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.
Almeida, de, P. M., Duarte, J. L., Ribeiro, P. F., & Barbosa, P. G. (2014). Repetitive controller for improving grid-connected photovoltaic systems. IET Power Electronics, 7(6), 1466-1474. https://doi.org/10.1049/iet-pel.2013.0546