Sequential loop closing identification of multivariable process models

Abstract

Sequential loop closing (SLC) method is one of the well-known methods to tune multiloop control systems for multivariable processes. In the method, each controller is designed sequentially with single-input single-output methods by finding the transfer function for the paired input and output while former loops have been closed. Utilizing the single-input single-output nature in tuning each controller, autotuning methods can also be applied. However, sometimes iterations are required for better performance. Especially, if pairing is undesirable, the multiloop control system designed with the autotuning SLC method does not show the best performance and tuning should be discarded and repeated totally for the correct pairing. Here, to avoid this, multivariable process models are identified while loops are being tuned. The identified models can be used to correct the pairing and to improve the multiloop control systems. Field experiments needed are just the same as the autotuning SLC method.