---
_id: '59805'
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%).
article_number: '1517'
author:
- first_name: Roland
  full_name: Unruh, Roland
  id: '34289'
  last_name: Unruh
- first_name: Joachim
  full_name: Böcker, Joachim
  id: '66'
  last_name: Böcker
  orcid: 0000-0002-8480-7295
- first_name: Frank
  full_name: Schafmeister, Frank
  id: '71291'
  last_name: Schafmeister
citation:
  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>
  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} }'
  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>.'
  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).
date_created: 2025-05-05T12:27:39Z
date_updated: 2025-05-05T12:34:00Z
department:
- _id: '52'
doi: 10.3390/electronics14081517
intvolume: '        14'
issue: '8'
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
main_file_link:
- url: https://www.mdpi.com/2079-9292/14/8/1517
publication: Electronics
publication_identifier:
  issn:
  - 2079-9292
publication_status: published
publisher: MDPI AG
status: public
title: Adaptive DC-Link Voltage Control for 22 kW, 40 kHz LLC Resonant Converter Considering
  Low-Frequency Voltage Ripple
type: journal_article
user_id: '34289'
volume: 14
year: '2025'
...
---
_id: '63157'
abstract:
- lang: eng
  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.
author:
- first_name: Roland
  full_name: Unruh, Roland
  id: '34289'
  last_name: Unruh
- first_name: Joachim
  full_name: Böcker, Joachim
  id: '66'
  last_name: Böcker
  orcid: 0000-0002-8480-7295
- first_name: Frank
  full_name: Schafmeister, Frank
  id: '71291'
  last_name: Schafmeister
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>'
  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>
  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} }'
  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>.'
  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>.
  short: 'R. Unruh, J. Böcker, F. Schafmeister, in: 2025 Energy Conversion Congress
    &#38;amp;Amp; Expo Europe (ECCE Europe), IEEE, 2025.'
conference:
  end_date: 2025-09-04
  location: Birmingham, United Kingdom
  name: 2025 Energy Conversion Congress & Expo Europe (ECCE Europe)
  start_date: 2025-09-01
date_created: 2025-12-16T15:20:55Z
date_updated: 2025-12-16T15:25:38Z
department:
- _id: '52'
doi: 10.1109/ecce-europe62795.2025.11238538
keyword:
- Cascaded H-Bridge
- Current Control
- dq Transformation
- Linear Regression
- Unbalanced Inductors
language:
- iso: eng
main_file_link:
- url: https://ieeexplore.ieee.org/document/11238538
publication: 2025 Energy Conversion Congress &amp;amp; Expo Europe (ECCE Europe)
publication_status: published
publisher: IEEE
status: public
title: Three-Phase Instantaneous Current Controller for Unbalanced Grid Inductors
  Without DQ Transform for Cascaded H-Bridge Converters
type: conference
user_id: '34289'
year: '2025'
...
---
_id: '54356'
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
  full_name: Unruh, Roland
  id: '34289'
  last_name: Unruh
- first_name: Joachim
  full_name: Böcker, Joachim
  id: '66'
  last_name: Böcker
  orcid: 0000-0002-8480-7295
- first_name: Frank
  full_name: Schafmeister, Frank
  id: '71291'
  last_name: Schafmeister
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>'
  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>
  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} }'
  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>.'
  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>.'
  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>.
  short: 'R. Unruh, J. Böcker, F. Schafmeister, in: ECCE Europe 2024; IEEE Energy
    Conversion Congress &#38; Exposition Europe, IEEE, Darmstadt, n.d.'
conference:
  end_date: 2024-09-06
  location: Darmstadt, Germany
  name: ECCE Europe 2024
  start_date: 2024-09-02
date_created: 2024-05-19T14:26:29Z
date_updated: 2024-11-28T14:16:05Z
department:
- _id: '52'
doi: https://doi.org/10.1109/ECCEEurope62508.2024.10751954
keyword:
- Cascaded H-Bridge
- Converter Losses
- Decentralized Control
- Full-Bridge Converter
- LLC Resonant Converter
language:
- iso: eng
main_file_link:
- url: https://ieeexplore.ieee.org/abstract/document/10751954
place: Darmstadt
publication: ECCE Europe 2024; IEEE Energy Conversion Congress & Exposition Europe
publication_identifier:
  isbn:
  - 979-8-3503-6444-6
publication_status: accepted
publisher: IEEE
status: public
title: Experimentally Verified 22 kW, 40 kHz LLC Resonant Converter Design with new
  Control for a 1 MW Cascaded H-Bridge Converter
type: conference
user_id: '34289'
year: '2024'
...
---
_id: '63497'
author:
- first_name: Nikolas
  full_name: Förster, Nikolas
  last_name: Förster
- first_name: Oliver
  full_name: Wallscheid, Oliver
  last_name: Wallscheid
- first_name: Frank
  full_name: Schafmeister, Frank
  last_name: Schafmeister
citation:
  ama: 'Förster N, Wallscheid O, Schafmeister F. Dual-Active Bridge Sequential Pareto
    Optimization for Fast Pre-Design and Final Component Selection. In: <i>2024 IEEE
    Design Methodologies Conference (DMC)</i>. ; 2024:1-8. doi:<a href="https://doi.org/10.1109/DMC62632.2024.10812131">10.1109/DMC62632.2024.10812131</a>'
  apa: Förster, N., Wallscheid, O., &#38; Schafmeister, F. (2024). Dual-Active Bridge
    Sequential Pareto Optimization for Fast Pre-Design and Final Component Selection.
    <i>2024 IEEE Design Methodologies Conference (DMC)</i>, 1–8. <a href="https://doi.org/10.1109/DMC62632.2024.10812131">https://doi.org/10.1109/DMC62632.2024.10812131</a>
  bibtex: '@inproceedings{Förster_Wallscheid_Schafmeister_2024, title={Dual-Active
    Bridge Sequential Pareto Optimization for Fast Pre-Design and Final Component
    Selection}, DOI={<a href="https://doi.org/10.1109/DMC62632.2024.10812131">10.1109/DMC62632.2024.10812131</a>},
    booktitle={2024 IEEE Design Methodologies Conference (DMC)}, author={Förster,
    Nikolas and Wallscheid, Oliver and Schafmeister, Frank}, year={2024}, pages={1–8}
    }'
  chicago: Förster, Nikolas, Oliver Wallscheid, and Frank Schafmeister. “Dual-Active
    Bridge Sequential Pareto Optimization for Fast Pre-Design and Final Component
    Selection.” In <i>2024 IEEE Design Methodologies Conference (DMC)</i>, 1–8, 2024.
    <a href="https://doi.org/10.1109/DMC62632.2024.10812131">https://doi.org/10.1109/DMC62632.2024.10812131</a>.
  ieee: 'N. Förster, O. Wallscheid, and F. Schafmeister, “Dual-Active Bridge Sequential
    Pareto Optimization for Fast Pre-Design and Final Component Selection,” in <i>2024
    IEEE Design Methodologies Conference (DMC)</i>, 2024, pp. 1–8, doi: <a href="https://doi.org/10.1109/DMC62632.2024.10812131">10.1109/DMC62632.2024.10812131</a>.'
  mla: Förster, Nikolas, et al. “Dual-Active Bridge Sequential Pareto Optimization
    for Fast Pre-Design and Final Component Selection.” <i>2024 IEEE Design Methodologies
    Conference (DMC)</i>, 2024, pp. 1–8, doi:<a href="https://doi.org/10.1109/DMC62632.2024.10812131">10.1109/DMC62632.2024.10812131</a>.
  short: 'N. Förster, O. Wallscheid, F. Schafmeister, in: 2024 IEEE Design Methodologies
    Conference (DMC), 2024, pp. 1–8.'
date_created: 2026-01-06T08:06:24Z
date_updated: 2026-01-06T08:07:50Z
department:
- _id: '52'
doi: 10.1109/DMC62632.2024.10812131
keyword:
- MOSFET
- Thermal resistance
- Surface resistance
- Bridge circuits
- Zero voltage switching
- Pareto optimization
- Capacitance
- Numerical simulation
- Optimization
- Resistance heating
- Pareto Optimization
- Dual-Active Bridge
- ZVS
- Inductor Optimization
- Transformer Optimization
- Heat Sink Optimization
language:
- iso: eng
page: 1-8
publication: 2024 IEEE Design Methodologies Conference (DMC)
status: public
title: Dual-Active Bridge Sequential Pareto Optimization for Fast Pre-Design and Final
  Component Selection
type: conference
user_id: '83383'
year: '2024'
...
---
_id: '48352'
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.
author:
- first_name: Roland
  full_name: Unruh, Roland
  id: '34289'
  last_name: Unruh
- first_name: Joachim
  full_name: Böcker, Joachim
  id: '66'
  last_name: Böcker
  orcid: 0000-0002-8480-7295
- first_name: Frank
  full_name: Schafmeister, Frank
  id: '71291'
  last_name: Schafmeister
citation:
  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>'
  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>
  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} }'
  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>.
  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>.'
  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>.
  short: 'R. Unruh, J. Böcker, F. Schafmeister, in: 2023 25th European Conference
    on Power Electronics and Applications (EPE’23 ECCE Europe), IEEE, 2023.'
conference:
  end_date: 2023-09-08
  location: Aalborg, Denmark
  name: 2023 25th European Conference on Power Electronics and Applications (EPE'23
    ECCE Europe)
  start_date: 2023-09-04
date_created: 2023-10-20T07:13:32Z
date_updated: 2023-10-20T10:01:02Z
department:
- _id: '52'
doi: 10.23919/epe23ecceeurope58414.2023.10264313
keyword:
- Cascaded H-Bridge
- Solid-State Transformer
- Capacitor voltage ripple
- Zero sequence voltage
- Third harmonic injection
language:
- iso: eng
main_file_link:
- url: https://ieeexplore.ieee.org/abstract/document/10264313
publication: 2023 25th European Conference on Power Electronics and Applications (EPE'23
  ECCE Europe)
publication_identifier:
  isbn:
  - 979-8-3503-1678-0
publication_status: published
publisher: IEEE
quality_controlled: '1'
status: public
title: An Optimized Third-Harmonic Injection Reduces DC-Link Voltage Ripple in Cascaded
  H-Bridge Converters up to 50% for all Power Factors
type: conference
user_id: '34289'
year: '2023'
...
---
_id: '34176'
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
    %.
author:
- first_name: Roland
  full_name: Unruh, Roland
  id: '34289'
  last_name: Unruh
- first_name: Frank
  full_name: Schafmeister, Frank
  id: '71291'
  last_name: Schafmeister
- first_name: Joachim
  full_name: Böcker, Joachim
  id: '66'
  last_name: Böcker
  orcid: 0000-0002-8480-7295
citation:
  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.'
  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.
  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} }'
  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.
  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.
  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.
  short: 'R. Unruh, F. Schafmeister, J. Böcker, in: 24th European Conference on Power
    Electronics and Applications (EPE’22 ECCE Europe), IEEE, 2022.'
conference:
  end_date: 2022-09-09
  location: Hanover, Germany
  name: 24th European Conference on Power Electronics and Applications (EPE'22 ECCE
    Europe)
  start_date: 2022-09-05
date_created: 2022-12-02T12:47:38Z
date_updated: 2023-10-23T09:04:23Z
department:
- _id: '52'
keyword:
- Cascaded H-Bridge
- Solid-State Transformer
- Zero sequence voltage
- Third harmonic injection
- Capacitor voltage ripple
language:
- iso: eng
main_file_link:
- url: https://ieeexplore.ieee.org/abstract/document/9907278
publication: 24th European Conference on Power Electronics and Applications (EPE'22
  ECCE Europe)
publication_identifier:
  isbn:
  - 978-9-0758-1539-9
publication_status: published
publisher: IEEE
status: public
title: Zero-Sequence Voltage Reduces DC-Link Capacitor Demand in Cascaded H-Bridge
  Converters for Large-Scale Electrolyzers by 40%
type: conference
user_id: '34289'
year: '2022'
...
---
_id: '29893'
abstract:
- lang: eng
  text: Phase-shift modulated full bridge converters suffer from thermal imbalances
    of the inverter switches. The lagging leg switches are subject to larger commutation
    currents compared to those of the leading leg as the transformer current reduces
    in the freewheeling interval. Furthermore, after this interval, the energy in
    the series inductance may not be large enough to achieve zero-voltage switching
    (ZVS) for the leading leg. Both effects result in thermal imbalances. This paper
    analyzes the alternating-asymmetrical phase-shift modulation to achieve balanced
    conduction and switching losses for all four switches while showing that this
    modulation is easily implemented on standard DSPs. The modulation has been implemented
    to LLC converters where experimental measurement results proved its effectiveness
    for LLC converters by reducing the temperature deviation from 6.3 K to only 0.2
    K such that the peak temperature is reduced from 95 °C to 92 °C. The paper also
    proves that the modulation can be utilized to improve the efficiency of LLC converters
    operated at very low gains while simultaneously reducing the junction temperature
    of all four switches compared to the conventional complementary modulation. Finally,
    EMI implications are analyzed, which show that the modulation may be beneficial
    for reducing the common-mode emissions around the operating frequency.
author:
- first_name: Philipp
  full_name: Rehlaender, Philipp
  id: '69469'
  last_name: Rehlaender
- first_name: Roland
  full_name: Unruh, Roland
  id: '34289'
  last_name: Unruh
- first_name: Frank
  full_name: Schafmeister, Frank
  id: '71291'
  last_name: Schafmeister
- first_name: Joachim
  full_name: Böcker, Joachim
  id: '66'
  last_name: Böcker
  orcid: 0000-0002-8480-7295
citation:
  ama: 'Rehlaender P, Unruh R, Schafmeister F, Böcker J. Alternating Asymmetrical
    Phase-Shift Modulation for Full-Bridge Converters with Balanced Switching Losses
    to Reduce Thermal Imbalances. In: <i>2021 IEEE Applied Power Electronics Conference
    and Exposition (APEC)</i>. IEEE; 2021. doi:<a href="https://doi.org/10.1109/apec42165.2021.9487104">10.1109/apec42165.2021.9487104</a>'
  apa: Rehlaender, P., Unruh, R., Schafmeister, F., &#38; Böcker, J. (2021). Alternating
    Asymmetrical Phase-Shift Modulation for Full-Bridge Converters with Balanced Switching
    Losses to Reduce Thermal Imbalances. <i>2021 IEEE Applied Power Electronics Conference
    and Exposition (APEC)</i>. 2021 IEEE Applied Power Electronics Conference and
    Exposition (APEC), Phoenix, AZ, USA. <a href="https://doi.org/10.1109/apec42165.2021.9487104">https://doi.org/10.1109/apec42165.2021.9487104</a>
  bibtex: '@inproceedings{Rehlaender_Unruh_Schafmeister_Böcker_2021, title={Alternating
    Asymmetrical Phase-Shift Modulation for Full-Bridge Converters with Balanced Switching
    Losses to Reduce Thermal Imbalances}, DOI={<a href="https://doi.org/10.1109/apec42165.2021.9487104">10.1109/apec42165.2021.9487104</a>},
    booktitle={2021 IEEE Applied Power Electronics Conference and Exposition (APEC)},
    publisher={IEEE}, author={Rehlaender, Philipp and Unruh, Roland and Schafmeister,
    Frank and Böcker, Joachim}, year={2021} }'
  chicago: Rehlaender, Philipp, Roland Unruh, Frank Schafmeister, and Joachim Böcker.
    “Alternating Asymmetrical Phase-Shift Modulation for Full-Bridge Converters with
    Balanced Switching Losses to Reduce Thermal Imbalances.” In <i>2021 IEEE Applied
    Power Electronics Conference and Exposition (APEC)</i>. IEEE, 2021. <a href="https://doi.org/10.1109/apec42165.2021.9487104">https://doi.org/10.1109/apec42165.2021.9487104</a>.
  ieee: 'P. Rehlaender, R. Unruh, F. Schafmeister, and J. Böcker, “Alternating Asymmetrical
    Phase-Shift Modulation for Full-Bridge Converters with Balanced Switching Losses
    to Reduce Thermal Imbalances,” presented at the 2021 IEEE Applied Power Electronics
    Conference and Exposition (APEC), Phoenix, AZ, USA, 2021, doi: <a href="https://doi.org/10.1109/apec42165.2021.9487104">10.1109/apec42165.2021.9487104</a>.'
  mla: Rehlaender, Philipp, et al. “Alternating Asymmetrical Phase-Shift Modulation
    for Full-Bridge Converters with Balanced Switching Losses to Reduce Thermal Imbalances.”
    <i>2021 IEEE Applied Power Electronics Conference and Exposition (APEC)</i>, IEEE,
    2021, doi:<a href="https://doi.org/10.1109/apec42165.2021.9487104">10.1109/apec42165.2021.9487104</a>.
  short: 'P. Rehlaender, R. Unruh, F. Schafmeister, J. Böcker, in: 2021 IEEE Applied
    Power Electronics Conference and Exposition (APEC), IEEE, 2021.'
conference:
  end_date: 2021-06-17
  location: Phoenix, AZ, USA
  name: 2021 IEEE Applied Power Electronics Conference and Exposition (APEC)
  start_date: 2021-06-14
date_created: 2022-02-20T21:19:46Z
date_updated: 2023-10-20T11:50:25Z
department:
- _id: '34'
- _id: '52'
doi: 10.1109/apec42165.2021.9487104
keyword:
- Phase-Shifted Full Bridge
- Full-Bridge Converter
- Phase-Shift Control
- Phase-Shift Modulation
- LLC Converter
- Thermal Balancing
language:
- iso: eng
main_file_link:
- url: https://ieeexplore.ieee.org/abstract/document/9487104
publication: 2021 IEEE Applied Power Electronics Conference and Exposition (APEC)
publication_identifier:
  isbn:
  - 978-1-7281-8950-5
publication_status: published
publisher: IEEE
status: public
title: Alternating Asymmetrical Phase-Shift Modulation for Full-Bridge Converters
  with Balanced Switching Losses to Reduce Thermal Imbalances
type: conference
user_id: '34289'
year: '2021'
...
---
_id: '29940'
abstract:
- lang: eng
  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.
author:
- first_name: Roland
  full_name: Unruh, Roland
  id: '34289'
  last_name: Unruh
- first_name: Frank
  full_name: Schafmeister, Frank
  id: '71291'
  last_name: Schafmeister
- first_name: Norbert
  full_name: Fröhleke, Norbert
  last_name: Fröhleke
- first_name: Joachim
  full_name: Böcker, Joachim
  id: '66'
  last_name: Böcker
  orcid: 0000-0002-8480-7295
citation:
  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.'
  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.
  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} }'
  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.
  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.
  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.'
conference:
  end_date: 2020-07-08
  location: Germany
  name: PCIM Europe digital days 2020
  start_date: 2020-07-07
date_created: 2022-02-21T16:42:30Z
date_updated: 2023-10-20T11:52:39Z
department:
- _id: '52'
keyword:
- Cascaded H-Bridge
- Solid-State Transformer
- Capacitor voltage ripple
- Zero sequence voltage
- Full-Bridge
language:
- iso: eng
main_file_link:
- url: https://ieeexplore.ieee.org/abstract/document/9178138
publication: PCIM Europe digital days 2020; International Exhibition and Conference
  for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management
publication_identifier:
  isbn:
  - 978-3-8007-5245-4
publication_status: published
publisher: VDE
status: public
title: 1-MW Full-Bridge MMC for High-Current Low-Voltage (100V-400V) DC-Applications
type: conference
user_id: '34289'
year: '2020'
...
---
_id: '29880'
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.
author:
- first_name: Roland
  full_name: Unruh, Roland
  id: '34289'
  last_name: Unruh
- first_name: Frank
  full_name: Schafmeister, Frank
  id: '71291'
  last_name: Schafmeister
- first_name: Joachim
  full_name: Böcker, Joachim
  id: '66'
  last_name: Böcker
  orcid: 0000-0002-8480-7295
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>'
  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>
  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} }'
  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>.
  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>.'
  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.'
conference:
  end_date: 2020-11-12
  start_date: 2020-11-09
date_created: 2022-02-18T16:29:08Z
date_updated: 2024-11-28T14:19:07Z
department:
- _id: '52'
doi: 10.1109/compel49091.2020.9265771
keyword:
- Full-bridge
- High voltage power converters
- LLC resonant converter
- Multilevel converters
- ZVS Converters
language:
- iso: eng
main_file_link:
- url: https://ieeexplore.ieee.org/abstract/document/9265771
publication: 2020 IEEE 21st Workshop on Control and Modeling for Power Electronics
  (COMPEL)
publication_identifier:
  unknown:
  - 978-1-7281-7160-9
publication_status: published
publisher: IEEE
quality_controlled: '1'
status: public
title: 11kW, 70kHz LLC Converter Design with Adaptive Input Voltage for 98% Efficiency
  in an MMC
type: conference
user_id: '34289'
year: '2020'
...