A power flow calculation method is proposed

and the steady state characteristics of the power system with fractional frequency wind power system (FFWPS) are analyzed. Firstly

the power flow model of cycloconverter is proposed. Then

a novel unified iterative method is introduced to calculate the power flow of a system with FFWPS. By this method

the admittances of transformers and transmission lines in lower frequency side are modified according to their operation frequency. Moreover

based on the model of cycloconverter

the Jacobi matrix is also extended. Finally

in the planning of power grid of Sichuan

the steady characteristics of the power system with FFWPS are analyzed

which includes the voltage fluctuation and reactive power demand. The steady characteristics of the FFWPS utilizing variable-frequency strategy are compared with that of FFWPS utilizing constant-frequency strategy. Analysis results for a typical day show that the aggregate indicators of the FFWPS utilizing variable-frequency strategy are better than that of constant-frequency strategy

because of the wind generators mainly operating at a low or medium wind speed.