Thermal Modeling Method With Identified Thermal Parameters and Core Loss Model for High-Voltage High-Power High-Frequency Transformers With Racetrack Spiral Windings

Power electronic transformers are widely used in railway traction and electric vehicles. High-voltage, high-power, high-frequency transformers (H³FTs) are key magnetic components of power electronic transformers. Efficient and accurate thermal prediction is important for the optimal design, condition monitoring, and thermal management of high-frequency transformers. This paper proposes a multi-scale boundary-coupled thermal modeling method with identified thermal parameters and a core loss model for H³FTs with racetrack spiral windings. The proposed method exhibits satisfactory accuracy and efficiency. A 2D FEM with the effective winding length for the racetrack spiral winding and a 3D FEM for the remaining region of the H³FT are coupled by their boundary temperatures to achieve the efficient simulation of the 3D thermal field of H³FTs. The 2D FEM reduces the number of FEM nodes required for the thin wires of the winding, which account for a significant proportion of the total number of FEM nodes in a detailed 3D FEM. A sensitivity analysis is conducted for the multi-scale boundary-coupled FEMs to understand the influence of the effective winding length, thermal parameters, and losses on the thermal analysis results. Furthermore, to enhance the thermal modeling accuracy, the uncertain thermal parameters and core loss model, which are influenced by process factors and are difficult to measure directly, are identified based on the surface and internal temperatures of the H³FT under short-circuit and open-circuit thermal tests, respectively. The identification is formulated as a single-objective optimization problem, which is solved by the particle swarm optimization algorithm. The experimental results for a 10 kV H³FT under practical operating conditions demonstrate the satisfactory accuracy and efficiency of the proposed method.