report of Improvement of the Electric Power Quality Using Series Active and Shunt Passive Filters

Improvement of the Electric Power Quality Using
Series Active and Shunt Passive Filters
REVA INSTITUTE OF TECHNOLOGY AND MANAGEMENT Page 1
CHAPTER 1
INTRODUCTION
INTRODUCTION
The increase of nonlinear loads due to the proliferation of electronic equipment causes power
quality in the power system to deteriorate. Harmonic current drawn from a supply by the
nonlinear load results in the distortion of the supply voltage waveform at the point of
common coupling (PCC) due to the source impedance. Both distorted current and voltage
may cause end-user equipment to malfunction, conductors to overheat and may reduce the
efficiency and life expectancy of the equipment connected at the PCC.
Harmonics and reactive power regulation and guidelines are upcoming issues and
increasingly being adopted in distributed power system and industries. Vital use of power
electronic appliances has made power management smart, flexible and efficient. But side by
side they are leading to power pollution due to injection of current and voltage harmonics.
Harmonic pollution creates problems in the integrated power systems. The researchers and
engineers have started giving effort to apply harmonic regulations through guidelines of IEEE
519-1992. Very soon customers have to pay and avail the facility for high performance, high
efficiency, energy saving, reliable, and compact power electronics technology. It is expected
that the continuous efforts by power electronics researchers and engineers will make it
possible to absorb the increased cost for solving the harmonic pollution. The thyristor
controlled reactors of various network configurations are widely used in industries and utility
systems for harmonic mitigation and dynamic power factor correction. These thyristor
controlled reactor operate as a variable reactance in both the inductive and capacitive
domains. By means these two parameters two types of problems are normally encountered.
The first problem is the reactive power (Var) that leads to poor power factor and the
harmonics appears due to presence of power converter devices and nonlinear loads for
example, electrics machines, fluctuating industrial loads, such as electric arc furnaces, rolling
mills, power converters etc. These types of heavy industrial loads are normally concentrated
in one plant and served from one network terminal, and therefore, can be handled best by a
local compensator connected to the same terminal.
The main emphasis of the investigation has been on compactness of configurations,
simplicity in control, reduction in rating of components, thus finally leading to saving in
overall cost. Based on these considerations, a wide range of configurations of power quality
mitigators are developed for providing a detailed exposure to the design engineer in selection
of a particular configuration for a specific application under the given constraints of economy
and the desired performance. Fig 1.1 shows a classical shunt passive filter is connected the

power system through common coupling point (PCC). Because of using non-linear load, the
load current is highly non-linear in nature. The compensating current which is the output of
the shunt passive filter is injected in PCC, by this process the harmonic cancellation take
place and current between the sources is sinusoidal in nature. The passive filter is popular in
cancellation of harmonic current in power system.
Fig.1.1 The Classical Shunt Passive Filter.
To control this process, there are two ways i.e.
(i)Harmonic extraction technique
(ii)Current modulator
1.1.2 Harmonic Extraction
The harmonic extraction is the process in which, reference current is generated by using the
distorted waveform. Many theories have been developed such as p-q theory (instantaneous
reactive power theory), d-q theory, P-I controller, adaptive controller etc. Out of these
theories more than 60% research works have been consider p-q theory and d-q theory due to
their accuracy, robustness and easy calculation.
1.1.3 Current Modulator
Current modulator mainly provides the gate pulse to the ac-dc converter. There may be many
techniques used for giving the gate signals to PWM VSI or CSI such as sinusoidal PWM,
triangular PWM etc. The above described two control techniques (harmonic extraction
technique and current modulator technique) are main research foci of many researchers in
recent years. It may be noted that either harmonics extraction technique or the current
modulator can be used individually or both at a time. Apart from these two techniques, most
of the research works are directed also in dealing with multi-level rectifier control problems.

1.2 SERIES ACTIVE POWER FILTER Series APF are operated mainly as a voltage
regulator and a harmonic isolator between the nonlinear load and the utility system. The
series connected filter protects benefit the consumer from an inadequate supply voltage
quality. This type of approach is mostly recommended for compensation of voltage
unbalances and voltage sags from the AC supply and for low applications and represents
economically attractive alternatives to utility power system, since no energy storage is energy
and the overall ratings of the components is smaller. The advantages of series active power
are- automatic compensation for varying loads, resonance free, does not affect power factor
and can be combined with passive filter network. inverter. The output of the series active
power filter is connected to the main lines through series transformers so as to make the load
voltage purely sinusoidal the harmonic voltage is absorbed or injected by the filter.
Fig.1.2 Circuit Configuration of Series active power filter (APF).

2.1 Traditionally, a passive LC power filter is used to eliminate current harmonics when it is
connected in parallel with the load. This compensation equipment has some drawbacks due to
which the passive filter cannot provide a complete solution. These disadvantages are mainly
the following.
The compensation characteristics heavily depend on the system impedance because the filter
impedance has to be smaller than the source impedance in order to eliminate source current
harmonics. Overloads can happen in the passive filter due to the circulation of harmonics
coming from nonlinear loads connected near the connection point of the passive filter. They
are not suitable for variable loads, since, on one hand, they are designed for a specific
reactive power, and on the other hand, the variation of the load impedance can detune the
filter. Series and/or parallel resonances with the rest of the system can appear.
Fig. 2.1 Series active filter and parallel passive filter.
An active power filter, APF, typically consists of a threephase pulsewidth modulation (PWM)
voltage source inverter. When this equipment is connected in series to the ac source
impedance it is possible to improve the compensation characteristics of the passive filters in
parallel connection. This topology is shown in Fig. 2.1, where the active filter is represented
by a controlled source, where Vc is the voltage that the inverter should generate to achieve
the objective of the proposed control algorithm.

Different techniques have been applied to obtain a control signal for the active filter One such
is the generation of a voltage proportional to the source current harmonics. With this control
algorithm, the elimination of series and/or parallel resonances with the rest of the system is
possible. The active filter can prevent the passive filter becoming a harmonics drain on the
close loads. Additionally, it can prevent the compensation features depending on the system
impedance. From the theoretical point of view, the ideal situation would be that the
proportionality constant, k, between the active filter output voltage and source current
harmonics, had a high value. However, at the limit this would be an infinite value and would
mean that the control objective was impossible to achieve. The chosen k value is usually
small so as to avoid high power active filters and instabilities in the system. However, the
choice of the appropriate k value is an unsolved question since it is related to the passive
filter and the source impedance values. Besides, this strategy is not suitable for use in systems
with variable loads because the passive filter reactive power is constant, and therefore, the set
compensation equipment and load has a variable power factor. In another proposed control
technique, the APF generates a voltage waveform similar to the voltage harmonics at the load
side but in opposition. This strategy only prevents the parallel passive filter depending on the
source impedance; the other limitations of the passive filter nevertheless remain.
Fig. 2.2 Transformation from the phase reference system (abc) to the 0αβ system.

Fig. 3.1. Three-phase system.
3.THE DUAL INSTANTANEOUS REACTIVE POWER THEORY
The instantaneous reactive power theory is the most widely used as a control strategy for the
APF. It is mainly applied to Fig. 3. Three-phase system. compensation equipment in parallel
connection. This theory is based on a Clarke coordinate transformation from the phase
coordinates (see Fig. 2.2).
In a three-phase system such as that presented in Fig.3, voltage and current vectors can be
defined by
The vector transformations from the phase reference system a-b-c to α-β-0 coordinates can be
obtained, thus
The instantaneous real power in the α-β-0 frame is calculated as follows:

Fig 3.2. Dual instantaneous power theory
In this case, the nonlinear load consists of an uncontrolled three-phase rectifier with an
inductance of 55 mH and a 25 resistor connected in series on the dc side. Fig. 7 shows the
phase “a” load current. The load current total harmonics distortion (THD) is 18.6% and the
power factor 0.947, when the system is not compensated. The 5th and 7th harmonics are the
most important in the current waveform. They are 16.3% and 8.4% of the fundamental
harmonic, respectively. Two LC branches were connected to mitigate the fifth and seventh
harmonics. The source current waveform with the passive filter connected is shown in Fig. 8.
The THD falls to 4.7%. The 5th and 7th harmonics decrease to 3.6% and 0.9%, respectively.

4. SIMULATION RESULTS
The system shown in Fig. 6 has been simulated in the Matlab- Simulink platform to verify the
proposed control. Each power device has been modeled using the SimPowerSystem toolbox
library. The power circuit is a three-phase system supplied by a sinusoidal balanced three-
phase 100-V source with a source inductance of 5.8 mH and a source resistance of 3.6ohm.
The inverter consists of an Insulated Gate Bipolar Transistor (IGBT) bridge. On the dc side,
two 100-V dc sources are connected. An LC filter has been included to eliminate the high
frequency components at the output of the inverter. This set is connected to the power system
by means of three single-phase transformers with a turn ratio of 1:1.
Fig. 4. Series active power and passive filter topology.
The passive filter is constituted by two LC branches tuned to the fifth and seventh harmonics.
Each element value is included in Table I.

CHAPTER 2
RESULTS AND DISCUSSIONS
Here simulation has been carried out for series active, shunt active, shunt passive, filters, by
using MATLAB SIMULINK.FFT analysis is done, THD is observed for various circuits.
Fig 5.FTT analysis of compensating voltage wave form
Fig 6: Representation of each and every harmonic

Fig 7: FFT analysis of compensating current.
. Fig 8: FFT analysis of Compensating voltage wave form at PCC

Simulation
Output waveform

CHAPTER 3
CONCLUSION & REFERENCE
CONCLUSION
 A control algorithm for a hybrid power filter constituted by a series active filter and a
passive filter connected in parallel with the load is proposed. The control strategy is
based on the dual vectorial theory of electric power. The new control approach
achieves the following targets. The compensation characteristics of the hybrid
compensator do not depend on the system impedance. The set hybrid filter and load
presents a resistive behavior. This fact eliminates the risk of overload due to the
current harmonics of nonlinear loads close to the compensated system.
 This compensator can be applied to loads with random power variation as it is not
affected by changes in the tuning frequency of the passive filter. Furthermore, the
reactive power variation is compensated by the active filter. Series and/or parallel
resonances with the rest of the system are avoided because compensation equipment
and load presents resistive behavior. Therefore, with the proposed control algorithm,
the active filter improves the harmonic compensation features of the passive filter and
the power factor of the load.
REFERENCES
Author(s)
1. P.Salmeron
Electric Engineering Department, Huelva Univ., Huelva, Spain
S. P. Litran
2. F. Z. Peng and D. J. Adams, “Harmonics sources and filtering approaches,in Proc.
Industry Applications Conf., Oct. 1999, vol. 1, pp. 448–455.
3. J. C. Das, “Passive filters-potentialities and limitations,” IEEE Trans. Ind. Appli., vol.
40, no. 1, pp. 232–241, Jan. 2004.
4. H. L. Ginn, III and L. S. Czarnecki, “An optimization based method for selection of
resonant harmonic filter branch parameters,” IEEE Trans.Power Del., vol. 21, no. 3,
pp. 1445–1451, Jul. 2006.
5. ieeexplore.ieee.org/iel5/61/5437451/05361356.pdf?arnumber.
6. www.ijmer.com
Feb. 2004.

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