Battery Management Systems Enhance Reliability and Safety In Electric Vehicles

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With the Indian government pushing for a larger number of electric vehicles on the country’s roads, the battery management system (BMS) industry is poised to grow significantly in the coming years.

By Potshangbam July

The growing concern about the environment has led to the Indian government making commitments to reduce its carbon footprint and the emission of greenhouse gases. This is expected to increase the demand for electric vehicles (EVs). With higher adoption of EVs, the impact on the battery management system (BMS) industry will be considerable, as EVs are powered by tens or hundreds of battery cells. A BMS is one of the fundamental components of electric vehicles, and plays a protective role by monitoring the voltage and temperature of battery cells. These systems oversee the operation of the battery packs, and ensure that the battery is operated in a safe and efficient manner.

Why battery management systems are needed in EVs
The battery systems in EVs are made up of hundreds of lithium battery cells that are packed together. These systems, with a voltage rating of 300V to 400V, supply current as high as 300A (approximately), and any mismanagement could trigger a massive disaster. That is why BMSs are critical in EVs for the safe operation of the high-voltage battery. They effectively monitor the state of the batteries, preventing overcharging and discharging that may reduce the battery’s life span, capacity and even cause explosions. A BMS checks the power voltage, and when the required voltage is reached, it stops the charging process. In case any irregular pattern in the power flow is traced, BMSs shut down and send out an alarm. The best part about BMSs is that they can relay the information about the battery’s condition to the energy and power management systems. In addition, they regulate the temperatures of the battery cells, and also the battery’s health, making it safe and reliable under all conditions.

Advantages of battery management systems in EVs

  • A BMS enhances the life span of the battery cells in EVs.
  • This is an effective system to measure and control the cell’s voltage.
  • It provides stability and reliability.
  • It ensures the safety of the battery pack, especially large format lithium-ion batteries.
  • It optimises the performance of the electric car battery.
  • It monitors the battery cells constantly to avoid the occurrence of failure or explosion.
  • A BMS helps to track any problems such as excessive heat, smoke, fire, etc, that can ruin the cells.
  • It controls the temperature, maintaining it at the ideal or optimum 45 degrees Celsius for EV batteries.
  • It gives an indication of how long the battery’s charge will last before it needs recharging.
  • It forecasts the battery pack’s capabilities in the near future.
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Determining the state-of-charge (SoC)

One of the important features of a BMS is to estimate the state-of-charge (SoC) of the battery. It is critical to efficiently maintain the SoC of the battery packs. The voltage of the battery should not be too high or too low. The battery should not be charged beyond 100 per cent or discharged to 0 per cent as this will reduce the capacity of the battery cells. Besides, a BMS not only provides precise information on the voltage and temperature of the battery, but also gives an idea of the energy available for use and the remaining battery charge.

Here are a few methods that can be followed to determine the SoC:

  • For direct measurement of SoC, a voltmeter is recommended because the battery
  • voltage decreases more or less linearly during the discharging cycle of the battery.
  • In the coulomb-counting process, to produce the relative value of its charge, the current going into or coming out of a battery is integrated.
  • The above two methods could be combined too. The voltmeter could be used to monitor the battery voltage and calibrate the SoC when the actual charge approaches either end. Meanwhile, the battery current could be integrated to determine the relative charge going into and coming out of the battery.

Trends and innovations in the BMS space
As the pace of EV adoption picked up across the globe, innovations in BMSs also increased. BMSs are now more intelligent. The most recent trend is the wireless BMS, for which neither a CAN bus cable nor an isoSPI twisted pair to interconnect the modules (as in the conventional BMSs) are used. This trend has enabled getting rid of the complexity and danger involved in wiring methods used for humongous multi-cell battery packs.

According to the EV team at Tata Elxsi, “Large automotive battery packs require monitoring of voltages and temperatures across multiple cells, which can result in complex wiring. In such scenarios, a wireless BMS is a great advantage as it reduces the risk of short circuits.” The best part of a wireless BMS is that it significantly reduces the cost and weight of a battery, while ensuring reliability and safety to a great extent. There are no requirements for cables, connectors and harnesses, for which maintenance is needed. It is easier to use sensors in the system, to collect data and improve the accuracy of SoC/SoH (state-of-health) calculations. Besides, a BMS with a wireless smart mesh network provides users flexibility in where to place the battery modules. Unlike the wired system, any extra sensors are easier to install in any location.

As per global market insights gathered for the period 2018 to 2027 by Fact.MR, investments are being made to develop battery management systems with smart microcontrollers that precisely monitor vital battery parameters. While efforts are under way to increase battery capacity to meet performance demands, the need for an efficient battery monitoring device has increased investments in the BMS space in the EV landscape.

Why is a BMS pivotal for EV batteries?
“The majority of conventional gasoline vehicles use lead acid batteries, which have a shorter life span, require higher maintenance and are bulkier. With the introduction of the lithium-ion cell chemistries, the demand for energy storage technology increased exponentially due to its higher energy density, longer life and compact size. The different chemistries of lithium-ion cells are capable of addressing the needs of a wide spectrum of applications, both for static machinery and moving vehicles. Static lithium-ion applications are in telecom, railways, the power grid, home appliances, etc, while moving lithium-ion applications are in electric vehicles, aviation, etc. The lithium-ion batteries are high performing, but quite unstable under certain temperature and load conditions. The biggest obstacle to these batteries being used in EVs is their unbalanced charging and discharging of individual cells. Individual cells need to be monitored closely, with constant checks on their health and behaviour under various temperature conditions. Therefore, the BMS is crucial in EVs to ensure that the battery packs are working at their maximum efficiency. It also provides safety by preventing overcharging, over discharging and ensuring the electrical safety of cells.”
—Venkat Gumpini, power electronics engineer at Autobot India“The lithium-ion battery is a critical element in the electric vehicle. The battery management system oversees the operation of the battery and ensures that it is operated in a safe and efficient manner. In a nutshell, a BMS’ core functions are to monitor, protect and optimise. Factors that have to be taken into consideration while monitoring are state-of-charge, state-of-health, temperature, voltage and current. In fact, a BMS plays the defining role of the regulator by controlling the excessive supply of voltage and current, consequently maximising battery life and balancing capacity utilisation.”
—Tata Elxsi EV team


Challenges

The BMS industry is yet to mature in India as there are not many big players, despite the government’s strong support for e-vehicles. It is still a fragmented market with no dominant players that can exercise enough influence to bring about healthy competition. And there are no reliable standards to guide the manufacturers or the consumers. The absence of technical standards has been a major barrier to the growth of the BMS industry. Besides, there are no clear policies and strategies that can propel growth in this segment.

The journey ahead
The Indian government has taken a strong initiative with the launch of its ‘National Electric Mission Plan’ to promote the electric mobility sector. The aim is to have 6-7 million electric vehicles on Indian roads by 2020. The government has also announced its commitment to ensure that by 2030, 30 per cent of the vehicles on Indian roads are electric vehicles. Indian automotive companies now need to take an active part by bidding for government tenders for the supply of EVs, and investing more on R&D to tap the full potential of modern technology—from IoT to artificial intelligence.

There is a rising awareness about the benefits of EVs, and experts believe that these vehicles will soon dominate the Indian market, which is likely to transform the automotive sector. With that, there will be a ripple effect across the battery industry as electric vehicles are powered by huge sets of battery cells. This will directly propel the growth of the BMS segment.

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