Impedance norton modelling of utility-interactive multilevel photovoltaic systems

This paper presents the Norton equivalence model of a multilevel photovoltaic (PV) system based on the well-known T-type Neutral-Point-Clamped inverter (3L-TNPC) connected to the grid by using a LCL filter. The contribution of this work is the development of a current harmonic injection model of this inverter operating under a polluted voltage grid for harmonic analysis. Furthermore, overall filtering design restriction due to impedance limits based on current and voltage standards are considered. The proposed impedance Norton model is compared with the switching model by using comprehensively simulations showing good match between both models.