A Robust Dual-mode MPC Approach to Ensuring Critical Quality Attributes in Quality-by-Design

In the Quality-by-Design (QbD) paradigm for pharmaceutical processes, critical quality attributes (CQAs) must meet specifications for all possible realizations of critical process parameters (CPPs) within a design space. During the startup of such a process, it is desired to begin meeting CQA specifications as quickly as possible and then robustly guarantee that specifications will continue to be met. This paper proposes a robust dual-mode model predictive controller (RDMPC) for meeting these objectives, for discrete-time linear systems with a linear fractional transformation (LFT) uncertainty description. The receding-horizon controller steers the system into a controlled invariant set in finite time, after which the terminal controller is applied to robustly guarantee specifications on CQAs for all time. The proposed control algorithm is demonstrated for a continuous stirred-tank reactor.