Analysis and design of a new active power filter to cancel neutral current harmonics in three phase four wire electric distribution systems

An active power filter for cancelling harmonic currents in the neutral of a three-phase four-wire system is proposed. This approach employs a star/delta transformer along with a two-switch PWM (pulse-width-modulated) controlled active filter. The closed-loop control of the active power filter guarantees cancellation of neutral current harmonics under varying load conditions. The proposed system greatly improves the overall system performance and virtually eliminates transformer overheating due to harmonics. Experimental results from a prototype active power filter confirm the suitability of the proposed approach.>