| As the reserves of petroleum energy on the earth are dwindling,fuel vehicles will gradually fade out of the historical stage in the future.The main power source of new energy vehicles is electric energy,which is classified as renewable energy and does not produce exhaust gas.It is great of significance to protect the environment and clean the air.Lithium batteries are often used as the main carrier for storing electrical energy,which has the advantages of high power density,no memory effect,and many cycles.However,due to factors such as differences in production processes and complex use environments the energy between cells will gradually be forced to change,the life of the entire battery pack will be affected,and even the safety of driving will be affected.To solve the above problems,a novel bidirectional battery voltage equalizer is proposed in this paper.Firstly,the reasons for the inconsistency of power between battery packs are analyzed,and the solutions currently used are summarized.Focusing on the non-energy dissipative equalization structure,a bidirectional battery voltage equalizer based on a flyback transformer was proposed in this paper.The forward operation of this structure can be equivalent to a dual switch flyback mode,which is realized the continuous balance of the battery pack to the low-battery cell,and the energy of the leakage inductance can be fed back to the battery pack.It not only reduces the equalization time but also improves the efficiency.Reverse operation of this structure can be equivalent to flyback mode.Two high-power cells can be balanced at the same time,and the leakage inductance energy can participate in the work of the next cycle through the conduction of the corresponding switch tube,thereby further reducing the balancing time and improving the energy utilization rate.The principle analysis and programmatic demonstration of the forward and reverse working modes are carried out,and then the parameters and working efficiency of the equalization circuit are calculated.Secondly,the physical construction and debugging of the new bidirectional battery voltage equalization system are carried out.The balance system is mainly divided into six parts: battery pack module,battery voltage detection and control module,main circuit module,switch array module,host computer monitoring module,and main control module.Different control strategies are formulated according to the forward and reverse working modes of the main circuit,and the corresponding energy transfer is carried out through the gating of the switch array.The power status of the entire battery pack is displayed by the host computer built by Lab VIEW.Finally,in order to verify the feasibility of the proposed new structure,a battery pack composed of 12 2800-m Ah 18650 lithium batteries is used to carry out an equilibrium test.The initial voltage distribution of each cell in the battery pack is set to be relatively dispersed,and then start voltage equalization.After 220 minutes,the overall voltage tends to be basically the same,the maximum voltage difference between the cells is reduced from the initial 1.111 V to the final 28 m V,and the equilibrium efficiency reaches 88.2%.The experimental results show that good equalization performance is proved by a new voltage equalization circuit proposed in this paper. |
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