EPE Association: EPE 2025 - LS5a: DC/DC Converter Topologies

EPE 2025 - LS5a: DC/DC Converter Topologies
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2025 - Conference > EPE 2025 - Topic 09: Power Converter Topologies > EPE 2025 - LS5a: DC/DC Converter Topologies

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   A High-Efficiency 5.5kW Battery Backup Unit for OCP Open Rack V3 Using Partial Power Conversion
By Martin WATTENBERG, Lars BOHLAENDER, Matthias J. KASPER, Ulf SCHWALBE, Gerald DEBOY [View]
[Download]

Abstract: Battery Backup Units (BBUs) are key components in modern, AI-centric data centers where uptime, efficiency, and high-power capability are critical.This paper presents a highly efficient BBU based on a 5.5 kW DC-DC converter using a partial power concept. The output power can be maintained for a battery voltage from 35 to 62 V according to OCP V3 (50V). A power density of 290 W/inch3 is achieved with a converter size of 75 x 128 x 36 mm while maintaining an efficiency above 99\%. A prototype has been built, and experimental resultsare presented.

   Design and Optimization of an Unbalanced-flux Transformer for 1 kW LLC Transformer
By Sobhi BARG, Adane HAILU, Souhaib BARG, Kent BERTILSSON [View]
[Download]

Abstract: Existing works to increase the power density of LLC transformer are mainly based on the MHzapproach. This paper proposes a new LLC transformer design based on the recent introducedconcept called the unbalanced-flux magnetics. The transformer was optimized using Genetic algorithm and iterative optimization approach. The unbalanced-flux transformer was designed and experimentally tested in 1 kW 400/48V LLC converter. The LLC converter is built, and the transformer is successfully up-to 750 W without heatsink and 1 kW with heatsink. The realized realizing power density is 224W/cm3 which is approximately 3x higher than the results in the state-of-the-art.

   Performance Evaluation of Three-Phase, Two-Level Medium Voltage Power Stack Based on 10 kV SiC MOSFETs
By Morten Rahr NIELSEN, Martin KJÆR, Gao LIU, Zhixing YAN, Asger Bjørn JØRGENSEN, Hongbo ZHAO, Michael Møller BECH, Stig MUNK-NIELSEN [View]
[Download]

Abstract: The performance of a 50 kVA three-phase, two-level medium voltage power stack based on 10 kV SiC MOSFETs has been evaluated under varying load conditions, i.e. voltage- and current-levels, coolant temperatures, and switching frequencies. A calorimetric measurement method is applied to estimate the power stack losses and its equivalent power stack efficiency. Experimental results from an inductive load test setup show an equivalent power stack efficiency of 98.8\% ± 0.56 at 6 kV DC-link voltage, 10 kHz switching frequency, and 40C coolant temperature with a maximum MOSFET junction temperature of less than 115C and thermal resistance of 0.38 K/W.

EPE 2025 - LS5a: DC/DC Converter Topologies
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2025 - Conference > EPE 2025 - Topic 09: Power Converter Topologies > EPE 2025 - LS5a: DC/DC Converter Topologies
	[return to parent folder]

	A High-Efficiency 5.5kW Battery Backup Unit for OCP Open Rack V3 Using Partial Power Conversion By Martin WATTENBERG, Lars BOHLAENDER, Matthias J. KASPER, Ulf SCHWALBE, Gerald DEBOY	[View] [Download]
Abstract: Battery Backup Units (BBUs) are key components in modern, AI-centric data centers where uptime, efficiency, and high-power capability are critical.This paper presents a highly efficient BBU based on a 5.5 kW DC-DC converter using a partial power concept. The output power can be maintained for a battery voltage from 35 to 62 V according to OCP V3 (50V). A power density of 290 W/inch3 is achieved with a converter size of 75 x 128 x 36 mm while maintaining an efficiency above 99\%. A prototype has been built, and experimental resultsare presented.

	Design and Optimization of an Unbalanced-flux Transformer for 1 kW LLC Transformer By Sobhi BARG, Adane HAILU, Souhaib BARG, Kent BERTILSSON	[View] [Download]
Abstract: Existing works to increase the power density of LLC transformer are mainly based on the MHzapproach. This paper proposes a new LLC transformer design based on the recent introducedconcept called the unbalanced-flux magnetics. The transformer was optimized using Genetic algorithm and iterative optimization approach. The unbalanced-flux transformer was designed and experimentally tested in 1 kW 400/48V LLC converter. The LLC converter is built, and the transformer is successfully up-to 750 W without heatsink and 1 kW with heatsink. The realized realizing power density is 224W/cm3 which is approximately 3x higher than the results in the state-of-the-art.

	Performance Evaluation of Three-Phase, Two-Level Medium Voltage Power Stack Based on 10 kV SiC MOSFETs By Morten Rahr NIELSEN, Martin KJÆR, Gao LIU, Zhixing YAN, Asger Bjørn JØRGENSEN, Hongbo ZHAO, Michael Møller BECH, Stig MUNK-NIELSEN	[View] [Download]
Abstract: The performance of a 50 kVA three-phase, two-level medium voltage power stack based on 10 kV SiC MOSFETs has been evaluated under varying load conditions, i.e. voltage- and current-levels, coolant temperatures, and switching frequencies. A calorimetric measurement method is applied to estimate the power stack losses and its equivalent power stack efficiency. Experimental results from an inductive load test setup show an equivalent power stack efficiency of 98.8\% ± 0.56 at 6 kV DC-link voltage, 10 kHz switching frequency, and 40C coolant temperature with a maximum MOSFET junction temperature of less than 115C and thermal resistance of 0.38 K/W.