Robust T-S Fuzzy Control of Electrostimulation for Paraplegic Patients considering Norm-Bounded Uncertainties

This manuscript presents a Takagi–Sugeno fuzzy control for a mathematical model of the knee position of paraplegic patients using functional electrical stimulation (FES). Each local model of the fuzzy system is represented considering norm-bounded uncertainties. After obtaining the model of FES with norm-bounded uncertainties, the fuzzy control strategy is designed through the solution of linear matrix inequalities (LMIs) using the conditions available in the literature, which consider these norm-bounded uncertainties. The strategy considers decay rate and constraints on the input signal. The model is simulated in the Matlab environment using the numerical parameters measured by experimental tests from a paraplegic patient.

Two-degree-of-freedom compensator design for disturbance attenuation problem via higher order sinusoidal input describing functions theory

In order to deal with disturbance attenuation problem in the presence of norm bounded uncertainties, different techniques involving [Formula: see text]/[Formula: see text] and linear quadratic regulator (LQR) designs exist in literature. The major drawbacks of these approaches may be classified as obtaining controllers with high order terms and too much computational load during the controller design. Hence, two-degree-of freedeom (2-DOF) controller design is taken into consideration in this study in order to avoid some of these drawbacks in the controller design and implementation process for disturbance attenuation problem. Here, the procedure for the design of 2-DOF structure is divided into two parts: designing [Formula: see text] controller to stabilize the closed loop system and implementing a higher order sinusoidal input describing functions (HOSIDF)-based compensator as a secondary controller in order to increase the disturbance attenuation performance of the overall closed loop system where the norm bounded uncertainties already exist. Thanks to the Lur’e type system definition that is also used in the design process of HOSIDF compensator, the research also proves that the proposed 2-DOF design structure is suitable to be implemented into the systems involving nonlinearities such as actuator saturation.