The algorithm of expanded current synchronous detection for active power filters considering three phase unbalanced power system

A new algorithm, expanded current synchronous detection (ECSD) theory, for three phase active power filters is proposed. It can detect symmetrically and equally active or fundamental reactive currents in each phase, based on decomposition of fundamental reactive component and harmonics of nonlinear load current under unbalanced power conditions. Nonlinear load is composed of a 2 hp three phase squirrel cage type induction motor and motor drives (invertor). To confirm the validity of the proposed algorithm, some experiments were accomplished in steady states under 15% unbalanced power condition. From the experimental results, active and fundamental reactive current components detected by the proposed theory, was balanced and equaled in each phase despite of unbalanced power source.