Alternate iteration method for power flow analysis of interconnected system of fractional frequency transmission system and main grid

Fractional frequency transmission system (FFTS) is utilized to transmit large-scale and remote wind power. By adopting a lower frequency (50/3 Hz), FFTS could reduce the electric distance of transmission lines, thus lowering the transmission loss. In order to analyze the interconnected system of FFTS and main grid, the power flow calculation should be conducted. This paper introduces a new method to calculate the power flow of the interconnected system and analyzes the control strategy of reactive power of FFTS. Firstly, a quasi- steady model of the cycloconverter is elaborated. Secondly, the validity of the model is verified through power flow calculation and PSCAD/EMTDC simulation of a simplified system. Finally, an alternate iteration method for power flow calculation of the interconnected system is proposed. Based on the IEEE-30 system, the power factor control of FFTS is discussed considering various integration buses of wind power.