Research Of Equalization For Series-connected Lithium-ion Batteries

With the development of lithium-ion battery technology and the popularization of the concept of energy conservation and environmental protection, the high-capacity lithium-ion batteries have been more and more wildly used in high power situations, such as electric cars, electric bicycles, hybrid driven vehicles, photovoltaic power generation systems—the new energy field and the aerospace field.The problem of capacity unbalance, which occurs when lithium-ion batteries are series connected, limits its application. Adding an equalization circuit is a good solution, especially for the expensive big capacity lithium-ion batteries, which need effective and reliable equalization circuits and control strategies. It is reasonable to say that to make the large-capacity lithium-ion batteries widely used in high power situation, effectively equalization in a single battery is one of the current technological bottlenecks. Therefore, it is magnificent to have in-depth study on the equalization circuits of the lithium-ion battery pack.The main contents of this paper are as followed:1. Summarization and comparison of the current equalization technique for series-connected lithium-ion batteries, including the equalization topology and control strategy.2. Combining with the need of the equalization circuits, detailed tests and research on lithium batteries' characteristics have been done and significant conclusions for equalization circuits are drawn.3. An equalization circuit for nine lithium-ion batteries is introduced, including the detailed design flow and the parameters.4. A new over equalization adding delay loop control program is put forward, based on lithium-ion electrical characteristics. Finally, the experiment and simulation results are presented to qualify the program.5. Some conclusion and prospect is put forward based on the research of this paper.