Analysis and design of a multiple-loop control system for a hybrid active filter

This paper investigates the control of a hybrid active filter consisting of a single tuned resonant branch and an active element. This filter is capable of suppressing multiple harmonics using a multiple-loop control system. Linear continuous-time models are first developed in the dq reference frame. This results in a two-input/two-output system with cross coupling. The continuous model is discretized and the design of a multiple-loop discrete-time controller is examined. Wideband current feedback loops are shown to affect the coupling between the d- and q-axis controllers and provide a resistance-like damping effect. Variations in stability with processing delay times are examined. Finally, this work is extended to include narrowband harmonic specific controls. The results of the control study are confirmed by simulation and experimental results.