Bidirectional Coupling of Electromagnetic and Temperature Fields for Power Electronic Transformer

The working conditions of the power electronic transformer (PET) are different to the typical power transformers due to its high switching frequency, high voltage and high current. To understand the behavior of the PETs, a Multiphysics model, which enables a bidirectional coupling of electromagnetic and temperature fields, needs to be considered during the design and operation. In this paper, a simulation-based study of power electronic transformer is carried out, especially for a bidirectional coupling of electromagnetic field and temperature distribution. Firstly, a model of transformer magnetic loss is developed. Based on this, a finite element method (FEM) model is then developed with a detailed structure of a transformer iron core and windings. Considering the influence of temperature on the material properties of transformer, the bidirectional coupling between the electromagnetic field and temperature field is established, and the parameters of electromagnetic field and temperature field are determined. The results of electromagnetic field and temperature field in transformer are analyzed by means of electromagnetic- thermal coupling analysis. The simulation results indicated that there is a significant difference between the simulation results of the temperature distribution of the core with or without the bidirectional coupling. The temperature of the hot spot of the transformer is increased by 7 °C when considering the bidirectional coupling. The bidirectional coupling model can be adopted for the design and asset management of the PETs with more reliability, and the temperature dependency of the material properties should be included in modelling PETs.