In order to solve the problem that the hybrid multi-terminal DC transmission system cannot operate in the optimal mode under arbitrary power when using the droop control

a loss optimization control strategy is proposed. The control strategy can be divided into two layers. The upper level is the optimization control

which calculates the droop control parameter according to the different inject power of hybrid multi-terminal DC transmission system. The lower level is the droop control to obtain the fast response to power fluctuation. This control scheme successfully obtains the minimum of multi-terminal DC loss and takes the limit of minimum extinguish angle into account for the inverter stations in the grid

which realizes the stable and economic operation of hybrid multi-terminal DC transmission system. In order to verify the effectivity of the proposed control strategy

a six-terminal hybrid DC transmission system is designed. Firstly

the proposed optimal method is used to calculate the stable and optimized results of this model. Then the simulation model is built in PSCAD/EMTDC. The simulation results in the field of power fluctuation and communication failure show that the optimization result of the proposed droop parameter design approach is consistent with the theoretical calculation and satisfies the system constrains. The hybrid multi-terminal DC transmission system not only has good dynamic response of loss optimization when the transmitter power changes but also remains stable during the communication failure.