9.14 Summary

With the increase of harmonic currents and voltages in present-day power systems, the installation of passive, active, and hybrid filters gains in importance. In the future, recommended practices such as IEEE-519 [11] will result in further increased use of filters within the distribution system. There are a great variety of filter configurations (Figs. 9.3 and 9.13 to 9.25). Classification of filters can be based on different criteria such as supply type, filter connection, number of filter elements, power rating, compensation type, speed of response, and control technique. In this chapter the classification of power filters is performed based on the type of supply (Fig. 9.3) and the control method (Section 9.7). Proper selection of filter configurations depends primarily on the properties of nonlinear loads, type of supply, and system rating:

• Passive filter blocks (Fig. 9.12 and 9.13) and a combination of passive filters (Figs. 9.19 and 9.20) are the most qualified candidates for single-phase systems – with high penetration of nonlinear loads – and low-power applications.

• Hybrid filters (Figs. 9.21 and 9.22) are considered as a cost-effective option for power quality improvement, compensation of the poor power quality effects of nonlinear loads, or to provide a sinusoidal AC supply to sensitive loads, especially for high-power applications. They are also good options for compensation of single-phase systems and high-power applications.

• A group of passive filters (Fig. 9.13a) or a combination of active and passive filters in different configurations (Figs. 9.23 to 9.25) should be used for the compensation of three-phase three-wire power systems that have a great amount of current or voltage harmonics due to a large number of small-and moderate-rating nonlinear loads, as well as feeding terminals of HVDC transmission systems.

Selection of the control approach (Sections 9.7.1 to 9.7.3 and 9.7.5) greatly depends on the choice of the control objective, for example, the required waveform of the supply current after compensation. The selection of the domain (e.g., time or frequency) and the reference frame (e.g., dq0 or αβ0) will affect the computational burden required to implement appropriate filters. All active filters perform harmonic mitigation. However, depending on the selected control strategies, additional forms of compensation (e.g., fundamental reactive power, negative-sequence, zero-sequence, phase balancing, sag, swell, and flicker) can be accommodated within the apparent power rating of an active filter. There exist three different definitions for the control objective:

First Definition: Supply currents (after filtering) should contain only fundamental frequency components. This is the main task of active filter controllers using waveform compensation (Section 9.7.1).

Second Definition: Supply currents (after filtering) should be such that the instantaneous active power is constant while the instantaneous reactive power is zero. This is performed by active filter controllers that use instantaneous power compensation (Section 9.7.2).

Third Definition: Supply currents (after filtering) should be entirely active. This is the main function of active filter controllers using impedance-based compensation (Section 9.7.3).

If the supply voltage is not distorted (with nearly sinusoidal waveform), the following remarks should be considered for the selection of the control method:

• The three aforementioned objective definitions are equivalent and the choice of the control method should be based on the ease of their implementation and their instrumentation requirements.

• Given the harmonic limits provided by relevant guidelines, recommended practices, or standards such as IEEE-519 [11], waveform compensation (first definition) is the most important approach. The techniques for this approach separate the fundamental from the harmonic components. Time-domain filters have the advantage of continuity during transient conditions, whereas frequency-domain filters have a better selectivity under steady-state conditions. The synchronous dq0 reference frame can ease the filter implementation of three-phase systems at the expense of longer processing time.

• The instantaneous power methods (second definition) are beneficial in three-phase systems due to their ease of filter design without the need for dq0 transformation.

• The active current approaches (third definition) are relatively easy to implement because they require only the identification of the (average) real power. These approaches are implicit in controllers that use the energy balance at the DC bus to identify the desired current.

Further complications regarding the selection of the control method for active filters arise if the supply voltage (before filtering) is distorted. This is the case for most practical power quality problems, for example, when active filters are operating on weak feeders of the distribution network. If the supply voltage is distorted, the following guidelines should also be considered for the selection of the control method:

• Distorted supply voltage may increase the apparent power rating of the active power filter.

• Waveform compensation approaches only draw fundamental current and do not generate extra distortion; however, they will not provide damping of the existing distortion.

• Instantaneous active power methods respond to harmonic supply voltages by introducing additional harmonic currents at other frequencies (Eq. 9-22). In particular, a negative-sequence fundamental voltage will cause these controllers to inject harmonic currents.

• Controllers with impedance-based compensation – resulting in active supply current – represent resistive characteristics at all frequencies, and therefore convert nonlinear loads into linear loads. They inherently provide damping and reduce the propagation of harmonic voltages. However, the design of active filters will have to be coordinated with existing approaches for the damping of network resonances.

Active filters can be designed to perform phase balancing if the exchange of instantaneous power between phases is within their ratings:

• All three control approaches (waveform compensation, instantaneous power compensation, and impedance synthesis) can enforce phase balancing. Waveform compensation and impedance synthesis (active current) methods can be implemented on a phase-by-phase basis to avoid rebalancing.

• Instantaneous power methods (in their original form) have an unacceptable response under unbalanced operating conditions, and will inject additional harmonic currents at different frequencies. Modifications (e.g., redefining the inverse transformation) are necessary to control harmonic generation.

• Waveform compensation methods result in balanced currents despite unbalanced voltages.

• Impedance synthesis methods present balanced impedances to unbalanced voltages. As a result, they draw the least current from the smallest phase voltage. In contrast, the constant instantaneous power approaches draw the greatest current from the smallest phase voltage.

The unified power quality conditioner (UPQC) is an advanced hybrid filter that consists of a series active power filter for compensation of voltage disturbances and a shunt active power filter for eliminating current distortions. This custom power device is mainly employed to protect a critical nonlinear load by improving the quality of voltage across it, and to improve the waveform of the supply current. Different control approaches may be implemented to simultaneously perform these tasks. This chapter introduces two commonly relied on UPQC control approaches based on the dq0 transformation and the instantaneous real and reactive powers. Detailed UPQC block diagrams are provided for these approaches and application examples are used to demonstrate their effectiveness. Using an appropriate control algorithm, a UPQC can improve the utility current and protect the critical load at the point of installation in distorted distribution systems by taking a number of actions including reducing harmonic distortions, voltage disturbance compensation, voltage regulation, reactive (harmonic) power flow, harmonic isolation, and neutral and negative-sequence current compensations.

References

[1] Peng FZ. Harmonic sources and filtering approaches. IEEE Ind Appl Mag. 2001;7:18–25.

[2] Das JC. Passive filters – potentialities and limitations. IEEE Trans Power Ind Appl. 2004;40(1):232–241.

[3] Akagi H. Active harmonic filters. Proc IEEE. 2005;93(12):2128–2141.

[4] Singh B, Verma V, Chandra A, Al-Hadded K. Hybrid filters for power quality improvement. IEE Proc Generat Transm Distrib. 2005;152(3):365–378.

[5] El-Habrouk M, Darwish MK, Mehta P. Active power filters: a review. IEE Proc Elec Power Appl. 2000;147(5):403–413.

[6] Green TC, Marks JH. Control techniques for active power filters. IEE Proc Elec Power Appl. 2005;152(2):369–381.

[7] Phipps JK. A transfer function approach to harmonic filter design. IEEE Ind Appl Mag. 1997;68–82.

[8] Singh B, Al-Haddad K, Chandra A. A review of active filters for power quality improvement. IEEE Trans Ind Electron. 1999;46(5):960–971.

[9] Grainger JJ, Civanlar S. Volt/VAr control on distribution systems with lateral branches using shunt capacitors and voltage regulators. Part III: the numerical result. IEEE Trans Power App Syst. 1985;104(11):3291–3297.

[10] Hu Z, Wang X, Chen H, Taylor GA. Volt/VAr control in distribution systems using a time-interval based approach. IEE Proc Generat Transm Distrib. 2003;150(5):548–554.

[11] IEEE recommended practice and requirements for harmonic control in electric power systems. IEEE Standard 519; 1992.

[12] Nilsson JW. Electric circuits. Reading, Massachusetts: Addison-Wesley Publishing Company; 1983.

[13] Thomas RE, Rosa AJ. The analysis and design of linear circuits. 4th ed. John Wiley & Sons, Inc; 2004.

[14] Masoum MAS, Ulinuha A, Islam S, Tan K. Hybrid passive filter design for distribution systems with adjustable speed drives. In: The seventh international conference on power electronics and drive systems (PEDS-2007); November 27–30, 2007 Bangkok, Thailand.

[15] Jou HL, Wu JC, Wu KD. Parallel operation of passive power filter and hybrid power filter for harmonic suppression. IEE Proc Generat Transm Distrib. 2001;148(1):8–14.

[16] Gholamrezaei M, Masoum MAS, Kalantar M. Parallel combination of passive and hybrid power filters for harmonic mitigation. 7–15. 18th International power system conference. 2003;vol. 1 PSC.

[17] Phipps JK. Phase shifting transformers and filters: interfacing for power electronic motor drive converters. MS. Thesis University of Colorado at Denver; May 1993.

[18] GyuGyi L. A unified flow control concept for flexible AC transmission systems. Proc Inst Elect Eng. 1992;139(4):323–331 Part C.

[19] Hingorani NG, GyuGyi L. Understanding FACTS – concepts and technology of flexible transmission systems. IEEE Press; 2000.

[20] Hingorani NG. Introducing custom power. IEEE Spectr. 1995;32(6):41–48.

[21] Ghosh A, Ledwich G. Power quality enhancement using custom power devices. Boston: Kluwer Academic Publishers; 2002.

[22] Peng FZ, Akagi H, Nabae A. A new approach to harmonic compensation in power system – a combined system of shunt passive and series active filters. IEEE Trans Ind Appl. 1990;26(6):983–990.

[23] Akagi H. New trends in active filters for power conditioning. IEEE Trans Ind Appl. 1996;32(6):1312–1322.

[24] Fujita H, Akagi H. The unified power quality conditioner: the integration of series and shunt–active power filters. IEEE Trans Power Electron. 1998;13(2):315–322.

[25] Kamran F, Habetler TG. Combined deadbeat control of a series-parallel converter combination used as universal power filter. In: Proceedings of the IEEE power electronic specialist conference (PESC); 1995:196–201 IEEE Trans Power Electron 1998;13(1):160–168.

[26] Aredes M, Heumann K, Watanabe EH. An universal active power line conditioner. IEEE Trans Power Deliv. 1998;13(2):545–551.

[27] Tolbert LM, Peng FZ. A multilevel converter-based universal power conditioner. IEEE Trans Ind Appl. 2000;36(6):596–603.

[28] Graovac D, Katic V, Rufer A. Power quality compensation using universal power quality conditioning system. IEEE Power Eng Rev. Dec. 2000;58–60.

[29] Ghosh A, Ledwich G. A unified power quality conditioner (UPQC) for simultaneous voltage and current compensation. Elec Power Syst Res. 2001;59:55–63.

[30] Mosavi SA, Masoum MAS. Mitigation of temporary and sustained power quality disturbances by UPQC. Int J Eng, Iran. 2004;15(3):109–120.

[31] Watanabe EH, Stephan RM, Aredes M. New concepts of instantaneous active and reactive powers in electrical systems with generic loads. IEEE Trans Power Deliv. 1993;8(2):697–703.

[32] Vilathgamuwa M, Zhang YH, Choi SS. Modeling, analysis and control of unified power quality conditioner. 1035–1040. Proceedings of the 8th international conference on harmonics and quality of power. 14–16 Oct, 1998;vol. 2.

[33] Montanari GC, Loggini M, Cavallini A, Pitti L, Zaninelli D. Arc furnace model for the study of flicker compensation in electrical networks. IEEE Trans Power Deliv. 1994;9:2026–2036.

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset