Adaptive Feedforward Sliding Curve-Based Hybrid Fixed-Time Extended-Order Terminal Sliding-Mode Control for DC Microgrids

This article describes a robust dual-loop proportional-integral-based control technique used in a dc microgrid. The proposed technique is implemented on a dc–dc half-bridge boost converter as a hybrid constant switching frequency pulse width modulation sliding-mode control (SMC) technique. The hybrid SMC includes a linear sliding manifold (SM)-based double-integral SMC (DI-SMC) technique combined with nonlinear nonsingular extended-order fixed-time terminal SMC (EOFT+DI-SMC). The dual-loop control structure includes an outer output voltage control loop and an inner average inductor current control loop. The proposed EOFT+DI-SMC technique is based on a modified equivalent control law derived by considering a specific orientation of a sliding curve given by the intersection of SM and its orthogonal manifold for faster response and reduced chattering. The EOFT principle is used to modify an equivalent control law derived using the sliding curve principle, to enable disturbance rejection with minimal dependency on an observer. Furthermore, feedforward gains of the control loop are tuned in real time adaptively using the existence condition of SMC considering state boundary value conditions and small-signal stability analysis. The novel EOFT+DI-SMC principle is proved mathematically in terms of the equivalent control law, Lyapunov stability analysis, and fixed-time convergence. The proposed control technique is simulated using MATLAB/Simulink tool. An experimental prototype of a half-bridge converter is developed and tested to validate the proposed technique.