Repetitive controller for improving grid-connected photovoltaic systems

This study presents the modelling and design steps of a discrete time recursive repetitive controller (RC) to be used in a grid-connected photovoltaic (PV) system. It is shown that the linear synchronous reference frame proportional-integral controller, originally designed to control the converter´s output currents, may have its effectiveness compromised because of non-linearities in the system components. A RC is introduced as an alternative to overcome this drawback and improve the system´s output currents. The performance of the designed hybrid controller is tested, under both steady-state and transient operations, for variations on the power generated by a 30 kWp PV power plant. Experimental results obtained from the operation of the PV system connected to a distribution network, without output passive filters, only through a transformer that operates in a non-linear region are presented. The results are used to evaluate the performance of the proposed compensation method and to validate the designed hybrid controller.