Design of a robust H∞ current controller for grid-connected photovoltaic systems based on cascaded multilevel inverter

This work proposes a design method for robust state feedback H-infinity grid current controller applied to single-phase grid-connected photovoltaic (PV) systems. The proposed method achieved high system reliability even dealing with grid distorted voltages and other power quality issues. The robustness of the H-infinity controller was verified in the face of parametric uncertainties at the first-order output filter, and also a satisfactory disturbance rejection performance was achieved. The proposed design is based on linear matrix inequalities associated with constraints involving H-infinity optimisation and a pole placement analysis on the continuous-time domain. A discrete-time analysis is also presented in order to indicate the simplicity of its implementation by a microcontroller or similar devices. Based on the presented results and in order to validate the proposed controller, its robust performance was compared with two linear and well-known control methods: a classical PI controller, in terms of robustness; and a robust H-infinity resonant controller, regarding the power quality at the connection point with the grid-utility. Although the conclusions were listed regarding a low voltage PV grid-interactive multilevel power converter, the proposed H-infinity control design (and its concepts) can be applied to a great variety of renewable energy resources systems.