| The stable transmission of electrical energy is a key technology for renewable energy generation systems.In order to achieve stable transmission of electrical energy,battery storage units are added to new energy generation systems.The charge and discharge control of the battery storage unit requires a bi-directional DC-DC converter,so the circuit structure of the bi-directional DC-DC converter and its control strategy become the focus of this research.The State of Charge(SOC)of the battery storage unit not only provides an accurate estimate of the remaining battery power,but also provides a basis for the charge/discharge control strategy of the battery storage unit.By comparing commonly used batteries,the lead-acid battery is chosen as the object of study.To realise the charge/discharge control and SOC estimation of lead-acid batteries,a charge/discharge topology based on a Dual Active Bridge DC-DC(DAB)converter and its control strategy,as well as a SOC estimation method based on the Extended Kalman Filter(EKF)algorithm,are designed.By improving the equivalent model of the DAB converter and comparing different modelling methods,a current linearisation model is selected and combined with a single-phase shift control strategy to achieve three-stage charging and constant voltage discharge control of the lead-acid battery.In order to achieve real-time online SOC estimation of the battery.Firstly,the lead-acid battery is modelled using the modeling method and a second-order RC equivalent circuit model is established to simulate the dynamic operating characteristics of the lead-acid battery.Secondly,the parameters of the equivalent circuit model are identified online through Forgetting Factor Recursive Least Squares(FFRLS).And finally,the battery SOC is estimated by combining the EKF algorithm.The simulation and experimental results show that the output voltage ripple of the DAB converter is small and the output is more stable;in the process of charging the battery,the charging efficiency and output steady-state accuracy of the DAB converter are improved.By comparing the Extended Kalman Filter algorithm with the Ansatz integration algorithm,the Extended Kalman Filter algorithm SOC estimation has high accuracy and small error. |
