DC Voltage Control Strategy In The VSC-MTDC System Based On Optimal AC/DC Power Flow

Multi-terminal flexible DC transmission is an important part of the smart grid,but also the current research hot spots.On the one hand,in order to ensure the safe and stable operation of the flexible DC transmission system,it needs to carry on the thorough research to its coordinated control strategy;On the other hand,the popularization and application of the multi-terminal flexible DC transmission system also needs to have the better economy,so the optimization of grid operation is needed.This paper studies the control strategy of multi-terminal flexible DC transmission system based on optimal power flow with voltage source converter,which has certain theoretical significance and engineering application value.In this paper,the structure and principle of the flexible DC transmission system are analyzed.The system level control strategy and the converter station control method of the flexible DC transmission system are studied.Based on the characteristics of these control strategies and the generalized droop control mode,Seamless switching of voltage source converter control strategy could be realized.Then,the optimal power flow of multi-terminal flexible DC transmission system is studied,and a multi-objective optimization model is proposed to reduce the active loss,reduce the system voltage deviation and increase the static voltage stability margin of the system.On the basis of this,a solution method based on interior point method and NSGA2 algorithm is proposed,which divides the multi-objective optimization problem into two parts: continuous optimization and discrete optimization.It can obtain multiple Pareto optimal solutions by one operation,and overcome the defect of the previous algorithm which need to run several times in order to get a set of approximate Pareto optimal solution and the results may be inconsistent.Finally,the control strategy of multi-terminal flexible DC transmission system based on optimal power flow is proposed by combining the trend optimization results of multi-terminal flexible DC transmission system with generalized droop control.Combined with the wind power forecast data,the control strategy is used to adjust the control coefficients of each converter station,optimization of the system operation,power flow,and simulation results show that the proposed method is effective and feasible.