Results are developed to ensure stability of a dissipative distributed model predictive controller in the case of structured or arbitrary failure of the controller communication network; bounded errors in the communication may similarly be handled. Stability and minimum performance of the process network is ensured by placing a dissipative trajectory constraint on each controller. This allows for the interaction effects between units to be captured in the dissipativity properties of each process, and thus, accounted for by choosing suitable dissipativity constraints for each controller. This approach is enabled by the use of quadratic difference forms as supply rates, which capture detailed dynamic system information. A case study is presented to illustrate the results. V C 2014 American Institute of Chemical Engineers AIChE J, 60: 1682-1699, 2014 Keywords: process control, model predictive control, distributed control
IntroductionModel predictive control (MPC) is one of the few advanced control techniques which has achieved wide spread use in the chemical industry, 1,2 due to its ability to handle constraints (both soft and hard), multivariable problems, and generate an optimal control action. Constraints, along with large scale and strong interactions (potentially inducing time-scale separation) are key problems in the control of chemical process networks. 3,4 These interactions between process units are due to material recycle and heat integration, which are common in modern chemical plants as a result of designs based upon steady-state efficiency concerns. These recycle loops can be thought of as positive feedback interconnections from a control point of view, which are well known present challenges in control practice.As such, a scalable approach to MPC for process networks which takes interaction effects into account is desired. Although centralized approaches can handle interaction effects, they suffer from poor scalability due to the computational complexity involved in modeling and design. Conversely, decentralized MPC offers a more scalable approach, although it may lead to poor performance or even instability if interaction effects are not accounted for. 5 Due to these short comings, distributed MPC has received much attention in the literature, as it attempts to realize the benefits of centralized and decentralized approaches, some recent examples include 6,7 and those by Rawlings and coworkers,8,9 and Christofides and coworkers, 10-12 a recent review is also available.
13In our previous work, 14 a dissipativity-based approach to noncooperative distributed MPC for systems with constant interconnection topology was presented. A dissipativity ensuring constraint is imposed on the individual controllers such that the closed loop process network satisfies a desired dissipativity condition. Dynamic supply rates in the form of quadratic difference forms (QdFs) were used to ensure stability and minimum performance bounds on the process network.In this work, the controller network is allowed to change to mode...