Lithium-ion Battery Management System (BMS) – A Detailed Coverage

WHAT IS IT SO CRUCIAL FOR LITHIUM-ION BATTERY PACKS? Its Functions & Analysis…

Lithium-ion BMS offers optimal battery protection- pretty similar to PCM and safeguards it against overcharging, over-discharging and increase in temperature. Lithium-ion BMS also plays a role in energy balance to compensate for the differences in specific battery cells by managing the active/passive discharge or charge. This aids in keeping the battery performance consistent and further extending its longevity.

BESIDES THESE FUNCTIONS…!

BMS also performs SOC calculations which helps determine the remaining power situation of lithium-ion batteries more immaculately. It uses the Ah method– which is regarded as the accurate, current integration method. Internal resistant method and Q=∫idt, Kalman method and neural network method exist as other methods.

That said, the typical method employed in the industry is the Current scoring method. In terms of communication, there are several systems which require varied communication interface. Those typical communication interfaces are as follows –

SPI
I2C
CAN
RS485
 And among them, the last two namely CAN, and RS485 apply for automobile and the energy storage systems.

Answer Section (300 characters)

Also, Dieter Zetsche, the CEO of Mercedes opines …

“The intelligence of a lithium-ion battery doesn’t merely lie in its cell, but its advanced management and monitoring system.

And this is pretty much reminiscent of those boxy computers in the 1970’s era having bulky hardware but very little software.”

A Gist of the Purpose/Uses of Lithium-ion BMS –

To ensure battery safety and its operational longevity of lithium-ion batteries.
 
Ensuring the advanced rate of charge and retention of its health capacity for quality operations/applications
 
Maintaining a high temperature and handing cell calibration or imbalance.
 
And it was pointing out a lithium-ion battery’s end of life when its capacity dips below its fixed target threshold.
 

BUT, All THESE ARE JUST A RUDIMENTARY COVERAGE.

And if you wish to learn more about lithium-ion BMS, then this post will be your perfect info-rich knowledge base.

So, continue reading the sections which follow to know all you need to know about lithium-ion BMS.

An In-Depth Coverage of Lithium-Ion Battery Management System

BMS AIDS IN FULFILLING A WIDE RANGE OF FUNCTIONS BASED ON SPECIFIC APPLICATIONS, THE TYPE, AND PARTICULAR SIZE LITHIUM-ION BATTERIES…”

That’s right!

The primary objective of BMS – battery management systems is to ensure the lithium-ion battery stays within its recommended safety confines in terms of –

  • Its temperature at the time of charge
  • Its cell voltage and current measurement and control
  • Isolation monitoring
  • For communications
  • For achieving an immaculate state of charge and health calculation
  • And also specific cases at open circuit

By this, the lithium-ion battery meets the predictable application requirements to the best of its ability and longevity without posing any risks that may hamper the energy system and its close inhabitants, working staff, and maintenances.

Experts label this BMS aspect as charging and discharging management.

FURTHERMORE…!

BMS also helps appropriately analyze the behavior of lithium-ion batteries periodically. It aptly transforms the monitored factors within the battery state data. And that is either fed to the battery’s upper system level or used directly to regulate the charge and discharge.

The lithium-ion battery’s upper system level can be its user itself, like, for example- the driver of an EV- electric vehicle or HE- hybrid electric vehicle. Plus, it can also be the hardware or software configuration, which aids in regulating the battery energy system.

As per the lithium-ion battery’s acquired state data, users can accordingly pick and execute their final call, which may as well be reduced to something as basic as restarting the charge or discharge process or its termination.

“THE CORRESPONDING BATTERY MANAGEMENT SYSTEM IS MAINLY SEGREGATED INTO 2 CATEGORIES – NON-AQUEOUS ELECTROLYTE BATTERY AND AQUEOUS ELECTROLYTE BATTERY…”

So, let’s begin by understanding Non-Aqueous Electrolyte Battery…

Non-Aqueous Electrolytes are primarily used in super-capacitors. They deliver electrochemical stability and can negate issues of current leakage in systems.

Generally, non-aqueous electrolytes are quaternary ammonium salts which are aptly circulated in carbonates as well as acetonitrile like –

  • Propylene carbonate/ tetraethyl ammonium tetrafluoroborate
  • Acetonitrile/, tetraethyl ammonium tetrafluoroborate
  • Triethylmethylammonium tetrafluoroborate/ propylene carbonate

Now, Let’s Understand Aqueous Electrolyte Batteries…

In aqueous electrolyte lithium-ion batteries, its energy storage operations are mainly accompanied by water decomposition-based electrochemical reactions such as –

  • HER – Hydrogen Evolution Reaction
  • And OER – Oxygen Evolution Reaction

Both OER and HER are parasitic processes that eventually lead to energy efficiency, Faradic decrease, and water. They even lead to progressive battery degradation.  That said, the aqueous electrolyte battery management mainly focuses on finding the appropriate balance between the discharge and charge reactions and the loss of water.

“THE OTHER CRUCIAL BUILDING BLOCKS OF BATTERY MANAGEMENT SYSTEM…”

The BMS – Battery Management System is one complex set-up. And besides what you have learned about it from the above sections, It Is Time to Look into Its Other Crucial Building Blocks.

They Are As Follows –

  • Battery authentication
  • Daisy Chain
  • A Memory
  • And RTC

Digging Deeper…

Memory and RTC are mainly employed to meet black-box applications.

Specifically, the memory is used to store all critical data and let the users be aware of the lithium-ion battery’s behavior before any catastrophic incidents occur.

The RTC is utilized for a timestamp. The authentication helps avert the BMS electronics from connecting to any 3rd party battery. Its voltage regulator is employed to power up the exterior circuitry circulating the BMS. And its daisy-chain circuitry is used to ease off the connection in between set devices.

Finally, the daisy-chain block aids in replacing the necessity for optical couplers or any other level-shifting circuitry!

(MORE INFO…) On How Lithium-ion Battery Management System Helps in CO2 Reduction & Its Importance in EV/HEV Applications

So, Let’s Keep At It & Learn More…!

HOW LITHIUM-ION BATTERY MANAGEMENT SYSTEM HELPS IN CO2 REDUCTION?

The BMS (as stated before) is one mean hardware and software system, and it serves as an essential part of any concerning high-voltage battery pack.

What’s more, each of these crucial parts helps ensure the electric vehicle’s proper safety, maintains an appropriate balance in the car’s performance, and battery life longevity.

  1. Its first crucial function is Cell Voltage and Measurement. BMS generally monitors the voltage across cell groups.  Preventing overcharge is the most critical reason for cell voltage monitoring.

They should never be excessively charged, or else they could lead to chemical reactions and a temperature rise, eventually leading to cell venting. Moreover, excess charging can also lead to a fire outbreak, simply because those vented cases are labelled highly flammable! Typically, the lithium-ion battery pack should consist of a robust model to monitor cell voltage to prevent excess charge and excess discharge.

  1. Next is the Isolation Monitoring, which is another critical safety aspect for high voltage vehicle units.

It checks the resistance between the chassis and the high voltage system. Ideally, the monitoring guidance states the valve to be more than 100ohm/volt for DC systems (as per the ISO 2011).

That means a 350 V unit must keep its resistance over 35kohms right in between the vehicle chassis and high voltage system. Keeping true to this will limit the current to roughly 10 milliamps. This may not be comfortable, but then again, it won’t be life-endangering either!

  1. Moving forward is Temperature Control. Lithium-ion BMS helps control temperature for battery pack and cell.

That said, the mode of monitoring and regulating the temperature for battery cells and packs vary from one application to another. However, the BMS does contain ample info concerning temperature deviations to ensure the controlling process aptly adjusts the cooling, heating, and even churn out the required amount of pack power levels!

  1. Lastly, Battery Management Systems also meet the functions of Communicating with vehicle users.

It requests for necessary changes in the EV’s operation after monitoring and determining the battery pack condition. It can even aid in predicting the performance and capability of the battery pack for the future.

Moreover, BMS communicates information to the controller about vehicle range, possible faults, and operating mode. Plus, it also serves useful when utilizing off-board DC chargers, which allow high recharge rates without putting any burden on the vehicle concerning the weight, price, and intricacy of powerful onboard chargers.

(FINALLY…) IT’S IMPORTANCE IN EV/HEV APPLICATIONS

It goes without saying that lithium-ion BMS is essential in EV and HEV applications. Not only do they have to handle the whole EV/HEV operating cycle, but it also needs to interface with numerous other on-board units, function properly in fluctuating discharge and charge situations whenever the EV/HEV brakes or accelerates. Most importantly, it has to function in the harshest, unregulated environment.

But… That’s Not All!

Take A Look At This Table!

The BMS gathers up all crucial information (like voltage temperatures and current) from the battery sensors. And then it uses that information to make sure the battery operation is optimal!
The BMS controls the charger to ensure an appropriate battery charge. It also reacts to data obtained from the sensors concerning every battery module or telemetry boards, and aptly responds as per the unique parameters and algorithms in the computer.
The BMS aids in managing proper cell balance to achieve quality battery performance. Proper balancing is crucial in case of multi-cell batteries- simply because even the weakest cells can potentially restrict the overall battery performance.  In simple terms, BMS properly controlling the electronic balancing devices incorporated within every telemetry board as per the prearranged algorithm or stratagem.
The BMS 0monitors collects and stores the battery measurement data, thus allowing easy data transfer to a PC/laptop or examining the results by using spreadsheets or other software tools.
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