This article presents design and evaluation of filtered proportional-integral controllers and filtered Smith predictorinspired constrained dead time compensators. Both are based on the integral plus dead time and on the first-order time delayed plant models. They are compared as for tuning simplicity, robustness and noise attenuation. Such a comparison, which presents a robustness test regarding the importance of the internal plant feedback approximation, may be carried out by performance measures built on deviations of the input and output transient responses from their ideal shapes. When combined with integral of absolute error measures of both solution types with the disturbance responses set as nearly equivalent, we can see that the filtered Smith predictor setpoint responses may be significantly faster than the filtered proportional-integral controller responses, more robust and, using higher-order filters, also sufficiently smooth. Furthermore, tuning of the possibly higher-order filters for filtered Smith predictor is simpler. Its overall design is more transparent and straightforward with respect to the control constraints, where the filtered Smith predictor requires some additional anti-windup measures.

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This paper treats a noise attenuation motivated position controller design outlined in [1]. This modular approach to a filtered PD and a disturbance observer based filtered PID (FPD and DO-FPID) control design, including an experimental evaluation of an optimal filter degree choice, is extended to a constrained control grounded in the invariant set approach [2]-[4]. Loop performance is evaluated by recently introduced measures for deviations from monotonic and two-pulse shapes of transients typical for control of plants with dominant 2nd order dynamics. The analysis shows that a simplified disturbance observer (DO) based constrained filtered PID controller (DO-CFPID) derived for a double integrator plant model gives an interesting performance also for constrained integral systems with a stable mode. It remains simple and it offers an excellent performance also from the point of view of the noise attenuation versus speed of transients.

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