CN104570729A - Improved smith predicting controller - Google Patents

Abstract

An improved Smith predicting controlling algorithm comprises the following steps: designing a fuzzy adaptive PID controller to replace an original PID controller, wherein the fuzzy adaptive PID controller mainly comprises a PID control regulator and a fuzzy inference engine, and modifying a PID control parameter according to a fuzzy control rule in real time by using an error e and the change rate ec of the error as the input of the controller and the kp, ki and kd of the PID control parameter as the output, so as to meet the requirements of e and ec for the self-regulation of the PID parameter at different moments; adding an inner feedback loop, sending a feedback signal to a predicting model and an input end of an actually-controller object by the inner feedback loop at the same time, comparing the feedback signal with the output of a main controller, using the difference as an input signal of the actually-controlled object and the predicting model and introducing an adaptive regulator. Therefore, the problem of deviation caused by the change of an open-loop gain parameter is solved by changing the value of a proportional controller continuously.

Description

A kind of follow-on Smith predictor controller

Art

The present invention relates to a kind of intelligent control algorithm, particularly relate to a kind of control algolithm of carrying out improving on the basis of conventional Smith prediction device.

Background technology

What the control system of current most numerical control device adopted is all PID controller, and PID controller design is simple, easy to operate, is convenient to realize, substantially meets the needs of most of control system.But, if there is larger time lag in system.Comprise delayed control system and usually there is larger overshoot, and regulating time is long, when there is extraneous factor interference, conventional PID controller cannot produce inhibiting effect substantially at once.Smith Prediction Control proposes the earliest specially for a kind of control program of delay system, and it is by pre-estimating the dynamic perfromance of system and compensating, and reduces overshoot and accelerate adjustment process.1974, Smith proposed a kind of predictor controller, i.e. Smith predictor controller.Smith predictor controller, on PID FEEDBACK CONTROL basis, introduces a predictive compensation link, makes closed loop transform function not containing purely retarded item.The ultimate principle of the method is the dynamic perfromance by estimating object, carries out the compensation of time lag with a prediction model, and compensator and controlled device form a not free delayed the generalized controlled object jointly.Thus the Traditional PID-Smith controller combined with Smith prediction device by PID controller is used widely.But PID controller and Smith prediction device all design based on mathematical models, poor to model parameter change adaptive faculty, and working conditions change is complicated in actual production process, be difficult to obtain accurate mathematical model, cause PID-Smith controller to be still difficult to obtain gratifying control effects.Current most research is all the Optimal flattening round PID controller and Smith prediction device.In the optimizing research of PID controller, a lot of research is all that PID controller and fuzzy control theory or neural network are combined together, and therefore various fuzzy composite controller, Fuzzy Self-adaptive PID, neuronal-acetylcholine receptor constantly appears in one's mind.What current use was many is Fuzzy Adaptive PID Control and this two large class of neuronal-acetylcholine receptor.The improvement of Smith prediction device also at development, and what use was more at present is the introducing that inner membrance controls prediction device and the adaptive controller combined with Smith prediction device, such as: gain-adaptive prediction device.The combination of various new technology and introducing, facilitate the development of control technology.

Summary of the invention

The object of this invention is to provide a kind of follow-on Smith predictor controller.For in shortage mathematical models and in the Large-lag System of parameter time varying, based on the Smith prediction device poor stability of PID controller and the large problem of overshoot, a kind of improved Fuzzy self-adaptive PID-Smith predictor controller is proposed.The program is on the basis of Traditional PID-Smith prediction device, traditional PID controller is replaced by Fuzzy Self-adaptive PID, and introduce an internal feedback ring and a self-adaptive regulator, and then ensure that the stability of system state, enhance the adaptive ability of changing environment during controller pair.This controller weakens the negative effect that controller brings model parameter sensitive, decreases the overshoot of system, and in model parameter change 40 percent, controller still can obtain good control effects.

In order to achieve the above object, the present invention adopts following technical scheme:

Modified Smith Prediction Control algorithm, comprises the following steps:

(1) design Fuzzy Self-adaptive PID and replace original PID controller, it is mainly made up of PID controlled adjuster and indistinct logic computer two parts, using the rate of change ec of error e and error as the input of controller, with the k of pid control parameter _p, k _i, k _das output, utilize fuzzy control rule to carry out real time modifying to the controling parameters of PID, meet not e and ec in the same time to the requirement of pid parameter Self-tuning System.

(2) before the long time delay link of conventional Smith prediction device controlled system model, an internal feedback ring is added, by internal feedback ring feedback signal delivered to simultaneously prediction model and actual controlled device input end and with the output of main control carry out poor, then using the input signal of difference as actual controlled device and prediction model, introduce a self-adaptive regulator simultaneously, by constantly changing the value of proportional controller, solve because open loop gain parameter changes the offset issue caused.

(3) transport function of the modified Smith predictor controller described in algorithm is: $\frac{Y\left(s\right)}{R\left(s\right)}=\frac{G_c\left(s\right)G_p\left(s\right)\exp (-\mathrm{Ls})}{1+G_c\left(s\right)[G_m\left(s\right)+G_p\left(s\right)\exp (-\mathrm{Ls})-G_m\left(s\right)\exp (-L_{m}s)},$ When model parameter is accurate, i.e. G _m(s)=G _c(s), L _mduring=L, show that the transport function of closed-loop system is: its secular equation is: 1+G _c(s) G _ps ()=0, can find out after Smith compensates from secular equation, no longer containing purely retarded item in the characteristic equation of closed-loop system, illustrating that purely retarded item has been eliminated, has been its lag output the time of a L; When actual controlled device and prediction model have error, secular equation is: 1+G _c(s) [G _m(s)+G _p(s) exp (-Ls)-G _m(s) exp (-L _ms)], the error of actual controlled device and prediction model is larger, i.e. G _p(s) and G _m(s) and L and L _mdiffer larger, compensation effect is poorer.Because purely retarded is exponential form, so the error ratio G of purely retarded _ms the error effect of () is large, i.e. L _mprecision more crucial.New departure is on the basis of Traditional PID-Smith prediction device, traditional PID controller is replaced by Fuzzy Self-adaptive PID, and introduce an internal feedback ring and a self-adaptive regulator, and then ensure that the stability of system state, enhance the adaptive ability of changing environment during controller pair.Even if model mismatch 40 percent time, still the large problem of overshoot in Large-lag System can be solved well, there is good stability and robustness.

Accompanying drawing explanation

Fig. 1 is the process flow diagram that modified Smith predictor controller is formed.

Fig. 2 is Model Matching is lmproved Smith Estimator and conventional Smith predictor controller response curve comparison diagram.

Lmproved Smith Estimator and conventional Smith predictor controller response curve comparison diagram when Fig. 3 is model mismatch 40%.

Embodiment:

Fig. 1 is the process flow diagram that modified Smith predictor controller is formed.Based Intelligent Control predictive algorithm of the present invention comprises the following steps:

(1) design Fuzzy Self-adaptive PID and replace original PID controller, it is mainly made up of PID controlled adjuster and indistinct logic computer two parts, using the rate of change ec of error e and error as the input of controller, with the k of pid control parameter _p, k _i, k _das output, utilize fuzzy control rule to carry out real time modifying to the controling parameters of PID, meet not e and ec in the same time to the requirement of pid parameter Self-tuning System.

(2) before the long time delay link of conventional Smith prediction device controlled system model, an internal feedback ring is added, by internal feedback ring feedback signal delivered to simultaneously prediction model and actual controlled device input end and with the output of main control carry out poor, then using the input signal of difference as actual controlled device and prediction model.The object adding internal feedback ring weakens time constant T and L dynamic change retardation time to the negative effect of system performance, increases the stability of system.Introducing a self-adaptive regulator simultaneously, by constantly changing the value of proportional controller, solving because open loop gain parameter changes the offset issue caused.

Fig. 2 is Model Matching is lmproved Smith Estimator and conventional Smith predictor controller response curve comparison diagram.

Lmproved Smith Estimator and conventional Smith predictor controller response curve comparison diagram when Fig. 3 is model mismatch 40%.

Claims (2)

1. a follow-on Smith Prediction Control algorithm, comprises the following steps:

(1) design Fuzzy Self-adaptive PID and replace original PID controller, it is mainly made up of PID controlled adjuster and indistinct logic computer two parts, using the rate of change ec of error e and error as the input of controller, with the k of pid control parameter _p, k _i, k _das output, utilize fuzzy control rule to carry out real time modifying to the controling parameters of PID, meet not e and ec in the same time to the requirement of pid parameter Self-tuning System.

(2) before the long time delay link of conventional Smith prediction device controlled system model, an internal feedback ring is added, by internal feedback ring feedback signal delivered to simultaneously prediction model and actual controlled device input end and with the output of main control carry out poor, then using the input signal of difference as actual controlled device and prediction model, introduce a self-adaptive regulator simultaneously, by constantly changing the value of proportional controller, solve because open loop gain parameter changes the offset issue caused.

(3) transport function of the modified Smith predictor controller described in algorithm is: $\frac{Y\left(s\right)}{R\left(s\right)}=\frac{G_c\left(s\right)G_p\left(s\right)\exp (-\mathrm{Ls})}{1+G_c\left(s\right)[G_m\left(s\right)+G_p\left(s\right)\exp (-\mathrm{Ls})-G_m\left(s\right)\exp (-L_{m}s)]},$ When model parameter is accurate, i.e. G _m(s)=G _c(s), L _mduring=L, show that the transport function of closed-loop system is: its secular equation is: 1+G _c(s) G _ps ()=0, can find out after Smith compensates from secular equation, no longer containing purely retarded item in the characteristic equation of closed-loop system, illustrating that purely retarded item has been eliminated, has been its lag output the time of a L; When actual controlled device and prediction model have error, secular equation is: 1+G _c(s) [G _m(s)+G _p(s) exp (-Ls)-G _m(s) exp (-L _ms)], the error of actual controlled device and prediction model is larger, i.e. G _p(s) and G _m(s) and L and L _mdiffer larger, compensation effect is poorer.

2. follow-on Smith Prediction Control algorithm according to claim 1, improvement project is on the basis of Traditional PID-Smith prediction device, traditional PID controller is replaced by Fuzzy Self-adaptive PID, and introduce an internal feedback ring and a self-adaptive regulator, and then ensure that the stability of system state, enhance the adaptive ability of changing environment during controller pair, even if model mismatch 40 percent time, still can solve the large problem of overshoot in Large-lag System well, there is good stability and robustness.