Abstract: This paper proposed a method for calculating the optimum output voltage of converter,and therefore realize the fixed-frequency control for the direct power control（DPC） method.Reactor parameters,voltage and current of the system, and the active and reactive power were also used to compute the estimated value of converter’s output voltage.The space vector modulation was adopted for the converter.By the proposed method,both high transient dynamics and constant-switching frequency control can be obtained.As the calculation process was completed only in static coordinates, phase-locked loop（PLL） is not required,which simplifies the control scheme.The correctness and feasibility of the proposed control scheme was verified by the simulating and experimental tests.