Analysis and Experimental Characterization of a Large-Bandwidth Triple-Loop Controller for Grid-Tied Inverters

This paper analyzes a large-bandwidth, triple-loop controller designed for single-phase, grid-tied, and voltage-source inverters with LCL output filter. The inner control loops regulate the inverter output current and the filter capacitor voltage, respectively, while the third, outer one regulates the current injected into the grid. The inner loops are given deadbeat type regulators, whose minimum response delay allows the third loop to achieve a relatively large regulation bandwidth. This organization provides several benefits, including a regulated local ac voltage, a large-bandwidth control of the power flowing to the grid, and a good robustness against different types of commonly encountered grid perturbations. In particular, grid voltage harmonic pollution, amplitude, and frequency fluctuations or connection impedance parameter variations can be tolerated without incurring into instability or unacceptable performance degradation. Besides, the proposed controller is inherently able to guarantee seamless transitions between grid-tied and islanded operation, showing good potential for application to nano- and microgrid utility interface converters.