Advances in DC microgrids

DC microgrids are the new buzz concept around the professional communities of power systems. The battle of AC and DC from the Edison and Tesla era is comming back with new advances in promoting the latest against the first, which dominated and is still in power for large applications in the power industry for almost 14 decades ("The War of Currents," 1880).

Microgrids are an important concept in the emerging power industry field, and they usually refer to distribution topologies that can work either as a stand-alone subsystem or connected to the main power grid. They are widely recognized as an innovative ecosystem when it comes to a flexible and reliable option for the integration of distributed energy renewable resources (DER).

Even though the vast majority of recent demonstrations for microgrids use AC power transfer, a traditional dominant scheme, DC power distribution systems are taking ground especially for applications where the end-use loads are natively DC. Industry drivers in ICT and Telecommunication Industry already took initiatives for standardization with respect to DC microgrids in these specific applications such as data centres for example. Furthermore, deployments and demonstration projects for plugged-in electric vehicles (PHV) as well as the exponential spreading of photovoltaic systems installed especially on residential buildings, with Germany leading the market, increased the research interest in LV-building level DC microgrids.

Several demonstrations for LV DC microgrids showed that when onsite renewable generation, electric vehicles and storage systems are present, DC-based microgrids may offer significant benefits compared to their AC counterparts, such as: higher power efficiency due to fewer conversion stages, higher reliability, lower capital cost, simpler control and more close to universal control strategies, higher power quality and disturbance survivability.

It is to be noted however, that the research on DC microgrids mainly focuses on either comparisons with AC counterpart configuration of the same microgrid in terms of operation (scheduling and optimal operation), or on improvements in the control methods. The current state of the art in the DC building level microgrids architecture is most of the time limited to a radial configuration with a single DC supply bus. As building level DC microgrids expand, it is expected that meshed clusters of microgrids connected at distribution feeders will emerge. A recently stated project, finaced by the European Commission under the Research and Innovation Scheme of Horizon 2020 Program, focuses on the analysis of several modelling, operation and control methods of clusters of DC microgrids in a more comprehensive range of possible architectures, where an important consideration in the design is reserved to power quality aspects. 

Power quality standards for DC systems are limitted to a small range of mobile systems such as matitime ships of airplanes or those that advanced in the Telecom Industry. Therefore, the current project also aims to advance proposals for standardization in PQ definitions for terrestrial DC microgrids. 

Reason for creating this blog

This blog has been created in order to help power Engineers find resources that are missing on the web or hard to find.

Wind energizer from Leviathan Energy Boosted the output of wind turbines with 30% by Breakthrough Design

Leviathan Energy has completed initial testing on their Wind Energizer unit and is reporting gains in wind turbine output in the range of 15 to 30% — and as much as 150% at lower wind speeds.

The theory behind this work is that by placing passive objects around a wind turbine ( wind farm according to http://cleantechnica.com/2009/04/29/wind-turbine-output-boosted-30-by-breakthrough-design) it will change the circulation around the wind turbine. The advancement is not in the turbine itself, but rather in the area around it, as such, units can be adapted to any wind turbine from any manufacturer.

 

wind energy

Interactive (visual) wind turbine (WT) operation.

I found it useful for a first start in understanding how wind turbines work and which are the main components of a WT.

 http://www.windpower.org/en/kids/intro/intronac.htm

Benchmark test systems in IEEE and PSS/E formats

We all know that for validating research studies in power engineering benchmark standardized systems might be used. Therefore, my intention on this blog was to provide web links to such Test (benchmark) Power Systems in IEEE and PSS/E formats for both load flow, power economics and signal dynamics analysis. Currently there is an ongoing project of the IEEE Task Force on Test Systems for Economic Analysis (IEEE-TEA), which has as aim to derive benchmark test systems specifically for energy economic studies. In this respect the group created a wiki web site where they intend to post those specific benchmark test systems: http://www.ieee-tea.ethz.ch/wiki 

However, the most cited link for benchmark test systems in IEEE Common Data Format/PTI Power Flow Data Format /PECO PSAP Format is the following:

http://www.ee.washington.edu/research/pstca/.

The above cited site is maintained by dr. Richard D. Christie, Associate Professor at the University of Washington, Seattle, Washington, USA, and was last updated in '99.

For power system reliability studies there are a couple of useful links, I found, that provide test systems in PPS/E format:

1. http://www.eleceng.adelaide.edu.au/Groups/PCON/PowerSystems/IEEE/BenchmarkData/index.html#TestSystemData,
2. Direct link to the IEEE 14 generator test system in PSS/E format:  http://www.eleceng.adelaide.edu.au/Groups/PCON/PowerSystems/IEEE/BenchmarkData/AUdata_Rev2_20080521.zip
3. Master Thesis example models in PSS/E format: http://www.ee.kth.se/php/modules/publications/reports/2007/XR-EE-EME_2007_009

Apparently, the test systems used in this Master thesis are from Kundur's book: "Power system stability and control". 

Other recent test systems, developed for dunamical studies were recently released by a small group of researchers form KIOS Research Center, Cyprus. 

Dynamic IEEE test systems similar to the ones described above and the IEEE 300 bus modified test system implemented in Powerworld can be downloaded from here:

http://www.kios.ucy.ac.cy/testsystems/index.php/dynamic-ieee-test-systems/ieee-300-bus-modified-test-system-2