JP2017034960A - Permanent magnet type rotary electric machine, and control method for permanent magnet type rotary electric machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a permanent magnet capable of predicting a field strength required for obtaining a desired magnetic flux density regardless of a value of a magnetic flux density of the permanent magnet at a time point of magnetization initiation.SOLUTION: A permanent magnet provided in a permanent magnet type rotary electric machine has such magnetization properties that a field strength at a point where a rate of change of magnetization becomes maximum relative to increase of the field strength in a minor loop within a first quadrant in a hysteresis curve of the permanent magnet is smaller than a field strength required for obtaining a magnetic flux density equal to the magnetic flux density at the point where the rate of change of magnetization becomes maximum, in a major loop within the first quadrant in the hysteresis curve and that the minor loop in the case of magnetization without polarity inversion with respect to a permanent magnet having a magnetic flux density smaller than a maximum residual magnetic flux density is settled on the substantially same line in a magnetization region including the point where the rate of change of magnetization becomes maximum, regardless of a magnitude of the magnetic flux density of the permanent magnet at the time point of magnetization initiation.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a permanent magnet type rotating electrical machine and a method for controlling a permanent magnet type rotating electrical machine.

  Conventionally, a permanent magnet type rotating electrical machine that changes the magnetization state of a permanent magnet according to the operating state of the rotating electrical machine is known (see Patent Document 1). This permanent magnet type rotating electrical machine includes a permanent magnet having asymmetric magnetization characteristics, and reduces the magnetizing current required at the time of increasing magnetization to the permanent magnet than at the time of demagnetizing control, thereby saving energy of the rotating electrical machine. ing.

JP 2011-172323 A

  However, the permanent magnet included in the rotating electrical machine disclosed in Patent Document 1 has a magnetizing curve that varies depending on the value of the magnetic flux density (magnetic flux amount) of the permanent magnet at the start of the magnetizing control. It is difficult to predict the magnetic field strength required to obtain a magnetic flux density of. Therefore, in order to obtain the desired magnetic flux density, the magnetic field strength is increased until the magnetization saturation point on the major loop is reached once, so that the magnetic flux density of the permanent magnet is increased to a saturation magnetic flux density that can be known in advance. There is a need to. For this reason, an excessive magnetization current related to the magnetization control is required.

  An object of the present invention is to provide a permanent magnet capable of predicting the magnetic field strength necessary to obtain a desired magnetic flux density regardless of the value of the magnetic flux density of the permanent magnet at the start of the magnetizing control.

  The permanent magnet type rotating electrical machine according to the present invention changes the magnetic flux density of the permanent magnet by magnetizing the permanent magnet by the action of the magnetic field formed by the current applied to the stator winding. This permanent magnet has a magnetic field strength at a point at which the rate of change of magnetization with respect to an increase in magnetic field strength is maximum in the minor loop in the first quadrant in the hysteresis curve of the permanent magnet, in the major loop in the first quadrant in the hysteresis curve. Without reversal of polarity for a permanent magnet having a magnetic flux density smaller than the maximum magnetic flux density required to obtain the same magnetic flux density as the magnetic flux density at the point where the rate of magnetization change is maximum. The minor loop in the case of magnetizing in the direction of magnetism converges on substantially the same line in the magnetized region including the point where the rate of magnetization change is maximum regardless of the magnitude of the magnetic flux density of the permanent magnet at the start of magnetizing. It has such a magnetization characteristic.

  According to the present invention, the permanent magnet minor loop of the permanent magnet type rotating electrical machine exhibits a magnetizing curve that converges on a single line at least at the point where the rate of magnetization change is maximum. This makes it possible to predict the magnetic field strength necessary to obtain a desired magnetic flux density regardless of the value of the magnetic flux density of the permanent magnet at the start of magnetizing, thereby reducing the magnetizing current related to magnetizing control. Can do.

FIG. 1 is a configuration diagram of the permanent magnet type rotating electrical machine according to the first embodiment viewed from a cross section perpendicular to the axial direction. FIG. 2 is a diagram illustrating the magnetization characteristics of the low coercivity magnet provided in the permanent magnet type rotating electrical machine of the first embodiment. FIG. 3 is a diagram for explaining the magnetization characteristics of the permanent magnet according to the first comparative example. FIG. 4 is a diagram illustrating the magnetization characteristics of the low coercivity magnet provided in the permanent magnet type rotating electrical machine of the first embodiment. FIG. 5 illustrates a control method associated with the magnetization increase control of the low coercivity magnet provided in the permanent magnet type rotating electrical machine of the first embodiment and a control method associated with the magnetization increase control of the low coercivity magnet according to Comparative Example 2. It is a figure for doing. FIG. 6 is a diagram for explaining the magnetization characteristics of the permanent magnet according to Comparative Example 3. FIG. 7 is a diagram for explaining a control method when magnetizing the low coercivity magnet in the second embodiment. FIG. 8 is a diagram for explaining a control method when magnetizing the low coercivity magnet in the second embodiment. FIG. 9 is a diagram illustrating the magnetization characteristics of the low coercive force magnet included in the permanent magnet type rotating electric machine according to the first embodiment. FIG. 10 is a diagram for explaining the magnetization characteristics of a conventional low coercivity magnet. FIG. 11 is a diagram for explaining initial magnetization according to the fourth embodiment. FIG. 12 is a diagram showing the magnetic field strength of the initial magnetization performed on the low coercive force magnet. FIG. 13 is a diagram showing measurement results showing the relationship between the magnetic field strength of the initial magnetization performed on the low coercive force magnet and the squareness of the minor loop. FIG. 14 shows measurement results obtained by measuring a minor loop related to increase / decrease after initial magnetization five times when initial magnetization is performed at a magnetic field strength of 13.5 [kOe]. FIG. 15 is a diagram for explaining the magnetic field strength of initial magnetization in the fourth embodiment.

[First embodiment]
FIG. 1 is a configuration diagram of a permanent magnet type rotating electrical machine 1 (hereinafter also simply referred to as a rotating electrical machine 1) according to a first embodiment as viewed from a cross section perpendicular to the axial direction, and shows a part of the entire configuration. It is. The rotating electrical machine 1 of the present embodiment includes an annular stator 2, a rotor 3 that is concentric with the stator 2, and is disposed so as to have an air gap 6 between the stator 2, And a permanent magnet unit 4 fitted in a corresponding portion of the rotor 3 in a state where the permanent magnets 4a and 4b are superposed in series in the magnetization direction to constitute an electric motor or a generator. This permanent magnet type rotating electrical machine 1 is used as a drive source of an electric vehicle, for example.

  The stator 2 includes a ring-shaped stator core 12, a plurality of teeth 9 protruding from the stator core 12 toward the inner peripheral side, and a stator winding 7 wound around the teeth 9. The stator core 12 is formed, for example, by laminating electromagnetic steel plates that are soft magnetic materials.

  The rotor 3 has a rotor core 13. The rotor core 13 is formed in a cylindrical shape by a so-called laminated steel plate structure in which a large number of electromagnetic steel plates formed by punching a metal plate having a high magnetic permeability into an annular shape are laminated in the axial direction. ing. Further, on the outer peripheral portion of the rotor core 13 facing the stator 2, the magnetic poles formed by the permanent magnet unit 4 are equally spaced along the circumferential direction, and the polarities of the adjacent magnetic poles are different from each other. It is provided to be polar. Note that the rotor core 13 according to the rotating electrical machine 1 of the present embodiment has a six-pole structure in which six permanent magnet units 4 are provided along the circumferential direction as inferred from the partial configuration shown in FIG. .

  Moreover, the rotor 3 has a low magnetic permeability layer 5 that is a space portion formed by punching a magnetic steel sheet forming the rotor core 13 between the magnetic poles. The low magnetic permeability layer 5 has a lower magnetic permeability than the electromagnetic steel sheet, that is, has a large magnetic resistance. Therefore, the low magnetic permeability layer 5 acts as a magnetic barrier (flux barrier) through which the magnetic flux (flux) is difficult to pass in the magnetic circuit formed by the permanent magnet unit 4 on the rotor 3. The low magnetic permeability layer 5 is formed for every fixed mechanical angle along the circumferential direction of the rotor 3, and the above-described permanent magnet unit 4 is disposed between these low magnetic permeability layers 5.

  The permanent magnet unit 4 is disposed by superposing permanent magnets 4 a and 4 b perpendicularly to the center direction of the rotor 3. The direction of the magnetic flux produced by the permanent magnet unit 4 is the d axis, and the direction perpendicular to the d axis electrically and magnetically is the q axis. That is, the permanent magnet unit 4 is disposed on the rotor 3 in a range sandwiched between two q axes.

  The permanent magnets 4a and 4b constituting the permanent magnet unit 4 have different coercive forces. The permanent magnet 4b is a permanent magnet having a coercive force that can be increased or demagnetized by a magnetic field formed by passing a d-axis current having a current value allowable by an inverter (not shown) to the stator winding 7. It is. A permanent magnet having such a coercive force is defined as a low coercive force magnet. The coercivity of the permanent magnet 4b (hereinafter referred to as the low coercivity magnet 4b) is desirably less than 8 kOe at room temperature, for example, but is not necessarily limited to this value. On the other hand, the coercive force of the permanent magnet 4a may be a value that is not magnetized by a magnetic field formed by a d-axis current having a current value that an inverter (not shown) can accept, and is, for example, 15.1 kOe or more at room temperature. The permanent magnet 4a having such a coercive force is defined as a high coercive force magnet.

  The rotating electrical machine 1 of the present embodiment is characterized by the magnetization characteristics of the low coercive force magnet 4 b constituting the permanent magnet unit 4. Here, before describing the details of the magnetization characteristics of the low coercivity magnet 4b according to the present embodiment, the magnetization characteristics of the conventional low coercivity magnet will be described with reference to FIG.

  2. Description of the Related Art Conventionally, a permanent magnet type rotating electrical machine that changes the magnetization state of a low coercive force magnet according to the operating state of the rotating electrical machine is known (see Patent Document 1). In order to change the magnetization state of the permanent magnet, that is, the magnetic flux density (magnetic flux amount) of the permanent magnet, it is necessary to apply an external magnetic field having a strength corresponding to the desired magnetic flux density to the permanent magnet. The greater the desired magnetic flux density, the greater the required magnetic field strength. And as the intensity of the magnetic field at the time of magnetization increases, the necessary magnetization current also increases and the energy consumption increases. Therefore, in Patent Document 1, in order to reduce the energy consumption during the magnetization increasing control, a low coercivity magnet having an asymmetric magnetization characteristic with respect to the intersection of the vertical axis and the horizontal axis in FIG. The magnetizing current required for the magnetic control is reduced more than the magnetizing current required for the demagnetizing operation to save energy.

  FIG. 10 is a diagram showing a hysteresis curve related to the magnetization characteristics of a low coercive force magnet in a conventional permanent magnet type rotating electrical machine. The horizontal axis represents the magnetic field strength [kOe] of the external magnetic field applied to the low coercivity magnet, and the vertical axis represents the magnetic flux density [kG] inside the low coercivity magnet. The curve represented by the solid line drawn asymmetrically around the intersection of the horizontal axis and the vertical axis is the relationship between the magnetic flux intensity [kG] and the magnetic field strength [kOe] when the magnetization of the low coercivity magnet is partially magnetized. This is a so-called minor loop, which is a magnetization curve representing (magnetization characteristics). A curve including a dotted line drawn approximately symmetrically about the intersection of the horizontal axis and the vertical axis shows a state in which the magnetization of the permanent magnet, for example, starting from A, is saturated in magnetic flux density in the opposite polarity (B in the figure). It is a so-called major loop (also referred to as a full loop) that represents the magnetization characteristics when changing over time.

  As can be seen from FIG. 10, in the conventional low coercivity magnet, the magnetization curve (magnetization curve) relating to the minor loop in the portion represented in the first quadrant is smaller than the magnetization curve represented by the full loop. It varies according to the magnetic field strength [kOe]. For this reason, the conventional low coercive force magnet reduces the magnetizing current required for the magnetizing control more than the magnetizing current required for the demagnetizing operation following the magnetization curve (demagnetization curve) shown in the second quadrant of FIG. can do.

  However, in the conventional low coercive force magnet, the magnetizing curve associated with the magnetizing control differs depending on the magnitude of the magnetic flux density [kG] at the start of magnetizing control (see the first quadrant in FIG. 10). For this reason, it is difficult to accurately predict the required magnetic field strength when it is desired to magnetize a magnetized state having a desired magnetic flux density, and the accuracy when changing the amount of magnetic flux of the low coercive force magnet is reduced. Therefore, when it is desired to change the magnetic flux density from the partial magnetization state Br1 to the partial magnetization state Br2 having larger magnetization, it is necessary to pass through the following magnetization path in order to ensure accuracy. That is, (a) the magnetic field strength of the external magnetic field is increased until the magnetic flux density of the low coercivity magnet in the magnetization state Br1 reaches the magnetization saturation point A on the full loop. (B) A magnetic field in the opposite direction is applied to the low coercive force magnet to cause transition from the magnetized state A to the magnetized state Br21. (C) A low coercivity magnet having a partial magnetization state Br2 is obtained by removing the external magnetic field.

  In this way, in the low coercivity magnet of the conventional permanent magnet type rotating electrical machine, when it is desired to increase the magnetization state to have a desired magnetic flux density, the magnetic field strength must be increased until reaching the major loop in order to ensure accuracy. Need to increase. For this reason, a larger amount of magnetizing current related to the magnetization control is required.

  The present invention has been made to solve such a problem, and does not require an excessive magnetizing current for ensuring accuracy as in the prior art in the magnetizing control. Hereinafter, details of the low coercive force magnet 4b according to the first embodiment of the present invention will be described with reference to the drawings.

  FIG. 2 is a diagram illustrating a hysteresis curve related to the magnetization characteristics of the low coercive force magnet 4b included in the permanent magnet type rotating electrical machine 1 according to the first embodiment. The horizontal axis represents the magnetic field strength [kOe] of the external magnetic field applied to the low coercivity magnet, and the vertical axis represents the magnetic flux density [kG] inside the low coercivity magnet. A curve represented by a solid line indicates that the low coercive force magnet 4b is magnetized in a negative direction after being magnetized from a partial magnetization state in which the magnetization is not saturated to a magnetization saturation state indicated by A in the figure. This is a minor loop representing the relationship between the magnetic field strength and the magnetic flux density when a magnetic flux density of 0 kG or more is obtained. The curve represented by the dotted line represents the relationship between the magnetic field strength and the magnetic flux density when the low coercive force magnet 4b is magnetized through a state (not shown) where the magnetic flux density is saturated on the opposite polarity side. It is a major loop.

  The alternate long and short dash line in FIG. 2 is obtained by differentiating one minor loop in the first quadrant and represents the magnitude of the inclination, that is, the magnetization change rate in the minor loop related to the low coercivity magnet 4b. It represents dB / dH. The magnetization change rate dB / dH at an arbitrary point on the minor loop is expressed by the following formula (1).

  However, B represents magnetic flux density [kG], and H represents external magnetic field strength [kOe]. (N) represents an arbitrary point on the minor loop. Note that 1 in (n-1) is a number used for convenience to express a point serving as a reference when calculating the magnetization change rate at an arbitrary point on the minor loop, and is not limited to an integer. Absent.

  As can be seen from FIG. 2, the low coercivity magnet 4b according to the present embodiment has a magnetic field strength on the minor loop that can obtain the magnetic flux density [kG] at the point where the magnetization change rate dB / dH is maximum in the first quadrant. However, it is comprised so that it may become a value smaller than the magnetic field intensity [kOe] on the major loop which can obtain the same magnetic flux density.

  That is, according to the low coercive force magnet 4b having such a magnetization characteristic, when the magnetization is increased from a partial magnetization state in which the magnetization is not saturated to a partial magnetization state having a higher magnetic flux density, Magnetization can be performed with a smaller magnetization current than in the major loop, so that the magnetization current related to the magnetization control can be reduced.

  Moreover, as the low coercive force magnet 4b having such magnetization characteristics, it is desirable to use an NdFeB-based magnet having a reduced coercive force that satisfies, for example, the following general formula (2).

  In order to reduce the coercive force, it is desirable to replace a part of Nd using REE (Rare Earth Elements) such as Y, La, and Ce. Further, from the viewpoint of improving magnetic properties and corrosion resistance, additional elements other than those described above may be included.

  The manufacturing method of the low coercive force magnet 4b is not particularly limited, but it is desirable that the magnetization curve has a flat minor loop shape that is closer to a quadrangle shape, so that fine crystal grains are obtained in the manufacturing process of the low coercive force magnet 4b. It is desirable to select a manufacturing method that can be used. For example, a low coercive force magnet having desired magnetization characteristics is manufactured using anisotropic magnetic powder having fine crystal grains obtained by the HDDR method. Alternatively, the isotropic magnetic powder having fine crystal grains obtained by the ultra-quenching method is densified by hot working molding at a temperature of 1000 ° C. or less, and at the same time imparting anisotropy to obtain desired magnetization characteristics. You may produce the low coercivity magnet which has.

  In addition, the coercive force may be adjusted by forming a low coercivity magnet created by the above method and then performing heat treatment. The low coercive force magnet 4b according to the present embodiment is an average obtained by forming a mother alloy using La as an REE for a NdFeB-based magnet into a powder having fine crystals by a super-quenching method, and forming and orienting it by a hot working method. A fine crystal magnet having a grain size of 0.1 to 1 μm is used. The permanent magnet 4a having a high coercive force is desirably an NdFeB-based permanent magnet.

[Comparative Example 1]
A comparative example for the low coercive force magnet 4b having the above-described magnetization characteristics is shown in FIG. The permanent magnet used as a comparative example is an SmCo magnet having a coercive force adjusted to less than 8 kOe by heat treatment. In FIG. 3, as in FIG. 2, the horizontal axis represents the magnetic field strength [kOe] of the external magnetic field, and the vertical axis represents the magnetic flux density [kG]. The curve in the figure represents a magnetization curve based on the magnetization characteristics of the permanent magnet according to the comparative example. The alternate long and short dash line in the figure represents the magnetization change rate dB / dH calculated based on the above formula (1).

  As can be seen from the figure, the magnetization curve of the permanent magnet according to the comparative example is such that there is no difference in the magnetized region between the major loop indicated by the dotted line and the minor loop indicated by the solid line, and the magnetization change rate dB / dH is maximum. The magnetic field strength is almost the same between the minor loop and the major loop. Therefore, there is little effect of reducing the magnetization current when the magnetization is increased from a partial magnetization state that is less than the saturation state to a partial magnetization state having a higher magnetic flux density.

  Next, the magnetization characteristic characteristic of the low coercive force magnet 4b of the first embodiment will be described with reference to FIG. In FIG. 4, as in FIG. 2, the horizontal axis represents the magnetic field strength [kOe] of the external magnetic field, and the vertical axis represents the magnetic flux density [kG]. A curve indicated by a solid line in the figure represents a minor loop based on the magnetization characteristics of the low coercive force magnet 4b, and a curve indicated by a dotted line represents a major loop. Then, the alternate long and short dash line in the figure represents the magnetization change rate dB / dH calculated by using the above formula (1) based on the magnetizing curve related to a certain minor loop of the low coercive force magnet 4b.

  The low coercive force magnet 4b of the present embodiment has the point that the inclination becomes maximum in the minor loop in the first quadrant representing the magnetization characteristic, that is, the point where the magnetization change rate dB / dH becomes maximum. It has a magnetization characteristic such that it is located on the same line (on the line segment EF in the figure) regardless of the magnitude of the magnetic flux density at the start of. In addition, in the magnetization curve in the first quadrant, a region drawn at approximately the vertical axis and including at least a point where the magnetization change rate dB / dH is maximum is defined as a magnetized region.

  More specifically, when an infinite number of minor loops having a magnetic flux density of 0 kG or more and less than the maximum residual magnetic flux density as the magnetic flux density at the start of the magnetizing control are drawn, The loops converge on the same line (on the line segment EF in the figure). In other words, when each of the points at which the magnetization change rate dB / dH in the magnetizing curve of each minor loop drawn innumerably is plotted, the curve drawn by the set of points is one on the magnetizing curve in the minor loop. (Line segment EF).

  Further, the strength of the magnetic field at the point where the magnetization change rate dB / dH is maximum falls within a predetermined magnetic field strength range of about 20% with respect to the coercive force of the low coercive force magnet 4b. For example, in the low coercive force magnet 4b of the present embodiment, the point at which the magnetization change rate dB / dH is maximum for a coercive force of about 2.1 kOe is about 0.4 [kOe] (about 1.8 kOe). [kOe] to 2.2 [kOe]).

  It should be noted that the magnetic field strength at the same magnetic flux density is related to the magnitude of the starting magnetization (for example, Br1 to Br4) in the magnetizing curve of the low coercive force magnet 4b according to the present embodiment, particularly in the line segment EF. It has a magnetization characteristic that falls within a range of ± 5%.

  As described above, the low coercivity magnet 4b has a magnetization characteristic that converges on substantially the same line in the minor loop magnetizing region, so that the magnetic flux density of the low coercivity magnet 4b at the start of the magnetizing control is increased. Whatever the value, the magnetic field strength necessary to obtain a desired magnetic flux density can be obtained on the basis of the magnetizing curve relating to the line segment EF that can be detected in advance. Therefore, it is possible to accurately predict the magnetic field strength required to magnetize to a desired magnetic flux density, regardless of the value of the magnetic flux density at the start of the magnetization increasing control.

  As described above, the permanent magnet type rotating electrical machine according to the first embodiment magnetizes the low coercive force magnet 4b by the action of the magnetic field formed by the current applied to the stator winding 7, thereby magnetic flux density of the low coercive force magnet 4b. To change. The low coercivity magnet 4b has a maximum magnetization change rate dB / dH with respect to an increase in magnetic field strength [kOe] in a minor loop in the first quadrant of the hysteresis curve (magnetization curve) of the low coercivity magnet 4b. The magnetic field strength is smaller than the magnetic field strength required to obtain the same magnetic flux density as the magnetic flux density at the point where the magnetization change rate dB / dH becomes maximum in the major loop in the first quadrant in the hysteresis curve. In addition, a minor loop in the case of magnetizing a permanent magnet having a magnetic flux density [kG] smaller than the maximum residual magnetic flux density without reversing the polarity of the low coercive force magnet 4b at the start of magnetizing control. Regardless of the magnitude of the magnetic flux density, they converge on substantially the same line in the magnetized region.

  As a result, when magnetizing from a partially magnetized state in which the magnetization is less than a saturated state to a partially magnetized state having a higher magnetic flux density, it is possible to increase the magnetization with a smaller magnetizing current than in the major loop. Therefore, it is possible to reduce the magnetization current related to the magnetization increase control.

  In addition, it is possible to accurately predict the magnetic field intensity required to magnetize to a desired magnetic flux density regardless of the value of the magnetic flux density at the start of the magnetizing control, and until the magnetization is saturated every time the magnetizing control is performed. Since it is not necessary to increase the magnetization, the magnetization current related to the magnetization control can be greatly reduced.

[Control Method for Permanent Magnet Type Rotating Electric Machine According to First Embodiment]
[Example 1]
Next, in the permanent magnet type rotating electrical machine 1 including the low coercive force magnet 4b having the magnetic characteristics described so far, a control method associated with the magnetization increase control of the low coercive force magnet 4b will be described.

  FIG. 5 is a diagram for specifically explaining a control method associated with the magnetization increase control of the low coercive force magnet 4b. This control method is characterized in that the magnetization is increased without passing through the state where the magnetization of the low coercive force magnet 4b is saturated. However, the “state in which the magnetization is saturated” in the present embodiment is not limited to the 100% magnetization state, that is, the point A in the figure in which the magnetic flux density of the low coercive force magnet 4b is the saturation magnetic flux density. It shall include a magnetization state equal to or greater than 90% of the magnetization state indicated by point D.

  Therefore, in this control method, the operation history of the magnetization control when the magnetization is increased from the partial magnetization state Br1 that is less than the saturation state to the partial magnetization state Br2 having a higher magnetic flux density is as follows. Control is performed so as to follow an arrow indicated by a one-dot chain line in FIG.

  First, by applying a positive magnetic field to the low coercive force magnet 4b in the magnetization state Br1 (magnetic flux density: 4.9 [kG]), the magnetization state is shifted to the point b in the figure. More specifically, the operating point in the magnetizing control in Br1 at the start of magnetizing control is that a positive magnetic field is applied to the low coercive force magnet 4b so that the magnetization is flat toward the point a. It changes while following the curve. The operating point at point a rises steeply toward point b. The locus of the operating point from the point a to the point b is a line that overlaps the line segment EF in FIG. 4 described above, that is, a magnetized region including a point where the magnetization change rate dB / dH is maximum.

  The point b has a magnetic flux density of 11.1 [kG], which is substantially the same as the magnetic flux density in the magnetized state Br2, and the magnetic field strength is 2.2 [kOe]. Accordingly, by applying a magnetic field of 2.2 [kOe] to the low coercive force magnet 4b, the magnetization state can be shifted from Br1 to point b in the figure. Then, by removing the external magnetic field that acts on the low coercive force magnet 4b (by setting the magnetic field strength to 0 [kOe]), the operating point moves toward the magnetization state Br2 while following the flat magnetization curve again. Thereby, the low coercive force magnet 4b having a desired magnetic flux density (11.1 [kG]) can be obtained. When the magnetic field strength [kOe] of the magnetic field required for the magnetization is converted into a magnetomotive force [kA / m], the magnetomotive force required for the magnetization control from the magnetization state Br1 to the magnetization state Br2 is 2.2 kOe≈175. 0 kA / m.

[Comparative Example 2]
On the other hand, even in the permanent magnet type rotating electrical machine 1 having the same low coercive force magnet 4b, the magnetization state is increased from the magnetization state Br1 to the magnetization state Br2 via the point D where the magnetization is 90%. When the control is performed, the following magnetization control is required. First, a positive magnetic field of 4.178 [kOe] is applied to the low coercive force magnet 4b in the magnetization state Br1, and the magnetization state is shifted to point D in the figure. Next, by applying a negative magnetic field of −1.43 [kOe], the magnetization state of the low coercive force magnet 4b is shifted to a point c at which the magnetic flux density is substantially the same as the magnetization state Br2. And the low coercive force magnet 4b which has magnetization state Br2 is obtained by removing the external magnetic field which acts on the low coercive force magnet 4b.

  The total magnetomotive force associated with such a magnetizing method is 4.178 [kOe] (≈332.5 kA / m; positive direction) + | −1.43 [kOe] | (≈113.8 kA / m; negative) Direction) = 446.3 kA / m. Therefore, in the control method according to Comparative Example 2, the magnetomotive force of 175.0 kA / m required for the control method according to Example 1 in which the magnetization is increased without going through the state where the magnetization is saturated is twice as large as that of the control method. It can be seen that magnetomotive force is required.

[Comparative Example 3]
Referring to FIG. 6, even when a control similar to the above control method of increasing the magnetism without going through a saturation state is performed, a permanent magnet having a different magnetization characteristic from that of the low coercive force magnet 4 b is used. Comparative Example 3 will be described. The permanent magnet used in this comparative example is the same SmCo-based magnet as used in comparative example 1, with the coercive force adjusted to less than 8 kOe by heat treatment.

  FIG. 6 is a diagram illustrating a method for controlling the permanent magnet in the third comparative example. As described in Comparative Example 1, the magnetization curve of the permanent magnet used in this comparative example has no difference between the major loop and the minor loop, and the magnetic field strength [kOe] at the point where the magnetization change rate is maximum is the minor loop. Almost matches with major loop.

  Therefore, when the magnetization state Br1 (magnetic flux density: 2.4 [kG]) shown in FIG. 6 is increased to the magnetization state Br2 (magnetic flux density: 6.36 [kG]), the magnetic field strength is 2.2 [kOe. It is necessary to apply a positive magnetic field. In the control method according to Example 1, considering that the magnetic flux density obtained by the magnetic field strength of 2.2 [kOe] is 11.1 [kG], the magnetization efficiency per unit magnetomotive force according to Comparative Example 3 is This is about 2/3 of the magnetization efficiency per unit magnetomotive force according to the control method of the first embodiment. Here, the magnetization efficiency is a value obtained by dividing the change in magnetization by the magnetomotive force required to form the applied magnetic field. Each magnetization efficiency is shown in Table 1 below.

  That is, in Example 1, the magnetization is saturated without a decrease in coercive force from a partial magnetization state in which the magnetization is not saturated to a partial magnetization state having a higher magnetic flux density. By using the low coercive force magnet 4b having a magnetization characteristic that can change the magnetization without going through the above state, the rotating electrical machine 1 is operated while repeating the magnetization from the partial magnetization state to the partial magnetization state. Thereby, compared with the comparative example 2 which passes through the state where magnetization was saturated, the magnetomotive force reduction of about 60% can be realized per one magnetizing control.

[Example 2]
Next, Example 2 relating to the magnetizing control of the low coercive force magnet 4b in the control method for the permanent magnet type rotating electrical machine according to the first embodiment will be described.

  In Example 2, from any partial magnetization state, the magnetization is increased to the partial magnetization state having a higher magnetic flux density via the same magnetization curve without passing through the saturation state. It is characterized in that magnetic control is performed. Hereinafter, a specific description will be given with reference to FIG.

  FIG. 7 is a diagram for specifically explaining a control method when magnetizing the low coercive force magnet 4b in the second embodiment. In the control method according to the second embodiment, in the minor loop related to the magnetization curve of the low coercive force magnet 4b shown by the solid line in the figure, when the magnetization state Br1 is magnetized to the magnetization state Br2, the magnetization state Br3 is magnetized to the magnetization state Br2. In both cases, and in the case of magnetizing from the magnetized state Br3 to the magnetized state Br1, control is performed so as to increase the magnetization via the same magnetizing curve (on the line segment EF). By controlling in this way, it is possible to know the magnetic field strength necessary to obtain a desired magnetic flux density with reference to the magnetizing curve related to the line segment EF. Therefore, it is possible to accurately predict the magnetic field strength necessary to obtain the magnetic flux density of the first magnetic field.

  That is, according to the control method according to the second embodiment, it is possible to predict the magnetization current associated with the magnetization increasing control regardless of the magnitude of the magnetic flux density of the low coercivity magnet at the start of the magnetization increasing control. For this reason, even when the magnetic flux density of the low coercive force magnet 4b at the start of the magnetizing control cannot be obtained, it is possible to accurately supply the magnetizing current necessary for magnetizing to the desired magnetization state. And the accuracy at the time of changing the magnetic flux density of the low coercive force magnet 4b can be ensured, and the reliability of the rotary electric machine 1 can be improved.

  The reason why such control is possible is that the low coercive force magnet 4b to be controlled has a magnetic flux at the point where the magnetization change rate dB / dH represented by the above formula (1) is maximum on the minor loop. The magnetic field strength of the external magnetic field that can obtain the density is smaller than the magnetic field strength of the external magnetic field that can obtain the same magnetic flux density in the major loop in the first quadrant, and the magnetization change rate dB / dH is the maximum in the minor loop. There is a magnetization characteristic in which the magnetized region including the point is converged on substantially the same single line. As a factor for obtaining such magnetic characteristics, as described in the description of the permanent magnet type rotating electric machine according to the first embodiment, the low coercive force magnet 4b is composed of a fine and uniform crystal structure. Can be mentioned.

  In addition, it is known that a permanent magnet composed of fine crystal particles of submicron order exhibits pinning-type magnetization fluctuations that require a magnetic field (magnetic field) having a magnetic field strength of a certain value or more for magnetization caused by domain wall movement. (For example, SmCo magnet). The minor loop indicated by such a permanent magnet has a flat shape with a small inclination. However, when the magnetization change rate dB / dH of the magnetic flux density with respect to the application of the external magnetic field becomes maximum, it is considered that the domain wall pinning is removed and a sudden domain wall movement occurs. When such a sudden domain wall movement occurs, the magnetization changes rapidly and the inclination of the minor loop also increases.

  As described above, the pinning by the crystal grain boundary (domain wall) is dominant in the magnetization mechanism of the low coercive force magnet 4b used in the present embodiment. In particular, the magnetic field strength at which domain wall movement suddenly occurs after pinning is removed is smaller than the magnetic field strength at which the same magnetic flux density is obtained in the major loop in the first quadrant. When the crystal grain size is small and the pinning force is strong, the inclination of the minor loop becomes small and the shape becomes linear regardless of the magnetization history (magnetization state at the start of magnetization increasing control). Furthermore, since the crystal is highly uniform, the locus of the maximum value of the magnetization change rate dB / dH can be predicted to increase or decrease in proportion to the magnetization even if the magnetization histories are different, and it converges on a single line on the magnetizing curve. It is thought that it is done.

  By using a permanent magnet having such a crystal structure, it is possible to control the magnetizing by predicting the magnetic field strength necessary to magnetize to a desired magnetic flux density even if the permanent magnet has a different magnetization history. Therefore, the reliability of the rotating electrical machine can be improved. In addition, since control is possible regardless of the magnetization history, it is not necessary to increase the magnetization until the magnetization is saturated every time the magnetization control is performed, so that the magnetization current can be greatly reduced.

  On the other hand, in the case of general NdFeB (crystal grain size of 5 to 10 μm) manufactured by the sintering method, the pinning force is weak and the domain wall movement continuously occurs, so the maximum value of the magnetization change rate dB / dH is It is difficult to approximate the locus on a single line on the magnetizing curve.

  As described above, in the control method of the permanent magnet type rotating electrical machine according to the first embodiment, the magnetization of the low coercive force magnet 4b is saturated in the magnetization increasing control for the low coercive force magnet 4b having a magnetic flux density smaller than the maximum residual magnetic flux density. Magnetize without going through the state. Thereby, when it is desired to change the magnetization of the low coercive force magnet 4b, the magnetization from the partial magnetization state to the partial magnetization state can be shifted without passing through the saturation state. The magnetomotive force per magnetizing control can be greatly reduced.

[Example 3]
In the control method of the permanent magnet type rotating electrical machine according to the first embodiment, Example 3 relating to the magnetization increase control of the low coercive force magnet 4b will be described.

  The third embodiment specifically shows a control method related to the magnetization increase control of the low coercive force magnet 4b. As shown in FIG. 9, the third embodiment is characterized in that the magnetization increase control of the low coercive force magnet 4b is performed only in a region not accompanied by polarity reversal. The reason will be described with reference to FIG.

  FIG. 8 is a diagram for explaining a method of controlling the low coercivity magnet 4b in the third embodiment. The one-dot chain line shown in FIG. 8 changes the magnetization from the partial magnetization state Br2 to the partial magnetization state Br4 having the opposite polarity, and then reverses the polarity again to cause the magnetization to the partial magnetization state Br1. The magnetization history in the case of changing is shown.

  The magnetization state of the low coercive force magnet 4b when following such a magnetization history is as follows. That is, (a) a magnetic field in a negative direction is applied to magnetize from the partial magnetization state Br2 to the partial magnetization state Br4, and the magnetic field strength is a strength (magnetic field) required to obtain a magnetic flux density in the magnetization state Br4. After reaching the intensity: about −3.5 [kOe]), the magnetic field is removed. (B) In order to magnetize from the partial magnetization state Br4 to the partial magnetization state Br1, a magnetic field in the positive direction is applied, and the magnetic field strength is the strength necessary to obtain the magnetic flux density in the magnetization state Br1 (magnetic field strength: After reaching 2.15 [kOe]), the magnetic field is removed.

  As can be seen from the figure, when the magnetization of the low coercive force magnet 4b is performed using a region with polarity reversal, the magnetizing curve in the magnetizing control of (b) above is a magnetizing curve when there is no polarity reversal. (The line segment EF indicated by a broken line) passes between the major loop. For this reason, as in the first and second embodiments described above, although the characteristic that the magnetization can be increased from the partially magnetized state to the larger magnetized state without going through the saturation state (A, B) is not changed, Since the magnetizing curve accompanying the control is shifted to the major loop side, the effect of reducing the magnetizing current is reduced as compared with the control according to the first and second embodiments.

  In addition, the magnetizing curve when the region with polarity reversal is used is the magnetizing curve that passes between the magnetizing curve without the polarity reversal (segment EF indicated by a dotted line) and the major loop. Varies with history. For this reason, it is difficult to predict a magnetizing curve when performing magnetizing control on a permanent magnet having a different magnetization history, that is, accurately predicting the intensity of an external magnetic field required to obtain a desired magnetic flux density. Therefore, the accuracy when changing the amount of magnetic flux is impaired, and the reliability of the rotating electrical machine 1 is lowered.

  Therefore, when controlling the magnetization of the low coercive force magnet 4b, it is desirable to control so that only the region without polarity reversal is used in the magnetization curve of the low coercive force magnet 4b.

  Therefore, in the control method of the permanent magnet type rotating electrical machine according to the first embodiment, the magnetization curve when magnetizing the low coercive force magnet 4b is as shown in the minor loop shown by the solid line in FIG. The magnetizing curve without the polarity reversal is characterized by passing on the line segment EF of the minor loop, regardless of the origin of any magnetization history less than the maximum residual magnetic flux density.

  As described above, according to the control method of the permanent magnet type rotating electric machine according to the first embodiment of Example 3, the magnetization of the low coercive force magnet 4b is performed only in the region where the polarity code of the low coercive force magnet 4b is the same. Thus, regardless of the magnitude of the magnetic flux density [kG] of the low coercive force magnet 4b at the start of the magnetizing control, it always converges on substantially the same line in the magnetizing region, so that a desired magnetic flux density can be obtained. The required strength of the external magnetic field can be accurately predicted, and accuracy when changing the amount of magnetic flux is ensured.

[Example 4]
Next, in the permanent magnet type rotating electrical machine 1 including the low coercive force magnet 4b having the magnetic characteristics described so far, in particular, at the first time when the low coercivity magnet 4b in a non-magnetized state is first magnetized. Magnetization control of magnetization (hereinafter referred to as initial magnetization) will be described.

  As described above, the permanent magnet type rotating electrical machine 1 according to the present invention constitutes an electric motor or a generator, and is used, for example, as a drive source for an electric vehicle. When the permanent magnet type rotating electrical machine 1 is used as a drive source for an electric vehicle, the permanent magnet type rotating electrical machine 1 is called a so-called variable magnetic force motor or the like. The variable magnetic force motor is reduced in accordance with the traveling state of the electric vehicle while the electric vehicle is traveling by increasing or decreasing the magnetism of the low coercive force magnet 4b by the control method described in the first to third embodiments. The magnetic force of the coercive force magnet 4b can be suitably changed.

  However, in the low coercivity magnet 4b according to the present invention, when the magnetization is performed with a small magnetic field that does not saturate the magnetic flux of the low coercivity magnet 4b during the initial magnetization from the non-magnetized state, There is a problem that the squareness of the minor loop is deteriorated. The problem will be described with reference to FIGS.

  Note that the squareness is a word representing the degree to which the demagnetization curve becomes a square, and in the magnetization curve (demagnetization curve) represented in the second quadrant, a residual ratio of a predetermined ratio or more (for example, 90% or more). This is a characteristic of the permanent magnet represented by the ratio of the magnetic field and the coercive force corresponding to the magnetic flux density (the value of the magnetic flux density [kG] when the magnetic field strength is 0 [kOe]).

  FIG. 11 is a diagram for explaining the initial magnetization. A curve indicated by a solid line in the figure represents a minor loop similar to that described in the first to third embodiments. In principle, the initial magnetization is performed for the first time on the non-magnetized low coercive force magnet 4b, and therefore G in the figure is the starting point of the magnetization. The magnetizing curve of the initial magnetization is represented by a curve (GA) that follows the full loop of the low coercive force magnet 4b from G in the figure to the set magnetic field. After the initial magnetization, the second and subsequent magnetizing curves are performed with a magnetic field smaller than the magnetic field strength related to the full loop, as described in the first to third embodiments, and follow the minor loop FE. The initial magnetization may be performed either after the motor 4 is assembled or before the motor 4 is assembled (rotor assembly state).

  12 and 13 are diagrams for explaining the measurement results showing the relationship between the magnetic field intensity of the initial magnetization performed on the low coercive force magnet 4b and the squareness of the minor loop. The measurement result was measured by using a low coercivity magnet 4b of φ2.5 × 4 mm and applying a demagnetizing field correction based on a permeance coefficient of 7.91.

  FIG. 12 is a diagram showing the magnetic field strength of the initial magnetization. The measurement was performed with four patterns of magnetic field strength. In other words, the magnetic field strength (3.7 [kOe], 5.6 [kOe], 8.5 [kOe]) for generating a magnetic flux below the saturation magnetic flux density in the low coercive force magnet 4b is shown in the figure. Although there is no magnetic field strength (13.5 [kOe]), the low coercive force magnet 4b generates a magnetic flux density equal to or higher than the saturation magnetic flux density.

  The saturation magnetic flux density referred to here is 90% or more, preferably 95% of the magnetic flux density based on the magnetic flux density when the magnetic flux density of the low coercivity magnet 4b reaches saturation when the magnetic field is increased. It is defined as showing the above magnetic flux density.

  FIG. 13 is a diagram for comparing the squareness of the minor loops when the initial magnetization is performed with the magnetic field strength shown in FIG. 12, and showing the second quadrant of each minor loop. is there. From the measurement result of FIG. 13, the squareness of the low coercive force magnet 4b indicates that the low coercive force magnet 4b is initially magnetized with a magnetic field strength (13.5 [kOe]) that generates a magnetic flux density higher than the saturation magnetic flux density. It is clear that the lower the magnetic field strength applied to the initial magnetization, the worse the case. For example, after the initial magnetization is performed with a magnetic field strength of 3.7 [kOe] and a reverse magnetic field of −1 [kOe] is applied to the low coercive force magnet 4b while the vehicle is traveling, the low coercive force magnet 4b. The magnetic flux density is lower by about 1 [kG] than when the initial magnetization is performed at 13.5 [kOe]. This means that when demagnetization is performed while the electric vehicle is running, the demagnetization may cause excessive demagnetization beyond the desired magnetic flux density, resulting in a decrease in torque. To do. According to the measured data, during the maximum torque operation when the magnetizing magnetic field strength during vehicle running is 2 [kOe], initial magnetization is performed with a magnetic field strength larger than the magnetizing magnetic field strength during vehicle running. The low coercive force magnet 4b is demagnetized by 30% or more compared to the low coercive force magnet 4b that has been initially magnetized with a magnetic field strength (10 [kOe]) that generates a magnetic flux that is equal to or higher than the saturation magnetic flux density.

  On the other hand, when the initial magnetization is performed at a magnetic field strength of 13.5 [kOe], the squareness of the minor loop does not deteriorate as shown in FIG.

  FIG. 14 shows measurement results obtained by measuring a minor loop related to increase / decrease after initial magnetization five times when initial magnetization is performed at a magnetic field strength of 13.5 [kOe]. As shown in the figure, the minor loops related to the five measurement results overlap, and no deterioration in squareness is observed. That is, from the viewpoint of the squareness of the minor loop, the initial magnetization of the low coercive force magnet 4b is preferably performed by applying a magnetic field strength that generates a magnetic flux density higher than the saturation magnetic flux density to the low coercive force magnet 4b. I understand.

  Therefore, in Example 4, as shown in FIG. 15, the initial magnetization magnetic field strength is set to be equal to or higher than the magnetic field strength that causes the low coercive force magnet 4 b to generate a magnetic flux density higher than the saturation magnetic flux density.

  As described above, according to the control method of the permanent magnet type rotating electrical machine according to the first embodiment of Example 4, in the magnetizing control for the low coercive force magnet 4b, in the magnetizing control (initial magnetization) at the first time, A magnetic field that generates a magnetic flux density exceeding the saturation magnetic flux density of the low coercive force magnet 4b is applied to the low coercive force magnet 4b. Even a small magnetic field acts. Thereby, for example, it is possible to prevent the low coercive force magnet 4b from being demagnetized excessively during traveling of the vehicle, and thus the torque can be improved.

  The present invention is not limited to the embodiment described above. For example, the permanent magnet type rotating electrical machine 1 is configured with one magnetic pole by the permanent magnet unit 4 including the low coercive force magnets 4b and 4a, but is not necessarily configured by the permanent magnet unit including two types of permanent magnets. The low coercive force magnet 4b may be composed of a single permanent magnet having the same magnetization characteristics as those described above. The low coercive force magnet 4b is not limited to application to a rotating electrical machine for an electric vehicle, and is a device including a permanent magnet, such as a washing machine, and can change the magnetization of the permanent magnet during use or manufacture. It can be applied to various devices.

DESCRIPTION OF SYMBOLS 1 ... Permanent magnet type rotary electric machine 2 ... Stator 3 ... Rotor 4 ... Permanent magnet unit 4b ... Low coercive force magnet 7 ... Stator winding

Claims (4)

A stator having a stator winding;
A rotor having a plurality of permanent magnets,
In the permanent magnet type rotating electrical machine that changes the magnetic flux density of the permanent magnet by magnetizing the permanent magnet by the action of the magnetic field formed by the current applied to the stator winding,
The magnetization characteristics of the permanent magnet are:
In the minor loop in the first quadrant in the hysteresis curve of the permanent magnet, the magnetic field strength at the point where the rate of change of magnetization with respect to the increase in the magnetic field strength of the magnetic field is the maximum in the major loop in the first quadrant in the hysteresis curve, Smaller than the magnetic field strength required to obtain the same magnetic flux density as the magnetic flux density at the point where the rate of change of magnetization is maximum, and
The minor loop in the case where the permanent magnet having a magnetic flux density smaller than the maximum residual magnetic flux density is magnetized without reversing the polarity is the magnitude of the magnetic flux density of the permanent magnet at the start of the magnetizing. Regardless, converge on substantially the same line in the magnetized region including the point where the rate of magnetization change is maximum,
A permanent magnet type rotating electrical machine. A control method for a permanent magnet type rotating electrical machine for controlling the magnetic flux density of a permanent magnet provided in the permanent magnet type rotating electrical machine according to claim 1,
In the magnetization control for the permanent magnet having a magnetic flux density smaller than the maximum residual magnetic flux density,
The magnetization control is performed without increasing the magnetization of the permanent magnet without saturation.
A control method for a permanent magnet type rotating electrical machine. A control method for a permanent magnet type rotating electrical machine for controlling the magnetic flux density of a permanent magnet provided in the permanent magnet type rotating electrical machine according to claim 1,
Magnetization of the permanent magnet is performed only in a region where the polarity code of the permanent magnet is the same.
A control method for a permanent magnet type rotating electrical machine. A control method for a permanent magnet type rotating electrical machine for controlling the magnetic flux density of a permanent magnet provided in the permanent magnet type rotating electrical machine according to claim 2,
In the magnetization control for the permanent magnet,
In the magnetizing control at the first time, a magnetic field that causes the permanent magnet to generate a magnetic flux density exceeding the saturation magnetic flux density of the permanent magnet is applied to the permanent magnet,
In the second and subsequent magnetizing control, a magnetic field smaller than the magnetic field in the first magnetizing control is applied to the permanent magnet.
A control method for a permanent magnet type rotating electrical machine.

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