Design And Research Of Energy Storage System Of Lithium Iron Phosphate Battery

Lithium battery is a new type of energy,which supports charging and discharging of high rate current,has many cycles and good stability,and is widely used in energy storage system.A low voltage and low power lithium battery energy storage system based on lithium iron phosphate battery is studied in this thesis.The system integrates BMS battery management unit and inverter unit.The BMS battery management unit is the core unit of the energy storage system.It detects and controls the input and output of the whole system,protects the battery,prolongs the battery life,and plays a crucial role in the stability and safety of the system.In the design of the battery management unit,the stability of the battery should be tested first,so as to determine the operating temperature and current within the normal range of the battery.Several charge-discharge cycle tests were carried out under different conditions to observe the effects of temperature,working current and aging degree on the stability of the battery.In order to accurately predict the working state of the battery,determine the relationship between external factors and the working state of the battery,and timely charge and discharge control and protection,the second-order modeling optimization and analysis of the battery was carried out.Secondly,SOC estimation is the key and difficult point of battery management system design.If the SOC estimation deviation is too large,the battery will be overcharged or overdischarged,which affects the battery life and poses security risks.In this thesis,the open circuit voltage method and ampere-hour integral method are used to estimate the SOC of the battery,and the estimate is modified during the working process,which solves the problem that the open circuit voltage method can not predict the SOC change,and the ampere-hour integral method can not predict the initial value.Finally,the improved passive equalization circuit is adopted in this thesis to improve the equalization efficiency and ensure the safety of the equalization.In the design of inverter unit,aiming at the problems that single-phase inverter is easy to be disturbed and switch timing control is difficult,this thesis adopts two-stage architecture design.The front and back stages of the inverter are separately controlled,which has strong anti-interference ability.The timing sequence of the front stage DC/DC is controlled by the chip with protection function,which ensures the safe and stable operation of the inverter unit.At the end of this thesis,the software design of the energy storage system,including battery management unit program and inverter program.The battery management unit program includes charge and discharge control program,SOC estimation program,SPI communication program and power consumption reduction sleep program.The inverter unit program includes SPWM signal modulation program and various protection programs.Through the experiment,the energy storage system software is stable and reliable,and meets the design requirements.