With the continuously increasing penetration of renewable energy, new power systems are increasingly characterized by reduced rotational inertia and heightened parameter variability. Relying solely on traditional frequency regulation resources may therefore lead to insufficient frequency control capability. Power-electronic-based frequency regulation resources offer much faster response speeds, providing an opportunity to realize rapid frequency regulation in new power systems. Accordingly, this paper proposes a coordinated frequency regulation strategy combining power-electronic-based distributed frequency regulation resources with conventional synchronous generators. However, power-electronics-based units exhibit pronounced distributed characteristics, and as renewable energy penetration fluctuates, system inertia and frequency response characteristics also change accordingly. To address these issues, a novel distributed model predictive automatic generation control (AGC) strategy for new power systems is developed, which accommodates parameter uncertainty and is suitable for distributed, heterogeneous, multi-source coordinated frequency regulation. The proposed distributed model predictive control strategy can fully exploit the fast frequency regulation potential of rapid-response resources, enabling prompt suppression of system frequency fluctuations. Moreover, an online event-triggered parameter identification method is designed to ensure that, when key system parameters undergo significant changes, the model predictive controller can timely update system parameters to achieve accurate predictive control. Finally, simulation studies under various scenarios demonstrate that the proposed method significantly enhances frequency regulation performance and achieves the expected outcomes.