Large-Signal Stability Analysis of AC Micro-Grid Under Quadratic Droop Control

Quadratic droop control is an innovative control strategy for power network, aiming to respect the inherently quadratic nature of reactive power flow. However, the system stability under quadratic droop control has not been addressed completely so far. This paper mainly focuses on the large-signal stability analysis of the AC network under quadratic droop control. We firstly analyze the stability of each equilibrium, it is concluded that the high-voltage equilibrium is stable as long as it exists while all low-voltage equilibria are unstable. Secondly, an analytical energy function for the system under quadratic droop control is established. It is proved that the high-voltage equilibrium is the local minimum of the proposed energy function while all the low-voltage equilibria are saddle points. Thirdly, to estimate the region of attraction (ROA) of the high-voltage equilibrium, an innovative method based on the analytical energy function is proposed. Comparing with the closest UEP method, the proposed ROA method significantly reduce the amount of computations. Simulation results verify the proposed theorems.