The power reference value and the droop coefficient determine power distribution of converter stations and the specific relationship between DC voltage and DC power

and then the power flow of the AC/DC hybrid system with flexible DC grid. So it is very important to select the power reference value and the droop coefficient. A power flow optimal control method for AC/DC hybrid system with flexible DC grid is proposed to minimize the network loss and DC voltage deviation rate. Firstly

the models of converter stations

AC system and DC grid for AC/DC hybrid system with flexible DC grid are built

and a unified expression for the governing equations of DC grid in master-slave control and droop control operation modes is put forward. Then

based on the optimal power flow of AC/DC hybrid system with flexible DC grid

the power reference value and the droop coefficient are corrected continuously in the system running process. Finally

the modified IEEE 39-bus system and IEEE 118-bus system containing five ends of flexible DC grid in different operating modes are simulated and analyzed

with the calculation results showing the effectiveness of the proposed method. This work is supported by State Grid Corporation of China(No. SGRIZLKJ［2015］457).