JPS59231602A - Control system of feedback loop control system - Google Patents

Abstract

PURPOSE:To improve the response of a feedback loop by holding a minor feedback at zero when the controlled variable of a controlled system is smaller than a specific value. CONSTITUTION:When a detector 35 detects the differential value of a current being larger than a specific reference value, the detector 35 turns on a switch 34. Consequently, a current variation rate control loop is constituted, and the variation rate of the current is brought under feedback control under a current variation command Vrr. In this case, a limiter operates, so the absolute value of a current variation rate command becomes constant, so only the current variation rate control loop operates. The variation rate of the current decreases below the specific reference value by following up a command Vcr, and then the feedback signal of the current variation rate control loop goes down to zero through the turning-off operation of the switch 34, so that only the current control loop is left. The current variation rate loop is turned off to increase the gain of the current control loop.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for a feedback control system including a major feedback loop and a minor loop located inside the loop.

[Background of the invention]

In general, a feedback control system includes a control element that obtains a manipulated variable from a control operation signal obtained by comparing a reference input signal with a feedback signal, a controlled object that is controlled by the manipulated variable from the control element, and control of the controlled object. and a feedback element for forming a feedback signal from the quantity. Furthermore, it is a well-known convention that a control element, a controlled object, and a feedback element are regarded as one loop, and this is called a feedback loop.

By the way, in order to improve the quality of control, there is a feedback control system in which another feedback loop is provided inside one feed pack loop for control. It is also well known that the former feedback loop is called a major feedback loop, and the latter feedback loop is called a minor feedback loop.

According to such a feedback control system, a control operation signal is formed based on the result of comparing a reference input signal and a major feedback signal, this control operation signal is compared with a minor feedback signal, and the operation obtained from the comparison result is Control the controlled object using quantity. According to such a feedback control system, the influence of disturbance can be significantly reduced compared to a single loop system. Therefore, in the case of a feedback control system having a major feedback loop and a minor feedback loop as described above, the response of the minor loose is set to be several times faster than the response of the major loop in order to avoid interference between the two loops. ing. Therefore, it is often impossible to provide a filter or other element that slows down the response for minor looseness.

Therefore, when the controlled variable of the controlled object changes intermittently and the average value of the controlled variable does not change, even though the minor loose feedback signal should originally be zero, It will be output. As a result, the control element outputs an operation amount corresponding to the minor feedback signal, which is undesirable for the operation of the control element.

[Purpose of the invention]

The present invention has been made in view of the above problems, and its purpose is to provide a control method for a feedback control system that increases the response of the feedback loop of the feedback control system.

[Summary of the invention]

In order to achieve the above object, the present invention is characterized in that the minor feedback signal is set to zero when the rate of change of the controlled variable of the controlled object is below a certain value.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings, but before that, the matters that are the basis of the present invention will be explained.

FIG. 1 is a block diagram showing a stationary Leonard speed control system as a specific example of the feedback control system that is the basis of the present invention.

In this figure, the symbol ■sr is a speed command that is compared with sb and a speed feedback signal vsb, and the deviation as a result of the comparison is applied to the speed controller 11. This speed controller 11 receives a limited current command.
It is configured to be able to output Crtl-. The current command vCr from the speed controller 11 and the current feedback signal vcb are compared, and the deviation as a result of the comparison is applied to the current controller 12. The current controller 12 is configured to output a limited current change rate command RR. The current change rate command ``rr'' from the current controller 12 is compared with the current change rate feedback signal, and the deviation of the comparison result is supplied to the current change rate controller 13. The current rate of change controller 13 is capable of supplying a control signal to the gate pulse generator 14 . The gate pulse generator 13 is
It has a function of controlling the phase of the gate pulse using the control signal, and is connected to supply the gate pulse to the thyristor power converter 15.

The power converter 15 outputs a voltage corresponding to the gate pulse and supplies it to the electric motor 19.

Reference numeral 16 denotes a speed feedback controller, and the controller 16 has a function of converting the voltage from the speed generator 20 connected to the rotating shaft of the electric motor 19 and detecting its speed into a speed feedback signal vsb. have.

Further, reference numeral 17 is a current feedback controller, and this controller 17 generates a current feedback signal v from a signal from a current detector CT that detects the current flowing through the motor 19.
It has a function to convert to cb. Reference numeral 18 denotes a current change rate feedback controller, and this controller 19 has a function of forming a current change rate feedback signal Vrb from the current feedback signal vcb. Although not shown, a voltage feedback loop is provided inside the current change rate feedback loop.

The operation of the device configured as described above will be explained.

In the figure, a speed command ysr and a speed feedback signal vsb are added by an adder 10, and the result is applied as a deviation to a speed controller 11 to control the speed. The speed controller 110 output VCr is a limited current command, and the deviation between this current command ver and the current field VCb is applied to the current controller 12 to control the current so that it does not exceed the allowable value of the motor. . Output of current controller 12 ■r
r is a limited current change rate command, and this current change rate command ■rr and current change rate feedback signal vrb
By applying the deviation from the current change rate to the current change rate controller 13, the current change rate is controlled so as not to exceed the allowable value of the motor.

The output of the current change rate controller 13 is connected to the gate pulse generator 14.
The generator 14 controls the phase of the gate pulse of the thyristor power converter 15 . This gate pulse controls the terminal voltage Vt applied from the power converter 15 to the DC motor 19, thereby controlling the terminal voltage Vt applied to the DC motor 19.
9 rotational speed is controlled.

By the way, if we take note of the above configuration and pay attention to the current control unit, we will find that there is a function to feedback control the current flowing to the motor 19 in response to the current command 19
There is a configuration that has a function of feedback controlling the rate of change of the current flowing through the circuit. It can be understood that in this configuration, the current feedback loop corresponds to a major feedback loop, and the current rate of change feedback loop corresponds to a minor feedback loop.

It can be understood that the current command ■Cr corresponds to a reference input signal, the feedback signal vcb corresponds to a minor feedback signal, the current change rate command vrr corresponds to a control operation signal, and the feedback signal vrb corresponds to a minor feedback signal.

FIG. 2 is a block diagram showing the current control loop with the above-mentioned major foot loop and minor foot loop using a transfer function, etc. In this diagram, reference numeral 22 indicates the control of the current controller 12. The content is proportional control (KC) with limit (lV'rl). 23 is the current change rate flitl. 31. is the transfer function of the generator 11 and the power converter 15, and proportional 32 is a transfer function from the output voltage Bt of the power converter 15 to the motor current Id, 33 is a transfer function from the current 1d to the motor transmitted electromotive force EC, and 27 is a current feedback gain; 28 is a current change rate feedback gain.

The operation of the current control loop with such a block configuration is explained in the first section.
This will be explained with reference to FIGS. 3 to 3. Note that FIG. 3 is a waveform diagram showing the current response waveform of FIG. 2, with the vertical axis representing the waveform of each part and the horizontal axis representing time.

In the figure, for example, if there is a large change in the speed command vsr or the speed feedback vsb, the current command ■Cr changes in a stepwise manner/(Time [0 in Figure 3) o At this time,
The current change rate command ■rr also changes stepwise, and the current Id
The output is output during the period in which there is a change in the flow until the current reaches a steady state (time 1o-1 in Figure 3). That is, the current command vCr, the current feedback signal VCb, the nine deviation ε, and the current Id are given as the following equation: Id(t)=Io+ -t, l t l >
-LM-a-r ΔT KC However, t≦t1・・・・・・・・・
・(1) KC Id(t)=Id(tt)+ΔId(1-exp((t
h) )+ΔT Vr1 1ε1ku□ KC However, 1>11 ・・・・・・・・・
・(2) Note that r is the current rated value, ΔI d = I
d-Id(to).

Δ'1'=t, -t.

By the way, the current d flowing through the DC motor 19 includes a large ripple value. Furthermore, the response of the current rate of change control loop is set to be several times faster than that of the current control loop in order to avoid the mutual interference between the control loops described above. Therefore, a filter cannot be connected to the current change rate feedback controller 18. As a result, the current I
Even if there is no change in the average value of d (that is, the current rate of change is zero), the current rate of change feedback signal vrb should be zero, but it does not become zero and a ripple value remains. Since this ripple value is applied to the generator 14 via the current rate of change controller 13, the gate pulse of the generator 14 fluctuates, and this fluctuation causes the power converter 15 to change.
output voltage fluctuates. Naturally, this fluctuation becomes larger as the gain of the current change rate control loop becomes larger. the result,
When the ripple fluctuation of the output voltage from the power converter 15 increases, it becomes impossible to stably commutate the switching elements of the power converter 15. Therefore, even though the gain of the current change rate control loop is originally required to be set high, it is actually limited. This is because tolerance is provided for ripple fluctuations in the output voltage of the power converter 15 so that the switching elements of the power converter 15 can stably commutate.

Furthermore, such a restriction suppresses the gain of the optical control loop, which in turn suppresses the gain of the speed control loop, which ultimately results in a suppressed speed response.

FIG. 4 is a block diagram showing an embodiment of the control method of the feedback control system according to the present invention. In Figure 4,
Components that are the same as those in the above configuration are given the same reference numerals, explanations thereof are omitted, and they will be handled in the same manner hereinafter.

The embodiment of FIG. 4 differs from the configuration of FIGS. 1 and 2 in that a switch 34 is provided at the output section of the current change rate feedback controller 18, and the output signal from the current change rate feedback controller 18 is from the differential value (i.e., the control l
A current change rate presence/absence detector 35 is provided to detect whether or not the current change rate (1d change) is present, and when the current change rate is within a certain reference value, the switch 34 is turned off and the current change rate feed/ vrb is set to zero, and when the current change rate exceeds a certain reference value, the switch 34 is turned on to supply the current feedback signal vrb to the abutting section.

The operation of such a configuration will be explained below with reference to FIGS. 5 and 6.

First, if the differential value of the current is above a certain reference value, the detector 3
5, the detector 35 turns on the switch 34. As a result, a current change rate control loop is formed, and the current is subjected to change rate feedback control in accordance with the current change rate command RR. In this case, a limiter is applied, so
Since the absolute value of the current change rate command becomes constant at yrr==lVrl, only the current change rate control loop operates (periods 1o to tl in FIG. 3).

This means that did/dt == constant, in other words,
Since this is a case where the rate of change of the current Id is constant, the current control loop becomes as shown in FIG. In other words, the current controller 22 continues to output a constant output yr (from 10 to t in FIG. 3).
, period), at this time, no current control is performed in the transfer function 22, and '7 r is set as the time constant T in the current change rate controller 23.
Since it is only integrated by r, the current Id changes with a time constant ΔT. Therefore, these relationships are given by the following equation 1. Next, when dId/dt is constant, in other words, when the rate of change of current d is not constant, the current control loop is as shown in FIG. It will be like this. That is, current controller 2
2 is a state in which the transfer functions 22 and 23 operate simultaneously after escaping from the constant output range (period from time t1 to time tl in FIG. 3). Therefore, these relationships are as shown in the following equation.

Therefore, in this embodiment, when the current feedback VCb follows the command vCr and the current change rate becomes below a certain reference value, the feedback signal in the current change rate control loop becomes zero because the switch 34 is turned off. No, there is only a current control loop (major feedback loop).

Turning off the current rate of change loop and making the feedback signal zero has the following meaning.

In other words, the closed loop gain between the command vrr and the controlled variable in the current rate of change control loop is about 1, whereas in the absence of the current rate of change control loop, the closed loop gain between the command ■rr and the controlled variable I
The gain with respect to d is much larger. As a result, the gain of the current control loop increases. In particular, considering that the output of the current rate of change loop controller 28 is essentially zero when the current is intermittent, there is no problem even if the current rate of change feedback loop is turned off, and the main When the switch 34 is turned off based on a command from the detector 35, the current change rate control loop is turned off, and the gain of the current control loop is reduced due to a sharp increase in circuit resistance. can be raised. As a result, the decrease in response can be improved.

FIG. 7 is a block diagram showing a second embodiment of the present invention. The difference between the embodiment shown in FIG. 7 and the configuration shown in FIG. 4 is that if the current change rate controller 23 is of an integral type,
The point of comparison with the current change rate feedback signal is set after the controller 23, the deviation input to the current controller 22 is input to the detector 35, and the change rate feedback signal is combined with the signal from the current detector 27. That's the point. Even with this configuration, the same effects can be achieved, and there is no need to provide a differentiator. Here, the current change rate is the deviation 1vcr+
I'm getting vcb+.

FIG. 8 is an application example of FIG. 7, and the difference from the configuration in FIG.
It is at the point where b was input.

With this configuration, the same effects as those of the above embodiment can be achieved.

The above configuration can be realized not only by an analog control method but also by a digital node control method. When the above current rate control is implemented using a microcomputer, the following problems arise.

(1) Analog systems use instantaneous current waveforms to determine the firing phase, whereas microcontrollers can only use intermittent current values.

(2) A smoothing filter is required to control the average current, so a delay occurs. For this reason, calculating the change in average current will result in poor response.

(3) The current waveform controlled by the thyristor converter pulsates, so sampling and detecting the value at an appropriate point will not yield the correct rate.

In consideration of the above, it was decided here that the current rate and average current would be controlled using the configuration shown in FIG. That is, (1) control is performed using two feedback amounts: average current If and instantaneous current l. (2) For the instantaneous current if, a value near the time when the ignition pulse is generated is used. The current value at this point is a value determined by control calculation. (3) To simplify current detection, the ignition pulse is used as an interrupt pulse.

The configuration of the digital control system using the microcomputer shown in FIG. 9 will be explained below. In FIG. 9, reference numeral 51 is a microcomputer, and the microcomputer 51 outputs a processed signal to a gate pulse generation circuit 52. The gate pulse generation circuit 52 can apply its output 100 to the microcomputer 51 as an interrupt signal, and can also supply its output to the power converter 15 via the gate pulse amplifier 53. Also, 54
is an AC power source) and is connected to the power converter 15. A current detector CT is connected between the AC power supply 54 and the power converter 15, and the current detected from the detector CT is rectified by a rectifier circuit 55, and the rectified value is converted into an instantaneous value of the current it. The current can be supplied to the analog-to-digital (AD) converter 56 as an average value If of the current, and can also be supplied to the AD converter 56 via a filter 57 and an average value If of the current. This AD converter 56 is configured so that its conversion output can be supplied to the microcomputer 51.

The current control system configured in this manner operates as follows.

First, the microcomputer 51 executes the process shown in FIG. 10 every time an ignition pulse is generated. First, the instantaneous value of the current i, (n),
Detect the average value I f (n) (step 5ioo)
. Immediately after the ignition pulse occurs (as it is detected, the instantaneous value i,
(n) means the current at the time of ignition. Note that n means the n-th sampling point.

Next, step 81 in which overcurrent and four-quadrant switching were determined.
01.8102), the following current control calculation is performed to obtain the current rate command fR@(n) (step 8103
).

'R@('')'''±111-(IIC(n) If(
n) When l≧ε1) (5) il, , (n)=k. (IC(n) −I f (n)
)(l I C(n) −I f(n) + <61
(6) where %jRsm is the rate limit value, and ε1 is the current deviation at the time when the limit value is reached.

The current rate feedback amount 1it(n) is determined using the following equation (step 8104).

i, , (n)=='l'r (11(n) t,
(n 1)/Td(”) =”(7)Td(n)
-("(n)-" (n-1) + ff/3)/2y
r f (8) where α(n) is the ignition phase and f is the power supply frequency.

Here, the current rate feedback amount shown in equation (7)! m t
It is determined whether (n) is less than or equal to a certain value (step 8105). In step 8105, current rate feedback ti
If it is determined that the drunkenness is below a certain value, step 5
The process moves to step 106, where the current rate feedback amount 1it=o is set, and the process moves to step 8107. However, if it is determined in step 5105 that the current rate feedback amount 1nt exceeds a certain value, the process moves to step 8107. Further, the current rate control calculation is performed using the following equation (step 8107).

VC(n)=VC(n 1)+(in-(n) 1
ir(n))/Ti...(9) Finally, inverse cosine correction is performed (step 8108),
□ Find α(n+1) using the following formula.

α(n+t) = cos-1vc(n),
, , , , , , Q(1 α(n
+1) is applied with a limiter in step 5109 and set in the gate pulse generation circuit, completing one process. By repeating this process every time a firing pulse is generated, current control including rate control is performed. Incidentally, this processing t is collectively represented by a block diagram in FIG. 11.

Note that step 5ito indicates current limiting processing when it is determined that an overcurrent occurs in step 5101, and step 511
1 indicates the switching control when it is determined in step 5102 that it is the four-quadrant switching point.

Here, FIG. 11 will be briefly described. Since this corresponds to about IIt to FIG. 4, the corresponding parts will be given the same reference numerals as the configurations in FIG. 4.

Also, ■Cr, ■Cb, ■rr and vr in FIG.
b corresponds to I'@I f@'IIs and ill, respectively. It also shows that the switch SW is closed for each ignition pulse, and is otherwise open.

The present invention can also be realized using the digital control method as described above.

〔Effect of the invention〕

As described above, according to the present invention, the control method performs feedback control using a major feedback signal and a minor feedback signal, and the minor feedback signal is set to zero when the rate of change of the control amount is below a certain value. This has the effect of improving feedback loose response.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the stationary Leonard speed control system that is the basis of the present invention, Fig. 2 is a block diagram showing the current control system with current change rate control loop of Fig. 1, and Fig. 3 is a block diagram showing the current control system with current change rate control loop. Waveform diagram shown to explain the operation of the control system in Figure 4.
5 is a block diagram showing the control method of the feedback control system according to the present invention, FIG. 5 is a block diagram showing the state when the control method shown in FIG. 4 has a constant current change rate, and FIG.
The figure is a block diagram showing a state when the control method shown in Fig. 4 cannot maintain a constant current change rate, Fig. 7 is a block diagram showing another embodiment of the present invention, and Fig. 8 is a block diagram showing another embodiment of the present invention. 9 is a block diagram showing a configuration when the embodiment of the present invention is realized using a microcomputer, and FIG. 10 is shown to explain the operation of the configuration of FIG. 9. Flowchart FIG. 11 is a block diagram showing a functional configuration to explain the operation of FIG. 9. 11... Speed controller, 12... Current controller, 13.
... Current change rate controller, 14... Gate pulse generator, 15... Thyristor power converter, 16... Feedback controller, 17... Current feedback controller, 18... Current change rate Feedback controller, 19.
... DC motor, 20... Speed generator, 22... Transfer function of current controller 12, 23... Transfer function of current change rate controller 13, 27... Current detection gain, 28...
・Transfer function of current change rate feedback controller 18, 3
1... Transfer function of gate pulse generator 14 and power converter 15, 34... Switch, 35... Current change rate presence/absence detector. Funeral figure 2 is also 30 Foil 4-Figure 7 Funeral figure 8 c6 Mo9 figure 5'/ 1tJy Funeral lI figure, Zt5'/

Claims (1)

[Claims] 1. A control signal formed based on the result of comparing a reference input signal and a major loop feedback signal is compared with a minor feedback signal, and a controlled object is controlled using the manipulated variable obtained from the comparison result. 1. A control method for a feedback control system, characterized in that the minor feedback signal is set to zero when the rate of change of the control amount in the controlled object is less than or equal to a predetermined value. 2. A control method for a feedback control system according to claim 1, wherein the rate of change of the control amount is obtained by performing a differential operation on a major feedback signal. 3. A control method for a feedback control system according to claim 1, characterized in that the rate of change of the control amount is obtained from a comparison result between a reference input signal and a major feedback signal. .