In the scenario where a renewable power generation (RPG) system disconnected from the power grid and directly supplies power to Islanded loads, the grid-following (GFL) control based on phase-locked loop (PLL) is prone to frequency unstable. Although the grid-forming (GFM) control can establish a stable frequency in islanded operation mode, multiple parallel GFM converters may cause large circulating currents due to the voltage deviations, deteriorating current instability of RPG. In this paper, a novel GFM method based on the PLL frequency limitation is proposed, by which the converter can establish a stable frequency reference, enabling other converters to follow it. But unlike strong grids, the terminal voltage of each converter under islanded conditions varies with current injection, incorrect current references lead to the absence of stable equilibrium point (SEP) and trigger loss of synchronization (LOS). Therefore, the existence of the SEP is further analyzed, and a current injection strategy based on the load impedance angle is adopted to ensure the stable operation. Finally, simulations verify the correctness and effectiveness of the proposed method.