Abstract: Owing to the fact that the operating point on the de-loading power curve will shift when the actual rotor speed changed during the frequency droop control,doubly-fed induction generators（DFIGs）cannot provide the desired primary frequency control ability.To solve this problem,firstly a novel low-order system frequency response model is established for distributed systems including DFIG and thermal generation unit based on the small signal analysis theory.And then the quantified formulas of the actual and desired primary frequency control abilities of DFIG are derived by using the proposed model.According to the derivation,this paper proposes that DFIGs provide the desired primary frequency control ability after multiplying a reduction factor for the original set of droop coefficients.Finally,the capability of the proposed droop coefficient modification method is tested on an actual distributed system.The simulation results show that,with the proposed method,not only has the system quasi-steady-state frequency deviation reached the expectation level,but also the system maximum frequency deviation has further improved.