Disturbance-Resilient Voltage/Power-Quality Management for Islanded Inverters Using Self-Tuning Type-3 Fuzzy Controller

Abstract

This paper proposes a disturbance-resilient adaptive fuzzy sliding-mode control (AFSMC) strategy for off-grid (islanded) inverters using an interval type-3 (IT3) fuzzy logic system (FLS). An integral sliding surface is formulated to eliminate the reaching phase and ensure robust output-voltage regulation under lumped uncertainties. A model-based inductor-current reference with an embedded limiter is incorporated to provide overcurrent protection during abnormal operating conditions. To mitigate the chattering associated with conventional sliding-mode switching and to avoid relying on tight uncertainty bounds, the discontinuous term is replaced by a continuous IT3-FLS compensator. The rule weights, membership-function (MF) parameters of the IT3-FLS, and translation width are tuned online via Lyapunov-based adaptation laws. Comparative simulations and real-time co-simulation under load variations, DC-link fluctuations, filter-parameter perturbations, and master–slave inverter connection/disconnection events demonstrate improved tracking and power quality. The proposed controller reduces output-voltage THD to 0.81% (vs. 1.59% for SMC and 4.85% for PID) and lowers the control-input chattering index from $2.2\times 10^3$ to $1.7\times 10^2$, while achieving up to 76.4% improvement in voltage MSE at the disturbance instant under parameter variations. The resulting IT3-FLS-based controller provides a practical and extensible framework for uncertain nonlinear power-electronic systems, with potential applicability to motor drives and related converter-based applications.