Research On Control Strategy In AC/DC Distribution Network

Distribution network is an important part of the power system and the key for users to obtain power from the power grid.The communication system has dominated the distribution for the advantage of simple structure and mature technology;But with the development of distributed generation and rapid growth of DC load,traditional AC power distribution gradually shows its limitations.Therefore,relevant scholars put forward the concept of AC-DC distribution network,which has been widely concerned with the development of energy Internet and the advantages of high power quality,low power loss,good controllability.In this context,this paper takes the AC-DC distribution network with power supply at both ends as the research object,and proposed a new optimization control strategy which makes the system have a better control effect under normal and fault conditions.Firstly,the topology of several common AC/DC distribution networks is introduced,and it is analyzed several aspects such as power supply reliability and power quality.This paper further established the topological structure of the two-end distribution network and the mathematical model of each unit in it;established an optimal scheduling model with minimum power loss and voltage deviation.Secondly,aiming at the characteristics of traditional master-slave control and peer-to-peer control,a hierarchical control based on different time scales is proposed,which combines the advantages of the two controls.In a short-term scale,the first layer control coordinating each converter stations to provide voltage support for DC subnet;the second layer control reduces the voltage deviation of the system under severe conditions by switching the control strategy of the energy storage system;as the third layer control,optimal energy dispatch system provides operational instruction set for the lower control by optimal power flow calculation in a long-term scale which allow the system runs at an optimal state when it is stable.Finally,the effectiveness of the control method in this paper is verified by the normal operation of the system,scheduling faults and DC disconnection faults.By analyzing the switching of the controllable units' control strategy and the adjustment of its output power when the operating state of the system changes,it can be known that the control strategy can improve the operating state of the system with low communication requirements and maintain stable operation of the system in the event of scheduling failure and DC disconnection fault operation.