[{"doi":"10.3390/electronics14081517","main_file_link":[{"url":"https://www.mdpi.com/2079-9292/14/8/1517"}],"volume":14,"author":[{"last_name":"Unruh","full_name":"Unruh, Roland","id":"34289","first_name":"Roland"},{"first_name":"Joachim","orcid":"0000-0002-8480-7295","last_name":"Böcker","full_name":"Böcker, Joachim","id":"66"},{"first_name":"Frank","id":"71291","full_name":"Schafmeister, Frank","last_name":"Schafmeister"}],"date_updated":"2025-05-05T12:34:00Z","intvolume":"        14","citation":{"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>.","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>.","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>","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>","short":"R. Unruh, J. Böcker, F. Schafmeister, Electronics 14 (2025).","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>.","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} }"},"publication_identifier":{"issn":["2079-9292"]},"publication_status":"published","article_number":"1517","department":[{"_id":"52"}],"user_id":"34289","_id":"59805","status":"public","type":"journal_article","title":"Adaptive DC-Link Voltage Control for 22 kW, 40 kHz LLC Resonant Converter Considering Low-Frequency Voltage Ripple","date_created":"2025-05-05T12:27:39Z","publisher":"MDPI AG","year":"2025","issue":"8","language":[{"iso":"eng"}],"keyword":["adaptive DC-link voltage","cascaded H-bridge","resonant operation","Full-Bridge Converter","loss minimization","LLC Resonant Converter","peak capacitor voltage reduction"],"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"},{"title":"Three-Phase Instantaneous Current Controller for Unbalanced Grid Inductors Without DQ Transform for Cascaded H-Bridge Converters","main_file_link":[{"url":"https://ieeexplore.ieee.org/document/11238538"}],"conference":{"end_date":"2025-09-04","location":"Birmingham, United Kingdom","name":"2025 Energy Conversion Congress & Expo Europe (ECCE Europe)","start_date":"2025-09-01"},"doi":"10.1109/ecce-europe62795.2025.11238538","publisher":"IEEE","date_updated":"2025-12-16T15:25:38Z","date_created":"2025-12-16T15:20:55Z","author":[{"id":"34289","full_name":"Unruh, Roland","last_name":"Unruh","first_name":"Roland"},{"first_name":"Joachim","last_name":"Böcker","orcid":"0000-0002-8480-7295","id":"66","full_name":"Böcker, Joachim"},{"last_name":"Schafmeister","id":"71291","full_name":"Schafmeister, Frank","first_name":"Frank"}],"year":"2025","citation":{"ama":"Unruh R, Böcker J, Schafmeister F. Three-Phase Instantaneous Current Controller for Unbalanced Grid Inductors Without DQ Transform for Cascaded H-Bridge Converters. In: <i>2025 Energy Conversion Congress &#38;amp;Amp; Expo Europe (ECCE Europe)</i>. IEEE; 2025. doi:<a href=\"https://doi.org/10.1109/ecce-europe62795.2025.11238538\">10.1109/ecce-europe62795.2025.11238538</a>","chicago":"Unruh, Roland, Joachim Böcker, and Frank Schafmeister. “Three-Phase Instantaneous Current Controller for Unbalanced Grid Inductors Without DQ Transform for Cascaded H-Bridge Converters.” In <i>2025 Energy Conversion Congress &#38;amp;Amp; Expo Europe (ECCE Europe)</i>. IEEE, 2025. <a href=\"https://doi.org/10.1109/ecce-europe62795.2025.11238538\">https://doi.org/10.1109/ecce-europe62795.2025.11238538</a>.","ieee":"R. Unruh, J. Böcker, and F. Schafmeister, “Three-Phase Instantaneous Current Controller for Unbalanced Grid Inductors Without DQ Transform for Cascaded H-Bridge Converters,” presented at the 2025 Energy Conversion Congress &#38; Expo Europe (ECCE Europe), Birmingham, United Kingdom, 2025, doi: <a href=\"https://doi.org/10.1109/ecce-europe62795.2025.11238538\">10.1109/ecce-europe62795.2025.11238538</a>.","bibtex":"@inproceedings{Unruh_Böcker_Schafmeister_2025, title={Three-Phase Instantaneous Current Controller for Unbalanced Grid Inductors Without DQ Transform for Cascaded H-Bridge Converters}, DOI={<a href=\"https://doi.org/10.1109/ecce-europe62795.2025.11238538\">10.1109/ecce-europe62795.2025.11238538</a>}, booktitle={2025 Energy Conversion Congress &#38;amp;amp; Expo Europe (ECCE Europe)}, publisher={IEEE}, author={Unruh, Roland and Böcker, Joachim and Schafmeister, Frank}, year={2025} }","short":"R. Unruh, J. Böcker, F. Schafmeister, in: 2025 Energy Conversion Congress &#38;amp;Amp; Expo Europe (ECCE Europe), IEEE, 2025.","mla":"Unruh, Roland, et al. “Three-Phase Instantaneous Current Controller for Unbalanced Grid Inductors Without DQ Transform for Cascaded H-Bridge Converters.” <i>2025 Energy Conversion Congress &#38;amp;Amp; Expo Europe (ECCE Europe)</i>, IEEE, 2025, doi:<a href=\"https://doi.org/10.1109/ecce-europe62795.2025.11238538\">10.1109/ecce-europe62795.2025.11238538</a>.","apa":"Unruh, R., Böcker, J., &#38; Schafmeister, F. (2025). Three-Phase Instantaneous Current Controller for Unbalanced Grid Inductors Without DQ Transform for Cascaded H-Bridge Converters. <i>2025 Energy Conversion Congress &#38;amp;Amp; Expo Europe (ECCE Europe)</i>. 2025 Energy Conversion Congress &#38; Expo Europe (ECCE Europe), Birmingham, United Kingdom. <a href=\"https://doi.org/10.1109/ecce-europe62795.2025.11238538\">https://doi.org/10.1109/ecce-europe62795.2025.11238538</a>"},"publication_status":"published","keyword":["Cascaded H-Bridge","Current Control","dq Transformation","Linear Regression","Unbalanced Inductors"],"language":[{"iso":"eng"}],"_id":"63157","user_id":"34289","department":[{"_id":"52"}],"abstract":[{"text":"Three-phase cascaded H-bridge converters (CHBs) in star configuration require reliable current controllers to evenly charge the module DC-link capacitors. Conventionally, a current control in dq-coordinates is utilized. At steady state, the resulting calculated reference arm voltages are sinusoidal, have identical amplitudes and show a phase shift of 120 degree to each other. For balanced grid inductors, the resulting grid currents also have the same amplitude. However, own simulations show that unbalanced grid inductors always lead to different grid current amplitudes (4% difference in this case). As a result, the averaged charging module powers differ and the peak DC-link capacitor voltage rises as well. In the first step, an adaptation of an existing zero-sequence voltage injection is proposed. For balanced grid inductors, it converges to the 3rd harmonic voltage injection which can reduce the peak-to-peak DC-link voltage ripple up by to 50% and balances the power between the phases. However, unbalanced grid inductors still lead to the same unbalanced grid currents of 4%. Therefore, a new method with 4 integrators based on linear regression is proposed to achieve sinusoidal grid currents for unbalanced inductors. The proposed method has a similar transient dynamic as the conventional dq control, but balances the grid currents nearly ideally. Simulation results of a 1MW cascaded H bridge and a scaled-down prototype verify the proposed method.","lang":"eng"}],"status":"public","type":"conference","publication":"2025 Energy Conversion Congress &amp;amp; Expo Europe (ECCE Europe)"},{"date_created":"2024-05-19T14:26:29Z","publisher":"IEEE","title":"Experimentally Verified 22 kW, 40 kHz LLC Resonant Converter Design with new Control for a 1 MW Cascaded H-Bridge Converter","year":"2024","language":[{"iso":"eng"}],"keyword":["Cascaded H-Bridge","Converter Losses","Decentralized Control","Full-Bridge Converter","LLC Resonant Converter"],"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."}],"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"},{"first_name":"Frank","full_name":"Schafmeister, Frank","id":"71291","last_name":"Schafmeister"}],"date_updated":"2024-11-28T14:16:05Z","conference":{"location":"Darmstadt, Germany","end_date":"2024-09-06","start_date":"2024-09-02","name":"ECCE Europe 2024"},"doi":"https://doi.org/10.1109/ECCEEurope62508.2024.10751954","main_file_link":[{"url":"https://ieeexplore.ieee.org/abstract/document/10751954"}],"publication_identifier":{"isbn":["979-8-3503-6444-6"]},"publication_status":"accepted","citation":{"short":"R. Unruh, J. Böcker, F. Schafmeister, in: ECCE Europe 2024; IEEE Energy Conversion Congress &#38; Exposition Europe, IEEE, Darmstadt, n.d.","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} }","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>.","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>","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>."},"place":"Darmstadt","department":[{"_id":"52"}],"user_id":"34289","_id":"54356","type":"conference","status":"public"},{"language":[{"iso":"eng"}],"keyword":["Cascaded H-Bridge","Solid-State Transformer","Capacitor voltage ripple","Zero sequence voltage","Third harmonic injection"],"department":[{"_id":"52"}],"user_id":"34289","_id":"48352","status":"public","abstract":[{"lang":"eng","text":"Star-connected cascaded H-bridge Converters require large DC-link capacitors to buffer the second-order harmonic voltage ripple. First, it is analytically proven that the DC-link voltage ripple is proportional to the apparent converter power and does not depend on the power factor for nominal operation with sinusoidal reference arm voltages and currents. A third-harmonic zero-sequence voltage injection with an optimal amplitude and phase angle transforms the 2nd harmonic to a 4th harmonic DC-link voltage ripple. This reduces the voltage ripple by exactly 50% for all power factors at steady-state at balanced conditions. However, this requires 54% additional modules for unity power factor operation and even 100% for pure reactive power operation to account for the increased reference arm voltages due to the large amplitude of the optimal third-harmonic injection. If not enough modules are available, an adaptive discontinuous PWM is utilized to still minimize the voltage ripple for the given number of modules and power factor. With a very limited number of modules (modulation index is 1.15), the proposed method still reduces the DC-link voltage ripple by 24.4% for unity power factor operation. It requires the same number of modules as the commonly utilized 3rd harmonic injection with 1/6 of the grid voltage amplitude and achieves superior results. Simulations of a 10 kV/1 MVA system confirm the analysis."}],"publication":"2023 25th European Conference on Power Electronics and Applications (EPE'23 ECCE Europe)","type":"conference","doi":"10.23919/epe23ecceeurope58414.2023.10264313","conference":{"location":"Aalborg, Denmark","end_date":"2023-09-08","start_date":"2023-09-04","name":"2023 25th European Conference on Power Electronics and Applications (EPE'23 ECCE Europe)"},"main_file_link":[{"url":"https://ieeexplore.ieee.org/abstract/document/10264313"}],"title":"An Optimized Third-Harmonic Injection Reduces DC-Link Voltage Ripple in Cascaded H-Bridge Converters up to 50% for all Power Factors","author":[{"id":"34289","full_name":"Unruh, Roland","last_name":"Unruh","first_name":"Roland"},{"first_name":"Joachim","id":"66","full_name":"Böcker, Joachim","last_name":"Böcker","orcid":"0000-0002-8480-7295"},{"first_name":"Frank","last_name":"Schafmeister","full_name":"Schafmeister, Frank","id":"71291"}],"date_created":"2023-10-20T07:13:32Z","publisher":"IEEE","date_updated":"2023-10-20T10:01:02Z","citation":{"ieee":"R. Unruh, J. Böcker, and F. Schafmeister, “An Optimized Third-Harmonic Injection Reduces DC-Link Voltage Ripple in Cascaded H-Bridge Converters up to 50% for all Power Factors,” presented at the 2023 25th European Conference on Power Electronics and Applications (EPE’23 ECCE Europe), Aalborg, Denmark, 2023, doi: <a href=\"https://doi.org/10.23919/epe23ecceeurope58414.2023.10264313\">10.23919/epe23ecceeurope58414.2023.10264313</a>.","chicago":"Unruh, Roland, Joachim Böcker, and Frank Schafmeister. “An Optimized Third-Harmonic Injection Reduces DC-Link Voltage Ripple in Cascaded H-Bridge Converters up to 50% for All Power Factors.” In <i>2023 25th European Conference on Power Electronics and Applications (EPE’23 ECCE Europe)</i>. IEEE, 2023. <a href=\"https://doi.org/10.23919/epe23ecceeurope58414.2023.10264313\">https://doi.org/10.23919/epe23ecceeurope58414.2023.10264313</a>.","ama":"Unruh R, Böcker J, Schafmeister F. An Optimized Third-Harmonic Injection Reduces DC-Link Voltage Ripple in Cascaded H-Bridge Converters up to 50% for all Power Factors. In: <i>2023 25th European Conference on Power Electronics and Applications (EPE’23 ECCE Europe)</i>. IEEE; 2023. doi:<a href=\"https://doi.org/10.23919/epe23ecceeurope58414.2023.10264313\">10.23919/epe23ecceeurope58414.2023.10264313</a>","short":"R. Unruh, J. Böcker, F. Schafmeister, in: 2023 25th European Conference on Power Electronics and Applications (EPE’23 ECCE Europe), IEEE, 2023.","bibtex":"@inproceedings{Unruh_Böcker_Schafmeister_2023, title={An Optimized Third-Harmonic Injection Reduces DC-Link Voltage Ripple in Cascaded H-Bridge Converters up to 50% for all Power Factors}, DOI={<a href=\"https://doi.org/10.23919/epe23ecceeurope58414.2023.10264313\">10.23919/epe23ecceeurope58414.2023.10264313</a>}, booktitle={2023 25th European Conference on Power Electronics and Applications (EPE’23 ECCE Europe)}, publisher={IEEE}, author={Unruh, Roland and Böcker, Joachim and Schafmeister, Frank}, year={2023} }","mla":"Unruh, Roland, et al. “An Optimized Third-Harmonic Injection Reduces DC-Link Voltage Ripple in Cascaded H-Bridge Converters up to 50% for All Power Factors.” <i>2023 25th European Conference on Power Electronics and Applications (EPE’23 ECCE Europe)</i>, IEEE, 2023, doi:<a href=\"https://doi.org/10.23919/epe23ecceeurope58414.2023.10264313\">10.23919/epe23ecceeurope58414.2023.10264313</a>.","apa":"Unruh, R., Böcker, J., &#38; Schafmeister, F. (2023). An Optimized Third-Harmonic Injection Reduces DC-Link Voltage Ripple in Cascaded H-Bridge Converters up to 50% for all Power Factors. <i>2023 25th European Conference on Power Electronics and Applications (EPE’23 ECCE Europe)</i>. 2023 25th European Conference on Power Electronics and Applications (EPE’23 ECCE Europe), Aalborg, Denmark. <a href=\"https://doi.org/10.23919/epe23ecceeurope58414.2023.10264313\">https://doi.org/10.23919/epe23ecceeurope58414.2023.10264313</a>"},"year":"2023","quality_controlled":"1","publication_identifier":{"isbn":["979-8-3503-1678-0"]},"publication_status":"published"},{"citation":{"apa":"Unruh, R., Schafmeister, F., &#38; Böcker, J. (2022). Zero-Sequence Voltage Reduces DC-Link Capacitor Demand in Cascaded H-Bridge Converters for Large-Scale Electrolyzers by 40%. <i>24th European Conference on Power Electronics and Applications (EPE’22 ECCE Europe)</i>. 24th European Conference on Power Electronics and Applications (EPE’22 ECCE Europe), Hanover, Germany.","short":"R. Unruh, F. Schafmeister, J. Böcker, in: 24th European Conference on Power Electronics and Applications (EPE’22 ECCE Europe), IEEE, 2022.","mla":"Unruh, Roland, et al. “Zero-Sequence Voltage Reduces DC-Link Capacitor Demand in Cascaded H-Bridge Converters for Large-Scale Electrolyzers by 40%.” <i>24th European Conference on Power Electronics and Applications (EPE’22 ECCE Europe)</i>, IEEE, 2022.","bibtex":"@inproceedings{Unruh_Schafmeister_Böcker_2022, title={Zero-Sequence Voltage Reduces DC-Link Capacitor Demand in Cascaded H-Bridge Converters for Large-Scale Electrolyzers by 40%}, booktitle={24th European Conference on Power Electronics and Applications (EPE’22 ECCE Europe)}, publisher={IEEE}, author={Unruh, Roland and Schafmeister, Frank and Böcker, Joachim}, year={2022} }","ama":"Unruh R, Schafmeister F, Böcker J. Zero-Sequence Voltage Reduces DC-Link Capacitor Demand in Cascaded H-Bridge Converters for Large-Scale Electrolyzers by 40%. In: <i>24th European Conference on Power Electronics and Applications (EPE’22 ECCE Europe)</i>. IEEE; 2022.","ieee":"R. Unruh, F. Schafmeister, and J. Böcker, “Zero-Sequence Voltage Reduces DC-Link Capacitor Demand in Cascaded H-Bridge Converters for Large-Scale Electrolyzers by 40%,” presented at the 24th European Conference on Power Electronics and Applications (EPE’22 ECCE Europe), Hanover, Germany, 2022.","chicago":"Unruh, Roland, Frank Schafmeister, and Joachim Böcker. “Zero-Sequence Voltage Reduces DC-Link Capacitor Demand in Cascaded H-Bridge Converters for Large-Scale Electrolyzers by 40%.” In <i>24th European Conference on Power Electronics and Applications (EPE’22 ECCE Europe)</i>. IEEE, 2022."},"year":"2022","publication_identifier":{"isbn":["978-9-0758-1539-9"]},"publication_status":"published","conference":{"start_date":"2022-09-05","name":"24th European Conference on Power Electronics and Applications (EPE'22 ECCE Europe)","location":"Hanover, Germany","end_date":"2022-09-09"},"main_file_link":[{"url":"https://ieeexplore.ieee.org/abstract/document/9907278"}],"title":"Zero-Sequence Voltage Reduces DC-Link Capacitor Demand in Cascaded H-Bridge Converters for Large-Scale Electrolyzers by 40%","date_created":"2022-12-02T12:47:38Z","author":[{"first_name":"Roland","id":"34289","full_name":"Unruh, Roland","last_name":"Unruh"},{"first_name":"Frank","last_name":"Schafmeister","id":"71291","full_name":"Schafmeister, Frank"},{"full_name":"Böcker, Joachim","id":"66","orcid":"0000-0002-8480-7295","last_name":"Böcker","first_name":"Joachim"}],"publisher":"IEEE","date_updated":"2023-10-23T09:04:23Z","status":"public","abstract":[{"lang":"eng","text":"Cascaded H-bridge Converters (CHBs) are a promising solution in converting power from a three-phase medium voltage of 6.6 kV...30 kV to a lower DC-voltage in the range of 100 V...1 kV to provide pure DC power to applications such as electrolyzers for hydrogen generation, data centers with a DC power distribution and DC microgrids. CHBs can be interpreted as modular multilevel converters with an isolated DC-DC output stage per module, require a large DC-link capacitor for each module to handle the second harmonic voltage ripple caused by the fluctuating input power within a fundamental grid period. Without a zero-sequence voltage injection, star-connected CHBs are operated with approximately sinusoidal arm voltages and currents. The floating star point potential enables to utilize different zero-sequence voltage injection techniques such as a third-harmonic injection with 1/6 of the grid voltage amplitude or a Min-Max voltage injection. Both well-known methods have the advantage to reduce the peak arm voltage and thereby the number of required modules by 13.4 % (to √ 3 2). This paper proves analytically that the third-harmonic injection with 1/6 of the grid voltage amplitude reduces the second harmonic voltage ripple by only 15.1 % compared to no-voltage injection for unity power factor operation and balanced grid voltages. Then it is shown, that the Min-Max injection has the often overlooked advantage of reducing the second harmonic voltage ripple by even 18.8 %. By applying the here proposed zero-sequence voltage injection in saturation modulation, the second harmonic voltage ripple of the DC-link capacitors is reduced by even 24.3 %, while still requiring the same number of modules as the Min-Max injection. For a realistic number of reserve modules, the overall energy ripple in the DC-link capacitors is reduced by 40 %."}],"publication":"24th European Conference on Power Electronics and Applications (EPE'22 ECCE Europe)","type":"conference","language":[{"iso":"eng"}],"keyword":["Cascaded H-Bridge","Solid-State Transformer","Zero sequence voltage","Third harmonic injection","Capacitor voltage ripple"],"department":[{"_id":"52"}],"user_id":"34289","_id":"34176"},{"date_updated":"2023-10-20T11:52:39Z","publisher":"VDE","date_created":"2022-02-21T16:42:30Z","author":[{"last_name":"Unruh","full_name":"Unruh, Roland","id":"34289","first_name":"Roland"},{"first_name":"Frank","last_name":"Schafmeister","full_name":"Schafmeister, Frank","id":"71291"},{"full_name":"Fröhleke, Norbert","last_name":"Fröhleke","first_name":"Norbert"},{"first_name":"Joachim","id":"66","full_name":"Böcker, Joachim","orcid":"0000-0002-8480-7295","last_name":"Böcker"}],"title":"1-MW Full-Bridge MMC for High-Current Low-Voltage (100V-400V) DC-Applications","main_file_link":[{"url":"https://ieeexplore.ieee.org/abstract/document/9178138"}],"conference":{"start_date":"2020-07-07","name":"PCIM Europe digital days 2020","location":"Germany","end_date":"2020-07-08"},"publication_status":"published","publication_identifier":{"isbn":["978-3-8007-5245-4"]},"year":"2020","citation":{"chicago":"Unruh, Roland, Frank Schafmeister, Norbert Fröhleke, and Joachim Böcker. “1-MW Full-Bridge MMC for High-Current Low-Voltage (100V-400V) DC-Applications.” In <i>PCIM Europe Digital Days 2020; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management</i>. VDE, 2020.","ieee":"R. Unruh, F. Schafmeister, N. Fröhleke, and J. Böcker, “1-MW Full-Bridge MMC for High-Current Low-Voltage (100V-400V) DC-Applications,” presented at the PCIM Europe digital days 2020, Germany, 2020.","ama":"Unruh R, Schafmeister F, Fröhleke N, Böcker J. 1-MW Full-Bridge MMC for High-Current Low-Voltage (100V-400V) DC-Applications. In: <i>PCIM Europe Digital Days 2020; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management</i>. VDE; 2020.","mla":"Unruh, Roland, et al. “1-MW Full-Bridge MMC for High-Current Low-Voltage (100V-400V) DC-Applications.” <i>PCIM Europe Digital Days 2020; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management</i>, VDE, 2020.","bibtex":"@inproceedings{Unruh_Schafmeister_Fröhleke_Böcker_2020, title={1-MW Full-Bridge MMC for High-Current Low-Voltage (100V-400V) DC-Applications}, booktitle={PCIM Europe digital days 2020; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management}, publisher={VDE}, author={Unruh, Roland and Schafmeister, Frank and Fröhleke, Norbert and Böcker, Joachim}, year={2020} }","short":"R. Unruh, F. Schafmeister, N. Fröhleke, J. Böcker, in: PCIM Europe Digital Days 2020; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, VDE, 2020.","apa":"Unruh, R., Schafmeister, F., Fröhleke, N., &#38; Böcker, J. (2020). 1-MW Full-Bridge MMC for High-Current Low-Voltage (100V-400V) DC-Applications. <i>PCIM Europe Digital Days 2020; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management</i>. PCIM Europe digital days 2020, Germany."},"_id":"29940","user_id":"34289","department":[{"_id":"52"}],"keyword":["Cascaded H-Bridge","Solid-State Transformer","Capacitor voltage ripple","Zero sequence voltage","Full-Bridge"],"language":[{"iso":"eng"}],"type":"conference","publication":"PCIM Europe digital days 2020; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management","abstract":[{"text":"A full-bridge modular multilevel converter (MMC) is compared to a half-bridge-based MMC for high-current low-voltage DC-applications such as electrolysis, arc welding or datacenters with DC-power distribution. Usually, modular multilevel converters are used in high-voltage DC-applications (HVDC) in the multiple kV-range, but to meet the needs of a high-current demand at low output voltage levels, the modular converter concept requires adaptations. In the proposed concept, the MMC is used to step-down the three-phase medium-voltage of 10 kV. Therefore, each module is extended by an LLC resonant converter to adapt to the specific electrolyzers DC-voltage range of 142-220V and to provide galvanic isolation. The proposed MMC converter with full-bridge modules uses half the number of modules compared to a half-bridge-based MMC while reducing the voltage ripple by 78% and capacitor losses by 64% by rearranging the same components to ensure identical costs and volume. For additional reliability, a new robust algorithm for balancing conduction losses during the bypass phase is presented.","lang":"eng"}],"status":"public"}]