Analytical calculation of the PV converter efficiency curve at non-unity power factors

This paper presents a new mathematical model for the power losses of the PV inverters for various PFs using the datasheet of the PV inverter manufacturer and basic knowledge of power electronics and semi-conductors. The mathematical model uses as parameters the input and output power of the inverter, the PF (inductive or capacitive), which the inverter operates at, and the efficiency curve of the inverter formed at unity PF using an already derived analytical expression. The effectiveness of the analytical calculation is validated through measurements of eight 17kVA SMA Sunny TriPower PV converters that are installed in a 1MWp PV installation in Trikala, Greece. The efficiency of those converters has been measured in August 2016 and concerns 8 different PFs: capacitive 0.8, 0.85, 0.9, 0.95 and inductive 0.8, 0.85, 0.9, 0.95. The good convergence with the efficiency curves taken by measurements and simulations proves that the mathematical model is valid for every PF down to 0.8 (over and under excitation). Smaller PFs are not examined since they lead to unreasonably large inverter oversizing.