Motor control method

Abstract

To provide a motor control method that can reduce motor vibration noise.SOLUTION: A control method for a motor 20 comprising a stator 30 and a rotor 40, includes: a drive current determination step of determining a waveform of a drive current to be applied to an iron core of the stator 30 based on magnetostriction of the iron core of the stator 30 so as to reduce vibration due to the magnetostriction of the iron core of the stator 30; and a drive current applying step of applying, to the iron core of the stator 30, the drive current determined in the drive current determination step.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a method for controlling a motor.

Background Art

[0002] Conventionally, a permanent magnet type rotating electric machine has been disclosed that reduces vibration and noise by canceling the unbalanced electromagnetic force in the radial direction.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Further reduction of vibration and noise of the motor is required.

[0005] In view of such circumstances, an object of the present disclosure is to reduce vibration and noise of a motor.

Means for Solving the Problems

[0006] (1) A method for controlling a motor according to an embodiment of the present disclosure is a method for controlling a motor including a stator and a rotor, a drive current determination step of determining a current waveform of a drive current applied to the iron core of the stator based on the magnetic distortion of the iron core of the stator so that the vibration due to the magnetic distortion of the iron core of the stator becomes small, a drive current application step of applying the drive current determined in the drive current determination step to the iron core of the stator and including.

[0007] (2) In the method for controlling a motor according to (1) above, the drive current determination step is A waveform assumption step of assuming a plurality of current waveforms of the drive current; A magnetic flux density calculation step of calculating, for each of the assumed current waveforms, a time change of the magnetic flux density generated in the iron core of the stator when the assumed current waveform is applied as the drive current to the iron core of the stator; A magnetic strain deformation amount calculation step of calculating, for each of the current waveforms, a time change of the magnetic strain deformation amount which is a deformation amount of the entire iron core of the stator due to magnetic strain based on the time change of the magnetic flux density generated in the iron core of the stator; A waveform determination step of determining, as the drive current to be applied to the iron core of the stator, a current waveform when the amplitude of the time change of the magnetic strain deformation amount of the entire iron core of the stator calculated for each of the current waveforms is less than a determination threshold value set based on the amplitude of the time change of the deformation amount of the entire iron core of the stator calculated for a current waveform determined without relying on magnetic strain; may be included.

[0008] (3) In the waveform assumption step of the motor control method according to (2) above, the current waveform may be assumed such that the torque acting on the rotor becomes a predetermined magnitude.

[0009] (4) In the magnetic flux density calculation step of the motor control method according to (2) or (3) above, the time change of the magnetic flux density at each of a plurality of elements set along the circumferential direction in the iron core of the stator may be calculated. In the magnetic strain deformation amount calculation step, the time change of the magnetic strain deformation amount of each of the plurality of elements may be calculated based on the time change of the magnetic flux density at each of the plurality of elements. The sum of the time changes of the magnetic strain deformation amounts of each of the plurality of elements may be calculated as the time change of the magnetic strain deformation amount of the entire iron core of the stator.

[0010] (5) In the waveform assumption step of the motor control method according to any one of (2) to (4) above, two or more currents may be assumed as the drive current. In the magnetic flux density calculation step, the time change of the magnetic flux density may be calculated for each phase current of the drive current. In the magnetostrictive deformation amount calculation step, the time change of the deformation amount of the entire core of the stator may be calculated for each phase current of the drive current.

[0011] (6) In the motor control method according to (5) above, for a period of at least half of the period during which each of the two or more currents flows, it may overlap with the period during which the current of another phase flows.

[0012] (7) In the motor control method according to (5) or (6) above, the shapes of the current waveforms of each phase of the drive current may be the same. The phases of the currents of each phase of the drive current may be different.

[0013] (8) In the motor control method according to any one of (2) to (7) above, the drive current determination step may further include an electromagnetic force deformation amount calculation step of calculating the time change of the electromagnetic force deformation amount, which is the deformation amount of the core of the stator due to the electromagnetic force acting on the stator. In the waveform determination step, the current waveform when the amplitude of the time change of the total deformation amount obtained by combining the magnetostrictive deformation amount of the entire core of the stator and the electromagnetic force deformation amount of the core of the stator is minimized may be determined as the drive current applied to the core of the stator.

Effect of the Invention

[0014] According to the motor control method according to the present disclosure, the vibration and noise of the motor are reduced.

Brief Description of the Drawings

[0015]

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[0016] Hereinafter, embodiments of the motor control method according to the present disclosure will be described with reference to the drawings. Each drawing is schematic and may be different from the actual one. Further, the following embodiments illustrate an apparatus or method for embodying the technical idea of the present disclosure, and do not specify the configuration to the following. That is, various changes can be made to the technical idea of the present disclosure within the technical scope described in the claims.

[0017] (Overview of Motor Control Method) As characteristics of an automotive motor or an industrial motor, not only high efficiency and high output but also low vibration and noise are required. For example, in a large-diameter and high-output motor used in an electric vehicle or the like, it is required to reduce the vibration and noise during driving of the motor.

[0018] As a cause of vibration and noise, it is known that vibration of components occurs when the electromagnetic force generated inside the motor acts on the components of the motor. As a method for reducing the vibration of components due to the electromagnetic force, for example, a method of flattening (reducing the time change) the sum of the electromagnetic forces acting on each part of the motor, or a method of appropriately controlling the electromagnetic force such as a method of reducing the pulsation of the electromagnetic force by injecting a harmonic current can be considered.

[0019] On the other hand, the iron core of the motor has magnetostrictive characteristics. The magnetostrictive deformation caused by the magnetostrictive characteristics of the iron core is one of the causes of the vibration and noise of the motor. Magnetostrictive deformation is a phenomenon in which an excited iron core expands due to the movement of magnetic domains, as illustrated in FIGS. 1A and 1B. As shown in FIG. 1B, compared to the state where the directions of the magnetic fluxes of the respective magnetic domains in the iron core are not aligned (demagnetized state) as shown in FIG. 1A, in the state where the directions of the magnetic fluxes of the respective magnetic domains are aligned (excited state), the length of the iron core extends from d to d + Δd along the direction of the magnetic flux. The amount of deformation due to the magnetostriction of the iron core is determined according to the magnitude of the magnetic flux density applied to the iron core. The motor includes a stator including an iron core and a rotor. That is, at least a part of the stator of the motor corresponds to the iron core of the motor. The stator and the rotor have an annular yoke. As illustrated in FIG. 2, the magnetic flux passing through the annular yoke of the stator of the motor in the circumferential direction generates circumferential magnetostriction in the annular yoke, and deforms the yoke so that the annular yoke expands outward in the radial direction. When the shape of the yoke is not annular, the magnetic flux passing along the tangential direction of the yoke generates tangential magnetostriction in the yoke, and deforms the yoke so that the yoke expands outward.

[0020] When the magnetic flux density applied to drive the motor inside the motor changes periodically, the annular yoke vibrates by repeating expansion and contraction due to the deformation caused by magnetostriction and deforming periodically. The vibration mode of the annular yoke is mode 0.

[0021] In other words, the periodic change in the magnetic flux density inside the motor serves as the excitation source. When the resonance frequency of the stator yoke matches the frequency of the excitation source (the frequency of the magnetic flux density), the stator yoke resonates and vibrates greatly, generating significant vibration noise. For example, when a stator with a large outer diameter is used to increase the output of a motor for an automobile, the resonance frequency of mode 0 of the stator yoke that constitutes the iron core becomes lower. As a result, the difference between the resonance frequency of mode 0 of the stator yoke and the frequency of the magnetic flux density applied to drive the motor becomes smaller, making the stator yoke more likely to resonate and increasing the vibration noise of the stator yoke, which has become a problem. In addition, an iron core made of amorphous metal with low iron loss or a permendur iron core with a high magnetic flux density has very large magnetostrictive characteristics. The vibration noise generated by the magnetostrictive deformation of the iron core with large magnetostrictive characteristics also becomes a problem as it becomes large enough to be non-negligible compared to the vibration noise generated by electromagnetic force.

[0022] As described above, the influence of magnetostrictive characteristics on the vibration noise of the motor has become non-negligible. The present disclosure proposes a method of controlling a motor so as to reduce the vibration noise during driving of the motor by reducing the vibration caused by the magnetostrictive deformation of the motor.

[0023] (Configuration example of control system 1) As illustrated in FIG. 3, a control system 1 according to an embodiment includes a control device 10 and a motor 20. The control device 10 controls the motor 20 so as to reduce the vibration noise during driving of the motor 20.

[0024] <Control device 10> The control device 10 includes a control unit 12, a storage unit 14, and an interface 16.

[0025] The control unit 12 generates a signal of drive current or drive voltage to be applied to the coil 36 (see FIG. 4) of each pole 34 (see FIG. 4) of the stator 30 in order to excite the iron core which is at least a part of the stator 30 (see FIG. 4) of the motor 20 and drive the motor 20. The control unit 12 may output, to the motor 20 from the interface 16, the signal of drive current or drive voltage itself to be applied to the coil 36 in order to excite the iron core of the motor 20 and drive the motor 20. When the control system 1 further includes an exciting device for exciting the iron core of the motor 20, the control unit 12 may output, from the interface 16, information for controlling the exciting device so that the exciting device applies a current or voltage corresponding to the signal of drive current or drive voltage generated by the control unit 12 to the coil 36.

[0026] The control unit 12 is configured to control and manage various functions of the control device 10 such as a function of generating a signal of drive current or drive voltage to be applied to the iron core of the motor 20. The control unit 12 may include at least one processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). The control unit 12 may be composed of only one processor or may be composed of a plurality of processors. The processor constituting the control unit 12 may realize the functions of the control device 10 by reading and executing a program stored in the storage unit 14.

[0027] The storage unit 14 stores various types of information, data, etc. The storage unit 14 may store, for example, a program executed in the control unit 12, or data or processing results used in the processing executed in the control unit 12. Further, the storage unit 14 may function as a work memory of the control unit 12. The storage unit 14 may be configured to include, for example, a semiconductor memory or the like, but is not limited thereto. For example, the storage unit 14 may be configured as an internal memory of a processor used as the control unit 12, or may be configured as a hard disk drive (HDD) accessible from the control unit 12. The storage unit 14 may be configured as a non-temporary readable medium. The storage unit 14 may be configured integrally with the control unit 12, or may be configured separately from the control unit 12.

[0028] The interface 16 may be configured as a terminal electrically connected to the coil 36 so as to be able to output to the coil 36 the drive current or the signal of the drive voltage applied to each pole 34 of the stator 30 of the motor 20 itself.

[0029] The interface 16 may be configured to include a communication interface that transmits to the excitation device information for controlling the excitation device so that the excitation device applies a current or voltage corresponding to the drive current or drive voltage signal generated by the control unit 12 to the coil 36. The communication interface may be configured to communicate with the excitation device by wire or wirelessly.

[0030] The communication interface is not limited to the excitation device, and may be configured to communicate with various other devices by wire or wirelessly. The communication interface may be configured to communicate with, for example, an external management device. The control unit 12 may acquire data or information necessary for generating a drive current or drive voltage signal applied to the iron core of the motor 20 from the external management device. The control unit 12 may output the result of generating a drive current or drive voltage signal applied to the iron core of the motor 20 to the external management device. The communication interface may be configured to support various communication standards.

[0031] The interface 16 may be configured to include a display device. The display device may notify the user of information by outputting visual information such as characters, figures, or images. The display device may include various displays such as, for example, a liquid crystal display. The control unit 12 may cause the display device to display the result of generating a signal of a drive current or a drive voltage applied to the core of the motor 20.

[0032] The interface 16 may be configured to include an input device that receives an input from the user. The input device may include, for example, a keyboard or physical keys, or may include a pointing device such as a touch panel or a touch sensor or a mouse. The input device is not limited to these examples and may include various other devices. The control unit 12 may acquire the data or information input by the user through the input device as the data or information necessary for generating a signal of a drive current or a drive voltage applied to the core of the motor 20.

[0033] <Motor 20> As illustrated in FIG. 4, the motor 20 includes a stator 30 and a rotor 40. In FIG. 4, the motor 20 is represented as a 1 / 6 partial model. The stator 30 has an annular yoke 32 and poles 34. The poles 34 project from the annular yoke 32 toward the inside of the ring. The rotor 40 has an annular yoke 42 and poles 44. The poles 44 project from the annular yoke 42 toward the outside of the ring. The yoke 42 of the rotor 40 is located inside the yoke 32 of the stator 30. The poles 34 of the stator 30 project toward the inner rotor 40. Also, the poles 44 of the rotor 40 project toward the outer stator 30. The poles 34 of the stator 30 and the poles 44 of the rotor 40 face each other.

[0034] The stator 30 may further include a coil 36 wound around the axis of the protruding direction of the pole 34 to generate a rotating magnetic field in the iron core composed of the yoke 32 and the pole 34 to continuously generate torque. When an exciting current flows through the coil 36, a magnetic flux is generated in the pole 34. The magnetic flux generated in the pole 34 passes through a magnetic circuit constituted by the yoke 32 and the pole 34 of the stator 30, the yoke 42 and the pole 44 of the rotor 40, and the air gap between the pole 34 and the pole 44. When the magnetic flux passes through the stator 30 and the rotor 40, the iron core is excited.

[0035] In the motor 20, when each pole 34 of the stator 30 is excited by the drive current flowing through the coil 36, an electromagnetic force (a magnetic force attracting the pole 44) acting on the pole 44 of the rotor 40 is generated. Among the electromagnetic forces acting on the pole 44 of the rotor 40, the component in the tangential direction of the yoke 42 (the direction in which the rotor 40 rotates) generates torque in the rotor 40. The motor 20 outputs the torque generated in the rotor 40 during driving.

[0036] The motor 20 according to this embodiment is assumed to be an 18 - 12 pole Switched Reluctance Motor (SRM). In the motor 20 according to this embodiment, the stator 30 has 18 poles 34. The rotor 40 has 12 poles 44. The motor 20 according to this embodiment applies three - phase drive currents with a phase shift of 120 degrees each to the coils wound around each of three adjacent poles 34 of the stator 30 to generate torque in the rotor 40. The phase of the drive current is also referred to as the electrical angle. On the other hand, the rotation angle around the rotation axis of the motor 20 (the rotation angle of the rotor 40) is also referred to as the mechanical angle. 360 degrees of electrical angle corresponds to the period during which one - cycle of drive current flows. When one - cycle of drive current flows through each coil, the rotor 40 of the motor 20 (18 - 12 pole SRM) according to this embodiment rotates by an amount corresponding to three poles 34 of the stator 30 (60 degrees). That is, when the electrical angle advances 360 degrees, the mechanical angle advances 60 degrees. The number of phases of the drive current is not limited to three - phase. The number of phases of the drive current may be one - phase, two - phase, or four - phase or more according to the configuration of the motor 20. In a reluctance motor, torque is generated in the direction in which the magnetic reluctance of the iron core becomes smaller. In other words, torque is generated in the direction in which the rotor 40 is rotated so that the length of the magnetic circuit from the pole 34 of the stator 30 to the pole 44 of the rotor 40 (the length of the magnetic flux lines passing through the pole 34 of the stator 30 and the pole 44 of the rotor 40) becomes the shortest. By changing the phase (electrical angle) of the drive current according to the rotation angle (mechanical angle) of the rotor 40, torque is continuously generated in the rotor 40.

[0037] (Operation example of control system 1) Hereinafter, an operation example of the control system 1 according to this embodiment will be described.

[0038] The control unit 12 of the control device 10 reduces the vibration of the stator 30 by reducing the time - change of the magnetic - strain deformation amount in the tangential direction of the yoke 32 generated by the magnetic flux passing through the yoke 32 of the stator 30 in the tangential direction of the yoke 32. When the yoke 32 is annular, the tangential direction of the yoke 32 is also referred to as the circumferential direction of the yoke 32.

[0039] The control unit 12 assumes a signal of drive current or drive voltage for exciting the pole 34 of the stator 30, and calculates the time change of the magnetostrictive deformation amount in the tangential direction of the yoke 32 of the stator 30 when the assumed signal is applied to the pole 34 of the stator 30. The control unit 12 assumes a signal of drive current or drive voltage so that the time change of the magnetostrictive deformation amount in the tangential direction of the yoke 32 of the stator 30 becomes small. The control unit 12 may determine a signal of drive current or drive voltage so that the amplitude of the time change of the magnetostrictive deformation amount in the tangential direction of the yoke 32 of the stator 30 becomes less than the determination threshold value. The control unit 12 may set the determination threshold value based on the amplitude of the time change of the deformation amount in the tangential direction of the yoke 32 of the stator 30 when a signal of drive current or drive voltage determined without relying on magnetostriction is applied to the pole 34 of the stator 30. That is, the control unit 12 may set the determination threshold value based on the amplitude of the time change of the deformation amount of the entire iron core of the stator 30 calculated for the current waveform determined without relying on magnetostriction. The control unit 12 may, for example, set half of the amplitude of the time change of the deformation amount of the entire iron core of the stator calculated for the current waveform determined without relying on magnetostriction as the determination threshold value. The control unit 12 may, for example, set the amplitude itself of the time change of the deformation amount of the entire iron core of the stator calculated for the current waveform determined without relying on magnetostriction as the determination threshold value. The control unit 12 may determine a signal of drive current or drive voltage so that the amplitude of the time change of the magnetostrictive deformation amount in the tangential direction of the yoke 32 of the stator 30 becomes extremely small or minimum.

[0040] The control unit 12 generates a magnetic flux in the pole 34 by applying the determined signal of drive current or drive voltage to the coil 36 wound around the pole 34 of the stator 30, and excites the iron core of the motor 20. The control unit 12 can drive the motor 20 by generating torque in the rotor 40 by exciting the iron core of the motor 20.

[0041] The magnetic flux generated in the pole 34 is proportional to the magnitude of the drive current flowing through the coil 36 wound around the pole 34. Therefore, the control unit 12 can control the magnetic flux generated in the pole 34 by controlling the drive current. Hereinafter, an example of a procedure for driving the motor 20 by the control unit 12 determining a signal of the drive current and applying the determined drive current to the iron core of the motor 20 will be described. Note that the control unit 12 may control the magnitude of the drive current flowing through the coil 36 by determining the drive voltage applied to the coil 36 in consideration of the inductance of the coil 36. Therefore, in the example of the procedure described below, the control unit 12 may determine a signal of the drive voltage instead of the drive current.

[0042] As exemplified in the flowchart of FIG. 5, the control method of the motor 20 executed by the control unit 12 includes a step S1 in which the control unit 12 determines a drive current, and a step S2 in which the control unit 12 applies the drive current to the iron core of the motor 20 to excite it. Step S1 is also referred to as a drive current determination step. Step S2 is also referred to as a drive current application step. The control unit 12 may determine a drive voltage instead of the drive current in the procedure of step S1, and apply the drive voltage to the iron core of the motor 20 in the procedure of step S2.

[0043] The step S1 in which the control unit 12 determines the drive current may be executed as a drive current determination method including the procedure exemplified in the flowchart of FIG. 6. The control method of the motor 20 or the drive current determination method may be realized as a control program of the motor 20 or a drive current determination program that causes a processor constituting the control unit 12 to execute. The control program of the motor 20 or the drive current determination program may be stored in a non-transitory computer-readable medium. Hereinafter, the operation of the control unit 12 will be described based on the procedure exemplified in the flowchart of FIG. 6.

[0044] <Assumption of current waveform> The control unit 12 assumes a current waveform of a drive current applied to the coil 36 of the pole 34 of the stator 30, which is used to calculate the magnetostrictive deformation amount of the stator 30 of the motor 20 (step S11). Step S11 is also referred to as a waveform assumption step. As described above, the motor 20 according to the present embodiment generates torque on the rotor 40 by applying three-phase drive currents with an electrical angle shifted by 120 degrees to the coils 36 of three adjacent poles 34 of the stator 30. The three-phase drive currents may be distinguished as drive currents of phase A, phase B, and phase C. The control unit 12 assumes the current waveforms of the drive currents of phase A, phase B, and phase C. In the present embodiment, the control unit 12 assumes the same current waveform as the current waveforms of the drive currents of phase A, phase B, and phase C. The control unit 12 makes the current waveforms of the drive currents of phase A, phase B, and phase C the current waveforms used in the examples described later (for example, the i in the graph of FIG. 13A A , i B and i C ). The control unit 12 may assume a current waveform such that the torque acting on the rotor 40 of the motor 20 becomes a predetermined magnitude. The control unit 12 may assume a current waveform of one phase according to the configuration of the motor 20, or may assume a current waveform of any number of phases of two or more phases.

[0045] <Calculation of the time change of the magnetic flux density> The control unit 12 calculates the time change of the magnetic flux density generated in the iron core of the motor 20 when the assumed current waveform is applied as a drive current to the coil 36 of each pole 34 of the stator 30 (step S12). Step S12 is also referred to as the magnetic flux density calculation step. Specifically, the control unit 12 calculates the magnetic flux density generated in the stator 30 with respect to the magnetic flux generated in the stator 30 when the current waveform assumed in the procedure of step S11 is applied as a drive current to the coil 36 by applying finite element analysis to the partial model of FIG. 4. For finite element analysis, various finite element analysis software such as JMAG (registered trademark) or Ansys Maxwell (registered trademark) may be used, for example. The control unit 12 sets a plurality of elements for finite element analysis in the partial model of the stator 30. The position in the tangential direction of each element set in the partial model of the stator 30 is specified with the mechanical angle θ m as a parameter. The control unit 12 applies finite element analysis to the plurality of elements set in the partial model of the stator 30, and sweeps the electrical angle of the current waveform assumed in the procedure of step S11 and the current value of each phase at regular intervals, thereby obtaining the absolute value |B t (θ m )| of the tangential component of the magnetic flux density at each element of the stator 30.

[0046] As shown in FIG. 7, as an example of the calculation result of the magnetic flux density by finite element analysis, the distribution of the magnitude of the absolute value of the tangential component of the magnetic flux density in the stator 30 at a certain time is represented in gray scale. In FIG. 7, the magnitude of the absolute value of the tangential component of the magnetic flux density in each element set in the stator 30 is represented by the shading of the pixel corresponding to each element. The pixel corresponding to the element with a large absolute value of the tangential component of the magnetic flux density is represented by a color close to black. Conversely, the pixel corresponding to the element with a small absolute value of the tangential component of the magnetic flux density is represented by a color close to white. Assume that the three poles 34 of the stator 30 include a pole 34A to which a driving current of phase A is applied, a pole 34B to which a driving current of phase B is applied, and a pole 34C to which a driving current of phase C is applied. Due to the phase shift of the electrical angles of the driving currents of each of phase A, phase B, and phase C, the magnitudes of the tangential components of the magnetic flux density in the portions adjacent to each of the poles 34A, 34B, and 34C of the yoke 32 are different from each other.

[0047] The control unit 12 calculates the magnetic flux density in the stator 30 at each time when the assumed current waveform is passed through the coil 36 for one cycle. By calculating the magnetic flux density at each time, the control unit 12 can calculate the time change of the magnetic flux density. The control unit 12 may appropriately set the interval between the times at which the magnetic flux density is calculated.

[0048] <Conversion to the time change of the magnetostrictive deformation amount> The control unit 12 converts the time change of the magnetic flux density generated in the iron core of the motor 20 when the assumed current waveform is applied as the driving current into the time change of the magnetostrictive deformation amount of the iron core (step S13). Step S13 is also referred to as the magnetostrictive deformation amount calculation step. The control unit 12 can convert the time change of the magnetic flux density generated in the iron core (stator 30) into the time change of the magnetostrictive deformation amount of the iron core (stator 30) by converting the result of calculating the magnetic flux density in the stator 30 at each time into the magnetostrictive deformation amount in the tangential direction of the yoke 32 of the stator 30 at each time.

[0049] An example of the tangential magnetic flux density distribution at a certain time is shown as a graph in FIG. 8. In the graph of FIG. 8, the horizontal axis is the mechanical angle θ mcorresponds to the position in the tangential direction within the stator 30 represented thereby. The vertical axis represents the absolute value |B t (θ m )| of the tangential component of the magnetic flux density at each position in the tangential direction. Based on the magnetostriction characteristics of the stator 30, the control unit 12 calculates, in the procedure of step S12, the absolute value |B t (θ m )| of the tangential component of the magnetic flux density at each position in the tangential direction of the stator 30, and converts it into the magnetostriction deformation amount λ t (θ m ) at each position in the tangential direction of the stator 30. The control unit 12 may use, as the magnetostriction characteristics of the stator 30, for example, a λ - B diagram that specifies the relationship between the magnetostriction amount λ and the magnetic flux density B, which is illustrated as a graph in FIG. 9. In FIG. 9, the horizontal axis corresponds to the magnetic flux density B. The unit of the magnetic flux density B is T (tesla). The vertical axis corresponds to the magnetostriction deformation amount λ. The unit of the magnetostriction deformation amount λ is ppm (parts per million).

[0050] The λ - B diagram may be generated based on, for example, data obtained by actually measuring the magnetostriction using the material of the stator 30 of the motor 20 that is the object of analysis of the magnetostriction deformation. The λ - B diagram may be generated based on data measured by exciting the stator 30 at a low frequency of 3 Hz. The λ - B diagram may be generated so as to be represented as a more complex butterfly - shaped graph than the graph illustrated in FIG. 9. The control unit 12 uses various relationships between the magnetostriction amount λ and the magnetic flux density B to convert the distribution of the absolute value |B t (θ m )| of the tangential component of the magnetic flux density into the magnetostriction distribution λ t (θ m ).

[0051] When the absolute value of the tangential component of the magnetic flux density illustrated in FIG. 8 is converted using the λ - B diagram illustrated in FIG. 9, the magnetostriction deformation amount λ t (θ m ) at each position in the tangential direction of the stator 30 is shown as a graph in FIG. 10. In the graph of FIG. 10, the horizontal axis corresponds to the position in the tangential direction of the stator 30 represented by the mechanical angle θ m . The unit of the mechanical angle is deg (degree). The vertical axis represents the tangential magnetostriction deformation amount λ at each position in the tangential direction of the stator 30t (θ m ) corresponds. The magnetostrictive deformation amount λ t in the tangential direction has the unit of ppm (parts per million).

[0052] <Calculation of the sum of magnetostrictive deformations> The control unit 12 calculates the time change of the sum of the magnetostrictive deformations of the core of the motor 20 when the assumed current waveform is applied as the drive current (step S14). Step S14 is also referred to as the sum-of-magnetostrictive-deformation calculation step. The sum of the magnetostrictive deformations of the core of the motor 20 is the sum of the magnetostrictive deformation amounts λ t (θ m ) in the tangential direction at each position in the tangential direction of the stator 30 of the motor 20. In other words, the control unit 12 calculates the sum of the time changes of the magnetostrictive deformation amounts of each of the plurality of elements set in the stator 30 of the motor 20, which were calculated in the magnetostrictive deformation amount calculation step, as the time change of the magnetostrictive deformation amount (sum of magnetostrictive deformations) of the entire core of the stator 30.

[0053] Specifically, the control unit 12 integrates the magnetostrictive deformation amount λ t (θ m ) in the tangential direction of the stator 30 (along the circumference) to calculate the sum of the magnetostrictive deformations at a certain electrical angle θ e . The sum of the magnetostrictive deformations at a certain electrical angle θ e depends on the excitation currents i A , i B , i C , and the electrical angle θ e , so it is represented as Λ t (i A , i B , i C , θ e ). The time change of the sum of the magnetostrictive deformations means the change in the sum of the magnetostrictive deformations corresponding to the change in the electrical angle θ e . That is, the time change of the sum of the magnetostrictive deformations is Λ e when the electrical angle θ t (i A , i B , i C , θ e is changed.) is represented as a change in the value.

[0054] <Determination of Driving Current Based on Magnetostrictive Deformation Sum> The control unit 12 determines whether the amplitude of the temporal change in the magnetostrictive deformation sum satisfies the condition (step S15). When the amplitude of the temporal change in the magnetostrictive deformation sum satisfies the condition (step S15: YES), the control unit 12 determines the current waveform that satisfies the condition as the driving current to be actually applied to the stator 30 of the motor 20 (step S16). Step S16 is also referred to as a waveform determination step. The control unit 12 may set, as a condition to be satisfied by the amplitude of the temporal change in the magnetostrictive deformation sum, a condition that can reduce the noise caused by the magnetostrictive vibration of the iron core of the motor 20, as described below.

[0055] The noise caused by the magnetostrictive vibration of the iron core of the motor 20 increases according to the amplitude of the magnetostrictive vibration of the iron core of the motor 20. The amplitude of the magnetostrictive vibration of the iron core of the motor 20 corresponds to the change width (amplitude of the temporal change in the magnetostrictive deformation sum) when the magnetostrictive deformation sum of the iron core of the motor 20 changes periodically. Therefore, the control unit 12 may set, as a condition that can reduce the noise caused by the magnetostrictive vibration of the iron core of the motor 20, a condition that the amplitude of the temporal change in the magnetostrictive deformation sum of the iron core of the motor 20 becomes small.

[0056] For example, when the amplitude of the temporal change in the magnetostrictive deformation sum calculated by executing the procedures from step S11 to step S14 is less than a predetermined value, the control unit 12 may determine that the current waveform assumed in the procedure of step S11 satisfies the condition, and determine that current waveform as the driving current to be actually applied to the stator 30 of the motor 20.

[0057] For example, the control unit 12 may repeatedly execute the procedures from step S11 to step S14 a plurality of times to calculate the amplitude of the temporal change in the magnetostrictive deformation sum corresponding to each of the assumed plurality of current waveforms. The control unit 12 may determine that the current waveform corresponding to the minimum amplitude among the amplitudes of the temporal change in the magnetostrictive deformation sum corresponding to each of the assumed plurality of current waveforms satisfies the condition, and determine that current waveform as the driving current to be actually applied to the stator 30 of the motor 20.

[0058] When the amplitude of the temporal change in the magnetostrictive strain sum does not satisfy the condition (step S15: NO), the control unit 12 returns to the procedure of step S11, and repeats the procedures from step S11 to S15 until the amplitude of the temporal change in the magnetostrictive strain sum newly calculated assuming a current waveform satisfies the condition.

[0059] After executing the procedure of step S16, the control unit 12 ends the execution of the procedure of the flowchart in FIG. 6. The control unit 12 drives the motor 20 by applying the drive current determined by executing the procedure of the flowchart in FIG. 6 to the excitation current application procedure in step S2 of the flowchart in FIG. 5 described above.

[0060] <Parentheses> As described above, the control unit 12 grasps the relationship between the driving conditions of the motor 20 and the magnetostrictive strain sum in order to obtain a current for making the magnetostrictive strain sum substantially constant. The driving conditions include the current waveforms of each phase of the assumed drive current. The current waveform is specified by the electrical angle and the current value at each electrical angle. The control unit 12 can determine a drive current in which the current value of the drive current at each electrical angle is adjusted so that the amplitude of the temporal change in the magnetostrictive strain amount becomes small, using data representing the relationship between a finite number of drive conditions and the magnetostrictive strain amount within a certain range. By applying the determined drive current to the iron core of the motor 20, the control unit 12 can reduce the magnetostrictive vibration of the iron core of the motor 20 and reduce the noise caused by the magnetostrictive vibration.

[0061] (Example) Hereinafter, an example of the model analysis of the motor 20 will be described.

[0062] <First Embodiment> As a first embodiment, a model analysis for determining the drive current of a switched reluctance motor (SRM) is verified. FIG. 11 shows a 1 / 6 partial model of a motor 20 (SRM) used for verifying a method for determining the drive current of the motor 20 according to the first embodiment. The motor 20 includes a stator 30 and a rotor 40. The stator 30 includes a yoke 32, poles 34A, 34B, and 34C, and coils 36A, 36B, and 36C. The yoke 32 is configured in an annular shape. Each of the poles 34A, 34B, and 34C protrudes from the yoke 32 toward the inside of the annulus. Each of the coils 36A, 36B, and 36C is wound around the poles 34A, 34B, and 34C. The rotor 40 includes a yoke 42 and a pole 44. The yoke 42 is configured in an annular shape having a radius smaller than that of the yoke 32. The pole 44 protrudes from the yoke 42 toward the outside of the annulus.

[0063] It is assumed that the motor 20 (SRM) to be verified is designed as a generator of a hybrid vehicle. It is assumed that the materials of the poles 34A, 34B, and 34C of the stator 30 are amorphous metal 2605SA1. It is assumed that the thickness (core stack thickness) of each of the poles 34A, 34B, and 34C is 50 mm. It is assumed that the outer diameter of the yoke 32 is 190 mm.

[0064] Current waveforms shown in FIG. 12A as rectangular current waveforms according to a comparative example are applied to each of the coils 36A, 36B, and 36C of the partial model of FIG. 11. In the graph of FIG. 12A, the horizontal axis is the electrical angle. The unit of the electrical angle is deg (degree). The vertical axis is the value of the exciting current flowing through each of the coils 36A, 36B, and 36C at each electrical angle. The unit of the exciting current is A (ampere). The currents applied to the coils 36A, 36B, and 36C are represented as i A , i B and i C respectively.

[0065] When the rectangular current waveform according to the comparative example is applied to the partial model, the sum of the magnetic strain deformations in the tangential direction (circumferential direction) of the yoke 32 of the stator 30 corresponding to the rectangular current waveform is calculated. The waveform of the time change of the sum of the magnetic strain deformations in the tangential direction (circumferential direction) of the yoke 32 corresponding to the rectangular current waveform according to the comparative example is shown as the graph in FIG. 12B. In the graph of FIG. 12B, the horizontal axis is the electrical angle. The unit of the electrical angle is deg (degree). The vertical axis is the sum of the magnetic strain deformations in the tangential direction (circumferential direction) of the yoke 32 at each electrical angle. The unit of the sum of the magnetic strain deformations is ppm (parts per million). As shown in FIG. 12B, the amplitude of the time change of the sum of the magnetic strain deformations when the rectangular current waveform according to the comparative example is applied to the partial model was 10.6 ppm.

[0066] On the other hand, the current waveform shown in FIG. 13A as the current waveform according to the first embodiment is applied to each of the coils 36A, 36B, and 36C of the partial model in FIG. 11. In the graph of FIG. 13A, the horizontal axis is the electrical angle. The unit of the electrical angle is deg (degree). The vertical axis is the value of the exciting current flowing through each of the coils 36A, 36B, and 36C at each electrical angle. The unit of the exciting current is A (ampere). The currents applied to the coils 36A, 36B, and 36C are respectively i A 、i B and i C as represented. The current waveform according to the first embodiment is determined using the driving current determination method described in the above-described embodiment.

[0067] When the current waveform according to the first embodiment is applied to the partial model, the sum of the magnetic strain deformations in the tangential direction (circumferential direction) of the yoke 32 of the stator 30 corresponding to the current waveform is calculated. The waveform of the time change of the sum of the magnetic strain deformations in the tangential direction (circumferential direction) of the yoke 32 corresponding to the current waveform according to the first embodiment is shown as the graph in FIG. 13B. In the graph of FIG. 13B, the horizontal axis is the electrical angle. The unit of the electrical angle is deg (degree). The vertical axis is the sum of the magnetic strain deformations in the tangential direction (circumferential direction) of the yoke 32 at each electrical angle. The unit of the sum of the magnetic strain deformations is ppm (parts per million). As shown in FIG. 13B, the amplitude of the time change of the sum of the magnetic strain deformations when the current waveform according to the first embodiment is applied to the partial model was 0.8 ppm.

[0068] According to the results described above, the amplitude of the time change of the sum of magnetostrictive deformations when the current waveform according to the first embodiment is applied is significantly smaller than the amplitude of the time change of the sum of magnetostrictive deformations when the rectangular current waveform according to the comparative example is applied. Specifically, the amplitude of the magnetostrictive vibration when the current waveform according to the first embodiment is applied is reduced to 1 / 10 or less of the amplitude of the magnetostrictive vibration when the rectangular current waveform according to the comparative example is applied. Further, by narrowing the sweep interval between the current and the electrical angle of each phase, the current waveform applied for excitation may be further finely adjusted. By the fine adjustment of the current waveform, the amplitude of the time variation of the magnetostrictive deformation amount is further reduced.

[0069] In the SRM to be verified, the third-order components are the main noise components. Therefore, from the viewpoint of noise suppression, it is prioritized to reduce the third-order vibration components. Thus, the deformation amounts of the third-order and sixth-order components of the magnetostrictive vibration of the stator 30 are compared between the case where the motor 20 is driven by applying the rectangular current waveform according to the comparative example and the case where the motor 20 is driven by applying the current waveform according to the first embodiment.

[0070] As shown in FIG. 14, the third-order component of the magnetostrictive vibration of the stator 30 is compared between the case where the rectangular current waveform according to the comparative example is applied and the case where the current waveform according to the first embodiment is applied. The displacement amount of each part of the stator 30 when the rectangular current waveform according to the comparative example is applied is about 1 μm. On the other hand, the displacement amount of each part of the stator 30 when the current waveform according to the first embodiment (this embodiment) is applied is close to 0 μm.

[0071] As shown in FIG. 15, the sixth-order component of the magnetostrictive vibration of the stator 30 is compared between the case where the rectangular current waveform according to the comparative example is applied and the case where the current waveform according to the first embodiment is applied. The displacement amount of each part of the stator 30 when the rectangular current waveform according to the comparative example is applied is about 2 μm. On the other hand, the displacement amount of each part of the stator 30 when the current waveform according to the first embodiment (this embodiment) is applied is close to 0 μm.

[0072] According to the results shown in FIGS. 14 and 15, it was confirmed that the deformation caused by the third and sixth components of the vibration was significantly reduced by adopting the current waveform according to the first embodiment.

[0073] FIG. 16 shows the analysis values of the sound pressure levels of the vibration noise generated from the motor 20 when the rectangular current waveform according to the comparative example is applied to drive the motor 20 and when the current waveform according to the first embodiment (this embodiment) is applied to drive the motor 20. In FIG. 16, the horizontal axis represents the order of the frequency components. The vertical axis represents the sound pressure level at each order. The unit of the sound pressure level is dB (decibel). The sound pressure level of the third component of the vibration noise in this embodiment is reduced by 16 dB compared to the sound pressure level of the comparative example. The sound pressure level of the sixth component of the vibration noise in this embodiment is reduced by 20 dB compared to the sound pressure level of the comparative example. The sound pressure level of the ninth component of the vibration noise in this embodiment is reduced by 14 dB compared to the sound pressure level of the comparative example. The sound pressure level of the twelfth component of the vibration noise in this embodiment is reduced by 17 dB compared to the sound pressure level of the comparative example.

[0074] As described above, the vibration noise when driving the motor 20 by applying the current waveform according to the first embodiment determined by executing the drive current determination method is reduced compared to the vibration noise when applying the rectangular current waveform.

[0075] The rectangular current waveform used in the comparative example hardly overlaps with other phases. On the other hand, each of the three-phase current waveforms i A , i B and i C in the first embodiment overlaps with the period during which the current of other phases flows for more than half of the period during which the current flows, as shown in FIG. 13A. Also, each of the three-phase current waveforms i A , i B and i C is configured such that the shapes of the respective current waveforms are the same and only the phases of the respective phases are different.

[0076] <Second Embodiment> The drive current determination method described above is also applicable to a Permanent Magnet Synchronous Motor (PMSM). Therefore, as a second embodiment, a model analysis for determining the drive current of a PMSM is verified. FIG. 17 shows a 1 / 8 partial model of a motor 20 (PMSM) used for verifying the method for determining the drive current of the motor 20 according to the second embodiment. The motor 20 includes a stator 30 and a rotor 40. The stator 30 includes a yoke 32, poles 34, and coils 36. The yoke 32 is configured in an annular shape. The poles 34 project from the yoke 32 toward the inside of the annulus. The coils 36 are wound around the poles 34. The rotor 40 includes a yoke 42, poles 44, and permanent magnets 46. The yoke 42 is configured in an annular shape having a radius smaller than that of the yoke 32. The poles 44 project from the yoke 42 toward the outside of the annulus. The permanent magnets 46 generate magnetic flux in the poles 44. In a PMSM, when each pole 34 of the stator 30 is excited by a drive current flowing through the coil 36, an electromagnetic force (a magnetic force that attracts or repels the pole 44) is generated between the pole 44 of the rotor 40 where magnetic flux is generated by the permanent magnet 46. Among the electromagnetic forces acting on the pole 44 of the rotor 40, the component in the tangential direction of the yoke 42 (the direction in which the rotor 40 rotates) generates torque in the rotor 40.

[0077] The motor 20 (PMSM) to be verified is designed as a generator for a hybrid vehicle. However, the effects obtained by the present invention are not limited to hybrid vehicle applications or power generation (regeneration) applications, and the effects can also be obtained in drive (power running) as long as the requirements of the invention are satisfied. Assume that the material of the pole 34 of the stator 30 is amorphous metal 2605SA1. Assume that the thickness (core stack thickness) of the pole 34 is 60 mm. Assume that the outer diameter of the yoke 32 is 190 mm.

[0078] The control of a PMSM is different from that of an SRM. The drive current input to a PMSM is not a three-phase current waveform, but a d-axis current, a q-axis current, and a zero-phase current. The d-axis current, q-axis current, and zero-phase current are represented as variables of vector control including the frequency components and phases of the respective currents. To the coil 36 of the partial model in FIG. 17, the d-axis current according to the comparative example and the d-axis current according to the second embodiment (this embodiment), which are shown in the graph of FIG. 18, are applied. In the graph of FIG. 18, the horizontal axis is the electrical angle. The unit of the electrical angle is deg (degree). The vertical axis is the value of the d-axis current flowing through the coil 36 at each electrical angle. The unit of the d-axis current is A (ampere). The d-axis current according to the comparative example is a DC current of -66 A. The d-axis current according to the second embodiment is a current obtained by superimposing a sixth-order current with an amplitude of 17.5 A and a phase of 70 deg on a DC current of -66 A in order to suppress the sixth-order component, which is the main vibration component. The d-axis current according to the second embodiment is determined using the drive current determination method described in the above-described embodiments. Note that the q-axis current is a DC current in both the comparative example and the second embodiment.

[0079] When the d-axis currents according to the comparative example and the second embodiment are applied to the partial model, the sum of the magnetic strain deformations in the tangential direction (circumferential direction) of the yoke 32 of the stator 30 corresponding to the respective d-axis currents is calculated. The waveforms of the time changes of the sum of the magnetic strain deformations in the tangential direction (circumferential direction) of the yoke 32 corresponding to the d-axis currents according to the comparative example and the second embodiment (this embodiment) are shown as the graph of FIG. 19. In the graph of FIG. 19, the horizontal axis is the electrical angle. The unit of the electrical angle is deg (degree). The vertical axis is the sum of the magnetic strain deformations in the tangential direction (circumferential direction) of the yoke 32 at each electrical angle. The unit of the sum of the magnetic strain deformations is ppm (parts per million).

[0080] As shown in FIG. 19, the amplitude of the time change of the magnetostrictive strain sum when the d-axis current according to the comparative example was applied to the partial model was 0.8 ppm. On the other hand, the amplitude of the time change of the magnetostrictive strain sum when the d-axis current according to the second embodiment (this embodiment) was applied to the partial model was 0.1 ppm. That is, it was confirmed that the amplitude of the time change of the magnetostrictive strain sum when a current with a sixth-order harmonic superimposed as the d-axis current was applied was smaller than the amplitude of the time change of the magnetostrictive strain sum when a direct current was applied as the d-axis current and the q-axis current.

[0081] In the PMSM under verification, the sixth-order vibration component is the main noise component. Therefore, from the perspective of noise suppression, reducing the sixth-order vibration component is prioritized. Therefore, the deformation amount of the sixth-order component of the magnetostrictive vibration of the stator 30 is compared between the case where the motor 20 is driven by applying the d-axis current according to the comparative example and the case where the motor 20 is driven by applying the d-axis current according to the second embodiment.

[0082] As shown in FIG. 20, the displacement amount of each part of the stator 30 when the d-axis current according to the comparative example was applied was about 0.4 μm. On the other hand, the displacement amount of each part of the stator 30 when the d-axis current according to the second embodiment (this embodiment) was applied was close to 0 μm. According to the results shown in FIG. 20, it was confirmed that the deformation due to the sixth-order component of the vibration was significantly reduced by adopting the d-axis current according to the second embodiment.

[0083] FIG. 21 shows the analysis values of the sound pressure levels of the vibration noise generated from the motor 20 when the motor 20 was driven by applying the d-axis current according to the comparative example and when the motor 20 was driven by applying the d-axis current according to the second embodiment (this embodiment). In FIG. 21, the horizontal axis represents the order of the frequency components. The vertical axis represents the sound pressure level at each order. The unit of the sound pressure level is dB (decibel). The sound pressure level of the sixth-order component of the vibration noise in this embodiment is reduced by 19 dB compared to the sound pressure level of the comparative example. On the other hand, although the sixth-order current component is superimposed on the d-axis current applied in this embodiment and the twelfth-order current component is not superimposed, the sound pressure level of the twelfth-order component of the vibration noise is not reduced much.

[0084] As described above, the vibration noise when driving the motor 20 by applying the d-axis current according to the second embodiment determined by executing the drive current determination method is reduced compared to the vibration noise when applying the DC d-axis current according to the comparative example.

[0085] As the d-axis current according to the second embodiment, a current with a superimposed 6th-order current component is used. Depending on the vibration component to be suppressed, a current with superimposed current components of various orders such as 12th order or 18th order may be used as the d-axis current.

[0086] (Other Embodiments) Hereinafter, examples of the drive current determination method according to other embodiments will be described.

[0087] In the motor 20, the electromagnetic force acting between the stator 30 and the rotor 40 acts not only in the tangential direction (circumferential direction) of the stator 30, but also in the direction orthogonal to the tangential direction (radial direction) by the stator 30 and the rotor 40 attracting and repelling each other. The electromagnetic force acting in the tangential direction of the stator 30 contributes to the torque output of the motor 20. On the other hand, the electromagnetic force acting in the direction intersecting the tangential direction of the stator 30 does not contribute to the torque output of the motor 20, but rather causes vibration noise by deforming the stator 30. Therefore, the control unit 12 may determine the drive current of the motor 20 in consideration of not only the magnetostrictive deformation amount but also the electromagnetic force deformation amount. The electromagnetic force deformation amount is determined based on the electromagnetic force acting on the stator 30 and the characteristics of the stator 30 (for example, Young's modulus, etc.).

[0088] In order for the control unit 12 to determine the drive current of the motor 20 in consideration of not only the magnetostrictive deformation amount but also the electromagnetic force deformation amount, a drive current determination method including the procedure illustrated in the flowchart of FIG. 22 may be executed.

[0089] The control unit 12 assumes a current waveform of the drive current applied to the coil 36 of the pole 34 of the stator 30, which is used to calculate the magnetostrictive deformation amount of the stator 30 of the motor 20 (step S21). The control unit 12 calculates the time change of the magnetic flux density generated in the iron core of the motor 20 when the assumed current waveform is applied as the drive current to the coil 36 of each pole 34 of the stator 30 (step S22). The control unit 12 converts the time change of the magnetic flux density generated in the iron core of the motor 20 when the assumed current waveform is applied as the drive current into the time change of the magnetostrictive deformation amount of the iron core (step S23). The control unit 12 calculates the time change of the sum of the magnetostrictive deformations of the iron core of the motor 20 when the assumed current waveform is applied as the drive current (step S24). The control unit 12 may execute each procedure from step S21 to S24 in the same manner as each procedure from step S11 to S14 in the flowchart of FIG. 6.

[0090] The control unit 12 converts the time change of the magnetic flux density generated in the iron core of the motor 20, which is calculated in the procedure of step S22, into the time change of the electromagnetic force deformation amount of the stator 30 (step S25). Step S25 is also referred to as an electromagnetic force deformation amount calculation step. Specifically, the control unit 12 can convert the time change of the magnetic flux density generated in the iron core (stator 30) into the time change of the electromagnetic force deformation amount of the iron core (stator 30) by converting the result of calculating the magnetic flux density in the iron core at each time into the electromagnetic force deformation amount of the stator 30 due to the electromagnetic force acting between the stator 30 and the rotor 40 at each time.

[0091] The control unit 12 calculates the time change of the total deformation amount obtained by adding the time change of the sum of the magnetostrictive deformations of the iron core of the motor 20 calculated in the procedure of step S24 and the time change of the electromagnetic force deformation amount of the iron core of the motor 20 calculated in the procedure of step S25 (step S26). The control unit 12 may convert the sum of the magnetostrictive deformations in the tangential direction of the stator 30 into the deformation amount in the direction intersecting the tangential direction of the stator 30 and add it to the electromagnetic force deformation amount of the stator 30.

[0092] The control unit 12 determines whether the amplitude of the temporal change in the total deformation amount satisfies the condition (step S27). When the amplitude of the temporal change in the total deformation amount satisfies the condition (step S27: YES), the control unit 12 determines the current waveform that has satisfied the condition as the drive current to be actually applied to the stator 30 of the motor 20 (step S28). As a condition that the amplitude of the temporal change in the total deformation amount should satisfy, the control unit 12 may set a condition that can reduce the noise caused by the deformation vibration of the iron core of the motor 20, as described below.

[0093] The noise caused by the deformation vibration of the iron core of the motor 20 increases according to the amplitude of the total deformation amount of the iron core of the motor 20. Therefore, the control unit 12 may set, as a condition that can reduce the noise caused by the deformation vibration of the iron core of the motor 20, a condition that the amplitude of the temporal change in the total deformation amount of the iron core of the motor 20 becomes small.

[0094] For example, when the amplitude of the temporal change in the total deformation amount calculated by executing the procedures from step S21 to step S26 is less than a predetermined value, the control unit 12 determines that the current waveform assumed in the procedure of step S21 satisfies the condition, and determines that current waveform as the drive current to be actually applied to the stator 30 of the motor 20.

[0095] For example, the control unit 12 may repeatedly execute the procedures from step S21 to step S26 a plurality of times to calculate the amplitude of the temporal change in the total deformation amount corresponding to each of the assumed plurality of current waveforms. The control unit 12 determines that the current waveform corresponding to the minimum amplitude among the amplitudes of the temporal change in the total deformation amount corresponding to each of the assumed plurality of current waveforms satisfies the condition, and may determine that current waveform as the drive current to be actually applied to the stator 30 of the motor 20.

[0096] When the amplitude of the temporal change in the total deformation amount does not satisfy the condition (step S27: NO), the control unit 12 returns to the procedure of step S21 and repeats the procedures from step S21 to S26 until the amplitude of the temporal change in the total deformation amount newly calculated by assuming a current waveform satisfies the condition.

[0097] After executing the procedure of step S28, the control unit 12 ends the execution of the procedure of the flowchart in FIG. 22. The control unit 12 drives the motor 20 by applying the drive current determined by executing the procedure of the flowchart in FIG. 22 to the excitation current application procedure of step S2 in the flowchart of FIG. 5 described above.

[0098] As described above, the drive current determination step according to another embodiment further includes an electromagnetic force deformation amount calculation step of calculating a time change of the electromagnetic force deformation amount, which is the amount of deformation of the iron core of the stator 30 due to the electromagnetic force acting on the stator 30 of the motor 20. Further, in the waveform determination step, the control unit 12 may determine, as the drive current to be applied to the iron core of the stator 30, the current waveform when the amplitude of the time change of the total deformation amount obtained by combining the magnetostrictive deformation amount (sum of magnetostrictive deformations) of the entire iron core of the stator 30 and the electromagnetic force deformation amount of the iron core of the stator 30 is minimized.

[0099] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications or alterations are included in the scope of the present disclosure. For example, the functions included in each component or each step, etc. can be rearranged so as not to be logically contradictory, and a plurality of components or steps, etc. can be combined into one or divided. The embodiments according to the present disclosure can also be realized as a program executed by a processor included in the device or a storage medium recording the program. It should be understood that these are also included in the scope of the present disclosure.

Explanation of Reference Numerals

[0100] 1 Control system 10 Control device (12: Control unit, 14: Storage unit, 16: Interface) 20 Motor 30 Stator (32: Yoke, 34, 34A - C: Poles, 36, 36A - C: Coils) 40 Rotor (42: Yoke, 44: Pole, 46: Permanent magnet)

Claims

1. A method for controlling a motor including a stator and a rotor, a drive current determination step of determining a current waveform of a drive current applied to the iron core of the stator based on an amplitude of a temporal change in a deformation amount of magnetic strain of the iron core of the stator so that vibration due to magnetic strain of the iron core of the stator is reduced; a drive current application step of applying the drive current determined in the drive current determination step to the iron core of the stator and including a method for controlling a motor.

2. The drive current determination step includes: a waveform assumption step of assuming a plurality of current waveforms of the drive current; a magnetic flux density calculation step of calculating a temporal change in magnetic flux density generated in the iron core of the stator for each of the assumed current waveforms when the assumed current waveforms are applied to the iron core of the stator as the drive current; a magnetic strain deformation amount calculation step of calculating a temporal change in a magnetic strain deformation amount, which is a deformation amount of the entire iron core of the stator due to magnetic strain, for each of the current waveforms based on the temporal change in magnetic flux density generated in the iron core of the stator; a waveform determination step of determining, as the drive current to be applied to the iron core of the stator, a current waveform when an amplitude of the temporal change in the magnetic strain deformation amount of the entire iron core of the stator calculated for each of the current waveforms is less than a determination threshold set based on an amplitude of the temporal change in the deformation amount of the entire iron core of the stator calculated for a current waveform determined without relying on magnetic strain and including a method for controlling a motor according to claim 1.

3. The method for controlling a motor according to claim 2, wherein in the waveform assumption step, the current waveform is assumed so that a torque acting on the rotor becomes a predetermined magnitude.

4. In the magnetic flux density calculation step, calculating a temporal change in magnetic flux density at each of a plurality of elements set along a circumferential direction in the iron core of the stator, in the magnetic strain deformation amount calculation step, calculating a temporal change in the magnetic strain deformation amount of each of the plurality of elements based on the temporal change in magnetic flux density at each of the plurality of elements, and calculating a sum of the temporal changes in the magnetic strain deformation amounts of each of the plurality of elements as the temporal change in the magnetic strain deformation amount of the entire iron core of the stator, and including a method for controlling a motor according to claim 2.

5. In the waveform assumption step, assuming two or more phases of current as the drive current, in the magnetic flux density calculation step, calculating a temporal change in magnetic flux density for each phase of the drive current. In the magnetic distortion amount calculation step, the time change of the deformation amount of the entire core of the stator is calculated for the current of each phase of the drive current. The method for controlling a motor according to claim 2.

6. The method for controlling a motor according to claim 5, wherein for a period of at least half of the period during which each of the two or more currents flows, the period overlaps with the period during which the current of another phase flows.

7. The method for controlling a motor according to claim 5 or 6, wherein the shapes of the current waveforms of each phase of the drive current are the same and the phases of the currents of each phase of the drive current are different.

8. The drive current determination step further includes an electromagnetic force deformation amount calculation step of calculating the time change of the electromagnetic force deformation amount, which is the deformation amount of the core of the stator due to the electromagnetic force acting on the stator. In the waveform determination step, the current waveform when the amplitude of the time change of the total deformation amount obtained by combining the magnetic distortion deformation amount of the entire core of the stator and the electromagnetic force deformation amount of the core of the stator is minimized is determined as the drive current to be applied to the core of the stator. The method for controlling a motor according to any one of claims 2 to 6.

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