Battle over NiMH No.7 battery management system balancing technology roadmap

　　As an important component of the electric vehicle NiMH No.7 battery system, the NiMH No.7 battery management system (BMS) controls the voltage, temperature, current, SOC, SOH and other parameters of the NiMH No.7 battery pack as a whole. Among them, since the NiMH No.7 battery pack is composed of several single cells, the BMS also plays the role of energy balance.

　　The need for balance

　　With the current NiMH No.7 battery manufacturing level and technology, there will be subtle differences in each cell during the production process, which is a consistency issue. This inconsistency will make the parameters of the NiMH No.7 battery cells very different. In order for them to fit together to form a whole, a balanced approach must be used in the process of action. Just like the wooden barrel effect, only by making up for shortcomings can performance be maximized.

　　On the other hand, when the cells are used to form a NiMH No.7 battery assembly vehicle, the inconsistency of the cells will also occur due to reasons such as self-discharge and part temperature. The inconsistency of the cells will also affect the charge and discharge characteristics of the NiMH No.7 battery pack. .

　　The battle for balanced technical routes

　　The debate on the BMS technical route mainly focuses on two aspects: passive balancing and active balancing.

　　As the name suggests, passive balancing is to consume the individual cells with slightly more capacity in the single NiMH No.7 battery to achieve overall balance. Active balancing is to transfer the slightly higher energy of the single unit to the slightly lower energy NiMH No.7 battery through the energy storage link. What is achieved is an active distribution effect.

　　Some people believe that passive balancing is more suitable for the current development status of power batteries and has less impact on NiMH No.7 battery life; others believe that active balancing can significantly help improve the overall operating results and driving experience of electric vehicles.

　　Currently, there are many BMS systems using passive balancing on the market. On the one hand, passive balancing appeared earlier than active balancing, and the technology is relatively mature and simple, and is widely used. The active balancing structure is more complex, and the design of the transformer scheme and the switch matrix will undoubtedly increase the cost significantly.

　　As mentioned before, the key point of passive equalization is that the structure is simple and the cost is low, but due to the use of resistors to consume energy, heat will be generated, thereby reducing the efficiency of the entire system.

　　Active balancing has a high energy utilization rate because its principle lies in the transfer and distribution of energy. However, it can generally only transfer energy between two adjacent single cells. The structure is relatively complex and the cost increases. The shortcomings lie.

　　BYD Qin’s BMS balancing technology inspiration

　　According to the official introduction, BYD Qin’s BMS not only has basic NiMH No.7 battery energy management and NiMH No.7 battery thermal management functions, but also has an automatic balancing function for NiMH No.7 battery cells. According to the introduction, during the operation of the vehicle, monitoring the single performance parameters of the entire NiMH No.7 battery pack and achieving timely and automatic maintenance through the NiMH No.7 battery balancing function can greatly reduce the cost of power NiMH No.7 battery maintenance, extend the service life, and improve each stage. performance.

　　Qin optimizes and extends the performance and life of the NiMH No.7 battery pack through an actively balanced BMS system. According to the introduction, Qin specifically uses the DMⅡ generation NiMH No.7 battery management system, and the MIⅡ generation adopts a distributed design. By collecting the temperature and voltage of NiMH No.7 battery cells, the distributed NiMH No.7 battery management system performs power NiMH No.7 battery energy management, thermal balance management, vehicle charge and discharge management, and vehicle high-voltage safety management to further improve the energy management efficiency of the NiMH No.7 battery while achieving lightweight design. Design requirements.

　　Each two single cells form a unit, which transfers energy through energy storage and balances the voltage.

　　summary

　　Whether it is active equilibrium or passive equilibrium, it has its application value. Balance technology is not a god-like existence either. The overall design of the BMS and its matching with the entire vehicle are the key. At the same time, the two BMS equalization methods have obvious advantages and disadvantages, and the main controversy at home and abroad is which method is more reasonable. But it still depends on the characteristics of the NiMH No.7 battery. When the consistency of the cells is strong, a small-capacity NiMH No.7 battery pack is more suitable for passive balancing. If the consistency of a large-capacity power NiMH No.7 battery is average, active balancing will be more suitable for use.

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