Common mode EMI noise modeling and prediction for a three-phase, three-level, grid tied photovoltaic inverter

Recently, transformerless photovoltaic (PV) systems become popular in industrial applications due to the demands of high efficiency and low cost inverters. However, the leakage ground current and common mode (CM) electromagnetic interference (EMI) noise becomes significant so they need to be addressed. In solving the problems, a simple CM noise model is widely used. However, the model does not include information on how the noise source will be influenced by modulation schemes and how the propagation path will affect the CM noise spectrum. This paper intends to improve the model. A complete CM noise modeling and prediction method is proposed for the three-phase three-level inverter. Modeling process starts from building a simple CM noise model for the inverter and is then improved by two steps. Step one is for CM noise source modeling and the step two is for noise propagation path modeling. For noise source modeling, the influence of two different modulation schemes on the generation of CM noise is discussed and simulation results are illustrated. For the noise path modeling, scattering parameters is used for parasitic parameter extraction. A circuit model for the prediction of the CM noise spectrum is then developed and an inverter prototype is built for the experimental verification of the proposed technique. The proposed modeling and prediction technique is validated by the comparison between the measured and the simulated CM EMI noise spectra.