JPH09271200A - Digital servo control equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve controllability by preventing change of output torque of a servo motor, in digital servo control. SOLUTION: A current forecasting means forecasts the d-axis component and the q-axis component of a load current in the actual control time by the calculation of the same dimension observer to digital servo control system, from the d-axis component and the q-axis component of a detected current, the d-axis component and the q-axis component of a calculated voltage, a detected rotation angle, and a detected angular velocity. A control means performs current control in response to feedback values of a current and the aimed value of a current which feedback values are the d-axis component and the q-axis component obtained by the current forecasting means, and the d-axis component and the q-axis component of a detected current. Time difference between the current detection time and the current control time can be eliminated, and the deviation of a current forecast value can be eliminated, so that torque vibration of a digital servo motor can be prevented and controllability is improved.

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, a target value and a feedback value are given as digital values, a deviation between the two is calculated by a digital computer, a command value corresponding to the deviation is given as a digital value, and a 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 feedback loop, the current is detected by the current transformer (CT), its output is amplified by the analog amplifier, and the output of the amplifier is sampled at a predetermined cycle and digitized.

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 a reactive current, and the q-axis component of the load current 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 a 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 excitation magnetic field and the reference axis of the armature coil, for example, in the rotary exciter-type synchronous motor, the rotation angle θ of the rotating magnetic field and the rotation armature-type synchronization. Regardless of the rotation angle of the armature in the motor and the rotation angle of the rotating magnetic field seen from the primary side (stationary coordinates) in the induction motor, only the DC component is present, which has the advantage of facilitating current control. The control cycle of the velocity feedback loop and the position feedback loop is set to an integral multiple of the current feedback loop.

In such a digital servo controller, current detection, current dq conversion, current deviation calculation, command voltage value calculation, dq inverse conversion, PWM control pattern output are calculated by a digital computer. As a result, because of the calculation time by the digital computer,
The actual current control time is delayed by the calculation time with respect to the current detection time. That is, at the current control time, the current value is already different from the detected value, and therefore current control is performed based on a value different from the actual current value, so that the control characteristics deteriorate and torque fluctuations occur. Will occur. In order to solve this problem, the d-axis component and the q-axis component of the load current at the actual control time are predicted by the calculation by the same-dimensional observer for the digital servo control system, and the d-axis component of the predicted load current and the A digital servo control device has been disclosed in which a q-axis component is used as a current feedback value, current control is performed according to the value and a target value of the current, and a time difference between a current detection time and a control time is eliminated. (Kaihei 5-204461).

[0005]

However, in the above disclosed technique, the predicted value used as the feedback value may deviate from the actual value due to the bus voltage fluctuation of the inverter, a non-linear element, an error in the motor constant, and the like. Therefore, there is a problem that the control characteristics of the digital servo control device are not good.

The present invention has been made to solve the above problems, and an object thereof is to prevent fluctuations in output torque of a servo motor due to fluctuations in the bus voltage of an inverter in a digital servo control device and to improve control performance. Is to improve.

[0007]

Means for Solving the Problems In order to solve the above problems, the means described in claim 1 can be adopted. According to this means, the load current of the polyphase AC servomotor is sampled at a predetermined control cycle, and the current feedback value is provided as a current feedback value. The current feedback loop digitally controls the load current according to the value and the target value of the current. In the digital servo control device, the current detecting means detects the d-axis component and the q-axis component of the load current of the AC servo motor at each sampling time. The angle detecting means detects the rotation angle of the servo motor at each sampling time, and the speed detecting means detects the rotation angular speed of the servo motor at each sampling time. Then, the digital servo control system is used by using the detection value by the current detection means, the d-axis component and the q-axis component of the voltage applied to the AC servo motor at each sampling time, the detection value by the angle detection means, and the detection value by the speed detection means. To the d-axis component and the q-axis component of the load current at the actual control timing by the current predicting means. The current control means performs the current control according to the respective values and the target value of the current, using the predicted value by the current predicting means and the detected value by the current detecting means as feedback values. The predicted value of the current may deviate from the actual value due to fluctuations in the inverter bus voltage, non-linear factors, or errors in the motor constants. The error due to the deviation is eliminated, the torque fluctuation is prevented, the gain can be increased, and the control performance is improved.

According to the second aspect of the invention, the first computing means for obtaining the proportional term from the deviation between the target value of the current and the feedback value from the current predicting means, the target value of the current and the current detecting means. The current control means is composed of the second calculation means for obtaining the integral term from the cumulative value of the deviation from the feedback value from and the third calculation means for obtaining the voltage command value for current control from the proportional term and the integral term. This makes it possible to implement the means described in claim 1 more effectively.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on specific embodiments. FIG. 1 is a block diagram showing the configuration of a digital servo controller according to the present invention. The digital servo controller 10 is mainly a CPU
11, ROM 12, RAM 13, digital signal processor (hereinafter referred to as "DSP") 14, common RAM 1
7. A / D converters 15a and 15b and current value counter 1
6. A keyboard (KB) 21 and a CR are provided to the CPU 11 via an interface (IF) 19.
The T display device 22 is connected.

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 servo motor 31, and the load voltage of the servo motor 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 determining 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 by the SP 14 as a current position feedback value, 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 target current value with the predicted current feedback value to calculate the current deviation. Based on the instantaneous current deviation at that time and the cumulative value of the instantaneous current deviation, that is, by the proportional-plus-integral calculation,
The instantaneous voltage command value at the current control time is calculated. The instantaneous voltage command value is compared with a 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 becomes 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. A lower feedback loop requires 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. If it is the position deviation calculation timing, 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
If it is the speed deviation calculation timing in the p speed 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 and the speed control cycle D are used to determine the electrical angular speed in the current speed control period. The current value ω (p) of is calculated by the following equation.

[0020]

[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 for the axis and q-axis components are calculated. This speed feedback control is executed at the timing indicated by the signal S2 in FIG.

Next, at step 114, 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, the electrical angle of this time is calculated. Acceleration A (p) is calculated by the following equation.

[0023]

[Equation 2] A (p) = (ω (p) −ω (p-1)) / D (2) Next, the process proceeds to step 116, where the current execution cycle is the nth time.
It is determined whether 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 the 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 the present embodiment, as shown in FIG. 3, the current control is delayed by one current control cycle by T 1 as compared with the current detection, and the time delay is performed after the current control of the Nth current control cycle is performed. Instead, the current detection in the (N + 1) th current control cycle is performed. That is, it is assumed that the current control time of the Nth current control cycle and the current detection time of the N + 1th current control cycle are the same.

[0025]

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

## EQU4 ## θ (n + 1) = θ (p) + ω (p) (n + 1) T (4) where T is the 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.

[0027]

(Equation 6)

As 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)
From the axis component Iq (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.

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 the induced voltage constant Φ of the servo motor and the electrical angular speed ω at the current detection time.
It is calculated by Eq (n) = Φ × ω (n) using (n).

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), speed electromotive force q-axis component Eq (n), voltage command value
From the d-axis component Vd (n) ^* and the q-axis component Vq (n) ^* , the current control time (n
D-axis component Id (n + 1) ', q-axis component of the predicted current value at (+1)
Iq (n + 1) 'is calculated.

Next, the same-dimensional observer will be described. Voltage d-axis component Vd, q-axis component Vq and current d-axis component I
The following relationship holds between the d and q axis components Iq.

(Equation 7)

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

[0034]

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

[0035]

[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. For this control system, a control system exhibiting similar transfer characteristics is constructed, and the same-dimensional observer is constructed as shown in FIG. In the actual control system and the same-dimensional observer, the transfer function of each block is the same. Regarding the transfer characteristics of the same-dimensional observer shown in FIG. 5, the following relational expression holds.

[0037]

(Equation 12) As the matrix tilt A and tilt B, the transfer matrix in the digital control system is used as defined by the equations (10) and (11). Thus, according to Eq. (12), the d-axis component Id (n + 1) 'and the q-axis component Iq (n +
1) 'can be obtained.

Next, returning to step 126 in FIG. 2, the d-axis component and the q-axis component of the current target value set in step 112 (
The current target value remains unchanged during the speed control cycle. That is, the current target 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.
The deviation of the q-axis component Iq (n + 1) 'and the d-axis component of the current target value
Depending on the accumulated value of the deviation between the d-axis component Id (n) and the q-axis component Iq (n) of the detected current value for the q-axis component, the current control time (n +
The d-axis component Vd (n + 1) ^* and the q-axis component Vq of the voltage command value in 1)
(n + 1) ^* and are calculated. The block diagram of the control system in step 126 is as shown in FIG. 6, and the d-axis component Vd (n + 1) ^* and the q-axis component Vq (n + 1) ^* of the voltage command value are (13) It is represented by a formula.

[0039]

(Equation 13) Here, Id ^* and Iq ^* represent the d-axis component and the q-axis component of the target current value, respectively. Also, K _I = K / T. Incidentally, (13)
In the equation, the first term and the second term on the right side correspond to the first computing means and the second computing means, respectively, and the entire right side corresponds to the third computing means. Then, in step 128,
The voltage command values Vd (n + 1) ^* , Vq (n + 1) ^* are subjected to inverse dq conversion, and the voltage command values Vu (n + 1) ^* , Vv (n for each phase at the current control time (n + 1) +1)
^* , Vw (n + 1) ^* is calculated.

[0040]

[Equation 14]

Next, in step 130, the level relationship between the phase voltage command values Vu (n + 1) ^* , Vv (n + 1) ^* , Vw (n + 1) ^* and the high frequency triangular wave is utilized. That is, the on-time of the PWM signal of each phase is calculated using the average voltage method. Then, in step 132, the on-time is set in each timer incorporated in the DSP 14, and the PWM signal of each phase which becomes high level for the set time is output to the inverter 25. Although not explicitly shown, dead time processing is performed so that 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, and 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 116 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, the known voltage value of the commercial power source may be used as the initial value in the current prediction calculation formula (12). Alternatively, instead of the command values Vd (n) ^* and Vq (n) ^* of the voltage when the current is detected (n), the voltage may be obtained by actual measurement. Further, the angular velocity ω (n) may be obtained by a tacho generator.

[0044]

As described above, 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 calculated voltage, the detected rotation angle, 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-dimensional observer for the digital servo control system from the detected rotational angular velocity, and the load obtained by the current predicting means. The d-axis component and the q-axis component of the current and the d-axis component and the q-axis component of the load current detected by the current detecting means are used as current feedback values, and the current control is performed according to those values and the target value of the current. Since the current control means is provided, the current value at the future current control time can be predicted, and the current can be controlled by using the predicted current value as the current feedback value. The ability. Therefore, the time difference between the current detection time and the current control time can be eliminated, so that torque vibration of the digital servo motor 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 the timing 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.

FIG. 6 is a block diagram of a control system when a current target value is input and a voltage command value is output.

[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

Front page continuation (72) Inventor Yuji Oba 1-1 Asahi-cho, Kariya city, Aichi Toyota Koki Co., Ltd. (72) Inventor, Katsuhiro Asano 1 41st Yokomichi, Nagakute, Nagakute-cho, Aichi-gun, Aichi Prefecture Toyota Central Research Institute Co., Ltd.

Claims (2)

[Claims] 1. A current feedback loop for digitally controlling a load current according to a value of a load current of a multi-phase AC servomotor sampled at a predetermined control cycle and used as a current feedback 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, d-axis component and q-axis of the current detected by the current detection means Component, dq locus of applied voltage of the AC servomotor at each sampling time From the d-axis component of the reactive voltage component and the q-axis component of the effective voltage component in the standard system, the rotation angle detected by the angle detection means, and the rotation angular velocity detected by the speed detection means, the same for the digital servo control system A current predicting unit that predicts a d-axis component and a q-axis component of the load current at an actual control time by a calculation by a dimensional observer; a d-axis component and a q-axis component of the load current obtained by the current predicting unit; A d-axis component and a q-axis component of the load current detected by the current detection means as current feedback values, and current control means for performing current control according to each value and the target value of the current. Characteristic digital servo controller. 2. The current control means, first computing means for obtaining a proportional term from a deviation between the target value of the current and the feedback value from the current predicting means, the target value of the current and the current detecting means. From the cumulative value of the deviation from the feedback value from the second calculation means for obtaining an integral term, and a third calculation means for obtaining a voltage command value for current control from the proportional term and the integral term. The digital servo control device according to claim 1, which is characterized in that.