Central Topologies
Central inverter configurations are mainly used to interface large PV systems to the grid. The most common inverter topology found in practice is the 2L-VSI, composed of three half-bridge phase legs connected to a single dc link. The inverter operates below 1,000 V at the dc side (typically between 500 and 800 V), limited by the PV module’s insulation, which prevents larger strings. Grid con- nection is done through a low-frequency transformer to elevate the voltage al- ready within the collector of the power plant to reduce losses. More recently, the three-phase 3L-NPC and the three-phase 3L-T converter have been also used for this configuration, as shown in Figure 3. The characteristics, advantages, and disadvantages analyzed for the single-phase versions of these topologies for PV string systems also hold for the central inverter version.