Grid code compliance of grid-side converter in wind turbine systems

Until recently, there were no specific requirements in the grid codes for connecting the wind turbines/farms to the electrical network. Nowadays the power system operators e.g. in Denmark, Germany and Spain, have started to issue new grid codes addressed to wind turbines/farms. The grid connection requirements are addressed both at distribution and transmission level and can be applied to on-shore units as well as to off-shore ones. The focus in these grid codes is on the power quality, grid stability, control capabilities and on the performances of the wind turbines/farms under fault conditions as well. These requirements can vary considerably from one specific grid code to another and one of the major goals for the wind turbine industry is to meet them without major changes in the control algorithms as well as in the hardware. The grid side converter is a key element in achieving the grid code requirements regarding the compatibility levels for voltages and currents in the Point of Common Coupling (PCC). An analysis of these compatibility levels for voltages and currents in the PCC for different control strategies of the grid side converter in large wind turbine applications is presented in this paper. Different grid conditions as well as different connection method to PCC are considered. The analysis is based on the existing recommendation within the grid codes.