Research On The Internalmodelcontrolin Multivariable Large Time Delay Systems

Multiple-input-multiple-output(MIMO) systems with multiple timedelays and coupling are common in chemical processes. However, thetraditional control method using dynamic decoupling matrix often leadsto differentiation element, which is physically unrealizable. So the maincontent of this paper is to investigate new controller design methods forMIMO systems with large time delays.In this paper, one of the advanced control strategies, i.e. the InternalModel Control(IMC) is applied to deal with both square and non-squaresystems. It can be seen from the simulation results that the two methodsproposed in this paper have smaller overshoot, fast tracking features, fastresponse capability as compared with other methods in the literatures.Additionally,the strong robustness when models mismatch confirmsbetter performance in the control of multiple time delays and couplingsystems.In this paper, the basic principle, characters of IMC are reviewedfirstly,then further study on controller design methods is discussed. Andthe IMC robustness is analyzed also. Much simulation work on first-order plus time delay system is done to implement the study of the IMCmethod.The design method proposed in this paper is capable of controllingthose industrial MIMO systems which are difficult for traditional ones. Amodified design of the Internal Model Control(IMC) based on robustfinal value decomposition is carried out for improving the controlperformance. This paper shows how expected diagonal decoupledtransfer function matrix can be combined with the stable IMC principle todesign compensator, thus obtaining the final decoupled controller. Usingthe proposed method, we can simplify the calculation by avoiding modelapproximation. Meanwhile the improvement in IMC filter structure cansignificantly enhance dynamic quality and robustness of the controlsystems. Moreover, this new method is suitable for square and non-squaresystems.A new method to design Smith delay compensator using equivalentmodel is also studied in this paper. A series of single loop systems can bederived through the equivalent transformation of the open-loop processmodel. In this way, this paper present a model reduction based method tofind a much simpler yet good approximation model in each single loop.Using the low-order equivalent models (normally in the form offirst-order plus time delay or second-order plus time delay), combiningthe IMC design method, the expected Smith delay compensator can beobtained easily. Simulation results are employed to prove the method hasthe advantages of high-order decoupling capability, fast response featuresand good control performance. Illustrative examples are given to showthe effectiveness and merits of the two proposed methods in this paper.