A Phase-Shifting MPPT Method to Mitigate Interharmonics from Cascaded H-Bridge PV Inverters

Interhamonics are an emerging issue in photo-voltaic (PV) systems. It has been revealed in the previous studies that the maximum power point tracking (MPPT) control is one of the responsibilities for interharmonic emissions. In cascaded H-bridge (CHB) PV inverters, if the MPPT perturbations of CHB cells are in-phase, the sum of the voltages of all CHB cells will oscillate with a higher amplitude, leading to large interharmonics in the grid. To address this, a phase-shifting MPPT method is proposed in this paper. By properly shifting the phase of the MPPT perturbation of each CHB cell, the oscillation of the equivalent total DC voltage can be effectively mitigated, and in turn, the interharmonics can be suppressed to a large extent. A 4-cell CHB PV inverter is examplified to demonstrate the proposed phase-shifting MPPT method, and n-cell CHB PV inverters have further been discussed regarding the implementation and control performances. The results have validated the effectiveness of the proposed method in terms of interharmonic suppression.