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Repetitive control has proven to be an efficient control technique in power factor correction by active filtering. Unfortunately, this technique shows a dramatic performance decay when the network frequency is not exactly known or it varies with time. In order to overcome the varying/uncertain frequency problem, a robust high-order repetitive control strategy can be used; however, most internal models obtained by these approaches are unstable. Although this fact does not compromise the closed-loop stability, practical problems can arise during the implementation. This study proposes and studies a stable second-order odd-harmonic repetitive control system, presents a stability analysis of high-order internal models and describes the performance degradation of the standard repetitive control in terms of the active filter (AF) application. In this way, an experimental validation has been carried out implementing the proposed internal model in a shunt AF current controller. As a result, this high-order controller allows dealing with the grid frequency variations without using adaptive schemes.