMSM). FIG. 2A shows an example of surface PMSM, where the magnets are disposed on an outer surface of the rotor, surrounding the laminations of the rotor’s core. FIG. 2B shows an example of a field weakening (FW) interior PMSM, also referred to herein as FW-IPMSM, in which the magnets are disposedwithin the rotor’s core, and flux barriers are disposed on both sides of each magnet. In some examples, there are two flux barriers for each magnet, such that when there are four magnets, there are eight total flux barriers. FIG. 2C shows an example of a field intensifying (Fl) interior PMSM, also referred to herein as FI-IPMSM, in which the magnets are disposed within the rotor’s core, and the flux barriers are disposed between neighboring magnets in the q-axis, such that there is at least one flux barrier between each neighboring pair of magnets. In some examples, when there are four magnets, there are at least four flux barriers. The number of flux barriers may be the same as the number of magnets or a multiple of the number of magnets. Also shown in each figure are arrows showing the d-axis (d) and the q-axis (q), and the north and south poles (N and S) associated with the magnets are also labeled. The d-axis is a direct axis which is the axis by which flux is produced by the field winding, and the q-axis is a quadrature axis which is the axis on which torque is produced.

[0066] The natural operation of Flux Intensification (Fl) machines favors the use of a high-Br, low-Hci (LCF) magnet material such as iron nitride (FeN). An FeN LCF magnet helps optimize the torque density of a Battery Operated Electric Vehicle (BEV) traction motor attainable from an Fl machine. The magnet is pushed up the load line during operation, reducing the possibility of demagnetization and increasing the airgap flux density, which is proportional to the motor torque. When Ld>Lq, there is a positive reluctance torque which significantly boosts the torque output of the motor. In this case, there is another significant boost in motor torque with minimal current input. It can be difficult to perform Fl operation with a high-Hci (HCF) magnet material such as NdFeB, because there is a negative reluctance torque, where the cogging torque works against the generated torque and causes noise and vibration. The higher recoil permeability of FeN (pr = 1.8 - 2.0) compared to NdFeB (pr = 1.05 - 1.10) also aids Fl operation by further increasing Ld.

[0067] An FeN LCF magnet may help optimize the torque density of a Flux Intensifying BEV traction motor by pushing the magnet higher up the load line and utilizing a positive reluctance torque to add to the stator torque. The increase in torque density of an Fl motor increases the efficiency of the BEV traction motor, though typically in thelower-speed ranges of operation. This leads to use of Variable Flux (VF) technology to help improve the motor efficiency at the high-speed, low-torque operating points.

[0068] Variable Flux (VF) operation is defined as the ability to adjust the magnetization of the permanent magnets on-the-fly, while the motor is operating. It is akin to having a knob to dial in the optimum magnetization level of the magnets to maximize efficiency at any torque and speed operating point on the BEV drive cycle. VF operation is enabled through the use of FeN LCF magnets and is not possible using NdFeB HCF magnets. The primary advantage of VF operation is at high speeds, where the magnetization of the magnets can be reduced to optimize the efficiency of the motor at low-torque, high-speed operating points, presently the Achilles heel of BEV traction motors. VF operation is activated by magnetizing and demagnetizing the permanent magnets in the rotor via pulsing the stator coils with appropriate phasing and magnitude of magnetizing current.

[0069] With an appropriate VF control scheme, the magnetization of the FeN LCF magnets can be varied in either a continuous or discrete manner, a magnetic analog to a Continuously Variable Transmission (CVT) vs. a 5-speed manual transmission on an Internal Combustion Engine (ICE) automobile. This control scheme is implemented as a digitally-programmed look-up table and integrated into the drive electronics controlling the inverter, which provides current to the 3 motor phases. The natural operation of Variable Flux (VF) machines favors the use of a high-Br, low-Hci (LCF) magnet material such as FeN.

[0070] An FeN LCF helps optimize the adjustability of the VF control of the motor. VF control is generally difficult, if impossible, to perform with a high-Hci (HCF) magnet material such as NdFeB. This is because the magnitude of the current required to magnetize and demagnetize the magnets is generally too great. The higher recoil permeability of FeN (pr = 1.8 - 2.0) compared to NdFeB (pr = 1 .05 - 1 .10) also aids VF operation by increasing the gain of the mag / demag current when adjusting the magnetization of the FeN LCF magnets.

[0071] An FeN LCF magnet optimizes the efficiency of a Flux Intensifying BEV traction motor by allowing the instantaneous adjustment of the rotor flux depending upon the varying torque / speed operating points of the motor. The increase in efficiency of anFeN LCF Variable Flux BEV traction motor applies across the full speed and torque drive cycle, but the greatest and most significant efficiency gains are at the higher-speed ranges of operation.

[0072] In the examples disclosed herein, the magnets in the electric motor of FIG. 1 are magnets with low coercive force (Hci), such as iron nitride (FeN) magnets that operate as low-coercive-force (LCF) magnets and are arranged in the configuration shown in FIG. 2C, also referred to as an inverse saliency or reverse saliency configuration, such that Ld > Lq, where Ld is direct-axis (d-axis) stator inductance, and Lq is quadrature-axis (q- axis) stator inductance. For example, each of the magnets may be arranged on a d-axis of the electric machine, and one or more of the flux barriers may be arranged on a q-axis of the electric machine. In the example shown in FIG. 2A, Ld is approximately the same as Lq (in which there is little or no magnetic saliency), and in FIG. 2B, Ld<Lq (larger magnetic saliency ratio). FIGs. 3A through 3C show diagrams illustrating the current vectors for maximum torque-per-ampere (MTPA) condition in the examples of FIGs. 2A through 2C, respectively, showing the positions of the stator current (Is) and the permanent magnet flux (Apm) associated therewith.

[0073] Another characteristic of the iron nitride (FeN) magnets is the mass-to- volume advantage of the magnet. Based on the volume-to-weight related to a common magnetic saturation of rare-earth magnets to FeN magnets, the FeN magnets have a volume-to-weight ratio (mm3 / grams) of greater than 0.1 , or in some examples greater than 0.2. In some examples, the magnets have a volume-to-weight ratio of from 0.1 to 0.15, from 0.15 to 0.2, from 0.2 to 0.25, from 0.25 to 0.3, or any other suitable value within the foregoing ranges or any other suitable range between any of the foregoing ranges, as compared to rare-earth magnets which have a volume-to-weight ratio of less than 0.07. The volume-to-weight ratio may be calculated by multiplying the thickness of the magnet by the width of the magnet, and divided by the mass of the magnet. Beneficially, having a greater volume-to-weight ratio allows for the magnet to be less dense when compared toa denser magnet of equal weight. The magnet with lesser density has more volume, which offers a greater area to facilitate demagnetization or to change variable flux of the magnet. Furthermore, denser magnets generally require more cooling due to generating more heat than a magnet of lesser density.

[0074] In a typical FW-IPMSM configuration, in order to develop positive reluctance torque (which is a “cogging” torque that works in favor of the generated torque), a portion of the stator current distribution is positioned to oppose the permanent magnet flux, negative d-axis current (-Id), as shown in FIG. 4A where the x-axis represents the angles and y-axis represents the torque. FIG. 4A shows that the overall torque (which is the sum of the permanent magnet torque, or PM torque, and the reluctance torque) for Ld < Lq reaches a maximum in a positive current angle in the field weakening range. Therefore, increasing the portion of the stator current in the negative d-axis reduces the terminal voltage for operation above the base speed at the expense of increased stator ohmic losses. In the FI-IPMSM configuration, a positive reluctance torque is developed when a portion of the stator current distribution is aligned with the positive d-axis (+ Id), as shown in FIG. 4B where the overall torque for Ld > Lq reaches a maximum in a negative current angle in the field intensifying range. Specifically, the positive d-axis current facilitates the use of LCF magnets, as the positive d-axis current reinforces the permanent magnet flux. For example, in the case of FeN magnets, the rather high permeability of the FeN magnets, which are placed in the d-axis, further increases Ld. The permeability (p) of a magnet is calculated by p = B / H, where B is the magnetic flux density and H is the magnetic field intensity (or magnetic field strength) of the magnet. For FeN magnets, the permeability (p) is approximately from 1 .8 to 2.0. Operation above the base speed is possible by reducing the positive d-axis current, thereby reducing the Ohmic losses with this rotor configuration. Reducing Lq also reduces the magnetic saturation caused by the load current (lq).

[0075] The high remnant flux density (Br, also referred to as residual magnetization) of FeN provides high torque density. To further leverage and to help best take advantage of the low Hci and high Br properties of FeN, the flux intensifying (Fl) control technique may be combined with variable flux (VF) control technique to achieve variable-flux-intensifying interior permanent magnet synchronous motors (VFI-IPMSM) to be used for traction motor applications. As referred to herein, traction motor applications refer to the use of motors to drive an electric vehicle such as a battery electric vehicle (BEV) or a hybrid electric vehicle (HEV) as known in the art. Beneficially, with VF control,LCF FeN magnets are more capable of operating with variable magnetomotive force and flux characteristics.

[0076] FIG. 5A shows a graph with a portion of a B / H curve, with the x-axis representing the magnetic field intensity or H and the y-axis representing the magnetic flux density or B, comparing the nominal operating point of a magnet with a current angle of 0 degree, and the operating points of an FW-controlled and an Fl-controlled magnet, where it is shown that the operating points align with the B / H curve.

[0077] FIG. 5B shows different magnetization states, with each magnetization state (MS) having a different B / H curve represented by a different percentage of magnetization. For example, the B / H curve of the magnet at 25% magnetization state has the same slope or permeability (p) as the magnet at 100% magnetization state but is located at a lower value along the y-axis than that of the 100% magnetization state. In some examples, the FeN magnets may be intentionally de-magnetized or re-magnetized so as to control the magnet flux linkage and the back (or counter) electromotive force (EMF) voltage of the motor, thereby allowing the traction motor to operate at a higher efficiency in the high-speed regions of operation, as shown in FIG. 5B, as compared to the magnet operating point during the FW or Fl operation as shown in FIG. 5A. For example, in FIG. 5B, a permanent magnet (PM) flux linkage is variable due to the MS of magnets being changed with the application of either an increasing MS manipulation d- axis current (+ld) or a decreasing MS manipulation d-axis current (-Id), resulting in an MS that is between 0% and 100% magnetization at any given time.

[0078] The VFI-IPMSM combines the benefits of the high torque density of permanent magnet machines, the variable flux attributes of nonpermanent magnet machines, and the flux intensification of inverse saliency via Ld > Lq. Because FeN magnets enable and enhance the design of such motors, all these positive attributes combine to allow for competitive cost and performance, with improved overall drive-cycle efficiency from a traction motor with no rare earth or strategic / critical mineral content.

[0079] FIG. 6 shows the graphical relationship between magnetic flux linkage and torque for a range of current vectors, where the x-axis represents the current angle, and the y-axis represents the torque. It is shown that the overlaid torque curve for a constant current magnitude increases in value, resulting in a positive reluctance torque when apositive current angle, also referred to as a flux-intensifying current +ld, is applied. The positive current angle also increases a PM flux linkage as shown by the topmost curve.

[0080] FIG. 7 shows an electric machine 102 according to embodiments disclosed herein. The electric machine 102 includes a rotor 104 and a stator 106. The stator 106 may include any suitable configuration of lamination 702 (for example, steel lamination or lamination stacks) and coils of insulated wire 704 inserted into the lamination 702. In some examples, the stator 106 may implement hairpin windings, oil spray, and / or liquid cooling, as suitable. The rotor 104 includes a plurality of FeN LCF magnets 700 inserted in a lamination 702 so as to align with the d-axis and a plurality of flux barriers 706 located between the magnets 700 and aligning with the q-axis. The rotor 104 is configured to be capable of rotating with speeds of at or greater than 20 kRPM as well as reaching at least 55 kW power (continuous) and 100kW (peak), torque of at least 300 Nm, and power density of at least 50 kW / L, to meet or exceed the targets of USDRIVE Partnership Plan 2025 set by the U.S. Department of Energy. In some examples, there may also be a d- axis flux bypass component 708 (which may be part of the lamination or an insertable component made of a different material from the lamination) located between two flux barriers 706. The shape of one or more of the flux barriers 706 may include for example a hemisphere, trapezoid, arch, or any other suitable configuration as known in the art.

[0081] FIG. 8 shows a B / H curve or de-magnetization curve, with the x-axis representing the magnetic field intensity or H and the y-axis representing the magnetic flux density or B, for de-magnetization of magnets as used in the embodiments disclosed herein. A recoil permeability represents the slope of the B / H curve in the working or operating region. As such, a recoil line shows the path of the operating point. Also shown are a nominal load line as well as two additional load lines for different configurations of constant permanent magnets (CPMs). Flux intensifying (Fl) adjusts the magnet flux by pushing the magnet up the load line, and flux weakening (FW) adjusts the magnet flux by pulling it down the load line. The CPMs may be arranged in a series or parallel configuration, for example. The nominal load line is the line that begins from the origin and intersects the B / H curve at the operating point (A). In a series CPM configuration, the load line retains the same slope as the nominal load line and shifts to the right to intersect the B / H curve at As, and in a parallel CPM configuration, the load line shifts tothe left to intersect the B / H curve at AP. In different paths of operating points, for example via the different recoil lines that either passes through point D or E (refer to FIG. 5B for such paths as shown by the arrows), the B / H curve may pass through points Cs, C, and CP(if via point D) or through points Fs, F, and FP(if via point E), with the curve passing through Cs, C, and CPhaving a lower magnetization than the curve passing through Fs, F, and FP.

[0082] FeN is built upon a compound of iron and nitrogen, a”-FeieN2, and the precursors of FeN are iron oxide and ammonia, both of which are abundant commodities. FeN is also distinguished by low temperature coefficients of both remanent magnetization (Br) and intrinsic coercivity (Hci). For comparison, Table 1 below shows the key performance metrics for FeN with bonded and sintered grades of NdFeB magnet, which implements neodymium which is a rare-earth metal. Because of the exceptional temperature stability (very low alpha and beta, which are the temperature coefficients for permanent magnets as shown in the table below) and higher electrical resistivity of FeN (such that, with high resistivity, eddy currents will not heat up the magnets at high speeds), the use of cooling for the rotor can also be minimized, which may be beneficial in simplifying the manufacturing process by eliminating the number of components in the final design of the motor.Table 1 : Key performance metrics for FeN with bonded and sintered grades of NdFeB

[0083] Benefits of implementing the VFI-IPMSM operation for electric machines using magnets with low Hci, or LCF magnets, are explained below.

[0084] Rare earth magnets such as neodymium magnets can maintain certain levels of magnetic strength as temperature rises up to a certain level, and the magnetic strength experiences a gradual drop with an increase in temperature. However, LCF magnets such as FeN magnets may experience a drastic drop in magnetic strength once the temperature increases past a certain threshold. The drastic drop may be, for example, at least 70% reduction, at least 80% reduction, or at least 90% reduction in magnetic strength as temperature increases past 210 degrees Celsius (for example, when reaching 220 degrees Celsius). FeN magnets, therefore, are typically eliminated as a candidate for the use as a voltage-generating current source, so as to prevent high voltage from building up on the motor housing, and to allow the failed electric machine to cool down to a safe temperature.

[0085] With the implementation of the Fl-controlled design (Ld > Lq) for the electric machine, the risk of demagnetization during operation in the electric machine can beminimized or mitigated, even when the electric machine utilizes FeN magnets that are naturally more susceptible to such demagnetization at higher temperatures, for example, as compared to the more commonly employed FW-controlled design (Lq > Ld), thus improving reliability of the electric machine. As such, the VFI-IPMSM operation combines the benefits of the high torque density of permanent magnet machines, the variable flux attributes of nonpermanent magnet machines, and the flux intensification of inverse saliency via Ld > Lq, possibly increasing the overall efficiency of the traction motor by more than 2 percentage points over the entire drive cycle of an EV, especially at higher speeds.

[0086] Such benefits are in addition to the advantages offered by significantly reducing the use of rare earth metals and / or strategic / critical minerals from traction motors, which is a more environmentally-friendly, ethically-sourced, as well as economically-affordable alternative to continuing the use of rare earth metals and / or strategic / critical minerals in electric machine or EV production. Because FeN magnets enable and enhance the design of such electric motors, all these positive attributes may be combined to allow for competitive cost and performance, with improved overall drivecycle efficiency over an entire drive cycle speed or torque range, from a traction motor with no rare earth or strategic metal content.

[0087] The U.S. Department of Energy, in its USDRIVE Partnership Plan 2025, indicates that one of key requirements for a traction motor to be marketable to the public is the capability of the traction motor to maintain a high efficiency over a whole driving cycle, targeting for a power density of greater than 50 kW / L. A bottleneck may exist for traction motors with nonadjustable PM flux linkage in conventional PM machines in that there is a conflict between high-speed and low-speed operations, due to the high torque demand at low speeds and the high power demand at high speeds, thereby causing a low efficiency in light-load or high-speed regions of operation during its driving cycle.

[0088] FIGs. 9A and 9B show two representations of efficiency / torque-speed profiles, where the x-axis represents the speed and the y-axis represents the torque / power, for two different PMSMs. In FIG. 9A, the efficiency / torque-speed profile of a conventional PMSM using high-coercive-force (HCF) magnets with nonadjustable PM flux linkage is shown, where the high efficiency area only lies within a small shaded regionlocated underneath both the torque curve and the power curve. This is due to HCF magnets generating too much flux at high speeds, thereby reducing motor efficiency.

[0089] In comparison, FIG. 9B shows the efficiency / torque-speed profile of a VFI- IPMSM as disclosed herein. There are three regions in which high efficiency may be achieved: a flux-enhanced (or flux-intensified) region at a high-torque / low-speed operation such as when driving in a metropolitan area, a zero-magnetized region at a mid-range torque / speed operation, and a flux-weakened region at a low-torque / high- speed operation such as when driving on a highway. Therefore, the VFI-IPMSM with FeN magnets is capable of improving the overall efficiency of the vehicle over a wide range of driving cycles and situations as compared to the conventional counterpart PMSM with nonadjustable PM flux linkage.

[0090] FIG. 10A, in which the x-axis represents speed and the y-axis represents voltage or percentage of magnetization state (MS), shows how the VFI-IPMSM may be controlled to allow higher speed operation by reducing the MS. During a low-speed operation, the induced voltage is increased at a higher MS percentage until the induced voltage reaches the maximum voltage of inverter drive. Upon detecting that the induced voltage reached the maximum voltage, the PM flux linkage is adjusted (“knocked down”) to achieve a lower MS percentage, resulting in a reduction of induced voltage, at which point the induced voltage increases. Each time the induced voltage reaches the maximum voltage with an increase in speed, the MS percentage is reduced by a certain level.

[0091] FIG. 10B shows a principle of loss reduction for the VFI-IPMSM, where the x-axis represents the speed. As speed increases, the PM flux linkage remains the same for a conventional PM machine with nonadjustable PM flux linkage, and the loss (for example, any amount of eddy currents) experienced by the conventional PM machine also increases, whereas the loss remains the same for the VFI-IPMSM machine as currently disclosed, which is capable of reducing the PM flux linkage as speed increases. Also, as speed increases, the flux-weakening current increases for the conventional PM machine, whereas such current is not generated for the VFI-IPMSM machine as currently disclosed. As such, the VFI-IPMSM machines can reduce losses and extend high-speed operation by changing the PM flux linkage, in view of the above FIGs. 10A and 10B.

[0092] FIG. 11A shows an optimum efficiency map for a VFI-IPMSM machine as experimentally calculated for a 30 kW vehicle class design. The figure shows a consistently high efficiency of 93% or greater from the speed of 0 rotation / m inute to 14,000 rotations / minute. FIG. 11 B shows an MS distribution map that corresponds to the optimum efficiency map of FIG. 11 A. According to FIG. 11 B, generally a higher MS percentage is used for a higher torque / lower speed operation, and a lower MS percentage is used for a lower torque / higher speed operation of the machine. Under the same motor sizing and power rating (peak power of 80 kW), it was calculated that the New European Driving Cycle (NEDC) efficiency of the VFI-IPMSM machine was 95.3%, whereas the NEDC efficiency of the baseline or conventional PM machine with nonadjustable PM flux linkage was 93.1 %, resulting in an efficiency increase of greater than 2%, and an overall driving-cycle-loss reduction of about 20%. As such, the VFI-IPMSM machine offers higher speed range and improved motor efficiency (and battery life) over the entire drive cycle, especially at freeway speeds.

[0093] Furthermore, low Hci value of the FeN magnet enables flux intensification (Fl) by allowing the FeN magnet to be “pushed up” along the load line as shown in FIG. 8, as opposed to flux weakening (FW) where higher-Hci magnets or HCF magnets are “pulled down” along the load line. High permeability (p) also enables flux intensification by allowing the FeN magnets to be “pushed up” along the load line, as opposed to flux weakening where higher-Hci magnets or HCF magnets are “pulled down” along the load line. Flux intensification beneficially yields higher efficiency at high operating speeds in comparison to flux weakening, providing higher overall efficiency over the full range of motor speed and torque operation. Excellent thermal properties of FeN also beneficially enhance the stability of the machine over a wide range of operating temperatures. Because the machine properties depend upon the magnet properties, if the magnet properties vary considerably with respect to temperature, then the machine’s performance will vary accordingly. Furthermore, low electrical conductivity beneficially minimizes eddy current losses in the FeN magnets, further enhancing machine efficiency.

[0094] In some examples, advantages of using flux intensification may include, but are not limited to, the capability of obtaining more torque out of the same motor and / or maintain the same amount of torque obtained while reducing the size of the motor. Abaseline motor may include the FeN permanent magnets whose identifying properties are shown below in Table 2.Table 2: Properties of Baseline FeN Magnet

[0095] According to embodiments, the baseline FeN magnets are implemented in the rotor of the electric machine as shown in FIG. 12, along with a plurality of flux barriers. FIG. 12 shows an electric machine 102 according to an alternate embodiment disclosed herein. The electric machine includes a rotor 104 and a stator 106. The stator 106 may include any suitable configuration of lamination (e.g., a steel lamination) and coils of insulated wire inserted into the lamination, such as windings 704. The lamination may be high-permeable material (e.g., steel). In some examples, the stator may implement hairpin windings, oil spray, and / or liquid cooling, as suitable.

[0096] The rotor 104 includes a plurality of FeN LCF magnets 700 inserted in a lamination so as to align with the d-axis and a plurality of flux barriers. The flux barriers are made of nonmagnetic and nonconductive material (e.g., plastic, resin, air, and / or vacuum) and are located between the magnets and aligning with the q-axis. The flux barriers are also referred to herein as first nonmagnetic nonconductive components 1202 and second nonmagnet nonconductive components 1204 as shown in FIG. 12, for example. The magnets 700 are in pairs with like poles facing each other. As such, the N poles 1206 face each other (e.g., such that a first N pole from a first magnet faces a second N pole from a second magnet in the pair of magnets) or the S poles 1208 faceeach other (e.g., such that a first S pole from a first magnet faces a second S pole from a second magnet in the pair of magnets) in a spoke configuration with the magnet placements arranged around the near outer surface area of the rotor.

[0097] The rotor 104 may have two (2), four (4), six (6), eight (8), ten (10), twelve (12) or more pairs of magnets. In some examples, it may be preferrable for the flux barriers to have a concave and curved configuration. The flux barriers may be curved or segmented to represent a curve and may be concave (inwardly curving) in nature. In some embodiments, the flux barrier may be concave curved flux barrier, and the system may comprise one or more concave flux barriers. In some examples, the smallest radius flux barrier is closest to the rotor surface (e.g., outer surface of the rotor) and the largest radius flux barrier may be farthest from the rotor surface. In some examples, the origin points of the one or more concave flux barriers are in a line to a line of the centers of the FeN LCF magnets. In some examples, the FeN LCF magnets are positioned in a spoke configuration around the rotor. In some examples, a flux barrier extends between each magnet.

[0098] In some configurations, the rotor 104 is be capable of rotating with speeds of at or greater than 20 kRPM as well as reaching at least 55 kW power (continuous) and 10OkW (peak), torque of at least 300 Nm, and power density of at least 50 kW / L, to meet or exceed the targets of USDRIVE Partnership Plan 2025 set by the U.S. Department of Energy. In some examples, there may also be a d-axis flux bypass component (which may be part of the lamination or an insertable component made of a different material from the lamination) located between two flux barriers. The shape of one or more of the flux barriers may include, for example, a hemisphere, trapezoid, arch, or any other suitable configuration as known in the art.

[0099] The rotor 104 includes a plurality of pairs of magnets 700 (shown in FIG. 12 with 4 pairs of magnets) disposed in the rotor near an outer portion 1210 of the rotor. The magnets 700 have a coercivity (Hci) of 2,000 Oe to 4,000 Oe. The coercivity of the magnets includes any range of from 2,000 Oe to 2,100 Oe, from 2,100 Oe to 2,200 Oe, from 2,200 Oe to 2,300 Oe, from 2,300 Oe to 2,400 Oe, from 2,400 Oe to 2,500 Oe, from 2,500 Oe to 2,700 Oe, from 2,700 Oe to 3,000 Oe, from 3,000 Oe to 3,200 Oe, from 3,200 Oe to 3,500 Oe, from 3,500 Oe to 3,700 Oe, from 3,700 Oe to 4,000 Oe, or any othersuitable value within the foregoing ranges or any other suitable range between any of the foregoing ranges. The magnets 700 are positioned such that magnetic poles (e.g., poles 1206 and 1208) are in line with a rotational axis of the rotor 104. The magnets 700 are affixed to the rotor 104 by a high-permeable material. Each pair of the magnets 700 has like magnetic poles facing each other (as shown by the positions of the N poles 1206 and S poles 1208). Each of the magnets 700 has a longitudinal axis 1212 that aligns with a d-axis of the rotor.

[0100] The rotor also includes a plurality of first nonmagnetic and nonconductive components disposed in the rotor. Each of the first nonmagnetic and nonconductive components has a longitudinal axis that aligns with a q-axis of the rotor 104. The rotor 104 also includes a plurality of second nonmagnetic and nonconductive components 1204 disposed in the rotor 104 near the outer portion 1210 of the rotor 104. Each of the second nonmagnetic and nonconductive components 1204 has a curved region 1214 that may be concave with respect to a surface 1216 of the rotor (such as an outer surface 1216 of the rotor), and an end portion 1218 near the surface 1216 of the rotor 104. The magnets 700 are centered relative to the second nonmagnetic and nonconductive components 1204 such that each of the magnets 700 is disposed in the curved region 1214.

[0101] In some examples, the second nonmagnetic and nonconductive components 1204 includes smaller-radius components 1204A and larger-radius components 1204B having greater radius than the smaller-radius components 1204A. The smaller-radius components 1204A are disposed closer to the outer surface 1216 of the rotor 104 than the larger-radius components 1204B. In some examples, there may be any suitable number of second nonmagnetic and nonconductive components 1204 for each magnet 700. For example, FIG. 12 shows two (2) components (a smaller-radius component closer to the outer surface of the rotor and a larger-radius component further from the outer surface), but it is to be understood that there may be three (3), four (4), five (5), or any larger number of components with different radii, as suitable, each of which is concave with respect to the outer surface 1216. The individual components may be substantially parallel to each other, such that the smaller-radius components 1204A do not overlap with the larger-radius components 1204B.

[0102] In some examples, the surface 1216 of the rotor has a plurality of indented portions 1220 in proximity to the magnets 700. The indented portions 1220 may define a non-circular cross-section for the rotor 104. In some examples, the magnets 700 are disposed adjacent to each other or side-by-side with respect to each other. In some examples, each of the magnets 700 has a volume-to-weight ratio of greater than 0.1 , greater than 0.15, greater than 0.2, or any other suitable value within the foregoing ranges or any other suitable range between any of the foregoing ranges. The magnets 700 and the first nonmagnetic and nonconductive components 1202 are disposed in an interspersed configuration in which each first nonmagnetic and nonconductive component 1202 is disposed between two neighboring magnets 700.

[0103] The rotor 104 may be substantially cylindrical or may include portions there of along the surface that are not circular, so as to have non-circular cross-sectional surfaces. The magnet 700 and one of the second nonmagnetic and nonconductive components 1204 may also form a configuration that resembles the Greek alphabet psi (“ip”) in that the longitudinal axis of the magnet is centered with respect to the curved region 1214 of the second nonmagnetic and nonconductive component, where the curved region is concave with respect to the surface 1216 of the rotor. Each of the magnets 700 and the first nonmagnetic and nonconductive components 1202 has a longitudinal axis 1222 as well as a transverse distance labeled as “T” that is measured perpendicular to the longitudinal axis 1222. In some examples, the transverse distance T of the magnet 700 or the first nonmagnetic and nonconductive component 1202 may be consistent along the longitudinal axis 1222, or the transverse distance T may vary, such as the measured distance T being longer near the outer portion 1210 of the rotor and shorter near an inner portion 1224 of the rotor, or vice versa (i.e. , shorter near the outer portion 1210 and longer near the inner portion 1224).

[0104] In some examples, the rotor 104 includes a rotor body 1226 with a plurality of slots 1228, 1230, 1232 into which different components of the rotor 104 may be disposed. The rotor body 1226 may include a plurality of laminations (such as the lamination 702 of FIG. 7) in a stacked configuration. The slots may be shaped and sized to accommodate the shapes and sizes of the respective components. The first slots 1228 may be formed in the rotor body 1226 to accommodate the magnets 700. The secondslots 1230 may be formed in the rotor body 1226 to accommodate the first nonmagnetic and nonconductive components 1202. The third slots 1232 may be formed in the rotor body 1226 to accommodate the second nonmagnetic and nonconductive components 1204.

[0105] FIG. 13 shows an operating point of the magnet, or more specifically, a position on the load line for conventional operation using the identified permanent magnets. The position on the load line for conventional operation is determined by: presenting the conventional load line current waveform for operating the motor and comparing the NdFeB FW configuration against the FeN Fl B / H configuration; defining the region on the load line for flux weakening operation; and presenting the flux weakening load line current waveform for three positions on the load line. As shown in FIG. 13, FW operation pulls the magnet lower down the load line, increasing the risk of irreversible demagnetization. FW operation is implemented by injecting current into the d-axis to reduce the magnet flux during high-speed operation. This d-axis current increases power losses according to P = lA2 * R, where P is the power, I is the current, and R is the resistance, and also reduces motor efficiency at high speeds.

[0106] Tables 3A through 3C below compare the specifications, material and operational parameters, and the losses and efficiency at load points of the NdFeB FW- IPM motor (Motor A) as known in the art, and of the FeN VFI-IPM motor (Motor B) as presently disclosed.Table 3A: Comparison of motor specificationsTable 3B: Comparison of motor materials and physical propertiesTable 3C: Comparison of load points, and losses and efficiency at ambient temperature

[0107] According to Table 3A, the physical dimensions and operational specifications of the two motors are the same. According to Table 3B, although the two motors have similar magnet masses, the magnet of Motor B has a greater volume-to- weight ratio (about 0.2) than that of Motor A (about 0.07). According to Table 3C, the efficiency of Motor B is 2.5% greater than that of Motor A in the same temperature range when operating at a high-speed / low-torque load point.

[0108] An FeN LCF optimizes the torque density of a Flux Intensifying BEV traction motor by pushing the magnet higher up the load line and utilizing a positive reluctance torque to add to the stator torque. The increase in torque density of an Fl motor increases the efficiency of the BEV traction motor, but mainly in the lower-speed ranges of operation. This leads to the need for Variable Flux (VF) technology to improve the motor efficiency at the high-speed, low-torque operating points.

[0109] Variable Flux (VF) operation is defined as the ability to adjust the magnetization of the permanent magnets on-the-fly, while the motor is operating. It is akin to having a knob to dial in the optimum magnetization level of the magnets to maximize efficiency at any torque and speed operating point on the BEV drive cycle. VF operation is enabled through the use of FeN LCF magnets and is not possible using NdFeB HCF magnets.

[0110] The primary advantage of VF operation is at high speeds, where the magnetization of the magnets can be reduced to optimize the efficiency of the motor at low-torque, high-speed operating points, presently the Achilles heel of BEV traction motors. VF operation is activated by magnetizing and demagnetizing the permanentmagnets in the rotor via pulsing the stator coils with appropriate phasing and magnitude of magnetizing current.

[0111] With regards to FIGs. 14 through 17 with an appropriate VF control scheme, the magnetization of the FeN LCF magnets can be varied in either a continuous or discrete manner, a magnetic analog to a Continuously Variable Transmission (CVT) vs. a 5-speed manual transmission on an Internal Combustion Engine (ICE) automobile. For example, FIGs. 14 through 17 illustrate different torque curves showing the relationship between electrical degrees and torque as explained herein. The relationship between electrical degree and mechanical degree is represented by the following formula: 0e = (P / 2) 0m, where 0e is the electrical angle (angular displacement of the rotor with respect to the stator’s magnetic field in electrical degree), P is the number of poles (such that P / 2 is the number of pole pairs) in the rotor, and 0m is the mechanical angle (angular displacement of the rotor in physical / mechanical degrees). For example, with 24 poles in the rotor, there are 12 pole pairs, and there are 30 mechanical degrees for each revolution.

[0112] In FIG. 14, the brushless DC motor torque curves are shown in which electrical signals are inputted to each phase without VF adjustments.

[0113] In FIG. 15, input electrical signals are applied to each phase as aligned with the timing of the VF pulse signals (shown as A, B, and C) for synchronization. The VF pulse signals include two consecutive positive pulse signals (A and B) that are separated by 360 / n electrical degrees, where n is a number of phases of the electric machine, such as at 0 electrical degree and 120 electrical degrees as shown in a three-phase machine. The VF pulse signals also include a negative pulse signal (C) occurring at a midpoint between the two consecutive positive pulse signals, such as at 60 electrical degrees as shown in the three-phase machine. Polarity and magnitude may depend upon the desired target magnetization level.

[0114] In FIG. 16, a brushless DC motor torque curves are shown, as well as the ideal output torque of each phase.

[0115] In FIG. 17, the ideal total motor output torque is shown, with the goal being to minimize the torque perturbations caused by the VF current pulses. The figure shows the effective torque ripple in a 3-phase 2-pole brushless motor.

[0116] FIGs. 18A through 18D illustrate the different configurations for stator winding as disclosed herein to implement the VF operations. FIG. 18A shows a 4-pole 6-slot winding diagram, FIG. 18B shows a 6-pole 9-slot winding diagram, FIG. 18C shows an 8-pole 9-slot winding diagram, and FIG. 18D shows an 8-pole 12-slot winding diagram. Other types of winding may be implemented as suitable. Using such winding diagrams in concert with the VF operations improves the efficiency of the motor that uses the FeN LCF magnets as the operation shifts between two different speeds. For example, conventionally, performing flux-weakening operation on LCF AINiCo magnets is problematic due to the risk of demagnetizing the magnets in an undesirable way. The location of the operating point along the load line (as shown in FIG. 5A) dictates the weight of the magnets necessary for the design of the motor, such that the load can be generated using a greater amount of magnets, such as at the high-speed, low-torque operating points.

[0117] FIG. 19 shows a portion of a magnetic hysteresis loop including the BH curve when an external magnetic field (x-axis) is applied to the FeN magnet resulting in the magnetization (y-axis). As shown, when there is no magnetic field applied, the FeN magnet has the magnetization of slightly above 10,000 gauss, and the magnet is demagnetized (at 0 gauss) when the magnetic field of about 2,100 Oe is applied in the opposite direction. The loop shows an initial curve and a return curve.

[0118] FIG. 20 shows a process or method 2000 of operating the rotor or the electric machine as disclosed herein. The method 2000 includes step 2002 of receiving a torque command. The torque command may be received by the controller 110 as shown in FIG. 1 , for example, which is operatively coupled with the rotor 104. In step 2004, flux-intensifying operation is performed by operating the rotor to develop a positive reluctance torque and align a current distribution of the stator with a positive d-axis of the rotor such that an overall torque reaches a maximum value at a negative current angle in a field intensifying operation range of the rotor, where inductance is greater in the d-axis of the rotor than in a q-axis of the rotor (Ld>Lq).

[0119] FIG. 21 shows a process or method 2100 of operating the rotor or the electric machine as disclosed herein. The method 2100 includes step 2102 of receiving a torque command and a speed command. The torque command and the speedcommand may be received by the controller 110 as shown in FIG. 1 , for example, which is operatively coupled with the rotor 104. In step 2104, the operation type for the rotor is determined based on the torque command and the speed command. The operation type may be selected from one of the following: a high-torque / low-speed operation 2104A in which the rotor operates in a flux-intensified region of electric current angle, a mid-range torque / speed operation 2104B in which the rotor operates in a zero-magnetized region of electric current angle, and a low-torque / high-speed operation 2104C in which the rotor operates in a flux-weakened region of electric current angle. The operation type may be changed or adapted during operation of the electric machine such that, as the torque and / or speed changes, the operation type is changed or newly selected, as suitable according to the new torque and / or speed command(s). In step 2106, the rotor is operated by applying electric current to the rotor according to the operation type as determined. The rotor includes a plurality of pairs of magnets disposed therein near an outer portion of the rotor. The magnets have a coercivity of 2,000 Oe to 4,000 Oe, the magnets are positioned such that magnetic poles are in line with a rotational axis of the rotor, each pair of the magnets has like magnetic poles facing each other, and each of the magnets has a longitudinal axis that aligns with a d-axis of the rotor.

[0120] In the operation types 2104A, 2104B, and 2104C, the specific values at which the rotor is determined to be operating in high-torque / low-speed, mid-range, or low- torque / high-speed may vary.

[0121] In some examples, the torque command may be interpreted as being “high- torque” if the value of the torque that is to be achieved is at least 60%, at least 70%, at least 80%, or any other suitable value within the foregoing ranges or any other suitable range between any of the foregoing ranges, with respect to a maximum (or peak) torque amount that can be safely and reliably delivered by the rotor. For example, if the rotor can safely deliver a maximum torque of up to 500 Nm, the high-torque region may be interpreted as being at least 300 Nm, at least 350 Nm, or at least 400 Nm.

[0122] In some examples, the torque command may be interpreted as being “low- torque” if the value of the torque that is to be achieved is no greater than 30%, no greater than 20%, no greater than 10%, or any other suitable value within the foregoing ranges or any other suitable range between any of the foregoing ranges, with respect to themaximum (or peak) torque amount. For example, if the maximum torque is 500 Nm, the low-torque region may be interpreted as being no greater than 150 Nm, no greater than 100 Nm, or no greater than 50 Nm. Accordingly, the mid-range torque may be the value between the two regions for the high-torque and low-torque values, as described above.

[0123] Similarly, in some examples, the speed command may be interpreted as being “high-speed” if the value of the speed that is to be achieved is at least 60%, at least 70%, at least 80%, or any other suitable value within the foregoing ranges or any other suitable range between any of the foregoing ranges, with respect to a maximum (or peak) speed value that can be safely and reliably achieved by the rotor. For example, if the rotor can safely operate at a maximum rotational speed of up to 20 kRPM, the high-speed region may be interpreted as being at least 12 kRPM, at least 14 kRPM, or at least 16 kRPM.

[0124] In some examples, the speed command may be interpreted as being “low- speed” if the value of the speed that is to be achieved is no greater than 30%, no greater than 20%, no greater than 10%, or any other suitable value within the foregoing ranges or any other suitable range between any of the foregoing ranges, with respect to the maximum (or peak) speed value. For example, if the maximum rotational speed is 20 kRPM, the low-speed region may be interpreted as being no greater than 6 kRPM, no greater than 4 kRPM, or no greater than 2 kRPM. Accordingly, the mid-range speed may be the speed value between the two regions for the high-speed and low-speed values, as described above. It is to be understood that the aforementioned maximum values for the torque and speed may be provided by the manufacturer as part of the original specification for the rotor. Alternatively, the maximum values may be determined experimentally.

[0125] In view of the above, according to some examples, in the high-torque / low- speed operation 2104A, the rotor is operated to provide torque that is at least 60% of a maximum torque of the rotor and speed that is no greater than 30% of a maximum speed of the rotor. In some examples, in the mid-range torque / speed operation 2104B, the rotor is operated to provide torque that is between 30% and 60% of a maximum torque of the rotor and speed that is between 30% and 60% of a maximum speed of the rotor. In some examples, in the low-torque / high-speed operation 2104C, the rotor is operated to providetorque that is no greater than 30% of a maximum torque of the rotor and speed that is at least 60% of a maximum speed of the rotor.

[0126] FIG. 22 shows a process or method 2200 of making or manufacturing a rotor of an electric machine as disclosed herein. The method 2200 includes step 2202 of providing a rotor body comprising a plurality of laminations in a stacked configuration. The rotor body has a plurality of first slots, a plurality of second slots, and a plurality of third slots. In step 2204, a plurality of pairs of magnets are disposed in the first slots of the rotor body near an outer portion of the rotor body. For example, the magnets have a coercivity of 2,000 Oe to 4,000 Oe, the magnets are positioned such that magnetic poles are in line with a rotational axis of the rotor, the magnets are affixed to the rotor body by a high-permeable material, each pair of the magnets has like magnetic poles facing each other, and each of the magnets has a longitudinal axis that aligns with a d-axis of the rotor. In step 2206, a plurality of first nonmagnetic and nonconductive components are disposed in the second slots of the rotor body. For example, each of the first nonmagnetic and nonconductive components has a longitudinal axis that aligns with a q-axis of the rotor. In step 2208, a plurality of second nonmagnetic and nonconductive components are disposed in the third slots of the rotor body near the outer portion of the rotor body. For example, each of the second nonmagnetic and nonconductive components has a curved region that is concave with respect to a surface of the rotor body, and an end portion near the surface of the rotor body, and the magnets are centered relative to the second nonmagnetic and nonconductive components such that each of the magnets is disposed in the curved region.

[0127] Numerous characteristics and advantages have been set forth in the preceding description, including various alternatives together with details of the structure and function of the devices and / or methods. Moreover, the scope of the various concepts addressed in this disclosure has been described both generically and with regard to specific examples. The disclosure is intended as illustrative only and as such is not intended to be exhaustive. It will be evident to those skilled in the art that various modifications may be made, especially in matters of structure, materials, elements, components, shape, size, and arrangement of parts including combinations within the principles of the disclosure, to the full extent indicated by the broad, general meaning ofthe terms in which the appended claims are expressed. To the extent that these various modifications do not depart from the spirit and scope of the appended claims, they are intended to be encompassed therein.

Claims

ClaimsWhat is claimed is:1 . A rotor for an electric machine, the rotor comprising: a plurality of pairs of magnets disposed in the rotor near an outer portion of the rotor, wherein: the magnets have a coercivity (Hci) of 2,000 Oe to 4,000 Oe; the magnets are positioned such that magnetic poles are in line with a rotational axis of the rotor; the magnets are affixed to the rotor by a high- permeable material; each pair of the magnets has like magnetic poles facing each other; and each of the magnets has a longitudinal axis that aligns with a d-axis of the rotor; a plurality of first nonmagnetic and nonconductive components disposed in the rotor, wherein each of the first nonmagnetic and nonconductive components has a longitudinal axis that aligns with a q-axis of the rotor; and a plurality of second nonmagnetic and nonconductive components disposed in the rotor near the outer portion of the rotor, wherein: each of the second nonmagnetic and nonconductive components has a curved region that is concave with respect to a surface of the rotor, and an end portion near the surface of the rotor; and the magnets are centered relative to the second nonmagnetic and nonconductive components such that each of the magnets is disposed in the curved region.

2. The rotor of claim 1 , wherein the second nonmagnetic and nonconductive components includes smaller-radius components and larger-radius components having greater radius than the smaller-radius components, wherein the smaller-radius components are disposed closer to the surface of the rotor than the larger-radius components.

3. The rotor of claim 1 or 2, wherein the surface of the rotor has a plurality of indented portions in proximity to the magnets.

4. The rotor of any one of claims 1-3, wherein the magnets are disposed adjacent to each other along the rotational axis of the rotor.

5. The rotor of any one of claims 1 -4, wherein each of the magnets has a volume- to-weight ratio of greater than 0.1 .

6. The rotor of any one of claims 1 -5, wherein each of the magnets has a permeability of from 1 .8 to 2.0.

7. The rotor of any one of claims 1-6, wherein the magnets include iron nitride (FeN) magnets.

8. The rotor of any one of claims 1-7, wherein a pair of the plurality of pairs of magnets includes a first magnet and a second magnet such that a first N pole of the first magnet faces a second N pole of the second magnet.

9. The rotor of any one of claims 1-7, wherein a pair of the plurality of pairs of magnets includes a first magnet and a second magnet such that a first S pole of the first magnet faces a second S pole of the second magnet.

10. The rotor of any one of claims 1 -9, wherein the each of the first nonmagnetic and nonconductive components has a transverse distance that is measured perpendicular to the longitudinal axis of the first nonmagnetic and nonconductive component, and the transverse distance measured along the longitudinal axis of the first nonmagnetic and nonconductive component is consistent.11 . The rotor of any one of claims 1 -9, wherein the each of the first nonmagnetic and nonconductive components has a transverse distance that is measured perpendicular tothe longitudinal axis of the first nonmagnetic and nonconductive component, and the transverse distance varies along the longitudinal axis of the first nonmagnetic and nonconductive component such that the transverse distance measured near the outer portion of the rotor is longer than the transverse distance measured near an inner portion of the rotor.

12. The rotor of any one of claims 1 -9, wherein the each of the first nonmagnetic and nonconductive components has a transverse distance that is measured perpendicular to the longitudinal axis of the first nonmagnetic and nonconductive component, and the transverse distance varies along the longitudinal axis of the first nonmagnetic and nonconductive component such that the transverse distance measured near the outer portion of the rotor is shorter than the transverse distance measured near an inner portion of the rotor.

13. The rotor of any one of claims 1 -12, wherein one or more of the first nonmagnetic and nonconductive components and the second nonmagnetic and nonconductive components are made of plastic or resin.

14. The rotor of any one of claims 1 -13, wherein the magnets and the first nonmagnetic and nonconductive components are disposed in an interspersed configuration in which each of the first nonmagnetic and nonconductive components is disposed between two neighboring magnets of the plurality of pairs of magnets.

15. An electric machine comprising: a stator; and the rotor of any one of claims 1 -14 disposed in the stator.

16. A method of operating an electric machine with the rotor of any one of claims 1 - 14, the method comprising: receiving, by a controller operatively coupled with the rotor, a torque command; andperforming, by the controller based on the torque command, flux-intensifying operation by operating the rotor to develop a positive reluctance torque and align a current distribution of the stator with a positive d-axis of the rotor such that an overall torque reaches a maximum value at a negative current angle in a field intensifying operation range of the rotor, where inductance is greater in the d-axis of the rotor than in a q-axis of the rotor.

17. A method of operating a rotor, the method comprising: receiving, by a controller operatively coupled with the rotor, a torque command and a speed command; determining, by the controller based on the torque command and the speed command, an operation type for the rotor, the operation type being selected from one of: a) a high-torque / low-speed operation in which the rotor operates in a flux- intensified region of electric current angle, b) a mid-range torque / speed operation in which the rotor operates in a zero- magnetized region of electric current angle, and c) a low-torque / high-speed operation in which the rotor operates in a flux- weakened region of electric current angle; and operating the rotor by applying electric current to the rotor according to the operation type as determined, the rotor comprising a plurality of pairs of magnets disposed therein near an outer portion of the rotor, wherein the magnets have a coercivity (Hci) of 2,000 Oe to 4,000 Oe, the magnets are positioned such that magnetic poles are in line with a rotational axis of the rotor, each pair of the magnets has like magnetic poles facing each other, and each of the magnets has a longitudinal axis that aligns with a d-axis of the rotor.

18. The method of claim 17, wherein, in the high-torque / low-speed operation, the rotor is operated to provide torque that is at least 60% of a maximum torque of the rotor and speed that is no greater than 30% of a maximum speed of the rotor.

19. The method of claim 17, wherein, in the mid-range torque / speed operation, the rotor is operated to provide torque that is between 30% and 60% of a maximum torque of the rotor and speed that is between 30% and 60% of a maximum speed of the rotor.

20. The method of claim 17, wherein, in the low-torque / high-speed operation, the rotor is operated to provide torque that is no greater than 30% of a maximum torque of the rotor and speed that is at least 60% of a maximum speed of the rotor.21 . A method of making a rotor of an electric machine, the method comprising: providing a rotor body comprising a plurality of laminations in a stacked configuration, the rotor body having a plurality of first slots, a plurality of second slots, and a plurality of third slots; disposing a plurality of pairs of magnets in the first slots of the rotor body near an outer portion of the rotor body, wherein the magnets have a coercivity (Hci) of 2,000 Oe to 4,000 Oe, the magnets are positioned such that magnetic poles are in line with a rotational axis of the rotor, the magnets are affixed to the rotor body by a high- permeable material, each pair of the magnets has like magnetic poles facing each other, and each of the magnets has a longitudinal axis that aligns with a d-axis of the rotor; disposing a plurality of first nonmagnetic and nonconductive components in the second slots of the rotor body, each of the first nonmagnetic and nonconductive components having a longitudinal axis that aligns with a q-axis of the rotor; and disposing a plurality of second nonmagnetic and nonconductive components in the third slots of the rotor body near the outer portion of the rotor body, wherein each of the second nonmagnetic and nonconductive components has a curved region that is concave with respect to a surface of the rotor body, and an end portion near the surface of the rotor body, and the magnets are centered relative to the second nonmagnetic and nonconductive components such that each of the magnets is disposed in the curved region.

22. The method of claim 21 , wherein disposing the second nonmagnetic and nonconductive components comprises disposing a plurality of smaller-radiuscomponents and a plurality of larger-radius components having greater radius than the smaller-radius components, wherein the smaller-radius components are disposed closer to the surface of the rotor than the larger-radius components.

23. The method of claim 21 or 22, wherein disposing the magnets comprises disposing the magnets adjacent to each other along the rotational axis of the rotor.

24. The method of any one of claims 21 -23, wherein a pair of the plurality of pairs of magnets includes a first magnet and a second magnet such that a first N pole of the first magnet faces a second N pole of the second magnet.

25. The method of any one of claims 21 -23, wherein a pair of the plurality of pairs of magnets includes a first magnet and a second magnet such that a first S pole of the first magnet faces a second S pole of the second magnet.

26. The method of any one of claims 21 -25, wherein the magnets and the first nonmagnetic and nonconductive components are disposed in an interspersed configuration in which each of the first nonmagnetic and nonconductive components is disposed between two neighboring magnets of the plurality of pairs of magnets.

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