Smart Battery Management System-Reason, Design and Requirements

Why smart battery management system is needed?

A battery management system is an electronic device that keeps a check and balance upon the charge, discharge rates, and temperature of the rechargeable battery packs. They can monitor single or multiple cells of battery systems. In multi-cell battery systems, the condition of individual cells is monitored and controlled. In these battery management systems, the system is not inside the battery pack and is wire-based.

When we talk about smart battery management systems, they are wireless systems integrating the battery pack from the inside. This system is based on wireless feedback from individual battery cells inside the pack and it is capable to be used in electronic vehicle applications. This wireless solution increases the useable capacity and the life cycle of the batteries as they integrate directly inside the battery pack.

How do you design a smart battery management system?

A smart battery management system can maximize the battery’s capacity and prevents undercharging and overcharging as well. With smart battery management, it ensures that all the cells of the battery have equal supply of charges and are discharged equally as well.

This brain of the battery pack measures and reports crucial information for the operation of the battery and protects the battery from damage from a wide range of operating conditions. Let us give you a little bit of familiarization with its components; the single most important function that BMS performs is “Cell Protection.” Lithium-ion cells have two critical design issues, if you over-charge, charge them you can cause overheating and damage them or could even cause explosion and flames, so it’s important to have a BMS to ensure over-voltage protection.

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Every battery protection circuit has two electronic switches known as MOSFETS. MOSFETS are semiconductors used to switch electronic signals on or off in a circuit. A BMS typically has a discharge MOSFET and a charge MOSFET. If the lithium-ion protector chip detects that the voltage across the cells exceeds the upper limit it will discontinue the charge by opening the charge MOSFET chip. Once the charge has gone back down to a safe level, the chip will close again. Similarly, when a cell drains to a certain voltage, the protector will cut off the charge by opening the discharge MOSFET.

Energy Management is the second most important function performed by a BMS. For Example; most laptops are not only able to tell you how much charge is left in the battery but also what your rate of consumption is and how much time you will have left to use the device before the battery needs to be recharged. Therefore, in practical terms, energy management is very important in portable electronic devices. Like knowing for how long you can play counter strike for before the controller dies in the middle of a battle and you’re scrambling to find extra batteries and… Never Mind.

The key to energy management is Coulomb counting. For Example; if you have five people in the room and two people leave you are left with three if three more people enter the room you now have six people. Also, if the room has a capacity of ten with six people inside then it's 60% full. A BMS tracks this capacity and the state of charge is communicated to the user electronically through a digital bus called an SM Bus, or through a state of charge display where you press a button and the LED display gives you an indication of the total charge in 20% increments. BMS for certain applications like handheld pointer cell terminals also included an embedded charger consistent with a control device i.e. an inductor that is a storage device and a discharger. The control device manages the charging algorithm. For lithium-ion cells, the ideal charging algorithm is the constant current and constant voltage.

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A battery patch usually consists of several individual cells that work together in combination. Ideally, all these cells in the battery pack are in the same state of charge. If the cells go outside of balance individual cells can be stressed and lead to premature charge termination and reduction in overall cycle life of the battery. The cell balance of the BMS extends the life of the battery by preventing the imbalance of charge in individual cells from occurring. Until now, we have gone through the basic components of the Battery Management System and what they do.

What are the requirements of battery management system?

There are certain building blocks of a smart battery management system. Some of them are listed below.

1.Cutoff FETs:A FET driver functional block is for providing connection and isolation of the battery pack.

2.A FUEL GAUGE MONITOR:A fuel gauge keeps a check and balance on the charge entering and exiting the battery pack.

3.CELL VOLTAGE BALANCE & MONITOR:?Monitoring and Balancing of cell voltage in individual cells is essential for the overall health of the battery pack.

4.TEMPERATURE MONITORS:Temperature monitors serve as multipurpose soldiers in a BMS. Their first and utmost duty is to keep a check and balance on the amount of current entering the battery at the time of charge because a lot of current at a constant voltage can cause a fire. The second function of these monitors is to determine if it is desirable to charge or discharge the battery.?

5.State Machine:For the sensing circuit most BMS require MCU or FPGA sensing circuitry and for making e=decisions with the recovered information.

6.OTHER BMS BUILDING BLOCKS:?Other BMS building blocks include authentication, a real-time clock, memory, and daisy chain. Memory is used for storing data, Real-Time Clock for a timestamp.

A BMS can be constructed using a variety of building blocks and design techniques. Battery requirements and battery life goals help us to determine the right architecture, functional blocks, and ICs to create our BMS and charging scheme to optimize battery life. If a BMS is designed in accordance with the battery requirements then it will have a long life as well as the battery it is designed for.