Migration Laws of Power System Out-of-Step Center with High-Penetration of Grid-Connected Photovoltaic

With the increased penetration of grid-connected photovoltaics, the mechanism of the out-of-step center needs careful investigations. To tackle that challenge, this paper proposes the impedance characteristics-based out-of-step center analysis. According to the photovoltaic power model and its different fault control strategies, the external characteristics of the PV power station is modelled by an equivalent dynamically changing negative impedance. Then the out-of-step center's position distribution can be derived and the migration laws are investigated. Theoretical analysis shows that as the PV output increases, the position distribution of the oscillation center shifts from one side of the line to its opposite side. Furthermore, in the process of gradually increasing photovoltaic output, the distribution range is gradually increased when the oscillation center position is away from the power supply. It is found that when the position is near the power supply, the distribution range is gradually reduced. In addition, the out-of-step center migrates in a direction away from the photovoltaic access point. Simulation results carried out on the IEEE 9-bus test system verify the correctness and effectiveness of the theoretical analysis.