Abstract：The grid frequently exhibits weak grid characteristics because the impedance fluctuation range of

the collector network is broad in high permeability distributed generation system. The coupling relationship

between the phase-locked loop and the grid impedance leads to desynchronizing between the grid-following（GFL）converter and grid，which seriously threatens the stability of the system. However，the slow power response of gridforming（GFM）converter is contradictory to the maximum power point tracking of source side，and the economy is poor. Consequently，in order to increase the grid-connected reliability of the system，some units are necessary to be configured flexibly，which will switch to the GFM mode. Concentrating on the grid-connected converters，a dualmode adaptive flexible switching control strategy for distributed energy was proposed considering friendly interaction between grid and converters to maximize the utilization of new energy under the premise of system stability. The grid impedance identification algorithm based on non-characteristic harmonic injection was applied to sense the power grid strength，and the control strategy was adaptively switched according to the strength of the grid.Under the circumstance of robust grid，the constant power control method was adopted，which can quickly respond to the maximum power point instruction and improve the utilization rate of renewable energy. During the weak grid，converters flexibly switch to the virtual synchronous generator（VSG）control strategy to enhance inertia and damping support capabilities，realizing the friendly interaction between converters and grid. The proposed strategy enhances the robustness of grid-connected converters during the variation of grid strength，ensuring the stable operation of the system. The effectiveness of the proposed dual-mode control strategy was validated by PLECS simulation.

      Key words：identification of grid impedance parameters；adaptive dual-mode switching；virtual synchronous

generator（VSG）