How to select Battery Management Systems
attery Management Systems (BMS) are the key to lithium-ion batteries' safe, reliable, and efficient functioning. It is an electronic supervisory system that manages the battery pack by measuring and monitoring the cell parameters, estimating the state of the cells and protecting the cells by operating them in the Safe Operating Area (SOA). Battery safety systems are an essential component of all lithium-ion battery packs. These battery packs can be classified into Low Voltage (LV) or High Voltage (HV). In automotive engineering, "high voltage" is defined to be within a range of 30 – 1000 VACS or 60 – 1500 VDC (UNECE 2013). Voltages under 30 VAC and 60 VDC are defined as “low voltage.” LV 112-1 presents three voltage classes, which are based on ISO 6469-3 class A and B: Low voltage class 1: ≤ 30 VAC and ≤ 60 VDC; High voltage class 2: ≤ 600 VAC and ≤ 900 VDC; High voltage class 3: ≤ 1000 VAC and ≤ 1500 VDC.
LV battery packs are typically used in light electric and hybrid vehicles, two and three-wheelers stated by Battery management courses. HV battery packs are usually used in traction applications for electric automotive and stationary applications in Energy Storage Systems (ESS). HV battery packs have many lithium-ion cells connected in series and parallel to build up the total voltage and capacity of the group. For example, an HV battery pack of a hybrid bus rated for 600V, 100kWh built of 18650 NMC cells will have about 160 cells in series and 55 cells in parallel, taking the total cell count to 8800.
Irrespective of the voltage, all lithium-ion battery packs require a BMS. Selection of the right type for the battery pack is essential. Several off-the-shelf BMSs are available in the market, and they are of different topologies. These BMSs can be fundamentally classified into – Centralized and Decentralized. Centralized BMS is one central pack controller that monitors, balances, and controls all the cells. The entire unit is housed in a single assembly, from which the wire harness (N + 1 wires for N cells in series and temperature sense wires) goes to the cells of the battery. Choose the right EV Batteries wires are used for cell voltage, temperature measurements and balancing.
The board is commonly powered from the battery output and does not require an external power supply. It consists of multiple Analog Digital Converters (ADC) channels as part of the cell monitoring circuitry. The voltage on each cell is referenced to the BMS ground, and this voltage grows with the number of cells and provides a high voltage at the ADC channels that measure the topmost cells in the stack. The cell monitoring circuitry is also coupled with intelligence circuitry. The intelligence circuitry is responsible for internal communication with the cell monitoring circuitry for data acquisition, computing the battery’s State of Charge (SoC) and State of Health (SoH), controlling the Power Distribution Unit (PDU) and for external communication. The Battery technology consulting is divided into multiple, identical modules, each with its bundle of wires going to one of the batteries in the pack. Typically, one of the modules is designated as a master, as it is the one that manages the entire collection and communicates with the rest of the system. In contrast, the other modules act as simple remote measuring devices. Readings from the other modules to the controller module are transferred via a communication link.