The Search And Application Of Internal Model Control In Complex System

With the rapid development of modern industry, the production process become much more complex than before, which always contains integrator and time delay process, variable structure object. And these controlled object often has the characteristics of uncertainty, time delay, multivariable coupling, input and output are constrained ect.. By using traditional internal model control method to solve these complex problems, the desired control effect can be hardly achieved. In order to fully play the advantages of internal model control, to develop some effective, simple and practical internal model control methods for a variety of special controlled objects has become one of the urgent needs for research area and modern industrial area. Based on this standpoint, taking internal model control as the basic control method, some solutions and improvements are proposed for the problems of complex systems. These solutions and improvements include the improvement of internal model control structure, the stability and robustness analysis of internal model structure, and the improvement of the filter. In this dissertation, the main study contents and the research results are as follows: (1) Represented the principles of system identification and several common identification methods. Mainly researched particle swarm optimization (PSO) and unconstrained multidimensional optimization algorithm(Powell), by analyzing the strengths and weaknesses of PSO algorithm and Powell algorithm, PSO-Powell identification algorithm was proposed. Through the simulation of chemical plant model illustrated the effectiveness and robustness of the proposed identification method. The unstandardized response situation of the industrial field had been researched, and this proposed method can carry out model identification in the condition of unsteady state initial value, unsteady final value, as well as Divergence output, ect.(2) The principle, structure and design method of internal model control are systematically represented. The relationship between IMC and classical feedback control, and the design method of filter are researched. A variety of time delay approximation methods had been researched. Based on these approximation methods internal model controllers were designed for the first order system with time delay and the second order system with time delay, derived the IMC-PID tuning formulas.(3) The decoupling and control problem of multivariable processes with time delays has been investigated. Two novel multivariable internal model control methods are adopted. The first method isâ…¤norm multivariable decoupling internal model control. The multivariable internal model controller has V norm structure, which has the functions of decoupling compensator and internal model controller. The controller design procedures were deduced, and the general formula of controller design was obtained. The second method is Max-Max internal model control method for multivariable system with multiple time delays. By calculating the inverse of transfer function matrix and the optimal diagonal matrix, the closed-loop system can be decoupled and the control response with minimum time delay. Finally the simulation results illustrated the effectiveness of these two methods.(4) In view of the limitation of the traditional internal model control method in the integrator and time delay process. Two improvement IMC structure had been proposed. The first method is that a proportional controller and a proportional differential controller were added to the traditional internal model control structure, to stabilize unstable object and control the disturbance rejection performance and robustness of the system respectively. Meanwhile, All-pole approximation method was adopted to approximate the delay item of the system. The second method is that to overcome the impact of external interference, the feedback signal is added to the control variables, that is equal to added a perturbation estimator to traditional IMC structure, the decoupling control of the system was realized, and the system has good dynamic characteristics. Finally, the simulation results illustrated the effectiveness of these two methods.(5) The internal model control method for non-square system has been investigated in the dissertation. Two internal model control methods had been proposed. The first method is that to analysis the stability of non-square system by non-square effective relative gain, and chosen the optimal subsystem which has the most relevant inputs and outputs. After analyzing this optimal subsystem, two internal model controllers and one strong robustness decentralized PID controller were designed based on the analysis result. The second method is that for the non-square system with time-delay and non-minimum phase zero, based on analytical analysis and generalized inverse a decoupling internal model control was proposed. This method can realize decoupling of non-square processes and eradicating unrealizable factors by inserting compensated terms. Meanwhile, a non diagonal filter is designed on the basis of SVD matrix theory, which makes control system could bear the capacity of high-dimensional decoupling and fast response, and has strong robustness. Finally the simulation results illustrated the effectiveness of these two methods.Though the researches of the above industrial objects, the advantage of internal model control is further developed, complete the internal model control in theory, and made the application of internal model control much wider in practical application.