In order to optimize the power flow of the high voltage direct current(HVDC)grid and reasonably distribute the unbalanced power after disturbance

this paper proposes a hierarchical coordinated adaptive droop control strategy in flexible DC grid. Based on the DC voltage and active power of converter stations

the system-level control layer takes minimum network loss and DC voltage deviation of DC grid as the optimization object. Then the references of DC voltage and active power are analyzed and optimized in real time

so that the DC power flow optimization can be achieved in steady state. The optimization of converter-level control layer is based on the local signals. Considering the power margin of converters and the voltage deviation factor

the droop coefficient is adjusted in real time to realize the reasonable distribution of unbalanced power in the DC grid after disturbance and reduce the deviation of DC voltage. The optimization of reference values on system-level control layer is coordinated with the optimization of droop coefficient on converter-level control layer

so the coordination control of power is realized. The simulation results of seven-terminal DC grid verify the effectiveness and superiority of the proposed strategy.