Output Impedance Modeling and Stability Prediction of Three-Phase Paralleled Inverters with Master-Slave Sharing Scheme Based on Terminal Characteristics of Individual Inverters

Paralleled inverters are widely employed as the power source in the AC distributed power system, whose output impedance and stability status are required in the impedance-based stability analysis of the whole system. This paper presents an output impedance model as well as a stability prediction method for three-phase paralleled inverters with master-slave sharing scheme. While the output impedance of three-phase paralleled inverters is generally modeled under synchronous reference frame (SRF), the terminal characteristics of individual inverters operating standalone are innovatively adopted in the proposed output impedance model, with no need for knowledge about inner parameters of the inverters. Furthermore, the stability criterion is derived with this model according to the generalized Nyquist criterion, where the stability of paralleled inverters can be predicted by investigating characteristic loci of two return ratios. Meanwhile, the terminal characteristics of individual inverters controlled under SRF is comprehensively modeled. Finally, the proposed output impedance model and stability criterion were experimentally verified.