Optimization of Robust PI Controllers for Grid-Tied Inverters

This paper contributes with a procedure that can provide PI current regulators for grid-tied inverters, with robustness against uncertain grid parameters ensured in the control design stage, without the need of a posteriori exhaustive tests of robust performance. The procedure is suitable for inverters with LCL output filters, taking into account the control delay and not using any approximation of lower order for the filter. The gains of fixed PI controllers are obtained offline, in an automated synthesis relying on particle swarm optimization with an objective function based on commonly used frequency domain design criteria, which is also different from similar works, based predominantly on time domain criteria. The results obtained are suitable, respecting the requirements of the IEEE 1547 Standard for grid currents, which makes the proposed procedure an alternative for providing robust PI controllers for grid-tied inverters, avoiding time consuming designs based on human-machine iterations.