Research On Power Coordinated Control Strategy Of DC/AC Hybrid Micro-grid

Micro-grid is an important means to solve the issue of large-scale renewable energy access in future smart grid systems.With the widespread use of DC power supplies and loads,as well as the increase mutual penetration rate of DC/AC loads,DC/AC micro-grid that combines the characteristics of AC micro-grid and DC micro-grid will become the mainstream of micro-grid technology in the future.How to allocate the power of DC/AC micro-grid reasonably to achieve coordinated operation is an important goal of DC/AC micro-grid control.Research has been carried out from different angles for the power control of DC/AC micro-grid,while still lacks the refinement and summary of key technology.Therefore,this paper designs a multi-mode power-coordination control strategy for DC/AC micro-grid applied to buildings.Firstly,this paper proposes a topological structure of DC/AC micro-grid for building since the high inter-permeability of AC and DC loads in building.The bus structure and voltage level as well as the allocate of the load are analyzed for the designed system.Photovoltaic power generation modules,battery module,and bi-directional DC/AC converter units are modeled and analyzed.Secondly,the power balance relations under two operating conditions,grid-connected and off-grid,were separately discussed.The operation case of the system are classified into different operation modes according to the power shortage of the micro-grid and the state of charge of battery.With the threshold of each unit converter,the system can be switched among the different modes to achieve power balance control.Finally,a multi-mode power-coordination control strategy is proposed based on the above operating modes.The working mode of the converters can be changed automatically according to the power shortage of the micro-grid and the state of charge of the battery in order to ensure the stability of the DC/AC micro-grid under all operating conditions.When the operation condition changes,each unit can change its operation mode according to its own threshold,in order to achieve reasonable power distribution among the units.A control strategy of reactive power compensation is proposed except for the active power control strategy to realize local balance of reactive power.Simulation is performed to verify the designed control strategy can achieve a reasonable power allocation among units in the DC/AC microgrid,so as to achieve the stable operation of the system.