Bus-based Active Equalisation Circuit Design For Low Power Battery Packs

The new energy industry is developing rapidly,and more and more industries are using lithium batteries to gradually replace traditional energy storage devices,while the safety of lithium battery packs in use is receiving more and more attention.In different scenarios,the battery equalization has different requirements.Taking small UAV and aerospace as examples,the main requirements for equalization are small size,light weight and high efficiency.To meet the above requirements,two bus-based equalization circuit topologies are proposed in this paper.The first capacitor-based bus-type equalization circuit can support any battery in series when the device withstand voltage is sufficient,and the equalization speed is independent of the number of series-connected batteries,but only related to the capacity of the batteries.The circuit structure is simple and does not require complex control scheme and algorithm,and only one way clock signal is needed to control the MOS tube switch to achieve equalization.It uses capacitors as a bridge for energy exchange,so that energy flows automatically from high-energy batteries to low-energy batteries.However,this topology still has disadvantages such as large switching losses,high requirements for driving signals,and poor anti-interference capability.The second topology is a bus-type equalization circuit that can realize zerocurrent switching.While having the advantages of the above topology,the softswitching technology is introduced to realize ZCS(zero-current switching)and reduce the switching losses.In this paper,the above two equalization topologies are optimized.The first one finds the best device parameters and control frequency by deriving the equivalent resistance,which reduces the capacitance value and circuit size without reducing the equalization efficiency and reduces the cost.The second equalization topology is derived by deriving the conditions for the equalization topology to achieve ZCS,finding the suitable Q value,and improving the equalization efficiency.In this paper,the effectiveness of the equalization topology and the improved scheme is demonstrated by theoretical analysis,circuit simulation,and circuit experiments that corroborate each other.In addition,this paper designs a circuit to monitor the voltage of a single battery,and chooses two sets of voltage acquisition schemes,resistive voltage divider type and integrated chip type,and makes a physical circuit for both schemes,conducts experimental verification,and analyzes and summarizes the advantages and disadvantages of the two schemes.