Series parallel topology of lithium battery pack

　　The typical connection modes of lithium battery pack include parallel connection first and then series connection, series connection first and then parallel connection, and hybrid connection.

　　Lithium battery packs for pure electric buses are usually connected in parallel and then in series.

　　Lithium battery packs for power grid energy storage are usually connected in series and then in parallel.

　　Advantages of lithium battery in parallel before in series

　　The lithium battery unit will automatically exit when it fails, except for the capacity reduction, which will not affect the use after parallel connection;

　　When a single lithium battery in parallel is short circuited, the current of the parallel circuit is very large, which is usually avoided with fuse protection technology.

　　Disadvantages of lithium battery in parallel before in series

　　Due to the difference of internal resistance of lithium battery cells and uneven heat dissipation, the cycle life of lithium battery packs after parallel connection will be affected.

　　Advantages of lithium batteries in series before in parallel

　　According to the capacity of single lithium battery, series connection is carried out first, such as 1/3 of the capacity of the whole group, and then parallel connection is carried out to reduce the failure probability of large capacity lithium battery modules; It is very helpful for the consistency of lithium battery pack to string first and then parallel.

　　From the perspective of the reliability of lithium battery pack connection, the development trend of voltage inconsistency and performance impact, the parallel to series connection is better than the series to parallel connection, and the series to parallel lithium battery topology is conducive to the detection and management of each lithium battery unit in the system.

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