| New energy power generation has the advantages of flexible power generation,low investment cost and environmental cleanliness,which has a good effect on alleviating the current severe environmental problems and energy crisis.But it has characteristics of intermittent and low energy density per unit area,so the micro-grid with intelligent adjustment ability has become an important form to promote the development of new energy power generation technology.At the same time,most of the current household appliances can be powered directly from the DC power supply,the photovoltaic,energy storage and other power supply units are connected to dc residential microgrid system by dc bus supplying for the appliances which could reduce the power loss because of multi-stage the ac to dc power conversion.By investigating the types,power and usage frequency of the household loads,the structure and capacity configuration of a residential dc microgrid is put forward in this paper,and the stability control of the system has been studied,The main contents and outcomes of the paper are as follows:1.The structure and capacity configuration of a residential dc microgrid is designed Then,according to the system capacity,voltage and current and control requirements,the parameters and control algorithms of PV power generation unit,energy storage unit and grid-connected power electronic interface are designed,including constant voltage and current control of the battery as well as MPPT and limit the power control of PV power generation unit.2.In the aspect of dc residential microgrid control,this paper proposes a control strategy based on master and slave control and hierarchical control frame which is divided into upper layer optimal control and bottom converter control.The upper layer optimization control is responsible for the system to optimize the operation,including to smooth line power,optimize the battery charge and discharge,and the bottom converter control is responsible for controlling the system converter to maintain the dc bus voltage stability.The proposed dc microgrid may operate in grid-connected mode and off-grid mode.When the system at grid connected mode,that is,the grid is stable and the power to grid power electronic interface is working normally,the control mode of the bottom converter uses the following manners which the grid-connected converter adopts voltage control to maintain the bus voltage stable and the photovoltaic and energy storage converters adopt current control method to regulate their output power.When the system at off-grid connected mode when grid or the grid-connected converter is in failure,the control mode of the bottom converter uses such manners that energy storage converters adopt voltage control to maintain the bus voltage stable and the photovoltaic converter using current control to control release power.3.A small signal model of the residential dc microgrid is established,and the influence of the controller parameters of the converters and load variation on the stability of the system is analyzed by the small disturbance characteristic analysis method.Finally,the simulation model of the residential dc microgrid system is established by using Matlab/Simulink,and the running conditions of the system in grid-connected mode,off-grid mode as well as the above two modes switching are analyzing.The simulation results show that the control strategy can effectively coordinate the system operation and the power distribution between PV and battery,to maintain the DC bus voltage stability. |
