Impact of phase-locked loop on stability of active damped LCL-filter-based grid-connected inverters with capacitor voltage feedback

Shichao Liu,Xiaoqiang Guo,Xiaoyu Wang

doi:10.1007/s40565-017-0302-3

Abstract

Active damped LCL-filter-based inverters have been widely used for grid-connected distributed generation (DG) systems. In weak grids, however, the phase-locked loop (PLL) dynamics may detrimentally affect the stability of grid-connected inverters due to interaction between the PLL and the controller. In order to solve the problem, the impact of PLL dynamics on small-signal stability is investigated for the active damped LCL-filtered grid-connected inverters with capacitor voltage feedback. The system closed-loop transfer function is established based on the Norton equivalent model by taking the PLL dynamics into account. Using an established model, the system stability boundary is identified from the viewpoint of PLL bandwidth and current regulator gain. The accuracy of the ranges of stability for the PLL bandwidth and current regulator gain is verified by both simulation and experimental results.

Highlights

LCL-filter-based grid-connected inverters have been widely discussed in [1,2,3,4]
In order to avoid the losses resulting from passive damping, capacitor-current feedback active damping was proposed in [8] to enhance the stability of LCL-type grid-connected inverters
Case 2 The inverter system is initially installed with a PI type current regulator and the active damping function, the damping function is removed at t = 0.25 s

Summary

Introduction

LCL-filter-based grid-connected inverters have been widely discussed in [1,2,3,4]. One of the important issues is their stability. [5] proposed a robust passive damping method for LLCL-filter-based grid-connected inverters, so as to minimize the effect of harmonic voltages on the grid. Another interesting filter was proposed in [6] for optimizing the system performance and stability. In order to avoid the losses resulting from passive damping, capacitor-current feedback active damping was proposed in [8] to enhance the stability of LCL-type grid-connected inverters. In [10], a virtual RC damping method was presented with extended selective harmonic compensation Note that these solutions are for voltage-source inverters.

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Results

Conclusion