Dual-loop H∞ controller design for a grid-connected single-phase photovoltaic system

A nonlinear dual-loop H∞ controller is presented in this paper synthesized with linear matrix inequality (LMI) method with primary objectives of generating switching signals for inverters for maximum power point tracking and improving dynamic response of a single-phase grid-connected photovoltaic (PV) system. A state-space model of the PV system is developed with parametric uncertainty in terms of linear fractional transformation. A dual control loop is implemented into the control structure: one is outer dc-link voltage control loop and the other is inner grid current control loop. Weighting functions are first selected and tuned to achieve minimum tracking error and robust performance. Next, control laws are obtained by synthesizing the controller. To facilitate practical implementation, model order of the controller is reduced by Henkel-norm method. The performance of the proposed controller is demonstrated on a test system through simulation results under different parametric, atmospheric and load conditions as well as system contingencies. From the simulation results, it is evident that the controller provides superior performance under various operating conditions.