Abstract: The double disks refiner has large time delay， large inertia and nonlinear characteristics during operation， whereas the internal model control， as an advanced control strategy， given its advantages of not requiring high accuracy in the process model. A PI control method was proposed based on internal model control principle， which has only one adjustable parameter in the designed controller， achieving tuning by maximum sensitivity indicator， thus the complexity and randomness of controller tuning could be effectively avoided. Simulation results show that， compared with the conventional PID control， the model parameters variations and alleviate various interference on system performancecan be effectively reduced by using the proposed method， and the requirements of mechanical pulping process for controller properties can be satisfied to ensure the stable control of the mill load， laying the foundation for the implementation of the integrated automation system for pulping process.

Key words: mechanical pulping process, refiner load, internal model control, PI control, robustness