WO2021081372A1

WO2021081372A1 - Variable-flux memory motor

Info

Publication number: WO2021081372A1
Application number: PCT/US2020/057129
Authority: WO
Inventors: Nicolaus Radford; Mohammadreza Barzegaranbaboli
Original assignee: Jacobi Motors LLC
Priority date: 2019-10-25
Filing date: 2020-10-23
Publication date: 2021-04-29

Abstract

A multi-pole rotor of a variable-flux memory motor (VFMM) includes: a rotor core; and a plurality of poles. Each of the plurality of poles includes: a plurality of soft magnets; a first ferrous wedge; and a second ferrous wedge. The plurality of soft magnets is disposed between the first and second ferrous wedges and along a radial direction of the rotor with respect to one another. At least two adjacent soft magnets among the plurality of soft magnets are spaced from one another in the radial direction of the rotor.

Description

VARIABLE-FLUX MEMORY MOTOR

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims priority, pursuant to 35 U.S.C. § 119(e), to U.S. Provisional Application No. 62/926,111 entitled, “A VARIABLE-FLUX MEMORY MOTOR,” filed on October 25, 2019. The contents of which are hereby incorporated by reference in its entirety.

BACKGROUND

[0002] Synchronous electric motors with permanent magnets such as variable- flux memory motors have a wide range of applications in industrial, commercial, and residential, applications, such as fans, pumps, compressors, elevators, and refrigerators, industrial machinery, and electric motor vehicles because of their high efficiencies. Also, because of using permanent magnets instead of windings in the rotors of the synchronous electric motors, there is no need for a rotor cooling. These advantages along with others (e.g., being brushless) make the synchronous electric motors popular where high torque, high efficiency, or low maintenance for electric motors is needed.

SUMMARY

[0003] In one aspect, embodiments of the invention are directed to a multi-pole rotor of a variable-flux memory motor (VFMM). The multi-pole rotor includes: a rotor core; and a plurality of poles. Each of the plurality of poles includes: a plurality of soft magnets; a first ferrous wedge; and a second ferrous wedge. The plurality of soft magnets is disposed between the first and second ferrous wedges and along a radial direction of the rotor with respect to one another. At least two adjacent soft magnets among the plurality of soft magnets are spaced from one another in the radial direction of the rotor. [0004] Other aspects of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

[0005] FIG. 1 shows a synchronous electric motor.

[0006] FIG. 2 shows a cross-sectional view of a variable-flux memory motor

(VFMM) in accordance with one or more embodiments of the invention.

[0007] FIGS. 3A-3B show Design A of a VFMM rotor in accordance with one or more embodiments of the invention.

[0008] FIG. 4A shows magnetization directions in a cross-sectional view of a portion of the VFMM in accordance with one or more embodiments of the invention.

[0009] FIG. 4B shows a cross-sectional view of a portion of the VFMM in accordance with one or more embodiments of the invention.

[0010] FIG. 4C shows a cross-sectional view of a portion of the VFMM in accordance with one or more embodiments of the invention.

[0011] FIGS. 5A-5B show distributions of magnetic fluxes in cross-sectional views of the VFMM in accordance with one or more embodiments of the invention.

[0012] FIG. 6A shows a magnetization diagram for Design A of a VFMM rotor in accordance with one or more embodiments of the invention.

[0013] FIG. 6B shows a magnetic field distribution corresponding to the VFMM rotor shown in FIG. 6B.

[0014] FIG. 7 shows a magnetization diagram.

[0015] FIG. 8 shows Design B of a VFMM rotor in accordance with one or more embodiments of the invention. [0016] FIG. 9A shows magnetization plots for Design A and Design B of VFMM rotors in accordance with one or more embodiments of the invention.

[0017] FIG. 9B shows magnetic field distributions for Design A and Design B of the VFMM rotors shown in FIG. 9A.

[0018] FIG. 10 shows magnetic field distributions for variations of Design B in accordance with one or more embodiments of the invention.

DETAILED DESCRIPTION

[0019] This Application discloses improvements to U.S. Patent Application No.

16/383,274 entitled “A VARIABLE-FLUX MEMORY MOTOR AND METHODS OF CONTROLLING A VARIABLE-FLUX MOTOR” and filed on April 12, 2019, which is incorporated by reference in its entirety.

[0020] Specific embodiments of the invention will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency.

[0021] In the following detailed description of embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it would have been apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0022] FIG. 1 shows an exploded view of a synchronous electric motor (100) (hereinafter, will be referred to as “synchronous motor”) including a rotor (101), a stator (102), and stator windings (103) arranged around a rotor hub (104). The synchronous motor may also include a terminal box for connecting input power, a cooling fan, a rotor position sensor, temperature sensors, liquid cooling housings, etc. The rotor (101) includes multiple poles, each including permanent magnets (105) (PM). [0023] The synchronous motor (100) operates via a three-phase AC input, in which each phase is delayed from the other two phases by 120 degrees. To create the three-phase AC input, a power converter may convert DC power fed to the power converter from a high voltage DC source (e.g., a battery). By applying the three-phase AC input to the synchronous motor, the stator windings create a three-phase magnetic field that interacts with the magnetic fields of the PMs (105) and cause the rotor (101) to rotate with a fixed number of revolutions per minute (RPM) speed in a steady-state (hereinafter, will be referred to as “RPM”). The RPM of the synchronous motor is fixed to limiting factors such as number of poles, available voltage, and flux linkage

which is provided and is fixed by the PMs. Synchronous motors have a wide range of applications in industrial, commercial, and residential, applications, such as fans, pumps, compressors, elevators, and refrigerators, industrial machinery, and electric vehicles.

[0024] In one or more embodiments, because the l_p1 provided by the PMs is fixed, the synchronous motors with PMs have a narrow constant power speed range (CPSR), which is the speed range at which the drive of the motor can maintain a constant power with limited values of input voltage and current of the motor. Thus, increasing the CPSR of the synchronous motors without using advanced control techniques such as implementing flux-weakening control methods is difficult. Because of the narrow range of CPSR for the synchronous motors, using a transmission system may be required to change a CPSR of a system driven by the synchronous motor. Even using such advanced methods extend the CPSR of the synchronous motors to 2 to 3. On the other hand, the CPSR of the VFMM according to one or more embodiments may achieve 4 to 6.

[0025] In general, embodiments of the invention relate to designs of VFMMs, rotors for VFMMs, and methods for magnetizing VFMMs. A VFMM is a type of synchronous motor in which magnetization of rotor magnets (RM) of the VFMM can be adjusted (/. e. , changed) during an operation of the VFMM. The adjustment of the magnetization of the RMs (hereinafter, will be referred to as “VFMM magnetization” for simplicity) changes the RPM of the VFMM. According to one or more embodiments, to facilitate the change in the VFMM magnetization, the RMs are made of a soft-ferromagnetic material such as aluminum nickel cobalt (AlNiCo) or some types of ceramics. Hereinafter, an RM made of a soft-ferromagnetic material will be referred to as “soft magnet,” which is a low coercive force magnet. According to one or more embodiments, the soft magnets may be AlNiCo with grades 1-9 or magnets comprised of AlNiCo, cast, ceramics, some grades of samarium cobalt, or sintered construction of these materials. It is apparent that one of ordinary skill in the art could use specific amounts of these materials to achieve a desired function of the VFMM.

[0026] The VFMM in accordance with one or more embodiments is a better substitute to a synchronous motor because a maximum achievable RPM with a limited voltage of the VFMM may be more efficiently attained through changing the VFMM magnetization. In other words, the CPSR of the VFMM could have a wider range compared to the CPSR of the synchronous motor. Thus, there is no need to couple the transmission system to the VFMM. Consequently, according to one or more embodiments, using the VFMM potentially reduces manufacturing costs of electric motor-equipped systems due to being magnetized or demagnetized during assembly.

[0027] Soft-ferromagnetic materials have high permeability (same as hard- ferromagnetic materials such as alloys of iron and nickel) but low coercivity (unlike hard-ferromagnetic materials). Because of the low coercivity of soft- ferromagnetic materials, changing the magnetization of soft-ferromagnetic materials requires relatively smaller magnetic field compared to hard- ferromagnetic materials. [0028] In one or more embodiments, only soft magnets may be used as the magnets of the rotor of the VFMM and there may be no hard magnets (i.e., magnets made of hard-ferromagnetic materials) mounted on the rotor. Alternatively, in one or more embodiments, both of the soft magnets and hard magnets may be used as the magnets of the rotor of the VFMM. Embodiments of the invention may have advantages over synchronous motors, which use only hard magnets, because hard magnets are made of rare-earth-materials and are significantly more expensive than soft magnets (e.g., AlNiCo). Thus, partially or entirely using soft magnets instead of hard magnets in the VFMM significantly reduces manufacturing costs of the VFMM compared to traditional synchronous motors.

[0029] Additionally, another advantage of using the soft magnets is that control and change of the overall magnetization of the overall magnets of the VFMM can be done in a wide range. According to one or more embodiments, the overall magnetization of the soft magnets can be changed to any value from 0% magnetization (i.e., the soft magnets are completely demagnetized) to 100% magnetization (i.e., the soft magnets are magnetized to their maximum capacity). This change in magnetization may occur in a short time (e.g., about 1 millisecond).

[0030] In contrast, hard magnets do not tend to change their magnetization easily. Accordingly, changing the magnetization of hard magnets requires significantly more power than the operating power of a VFMM or other types of synchronous motors. For example, changing magnetization of hard magnets, such as some grades of neodymium iron boron (NdFeB) and samarium cobalt (SmCo) may require a power more than 10 folds higher that a power required for changing magnetization of the soft magnets. Thus, if the hard magnets are used in the VFMM, the magnetization of the hard magnets cannot be changed, unless a high current is applied to the stator windings. However, such a high current may damage the windings or other components of the electric motor.

[0031] According to one or more embodiments, if a current that is significantly higher than operational current of the stator windings passes the stator windings, this current may temporarily change the magnetization of the soft magnets to an unwanted value. This current (hereinafter, will be referred to as the “glitch current”) may be generated due to an unwanted glitch in the VFMM or a controller that controls the VFMM. However, it will be easy to revive the magnetization of the soft magnets by another current that is bearable by the stator windings. No matter how high the glitch current be, the magnetization of the soft magnets can be revived via a relatively smaller current than the glitch current because soft magnets can easily accept a different magnetization (compared to hard magnets).

[0032] On the other hand, if a synchronous motor that has soft magnet (such as a VFMM) includes hard magnets and the glitch current changes the magnetization of the hard magnets, reviving the magnetization of the hard magnets via a current in the stator windings will be difficult. Such a current capable of reviving the hard magnets may be too high to bear for the stator windings or other parts of the synchronous motor. For example, such a high current may bum the stator windings or may dislocate various components of the synchronous motor such as the rotor and the windings. To revive the hard magnets, the synchronous motor must be opened and the hard magnets must be separated from the synchronous motor to be placed under a high magnetic field.

[0033] In one or more embodiments, a certain number or amount of hard magnets may be used to create a magnetization baseline for the VFMM. Because the magnetization of the hard magnets is reluctant to change, the magnetization of the hard magnets will be the magnetization baseline, and the magnetization of the soft magnets will change the overall magnetization from the magnetization baseline (to higher or lower magnetization from the baseline, depending on the torque and RPM of the VFMM).

[0034] FIG. 2 shows a cross-sectional view of the VFMM (200) in accordance with one or more embodiments of the invention. The VFMM (200) of FIG. 2 includes a stator (201) that holds the stator windings in slots between adjacent stator teeth (202), and a rotor (203). The rotor (203) includes the soft magnets (204) and ferrous wedges (205) that are mounted on a rotor core (206). The rotor (203) is mounted on a shaft (208). The rotor (203) includes a sleeve (207) that keeps the soft magnets (204) and ferrous wedges (205) together. The sleeve (207) may be 0.5 to 3 millimeter (mm) thick in the radial direction. The thickness is determined by the centrifugal force exerted by the soft magnets (204) and the ferrous wedges (205). Alternatively, in one or more embodiments, the sleeve (207) may adhere to any one of the soft magnets

(204), the ferrous wedges (205), and/or the rotor core (206).

[0035] In these embodiments, the sleeve (207) may be from a non-binding material, which does not adhere to the soft magnets (204), the ferrous wedges

(205), and/or the rotor core (206). The non-binding sleeve (207) may be from carbon fiber HEX TOW IM10 or a Kevlar tow (i.e., Kevlar twine). Alternatively, the sleeve (207) may be a part of the rotor assembly.

[0036] The d-axis (direct axis) and q-axis (quadrature axis) are shown in FIG. 2. D-axis is the axis in which the magnetic field of the rotor is at its peak. For example, d-axis in FIG. 2 is in the middle of the adjacent poles that is between the adjacent ferrous wedges (205) where the magnetic field of the rotor (203) is the highest. The q-axis is away from the d-axis by 90 degrees phase. For example, q-axis in FIG. 2 is between the soft RMs (204) of each of the poles where the magnetic field of the rotor (203) is the lowest.

[0037] According to one or more embodiments, the rotor includes multiple poles and each of the poles includes one or more of the soft magnets. In one or more embodiments, each of the poles may include a plurality of the soft magnets. For example, the rotor (300) shown in FIGs. 3A-3B includes ten poles around a rotor core (306), and each of the poles includes eight soft magnets (302) (i.e., segments) disposed next to each other in the circumferential direction (308) and in the along the axial direction (312) between two ferrous wedges (304). In a viewing direction along the axial direction (312) (view of FIG. 3B), there are rows of soft magnets (302) disposed next to each other such that four soft magnets (302) are disposed next to each other in each of the rows.

[0038] FIGs. 3A-3B show examples of Design A of the rotor (300) in accordance with one or more embodiments of the invention. In Design A, the rows of soft magnets (302) are disposed next to each other in the circumferential direction (308) of the rotor (300). This arrangement of the rows of soft magnets (302) in Design A is different from Design B, which will be explained further below.

[0039] In other embodiments, the number of the rows of soft magnets (302) may be more or less than two and the number of the soft magnets (302) in each of the rows may be more or less than four depending on a specific design and function, as well as manufacturing constraints, of the VFMM.

[0040] According to one or more embodiments, an advantage of having multiple soft magnets (302) in a pole over having a single RM is reducing eddy currents in the soft magnets (302) during the VFMM operation as well as more defined control of magnetic field orientation inside the VFMM. When the soft magnets (302) or other conductive components of the VFMM are in a time-varying magnetic flux such as an AC magnetic flux, eddy currents are induced in the soft magnets (302) and in other conductive components of the VFMM. Eddy currents in the soft magnets (302) produce heat. Using multiple soft magnets (302) helps to reduce the eddy currents because small airgaps at the interface of adjacent soft magnets (302) stop the eddy currents from conducting between the adjacent soft magnets (302). Thus, the eddy currents and resistive losses will be reduced. From reading the embodiments of this disclosure, one of ordinary skill in the art will understand that the row of soft magnets as disclosed herein may include one or more segments depending on a specific design and function of the VFMM.

[0041] According to one or more embodiments, the rotor core (306) may be entirely or partially non-conductive and/or non-magnetic. For example, the rotor core (306) may be made of polyamide-imide, G10, thermoplastic materials, three-dimensional printed materials, Delrin, etc. A non-conductive rotor core (306) could be significantly lighter than traditional rotor cores that are made of metals such as aluminum and laminated or solid magnetic steel. According to one or more embodiments, the eddy currents cannot be generated in the non-conductive rotor core (306). Thus, the non-conductive rotor core (306) remains cooler than the traditional metallic rotor cores. In addition, reducing or omitting the eddy currents in the rotor core (306) is advantages because of reducing parasitic magnetic flux generated by the eddy currents that interfere with the magnetic flux generated by the stator windings. The interference of the magnetic fluxes may reduce the efficiency and controllability of the magnetization of the VFMM.

[0042] According to one or more embodiments, the rotor (300) may be mounted on a polygon (e.g, a hexagon) shaft (314) for a better grip between the rotor (300) and the shaft (314) or in other words, a better torque transfer between the shaft (314) and the rotor (300). Those skilled in the art will appreciate that other shapes may be employed for the shaft (314) depending on the purposes of the rotor (300).

[0043] According to one or more embodiments, the soft magnets and the ferrous wedges are designed to magnetize the soft magnets more efficiently than before. When the magnetic flux outside of the soft magnets (dissipated magnetic flux) is eliminated and instead, the magnetic flux is guided toward the soft magnets via the ferrous wedges, the efficiency of the VFMM magnetization increases. To eliminate the magnetic flux dissipation, the soft magnets and the ferrous wedges are designed to create the most efficient path for the magnetic flux inside the soft magnets. Hereinafter, the average direction of the magnetic flux inside the soft magnets will be referred to as the “magnetization direction.” According to one or more embodiments, the ferrous wedges may have a triangular shape to efficiently guide the magnetic flux to the soft magnets. For example, the ferrous wedges may be similar to the ferrous wedges (304) shown in FIGs. 3A-3B.

[0044] FIG. 4A shows various magnetization directions inside the soft magnets (402) in a cross-sectional view of the VFMM that includes the soft magnets (402), the ferrous wedges (404), the rotor core (406), the stator teeth (408), and the stator slots (410) that accommodate ends of the stator windings (412).

[0045] The magnetization directions in FIG. 4A are indicated by the slope of the magnetization directions in a Cartesian coordination in which “X” and “Y” axes are defined in FIG. 4A. The X axis is parallel to the interface between the soft magnets (402) and the Y axis is perpendicular to the X axis and the axial direction of the rotor. When the slope of a magnetization direction in the Cartesian coordination is “S,” the magnetization direction is defined as “+X/S+Y” and “-X/S+Y” in the upper and lower soft magnets (402), respectively.

[0046] According to one or more embodiments, a current conducting in the stator windings (412) creates a magnetic flux in the airgap (414) between the rotor and the stator. The ferrous wedges (404) guide the magnetic flux in the airgap (414) to the soft magnets (402) to magnetize the soft magnets (402).

[0047] According to one or more embodiments, the efficiency of the VFMM, which is the percentage of the total output mechanical power of the VFMM over the input electrical power of the VFMM, depends on the magnetization direction. Increasing the efficiency of electric motors is highly important in industry, and improvements of the efficiency even within 1% is considered substantial in the art. The efficiency is calculated using a numerical software (Finite Element Analysis) and is verified experimentally. All known losses of the machine including electrical and mechanical losses are considered in the calculation of the efficiency. The effect of the VFMM magnetization on the efficiency is more notable in electromagnetic losses. Electromagnetic losses include resistive losses in the stator windings, resistive losses by the eddy currents, and losses that are due to dissipation of the magnetic flux by straying out of the permeable areas (e.g., ferrous wedges and RMs) (hereinafter, will be referred to as stray losses).

[0048] Table 1 below shows the efficiency for various magnetization directions in accordance with one or more embodiments.

Table 1:

[0049] In Table 1, the magnetization direction for “test case 1” is circumferential, which means the average direction of the magnetic flux inside the soft magnets is along the circumference of the rotor. For example, with reference to FIG. 3B, the average direction of the magnetic flux inside the soft magnets (302) may be along the circumferential direction (308).

[0050] According to one or more embodiments, the geometries of the soft magnets (402), ferrous wedges (404), and the rotor core (406) are optimized to achieve the magnetization directions in Table 1.

[0051] Table 2 below shows five different designs each including exemplified geometrical factors of the soft magnets and ferrous wedges with reference to FIG. 4B that result to optimal magnetization directions to achieve the highest power efficiency at minimum mass of the VFMM. The geometrical factors in Table 2 correspond to various magnetization directions in accordance with one or more embodiments. These geometrical factors have been achieved through optimization methods to obtain the efficiencies in Table 1.

Table 2

[0052] FIG. 4B corresponds to the examples in Table 2. As shown in FIG. 4B, the magnet depth (422) in Table 2 is the radial thickness of the soft magnets (402). The magnet fraction in Table 2 is a percentage ratio between the angle (0m) that corresponds to the soft magnets (402) for each pole and of the angle (qr) that corresponds to the entire pole in the cross-sectional view of the rotor. For example, if the rotor includes 10 poles, q will be 36 degrees = 360/P, where “P” is the number of poles. In this example, the magnet fraction of 58% is equal to lOOx0_m/0_P. Thus, 0_m of this example will be 20.88 degrees. The rotor inert radius (424) is the radial distance between the RMs (402) and the center of the rotor, as shown in FIG. 4B. As shown in FIG. 4B, in the examples of Table 2, each of the ferrous wedges (404) has the triangular-type shape.

[0053] Although the designs shown in Table 2 are examples of the rotor to achieve the corresponding magnetization directions, one of ordinary skill in the art appreciates that the embodiments of the invention are not limited to these examples and that values of the geometrical factors in Table 2 can be achieved through optimization and computational simulations to achieve a specific magnetization direction depending on a design or manufacturing constraints of the VFMM.

[0054] For example, the magnetization direction may be determined via simulations using a commercial finite element method (FEM) software. In the FEM software, the geometries of the VFMM can be defined by building a three-dimensional model of the VFMM, and the magnetization direction can be determined by computationally solving electromagnetic equations for the VFMM model in an electromagnetic module of the FEM software. The FEM software may have multiple modules such as thermal transfer module and mechanical stress module that may be coupled to the electromagnetic module of the FEM software to determine a more accurate and universal performance of the VFMM.

[0055] In one or more embodiments, the variables in Table 2 can be varied in the FEM simulations to obtain different magnetization directions. For example, magnet depth, magnet fraction, or rotor inert radius for Design 1 can be changed (i.e., adjusted) to achieve a magnetization direction different than - X/16+Y.

[0056] In one or more embodiments, the geometries of the rotor can be formulized, and optimization methods can be applied to the formulized geometries to achieve the optimal magnetization direction. For example, the edges of the RMs (402) and the ferrous wedge (404) in FIG. 4C can be define via formulas (l)-(7) below.

(1) The first end of edge (4021) is at point “A” in FIG. 4C, which is at x=(ri+drb+dm) ^c cos(-a_m ^x 180degree/P+qrr- 180degree/P) and y=(ri+drb+dm)xsin(-a_m ^x180degree/P+qrr-180degree/P). The second end of edge (4021) is at point “C,” which is at x=(ri+drb+dm) ^c cos(a_m ^x 180degree/P+qrr- 180degree/P) and y=(ri+drb+dm)xsin(a_m ^x180degree/P+qrr-180degree/P). The curvature of edge (4021) between the first and second ends of edge (4021) is 360degree/P.

(2) The first end of edge (4022) is at point “B,” which is at x=(ri+drb)xcos(- a_m ^x180degree/P+qrr-180degree/P) and y=(ri+drb)xsin(- a_m ^x180degree/P+qrr-180degree/P). The second end of edge (4022) is at point “D,” which is at x=(ri+drb)xcos(a_m ^x180degree/P+qrr-180degree/P) and y=(ri+drb)xsin(a_m ^x180degree/P+qrr-180degree/P). The curvature of edge (4022) between the first and second ends of edge (4022) is 360degree/P.

(3) The edge (4023) is a straight line between points A and B.

(4) The edge (4024) is a straight line between points C and D.

(5) The ferrous wedge (404) shares the edge (4024) with the soft PMs (402).

(6) The edge (4042) of the ferrous wedge (404) is starts at points C and ends with a curve of (ai-a_m)^x 180degree/P at E.

(7) The edge (4041) of the ferrous wedge (404) is a straight line between point D and point E.

[0057] In the above formulas (l)-(7), “ri” is the rotor inert radius, “drb” is rotor back iron, “dm” is magnet depth (4025), “a_m” is scaled magnet fraction. For example, for a magnet fraction of 58%, a_m is 0.58. “cci” is equal to l-a_m. “P” is the number of poles “qrr” is equal to cot+q, where theta is “co” is the angular velocity of the rotor and, “t” is time, and “Q” is an angle offset.

[0058] In one or more embodiments, the gap (418) between the soft magnets or the ferrous wedges and the stator (hereinafter will be referred to as “gap”) that may include the airgap (414) and a non-magnetic sleeve (420) may not directly affect the magnetization direction. However, the gap (418) may affect the efficiency because more energy is required to pass the magnetic flux from the stator windings through the gap (418), which may have a magnetic permeability of about 1. In one or more embodiments, the gap (418) may be about 2.25 mm such that 0.9 mm of the gap may be occupied by sleeve (420) and 1.35 mm is the airgap (414) between the sleeve (420) and the stator.

[0059] FIGS. 5 A and 5B show magnetic fluxes in cross-sectional views of the VFMM for magnetization directions of ±X/4+Y and ±X/ 16+Y, respectively. These figures illustrate how the magnetization direction affects the VFMM efficiency. In these figures, the ferrous wedges (504) conduct the magnetic flux generated by the stator windings to the soft magnets (502). The rotor core (506) is chosen from non-conductive/non-magnetic polyamide-imide to prevent shunting the magnetic flux by the rotor core (506). Thus, most of the magnetic flux enters and magnetizes the soft magnets (502).

[0060] According to one or more embodiments, the shapes and sizes of the soft magnets (502) and the ferrous wedges (504) determine the efficiency of magnetizing the soft magnets (502) and dissipation of the magnetic flux to outside of the soft magnets (502). For example, there is less stray (508) of the magnetic flux for magnetization directions of ±X/16+Y (shown in FIG. 5B) than for the magnetization directions of ±X/4+Y (shown in FIG. 5A). Consequently, the magnetization of the soft magnets (502) is more efficient with magnetization directions of ±X/16+Y than with magnetization directions of ±X/4+Y. The stray (508) of the magnetic flux is an example of the stray losses described above. [0061] High-power VFMMs, for example higher than 50 kW, require large pulses of electrical current to magnetize soft magnets used in the VFMMs. For example, FIG. 6 A shows Design A of a rotor (600) for a 175 kW VFMM and a magnetization diagram for soft magnets (602) in the rotor (600). Upon applying a current pulse with a peak amplitude of 5500 Ampere (A), the magnetization of the soft magnets (602) can reach a maximum magnetization state (MS) of 92%. Even at such a high current, the MS does not reach 100% because the soft magnets (602) are not homogenously magnetized, as explained below with reference to FIG. 6B.

[0062] FIG. 6B shows magnetic field distribution in the portion of the rotor (600) shown in FIG. 6A at the current peak of 5500 A. At the current peak, the inner portion of the soft magnets (602) (circled) is not as magnetized as the outer portion of the soft magnets (602) (i.e., on the right side of the circled area). This is because the magnetic permeability (p_r) of the soft magnets (602) such as AlNiCo are relatively low compared to iron and is comparable with magnetic permeability of non-magnetic materials such as air and plastic (p_r ~ 1.0). FIG. 7 shows magnetic field (“B”) as a function of auxiliary magnetic field (“H”) for various types of AlNiCo. The slope of the curves shown in FIG. 7 is the magnetic permeability of AlNiCo, which is between 1.1 to 1.5 above the knee for AlNiCo-9.

[0063] FIG. 8 shows an example of Design B of a VFMM rotor in which an arrangement of soft magnets is different from in Design A. In Design B, for each pole of the rotor, the soft magnets are spaced from each other in a radial direction of the rotor. For example, in FIG. 8, the soft magnets (802) are disposed between two ferrous wedges (804) such that the soft magnets (802) are spaced from each other in the radial direction of the rotor (800), which is along the “X.”

[0064] According to one or more embodiments, the radial thicknesses of the soft magnets (802) (dm_l, dm 2, and dm 3), the spaces (806) for disposing the soft magnets (802) (dg_l, dg_2, and dg_3), and the edge angle (Q) of the soft magnets (802) can be obtained through optimization methods to achieve a more efficient VFMM.

[0065] The example shown in FIG. 8 is designed for a 175 kW VFMM. In this example, each pole includes three soft magnets (802), the radial thicknesses of the soft magnets (802) and the spaces (806) between adjacent soft magnets (802) may be the same. In one or more embodiments, the radial thicknesses of the soft magnets and the spaces between adjacent soft magnets may be different from one another but substantially similar. For example, a variation between the thicknesses may be less than 10% of the mean thickness for all of the thicknesses. One of ordinary skill in the art acknowledges that the above parameters such as the number of soft magnets, the space between the soft magnets, and edge angle may be chosen differently from the examples disclosed herein based on specific designs and functions of the VFMM.

[0066] In one or more embodiments, the spaces (806) may be air. One of ordinary skill in the art acknowledges that the spaces (806) may be from another non-magnetic material such as a polymer.

[0067] According to one or more embodiments, each of the soft magnets in Design B may include one or more segment of soft magnets along the “Z” axis similar to the embodiments disclosed above with reference to FIGs. 3A-3B. For example, each of the soft magnets (802) shown in FIG. 8 includes four segments of soft magnets along the “Z” axis.

[0068] FIG. 9A compares magnetizations of soft magnets (902) in Design A and Design B in VFMM rotors (900) with relative dimensions of the soft magnets (902), spaces (904), ferrous wedges (906), and rotor cores (908) shown in FIG. 9. Specifically, the soft magnets (902) have the same radial thicknesses and the spaces (904) between the soft magnets (902) are substantially the same size as the radial thickness of the soft magnets (1002). In this comparison, a current pulse with a peak of 1000 A is fed to the VFMMs corresponding to the designs. Although the total amount of soft magnets (902) in Design B is about half of the total amount of soft magnets (902) in Design A, the average magnetic field in the soft magnets (902) in Design B is much higher than in Design A and more closely matches the ideal magnetization curve of AlNiCo.

[0069] Higher magnetization of the soft magnets (902) in Design B (compared to Design A) is because the magnetic field in Design B shunts to areas other than the soft magnets (902) less than in Design A. FIG. 9B shows magnetic field density maps for the rotors (900) shown in FIG. 9A. The color variation in the soft magnets (902) of Design A shows that the magnetic field shunts to the rotor core (908). On the other hand, the magnetic field in the soft magnets (902) of Design B is distributed homogenously and has a higher contrast with the magnetic field in the rotor core (908).

[0070] FIG. 10 shows Designs B1 and B2 of VFMM rotors (1000), which are examples of Design B. Design Bl, which shows the VFMM rotor (900) of Design B shown in FIGs. 9A-9B, includes three soft magnets (1002) in each pole, and the soft magnets (1002) have the same radial thicknesses and are spaced with spaces (1004) that are substantially the same size as the radial thicknesses of the soft magnets (1002). Design B2 includes two soft magnets (1002) in each pole and the soft magnets (1002) have the same radial thicknesses and are spaced with a space that is smaller than the radial thickness of the soft magnets (1002). FIG. 10 shows that the magnetic field in the soft magnets (1002) of Design B 1 is distributed more homogenously than in Design B2.

[0071] While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

CLAIMS What is claimed is:

1. A multi-pole rotor of a variable-flux memory motor (VFMM), comprising: a rotor core; and a plurality of poles, each comprising: a plurality of soft magnets; a first ferrous wedge; and a second ferrous wedge, wherein the plurality of soft magnets is disposed: between the first and second ferrous wedges, along a radial direction of the rotor with respect to one another, and such that at least two adjacent soft magnets among the plurality of soft magnets are spaced from one another in the radial direction of the rotor.

2. The multi-pole rotor according to claim 1, wherein all of the plurality of soft magnets are spaced from one another.

3. The multi-pole rotor according to claim 2, wherein thicknesses of the plurality of soft magnets are substantially similar.

4. The multi-pole rotor according to claim 2, wherein thicknesses of spaces between all adjacent soft magnets among the plurality of soft magnets are substantially similar.

5. The multi-pole rotor according to claim 2, wherein thicknesses of the plurality of soft magnets and of spaces between all adjacent soft magnets among the plurality of soft magnets are substantially similar.

6. The multi-pole rotor according to claim 1, wherein the space between the at least two adjacent soft magnets is a non-magnetic material.

7. The multi-pole rotor according to claim 1, wherein the space between the at least two adjacent soft magnets is air.

8. The multi-pole rotor according to claim 1, wherein the plurality of soft magnets comprises a combination of aluminum, nickel, and cobalt.

9. The multi-pole rotor according to claim 8, wherein the plurality of soft magnets is AlNiCo with one of the grades 1-9.

10. The multi-pole rotor according to claim 1, wherein the rotor core is non-conductive.

11. The multi-pole rotor according to claim 10, wherein the rotor core is a polyamide- imide.

12. The multi-pole rotor according to claim 1, wherein at least one of the plurality of soft magnets comprises a plurality of magnet segments disposed next to each other in an axial direction of the rotor.

13. The multi-pole rotor according to claim 1, wherein each of the plurality of soft magnets comprises a plurality of magnet segments disposed next to one another in an axial direction of the rotor.

14. The multi-pole rotor according to claim 1, further comprising a sleeve that keeps the plurality of soft magnets and the first and second ferrous wedges from disassociation from the rotor core.

15. The multi-pole rotor according to claim 1, wherein the multi -pole rotor does not include a rare-earth-material magnet as a rotor magnet.

16. The VFMM comprising the multi-pole rotor according to claim 1.

17. The VFMM comprising the multi-pole rotor of claim 3.

18. The VFMM comprising the multi-pole rotor of claim 4.

19. The multi-pole rotor according to claim 3, wherein the multi-pole rotor does not include a rare-earth-material magnet as a rotor magnet.

20. The multi-pole rotor according to claim 4, wherein the multi-pole rotor does not include a rare-earth-material magnet as a rotor magnet.