PID-DTC Controller for Nonlinear Knee Extension Model with Time Delay Effect in Closed-Loop FES

Functional Electrical Stimulation (FES) is a crucial device in neuromuscular applications, facilitating restoring functionality of paralyzed muscles and limbs. However, its practical utilization encounters significant nonlinear challenges, predominantly arising from factors like muscle fatigue and time delay. These challenges impede the optimal performance of FES controllers, such as proportional-integral-derivative (PID), sometimes resulting in suboptimal outcomes or complete failure. The nonlinearities introduced by these factors necessitate system adaptability, but traditional controller retuning is often impractical due to its adverse effects on muscle performance. Moreover, introducing time delays can induce instability and oscillations in the system. This study explores the application of direct torque control (DTC) with PID controller to leverage FES-induced muscle torque for knee rehabilitation. Through a simulation model developed in MATLAB/Simulink, we empirically demonstrate the effectiveness of the PID-DTC approach in managing the knee extension model with nonlinear time delay in closed-loop FES. The results demonstrate the absence of oscillations, reduced overshoot, and minimal steady-state error, suggesting potential for successful real-world hardware implementation in rehabilitation applications.