A practical design procedure for robust H2 controllers applied to grid-connected inverters

This paper provides as contribution an efficient design procedure based on the choice of only one parameter, leading to robust H-2 current controllers suitable for three-phase grid-connected inverters operating under grid variations. As the main advantage, the procedure proposed here provides performances similar to suitably designed discrete linear quadratic regulators, but with a significantly lower design effort. The controller relies on the robust H-2 design paradigm in terms of linear matrix inequalities, in the scenario of uncertain and time-varying grid parameters, also considering the rejection of broad-band frequency disturbances. Experimental and real-time simulation results show grid currents with low harmonic content, complying with the requirements of the IEEE 1547 Standard. The approach can also cope with grid impedance variations over large intervals and be applied for different sets of filters parameters. The good trade-off between robustness, suitable experimental results, and low control design effort, as demonstrated by design examples in the paper, makes the proposed procedure a useful alternative for robust current control in this application.