Analysis of harmonic interactions between DG inverters and polluted grids

This paper proposes an impedance-based analytical method for modeling and estimation of harmonic interactions between the grid and DG inverters. The root cause of harmonic interaction/resonance problems is introduced. Starting with a simple PI regulator controlled inverter, the output impedance of the converter is modeled and proven by simulations to be operative for forecasting harmonic interactions. Moreover, another test case based on an inverter with multiple PR controllers is designed and modeled to clarify impedance-based design and harmonic interaction analysis. Assuming the impedance models of individual inverters and local loads within a distribution grid are knowledgeable, especially in the case of new grids under construction, harmonic interactions between the grid and a certain number of DG inverters can be preliminarily estimated.