Harmonics Cancellation in Distribution Systems by Using a Hybrid Four-Branch Star Filtering Topology

Abstract

This paper presents a new solution for filtering current harmonics in three-phase four-wire networks. The original four-branch star (FBS) filter topology presented in this paper is characterized by a particular layout of single-phase inductances and capacitors, without using any transformer or special electromagnetic device. Via this layout, a power filter, with two different and simultaneous filter resonance frequencies and sequences, is achieved—one frequency for positive-/negative-sequence and another one for zero-sequence components. This filter topology can work either as a passive filter, when only passive components are employed, or as a hybrid filter, when its behavior is improved by integrating a power converter into the filter structure.. The paper analyzes the proposed topology, and derives fundamental concepts about the control of the resulting hybrid power filter. From this analysis, a specific implementation of a three-phase four-wire hybrid power filter is presented as an illustrative application of the filtering An extensive evaluation using simulation designed and experimental results from a DSP-based laboratory prototype is conducted in order to verify and validate the good performance achieved by the proposed FBS passive/hybrid power.

Introduction

The text addresses the growing problem of current harmonics in low- and medium-voltage power distribution networks, which arise mainly from widespread nonlinear loads such as power-electronic equipment, discharge lamps, furnaces, and rectifiers. These harmonics degrade power quality by causing voltage distortion, overheating, increased losses, equipment malfunction, premature aging, and reduced reliability of supply. In three-phase systems, nonlinear loads generate both positive/negative-sequence (pn-seq) harmonics and zero-sequence (z-seq) harmonics. Z-seq harmonics, especially third-order and its multiples, accumulate in the neutral conductor, leading to neutral overloading, transformer overheating, and voltage distortion.

The text reviews existing harmonic mitigation techniques, including shunt passive power filters (SPPFs), shunt active power filters (SAPFs), and shunt hybrid power filters (SHPFs). Passive filters are simple and low-cost but suffer from resonance issues, grid-impedance dependence, and poor performance for third-order harmonics. Active filters provide precise harmonic compensation but are expensive. Hybrid filters combine the advantages of both, offering good performance at reduced cost.

A major contribution discussed is the four-branch star (FBS) power filter topology for three-phase four-wire systems. This topology uses a specific arrangement of single-phase inductors and capacitors without transformers, enabling simultaneous and independent filtering of pn-seq and z-seq harmonics at different resonance frequencies. The FBS filter can operate in passive or hybrid mode and can be configured in multiple variants to suit different harmonic compensation and reactive power needs. Simulation and experimental results show that it offers effective harmonic filtering with lower cost, higher modularity, and reduced sensitivity to grid conditions.

The literature survey further places the work in the broader context of filter evolution, covering passive, active, hybrid, digital, and electromechanical filters (such as quartz, SAW, BAW, and YIG filters). Overall, the text highlights the significance of harmonic mitigation in modern power systems and presents the FBS topology as a practical, economical, and effective solution for improving power quality in distribution networks.

Conclusion

A new filter based on the FBS topology was presented in this paper. Analysis, simulations, and experiments conducted in this paper proved the FBS power filter topology as an effective and economical solution for current conditioning in three-phase four- wire networks. Connection of resonant cells according to FBS topology results in independent low-impedance paths for both pn- and z-seq components at specific frequencies, which allows performing selective filtering of current harmonics in both the phases and the neutral conductor of a three-phase four-wire system. The FBS power filter topology can operate in either passive or hybrid mode. In this second mode, a very simple VSI with a dc-link voltage around 10% of the grid line voltage extends further filtering capability of the passive network as well as it avoids overloads and unexpected resonances. A three-phase four-wire hybrid power filter was presented in this paper as an attractive application of the FBS filtering topology. The proposed solution allows low cost implementation of the neutral current conditioning functionality in a conventional wye-connected three-phase passive filter.

References

[1] IEEE Recommended Practices and Requirements for Harmonic Controlling Electrical Power Systems. IEEE,IEEE Standard 519-1992, 1992. [2] Electromagnetic Compatibility (EMC), Part3: Limits,Section2:LimitsforHarmonicsCurrent Emissions (Equipment Input Current ?16A Per Phase), IEC Standard 61000-3-2, 1997. [3] Electromagnetic Compatibility (EMC), Part3: Limits,Section4:LimitationofEmissions of Harmonics Currents in Low-Voltage Power Supply Systems for Equipment with Rated Currents Greater Than 16A, IEC Standard61000-3-4. [4] R. C. Dugan, M. F. McGranaghan, S. Santoso, and H. W. Beaty, Electrical Power Systems Quality, 2nd ed. New York: McGraw-Hill, 2002 [5] J. C. Das, “Passive filters—Potentialities and limitations,” IEEE Trans. Ind. App., vol. 40, no. 1, pp. 232–241, Jan./Feb. 2004.

Copyright

Copyright © 2026 Miss. Prajkta R. Gangurde, Miss. Pratiksha A. Shinde. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.