Influence of DC/DC Stage on the Design of the Output Filter of the Inverter Stage in Two-Stage Grid-Connected PV Systems

One-stage and two-stage grid connected PV systems are compared in terms of compactness for both, 1000-V and 1500-V PV string voltage levels. Design space of the inverter's output filter is investigated for case when dc bus voltage is very well controlled to its minimum value and when it varies in the full operating range. Full multivariable optimization is conducted for the analyzed design spaces in order to investigate possible compensation of the increase of the total system volume caused by the addition of a dc/dc stage by achieving more compact inverter stage for better controlled dc bus voltage. It is concluded that for the same efficiency, filter designs with lower dc bus voltage can occupy approximate to 50% less volume compared to the case when dc bus varies in the full operating range. Hybrid, multilevel, partial power processing topologies that employ new classes of 650-V and 900-V WBG devices, that are already reported in the literature and that occupy approximate to 0.8 - 0.9 dm(3) for the design rated for 1500-V PV system and 20kW of the output power are very good candidates for a dc/dc stage that can control dc bus voltage at the input of the inverter stage and that can improve significantly compactness of the inverter stage and of the whole system. All the analysis and estimations are justified by comprehensive simulations of the 1500-V grid-connected PV inverter in PSIM package.