Observer-based second-order sliding mode control for grid-connected VSI with LCL-type filter under weak grid

•System cost is reduced with only grid-side current and voltage are sensed.•Desired system resonance damping and dynamic performance are achieved through arbitrary poles placement.•The adaptability of LCL-type inverters in weak grid is significantly enhanced.•System stability and satisfactory performance are ensured by SMO-based SOSMC strategy.•Detailed guidelines of parameters design and stability proof are provided.