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Propagation of supraharmonics in a data center with different operating modes of UPS
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0001-5558-7708
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0002-4004-0352
2023 (English)In: IEEE Access, E-ISSN 2169-3536, Vol. 11, p. 36823-36833Article in journal (Refereed) Published
Abstract [en]

A data center is a major hub of different converters ensuring continuous power to the server loads. The pulse width modulation switching techniques with frequency emission from 2 to 150 kHz (i.e., supraharmonics) in these converters call for a study of the magnitude and propagation of this emission within data centers where UPS is one of the main contributors of supraharmonics. The paper shows, with measurements and model, the change in magnitude and propagation of supraharmonics with the change in the operating mode of the UPS. The magnitude of supraharmonics shows a non-linear dependency on the power consumed in the online mode. In bypass mode, the magnitude of supraharmonics shows a dependency on the type of load connected. The filter connected between PE-N at the input side of the UPS can cause resonance in the phase conductors. The results show that to study the emission, immunity, and electromagnetic compatibility of supraharmonics for UPS, the factors such as operating mode, the type of load connected, and the input and output impedance need to be considered.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2023. Vol. 11, p. 36823-36833
Keywords [en]
Data center, electromagnetic compatibility, power quality, power conditioning, uninterruptible power supply, pulse width modulation, resonance, supraharmonics
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-96639DOI: 10.1109/access.2023.3266092ISI: 000975054100001Scopus ID: 2-s2.0-85153356418OAI: oai:DiVA.org:ltu-96639DiVA, id: diva2:1751248
Funder
Swedish Energy Agency, 43090-2
Note

Validerad;2023;Nivå 2;2023-07-04 (hanlid)

Available from: 2023-04-17 Created: 2023-04-17 Last updated: 2023-09-05Bibliographically approved
In thesis
1. On the supraharmonics in single-phase and three-phase installations
Open this publication in new window or tab >>On the supraharmonics in single-phase and three-phase installations
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Society has increasingly started depending on the continuity of internet services, the interruption can be crucial for vital societal functions. It is therefore important to maintain continuous and reliable operations of e.g., installations housing sensitive IT (Information Technology) loads. The establishment of a data center attracts huge investments, thereby boosting the economy. The electrical load within the data center is more structured with a similar type of load, i.e., power supplies supplying the servers connected repetitively. They also use power-conditioning equipment such as an uninterruptible power supply (UPS), which ensures uninterrupted power to the servers. The power supplies use switching techniques to modulate and condition the power supplied to the IT load. The switching residues from the power supplies are often in the frequency range from 2 kHz to 150 kHz, known as supraharmonics. The switching frequency of power electronic converters and power line communication are identified as the main contributors to supraharmonics. The increase in the number of power electronic converters in the power system has sparked interest in supraharmonics. Limited standards are available on the magnitude of supraharmonics allowed in the system. For installations that house multiple power converters, prior knowledge about the propagation and consequences of the supraharmonics can be an advantage in increasing their reliability. This work is focused on supraharmonics within data centers, but the results of the study can be applied to other installations.

The data centers are usually three-phase installations where single-phase devices, i.e., servers are distributed over three phases. To understand the holistic view of the system, it is important to understand the spread of supraharmonics in phase, neutral, and protective earth conductors. A perspective on the behaviour of supraharmonics in three-phase installation is presented in this work. The focal point of the work is the summation of supraharmonics in the neutral conductor and conductor crosstalk. The behaviour of the device connected in single-phase installation and when the same devices are spread over three phases may differ depending on the design of the installation. Since the focus is on a greater number of devices, analysis for the change in the magnitude of supraharmonics in a neutral conductor with the change in the number of devices is also undertaken. The IT workload in a data center changes continuously, thus a constant unbalance in the electrical load between the three phases can exist. The thesis aims to understand the factors influencing the change in supraharmonic magnitude and propagation in phase and neutral conductors according to a balanced and unbalanced voltage supply and loading conditions. The presence of a supraharmonic emitting load in one phase can cause interference on the adjacent phase due to conductor crosstalk. Crosstalk leads to the propagation of supraharmonics between the phases. The work focuses on the parameters influencing the crosstalk phenomena for supraharmonics. Among the parameters studied, the type of cable used in an installation and the cable length is dominating. The measurement of supraharmonic emission from the device connected as single-phase and connected as three-phase would differ because of crosstalk.

A large number of servers in data centers connected close by may lead to an increased leakage current. The composite leakage current can comprise subharmonics, harmonics, and supraharmonics. This can cause unwanted tripping of the residual current device (RCD), which is installed for human protection. The work aims to understand the impact of the composite residual current on the operation of the residual current devices.

The main contributions of this work are summarized as:

• A sensitivity analysis is presented based on the parameters impacting the propagation of supraharmonics for different operating modes of a UPS.

• A characterization of supraharmonics emission from different devices according to their time and frequency varying behaviour.

• A mathematical model to predict the change in the supraharmonic emission in the neutral conductor.

• An increased understanding of the behaviour of supraharmonics for constant powerloads under voltage reduction conditions in three-phase installations.

• Introduction and definition of the terms induced primary emission and induced secondary emission to explain conductor crosstalk for supraharmonic emission.

• A mathematical model to show the factors influencing the magnitude of induced primary emission and induced secondary emission.

• The frequency response of RCDs of type AC, A, B, and F under residual currents comprising pure tones and composite currents is presented by measurements andmodeling.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2023. p. 70
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-96668 (URN)978-91-8048-321-6 (ISBN)978-91-8048-322-3 (ISBN)
Public defence
2023-05-30, Hörsal A, Luleå tekniska universitet, Skellefteå, 09:00 (English)
Opponent
Supervisors
Available from: 2023-04-20 Created: 2023-04-19 Last updated: 2023-09-05Bibliographically approved

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Sutaria, JilRönnberg, Sarah

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