JP2016019457A - Method and device for estimating motor torque - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately estimate a torque of a motor to which demagnetization occurs.SOLUTION: A method is for estimating a torque of a motor where in a rotor, permanent magnets are arranged. At a reference temperature and a target temperature, demagnetization curves of permanent magnets are actually measured and demagnetization functions are acquired. By a magnetic field analysis by a finite element method, position data at operation points on the demagnetization curve at the target temperature where demagnetization can occur to each element of the permanent magnets is calculated at every rotation angle. A minimum value of magnetization of each element is acquired on the basis of the position data of the operation points, the minimum value is substituted for the demagnetization function, and a demagnetization ratio is calculated. The demagnetization curve after demagnetization is acquired by applying the demagnetization ratio to the demagnetization curve at the reference temperature, and a torque is calculated by the magnetic field analysis by the finite element method using the demagnetization curve.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a method and apparatus suitable for estimating the torque of a permanent magnet type synchronous motor (PM motor) that tends to cause demagnetization, such as a drive motor of an automobile.

  Regarding the present invention, a method is disclosed in which the torque after demagnetization can be calculated with high accuracy (Patent Document 1).

  In principle, since the demagnetization curve after demagnetization cannot be measured, a method for obtaining a demagnetization function from experimental data and calculating the demagnetization torque using the demagnetization function is disclosed. Has been.

JP 2013-165554 A

  Generally, PM motors can be broadly classified into SPM motors in which permanent magnets are attached to the surface of the rotor and IPM motors in which permanent magnets are embedded in the rotor. In particular, the latter can use a reluctance torque generated by magnetic saliency in addition to a magnet torque caused by a magnet magnetic flux, so that a high torque of the motor can be achieved. In the method of Patent Document 1, “reluctance torque” calculated by replacing the permanent magnet of the rotor core with an air layer (non-magnetic material) and performing magnetic field analysis in that state is used for calculating the torque. The value of the reluctance torque is unchanged before and after demagnetization and is treated as the same.

  Further, in the method of Patent Document 1, when calculating the magnetic flux after demagnetization, the sum of the magnetic fluxes of each element by the finite element method of the permanent magnet and the magnetic flux of the entire permanent magnet are considered to be equivalent. The magnetic interaction between the elements is not considered.

  In practice, however, the magnetic flux density distribution inside the motor core changes after demagnetization, so that the reluctance torque also changes and there is a magnetic interaction between the elements. Therefore, the method of Patent Document 1 has room for improvement in terms of accuracy.

  Particularly in recent years, the amount of permanent magnets used has been decreasing. For this reason, the ratio of the reluctance torque in the total torque is increasing, and there is a concern that the accuracy of the method of Patent Document 1 will further decrease in the future.

  Accordingly, an object of the present invention is to provide a method and an apparatus that can estimate the torque of a motor with high accuracy.

  The method according to the present invention is a method for estimating the torque of a motor in which a plurality of permanent magnets are arranged at the facing portion between the rotor and the stator. In this method, at least a reference temperature and a target temperature at which irreversible demagnetization can occur, a demagnetization curve of the permanent magnet is actually measured, and a demagnetization curve for each temperature is converted into data and stored. A demagnetization function acquisition step of acquiring a demagnetization function of the permanent magnet having a correlation between an irreversible demagnetization factor and a ratio of magnetization and residual magnetic flux density, and storing the demagnetization function as data, and the demagnetization curve And a torque estimation step of estimating torque using the demagnetization function.

  Then, in the torque estimation step, the position data of the operating point on the demagnetization curve at the target temperature for each of the plurality of elements set in the permanent magnet is obtained with respect to the stator by magnetic field analysis by a finite element method. Based on the operating point information acquisition step calculated for each rotation angle of the rotor and the calculated position data of the operating point, a minimum magnetization value is acquired in each of the elements, and the minimum magnetization value is reduced. Demagnetization by applying the irreversible demagnetization factor to the demagnetization curve of the reference temperature stored in the element and the stored demagnetization curve of the reference temperature by substituting in the magnetic function After demagnetization to calculate torque by obtaining a demagnetization curve after demagnetization to obtain a later demagnetization curve and a magnetic field analysis by a finite element method using the demagnetization curve after demagnetization A torque calculation step includes the.

  That is, according to this method, the irreversible demagnetization factor is obtained using the actually measured demagnetization curve and the demagnetization function, and the demagnetization curve after demagnetization obtained based on the irreversible demagnetization factor is used. Torque is calculated by magnetic field analysis by the element method.

  Therefore, according to this method, since the torque is calculated by the magnetic field analysis using the demagnetization curve after demagnetization, in addition to the change in the magnetic flux density distribution inside the motor core due to the demagnetization of the permanent magnet, Since the influence of the magnetic interaction between each element of the magnet is also taken into consideration, the total torque of the motor including the reluctance torque can be estimated with high accuracy.

  The demagnetization function acquisition step includes an actual measurement step of measuring an irreversible demagnetization factor for each temperature by a thermal demagnetization test using a test piece of the permanent magnet, and a magnetization of the test piece at each temperature by a finite element method. It is preferable to include an analysis step that is calculated by magnetic field analysis according to the above.

  Then, since the calculation error of the test piece magnetization is smaller than using the average permeance coefficient and demagnetization curve of the test piece calculated by the approximate expression, it is possible to obtain a more accurate demagnetization function. it can.

  In particular, when the motor is a motor that performs flux-weakening control, in the operating point information acquisition step, the current and current phase conditions during the flux-weakening control are input to the calculation of the position data of the operating point. It is preferable to provide it as a condition.

  Then, torque can be estimated in consideration of not only irreversible demagnetization due to a thermal load but also irreversible demagnetization due to an external magnetic field, so that the torque after demagnetization can be estimated with higher accuracy.

  Furthermore, when the motor is an automobile drive motor, the permanent magnet is preferably an Nd—Fe—B based sintered magnet.

  With Nd-Fe-B sintered magnets, motor characteristics suitable for automobile drive motors can be obtained, but on the other hand, there is a characteristic that demagnetization is likely to occur due to the influence of temperature, and demagnetization is considered. This is because the torque cannot be estimated properly.

  In this case, the target temperature is preferably selected within a range of −40 to 200 ° C.

  Since the motor drive motor has a practical temperature range in which demagnetization can occur, the torque of the car drive motor can be appropriately evaluated.

  By using such a torque estimation method, a device capable of estimating the motor torque can be easily realized. Specifically, the apparatus includes each data of the demagnetization curve and the demagnetization function, a demagnetization analysis program that executes demagnetization analysis using the data, and a magnetic field analysis program that executes the magnetic field analysis. And a calculation unit that performs calculation processing of each step of the torque estimation step in cooperation with the storage unit.

  If it does so, since highly accurate torque evaluation can be easily performed using this apparatus, it is excellent in convenience.

  According to the method of the present invention, the torque of the motor can be estimated with high accuracy.

It is a figure for demonstrating a magnetic field etc. FIG. It is a figure for demonstrating a hysteresis curve. It is a figure for demonstrating a demagnetization curve, an operating point, etc. FIG. It is the schematic (sectional drawing) which shows an example of the motor which this invention makes object. It is the schematic which shows an example of the torque estimation apparatus of this embodiment. It is a flowchart which shows the flow of the torque estimation method of this embodiment. It is a graph which shows an example of a demagnetizing function. It is a conceptual diagram for demonstrating the magnetic field analysis in an operating point information acquisition step. It is a figure for demonstrating the demagnetization factor calculation step classified by element. It is a figure for demonstrating the demagnetization curve acquisition step after a demagnetization.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the following description is merely illustrative in nature and does not limit the present invention, its application, or its use.

<Related art of the present invention>
(Magnetic field, etc.)
FIG. 1 shows a cross section of a plate-like permanent magnet. The permanent magnet is magnetized in the thickness direction, and a magnetic field (magnetic field) from the north pole to the south pole is formed around the permanent magnet. Here, the strength of the magnetic field in the direction in which the permanent magnet is magnetized is represented by the symbol H.

  The magnetic field is formed not only outside the permanent magnet but also inside. The magnetic field inside the permanent magnet is called a demagnetizing field because it works in the direction of demagnetizing the permanent magnet. The strength (Hd) of the demagnetizing field varies depending on the shape and size of the permanent magnet and the location of the permanent magnet. Normally, the demagnetizing field strength Hd increases as the thickness of the permanent magnet decreases.

  Arrow lines in the figure represent magnetic flux lines that are bundles of magnetic field lines. The magnetic flux is the flux of the magnetic field. Here, the magnetic flux density per unit area (magnetic flux density) on the surface of the permanent magnet is represented by the symbol B.

Magnetization (magnetic polarization) is a magnetic flux per unit area by the permanent magnet itself, and is represented by the symbol J. The magnetic flux density B is obtained by adding the strength of the external magnetic field to the magnetization J, and has a relationship of B = μ ₀ · H + J (μ ₀ : permeability of vacuum).

(Hysteresis curve)
FIG. 2 schematically shows a hysteresis curve (magnetic history curve) of the magnetic material. The solid line is a BH curve with the vertical axis represented by magnetic flux density B, and the broken line is a JH curve with the vertical axis represented by magnetization J, obtained by converting the BH curve. The hysteresis curve can be measured using a DC magnetization characteristic measuring device (BH tracer) or the like.

Specifically, a magnetic field is applied to the magnetic material to cause magnetic saturation (point a in the figure). When the magnetic field is decreased from this state, the magnetization J remains (point b in the figure) even when the magnetic field strength H becomes zero. The magnetization J at this time is called a residual magnetic flux density and is represented by the symbol Br. Further, when the magnetic field is decreased, the magnetization becomes 0 (point c in the figure). The magnetic field strength H at this time is called coercive force, and is represented by the symbol H _cj .

  When the magnetic field strength H is further increased in the reverse direction, the magnetic saturation is performed in the reverse direction (point d in the figure), and from this state, the magnetic field direction is reversed to increase the magnetic field strength H. As in the beginning, the magnetic saturation occurs and a hysteresis curve is obtained. Of this hysteresis curve, the portion in the second quadrant is called a demagnetization curve.

(Demagnetization curve)
FIG. 3 schematically shows a demagnetization curve (BH curve). The demagnetization curve changes with temperature, C1 represents a demagnetization curve at room temperature, and C2 represents a demagnetization curve at a high temperature of 100 ° C. or higher. L1 and L2 represent operation lines whose slope is a ratio (B / Hd) between the demagnetizing field Hd and the magnetic flux density B. The inclinations of these operation lines L1 and L2 are determined by the shape and dimensions of the magnet and are called permeance coefficients.

  The intersection of the operation lines L1, L2 and the demagnetization curves C1, C2 is called an operation point Pw. This operating point Pw is an important factor in evaluating the demagnetization of the permanent magnet.

  That is, as shown in the demagnetization curve C2, the demagnetization curve has an inflection point (called a knick point K) at which the decrease of the magnetic flux density B suddenly increases. Depending on the position of the operating point Pw with respect to the knick point K, This is because it is determined whether reversible demagnetization or irreversible demagnetization.

  Specifically, when the operation line L1 is viewed, when the heating line is heated from room temperature to C2, the magnetic flux density B decreases from B1 to B2. In both C1 and C2, since the operating point Pw is located above the knick point K, the magnetic flux density B recovers to almost B1 when the temperature returns to room temperature (reversible demagnetization).

  However, when the operating point Pw enters the lower side of the knick point in C2 as in the operating line L2, the magnetic flux density B does not recover to the original state even if the operating temperature returns to room temperature, and a certain irreversible demagnetization occurs. (Irreversible demagnetization).

  Irreversible demagnetization proceeds only in the direction in which the amount of demagnetization increases. That is, after demagnetization occurs, demagnetization does not proceed even if demagnetization with a smaller demagnetization amount occurs, but if demagnetization with a larger demagnetization amount occurs, the demagnetization amount increases. Demagnetization proceeds by the amount.

  Such irreversible demagnetization (hereinafter also simply referred to as demagnetization) can be caused not only by heating but also by cooling, and can also be caused by an external magnetic field acting in the opposite direction.

  When demagnetization occurs in the permanent magnet that constitutes the magnetic pole of the motor, the torque also decreases. Therefore, in the case of a motor that is used under conditions where demagnetization can occur, the torque after the start of use is less than the torque before the start of use, so in order to estimate the effective torque with high accuracy at the time of design. Therefore, it is necessary to reflect the effect of demagnetization in the estimation.

<Motor targeted by the present invention>
The main object of the present invention is a permanent magnet motor (PM motor) that can cause demagnetization.

  FIG. 4 shows an example of such a motor (motor 50). The motor 50 is an embedded magnet type inner rotor type motor, and includes a shaft 51, a rotor 52, a stator 53, a motor case 54 that accommodates these, and the like.

  The rotor 52 mainly includes a rotor core 52a formed in a cylindrical shape by stacking soft magnetic materials such as electromagnetic steel plates, and a plurality of plate-like permanent magnets 55. The rotor core 52a is fixed to a shaft 51 that is rotatably supported by the motor case 54 in a state where the centers coincide with each other. The permanent magnet 55 is embedded in the outer peripheral portion of the rotor 52 so as to extend in the direction of the rotation axis, and is arranged such that N poles and S poles are alternately arranged in the circumferential direction at equal intervals.

  A plurality of teeth 53a project at equal intervals on the inner peripheral portion of the stator 53 facing the outer peripheral surface of the rotor 52 with a slight gap therebetween, and a plurality of coils 56 are wound by winding a wire around each of the teeth 53a. Is formed. When a controlled current is applied to these coils 56, the rotor 52 rotates and the rotational force is output through the shaft 51.

  In the present invention, the type of the motor is not limited as long as the motor uses a permanent magnet for the magnetic poles of the rotor. The structure of the motor is not particularly limited, such as the number, shape, and arrangement of permanent magnets, the number of coils, and the manner of winding the wire.

  The present invention is particularly suitable for an automobile drive motor.

  In other words, a drive motor for an automobile is required to have motor characteristics corresponding to a wide range of driving conditions from high torque low rotation to low torque high rotation. Furthermore, the permanent magnet used is required to have heat resistance that can withstand a wide temperature range of, for example, −40 ° C. to 200 ° C., and the influence of demagnetization is large.

  For example, as the permanent magnet, an Nd—Fe—B sintered magnet is preferable. In the case of the Nd—Fe—B based sintered magnet, a high residual magnetic flux density Br is obtained, so that motor characteristics suitable for a drive motor of an automobile can be obtained. On the other hand, the Nd—Fe—B based sintered magnet is susceptible to temperature and has the property of easily causing demagnetization, and the torque estimation accuracy is likely to decrease.

  In contrast, the method and apparatus of the present invention can appropriately reflect the effect of demagnetization, so that even if the permanent magnet of the rotor is an Nd-Fe-B sintered magnet, the torque can be accurately measured. Can be estimated.

In that case, the coercivity H _cj of the permanent magnet is preferably in the range of 20 to 35 kOe. If the coercive force H _cj is within this range, even if demagnetization occurs, the motor characteristics required for the drive motor of the automobile can be maintained, and the method of the present invention can be effectively applied.

  Furthermore, it is more effective when the flux-weakening control is performed by the motor.

  The magnetic flux generated by the permanent magnet on the rotor side is constant. Therefore, the counter electromotive voltage generated by the magnetic flux increases with the increase in the rotational speed of the motor. When this counter electromotive voltage becomes equal to the voltage applied to the stator side coil, a phenomenon occurs in which the current stops flowing and the rotational speed does not increase any more.

  In the flux weakening control, in order to suppress the increase in the counter electromotive voltage, the phase of the current supplied to the coil is advanced, and a reverse magnetic field is applied to the permanent magnet from the stator side. Thereby, the motor can be increased to a higher rotational speed.

  However, in this case, a demagnetization can occur in the permanent magnet due to a reverse magnetic field (external magnetic field) acting on the permanent magnet. Therefore, when the flux weakening control is performed by the target motor, it is necessary to consider not only the temperature but also the influence of demagnetization by the external magnetic field.

  On the other hand, in the method of the present invention, since the influence of demagnetization due to the external magnetic field is also reflected, the torque can be estimated with high accuracy even for a motor that performs flux-weakening control. .

<Torque estimation device>
FIG. 5 shows an example of the torque estimation device of the present embodiment (hereinafter also simply referred to as device 1). The hardware of the apparatus 1 is a so-called computer system, and includes a CPU 2 (corresponding to a calculation unit), a memory 3 (corresponding to a storage unit) such as ROM, RAM, HDD, a display 4 (display unit), a keyboard 5 and a mouse 6. Etc. (input unit).

  The memory 3 stores software such as an operating system, a magnetic field analysis program, and a demagnetization analysis program, which can be executed. The memory 3 may be temporarily configured by taking in a storage medium such as a disk on which the software is recorded into the apparatus 1. As the magnetic field analysis program, for example, known software such as “JMAG” manufactured by JSOL Corporation can be used.

  The memory 3 also stores various data such as finite element model data, demagnetization curve data, demagnetization function data, and calculation results created by each program.

  By starting the operating system and executing the magnetic field analysis program and the demagnetization analysis program, this computer system exhibits the function as the torque estimation device 1. As a result, the CPU 2 executes each process and calculation processing of each step based on the torque estimation method described below in cooperation with the memory 3 based on instructions and information input through the keyboard 5 and the like.

<Torque estimation method>
A method for estimating the torque of the motor by the torque estimation device 1 will be described with reference to the flowchart of FIG. This torque estimation method is devised so that the torque of the motor can be estimated with high accuracy by appropriately reflecting demagnetization. For convenience, the description uses a two-dimensional analysis model, but the present invention can also be applied to a three-dimensional analysis model.

  The main body of this torque estimation method includes a material property acquisition step 10, a demagnetization function acquisition step 20, and a torque estimation step 30. Among these, the material property acquisition step 10 and the demagnetization function acquisition step 20 are performed prior to the torque estimation step 30, and data obtained in these steps is stored in the memory 3 before the torque estimation step 30 is performed. Is done.

(Material property acquisition process)
In this process, at least at the reference temperature and the target temperature, the demagnetization curve of the permanent magnet of the motor to be analyzed (hereinafter also simply referred to as a permanent magnet) is measured, and the demagnetization curve for each temperature is converted into data. The storing process is performed.

  The reference temperature is the normal temperature of the permanent magnet, and is usually room temperature (20 ± 15 ° C.). The target temperature is the temperature farthest from the reference temperature that the permanent magnet can reach, and is usually a high temperature at which demagnetization can occur.

  A demagnetization curve is obtained by actually measuring a hysteresis curve at each temperature. The demagnetization curve thus obtained is converted into data usable by the magnetic field analysis program and the demagnetization analysis program as a collection of point data on coordinates and stored in the memory 3.

  The demagnetization curve is preferably measured not only at the reference temperature and the target temperature but also at a plurality of temperatures, converted into data, and stored in the memory 3. Then, since it can utilize as needed among these demagnetization curves according to temperature, it is excellent in versatility.

  Furthermore, it is preferable to store these demagnetization curves as data for a plurality of permanent magnets of different materials. Then, even if the material of the permanent magnet changes, it can respond immediately, so it is more versatile.

(Demagnetization function acquisition process)
In this step, a process of acquiring a demagnetization function of the permanent magnet having a correlation between the ratio of the magnetization J and the residual magnetic flux density Br and the irreversible demagnetization rate, and storing the demagnetization function as data is performed.

  Preliminary experiments are performed to obtain the demagnetization function. The preliminary experiment mainly includes an actual measurement step 21 and an analysis step 22.

  In the actual measurement step 21, the irreversible demagnetization factor for each temperature is actually measured by a thermal demagnetization test in which a heat load using a test piece is applied. Specifically, the test piece used is made of the same magnetic material as the permanent magnet.

  In this step, first, the amount of magnetic flux at room temperature (the amount of magnetic flux before heating) of each test piece is measured. These test pieces are heated to different predetermined temperatures to give a sufficient heat load, then returned to room temperature, and the amount of magnetic flux (the amount of magnetic flux after heating) is measured.

  The demagnetization amount of each test piece is calculated from the difference between the pre-heating magnetic flux amount and the post-heating magnetic flux amount of each test piece obtained in this way, and the irreversible demagnetization factor ( Hereinafter, it is also simply referred to as a demagnetization factor.

  At the same time, a demagnetization curve at each temperature of room temperature and a predetermined temperature at which the test piece is heated is also measured. In addition, when the data of these demagnetization curves are already memorize | stored in the memory 3, the data can be utilized.

  In the analysis step 22, the magnetization J of the test piece at each temperature is calculated by magnetic field analysis by the finite element method. In addition, since a well-known method can be used for the magnetic field analysis here, the specific description is abbreviate | omitted.

  In this step, since the magnetization J of the test piece at each temperature is calculated using the magnetic field analysis by the finite element method, the calculation is performed using the average permeance coefficient and the demagnetization curve of the test piece calculated by the approximate expression. , The calculation accuracy increases.

  Then, the magnetization parameter (J / Br), which is the ratio of these, is obtained from the magnetization J and the residual magnetic flux density Br of the demagnetization curve at the corresponding heating temperature.

  FIG. 7 shows an example of a graph showing the relationship between the acquired magnetization parameter and the demagnetization factor at the corresponding heating temperature. A high-order first-order correlation is recognized between them, and a linear equation can be expressed by using both as variables (demagnetization function). This demagnetization function is converted into data and stored in the memory 3.

(Torque estimation process)
In this step, torque is estimated using the acquired demagnetization curve and demagnetization function. The torque estimation step 30 mainly includes an operating point information acquisition step 31, an element-specific demagnetization factor calculation step 32, a demagnetization curve acquisition step 33 after demagnetization, and a torque calculation step 34 after demagnetization.

(Operation point information acquisition step)
In this step, the target temperature and the control condition (current condition) are input for each of a plurality of elements set in the permanent magnet by the magnetic field analysis by the finite element method, and the position data of the operating point Pw at that time is A process of calculating for each rotation angle of the rotor is performed.

  Specifically, first, the finite element model required for magnetic field analysis, such as the material and shape of the rotor core, the shape and arrangement of the permanent magnet, the number of turns of the coil, the motor drive conditions, the rotation angle of the rotor, and the number of divided elements Is input through the keyboard 5 or the like.

  Then, the magnetic field analysis program is instructed to calculate the position data of the operating point Pw at the target temperature. Then, the virtual motor whose cross section is configured by a plurality of elements (mesh) is set by the CPU 2 and displayed on the display 4. In this virtual motor, magnetic field analysis is performed while rotating the rotor by a predetermined angle with respect to the stator.

  In the case of a motor, since the magnetic field changes periodically, it is not necessary to analyze the entire circumference of the motor. It is efficient to analyze within the range of the electrical angle for one cycle.

  FIG. 8 shows a conceptual diagram of processing performed in this step. In FIG. 8, only the permanent magnet is represented by a plurality of elements s1,. First, position data of the operating point Pw at the initial position is calculated for each element s1,... Of the permanent magnet by magnetic field analysis.

  FIG. 8 illustrates an image in which the operating points Pw1 and Pwn are acquired for the elements s1 and sn among the elements s1,... In the permanent magnet at the initial position.

  Next, the rotor is rotated by the set predetermined angle θ. Also at the rotation angle, as in the case of the initial position, the position data of the operating point Pw of each element s1,. FIG. 8 illustrates an image in which the operating point Pw1 'is acquired for the element s1' among the elements s1, ... at the rotation angle.

  Thereafter, by repeating this processing, the position data of the operating point Pw at the target temperature is acquired for each rotation angle for each element s1,.

(Demagnetization factor calculation step by element)
In this step, the minimum value of the magnetization J at each element is acquired based on the position data of the operating point Pw calculated in the operating point information acquisition step 31, and the minimum value of the magnetization J is substituted into the demagnetization function. Thus, processing for calculating the maximum value of the demagnetization factor for each element is performed.

  FIG. 9 shows a JH curve at the target temperature of the permanent magnet. The JH curve is obtained by converting the data of the BH curve.

  In the operating point information acquisition step 31, the position data of the operating point Pw at each rotation angle (located on the BH curve at the target temperature) is acquired for each element. Here, first, for each element, the position data of the operating point Pw at each rotation angle is converted into the position data of the magnetization J, and the converted position data is plotted on the JH curve. A plurality of white circles shown in FIG. 9 represent these plotted points.

  Of these points, the point having the smallest magnetization J is identified (Jd). A magnetization J parameter (Jd / Br) is calculated from the magnetization Jd at this time and the residual magnetic flux density Br. By substituting the calculated magnetization J parameter (Jd / Br) into the demagnetization function, the maximum value of the demagnetization factor (the largest demagnetization factor in the rotation angle) is calculated. Such a process is performed for each element, and the demagnetization factor of each element is calculated.

(Demagnetization curve acquisition step after demagnetization)
In this step, a process of obtaining a demagnetization curve after demagnetization is performed by applying the calculated demagnetization factor to the stored demagnetization curve of the reference temperature.

  FIG. 10 shows the JH curve Cs at the reference temperature and the JH curve Ct at the target temperature of the permanent magnet. By applying the demagnetization factor of each element to the value of the magnetization J on the vertical axis among the coordinate data constituting the JH curve Cs of the reference temperature, J− after demagnetization at the reference temperature is obtained. The H curve Cs ′ is acquired and stored in the memory 3.

(Torque calculation step after demagnetization)
In the demagnetization curve acquisition step 33 after demagnetization, the JH curve Cs ′ after demagnetization at the reference temperature is obtained for each element. Therefore, in this step, the demagnetization curve Cs ′ after demagnetization is obtained. A process of calculating torque is performed by magnetic field analysis by the finite element method used.

  Specifically, the JH curve Cs ′ after demagnetization of each element is converted into a BH curve after demagnetization. The magnetic field analysis by the finite element method is performed again using the BH curve after demagnetization of each element thus obtained, and the torque after demagnetization is calculated.

  Therefore, according to the method and apparatus 1 for estimating the torque, it is possible to estimate the torque of the motor in which the irreversible demagnetization has occurred due to the influence of a thermal load or an external magnetic field with high accuracy. It becomes possible to judge.

  As a result, it is possible to obtain an excellent effect such as an increase in cost due to an excessive design for safety.

DESCRIPTION OF SYMBOLS 1 Torque estimation apparatus 10 Material characteristic acquisition process 20 Demagnetization function acquisition process 30 Torque estimation process 50 Motor 55 Permanent magnet

Claims (6)

A method for estimating the torque of a motor in which a plurality of permanent magnets are arranged at opposite portions of a rotor and a stator,
At least at a reference temperature and a target temperature at which irreversible demagnetization can occur, the demagnetization curve of the permanent magnet is actually measured, and the material property acquisition step for storing and storing these demagnetization curves for each temperature,
A demagnetization function acquisition step of acquiring a demagnetization function of the permanent magnet consisting of a correlation between an irreversible demagnetization factor and a ratio of magnetization and residual magnetic flux density, and storing the demagnetization function as data;
A torque estimation step of estimating torque using the demagnetization curve and the demagnetization function;
Including
The torque estimation step includes
The position data of the operating point on the demagnetization curve at the target temperature is calculated for each rotation angle of the rotor relative to the stator for each of a plurality of elements set in the permanent magnet by magnetic field analysis using a finite element method. An operating point information acquisition step;
Based on the calculated position data of the operating point, the minimum value of the magnetization is obtained in each of the elements, and the minimum value of the magnetization is substituted into the demagnetization function, whereby the irreversible demagnetization factor is determined for each element. Demagnetization factor calculation step for each element to be calculated in
Applying the irreversible demagnetization factor to the stored demagnetization curve of the reference temperature to obtain a demagnetization curve after demagnetization to obtain a demagnetization curve after demagnetization;
Torque calculation step after demagnetization for calculating torque by magnetic field analysis by a finite element method using the demagnetization curve after demagnetization,
A method for estimating torque including The torque estimation method according to claim 1,
The demagnetization function acquisition step includes
An actual measurement step of actually measuring the irreversible demagnetization rate for each temperature by a thermal demagnetization test using the permanent magnet test piece,
An analysis step of calculating the magnetization of the test piece at each temperature by a magnetic field analysis by a finite element method;
A method for estimating torque including In the torque estimation method according to claim 1 or 2,
The motor is a motor that performs flux-weakening control,
In the operating point information acquisition step,
A torque estimation method in which an external magnetic field acting in a reverse direction on the permanent magnet is applied to the permanent magnet by the flux-weakening control in calculating the position data of the operating point. The torque estimation method according to claim 3,
The motor is an automobile drive motor,
A method for estimating torque, wherein the permanent magnet is an Nd—Fe—B based sintered magnet. The torque estimation method according to claim 4,
A torque estimation method in which the target temperature is within a range of −40 to 200 ° C. An apparatus capable of estimating the torque of the motor by using the torque estimation method according to any one of claims 1 to 5,
Each data of the demagnetization curve and the demagnetization function,
A demagnetization analysis program for performing demagnetization analysis using each of the data;
A magnetic field analysis program for executing the magnetic field analysis;
A storage unit for storing
A calculation unit that performs calculation processing of each step of the torque estimation step in cooperation with the storage unit;
A device comprising:

Images