Interharmonics Reduction in Photovoltaic Systems with Random Sampling MPPT Technique

An increasing penetration level of grid-connected Photovoltaic (PV) systems raises a concern regarding power quality problem, in particularly, interharmonics. According to previous research, the perturbation from the Maximum Power Point Tracking (MPPT) algorithm is one of the main root-cause of interharmonic emission in PV systems. In general, the interharmonic characteristics are strongly dependent on the sampling rate of the MPPT algorithm. A slow sampling rate of the MPPT algorithm can minimize the interharmonic emission but it results in poor tracking performance of the MPPT algorithm. Thus, there is a trade-off between the interharmonic emission and the MPPT efficiency when selecting the MPPT sampling rate. To overcome this problem, a new MPPT technique implemented with a random sampling rate is proposed in this paper. The proposed method randomly selects the MPPT algorithm sampling rate during each perturbation. This method is simple to be implemented but results in a significant reduction in the interharmonics of the output current and, at the same time, a high MPPT efficiency. The effectiveness of the proposed method has been validated experimentally with a single-phase grid-connected PV system. Moreover, the effect of interharmonic cancellation when implementing the proposed random sampling MPPT technique with parallel-connected PV inverters has also been demonstrated.