---
_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: '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: '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'
...