Study Of A Zone Control Algorithm With Unequal Limits In The Model Predictive Control

As a common control strategy in the industrial process,set point control is to maintain the controlled variables equal to the rigorous set point.However,in many situations,some of the output variables are not controlled to track the set point strictly,but only need to be controlled within a zone concerning the products output and quality,energy and material consumption,etc.Using zone control strategy,system has great degree of freedom to restrain disturbance and reduce the control frequency.When the outputs lie outside the boundary of the specified zones,especially run to the dangerous directions,they are quickly withdrawed into the zones under the hard regulating actions.When the outputs lie in the specified zones,control actions just remain unchanged.Besides,during some chemical control processes,controllers can take various regulating actions to different deviations from the specified zones.This kind of zone control strategy we usually call unequal zone control.The thesis made a study centred on unequal zone control.Although most of the existing zone control algorithms can make the outputs violating the target zones return to the zones,they can not ensure the outputs to be kept within the target zones during the entire control process.Therefore,aimed at zone control objective with no output overshoot,a zone control algorithm with unequal limits in the model predictive control was proposed which could not only realized unequal-boundary zone control but also realized equal-boundary zone control.Furthermore,the thesis improved this zone control algorithm by which we could deal with the constraints conditions to get an explicit control law with less online time and less calculation.There we should recognize that both the original algorithm and the improved algorithm can not ensure the outputs to realize the zone control objective with no overshoot.This mainly depends on the outputs expected zones.So the thesis lastly conducted a study on the selection of outputs expected zones.A method for selecting optimal outputs expected zones was discussed based on convex polynedron geometry and by this method,we could get the optimal outputs expected zones.Combined with optimal outputs expected zones,improved unequal zone control algorithm could make the outputs realize the zone control objective with no overshoot.The thesis includes the following aspects:Firstly,the thesis made a overview of zone control strategy and a summary about the domestic and international's study on zone control algorithms as well as some other related theoretical issues.The basic knowledge and the basic ideas about zone control had been introduced in details in this thesis.Meanwhile,four existing zone control algorithms had been introduced.Secondly,the thesis proposed a zone control algorithm with unequal limits on the base of the theory of MPC,including its description and its solution,which took various control to different devious from the object through distinguishing the devious directions by different weights.Simulation results showed that this zone control algorithm presented in this thesis possessed good performance.Thirdly,the thesis improved this algorithm by adding a attenuation factor in order to shorten the online computing time and reduce the algorithm's complexity.Simulation results validated the effectiveness of the improved algorithm.Lastly,according to OCI,the thesis made a study on the selection of outputs expected zones on the base of improved zone control algorithm with unequal limits.On the one hand,a judgement basis about the rationality of outputs expected zones was proposed,On the other hand,a method for selecting the optimal outputs expected zones when the initial outputs expected zones were not reasonable was proposed,too.This kind of output expected zone is the maximal output expected zone.Moreover,the method established in this thesis both avoids the waste of energy and eliminates the manual intervention.Simulation results showed that all the outputs zones constraints conditions could be satisfied and the control performance was perfect,without overshoot,smooth change of control actions,during the whole horizon by this method.In the end,the thesis made a whole summary and presented the future prospect on zone control further study.