Active power filtering for a three-phase four-wire network with unidentifiable harmonic loads

Harmonic characteristics of a number of widely used appliances are investigated. Their cumulative effect on a 3-phase 4-wire distribution network, in terms of severity of harmonic disturbance and current unbalance, is explored. This data is used in designing an active power filter based on a 3-phase 4-leg flying capacitor multilevel converter to eliminate the harmonics and current unbalance. The controller is tuned according to an emulation of the measured current. The algorithm employs a modified dead-beat control law to overcome the response delays caused by harmonic extraction loop. Simulation results have shown significant improvement in current waveforms.