Abstracto
- A design approach for Two-Degree-of-Freedom (2-DoF) PID controllers within a cascade control config-uration that guarantees robust and smooth control is presented in this paper. The use of a cascade controlconfiguration comes into place when the use of an additional (intermediate) sensor provides the possi-bility for a compensation of a load-disturbance before it affects the output variable. The rationale ofoperation associated to both the inner and outer controllers determines the need of good performancefor disturbance attenuation (regulation) as well as set-point following (tracking). Therefore, the use of2-DoF controllers is introduced. However, the use of 2-DoF controllers, introduces additional parametersthat need to be tuned appropriately. Specially for the case of PI/PID controllers there are not known clearauto-tuning guidelines for such situation. The approach undertaken in this paper provides the completeset of tuning parameters for the inner (2-DoF PI) controller and the outer (2-DoF PID) controller. Thetrade-off among control system performance (measured in terms of closed-loop response speed) androbustness allows to derive a recommendation for the design-parameter lower limit. The design equa-tions are formulated in such a way that a non-oscillatory response is specified for both the inner andouter loop. A side advantage of providing the complete set of parameters is that it avoids the need forthe usual identification experiment for the tuning of the outer controller.