The rapid development of powerful generators for wind power plants leads producers of power converters search ways to maximize the nominal power and availability of their converter units. The cooling solutions of a medium voltage converter with rated power of 3MVA are designed and assessed here from thermal and reliability points of view. Cooling becomes the limiting factor in meeting the weight, volume and reliability objectives of high power devices. The 3D FEM thermal modeling of the power module and analytical reliability analysis on the cooling systems’ equipments are used to compare the cooling systems based on single-phase cold plates, heat pipes with water pools and two-phase cold plates.