Power Control Strategy Of Inter-linking Converter In Hybrid Microgrid

Microgrid can realize centralized management of load and distributed power supply,and can solve the problem of access and absorption of renewable energy and unconventional power supply.It is one of the important directions for the development of power grid technology in the future.The hybrid AC/DC microgrid connects the AC microgrid and the DC microgrid through interlinking converters,which combines their respective advantages and has higher efficiency and compatibility in integrating distributed power and AC and DC loads;moreover,relying on interlinking converters can achieve mutual support of power and improve the reliability of power supply of the system,so it has become a hot research topic in recent years.In this paper,the following research work is carried out on the power control problem of interlinking converters in hybrid AC/DC microgrid.This paper mainly studies the power control of interlinking converters in hybrid AC/DC microgrid,including the following aspects:Firstly,the advantages and disadvantages of four common topologies of hybrid AC/DC microgrid and their applicable scenarios are compared and analyzed.The operation mode,internal micro-source control strategy and control strategy of hybrid microgrid are discussed in detail,and three principles of system control are proposed.Secondly,for the hybrid microgrid with master-slave control,the power balance relationship and the control strategy of the interlinking converter in the two subnets are studied.The main control unit bears the power fluctuation of the system and affects the stability of the system.Therefore,the concept of the capacity occupancy rate of the main control unit is proposed to reflect the operating state of the microgrid on both sides.According to this concept,the mathematical relationship between AC and DC sides is established,and the sectional control strategy is designed to regulate the flow of power between the microgrids,so as to realize the mutual support of power on both sides.In order to avoid frequent switching of the operation mode of the interlinking converter,a hysteresis function is introduced to improve the stability of the system.The simulation model of the master-slave control hybrid microgrid was built in PSCAD/EMTDC,and the effectiveness of the proposed control strategy was verified.Finally,for the hybrid microgrid with peer-to-peer control,based on the three principles of hybrid microgrid control,the droop characteristic curve of the energy storage unit is improved,and the segmentation control strategy is designed.The segmentation control includes a sub-microgrid independent operation section,an inter-network power exchange section,and an over-constrained operation section.Taking the difference between the AC side frequency and the DC side voltage of the standardization process as the action criterion,and considering the state of charge of the energy storage unit,the working principle of each segment control is analyzed in detail;the action criterion is compensated for the possible exchange power oscillation between the microgrids and the frequent switching of the ILC operating mode.The simulation model of the peer-to-peer hybrid microgrid was built in PSCAD/EMTDC,and the effectiveness of the proposed segmentation control strategy was verified.