Mitigation of Interharmonics in PV Systems With Maximum Power Point Tracking Modification

Abstract

Interharmonics are emerging power quality challenges in grid-connected photovoltaic (PV) systems. Previous studies and field measurements have confirmed the evidence of interharmonic emission from PV inverters, where the maximum power point tracking (MPPT) is one of the main causes for interharmonics. In that regard, the MPPT parameters such as their sampling rate has a strong impact on the interharmonic characteristic of the PV system. In general, there is a trade-off between the interharmonic emission and the MPPT performance when selecting the sampling rate of the MPPT algorithm. More specifically, employing a faster MPPT sampling rate will improve the MPPT efficiency, but it will also increase the interharmonic emission level. To solve this issue, a new mitigating solution for interharmonics in PV systems is proposed in this paper. The proposed method modifies the MPPT algorithm in a way to randomly select the sampling rate between the fast and the slow value. By doing so, the interharmonics in the output current can be effectively reduced due to the distribution of the frequency spectrum. On the other hand, the MPPT performance of the proposed method can be maintained similar to the case when employing a fast MPPT sampling rate. The effectiveness of the proposed interharmonic mitigation has been validated experimentally on a single-phase grid-connected PV system.