In order to maintain the voltage stability and the balance of power between converter stations for MMC-MTDC

a differential flatness based on adaptive droop control strategy is proposed.The controller consists of a feed-forward double loop control and dynamic error feed-back control.The feed-forward control is based on the reference trajectory according to the system flat output expected and the functional relationship between system state variables and input variables.First

the dominant control of the control system is obtained.The linear feed-back error control eliminates the impacts of system disturbance and external disturbance on the trajectory of the system.Then

the system response speed and transient and steady-state characteristics are enhanced.Finally

an MMC-MTDC simulation model including five stations is established in PSCAD/EMTDC.Simulations are performed to validate the feasibility of power flow inversion in steady state and the outage broken main station.The results show that the control strategy can be adopted to control the droop coefficient according to the direction of DC voltage variation and converter margin.Converters can avoid the full or overload operation.All the converters can achieve their optimal power sharing.