Research On The Active Power Optimal Dispatch And Coordinated Control For VSC-MTDC

The demands of large-scale renewable energy integration and regional grids interconnection promote the rapid development of the voltage-source converter based high voltage direct current(VSC-HVDC)technology.The newly-developed VSC-HVDC system has the following features and characteristics:(1)Bipolar configuration;(2)Different DC network topologies;(3)Varieties of control strategies.These characteristics increase the reliability,flexibility and efficiency of the power grids;on the other hand,it also increases the complexity of the control system.Therefore,it shows research significance and application value to study the active power optimal dispatch and coordinated control strategy for VSC-MTDC.The main research work and achievements are as follows:(1)An active power optimal dispatch method for bipolar operating VSC-MTDC system is proposed.As the positive and negative grids can be independently controlled,power surplus of the fault grid can be transferred to the non-fault one under abnormal operating conditions.This strategy improves the reliability and transmission capability of power grid.(2)In order to provide the rapid and accurate DC power flow,this paper develops a universal power flow algorithm for bipolar VSC-MTDC.The bipolar configuration is fully explored,and different structures and topologies and the new control strategies as well as the existing control strategies are implemented.(3)A novel coordinated control strategy is proposed where the amplitude-phase control and active/reactive power decoupled control can be applied to the positive and negative poles,respectively.The coordinated strategy combines the advantages of two control modes and can be adapted to bipolar VSC-MTDC for wind farm integration.(4)An electromagnetic transient simulation model is built in PSCAD/EMTDC.It is a research platform for the bipolar active power optimal dispatch,coordinated control strategy and the DC power flow algorithm;it also verifies the efficiency and accuracy of the proposed strategies and algorithm.