JP2013223333A - Motor controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor controller that is able to highly efficiently drive a synchronous reluctance motor.SOLUTION: A current phase angle calculation unit 42 calculates a current phase angle β by which motor torque T relative to a current command value Ibecomes a value close to the maximum value on the basis of the current command value Igiven by a current command value setting unit 41 and a preset current phase angle calculation expression. The current phase angle calculation expression is made as follows: acquiring characteristic data of the motor torque T relative to the current phase angle β for each of a plurality of armature currents I; and obtaining the current phase angle calculation expression on the basis of an approximate expression obtained by linear approximation of a curve connecting maximum torque values on current phase angle-motor torque characteristic curves corresponding to respective armature currents I.

Description

  The present invention relates to a motor control device, and more particularly to a motor control device that controls a synchronous reluctance motor.

  A reluctance motor that rotates a rotor using only reluctance torque generated by a change in the position of electromagnetic energy is known. The reluctance motor includes a switched reluctance motor (SRM) having a salient pole and stator structure, and a synchronous reluctance motor (SynRM) having a stator structure similar to a brushless motor. .

JP 2002-305900 A

Masaru Hasegawa (Chubu University), Shinji Michiki (Nagoya University), Akiyoshi Satake (Okuma), Hiroshi Wang (Gifu University), "Drive circuit technology and drive control technology for permanent magnet motors and reluctance motors-6. Reluctance motor control Technology- ", Proceedings of 2004 Annual Conference of the Institute of Electrical Engineers of Japan, I-119 to I-124 (2004)

  A synchronous reluctance motor (SynRM) has a salient pole structure only in a rotor among a stator and a rotor. In the SynRM, there are a salient pole direction in which magnetic flux easily flows (hereinafter referred to as “d-axis direction”) and a non-salient pole direction in which magnetic flux does not easily flow (hereinafter referred to as “q-axis direction”). Therefore, a reluctance torque is generated due to a difference between an inductance in the d-axis direction (hereinafter referred to as “d-axis inductance”) and an inductance in the q-axis direction (hereinafter referred to as “q-axis inductance”), and the rotor is rotated by the reluctance torque. To do.

It is conceivable to control SynRM in the same way as a brushless motor. That is, a current command value I _a ^*, which is an armature current command value, is set, and a q-axis current command value i _q ^* and a d-axis current command value i _q ^* are calculated from the set current command value I _a ^*. Based on the deviation between the q-axis current command value i _q ^* and the actual q-axis current and the deviation between the d-axis current command value i _q ^* and the actual d-axis current, it is conceivable to perform current feedback control of the SynRM.

In SynRM, q-axis current _{i q} and d-axis current _{i d} are respectively the following formulas (1), represented by (2).
i _q = I _a · sin β (1)
i _d = I _a · cos β (2)
_Ia is the magnitude of the current vector (armature current) for creating the rotating magnetic field. β is a current phase angle, which is a phase difference between a current vector (armature current vector) for generating a rotating magnetic field and the d-axis.

Therefore, the q-axis current command value i _q ^* and the d-axis current command value i _q ^* can be calculated using the current command value I _a ^* , the current phase angle β, and the above equations (1) and (2). Conceivable.
Current phase angle β is a value related to the d-axis inductance L _d and q-axis inductance L _q, can be the value of d-axis inductance L _d and q-axis inductance L _q is calculates the current phase angle β Knowing It is. However, in SynRM, the d-axis inductance and the q-axis inductance are not constant and vary during motor driving. In addition, it is difficult to measure the d-axis inductance and the q-axis inductance in real time. Therefore, the d-axis inductance and the q-axis inductance are measured while the motor is driven, the current phase angle β is calculated based on the measured values, and the q-axis current command value is calculated using the above equations (1) and (2). It is difficult to obtain i _q ^* and d-axis current command value i _q ^* .

  An object of the present invention is to provide a motor control device capable of driving a synchronous reluctance motor with high efficiency.

  The invention according to claim 1 is a motor control device (12) for controlling a synchronous reluctance motor (18), wherein a current command value setting for setting a current command value which is a current command value of the synchronous reluctance motor is provided. Based on the means (41), a map storing the relationship between the current command value and the current phase angle, or an arithmetic expression representing these relationships, and the current command value set by the current command value setting means, the current A current phase angle calculating means (42) for calculating a current phase angle at which the motor torque is close to the maximum value with respect to the command value; a current command value set by the current command value setting means; and the current phase angle calculation Two-phase indicating current calculating means (43, 44) for calculating a d-axis current command value and a q-axis current command value based on the current phase angle calculated by the means; and the two-phase indicating Based on the calculated d-axis current command value and the q-axis current command value by the flow calculation unit, wherein and a synchronous reluctance motor drive control controlling means (45 to 48), a motor control device. In addition, although the alphanumeric character in parentheses represents a corresponding component in an embodiment described later, of course, the scope of the present invention is not limited to the embodiment. The same applies hereinafter.

According to this invention, it is possible to calculate the d-axis current command value and the q-axis current command value at which the motor torque is close to the maximum value with respect to the current command value set by the current command value setting means. As a result, the synchronous reluctance motor can be driven with high efficiency.
According to a second aspect of the present invention, the map or the arithmetic expression is created based on a straight line that approximately represents a relationship between an armature current and a current phase angle at which a maximum motor torque is obtained. The motor control device according to claim 1, wherein the motor control device is obtained by linearly approximating actual measurement data of a current phase angle obtained for each of a plurality of armature currents to obtain a maximum motor torque.

FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering device to which a motor control device according to an embodiment of the present invention is applied. FIG. 2 is a schematic diagram showing an electrical configuration of the ECU. FIG. 3 is a graph showing a setting example of the current command value I _a ^* with respect to the detected steering torque Th. Figure 4 is a graph showing an example of the characteristic data of the motor torque T for the current phase angle β obtained for each of the plurality of armature current I _a. Figure 5 is a relationship between the motor and the measured data of the current phase angle β of torque T becomes the maximum, and the current phase angle β of the armature current I _a and the motor torque T is maximized for each armature current I _a It is a graph which shows the straight line which represented approximately.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering device to which a motor control device according to an embodiment of the present invention is applied.
The electric power steering apparatus 1 includes a steering wheel 2 as a steering member for steering the vehicle, a steering mechanism 4 that steers the steered wheels 3 in conjunction with the rotation of the steering wheel 2, and steering by the driver. And a steering assist mechanism 5 for assisting. The steering wheel 2 and the steering mechanism 4 are mechanically coupled via a steering shaft 6 and an intermediate shaft 7.

  The steering shaft 6 includes an input shaft 8 connected to the steering wheel 2 and an output shaft 9 connected to the intermediate shaft 7. The input shaft 8 and the output shaft 9 are connected via a torsion bar 10 so as to be relatively rotatable on the same axis. That is, when the steering wheel 2 is rotated, the input shaft 8 and the output shaft 9 rotate in the same direction while rotating relative to each other.

A torque sensor 11 is provided around the steering shaft 6. The torque sensor 11 detects the steering torque applied to the steering wheel 2 based on the relative rotational displacement amount of the input shaft 8 and the output shaft 9. The steering torque detected by the torque sensor 11 is input to an ECU (Electronic Control Unit) 12.
The steered mechanism 4 includes a rack and pinion mechanism including a pinion shaft 13 and a rack shaft 14 as a steered shaft. The steered wheel 3 is connected to each end of the rack shaft 14 via a tie rod 15 and a knuckle arm (not shown). The pinion shaft 13 is connected to the intermediate shaft 7. The pinion shaft 13 rotates in conjunction with the steering of the steering wheel 2. A pinion 16 is connected to the tip of the pinion shaft 13.

  The rack shaft 14 extends linearly along the left-right direction of the automobile (a direction orthogonal to the straight-ahead direction). A rack 17 that meshes with the pinion 16 is formed at an intermediate portion in the axial direction of the rack shaft 14. By the pinion 16 and the rack 17, the rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. The steered wheels 3 can be steered by moving the rack shaft 14 in the axial direction.

When the steering wheel 2 is steered (rotated), this rotation is transmitted to the pinion shaft 13 via the steering shaft 6 and the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into an axial movement of the rack shaft 14 by the pinion 16 and the rack 17. Thereby, the steered wheel 3 is steered.
The steering assist mechanism 5 includes an electric motor 18 for assisting steering and a speed reduction mechanism 19 for transmitting the output torque of the electric motor 18 to the steering mechanism 4. In this embodiment, the electric motor 18 is a synchronous reluctance motor (SynRM). The speed reduction mechanism 19 includes a worm gear mechanism that includes a worm shaft 20 and a worm wheel 21 that meshes with the worm shaft 20. The speed reduction mechanism 19 is accommodated in a gear housing 22 as a transmission mechanism housing.

The worm shaft 20 is rotationally driven by the electric motor 18. The worm wheel 21 is coupled to the steering shaft 6 so as to be rotatable in the same direction. The worm wheel 21 is rotationally driven by the worm shaft 20.
When the worm shaft 20 is rotationally driven by the electric motor 18, the worm wheel 21 is rotationally driven and the steering shaft 6 rotates. The rotation of the steering shaft 6 is transmitted to the pinion shaft 13 via the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. Thereby, the steered wheel 3 is steered. That is, the wheel 3 is steered by rotating the worm shaft 20 by the electric motor 18.

The rotation angle of the rotor of the electric motor 18 (rotor rotation angle) is detected by a rotation angle sensor 25 such as a resolver. An output signal of the rotation angle sensor 25 is input to the ECU 12. The electric motor 18 is controlled by the ECU 12 as a motor control device.
FIG. 2 is a schematic diagram showing an electrical configuration of the ECU 12.
The ECU 12 drives the electric motor 18 in accordance with the steering torque Th detected by the torque sensor 11, thereby realizing appropriate steering assistance according to the steering situation.

As described above, the electric motor 18 is a synchronous reluctance motor, and includes a rotor (not shown) having a salient pole structure and a stator (not shown) having an armature winding (not shown). The armature winding is constituted by a star connection of a U-phase stator winding, a V-phase stator winding, and a W-phase stator winding.
The ECU 12 is controlled by the microcomputer 31, a drive circuit (inverter circuit) 32 that supplies power to the electric motor 18, and a current that detects a current flowing through the stator windings of each phase of the electric motor 18. And a detector 33.

The current detection unit 33 includes phase currents i _U , i _V , i _W (hereinafter, collectively referred to as “three-phase detection currents i _U , i _V , i _W ) flowing in the stator windings of the respective phases of the electric motor 18. Is detected. These are current values in the coordinate axis directions in the UVW coordinate system.
The microcomputer 31 includes a CPU and a memory (ROM, RAM, etc.), and functions as a plurality of function processing units by executing a predetermined program. The plurality of function processing units include a current command value setting unit 41, a current phase angle calculation unit 42, a d-axis current command value calculation unit 43, a q-axis current command value calculation unit 44, and a d-axis current deviation calculation. Unit 45, q-axis current deviation calculation unit 46, d-axis PI (proportional integration) control unit 47, q-axis PI (proportional integration) control unit 48, d-axis command voltage generation unit 49, q-axis command voltage A generation unit 50, a first coordinate conversion unit 51, a PWM control unit 52, a rotation angle calculation unit 53, and a second coordinate conversion unit 54 are included.

The current command value setting unit 41 sets a current command value I _a ^* that is a command value of the armature current of the electric motor 18. Specifically, the current command value setting unit 41 sets the current command value I _a ^* based on the steering torque (detected steering torque Th) detected by the torque sensor 11. An example of setting the current command value I _a ^* for the detected steering torque Th is shown in FIG. For the detected steering torque Th, for example, the torque for steering in the left direction is a positive value, and the torque for steering in the right direction is a negative value. The current command value I _a ^* is a positive value when a steering assist force for leftward steering is to be generated from the electric motor 18, and a steering assist force for rightward steering is generated from the electric motor 18. When power is to be negative.

The current command value I _a ^* is positive with respect to a positive value of the detected steering torque Th, and is negative with respect to a negative value of the detected steering torque Th. When the detected steering torque Th is zero, the current command value I _a ^* is zero. The absolute value of the current command value I _a ^* is increased as the absolute value of the detected steering torque Th increases. Thereby, the steering assist force can be increased as the absolute value of the detected steering torque Th increases.

The current command value setting unit 41 uses, for example, a map that stores the relationship between the steering torque Th and the current command value I _a ^* as shown in FIG. 3 or an arithmetic expression that expresses the relationship to the steering torque Th. A corresponding current command value I _a ^* is set. The current command value I _a ^* set by the current command value setting unit 41 is supplied to the current phase angle calculation unit 42 and also to the d-axis current command value calculation unit 43 and the q-axis current command value calculation unit 44.

Based on the current command value I _a ^* given from the current command value setting unit 41 and a preset current phase angle calculation formula, the current phase angle calculation unit 42 generates _a motor for the current command value I _a ^* . A current phase angle β at which the torque is close to the maximum value is calculated. A method for creating the current phase angle calculation formula will be described.
In order to drive the electric motor 18 with high efficiency, the electric motor 18 may be controlled so that the ratio of the motor torque to the armature current is increased.

The motor torque T in the synchronous reluctance motor having the _number of pole pairs _Pn is expressed by the following equation (3).
_{T = P n · (L d} -L q) · i d · i q ... (3)
L _d is the d-axis inductance [H], and L _q is the q-axis inductance [H]. Further, _id is a d-axis current [A], and i _q is a q-axis current [A].

If the magnitude of the armature current is I _a and the current phase difference is β, then i _q = I _a · sin β and i _d = I _a · cos β, so the motor torque T is expressed by the following equation (4). Is done. The current phase difference β is a phase difference between a current vector (armature current vector) for generating a rotating magnetic field and the d-axis.
_{T = (1/2) · P n} · (L d -L q) · I a 2 sin2β ... (4)
Therefore, if the d-axis inductance L _d and the q-axis inductance L _q do not vary with the current phase angle β, the motor torque T is maximized when the current phase angle β is 45 degrees. However, in SynRM, since the d-axis inductance L _d and the q-axis inductance L _q fluctuate due to the magnetic saturation of the rotor core, the motor torque T is not necessarily maximized when the current phase angle β is 45 degrees.

Therefore, in this embodiment, by performing the experiment in advance to the electric motor 18, the range of the armature current I _a to be used _(* current command value I ^_a), the current phase for each of a plurality of the armature current I _a The characteristic data of the motor torque T with respect to the angle β is acquired.
Figure 4 is a graph showing an example of the characteristic data of the motor torque T for the current phase angle β obtained for each of the plurality of armature current I _a. The characteristic data in FIG. 4 is obtained by diverting data published in Non-Patent Document 1. In Figure 4, taking the current phase angle β to the horizontal axis, the vertical axis represents the motor torque T, which represents the characteristics of the motor torque T, respectively curves for the current phase angle β of the armature current I _a.

In the graph of FIG. 4, the current phase angle corresponding to the armature current I _a - by linear approximation curve connecting up torque value on the motor torque curve, the armature current I _a and the armature current I _a , An approximate expression representing the relationship with the current phase angle β at which the motor torque is close to the maximum value is obtained. Specifically, an approximate expression representing the relationship between the armature current _Ia and the current phase angle β is obtained based on the following expression (5). It is assumed that the current phase angle β at which the motor torque is maximum when the armature current _Ia is zero is 45 degrees.

β = {(β _max −β _min ) / I _amax } · I _a + β _min (5)
I _amax is the maximum value of the armature current I _a (the maximum value of the current command value I _a ^* ), and in this example, I _amax = 50 [A]. β _max is a current phase angle β at which the motor torque T becomes the maximum value when the armature current I _a is the maximum value I _amax , and in this example, β _max = 66 [deg]. β _min is the current phase angle β at which the motor torque T is the maximum when the armature current I _a is the minimum value (zero). In this example, β _min = 45 [deg]. .

Substituting I _amax = 50 [A], β _max = 66 [deg], and β _max = 45 [deg] into the equation (5) yields an approximate equation represented by the following equation (6). .
β = (21/50) · I _a +45 (6)
Polygonal line a in FIG. 5, the motor torque T for each armature current I _a is a graph showing measured data of the current phase angle β becomes maximum. A straight line b in FIG. 5 represents an approximate straight line represented by the above formula (6).

The approximate expression (6) the current command value I _a in I _a ^* of the absolute value | I a _* ^| by replacing, as indicated by the following equation (7), current command value I _a ^* from the current phase An arithmetic expression (current phase angle arithmetic expression) for calculating the angle β is obtained.
β = (21/50) · | I _a ^* | +45 (7)
In the current phase angle calculation unit 42, the current phase angle calculation formula (for example, the formula (7)) obtained as described above is set in advance. Current phase angle calculation unit 42 includes a current phase angle arithmetic expression that has been set in advance, based on the current command value I _a ^* given from the current command value setting unit 41, with respect to the current command value I _a ^* The current phase angle β at which the motor torque is close to the maximum value is calculated. The current phase angle β calculated by the current phase angle calculation unit 42 is given to the d-axis current command value calculation unit 43 and the q-axis current command value calculation unit 44.

The d-axis current command value calculation unit 43 uses the armature current command value I _a ^* given from the current command value setting unit 41 and the current phase angle β given from the current phase angle calculation unit 42, and Based on 8), the command value i _d ^* of the d-axis current is calculated.
i _d ^* = I _a ^* · cos β (8)
The q-axis current command value generation unit 44 uses the armature current command value I _a ^* given from the current command value setting unit 41 and the current phase angle β given from the current phase angle calculation unit 42, and Based on 9), the command value i _q ^* of the q-axis current is calculated.

i _q ^* = I _a ^* · sin β (9)
The d-axis current command value i _d ^* and the q-axis current command value i _q ^* may be collectively referred to as “two-phase command current i _d ^* , i _q ^* ”.
The rotation angle calculation unit 53 calculates the rotation angle (rotor rotation angle) θ of the rotor of the electric motor 18 based on the output signal of the rotation angle sensor 25.

The three-phase detection currents i _U , i _V , i _W detected by the current detection unit 33 are given to the second coordinate conversion unit 54. The second coordinate conversion unit 54 uses the rotor rotation angle θ calculated by the rotation angle calculation unit 53 to convert the three-phase detection currents i _U , i _V , i _W into the d-axis current i _d on the dq coordinate. And q-axis current i _q (hereinafter collectively referred to as “two-phase detection current i _d , i _q ”). D-axis current i _d obtained by the second coordinate conversion unit 54 is given to the d-axis current deviation calculation unit 45. The q-axis current i _q obtained by the second coordinate converter 54 is given to the q-axis current deviation calculator 46.

d-axis current deviation calculation unit 45 calculates the deviation of the d-axis current _{i d} for the d-axis current command value _i ^{d *.} The current deviation calculated by the d-axis current deviation calculation unit 45 is given to the d-axis PI control unit 47 and subjected to PI calculation processing. The d-axis command voltage generator 49 generates a d-axis command voltage v _d ^* according to the calculation result of the d-axis PI controller 47.
The q-axis current deviation calculator 46 calculates the deviation of the q-axis current i _{q from} the q-axis current command value i _q ^* . The current deviation calculated by the q-axis current deviation calculation unit 46 is given to the q-axis PI control unit 48 and subjected to PI calculation processing. The q-axis command voltage generation unit 50 generates a q-axis command voltage v _q ^* according to the calculation result of the q-axis PI control unit 48.

The d-axis command voltage v _d ^* and the q-axis command voltage v _q ^* are given to the first coordinate conversion unit 51. The first coordinate conversion unit 51 uses the rotor rotation angle θ calculated by the rotation angle calculation unit 53 to convert the d-axis command voltage v _d ^* and the q-axis command voltage v _q ^* into the command voltage of the UVW coordinate system, That is, the U-phase, V-phase, and W-phase command voltages v _U ^* , v _V ^* , and v _W ^* (hereinafter, collectively referred to as “three-phase command voltages v _U ^* , v _V ^* , and v _W ^* ”). Convert.

The PWM control unit 52 includes a U-phase PWM control signal, a V-phase PWM control signal, and a W-phase with duty ratios corresponding to the U-phase command voltage v _U ^* , the V-phase command voltage v _V ^*, and the W-phase command voltage v _W ^* , respectively. A PWM control signal is generated and supplied to the drive circuit 32.
The drive circuit 32 includes a three-phase inverter circuit corresponding to the U phase, the V phase, and the W phase. By the power elements that constitute the inverter circuit are controlled by the PWM control signals provided from the PWM control unit 52, the three-phase command voltage ^{_{v U *, v V *,}} v W voltage corresponding to ^* of the electric motor 18 It is applied to the stator winding of each phase.

The current deviation calculation units 45 and 46 and the PI control units 47 and 48 constitute current feedback control means. By the action of the current feedback control means, the motor current flowing through the electric motor 18 approaches the two-phase indicating currents i _d ^* and i _q ^* calculated by the d-axis and q-axis current command value calculation units 43 and 44. Be controlled.
According to the embodiment, the d-axis current command value i _d ^* and the q-axis current command value at which the motor torque is close to the maximum value with respect to the current command value I _a ^* set by the current command value setting unit 41. i _q ^* can be calculated. Thereby, the electric motor 18 can be driven with high efficiency.

As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above-described embodiment, the current phase angle calculation unit 42 and the current command value I _a ^* given from the current command value setting unit 41 and a preset current phase angle calculation formula (for example, see formula (7)). ), The current phase angle β at which the motor torque is close to the maximum value is calculated for the current command value I _a ^* . However, the current phase angle calculation unit 42 is supplied from the current command value setting unit 41 and a map that stores the relationship between the current command value I _a ^* and the current phase angle β expressed by the current phase angle calculation formula. based on the current command value I _a ^*, the motor torque may be calculated current phase angle β to a value close to the maximum value for the current command value I _a ^*.

In the above-described embodiment, the curve connecting the maximum torque values on the current phase angle-motor torque characteristic curve corresponding to each armature current _Ia is obtained by linear approximation based on the equation (5). The current phase angle calculation formula is obtained based on the approximate formula. However, by another method such as a least square method, _a curve connecting the maximum torque values on the current phase angle-motor torque characteristic curve corresponding to each armature current Ia is linearly approximated, and based on the obtained approximate expression A current phase angle calculation formula may be obtained.

  In addition, various design changes can be made within the scope of matters described in the claims.

  DESCRIPTION OF SYMBOLS 11 ... Torque sensor, 12 ... ECU, 18 ... Electric motor, 25 ... Rotation angle sensor, 31 ... Microcomputer, 33 ... Current detection part, 41 ... Current command value setting part, 42 ... Current phase angle calculating part, 43 ... d Axis current command value calculation unit, 44 ... q-axis current command value calculation unit, 45 ... d-axis current deviation calculation unit, 46 ... q-axis current deviation calculation unit, 47 ... d-axis PI control unit rotation angle calculation unit, 48 ... q Axis PI controller

Claims (2)

A motor control device for controlling a synchronous reluctance motor,
Current command value setting means for setting a current command value which is a command value of the current of the synchronous reluctance motor;
Based on a map storing the relationship between the current command value and the current phase angle or an arithmetic expression representing these relationships and the current command value set by the current command value setting means, the motor is applied to the current command value. Current phase angle calculating means for calculating a current phase angle at which the torque is close to the maximum value;
Two-phase indicating current for calculating the d-axis current command value and the q-axis current command value based on the current command value set by the current command value setting means and the current phase angle calculated by the current phase angle calculation means Computing means;
And a control means for driving and controlling the synchronous reluctance motor based on the d-axis current command value and the q-axis current command value calculated by the two-phase command current calculation means.   The map or the calculation formula is created based on a straight line that approximately represents the relationship between the armature current and the current phase angle at which the maximum motor torque can be obtained, and the straight line corresponds to each of a plurality of armature currents. The motor control device according to claim 1, wherein the motor control device is obtained by linearly approximating actually measured data of the current phase angle obtained for the maximum motor torque.

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