On flatness-based controller for shunt-connected VSC with LCL-filter for voltage dip mitigation in a weak grid

In this paper, a grid connected shunt converter for mitigation of voltage sags in weak grids is described. The VSC keeps the grid voltage magnitude at the point of connection constant by injecting reactive power to compensate for the voltage dip. A novel flatness-based control (FBC) is proposed for this purpose that gives higher performance and robustness with an inductor/capacitor/inductor (LCL)-filter in between the VSC and the grid. Simulation model includes the practical limitation of voltage source converter output voltage. Then, the simulation results for the FBC under balanced voltage dips are presented and compared with traditional proportional integral controller. Finally, the sensitivity analysis of the FBC for grid impedance and to system parameter variations is presented.