JP2001025283A - Electricity controller for ac motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of servo control on a brushless motor by taking resolution of a rotational angle sensor and errors caused by the sampling period of detected rotational angle into consideration. SOLUTION: A brushless motor 11 is servo-controlled according to the steering torque detected by means of a steering torque sensor 15. In this servo control, an electrical angle correcting section 44 corrects the electrical angle θ0 of a rotor detected by means of a rotational angle sensor 16 and an electrical angle converting section 43. In this correction, a corrected electrical angle θ=θ0+a.δ+b.ω.Δ or θ=θ0-a.δ+b.ω.Δ is calculated, according to the rotational angle of the rotor, based on coefficients (a) and (b) corresponding to the operated state, the controlled state, etc., of the motor 11, a correction value a.δ which varies depending upon the resolution of detected rotational angles, a sampling period Δ of the detected rotational angles, and a correction value b.ω.Δwhich varies, depending upon the angular velocity ω of the rotor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electric control device for an AC motor.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Patent Laid-Open Publication No.
As disclosed in Japanese Patent Laid-Open Publication No. 0-205, electric control of an AC motor including rotation angle detection means for detecting the rotation angle of the rotor, and controlling the rotation of the rotor using the rotation angle detected by the rotation angle detection means. The device is well known.

[0003]

The above-described control is as follows.
Generally, digital processing is performed by a computer or the like. In this case, the resolution of the rotation angle detected by the rotation angle detecting means and an error due to the sampling period are problematic. However, in the above-described conventional apparatus, errors due to the resolution and the sampling period are not considered,
There is a problem that the accuracy of the detected rotation angle is poor, and that the rotation control of the AC motor is not accurately performed.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to address the above problems, and has as its object to correct the detected rotation angle by correcting the detected rotation angle in consideration of the error due to the resolution or sampling period of the detected rotation angle. An object of the present invention is to provide an electric control device for an AC motor that improves the accuracy of the angle.

In order to achieve the above object, a structural feature of the present invention is that a rotation angle detecting means for detecting a rotation angle of a rotor in an AC motor is provided, and a rotation angle detected by the rotation angle detecting means is used. In an electric motor control device for an AC motor for controlling rotation of a rotor, a correction means for correcting an error in the detected rotation angle by adding or subtracting a predetermined correction value to or from the detected rotation angle in accordance with the rotation direction of the rotor is provided. It is in. In this case, the correction means may add or subtract a value depending on the resolution of the rotation angle detected by the rotation angle detection means as a correction value to or from the detected rotation angle, or a value depending on the sampling period of the detected rotation angle and the angular velocity of the rotor. Is added to or subtracted from the detected rotation angle as a correction value.

In the present invention configured as described above,
By adding or subtracting a predetermined correction value to or from the rotation angle detected by the rotation angle detection means according to the rotation direction of the rotor,
The detected rotation angle is corrected. Therefore, even if the resolution of the rotation angle detected by the rotation angle detecting means is somewhat large or the sampling period is slightly long, the detection error depending on the resolution or the sampling period is corrected, and the accuracy of the detected rotation angle is improved. As a result, the accuracy of the rotation control of the AC motor using the detected rotation angle is also improved.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example in which an electric control device for an AC motor according to the present invention is applied to an electric power steering device for a vehicle. This is shown in the figure.

This electric power steering apparatus has a brushless motor 11 composed of a three-phase synchronous permanent magnet motor as an AC motor. Brushless motor 1
Reference numeral 1 denotes an assisting force applied to the steering of the front wheel by the turning operation of the steering handle 12, and the tie rod 13 connecting the front wheel at the outer end is driven in the axial direction according to the rotation. A steering torque sensor 15 is mounted on a steering shaft 14 connected to the steering handle 12 at an upper end and connected to a tie rod 13 at a lower end. The sensor 15 detects a steering torque acting on the steering shaft 14. And outputs a detection signal indicating the same torque. Further, a rotation angle sensor 16 constituted by an encoder for detecting the rotation angle of the motor 11 is assembled with the brushless motor 11. The rotation angle sensor 16 has a phase difference of π / 2 according to the rotation of the rotor of the brushless motor 11.
A phase pulse train signal and a zero-phase pulse train signal representing the reference rotational position are output.

The electric control device for controlling the rotation of the brushless motor 11 includes a basic assist force calculation unit 21, a return force calculation unit 22, and a calculation unit 23 for calculating the command torque T *. The basic assist force calculation unit 21 receives the steering torque from the steering torque sensor 15 and the vehicle speed from a vehicle speed sensor (not shown), and calculates an assist torque that increases as the steering torque increases and decreases as the vehicle speed increases. The return force calculation unit 22 inputs a corrected electrical angle θ (corresponding to a rotation angle) and an angular speed ω of a rotor described later together with the vehicle speed, and based on these input values, a return force of the steering shaft 14 to the basic position and The return torque corresponding to the resistance to the rotation of the steering shaft 14 is calculated.
The calculation unit 23 calculates the command torque T * by adding the assist torque and the return torque, and supplies the command torque T * to the command current determination unit 24.

The command current determining section 24 determines the command torque T
Based on *, two-phase command currents Id * and Iq * are calculated. The command currents Id * and Iq * correspond to the d-axis in the same direction as the permanent magnet and the q-axis orthogonal to the same in the rotating coordinate system synchronized with the rotating magnetic flux generated by the permanent magnet on the rotor of the brushless motor 11. These command currents Id
* And Iq * are referred to as d-axis and q-axis command currents, respectively. The command current determination unit 24 also receives values detected by various sensors and corrects and outputs both command currents Id * and Iq *. For example, when a battery voltage value is input, the d-axis and q-axis command currents Id * and Iq * are corrected for magnetic flux weakening when the battery voltage value is low.

The corrected d-axis and q-axis command currents Id
*, Iq * are supplied to arithmetic units 25 and 26,
26 calculates difference values ΔId and ΔIq by subtracting the d-axis and q-axis detection currents Id and Iq from the d-axis and q-axis command currents Id * and Iq *, respectively, and calculates a proportional integral control unit (PI control unit). ) 27 and 28. Proportional-integral controller 27, 2
8, the d-axis and q-axis command voltages Vd *, Vd *, and the d-axis and q-axis detection currents Id, Iq follow the d-axis and q-axis command currents Id *, Iq * based on the difference values ΔId, ΔIq. Calculate Vq *.

These d-axis and q-axis command voltages Vd *, Vq *
Are corrected by the non-interference correction value calculation unit 31 and the calculation units 32 and 33 and supplied to the two-phase / three-phase coordinate conversion unit 34 as d-axis and q-axis correction command voltages Vd * 'and Vq *'. The non-interference correction value calculator 31 calculates the d-axis and q-axis command voltages V based on the d-axis and q-axis detection currents Id and Iq and the angular velocity ω of the rotor.
Non-interference correction values ω · La · Iq, −ω · (φa
+ La · Id) is calculated. The inductance La
And the magnetic flux φa are predetermined constants. Arithmetic unit 3
Reference numerals 2 and 33 denote the d-axis and q-axis correction command voltages by subtracting the non-interference correction values ω · La · Iq and −ω · (φa + La · Id) from the d-axis and q-axis command voltages Vd * and Vq *, respectively. Vd * '= Vd * -ω
La · Iq, Vq * ′ = Vq * + ω · (φa + La · Id) is calculated.

The two-phase / three-phase coordinate converter 34 includes a d-axis and a q-axis
Axis correction command voltages Vd * ', Vq *' are converted to three-phase command voltages Vu *, Vv
*, Vw *, and the converted three-phase command voltages Vu *, Vv
*, Vw * are supplied to the PWM voltage generator 35. The PWM voltage generator 35 converts the PWM control voltage signals UU, VU, WU corresponding to the three-phase command voltages Vu *, Vv *, Vw * into inverter circuit 3
6 is output. The inverter circuit 36 includes a three-phase excitation voltage signal V corresponding to the PWM control voltage signals UU, VU, and WU.
u, Vv, Vw to generate the excitation voltage signals Vu, Vv, Vw.
Are supplied to the brushless motor 11 via three-phase excitation current paths. Current sensors 37 and 38 are provided in two of the three-phase excitation current paths.
8 is a three-phase excitation current I for the brushless motor 11
The two exciting currents Iu and Iw among u, Iv and Iw are detected and output to the three-phase / two-phase coordinate converter 41. This 3 phase / 2
In the phase coordinate conversion unit 41, the detection current I
The excitation current Iv calculated based on u and Iw is also supplied. The three-phase / two-phase coordinate converter 41 converts these three-phase detection excitation currents Iu, Iv, Iw into two-phase detection excitation currents Id, Iq.

The two-phase pulse train signal and the zero-phase pulse train signal from the rotation angle sensor 16 are continuously supplied to the electrical angle converter 43 at a predetermined sampling cycle. The electrical angle converter 43 calculates the electrical angle θo of the rotor of the brushless motor 11 with respect to the stator based on the pulse train signals, and supplies the electrical angle θo to the electrical angle corrector 44. The electrical angle correction unit 44 corrects the calculated electrical angle θo,
The corrected electrical angle θ is supplied to the angular velocity converter 45. The angular velocity converter 45 differentiates the corrected electrical angle θ to calculate an angular velocity ω of the rotor with respect to the stator. Note that the angular velocity ω
Represents positive rotation of the rotor in the positive direction and negative rotation of the rotor in the negative direction.

As shown in FIG. 2, the electrical angle correction unit 44
A correction operation unit 44a, a first coefficient determination unit 44b, and a second coefficient determination unit 44c are provided. The correction calculation unit 44a receives the electrical angle θo from the electrical angle conversion unit 43 and the angular velocity ω from the angular velocity conversion unit 45, and inputs the first and second coefficients a from the first and second coefficient determination units 44b and 44c. , B, and if the rotation direction of the rotor is positive (ω ≧ 0), the correction electrical angle θ is calculated by executing the calculation of the following equation (1). If the rotation direction of the rotor is negative (ω <0),
By executing the above calculation, the corrected electrical angle θ is calculated.

[0016]

[Equation 1] θ = θo + a · δ + b · ω · Δ

[0017]

[Equation 2] θ = θo−a · δ + b · ω · Δ

Here, δ is a positive constant representing the resolution of the rotation angle sensor 16, and Δ is a positive constant representing the sampling period for taking the signal from the rotation angle sensor 16 into the electrical angle converter 43. In the above equations (1) and (2), the third term b · ω · Δ also takes a positive or negative value according to the rotation direction of the rotor depending on whether the angular velocity ω is positive or negative.

The first coefficient determination unit 44b inputs coefficient determination information including the rotation state (operating state) of the brushless motor 11, such as the battery voltage, the control state, and the like, in addition to the angular velocity ω. Therefore, the first coefficient a
To determine. Note that the first coefficient a ranges from “0.0” to “1.
The value changes between "0" and is set to a value close to "0.0", which means that the electrical angle θ is delayed, which means that the control on the stronger magnetic flux side is performed. The setting of the first coefficient a to a value close to “1.0” means that the electrical angle θ
Therefore, the control on the side of the weak magnetic flux is performed.

Since the error due to the resolution of the rotation angle sensor 16 takes a random value between 0 and δ, the first coefficient a is basically set to an average value of “0.5”. Thereby, during the normal operation of the brushless motor 11, the variation in torque can be reduced, and the average efficiency can be improved.

When the rotational speed of the rotor is low (angular speed ω
(When the absolute value | ω | is equal to or smaller than the predetermined minute value ε), the first coefficient a is set to “0.0” regardless of the above. As a result, it is possible to avoid hunting of the correction rotation angle θ due to repetition of positive and negative when the angular velocity ω is close to “0.0”, and the influence of the above-described correction under the situation where the influence of the error due to the resolution is small and the correction is small is small. Can be avoided.

If the battery voltage is lower than normal and lower than a predetermined value, the first coefficient a is set to "1.0" regardless of the above. As a result, the brushless motor 11 is controlled to the weak magnetic flux side, so that the excitation voltage can have a margin of control.

Further, regardless of the above conditions, the first coefficient a may be set to "0.5" during the magnetic flux weakening control (displayed by the coefficient determination information). this is,
If the corrected rotation angle θ fluctuates with an error, the d-axis and q-axis command currents Id * and Iq * fluctuate. Therefore, the correction rotation angle θ is calculated using an average value as described in the above condition. This is to suppress the fluctuation of as small as possible.

The second coefficient determination unit 44c inputs coefficient determination information including the rotation state (operating state) of the brushless motor 11, such as the battery voltage, and the control state, in addition to the angular velocity ω, according to the following conditions. Determine the second coefficient b.

When the rotation speed of the rotor is low (when the absolute value | ω | of the angular speed ω is equal to or smaller than the predetermined minute value ε), the second coefficient b is set to “0.0”. At other times,
The second coefficient b is set to “1.0”. In addition, the fact that the second coefficient b is “1.0” means that the influence of the delay due to sampling is considered, and that the coefficient b is “0.0” means that the influence of the delay due to sampling is ignored. .

Therefore, when the rotor is rotating at medium to high speed under the above conditions, the correction value ωΔ
Delay errors for various calculations depending on the sampling period can be eliminated. Further, when the rotation speed of the rotor is low, that is, when the correction value ωΔ is small and the influence on the error is small and the necessity of correction is small, It is possible to avoid the influence of disturbance caused by the repetition (the cause of the oscillation of the corrected electrical angle θ).

The first and second coefficient determining units 44
b, 44c, when the first and second coefficients a, b are changed, abrupt changes in the corrected electrical angle θ and the angular velocity ω may cause torque oscillation. , B after a low-pass filter process or a change regulation process for limiting the change or the rate of change of the correction coefficients a and b to within a predetermined value.
Should be output.

The electric control device having the above-described configuration includes various sensors 1
4, 16, 37, 38 and the inverter circuit 36 are housed in an electronic circuit unit, and the circuit in the unit may be constituted by a hardware circuit for performing digital processing. It is composed of a computer device. And each function in each part 21-28, 31-35, 41-45 in an electronic circuit unit is implement | achieved by program processing. Therefore, the detection signals from the various sensors 14, 16, 37, and 38 are input to each section of the electronic circuit unit in the form of detection values sampled at a predetermined sampling rate (sampling cycle).

Next, the operation of the embodiment configured as described above will be described. When the driver turns the steering wheel 12, the turning operation is transmitted to the tie rod 13, and the front wheel is steered by the axial movement of the rod 13. At the same time, the steering torque sensor 15
The brushless motor 1 detects the steering torque applied to the
1 is servo-controlled by the electric control device and drives the tie rod 13 with an assist torque corresponding to the steering torque, so that the front wheels are steered while being assisted by the driving force of the brushless motor 11.

In the servo control by this electric control device, the basic assist force calculation unit 21, the return force calculation unit 22, and the calculation unit 23 are based on the detected steering torque, vehicle speed, and corrected electric angle θ and angular speed ω of the rotor. Command current T *, and the command current determining unit 24 calculates the d-axis and q based on the command torque T * and other various sensor values.
The axis command currents Id * and Iq * are determined. And the operation unit 2
5, 26, proportional-integral controllers 27, 28, two-phase / 3-phase coordinate converter 34, PWM voltage generator 35, and inverter circuit 36 include current sensors 37, 38, three-phase / 2-phase coordinate converter 41, and arithmetic operation. The brushless motor 11 is controlled using the d-axis and q-axis detection currents Id and Iq fed back by the unit 42. In this case, the non-interference correction value calculation unit 31 and the calculation units 32 and 33 use the d-axis and q-axis command voltages from the proportional-integral control units 27 and 28 to cancel the speed electromotive force that interferes between the d and q axes. Vd * and Vq * are corrected.

In such servo control, the return force calculation unit 22, the non-interference correction value calculation unit 31, the two-phase / 3-phase coordinate conversion unit 34, and the three-phase / 2-phase coordinate conversion unit 34 have an electrical angle correction unit 44. Electrical angle θ or angular velocity converter 4 corrected by
The angular velocity ω converted in step 5 is used. In this case, the electrical angle correction unit 44 executes the calculation of Equations 1 and 2 to add a predetermined correction value (detection rotation) to the detected electrical angle θo calculated by the electrical angle conversion unit 43 according to the rotation direction of the rotor. A correction value a · δ depending on the angular resolution, and a correction value b · ω · depending on the sampling period Δ of the detected rotation angle and the angular velocity ω of the rotor.
Δ) is added or subtracted to correct the detected electrical angle θo. Accordingly, even if the resolution of the rotation angle detected by the rotation angle sensor 16 is somewhat large, or if the sampling period Δ input from the sensor 16 to the electrical angle conversion unit 43 is slightly longer, it depends on the same resolution δ or the sampling period Δ. The detected error is corrected, the accuracy of the corrected electrical angle θ and the angular velocity ω is improved, and the control accuracy of the brushless motor 11 and the electric power steering device is improved.

Further, in the correction, a correction value a ·
The coefficients a and b of δ, b, ω, and Δ are calculated using the above-described conditions.
The control is performed according to the rotation state (operation state), control state, and the like of the brushless motor 11 as described above.
The correction is accurately performed, and the accuracy of the corrected electrical angle θ and the angular velocity ω is further improved, and the control accuracy of the brushless motor 11 and the electric power steering device is further improved.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram of an electric power steering device for a vehicle to which an electric control device for an AC motor according to an embodiment of the present invention is applied.

FIG. 2 is a detailed block diagram of an electrical angle correction unit of FIG.

[Explanation of symbols]

11 ... brushless motor, 12 ... steering wheel, 15 ...
Steering torque sensor, 16: rotation angle sensor, 24: command current determination unit, 27, 28: proportional integral control unit (PI control unit), 31: non-interference correction value calculation unit, 34: 2-phase / 3-phase coordinate conversion unit , 35 PWM voltage generator, 36 inverter circuit, 37, 38 current sensor, 41 three-phase / two-phase coordinate converter, 43 electrical angle converter, 44 electrical angle corrector, 4
5. Angular velocity conversion unit.

Claims (3)

[Claims] An AC motor electric control device, comprising: a rotation angle detecting means for detecting a rotation angle of a rotor in an AC motor; and controlling rotation of the rotor using a rotation angle detected by the rotation angle detection means. An electric motor control device for an AC motor, further comprising a correction means for correcting an error of the detected rotation angle by adding or subtracting a predetermined correction value to or from the detected rotation angle in accordance with a rotation direction of a rotor. 2. The electric control device for an AC motor according to claim 1, wherein the correction means adds or subtracts a value depending on the resolution of the rotation angle detected by the rotation angle detection means as a correction value to the detected rotation angle. Motor electric control device. 3. The electric motor control device for an AC motor according to claim 1, wherein the correction unit sets a value dependent on a sampling cycle of the detected rotation angle and an angular velocity of a rotor as a correction value to the detected rotation angle. An electric motor control unit for adding and subtracting AC motors.