To solve the problem of overloaded DC voltage and power inappropriate allocation in VSC-MTDC transmission system

we proposed a coordinated control strategy combined with the scheduling system. The short-term load forecasting is carried out by the scheduling system

and the droop coefficients

DC voltage reference values and DC power reference values of all droop-control stations are considered as decision variables

while the DC voltages

DC powers and DC line currents are not limited as inequality constraints

so that a multi-target optimization model for the minimum system loss and the minimum DC voltage deviation is established. In addition

in order to ensure the stability of the system

with an established state space model reflecting the response of the VSC-MTDC DC side

the equality constraint of the sum of all droop coefficients as a constant value is introduced. In the example

a four-terminal VSC-MTDC system is built to be tested under the cases of the power invariance

power mutation and planned outage of the fixed power station. The results show that the proposed algorithm can ensure that the DC voltage of each node is between –5% and 5% of the rated value

ensuring that the DC power of each station is not full

on the premise of ensuring the stability of the system. Therefore

the proposed algorithm can optimize the operation characteristics of VSC-MTDC

and can be used as a control means for steady state control or planned outage.