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 risk of explosion when the lithium battery is severely
overcharged, causing damage to the lithium battery and posing a threat to the
life safety of the user. Therefore, lithium batteries must be equipped with a
targeted lithium battery management system BMS to effectively monitor, protect,
energy balance and fault alarms for the battery pack, thereby improving the
efficiency and service life of the entire lithium battery.
What is BMS?
The battery management system (English: Battery Management System,
abbreviation BMS) is a system that manages batteries. It usually has the
function of measuring battery voltage to prevent or avoid abnormal conditions
such as battery over-discharge, over-charging, 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 electric vehicles. It uses sensors to detect the voltage, current, and
temperature of the battery in real time. It also performs leakage detection,
thermal management, battery balance management, alarm reminders, and calculation
of remaining capacity (SOC). , discharge power, report battery deterioration
(SOH) and remaining capacity (SOC) status, and also use algorithms to control
the maximum output power according to the voltage, current and temperature of
the battery to obtain the maximum mileage, and use algorithms to control the
charger for optimal current Charging, real-time communication with the vehicle
main controller, motor controller, energy control system, vehicle display
system, etc. through the CAN bus interface.
The functions of the BMS should include basic battery protection functions,
battery balancing functions, battery reserve energy measurement functions and
network communication functions.
Why do lithium batteries need BMS?
The power lithium battery management system can effectively monitor,
protect, energy balance and fault alarm 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 many advantages such as high operating voltage, small size, light weight,
high energy density, no memory effect, no pollution, small self-discharge, and
long cycle life. However, lithium batteries have serious shortcomings. In
summary, they have the following two aspects:
(1)Safety
Lithium batteries have defects such as poor safety and occasional
explosions. In particular, lithium batteries with lithium cobalt oxide as the
cathode material cannot be discharged at high currents and have poor safety. In
addition, overcharging or overdischarging almost all types of lithium batteries
can cause irreversible damage to the cells. Lithium batteries are also extremely
sensitive to temperature: if used at too high a temperature, the electrolyte may
decompose, burn or even explode; if the temperature is too low, the performance
of the lithium battery will significantly deteriorate, affecting the normal use
of the equipment.
Due to the limitations of the battery manufacturing process, the internal
resistance and capacity of each battery unit will vary. When multiple battery
units are used in series, the charge and discharge rates of each battery cell
will be inconsistent, which leads to low utilization of battery capacity. In
view of this, lithium batteries usually require a specialized protection system
to monitor the health of the battery during actual use to manage the use process
of lithium batteries.
(2)Maintainability
The capacity fading of lithium batteries at low temperatures and the
inability to accurately predict the power level make the maintainability of the
equipment poor. Instruments that are online for a long time require regular
battery replacement, and the working sites of remote monitoring equipment are
scattered and the distances between sites are long, so battery replacement is a
huge workload and costly.
In order to reduce the maintenance workload and maintenance costs, the
lithium battery BMS management system is required to have an accurate charge
state estimation function to accurately grasp the battery charge state and
perform battery replacement more purposefully; at the same time, the battery
management system is also required to have a relatively high charge state
estimation function. Low self-power consumption to reduce maintenance frequency
and extend battery life. Therefore, for remote monitoring instruments that are
continuously powered for a long time, 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 is similar to PCM, including overcharge,
over-discharge, over-temperature, over-current, and short-circuit protection.
Like ordinary lithium manganese batteries and ternary lithium batteries, once it
detects that the voltage of any battery exceeds 4.2V or the voltage of any
battery falls below 3.0V, the system will automatically cut off the charging or
discharging circuit. If the battery temperature exceeds the battery's operating
temperature or the current is greater than the battery's discharge current, the
system will automatically cut off the current path to ensure the safety of the
battery and system.
2. Energy balance. Since many batteries are connected in series, the entire
battery pack will eventually show great differences after working for a certain
period of time due to the inconsistency of the cells themselves and the
inconsistency of the operating temperature. It has a huge impact on the life of
the battery and the use of the system. Energy balancing is to make up for the
differences between individual cells and do some active or passive charge or
discharge management to ensure the consistency of the battery and extend the
life of the battery.
There are safety issues in power lithium batteries from the time they are
produced until they are recycled at the end of their life. Even if they fully
comply with international safety standards when they leave the factory, they
will evolve from a safe state to an unsafe state during use. The performance of
good-quality single cells will gradually decline and reach The performance of
single batteries with limited lifespan and poor quality will gradually undergo
various abnormal degradations and declines during use, and enter the feared
unsafe state. This is a gradual and cumulative process of change.
The lithium battery BMS management system is not dispensable as some
battery manufacturers say, but a must, and it must be present throughout 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 has put forward higher requirements for 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 enables the
battery to be in a safe and controllable charging and discharging process at all
times, which greatly improves the cycle life of the battery in actual use. In
the rapid development of new energy vehicles, BMS plays a decisive role as the
core technology.
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