With the increase of nonlinear devices connected to the power grid, there are rich background harmonics in the grid voltage. These background harmonics are introduced into the grid current through the control loop of the grid-tied inverter, leading to a decrease in the quality of the grid current (Zhong et al. in IEEE J Emerg Select Top Power Electron 9:4236–4247, 2020; Lin et al. in IEEE Trans Power Electron 35:9784–9793, 2020). Although grid voltage feedforward can effectively solve this problem, in weak power grids, the voltage feedforward of the grid impedance voltage will be introduced into the PCC voltage measurement feedforward, which will reduce the phase margin of the grid-tied inverter and may lead to system instability (Cai et al. in IEEE Trans Industr Electron 67:7789–7797, 2019; Shen et al. in IEEE Trans Power Electron 23:1899–1906, 2008). Therefore, this chapter will study how to use differential feedforward of the grid voltage to improve the quality of the grid-tied inverter's grid-side current under severe grid voltage distortion. Through the study in this chapter, it can be proved that if differential feedforward can be applied reasonably when feeding back the grid voltage, it will be beneficial to improve the quality of the grid-tied inverter's grid-side current.