A flexible DC-DC converter achieves a record efficiency of 98.3%

A new converter paves the way for more efficient and sustainable energy storage and conversion solutions.


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A new DC-DC power converter surpasses earlier designs and sets the stage for improved, dependable, and eco-friendly energy storage and conversion options. The Kobe University innovation can effectively connect with various energy sources while bolstering system stability and ease of use with unparalleled efficiency.

There are two types of electric power, AC (alternating current) and DC (direct current). The “Current War” in the late 19th century was famously a debate over which type should be used for national power grids, and AC emerged as the favored choice.

Today, most power plants generate AC, but DC is essential for solar power, batteries, electric vehicles, and computers, necessitating the conversion from AC to DC, which incurs a loss. An alternative approach is the implementation of DC microgrids that combine different renewable DC energy sources and storage devices to directly supply energy to data centers and other DC-powered appliances.

This eliminates the need for AC-to-DC conversion, but a device capable of flexibly converting various voltages is required because each DC device typically operates at a different voltage, and batteries supply different voltages based on their charge and capacity. Furthermore, the voltage conversion must work in both directions since batteries serve as both energy sources and sinks.

MISHIMA Tomokazu from Kobe University (Japan) and LAI Ching-Ming from the National Chung Hsing University (Taiwan) collaborated on a project to develop essential technologies for high power density power distribution systems that contribute to low-carbon data centers. Their joint effort has resulted in a significant breakthrough.

“Our diverse team with expertise spanning across relevant disciplines allowed us to approach the problem from multiple perspectives, and our access to cutting-edge facilities and resources enabled us to conduct thorough experiments, simulations, and analyses. Additionally, our group has a track record of successful collaborations with industry partners and other research institutions, providing valuable insights and support for our endeavors,” explains Kobe University student team member LIU Shiqiang.

Liu, who is the first author of the study, explains its main advantages over previous designs: “Its superior voltage ratio means it can efficiently interface with a wide range of energy sources, while the self-balancing of inductor currents enhances system stability and simplicity. Moreover, the asymmetrical duty limit control offers enhanced performance, especially for electric vehicle-connected DC microgrids.”

Their prototype was found to be highly efficient, achieving an impressive 98.3% efficiency. “This highlights the practical feasibility and scalability of the proposed topology for real-world applications, paving the way for future advancements in bidirectional DC-DC conversion technology,” comments Liu.

The team has filed for a patent for the design in Japan and is now preparing for its commercialization with UPE-Japan, a Kobe University startup. Naturally, they also want to keep improving their design, including for higher power densities and a wider variety of applications.

Liu says, “Ultimately, our long-term objective is to contribute to the transition towards more efficient, reliable, and sustainable energy storage and conversion solutions, particularly in the context of electric vehicles and renewable energy integration.”

Journal reference:

  1. Shiqiang Liu, Guiyi Dong, Tomokazu Mishima, Ching-Ming Lai. Over 98% Efficiency SiC-MOSFET based Four-Phase Interleaved Bidirectional DC-DC Converter Featuring Wide-Range Voltage Ratio. IEEE Transactions on Power Electronics, 2024. DOI: 10.1109/TPEL.2024.3389052