A PLC-based Generalized Predictive Control Universal Module Design

Generalized predictive control is one of the most representative model predictive controlalgorithms. It is developed on the study of adaptive control and inherited its advantages.Furthermore, we could get a good control effect from using the algorithm for nonlinear,time-varying, and multivariable coupling system with multi-step prediction, rolling optimizationand feedback correction strategy.As a kind of computer control algorithm, generalized predictive control is based on generalcomputer platform which is in the form of commercial design software used in the processcontrol system. However, the high cost of implementations, long development cycle of thesystems, complex optimization solution algorithm exist in the systems based on computerplatform, so it can hardly adapt to the industrial control field of the existing platform, and thedegree of the fusion between model predictive control theory and industrial field will be reducedto some extent.The transplant of advanced control algorithms to PLC are greatly promoted by developmentand application of software and hardware in field for the past few years. It makes more and moreadvanced control strategies are applied to the industrial field by experts and scholars.The experience of the transplant from typical advanced process control to PLC platform issummarized in this paper. An improved direct algorithm is proposed for the defect ofrequirement of high dimension matrix inversion in conventional multivariable generalizedpredictive control algorithms. The results of inversion with high dimension matrix will beachieved by identification, and the problem of divergence which is caused by matrix inversionwill be solved fundamentally as well. In addition, a user oriented universal GPC module isproposed in the SIEMENS S7-300PLC platforms originally, it aims at provide a new kind ofadvanced control schemes to PLC-dedicated technical staff.An improved multivariable generalized predictive control algorithm is deduced first, andthe algorithm flow is given at the same time. The control performance and portability on PLCplatform is proved by a simulation example which is modeled by structured control language thatcomply with IEC61131-3. And then, the independent function block with the improved algorithmis worked out and the parameters description of input and output will on the SIEMENS S7-300PLC be provided. Finally, an experimental platform is built to realize the control algorithm, andconfiguration software is used for real-time monitoring and curve records. Experimental resultsshow the effectiveness and universalness of the presented module.