Odd-harmonic repetitive control of an active filter under varying network frequency: Practical considerations

This work deals with the design and analysis of a controller for a shunt active power filter. The design is based on combined feedforward and feedback actions, the last using odd-harmonic repetitive control, and aims at obtaining good closed-loop performance in spite of the possible frequency variations that may occur in the electrical network. As these changes affect the performance of the controller, the proposal includes a compensation technique consisting of an adaptive change of the sampling time of the digital controller according to the network frequency variation. However, this implies structural changes in the closed-loop system that may eventually destabilize it. Hence, this article is also concerned with closed-loop stability of the resulting system, which is analyzed using a robust control approach that takes advantage of the small gain theorem. Experimental results reporting good performance of the closed-loop system are provided.