Droop control is an important DC distribution network control mode. A voltage source converter(VSC)substation local control mathematical model and its linearized small-signal analysis model are deduced. Furthermore

by referring to coordinated control

a general small-signal analytic model of droop control strategies

along with its two typical situations

is analyzed. Based on the VSC small-signal analysis model

the linearized equivalent impedance is devised

by which the whole DC distribution network can be simplified to a system comprising one VSC and several linearized equivalent impedances one by one. Finally the root locus method is adopted to discuss the small-signal stability and its factors of two droop control modes quantitatively

whose validity is verified with PSCAD/EMTDC digital simulation software. This work is supported by National High Technology Research and Development Program of China(863 Program)(No. 2015AA050104).