Enhanced Q-axis Voltage Integral Damping Control for Fast PLL-Synchronized Inverters in Weak Grids

The phase-locked loop (PLL) is a commonly used synchronization control method for grid-tied inverters. The PLL-synchronized inverters tend to have poor stability robustness with weak grid interconnections, especially when the PLL is designed with a high control bandwidth. To tackle this challenge, this paper proposes an enhanced q-axis voltage integral damping (Q-VID) control, which not only stabilizes PLL-synchronized inverters in weak grids but also lifts the restriction on PLL bandwidth. This superior feature enables inverters to operate stably in ultraweak grids and with a superior transient response. Experimental tests confirm the performance of the method with 400-Hz PLL bandwidth under a short circuit ratio of 1.28 of the grids.