A combined control scheme of improved deadbeat control and plug-in repetitive control is proposed for grid-connected three-phase four-leg inverters to control the grid-connected current. The deadbeat current control can quickly and accurately track a given signal

and the repetitive control based on the internal model principle can quickly eliminate the steady-state error in each cycle by providing high gain at the fundamental frequency and its integral multiples. Based on the mathematical model of grid-connected voltage-type three-phase four-leg inverter

the deadbeat control algorithm is derived

and the effect of control delay in the deadbeat control on the stability of the system is analyzed. The plug-in repetitive controller is able to reduce the sensitivity of the deadbeat control to the inductance parameters and the dependence on the model accuracy. Thus

the periodic steady-state error can be eliminated. The optimal compensation step is obtained by analyzing the transfer function of the model. Finally

the simulation and experimental results show that the proposed control strategy can achieve fast and accurate tracking of the reference current.