JPH05204461A - Digital servo control device - Google Patents

Abstract

PURPOSE:To improve the control performance by preventing the output torque fluctuation of a servo motor by performing a feedback control by predicting current value at a future current control time from the current/voltage at a sampling time for current detection by a calculation by the same dimension observer. CONSTITUTION:The load current of a servo motor 31 is detected by CT 32a, 32b and a sampling is performed for the current by A/D conversions 15a, 15b after it is amplified. As for the servo motor 31, the present location is detected in a pulse encoder 33, it is inputted in a present value counter 16 via a waveform forming/direction discrimination circuit 34, and speed and current target value are calculated based on the target value from a CPU 11 by a DSP 14. A dq conversion is performed for the sampled load current by the DSP 14 and the current value at the time is predicted and calculated based on the detection value. Then, based on the current target value and the predicted current value, an instantaneous current command value at the control time is calculated, a voltage control PWM signal is generated and load current is controlled to the target value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital servo control device for digitally controlling an AC servo motor, and more particularly to a device for preventing torque fluctuation.

[0002]

2. Description of the Related Art In recent years, digital servo control devices have come to be used in order to solve the drawbacks of analog control systems. In this digital servo control device, the target value and the feedback value are given as digital values, the deviation between them is calculated by a digital computer, the command value corresponding to the deviation is given as a digital value, and the control amount is adjusted according to the value. It is digitally controlled. Such servo controllers typically include position, velocity and current feedback loops.

In the current feedback loop of the above feedback loops, current is detected by a current transformer (CT), its output is amplified by an analog amplifier, and the output of the amplifier is sampled at a predetermined cycle and digitized. It

Then, the detected currents of the respective phases are dq-converted, and the d-axis component and the q-axis component thereof are controlled so as to be equal to the target value of each axis. The d-axis component of the load current means the reactive current, and the q-axis component is proportional to the torque of the servo motor when the servo motor is a synchronous motor and the magnitude of the exciting magnetic field is constant. Therefore, in the case of the synchronous motor, the current feedback control is controlled so that the d-axis component of the detected load current becomes zero and the q-axis component becomes equal to the target value of the output torque.

As described above, the d-axis component and the q-axis component are the electrical angle formed by the exciting magnetic field and the reference axis of the armature coil. For example, in a rotary exciter type synchronous motor, the rotating angle θ of the rotating magnetic field In the armature type synchronous motor, the rotation angle of the armature,
An induction motor has the advantage of facilitating current control because it has only the DC component regardless of the rotation angle of the rotating magnetic field seen from the primary side (stationary coordinates). The control cycle of the velocity feedback loop and the position feedback loop is set to an integral multiple of the current feedback loop.

[0006]

However, in the above digital servo control device, current detection and current d
q conversion, current deviation calculation, command current value calculation, dq inverse conversion,
The PWM control pattern output is calculated by the digital computer. As a result, the actual current control time is delayed from the current detection time by the calculation time due to the calculation time by the digital computer. That is,
At the current control time, the current value is already different from the detected value, so current control will be performed based on a value different from the actual current value, resulting in poor control characteristics and torque fluctuations. It will be.

The present invention has been made to solve the above problems, and an object thereof is to prevent fluctuations in output torque of a servomotor in digital servo control and improve control performance.

[0008]

The configuration of the invention for solving the above-mentioned problems is to sample a load current of a multi-phase AC servomotor at a predetermined control cycle and set it as a current feedback value, and to set that value and the target of the current. In a digital servo control device having a current feedback loop for digitally controlling the load current according to the value, the d-axis component and q of the load current of the AC servo motor at each sampling time
Current detecting means for detecting the axis component, angle detecting means for detecting the rotation angle of the servo motor at each sampling time, speed detecting means for detecting the rotational angular speed of the servo motor at each sampling time, and alternating current at each sampling time Voltage detection means for detecting the d-axis component and the q-axis component of the voltage applied to the servo motor, and d of the detected current.
Axis component and q-axis component, d-axis component of detected voltage and q
A current predicting means for predicting the d-axis component and the q-axis component of the load current at the actual control timing by the calculation by the same dimension observer for the digital servo control system from the shaft component, the detected rotation angle, and the detected rotation angular velocity. The d-axis component and the q-axis component of the load current obtained by the current predicting means are used as current feedback values, and current control means is provided for performing current control according to the values and the target value of the current. .

[0009]

The current value at the future current control time is predicted and calculated from the current value and the voltage value at the sampling time of the current detection by the operation by the same dimension observer for the digital control system. The predicted current value is used as a current feedback value, a current command value is calculated from the value and a current target value, and the current is controlled according to the command value.

Therefore, the current value of the current at the actual control time is predicted and calculated, and the current is controlled based on the current value at that time. Therefore, since the time difference between the current detection time and the current control time can be eliminated, torque vibration of the digital servomotor is prevented and the control performance is improved.

[0011]

EXAMPLES The present invention will be described below based on specific examples. FIG. 1 is a block diagram showing the configuration of a digital servo controller according to the present invention. The digital servo control device 10 mainly includes a CPU 11 and a ROM.
12, RAM 13, digital signal processor (hereinafter referred to as "DSP") 14, common RAM 17, A / D converters 15a and 15b, and a current value counter 16. A keyboard 21 and a CRT display device 22 are connected to the CPU 11 via an interface 19.

The output of the DSP 14 is input to the inverter 25, which drives the servo motor 31 in accordance with the output signal of the DSP 14. A synchronous motor is used as the servomotor 31, and the load current of the servomotor 31 is controlled by the PWM voltage control of the inverter 25, and as a result, the output torque is controlled.

The u-phase and v-phase load currents of the servomotor 31 are detected by the CTs 32a and 32b, and the amplifier 18
It is amplified by a and 18b. The amplifiers 18a, 18
The output of b is input to the A / D converters 15a and 15b,
It is sampled at a predetermined cycle and converted into a digital value. The sampled value is input to the DSP 14 as a feedback value of the instantaneous load current. Further, a pulse encoder 33 is connected to the servo motor 31,
Its current position is detected. The output of the pulse encoder 33 is connected to the current value counter 16 via the waveform shaping / direction discrimination circuit 34.

The output signal from the pulse encoder 33 input to the current value counter 16 via the waveform shaping / direction discriminating circuit 34 adjusts the value of the current value counter 16. D
The value of the current value counter 16 is read as a current position feedback value by the SP 14, and the DSP 14
The position deviation is calculated by comparison with the target value output from the CPU 11. Then, the DSP 14 calculates the speed target value based on the position deviation.

The current position feedback value input to the DSP 14 is differentiated to calculate the speed feedback value. The DSP 14 compares the speed target value determined according to the position deviation with the speed feedback value to calculate the speed deviation, and calculates the current target value based on the speed deviation.

On the other hand, the load current detected by the CTs 32a and 32b is supplied to the amplifiers 18 and 18b and the A / D converter 15.
Input to the DSP 14 via a and 15b. Then, as will be described later in detail, the current value at the current control time is predicted and calculated as the current feedback value based on the detected current value at the current sampling time.

Then, the DSP 14 compares the current target value with the predicted current feedback value to calculate the current deviation. The instantaneous current command value at the current control time is calculated based on the instantaneous current deviation at that time, the cumulative value of the instantaneous current deviation, and the current target value, that is, by the proportional integral calculation. The instantaneous current command value is compared with the high frequency triangular wave, and a voltage control PWM signal for controlling on / off of each phase transistor of the inverter 25 is generated.

The voltage control PWM signal is sent to the inverter 2
5, and the transistors of each phase of the inverter 25 are driven. By the switching of the inverter 25, the load current of each phase is controlled to the current target value. The positioning of the servo motor 31 is C
The process is completed when the PU 11 determines that the output value of the current value counter 16 has become equal to the target position value.
The u-phase and v-phase load current values sampled by the A / D converters 15a and 15b are dq converted by the DSP 14.

The digital servo controller of this embodiment is
As described above, it is composed of three feedback loops of position, velocity and current. Lower feedback loops require higher responsiveness.For example, the lowest current feedback loop is 100 μs, the velocity feedback loop is several times that, and the position feedback loop is several times more synchronized. Data sampling is performed, and the processing of each feedback loop is performed.

Next, the operation of the apparatus of this embodiment will be described. The program of FIG. 2 is repeatedly executed by the DSP 14 at every predetermined minimum period. In step 100,
It is determined whether or not the current execution cycle is the position deviation calculation timing, and if it is the position deviation calculation tamming, step 102
At, the current value of the position held in the current value counter 16 is read, and the position deviation from the target value is calculated. next,
In step 104, a velocity target value is calculated according to the position deviation. This position feedback control is executed at the timing indicated by the signal S1 in FIG.

Next, at step 106, it is judged if the current execution cycle is the speed deviation calculation timing. First
In the case of velocity deviation calculation tamming in the p velocity control cycle, in step 108, the current value (electrical angle) θ (p) of the position held in the current value counter 16 is read. next,
In step 110, the current angular velocity (electrical angle) θ (p-1) of the position read at the time of the speed deviation calculation timing in the p-1st speed control cycle last time, and the speed control cycle D are used to determine the electrical angular speed in the current speed control period. The present value ω (p) of is calculated by the following equation.

[0022]

[Equation 1] ω (p) = (θ (p) -θ (p-1)) / D (1)

Further, the deviation from the speed target value set in step 104, that is, the speed deviation is calculated. And
In the next step 112, depending on the speed deviation, d
The target current values of the axis component and q-axis component are calculated. This speed feedback control is executed at the timing shown by the signal S2 in FIG.

Next, at step 114, the current electrical angle is calculated using the angular velocity ω (p-1) detected in the previous speed control cycle and the angular velocity ω (p) detected in the current speed control cycle. Acceleration A (p) is calculated by the following equation.

[0025]

[Equation 2] A (p) = (ω (p) -ω (p-1)) / D (2)
Next, in step 116, the current execution cycle is the nth
It is determined whether or not it is the current deviation calculation timing in the current control cycle. Note that n is one speed control cycle,
It is a value that changes from 1, 2, ..., and is related to the time of current detection and current control. If it is the current deviation calculation timing,
Go to step 118. Step 118 and subsequent steps are current feedback control, and this control is executed at the timing shown by the signal S3 in FIG.

In step 118, the electrical angle θ (n) during current detection and the electrical angle θ (n + 1) during current control in the nth current control cycle in the pth speed control cycle are calculated by the following equations.
In this embodiment, as shown in FIG. 3, the current control is delayed by one current control cycle compared to the current detection.
After the current control of the nth current control cycle is performed, the current detection of the (n + 1) th current control cycle is performed without a time delay. That is, the current control time of the nth current control cycle and the n + th
1 It is assumed that the current detection time of the current control cycle is the same.

[0027]

[Equation 3] θ (n) = θ (p) + ω (p) nT (3)

(4) θ (n + 1) = θ (p) + ω (p) (n + 1) T (4)
However, T is a current control period. Further, the electrical angular velocity ω (n) at the current detection time is interpolated by the following equation.

[Equation 5] ω (n) = ω (p) + A (p) nT (5)

Next, the routine proceeds to 120, where the current values Iu (n), Iv (n) of the u-phase and v-phase instantaneous load currents are converted into A / D converters 15a,
It is read from 15b. The current value Iw (n) of the w-phase instantaneous load current is calculated by Iw (n) =-(Iu (n) + Iv (n)). Then, in step 122, the current value of the current Iu
(n), Iv (n), and Iw (n) are dq converted, and the d-axis component Id (n) and the q-axis component Iq (n) at the current detection time are calculated by the following equation.

[0029]

[Equation 6]

As is well known, the dq coordinate system is d
The axis is in phase with the exciting magnetic field, and the q axis is the coordinate system with a 90 ° phase difference in electrical angle from the exciting magnetic field. The d-axis component represents the ineffective component and the q-axis component represents the effective component.

Next, at step 124, the d-axis components Id (n) and q of the current value of the detected current at the current detection time (n)
The d-axis component Id (n + 1) 'and the q-axis component Iq (n + 1)' of the predicted value of the load current at the current control time (n + 1) are calculated from the axis component Iq (n).

Next, the procedure will be described with reference to FIG.
In step 200, the q-axis component Eq (n) of the speed electromotive force of the servo motor at the current detection time is calculated by Eq (n) = Φ × ω (n) using the electrical angular velocity ω (n) at the current detection time. Is calculated.

Next, in step 202, by the operation by the same-dimensional observer for the digital control system,
D-axis component of detected current at current detection time (n) Id (n) _,
q-axis component Iq _(n), the speed electromotive force of the q-axis component Eq _(n), d-axis component Vd of the voltage command value (n) ^*, from the q-axis component Vq (n) ^*, the current control time (n + 1) d-axis component of the predicted value of current Id (n + 1) '
_, q-axis component Iq (n + 1) 'is calculated.

Next, the same-dimensional observer will be described. D-axis component of voltage Vd, q-axis component Vq and d-axis component of current
The following relationship holds between Id _{and the} q-axis component Iq.

[Equation 7]

Rewriting equation (7) above into a first-order differential equation for (Id, Iq),

[0036]

[Equation 8] Becomes Furthermore, by discretizing the above equation (8),
The following equation is obtained.

[0037]

[Equation 9] However,

[Equation 10]

[Equation 11]

The above equation (9) shows the characteristic between the current and the voltage of the servo motor, and shows that the current at the time (n + 1) can be predicted from the voltage and the current at the time (n). The transfer characteristic relating to the digital current control of the servo motor by the above equation (9) is expressed as shown in FIG.
FIG. 5 shows a same-dimensional observer in which a negative feedback circuit (a circuit having a transfer function tilt K) in which a control system showing similar transfer characteristics is configured is added to this control system, and error convergence is taken into consideration. To configure. In the actual control system and the same-dimensional observer, the transfer function of each block is the same except that the error feedback block is added to the same-dimensional observer.

Regarding the transfer characteristics of the same-dimensional observer shown in FIG. 5, the following relational expression holds.

[Equation 12] However,

[Equation 13] Is. As the matrix tilts A and B, the transfer matrix in the digital control system is used as defined by the equations (10) and (11). Further, the matrix tilt K is set appropriately in consideration of the convergence of the error. The matrix tilt e represents the prediction error at the n-th control, and should be converged to zero. Thus, using equation (12), it is possible to obtain the d-axis component Id (n + 1) 'and the q-axis component Iq (n + 1)' of the predicted current value during the n + 1st control without error. Becomes

Next, returning to step 126 of FIG. 2, the d-axis component and the q-axis component of the current target value set in step 112 (
The current target value is unchanged during the speed control cycle. That is, the target current value is equal to the current detection time (n) and the current control time (n + 1)) and is the d-axis component Id (n + 1) 'of the predicted current value.
Depending on the deviation of q-axis component Iq (n + 1) ', current control time (n + 1)
D-axis component Vd (n + 1) ^* and q-axis component Vq (n
+1) ^* and are calculated. Next, in step 128, the voltage command values Vd (n + 1) ^* , Vq (n + 1) ^* are inversely dq-converted by the following equation to obtain the voltage command values for each phase at the current control time (n + 1). Vu (n +
1) ^* , Vv (n + 1) ^* , Iw (n + 1) ^* are calculated.

[0041]

[Equation 14]

Next, at step 130, the level relationship between each phase voltage command value Vu (n + 1) ^* , Vv (n + 1) ^* , Vw (n + 1) ^* and the high frequency triangular wave is utilized. , That is, using the average voltage method,
The ON time of the PWM signal of each phase is calculated. Then, in step 132, by setting the ON time of each timer incorporated in the DSP 14, the PWM signal of each phase which becomes high level for the set time is output from the inverter 25.
Is output to. Although not explicitly shown, dead time processing is performed so that the two transistors in the same phase do not turn on at the same time when the PWM signal for each phase is generated.

In this way, the processing of one execution cycle is completed. This execution cycle is executed with the minimum control period, so that the current feedback loop is controlled by an integral multiple thereof, the velocity feedback loop is controlled by that integral multiple, and the position feedback loop is controlled by that integral multiple. , Steps 100, 106, and 114 set the number of times of judgment. By repeatedly executing the above-described cycle, the position, speed, and current feedback control is performed at the timing shown in FIG.

In the above embodiment, in the current prediction calculation formula (12), the command value of the voltage at the time of current detection (n)
The voltage may be obtained by actual measurement instead of Vd (n) ^* and Vq (n) ^* . Alternatively, the angular velocity ω (n) may be obtained by a tacho generator.

[0045]

According to the present invention, the d-axis component and the q-axis component of the detected current, the d-axis component and the q-axis component of the detected voltage,
Current predicting means for predicting the d-axis component and the q-axis component of the load current at the actual control time by the operation of the same dimension observer for the digital servo control system from the detected rotation angle and the detected rotation angular velocity, and the current prediction. Since the d-axis component and the q-axis component of the load current obtained by the means are used as the current feedback value, and the current control means for controlling the current according to the value and the target value of the current is provided,
It is possible to predict the current value at the future current control time,
The current can be controlled by using the predicted current value as the current feedback value. Therefore, the time difference between the current detection time and the current control time can be eliminated, so that torque vibration of the digital servomotor can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a digital servo controller according to a specific embodiment of the present invention.

FIG. 2 is a flowchart showing a processing procedure by a DSP used in the apparatus of the embodiment.

FIG. 3 is a timing chart showing timings of position, speed, and current feedback control by the DSP.

FIG. 4 is a flowchart showing a procedure for predicting a current value by the same dimension observer.

FIG. 5 is a block diagram showing a relationship between the same-dimensional observer and a digital control system.

[Explanation of symbols]

10 ... Digital servo control device 11 ... CPU 12 ... ROM 13 ... RAM 14 ... DSP (digital signal processor) 15a, 15b ... A / D converter 16 ... Current value counter 25 ... Inverter 31 ... Servo motor 32a, 32b ... Current transformer (CT) 33 ...
Pulse encoder

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[Procedure amendment]

[Submission date] October 19, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

[Title of the Invention] di di Tarusabo control device

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

Claims (1)

[Claims] 1. A current feedback loop for sampling a load current of a multi-phase AC servomotor at a predetermined control cycle to obtain a current feedback value, and digitally controlling the load current according to the value and a target value of the current. In the digital servo control device, the current detection means for detecting the d-axis component of the reactive current component and the q-axis component of the active current component in the dq coordinate system of the load current of the AC servomotor at each sampling time, and each sampling Angle detection means for detecting the rotation angle of the servo motor at time, speed detection means for detecting the rotation angular speed of the servo motor at each sampling time, and dq coordinate system of the applied voltage of the AC servo motor at each sampling time. D-axis component of reactive current component and q-axis component of active current component A voltage detecting means for detecting the voltage, a d-axis component and a q-axis component of the current detected by the current detecting means, and a d of the voltage detected by the voltage detecting means.
The load at the actual control time is calculated from the axis component and the q-axis component, the rotation angle detected by the angle detection means, and the rotation angular velocity detected by the speed detection means by the same-dimensional observer for the digital servo control system. A current predicting means for predicting a d-axis component and a q-axis component of the current, and a d-axis component and a q-axis component of the load current obtained by the current predicting means as a current feedback value, and the value and the target value of the current A digital servo control device having a current control means for performing current control according to the following.