Contribuição ao estudo do inversor multinível em cascata aplicado a sistemas fotovoltaicos sujeitos a sombreamentos parciais.

Abstract

This work presents a theoretical and experimental study about Cascaded Cell Multilevel Inverter (CCMLI) as the power interface between a set of photovoltaic (PV) panels and the commercial grid. The choice for this topology results from the higher voltage quality synthesized by the multilevel system, combined with the superior control modularity obtained by the proposed data processing methodology. Although this kind of converter can be applied at any power level and phase number, the analysis inside this thesis is restricted to single-phase small power systems, as typically found in residences or in other distributed microgeneration environments. In these places, usually located in urban areas, the set of panels can be exposed to partial shading with short or long duration, differences in sunlight relative angle orientation or differences between panel’s characteristics (panels mismatches), causing asymmetric power distribution between system elements. In this text, such asymmetry is compensated on power switches command structure, by acting on modulation controller of each converter cell. The average reference voltage at each DC link is calculated by a MPPT algorithm which seeks the highest value of average power provided by the PV source. Obtaining the maximized power in each cell carries the entire system to operate on global maximum power point. An approach to dynamic operation of grid connected converter is also presented, using simulation environments and experimental results from a 9 levels prototype, developed according to the suggested control methodology. These results confirms the expected voltage quality at inverter output, as well his capability to adapt readily to irradiation level changes over the panels.