Inherent Interaction Analysis for Harmonic Oscillations in the Multi-Paralleled Grid-Connected Inverter System Using a Sum Type Criterion: Global Admittance (GA)

With the extensive use of power electronics converters, harmonic oscillation issues in the multi-paralleled grid-connected inverter system have drawn much attention. Apart from the stability analysis using the impedance-based stability analysis method, the interaction analysis is aimed at revealing the changing process of the system state under the variation of some parameters such as the grid impendence, the number of grid-connected inverters and the control parameter of the inverter current control, etc. In this paper, after comparing the ratio type stability criterion and the sum type stability criterion, the interaction analysis using global admittance is presented in two frequency-domain dimensions. It shows that the harmonic instability depends on both the imaginary part of global admittance which determines the appearance of the resonance point and the real part of global admittance which reflects the property of such resonance point. The essence of this approach is to reveal the appearance of the resonance point and its influence on the system stability. The inherent changing rules of the resonance point are illustrated in the following typical occasions: different grid impendence, different number of grid-connected inverters and different control parameters of the current control loop. Finally, detailed simulations and experimental results validate the effectiveness of the proposed approach.