Discrete-Time Integral Variable Structure Control of Grid-Connected PV Inverter

In the paper a new discrete-time integral variable structure control of grid-connected PV inverter is proposed in order to maximize the input power given by PV arrays and at the same time for using the grid-inverter as a reactive power compensator. In the last years different variable structure controls (VSC) have been proposed in literature. In spite these algorithms have been implemented on digital hardware, they have been developed by means of a time-continuous formulation neglecting the effects of a microprocessor-based implementation. Such approach can cause an increasing amplitude chatter of the state trajectories which means instability. The proposed VSC is fully formulated in discrete-time, taking into account the effects introduced by a microprocessor-based implementation. Moreover it introduces respect to the classical formalization of the VSC an integral action that improve the performance of the controlled system. After a detailed formalization of the proposed control algorithm, several numerical and experimental results on a three-phase grid-connected inverter prototype are shown, proving the effectiveness of the control strategy. Thanks to the proposed control law the controlled system exhibits fast dynamic response, strong robustness for modelling error and good current harmonic rejection.