A hybrid random parameters modification to MPPT algorithm to mitigate interharmonics from single-phase grid-connected PV systems

Abstract

As the on-grid photovoltaic (PV) system's penetration level increases, the utility grid power quality (PQ) becomes a vital emerging issue to spot the lights on. The recent studies confirmed that one source of interharmonics emission from PV inverters is the maximum power point tracking (MPPT) algorithms. Following this issue, a strong relationship has been found between the interharmonics generating characteristics and the MPPT parameters, such as the sampling rate and perturbation step size. Utilizing a big step size and fast sampling rate will enhance the tracking performance but will raise the level of interharmonics injected into the grid and lower the overall efficiency. Therefore, there is a trade-off between MPPT parameters, efficiency, and interharmonics characteristics in PV systems. To alleviate mentioned issue, this paper investigates the mechanism of interharmonics generation and emission under different power operating conditions. Accordingly, a new mitigation technique is presented for interharmonics generation in grid-connected PV systems. The proposed method is based on modifying the MPPT algorithm in a way that maintains its performance characteristic while effectively minimizing the generated interharmonics by a random selection of big or small perturbation step sizes and fast or slow sampling rate, respectively. Thereby, the frequency spectrum distribution is modified, and interharmonics peaks are reduced in the output injected current to the grid by 27 % compared to the other conventional and modified perturb and observe (P&O) MPPT algorithms found in the literature. The effectiveness of the proposed method is verified by simulation studies on a single-phase grid-connected PV system.