Robust control of grid-connected converters under wide grid impedance variation

This paper investigates the robust current control of grid-connected converters operating under wide grid impedance variation. Digital state feedback control gains are obtained based on linear matrix inequalities that ensure the location of the closed-loop poles inside a circle with radius r, included in the unit circle. To guide in the choice of r, here it is proposed the use of a criterion based on the grid-current tracking errors. The proposed procedure leads to control gains which ensure performance complying with IEEE 1547 Std., which is confirmed by means of experimental results and also by real time domain simulations, in conditions that encompass operation under stiff and weak grid, and also grid voltages distorted by harmonics.