Research On Multiple Degree Of Freedom Energy Management Of Battery Pack Based On Partial Power Conversion

With the wide application of new energy,the research on battery energy storage systems has developed rapidly.The echelon utilization of ecommissioned batteries is a topic that draws attention.For the decommissioned batteries,the parameters difference are large such as capacity,voltage and internal resistance.In this paper,a multi-degree-of-freedom battery pack energy management system based on partial power conversion is proposed.The proposed multi-degree-of-freedom battery pack energy management system based on partial power conversion is firstly analyzed.The inductor currents of the the front-end Dual Half Bridge(DHB)and the back-end Buck/Boost converter are analyzed based on the different switching subinterval.The constraint required for zero voltage turn-on(ZVS)of the DHB are presented based on the inductor currents expression,and six schemes with different frequencies,inductor values and control methods are compared for the Buck/Boost converter in the back-stage of the system,and a optimized converter scheme is selected.Secondly,the start-up process,control scheme and protection functions of the system are studied.Control scheme mainly including current mode and power mode,and the front DHB are closed-loop control of the secondary bus voltage based on the realization of soft switching.The current mode controls the inductor current of the Buck/Boost module connected to the battery pack to achieve arbitrary output current control objectives such as current sharing.The power mode samples the current and voltage of the battery and then controls their product to achieve a constant set power.The protection functions of the system are mainly divided into voltage and current protection,short circuit protection and fault protection.The transfer functions of the front-stage half-bridge converter and the back-stage Buck/Boost converter are derived separately,and the stability of the current mode and power mode control schemes is verified by drawing a bode diagram using MATLAB software.Then the parameters of the proposed system are designed,mainly including the design of the transformer and phase shifting inductor of the front stage DHB converter,the design of the Buck/Boost inductor of the back-stage,and the design of the bridge arm capacitor and filter capacitor of the system.The parameters such as voltage and current of the system are determined according to the charge/discharge current of the battery pack,the voltage range of the battery pack and the DC bus voltage.Then the front stage transformer and inductor are designed according to the calculated system parameters,followed by the design and selection of the inductor of the back-stage Buck/Boost,and finally the capacitance of the system is calculated.Finally,the proposed multi-degree-of-freedom energy management system based on partial power conversion is simulated and analyzed based on PLECS software,and the experimental verification is carried out by building a battery pack control experimental platform with DSP28335 as the core.