An Improved Impedance Modeling Method of Grid-Tied Inverters With White-Box Property

Abstract

Small-signal modeling of grid-tied inverters (GTIs) is an essential work in stability analysis of GTIs-weak grid coupling system. Different from the previous small-signal modeling methods of GTIs with black-box property, a reduced-order modeling method has been proposed in this article to provide an impedance model with white-box property. First, impedance and admittance are seamlessly incorporated into the modeling method, where concepts of partial admittances, partial impedance, active power admittance, and reactive power admittance are especially introduced. As a result, simplified expressions of impedance model of GTIs have been obtained with physical interpretations of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> impedances strengthened. After that, dominated relationships between terms of GTI's impedance matrix and its internal physical parts are explicitly revealed to represent white-box property of the proposed impedance model. Specifically, the influence and effect mechanism of feedforward voltage compensation, current controller, phase lock loop, and power points ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_d</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_q</i> ) are emphasized based on the proposed impedance model. Finally, perturbations generated independent with PLL are injected into a hardware in-loop experiment platform, and impedance measurement results are provided to verify the conclusions drawn from the improved modeling method.