Hardware Demonstration of Weak Grid Oscillations for IBR with DC-Link Voltage Control

Inverter-based resources (IBRs) may exhibit oscillations when integrated in a weak grid. In this paper, a hardware testbed is built to demonstrate weak grid oscillations for an IBR with dc-link voltage control. Both electromagnetic transient (EMT) simulation and experimental results illustrate that a higher phase-locked-loop (PLL) bandwidth leads to oscillations at about18-Hz, while a lower bandwidth PLL leads to low-frequency oscillations at 2.2-Hz or 4.5-Hz. An analytical model is developed to investigate the effects of PLL bandwidth on stability performance. Analysis results based on a two-block diagram’s Bode plots show that the lower-frequency oscillation is caused by operation condition and low-bandwidth outer controls, while the high-frequency oscillation is caused by PLL.