Power Asymmetry Characteristic and Stability Analysis of Grid-Connected Inverter under Weak Grid Condition

The active and reactive power of grid-connected inverter (GCI) under weak grid condition supports the operation at the same time, so its operating characteristic under different power factors are particularly important. Therefore, from the perspective of system damping ratio, the small signal models of GCI under three control methods are respectively constructed. It is found that when the current vector is a circular trajectory, its damping ratio characteristic is a non-circular trajectory, namely stability ‘asymmetry’ phenomenon of active and reactive power; Based on that, it is found that when power factor changes from -90°-0°-90°, the participation factor of the PLL angle increases first and then decreases, and vice versa for VSG angle. And compared with current-loop vector control and VSG control, the power ‘asymmetry’ of the double-loop vector control strategy is the most obvious. Finally, the accuracy of the analysis is verified by Matlab simulation and experimental platform.