Use of Resonant Terms in a 2DOF Control Scheme for the Current Control of an Active Power Filter.

This paper proposes a control scheme for the current injected by an Active Power Filter (APF) that has an LCL filter at its output. The proposed structure relies in a Two-Degrees-of-Freedom (2DOF) controller in which resonant terms are included. The 2DOF scheme follows the current reference at the fundamental frequency of the grid and damps the resonance phenomenon of the LCL filter, whereas the resonant regulators allow a proper tracking of the harmonics. This is achieved with only the measurement of the current injected by the APF into the grid, without the need for additional measurements or observers. In order to assess the performance of the controllers, a Hardware-In-the-Loop (HIL) emulation has been carried out. The results show a good time response, allowing the compensation of current disturbances at both the fundamental frequency and its harmonics.