Variable Flux Memory Motor and Method for Controlling a Variable Flux Motor

Abstract

In one aspect, an embodiment of the present invention is directed to a multi-pole rotor for a variable flux memory motor (VFMM), including a rotor core and a plurality of magnetic poles, each of which includes one or more soft rotor magnets, a first iron wedge, and a second iron wedge, the one or more soft rotor magnets being disposed circumferentially between the first iron wedge and the second iron wedge.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority under 35 U.S.C. § 119(e) to U.S. Patent Application No. 16 / 383,274, filed on Apr. 12, 2019. The content thereof is incorporated herein by reference in its entirety.

Background Art

[0002] Synchronous electric motors including 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, due to their high efficiency. Also, since permanent magnets are used instead of windings in the rotors of synchronous electric motors, there is no need for rotor cooling. These advantages, along with other advantages (e.g., being brushless), promote the use of synchronous electric motors where high torque, high efficiency, or low maintenance is required for electric motors.

Summary of the Invention

[0003] In one aspect, embodiments of the present invention are directed to a multi - pole rotor of a variable - flux memory motor (VFMM) including a rotor core and a plurality of magnetic poles. Each of the magnetic poles includes one or more soft rotor magnets, a first ferrous wedge, and a second ferrous wedge. The one or more soft rotor magnets are disposed between the first ferrous wedge and the second ferrous wedge in the circumferential direction of the rotor.

[0004] In one aspect, embodiments of the present invention are directed to a method for controlling the magnetization state of a VFMM. The method includes receiving an instruction to change the magnetization state, determining an ideal magnetization state based on the instruction, measuring the back electromotive force generated by the magnets of the VFMM, determining the real-time magnetization state of the magnets based on the measured back electromotive force, determining a d-axis current pulse based on the difference between the ideal magnetization state and the real-time magnetization state, and sending a d-axis current pulse to the stator windings of the VFMM to adjust the real-time magnetization state such that the absolute value of the difference between the ideal magnetization state and the adjusted real-time magnetization state falls within a predetermined threshold range.

[0005] In one aspect, embodiments of the present invention are directed to a method for automatically controlling the magnetization state of a VFMM. The method includes measuring the speed of the VFMM, determining the torque of the VFMM, determining an ideal magnetization state based on the speed and torque of the VFMM, measuring the back electromotive force generated by the magnets of the VFMM, determining the real-time magnetization state of the magnets based on the measured back electromotive force, determining a d-axis current pulse based on the difference between the ideal magnetization state and the real-time magnetization state, and sending a d-axis current pulse to the stator windings of the VFMM to adjust the real-time magnetization state with respect to the ideal magnetization state such that the absolute value of the difference between the ideal magnetization state and the adjusted real-time magnetization state falls within a predetermined threshold range.

[0006] In one aspect, embodiments of the present invention are directed to a system for a VFMM. The system includes a VFMM and a control device. The VFMM includes a rotor including a rotor core and a plurality of magnetic poles, and a stator. Each of the magnetic poles of the rotor includes one or more soft rotor magnets, a first iron wedge, and a second iron wedge. The one or more soft rotor magnets are disposed between the first iron wedge and the second iron wedge. The stator includes first, second, and third stator windings respectively corresponding to first, second, and third magnetization phases, and at least one sense coil for measuring the magnetization state of the VFMM. The control device controls the magnetization state of the VFMM based on the magnetization state of the VFMM measured via the sense coil. The control device adjusts the magnetization state of the VFMM via a current pulse in at least one of the first, second, and third stator windings.

[0007] Other aspects of the present invention will become apparent from the following description and the appended claims.

Brief Description of the Drawings

[0008]

Figure 1

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DETAILED DESCRIPTION OF THE INVENTION

[0009] Next, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. Similar elements in the various figures are denoted by similar reference numerals for consistency.

[0010] In the following detailed description of the embodiments of the present invention, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. However, it would have been apparent to those skilled in the art that the present invention could be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0011] FIG. 1 shows an exploded view of a synchronous electric motor (100) (hereinafter referred to as "synchronous motor") including a rotor (101), a stator (102), and a stator winding (103) disposed around a rotor hub (104). The synchronous motor may also include a terminal box for connecting to an input power source, a cooling fan, a rotor position sensor, a temperature sensor, a liquid cooling housing, etc. The rotor (101) includes a plurality of magnetic poles, each of which includes a permanent magnet (105) (PM).

[0012] The synchronous motor (100) operates via a three-phase AC input where each phase lags the other two phases by 120°. To create the three-phase AC input, a power conversion device may convert DC power supplied to the power conversion device from a high voltage DC source (e.g., a battery). By applying a three-phase AC input to the synchronous motor, the stator winding creates a three-phase magnetic field that interacts with the magnetic field of the PM (105) and rotates the rotor (101) at a constant number of revolutions per minute (RPM) speed (hereinafter referred to as "RPM") in the steady state. The RPM of the synchronous motor is fixed by limiting factors such as the number of magnetic poles, the available voltage, and the magnetic flux linkage number (λ m ) provided and fixed by the PM. The synchronous motor has a wide range of applications in industrial, commercial, and residential applications, such as fans, pumps, compressors, elevators, and refrigerators, industrial machinery, and electric vehicles.

[0013] In one or more embodiments, λ provided by the PM mSince it is fixed, a synchronous motor including a PM has a narrow constant power speed range (CPSR), which is a speed range in which the driving of the motor can maintain a constant output with limited motor input voltage and current values. Therefore, it is difficult to increase the CPSR of a synchronous motor without using advanced control techniques such as implementing a field weakening control method. Due to the narrow CPSR range for synchronous motors, it may be necessary to use a power transmission system to vary the CPSR of a system driven by a synchronous motor. Even by using such advanced methods, the CPSR of a synchronous motor is expanded from 2 to 3. On the other hand, the CPSR of the VFMM according to one or more embodiments can achieve from 4 to 6.

[0014] Generally, embodiments of the present invention relate to the design of a VFMM, a rotor for the VFMM, and a method of magnetizing the VFMM. The VFMM is a type of synchronous motor in which the magnetization of the rotor magnet (RM) of the VFMM can be adjusted (i.e., changed) during the operation of the VFMM. Adjustment of the magnetization of the RM (hereinafter referred to as "VFMM magnetization" for simplicity) changes the RPM of the VFMM. According to one or more embodiments, to facilitate changes in VFMM magnetization, the RM is made of a soft ferromagnetic material such as aluminum-nickel-cobalt (AlNiCo) or some types of ceramics. Hereinafter, the RM made of a soft ferromagnetic material is referred to as a "soft RM". According to one or more embodiments, the soft RM can be a magnet composed of grade 1 to 9 AlNiCo, or a sintered structure of AlNiCo, castings, ceramics, samarium cobalt of the same grade, or these materials. It is obvious that those skilled in the art can use a specific amount of these materials to obtain the desired functions of the VFMM.

[0015] The maximum achievable RPM with the limited voltage of the VFMM can be obtained more efficiently by changing the VFMM magnetization. Thus, the VFMM according to one or more embodiments is a superior alternative to synchronous motors. In other words, the CPSR of the VFMM can have a wider range compared to the CPSR of synchronous motors. Therefore, there is no need to couple a power transmission system to the VFMM. As a result, according to one or more embodiments, by using the VFMM, since it is magnetized or demagnetized during assembly, the manufacturing cost of a system equipped with an electric motor is potentially reduced.

[0016] Soft ferromagnetic materials have high permeability (the same as hard ferromagnetic materials such as alloys of iron and nickel), but have low coercivity of saturation (different from hard ferromagnetic materials). Due to the low coercivity of saturation of soft ferromagnetic materials, changing the magnetization of soft ferromagnetic materials requires a relatively smaller magnetic field compared to hard ferromagnetic materials.

[0017] In one or more embodiments, only soft RM may be used as the magnet of the rotor of the VFMM, and hard magnets (i.e., magnets made of hard ferromagnetic materials) may not be attached to the rotor. Alternatively, in one or more embodiments, both soft RM and hard magnets can be used as the magnets of the rotor of the VFMM. Since hard magnets are made of rare earth materials and are much more expensive than soft RM (e.g., AlNiCo), embodiments of the present invention can have advantages over synchronous motors that use only hard magnets. Therefore, by partially or entirely using soft RM instead of hard magnets in the VFMM, the manufacturing cost of the VFMM is significantly reduced compared to conventional synchronous motors.

[0018] Furthermore, another advantage of using soft RM is that the overall magnetization of all the magnets in the VFMM can be controlled and varied over a wide range. According to one or more embodiments, the overall magnetization of the soft RM can be varied to any value from 0% magnetization (i.e., the soft RM is completely demagnetized) to 100% magnetization (i.e., the soft RM is magnetized to its maximum capacity). This change in magnetization can occur in a short time (e.g., about 1 millisecond).

[0019] In contrast, hard magnets do not easily change their magnetization. Thus, changing the magnetization of hard magnets requires much more power than the operating power of a VFMM or other types of synchronous motors. For example, changing the magnetization of some grades of neodymium iron boron (NdFeB) and samarium cobalt (SmCo) and other hard magnets may require more than 10 times the power required to change the magnetization of soft RM. Therefore, when hard magnets are used in a VFMM, the magnetization of the hard magnets cannot be changed unless a large current is applied to the stator winding. However, such a large current can damage the windings or other components of the electric motor.

[0020] According to one or more embodiments, when a current significantly larger than the operating current of the stator winding passes through the stator winding, this current can temporarily change the magnetization of the soft RM to an undesirable value. This current (hereinafter referred to as "glitch current") can be generated due to an undesirable glitch in the VFMM or the control device that controls the VFMM. However, it will be easier to restore the magnetization of the soft RM by another current that the stator winding can withstand. Since the soft RM can easily accept different magnetizations (compared to hard magnets), no matter how large the glitch current is, the magnetization of the soft RM can be restored via a current relatively smaller than the glitch current.

[0021] On the other hand, a synchronous motor having a soft magnet (such as a VFMM) includes a hard magnet, and when a glitch current changes the magnetization of the hard magnet, it will be difficult to recover the magnetization of the hard magnet through the current in the stator winding. Such a current that can recover the hard magnet may be too large for the stator winding or other components of the synchronous motor to withstand. For example, such a large current may burn the stator winding or displace various components of the synchronous motor such as the rotor and winding. To recover the hard magnet, the synchronous motor must be opened, and the hard magnet must be separated from the synchronous motor placed under a high magnetic field.

[0022] In one or more embodiments, a specific number or amount of hard magnets may be used to create a magnetization baseline for the VFMM. Since the magnetization of the hard magnet is difficult to change, the magnetization of the hard magnet becomes the magnetization baseline, and the magnetization of the soft magnet changes the overall magnetization from the magnetization baseline (higher or lower magnetization from the baseline depending on the torque and RPM of the VFMM).

[0023] FIG. 2 shows a cross-sectional view of a VFMM (200) according to one or more embodiments of the present invention. The VFMM (200) of FIG. 2 includes a stator (201) that holds a stator winding in a slot between adjacent stator teeth (202), and a rotor (203). The rotor (203) includes a soft RM (204) and a pole piece (205) attached on a rotor core (206). The rotor (203) is attached on a shaft (208). The rotor (203) includes a sleeve (207) that holds the soft RM (204) and the pole piece (205) together. The sleeve (207) may have a thickness of 0.5 to 3 millimeters (mm) in the radial direction. The thickness is determined by the centrifugal force exerted by the soft RM (204) and the pole piece (205). Alternatively, in one or more embodiments, the sleeve (207) may be attached to any one of the soft RM (204), the pole piece (205), and / or the rotor core (206).

[0024] In these embodiments, the sleeve (207) can be made of a non-bonding material that does not adhere to the soft RM (204), the iron wedge (205), and / or the rotor core (206). The non-bonding sleeve (207) can be made of carbon fiber HEX TOW IM10 or Kevlar tow (i.e., Kevlar twisted yarn). Alternatively, the sleeve (207) can be part of the rotor assembly.

[0025] The d-axis (direct axis) and q-axis (quadrature axis) are shown in Figure 2. The D-axis is the axis where the magnetic field of the rotor is located at its peak. For example, the d-axis in Figure 2 is in the middle of adjacent magnetic poles existing between adjacent iron wedges (205), where the magnetic field of the rotor (203) is the highest. The Q-axis is 90 degrees out of phase from the d-axis. For example, the q-axis in Figure 2 is between the soft RMs (204) of each magnetic pole, where the magnetic field of the rotor (203) is the lowest.

[0026] According to one or more embodiments, the rotor includes a plurality of magnetic poles, and each of the magnetic poles includes one or more of the soft RMs. In one or more embodiments, each of the magnetic poles can include a plurality of soft RMs. For example, the rotor (300) shown in Figures 3A - 3B includes ten magnetic poles around the rotor core (306), and each of the magnetic poles includes eight soft RMs (302) (i.e., segments) arranged adjacent to each other in the circumferential direction (308) and along the axial direction (312) between two iron wedges (304). In the viewing direction along the axial direction (312) (the view in Figure 3B), there are rows of soft RMs (302) arranged adjacent to each other such that four soft RMs (302) are arranged adjacent to each other in each row.

[0027] In other embodiments, depending on the specific design and function of the VFMM as well as manufacturing constraints, the number of rows of soft RMs (302) can be more or less than two, and the number of soft RMs (302) in each row can be more or less than four.

[0028] According to one or more embodiments, the advantage of having a plurality of soft RMs (302) within a magnetic pole over having a single RM is to reduce eddy currents in the soft RMs (302) during VFMM operation and to provide more precise control of the magnetic field orientation within the VFMM. When the soft RM (302) or other conductive components of the VFMM are within a time-varying magnetic flux such as an AC magnetic flux, eddy currents are induced within the soft RM (302) and other conductive components of the VFMM. Eddy currents in the soft RM (302) generate heat. Using a plurality of soft RMs (302) helps reduce eddy currents because small gaps at the contact surfaces of adjacent soft RMs (302) prevent eddy currents from conducting between adjacent soft RMs (302). Thus, eddy currents and resistive losses are reduced.

[0029] According to one or more embodiments, the rotor core (306) can be wholly or partially non-conductive and / or non-magnetic. For example, the rotor core (306) can be made of polyamideimide, G10, a thermoplastic material, a 3D printed material, Delrin, etc. A non-conductive rotor core (306) can be significantly lighter than a conventional rotor core made of a metal such as aluminum or laminated or solid magnetic steel. According to one or more embodiments, eddy currents cannot be generated in a non-conductive rotor core (306). Thus, the non-conductive rotor core (306) remains cooler than a conventional metal rotor core. Further, reducing or eliminating eddy currents in the rotor core (306) is advantageous for reducing parasitic magnetic fluxes generated by eddy currents that interfere with the magnetic flux generated by the stator windings. Interference of the magnetic flux can reduce the efficiency and controllability of magnetization of the VFMM.

[0030] According to one or more embodiments, the rotor (300) can be mounted on a polygonal (e.g., octagonal) shaft (314) for a good grip between the rotor (300) and the shaft (314), in other words, for good torque transmission between the shaft (314) and the rotor (300). Those skilled in the art will understand that other shapes can be used for the shaft (314) depending on the purpose of the rotor (300).

[0031] According to one or more embodiments, the soft RM and the iron wedge are designed to magnetize the soft RM more efficiently than before. The efficiency of VFMM magnetization is increased when the magnetic flux (dissipated magnetic flux) outside the soft RM is eliminated and instead the magnetic flux is guided through the iron wedge towards the soft RM. To eliminate magnetic flux dissipation, the soft RM and the iron wedge are designed to create the most efficient path for the magnetic flux inside the soft RM. Hereinafter, the average direction of the magnetic flux inside the soft RM is referred to as the "magnetization direction". According to one or more embodiments, the iron wedge can have a triangular shape to efficiently guide the magnetic flux to the soft RM. For example, the iron wedge can be similar to the iron wedge (304) shown in FIGS. 3A - 3B.

[0032] FIG. 4A shows various magnetization directions inside the soft RM (402) in a cross-sectional view of a VFMM including the soft RM (402), the iron wedge (404), the rotor core (406), the stator teeth (408), and the stator slots (410) that accommodate the ends of the stator windings (412).

[0033] The magnetization directions in FIG. 4A are indicated by the inclination of the magnetization direction in the Cartesian coordinate system, and the "X" and "Y" axes of the Cartesian coordinate system are defined in FIG. 4A. The X-axis is parallel to the contact surface between the soft RMs (402), and the Y-axis is perpendicular to the X-axis and the axial direction of the rotor. When the inclination of the magnetization direction in the Cartesian coordinate system is "S", the magnetization direction is defined as "+X / S + Y" for the upper soft RM (402) and "-X / S + Y" for the lower soft RM (402), respectively.

[0034] According to one or more embodiments, the current passing through the stator winding (412) creates a magnetic flux within the air gap (414) between the rotor and the stator. The iron wedge (404) guides the magnetic flux within the air gap (414) to the soft RM (402) in order to magnetize the soft RM (402).

[0035] According to one or more embodiments, the efficiency of the VFMM, which is the ratio of the total output mechanical force of the VFMM to the input power of the VFMM, depends on the magnetization direction. Improving the efficiency of an electric motor is of great importance in the industry, and even an improvement in efficiency within the range of 1% is considered significant in the art. The efficiency is calculated using numerical calculation software (finite element analysis) and experimentally verified. All known losses of the machine, including electrical losses and mechanical losses, are considered in the calculation of the efficiency. The influence of VFMM magnetization on the efficiency is more prominent in electromagnetic losses. Electromagnetic losses include resistance losses in the stator winding, resistance losses due to eddy currents, and losses caused by the dissipation of magnetic flux (hereinafter referred to as stray losses) that drift outside the ferromagnetic regions (e.g., iron wedges and RM).

[0036] Table 1 below shows the efficiency for various magnetization directions according to one or more embodiments.

Table 1

[0037] In Table 1, the magnetization direction for "Test Case 1" is the circumferential direction, which means that the average direction of the magnetic flux inside the soft RM is along the circumference of the rotor. For example, referring to FIG. 3B, the average direction of the magnetic flux inside the soft RM (302) can be along the circumferential direction (308).

[0038] According to one or more embodiments, the geometries of the soft RM (402), the iron wedge (404), and the rotor core (406) are optimized to obtain the magnetization directions in Table 1.

[0039] Table 2 below shows five different designs, each of which results in an optimal magnetization direction for obtaining maximum power efficiency at the minimum mass of the VFMM, and includes the illustrated geometric factors of the soft RM and the iron wedge related to FIG. 4B. The geometric shape factors in Table 2 correspond to various magnetization directions according to one or more embodiments. These geometric shape factors were obtained through the optimization method for obtaining the efficiency in Table 1.

Table 2

[0040] FIG. 4B corresponds to the example in Table 2. As shown in FIG. 4B, the magnet depth (422) in Table 2 is the radial thickness of the soft RM (402). The magnet ratio in Table 2 is the percentage ratio of the angle (θ m ) corresponding to the soft RM (402) for each pole to the angle (θ p ) corresponding to the entire pole in the cross-sectional view of the rotor. For example, when the rotor includes 10 poles, θ p is 36 degrees = 360 / P, where "P" is the number of poles. In this example, a magnet ratio of 58% is equal to 100×θ m / θ p . Thus, θ m in this example is 20.88 degrees. The rotor inactive radius (424) is the radial distance between the rotor RM (402) and the center of the rotor, as shown in FIG. 4B. As shown in FIG. 4B, in the example of Table 2, each of the iron wedges (404) has a triangular shape.

[0041] The designs shown in Table 2 are examples of rotors for obtaining the corresponding magnetization directions, but those skilled in the art will understand that the embodiments of the present invention are not limited to these examples, and that the values of the geometric shape factors in Table 2 can be obtained through optimization and computational simulations to obtain a specific magnetization direction according to the design or manufacturing constraints of the VFMM.

[0042] For example, the magnetization direction can be determined through simulations using commercially available finite element method (FEM) software. In the FEM software, the geometry of the VFMM can be defined by constructing a three-dimensional model of the VFMM, and the magnetization direction can be determined by computationally solving the electromagnetic equations for the VFMM model in the electromagnetic module of the FEM software. The FEM software can have multiple modules, such as a heat transfer module and a mechanical stress module, that can be coupled to the electromagnetic module of the FEM software to determine more accurate and general performance of the VFMM.

[0043] In one or more embodiments, the variables in Table 2 can be changed in the FEM simulation to obtain various magnetization directions. For example, to obtain a magnetization direction different from -X / 16 + Y, the magnet depth, magnet ratio, or rotor inactive radius for Design 1 can be changed (i.e., adjusted).

[0044] In one or more embodiments, the geometry of the rotor can be formulated, and the optimization method can be applied to the formulated geometry to obtain an optimal magnetization direction. For example, the edges of the rotor RM(402) and the iron wedge (404) in FIG. 4C can be defined through the following equations (1) to (7). (1) The first end of the edge (4021) is located at point "A" in FIG. 4C, which is x = (ri + drb + dm) × cos(-α m × 180 degrees / P + qrr - 180 degrees / P) and y = (ri + drb + dm) × sin(-α m × 180 degrees / P + qrr - 180 degrees / P). The second end of the edge (4021) is located at point "C", which is x = (ri + drb + dm) × cos(α m × 180 degrees / P + qrr - 180 degrees / P) and y = (ri + drb + dm) × sin(α m × 180 degrees / P + qrr - 180 degrees / P). The curvature of the edge (4021) between the first end and the second end of the edge (4021) is 360 degrees / P. (2) The first end of the edge portion (4022) is located at point "B", which is at x = (ri + drb) × cos(-α m × 180 degrees / P + qrr - 180 degrees / P) and y = (ri + drb) × sin(-α m × 180 degrees / P + qrr - 180 degrees / P). The second end of the edge portion (4022) is located at point "D", which is at x = (ri + drb) × cos(α m × 180 degrees / P + qrr - 180 degrees / P) and y = (ri + drb) × sin(α m × 180 degrees / P + qrr - 180 degrees / P). The curvature of the edge portion (4022) between the first end and the second end of the edge portion (4022) is 360 degrees / P. (3) The edge portion (4023) is a straight line between point A and point B. (4) The edge portion (4024) is a straight line between point C and point D. (5) The wedge (404) shares the edge portion (4024) with the soft PM (402). (6) The edge portion (4042) of the wedge (404) starts from point C and has a curve of (α i -α m ) × 180 degrees / P and ends at E. (7) The edge portion (4041) of the wedge (404) is a straight line between point D and point E.

[0045] In the above formulas (1) to (7), "ri" is the rotor inactive radius, "drb" is the rotor back iron, "dm" is the magnet depth (4025), "α m " is the scaled magnet fraction. For example, in the case of a 58% magnet fraction, α m is 0.58. "α i " is equal to 1 - α m . "P" is the number of poles. "qrr" is equal to ωt + θ, where "ω" is the angular velocity of the rotor, "t" is the time, and "θ" is the angle offset.

[0046] In one or more embodiments, the gap (418) (hereinafter referred to as the "gap") between the soft RM or armature and the stator, which may include a void (414) and a non-magnetic sleeve (420), cannot directly affect the magnetization direction. However, since more energy is required to pass the magnetic flux through the gap (418) which may have a permeability of about 1 from the stator winding, the gap (418) can affect the efficiency. In one or more embodiments, the gap (418) can be about 2.25 mm such that 0.9 mm of the gap can be occupied by the sleeve (420) and 1.35 mm is the void (414) between the sleeve (420) and the stator.

[0047] Figures 5A and 5B show the magnetic flux in cross-sections of the VFMM for magnetization directions of ±X / 4 + Y and ±X / 16 + Y respectively. These figures show how the magnetization direction affects the VFMM efficiency. In these figures, the armature (504) guides the magnetic flux generated by the stator winding to the soft RM (502). The rotor core (506) is selected from non-conductive / susceptible polyamide-imide to prevent shunting the magnetic flux from the rotor core (506). Thus, most of the magnetic flux enters the soft RM (502) and magnetizes the soft RM (502).

[0048] According to one or more embodiments, the shape and size of the soft RM (502) and the armature (504) determine the efficiency of magnetizing the soft RM (502) and the dissipation of the magnetic flux to the outside of the soft RM (502). For example, there is less magnetic flux wandering (508) in the case of the magnetization direction of ±X / 16 + Y (shown in Figure 5B) than in the case of the magnetization direction of ±X / 4 + Y (shown in Figure 5A). Thus, magnetizing the soft RM (502) is more efficient using the magnetization direction of X / 16 + Y than using the magnetization direction of ±X / 4 + Y. The magnetic flux wandering (508) is an example of the wandering loss described above.

[0049] According to one or more embodiments, the stator winding creates the magnetic flux necessary to magnetize the VFMM and rotate the rotor. FIG. 6A shows a simplified circuit model of a stator winding wound in a Y-shaped configuration. There are three stator windings (i.e., a first stator winding (601A), a second stator winding (601B), and a third stator winding (601C)) having phases A, B, and C that are 120 degrees out of phase with each other. For example, when phase A is zero, phase B is 120 degrees, and phase C is -120 degrees. The three stator windings are connected to ground. Each of the three stator windings may include a plurality of winding coils wound in the same direction and connected to each other.

[0050] FIG. 6B shows, as an example according to one or more embodiments, how the three stator windings are wound around the stator. Each of the stator windings includes a plurality of winding coils. In the example shown in FIG. 6B, each of the stator windings for phases A, B, and C includes 20 winding coils. For each of the three phases, the winding coils carry a single phase (i.e., one of phases A, B, and C).

[0051] In the example shown in FIG. 6B, each of the stator slots (602) houses one end of one winding coil and one end of another winding coil. For example, stator slot 2 shown in the enlarged view of FIG. 6B includes an upper section (2T) that houses the end of the winding coil for phase A and a bottom section (2B) that houses the end of the winding coil for phase B.

[0052] Table 3 below shows an example of the winding coils for the stator winding in FIG. 6B.

Table 3

[0053] In Table 3, phase groups A1 - A5 possess the same phase A, phase groups B1 - B5 possess the same phase B, and phase groups C1 - C5 possess the same phase C. The winding coils in each of the phase groups (e.g., phase group A1) are connected in series with each other, and the phase groups for each phase (e.g., A) can be connected in parallel with each other. For example, the winding coils for phase group A1 are connected in series with each other, and phase groups A1 - A5 are connected in parallel with each other.

[0054] In the example shown in Table 3, coil - 1 (the winding coil of phase group A1) is wound 5 times between the upper part of slot 2 (2T) and the bottom part of slot 11 (11B). Then, the same wire continues to wind coil - 2 for the same phase group A1 14 times in the same direction as coil - 1 between 3T and 10B. Similarly, coil - 3 and coil - 4 for phase group A1 are wound in the same direction and in series with coil - 1 and coil - 2. The lead wire end and finish wire end of phase group A1 are located in slots 2T and 8B respectively.

[0055] In Table 3, the other phase groups are wound in the same way as phase group A1.

[0056] According to one or more embodiments, each of phases A, B, and C may have sense coils (in addition to the winding coils) for measuring the magnetization state (MS) of the soft RM. Thus, three sense coils (i.e., the first, second, and third sense coils) may exist. The sense coils may be arranged on or incorporated into the stator winding, but the sense coils are electrically insulated from the stator winding. FIG. 6C shows a simplified circuit model of the first, second, and third stator windings (601A, 601B, 601C respectively), each including the first, second, and third sense coils (604A, 604B, 604C respectively) wound in a Y - shaped configuration and corresponding to phases A, B, and C respectively. Those skilled in the art will understand that the stator winding and sense coils can be wound in a Δ (delta) configuration to obtain a specific function.

[0057] In one or more embodiments, since a large current pulse may be required to magnetize or demagnetize the soft RM, the stator windings can be wound in a Y-configuration because in a Y-configuration, the current pulse in the power line for each phase of the VFMM is equal to the current in the stator winding for that phase. Thus, the current in the stator winding can be directly controlled and easily measured by controlling and measuring the current in the power line. However, in a Δ-configuration, the current in the stator winding is not necessarily equal to the current in the power line.

[0058] In one or more embodiments, the sense coil inductively generates a back electromotive force (bemf) using the magnetic flux of the soft RM. The strength (amplitude) of the bemf indicates the MS of the soft RM and the rotor position. The bemf has parameters including fixed values such as inductance and resistance. The bemf also has parameters including variable values such as angular velocity, angular position, and current. In one or more embodiments, these fixed-value and variable-value parameters must be known in order to measure the MS of the soft RM.

[0059] Table 4 shows an example of winding the sense coil according to one or more embodiments. [Table 4]

[0060] The windings of the sense coil in Table 4 should be mapped in the same way as the winding coil in Table 3. For example, the sense coils for phase group A1 may be connected in series with each other, and phase groups A1 - A5 may be connected in parallel with each other.

[0061] Those skilled in the art will understand that the winding of the winding coil and the sense coil can be different from Tables 3 and 4 based on the desired design to obtain a specific function.

[0062] According to one or more embodiments, the voltage between three wires of the sense coil shown in FIG. 6C is measured, and then a conversion ratio is applied to obtain the actual voltage between the phases of the stator winding. The conversion ratio is the ratio of the number of turns of the sense coil to the number of turns of the stator winding. For example, when the stator winding is wound according to Table 3, the number of turns for each of the stator windings is 190. If a sense coil with only one turn for each of the winding coils in Table 3 is used, the number of turns of the sense coil for each phase is 20. Therefore, the conversion ratio in this case is 20 / 190 ≈ 0.105. In one or more embodiments, the conversion ratio for a 175 kW VFMM can be 0.0874.

[0063] In one or more embodiments, the MS of the soft RM is determined based on the equation λ m =V s / (K × ω), where λ m is the magnetic flux linkage, V s is the measured voltage of the sense coil, ω is the RPM and is constant in the steady state, and K is a constant related to the resistance and inductance of the d-axis and q-axis of the VFMM and the conversion ratio, etc. The configuration values are invariant in the steady state of the VFMM. With a constant K and ω in the steady state, and the induced V s in the sense coil, λ m can be determined. Then, the MS can be obtained from λ m by multiplying λ m by the conversion ratio, and the conversion ratio is a constant and depends on the design of the VFMM.

[0064] In one or more embodiments, the above equation can be expanded as follows. V q =(r s × I q )+(λ m × ω)+(ω × L d × I d ) where V q is the q-axis voltage induced on the sense coil, Ld is the d-axis inductance, and I d is the d-axis current, and I q is the q-axis current, and r s is the resistance of the sense coil at each of the phases and is constant. λ m To measure, I d should be considered zero, and I q is equal to the phase current passing through the field-oriented control device that controls the VFMM. Therefore, knowing V q measured by the sense coil, and the constant r s in the steady state, I q and having ω, λ m can be determined.

[0065] According to one or more embodiments, a pulse of I d supplied to the stator winding can change the VFMM magnetization, and thus can change the RPM of the VFMM. By the ability to change the MS of the soft RM, the maximum RPM of the VFMM can be changed. Therefore, the VFMM can be used without requiring a power transmission system to change the torque-to-speed ratio of the electric motor.

[0066] According to one or more embodiments, a control device controls the magnetization of the soft RM. The control device can determine the MS of the soft RM based on the back-EMF waveform (hereinafter referred to as "bemf"). In one or more embodiments, the control device can store and compile information and command a VFMM drive (e.g., the inventor, power supply, etc.) to change the magnetization of the soft RM according to the information. The control device can be a computer including a processing device (e.g., a CPU) connected to a storage device (e.g., a RAM) for controlling the MS.

[0067] Figure 7 shows a flowchart representing a method of manual control of the MS of the soft RM, and thus shows a method of manually controlling the torque of the VFMM using a control device. Hereinafter, the manual control of the MS is a control procedure in which an initial command for changing the torque, and thus the MS, is initiated by a human. As a non-limiting example, if the VFMM is a motor of an electric vehicle, the command can be a gear shift or a command to increase the speed of the electric vehicle from the driver. Alternatively, if the VFMM is a motor of an industrial machinery device, the command can be made via an input on the operator's control panel.

[0068] In step 705 (S705), the control device receives a command to change the MS. For example, the command can be an increase or decrease in motor torque / RPM that requires changing the MS.

[0069] In S710, the control device determines and sets the ideal MS based on the command received in S705. For example, if the command is a gear shift, the ideal MS is determined based on a preliminary analysis (e.g., a table) that is most optimal for the ideal MS for the selected gear. For example, gear 1 may be related to 100% MS, while gear 2 may be related to 80% MS.

[0070] According to one or more embodiments, 100% MS can be the MS of the soft RM where the soft RM is magnetized up to their full capacity or up to the magnetization of the soft RM determined (or limited) as the maximum magnetization based on a particular design or function of the VFMM. On the other hand, 0% MS is the MS of the soft RM where the soft RM is completely demagnetized.

[0071] In another example according to one or more embodiments, when a command to obtain a desired RPM / torque is received, the control device can find the ideal MS from a table that associates the desired RPM / torque with the ideal MS. Table 5 below shows an exemplary table that associates the desired RPM / torque with the ideal MS.

Table 5

[0072] In S715, the control device measures the back-EMF of the VFMM. According to one or more embodiments, the back-EMF is the voltage generated in the sensor coil by the rotor. The back-EMF is proportional to λ by a certain factor. m Therefore, the back-EMF indicates the real-time MS (i.e., the actual MS of the soft RM at the time of measurement).

[0073] In S720, the control device can correct the value of the back-EMF measured in S715 from transient errors. For example, due to the transient operation of the VFMM or the power conversion device, the measured back-EMF may include transient errors / noise (e.g., sparks, vibrations, etc.) that do not give the real-time MS. The control device can remove the transient errors / noise from the back-EMF to obtain a more realistic value of the real-time MS.

[0074] In S725, the control device determines the real-time MS based on the back-EMF. For example, the control device can determine the real-time MS based on a table that associates various back-EMF values with the values of the real-time MS. In one or more embodiments, the control device determines the real-time MS based on the corrected back-EMF from S720. Alternatively, the control device can use the uncorrected value of the back-EMF to determine the real-time MS.

[0075] In one or more embodiments, the control device can determine the real-time MS from the uncorrected or corrected back-EMF, and then the control device can apply some correction (e.g., noise discrimination) to the value of the real-time MS to obtain the final value of the real-time MS.

[0076] According to one or more embodiments, after the instruction from S705, the real-time MS and the ideal MS can be determined simultaneously. To do this, S715 to S725 can be performed simultaneously with S710.

[0077] In S730, the control device subtracts the ideal MS obtained from S710 from the real-time MS obtained from S725 to obtain the magnetization difference (ΔMS). If the absolute value of ΔMS ≤ the threshold value (for example, 5% of the ideal MS), the real-time MS is close enough to the ideal MS and there is no need to change the real-time MS. Otherwise, the control device proceeds with S735 described below.

[0078] In S735, the control device determines and sets the I d pulse based on the ΔMS obtained from S730. For example, the control device can determine the I d pulse based on a table associating various values of ΔMS with the values of the I d pulse.

[0079] In S740, the control device commands to send the I d pulse determined from S735 to the stator windings of the VFMM. For example, this command can be sent to the power conversion device to generate and send the I d pulse to the stator windings.

[0080] According to one or more embodiments, the duration, shape, or number of the I d pulse can be determined based on the torque / RPM of the VFMM. According to one or more embodiments, the duration of the I d pulse can be about 1 millisecond (ms).

[0081] In one or more embodiments, after S740, the control device can return to S715 and repeat the steps after S715 to determine whether ΔMS is within the threshold range. If ΔMS is not within the threshold range, the control device applies another I d pulse to adjust the real-time MS. This process can continue until the real-time MS is adjusted so that ΔMS is within the threshold range.

[0082] FIG. 8 shows a flowchart depicting a method for automatically controlling the MS of a soft RM using a control device. Hereinafter, the automatic control of the MS is a control process that automatically adjusts the MS based on the RPM and torque of the VFMM to maintain the highest power efficiency of the VFMM.

[0083] In S805, the control device measures the RPM of the VFMM.

[0084] In S810, the control device determines the torque of the VFMM. According to one or more embodiments, the control device can determine the torque based on the back-EMF measured in S820 and / or S825 described below.

[0085] In S815, the control device determines and sets an ideal MS corresponding to the criteria set for the VFMM. For example, the criteria can be the maximum efficiency (e.g., output efficiency) based on the RPM determined in S805, the torque determined in S810, the minimum magnetic characteristic diagram, the lowest coil temperature, etc. For example, the control device has access to a table that associates the values of RPM and torque with the values of the ideal MS, which results in the set criteria. From this table, the control device determines the ideal MS corresponding to the measured RPM and torque.

[0086] FIG. 9 shows a thermal graph of the power efficiency of the VFMM with respect to RPM and torque for an example where the set criteria is output efficiency. In one or more embodiments, each point on the efficiency map of the VFMM indicates the power efficiency, and the ideal MS is associated with that point.

[0087] In S820, the control device measures the back-EMF of the VFMM. This is the same as S715 described above. According to one or more embodiments, the control device can also calculate the λ m of the VFMM based on the back-EMF. Then, the control device can determine the torque for S810 based on the λ m .

[0088] For example, torque can be calculated based on the following equation: Torque = (3 / 2) × (number of magnetic poles / 2) × λ m × I q , where λ m is determined based on the back-EMF.

[0089] In S825, the control device can correct the measured back-EMF in S715 from the transient error. This can be similar to S720 described above. According to one or more embodiments, the control device can calculate λm based on the corrected back-EMF. Alternatively, the control device can calculate λm based on the uncorrected back-EMF and then correct λ m from the transient error.

[0090] In S830, the control device determines the real-time MS based on the corrected back-EMF. This can be similar to S725 described above. According to one or more embodiments, the control device can determine the real-time MS based on λ m . For example, the control device can look up the real-time MS in a table that associates various λ m values with the value of the real-time MS.

[0091] S835 is similar to S730. Further, according to one or more embodiments, if the absolute value of ΔMS ≤ the threshold value, the real-time MS is ideal and there is no need to change the real-time MS. In this case, the control device can return to S805. Otherwise, the control device proceeds to S840.

[0092] S840 is similar to S735 described above.

[0093] S845 is similar to S740 described above.

[0094] In one or more embodiments, after S845, the control device can return to S820 and repeat the steps after S820 in order to determine whether ΔMS is within the threshold range. If ΔMS is not within the threshold range, the control device applies another I d pulse. This process can continue to adjust the real-time MS so that ΔMS falls within the threshold range.

[0095] In one or more embodiments, the steps in each of the manual and automatic control of MS described with reference to FIGS. 7-8 can be performed in an order different from the order described above, unless otherwise specified. Steps can be omitted or performed multiple times in order to obtain the desired control of MS.

[0096] Although the present invention has been described with respect to a limited number of embodiments, those skilled in the art having the benefit of this disclosure will understand that other embodiments may be devised that do not depart from the scope of the invention disclosed herein. Accordingly, the scope of the present invention shall be limited only by the appended claims.

Claims

1. A variable flux memory motor (VFMM) comprising: a multi-pole rotor; and a stator, wherein the multi-pole rotor comprises: a rotor core; and a plurality of magnetic poles, each of the magnetic poles including: a plurality of soft rotor magnets; a first iron wedge; and a second iron wedge, wherein gaps are provided in contact surfaces of adjacent ones of the plurality of soft rotor magnets, and the same number of the plurality of soft rotor magnets are arranged between the first iron wedge and the second iron wedge in a circumferential direction of the rotor, the stator comprising: a first, a second, and a third stator winding respectively corresponding to first, second, and third magnetization phases, wherein the first, second, and third stator windings create magnetic fluxes to magnetize the plurality of soft rotor magnets, during the magnetization, the magnetic fluxes enter the one or more soft rotor magnets from the first and second iron wedges, the stator further comprising: a first sense coil disposed on or within the first stator winding; a second sense coil disposed on or within the second stator winding; and a third sense coil disposed on or within the third stator winding, wherein the first, second, and third sense coils are electrically insulated from the first, second, and third stator windings, and the first, second, and third sense coils inductively generate back electromotive forces via inductances of magnetic fluxes generated by the first, second, and third stator windings and the plurality of soft rotor magnets, and the back electromotive forces are indicators of magnetization states of the plurality of soft rotor magnets.

2. The variable flux memory motor (VFMM) according to claim 1, wherein the plurality of soft rotor magnets include a combination of aluminum, nickel, and cobalt.

3. The variable flux memory motor (VFMM) according to claim 2, wherein the plurality of soft rotor magnets are AlNiCo having one of grades 1 to 9.

4. The variable flux memory motor (VFMM) according to claim 1, wherein the rotor core is non-conductive.

5. The variable flux memory motor (VFMM) according to claim 4, wherein the rotor core is polyamide-imide.

6. ​ ​ The variable flux memory motor (VFMM) according to claim 1, wherein the plurality of soft rotor magnets include a plurality of the soft rotor magnets arranged adjacent to each other in the axial direction of the rotor or in the circumferential direction of the rotor.

7. The variable flux memory motor (VFMM) according to claim 1, further comprising a sleeve for preventing the plurality of soft rotor magnets and the first and second iron wedges from separating from the rotor core.

8. The variable flux memory motor (VFMM) according to claim 1, wherein the magnetization direction is inclined with respect to a direction perpendicular to the radial direction in the plurality of soft rotor magnets.

9. A system for a variable flux memory motor (VFMM), VFMM comprising a rotor comprising a rotor core and a plurality of magnetic poles, each magnetic pole including a plurality of soft rotor magnets, a first iron wedge, and a second iron wedge wherein the plurality of soft rotor magnets are provided with gaps at the contact surfaces of the adjacent soft rotor magnets, and are arranged in the same number between each of the first iron wedge and the second iron wedge, a rotor, a stator comprising first, second, and third stator windings respectively corresponding to first, second, and third magnetization phases, and at least one sense coil wherein the sense coil measures the magnetization state of the VFMM, a stator, a control device for controlling the magnetization state of the VFMM based on the magnetization state of the VFMM measured via the sense coil and wherein the control device adjusts the magnetization state of the VFMM via a current pulse in at least one of the first, second, and third stator windings. ​

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