The　inverters　controlled　by　virtual　synchronous　generator　(VSG)　can　supply　inertia　and　damping,　and　participate　in　the　regulation　of　voltage　and　frequency.　But　they　face　the　risk　of　overcurrent　when　grid　voltage　sags　occur.　Although　existing　literatures　have　applied　virtual　impedance　to　VSG,　aiming　at　suppressing　overcurrent,　how　to　meet　the　requirements　for　the　inverters　to　output　sufficient　reactive　current　to　the　power　grid　is　rarely　available　in　the　literatures.　This　paper　proposes　a　low　voltage　ride-through　(LVRT)　strategy　for　VSG　based　on　the　quantitative　design　of　virtual　impedance.　When　the　grid　voltage　sags,　the　strategy　firstly　freezes　the　power　loop,　and　then　the　virtual　impedance　calculated　according　to　the　proposed　method　is　added　to　ensure　stable　operation.　After　the　grid　voltage　is　restored,　the　reactive　power　loop　is　returned　to　the　normal　control　mode,　and　a　new　active　power　reference　is　set　while　the　virtual　recovery　resistance　is　added　to　avoid　the　overcurrent.　The　system　recovers　to　the　normal　mode　gradually　with　the　virtual　recovery　resistance　decreasing　to　zero.　Finally,　the　correctness　of　the　virtual　impedance　and　the　feasibility　of　the　proposed　LVRT　strategy　are　proved　through　the　hardware-in-the-loop　experiments.　©　2022,　High　Voltage　Engineering　Editorial　Department　of　CEPRI.　All　right　reserved.