Source current detection control of active filter for preventing current oscillation

Recently parallel-connected-type active filters have been developed for useful method of harmonic current compensation. Authors have developed the active filter which compensates the source current harmonics directly by detecting the source current itself. However the active filter may cause oscillation by capacitors inserted as a power line filter or for power factor correction. This paper proposes a control method that the derivative of source current is employed as an additional feedback signal in order to prevent this oscillation. First, the transfer function of the power system with the active filter is derived. The effectiveness of the modified control system is discussed on the Bode diagram of the open-loop transfer function. A control gain of the feedback loop is chosen as matched with given system parameters. The designed active filter is verified by both simulation and experimental studies. The active filter was operated under both no load and full load condition, and accomplished desirable compensation results without any oscillation. The transient characteristics of the active filter were also tested and achieved good characteristics against sudden load changes.