Uppsala universitet

On Compensation for Saturation in Input Rate and Input Amplitude - A Case Study for the Control of a Paper Machine Headbox.

Jonas Öhr, John Erik Larsson and Mikael Sternad

Report, Signals and Systems Group, Uppsala University, Sweden, 1999.

A headbox is the initial part of paper machines. It distributes liquid pulp into the machine, where it is then dried and converted into paper. The headbox is one of the most important subprocesses on a paper machine, and considerable economic gains can be attained by operating it well. Amplitude saturation in the outlet-air valve, and rate saturation in the stock-pump system both cause performance degradation if not compensated for. This motivates our effort to develop better control strategies, including saturation compensation.

This discussion introduces a general compensator structure and design scheme, and then focuses on design, tuning and synthesis of a compensator applied to a LQR-based control system to be used for the control of a paper machine headbox.

A model-based controller us proposed for minimizing effects caused by saturation in input rate and input amplitude in a headbox control system. The headbox is here considered as having two inputs and two outputs.

The proposed controller constitutes of a pre-existing controller and a saturation compensator. The design of the compensator can be carried out using the same approach as used for the design of the pre-existing controller.

Related publications:
ECC'97 paper on anti-windup compensators for multivariable control systems.

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