A Series Interharmonic Filter for Cascaded H-bridge PV Inverters

Interharmonics have become one of the challenging issues in photovoltaic (PV) systems. One of the reasons for interharmonic emissions is the maximum power point tracking (MPPT) control. In cascaded H-bridge (CHB) PV inverters, due to the potential superposition of the MPPT perturbations of individual PV cells, a higher oscillation may appear in the equivalent total DC voltage, leading to large interharmonics in the grid. To mitigate the interharmonics from CHB PV inverters, a series interharmonic filter is proposed in this paper, which employs a series H-bridge cell as an active filter. With the proposed control, the equivalent DC voltage can be maintained oscillation-free, thereby suppressing the interharmonics. In practice, the interharmonic filter can be either an additional unit, or a redundant cell in the cascaded PV converter. Simulations and experimental results have validated the effectiveness of the proposed solution.