Synergic control method and system of multi-end flexible DC power transmission

The invention provides a synergic control method and system of multi-end flexible DC power transmission. The synergic control system comprises a plurality of converter stations employing multi-point voltage control strategies, wherein at least one of the converter stations is selected as a main power balancing station, the other converter stations are auxiliary power balancing stations, the main power balancing station is used for adjusting a power reference value according to power reference values or actual-measurement powers of the other converter stations and rapidly adjusting the system power when power flow of a DC system is changed so that a DC power grid is maintained to run at a standard voltage in a steady state, the auxiliary power balancing stations participate in adjustment during the dynamic adjustment, and the auxiliary power balancing stations are used for accurately transmitting an active power in steady states according to the power reference value designated by the system. The main power ba