‏ ‏Mitigation of 3rd Harmonic in Three-Phase Four-Wire Distribution Power ‎Systems Based on Zigzag Transformer with Passive Filter

Abstract

 The broad usage of nonlinear loads in 3-phase 4-wire distribution systems defines significant 3rd-harmonic currents that accumulate in the neutral conductor and diminish quality of power. The present study examines a hybrid model of mitigation integrating Zigzag transformer connected in shunt with the load and a series passive filter installed on the utility side in the neutral conductor. The novelty of the proposed approach lies in controlling the neutral current path by shaping the frequency-dependent impedance, such that third-harmonic components are blocked from propagating toward the utility and are instead forced to circulate through the Zigzag transformer. The filter is tuned to show high impedance at the 3^rd-harmonic frequency, so restricting triplen harmonic propagation to the load and directing such harmonics again via Zigzag transformer. Simulations in MATLAB/Simulink under unbalanced as well as balanced nonlinear loading validate the substantial reduction in neutral current distortion and utility-side 3rd-harmonic currents. Specifically, the proposed method achieves a reduction of more than 97–99% in third-harmonic current on the utility side under balanced conditions, while under unbalanced loading the neutral current total harmonic distortion (THD) is reduced from 438.4% to approximately 49.95%, showing the efficiency of the proposed configuration.