Reseach On Coordinated Control Strategy For Multi-terminal AC/DC Hybrid Distribution Network

In recent years,with the increasing load density of urban distribution networks,traditional centralized power generation,high-voltage transmission,and medium-and low-voltage power distribution modes have exposed more and more serious problems,such as poor power supply capability,high harmonic content,and transmission corridor tension and environmental pollution;on the other hand,a large number of distributed power sources and DC loads are connected to the distri bution network,which changes the topology and tidal current distribution of the original distribution network,resulting in poor power supply quality,severe power loss and c omplex control.AC/DC hybrid distribution network can minimize the use of commuta tion equipment and reduce the construction cost of distribution network.It has become a feasible way to transition from AC distribution to DC distribution.In this context,the basic composition and topology of the AC/DC hybrid distribution network for double-ended and multi-terminal power supply are described.In order to ensure the safe and stable operation of the system,the control strategy of the system is mainly studied.Firstly,the topology,optimal scheduling,control strategy and protection technology of AC/DC hybrid distribution network are briefly summarized.The topology structure and related control methods of various power distribution units are proposed,and double-ended power supply and multi-end are established.The topology of the AC-DC hybrid distribution network is given,and the optimal scheduling model of AC/DC hybrid distribution network is given.Secondly,for the double-ended power supply AC/DC hybrid distribution network,an optimization control strategy based on different time sca les is proposed.In the short time scale,each grid-connected converter operates in the droop control mode according to the upper-level scheduling instructions.When the system is stable,it works in an optimized state;when a bad working condition occurs,the control strategy of the interconnecting converter and the energy storage unit converter is switched to maintain the DC side voltage stability of the distribution network.In the longer time scale,the corresponding optimization objectives are establis hed for the normal operation of the system and the DC disconnection fault.The scheduling algorithm is used to provide the scheduling instruction for the lower layer.The simulation results verify the effectiveness of the proposed control strategy.Finally,for the multi-terminal power supply AC/DC hybrid distribution network,a centralized-distributed control strategy is proposed.In the centralized control layer,the energy management system gives the optimal power reference value of each controllable element in the system;The layer provides initial operation instructions;in the decentralized control layer,the units participating in the power adjustment in the system are hierarchically controlled to ensure that the system can flexibly and efficiently adjust the system under different operating conditions,and the simulation model is set up.The control strategy was verified.