Thermal analysis of multi-MW two-level generator side converters with reduced common-mode-voltage modulation methods for wind turbines

Thermal performance influences both the cost of cooling system and the reliability of the power converter. Moreover, common-mode voltage in a generator drive may damage the bearing of the generator and also cause failure in a longer term. Therefore, both the thermal performance and common-mode voltage of the converter should be taken into account during the selection process of the modulation strategy. In this paper, two modulation strategies developed to reduce the common-mode-voltage reduced are compared based on the generator side converter of a 3 MW wind power system using the conventional-60° discontinuous PWM, where the common-mode voltage, power losses and thermal performance are all taken into account. The junction temperature and temperature of the power devices in the converter are obtained based on the thermal model by simulations and compared between the two modulation strategies.