The fault of unbalance in the power grid is sometimes happened under certain conditions

and the three-phase grid connected inverter will be affected

leading to high harmonic contents of the output grid current and pollution to the grid and

in case of serious cases

the grid inverter cannot operate properly and even damaged components. Therefore

it is necessary to study the control strategy of the three-phase grid inverter at the unbalance fault of grid. In this paper

the control strategy based on suppressing the negative sequence current on the AC side of inverter and the control strategy based on the secondary harmonics of voltage on the DC side of the inverter are described. The control results of two control strategies are analyzed and compared theoretically

meanwhile

the two control strategies are simulated and analyzed by PSCAD simulation software.