Research On Active Equalization Technology Of B-C Hybrid Energy Storage System Under The Background Of Echelon Utilization

Battery is the core energy storage component of electric vehicles.After a certain period of use,the battery charging capacity will decline,and it will no longer be suitable for electric vehicles,facing retirement.The retirement of a large number of batteries will bring great pressure to resource recovery.Therefore,some scholars put forward the concept of "battery echelon utilization",which includes the batteries retired from electric vehicles into energy storage power stations for recycling and reuse,so as to prolong the service time.Whether it is used as the first stage of power battery in electric vehicles or as the second stage of energy storage power stations,lithium-ion battery packs are inconsistent.The inconsistency of lithium-ion battery pack is solved by equalization technology.At present,a large number of scholars have conducted relevant research on the battery equalization technology of pure battery energy storage system,while the research on the battery equalization topology of battery super capacitors(B-C)hybrid energy storage system is relatively lacking.The characteristic of electric vehicle load is that it changes violently and often needs large current output.In order to prolong the service life of the energy storage system,B-C hybrid energy storage system is usually used to provide energy for electric vehicles.Therefore,it is necessary to build a battery equilibrium topology suitable for B-C hybrid energy storage system.According to the characteristics that the energy transmission demand from lithium-ion battery pack to super capacitor is prior to the battery equalization demand in the application scenario of electric vehicle,a transformer based equalization circuit suitable for the hybrid energy storage system of electric vehicle is proposed.Under the condition of using only one MOSFET,the equalization circuit uses a transformer to realize the function of transmitting energy from the lithium-ion battery pack to the super capacitor and the function of battery equalization.When the MOSFET switch is on,the transformer forms a forward converter to realize the high-speed transmission of energy from the lithium-ion battery pack to the super capacitor;When the MOSFET switch is turned off,the transformer constitutes a flyback converter to realize the degaussing of the transformer core,and the degaussing current is automatically distributed according to the voltage of each battery cell to achieve battery balance.In the application scenario of energy storage power station,the battery equalization demand takes priority over the energy transmission demand from lithium-ion battery pack to super capacitor.A transformer based equalization circuit suitable for the hybrid energy storage system of energy storage power station is proposed.When the MOSFET switch is turned on,the transformer forms a forward converter.The battery whose voltage is higher than the average voltage transmits energy to the battery whose voltage is lower than the average voltage to achieve high-speed battery energy balance;When the MOSFET switch is turned off,the transformer constitutes a flyback converter,which absorbs the excitation current of the transformer through the super capacitor to demagnetize the transformer core and realize the energy transmission from the lithium-ion battery pack to the super capacitor.In this paper,the topology and working principle of the two proposed active equalization circuits are introduced in detail,and the derivation of the mathematical model and the construction of the simulation model are completed to verify the effectiveness of the two proposed equalization circuits.Finally,an experimental platform is built to verify the performance of the circuit.