What is the working principle of the lithium battery protection board?

Date:Jul 23, 2019

The lithium battery is mainly composed of two large blocks, the battery core and the protection board PCM (the power battery is generally called the battery management system BMS), the battery core is equivalent to the heart of the lithium battery, and the management system is equivalent to the brain of the lithium battery. The battery core is mainly composed of a positive electrode material, a negative electrode material, an electrolyte solution, a separator and an outer casing, and the protection plate is mainly composed of a protection chip (or a management chip), a MOS tube, a resistor, a capacitor, and a PCB board.

Power BMS lithium battery protection board

Second, the advantages and disadvantages of lithium batteries

Lithium batteries have many advantages, high voltage platform, high energy density (light weight, small size), long service life and environmental protection.

The disadvantage of lithium batteries is that the price is relatively high, the temperature range is relatively narrow, and there is a certain safety hazard (requires protection system).

Third, lithium battery classification

Lithium batteries can be divided into two broad categories: disposable non-rechargeable batteries and secondary rechargeable batteries (also known as batteries).

Non-rechargeable batteries such as lithium manganese dioxide batteries, lithium-sulfuramide batteries.

Fourth, a variety of power battery comparison

Power batteries are mainly considered for their applications, mainly used in electric electric vehicles, electric bicycles, power tools and so on.

The power battery is different from the ordinary battery and has certain special characteristics:

1. Parallel connection of batteries

2. The battery capacity is larger

3. The battery has a large discharge rate (hybrid and power tools)

4. Battery safety requirements are higher

5. The battery has a wide operating temperature range

6. The battery has a long service life and generally requires 5 to 10 years.

V. Introduction and analysis of BMS functions

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

2. Energy balance, the entire battery pack, because many batteries are connected in series, after working for a certain period of time, due to the inconsistency of the battery itself, the inconsistency of the working temperature, etc., the final will show a big difference, the battery The life and the use of the system have a huge impact. Energy balance is to make up for the difference between the individual 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.

There are two types of passive equalization and active equalization in the industry. The passive equalization is mainly to balance the power consumption of the power through the resistance. The active balance is mainly to transfer the power of the battery with more power to the battery through the capacitor, inductor or transformer. The battery is balanced.

Since the active equalization system is relatively complex and the cost is relatively high, the mainstream is still passively balanced.

3. SOC calculation, battery power calculation is a very important part of BMS, many systems need to know the remaining power more accurately. Due to the development of technology, many methods of SOC calculation accumulate, the accuracy requirement is not high, and the remaining power can be judged according to the battery voltage. The accurate method is mainly the current integration method (also called Ah method), Q=∫idt, and Internal resistance method, neural network method, Kalman filter method, etc. The mainstream in the industry is still the current scoring method.

4. Communication, different systems have different requirements for communication interfaces. The mainstream communication interfaces are SPI, I2C, CAN, RS485, etc. Among them, the automotive and energy storage systems are mainly CAN and RS485.

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