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Load modelling for steady-state and transient analysis of low-voltage dc systems
KTH, School of Electrical Engineering (EES), Electric Power Systems.
ABB, Corporate Research, Power Technologies.
2007 (English)In: IET Electric Power Applications, ISSN 1751-8660, Vol. 1, no 5, 690-696 p.Article in journal (Refereed) Published
Abstract [en]

The modelling of loads for low-voltage (LV) DC system studies is treated. Results from measurements on 63 different loads supplied with DC are presented. The measurement results are used to derive simplified load models, which can be used for steady-state and transient analysis of LV DC systems. These load models extend existing standards for load flow and short circuit current calculations.

Place, publisher, year, edition, pages
2007. Vol. 1, no 5, 690-696 p.
Keyword [en]
Electric current measurement, Electric loads, Mathematical models, Short circuit currents, Transient analysis, Load models, Low voltage DC systems
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-8092DOI: 10.1049/iet-epa:20060418ISI: 000249908600006Scopus ID: 2-s2.0-34548029928OAI: oai:DiVA.org:kth-8092DiVA: diva2:13321
Note
QC 20100908Available from: 2008-03-10 Created: 2008-03-10 Last updated: 2010-09-08Bibliographically approved
In thesis
1. Modeling, Control and Protection of Low-Voltage DC Microgrids
Open this publication in new window or tab >>Modeling, Control and Protection of Low-Voltage DC Microgrids
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Current trends in electric power consumption indicate an increasing use of dc in end-user equipment, such as computers and other electronic appliances used in households and offices. With a dc power system, ac/dc conversion within these loads can be avoided, and losses reduced. AC/DC conversion is instead centralized, and by using efficient, fully controllable power-electronic interfaces, high power quality for both ac and dc systems during steady state and ac grid disturbances can be obtained. Connection of back-up energy storage and small-size generation is also easier to realize in a dc power system.

To facilitate practical application, it is important that the shift from ac to dc can be implemented with minimal changes. Results from measurements carried out on common household appliances show that most loads are able to operate with dc supply without any modifications. Furthermore, simple, and yet sufficiently accurate, load models have been derived using the measurement results. The models have been used for further analysis of the dc system, both in steady state and during transients.

AC microgrids have gained research interest during the last years. A microgrid is a part of power systems which can operate both connected to the ac grid, and autonomously in island mode when the loads are supplied from locally distributed resources. A low-voltage dc microgrid can be used to supply sensitive electronic loads, since it combines the advantages of using a dc supply for electronic loads, and using local generation to supply sensitive loads. An example of a commercial power system which can benefit from using a dc microgrid is data center. The lower losses due to fewer power conversion steps results in less heat which need to be cooled, and therefore the operation costs are lowered.

To ensure reliable operation of a low-voltage dc microgrid, well-designed control and protection systems are needed. An adaptive controller is required to coordinate the different resources based on the load-generation balance in the microgrid, and status of the ac grid. The performance of the developed controller has been studied and evaluated through simulations. The results show that it is possible to extend use of the data center dc microgrid to also support a limited amount of ac loads close to the data center, for example an office building.

A protection-system design for low-voltage dc microgrids has been proposed, and different protection devices and grounding methods have been presented. Moreover, different fault types and their impact on the system have been analyzed. The type of protection that can be used depends on the sensitivity of the components in the microgrid. Detection methods for different components have been suggested in order to achieve a fast and accurate fault clearing.

An experimental small-scale dc power system has been used to supply different loads, both during normal and fault conditions. A three-phase two-level voltage source converter in series with a Buck converter was used to interconnect the ac and the dc power systems. Together the converters have large controllability, high power quality performance, and allow bi-directional power flow. This topology can preferably be used together with energy storage. The tests confirm the feasibility of using a dc power system to supply sensitive electronic loads.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. xiv, 52 p.
Series
Trita-EE, ISSN 1653-5146 ; 2008:007
Keyword
circuit transient analysis, dc power systems, dispersed storage and generation, load modeling, power conversion, power distribution control, power distribution faults, power distribution protection, power electronics
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-4666 (URN)978-91-7178-867-2 (ISBN)
Public defence
2008-04-04, H1, Teknikringen 33, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100908Available from: 2008-03-10 Created: 2008-03-10 Last updated: 2010-09-08Bibliographically approved

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