Investigation of Parallel Active Filters’ Limitations for Power Decoupling on Single-Stage/Single-Phase Microinverters

During the last decade, microinverters have gained a considerable share in residential photovoltaic (PV) systems' market. However, in order to be accepted by the marketplace, the reliability of microinverters must be comparable with that of traditional PV string and multistring inverters. A typical reliability issue that these systems experience, particularly in single-stage/single-phase topologies, is the presence of a large electrolytic capacitor for decoupling the power pulsation caused by the single-phase power generation. For this reason, several decoupling topologies have been introduced, which manage to decouple the power pulsation by using high reliability components, i.e., small capacitors (usually film ones) and power MOSFET transistors. Among these topologies, the family of bidirectional buck-boost-based parallel active filter (PAF) converters has been highlighted due to their minimum counterparts and their robust design. The main contribution of this paper is the unified theoretical analysis and the investigation of the operational limitations of this family of PAF converters, as well as the introduction of a control technique, which overcomes those restrictions. Simulation and experimental results validate the derived PAF family analysis and also prove the effectiveness of the introduced control technique.