Papers and citations

The experience behind CLEPS has been documented in technical literature and conference work. The items below concern wind power grid connection, HVDC and the operation of power systems with a large share of connected generation. They are explained here to show which questions the competence is built on, and so that each one can be traced to its source.

1. HVDC Light Experiences Applicable for Power Transmission from Offshore Wind Power Parks

   Kjell Eriksson (ABB), Christer Liljegren (Cleps AB) and Kent Söbrink (Eltra). 2004. 42nd AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, published by the American Institute of Aeronautics and Astronautics.

   The work carries operating experience from the first voltage source converter based direct current links over to the question of power transmission from offshore wind power. It is the only one of these works where CLEPS is the stated affiliation.

   Why it matters today: a converter based connection can control active and reactive power independently and thereby support the voltage at a weak connection point. That is the same question facing an installation with long cable feeds or a weak grid.

   Publisher record, DOI 10.2514/6.2004-1010

2. Wind Power on the Swedish Island of Gotland

   Christer Liljegren and Thomas Ackermann. 2005. Chapter 13 in the book Wind Power in Power Systems, pages 283 to 297, published by Wiley.

   A book chapter, not a conference paper. It treats Gotland as a case study of large scale wind power in an island grid: how the system is built, what limits the grid places on how much generation can be connected, and which measures have been used to handle that.

   Why it matters today: how much generation a constrained grid can take is the same question for an industrial installation in a connection queue as for an island.

   Publisher record, DOI 10.1002/0470012684.ch13

3. Co-ordination of Parallel AC-DC Systems for Optimum Performance

   Ana Diez Castro and Rickard Ellström (Vattenfall Utveckling AB), Ying Jiang Häfner (ABB Power Systems) and Christer Liljegren (Gotlands Energiverk AB). 1999. The document does not state a publisher or conference, and none is given here.

   The work describes how the parallel alternating and direct current systems on Gotland are co-ordinated when a large share of wind power is connected in a weak grid. It covers converter control principles, how the grid protection must be designed, and how the short circuit contribution from both converters and wind power affects protection selectivity.

   Why it matters today: short circuit power at the connection point still sets the ceiling for how much can be connected, and protection settings still have to be recalculated when converter connected installations are added behind existing protection.

   The document is available as a historical full text in the CLEPS archive. The affiliations above are the ones that applied when the work was written and are reproduced unchanged.

   Historical full text in the CLEPS archive, PDF

One verified historical full text is available in the CLEPS archive and is linked above. The other works are published by conferences and publishers, and where the official publisher record is verified it is linked. A fourth title from the earlier list has been removed for now, because neither authors, year nor publisher could be established against any source.

1. Power Quality Disturbances in Production Facilities, Emanuel Widlund, 2012, Department of Energy and Environment, Chalmers University of Technology. The thesis thanks Christer Liljegren at Cleps AB for an interview, alongside representatives of other actors in the power system. Read the thesis at Chalmers
2. En möjlig framtid för Gotlands elnät; smarta vindkraftverk med frekvensreglering, Erik Håkansson, Linnea Johansson, Fredrik Juthe and Sara Rutfjäll, 2021, Department of Electrical Engineering, Chalmers University of Technology. The work thanks Christer Liljegren, power engineering consultant at Cleps, for an interview. Read the work at Chalmers
3. Nätanslutning av vindkraft, Alexander Wegener, thesis number 489, 2007, Department of Economics, Swedish University of Agricultural Sciences. The work states that Cleps AB represents an independent consultant in the wind power industry. Read the thesis at SLU
4. Pre study on hydrogen and energy storage on Gotland. Christer Liljegren at Cleps is named among those who authored parts of the report. According to the report, the work was carried out between 2019 and 2020. Read the report