JP2003189652A - Servomotor controllor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a servomotor control device which can perform stable operation in all the regions with magnetic saturation appearing so as to sufficiently attain miniaturization. <P>SOLUTION: A control gain reduction part 13 receiving a detected speed ωof a motor 1 is provided, a proportional gain Kp of a current control integration arithmetic part in a current control unit 9 is made to be reduced in accordance with decrease in a rotational speed of the motor 1. Including the situation even when it is servo locked, the motor 1 is controlled so as to suppress generation of control instability due to magnetic saturation of the motor 1 in a low speed condition. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedback control type servo motor control device, and more particularly to a servo motor control device of a type which controls a loop gain in accordance with a change in inductance of a motor winding.

[0002]

2. Description of the Related Art Servo motors are used in numerical control type machine tools, robots, etc. At this time, high-precision and responsive rotation speed control is required, so feedback control by a current control loop is generally used. Has been adopted as

FIG. 11 is a schematic block diagram showing an example of a conventional servo motor control device using a permanent magnet type synchronous motor. In this prior art example, first, a position detector 2 is used as a speed detection system. A speed calculator 3 is provided.

Position detector 2 such as a rotary encoder
Is attached to the motor 1 for the servo, so that the motor 1
The rotation speed information of is detected. Then, in the speed calculation unit 3, the detected speed ω is calculated based on this rotation speed information and is supplied to one input of the comparator 4.

A speed command value ωref is externally input to the other input of the comparator 4, and the difference between the detected speed ω and the speed command value ωref is taken out as a speed deviation, and the speed control section 5 receives the difference. Supplied. Then, with this speed control unit 5,
For example, the proportional-plus-integral calculation is performed and the current command iref is output,
It is supplied to one input of the second comparator 8.

On the other hand, as the current detection system, the current detector 6
And a current detector 7 are provided. Then, first, the current of the motor 1 is detected by the current detector 6 such as CT (current transformer), and the detected current i is output from the current detection device 7 based on this, and the detected current i is output to the other input of the second comparator 8. Is being supplied.

As a result, the deviation between the current command iref and the detected current i is calculated and input to the current control unit 9, where the voltage command is obtained by proportional-plus-integral control, and the PWM control unit 10 is operated.
Is supplied to.

The PWM control unit 10 performs phase conversion based on the input voltage command, creates a PWM signal using a triangular wave comparison PWM method, etc., and supplies this to a power element 11 of a power conversion device such as an inverter device. To do.

As a result, the three-phase AC power is supplied to the motor 1, and the motor 1 generates torque. At this time, the rotation speed ω converges to the speed command value ωref input from the outside. As described above, it is possible to operate a numerical control system machine tool, robot, or the like.

At this time, for example, JP-A-6-335279.
The publication discloses a current control method for a synchronous motor in which the feedback gain of the current control system is controlled in accordance with the current command value in consideration of the magnetic saturation appearing in the motor so that oscillation in the control system can be suppressed. This is the conventional technology.

[0011]

The above-mentioned prior art cannot be said to give sufficient consideration to magnetic saturation in the servo motor, and there is a problem in miniaturizing the servo motor control device.

When controlling the servomotor, it is necessary to give a torque current proportional to the load torque. At this time, the torque current and the torque constant which is a proportional coefficient of the torque are usually fixed and fixed. It constitutes the control system as a thing.

However, when the current supplied to the motor becomes large and magnetic saturation occurs in the magnetic circuit of the motor, the torque constant decreases, and the torque according to the torque command cannot be generated. Then, the feedback control is performed in the direction in which the current is further increased so that the torque according to the command is obtained, and the saturation further progresses.

Here, normally, it is general to design the servo motor control device so that the motor operates in a region where magnetic saturation does not appear. At this time, the current is increased to use up to the saturation region. If it is made possible, a larger torque can be generated and the motor can be downsized.

However, at this time, the operation of the current control system becomes unstable in the region where the current increases and the magnetic saturation appears, and in an extreme case, oscillation occurs. Cannot be fully utilized, which causes a problem in downsizing of the servo motor control device.

Here, in the above-mentioned prior art, the feedback loop gain of the current control system is lowered according to the current command value so that the oscillation of the control system can be suppressed. No consideration is given to the point that the saturation also depends on the rotation speed of the motor, and therefore the above-mentioned problems occur in the conventional technology.

An object of the present invention is to provide a servo motor control device which can perform stable operation in all regions where magnetic saturation appears and can be sufficiently miniaturized.

[0018]

The above object is to provide a means for detecting the rotation speed of a motor in a servo motor control device of a system for controlling a feedback gain of a current control system according to a change in inductance of a motor winding. This is achieved by reducing the feedback gain at least when the rotation speed of the motor is in the low speed range including zero.

Similarly, in the servo motor control device of the type in which the feedback gain of the current control system is controlled according to the change in the inductance of the motor winding, a means for detecting the rotation speed of the motor and a detection of the current of the motor are also provided. The feedback gain is reduced in at least one of a low speed region in which the rotation speed of the motor is 0 and a region in which the motor current is equal to or higher than the rated value of the motor. Even if it is done, it will be achieved.

At this time, the reduction of the feedback gain may be given by a preset reduction pattern, and the reduction of the feedback gain causes the current given to the motor whose inductance decreases at high torque. It may be performed according to the variation of the inductance so as not to be excessive.

Further, at this time, the reduction of the feedback gain is executed at least in the region where the rated torque of the motor is exceeded and the maximum torque is reached, ensuring the responsiveness during the rated operation of the motor and Suppression of oscillation at high torque may be obtained.

Further, at this time, the reduction of the feedback gain is controlled by a combination of at least the control gain reduction rate based on the motor current detection value and the control gain reduction rate based on the speed detection value, It may be possible to obtain both prevention of oscillation due to a decrease in winding inductance when the motor has high torque and suppression of oscillation when the motor is stopped.

According to the embodiment, according to the present invention, the control gain of the current control system is changed so as to match the change of the inductance of the actual machine, the control gain is prevented from becoming excessive, and the current control system is changed. The control gain is reduced by adding a current control gain reducing section to a current control system having a proportional-plus-integral control calculating section.

This gain reduction unit refers to the current detection value to perform a gain reduction rate according to the change in torque, and the speed reduction value to reduce the gain so that oscillation at stop does not occur. The gain is reduced by combining them so as to be stable in all the operation regions according to the characteristics of the servo motor.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION A servo motor control device according to the present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 shows an embodiment of the present invention. In this figure, 13 is a current control gain reduction unit, and other configurations are the same as those of the conventional technique described in FIG. Therefore,
The basic configuration and operation for controlling the motor 1 are also shown in FIG.
Although it is the same as the prior art, the details will be described here.

A position detector 2 is attached to the motor 1, a detected speed ω is calculated by a speed calculator 3 on the basis of information detected by the position detector 2, and the detected speed ω is input by a comparator 4 from a host control system. The deviation between the present speed command value ωref and the detected speed ω is calculated. Then, this deviation is input to the speed control unit 5 and, for example, a proportional-plus-integral calculation is performed, and the torque current command iref is output.

At this time, first, the current detector 6 detects only the u-phase and w-phase currents of the motor 1. The v-phase current is detected from the u-phase and w-phase currents by utilizing the fact that the sum of the three-phase currents becomes zero.

The u-phase, w-phase, and v-phase currents thus detected are first subjected to 3-phase to 2-phase conversion with reference to the u-phase current direction and the current direction orthogonal thereto, and then,
Based on the electrical angle information of the motor 1 obtained from the position detector 2, the d-axis current and π in the motor axis direction in the rotating coordinate system
The coordinates are converted to the q-axis current in the / 2 lead direction.

Therefore, in this rotating coordinate system, the d-axis current is set to zero, and then the q-axis current is controlled so that it becomes the torque current command iref calculated by the speed control section. The current of 1 will be feedback-controlled.

Therefore, the current controller 9 obtains the d-axis voltage command and the q-axis voltage command by proportional-plus-integral control,
2-phase to 3-phase conversion is performed to obtain a 3-phase voltage command value, and P
It is supplied to the WM control unit 10.

The PWM control section 10 creates a PWM signal by a triangular wave comparison PWM method or the like, and when this is given to the power element 11 as a command voltage, a three-phase current is supplied to the motor 1 to control it as a servo motor. Will be obtained.

Here, the voltage equation of the permanent magnet type synchronous motor by the current control system using the rotating coordinate system is given by the following equations (1) and (2). vd = (R + sL) ・ id + ω ・ L ・ iq ………… (1) vq = (R + sL) ・ iq + ω ・ (M _If −L ・ id) ………… (2) R: Motor winding resistance L: Inductance of motor winding M _If : Induced voltage coefficient ω: Detection speed id: d-axis armature current iq: q-axis armature current vd: d-axis armature voltage vq: q-axis armature voltage

FIG. 2 is a control block diagram of the q-axis side of the current control unit 9 based on the proportional-plus-integral calculation. In this case, the deviation between the current command input from the speed control system and the q-axis current is input, The current control unit 14 performs a proportional-plus-integral calculation to obtain a voltage command, and by inputting this voltage command to the motor winding unit 15, the time constant L / R determined by the winding resistance R and the inductance L of the motor is calculated. The q-axis current that it has is output.

The open loop transfer function G ₀ (s) at this time is given by the following equation (3). G ₀ (s) = Ki / sR · (1 + sKp / Ki) / (1 + sL / R) (3) where Kp and Ki are the proportional gain and the integral gain of the proportional integral calculation in the feedback control, respectively. Represent.

Assuming that the cutoff frequency of the current control system is 2πf _C and Kp / Ki = L / R is set so that the transfer function G ₀ (s) is an integral element, these control gains are set. Kp and Ki are given by the following equation (4). Kp = 2πf _C L, Ki = 2πf _C R (4) Therefore, the proportional gain Kp is determined by the cutoff frequency and the inductance of the control system.

By the way, FIG. 3 shows the change in the inductance of the winding with respect to the output torque of the motor. This is the measured value when a current is passed so as to maintain a proportional relationship between the torque command and the output torque. In the plot, as shown in the figure, the inductance of the motor winding is not constant but changes according to the torque (∝ current).

That is, in such a motor, the inductance L decreases as the output torque increases until the torque reaches a certain value. This is because magnetic saturation naturally appears in the area exceeding the rated torque, and saturation partially appears in the magnetic circuit of the motor even in the area before that.

If the motor inductance L decreases as the torque current increases, the motor time constant L / R also changes from the set value, and the time constant L / R changes as the torque increases. Will decrease.

Here, the proportional gain of the current control system is (4)
As expressed by the formula, cutoff frequency (response frequency) 2
It is determined by the value of πf _C and the inductance L. At this time, if the time constant L / R decreases with the increase in torque, the control gain is constant and does not change, so it should be given to the actual motor. The gain becomes relatively larger than the set value, so that in this case, the control system becomes unstable and oscillation occurs as described in the related art.

By the way, at this time, particularly in the case of a servomotor using a permanent magnet type synchronous motor, when the rotation speed thereof is extremely low, or when it is positioned and locked.
In the (servo-locked state), the magnetic flux concentrates in a part, so magnetic saturation occurs even if the motor current is not so large.

That is, the winding inductance of the motor also changes depending on the rotation speed, so that even when the detection speed ω decreases, the inductance L decreases as shown in FIG. 4, and therefore the gain becomes relatively large. As a result, the control system becomes unstable and oscillation occurs. Here, this Figure 4
Is also a plot of measured values.

Therefore, in this embodiment, the gain reducing section 13 is provided so that the proportional control gain of the current control system is reduced according to the rotation speed.
Specifically, the gain reduction unit 13 is configured to control the proportional gain Kp in the proportional-plus-integral calculation unit of the current control unit 9.

As described above, in the above-mentioned conventional technique, no particular consideration is given to the fact that the winding inductance of the motor depends on the rotation speed.

Therefore, not only the detection current i but also the detection speed ω is input to the gain reducing section 13 and is adjusted at least by the detection speed ω or by a combination of both the detection speed ω and the detection current i. The gain is output, and the proportional gain reduction rate of the current controller 9 is determined.

In this case, first, the change in the inductance L in the actual motor shown in FIGS. 3 and 4 is stored in advance in the memory as a data table, and the data table is referred to by the detected current i and the detected speed ω. A method of determining the gain reduction rate can be considered. However, in this case, a large amount of memory is required because it has a data table, and a data table must be prepared every time the characteristics of the permanent magnet type synchronous motor change.

Therefore, in this embodiment, a reduction pattern for the gain reduction rate is given in advance, and the current control gain is reduced based on the detected speed ω, or based on this and the output torque or the detected current i. The gain reducing unit 13 according to this embodiment will be specifically described below.

As described above, in this embodiment, the gain reduction rate is given from the pattern given in advance, but at this time, some methods using different patterns can be applied. Has become.

First, FIG. 5 (a) shows an example in which the proportional gain of the current control gain is changed based on the rotation speed of the motor. In this case, the detection speed ω is near 0, that is, near the stop. This is the case when the reduction is applied to. In the above-described servo lock state, the current is direct current, and therefore oscillation can be prevented by reducing the set control gain by about 60 to 70%.

Here, in the case of FIG. 5 (a), the two points of reduction start and end are, for example, a rotational speed of 0 and a rated rotational speed of about 15
%, The gain reduction rate based on the rotation speed is set to, for example, about 60% of the set gain when stopped, and then the gain is gradually increased to about 15% of the rated rotation speed. It is set to be%.

On the other hand, FIG. 5B shows an example in which the current control gain is reduced against the increase of the rotation speed to stabilize the entire current control system. Here, the control gain at the time of stop is shown. Is set to, for example, 100%, and when the detected speed ω becomes equal to or higher than the rated speed, the value is reduced to 70%, for example, and the inductance characteristic shown in FIG. 4 is linearly approximated.

Therefore, according to the embodiments shown in FIGS. 5 (a) and 5 (b), even when the rotation speed of the motor 1 is reduced, there is no fear that the control system becomes unstable, and the control system is stable even in the servo lock state. Can be positioned.

Next, FIG. 6A shows a pattern for calculating the proportional gain reduction rate from the detected current i. Here, the q-axis current is used in place of the detected current i. This is because in the case of a current control system using a different rotating coordinate system, the q-axis current is dominant in the torque of the motor, and the detected current i can be set to the q-axis current.

FIG. 6A shows the case where the proportional gain is reduced based on the torque command value or the torque current. For example, in accordance with the inductance change of the actual motor shown in FIG. Up to 125%, the gain reduction rate is gradually reduced by linearly approximating the increase in output torque, and when it exceeds 125%, the control gain is reduced to a constant value of about 60% of the initial value. This is the case.

By this gain reduction, the oscillation due to the reduction of the inductance at high torque is suppressed, and the operation of the current control system can be stabilized. Further, in the case of this method, since it suffices to set the gain reduction value, set the reduction start point and the reduction point, and perform linear approximation, it can be realized relatively easily.

Next, FIG. 6 (b) also shows the case where the proportional gain is reduced based on the torque command value or the torque current. In this case, the current at the rated torque is secured and then the proportional gain at the time of the high torque is secured. This is an example of the case where the gain is reduced by suppressing the current. For example, the current control gain is not reduced up to a torque current of 125%, and the output torque increases from about 125% to linearly increase the current control system. By reducing the proportional gain, the control gain is reduced to about 60% at the maximum output torque.

By reducing the proportional gain of the current control system shown in FIG. 6 (b), the oscillation phenomenon at high torque can be suppressed and stable operation can be obtained. On the other hand, the reduction is not performed near the rated torque. There is no fear that the responsiveness of the current control system will deteriorate, and sufficient responsiveness can be ensured in the region where the motor is continuously used.

By the way, FIGS. 3 and 4 described above measure the amount of change in the inductance with respect to the motor rotation speed and the torque current, but these fluctuation rates vary depending on the motor model, and the torque current is large. In many cases, the torque current and the rotational speed fluctuate in association with each other, such that the fluctuation with respect to the rotational speed becomes small.

Therefore, in this embodiment, as described above, both the detected current i and the detected speed ω are input to the current control gain reduction section 13, and this causes the above-mentioned FIG.
The characteristics of the respective motors are combined by combining the reduction of the current control gain based on the torque current shown in (a) and (b) with the reduction of the current control gain based on the speed shown in FIGS. 6 (a) and (b). In addition, the combination of these two types of gain reduction can be selected from the case of addition and the case of multiplication.

First, FIG. 7 shows an embodiment in which the gain reduction based on the torque current shown in FIG. 5A and the gain reduction based on the rotation speed shown in FIG. 6B are combined. ) Is an embodiment in which both gains are added, and FIG. 7B is an embodiment in which gains are multiplied.

In the case of FIG. 7, as the torque current increases based on the inductance variation of the actual machine shown in FIG. 3, the gain is reduced from the maximum to about 60% in the region where the torque current is, for example, 125% of the rated value. At the same time, based on the variation of the inductance with respect to the speed change in FIG. 4, the gain is reduced along with the speed increase from the stop time to the rated speed.

Here, the minimum is about 70 with respect to the set gain.
% Has been reduced. Therefore, when these are combined,
At high speed and high torque, the gain reduction becomes stronger, and as shown in FIG.
When both gain reduction rates are multiplied as shown in (b), the control gain decreases to a minimum of about 42% of the set value, so the reduction rate is adjusted according to the characteristics of the actual machine so that the responsiveness does not deteriorate. Need to decide.

Next, FIG. 8 shows an embodiment in which the reduction based on the torque current of FIG. 5 (a) and the reduction based on the speed of FIG. 6 (a) are combined. Here, FIG. ) Is a case where both are added, and FIG. 7B is a case where both are multiplied. In these cases, the gain reduction rate at high torque and the gain reduction rate in the locked state can be adjusted almost individually.

For example, in the case of the multiplication of FIG. 8 (b), the control gain at high speed and high torque is the reduction rate up to 60% set in FIG. 5 (a), while the control gain at stop is For example, referring to the speed in Fig. 5 (b), the speed is set to about 60%. If more torque is applied in the locked state, the current increases and the gain decreases in Fig. 5 (a), which causes the control system to oscillate. It can operate without doing.

Next, FIG. 9 shows a case in which the reduction based on the torque current shown in FIG. 5 (b) and the reduction based on the speed shown in FIG. 6 (a) are combined, and the gains of both are added here. The embodiment in the case is FIG. 9 (a), and the embodiment in the case of multiplication is FIG. 9 (b). With this combination, oscillation at high torque is suppressed, and oscillation at stop is suppressed and stabilized. At this time, since the gain is not reduced at the rated time, the responsiveness in the rated area can be secured.

For example, in the case of the multiplication shown in FIG. 9 (b), the reduction rate at high torque is about 60 at minimum as compared with FIG. 5 (b).
%, And the reduction rate in the locked state at stop is about 60 to 70% set in (a) of FIG.

Further, FIG. 10 shows an embodiment in which the reduction based on the torque current of FIG. 5 (b) and the reduction based on the speed of FIG. 6 (b) are combined, and the gains of both are added. In FIG. 10A, and the embodiment in the case of multiplication is shown in FIG.
(b) In this combination, the reduction rate becomes strong at high torque, the reduction with respect to speed change decreases as the speed increases, and at high speed it is reduced to about 50%.

It should be noted that the control gains combined at this time become small, as is apparent from FIGS. 10 (a) and 10 (b), and the response becomes worse. Especially Figure 1
In the case of the embodiment in which 0 (b) is multiplied, the change in the gain reduction becomes strong.

In the above embodiment, the gain reduction based on the torque current and the gain reduction based on the rotation speed are selected one by one, and two systems are combined. However, the present invention reduces the reduction at the time of stop. It is also possible to combine three or more systems to achieve gain reduction, such as reduction in high speed range and reduction at high torque.

However, when any control gain reduction is used, it is important to select an appropriate combination of reductions according to the actual motor characteristics and intended use and to set the gain reduction rate.

[0070]

According to the present invention, the reduction rates corresponding to the rotation speed and the current are set in advance, respectively, and the gain of the current control system is reduced by combining these, so that the rotation speed is high and high. Even in a region where rapid acceleration / deceleration is repeated by torque and when high torque is applied during servo lock, oscillation can be sufficiently prevented and stable operation can be performed.

[Brief description of drawings]

FIG. 1 is a control block diagram schematically showing an embodiment of a servo motor control device according to the present invention.

FIG. 2 is a control block diagram schematically showing an example of a q-axis current control system in an embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between motor output torque and winding inductance.

FIG. 4 is a characteristic diagram showing a relationship between a motor rotation speed and winding inductance.

FIG. 5 is a characteristic diagram showing the relationship between the torque current and the gain reduction rate of the current control system in the present invention.

FIG. 6 is a characteristic diagram showing the relationship between the detected speed value and the gain reduction rate of the current control system in the present invention.

FIG. 7 is a characteristic diagram showing an example of current control gain reduction characteristics according to the embodiment of the present invention.

FIG. 8 is a characteristic diagram showing another example of the current control gain reduction characteristic according to the embodiment of the present invention.

FIG. 9 is a characteristic diagram showing another example of current control gain reduction characteristics according to the embodiment of the present invention.

FIG. 10 is a characteristic diagram showing still another example of the current control gain reduction characteristic according to the embodiment of the present invention.

FIG. 11 is a control block diagram schematically showing an example of a servo motor control device according to a conventional technique.

[Explanation of symbols]

1 motor 2 Position detection device 3 speed detector 4 comparator 5 Speed control section 6 CT 7 Current detector 8 comparator 9 Current control section 10 PWM control unit 11 Power element 12 Servo motor controller 13 Current control gain reduction unit 14 Current control proportional integral calculation unit 15 Motor winding part

Continued front page    F term (reference) 5H303 AA01 AA10 BB06 CC03 DD01                       EE03 EE09 FF10 HH05 JJ02                       KK02 KK03 KK20 LL03 LL09                       MM05 QQ09                 5H550 AA18 BB04 DD04 FF07 GG03                       GG05 GG10 HA06 HB08 HB16                       JJ24 LL07 LL22 LL34                 5H576 AA17 BB03 DD02 DD07 EE01                       EE11 FF07 GG02 GG04 GG08                       HA01 HB01 JJ24 LL07 LL22                       LL41

Claims (6)

[Claims] 1. A servomotor control device for controlling a feedback gain of a current control system according to a change in inductance of a motor winding, wherein a means for detecting a rotation speed of the motor is provided, and at least the rotation speed of the motor is 0. The servo motor control device is configured such that the feedback gain is reduced in a low speed region including the. 2. A servo motor control device of a type that controls a feedback gain of a current control system according to a change in inductance of a motor winding, a means for detecting a rotation speed of a motor, and a means for detecting a current of the motor. And the feedback gain is reduced in at least one of a region where the rotation speed of the motor is in a low speed region including 0 and a region where the current of the motor is equal to or higher than the rated value of the motor. A servo motor control device having the above-mentioned configuration. 3. The servo motor control device according to claim 2, wherein the feedback gain is reduced by a preset reduction pattern. 4. The invention according to claim 2, wherein the reduction of the feedback gain is performed in accordance with the variation of the inductance so that the current given to the motor whose inductance decreases at high torque does not become excessive. A servo motor control device having the following configuration. 5. The invention according to claim 2, wherein the reduction of the feedback gain is executed at least in a region where the rated torque of the motor is exceeded and the maximum torque is reached. A servo motor control device, characterized in that the servo motor control device is configured so as to secure and suppress oscillation at high torque of the motor. 6. The invention according to claim 2, wherein the feedback gain is reduced by a combination of at least a control gain reduction rate based on a current detection value of the motor and a control gain reduction rate based on a speed detection value. The servo motor control device is configured so as to be both controlled by the adjustment and to prevent oscillation due to a decrease in winding inductance when the motor has a high torque and to suppress oscillation when the motor is stopped. .