The Control Methods Study Of Large Disturbance

Nowadays many advance control strategies have come out one after another,such as:Smith predictor control,internal model control algorithm,feed-forward compensation,predictive PI control programs Bang-Bang control programs.However,actual industrial production process system,such as temperature control redrying process barn,using conventional control strategies is difficult to achieve a good control effect.Therefore,on the basis of existing policies on further interference for real industrial situation,then carry out a predictive PI-based control strategy for large conventional disturbance,and control strategy for periodic disturbance systems.Based on the predicted PI large disturbance control algorithm use the PI controller as the primary loop controller in time delay inertial industrial process control object,and add the comparator as a switching controller.The main idea of this algorithm is as follows: When the controlled variable within the desired control range,predictive PI control algorithm can be effectively controlled,when the controlled variable exceeds the expected range,the comparator switches to the controller output increase or reduced to a tolerable limit,so the controlled object can rapidly approaching to set point.Simulation results show that: the use of the algorithm can effectively improve the adjusted rate,reduce volatility and other issues.Even in the case of large disturbance model mismatch,the control of the accuracy of the output remains within reasonable limits.Effective solution to the big lag characteristic of the controlled object with large inertial output at high disturbance fluctuations,slow response,adjusting a long time difficult.When disturbance is a periodic big disturbance,the algorithm can effectively reduce the influence of large disturbance.When disturbance is a periodic signal,the control strategy is still able to limit the scope of a small error,but it will be accompanied by a certain little shock.Further,for a certain periodicity large disturbance compensation control is not performed if the output is generated shock unquenchable,only using the main circuit control methods can not get good control effect.For large inertia lag with a periodic disturbance of the control object,this paper introduces the control scheme with a online frequency identification device.Most industry‘s disturbance is unknown.Therefore,the algorithm is different with the feed-forward compensation control,feed-forward compensation control requires disturbance is known,there are many limitations in practical applications,and traditional repetitive control needs to know the frequency of disturbance and other conditions,so as the unknown frequency disturbance traditional repetitive control becomes powerless.Therefore,here carried out some improvements on the basis of the traditional repetitive control,adding a online identification process which calculated the frequency of disturbance signals with the frequency identification devices then generates a periodic signals which has the same frequency of disturbance signals.Finally the control output stable at set point.The simulation showed that: this online identification algorithms has a good tracking system and high accuracy.In actual redrying process,due to the vacuum reversion process,cause a large pressure fluctuations in steam pipe network,resulting in a large disturbance to the barn temperature control system.If the steam valve position has not be good controlled,the barn temperature would be difficult to stabilize at the set point,but a barn temperature fluctuations,so the moisture content of the moisture content of the cold room and exports would be difficult to maintain at a stable point,result in the moisture content of sheet tobacco substandard and need to be redry again,reducing the productivity of redrying process.In the present situation,there hasn't a good program for large industrial disturbance control,use large disturbance temperature control algorithm based on predictive PI to control barn redrying process which introduced in this paper.According to the data in actual redrying process,the program can effectively reduce the large fluctuations and other issues,so that the temperature control precision of each drying zone have reached the technological requirements,achieve an automated industry production process.The control program has a good prospects in the future industrial applications.