A new approach to design and tune sliding mode controllers for chemical processes

This work reports on the application of Sliding Mode Control (SMC) theory to chemical engineering processes. SMC theory has been applied mainly to electrical engineering type systems. The most significant characteristic of controllers designed based on the SMC theory is their robustness to uncertainties. This robustness characteristic makes the application of Sliding Mode Controllers (SMCr's) very appealing to chemical processes, since they tend to be nonlinear in nature, and of higher-order.; As it has been applied to electrical systems, the design of SMCr requires a process model relating the controlled and manipulated variables. The development of a complete model of chemical engineering type processes is rather difficult due mainly to the nonlinearity characteristics, and to the lack of understanding and/or knowledge of some process parameters. In addition, the complexity of the SMCr also depends on the order of the system. Chemical processes tend to be of higher-order and it is common to find processes of fourth, or higher, order. Finally, another important characteristic of chemical processes is the presence of dead time. As of today there is no information about a methodology to handle dead time in the SMC theory. Thus, the nonlinear characteristic, the order of the process, and the presence of dead time make the application of SMC theory, as developed and applied up to the present, to chemical processes, rather difficult.; The contributions presented in this work include (1) A methodology to handle dead time in the designing of SMCr. (2) The design of a fixed structure SMCr based on a first-order-plus-dead-time (FOPDT) approximation of self-regulating processes. (3) Tuning relations as a function of the FOPDT parameters are developed for the controller.