A Harmonics Suppression Technique in Neutral Conductor for Three-Phase-Four-Wire Distribution Systems

Abstract

This paper presents a harmonic mitigation technique in a neutral conductor for a three-phase-four-wires power distribution system in industries using an active filter connected in series with the neutral conductor. The controller has a combination between analogue and digital microprocessor. A connection hard switch IGBT inverter operates in pulse width modulation (PWM) mode. The proposed system is capable of mitigating odd components of harmonic currents particularly for the 3^rd, 5^th, 7^th and 9^th harmonic current produced by these loads which tends to accumulate in the neutral conductor due to its zero sequence nature, thus resulting in overloading of the neutral conductor and the distribution transformer.  The existing harmonic mitigation schemes focus on re-directing zero sequence current harmonic back to the three-phase conductors.  Although such schemes could prevent overloading of the distribution transformer, the neutral conductor is still burdened by the excessive current of the 3^rd harmonic. The inverter therefore plays a key role in suppressing harmonic current in the neutral conductor to prevent overloading. The active filter operation will not affect the fundamental component due to the unbalanced loading, in which the neutral conductor is sized.  Experimental results show that the proposed scheme can eliminate current harmonics overloading in both the neutral conductor and the distribution transformer with only a single active filter installation.

Keywords: Harmonics mitigation; neutral conductor; active filter; 4P4W.