The frequency regulation previously undertaken by Synchronous Generators (SGs) may be provided by the Doubly-Fed Induction Generator (DFIG). To estimate the control effect, Dynamic Power Flow (DPF) is used to save the calculation effort of the detailed time domain analysis. A hierarchical frequency control with the upper level of the frequency prediction and the lower level of the DFIG control is proposed. Model Predictive Control (MPC) is applied to both levels to determine the control target with pre-evaluation of the control effect. At the upper level, the governor of the SG is included in the DPF to improve the accuracy of the frequency prediction, based on which the active power reference of the DFIG is determined. The mechanical transient of the DFIG with the change rate constraints is included. At the lower level, the MPC-based direct rotor current control of the DFIGs coordinated with frequency control is proposed to track the power reference, whose response is included in the frequency prediction. This work is supported by National Natural Science Foundation of China (No. 51877061).