Harmonic analysis of multi-parallel grid-connected inverters in distribution networks: Emission and immunity issues in the frequency range of 0-150 kHz

Abstract

Grid-connected inverters based on active front end technology are of the most important components in renewable energy systems. In large scale solar farms, a set of parallel grid-connected inverters are used to scale up the amount of injecting current to the network. Contrary to a single grid-connected inverter, each inverter based on its impedance consumes other inverters output current. Therefore, the main challenge in multi-parallel grid-connected inverters is to analyze the interaction between the inverters. The harmonic rejection ability of an inverter in a set of parallel grid-connected inverters differs from that of a single grid-connected inverter. In this paper, the harmonic behavior of a set of parallel grid-tied inverters equipped with LCL filter against the background voltage of the grid is investigated. The main aim of this paper is to find the harsh circumstances of the multi-parallel grid-connected inverters from the viewpoint of power quality. For this purpose, the electrical model of an inverter is initially derived. Then, the grid current is calculated based on the share of each inverter. The investigations are performed for two main case studies including identical and different types of inverters. The mentioned case studies are examined by using three different typical inverters to justify the achievements in this paper. Besides, for each case the effect of grid condition, i.e., the value of grid impedance is studied. Finally, using the grid current frequency response, the harmonic and power quality assessment of the inverters are analyzed.