Purpose - The frequency simulation and optimisation of electromagnetic compatibility (EMC) filter is often computation time consuming. Design/Methodology/approach -The paper proposes an approach for easy and fast modelling and optimization of power electronics structures. It focuses on the EMC filter design. To achieve this task time simulation, FFT and automatic frequency modelling are combined. Findings -An automatic frequency modelling is proposed and also gives automatically the model gradients. Therefore, the model can be used to optimize the EMC filter, but also can help in choosing its topology. Several optimization algorithms are used and compared. Research limitations/implications -The power electronics load is supposed to be a set of predefined harmonic sources, obtained by time simulation + FFT before the optimisation process. Practical implications -The aid to build the frequency model, and their automatic translation for sizing by optimisation allow to design and to compare rapidly several structures or modelling hypothesis on the parasitic elements and circuit imperfections. Originality/value - The frequency model is automatically generated, and sizing criteria on the component (e.g. inductors, capacitor) can be added in an analytical form, for example, to deal with volume or mass criteria.