Measurable Disturbances Compensation: Analysis and Tuning of Feedforward Techniques for Dead-Time Processes

Abstract

Abstract:In this paper, measurable disturbance compensation techniques are analyzed, focusing the problem on the input-output and disturbance-output time delays. The feedforward compensation method is evaluated for the common structures that appear between the disturbance and process dynamics. Due to the presence of time delays, the study includes causality and instability phenomena that can arise when a classical approach for disturbance compensation is used. Different feedforward configurations are analyzed for two feedback control techniques, PID (Proportional-Integral-Derivative) and MPC (Model Predictive Control) that are widely used for industrial process-control applications. The specific tuning methodology for the analyzed process structure is used to obtain improved disturbance rejection performance regarding classical approaches. The evaluation of the introduced disturbance rejection schemes is performed through simulation, considering process constraints in order to highlight the advantages and drawbacks in common scenarios. The performance of the analyzed structure is expressed with different indexes that allow us direct comparisons. The obtained results show that the proper design and tuning of the feedforward action helps to significantly improve the overall control performance in process control tasks.

Application of Predictive Feedforward Compensator to Microalgae Production in a Raceway Reactor: A Simulation Study

“…In this case, the disturbance compensation is performed through a feedback loop, since no additional compensator is included. The disturbance compensation oriented design (allowing quick change in control signal) results in overshoot in the initial stage of the day [20]. Notice that, in all analyzed configurations, the feedback controller has the same tuning, and the disturbance compensation technique consideration improves the performance.…”

“…This issue makes the classical feedforward compensator less effective and a more complex compensator is required. This is due to dead time inversion issues (see [20] for more details). Moreover, for simplicity, the process, P u , and the disturbance dynamics, P v , are represented by a first order system with dead time using the following representation:…”

“…For the carbon dioxide, an analogous mass balance can be defined (20), where Y CO 2 is the carbon dioxide to nitrogen molar ratio in the gas phase:…”

Transient response comparison of feedback and feed‐forward compensation methods in systems with zero steady state error

“…Feed-forward compensation for the design of high-frequency trans-conductance amplifiers was also used in [24], in an attempt to reduce the settling-time. Disturbance compensation methods were analyzed in [25], focusing on time delays, in the case of both PID and Model Predictive Control structures.…”