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

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.

Stability analysis of a PMSG based Virtual Synchronous Machine

“…It can be observed that for Kp ≥ 3, the VSM becomes unstable. This corroborates earlier works [25], [26] which stipulate that, for stable operation in islanded operation PLL bandwidth should be small.…”

“…In this scheme, the PLL is used in both grid and islanded modes [19]. The PLL dynamics may be neglected for stiff grids, however they play a crucial role on the system stability for weak grids and islanded operation [25], [26]. The synchronously-rotating-frame (SRF) PLL is implemented in this study [19].…”

“…The PLL bandwidth has a dominant effect on the stability of the VSM. Although a fast PLL is required for grid synchronization, it can greatly reduce stability, increase phase tracking error and lead to poor harmonics filtering [26], [35]. Hence, a compromise is required between a fast synchronizing PLL and a desirable dynamic performance.…”

Design and Control of Virtual Synchronous Machine Based Energy Systems

“…The PLL tracks the phase angle of the filter capacitor voltage V c (Fig. 3.1) to achieve synchronization with the grid [165], [166]. This ensures the voltage magnitude V is locked with the d -axis, V cd ≈ 1 pu and V cq ≈ 0 [167].…”

“…In this scheme, the PLL is used in both grid-connected and islanded modes [86]. The PLL dynamics may be neglected for stiff grids, however, it plays a crucial role on the system stability for weak grids and in islanded operation [165], [168]. The synchronously-rotating-frame (SRF) PLL is implemented in this study [86].…”