Robust back-stepping sliding mode control for LCL-type grid-connected inverters in weak grids.

Gird impedance variations in a weak grid can easily lead to the instability of grid-connected inverters with an LCL filter. In this paper, a robust back-stepping sliding mode control strategy for the LCL-type grid-connected inverter is proposed to ensure local asymptotic stability. First, due to its nonlinear switching problem, the model is transformed into the Brunovsky canonical form of a linear system, using the exact feedback linearization theory. Then, to ensure global stability and rapid dynamic performance, a back-stepping sliding mode control strategy is recursively derived. Furthermore, under the premise of asymptotic stability, a robust scheme is developed to obtain appropriate parameters against grid impedance variations. Hence, the expected stability performance can be achieved and the dynamic performance can be improved in a weak grid. Finally, a 2 kW prototype is constructed, and experimental results demonstrate the effectiveness of the proposed controller when compared with the conventional back-stepping scheme. [ABSTRACT FROM AUTHOR]