Abstract: The virtual synchronous generator (VSG) not only simulates the swing characteristics of synchronous generator (SG), but also introduces the problem of low-frequency oscillations. Typically, smaller damping coefficients will suffice to provide effective damping for SG, whereas VSG requires larger damping coefficients to maintain stability, resulting in undesirable droop characteristics. Therefore, this paper first compares the impedance models and damping torque models of SG and VSG, and reveals the mechanism which SG provides positive damping through transient/subtransient impedance while VSG voltage outer loop generates negative damping. Thereby, this paper simulates the positive damping mechanism of SG and proposes a damping enhancement control (DEC) based on dynamic virtual impedance. Parameter tuning is achieved using the \mathcalH-infinity control theory. Compared to traditional methods, DEC effectively suppresses VSG low-frequency oscillations without altering droop characteristics. Finally, the effectiveness of the proposed control is verified by digital simulation based on Matlab/Simulink and hardware-in-the-loop simulation based on RT-LAB. The research results show that, compared with the traditional method, the proposed DEC can effectively suppress low-frequency oscillation without changing the droop characteristics of VSG, and has good robustness under strong/weak power grids.