A Research Of Stable Operation And Autonomous Control For DC Microgrids

Nowadays,with the increasing penetration of renewable energy generations and growing demand for more reliable and efficient power supply,microgrid has attracted increasing attention.In such microgrid,from the generation side,most renewable sources like photovoltaic(PV)modules,super capacitors,and wind turbines are either inherently DC sources or converted to DC.And from the load side,most appliances we use today are also based on DC energy,such as household appliances and office equipment.Therefore,compared to AC system,DC microgrid may have higher efficiency and better reliability by eliminating DC-AC converters.Recently,as a key factor for stable control,the research of stable operation and autonomous control for DC microgrids has gradually become a hot area.It has a great practical significant to design a control strategy with high stability and flexibility.This paper is organized as follows.Firstly,the theories of system operation in DC microgrid are introduced based on the research status,topologies,and operation modes.Secondly,the modeling and control strategies of component units in DC microgrid are analyzed,including DC-DC converter and DC-AC converter.Thirdly,the small-signal models of droop-control DC microgrid are derived in the s plane.Eigenvalue analysis results reveal the relationship between system stability and the parameters of DC system,such as DC load power,the type of DC load and the droop gains.A low-pass-based active damping method is proposed to overcome the unstable oscillations and improve the stability.For rational power sharing and autonomous operation,a TOU-price-based hierarchical coordination control strategy is proposed in this paper,whose control architecture is divided into three levels: converter control level,bus regulation level,and power dispatch level.The proposed strategy can not only implement distributed autonomous operation,but also improve system economy.Finally,the effectiveness of proposed active damping method and hierarchical coordination control strategy is verified by the lab-scale DC microgrid platform in Tianjin University.