25th April 2019
Battery and BMS: The Key to Making EVs Mainstream
The most obvious difference between an EV and a conventional 4 wheeler is the fuel tank or rather the lack of one. Electric vehicles are powered by batteries, which need careful monitoring and maintenance. They come with fixed lifespans, safe operating levels, and charge/discharge cycle track.
Due to their high energy density, long lifespan and lightweight, lithium-ion batteries are favored by EV manufacturers.
Here, criteria such as voltage rating and Ah (ampere-hour) rating indicate when the battery must be charged. To attain higher voltage and Ah ratings, the cells are connected in series or parallel combinations. In fact, manufacturers often custom design the cell for improvising on application-specific characteristics.
But what really sets the battery of an electric vehicle apart from the fuel tank of a conventional vehicle? (Spoiler alert: BMS)
Firstly, safety. When operated at a constant voltage, while drawing large amounts of current, the temperature of the vehicle may sharply rise due to thermal runaway. Thanks to the volatile composition of a lithium-ion battery, it might even catch fire. This obviously risks the safety of the vehicle and passengers.
Further, the chemical composition of a Li-ion battery tends to deteriorate over time and intensity of usage. The charge/discharge rates, as well as the efficiency, begins to decrease with age and usage. When crucial performance parameters dip below/ shoot above normal value, the user must be notified. Thus timely repair or replacement can be initiated.
With all these affecting factors, to preserve the health and lifespan of a battery, a battery management system is essential. If the battery is the heart of the vehicle, the BMS is its brain. It maintains optimum performance and notifies the user in case the health fails. It monitors various parameters to collect data for enhanced battery life and health. Be it simply alerting in case of under/overcharging, a sudden spike in temperature or a prediction for battery aging, a timely notification from the BMS can enable the user to take steps to prevent further damage.
This brings us to the important question of maintenance.
What kind of care do these lithium-ion batteries need?
Firstly there’s voltage, charge/discharge current and temperature levels of the battery which a BMS monitors. On surpassing the threshold value of any of these quantities, the battery health begins to deteriorate. Along with it, the safety of the vehicle is threatened. In case of under-voltage/ current levels during usage or over-voltage/charge beyond permissible limits, the user is notified.
Similarly, the BMS also provides thermal control where it keeps the temperature of each individual cell under check. It prevents the occurrence of thermal runaway. Unlike an IC engine, external environmental conditions have higher intensity effects. Lithium-ion batteries tend to discharge faster in high-temperature surroundings. Thus the temperature of the entire battery pack is controlled.
Then there’s the SOC i.e. State of Charge levels which indicate the capacity remaining in the lithium-ion battery. This is analogous to the fuel tank of a fuel-driven vehicle. This should always be monitored to predict the capacity of the battery. Likewise, SOH i.e. State of Health and SOP i.e. State of Power levels represent battery health and battery performance respectively. The BMS measures these levels and keeps the vehicle’s users informed about battery health, charge levels and age.
Another critical feature is cell balancing. This means that all the cells in the battery must be maintained at equal voltage levels. If there are different voltage levels, the entire battery’s efficiency is compromised on. The BMS maintains balance using active and passive cell balancing techniques.
The BMS must also track the charge and discharge cycles, to keep a track of abnormal spikes or undercharging. Since charging is analogous to refueling in an IC engine vehicle, the user must be given alerts whenever it is under/overcharged. Aging affects the charging cycles of Li-ion batteries and not maintaining charge within operating limits can be very damaging to battery health.
Keeping all of these factors in mind, designing an appropriate BMS for your battery can be challenging. It must satisfy all of these requirements for you to safely use, relay information about battery parameters accurately and save you from incurring costs by saving your battery from damage.
Battery management systems such as FS-XT have been designed and built keeping in mind the high voltage requirements of electric vehicles. It’s precision and reliability, makes it ideal for applications in the automotive sector. Its stackable architecture with master-slave configuration helps to deliver high precision performances.
The Master BMS hosts 4 channels which can each be connected to 10 Slave BMS in a daisy chain formation. This allows the BMS to be scaled up to 720 cells in series, which enables its usage for any applicable between 100-1000V. Customized features can be added on each slave board such as additional temperature measurements, a current sensor, balancing current up to 1A and heater. Plus it supports multiple battery chemistries and supercapacitors.
Not just electric cars, the FS-XT can be used for buses, trucks, other heavy four-wheelers, and even industrial moving equipment. It employs the Columb-counting algorithm to estimate the SOC of your battery. Our SoH predictive algorithms are reconfigurable and compatible with over the air updates. They predict aging and provide continuous recalibration to enhance battery life.
Another major feature is that the FS-XT supports paralleling up to 16 batteries. Its cell balancing capabilities are twice as good as our competitors, at 410 mA. It hosts an individual cell voltage of 1V to 5V and can handle pre-charge up to 50 times compared to other BMS. Built with compression algorithms to reduce battery data acquisition by a factor of 20, the FS-XT can store up to 20 years of battery data.
A high-performance BMS is just not enough to completely utilize a battery’s capabilities. A battery intelligence platform is required which can measure the performance of the battery in real-time and provide diagnostics as well as prognostics.
Edison Analytics analyzes and interprets the vehicle’s performance data. With the help of compression algorithms in the platform, the BMS monitors and stores large amounts of data regarding regular usage as well as any unusual activity. This is particularly useful to keep track of deployed assets remotely.
Remotely, it can be particularly tricky to make necessary repairs. With a cloud-based battery intelligence platform, relevant data from the vehicle can be examined to rectify and diagnose problems remotely. In fact, Edison’s fleet monitoring technology makes it easy for the fleet manager of electric 4-wheelers to watch over the operating parameters of the vehicles.
So, for example, if there is a dip in the SOC levels, the vehicle owner or the battery manufacturer will be notified. This way, even for measuring other levels, in case of dips or sudden rises, the user can be alerted and timely maintenance can save the vehicle battery from damage. In order to increase the lifespan of the battery, and keep the vehicle within safe operating limits, this is crucial.
Edison uses machine learning and artificial algorithms to constantly monitor battery performance and send over the air updates. In fact, many BMS do not possess a dashboard that can simply convey information about battery status. With Edison, the battery status can be communicated without technicians having to open up the battery to perform maintenance audits.
Another growing trend in the electric mobility space is the second life application of batteries. While the Nexus LEAF may lead this trend currently, it is projected to grow over 100GWh storage capacity by 2029. Edison’s ability to predict lifespan can thus beneficial to plan the retirement of your vehicle’s lifespan and utilize it for second-life applications.
As the world cruises into an electric mobility revolution, we are collectively dependant on high performing lithium-ion batteries. Advancements in battery technology are the need of the hour and ION Energy is committed to helping companies build world-class batteries. Our licensees have utilized our cutting edge BMS technologies to design, manufacture and sell their products, making the best use of the benefits we have to offer.
With progressive schemes such as FAME 2, and companies like Shell expanding into the electric mobility market, the near future of 4 wheeler EV adoption seems bright and lucrative. With this automobile revolution, the grass is green for both our planet and electric vehicle enthusiasts.
[Battery Safety] Top 5 Reasons Why Lithium-Ion Batteries Catch Fire22nd January 2020/