E-ISSN: 2278–179X
JECET; March 2016- May 2016; Sec. C; Vol.5. No.2, 187-193.
Journal of Environmental Science, Computer Science and
Engineering & Technology
An International Peer Review E-3 Journal of Sciences and Technology
Available online at www.jecet.org
Section C: Engineering & Technology
Research Article
Harmonics Mitigation Techniques Using Shunt Active
Power Filters
1Nitesh Agrawal, 2Monika
Vardia
1
M. Tech Student, Geetanjali Institute of Technical Studies, Udaipur
2
Assistant Professor, Geetanjali Institute of Technical Studies, Udaipur
Received: 03 March 2016; Revised: 06 April 2016; Accepted: 13 April 2016
Abstract: The control of a shunt active power filter (APF) designed for harmonic and
reactive current mitigation. This paper briefly describes harmonic mitigation methods
for low voltage and medium voltage power distribution systems. It presents the
progress in harmonic mitigation methods starting from passive filtering, active
filtering to hybrid filtering and control techniques for shunt active filter (SAF) for low
voltage power distribution system.
Keywords: Active power filter, harmonic currents, reference source current, nonlinear loads.
INTRODUCTION
Rapid advancements in the power electronics technology have resulted in the usage of various power
electronics equipment’s for both industrial and commercial applications. This widespread use of
power electronics equipment pollutes the power system with harmonic currents due to its nonlinear
nature. The harmonic currents causes many adverse effects such as low power factor, overheating of
power system components, EMI problems1, 2 .Conventionally shunt passive LC filters are used to
compensate harmonic currents and improvement of power factor. However they offer many
disadvantages like large size, possibility of resonance and fixed compensation characteristics3, 4.
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Conventionally, passive filters have been used to limit the harmonic currents in power distribution
systems. However, they have several drawbacks such as the inability to compensate random
frequency variations in currents, degradation of the filtering performance due to parameter variations,
tuning problems, and parallel resonance5. In order to solve these problems, the APF has been designed
to cancel the current harmonic distortion by injecting the same distortion, but with the opposite
polarity, thereby improving power quality6, 7.
HARMONIC MITIGATION IN LOW VOLTAGE POWER DISTRIBUTION SYSTEM
Harmonic distortion in a power distribution system can be suppressed through three basic approaches
namely:
(1) Passive filtering
(2) Active power filtering and
(3) Hybrid active power filtering.
2.1 Passive Filtering of Harmonics: Shunt passive filters are configured with inductance,
capacitance and resistance elements and tuned to control harmonics. Common types of passive filters
and their configurations are shown in Fig.1.
(a)
(b)
Fig.1: (a) A passive high pass filter made using a capacitor and a resistor (b) A passive low pass filter
made using a capacitor and a resistor
Shunt passive filters are advantageous over series compensators as they will compensate for
harmonics as well as reactive power, in addition they will not carry large currents hence associated
losses are less. Notch reduction is used in a power distribution system having large electronic loads.
Notch filter will buy pass the high frequency harmonics to ground. Single tuned filters are more
effective to suppress harmonics of selected frequency. The first-order filter, which is characterized by
large power losses at fundamental frequency but it is simple to implement. The second-order HPF
provides good filtering action and fundamental frequency losses are less. The filtering performance of
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the third-order HPF is superior to that of the second-order HPF. However, it is found that the thirdorder HPF is not commonly used for low-voltage or medium-voltage applications since the economic,
complexity, and reliability factors do not justify them. Although simple and least expensive, the
passive filter inherits several shortcomings. The filter components are very bulky because the
harmonics that need to be suppressed are usually of the low order. Furthermore the compensation
characteristics of these filters are influenced by the source impedance and filter design is heavily
dependent on the power system in which it is connected. The passive filter is also known to cause
resonance, thus affecting the stability of the power distribution systems. Frequency variation of the
power distribution system and tolerances in components values affect the filtering characteristics. The
size of the components become impractical if the frequency variation is large.8, 9.
2.2 Active Filtering of Harmonics: The progress in power electronics had spurred interest in active
power filter (APF) for harmonic distortion mitigation. The hybrid filter topologies include series
active filter and shunt passive filter, shunt active filter connected in series with shunt passive filter.
The basic principle of APF is to produce specific harmonic current components that cancel the
harmonic current components caused by the nonlinear load. Fig. 2 shows the components of a typical
APF system and their connections.
Fig.2: Generalized block diagram for APF.
The information regarding the harmonic currents and other system variables are passed to the
compensation current/voltage reference signal estimator. The compensation reference signal from the
estimator drives the overall system controller. This in turn provides the control for the gating signal
generator. The output of the gating signal generator controls the power circuit. Finally, the power
circuit in the generalized block diagram can be connected in parallel, series or parallel/series
configurations depending on the interfacing inductor/transformer used.10.
APFs have a number of advantages over the passive filters. First of all, they can suppress not only the
supply current harmonics, but also the reactive currents. Moreover, unlike passive filters, they do not
cause harmful resonances with the power distribution systems. Consequently, the APF performances
are independent of the power distribution system properties. On the other hand, APFs have some
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drawbacks. APF necessitates fast switching of high currents in the power circuit resulting high
frequency noise that may cause an electromagnetic interference (EMI) in the power distribution
systems. APF can be mainly connected in three circuit configurations, namely shunt APF, series APF
and hybrid APF.
Shunt Active Power Filter (SAPF): This is the most important configuration widely used in active
filtering applications for current harmonic reduction and power factor improvement9. A shunt APF
consists of a controllable voltage or current source inverter. The voltage source inverter (VSI) based
shunt APF is the most commonly used type, due to its well-known topology and straight forward
installation procedure. SAPF acts as harmonic current source which injects an anti-phase but equal
magnitude of the harmonic and reactive current as that of nonlinear load. As a result components of
harmonic currents contained in the load current are cancelled and the source current remains
sinusoidal and in phase with the respective phase to neutral voltage. The principle configuration of a
VSI based shunt APF is shown in Fig. 3. It consists of a three leg six- Switch Bridge connected at the
point of common coupling (PCC) through an interfacing inductor (Lf) and with capacitor (Cdc)
connected on DC-side. A three phase diode bridge rectifier with an inductive load on DC side is
assumed as nonlinear load. This is achieved by “shaping” the compensation current waveform (if),
using the VSI switches. The shape of compensation current is obtained by measuring the load current
(iL) and subtracting it from a sinusoidal reference.
Fig. 3: Principle configuration of a VSI based shunt APF.
The aim of shunt APF is to obtain a sinusoidal source current (Is) as per the equation (2.1).
Is= IL− I f
(2.1)
Suppose the nonlinear load current is written as the sum of fundamental current component (IL,f) and
the harmonic current component (IL,h) as shown in Equation (2.2).
IL = IL,f + IL,h
(2.2)
If the injected compensation current of the shunt APF is equal to load harmonic current then the
resulting source current contains only fundamental component of load current as shown in equation
(2.3) and thus free from harmonics.
Is = IL − I f = IL,f
(2.3)
Shunt APFs have the advantage of carrying only the compensation current plus a small amount of
active fundamental current supplied to compensate for system losses. It can also contribute to reactive
power compensation. Moreover, it is also possible to connect several shunt APFs in parallel to cater
for higher currents, which makes this type of circuit suitable for a wide range of power ratings. The
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advantage of active filtering is that it automatically adapts to changes in the network characteristics,
eliminating the risk of resonance between the filter and network impedance.11, 12.
Series Active Power Filter: The configuration of series APF is shown in Fig. 4. It is connected in
series with the distribution line through a matching transformer. VSI is used as the controlled source,
thus the principle configuration of series APF is similar to shunt APF, except that the interfacing
inductor is replaced with the interfacing transformer as shown in Fig.4.
Fig. 4: Principle configuration of a VSI based series APF.
The operation principle of series APF is based on isolation of the harmonics in between the nonlinear
load and the source. This is obtained by the injection of harmonic voltage (vf) across the interfacing
transformer. The injected harmonic voltages are added/subtracted, to/from the source voltage to
maintain a pure sinusoidal voltage waveform across the nonlinear load.
It is controlled in such a way that it presents zero impedance for the fundamental component, but
appears as a resistor with high impedance for harmonic frequency components. That is, no current
harmonics can flow from nonlinear load to source, and vice versa. Series APFs are less common than
the shunt APF. This is because they have to handle high load currents which will increase their current
rating considerably compared with shunt APF especially on the secondary side of the interfacing
transformer. This increases the I2R losses. However, the main advantage of series APF over shunt APF
is that they are ideal for voltage harmonics elimination. It provides the load with a pure sinusoidal
waveform, which is important for voltage sensitive devices such as power system protection devices.
With this feature, series APF is suitable for improving the quality of the distribution source voltage.13
2.3 Hybrid Active Power Filter: The utilization of fast switching devices in APF application causes
switching frequency noise to appear in the compensated source current and interference with
neighboring sensitive equipment. To overcome the limitations of active filters a series hybrid active
filter topology which consists of a series active filter and shunt passive filter can be used. A series
hybrid active filter topology uses a current source inverter as series active filter and shunt high pass
filter due to excellent superior controllability and reliability of CSI inverter. The system configuration
of series hybrid APF is shown in Fig. 5, in which the series APF is coupled to the distribution line by
an interfacing transformer and passive filter is connected in parallel with the load. The shunt passive
filter consists of one or more single-tuned passive filters and/or a HPF. The series hybrid APF is
controlled to act as harmonic isolator between the source and nonlinear load by injection of controlled
harmonic voltage, thus eliminating harmonic voltages. It is controlled to offer zero impedance at the
fundamental frequency and high impedance (ideally open circuit) at all undesired harmonic
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frequencies. This constrains all the nonlinear load current harmonics to flow into the passive filter,
decoupling the source and nonlinear load at all frequencies, except at the fundamental. This
configuration is rarely used for harmonic mitigation as it requires high current rated transformer and
leading costly and bulky system.
The function of the hybrid APF thus can be divided into two parts: the passive high pass filter byepasses all higher order harmonics (Ihf) while the shunt active filter compensates for low order
harmonics (Ilf) in the load current(IL). This topology lends itself to retrofit applications with the
existing shunt APF and is used for compensating current harmonics and reactive currents Hybrid
APFs, inheriting the advantages of both passive filters and APFs, provide improved performance and
cost-effective solution. The idea behind this scheme is to simultaneously reduce the switching noise
and electromagnetic interference.
(a)
(b)
Fig.5: Hybrid APFs (a) Combination of series APF and shunt passive filter and b) Combination of
shunt APF and shunt passive filter.
CONCLUSION
The overall aim of this paper was to consider methods of achieving better utilization and control of
active power filters dealing with harmonic and reactive current compensation. Alternative schemes
based on soft computing techniques have been proposed. Nonmodel-based controllers designed
around fuzzy logic, neural network were applied to control the switching of the active power filter and
were found to provide much better response under varying load and supply conditions.
REFERENCES
1. V.E. Wagner, “Effects of Harmonics on Equipment,” IEEE Trans. on Power Delivery,
Vol. PWRD, 1993, 8, 2, 672-680.
2. C.Y. Hsu and H.Y. Wu, “A new single-phase active power filter with reduced energystorage capacity,” IEE Proc. Electr. Power appl, 1996, 143, 1, 25-30.
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Harmonics…
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3. M. TAKEDA, K. IKEDA, A. TERAMOTE and T. ARITSUKA, “Harmonic current
and reactive power compensation with an active filter,” IEEE PESC '88 conference
record, 1988, 1174-1 179
4. L. GYUGYI “Power electronics in electric utilities: static VAR compensations,” Proc.
IEEE, 1988, 76, (4), 484-494
5. H. Fujita, T. amasaki and W. Akagi, “A hybrid active filter for damping of harmonic
resonance in industrial power systems,” IEEE Trans. Power Electron., 2000, 15, 2,
215-222.
6. H. Akagi, “New trends in active filters for power conditioning,” IEEE Trans. Ind.
Appl., Nov./Dec. 1996, 32, 6, 1312-1322.
7. B. S. Rajpurohit and S. N. Singh, “Performance evaluation of current control
algorithms used for active power filters,” EUROCON, The International Conference
on ‘Computer as a Tool’, 2007, 2570-2575.
8. S. Rahmani, K. Al-Haddad & F. Fnaiech, "A hree- phase shunt active power filter for
damping of harmonic propagation in power distribution networks", Proc. IEEE
International symposium on Industrial Electronics, 2006, 3, 1760-1764.
9. M. TAKEDA, K. IKEDA, A. TERAMOTE and T. ARITSUKA, “Harmonic current
and reactive power compensation with an active filter,” IEEE PESC '88 conference
record, 1988, 1174-1 179.
10. J. C. Wu and H.J. Jou, “Simplified control method for single-phase active power
filter,” IEE proc. Electric Power Application, May. 1996, 143, 3, 219-224.
11. J. Doval, A. Nogueiras, C.M. Penalver and A. Lago, “Shunt active power filter with
harmonic current control strategy,” Proc. PELS Power Electronics Specialist
Conference (PESC),Fukuoka, Japan 1998, 1631–1635
12. E. J. Acordi, A. Goedtel and L. C. B. Nascimento, “A Study of Shunt Active Power
Filters Applied to three-Phase Four-Wire Systems”, ICREPQ’12- Spain, March, 2012,
28-30
13. Mr. S.N. Gohil, Prof. M.V. Makwana, Mr. K. T. Kadivar, Prof. G.J.Tetar, “Series
Active Power Filter with UVTG Technique for Voltage Sag and Swell
Compensation”, Journal of Information, Knowledge and Research in Electrical
Engineering, Nov 12 Oct 2013, 02, 02, ISSN: 0975-6736.
Corresponding author: Nitesh Agrawal
M. Tech Student, Geetanjali Institute of Technical Studies, Udaipur
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