Battery Management Systems (BMS) are the answer to the secure, reliable, and efficient functioning of lithium-ion batteries. A lithium-ion battery is an advanced battery technology that uses lithium ions as a key component of its electrochemistry. In other words, the Battery Management System is an electronic supervisory apparatus that manages the battery pack by measuring and monitoring the cell specifications, gauging the state of the cells, and protecting the cells by operating them in the Safe Operating Area (SOA). The safe operating area curve is a graphical representation of the power maneuvering capability of the device under various conditions.
A Battery Management System is an electronic board consisting of heterogeneity of components and circuitry. However, After dredging a problem in operational parameters (voltage, temperature, etc.) the Battery Management System engenders input to the alarm system followed by disengaging the battery pack from the load or charger.
Battery Management Systems (BMS) mainly include three parts: hardware, bottom layer software, and application layer software.
The hardware of the Battery Management System (BMS)
The framework of Battery Management System(BMS) hardware is divided into two types: centralized and distributed.
(1) Centralized Battery Management System
A centralized Battery Management System is one central pack controller that monitors, stabilizes, and controls all the cells. Moreover, a single assembly contains the entire unit, from which the wire harness (N + 1 wires for N cells in series and temperature sense wires ) goes to the cells of the battery. Evaluation of cell voltage, temperature measurements, and cell balancing prerequisites the wire harnesses.
(2) Distributed Battery Management System
In contrast to the centralized Battery Management System, distributed Battery Management System incorporates a mainboard and a slave board. A battery module may be accoutred with a slave board.
In other words, a decentralized BMS, fundamentally, does not have the entire cell monitoring and intelligence circuitry on a single assembly. This architecture contrivances through various topologies as explained below:
Modular: The battery management system segregates into various, identical modules, each with its bundle of wires going to one of the batteries in the pack. Moreover, one of the modules is designated as a master, as it is the one that manages the entire pack and liaises with the rest of the system, while the other modules behave as simple remote measuring devices.
Master-Slave: Master-Slave handles computation and communications.
This structure encompasses the Master and Slave BMS units. The slave unit monitors, equalizes, and controls a group of battery cells within the battery module. Moreover, it interacts with the master unit through a communication interface. State estimation, control of the Power Distribution Unit (PDU), and external communication hold the Master unit responsible. A master-slave BMS is similar to a modular system, as it uses multiple identical modules, each reckoning the voltage of a few cells. However, the master is different from the modules and does not measure voltages.
The prevalent functions predominantly include collection functions (such as voltage, current, and temperature collection), charging port detection (CC and CC2), and charging wake-up (CP and A+) ), relay control and status diagnosis, insulation detection, high voltage interlock, collision detection, CAN communication and data storage requirements.
(1) Main controller
The main controller processes the information reported from the controller and the high-voltage controller, and at the same time judges and controls the battery operating status according to the reported information. In addition, it helps to realize the BMS-related control strategy and makes the analogical fault diagnosis and processing.
(2) High voltage controller
The high voltage controller collects and delineates the total voltage and current information of the battery in real-time, perceives timely integration through its hardware circuit, and dispenses precise data to estimate the state of charge (SOC) and the state of health (SOH) for the motherboard. It is also responsible for the charge detection and insulation detection function.
(3) Slave controller
The slave controller is accountable for real-time collection and outlining of battery cell voltage and temperature information, feedback of the SOH and SOC of each string of cells, and a passive equalization function, which effectively ensures the consistency of cells during power use.
(4) Sampling control harness
The sampling control harness allocates hardware support for battery information collection and information interaction between controllers. Further, it adds a redundant insurance function to each voltage sampling line, effectively avoid battery short circuits caused by wiring harness or management system.
There are two ways to transfer information between the sampling chip and the main chip:
(1) CAN communication
Numerous control units and the BMS uses CAN communication for interaction. The implementation of CAN bus-based communication is essential as it reduces the wiring required between the control units. Moreover, CAN communication is the most stable.
(2) Daisy Communication
The typical wired solution connects battery monitors in a daisy-chain cable with twisted-pair cabling between battery modules. Moreover, The cost is very low, and the stability is relatively poor. However, as the pressure on cost control is increasing, many manufacturers are changing to the daisy chain mode.
BMS(Battery Management System) hardware comprises of power supply IC, CPU, sampling IC, high-drive IC, other IC components, CAN module, etc. Above all, the CPU is the core component, and IC manufacturers mainly include Linear Technology, Maxim, Texas Instruments, etc., including collecting cell voltage, module temperature, and peripheral configuration equalization circuits.
The design of the BMS is board is a bit complicated. Moreover, the working of a battery management system is stimulated by the entanglement of the electronic components available on board.
To sum up, it must function somewhere between the maximum and minimum rated values for a battery to operate at its best, i.e. current, voltage, temperature, etc.
As we learned earlier, a BMS helps batteries to operate within these critical rated values.
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