Rourkela: Professor Monalisa Pattnaik, Associate Professor, Department of Electrical Engineering and her research team including Dr Pradyumna Kumar Behera and Mr Karan Gupta at National Institute of Technology (NIT), Rourkela have developed a hybrid energy storage system to improve the efficiency and lifespan of batteries used in electric vehicles. This is a relevant development for India given the growing demand for electric vehicles in the country.
The NIT Rourkela team has secured a patent for the developed technology and are open to collaboration with EV original equipment manufacturers (OEMs), powertrain system integrators, fleet operators, and EV retrofit start-ups.
India is among the largest automobile markets in the world. Dwindling petroleum reserves, coupled with government initiatives such as the National Electric Mobility Mission Plan and the FAME schemes, have accelerated the adoption of electric vehicles across the country. In 2022 alone, electric vehicle sales in India crossed the one-million mark, reflecting the rapid pace of electrification of the domestic fleet.
EVs are powered by a battery pack, a large, rechargeable energy storage system made of thousands of individual cells linked together. Battery packs suffer from low power density, limited cycle life, and high thermal stress when exposed to rapid current spikes. These are particularly serious in cities where the vehicles have to start and stop frequently and have to face sudden and rapid speed increases and decreases, all of which could degrade battery cells.
To mitigate these limitations, the battery pack is often paired with a high-power-density supercapacitor to form a hybrid energy storage system (HESS). Supercapacitors store charge electrostatically at the electrode–electrolyte interface, enabling charge and discharge within seconds and delivering specific power an order of magnitude higher than that of conventional batteries. They also exhibit exceptional cycle life, typically exceeding one million charge–discharge cycles with negligible degradation. Consequently, during sudden acceleration, deceleration, and regenerative braking events, the supercapacitor absorbs and supplies the transient power demand, thereby relieving the battery of high-rate current stress and extending its service life.
The battery pack and supercapacitors are usually connected in three ways. These are, passive, semi-active and active.
In a passive connection, the two are connected directly, which makes the supercapacitor less capable of responding quickly to changes in power demand.
In active connections, there are separate electronic converters that manage the battery and supercapacitor, but these extra components increase complexity and reduce efficiency.
To overcome the above problems, the NIT-R researchers have developed a hybrid energy storage architecture that protects the battery from sudden power requirement surges, efficiently uses supercapacitor energy, and minimises the number of components, thereby minimising complexity.
Explaining the design, Prof. Monalisa Pattnaik said, “Our architecture contains three main components, one converter to connect both battery and supercapacitor to the vehicle’s electrical system, an inductor that is placed in the electrical path, and a single control system to handle the power flow.”
Each of these components serves a specific function. The single converter for both battery and supercapacitor reduces the number of switches and control components, thereby reducing complexity. The inductor protects against sudden surges in current, thereby increasing life of the battery. The single control system handles both speeding up and slowing down of the vehicle, thereby reducing the hardware requirements.
The researchers tested this hybrid system under conditions of sudden brakes, rapid acceleration and deceleration. The system retained stable 48 V voltage, enabled smooth battery current changes, and also helped the supercapacitor handle sudden power changes efficiently.
Professor Pattnaik added, “Our design is highly optimized for low-voltage EV platforms operating in the 24 V to 60 V DC range. This includes urban light electric vehicles such as electric scooters, electric motorcycles, electric rickshaws (e-rickshaws), cargo tricycles, and campus/industrial utility vehicles.”
This hybrid system can also be used in automated guided vehicles (AGVs) and warehouse carts, DC microgrids and renewable-energy charging stations.
