Analysing Harmonic Resonance Behaviour of a Grid-Connected PV Plant

The incorporation of inverter-based resources (IBR) into the power grid has led to new power quality challenges, including higher-order harmonics (supraharmonics), frequent transient voltages, power oscillations, etc. The supra-harmonics could damage assets that were originally designed to operate under power frequency. Furthermore, power quality standards have not yet set limits for higher-order harmonics. Moreover, the configuration of IBRs may result in higher-order resonance, potentially exacerbating these harmonic levels. Hence, in this paper, the effect of harmonics due to resonance characteristics of a grid-connected PV plant has been studied through simulations to understand the factors that affect forming resonance conditions at supra-harmonics levels. This study was extended by incorporating measured harmonic currents to understand the level of harmonic voltages that could appear at the transformer terminal under these resonance conditions. The results show the significance of considering the higher-order harmonics in Voltage Total Harmonic Distortion (Vthd) calculations, where existing limits by the standards could be violated at these resonance conditions.