This project is focused on the design of reliable yet efficient thermal models underpinning an optimal design framework for power electronic converters. Due to the high number of times these models must be evaluated during the optimisation process, they are required to be of low computational cost (so-called ‘optimisable’). These models are intended to be efficient representations of the complex thermal management systems found in real power converters. Accuracy is to be progressively increased by relaxing simplifying assumptions whilst ensuring a reasonable computational cost is maintained. Computational efficiency is required so that it is feasible to embed these models in the optimal design framework of the converter, whilst accuracy is paramount because thermal constraints are typically active and therefore drive the design. In order to assess their accuracy, the optimisable models will be ‘validated’ against computationally intensive simulations performed with commercial software.