The integration of renewable energy sources and the rising load demand has introduced significant challenges to the secure operation of interconnected power systems. To address these issues, a novel grid-connected microgrid control strategy based on higher-order sliding mode observer (HOSMO) and fractional-order sliding mode controller (FOSMC) is proposed for a grid-connected microgrid incorporating photovoltaic (PV) system, wind energy conversion system (WECS), and battery energy storage system (BESS). The proposed control strategy ensures effective DC bus voltage regulation by optimally managing the PV, WECS, and battery converter units. The HOSMO is designed to accurately estimate the current of PV or WECS converter, enhancing system robustness, while the FOSMC minimizes the chattering in DC bus voltage deviations. The performance of FOSMC is rigorously evaluated through extensive MATLAB/Simulink simulation under various uncertainties, including generation fluctuations, DC load variations, and DC faults. Stability analysis and comparative studies have been presented to demonstrate the superiority of the proposed control strategy. For comparative analysis, advanced control techniques such as finite time disturbance observer (FTDO)-based fixed time terminal sliding mode controller (FTTSMC) and nonlinear disturbance observer (NDO)-based back-stepping sliding mode controller (BSMC) are considered. Additionally, real-time validation of the proposed FOSMC is executed using the OPAL-RT (OP4510) platform to confirm the feasibility and reliability under practical operation conditions.