Hybrid damping adaptive control scheme for grid‐connected inverters in a weak grid

Abstract

The distributed generation system (DGS) located far away from load centres leads to the existence of long distance transmission lines and several transformer devices. Consequently, the equivalent impedance is introduced to a grid, which is called a weak grid and shows high impedance characteristic. A weak grid will affect the control loop stability of grid-connected inverters in DGS. To study the effects of a weak grid, the small signal model of single-phase LCL-type grid-connected inverters is first derived in this study. Then, the stability of grid-connected inverters caused by the grid impedance is analysed. Second, two common control schemes of passive and active damping are further studied. Then, the effects of the grid impedance on the damping coefficients under different damping options are analysed in quantity. A novel hybrid-damping control scheme is thereby proposed. Meanwhile, an adaptive control scheme of grid-connected inverters based on the hybrid damping is introduced in combination with the grid impedance online measurement, which ensures the stable performance of grid-connected inverters with different grid impedances. Finally, a prototype is built to verify the effectiveness of the proposed adaptive control scheme.