Abstract: Under the background of large-scale renewables being connected to the grid, voltage source converters have been widely used. In order to explore the power control stability problem in weak grids, the influences of the converter's reactive power support capability on the static stability limit of the system under different outer loop control strategies are compared and analyzed. Based on the relationship between key electrical quantities, this paper explores the instability mechanism of active power control, and puts forward the impact index of active power control changes on reactive power control. The conclusion is drawn that the PQ control can better adapt to changing primary energy output scenarios, and has strong anti-interference ability in the face of active power output changes; however, the PV control is more suitable for the weak grids due to its higher static stability limit. In addition, in order to deal with the scenario of renewable energy fluctuations, an improved control strategy is proposed. This strategy has high static stability limit and fast response speed of reactive power control, and its anti-interference ability is improved compared with that by the PV control. Finally, the results are verified by time domain simulation.