Attenuation of low-order current harmonics in three-phase LCL-filtered grid-connected inverters

A direct grid-current control method is proposed to attenuate low-order current harmonics in three-phase LCL-filtered grid-connected inverters. This method allows the use of a distorted reference current, thus the reference can be generated directly from grid voltage or by a simple phase-locked loop (PLL). It is found that the direct control is necessary for effectively attenuating the current harmonics caused by the distortion in the grid voltage. Active damping is achieved with an inner inverter-current feedback loop, which is found to be superior to the widely used capacitor-current feedback damping in improving system stability. A systematic controller design procedure is proposed to optimize system performance. Experimental results confirm the improved harmonic attenuation ability of the proposed method in comparison to that of conventional control methods.