This paper presents an improved thermal network model of insulated-gate bipolar transistor (IGBT) module, which considers the effects of base-plate solder fatigue on the junction temperature of the said module used in wind power converters. First, the coupling thermal structure 3-D finite-element model of the IGBT module is established based on the structure and material parameters of the module used in the wind power converters of a doubly fed induction generator. The junction temperature of the module is investigated at different thermal desquamating degrees of the base-plate solder. Second, the thermal resistance parameters are determined at different desquamating degrees, and the improved thermal network model that considers the effects of the base-plate solder fatigue is established. Finally, the IGBT junction temperature results through the improved thermal network, and the 3-D FEM models are compared.

The base-plate solder fatigue of the IGBT module is one of the failures of the wind power converter; however, the existing health condition monitoring method based on infrared thermography is difficult to be applied to the actual applications. In this paper, a health condition assessment method of the base-plate solder fatigue for the IGBT module is introduced based on the case temperature difference. First, according to the structure of the IGBT module, a 3D finite element model is established, and the junction and case temperatures at different delamination degrees are investigated. Second, for defining the degradation degree, identifying the steady-state process, and acquiring the case temperature, an assessment method of the base-plate solder fatigue based on the case temperature difference is established. Finally, taking the experiment of a practical wind turbine converter IGBT module as an example, the assessment process of base-plate solder of the IGBT module is demonstrated, and the results show that the proposed assessment method is correct and effective.