Power electronic (PE) penetration in energy networks has been increasing rapidly in recent years due to the campaign to rely on distributed generation as a clean, sustainable energy source. This increase leads to new challenges and stability problems occurring because of the increase in the harmonic current injected into the power network. To study and address such issues, accurate and computationally efficient models are required. In this article, a Hammerstein–Wiener-based approach is proposed to develop black-box models for PE devices capable of capturing the devices’ harmonic characteristics. A novel method based on magnitude square coherence is also proposed to compare the results of different models in the frequency domain. The method is implemented in a simulation environment and was further tested and validated through laboratory measurements.