A Study on Power Transmission Techniques for Marine Airborne Wind Energy Farms

Mahdi Ebrahimi Salari Postdoctoral Researcher

University of Limerick Department of Electronic and

Computer Engineering Centre for Robotics & Intelligent

Systems (CRIS)

Limerick V94 T9PX Ireland

mahdi.ebrahimisalari@ul.ie www.cris.ul.ie

A Study on Power Transmission Techniques

for Marine Airborne Wind Energy Farms

The slender structure of airborne wind energy (AWE) sys-tems has made them ideal for floating offshore appli-cations although the limited maximum distance of cur-rent marine high voltage AC (HVAC) technology (<50 km) can be a barrier for their development [1]. This research work is a literature review to study advanced marine power transmission technologies including high voltage DC (HVDC), low-frequency AC (LFAC) and direct intercon-nection technique (DIT), and their compatibility with AWE technologies. The absence of reactive power in HVDC has led to fewer power losses and higher transmission dis-tance compared to marine HVAC. However, high cost and failure rate of power electronic converters (PEC) nega-tively affects the economy and reliability of HVDC [2]. Ma-rine LFAC has higher loadability and distance compared to subsea HVAC [3]. The low operating frequency of LFAC (16.7 Hz) is compatible with the generated frequency of AWE devices; therefore, there is no need for PECs and their associated equipment in the offshore substation. However, LFAC requires shunt reactors and larger power transformers [3]. DIT relocates marine-based PECs to the onshore site to relieve the negative effects of offshore PECs on the cost and reliability [4]. Considering the cost of PECs between e111/kVA and e150/kVA [5], DIT can save e22.2M-e30M in capital cost of a 200 MW offshore AWE farm. The development of DIT for AWE systems needs more investigation as challenges like mechanical torque regulation, reactive power exchange, and flight control complexity are reported [6]. Less power losses and better

economy of LFAC compared to HVDC [7] and its frequency compatibility with AWE devices show a significant poten-tial for LFAC to be used as a marine power transmission for future floating offshore AWE systems. However, more investigation is necessary to examine this technology for AWE devices.

References:

[1] Reed, G.F. et al.: Comparison of HVAC and HVDC Solutions for Off-shore Wind Farms with a Procedure for System Economic Evalua-tion. IEEE Energytech conference, Cleveland, OH, USA (2013) [2] Zhao et al.: Fault Prediction and Diagnosis of Wind Turbine Gen-erators Using SCADA Data. Energies 10 (2017).

[3] Fischer et al.: Low Frequency High Voltage Offshore Grid for Transmission of Renewable Power. 3rd IEEE PES Innovative Smart Grid Technologies Europe (ISGT Europe), Berlin (2012).

[4] Pican et al.: Direct interconnection of offshore electricity gener-ators. Energy 36, 11 (2011).

[5] Parker, M. A. et al.: Cost and losses associated with offshore wind farm collection networks which centralise the turbine power elec-tronic converters. IET Renew. Power Gener. 7(4), 390ś400 (2013). [8] Ebrahimi Salari, M. et al.: Power Control of Direct Interconnec-tion Technique for Airborne Wind Energy System. Energies 11(11) (2018).

[7] Ruddy et al.: A Comparison of VSC-HVDC with Low Frequency AC for Offshore Wind Farm Design and Interconnection. Energy Proce-dia 80 (2015).