Gain Delay Retune in Multivariable Controls for the Paper Making Process, 2011 PaperCon Conference

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The paper making process, like many industrial processes, exhibits nonlinear behavior. The nonlinearities can become more severe in situations where large operating condition changes take place. Performing multivariable MD (machine direction) control based on linear process models formulated as first or higher order transfer functions in the Laplace domain becomes insufficient and inaccurate when these large operating condition changes are encountered. The problem is that a multivariable MD control transfer function uses a static gain and time delay, which will vary with operating conditions in a nonlinear process.

This paper examines a solution that involves automatically retuning the gain and time delay based on nonlinear mass balance and process interactions. The studied paper machine was in “slow-back” mode due to production limitations where the machine speed was almost half of its nominal speed.