Batch-to-Batch and Within-Batch Control Design for Final Product Quality Under MPLS Model Structure

• Main Authors: Kuen-Chi Lin, 林昆棋
• Other Authors: Junghui Chen
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/42269852675189108569

碩士 === 中原大學 === 化學工程研究所 === 94 === The two novel design strategies, one-stage MPLS based dEWMA control and two-stage MPLS based dEWMA control, respectively, are proposed for maintaining final product properties. They are model-based control algorithms using multi-way partial least squares (MPLS) models and double exponentially weighted moving average (dEWMA). In one-stage MPLS based dEWMA control, only one MPLS model is used to relate the final quality with the on-line measured and the manipulated variables. On the other hand, in two-stage MPLS based dEWMA control, one MPLS model is used to relate the final quality with the on-line measured variables while the other can relate the on-line measured variables with the manipulated variables. The MPLS based model utilizes input/output trajectory information as historical databases. It can address the difficulties in developing detailed mechanistic models. Rather than dealing with the high dimensional manipulated variable trajectories in the real space, MPLS takes the advantage of extracting the strongest relationship between the input and the output variables in the reduced space of the latent variables model. It is particularly useful for inherent noise suppression and removal of interaction of variables. Also, it can break the MIMO process into a series of univariate processes. However, MPLS may have the problems of the model-plant mismatches, so the dEWMA control algorithm is applied separately and directly to each SISO control loop based on model prediction errors from the previous batch run. With the updated process model, the feedback control of the output quality is introduced to find out the adjusted manipulated variables and track the desired quality at the end-point of a batch run. The batch-to-batch scheme can not only reduce the model mismatch but also make the end point quality gradually reach the desired quality. Furthermore, in order to adjust the operation in time, the MPLS based dEWMA control strategy is developed to explore the possible adjustments of the future input trajectories. It fixes up the disturbances just in time instead of until the next batch run and keep the product within specifications when this batch is finished. The effectiveness of the proposed design strategy is demonstrated through three cases of a simulated batch process, including setpoint changes, disturbance changes within a batch run, and disturbance changes occurred at batch-to-batch. These cases are used to investigate the potential applications of the proposed method and make a comparison with some conventional methods recently reported in the literature.