JP3668866B2 - Electric control device for AC motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric control device for an AC motor.
[0002]
[Prior art]
Conventionally, as disclosed in, for example, Japanese Patent Laid-Open No. 4-257770, a rotation angle detection unit that detects a rotation angle of the rotor has been provided, and the rotation of the rotor is performed using the rotation angle detected by the rotation angle detection unit. An electric control device for an AC motor for controlling the motor is well known.
[0003]
[Problems to be solved by the invention]
The above control is generally performed by digital processing by a computer or the like. In this case, the resolution of the detected rotation angle by the rotation angle detecting means and the error due to the sampling period become a problem. However, the conventional apparatus has a problem that the error due to the resolution and the sampling period is not taken into account, the accuracy of the detected rotation angle is poor, and 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 its purpose is to improve the accuracy of the detected rotational angle by correcting the detected rotational angle in consideration of the resolution of the detected rotational angle or the error due to the sampling period. An object of the present invention is to provide an electric control device for an AC motor.
[0005]
In order to achieve the above object, a structural feature of the present invention is provided with a rotation angle detection means for detecting a rotation angle of a rotor in an AC motor, and using the rotation angle detected by the rotation angle detection means, In an electric control device for an AC motor that controls rotation, angular velocity calculation means for calculating the angular velocity of the rotor using the detected rotation angle , and detected rotation angle by the rotation angle detection means according to the rotation direction of the rotor. Correction means for correcting an error of the detected rotation angle by adding or subtracting a correction value depending on the resolution of the resolution, and when the calculated angular velocity of the rotor is equal to or less than a predetermined minute value, the correction means This is because addition / subtraction is not performed .
According to this, by adding or subtracting a correction value depending on the resolution of the rotation angle detected by the rotation angle detection means according to the rotation direction of the rotor to the rotation angle detected by the rotation angle detection means, the detected rotation angle is obtained. It is corrected. Therefore, even if the resolution of the detected rotation angle by the rotation angle detecting means is somewhat large, the detection error depending on the resolution 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. Further, since the correction means does not perform addition / subtraction of the correction value when the angular velocity of the rotor is equal to or less than a predetermined minute value, it is possible to avoid hunting of the corrected rotation angle by repeating positive and negative in the vicinity of the angular velocity “0”, It is possible to avoid adverse effects due to addition and subtraction of correction values in a situation where there is little influence of errors due to resolution and there is little necessity for correction.
[0006]
Another feature of the present invention is that the AC motor includes rotation angle detection means for detecting the rotation angle of the rotor in the AC motor, and controls the rotation of the rotor using the rotation angle detected by the rotation angle detection means. In the electric control device, the angular velocity calculation means for calculating the angular velocity of the rotor using the detected rotation angle, the detected rotation angle according to the rotation direction of the rotor, the detected rotation angle sampling period and the calculated rotor angular velocity Correction means for correcting an error of the detected rotation angle by adding and subtracting the dependent correction value, and the correction means performs addition and subtraction of the correction value when the calculated angular velocity of the rotor is equal to or less than a predetermined minute value. There is to be not.
According to this, by adding or subtracting a correction value depending on the sampling period of the detected rotation angle and the angular velocity of the rotor according to the rotation direction of the rotor to the rotation angle detected by the rotation angle detecting means, the detected rotation angle Is corrected. Therefore, even if the sampling period is somewhat long, the detection error depending on the sampling period is corrected, and the accuracy of the detection 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. In addition, the correction means does not perform addition / subtraction of the correction value when the angular velocity of the rotor is equal to or less than a predetermined minute value. Therefore, the rotation speed of the rotor is low and the influence on the delay error for various calculations depending on sampling is small. When the necessity for correction is small, it is possible to avoid the influence of disturbance caused by repeating positive and negative in the vicinity of the angular velocity “0”.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described 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.
[0008]
This electric power steering apparatus includes a brushless motor 11 formed of a three-phase synchronous permanent magnet motor as an AC motor. The brushless motor 11 gives an assist force to the steering of the front wheel by the turning operation of the steering handle 12, and drives the tie rod 13 connecting the front wheel at the outer end in the axial direction according to the rotation. A steering torque sensor 15 is assembled to the steering shaft 14 connected to the steering handle 12 at the upper end and connected to the tie rod 13 at the lower end. The sensor 15 detects the steering torque acting on the steering shaft 14. Output a detection signal representing the same torque. Further, the brushless motor 11 is assembled with a rotation angle sensor 16 composed of an encoder for detecting the rotation angle of the motor 11. The rotation angle sensor 16 outputs a two-phase pulse train signal having a phase different by π / 2 in accordance with the rotation of the rotor of the brushless motor 11 and a zero-phase pulse train signal representing the reference rotational position.
[0009]
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 a command torque T *. The basic assist force calculation unit 21 inputs the steering torque from the steering torque sensor 15 and the vehicle speed from a vehicle speed sensor (not shown), and calculates the 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 electric angle θ (corresponding to a rotation angle) and an angular velocity ω of the rotor, which will be described later, together with the vehicle speed, and a return force to the basic position of the steering shaft 14 based on these input values and A return torque corresponding to the resistance force against 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.
[0010]
The command current determination unit 24 calculates two-phase command currents Id * and Iq * based on the command torque T *. The command currents Id * and Iq * correspond to the d-axis in the same direction as the permanent magnet and the q-axis orthogonal thereto in the rotating coordinate system synchronized with the rotating magnetic flux created 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 inputs detection values from various sensors, corrects and outputs both command currents Id * and Iq *. For example, when the battery voltage value is input, the d-axis and q-axis command currents Id * and Iq * are corrected for the magnetic flux control when the battery voltage value is low.
[0011]
The corrected d-axis and q-axis command currents Id * and Iq * are supplied to the calculation units 25 and 26. The calculation units 25 and 26 calculate the d-axis and q-axis from the d-axis and q-axis command currents Id * and Iq *. Difference values ΔId and ΔIq are calculated by subtracting shaft detection currents Id and Iq, respectively, and supplied to proportional-integral control units (PI control units) 27 and 28. Based on the difference values ΔId and ΔIq, the proportional-integral control units 27 and 28 adjust the d-axis and q-axis so that the d-axis and q-axis detection currents Id and Iq follow the d-axis and q-axis command currents Id * and Iq *. Axis command voltages Vd * and Vq * are calculated.
[0012]
These d-axis and q-axis command voltages Vd * and Vq * are corrected by the non-interference correction value calculation unit 31 and the calculation units 32 and 33 to be 2 as d-axis and q-axis correction command voltages Vd * ′ and Vq * ′. The phase / three-phase coordinate conversion unit 34 is supplied. The non-interference correction value calculation unit 31 determines the non-interference correction value ω · for the d-axis and q-axis command voltages Vd * and Vq * based on the d-axis and q-axis detection currents Id and Iq and the angular velocity ω of the rotor. La · Iq, −ω · (φa + La · Id) is calculated. The inductance La and the magnetic flux φa are predetermined constants. The calculation units 32 and 33 subtract 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, to correct the d-axis and q-axis. Command voltage Vd * ′ = Vd * −ω · La · Iq, Vq * ′ = Vq * + ω · (φa + La · Id) is calculated.
[0013]
The two-phase / three-phase coordinate conversion unit 34 converts the d-axis and q-axis correction command voltages Vd * ′ and Vq * ′ into the three-phase command voltages Vu *, Vv * and Vw *, and the converted three-phase command. The voltages Vu *, Vv *, and Vw * are supplied to the PWM voltage generator 35. The PWM voltage generator 35 outputs PWM control voltage signals UU, VU, WU corresponding to the three-phase command voltages Vu *, Vv *, Vw * to the inverter circuit 36. The inverter circuit 36 generates three-phase excitation voltage signals Vu, Vv, Vw corresponding to the PWM control voltage signals UU, VU, WU, and outputs the excitation voltage signals Vu, Vv, Vw to the three-phase excitation current path. Are supplied to the brushless motor 11 respectively. Current sensors 37 and 38 are provided in two of the three-phase excitation current paths, and each of the current sensors 37 and 38 is an excitation of two of the three-phase excitation currents Iu, Iv, and Iw for the brushless motor 11. The currents Iu and Iw are detected and output to the three-phase / two-phase coordinate conversion unit 41. The three-phase / two-phase coordinate conversion unit 41 is also supplied with the excitation current Iv calculated by the calculation unit 42 based on the detection currents Iu and Iw. 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.
[0014]
Further, 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 period. The electrical angle conversion unit 43 calculates the electrical angle θo of the rotor of the brushless motor 11 with respect to the stator based on each pulse train signal, and supplies it to the electrical angle correction unit 44. The electrical angle correction unit 44 corrects the calculated electrical angle θo and supplies the corrected electrical angle θ to the angular velocity conversion unit 45. The angular velocity conversion unit 45 calculates the angular velocity ω of the rotor relative to the stator by differentiating the corrected electrical angle θ. 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.
[0015]
As shown in FIG. 2, the electrical angle correction unit 44 includes a correction calculation unit 44a, a first coefficient determination unit 44b, and a second coefficient determination unit 44c. The correction calculation unit 44a inputs the electrical angle θo from the electrical angle conversion unit 43 and the angular velocity ω from the angular velocity conversion unit 45, and the first and second coefficients a from the first and second coefficient determination units 44b and 44c. , B are input, and if the rotation direction of the rotor is positive (ω ≧ 0), the corrected electrical angle θ is calculated by executing the calculation of Equation 1 below. If the rotation direction of the rotor is negative (ω <0), the corrected electrical angle θ is calculated by executing the calculation of the following formula 2.
[0016]
[Expression 1]
θ = θo + a · δ + b · ω · Δ
[0017]
[Expression 2]
θ = θo−a · δ + b · ω · Δ
[0018]
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 conversion unit 43. In the above formulas 1 and 2, the third term b · ω · Δ also takes a positive or negative value depending on the rotational direction of the rotor, depending on whether the angular velocity ω is positive or negative.
[0019]
The first coefficient determination unit 44b inputs coefficient determination information including the rotation state (operating state) and control state of the brushless motor 11 such as battery voltage in addition to the angular velocity ω, and the following (1) to (4) The first coefficient a is determined according to the conditions of The first coefficient a varies between “0.0” and “1.0”, and setting the value close to “0.0” delays the electrical angle θ, so that the strong magnetic flux is increased. It means to perform the control of the side. In addition, setting the first coefficient a to a value close to “1.0” means that the electric angle θ is advanced, and therefore, the weak flux side control is performed.
[0020]
(1) 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 “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.
[0021]
(2) When the rotational speed of the rotor is low (when the absolute value | ω | of the angular velocity 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 (1). . As a result, it is possible to avoid hunting of the correction rotation angle θ due to repeated positive and negative in the vicinity of the angular velocity ω of “0.0”, and the effect of the above (1) in the situation where the influence of the error due to the resolution is small and the necessity for correction is small. The adverse effects of correction can be avoided.
[0022]
(3) When the battery voltage is lower than a normal value and smaller than a predetermined value, the first coefficient a is set to “1.0” regardless of the above (1) and (2). Thereby, the brushless motor 11 is controlled to the magnetic flux weakening side, and it is possible to give a control margin to the excitation voltage.
[0023]
Regardless of the above conditions (2) and (3), the first coefficient a may be set to “0.5” during the magnetic flux weakening control (displayed by coefficient determination information). This is because the d-axis and q-axis command currents Id * and Iq * fluctuate when the correction rotation angle θ fluctuates including an error, so that an average value is obtained as described in the condition (1). This is to suppress the variation of the correction rotation angle θ as much as possible.
[0024]
The second coefficient determination unit 44c receives coefficient determination information including the rotation state (running state) and control state of the brushless motor 11 such as the battery voltage in addition to the angular velocity ω, and according to the following conditions (5) The second coefficient b is determined.
[0025]
(5) When the rotational speed of the rotor is low (when the absolute value | ω | of the angular velocity ω is equal to or smaller than the predetermined minute value ε), the second coefficient b is set to “0.0”. Otherwise, the second coefficient b is set to “1.0”. Note that the second coefficient b being “1.0” means that the influence of delay due to sampling is taken into account, and the coefficient b being “0.0” means that the influence of delay due to sampling is ignored. .
[0026]
Therefore, when the rotor is rotating at medium and high speeds under the condition (5), the correction value ωΔ can eliminate delay errors for various calculations depending on the sampling period. In addition, when the rotational speed of the rotor is low, that is, when the correction value ωΔ is very small and the influence on the error is small, and the necessity for correction is small, the angular speed ω is positive or negative in the vicinity of “0.0”. It is possible to avoid the influence of disturbance (cause of the oscillation of the corrected electrical angle θ) caused by repetition.
[0027]
When the first and second coefficients a and b are changed in the first and second coefficient determination units 44b and 44c, sudden changes in the corrected electrical angle θ and the angular velocity ω may cause torque vibration. The correction coefficients a and b determined according to the above conditions (1) to (5) are subjected to low-pass filter processing, change regulation processing for limiting the change or change rate of the correction coefficients a and b to a predetermined value, or the like. It is preferable to output the corrected electrical angle θ later.
[0028]
The electrical control device having the above configuration is housed in an electronic circuit unit except for the various sensors 14, 16, 37, and 38 and the inverter circuit 36, and the circuit in the unit is configured by a hardware circuit that performs digital processing. However, in this embodiment, it is constituted by a microcomputer device. And each part 21-28, 31-35, 41-45 in an electronic circuit unit implement | achieves each function by program processing. Therefore, detection signals from the various sensors 14, 16, 37, and 38 are input to each part of the electronic circuit unit in the form of detection values sampled at a predetermined sampling rate (sampling period).
[0029]
Next, the operation of the embodiment configured as described above will be described. When the driver turns the steering handle 12, the turning operation is transmitted to the tie rod 13, and the front wheel is steered by the movement of the rod 13 in the axial direction. At the same time, the steering torque sensor 15 detects the steering torque applied to the steering shaft 14, and the brushless motor 11 is servo-controlled by the electric control device to drive the tie rod 13 with the assist torque according to the steering torque. The front wheels are steered while being assisted by the driving force of the brushless motor 11.
[0030]
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 perform a command torque based on the detected steering torque, the vehicle speed, the corrected electric angle θ of the rotor and the angular velocity ω. While calculating T *, the command current determination unit 24 determines the d-axis and q-axis command currents Id * and Iq * based on the command torque T * and other various sensor values. Then, the calculation units 25 and 26, the proportional integration control units 27 and 28, the two-phase / three-phase coordinate conversion unit 34, the PWM voltage generation unit 35, and the inverter circuit 36 are converted into current sensors 37 and 38, three-phase / 2-phase coordinate conversion. The brushless motor 11 is controlled using the d-axis and q-axis detection currents Id and Iq fed back by the unit 41 and the calculation unit 42. In this case, the non-interference correction value calculation unit 31 and the calculation units 32 and 33 are configured so that the d-axis and q-axis command voltages from the proportional-integral control units 27 and 28 are used to cancel out the speed electromotive force that interferes between the d and q axes. Correct Vd * and Vq *.
[0031]
In such servo control, in the return force calculation unit 22, the non-interference correction value calculation unit 31, the 2 phase / 3 phase coordinate conversion unit 34, and the 3 phase / 2 phase coordinate conversion unit 34, correction is performed by the electrical angle correction unit 44. The corrected electrical angle θ or the angular velocity ω converted by the angular velocity converter 45 is used. In this case, the electrical angle correction unit 44 performs a predetermined correction value (detection rotation) on the detected electrical angle θo calculated by the electrical angle conversion unit 43 according to the rotation direction of the rotor by performing the calculations of the above formulas 1 and 2. The detected electrical angle θo is corrected by adding or subtracting the correction value a · δ depending on the angular resolution and the sampling period Δ of the detected rotation angle and the correction value b · ω · Δ depending on the angular velocity ω of the rotor. As a result, even if the resolution of the rotation angle detected by the rotation angle sensor 16 is somewhat large or the sampling period Δ input from the sensor 16 to the electrical angle converter 43 is somewhat long, it depends on the 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.
[0032]
Furthermore, in the correction, the coefficients a and b of the correction values a, δ, b, ω, and Δ are used to determine the rotational state (operating state) of the brushless motor 11 as in the above-described conditions (1) to (5). Since the control is performed according to the control state, the correction is performed accurately, the accuracy of the correction 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 also improved. improves.
[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 in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Brushless motor, 12 ... Steering handle, 15 ... Steering torque sensor, 16 ... Rotation angle sensor, 24 ... Command current determination part, 27, 28 ... Proportional integral control part (PI control part), 31 ... Non-interference correction value calculation 34, 2-phase / 3-phase coordinate conversion unit, 35 ... PWM voltage generation unit, 36 ... inverter circuit, 37, 38 ... current sensor, 41 ... 3-phase / 2-phase coordinate conversion unit, 43 ... electrical angle conversion unit, 44: electrical angle correction unit, 45: angular velocity conversion unit.

Claims (2)

In an electric control device for an AC motor that includes rotation angle detection means for detecting the rotation angle of the rotor in the AC motor, and controls the rotation of the rotor using the rotation angle detected by the rotation angle detection means.
Angular velocity calculation means for calculating the angular velocity of the rotor using the detected rotation angle;
Correction means for correcting an error of the detected rotation angle by adding or subtracting a correction value depending on the resolution of the detected rotation angle by the rotation angle detection means according to the rotation direction of the rotor according to the rotation direction of the rotor ;
The AC control apparatus for an AC motor, wherein the correction means does not perform addition / subtraction of the correction value when the calculated angular velocity of the rotor is a predetermined minute value or less . In an electric control device for an AC motor that includes rotation angle detection means for detecting the rotation angle of the rotor in the AC motor, and controls the rotation of the rotor using the rotation angle detected by the rotation angle detection means.
Angular velocity calculation means for calculating the angular velocity of the rotor using the detected rotation angle;
Correction means for correcting an error of the detected rotation angle by adding or subtracting a correction value depending on a sampling period of the detected rotation angle and the calculated angular velocity of the rotor in accordance with a rotation direction of the rotor to the detected rotation angle; Provided,
The AC control apparatus for an AC motor, wherein the correction means does not perform addition / subtraction of the correction value when the calculated angular velocity of the rotor is a predetermined minute value or less .

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