Abstract: With the increasing permeability of distributed generation，the grid becomes weaker and weaker. It

is very important to help the system achieve low voltage ride through（LVRT）when the grid voltage drops under

weak grid. Aiming at a series of problems such as over-current，voltage collapse and system oscillation caused by

the drop of grid voltage under weak grid，a control strategy of LVRT dual-mode switching for grid-connected

inverter was proposed. When the grid voltage was in the range of 0.7~1.0（per unit），the constant AC voltage

control mode was adopted；when the grid voltage was in the range of 0~0.7（per unit），the constant reactive current control mode was adopted. In addition，to solve the problem of system oscillation during voltage recovery，the active current ramp control was proposed during voltage recovery. Finally，dual-mode switching control strategy

was simulated in Matlab to verify the feasibility of the control strategy.

      Key words: weak grid；grid-connected inverter；low voltage ride through（LVRT）；constant AC voltage；control strategy