International Journal of Electrical and Electronics Research ISSN 2348-6988 (online)
Vol. 4, Issue 3, pp: (14-23), Month: July - September 2016, Available at: www.researchpublish.com
Harmonic Reduction and Power Factor
Improvement Using Shunt Active Filter in
Wind Power Generating System
K.Ramesh1, G.Tholkappia Arasu2
1
Jayam College of Engineering and Technology South India-636813
2
AVS College of Technology South India-636106
Abstract: This paper work concentrates on augmentation of power quality in wind energy system (WES) using
3-Phase, Seven Level -Shunt Active Filter (SL-SAF). In this surroundings, the permanent magnet synchronous
generator (PMSG) based 2.5 kW WES is considered to implement SL-SAF. The main intention of this SL-SAF is
to enhance the power quality in the proposed system, when WES output changes with the wind speed and also to
the variation in load condition. Furthermore, it reduces the power loss during low wind velocity and also due to
total harmonic distortions (THD) with improved power factor. In this work, the proposed system performance
parameters like output voltage frequency and THD levels are analyzed for various wind velocities and unbalanced
load conditions. In addition, the validity of SL-SAF is analyzed with the intelligent fuzzy logic based pulse width
modulation techniques (FL-PWM). The MATLAB/Simulink modeling of proposed system is evaluated and the
proportional results are used to authenticate the parameters of the SL-SAF converter.
Keywords: Multi level inverter, Non-linear load, Shunt Active Filter, Total Harmonic Distortion, Wind Energy
System, Pulse width modulation.
1. INTRODUCTION
In recent times, the power quality is becoming a serious issue in electrical systems due to extensive use of non-linear
loads, such as adjustable speed drives, uninterruptible power supply systems, battery charging system, etc. These
equipments usually use either diode or thruster to realize power conversion on the basis of lower component cost and less
control complexity. However, the converters to generate a large amount of harmonic current into the electrical supply
system and the resulting harmonic distortion may leads to failure of sensitive equipments. In order to reduce the harmonic
content in the system, the passive filters have been installed. Moreover, the harmonics are amplified and it may degrades
the power quality of the system [1], [3], [4].The researchers identified various active filtering approaches have been
presented to address the harmonic issues in the power system [5]–[8], [15]. The active filters are proposed for
compensating harmonic current and also to maintain the most optimum performance in terms of power factor.
However, the requirements of harmonic free current waveforms and good power factor, under non-sinusoidal voltage
conditions are contradictory to each other. When the supply voltage is non-sinusoidal and it is connected to an unbalanced
non-linear load. Hence, an attempt was made to get harmonic free current by installing a shunt filter which resulted in a
poor power factor. Similarly, any attempt to improve the power factor will result in distorted current waveforms. Under
these conditions, an optimum performance is the best one which can achieve. Many researchers in the past have worked
with different methodologies but, there was always an avenue for new methods to improve upon their work. In this
research a methodology by using seven level shunt active filters is developed to address both mitigation of harmonics and
enhancement in power factor.In this context, the application of active filters, both series and shunt type have been widely
researched by various researchers. The context of application and the scheme is explained for identifying the harmonic
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International Journal of Electrical and Electronics Research ISSN 2348-6988 (online)
Vol. 4, Issue 3, pp: (14-23), Month: July - September 2016, Available at: www.researchpublish.com
content, which varies from one scheme to the other in [6], [7]. Generally, a SAF employs a pulse width modulation based
switching strategy for the inverter devices in order to dynamically counter the fundamental reactive compon ent and also
the harmonic components in the source current in [3]. This target is obtained by implementing control algorithms of the
reference current and a quick response procedure to get the control signal and simultaneously quick controlling DC-side
capacitor voltage of the inverter as explained in [2], [10], [11], [12].
In this connection various control algorithms namely Fuzzy logic Controller (FLC) and other intelligent controllers has
been proposed by the researchers [2], [9],[ 16]. The advantages of FLC over conventional controllers are that, they do not
need an accurate mathematical model. In this work, fuzzy logic based PWM controller is implemented for shunt active
power filter for the harmonics compensation under non-linear loads.
1.1 Methods of WES:
The power converters behave as nonlinear loads to AC supply system and cause harmonic injection, lower power-factor
and poor voltage regulation in AC network. Moreover, single-phase loads on a 3-phase supply system result in an
unbalanced system voltage and supply current. The unbalanced voltage and non linear current affects the performance of
other loads which is connected to this particular system. The foresaid issues were discussed by many researchers and the
implementation of active filters provided better results than conventional methods. Several filters were used to eliminate
harmonics and lossless in the system using passive elements inductance and capacitance (L and C) or active elements
namely solid state Voltage source Inverter (VSI) and Current Source Inverter (CSI).
1.2 Configuration of Proposed WES
In this work, a 3-bus WES test system is considered to implement and analyse the proposed
simulink tool. In this system consists of a small wind turbine is coupled with a PMSG.
SL-SAF using MATLAB
(a). Proposed WES system configuration
In the above mentioned WES system configuration , the bus 1 and bus 3 have PMSG generator of 3 kW capacities, the
generator output power changes with respect to different wind velocities and loading conditions. In this the oscillating
generator output power is delivered to the load at bus 2.
1.2.1 Mathematical Model of the PMSG:
A permanent magnet synchronous generator (PMSG) rated 3 kW, 440 V and rated speed of 600 rpm is employed in the
WES. The output voltage of the generator varies with respect to the wind speed variation. The equation (1) shows the
mechanical output power of the wind turbine and it is given by cube law:
Pw =
S.
𝝀 ………………… (1)
where ρ is the air density (kg/m3 ), S is the surface of the turbine blades (m2 ) and VW is the average wind velocity in (m/s),
Cp is the power coefficient.
The equation (2) gives the tip speed ratio function.
𝝀=
………………………………….. (2)
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International Journal of Electrical and Electronics Research ISSN 2348-6988 (online)
Vol. 4, Issue 3, pp: (14-23), Month: July - September 2016, Available at: www.researchpublish.com
where 𝝎m is the rotor mechanical speed (rad/s) and R is the blade radius. The equation (3) shows the wind turbine output
torque Tw .
Tw
……………….. (3)
The line to line voltage of an ideal (unloaded and loss -less) PMSG is given as:
VL
………………………………… (4)
Where KV is the voltage constant and 𝝎e is the electrical frequency related to the mechanical speed 𝝎m by the relation
𝝎e
…………………………… (5)
where, NP is the number of poles in PMSG.
The mathematical expressions from equations (1) - (5) are used to develop the MATLAB simulink model. In simulation
model, the 3-phase PMSG is considered which provides maximum power of 3 kW at wind velocity of 12 m/s. The voltage
rating is 440V, when speed of generator nearly 500 rpm. The speed of the generator changes from 160 rpm to
560
rpm at various wind velocities.
1.3 Configuration of SL-SAF system:
The proposed SL-SAF is to improve the quality output voltage in the test system. The power rating of VSIs is not capable
to carry out the huge and sudden changes in the load. This may produce a change in system voltage level and generating
harmonics to the system. The multilevel inverter is designed to generate nearly sinusoidal output voltage waveform and to
eliminate THD. In this context, a key concern in the fundamental switching scheme is to determine the switching angles
in order to generate the voltage with fundamental frequency.
(b). Proposed 3- phase Seven Level-SAF inverter
Hence, the proposed SL-SAF topology as shown in above, the number of output voltage levels (Nlevel ) of the generated
voltage (V) are calculated from equations (6) and (7).The voltage level equations are expressed as follows:
……………………. (6)
Where, n=1,
Hence,
=7 ………………………………. (7)
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International Journal of Electrical and Electronics Research ISSN 2348-6988 (online)
Vol. 4, Issue 3, pp: (14-23), Month: July - September 2016, Available at: www.researchpublish.com
Modulation Index (MI)
(
)
................... (8)
Where,
Am=Amplitude of modulating wave
Ac=Amplitude of carrier
Nlevel =Number of voltage levels
The modulation index (MI) of the SL-SAF is varied on the basis of equation (8) in PWM signal of fixed 10 kHz
frequency to reduce harmonic content. Hence, the generated signal will give the needed voltage level and also mitigate the
harmonics in the proposed SL-SAF system.
1.3.1 Control Schemes for SL-SAF:
In this control method, PWM signal is generated to control the Shunt Active Filter (Inverter). In this context, the 3-phase
load current has been considered. Moreover, controller is converted into αβ and dq using Park and Clarke transformation.
This dq- axis indicates the active, reactive and reference components of the three phase currents respectively.
The disparity in active element from the load current and shunt converter current has been analyzed with the difference in
reactive components of the both proposed SAF converter and load currents. Subsequently, this variation will provide the
available active and reactive current to overcome the requirement.
(c). PWM control structure for SL-SAF
The PWM pulse is generated by converting this resultant dq component into three phases (ABC) component using inverse
Park and Clarke transformation. The generated three phase reference signal with (αβ) and voltage magnitude is used to
select suitable switching sector of a SL-SAF inverter using fuzzy based PWM control schemes.
1.4 Fuzzy logic implementation”
Consequently, the various control algorithms are discussed for controlling the pulse width in [8]. In this work, Fuzzy logic
controller is used for finding suitable MI to the PWM signal. Hence, if the mathematical model of the system is
acknowledged. It is not essential to design the fuzzy logic controller.
In the membership function, seven linguistic values namely, {Negative Big (NB), Negative Middle (NM), Negative Small
(NS), Zero (ZE), Positive Small (PS), Positive Middle (PM) and Positive Big (PB)}. The output variable u (the control
value), which also have seven language values {Negative Big (NB), Negative Middle (NM), Negative Small (NS), Zero
(ZE), Positive Small (PS), Positive Middle (PM), Positive Big (PB)}.
Tab. (i) Fuzzy logic rules to select MI
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International Journal of Electrical and Electronics Research ISSN 2348-6988 (online)
Vol. 4, Issue 3, pp: (14-23), Month: July - September 2016, Available at: www.researchpublish.com
CE/E
NB
NM
NS
ZE
PS
PM
PB
NB
ZE
NB
NB
NB
NS
NS
NM
NM
NB
NB
NS
NS
NS
ZE
ZE
NS
NB
NM
NS
NS
ZE
PS
ZE
ZE
PM
PS
PS
ZE
PS
ZE
NS
PS
ZE
ZE
ZE
PS
PB
PM
ZE
PM
ZE
ZE
ZE
PB
PB
PB
PS
PB
PM
PM
PS
PB
PB
PM
ZE
The main objective function is proposed in eqn. (8), based on that fuzzy controller was designed and the fuzzy sets are
presented in Tab. (i), based on the defined linguistic values.
(d). Structure of fuzzy logic controller
There are 49 consequent rules for this fuzzy controller is implemented to control the output voltage level and also to
reduce THD in the system.
(e). Input and output membership function for proposed FL-PWM
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International Journal of Electrical and Electronics Research ISSN 2348-6988 (online)
Vol. 4, Issue 3, pp: (14-23), Month: July - September 2016, Available at: www.researchpublish.com
The range of the input 1 (CE) and input 2 (E) is [-100, +100]. The corresponding MI output from the FLC is varies from
0.4 to 1.
2. RESULTS AND DISCUSSIONS
The proposed SL-SAF with FL-PWM is modeled in MATLAB simulink tool. The simulink parameters are listed in Tab.
(ii).The tab. (ii) shows that, the modeling parameters of power supply and SL-SAF. The proposed system configuration is
tested for various loads such as squirrel cage induction motor, uncontrolled diode bridge rectifier with resistive load and
three phase star connected loads. Further, the control of the system is analyzed which based on with and without Shunt
Active Filter. Hence, the results have been compared for both conditions.
(f). Simulink model of proposed WES with SL-SAF
Tab. (ii)Simu lin k parameters of non-linear loads
SL-SAF Parameter
DC source (Vdc)
100 V
Parameters of induction motor
Machine type
Wound rotor
Power rating
4 KVA
Supply voltage
400 Volts
Frequency
50 Hz
Rated Speed
1500 RPM
Stator resistance
1.405 Ω
Stator Inductance
5.839 mH
Rotor resistance
1.395 Ω
Rotor Inductance
5.839 mH
Mutual Inductance (Lm)
0.1722 H
Parameters of 3-phase resistive load
Connection Type
Star connected
Resistance ( Ra & Rc)
50 Ω
Resistance (Rb )
100 Ω
Uncontrolled diode bridge rectifier
Resistance (RL )
50 Ω
This simulink model shows that, the 3- phase supply system associated with the non-linear loads such as Squirrel cage
induction motor, Diode bridge rectifier and star connected load. Due to the non -linear load characteristics the system will
drawn different currents from the system. This non-linear load also injects the harmonics in the system. This will leads to
poor power factor and high THD content.
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International Journal of Electrical and Electronics Research ISSN 2348-6988 (online)
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The results of the proposed system without Shunt active filter is indicated in the waveform. This harmonic spectrum
shows that, the fundamental current of 25 Amps in magnitude. In this context, there is no even order harmonic present in
this system. So the effect of even order harmonic is vanished. But it contains the 5 Amps of DC component.
Tab.(iv) Comparison of THD% for various MI
THD in %
Modulation
SL-SAF
SL-SAF
Index
with
with
(MI)
conventional
fuzzy based PWM
PWM
1
13.82
4.307
0.9
12.93
4.358
0.8
10.66
4.923
0.7
11.61
5.030
(1)
(2)
(g). (1) Seven level converter current waveform (2) Individual phase currents without passive components
The SL-SAF without filter is shown in the seven level converter current waveform and individual phase currents without
passive components are applied through RLC elements to get the pure sinusoidal waveform. The amount of THD
generated in the system before and after SL-SAF compensation is given in Tab.(iii) and injected waveforms are illustrate.
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International Journal of Electrical and Electronics Research ISSN 2348-6988 (online)
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Tab. (iii). Harmonic analysis before and after SL-SAF
Compensation
After Compensation
Before
Order of
Harmonics
1st
3rd
5th
7th
9th
11th
13th
15th
17th
19th
Compensation
Current Magnitude
in (Amps)
Current Magnitude in
(Amps)
28.000
0.1507
0.4520
0.3160
0.0303
0.2808
0.0048
0.3177
0.2612
0.0245
25.000
0.0316
0.6490
1.1790
0.0125
0.2356
0.0054
0.0084
0.1686
0.0183
(h).Injected current using SL-SAF under load disturbance
(i). Harmonic spectrum for Non-linear Load without SL- SAF (Modulation Index=1)
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International Journal of Electrical and Electronics Research ISSN 2348-6988 (online)
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(j). Harmonic spectrum for non-linear load with SL-SAF (Modulation Index =1)
In this context, the effect of 5th order harmonic is higher than that of other odd order harmonics. The system has 12.82 %
current THD before SL-SAF compensation. This THD% is eliminated into 3.307% after implementing the SL-SAF with
fuzzy logic based PWM. Similarly THD analysis has been carried out for various loading conditions; the Fuzzy based
SL-SAF improves the power factor in the system and also reduces the THD by tuning the modulation index of PWM
signal. The results for various MI are illustrated in Tab. (iv).
The harmonic spectrum for non linear load without and with SL-SAF for MI as one (MI=1) are shown in Diagram. (i) and
(j), respectively. It is found that, the power factor in the proposed WES system has been improved to the standard level
(nearly 0.9) by implementing SL-SAF. Consequently, the total harmonic content in the system under various loading
conditions has been reduced by tuning MI of the PWM signal with the help of FL-PWM.
3. CONCLUSION
This research reveals that, the conventional SAF with traditional PWM control is simple and gives the required output
levels but also introduces a considerable ripple in the output with lower order harmonics . This paper discussed these
issues and addressed it with the new SL-SAF inverter mitigate the THD in the proposed WES. The FL-PWM is
implemented to optimize the suitable Modulation Index (MI). The simulation results obtained through this proposed
method indicates that, the voltage ripple and current THD is reduced to 4.3% under various load disturbance and
unbalanced load conditions . The simulation study also highlights that the proposed SL-SAF with FL-PWM method which
gives good control over the power quality of the system. In summary, the power quality improvement was completed by
employing SL-SAF in WES through the reduction of THD and enhancement in power factor to the standard level as
compared to the existing system.
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