A groundbreaking EV charging technology uses compact, transformer-free megawatt-scale converters to deliver ultra-fast charging, reducing vehicle charge times from hours to just minutes.
Bengaluru:
Published in IEEE Transactions on Industrial Electronics, the work demonstrates a 3–5 per cent efficiency gain at the megawatt scale—resulting in significant energy, cost, and material savings. Researchers at the Indian Institute of Science’s (IISc) Department of Electrical Engineering, in collaboration with Delta Electronics India, have developed a cascaded H-bridge (CHB) multiport DC converter that connects directly to the medium-voltage AC grid, eliminating the need for large LFTs.
With EV adoption surging, fast charging stations now demand power levels exceeding one MW—comparable to supplying 1,000 homes. Conventional stations rely on bulky, copper- and iron-intensive line-frequency transformers (LFTs) and multiple AC–DC conversion stages, which drive up costs, material use, energy loss, and footprint. The solid-state system can charge multiple EVs, integrate renewables, store energy locally, and—through its bidirectional design—feed power back to the grid during peak demand or outages, potentially supporting critical facilities such as hospitals. “We’ve replaced bulky transformers with a compact, solid-state solution,” said Kaushik Basu, Associate Professor, IISc.
In traditional systems, multiple power-conversion stages reduce efficiency and increase the carbon footprint. The new approach streamlines power delivery by cutting out these extra stages, resulting in a lighter, more efficient, and environmentally friendlier charging solution.
How is a CHB-based multiport DC converter different?
Professor Kaushik Basu discussed this innovative approach in detail. When asked how the CHB-based multiport DC converter differs from traditional transformer-based charging systems, Basu explained, “Thermal plants transmit electricity at high voltages, which transformers step down to about 230 volts for household use. In EVs, the battery is like the petrol tank, storing energy as an electrical charge. Charging speed depends on the charger's power."
First, battery technology itself limits safe charging speed due to thermal constraints and cell chemistry. Second, the charger must also deliver very high power. Delivering 500 kW requires substantial grid capacity, equivalent to the instantaneous demand of a small commercial building or multiple residential blocks.
Without adequate grid infrastructure, this can cause overload, Basu said, adding that some charging stations address this with battery energy storage systems—they charge batteries slowly from the grid and discharge rapidly into EVs when needed, though this approach is still emerging rather than widespread.
He further explained that current DC fast chargers typically take 30-60 minutes to charge an EV battery to 80 per cent—a much slower process than filling a petrol tank, which takes only a few minutes. "To charge faster, you need to deliver the same amount of energy at a higher current or higher power. For example, the battery capacity of a four-wheeler is measured in kilowatt-hours (kWh). If we charge it at 50 kW, roughly ‘1C’ charging, it takes about an hour. With a 350-500 kW ultra-fast charger, the same battery could reach 80 per cent charge in 15-20 minutes, though actual charging speeds depend on battery chemistry, temperature, and state of charge," he said while highlighting two key challenges.
Large consumers such as hospitals or commercial complexes draw power at higher voltages—typically 11 kV in India—because supplying 500 kW at 230 V would require enormous currents. Transformers at each charging station step this 11 kV supply down to 400 V (three-phase) or 230 V per single phase, which then feeds the individual EV chargers, he explained.
However, this conventional setup has two major drawbacks:
Bulky, costly transformers: They are mainly made of copper and iron, both of which are heavy and expensive, with copper prices rising sharply.
Poor efficiency: Charging the main storage battery from the grid at a slower rate and then transferring the energy from the storage battery to multiple EV batteries happens through multiple power conversion stages, reducing efficiency.
The IISc innovation—the CHB-based multiport DC converter—addresses both issues. It connects directly to the medium-voltage (11 kV) supply, eliminating the need for large transformers. By operating at high frequencies, the converter becomes compact and lightweight. It also provides multiple isolated output ports, so several vehicles can be charged in parallel.
Lab prototype and efficiency milestone:
A 1.2 kW lab prototype has been achieved, and it can supply DC power for charging EVs at over 95 per cent efficiency; the team now aims to scale to megawatt levels. Discussing the key hurdles in scaling the prototype from 1.2 kW to megawatt levels, Professor Basu explained that this concept is essentially a solid-state transformer, where semiconductors are used to convert power from high voltage to low voltage levels.
“The concept is not new,” Professor Basu said. "Researchers worldwide are working on how to match or exceed the efficiency of state-of-the-art conventional transformers. Our research shows that it is possible to meet or even beat the losses of traditional systems.”
In a traditional system, 11 kV is stepped down to 400 V and then supplied to a single charger that charges the car battery. This type of transformer is highly efficient. However, when power electronics are introduced to change the frequency from 50 Hz to 100 kHz, a larger number of semiconductor devices are required, compromising efficiency. He noted two main hurdles:
One is cost, as copper is expensive, but the cost of semiconductor-based solutions is gradually coming down as silicon processing improves. Initially, however, building these systems at scale is costly.
Second is the losses at higher frequencies. To make transformers smaller, the power electronics increase the frequency that the transformer “sees”—for example, to 100 kHz. This reduces the size of the transformer but also introduces additional power conversion stages, which can increase losses.
The IISc team has already demonstrated this technology at a prototype scale of 1.2 kW, but scaling up to the megawatt level poses significant challenges. Basu said, “The concept has been verified at a smaller scale, and the next step is to translate it into a high-power system,” he added.
New lab facility:
“With funding from the Department of Science and Technology (DST) and in partnership with Delta Electronics, we are establishing a 2,500 to 3,000 square foot lab at IISc,” added Basu. “The lab would be Delta-IISc’s centre of excellence on medium-voltage power electronics. We are planning to build a system in the 250 kW to 500 kW (half-megawatt) range and test it using car emulators.
Delta, which manufactures such systems for testing EV batteries and chargers, is providing the emulators for our project. The facility will be used to demonstrate a megawatt-level converter capable of simultaneously charging a 200 kW bus and a 50 kW car directly from an 11 kV grid line.”
When asked about the timeline for a commercial pilot, Professor Basu said the lab would be ready within a month, with field trials expected in about a year.
Beyond EV charging, this technology could also power next-generation data centres, wind systems, and railway traction by enabling high-efficiency conversion directly at medium voltages.
Basu said that large AI-driven data centres have soaring power demands. Instead of stepping voltage down outside and losing 2–3 per cent in transmission, our system converts directly from 11 kV to low-voltage DC inside the building — eliminating bulky transformer rooms and delivering power to chargers or servers far more efficiently.
Speaking about IP protection and licensing for broader adoption outside India, the professor said, “Together with Delta, we have filed several patents—some already extended to other countries—and many more are in the pipeline, as this is truly cutting-edge technology.”
Alignment with India’s EV Policy:
Replying to a question on how this work aligns with India’s national EV policy and charging infrastructure goals, he said, “The government aims to equip national highways with high-power EV charging stations. Our innovation, with its multiple ports, can integrate renewable sources such as solar power into this network, directly supporting that vision.”
Replying to what excites him most about this technology’s long-term impact on power infrastructure, the professor said, “Electric vehicles aim to cut petrol use and its harmful emissions, but charging them with coal-based power only shifts the pollution elsewhere. The real breakthrough will come from integrating renewable energy for charging — a true win-win. With climate change challenges, we must rely on indigenous technologies and inspire the next generation, especially in electrical engineering, to innovate and solve these problems.”
The road ahead:
“Within 5–10 years, vehicles could charge in under 10 minutes. As power electronics spread across generation and consumption, efficiency will rise and converters will shrink, paving the way for a fully renewable, low-carbon energy system," Basu added.
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