[{"abstract":[{"lang":"eng","text":"The LLC converter achieves the highest efficiency in resonant operation. Conventionally, the input DC-link voltage is controlled to operate the LLC converter at resonance for the given operating point. However, the DC-link capacitor voltage shows a low-frequency voltage ripple (typically the second harmonic of grid frequency) in cascaded converters so that the LLC has to adapt its switching frequency within the grid period. Conventionally, the LLC converter operates 50% of the time above the resonant frequency of 40 kHz and 50% below resonance. Both operating conditions cause additional losses. However, experimental measurements indicate that the below-resonance operation causes significantly higher losses than above-resonance operation due to much higher primary and secondary transformer currents. It is better to increase the DC-link voltage by 30% of the peak-to-peak low-frequency voltage ripple to mostly avoid below-resonance operation (i.e., from 650 V to 680 V in this case). With the proposed control, the LLC converter operates about 75% of time over resonance and only 25% of time below resonance. The overall efficiency increases from 97.66% to 97.7% for the average operating point with an 80% load current. This corresponds to a 2% total loss reduction. Finally, the peak resonance capacitor voltage decreases from 910 V to 790 V (−13%)."}],"publication":"Electronics","keyword":["adaptive DC-link voltage","cascaded H-bridge","resonant operation","Full-Bridge Converter","loss minimization","LLC Resonant Converter","peak capacitor voltage reduction"],"language":[{"iso":"eng"}],"year":"2025","issue":"8","title":"Adaptive DC-Link Voltage Control for 22 kW, 40 kHz LLC Resonant Converter Considering Low-Frequency Voltage Ripple","publisher":"MDPI AG","date_created":"2025-05-05T12:27:39Z","status":"public","type":"journal_article","article_number":"1517","_id":"59805","user_id":"34289","department":[{"_id":"52"}],"citation":{"apa":"Unruh, R., Böcker, J., &#38; Schafmeister, F. (2025). Adaptive DC-Link Voltage Control for 22 kW, 40 kHz LLC Resonant Converter Considering Low-Frequency Voltage Ripple. <i>Electronics</i>, <i>14</i>(8), Article 1517. <a href=\"https://doi.org/10.3390/electronics14081517\">https://doi.org/10.3390/electronics14081517</a>","mla":"Unruh, Roland, et al. “Adaptive DC-Link Voltage Control for 22 KW, 40 KHz LLC Resonant Converter Considering Low-Frequency Voltage Ripple.” <i>Electronics</i>, vol. 14, no. 8, 1517, MDPI AG, 2025, doi:<a href=\"https://doi.org/10.3390/electronics14081517\">10.3390/electronics14081517</a>.","short":"R. Unruh, J. Böcker, F. Schafmeister, Electronics 14 (2025).","bibtex":"@article{Unruh_Böcker_Schafmeister_2025, title={Adaptive DC-Link Voltage Control for 22 kW, 40 kHz LLC Resonant Converter Considering Low-Frequency Voltage Ripple}, volume={14}, DOI={<a href=\"https://doi.org/10.3390/electronics14081517\">10.3390/electronics14081517</a>}, number={81517}, journal={Electronics}, publisher={MDPI AG}, author={Unruh, Roland and Böcker, Joachim and Schafmeister, Frank}, year={2025} }","ama":"Unruh R, Böcker J, Schafmeister F. Adaptive DC-Link Voltage Control for 22 kW, 40 kHz LLC Resonant Converter Considering Low-Frequency Voltage Ripple. <i>Electronics</i>. 2025;14(8). doi:<a href=\"https://doi.org/10.3390/electronics14081517\">10.3390/electronics14081517</a>","ieee":"R. Unruh, J. Böcker, and F. Schafmeister, “Adaptive DC-Link Voltage Control for 22 kW, 40 kHz LLC Resonant Converter Considering Low-Frequency Voltage Ripple,” <i>Electronics</i>, vol. 14, no. 8, Art. no. 1517, 2025, doi: <a href=\"https://doi.org/10.3390/electronics14081517\">10.3390/electronics14081517</a>.","chicago":"Unruh, Roland, Joachim Böcker, and Frank Schafmeister. “Adaptive DC-Link Voltage Control for 22 KW, 40 KHz LLC Resonant Converter Considering Low-Frequency Voltage Ripple.” <i>Electronics</i> 14, no. 8 (2025). <a href=\"https://doi.org/10.3390/electronics14081517\">https://doi.org/10.3390/electronics14081517</a>."},"intvolume":"        14","publication_status":"published","publication_identifier":{"issn":["2079-9292"]},"main_file_link":[{"url":"https://www.mdpi.com/2079-9292/14/8/1517"}],"doi":"10.3390/electronics14081517","date_updated":"2025-05-05T12:34:00Z","author":[{"full_name":"Unruh, Roland","id":"34289","last_name":"Unruh","first_name":"Roland"},{"full_name":"Böcker, Joachim","id":"66","last_name":"Böcker","orcid":"0000-0002-8480-7295","first_name":"Joachim"},{"first_name":"Frank","full_name":"Schafmeister, Frank","id":"71291","last_name":"Schafmeister"}],"volume":14},{"keyword":["Cascaded H-Bridge","Converter Losses","Decentralized Control","Full-Bridge Converter","LLC Resonant Converter"],"language":[{"iso":"eng"}],"publication":"ECCE Europe 2024; IEEE Energy Conversion Congress & Exposition Europe","abstract":[{"lang":"eng","text":"Although there are numerous design and control methodologies for the LLC resonant converter,\r\nthey often do not consider decentralized control strategies to operate them as isolated DC-DC converters within a\r\ncascaded H-bridge. The total output power of all LLC converters must be constant to supply a load such as a wa-\r\nter electrolyzer. However, each individual LLC converter can vary its output power as long as the total output\r\npower remains constant. This opens new possibilities in increasing the system efficiency and robustness. Usually,\r\nthe DC-link voltage of each module capacitor shows a 2nd harmonic voltage ripple. However, the total stored energy\r\nin all DC-link capacitors is constant within a grid period for a balanced three-phase system. By controlling each\r\nLLC converter’s output power locally to be proportional to the energy stored in its DC-link capacitor, modules with\r\na lower instantaneous DC-link voltage transfer less power to the load than modules with a higher DC-link voltage.\r\nAs a result, a higher efficiency, voltage gain and lower peak resonant capacitor voltage can be achieved with the\r\nsame components. The 22.2kW experimental prototype of the LLC converter reaches an efficiency of over 97% at\r\nresonance which is similar to the precalculated value."}],"publisher":"IEEE","date_created":"2024-05-19T14:26:29Z","title":"Experimentally Verified 22 kW, 40 kHz LLC Resonant Converter Design with new Control for a 1 MW Cascaded H-Bridge Converter","year":"2024","_id":"54356","department":[{"_id":"52"}],"user_id":"34289","type":"conference","status":"public","date_updated":"2024-11-28T14:16:05Z","author":[{"first_name":"Roland","last_name":"Unruh","id":"34289","full_name":"Unruh, Roland"},{"full_name":"Böcker, Joachim","id":"66","last_name":"Böcker","orcid":"0000-0002-8480-7295","first_name":"Joachim"},{"id":"71291","full_name":"Schafmeister, Frank","last_name":"Schafmeister","first_name":"Frank"}],"doi":"https://doi.org/10.1109/ECCEEurope62508.2024.10751954","conference":{"end_date":"2024-09-06","location":"Darmstadt, Germany","name":"ECCE Europe 2024","start_date":"2024-09-02"},"main_file_link":[{"url":"https://ieeexplore.ieee.org/abstract/document/10751954"}],"publication_identifier":{"isbn":["979-8-3503-6444-6"]},"publication_status":"accepted","place":"Darmstadt","citation":{"ama":"Unruh R, Böcker J, Schafmeister F. Experimentally Verified 22 kW, 40 kHz LLC Resonant Converter Design with new Control for a 1 MW Cascaded H-Bridge Converter. In: <i>ECCE Europe 2024; IEEE Energy Conversion Congress &#38; Exposition Europe</i>. IEEE. doi:<a href=\"https://doi.org/10.1109/ECCEEurope62508.2024.10751954\">https://doi.org/10.1109/ECCEEurope62508.2024.10751954</a>","ieee":"R. Unruh, J. Böcker, and F. Schafmeister, “Experimentally Verified 22 kW, 40 kHz LLC Resonant Converter Design with new Control for a 1 MW Cascaded H-Bridge Converter,” presented at the ECCE Europe 2024, Darmstadt, Germany, doi: <a href=\"https://doi.org/10.1109/ECCEEurope62508.2024.10751954\">https://doi.org/10.1109/ECCEEurope62508.2024.10751954</a>.","chicago":"Unruh, Roland, Joachim Böcker, and Frank Schafmeister. “Experimentally Verified 22 KW, 40 KHz LLC Resonant Converter Design with New Control for a 1 MW Cascaded H-Bridge Converter.” In <i>ECCE Europe 2024; IEEE Energy Conversion Congress &#38; Exposition Europe</i>. Darmstadt: IEEE, n.d. <a href=\"https://doi.org/10.1109/ECCEEurope62508.2024.10751954\">https://doi.org/10.1109/ECCEEurope62508.2024.10751954</a>.","apa":"Unruh, R., Böcker, J., &#38; Schafmeister, F. (n.d.). Experimentally Verified 22 kW, 40 kHz LLC Resonant Converter Design with new Control for a 1 MW Cascaded H-Bridge Converter. <i>ECCE Europe 2024; IEEE Energy Conversion Congress &#38; Exposition Europe</i>. ECCE Europe 2024, Darmstadt, Germany. <a href=\"https://doi.org/10.1109/ECCEEurope62508.2024.10751954\">https://doi.org/10.1109/ECCEEurope62508.2024.10751954</a>","short":"R. Unruh, J. Böcker, F. Schafmeister, in: ECCE Europe 2024; IEEE Energy Conversion Congress &#38; Exposition Europe, IEEE, Darmstadt, n.d.","mla":"Unruh, Roland, et al. “Experimentally Verified 22 KW, 40 KHz LLC Resonant Converter Design with New Control for a 1 MW Cascaded H-Bridge Converter.” <i>ECCE Europe 2024; IEEE Energy Conversion Congress &#38; Exposition Europe</i>, IEEE, doi:<a href=\"https://doi.org/10.1109/ECCEEurope62508.2024.10751954\">https://doi.org/10.1109/ECCEEurope62508.2024.10751954</a>.","bibtex":"@inproceedings{Unruh_Böcker_Schafmeister, place={Darmstadt}, title={Experimentally Verified 22 kW, 40 kHz LLC Resonant Converter Design with new Control for a 1 MW Cascaded H-Bridge Converter}, DOI={<a href=\"https://doi.org/10.1109/ECCEEurope62508.2024.10751954\">https://doi.org/10.1109/ECCEEurope62508.2024.10751954</a>}, booktitle={ECCE Europe 2024; IEEE Energy Conversion Congress &#38; Exposition Europe}, publisher={IEEE}, author={Unruh, Roland and Böcker, Joachim and Schafmeister, Frank} }"}},{"keyword":["Full-bridge","High voltage power converters","LLC resonant converter","Multilevel converters","ZVS Converters"],"language":[{"iso":"eng"}],"_id":"29880","user_id":"34289","department":[{"_id":"52"}],"abstract":[{"lang":"eng","text":"Although there are numerous design methodologies for the LLC resonant converter, they often do not consider the possibility of input voltage adjustment. In the proposed concept, a modular multi-level converter (MMC) is used to step-down the three-phase medium voltage of 10 kV, and provide up to 1 MW of pure DC power to the load consisting of electrolyzers for hydrogen generation. Therefore, each module is extended by an LLC resonant converter to adapt to the specific electrolyzers DC voltage range of 142...220 V and to provide galvanic isolation. In order to achieve a high efficiency for a wide range of load conditions, the input voltage of the LLC converter is adjusted between 600 V and 770 V while operating at resonance or close to resonance. The parameters of the 11kW LLC resonant converter with an integrated leakage inductance are systematically optimized to maximize the efficiency for all loads while achieving zero-voltage switching. For a fast estimation of eddy current losses, a new method is proposed, which uses a single FEM simulation to fit newly developed loss equations. The calculated average efficiency is 97.8%. The prototype of the LLC converter reaches a peak efficiency of over 98% at resonance at half load which is similar to the precalculated value."}],"status":"public","type":"conference","publication":"2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)","title":"11kW, 70kHz LLC Converter Design with Adaptive Input Voltage for 98% Efficiency in an MMC","main_file_link":[{"url":"https://ieeexplore.ieee.org/abstract/document/9265771"}],"doi":"10.1109/compel49091.2020.9265771","conference":{"start_date":"2020-11-09","end_date":"2020-11-12"},"date_updated":"2024-11-28T14:19:07Z","publisher":"IEEE","date_created":"2022-02-18T16:29:08Z","author":[{"first_name":"Roland","full_name":"Unruh, Roland","id":"34289","last_name":"Unruh"},{"id":"71291","full_name":"Schafmeister, Frank","last_name":"Schafmeister","first_name":"Frank"},{"full_name":"Böcker, Joachim","id":"66","orcid":"0000-0002-8480-7295","last_name":"Böcker","first_name":"Joachim"}],"year":"2020","citation":{"ama":"Unruh R, Schafmeister F, Böcker J. 11kW, 70kHz LLC Converter Design with Adaptive Input Voltage for 98% Efficiency in an MMC. In: <i>2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)</i>. IEEE; 2020. doi:<a href=\"https://doi.org/10.1109/compel49091.2020.9265771\">10.1109/compel49091.2020.9265771</a>","ieee":"R. Unruh, F. Schafmeister, and J. Böcker, “11kW, 70kHz LLC Converter Design with Adaptive Input Voltage for 98% Efficiency in an MMC,” 2020, doi: <a href=\"https://doi.org/10.1109/compel49091.2020.9265771\">10.1109/compel49091.2020.9265771</a>.","chicago":"Unruh, Roland, Frank Schafmeister, and Joachim Böcker. “11kW, 70kHz LLC Converter Design with Adaptive Input Voltage for 98% Efficiency in an MMC.” In <i>2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)</i>. IEEE, 2020. <a href=\"https://doi.org/10.1109/compel49091.2020.9265771\">https://doi.org/10.1109/compel49091.2020.9265771</a>.","bibtex":"@inproceedings{Unruh_Schafmeister_Böcker_2020, title={11kW, 70kHz LLC Converter Design with Adaptive Input Voltage for 98% Efficiency in an MMC}, DOI={<a href=\"https://doi.org/10.1109/compel49091.2020.9265771\">10.1109/compel49091.2020.9265771</a>}, booktitle={2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)}, publisher={IEEE}, author={Unruh, Roland and Schafmeister, Frank and Böcker, Joachim}, year={2020} }","mla":"Unruh, Roland, et al. “11kW, 70kHz LLC Converter Design with Adaptive Input Voltage for 98% Efficiency in an MMC.” <i>2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)</i>, IEEE, 2020, doi:<a href=\"https://doi.org/10.1109/compel49091.2020.9265771\">10.1109/compel49091.2020.9265771</a>.","short":"R. Unruh, F. Schafmeister, J. Böcker, in: 2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL), IEEE, 2020.","apa":"Unruh, R., Schafmeister, F., &#38; Böcker, J. (2020). 11kW, 70kHz LLC Converter Design with Adaptive Input Voltage for 98% Efficiency in an MMC. <i>2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)</i>. <a href=\"https://doi.org/10.1109/compel49091.2020.9265771\">https://doi.org/10.1109/compel49091.2020.9265771</a>"},"publication_status":"published","publication_identifier":{"unknown":["978-1-7281-7160-9"]},"quality_controlled":"1"}]