Details

High-proportion inverter-type distributed energy grid integration introduces harmonics, power fluctuations, and three-phase imbalance, affecting the electromagnetic-thermal performance and lifespan of distribution transformers. Existing research lacks systematic electromagnetic-thermal coupling models and multi-scenario assessments considering different harmonic levels, permeability, filter types, imbalance, and power transients under real-world grid conditions. Therefore, this paper establishes MATLAB/Simulink models of a 20/0.4kV distribution transformer under various operating conditions (THD 2%–10%, permeability 50%–100%, L/LCL filter, imbalance 5%–15%, cloud-induced power step), and imports the output current into a COMSOL three-dimensional finite element electromagnetic-thermal coupling model to calculate losses, temperature rise, and hotspot locations. The results show that compared to no filter, the LCL filter can reduce the hotspot temperature by 23°C. When the permeability increases to 100% (THD=10%), the hotspot temperature rises from 85°C to 118°C, approaching the insulation limit of 120°C. A sudden power drop (100% → 20%) can generate a 30°C thermal shock, with a cooling rate of 60°C/s; a 15% imbalance can cause a 20°C temperature difference between phases. To ensure safe operation, the total inverter power should not exceed 80kW (without a filter) or 100kW (with an LCL filter); it is recommended to use an LCL filter (THD ≤ 2%), control the imbalance within 10%, and employ slow power control to reduce thermal shock.