Analysis and Modeling of Interharmonics From Grid-Connected Photovoltaic Systems

Abstract

The industry of solar photovoltaic (PV) energy and its application is still booming to enhance the sustainability of the society. When PV systems are connected to the grid, challenging issues should be addressed. One of the challenges is related to interharmonics in PV systems, especially with a large-scale adoption of PV systems. However, the origins of interharmonics remain unclear, although the impact of interhamonics has been reported in the literature. Thus, this paper explores the generation mechanisms of interharmonics in PV systems and the characteristics. The exploration reveals that the perturbation from the maximum power point tracking (MPPT) algorithm is one of the origins of interharmonics appearing in the grid current. Accordingly, the MPPT controller parameters such as the perturbation step size and the sampling rate have an inevitable impact on the interharmonic characteristics. Furthermore, an approach to characterize the interharmonics in the grid current is proposed. With the proposed model, interharmonics can be predicted according to the designed controller parameters in terms of frequencies and amplitudes. Experimental tests are performed on a single-phase grid-connected PV system. The results are in a close agreement with the analysis and, thus, validate the effectiveness of the proposed model. Index Terms-Interharmonics, inverters, maximum power point tracking (MPPT), modeling, photovoltaic (PV) systems, power quality. I. INTRODUCTIONI N RECENT years, more and more photovoltaic (PV) systems have been installed and connected to the grid due to the increasing demand of greener and more sustainable energy systems. However, at the same time, massive connections of PV systems to the grid bring several challenges, e.g., power quality and grid stability issues [1]-[6]. It has been reported that the

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“…In general, harmonics are generated by inverters due to the pulse width modulation, nonideal switching behaviors of the power devices and also the interaction among different controllers [31]- [33]. When the inverter works at the gridconnected mode, the harmonic currents produced by the inverter will flow out into the low-impedance grid to produce only a very small amount of distortion in the PCC voltage.…”

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“…To address this issue, a model to predict the interharmonic characteristic in PV systems has been proposed in [8], where the results from the interharmonic model agree well with the field observation in [6]. It has been demonstrated in [8] that the interharmonic characteristic is strongly dependent on the MPPT algorithm parameters such as the perturbation step-size v step and the sampling rate f MPPT . As discussed in [8], the interharmonic emission can be effectively alleviated by reducing the sampling rate of the MPPT algorithm.…”

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“…Although it is known that inter-harmonics are produced by non-linear loads, there are a few studies which focus on their creation mechanism [21][22][23][24]. According to these works, harmonic sources can be classified in four sub-concepts.…”