Equalization Of Lithium Battery Pack For Electric Vehicle Based On Bidirectional Cuk Converter

With the development of global economy,fossil energy is being depleted gradually,along with environmental pollution and other problems.Under such great pressure,people vigorously develop new energy,new energy vehicles because of its low energy consumption,light pollution and other advantages have been favored by governments around the world.With the progress of technology,lithium battery has gradually become the preferred power source of new energy vehicles due to its excellent energy density,long service life,convenient charging process,extremely low self-discharge rate and green environmental friendliness.In order to meet the normal use of a new energy vehicle,due to the low voltage of a single battery,it is necessary to series several batteries into a battery pack to provide energy for the electric vehicle.Due to the errors in the production process of lithium battery in the factory and the influence of environmental factors,there will be inconsistent conditions in the use of lithium battery pack.The inconsistency of battery pack will lead to the decrease of battery life,low energy utilization rate,and even cause explosion.Therefore,the battery equalization technology must be used in the use of lithium battery pack.Firstly,the causes of the inconsistencies of lithium battery are analyzed,and the advantages and disadvantages of different equilibrium evaluation indexes are analyzed.The terminal voltage is selected as the equilibrium evaluation index.Secondly,various balancing topologies are analyzed and compared in detail,and the active balancing system of lithium battery pack based on bidirectional Cuk converter and flyback converter is selected.In this paper,the working principle of bidirectional Cuk converter is analyzed and the formula is derived,and the difference between it and unidirectional Cuk converter is explained.The working principle of flyback converter is analyzed and its formula is deduced.Thirdly,the equilibrium scheme combining bidirectional Cuk converter and flyback transformer is introduced,the basic working principle of this grouped equalization scheme is analyzed,including intra-group equalization and inter-group equalization system,and the working process of equalization circuit is introduced.Subsequently,using voltage as the control variable,suitable control strategies were proposed for the duty cycle setting of MOSFET switches in intra group and inter group balancing.A simulation model is established in MATLAB to prove the effectiveness of this topology and the correctness of the equalization strategy,and to test the equilibrium efficiency of the equalizer.Finally,according to the principle analysis mentioned above,the hardware and software are designed,and a hardware experimental platform is built.The hardware circuit and control strategy of the balancing system are integrated into the built power battery equalization test system to verify the effectiveness of the designed equalization topology and equilibrium strategy.