Abstract: Under weak grid conditions,the digital control delay will cause the virtual impedance to show negative resistance and cannot achieve the damping effect. Therefore,the grid-connected inverter cannot operate stably under the change of grid impedance,and its robustness is seriously threatened. In response to the above problems,this paper proposes a bilinear positive feedback active damping strategy to expand the effective damping zone of the system. To save the cost the sensors,it is optimized as a capacitive voltage positive feedback active damping strategy,adding appropriate positive feedback damping links at both ends of the capacitor voltage,so that the effective damping area of the system is expanded to（0,0.477fs）. The analysis results show that this strategy makes the grid-connected inverter always have good robustness under weak grid conditions,and the system has good stability even when the resonance frequency is equal to 1/6 of the sampling frequency. Finally,a three-phase LCL grid-connected inverter is taken as an example to carry out experimental verification,and the experimental results verify the correctness of the strategy.