Control of high temperature short time milk pasteurization plant with centralized and decentralized linear quadratic regulators

Abstract

ABSTRACT Precise temperature control in each stage of the pasteurization process is important to deactivate pathogenic bacteria, and any temperature fluctuations during milk processing may affect the nutritional value and quality of the milk. Hence, maintaining stable temperature and minimizing disturbance effects is essential for improved quality of the milk. This necessitates an efficient controller that may provide precise temperature control despite process disturbances. Here, a mathematical model representing the high-temperature short-time (H.T.S.T) milk pasteurization process is simulated. The proposed model is simulated without a pre-cooling stage, thereby contributing to energy minimization but without compromising the operating conditions of the process. The design of a Linear Quadratic Regulator (L.Q.R)-based centralized and decentralized control for the H.T.S.T milk pasteurization process is implemented. The L.Q.R exhibits good results at disturbance rejection and targets mainly the objective function minimization. So, minimizing the energy is the prime objective of the L.Q.R. The centralized and decentralized L.Q.R structures were designed for the proposed plant, and the control scheme efficiencies are analyzed. The juxtaposition of these two control schemes reveals that the decentralized L.Q.R structure outperforms the centralized structure for the H.T.S.T milk pasteurization process.