Role of Battery Management System on the performance of electric vehiclesUPDATED AUG 30, 2021 - 15 MIN READ
Table of Contents
- Need for a Battery Management System
- Functions performed by Battery Management System
- Esmito's Smart Battery Management System
To conserve our environment from harmful emissions, electric cars have emerged as best alternative for a sustainable environment. With the increasing awareness about the benefits achieved through electric vehicles, there is a widespread adoption of e-mobility. There have been a lot of research initiatives going on to improve the performance of electric vehicles in the coming decade.
Fig 1: Battery Management System in an electric vehicle
The performance of electric vehicles depends on a lot of factors such as cell voltage, battery life and health, safety, charging-discharging rates, etc. All these factors, one way or the other, Battery Management System are linked to the rechargeable batteries in electric vehicles. Therefore, to achieve an efficient output from these batteries, there is a need for monitoring and controlling various battery parameters. This role is performed by a Battery Management System (BMS) in all the electric vehicles, which ensures the complete tracking of all the functions performed by the battery.
Performs the task of managing and controlling the batteries for reliable and safe operation. The real time information obtained from these batteries helps in timely actions for an improved battery life and safe operation, finally contributing to improved performance and durability of electric vehicles.
Need for a Battery Management System
In the last two decades, there has been a continuous improvement in power and energy of Lithium ion batteries, resulting in the opening of new application areas across all industries. The features of high power density, low self-discharge, and reduced cost, make them a good option for electric vehicle batteries. Along with all the benefits available from these batteries, safety issues related with these batteries need to be considered for adoption of electric vehicles. Battery Management System in electric vehicles, is a specially designed electronic circuit that ensures the safety and stability of these battery packs.
A battery pack in an electric vehicle is a combination of multiple modules of cells and each module is a collection of individual cells. It is difficult to manage performance of a battery pack because each cell in each module can get charged and discharged at varying rates. In addition, each cell has a different operational state because of the difference in temperature, state of health and state of charge. Therefore, for an efficient and safe operation, each battery cell needs to be monitored independently.
Battery Management System is required to monitor the charge rate across the whole pack up to cell level. This monitoring ensures safe and reliable battery operation resulting in the production of more efficient and safer electric vehicles.
Battery Management System can be categorized depending on the type of circuit design, topology and the voltage range.
1) Based on Design
a. PCM (Protection Circuit Model) - PCM is an electronic circuit which protects every single cell in the lithium battery pack against extremely high and low values of voltage, current and temperature. This also maintains the operating range for each cell resulting in safe operation and enhanced battery life. The typical applications include low-cost products like e-bikes or small electric tools.
b. BMS (Battery Management System) - BMS is a more sophisticated and intelligent protecting circuit. It incorporates additional modules like control circuitry, management and display modules. These modules other than controlling provide real time information of the battery pack. It includes a range of 2-wheeler, 3-wheeler, public and private vehicles, stationary applications, etc.
2) Based on Topology
a. Centralized BMS - In centralized BMS, there is a single board comprising a centralized controller and a smart circuit for all the operations and internal communication. The centralized controller performs the functions of monitoring, maintaining cell voltages, temperature and cell balancing by a direct connection with each cell of the battery.
The entire board is commonly powered from battery output. The wire harness collected information related to battery state of health and state of charge are communicated internally and externally by the smart circuit board.
b. Decentralized BMS - In decentralized BMS, the cell monitoring and smart circuit board are part of different assembly units. There are two approaches, namely modular and master slave, for implementation of this kind of BMS. These topology ensures high reliability compared to centralized BMs.
Fig 2: Classification of Battery Management System
3) Based on Voltage
a. Low Voltage (LV) BMS - LV Battery management System comprises low voltage class 1 which is less than or equal to 60 V DC. It involves all the electric vehicles covering 2 wheeler and 3 wheeler range.
b. High Voltage - HV Battery management System comprises high voltage class 2 which is less than or equal to 900 V DC and high voltage class 3 which is less than or equal to 1500 V DC. The applications include automotive vehicles and energy storage systems.
Functions Performed by Battery Management System
Battery Management System needs to be more advanced and powerful with the increasing demands of high-performance electric vehicles. In the current scenario, Lithium-ion batteries are the heart of electric vehicles providing high performance and increased energy density. However, Lithium ion batteries also pose some challenges as they are susceptible to some serious issues such as overheating, thermal imbalance which can result in complete damage of the battery pack. Battery Management System performs following functions to manage the battery operation and ensure safety and reliability for the smooth running of electric vehicles over an expected period of life.
1) Monitoring Function
Battery Management System performs following functions to manage the battery operation and ensure safety and reliability for the smooth running of electric vehicles over an expected period of life.
Depending on their state of charge, each cell in a module experiences a different temperature affecting the performance of the pack as a unit. The sensors are employed for the direct measurement of current, voltage and temperature parameters of each cell. Further these readings are used to evaluate parameters such as State of Charge (SoC), State of Health (SoH), energy calculation, current threshold, energy delivered and the consumption of energy and power. The continuous monitoring of these parameters plays a significant role in maintaining the safety of the battery pack and improved life span.
2) Protection Function
In the safe working of a battery pack, Safe Operating Area (SoA) is of real importance. It is defined as the voltage, current and temperature conditions over which the device can be expected to operate without any self-damage. An intelligent BMS must ensure the safety of its battery pack from external environments such as overheating and thermal management of the battery pack. These situations may give rise to failure and damage. To prevent such conditions BMS make sure the working of the battery in the safe operating area.
Fig 3: Functions of Battery Management System
3) Cell Balancing
Cell balancing is one of the major activities that is performed in the battery pack to achieve an improvement in battery life by reducing the number of battery charge- discharge cycles. This is a kind of optimization process where BMS balances the charging and discharging values of each cell in a module. The variation in the charging-discharging rate of each cell results into significant energy imbalance among the cells while discharging which limits the capacity of the battery pack during the charging process. Thus the number of battery charge discharge cycles increase affecting the battery life of the electric vehicle.
Battery Management System incorporates either the active balancing or the passive balancing technique to equalize the cells and take care of all the cells from overstressing.
Passive Balancing -
A conventional method of balancing the energy among the cells in a module. The excess energy from the cells is removed by providing a single point of drainage for all the cell. This helps in complete recharging of all the cells at same rate. The capacity of a module is still limited by the weakest cell in passive balancing method therefore an additional coolant technique is required with it. In this method, the function of this coolant is to take care of this excess energy which is dissipated as heat or external resistance
Active Balancing -
Active balancing is a complex and efficient process of balancing cell energy. It redistributes the energy among cells rather than dissipate and waste it, as in case of passive balancing technique. For the balancing operation in this technique, the excess energy is moved from strong cells to weak cells with the help of power devices. This is helpful in maximizing the available energy and increasing the effects of capacity of the module. There are different types of active balancing system for different applications.
All the major functions of a Battery Management Systems such as monitoring, collecting information about cell parameters and connected circuitry diagnostics etc. are timely performed because of the communication between them. The type of communication media depends on the requirement of application. In electric vehicles, the information about the battery and vehicle performance is also communicated to driver for timely actions.
Esmito's Smart Battery Management System:
Esmito offers the latest technology in smart BMS for lithium ion batteries in both NMC and LFP chemistries. We are proud to be one of the few companies in India who have developed a completely indigenous CAN enabled smart BMS. Our BMS technology maximizes the battery life by effective cell balancing and continuous monitoring of the state of charge and state of health of the battery packs. We offer BMS across 48V, 60V, 72V for both two wheeler and three wheeler applications.
1) Safety and Electrical Protection
Esmito’s BMS has a mechanism for safety in situations of overheating, heat accumulation, etc. Continuous tracking and controlling of the voltage, current and temperature parameters allows the battery operation in the safe operating area. This ensures the safety of electric vehicle user in situations of battery failure or damage.
2) Thermal Protection
Robust mechanical design and battery packaging provide great degree of protection against mechanical vibrations, exposure to high impact forces and thermal runway.
3) Cell Balancing
Implementation of active and passive balancing mechanism ensures the efficient utilization of the energy among all the cells in the battery modules resulting into increased life span of the electric vehicles.
4) On-Board Diagnostics
SoC and SoH are calculated as per the voltage, current and temperature parameters recorded. These values significantly indicate the battery condition for the smooth running of electric vehicles. In addition, BMS take corrective measures to fix any issues related to the change behavior of cells and battery pack.
State of Charge (SoC) indicates the available charge in the battery and gives an estimate for the next recharge.
State of Health (SoH) gives the current state of battery. It is determined by the battery’s ability to give desired range and power.
5) Cloud Connectivity for Battery Analytics
Battery Management System maintains communication from vehicle to battery, battery to charger and other communications which are required in the electric vehicle. This is helpful in achieving high performance from electric vehicles through effective and timely information among all units of electric vehicle.
BMS - Battery Management System
SoC - State of Charge
SoH - State of Health
PCM - Protection Circuit Module
NMC - Nickel Manganese Cobalt Oxide
LFP - Lithium Ion Phosphate
CAN - Controller Area Network