Suppression of Low- and High-Frequency Instabilities and Grid-Induced Disturbances in Distributed Generation Inverters

This paper presents a robust current control scheme for inductor-capacitor-inductor (LCL)-filtered distributed generation (DG) inverters featuring effective suppression of low- and high-frequency instabilities and grid-induced distortion and disturbances. The conceptual design of the proposed control scheme is to maximize the disturbance rejection performance against grid disturbances and parametric uncertainties, and minimize the coupling among active damping, disturbance rejection, and tracking controllers. First, a simple and robust active damping controller is realized by drooping the inverter control voltage with the capacitor current. Second, the augmented damped dynamics is used to design a robust controller, which is composed of a tracking controller, dynamic grid-disturbance rejection controller, and uncertainty rejection controller. The tracking controller is designed to yield deadbeat control performance to maximize the dynamic performance of the converter. The grid-disturbance rejection controller is designed to provide a base-line of grid-induced dynamics within the closed-loop system as an internal model; therefore, effective mitigation of grid-induced distortion can be achieved without a priori knowledge of the frequency modes to be eliminated. The uncertainty rejection controller is designed to reject voltage disturbances associated with parameter variation and imperfect compensation of the grid-disturbance-rejection controller. Theoretical analysis and comparative test results are presented to demonstrate the effectiveness of the proposed control scheme.