Mitigation of harmonics in a neutral conductor for three-phase four-wire distribution system using series active power filter

The nonlinear loads connected to three-phase four-wire distribution systems causes an unbalance current which results in the flow of zero sequence harmonic current in the neutral conductor. This leads to number of serious problems such as voltage distortion, over-burden on neutral conductor and derating of distribution transformer. Most of the existing harmonic mitigation schemes mainly focus on re-directing zero sequence current harmonics back to the phase conductor which can prevent overloading of distribution transformer, but the neutral conductor is still burdened by the excessive current harmonics. In this paper, a series active power filter is proposed to be placed in series with the neutral conductor of a three-phase four-wire distribution system. This filter interacts with neutral by injecting proper current in order to suppress the excessive current harmonics, this in turn will prevent the overloading of the neutral conductor and the distribution transformer with only one active filter installation and will not affect the fundamental component due to unbalanced loading, which the neutral conductor is sized for. This approach has been simulated using MATLAB/SIMULINK.