New circuit topology could lead to more efficient solid-state heat pumps

In the Fraunhofer lighthouse project ElKaWe, researchers are making significant progress in developing electrocaloric heat pumps as an alternative to traditional compressor technology. These new heat pumps promise higher efficiency without the need for refrigerants.

At Fraunhofer IAF, researchers achieved a remarkable milestone in power electronics by creating an ultra-efficient circuit topology for voltage converters with over 99.74% electrical efficiency. This breakthrough sets a global standard and is a crucial step towards more efficient solid-state heat pumps. The results have been published in the IEEE Journal of Emerging and Selected Topics in Power Electronics.

Heat pumps play a vital role in the heat transition, offering highly efficient heat generation. In the ElKaWe project, scientists aim to improve heat pump efficiency further by exploring new compressor-less designs. The electrocaloric heat pump, with its theoretical potential to reach 85% of the Carnot limit, shows promise in achieving higher efficiencies, where power electronics efficiency also plays a significant role.

Ultra-efficient power electronics due to gallium nitride

In the ElKaWe project, the Fraunhofer Institute for Applied Solid State Physics IAF leads the development of drive electronics for electrocaloric heat pumps. To enhance power density and efficiency, the institute focuses on researching devices utilizing gallium nitride (GaN) semiconductor technology.

For the first time, researchers have successfully designed and optimized power electronics specifically tailored for electrocaloric heat pumps. Through the use of GaN transistors, they have achieved an impressive electrical efficiency of 99.74% in the power path of voltage converters. This GaN-based multilevel DC/DC converter sets new global standards, significantly surpassing the previous research state with conversion efficiencies of less than 90% for the electrical control of these innovative heat pumps.

More efficient electronics provide more efficient heat pumps

The significant increase in efficiency of the drive electronics directly impacts the coefficient of performance of the entire system, marking a milestone in advancing heat pump technology. Previously, electrocaloric heat pump systems faced limitations due to electronics losses. However, the enhanced electrical efficiency now leads to a higher coefficient of performance for the entire heat pump system, making it a promising step towards more efficient heating and cooling solutions.

Dr. Stefan Mönch, a power electronics researcher at Fraunhofer IAF, notes that their ultra-efficient power electronics allow them to achieve well over 50% of the maximum theoretical coefficient of performance with electrocaloric heat pumps, even at the system level. This breakthrough brings the prospect of a more efficient and emission-free solution for heating and cooling.

Dr. Kilian Bartholomé, project manager of ElKaWe and researcher at Fraunhofer Institute for Physical Measurement Techniques IPM, highlights that achieving a high coefficient of performance for electrocaloric heat pumps relies on high efficiency in materials, electronics, and heat transfer. Successfully controlling these aspects unlocks the enormous potential of electrocalorics.

The electrocaloric heat pump operates based on the electrocaloric effect, where applying an electrical voltage to special ceramics or polymers causes the material to heat up. Upon removing the voltage, the material cools down, and the process is almost completely reversible. The power electronics in the system must efficiently charge and discharge the electrocaloric capacitances multiple times per second to pump heat in each cycle, as loss-free as possible.

The results stem from the Fraunhofer lighthouse project ElKaWe, involving six Fraunhofer Institutes exploring electrocaloric heat pumps for heating and cooling. Led by Fraunhofer IPM, they develop efficient heat pumps without compressor technology and refrigerants, aiming to showcase their potential for future emission-free heating and cooling applications.

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