Research On Flexible Interconnection Technology Of AC/DC Hybrid Distribution Network

The AC/DC hybrid distribution network meets the development trend of the future smart grid.The flexible interconnection technology can independently control the active and reactive power and improve the flexibility of power transmission,which is one of the key technologies for constructing AC/DC hybrid distribution network.As a power electronic device,Soft Open Point(SOP)and Flexible loop network controller(FLNC)can flexibly control the power of the system and effectively cope with grid fluctuations when distributed power supply is connected.However,compared with the traditional distribution network,the research on the optimized operation technology of AC/DC hybrid distribution network with power electronic components faces great challenges in control strategy and optimization scheduling.This paper analyzed the current AC/DC hybrid distribution network in China,which has three connection modes: radiation mode,power supply at both ends mode and ring mode.The voltage level of the distribution network,the structure selection and control method of the converter were studied.The AC/DC hybrid distribution network based on soft open point and the AC/DC hybrid distribution network based on flexible loop network controller were constructed.Firstly,in order to solve the problems of system loss increase and node voltage limit caused by massive access of distributed power supply,according to the operating characteristics of B2 B VSC,An optimal control strategy for AC/DC hybrid distribution network based on SOP was proposed.The strategy built a mathematical model to improve power loss and adjust voltage over-limit.The improved genetic algorithm was used to solve the problem.The simulation results demonstrated the rationality of the proposed optimal control strategy.Secondly,the three-terminal flexible loop network controller was taken as an example to introduce the topology structure and operation principle of the flexible loop network controller.For the three-terminal flexible ring network device,two power distribution methods were proposed,in which one end acts as a rectifier and the others act as inverter or two end act as rectifier and the remaining end act as a inverter.An idea of reducing power order was given for the four-terminal flexible loop network controller.Finally,aiming at the problem that it is difficult to achieve rapid optimization of local control of distribution network,based on the global optimization of the system,a hierarchical control method of AC/DC hybrid distribution network based on flexible ring network was proposed.The method divides the system into two situation: normaloperation and single-ended fault of the FLNC.In normal operation,the system set up a mathematical model with the minimum network loss as the target and to find optimal operating state of the system;When the FLNC has a single-ended fault,the device automatically switched the control strategy according to different types of faults,so as to reduce the voltage fluctuation and ensue the smooth operation of the system.The simulation results verified that the hierarchical control strategy not only optimizes the system operation from the global perspective,but also solves the failures of grid quickly,and meets the requirements of economic operation and green development of flexible distribution network in the future.