Reducing the Dc-Link Capacitance for Grid-Connected Solar Inverters with Shunt Power Decoupling Circuit

Single phase grid-tied inverters are remarkably increasing in low-power applications such as residential and industrial power supplies. In the single phase system, the inherent ripple power at twice the line frequency results in undesirable low-frequency ripple in the dc-link voltage and output ac current. This issue can be eased through the installation of bulky electrolytic capacitors in the dc link. However, such passive filtering approach may inevitably lead to limited system lifetime and reliability. To overcome these problems, auxiliary power decoupling methods are used to reduce the size of the electrolytic capacitor and replace it with film capacitor. In this paper, By introducing a shunt switching compensator (SSC) and exploiting instantaneous power theory (pq theory), the size of the required capacitance remarkably decreased.The proposed controlling system, based on the modified pq theory and single-phase modeling, was similar to a three-phase unbalanced system regarding the structure. The system simulation was according to the 3Kw photovoltaic system used at the Birjand University. The simulation results verify the proposed power decoupling technique. At the end, a cost comparison between the proposed structure and prevalent structure is also done.