2 core functions of the battery management system
2.1 SOC estimation
2.2 Balance Management
There are many processes in the process of producing a battery, and differentiation can cause inconsistencies. The difference in battery cells is mainly reflected in the change in internal resistance and capacity over time and temperature. Large differences between cells are more likely to cause overcharge or overdischarge, resulting in battery damage. Achieving battery balance maximizes the utility of the power battery, extending battery life and increasing safety. At this stage, the mainstream balance methods at home and abroad are as follows:
(1) Resistance equalization method. This method is the main representative of the energy dissipation type equalization method. The method is simple and the cost is low, but the energy loss is relatively large and the efficiency is low. It is only suitable for systems with small current charge and discharge.
(2) Switched capacitance method. This method is the main representative of the non-energy dissipative type equalization method, which makes up for the shortcomings of resistance equalization. However, its control circuit is complicated, the equalization speed is slow, and it takes a long time, which is not suitable for large current use.
(3) Transformer equalization method. This method is based on a symmetrical multi-winding transformer structure of a series battery pack active equalization control method. Its shortcomings are complicated circuits, many devices, and too large a volume, which is not easy to expand the battery pack. Generally suitable for charging and discharging of large currents.
(4) Centralized equilibrium. The method can quickly transfer the entire battery pack to the battery cells, and the centralized equalization module is smaller in size. However, the balancing operation of multiple batteries cannot be performed in parallel, and a large number of cable connections are required, which is not suitable for a battery pack having a large number of batteries.
2.3 Thermal Management
Temperature has an impact on all aspects of battery performance. Temperature field non-uniformity will exacerbate the inconsistency of the battery pack, so it is necessary to manage it. The purpose of thermal management is to maintain the temperature of the battery system within a certain range by heating or heat dissipation, and to maintain the temperature uniformity within the battery as much as possible.
Temperature management mainly completes the following four functions: (1) rapid heating of the battery pack under low resistance conditions; (2) ensuring uniform distribution of the battery temperature field; (3) accurate measurement and monitoring of the battery temperature; (4) in the battery pack When the temperature is too high, the amount of heat is effectively dissipated. Commonly used cooling methods include natural convection method, forced air convection method, liquid flow method, phase change material method and thermal management method. Common heating methods include battery internal heating method, heating plate method, heating jacket method and heat pump method.
