IIT Guwahati researchers develop method to provide accurate SOC for EVs

A team of researchers from the Indian Institute of Technology (IIT) Guwahati, India have developed an advanced technique that they say can precisely estimate the state of charge (SOC) in battery-powered electric vehicles.

The research team consisting of three members – Gautam Sethia, Research Scholar; Dr. Sisir Kumar Nayak, Associate Professor, and Prof. Somanath Majhi – are associated with the Department of Electronics and Electrical Engineering, IIT Guwahati.

The research findings were recently published in IEEE Transactions on Circuit and System I: Regular Papers, which is among a highly reputed international scientific journal. The research team is currently also working on various other important battery issues such as cell balancing, monitoring state of health and state of power among others.

State of Charge (SOC) reflects the remaining capacity of the battery, how much more power can be withdrawn from the battery before it gets fully discharged. The report says that having the knowledge of remaining capacity helps to optimise battery’s capacity utilisation, prevent overcharging and undercharging of the battery, increases its lifespan, reduces cost, and ensures safety of the battery and its surroundings.

The researchers say that unfortunately, such a vital parameter cannot be directly measured by any sensor. It is only possible to infer SOC by using the available measured quantities such as battery terminal voltage and current. However, the highly non-linear characteristic of the lithium-ion battery makes it difficult to estimate the SOC accurately. Hence, a well-developed estimation algorithm is crucial, which can ensure precise, reliable, and cost-effective SOC estimation.

In recent years, lithium-ion batteries have been widely popularised in various applications due to their low carbon emission, high energy density, low self-discharge rate, and low maintenance cost. Apart from the various day-today small devices such as cell phones, laptops, they have been also widely used in various other important applications such as electric vehicles, Renewable Energy Sources (RES) integrated smart grids and micro grids among others.

Speaking about the work with the research team, the researchers at IIT Guwahati briefly explained the technical/methodology part as follows: “In our work, we have divided the problem into two parts. First was to derive the mathematical model of the lithium-ion battery, which can closely exhibit its dynamic characteristics. Then, using few advanced system control and mathematical concepts such as sliding mode theory, we have tried to estimate the battery internal states precisely. The proposed technique shows the highly robust characteristics and works accurately even in the presence of various external disturbances such as sensor inaccuracy, temperature variation. Compared to the existing techniques, the proposed technique not only increases the accuracy but also reduces the computational time, and hence needs a cost-effective microcontroller chip for its implementation/commercialisation.”