Harmonic emissions of power electronic (PE) devices connected to transmission networks are introducing new and rising trends of harmonic distortion. Analyses, which focus on assessing the harmonic levels in PE-rich power networks of the future, are mostly based on digital simulations, which require accurate models of the power system and connected devices. The simulations are usually performed with the use of EMT models, resulting in long simulation times, or the use of over-simplified load-flow models. In this paper, we propose a methodology that can be used to define accurate frequency-domain simulation models of PE devices. The models are derived by frequency-dependent multi-parameter scanning. The resulting models can be employed for harmonic load-flow simulations in different network and PE-device operating conditions. They enable the assessment of the impact of frequency-dependent network-impedance characteristics and, moreover, the effect of cross-coupling between different frequency components. The analysis is focused on high-power, high-voltage power-electronic devices, which cannot be easily measured or analyzed for harmonic characteristics. Therefore, the methodology requires detailed EMT models of the devices, which are analyzed within different operating conditions. The accurate equivalent models of PE devices represent a crucial element within the context of harmonic emission studies in large transmission networks.

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