MIMO PID Control Design for Second Order Systems with Time-Delay
PID Control; MIMO systems; Second-order systems; Time-delay systems; Frequency response; Genetic Algorithm.
Systems that originate from second-degree differential equations, or simply second-order systems, are highly relevant in the study of control systems, due to their broad power to model practical situations, such as mechanical vibrations, resonance, and even specific processes in areas such as fermentation in certain biological processes. Working with this type of model, instead of first-order state models, can bring some benefits, such as the possibility of developing more sophisticated controls and a clearer frequency analysis. In practice, these systems suffer from delays inherent in several parts, such as actuators and sensor measurements, which can generate harmful effects, such as reduced performance, instability, and oscillations. Considering that even small delays can generate significant disturbances in the system, it is valid to use an approach based on the system's receptances, which can accurately represent the delay through a study in the frequency domain. This dissertation aims to develop multivariable PID controllers for linear dynamic systems with multiple inputs and outputs (MIMO) that present delay in actuation and are described by a system of second-order differential equations. The proposed technique uses the frequency domain model known as the receptance matrix, which can be obtained accurately experimentally and which allows the delay effect to be treated without approximations. Closed-loop stability is ensured using the so-called generalized Nyquist criterion, verified by the so-called eigenloci diagrams. A given stability margin is obtained by imposing a minimum distance between the eigenloci and the critical point for stability. An optimization problem is formulated to calculate the PID controller gains that impose this margin and minimize a time response performance index, which is solved by Genetic Algorithm. Different delays for each actuator and different PID controller schemes are considered. Numerical examples illustrate the proposed approach.