Abstract: The fact that ultra high voltage direct current (UHVDC) transmission system commutation failure causes the transient overvoltage at the sending terminal grid has threatened the safe and stable operation of the wind turbine. It is urgent to conduct research on the transient overvoltage suppression measures. Combined with the analysis of the transient reactive power-voltage characteristics and mechanism of wind turbines in the second part of this series paper, this paper proposed a control strategy for permanent magnet synchronous generator (PMSG), considering the virtual magnetic flux to suppress the transient overvoltage under the condition of UHVDC commutation failure. By revising the reactive current reference value of current loop in the grid side converter (GSC) of PMSG, the analytical model of transient reactive power of PMSG with virtual flux was established, and the model's accuracy was verified. Taking the transient characteristic of absorbing reactive power of the voltage component analyzed in the second part of the series papers into consideration, the transient reactive power was optimized by designing the controller parameters of the voltage component transient reactive power, the overvoltage suppression capability of PMSG under UHVDC commutation failure was improved. Based on the control hardware-in-the-loop (CHIL) real-time simulation platform in the first part of the series papers, the effectiveness of the transient overvoltage suppression and parameter optimization method considering the virtual flux for PMSG can be verified.