power conditioning by shunt active filter

IJIRST –International Journal for Innovative Research in Science & Technology| Volume 2 | Issue 06 | November 2015 ISSN (online): 2349-6010

All rights reserved by www.ijirst.org 105

Power Conditioning by Shunt Active Filter

Prof. Sumita D Chakrabortty Prof. Naimesh Zaveri

Assistant Professor (Head of Department) Professor(Head of Department)

Department of Electrical Engineering Department of Electrical Engineering

Mahavir Swami College of Engineering & Technology, Surat C K Pithawala College of Engineering & Technology, Surat

Abstract

In modern distribution systems the proliferation of non-linear loads results in a deterioration of the quality of voltage waveforms

at the point of common coupling (PCC) of various consumers. Therefore, power-conditioning equipment is becoming more

important for electric utilities and their customers. With the rapid development of semiconductor devices in power and control

circuits, a new generation of equipment for power quality, the active power filters, has been developed. Their advantages over

conventional means are more flexibility and very fast control response. The control of an active filter comprises two major parts:

the reference current computation and the current control. There are two fundamental methods of generating the reference

current: (i) frequency–domain methods, based on the Fourier analysis and (ii) time-domain analyze, based on the theory of

instantaneous imaginary power in the three-phase circuits, often called p-q theory.

Keywords: Active Filters, PWM-VSI, Point of common coupling (PCC), Current Reference, Harmonic compensation,

and IEEE-519 etc.

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I. INTRODUCTION

In view of the wide spread use of harmonics-sensitive electronic equipment, power conditioning equipment is becoming more

important for both electric utilities and their customers. With rapid development of power semiconductor devices in power and

control circuits, a new generation of equipments that help maintaining a good level of power quality, namely active power filters,

has been developed. Theirs advantages over conventional means are more flexibility and very fast control response. This paper

aim to present the actual status of active power filters based on state of the art power electronics technology and also their future

prospects and directions.

The wide use of power devices (based on semi-conductor switches) in power electronic appliances (diode and thyristor

rectifiers, electronic starters, UPS and HVDC systems, arc furnaces, etc…) induces the appearance of the dangerous

phenomenon of harmonic currents flow in the electrical feeder networks, producing distortions in the current/voltage waveforms.

As a result, harmful consequences occur: equipment overheating, malfunction of solid-state material, interferences with

telecommunication systems, etc... Damping harmonics devices must be investigated when the distortion rate exceeds the

thresholds fixed by the ICE 61000 and IEEE 519 standards.

The common application of active filtering combines the tasks of harmonic filtering and power factor compensation. Apart

from this complex comprehensive active filters have been proposed in the context of total power quality management concept.

Some of the powers filtering applications are categorized as custom power devices.

Advantages of active filters over conventional mean of compensation such as passive filters, special transformer connections and

specially designed transformers are mainly:

Flexibility in defining and implementing the functions of the filter, a very fast control response, and no additional problems

caused by possible resonant frequencies or network configuration.

II. ACTIVE FILTERS CLASSIFICATION

The technical literature proposes various types of active filters and their classification can be made from different points of view,

like as:

Electrical System Type A.

Related to the type of electrical system where they are functioning, active filters are divided into ac and dc filters. Active dc

filters have been proposed to compensate current and/or voltage harmonics on the dc side of power converters, and are mainly

applied in HVDC and traction systems. However, in most of the cases, the term active filter refers to active filters.

Power Circuit B.

Active filters in power systems applications are implemented as voltage-source or current source PWM inverters.

System Configuration C.

There are two basic active filter configurations: shunt and series; complex structures obtained by integration of the two above

mentioned configurations, referred as unified power quality conditioner, are also used.

Power Conditioning by Shunt Active Filter (IJIRST/ Volume 2 / Issue 06/ 018)


Control Strategy D.

The control strategies of active filters are mainly based on the Fourier analysis and instantaneous reactive power theory.

III. ACTIVE FILTER POWER CIRCUIT

Active filters are basically static power converters designed to synthesize a current or voltage source. There are two types of

power circuits used for active filters implementation:

Voltage Source Inverters A.

Which have a voltage source on the dc bus (a capacitor working as energy storage device). The inverter output delivers the

voltage waveform required for compensation purpose. For high power applications, where efficiency and losses are of primary

concern, a single pulse of voltage, for each cycle, can be used to synthesize an Ac voltage. For application requiring dynamic

performances, the pulse width modulation technique is mostly used.

Current Source Inverters B.

It is characterized by a current source inverter on the dc bus (an inductor working as energy storage device). The circuit results

from rectifier topology, using force commutated devices with reverse blocking capacity as switches, and are typically driven by

using pulse width modulation techniques.

Fig. 1: Shunt active filtering of non-linear loads.

A shunt active filter is designed to be connected in parallel with the load. It detects the harmonic current of load and injects

into the system a compensating current, identical with the load harmonic current but in opposite phase. Therefore, the net current

drawn from the distribution network at the point of coupling of filter and the load will be a sinusoidal current of only

fundamental frequency. Fig.1 shows the principle of operation and the connection scheme of a shunt active filter (made of a

static power converter).

IV. ACTIVE FILTERS CONTROL

Active filter control is an important tool in achieving the overall compensation objectives. There are mainly two kinds of control

strategies for analyzing and extracting current or voltage harmonics from distorted waveforms:

Frequency-Domain A.

That is based on the Fourier analysis in the frequency-domain;

Time-Domain B.

That is based on the theory of instantaneous reactive power in the three-phase circuits and is often called p-q theory.

Regarding the quantity that has to be measured and analyzed in order to generate the reference signal required by the active

control system, there are three kinds of approaches:

load current detection;

supply current detection;

Voltage detection.



Load current detection and supply current detection are recommended for shunt active filters working locally, for individual

non-linear high-power consumers. Voltage detection is suggested for: (a) shunt active filters functioning in complex equipments,

so called uniform power quality conditioner, whose destination is mostly to equip the distribution substations; (b) shunt active

filters located in the distribution system and supported by utilities. The series active filters are mostly controlled on the basis of

supply current detection.

V. P-Q THEORY DESCRIPTION

The p-q theory, or “Instantaneous Power Theory”, was developed by Akagi et al in 1983, with the objective of applying it to the

control of active power filters.

Initially, it was developed only for three-phase systems without neutral wire, being later worked by Watanabe and Aredes, for

three-phase four wires power systems.

This theory is based on time-domain, what makes it valid for operation in steady-state or transitory regime, as well as for

generic voltage and current power system waveforms, allowing to control the active power filters in real-time. Another important

characteristic of this theory is the simplicity of the calculations, which involves only algebraic calculation (exception done to the

need of separating the mean and alternated values of the calculated power components).

The p-q theory performs a transformation (known as “Clarke Transformation”) of a stationary reference system of coordinates

a – b - c to a reference system of coordinates α - β - 0, also stationary.

Fig. 2: Generation of reference compensating current by p-q method

VI. SIMULATION AND ANALYSIS

Simulation of Shunt Active Filter Based On P-Q Theory for Steady State Condition A.

Fig. 3: Simulation Diagram of Shunt Active Filter Based On p-q Theory



Fig. 4: waveforms of phase-A (a) distorted load current (b) compensating current by filter (c) source current after compensation

Fig. 5: harmonics spectrum of phase-A (a) distorted load current (b) compensating current by filter (c) source current after compensation

Fig. 6: Wave Forms of (a) Distorted Load Current in Phase-A and (b) THD of Load Current (28.66%)



Fig. 7: Wave Forms of (a) Compensated Source Current in Phase-a, and (b) THD of Source Current (2.57%)

Fig. 8: Wave Form of the Voltage across Capacitor Connected on D.C. Side of Inverter

VII. CONCLUSIONS

Proliferation of the power electronic equipments leads to an increasing harmonic contamination in power transmission or

distribution systems. Many researchers from the field of the power systems and automation have searched for different

approaches to solve the problem. One way was open by introducing the harmonic compensation by using active filters.

Simulation results were obtained before and after the use of the active filtering. From the analysis of the experimental data, in

case of a nonlinear load of rectifier type, one may observe that there are different levels of current distortion produced depending

on the load and its control mode, with high values of the total current harmonic distortion and low power factor.

Using the active filter, the experimental data show that the total harmonic distortion of current (THDi) decreases to 1%-4%, and

the power factor rises up to 0.98-1. A 30% decrease of the r.m.s. value of the current was also recorded.

REFERENCES

[1] Akagi, H., “Modern active filters and traditional passive filters”; Bulletin of The Polish Academy of Sciences Technical Sciences; Vol. 54, No. 3, pp. 255-

269; 2006. [2] Akagi, H., ”New trends in active filters for improving power quality”, in Proc. of the International Conference on Power Electronics, Drives and Energy

Systems for Industrial Growth, 1996,Vol. 1, Issue 8-11, Jan. 1996, pp. 417 - 425.

[3] Gligor, A., “Contribuţii privind sistemele avansate de conducere şi optimizare a proceselor energetice în instalaţiile electrice la consumatori”, PhD Thesis, Universitatea Tehnică Cluj-Napoca, 2007.



[4] Codoiu, R., “Selection of the representative non-active power theories for power conditioning”, Proceedings of the International Scientific Conference

Inter-Ing. 2007, Tg. Mureş, 2007, pp.V-6-1 - V-6-14.

[5] Codoiu, R., Gligor, A., “Current and power components simulation using the most recent power theories”, Proceedings of the International Scientific

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[6] A. E. Emanuel, “Summary of IEEE Standard 1459: definitions for the measurement of electric power quantities under sinusoidal, nonsinusoidal, balanced, or unbalanced conditions,” IEEE Trans. Ind. Appl., vol. 40, no. 3, May- 2004,pp. 869–876.

[7] IEEE Recommended Practices and Requirements for Harmonic Control of Electrical Power systems, IEEE Standards. 519-1992, 1993.

[8] H.Akagi, “New trends in active filters for power conditioning,” IEEE Industry Applications., vol. 32, No-6,1996, pp. 1312-1322. [9] J.Afonso, C. Couto, and J.Martins, “Active filters with control based on the p–q theory,” IEEE Ind. Electron. Soc. Newslett., Sep.2000, pp. 5–11.

[10] V.Soares,P.Verdelho,and G.D.Marques,“An instantaneous active and reactive current component method for active filters,” IEEE Trans. Power Electron.,

vol. 15, no. 4, July- 2000, pp. 660–669. [11] Naimish Zaveri, A.R.Chudasama, “Simulation Study andComparative Analysis of Different Control Techniquesused for Three Phase Three Wire Shunt

Active FiltersIJEE, Vol-1,No.-2, In press.

power conditioning by shunt active filter

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