Multi-Time Scale and Electro-Thermal Model Based Reliability and Efficiency Evaluations for Resonant Converter

This paper presents a modeling method to build the complete and accurate multi-time scale model for LLC resonant converter. Three switching types including zero voltage switching (ZVS), incomplete ZVS (i-ZVS) and hard switching (HS) are considered as switching transient in nano second time scale, as well as nine steady-state operation modes representing the LLC resonant converter in micro second time scale. The key waveforms are verified by LTspice. Meanwhile, the mission profile in second time level is considered to evaluate the thermal performance. Then combine the electrical model with the thermal network of switching device, an electro-thermal model for LLC is developed, in which electro-thermal coupling is considered by modelling temperature dependency of power device. Based on the electro-thermal model, the LLC resonant converter's efficiency and reliability (lifetime) evaluations are performed. Finally, a case study is presented to demonstrate the application of the proposed method. The results show that the two different LLC design parameters have close efficiency performance, while the reliability performances under the same mission profile are quite different. It can be concluded that the efficiency and reliability based multi-objective optimization for LLC converter is feasible by using the proposed model to further improve the converter performance.