With the growing popularity of distributed generation in recent years

the problem of suppressing DC component to inject into the grid connect system must be solved firstly. DC component is divided into common mode and differential mode. The isolation of DC component is normally achieved by the use power frequency transformer. However

the transformer increases the system cost

size and loss. In the Nonisolation grid-connected system

the inverter can in theory keep the differential DC component of output current to zero by way of accurate control. In fact

the differential DC component is included in the output current of inverter due to such reasons as measurement error in the loop system（including modulus transfer error and the measurement error of sensor）. In this paper

the use of moving average filter is proposed to detect the differential DC component of the output current by the comparison with the harmonic detection suppression differential DC component method based on instantaneous reactive power theory

then it is fed to the system for loop ring control

thus keeping the differential DC component reach the permitted range.The 40 kW simulation and experimental platform is set up and the effectiveness of the method is proved.