@article{59805, abstract = {{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%).}}, author = {{Unruh, Roland and Böcker, Joachim and Schafmeister, Frank}}, issn = {{2079-9292}}, journal = {{Electronics}}, keywords = {{adaptive DC-link voltage, cascaded H-bridge, resonant operation, Full-Bridge Converter, loss minimization, LLC Resonant Converter, peak capacitor voltage reduction}}, number = {{8}}, publisher = {{MDPI AG}}, title = {{{Adaptive DC-Link Voltage Control for 22 kW, 40 kHz LLC Resonant Converter Considering Low-Frequency Voltage Ripple}}}, doi = {{10.3390/electronics14081517}}, volume = {{14}}, year = {{2025}}, } @inproceedings{63157, abstract = {{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.}}, author = {{Unruh, Roland and Böcker, Joachim and Schafmeister, Frank}}, booktitle = {{2025 Energy Conversion Congress & Expo Europe (ECCE Europe)}}, keywords = {{Cascaded H-Bridge, Current Control, dq Transformation, Linear Regression, Unbalanced Inductors}}, location = {{Birmingham, United Kingdom}}, publisher = {{IEEE}}, title = {{{Three-Phase Instantaneous Current Controller for Unbalanced Grid Inductors Without DQ Transform for Cascaded H-Bridge Converters}}}, doi = {{10.1109/ecce-europe62795.2025.11238538}}, year = {{2025}}, } @inproceedings{54353, author = {{Piepenbrock, Till and Keuck, Lukas and Schachten, Sebastian and Böcker, Joachim and Schafmeister, Frank}}, booktitle = {{PCIM Europe 2024; IEEE International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management}}, location = {{Nuremberg}}, title = {{{Study on Sample Geometries for Ferrite Characterisation in the MHz-Range}}}, year = {{2024}}, } @article{53309, author = {{Hölsch, Lukas and Brosch, Anian and Steckel, Richard and Braun, Tristan and Wendel, Sebastian and Böcker, Joachim and Wallscheid, Oliver}}, issn = {{0885-8969}}, journal = {{IEEE Transactions on Energy Conversion}}, keywords = {{Electrical and Electronic Engineering, Energy Engineering and Power Technology}}, pages = {{1--12}}, publisher = {{Institute of Electrical and Electronics Engineers (IEEE)}}, title = {{{Insights and Challenges of Co-Simulation-Based Optimal Pulse Pattern Evaluation for Electric Drives}}}, doi = {{10.1109/tec.2024.3374962}}, year = {{2024}}, } @inproceedings{54357, author = {{Piepenbrock, Till and Schafmeister, Frank and Böcker, Joachim}}, booktitle = {{SPEEDAM 2024; 27th International Symposium on Power Electronics, Electrical Drives, Automation and Motion}}, location = {{Ischia, near Naples, Italy}}, title = {{{FEM Modelling of Dimensional-Resonant Inductors for LLC Converters in MHz Range}}}, doi = {{10.1109/SPEEDAM61530.2024.10609111}}, year = {{2024}}, } @inproceedings{54356, abstract = {{Although there are numerous design and control methodologies for the LLC resonant converter, they often do not consider decentralized control strategies to operate them as isolated DC-DC converters within a cascaded H-bridge. The total output power of all LLC converters must be constant to supply a load such as a wa- ter electrolyzer. However, each individual LLC converter can vary its output power as long as the total output power remains constant. This opens new possibilities in increasing the system efficiency and robustness. Usually, the DC-link voltage of each module capacitor shows a 2nd harmonic voltage ripple. However, the total stored energy in all DC-link capacitors is constant within a grid period for a balanced three-phase system. By controlling each LLC converter’s output power locally to be proportional to the energy stored in its DC-link capacitor, modules with a lower instantaneous DC-link voltage transfer less power to the load than modules with a higher DC-link voltage. As a result, a higher efficiency, voltage gain and lower peak resonant capacitor voltage can be achieved with the same components. The 22.2kW experimental prototype of the LLC converter reaches an efficiency of over 97% at resonance which is similar to the precalculated value.}}, author = {{Unruh, Roland and Böcker, Joachim and Schafmeister, Frank}}, booktitle = {{ECCE Europe 2024; IEEE Energy Conversion Congress & Exposition Europe}}, isbn = {{979-8-3503-6444-6}}, keywords = {{Cascaded H-Bridge, Converter Losses, Decentralized Control, Full-Bridge Converter, LLC Resonant Converter}}, location = {{Darmstadt, Germany}}, publisher = {{IEEE}}, title = {{{Experimentally Verified 22 kW, 40 kHz LLC Resonant Converter Design with new Control for a 1 MW Cascaded H-Bridge Converter}}}, doi = {{https://doi.org/10.1109/ECCEEurope62508.2024.10751954}}, year = {{2024}}, } @article{48059, author = {{Winkel, Fabian and Wallscheid, Oliver and Scholz, Peter and Böcker, Joachim}}, issn = {{2644-1284}}, journal = {{IEEE Open Journal of the Industrial Electronics Society}}, keywords = {{Electrical and Electronic Engineering, Industrial and Manufacturing Engineering, Control and Systems Engineering}}, pages = {{1--14}}, publisher = {{Institute of Electrical and Electronics Engineers (IEEE)}}, title = {{{Pseudo-Labeling Machine Learning Algorithm for Predictive Maintenance of Relays}}}, doi = {{10.1109/ojies.2023.3323870}}, year = {{2023}}, } @article{48058, author = {{Winkel, Fabian and Deuse-Kleinsteuber, Johannes and Böcker, Joachim}}, issn = {{0018-9529}}, journal = {{IEEE Transactions on Reliability}}, keywords = {{Electrical and Electronic Engineering, Safety, Risk, Reliability and Quality}}, pages = {{1--14}}, publisher = {{Institute of Electrical and Electronics Engineers (IEEE)}}, title = {{{Run-to-Failure Relay Dataset for Predictive Maintenance Research With Machine Learning}}}, doi = {{10.1109/tr.2023.3255786}}, year = {{2023}}, } @inproceedings{48352, abstract = {{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.}}, author = {{Unruh, Roland and Böcker, Joachim and Schafmeister, Frank}}, booktitle = {{2023 25th European Conference on Power Electronics and Applications (EPE'23 ECCE Europe)}}, isbn = {{979-8-3503-1678-0}}, keywords = {{Cascaded H-Bridge, Solid-State Transformer, Capacitor voltage ripple, Zero sequence voltage, Third harmonic injection}}, location = {{Aalborg, Denmark}}, publisher = {{IEEE}}, title = {{{An Optimized Third-Harmonic Injection Reduces DC-Link Voltage Ripple in Cascaded H-Bridge Converters up to 50% for all Power Factors}}}, doi = {{10.23919/epe23ecceeurope58414.2023.10264313}}, year = {{2023}}, } @inproceedings{48093, author = {{Pena, Mario and Meyer, Michael and Wallscheid, Oliver and Böcker, Joachim}}, booktitle = {{2023 IEEE International Electric Machines and Drives Conference (IEMDC)}}, location = {{San Francisco}}, publisher = {{IEEE}}, title = {{{Fade-Over Strategy for use of Model Predictive Direct Self-Control with Field-Oriented Control}}}, doi = {{10.1109/iemdc55163.2023.10239056}}, year = {{2023}}, } @article{48092, author = {{Pena, Mario and Meyer, Michael and Wallscheid, Oliver and Böcker, Joachim}}, issn = {{0885-8993}}, journal = {{IEEE Transactions on Power Electronics}}, keywords = {{Electrical and Electronic Engineering}}, number = {{10}}, pages = {{12416--12429}}, publisher = {{Institute of Electrical and Electronics Engineers (IEEE)}}, title = {{{Model Predictive Direct Self-Control for Six-Step Operation of Permanent-Magnet Synchronous Machines}}}, doi = {{10.1109/tpel.2023.3286713}}, volume = {{38}}, year = {{2023}}, } @inproceedings{53310, author = {{Gedlu, Emebet Gebeyehu and Wallscheid, Oliver and Böcker, Joachim and Nelles, Oliver}}, booktitle = {{2023 IEEE 14th International Symposium on Diagnostics for Electrical Machines, Power Electronics and Drives (SDEMPED)}}, publisher = {{IEEE}}, title = {{{Online system identification and excitation for thermal monitoring of electric machines using machine learning and model predictive control}}}, doi = {{10.1109/sdemped54949.2023.10271427}}, year = {{2023}}, } @article{53543, author = {{Winkel, Fabian and Scholz, Peter and Wallscheid, Oliver and Böcker, Joachim}}, issn = {{1545-5955}}, journal = {{IEEE Transactions on Automation Science and Engineering}}, keywords = {{Electrical and Electronic Engineering, Control and Systems Engineering}}, pages = {{1--11}}, publisher = {{Institute of Electrical and Electronics Engineers (IEEE)}}, title = {{{Reducing Contact Bouncing of a Relay by Optimizing the Switch Signal During Run-Time}}}, doi = {{10.1109/tase.2023.3322762}}, year = {{2023}}, } @inproceedings{54352, author = {{Urbaneck, Daniel and Böcker, Joachim and Schafmeister, Frank}}, booktitle = {{PCIM Europe 2023; IEEE International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management }}, isbn = {{978-3-8007-6091-6}}, location = {{Nuremberg}}, title = {{{Advanced Synchronous Rectification for an IGBT-Based ZCS LLC Converter with High Output Currents for a 2 kW Automotive DC-DC Stage}}}, year = {{2023}}, } @book{41369, author = {{Böcker, Joachim}}, publisher = {{Paderborn University}}, title = {{{Mechatronik und elektrische Antriebe / Mechatronics and electrical drives}}}, doi = {{10.17619/UNIPB/1-1640}}, year = {{2023}}, } @article{43456, author = {{Brosch, Anian and Wallscheid, Oliver and Böcker, Joachim}}, issn = {{0885-8993}}, journal = {{IEEE Transactions on Power Electronics}}, keywords = {{Electrical and Electronic Engineering}}, pages = {{1--14}}, publisher = {{Institute of Electrical and Electronics Engineers (IEEE)}}, title = {{{Time-Optimal Model Predictive Control of Permanent Magnet Synchronous Motors Considering Current and Torque Constraints}}}, doi = {{10.1109/tpel.2023.3265705}}, year = {{2023}}, } @article{46147, author = {{Brosch, Anian and Tinazzi, Fabio and Wallscheid, Oliver and Zigliotto, Mauro and Böcker, Joachim}}, issn = {{0885-8993}}, journal = {{IEEE Transactions on Power Electronics}}, keywords = {{Electrical and Electronic Engineering}}, publisher = {{Institute of Electrical and Electronics Engineers (IEEE)}}, title = {{{Finite Set Sensorless Control With Minimum a Priori Knowledge and Tuning Effort for Interior Permanent Magnet Synchronous Motors}}}, doi = {{10.1109/tpel.2023.3294557}}, year = {{2023}}, } @inproceedings{30349, author = {{Förster, Nikolas and Rehlaender, Philipp and Wallscheid, Oliver and Schafmeister, Frank and Böcker, Joachim}}, booktitle = {{Proc. 37th IEEE Applied Power Electronics Conference (APEC)}}, location = {{Houston, TX, USA}}, publisher = {{IEEE}}, title = {{{An Open-Source Transistor Database and Toolbox as an Unified Software Engineering Tool for Managing and Evaluating Power Transistors}}}, year = {{2022}}, } @inproceedings{30350, author = {{Keuck, Lukas and Schafmeister, Frank and Böcker, Joachim}}, booktitle = {{Proc. IEEE International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management (PCIM)}}, location = {{Nuremberg, Germany}}, publisher = {{IEEE}}, title = {{{Robust Hysteresis Control for LLC Resonant Converters Using a Fully Isolated Measurement Scheme}}}, year = {{2022}}, } @article{34533, author = {{Brosch, Anian and Wallscheid, Oliver and Böcker, Joachim}}, journal = {{IEEE Transactions on Power Electronics}}, keywords = {{Electrical and Electronic Engineering}}, publisher = {{Institute of Electrical and Electronics Engineers (IEEE)}}, title = {{{Model Predictive Torque Control for Permanent Magnet Synchronous Motors Using a Stator-Fixed Harmonic Flux Reference Generator in the Entire Modulation Range}}}, doi = {{10.1109/tpel.2022.3229619}}, year = {{2022}}, }