To address the limitations of conventional extended state observers (ESOs), which suffer from bandwidth constraints leading to poor estimation of sinusoidal signals and low utilization of system models, a novel model-assisted quasi-proportional resonant extended state observer (MA-QPRESO)-based active disturbance rejection control (ADRC) scheme is proposed. Specifically, the quasi-proportional resonant control is embedded into the ESO to improve its capability for estimating sinusoidal signals, while model-assisted compensation is introduced to account for known disturbances, thereby reducing the observer burden. Subsequently, the disturbance rejection performances of the proposed MA-QPRESO and the conventional ESO is compared through frequency-domain analysis to theoretically demonstrate the superiority of the proposed method. Finally, the effectiveness of the proposed method is verified by experiments on a single-phase grid-forming inverter. The method achieves robust control under variations in electrical parameters while maintaining excellent steady-state and dynamic performance.