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EP-4049361-B1 - METHODS OF MODIFYING THE MAGNETIZATION STATE AND CONTROLLING A VARIABLE-FLUX MEMORY MOTOR

EP4049361B1EP 4049361 B1EP4049361 B1EP 4049361B1EP-4049361-B1

Inventors

  • RADFORD, NICOLAUS
  • BARZEGARANBABOLI, MOHAMMADREZA

Dates

Publication Date
20260513
Application Date
20201023

Claims (11)

  1. A method for modifying the magnetization state of a soft magnet (204) mounted on a rotor (203) of a variable-flux memory motor (VFMM), wherein the VFMM comprises three stator windings (701A, 701B, 701C) that carry three phases, wherein each of the three phases has a sense coil (704A, 704B, 704C), the method comprising: measuring a back electromotive force generated in the sense coil by the rotor; determining in real-time a first magnetization state of the soft magnet based on the measured back electromotive force; obtaining a second magnetization state of the soft magnet; determining a magnetization difference between the second magnetization state and the first magnetization state; generating a first pulse of electric current based on the magnetization difference, wherein the first pulse has a duration of equal to or more than 0.1 millisecond (ms) and equal to or less than 2 ms; and applying the first pulse to a stator winding of the three stator windings of the VFMM to set a magnetization state of the soft magnet to the second magnetization state when the first pulse ends.
  2. The method of claim 1, wherein the duration of the first pulse is equal to or less than 1 ms.
  3. The method of claim 1, wherein the duration of the first pulse is equal or greater than 0.3 ms.
  4. The method of claim 1, wherein the duration of the first pulse is less than 1 ms, and one or more consecutive pulses with a duration of equal to or more than 0.3 ms and less than 1 ms modifies the magnetization state of the soft magnet.
  5. The method of claim 1, wherein the duration of the first pulse is equal to or more than 1 ms, and only the first pulse modifies the magnetization state of the soft magnet.
  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 a shape of the first pulse is triangular.
  9. The method of claim 1, further comprising: generating a plurality of consecutive pulses based on the magnetization difference, wherein plurality of consecutive pulses of electric current each has a duration of equal to or more than 0.1 ms and equal to or less than 2 ms; and applying the plurality of consecutive pulses to the stator winding of the VFMM to set the magnetization state of the soft magnet to the second magnetization state when the plurality of consecutive pulses ends, wherein the second magnetization state is higher than the first magnetization state.
  10. A method of controlling the magnetization state of the soft magnet of the VFMM comprising the method according to either claim 1 or claim 4, the method of controlling the magnetization state of the soft magnet of the VFMM further comprising: receiving a command to change the magnetization state of the soft magnet; determining the second magnetization state of the soft magnet based on the command; and sending the first pulse to the stator winding of the VFMM to adjust the first magnetization state of the soft magnet such that an absolute value of the difference between the second magnetization state and the first magnetization state falls within a predetermined threshold.
  11. A method of automatically controlling the magnetization state of the soft magnet of the VFMM comprising the method according to claim 1, the method of automatically controlling the magnetization state of the soft magnet of the VFMM further comprising: measuring a speed of the VFMM; determine a torque of the VFMM; determining the second 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 first magnetization state such that an absolute value of the difference between the second magnetization state and the first magnetization state falls within a predetermined threshold.

Description

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 entitled, "METHODS OF MAGNETIZING AND CONTROLLING A VARIABLE-FLUX MEMORY MOTOR," filed on October 25, 2019. BACKGROUND Synchronous electric motors with permanent magnets such as variable-flux memory motors have a wide range of applications in industrial, commercial, and residential, applications, such as fans, pumps, compressors, elevators, and refrigerators, industrial machinery, and electric motor vehicles because of their high efficiencies. Also, because of using permanent magnets instead of windings in the rotors of the synchronous electric motors, there is no need for a rotor cooling. These advantages along with others (e.g., being brushless) make the synchronous electric motors popular where high torque, high efficiency, or low maintenance for electric motors is needed. JP2013106480A discloses a conveyer driving device. JP4337989B1 discloses a magnetic flux amount variable rotating electric machine system excited by magnet. Athavale Apoorva et al. IEEE Energy Conversion Congress and Exposition (ECCE), 1 October 2017, pages 1932-1939, XP033247044, doi: 10.1109/ECCE.2017.8096031 discloses enabling driving cycle loss reduction in variable flux PMSMs via closed-loop magnetization state control. SUMMARY The invention is defined by the method of independent claim 1. The method includes: generating a first pulse of electric current that has a duration of equal to or more than 0.1 millisecond (ms) and equal to or less than 2 ms; and applying the first pulse to a stator winding of the VFMM to set a magnetization state of the soft magnet to a first magnetization state when the first pulse ends. Other aspects of the invention will be apparent from the following description and the appended claims. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows a synchronous electric motor.FIG. 2 shows a cross-sectional view of a variable-flux memory motor (VFMM) in accordance with one or more embodiments of the invention.FIG. 3 shows magnetization curves of VFMM rotors in accordance with one or more embodiments of the invention.FIG. 4A shows pulses of electric current to magnetize a soft magnet in accordance with one or more embodiments of the invention.FIG. 4B shows magnetization curves of the soft magnet in response to the pulses of electric current shown in FIG. 4A.FIG. 4C shows residual magnetizations corresponding to the magnetization curves shown in FIG. 4B.FIG. 5A shows magnetization of a soft magnet in response to pulses of electric current in accordance with one or more embodiments of the invention.FIG. 5B shows current pulses for magnetization of a soft magnet in accordance with one or more embodiments of the invention.FIGs. 6A-6B show devices for measuring magnetization of a soft magnet.FIG. 7A shows a simplified circuit model of stator windings of the VFMM in accordance with one or more embodiments of the invention.FIG. 7B shows stator windings of the VFMM in accordance with one or more embodiments of the invention.FIG. 7C shows a simplified circuit model of stator windings and sense coils of the VFMM in accordance with one or more embodiments of the invention.FIG. 8 shows a flowchart depicting a method for magnetization of a VFMM in accordance with one or more embodiments of the invention.FIG. 9 shows a flowchart depicting a method for magnetization of a VFMM in accordance with one or more embodiments of the invention.FIG. 10 shows a diagram in accordance with one or more embodiments of the invention. DETAILED DESCRIPTION Specific embodiments of the invention will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency. In the following detailed description of embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it would have been apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description. FIG. 1 shows an exploded view of a conventional synchronous electric motor (100) (hereinafter, will be referred to as "synchronous motor") including a rotor (101), a stator (102), and stator windings (103) arranged around a rotor hub (104). The synchronous motor may also include a terminal box for connecting input power, a cooling fan, a rotor position sensor, temperature sensors, liquid cooling housings, etc. The rotor (101) includes multiple poles, each including permanent magnets (105) (PM). The synchronous motor (100) operates via a three-phase AC input, in which each phase is delayed from the other two phases by 120 degrees. To create the three-phase AC input, a power converter may convert DC power fed to