What are the general requirements of BMS?
In the lithium battery management system, the key word is "management". To realize the management function, two modules are necessary:
I can control this system only if I can monitor it.
From this as the core point, I can slowly list the general requirements:
1. Monitoring the energy system, able to read all the status of the lithium battery in real time.
2. Control the energy system, and intervene when needed according to the status of the lithium battery (such as opening/closing the MOS of the charge and discharge loop).
The general requirements of the battery system are divided into acquisition and control, so what data will be collected?
As a system that manages lithium batteries, the above 3 points are the data we need to monitor. If the system is super simple and only 3 or 4 points are collected, then the AD interface of the MCU can be used to read the information directly. But in reality, it is almost impossible to have such a situation, and the acquisition method usually used is generally to use an analog front end.
Voltage: The chemical characteristics of the lithium battery itself determine that we must protect the voltage. The so-called voltage protection means that we must ensure that the voltage of the lithium battery is always in the appropriate range. The voltage cannot be too low because of its internal storage. Electricity is realized by a reversible chemical change in electrochemistry. Excessive discharge will cause irreversible reactions of this chemical change. Therefore, lithium batteries are most afraid of overdischarge. Once the discharge voltage is lower than 2.7V, the battery may become permanent. Sexual damage, which is scrap. At the same time, the voltage should not be allowed to be too high, because once the battery is overcharged, the damage caused is far greater than the overdischarge. Overdischarge can damage the battery at most and will not cause harm to the surroundings. Overcharge may cause the battery temperature to rise to the point. Spontaneous combustion or even explosion, this hazard is fatal.
Current: The so-called current protection is also we must ensure that the current cannot be too large whether it is charging or discharging. Everyone knows that a short circuit is a manifestation of overcurrent. When the positive and negative poles of the system are in direct contact, the resistance of the wire Small, resulting in a very large current, and a very large current will generate a lot of heat, and the resulting combustion and explosion are very fatal. In fact, even if it is not a short circuit, the excessive current will still cause the internal heating of the battery, which is very likely to cause permanent damage.
Temperature: Needless to say, temperature protection. Except for the chemical characteristics of the lithium battery itself which makes it unable to be used at extreme temperatures, I think any similar system should take temperature into consideration for the sake of safety.