IEEE Energy2030 Atlanta, GA USA 17-18 November, 2008 DC Collection for Wind Farms Anish Prasai Deepak Divan Georgia Institute of Technology, Atlanta, GA 777 Atlantic Drive NW, VL 275 Atlanta, GA 30332 Abstract – In the US, much of the wind resource is located a significant distance from population centers. Existing AC grids, if available, are weak and incapable of carrying large amounts of wind power. Use of proven HVDC technology using Voltage Source Converters (VSC) to perform the long haul for wind energy offers significant advantages at the system level. If one maintains the existing architecture with 60 hertz ac machines (DFIG or PM) connected in parallel, with another VSC converter station at the wind-farm, then the approach appears to be very expensive. This paper proposes a cost effective approach that is based on a compact and light HVDC architecture where individual turbine output is directly converted to DC, using PM generators, medium frequency transformers and simple power converters. I. INTRODUCTION In an effort to decrease reliance on foreign fuel, and to reduce carbon emissions, there is a strong drive to increase installed wind capacity in the US. Wind energy presently comprises <2% of the total generated electricity in the US, with a push to increase it to 20% by 2030 [1]. In the US, much of the wind resource is located in the Midwest, a significant distance from population centers, as shown in Fig. 1. Existing AC grids, if available, are weak and incapable of carrying large amounts of power over long distances. The inability to control how power flows on the network, constrains the ability to direct the current along available pathways in the AC grid. Difficulty of permitting, siting and building new overhead lines can limit the ability to transfer large amounts of power. Use of proven HVDC technology using Voltage Source Converters (VSC) to perform the long haul for wind energy offers significant advantages at the system level. HVDC Light cables from ABB can be deployed underground, creating less of an environmental impact [4]. Use of existing right of way using DC has been shown to handle significantly higher levels of power than using AC systems. The converter stations at the receiving end can regulate watts and vars, supporting the grid very well, even allowing for black-start capability. For AC system side faults, the VSC converter stations can effectively isolate the wind-farms from major disturbances. Finally, VSC based HVDC systems can be configured in a multi- point system, with multiple wind-farms and load centers connected to the dc bus, giving high level of flexibility when compared with conventional HVDC systems [5]. (a) (b) Figure 1. Distances are great between location of a) on- shore wind resources [2] and b) load centers (map of population density where lightest is lowest and darkest is highest) [3]. From the system side, it is very clear that the use of VSC- HVDC architecture provides significant performance advantages. However, these systems are often installed using building blocks, where the final system is often redundant, increasing cost and decreasing efficiency. At the wind-farm level, if one maintains the existing architecture with a PM machine and a back-to-back converter rated at full power, operating at 60 hertz, with another VSC converter station at the wind-farm level to go from AC to HVDC, then the approach appears to be very expensive. This paper proposes a different approach, where the entire wind-farm is designed around the concept of interfacing to a HVDC bus directly out