Improved Disturbance Observer for Grid Current Harmonic Suppression

Aiming at the harmonic disturbance caused by low-order harmonics in the power grid, an internal model principle based improved disturbance observer is presented in this paper, by implanting the internal model of sinusoidal signal with specific frequencies into the disturbance observer, it can selectively suppress the specific order grid current harmonics, reducing the influence on the current output by the grid-connected inverter from grid voltage harmonics. After analysis and simulation verification, compared with the traditional low-pass filter based disturbance observer, the enhanced disturbance observer demonstrates increased efficacy in mitigating harmonics of a specific order, thereby elevating the grid current’s quality. Concurrently, the experimental outcomes from perturbations in LCL filter parameters indicate that the system maintains performance despite variations in device parameters. the improved disturbance observer can still maintain stable output and effective suppression of the harmonics in the grid current, which has strong robustness.