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Purely inductive ripple power storage for improved lifetime in solar photovoltaic micro-inverter topology

Abstract:

In a solar photovoltaic (PV) system, decoupling of power ripple is necessary in order to maximize the energy harvest because the power flowing to the grid is time varying while the power extracted from the photovoltaic panel needs to be maintained constant. This necessitates the requirement of energy storage elements between the input and output to decouple the unbalance of power. The location of the decoupling element can be either at the PV-side or the AC-side. The traditionally used energy storage element is the electrolytic capacitor. Due to its fast degradation, it is often replaced by film capacitors with active decoupling schemes that perform better at higher temperatures with less degradation, however at significantly higher cost. From an economic perspective, both electrolytic and film capacitors have similar lifetimes, which are substantially lower than the typical warranty of the solar module (20-25 years) though. An inductor, in contrast, is an energy storage element with aging of less than 0.5 percentage over a 20-year lifecycle. Further, the reduced temperature drift compared to a capacitor makes it a highly suitable candidate for storage of power ripple in solar photovoltaic power converters. This paper demonstrates a proof-of-concept decoupling scheme using an inductor as the energy storage element at the PV-side of a DC-AC single stage power converter.