Control and Safe Steering of Batch Processes Under Uncertainty

This work considers the problem of controlling batch processes to achieve a desired final product quality subject to input constraints, faults in the control actuators and process uncertainties. Specifically, faults are considered that cannot be handled via robust control approaches, and preclude the ability to reach the desired end-point, necessitating fault-rectification. A safe-steering framework was developed previously to address the problem of determining how to utilize functioning inputs during fault rectification to ensure desired product properties can be reached upon batch termination after fault-rectification. To this end, first a novel reverse-time reachability region (we define the reverse-time reachability region (RTRR) as the set of states from where the desired end point can be reached by batch termination) based MPC was formulated that reduces online computations, as well as provides a useful tool for handling faults. Next, a safe-steering framework was developed that utilized the reverse-time reachability region based MPC in steering the state trajectory during fault rectification to enable (upon fault recovery) the achieving of the desired end point properties by batch termination. In this work, the framework is generalized to handle uncertainties through the development of an algorithm to generate robust RTRRs, which can be defined as the set of states from where the process can be driven to a desired neighbourhood of the desired end point in the presence of uncertainty. The efficacy of the robust RTRR based predictive controller is illustrated through a simulation example of a fed-batch bioreactor.