Interaction resonance mechanism of the parallel-inverter system containing multiple types of inverters

Almost all existing relevant literatures are focused on the multi-inverter system that only contains one type of inverter. Till now, the interactions in multi-inverter system consisting of polytype inverters have been not investigated systematically. To fill this gap, the paper is aimed at the stability study of the generic system containing multiple types of inverters. The mathematic model of interactions between different types of inverters as well as between the inverter and the power grid are divided into the admittance network and the excitation source. Based on the division stabilities of those interactions are investigated by root locus and a commonly used stability criterion is proposed for the multi-inverter system. To guarantee the system stable, the following two conditions should be satisfied: (a) the admittance network is stable; (b) any two inverters don't have the same unstable poles. The stability of the interaction between the inverter and the power grid is only depended on the criterion (a), whereas the stability of the interaction between different inverters is determined by both conditions. The theoretical analysis is verified by experimental results.