This paper describes the design procedure andperformance of an LCL grid filter for a medium-voltage neutralpoint clamped (NPC) converter to be adopted for a multimegawattwind turbine. The unique filter design challenges in thisapplication are driven by a combination of the medium voltageconverter, a limited allowable switching frequency, componentphysical size and weight concerns, and the stringent limitsfor allowable injected current harmonics. Traditional designprocedures of grid filters for lower power and higher switchingfrequency converters are not valid for a multi-megawatt filterconnecting a medium-voltage converter switching at low frequencyto the electric grid. This paper demonstrates a frequencydomain model based approach to determine the optimum filterparameters that provide the necessary performance under alloperating conditions given the necessary design constraints. Toachieve this goal, new concepts such as virtual harmonic contentand virtual filter losses are introduced. Moreover, a new passivedamping technique that provides the necessary damping withlow losses and very little degradation of the high-frequencyattenuation is proposed.