Why do lithium batteries need BMS?

2021-09-02 09:00:24 0

Why do lithium batteries need BMS? The role of lithium battery protection board BMS. Although lithium batteries have more advantages than other types of batteries, there is a danger of explosion when lithium batteries are in a severely overcharged state, which can cause damage to the lithium battery and threaten the safety of users. Therefore, it is necessary to equip the lithium battery with a set of targeted lithium battery management system BMS to effectively monitor, protect, energy balance and fault alarm of the battery pack, thereby improving the working efficiency and service life of the entire lithium battery.

What is BMS?

The battery management system, abbreviated BMS, is a system for battery management. It usually has the function of measuring battery voltage to prevent or avoid abnormal conditions such as battery over-discharge, over-charge, and over-temperature. With the development of technology, many functions have been gradually added.

The battery management system is closely integrated with the power battery of the electric vehicle, and the voltage, current, and temperature of the battery are detected in real time through sensors. At the same time, it also performs leakage detection, thermal management, battery balance management, alarm reminder, and calculation of remaining capacity (SOC) , Discharge power, report the battery deterioration degree (SOH) and remaining capacity (SOC) status, also use the algorithm to control the maximum output power according to the battery voltage, current and temperature to obtain the maximum mileage, and use the algorithm to control the charger for the best current For charging, real-time communication with on-board master controller, motor controller, energy control system, on-board display system, etc. is carried out through the CAN bus interface.

The function of BMS should include basic battery protection function, battery equalization function, battery reserve energy calculation function and network communication function.

Why do lithium batteries need BMS?

The power lithium battery management system can effectively monitor, protect, energy balance and fault alarms on the lithium battery pack, thereby improving the working efficiency and service life of the entire power battery pack. Lithium batteries are widely used in various precision equipment due to their high working voltage, small size, light weight, high energy density, no memory effect, no pollution, low self-discharge, long cycle life and many other advantages. However, lithium batteries have serious shortcomings. In summary, there are the following two aspects:

(1) Security

Lithium batteries have poor safety and have defects such as explosions from time to time. In particular, lithium batteries with lithium cobalt oxide as the cathode material cannot be discharged at a large current, and their safety is poor. In addition, overcharging or over-discharging almost all kinds of lithium batteries can cause irreversible damage to the cells. Lithium batteries are also extremely sensitive to temperature: if they are used at too high a temperature, they may cause the electrolyte to decompose, burn or even explode; if the temperature is too low, the performance of the lithium battery will deteriorate significantly and affect the normal use of the device.

Due to the limitations of the battery manufacturing process, the internal resistance and capacity of each battery cell will vary. When multiple battery cells are used in series, the charging and discharging rate of each battery cell will be inconsistent, which leads to low utilization of battery capacity. In view of this, the lithium battery usually needs a special protection system to monitor the health of the battery in the actual use process, so as to manage the use process of the lithium battery.

(2) Maintainability

The capacity decay and power of lithium batteries cannot be accurately predicted at low temperatures, which makes the maintainability of the equipment poor. Long-term online meters need to replace batteries regularly, but remote monitoring equipment has scattered work sites and long distances between sites. Therefore, the workload of battery replacement is huge and the cost is high.

In order to reduce maintenance workload and maintenance costs, it is necessary for the lithium battery BMS management system to have an accurate state of charge estimation function to accurately grasp the state of charge of the battery, and to perform battery replacement work more purposefully; at the same time, the battery management system is also required Low self-power consumption to reduce maintenance frequency and extend battery life. Therefore, for the long-term continuous power supply remote monitoring instrument, the reasonable design of the lithium battery BMS management system is of great significance to the maintenance of the equipment.

The role of lithium battery protection board BMS

1. Battery protection, similar to PCM, overcharge, overdischarge, overtemperature, overcurrent, and short circuit protection. Like ordinary lithium manganese batteries and ternary lithium batteries, once the voltage of any battery exceeds 4.2V or the voltage of any battery is lower than 3.0V, the system will automatically cut off the charging or discharging circuit. If the battery temperature exceeds the battery operating temperature or the current is greater than the battery discharge current, the system will automatically cut off the current path to ensure the safety of the battery and the system.

2. Energy balance, the entire battery pack, because many batteries are connected in series, after a certain period of work, due to the inconsistency of the battery cell itself, the inconsistency of the working temperature and other reasons, it will eventually show a big difference, which will affect the battery. The life of the battery and the use of the system have a huge impact. Energy balance is to make up for the differences between individual battery cells to do some active or passive charging or discharging management to ensure the consistency of the battery and extend the life of the battery.

Power lithium batteries have safety problems from the production to the end of their life and recovery. Even if they are in full compliance with international safety standards when they leave the factory, they will evolve from a safe state to an unsafe state during use, and the performance of good quality single cells will gradually decline. Life limit, poor quality single battery, its performance will gradually appear various abnormal deterioration and decline during use, and enter the unsafe state of concern. This is a cumulative process of change.

Lithium battery BMS management system is not as dispensable as some battery manufacturers say, but must have, and it also runs through the battery pack application. There have been many studies on lithium battery management systems at home and abroad, and they have begun to be applied in many fields. They have been able to meet the needs of some markets. The application of lithium power batteries puts forward higher requirements on battery management systems to ensure the safety of power battery packs. , Is the primary task of the lithium power battery management system.

As a powerful guarantee for the safe use of batteries, BMS keeps the battery in a safe and controllable charge and discharge process at all times, greatly improving the cycle life of the battery in actual use. In the rapid development of new energy vehicles, BMS plays a pivotal role as the core technology.