Online Shape Modification of Molecular Weight Distribution Based on the Principle of Active Disturbance Rejection Controller

Abstract

Molecular weight distribution (MWD), an important microcosmic quality index of high polymer, is online unmeasurable, which makes its closed-loop control extremely difficult. To solve this problem, an online shape modification strategy for polymer MWD is proposed based on the active disturbance rejection controller (ADRC). The temporal-spatial property of MWD is estimated in real time by a three-layers forward network based on orthogonal polynomials basis function, and the shape modification of distribution function is transformed into the tracking control of moment statistics in the state-space description. Taking full advantage of the online measured lower-order moments, dual ADRCs are constructed with two manipulated variables (the flow rate of monomer and initiator) to achieve the high precision tracking of lower-order moments and distribution functions, simultaneously. Furthermore, the stability condition of the closed loop system is proved which can guide the parameter tuning of ADRCs. The proposed control strategy is implemented on the polymerization reaction in the laboratory scale continuous stirred tank reactor (CSTR). The feasibility and robustness are verified in the simulation.