---
_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: '58648'
author:
- first_name: Roland
  full_name: Unruh, Roland
  id: '34289'
  last_name: Unruh
- first_name: 'Joachim '
  full_name: 'Böcker, Joachim '
  last_name: Böcker
- 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>Proceedings of the Energy Conversion Congress &#38; Expo (ECCE Europe)</i>.
    IEEE; 2024. doi:<a href="https://doi.org/10.1109/ECCEEurope62508.2024.10751954">10.1109/ECCEEurope62508.2024.10751954</a>'
  apa: Unruh, R., Böcker, J., &#38; Schafmeister, F. (2024). Experimentally Verified
    22 kW, 40 kHz LLC Resonant Converter Design with new Control for a 1 MW Cascaded
    H-Bridge Converter. <i>Proceedings of the Energy Conversion Congress &#38; Expo
    (ECCE Europe)</i>.  Energy Conversion Congress &#38; Expo (ECCE Europe), Darmstadt.
    <a href="https://doi.org/10.1109/ECCEEurope62508.2024.10751954">https://doi.org/10.1109/ECCEEurope62508.2024.10751954</a>
  bibtex: '@inproceedings{Unruh_Böcker_Schafmeister_2024, 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">10.1109/ECCEEurope62508.2024.10751954</a>},
    booktitle={Proceedings of the Energy Conversion Congress &#38; Expo (ECCE Europe)},
    publisher={IEEE}, author={Unruh, Roland and Böcker, Joachim  and Schafmeister,
    Frank}, year={2024} }'
  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>Proceedings of the Energy Conversion Congress
    &#38; Expo (ECCE Europe)</i>. IEEE, 2024. <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  Energy Conversion Congress &#38; Expo (ECCE Europe),
    Darmstadt, 2024, doi: <a href="https://doi.org/10.1109/ECCEEurope62508.2024.10751954">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>Proceedings
    of the Energy Conversion Congress &#38; Expo (ECCE Europe)</i>, IEEE, 2024, doi:<a
    href="https://doi.org/10.1109/ECCEEurope62508.2024.10751954">10.1109/ECCEEurope62508.2024.10751954</a>.
  short: 'R. Unruh, J. Böcker, F. Schafmeister, in: Proceedings of the Energy Conversion
    Congress &#38; Expo (ECCE Europe), IEEE, 2024.'
conference:
  end_date: 2024-09-06
  location: Darmstadt
  name: ' Energy Conversion Congress & Expo (ECCE Europe)'
  start_date: 2024-09-02
date_created: 2025-02-14T15:30:36Z
date_updated: 2025-02-14T15:33:10Z
ddc:
- '620'
department:
- _id: '52'
doi: 10.1109/ECCEEurope62508.2024.10751954
file:
- access_level: closed
  content_type: application/pdf
  creator: schafmei
  date_created: 2025-02-14T15:32:17Z
  date_updated: 2025-02-14T15:32:17Z
  file_id: '58649'
  file_name: EPE_2024_09_02-Experimentally Verified 22 kW, 40 kHz LLC Resonant Converter
    Design with new Control for a 1 MW Cascaded H-Bridge Converter.pdf
  file_size: 3829411
  relation: main_file
  success: 1
file_date_updated: 2025-02-14T15:32:17Z
has_accepted_license: '1'
language:
- iso: eng
publication: Proceedings of the Energy Conversion Congress & Expo (ECCE Europe)
publication_status: published
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: '71291'
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: '29938'
abstract:
- lang: eng
  text: Modular solid-state transformers (SSTs) are a promising technology in converting
    power from a 10kV three-phase medium voltage to a lower DC-voltage in the range
    of 100…400V to provide pure DC power to applications such as electrolyzers for
    hydrogen generation, data centers with a DC power distribution and DC micro grids.
    Modular SSTs which can be interpreted as modular multilevel converters with an
    isolated DC-DC output stage per module, are designed with redundant modules to
    increase reliability. Usually, each of the three arms operates independently,
    and therefore, only a fixed number of faulty modules can be compensated in each
    arm, even if all modules are operational in the remaining two arms. With the proposed
    zero-sequence voltage injection, up to 100% more faulty modules can be compensated
    in an arm by employing the same hardware. In addition, module power imbalances
    are nearly eliminated by utilizing a fundamental frequency zero-sequence voltage.
    A dominant 3rd harmonic zero-sequence voltage injection in combination with the
    5th, 7th and several higher order harmonics with adaptive (small) amplitudes minimize
    the required arm voltages at steady-state. For nominal operation or symmetrical
    faults, the proposed technique is equivalent to the well known Min-Max voltage
    injection, which already reduces the peak arm voltage by 13.4% compared to a constant
    star point potential. A statistical analysis proves, that the expected number
    of tolerable faulty modules of the 1MW SST increases by 12% without the need for
    additional hardware.
author:
- first_name: Roland
  full_name: Unruh, Roland
  id: '34289'
  last_name: Unruh
- first_name: Jarren
  full_name: Lange, Jarren
  id: '78801'
  last_name: Lange
- 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, Lange J, Schafmeister F, Böcker J. Adaptive Zero-Sequence Voltage
    Injection for Modular Solid-State Transformer to Compensate for Asymmetrical Fault
    Conditions. In: <i>23rd European Conference on Power Electronics and Applications
    (EPE’21 ECCE Europe)</i>. IEEE; 2021. doi:<a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542">https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542</a>'
  apa: Unruh, R., Lange, J., Schafmeister, F., &#38; Böcker, J. (2021). Adaptive Zero-Sequence
    Voltage Injection for Modular Solid-State Transformer to Compensate for Asymmetrical
    Fault Conditions. <i>23rd European Conference on Power Electronics and Applications
    (EPE’21 ECCE Europe)</i>. 23rd European Conference on Power Electronics and Applications
    (EPE’21 ECCE Europe), Ghent, Belgium. <a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542">https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542</a>
  bibtex: '@inproceedings{Unruh_Lange_Schafmeister_Böcker_2021, title={Adaptive Zero-Sequence
    Voltage Injection for Modular Solid-State Transformer to Compensate for Asymmetrical
    Fault Conditions}, DOI={<a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542">https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542</a>},
    booktitle={23rd European Conference on Power Electronics and Applications (EPE’21
    ECCE Europe)}, publisher={IEEE}, author={Unruh, Roland and Lange, Jarren and Schafmeister,
    Frank and Böcker, Joachim}, year={2021} }'
  chicago: Unruh, Roland, Jarren Lange, Frank Schafmeister, and Joachim Böcker. “Adaptive
    Zero-Sequence Voltage Injection for Modular Solid-State Transformer to Compensate
    for Asymmetrical Fault Conditions.” In <i>23rd European Conference on Power Electronics
    and Applications (EPE’21 ECCE Europe)</i>. IEEE, 2021. <a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542">https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542</a>.
  ieee: 'R. Unruh, J. Lange, F. Schafmeister, and J. Böcker, “Adaptive Zero-Sequence
    Voltage Injection for Modular Solid-State Transformer to Compensate for Asymmetrical
    Fault Conditions,” presented at the 23rd European Conference on Power Electronics
    and Applications (EPE’21 ECCE Europe), Ghent, Belgium, 2021, doi: <a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542">https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542</a>.'
  mla: Unruh, Roland, et al. “Adaptive Zero-Sequence Voltage Injection for Modular
    Solid-State Transformer to Compensate for Asymmetrical Fault Conditions.” <i>23rd
    European Conference on Power Electronics and Applications (EPE’21 ECCE Europe)</i>,
    IEEE, 2021, doi:<a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542">https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542</a>.
  short: 'R. Unruh, J. Lange, F. Schafmeister, J. Böcker, in: 23rd European Conference
    on Power Electronics and Applications (EPE’21 ECCE Europe), IEEE, 2021.'
conference:
  end_date: 2021-09-10
  location: Ghent, Belgium
  name: 23rd European Conference on Power Electronics and Applications (EPE'21 ECCE
    Europe)
  start_date: 2021-09-06
date_created: 2022-02-21T16:31:34Z
date_updated: 2022-09-09T12:01:42Z
department:
- _id: '52'
doi: https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542
keyword:
- Solid-State Transformer
- Zero sequence voltage
- Fault handling strategy
- Power balance control technique
- Three-phase system
language:
- iso: eng
main_file_link:
- url: https://ieeexplore.ieee.org/abstract/document/9570542
publication: 23rd European Conference on Power Electronics and Applications (EPE'21
  ECCE Europe)
publication_identifier:
  isbn:
  - 978-9-0758-1537-5
publication_status: published
publisher: IEEE
status: public
title: Adaptive Zero-Sequence Voltage Injection for Modular Solid-State Transformer
  to Compensate for Asymmetrical Fault Conditions
type: conference
user_id: '34289'
year: '2021'
...
---
_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: '29899'
abstract:
- lang: eng
  text: LLC resonant converters are typically unsuitable to be applied for wide voltage-transfer
    ratio applications. With a full-bridge inverter, however, they can be operated
    in a variety of different modulations. Most notably, by permanently turning on
    one MOSFET and turning off the other MOSFET of the same bridge leg, the LLC can
    be operated in half-bridge configuration reducing the gain by a factor of two.
    The resonant capacitor is hereby charged to an average voltage of half the input
    voltage. In this modulation, however, the switch that is permanently turned on
    is stressed by the complete resonant current while exhibiting no switching losses.
    This paper proves that the frequency-doubler modulation can better balance the
    losses among all MOSFETs and should be the preferred mode of operation favored
    over the conventional half-bridge modulation. This paper analyzes the beneficial
    loss distribution, proposes an on-the-fly morphing modulation and discusses potential
    operating strategies to further reduce the junction temperature. Furthermore,
    it is shown that this modulation can also be altered to achieve the asymmetrical
    LLC operation. Experimental measurement results show that the modulation results
    in a substantial decrease of the maximum MOSFET temperature and shows that the
    converter can be smoothly transitioned during operation from full-bridge modulation
    to the frequency-doubler half-bridge operation and back.
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: Lars
  full_name: Hankeln, Lars
  last_name: Hankeln
- 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, Hankeln L, Schafmeister F, Böcker J. Frequency-Doubler
    Modulation for Reduced Junction Temperatures for LLC Resonant Converters Operated
    in Half-Bridge Configuration. In: <i>23rd European Conference on Power Electronics
    and Applications (EPE’21 ECCE Europe)</i>. IEEE; 2021. doi:<a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570674">10.23919/EPE21ECCEEurope50061.2021.9570674</a>'
  apa: Rehlaender, P., Unruh, R., Hankeln, L., Schafmeister, F., &#38; Böcker, J.
    (2021). Frequency-Doubler Modulation for Reduced Junction Temperatures for LLC
    Resonant Converters Operated in Half-Bridge Configuration. <i>23rd European Conference
    on Power Electronics and Applications (EPE’21 ECCE Europe)</i>. 23rd European
    Conference on Power Electronics and Applications (EPE’21 ECCE Europe), Ghent,
    Belgium. <a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570674">https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570674</a>
  bibtex: '@inproceedings{Rehlaender_Unruh_Hankeln_Schafmeister_Böcker_2021, title={Frequency-Doubler
    Modulation for Reduced Junction Temperatures for LLC Resonant Converters Operated
    in Half-Bridge Configuration}, DOI={<a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570674">10.23919/EPE21ECCEEurope50061.2021.9570674</a>},
    booktitle={23rd European Conference on Power Electronics and Applications (EPE’21
    ECCE Europe)}, publisher={IEEE}, author={Rehlaender, Philipp and Unruh, Roland
    and Hankeln, Lars and Schafmeister, Frank and Böcker, Joachim}, year={2021} }'
  chicago: Rehlaender, Philipp, Roland Unruh, Lars Hankeln, Frank Schafmeister, and
    Joachim Böcker. “Frequency-Doubler Modulation for Reduced Junction Temperatures
    for LLC Resonant Converters Operated in Half-Bridge Configuration.” In <i>23rd
    European Conference on Power Electronics and Applications (EPE’21 ECCE Europe)</i>.
    IEEE, 2021. <a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570674">https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570674</a>.
  ieee: 'P. Rehlaender, R. Unruh, L. Hankeln, F. Schafmeister, and J. Böcker, “Frequency-Doubler
    Modulation for Reduced Junction Temperatures for LLC Resonant Converters Operated
    in Half-Bridge Configuration,” presented at the 23rd European Conference on Power
    Electronics and Applications (EPE’21 ECCE Europe), Ghent, Belgium, 2021, doi:
    <a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570674">10.23919/EPE21ECCEEurope50061.2021.9570674</a>.'
  mla: Rehlaender, Philipp, et al. “Frequency-Doubler Modulation for Reduced Junction
    Temperatures for LLC Resonant Converters Operated in Half-Bridge Configuration.”
    <i>23rd European Conference on Power Electronics and Applications (EPE’21 ECCE
    Europe)</i>, IEEE, 2021, doi:<a href="https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570674">10.23919/EPE21ECCEEurope50061.2021.9570674</a>.
  short: 'P. Rehlaender, R. Unruh, L. Hankeln, F. Schafmeister, J. Böcker, in: 23rd
    European Conference on Power Electronics and Applications (EPE’21 ECCE Europe),
    IEEE, 2021.'
conference:
  end_date: 2021-09-10
  location: Ghent, Belgium
  name: 23rd European Conference on Power Electronics and Applications (EPE'21 ECCE
    Europe)
  start_date: 2021-09-06
date_created: 2022-02-20T21:29:48Z
date_updated: 2023-02-09T11:01:11Z
department:
- _id: '34'
- _id: '52'
doi: 10.23919/EPE21ECCEEurope50061.2021.9570674
keyword:
- Resonant converter
- High frequency power converter
- Switched-mode power supply
- Converter control
- Control methods for electrical systems
language:
- iso: eng
main_file_link:
- url: https://ieeexplore.ieee.org/abstract/document/9570674
publication: 23rd European Conference on Power Electronics and Applications (EPE'21
  ECCE Europe)
publication_identifier:
  isbn:
  - 978-9-0758-1537-5
publication_status: published
publisher: IEEE
status: public
title: Frequency-Doubler Modulation for Reduced Junction Temperatures for LLC Resonant
  Converters Operated in Half-Bridge Configuration
type: conference
user_id: '34289'
year: '2021'
...
---
_id: '29939'
abstract:
- lang: eng
  text: In this paper, a full-bridge modular multilevel converter (MMC) and two half-bridge-based
    MMCs are evaluated for high-current low-voltage e.g. 100 - 400V 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 10kV, and provide up to 1 MW to the load. 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 six-arm MMC converter
    with half-bridge modules can be simplified and optimized by removing three arms,
    and thus halving the number of modules. In addition, the module voltage ripple
    and capacitor losses are decreased by 22% and 30% respectively. By rearranging
    the components of the half-bridge MMC to build a MMC consisting of grid-side full-bridge
    modules, the voltage ripple is further reduced by 78% and capacitor losses by
    64%, while ensuring identical costs and volume for all MMCs. Finally, the LLC
    resonant converter is designed for the most efficient full-bridge MMC. The LLC
    can not operate at resonance with a fixed nominal module voltage of 770V because
    the output voltage is varying between 142 - 220V. By decreasing the module voltage
    down to 600V, additional points of operation can be operated in resonance, and
    the remaining are closer to resonance. The option to decrease the module voltage
    down to 600V, increases the number of required modules per arm from 12 to 15,
    which requires to balance the losses of the LLCs and the grid-side stages.
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. Evaluation of MMCs for High-Power Low-Voltage
    DC-Applications in Combination with the Module LLC-Design. In: <i>2020 22nd European
    Conference on Power Electronics and Applications (EPE’20 ECCE Europe)</i>. IEEE;
    2020. doi:<a href="https://doi.org/10.23919/epe20ecceeurope43536.2020.9215687">10.23919/epe20ecceeurope43536.2020.9215687</a>'
  apa: Unruh, R., Schafmeister, F., &#38; Böcker, J. (2020). Evaluation of MMCs for
    High-Power Low-Voltage DC-Applications in Combination with the Module LLC-Design.
    <i>2020 22nd European Conference on Power Electronics and Applications (EPE’20
    ECCE Europe)</i>. 22nd European Conference on Power Electronics and Applications
    (EPE’20 ECCE Europe), Lyon, France. <a href="https://doi.org/10.23919/epe20ecceeurope43536.2020.9215687">https://doi.org/10.23919/epe20ecceeurope43536.2020.9215687</a>
  bibtex: '@inproceedings{Unruh_Schafmeister_Böcker_2020, title={Evaluation of MMCs
    for High-Power Low-Voltage DC-Applications in Combination with the Module LLC-Design},
    DOI={<a href="https://doi.org/10.23919/epe20ecceeurope43536.2020.9215687">10.23919/epe20ecceeurope43536.2020.9215687</a>},
    booktitle={2020 22nd European Conference on Power Electronics and Applications
    (EPE’20 ECCE Europe)}, publisher={IEEE}, author={Unruh, Roland and Schafmeister,
    Frank and Böcker, Joachim}, year={2020} }'
  chicago: Unruh, Roland, Frank Schafmeister, and Joachim Böcker. “Evaluation of MMCs
    for High-Power Low-Voltage DC-Applications in Combination with the Module LLC-Design.”
    In <i>2020 22nd European Conference on Power Electronics and Applications (EPE’20
    ECCE Europe)</i>. IEEE, 2020. <a href="https://doi.org/10.23919/epe20ecceeurope43536.2020.9215687">https://doi.org/10.23919/epe20ecceeurope43536.2020.9215687</a>.
  ieee: 'R. Unruh, F. Schafmeister, and J. Böcker, “Evaluation of MMCs for High-Power
    Low-Voltage DC-Applications in Combination with the Module LLC-Design,” presented
    at the 22nd European Conference on Power Electronics and Applications (EPE’20
    ECCE Europe), Lyon, France, 2020, doi: <a href="https://doi.org/10.23919/epe20ecceeurope43536.2020.9215687">10.23919/epe20ecceeurope43536.2020.9215687</a>.'
  mla: Unruh, Roland, et al. “Evaluation of MMCs for High-Power Low-Voltage DC-Applications
    in Combination with the Module LLC-Design.” <i>2020 22nd European Conference on
    Power Electronics and Applications (EPE’20 ECCE Europe)</i>, IEEE, 2020, doi:<a
    href="https://doi.org/10.23919/epe20ecceeurope43536.2020.9215687">10.23919/epe20ecceeurope43536.2020.9215687</a>.
  short: 'R. Unruh, F. Schafmeister, J. Böcker, in: 2020 22nd European Conference
    on Power Electronics and Applications (EPE’20 ECCE Europe), IEEE, 2020.'
conference:
  end_date: 2020-09-11
  location: Lyon, France
  name: 22nd European Conference on Power Electronics and Applications (EPE'20 ECCE
    Europe)
  start_date: 2020-09-07
date_created: 2022-02-21T16:33:14Z
date_updated: 2022-02-21T17:00:16Z
department:
- _id: '52'
doi: 10.23919/epe20ecceeurope43536.2020.9215687
keyword:
- Multilevel converters
- Resonant converter
- High voltage power converters
- ZVS Converters
- Combination MMC LLC
language:
- iso: eng
main_file_link:
- url: https://ieeexplore.ieee.org/abstract/document/9215687
publication: 2020 22nd European Conference on Power Electronics and Applications (EPE'20
  ECCE Europe)
publication_status: published
publisher: IEEE
status: public
title: Evaluation of MMCs for High-Power Low-Voltage DC-Applications in Combination
  with the Module LLC-Design
type: conference
user_id: '34289'
year: '2020'
...
---
_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'
...
---
_id: '29942'
abstract:
- lang: eng
  text: Due to recent developments in MMCs, they are used in many medium-voltage and
    high-power applications today, but efficient and modular solutions for high-power
    at low-voltage such as for electrolysis are still required. The proposed Y-MMC
    converts the grid AC-voltage into a DC-voltages, and an LLC converter is connected
    to each submodule capacitor to provide the required current to the DC-load. This
    paper proposes a topology that uses only half the number of submodules and moreover
    to reduce the effective switching frequency by a third, while preserving the same
    THD und output power of an YY-MMC.
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. MMC-Topology for High-Current
    and Low-Voltage Applications with Minimal Number of Submodules, Reduced Switching
    and Capacitor Losses. In: <i>PCIM Europe 2019; International Exhibition and Conference
    for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management</i>.
    VDE; 2019.'
  apa: Unruh, R., Schafmeister, F., Fröhleke, N., &#38; Böcker, J. (2019). MMC-Topology
    for High-Current and Low-Voltage Applications with Minimal Number of Submodules,
    Reduced Switching and Capacitor Losses. <i>PCIM Europe 2019; International Exhibition
    and Conference for Power Electronics, Intelligent Motion, Renewable Energy and
    Energy Management</i>. PCIM Europe 2019, Nuremberg, Germany.
  bibtex: '@inproceedings{Unruh_Schafmeister_Fröhleke_Böcker_2019, title={MMC-Topology
    for High-Current and Low-Voltage Applications with Minimal Number of Submodules,
    Reduced Switching and Capacitor Losses}, booktitle={PCIM Europe 2019; 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={2019} }'
  chicago: Unruh, Roland, Frank Schafmeister, Norbert Fröhleke, and Joachim Böcker.
    “MMC-Topology for High-Current and Low-Voltage Applications with Minimal Number
    of Submodules, Reduced Switching and Capacitor Losses.” In <i>PCIM Europe 2019;
    International Exhibition and Conference for Power Electronics, Intelligent Motion,
    Renewable Energy and Energy Management</i>. VDE, 2019.
  ieee: R. Unruh, F. Schafmeister, N. Fröhleke, and J. Böcker, “MMC-Topology for High-Current
    and Low-Voltage Applications with Minimal Number of Submodules, Reduced Switching
    and Capacitor Losses,” presented at the PCIM Europe 2019, Nuremberg, Germany,
    2019.
  mla: Unruh, Roland, et al. “MMC-Topology for High-Current and Low-Voltage Applications
    with Minimal Number of Submodules, Reduced Switching and Capacitor Losses.” <i>PCIM
    Europe 2019; International Exhibition and Conference for Power Electronics, Intelligent
    Motion, Renewable Energy and Energy Management</i>, VDE, 2019.
  short: 'R. Unruh, F. Schafmeister, N. Fröhleke, J. Böcker, in: PCIM Europe 2019;
    International Exhibition and Conference for Power Electronics, Intelligent Motion,
    Renewable Energy and Energy Management, VDE, 2019.'
conference:
  end_date: 2019-05-09
  location: Nuremberg, Germany
  name: PCIM Europe 2019
  start_date: 2019-05-07
date_created: 2022-02-21T16:57:29Z
date_updated: 2022-02-23T15:49:43Z
department:
- _id: '52'
language:
- iso: eng
main_file_link:
- url: https://ieeexplore.ieee.org/document/8767739
publication: PCIM Europe 2019; International Exhibition and Conference for Power Electronics,
  Intelligent Motion, Renewable Energy and Energy Management
publication_identifier:
  isbn:
  - 978-3-8007-4938-6
publication_status: published
publisher: VDE
status: public
title: MMC-Topology for High-Current and Low-Voltage Applications with Minimal Number
  of Submodules, Reduced Switching and Capacitor Losses
type: conference
user_id: '66'
year: '2019'
...