Comparative analysis of high voltage alternating current & high voltage direct current offshore collection grid systems

Abstract

An increase in industries as well as the world’s population, is causing a strain on the electricity supply. This coupled with the fact that fossil fuel supplies are decreasing, is leading the world to new, greener methods of electrical energy generation. Offshore wind farms are being developed far offshore and solar farms are being developed in remote locations with intense sunlight. This allows for the optimal operation of these systems. HVAC collection systems for offshore wind farms have traditionally been used but imposes limitations on the transmission distance. Exuberant amounts of capital are required for greater distances. HVDC systems have started to be recognised as a viable method of transmitting this electrical energy at a much lower cost on longer distances. This study shows a comparative performance and cost evaluation of both HVAC and HVDC collection systems for offshore wind farms. It evaluates the efficiency of the wind farm based on system losses, determines the advantages, disadvantages, and cost implications of each system, and determines the best type of technology to be used in offshore applications. The study looks at a case of a 40 MW wind farm at a distance of 120 km offshore. A simulation is developed for each system using MATLAB simulation software to determine the performance of each system during normal operation and fault conditions. From these simulations, it was found that HVDC collection systems have much higher efficiency when compared to HVAC systems and perform better under both normal operation and fault conditions. HVDC systems also have a lower cost once the break-even distance point is passed. From the study, it is found that HVDC collection systems are much better suited to allow offshore wind farms to have a high efficiency as well as be located further offshore to allow for maximum wind usage. The technology can be used for other long-distance transmission systems and incorporated for other renewable energy generation systems.