Method for magnetizing and controlling a variable flux memory motor

Abstract

A method for magnetizing a soft magnet in a rotor of a variable flux memory motor (VFMM) includes generating a first pulse of current having a duration of greater than or equal to 0.1 milliseconds (ms) and less than or equal to 2 ms, and applying the first pulse to a stator winding of the VFMM to set the magnetization state of the soft magnet to a first magnetization state.

Description

[Technical Field]

[0001] Cross-reference to related applications This application claims priority pursuant to 35 U.S.C. §119(e) to U.S. Provisional Application No. 62 / 926,126, filed October 25, 2019, and entitled "METHODS OF MAGNETIZING AND CONTROLLING A VARIABLE-FLUX MEMORY MOTOR," the contents of which are incorporated herein by reference in their entirety. [Background technology]

[0002] Due to their high efficiency, synchronous electric motors containing permanent magnets, such as variable flux memory motors, have a wide range of applications in industrial, commercial, and residential applications, such as electric fans, pumps, compressors, elevators, and refrigerators, industrial machinery, and electric motor vehicles. Furthermore, because synchronous electric motors use permanent magnets instead of windings in their rotors, rotor cooling is not required. These advantages, along with others (e.g., brushlessness), have made synchronous electric motors popular where high torque, high efficiency, or low maintenance are required in an electric motor. Summary of the Invention

[0003] In one aspect, an embodiment of the present invention is directed to a method of magnetizing a soft magnet in a rotor of a variable flux memory motor (VFMM), the method including generating a first pulse of current having a duration of greater than or equal to 0.1 milliseconds (ms) and less than or equal to 2 ms, and applying the first pulse to a stator winding of the VFMM to set the magnetization state of the soft magnet to a first magnetization state when the first pulse terminates.

[0004] Other aspects of the present invention will become apparent from the following description and appended claims. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 shows a synchronous electric motor. [Figure 2] FIG. 1 is a cross-sectional view of a variable flux memory motor (VFMM) according to one or more embodiments of the present invention. [Figure 3A] FIG. 10 illustrates the magnetization curve of a VFMM rotor in accordance with one or more embodiments of the present invention. [Figure 3B] FIG. 10 illustrates the magnetization curve of a VFMM rotor in accordance with one or more embodiments of the present invention. [Figure 3C] FIG. 10 illustrates the magnetization curve of a VFMM rotor in accordance with one or more embodiments of the present invention. [Figure 4A] FIG. 1 illustrates pulses of current for magnetizing a soft magnet according to one or more embodiments of the present invention. [Figure 4B] FIG. 4B shows the magnetization curve of a soft magnet in response to the pulse of current shown in FIG. 4A. [Figure 4C] FIG. 4C shows the residual magnetization corresponding to the magnetization curve shown in FIG. 4B. [Figure 5A] FIG. 1 illustrates the magnetization of a soft magnet in response to a pulse of current in accordance with one or more embodiments of the present invention. [Figure 5B] FIG. 2 illustrates current pulses for magnetization of a soft magnet according to one or more embodiments of the present invention. [Figure 6A] FIG. 1 shows a device for measuring the magnetization of a soft magnet. [Figure 6B] FIG. 1 shows a device for measuring the magnetization of a soft magnet. [Figure 7A] FIG. 1 illustrates a simplified circuit model of a stator winding of a VFMM in accordance with one or more embodiments of the present invention. [Figure 7B] FIG. 2 illustrates a stator winding of a VFMM in accordance with one or more embodiments of the present invention. [Figure 7C] FIG. 1 illustrates a simplified circuit model of the stator windings and sense coils of a VFMM in accordance with one or more embodiments of the present invention. [Figure 8]1 is a flow diagram illustrating a method for magnetizing a VFMM in accordance with one or more embodiments of the present invention. [Figure 9] 1 is a flow diagram illustrating a method for magnetizing a VFMM in accordance with one or more embodiments of the present invention. [Figure 10] 1 is a diagram according to one or more embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0006] Specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which like elements in the various figures are designated by like reference numerals for consistency.

[0007] In the following detailed description of 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 will be apparent to those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known features have not been described in detail in order to avoid unnecessarily complicating the description.

[0008] 1 shows an exploded view of a conventional synchronous electric motor (100) (hereinafter referred to as a "synchronous motor") including a rotor (101), a stator (102), and stator windings (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-cooled housing, etc. The rotor (101) includes multiple magnetic poles, each of which includes a permanent magnet (105) (PM).

[0009] The synchronous motor (100) operates via a three-phase AC input, with each phase lagging the other two by 120°. To create the three-phase AC input, a power converter may convert DC power supplied 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 causes the rotor (101) to rotate at a steady-state rotations per minute (RPM) speed (hereinafter referred to as "RPM"). The RPM of a synchronous motor is determined by the number of poles, the available voltage, and the flux linkage (λ) provided and fixed by the PMs. m Synchronous motors have a wide range of applications in industrial, commercial, and residential applications, such as electric fans, pumps, compressors, elevators, and refrigerators, industrial machinery, and electric vehicles.

[0010] In one or more embodiments, the λ provided by the PM m Because the CPSR is fixed, a synchronous motor including a PM has a narrow constant power speed range (CPSR), which is the speed range over which the motor drive can maintain constant output power at 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 flux-weakening control method. Due to the narrow CPSR range for a synchronous motor, it may be necessary to use a power transmission system to change the CPSR of the system driven by the synchronous motor. Even using such advanced methods increases the CPSR of a synchronous motor by 2 to 3. On the other hand, the CPSR of a VFMM according to one or more embodiments can achieve 4 to 6.

[0011] Generally, embodiments of the present invention relate to a VFMM design, a rotor for a VFMM, and a method for magnetizing a VFMM. A VFMM is a type of synchronous motor in which the magnetization of the rotor magnet of the VFMM can be adjusted (i.e., changed) during operation of the VFMM. Adjusting the magnetization of the rotor magnet (hereinafter referred to as "VFMM magnetization" for simplicity) changes the RPM of the VFMM. According to one or more embodiments, to facilitate the change in VFMM magnetization, the rotor magnet is made of a soft ferromagnetic material, such as aluminum-nickel-cobalt (AlNiCo) or some types of ceramics. Hereinafter, rotor magnets made of soft ferromagnetic materials are referred to as "soft magnets." Soft magnets are low-coercivity magnets (LCF). According to one or more embodiments, the soft magnet can be a magnet constructed of grades 1-9 AlNiCo, or AlNiCo, cast, ceramic, the same grades of samarium-cobalt, or a sintered structure of these materials. It will be apparent that one skilled in the art may use specific amounts of these materials to obtain the desired functionality of the VFMM.

[0012] The VFMM according to one or more embodiments is a better substitute for a synchronous motor because the maximum achievable RPM due to the limited voltage of the VFMM can be obtained more efficiently through varying the VFMM magnetization. In other words, the CPSR of the VFMM can have a wider range compared to the CPSR of a synchronous motor. Therefore, there is no need to couple the VFMM to a power transmission system.

[0013] According to one or more embodiments, soft magnets can be quickly and efficiently magnetized and demagnetized when they are assembled inside the motor. Thus, by using a VFMM, manufacturing costs for systems equipped with electric motors can potentially be reduced because they are magnetized or demagnetized during assembly.

[0014] Soft ferromagnetic materials have high magnetic permeability (similar to hard ferromagnetic materials such as iron-nickel alloys), but low coercivity (unlike hard ferromagnetic materials). Due to the low coercivity of soft ferromagnetic materials, changing the magnetization of a soft ferromagnetic material requires a relatively smaller magnetic field compared to a hard ferromagnetic material.

[0015] In one or more embodiments, only soft magnets may be used as rotor magnets in a VFMM, and no hard magnets (i.e., magnets made of hard ferromagnetic materials) may be attached to the rotor. Alternatively, in one or more embodiments, both soft and hard magnets may be used as rotor magnets in a VFMM. Because hard magnets are made of rare earth materials and are much more expensive than soft magnets (e.g., AlNiCo), embodiments of the present invention may have advantages over synchronous motors that use only hard magnets. Therefore, by partially or entirely using soft magnets instead of hard magnets in a VFMM, the manufacturing costs of the VFMM are significantly reduced compared to conventional synchronous motors.

[0016] Furthermore, another advantage of using soft magnets is that the overall magnetization of all magnets in a VFMM can be controlled and varied over a wide range. According to one or more embodiments, the overall magnetization of the soft magnets can be varied 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 can occur in a short time (e.g., about 1 millisecond).

[0017] In contrast, hard magnets do not change their magnetization easily. Therefore, changing the magnetization of a hard magnet requires much more power than the operating power of a VFMM or other type of synchronous motor. For example, changing the magnetization of hard magnets such as some grades of neodymium iron boron (NdFeB) and samarium cobalt (SmCo) can require more than 10 times the power required to change the magnetization of a soft magnet.

[0018] According to one or more embodiments, a current (hereinafter referred to as a "glitch current") may be generated due to an undesired glitch in the VFMM or a controller controlling the VFMM. If a current significantly larger than the operating current of the stator winding passes through the stator winding, this current may temporarily change the magnetization of the soft magnet to an undesired value. However, a different current that the stator winding can withstand may make it easier to restore the magnetization of the soft magnet. Because soft magnets can easily accept a different magnetization (compared to hard magnets, which require a large current to change their magnetization), no matter how large the glitch current is, the magnetization of the soft magnet may be restored via a current relatively smaller than the glitch current.

[0019] On the other hand, if a synchronous motor with soft magnets (such as a VFMM) includes hard magnets, and a glitch current changes the magnetization of the hard magnets, restoring the magnetization of the hard magnets through current in the stator windings would be difficult. Such currents that could restore the hard magnets may be too large for the stator windings or other components of the synchronous motor to withstand. For example, such large currents could burn the stator windings or displace various components of the synchronous motor, such as the rotor and windings. To restore the hard magnets, the synchronous motor must be opened, and the hard magnets must be separated from the synchronous motor and placed under a high magnetic field. However, as mentioned above, restoring the soft magnets does not require disassembling the VFMM.

[0020] 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 difficult to change, the magnetization of the hard magnets becomes 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).

[0021] FIG. 2 illustrates 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), which holds stator windings in slots between adjacent stator teeth (202), and a rotor (203). The rotor (203) includes soft magnets (204) and iron wedges (205) mounted on a rotor core (206). The rotor (203) is mounted on a shaft (208). The rotor (203) includes a sleeve (207) that holds the soft magnets (204) and iron wedges (205) together. The sleeve (207) can be 0.5 to 3 millimeters (mm) thick in the radial direction. The thickness is determined by the centrifugal force exerted by the soft magnets (204) and iron wedges (205). Alternatively, in one or more embodiments, the sleeve (207) may be attached to any one of the soft magnet (204), the iron wedge (205), and / or the rotor core (206).

[0022] In these embodiments, the sleeve (207) may be made of a non-bonding material that does not adhere to the soft magnets (204), iron wedges (205), and / or rotor core (206). The non-bonding sleeve (207) may be made of carbon fiber HEX TOW IM10 or Kevlar tow. Alternatively, the sleeve (207) may be part of the rotor assembly.

[0023] The d-axis (direct axis) and q-axis (quadrature axis) for the VFMM (200) are shown in FIG. 2. The d-axis is the axis where the rotor's magnetic field is located at its peak. For example, the d-axis in FIG. 2 is midway between adjacent poles, between adjacent iron wedges (205), where the rotor's (203) magnetic field is highest. The q-axis is 90 degrees out of phase with the d-axis. For example, the q-axis in FIG. 2 is midway between the soft RMs (204) of each pole, where the rotor's (203) magnetic field is lowest.

[0024] Further details regarding embodiments of the VFMM are disclosed in U.S. Patent Application No. 16 / 383,274, filed April 12, 2019, and entitled "A VARIABLE-FLUX MEMORY MOTOR AND METHODS OF CONTROLLING A VARIABLE-FLUX MOTOR," which is incorporated by reference in its entirety.

[0025] In one or more embodiments of the present invention, the effect of the inductance of a VFMM is disclosed. FIG. 3 shows VFMM Design 1, corresponding to an inductance of 200 microhenries (μH), and VFMM Design 2, corresponding to an inductance of 33 μH. A step electric current having a constant amplitude of 1.5 kiloamperes (kA) is supplied to the VFMM, and the magnetization (i.e., B-H curve) of the VFMM in response to the step current is displayed, as shown in FIG. 3. In the magnetization plot, the area below the magnetization curve (i.e., the area between the magnetization curve and the "B" (magnetic field) axis) indicates the energy consumed by the VFMM. Thus, the energy consumed by the VFMM of Design 2 (which has a lower inductance) is approximately 50% lower than that of Design 1 (which has a higher conductance). This reduction in power consumption is significant considering that the maximum magnetization (i.e., the highest magnetic field (B)) of the VFMM for Design 2 is only approximately 16% lower than that of the VFMM for Design 1.

[0026] To magnetize the VFMM, a current is applied at the d-axis of the soft magnet. The current is then removed to maintain a high torque on the VFMM. Therefore, pulses of current are typically supplied to the VFMM. In one or more embodiments of the present invention, the duration of the current pulses is reduced to increase the efficiency of the VFMM (i.e., reduce the power consumed by the VFMM to obtain a given level of magnetization of the soft magnet). These findings are explained below with reference to FIGS. 4A-4C and 5.

[0027] FIG. 4A shows a triangular-shaped long pulse (long pulse) having a duration of about 18 milliseconds (ms), a typical pulse duration for magnetizing low-power VFMMs (i.e., less than 30 kilowatts (kW)), and a triangular-shaped short pulse (short pulse) having a duration of about 1 ms. The 1 ms pulse is significantly shorter than the typical pulse duration for high-power VFMMs (i.e., greater than 100 kW), which is greater than 2 ms. In one or more embodiments, the pulse duration is the period during which the amplitude of the pulse of current is 10% or greater than the peak amplitude of the pulse. The short pulse in FIG. 4A has a negative overshoot that can be filtered.

[0028] FIG. 4B shows the magnetization curve of an AlNiCo-9 soft magnet in response to the pulse shown in FIG. 4A. As the current increases from zero to the peak amplitude of the pulse, the average magnetic flux in the soft magnet increases. At the peak amplitude, the average magnetic flux of the soft magnet corresponding to the longer pulse (having an 18 ms duration) is 0.3 Tesla (T) higher than the average magnetic flux of the soft magnet corresponding to the shorter pulse (having a 1 ms duration). However, as the pulse decays from the peak amplitude to zero, the average magnetic flux of the soft magnet corresponding to the longer pulse decreases more than the average magnetic flux corresponding to the shorter pulse. As shown in FIG. 4B, as the pulse decays to zero before going negative in the overshoot, the average magnetic flux of the soft magnet corresponding to the longer pulse is only about 0.05 T higher than the average magnetic flux corresponding to the shorter pulse.

[0029] 4B and 4C are provided for an AlNiCo-9 soft magnet, those skilled in the art will appreciate that the present invention is not limited to AlNiCo-9 and that embodiments of the present invention may extend to other types of soft magnetic materials, for example, other grades of AlNiCo.

[0030] As shown in Figure 4B, the shorter pulse becomes negative during the negative overshoot and then stabilizes at zero (i.e., a stable zero current). Even after the negative overshoot, the average magnetic flux of the soft magnet corresponding to the longer pulse is only about 0.15 T higher than the average magnetic flux of the soft magnet corresponding to the shorter pulse. In other words, when the two pulses decay from the same peak amplitude to zero, the soft magnet demagnetizes less in response to the shorter pulse. Hereinafter, the average magnetic flux at a stable zero current after the pulse is referred to as "residual magnetization." Figures 4B and 4C show the remanent magnetization of the soft magnet corresponding to the longer and shorter pulses shown in Figure 4A.

[0031] According to Figure 4B, the remanence of the soft magnet in response to the shorter pulse is about 16% lower than that in response to the longer pulse, but the power consumed by the shorter pulse is about 5% of the power consumed by the longer pulse. Thus, high magnetization of the soft magnet can be achieved with significantly less power.

[0032] In one or more embodiments of the present invention, the duration of the pulse of current may be 0.1 ms or more. In one or more embodiments of the present invention, the duration of the pulse of current may be 0.3 ms or more and 2 ms or less. More specifically, the duration of the pulse may be 1 ms or more. In one or more embodiments, as shown in Figures 4A-4C, the duration of the pulse may be 1 ms or more, and only one pulse magnetizes the soft magnet.

[0033] In one or more embodiments of the present invention, multiple consecutive pulses, each having a duration of less than 1 ms, can magnetize a soft magnet. By using multiple consecutive short pulses, the remanence of the soft magnet can be increased while keeping power consumption low. One example of these embodiments, FIG. 5, shows two consecutive pulses, each having a duration of about 0.5 ms, being used to magnetize a soft magnet. After the first pulse, the remanence of the soft magnet remains at about 0.8 T. The second pulse then increases this remanence to a higher remanence of about 0.9 T. While the amount of power consumed by the pulse combination in FIG. 5 is about 8% of the power consumed by the longer pulse shown in FIG. 4A, the remanence in response to the pulse combination in FIG. 5 and the longer pulse shown in FIG. 4A is approximately the same.

[0034] In one or more embodiments of the present invention, three or more consecutive pulses may be used to magnetize the soft magnet. For example, ten consecutive pulses, each with a duration of 0.5 ms, may be used over a period of 10 ms. Even with ten consecutive pulses, the total power consumed by the pulses would be approximately 30% of the 18 ms long pulse shown in FIG. 4A. Therefore, by using short pulses, high magnetization of the soft magnet in the VFMM may be achieved, while the power consumed to magnetize the soft magnet may be significantly reduced.

[0035] The duration and shape of the current pulse may depend on the practical limitations of the power supply to provide the required amount of energy to magnetize the soft magnet. For example, it may be necessary to magnetize the soft magnet to a fully demagnetized state (soft magnet current MS is 0%) and to magnetize the soft magnet to 20% MS and 100% MS with direct axis currents (I) of 1000 A and 4000 A. d ) respectively. If these two currents are applied to a soft magnet in pulses of the same duration, the shape of the current pulsing the power supply may differ depending on the power supply capabilities, as shown in FIG. 5B.

[0036] The ability of a power supply to provide short current pulses depends on the inductance of the circuit through which the current pulses are provided (e.g., the extensions used to magnetize the soft magnet). For example, for larger windings with higher inductance, the time constant of the current pulse will be higher. In other words, for larger winding inductance, the current pulse will take longer to reach the target current peak.

[0037] 6A-6B show an arrangement for magnetizing a soft magnet and measuring the magnetization curves shown in FIGS. 4B and 5. In FIG. 6A, two ferrous parts (602) are positioned next to each other. An electromagnetic coil (604) is disposed around the ferrous parts (602) to induce magnetic flux inside the ferrous parts (602) in response to application of a current (e.g., a current pulse) to the electromagnetic coil (604). The soft magnet to be magnetized is disposed in the gap (606) between the ferrous parts (602). The induced magnetic flux inside the ferrous parts (602) magnetizes the soft magnet. To measure the magnetization curve of the soft magnet, one or more measuring coils (608) are disposed in the small air gaps (610) between the ferrous parts (602). The magnetic flux of the soft magnet is measured via an electrical signal induced in the measuring coil by the magnetic flux of the ferrous parts (602).

[0038] According to one or more embodiments, the stator windings create the magnetic flux necessary to magnetize the VFMM and rotate the rotor. Figure 7A shows a simplified circuit model of the stator windings wound in a wye configuration. There are three stator windings (i.e., a first stator winding (701A), a second stator winding (701B), and a third stator winding (701C)) possessing phases A, B, and C that lag each other by 120 degrees. 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 null. Each of the three stator windings may include multiple winding coils wound in the same direction and connected to each other.

[0039] 7B shows, as an example according to one or more embodiments, how three stator windings are wound on a stator. Each of the stator windings includes multiple winding coils. In the example shown in FIG. 7B, each of the stator windings for phases A, B, and C includes 20 winding coils. For each of the three phases, a winding coil carries a single phase (i.e., one of phases A, B, and C).

[0040] In the example shown in Figure 7B, each of the stator slots (702) accommodates one end of one winding coil and one end of another winding coil. For example, stator slot 2 shown in the close-up of Figure 7B includes a top section (2T) that accommodates the end of the winding coil for phase A and a bottom section (2B) that accommodates the end of the winding coil for phase B.

[0041] According to one or more embodiments, each of phases A, B, and C may have a sense coil (in addition to the winding coils) to measure the MS of the soft magnet. Thus, there may be three sense coils (i.e., first, second, and third sense coils). The sense coils may be disposed on or integrated into the stator windings, but the sense coils are electrically isolated from the stator windings. FIG. 7C shows a simplified circuit model of the first, second, and third stator windings (701A, 701B, 701C, respectively) including first, second, and third sense coils (704A, 704B, 704C, respectively) corresponding to phases A, B, and C, respectively, wound in a wye configuration. Those skilled in the art will understand that the stator windings and sense coils may be wound in a delta configuration to achieve specific functions.

[0042] In one or more embodiments, because large current pulses may be required to magnetize or demagnetize the soft magnets, the stator windings may be wound in a wye configuration because, in the wye configuration, the current pulse in the power line of the VFMM for each phase is equal to the current in the stator winding for that phase. Therefore, 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 delta configuration, the current in the stator winding is not necessarily equal to the current in the power line.

[0043] In one or more embodiments, a sense coil inductively generates a back electromotive force (BEMF) using the magnetic flux of the soft magnet. The strength (amplitude) of the BEMF indicates the MS of the soft magnet and rotor position. The BEMF has parameters that include fixed values, such as inductance and resistance. The BEMF also has parameters that include variable values, such as angular velocity, angular position, and current. In one or more embodiments, these fixed and variable parameters must be known to measure the MS of the soft magnet.

[0044] According to one or more embodiments, the voltage between the three wires of the sense coil shown in FIG. 7C 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 in the sense coil to the number of turns in the stator winding. For example, the number of turns for each of the stator windings may be 190. In this example, if only one turn of sense coil is used for each winding coil, the number of turns of the sense coil for each phase is 20. Therefore, the conversion ratio in this example is 20 / 190 ≈ 0.105. In one or more embodiments, the conversion ratio for a 175 kW VFMM may be 0.0874.

[0045] In one or more embodiments, the MS of a soft magnet can be calculated using the equation λ m =V s / (K×ω), where λ m is the magnetic flux linkage, and V sis the measured voltage of the sense coil, ω is the RPM and is constant at steady state, and K is a constant related to the constructional values ​​such as the resistance and inductance of the d-axis and q-axis of the VFMM and the transformation ratio, which are invariant at steady state of the VFMM. s By having m Then, the MS can determine λ m By multiplying by the conversion ratio, λ m where the conversion ratio is a constant and depends on the design of the VFMM.

[0046] 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 ) In the formula, V q is the q-axis voltage induced on the sense coil, and L d is the d-axis inductance, and I d is the d-axis current, and I q is the q-axis current, and r s λ is the resistance of the sense coil in each of the phases and is constant. m To measure I d should be considered to be zero, and I q is equal to the phase current passing through the field-oriented control device that controls the VFMM. Therefore, V measured by the sense coil q and constant r in the steady state. s , I q , and ω, so that λ m It is possible to determine:

[0047] According to one or more embodiments, the I supplied to the stator windings dPulses of 0.01 V can change the VFMM magnetization and therefore the RPM of the VFMM. With the ability to change the MS of the soft magnet, 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.

[0048] According to one or more embodiments, a controller controls the magnetization of the soft magnet. The controller can determine the MS of the soft magnet based on the BEMF waveform (hereinafter referred to as "BEMF"). In one or more embodiments, the controller can store and compile information and instruct a VFMM drive (e.g., a power supply, etc.) to modify the magnetization of the soft magnet according to the information. The controller can be a computer including a processing unit (e.g., a CPU) connected to a storage unit (e.g., RAM) for controlling the MS.

[0049] FIG. 8 shows a flow diagram depicting a method for manual control of a soft magnet MS, and thus a method for manually controlling the torque of a VFMM using a controller. Hereinafter, manual control of the MS is a control procedure in which the initial command to change the torque, and therefore the MS, is initiated by a human. As a non-limiting example, if the VFMM is a motor in an electric vehicle, the command could be a gear shift or a command from the driver to increase the speed of the electric vehicle. Alternatively, if the VFMM is a motor in industrial machinery, the command could be via an operator's input at a control panel.

[0050] In step 805 (S805), the controller receives a command to change the MS. For example, the command may be an increase or decrease in motor torque / RPM, which requires changing the MS.

[0051] In S810, the controller determines and sets an ideal MS based on the command received in S805. For example, if the command is to shift gears, the ideal MS is determined based on a preliminary analysis (e.g., a table) relating the most optimal MS as the ideal MS for the selected gear. For example, gear 1 may be associated with an MS of 100%, while gear 2 may be associated with an MS of 80%.

[0052] According to one or more embodiments, 100% MS may be a soft magnet MS where the soft magnets are magnetized to their full capacity or to a soft magnet magnetization determined as (or limited to) the maximum magnetization based on the particular design or functionality of the VFMM, while 0% MS is a soft magnet MS where the soft magnets are completely demagnetized.

[0053] In another example, according to one or more embodiments, when a command to obtain a desired RPM / torque is received, the controller can find the ideal MS from a table relating the desired RPM / torque to the ideal MS. Table 1 below shows an example table relating the desired RPM / torque to the ideal MS. [Table 1]

[0054] In S815, the controller measures the bemf of the VFMM. According to one or more embodiments, bemf is the voltage generated in the sense coil by the rotor. bemf is multiplied by a constant factor, λ m Therefore, bemf represents the real-time MS (i.e., the actual MS of the soft magnet at the time of measurement).

[0055] In S820, the controller can correct the value of bemf measured in S815 from transient errors. For example, due to transient operation of the VFMM or power converter, the measured bemf may contain transient errors / noise (e.g., sparks, vibrations, etc.) that do not provide a real-time MS. The controller can remove the transient errors / noise from bemf to obtain a more realistic value of the real-time MS.

[0056] In S825, the controller determines the real-time MS based on bemf. For example, the controller may determine the real-time MS based on a table that associates various bemf values ​​with values ​​of real-time MS. In one or more embodiments, the controller determines the real-time MS based on the modified bemf from S820. Alternatively, the controller may use an unmodified value of bemf to determine the real-time MS.

[0057] In one or more embodiments, the control device can determine the real-time MS from the uncorrected or corrected bemf, and then the control device can apply some correction (e.g., noise filtering) to the value real-time MS to obtain a final value of the real-time MS.

[0058] According to one or more embodiments, after instruction from S805, the real-time MS and the ideal MS may be determined simultaneously. To do this, S815 through S825 may be performed simultaneously with S810.

[0059] In S830, the controller subtracts the ideal MS obtained from S810 from the real-time MS obtained from S825 to obtain the magnetization difference (ΔMS). If the absolute value of ΔMS is less than or equal to a threshold value (e.g., 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 controller continues with S835, described below.

[0060] In S835, the control device calculates I based on the ΔMS obtained in S830. dFor example, the controller may determine and set various values ​​of ΔMS to I d Based on the table relating the pulse value to the I d In another example, the pulse d The pulses may be considered similar to the pulses of current described above with reference to FIGS. 4A-4C and 5.

[0061] In S840, the control unit determines the I determined from S835. d This command sends a pulse to the stator winding of the VFMM. For example, this command d This may be sent to a power converter to generate and send pulses to the stator windings.

[0062] According to one or more embodiments, I d The duration, shape, or number of pulses may be determined based on the torque / RPM of the VFMM. d The pulse duration may be about 1 millisecond (ms).

[0063] In one or more embodiments, after S840, the controller may return to S815 and repeat steps S815 and after S815 to determine whether ΔMS is within the threshold range. If ΔMS is not within the threshold range, the controller may perform another I d This process may continue until the real-time MS is adjusted so that ΔMS falls within the threshold range.

[0064] Figure 9 shows a flow diagram illustrating a method for automatically controlling the MS of a soft magnet using a controller. Hereinafter, 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.

[0065] In S905, the controller measures the RPM of the VFMM.

[0066] In S910, the controller determines the torque of the VFMM. According to one or more embodiments, the controller can determine the torque based on the measured bemf in S920 and / or S925, described below.

[0067] In S915, the controller determines and sets an ideal MS corresponding to the criteria set for the VFMM. For example, the criteria can be maximum efficiency (e.g., power efficiency) based on the RPM determined in S905, the torque determined in S910, a minimum magnetic signature, a minimum coil temperature, etc. For example, the controller has access to a table that associates RPM and torque values ​​with values ​​of the ideal MS, which results in the set criteria. From this table, the controller determines the ideal MS corresponding to the measured RPM and torque.

[0068] 10 shows a thermal graph of VFMM power efficiency with respect to RPM and torque for an example where the set criterion is power efficiency. In one or more embodiments, each point on the VFMM efficiency map represents a power efficiency and an ideal MS is associated with that point.

[0069] In S920, the controller measures the bemf of the VFMM, which is similar to S815 described above. According to one or more embodiments, the controller also measures the λ of the VFMM based on the bemf. m The controller can then calculate λ m The torque for S910 may be determined based on:

[0070] For example, the torque can be calculated based on the following equation: Torque = (3 / 2) x (number of poles / 2) x λ m ×I q , In the formula, λ m is determined based on bemf.

[0071] In S925, the controller can correct the measured bemf in S815 from transient errors. This can be similar to S820 described above. According to one or more embodiments, the controller can calculate λ based on the corrected bemf. Alternatively, the controller can calculate λ based on the uncorrected bemf and then calculate λ. m can be corrected from transient errors.

[0072] In S930, the controller determines the real-time MS based on the modified bemf, which may be similar to S825 described above. According to one or more embodiments, the controller determines λ m For example, the controller may determine the real-time MS based on various λ m The real-time MS can be looked up in a table that relates values ​​to the real-time MS values.

[0073] S935 is similar to S830. Furthermore, according to one or more embodiments, if the absolute value of ΔMS is less than or equal to the threshold, 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 S905. Otherwise, the control device continues to S940.

[0074] S940 is similar to S835 described above.

[0075] S945 is similar to S840 described above.

[0076] In one or more embodiments, after S945, the controller may return to S920 and redo the steps of S920 and after S920 to determine whether ΔMS is within the threshold range. If ΔMS is not within the threshold range, the controller may perform another I d Apply a pulse. This process can continue to adjust the real-time MS so that ΔMS falls within the threshold range.

[0077] In one or more embodiments, the steps in each of the manual and automatic control of the MS described with reference to Figures 8-9 may be performed in an order different from that described above, unless otherwise specified. Steps may be omitted or performed multiple times to obtain the desired control of the MS.

[0078] While 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 appreciate that other embodiments may be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the present invention is intended to be limited only by the appended claims.

Claims

1. 1. A method for controlling soft magnets in a rotor of a variable flux memory motor (VFMM), comprising: measuring the back electromotive force generated by the soft magnet; determining the magnetization state of the soft magnet at the time of measurement based on the measured back electromotive force; determining a first pulse based on a difference between an ideal magnetization state of the soft magnet and the measured magnetization state, the first pulse having a duration of 0.1 milliseconds (ms) or more and 2 ms or less for application to a stator winding of the VFMM; applying the generated first pulse to the stator winding of the VFMM, wherein the first pulse sets the magnetization state of the soft magnet to a first magnetization state when application of the generated first pulse is terminated; generating a plurality of successive pulses of current for application to the stator winding of the VFMM, each pulse having a duration of not less than 0.1 ms and not more than 2 ms; and applying the generated plurality of successive pulses to the stator winding of the VFMM. Including, The plurality of consecutive pulses are terminated when the application of the plurality of consecutive pulses is completed. setting the magnetization state of the soft magnet to a target magnetization state; the target magnetization state is higher than the first magnetization state; The method, wherein the plurality of consecutive pulses includes the first pulse.

2. The method of claim 1 , wherein the duration of the first pulse is 1 ms or less.

3. 2. The method of claim 1, wherein the duration of the first pulse is 0.3 ms or greater.

4. one or more successive pulses, each having a duration of at least 0.3 ms and less than 1 ms, magnetize the soft magnet; the one or more consecutive pulses including the first pulse; The method of claim 1.

5. the duration of the first pulse is 1 ms or greater; Only the first pulse magnetizes the soft magnet. The method of claim 1.

6. The method of claim 1 , wherein the soft magnet is AlNiCo.

7. The method of claim 1, wherein the soft magnet is AlNiCo-9.

8. The method of claim 1 , wherein the first pulse has a triangular shape.

9. generating a second pulse of current having a duration of not less than 0.1 ms and not more than 2 ms for application to the stator winding of the VFMM after determining the first pulse; and applying the generated second pulse to the stator winding of the VFMM after applying the first pulse. further comprising the second pulse sets the magnetization state of the soft magnet to a second magnetization state when application of the generated second pulse is terminated; The method of claim 1 , wherein the second magnetization state is higher than the first magnetization state.

10. 10. A method of controlling the magnetization state of the soft magnet of the VFMM, comprising the method of claim 1, comprising: receiving a command to change the magnetization state of the soft magnet; determining the ideal magnetization state of the soft magnet based on the command; sending the first pulse to the stator winding of the VFMM to adjust the measured magnetization state of the soft magnet to the first magnetization state so that the absolute value of the difference between the ideal magnetization state and the first magnetization state falls within a predetermined threshold range; The method further comprises:

11. 10. A method for automatically controlling the magnetization state of the soft magnet of the VFMM, comprising the method of claim 1, measuring the velocity of said VFMM; determining the torque of the VFMM; determining the ideal magnetization state of the soft magnet based on the speed and the torque of the VFMM; and sending the first pulse to the stator winding of the VFMM to adjust the magnetization state during measurement to the first magnetization state so that the absolute value of the difference between the ideal magnetization state and the first magnetization state is within a predetermined threshold range; The method further comprises:

12. 5. A method for automatically controlling the magnetization state of the soft magnet of the VFMM, comprising the method of claim 4, measuring the velocity of said VFMM; determining the torque of the VFMM; determining the ideal magnetization state of the soft magnet based on the speed and the torque of the VFMM; and sending the first pulse to the stator winding of the VFMM to adjust the magnetization state during measurement to the first magnetization state so that the absolute value of the difference between the ideal magnetization state and the first magnetization state is within a predetermined threshold range; The method further comprises:

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