A Multi-port Converter Of Photovoltaic-battery Energy System Application

With the reduction of fossil energy and the aggravation of global environmental pollution,the renewable energy represented by the solar energy has received more and more attention.Minimum micro grid system,which is composed of distributed photovoltaic,energy storing device,the local load,converters and control units,monitoring and protecting units,is one of the most effective ways to manage distributed generation system for intelligent distribution network.Under such circumstances,this paper seeks to study photovoltaic-battery energy system integrated of a multiport converter.Firstly,this paper summarizes the research status of integrated photovoltaic-battery energy system from two aspects of system structure and control strategy.The system structure of photovoltaic inverter,standalone and grid-connected/stand-alone integrated photovoltaic-battery energy system are summarized.The control strategy of maximum power tracking control method for photovoltaic inverters are also reviewed.Then,this paper studies a multi port converter of photovoltaic-battery energy system based on common DC bus.The working principle of the bidirectional DC/DC converter and Boost converter is analysed,and the input-output relationships of two converters in steady-state condition are derived.The working principle of the three phase four wire inverter is also analysed.The mathematical model of these three converters is established.Secondly,this paper analyses the system operating modes,which are divided by energy flows,and the control strategy of each converter in every operating modes.Then,system operating modes transitions in gridconnected state and off-grid state are proposed,and changes of the control strategy of each converter during operating modes transitions are discussed.The control strategy of the bidirectional DC/DC converter,Boost converter and three phase four wire inverter in grid-connected state and off-grid state are discussed in detail.Lastly,a 50 kW prototype of the multi-port converter of photovoltaicbattery energy system is built.The design of experimental prototype mainly contains three aspects: the main circuit design,control circuit design and software design.The operating modes and control strategy of each converter in the system energy flows are verified by the prototype test.Both steady state experimental results and transient experimental results verify the reliability of converter and feasibility of the theoretical analysis above.