Converters are the essential devices in the energy transformation process from the wind generators to the grid. Power electronic semiconductors have a high share of failures in the power electronic converters. Therefore, the reliability based on lifetime of power semiconductor generates more and more attention. This thesis presents a comparison of different active control methods to control the lifetime of power semiconductors in wind turbines. This investigation is implemented through simulations on a 10 MW direct drive permanent magnet wind generator with three-level neutral point clamped converters. The study shows that both switching frequency control and reactive current control can improve semiconductor lifetime to certain extents. As for which control method is more effective depends on the surrounding wind environment.