Research On Control Strategy Of Photovoltaic AC-DC Hybrid Microgrid

Nowadays,China is in the transition period from traditional energy to new energy.How to use clean energy more effectively and conveniently has become an urgent problem to be solved.The common clean energy,such as wind and light,is different from traditional energy such as coal.It has the characteristics of unstable output power and diverse output forms.It has always been a difficult problem in grid-connected operation.It is difficult for a single AC microgrid to accept clean energy such as wind and light,and for a single DC microgrid to meet the needs of AC electrical appliances.In order to solve this problem,following the concepts of reducing AC/DC conversion and local energy absorption,AC/DC hybrid microgrid has become a more appropriate solution.In view of the problems existing in the separate AC and DC microgrids,a photovoltaic AC/DC hybrid microgrid with photovoltaic as the main power source is designed.The hybrid microgrid consists of a DC system with photovoltaic cells,storage batteries and DC loads,and an AC system with AC loads and grid-connected points.Using bidirectional half-bridge DC-DC converter,this paper designs a battery sag control scheme to achieve power stability of DC system.In order to solve the problem that the traditional AC-DC sag control bidirectional AC-DC converter frequently operates near the rated voltage,the AC-DC converter is improved to the subsection sag control by the cooperation of AC-DC converter and battery.In this paper,a unified AC/DC Z/P droop control is proposed,which combines AC side and DC side to improve droop control.The scheme considers the operation status of both DC and AC systems,and determines the operation mode of bidirectional AC-DC converter by collecting bus information at both DC and AC sides.In order to verify the feasibility of the photovoltaic AC/DC hybrid microgrid and its control system designed in this paper,a simulation model is built in Matlab/Simulink,and simulation experiments are carried out to analyze the changes of illumination intensity,load switching and grid-connected/island operation of the system.The experimental results show that the bidirectional AC-DC converter with uniform sag control of AC and DC can simultaneously monitor the operation status of DC and AC systems,thus realizing the unification of AC and DC system control,and realizing the coordinated control with storage batteries,thus maintaining the stable operation of the system.