Distributed Active Damping for Harmonic Instability Suppression in the Multi-paralleled Grid-connected Inverter System

Aiming at the harmonic instability problem of multi-paralleled grid-connected inverter system, which is caused by the interaction among the fast inner current or voltage control loops of inverters and grid impendence, distributed active damping is proposed in this paper. This approach is based on the grid voltage feedforward strategy and increase the damping of the global admittance (GA), which effectively improves the system stability. One of the advantages of this approach is that when some of the active damping fail to work, the remaining active damping can still maintain the system stability. Another is the employment of a second-order lag corrector which can alleviate the influence of the ignorance the prediction component and improve the characteristic of inverter output admittance at the harmonic controlled frequencies. Simulations are carried out and the results verify the effectiveness of the proposed method.