Research On Equalizers And Balancing Strategies For Battery Packs

So far the energy crisis and environmental pollution is a grave threat to humansurvival and sustainable development. In order to alleviate the energy crisis andmaintain the survival environment, on the one hand the renewable energy, such assolar power and wind power, are used to generate electricity, on the other hand a largenumber of electric vehicles are developed and produced to achieve zero discharge ofthe vehicle exhaust. The battery management system (BMS) is the key technology ofthe wind-solar energy storage battery system and the electric vehicle power batterysystem, which can improve the performance of the battery and ensure that the batteryis safe and reliable to be used. The balancing management system is the coretechnology of the BMS. Based on this background, the equalizers and balancingstrategies for battery packs are carefully studied in this paper, and the main researchcontents are listed as follows:1) The development status and the market application of the power and storagebattery are described in this papper. After analysizing the different batteries, thefunctions of the battery management system are described simply. The batterybalancing management is a core thecnology of the BMS, so according to thecurrent research several typical balancing schemes are briefly described, andsimultaneously the advantages and disadvantages of the balancing schemes arediscussed.2) A new balancing topology circuit based on LC oscillation circuit is suggested inthis paper. The voltage of the capacitor is improved by the LC oscillation circuit,so the shortcoming of the capacitor balancing scheme is overcomed. The abovebalancing circuit loss is bigger and the balancing current is difficult to becontrolled, so the balancing circuit is changed. The simulation results verify thebalancing efficiency of the changed circuit has been improved obviously. Theexisting balancing circuit based on cuk chopper circuit is improved in this paper,the number of the switches is reduced to one half and the driving circuits of theswitches are greatly simplified.3) An internal equalizer of battery pack is suggested in this paper, and it is composed of an inductor and a switching bridge matrix. The balancing energy is transferredwithin the battery pack. The balancing current is controllable, the balanced batterycell is selectable, and the balancing energy is bidirectional. In order to furtherimprove the discharging capacity of the battery pack and make the equalizer moreeasily achieved, the power supply is introduced to the above equalizer, which isthe internal and external equalizer of battery pack. The balancing strategy ofbattery discharging, the balancing energy is from the external equalizer of thebattery pack. In order to simplify the switching control of the charging balancingcircuit, a freewheeling diode is added to the above equalizer, which is the externalequalizer of battery pack. The balacing energy is transferred between the batterypack and the equalizer. The switching control is simpler and the equalizer is easilyachieved.4) Using the the external equalizer of battery pack and its balancing strategies, thebalancing experiment of charging and discharging for four serially connectedbattery cells has been completed. The corresponding experimental results showthat the equalizer improves the inconsistency degree of the battery cells andincrease the battery pack capacity of the charging and discharging.