Active-Capacitor for Power Decoupling in Single-Phase Grid-Connected Converters

In power conversion systems connected to the single-phase power grid it is usual the utilization of electrolytic capacitors to handle with low-frequency power ripple. However, such capacitors have a limited lifetime. Thereby, this paper proposes the application of an active power decoupling cell (PDC) connected to the dc bus of a two-stage photovoltaic microinverter, operating as an active-capacitor. The purpose of the PDC is to shift the power ripple from the dc bus to a decoupling capacitor, whose voltage ripple may oscillate more than the voltage of the main bus, allowing the use of low capacitance and high lifetime capacitors. Thus, the paper presents an analysis of the active-capacitor based on PDC and a new control structure to meet all the aforementioned objectives. Experimental results obtained from the prototype of a photovoltaic microinverter with PDC validate the performance of the active-capacitor.