A New Hybrid Power Conditioner for Suppressing Harmonics and Neutral-Line Current in Three-Phase Four-Wire Distribution Power Systems

ABSTRACT:

In this paper, a new hybrid power conditioner is proposed for suppressing harmonic currents and neutral-line current in three-phase four-wire distribution power systems. The proposed hybrid power conditioner is composed of a neutral-line current attenuator and a hybrid power filter. The hybrid power filter, configured by a three-phase power converter and a three-phase tuned power filter, is utilized to filter the nonzero-sequence harmonic currents in the three-phase four-wire distribution power system. The three-phase power converter is connected to the inductors of the three-phase tuned power filter in parallel, and its power rating can thus be reduced effectively. The tuned frequency of the three-phase tuned power filter is set at the fifth harmonic frequency. The neutral- line current suppressor is connected between the power capacitors of the three-phase tuned power filter and the neutral line to suppress the neutral-line current in the three-phase four-wire distribution power system. With the major fundamental voltage of the utility dropping across the power capacitors of the three-phase tuned power filter, the power rating of the neutral-line current suppressor can thus be reduced. Hence, the proposed hybrid power conditioner can effectively reduce the power rating of passive and active elements. A hardware prototype is developed to verify the performance of the proposed hybrid power conditioner. Experimental results show that the proposed hybrid power conditioner achieves expected performance.

 KEYWORDS:

  1. Harmonic
  2. Neutral-line current
  3. Power converter

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

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Fig. 1. Configuration of the advanced hybrid power filter.

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Fig. 2. System configuration of the proposed hybrid power conditioner.

EXPECTED SIMULATION RESULTS:

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 Fig. 3. Experimental results of the balanced three-phase load: (a) phase a load current, (b) phase b load current, (c) phase c load current, and (d) neutral line current of load.

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Fig. 4. Experimental results of the hybrid power conditioner under the balanced three-phase load: (a) phase a utility current, (b) phase b utility current, (c) phase c utility current, and (d) neutral line current of the utility.

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Fig. 5. Experimental results of the three-phase four-wire hybrid power conditioner under the transient of applying the neutral-line current attenuator: (a) phase a utility voltage, (b) phase a utility current, (c) phase a load current, and (d) neutral line current of the utility.

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Fig. 6. Experimental results of the unbalanced three-phase load, (a) phase a load current, (b) phase b load current, (c) phase c load current, and (d) neutral line current of the load.

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Fig. 7. Experimental results of the hybrid power conditioner under the unbalanced three-phase load: (a) phase a utility current, (b) phase b utility current, (c) phase c utility current, and (d) neutral line current of the utility.

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Fig. 8. Experimental results of the hybrid power conditioner under the transient of increasing load: (a) phase a utility voltage, (b) phase a utility current, (c) phase a load current, and (d) neutral line current of the utility.

 CONCLUSION:

Three-phase four-wire distribution power systems have been widely applied to low-voltage applications; however, they encounter serious problems of harmonic current pollution and large neutral-line current. In this paper, a new hybrid power conditioner, composed of a hybrid power filter and a neutral- line current attenuator, is proposed. In the proposed hybrid power conditioner, the power capacity of power converters in the hybrid power filter and neutral-line current attenuator can be effectively reduced, thus increasing its use in high-power applications and enhancing the operation efficiency. A prototype is developed and tested. Experimental results verify that the proposed hybrid power conditioner can suppress the harmonic currents and attenuate the neutral-line current effectively whether the loads are balanced or not. Hence, the proposed hybrid power conditioner is an effective solution to the problems of harmonic currents and neutral-line current in three-phase four-wire distribution power systems. Besides, the output current of the three-phase power converter is much smaller than the conventional hybrid power filter, and the power rating of the zig-zag transformer is smaller than the rating of the conventional neutral-line current attenuator.

REFERENCES:

[1] B. Singh, P. Jayaprakash, T. R. Somayajulu, and D. P. Kothari, “Reduced rating VSC with a zig-zag transformer for current compensation in a three-phase four-wire distribution system,” IEEE Trans. Power Del., vol. 24, no. 1, pp. 249–259, Jan. 2009.

[2] R. M. Ciric, L. F. Ochoa, A. Padilla-Feltrin, and H. Nouri, “Fault analysis in four-wire distribution networks,” Proc. Inst. Elect. Eng., Gen., Transm. Distrib., vol. 152, no. 6, pp. 977–982, 2005.

[3] J. C. Meza and A. H. Samra, “Zero-sequence harmonics current minimization using zero-blocking reactor and zig-zag transformer,” in Proc. IEEE DRPT, 2008, pp. 1758–1764.

[4] H. L. Jou, J. C.Wu,K.D.Wu,W. J. Chiang, andY. H. Chen, “Analysis of zig-zag transformer applying in the three-phase four-wire distribution power system,” IEEE Trans. Power Del., vol. 20, no. 2, pt. 1, pp. 1168–1178, Apr. 2005.

[5] S. Choi and M. Jang, “Analysis and control of a single-phase-inverterzigzag- transformer hybrid neutral-current suppressor in three-phase four-wire systems,” IEEE Trans. Ind. Electron., vol. 54, no. 4, pp. 2201–2208, Aug. 2007.