Cascade sliding mode control with applications

This study has comprehensively investigated the applicability and performance of the Sliding Mode Control (SMC) method within a cascade control structure. The primary objective of the present study is to evaluate the viability of SMC-based controllers as a reliable and robust alternative to conventional proportional–integral–derivative (PID) controllers in nonlinear and time-varying systems. In order to this end, single-loop P, PI and PID controllers, as well as SMC-1 (First-Order Sliding Mode Control) and SMC-2 (Second-Order Sliding Mode Control) controllers were designed. Various cascade and hybrid SMC-based control structures incorporating different outer-loop and inner-loop combinations were also developed. These were then subjected to comparative performance analyses. A fundamental objective of the study was to mitigate the inherent oscillations (chattering) observed in SMC systems. In order to achieve this objective, a hyperbolic tangent (tanh) function within a boundary layer approach was utilised as an alternative to the classical sgn\ function. This modification has been shown to reduce switching noise, ensure smoother control signals, and improve the robustness and stability of the system against disturbances and model uncertainties. The control algorithms were implemented on a DC motor system using the DIGIAC 1750 training set with experimentally determined parameters, and were validated through simulation and real-time testing in MATLAB/Simulink. The system's responses were evaluated using standard performance criteria, including rise time, settling time, overshoot and delay. The findings indicate that Cascade Sliding Mode Control (CSMC) structures, particularly those employing an SMC-2 controller in the outer-loop, exhibit a faster transient response, reduced overshoot, diminished steady-state error, and enhanced disturbance rejection capability. Consequently, CSMC can be regarded as a reliable and effective alternative to conventional PID-based control methods.