International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 22 Issue 2 – MAY 2016.
143
Abstract— This paper proposes the concept of Paralleling of
four leg Shunt Active Power Filter (SAPF) in order to
compensate the four wire electrical network without disturbing
the others Performance. A New Control Strategy of Space Vector
Pulse Width Modulation (SVPWM) is introduced for an effective
Operation of SAPF in Distribution Side. Fuzzy Logic Controller
(FLC) is used to maintain the same Amplitude and Frequency of
each inverter output. Both Fuzzy Logic Controller (FLC) and
Space Vector Modulation (SVM) together provides robustness,
Reactive Power Compensation, DC Voltage Stabilization and also
used to minimizing the Source Current Harmonics, reducing the
magnitude of Neutral Current, eliminating the Zero-Sequence
Current, reducing the Switching Losses. Analysis of mentioned
devices includes theoretical calculations and simulations
performed in MATLAB/Simulink software.
Index Terms—Shunt Active Power Filter (SAPF), Harmonic
Elimination, Paralleling of SAPF, Space Vector Modulation
(SVM), Fuzzy Logic Controller (FLC).
I. INTRODUCTION
Harmonic voltages and currents present in an electrical
power system are a result of non-linear electric loads.
Harmonic frequencies are the major cause of power quality
problems in the power grid [1]. Harmonics in power systems
results in increased heating effect in both an equipment and
conductors, misfiring in variable speed drives, and torque
pulsations in motors. When a non-linear load, for example
a rectifier, is connected to the system, it draws an unequal
current that is not necessarily sinusoidal. According to the
type of load and its interaction with other equipments of the
system, the current waveform will get distorted. Even though
it is very complex the current waveform becomes, as
described through Fourier series analysis, it is possible to split
it into a number of simple sinusoids, which start at the power
system fundamental frequency and occurs at integer multiples
of the fundamental frequency (50 Hz). With increasingly
higher density of loads basing on rectifiers and switched mode
power supplies, harmonic content in supply networks becomes
widely discussed and analyzed. This leads to current
harmonics mitigation devices application. Historical approach
to mitigate an harmonic current based on passive power filters.
Semiconductor switches development allowed researchers and
engineers to introduce more sophisticated devices offering
much higher accuracy active power filters as shown in Fig.1.
As the effectiveness of these devices is in most cases more
than sufficient, the problem with their application is related
with their significant costs, especially for compensation of
industrial loads harmonic currents. In this paper an approach
to reduce transistor current and voltage rating is based on
installing additional passive power filter. Proposed passive
power filter is tuned to mitigate 5th
and 7th
harmonic current
expected highest amplitude harmonic orders [2]. As highest
harmonic currents are compensated by the passive power
filter, required converter power rating is reduced.
The potential benefits of paralleled VSI systems have led to
the investment of considerable development effort. Many of
the early systems were passive in nature, relying entirely on
incidental load balancing actions in combination with standard
control methods, sometimes combined with output filter
impedances, to keep the circulating current within reasonable
limits. These systems are still widely employed due to their
simplicity and robust nature; however their poor performance
with respect to load sharing demands significant concessions
are made during the design process.
PARALLELING OF FOUR-LEG SHUNT
ACTIVE POWER FILTERS BASED ON SVPWM
USING FUZZY LOGIC CONTROL
1G.Shobana*,
2 Dr. R.Arivalahan
#
*PG Scholar,
#Associate Professor
Department of Electrical and Electronics Engineering
Valliammai Engineering College, Kattankulathur-603 203, Tamilnadu, India.
[email protected], [email protected]
Three
Phase
Source
Harmonic
Loads
Shunt
Active
Power Filter
IS IL
IF
Vpcc
International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 22 Issue 2 – MAY 2016.
144
Fig. 1: SAPF Connection Diagram
An improvement in manufacturing methods has lead to a
reduction in variances between components of the same
model, which has important implications for passive
paralleling. However, as it has been proven, installation of
passive power filter in shunt connection with active power
filter is not an effective solution. Inverter power rating can
become the subject of further reduction by applying other
possible connections of filters. The implementation of the
control is almost the same in complexity for all the selected
topologies and obtained harmonic mitigation performance is
similar maintaining system current THD below 5 %.
II. THEORETICAL CONSIDERATIONS
A. SHUNT ACTIVE POWER FILTER
The APF is an effective means of Harmonic Suppression,
it utilizing the pulse width modulation (PWM) technique is
used to generate switching harmonic current, which is power
grid leakage at high frequency and it should be eliminated by
output filter [3]. Output filter connected between the inverter
and grid connection, as shown in Fig 2. As the complexity of
its working principle, must be synthetically considered the
compensation performance of APF and filtering performance
of output filter etc, and this is a multi-objective optimization
problems..
Fig. 2: General Topology for Shunt Active Filter
Active filters are designed using passive and active
components, and require an outside power source. Operational
amplifiers are used in design of active filter [4]. These can
have high reactive power and quality factor, and can achieve
resonance without using inductors. However, their higher limit
is limited by the bandwidth of the amplifiers used in that
system. Filters having multiple elements are usually
constructed as a sequence network. These can be designed as a
continuation of the L, T and π format of filters. More elements
are required when it is desired to improvise some parameters
of the filter like stop-band rejection, slope of transition from
pass band to stop band.
A three-phase system connected with an inverter load has
been considered to study the operation of the SAPF. It has
been concluded that due to the characteristics change of power
electronics loads the Total Harmonic Distortion of source
current and terminal voltage fall below the IEEE-519 standard
and in main APF system is used to inject a current with equal
magnitude but opposite in phase to harmonic current to get a
pure sinusoidal current waveform in phase with the supply
voltage [7]. Fig. 3 shows the control strategy for proposed
method. The main component of the Active Power Filter is the
IGBT based Voltage Source Inverter. A dc capacitor is used to
deliver power for the inverter circuit. For the desired operation
of APF, capacitor voltage should be minimum of 150 % of
maximum line to line supply voltage.
B. SPACE VECTOR PULSE WIDTH MODULATION
TECHNIQUE
The voltage space vector synthesization is critical in the
conventional SVPWM method. As it uses Clarke
transformation to transform the reference voltages to d-q
coordinates in order to generate reference vectors.
Fig. 3: Phase Voltage Space Vector
Subsequently, the reference vectors are synthesized by
some optimally selected basic vectors with specific time
duration. In that method, the sectors of reference vectors are
determined by their phase angles, and the time duration of
basic vectors are calculated through the computation of phase
angles and reference vectors as shown in Fig. 4.
a1Vr
0Vr
3Vr
2Vr
4Vr
5Vr
6Vr
bj
POO
PPOOPO
OPP
OOP POP
refVr
q
OOOPPP
SECTOR ISECTOR III
SECTOR IV SECTOR VI
SECTOR V
SECTORII
w
International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 22 Issue 2 – MAY 2016.
145
Fig. 4: Control Scheme model of SVPWM Technique
As these computations involve huge quantities of irrational
numbers and trigonometric functions, the computation burden
would be enormous. These operations may bring about major
calculation errors which would corrupt the performance of
shunt APF. To solve this problem, an effective time concept
based SVPWM is used to generate the switching signals. It is
possible to reconstruct the actual gating time without
separation and recombination effort. The switching state
diagram of the VSI is shown in Fig. 3. The six non-null states
are represented by space vectors mathematically represented
as follows
Reference Vector Voltage is calculated using
where,
Rotating in space at w =2πf
C. FUZZY LOGIC CONTROLLER TECHNIQUE
Your unclear controller will be characterized as follows:
1) Seven fuzzy sets for each input and output.
2) Fuzzification using continuous universe of discourse.
3) Implication using Mamdani’s “min” operator.
4) De-fuzzification using the “centroid” method.
The block diagram of Fuzzy logic controller is shown in
Fig. 5. It consists of following blocks
Fuzzification Interface.
Knowledge base.
Decision making logic.
Defuzzification.
Fig 5: Block Diagram Of Fuzzy Logic Controller
A new fuzzy controller switches some sort of linguistic control
approach straight into a computerized control approach[12], in
addition to fuzzy guidelines usually are created by simply
specialist practical knowledge or maybe knowledge data-base
[13].
Table 1: Rule Base for Fuzzy Logic Controller
(de/dt)/e NB NM NS Z PS PM PB
NB NB NB NB NB NM NS Z
NM NB NB NB NM NS Z PS
NS NB NB NM NS Z PS PM
Z NB NM NS Z PS PM PB
PS NM NS Z PS PM PB PB
PM NS Z PS PM PB PB PB
PB Z PS PM PB PB PB PB
To start with, input mis-calculation E in addition to change
with mis-calculation are already placed with the angular
velocity to become the actual input parameters with the fuzzy
reason controller. Then your output changing [13] with the
fuzzy reason controller is usually offered through the control
Current Imax.
)()()( tvjtvtVba
r(1)
qj
refrefeVV
r (2)
International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 22 Issue 2 – MAY 2016.
146
The above graphs shows that the how the fuzzy Parameter
changes its ranges at each value. According to that the system
will perform its function.
To be able to change these numerical parameters straight into
linguistic parameters, these several fuzzy ranges or maybe sets
usually are decided on as: NB (negative big), NM (negative
medium), NS (negative small), ZE (zero), PS (positive small),
PM (positive medium), in addition to PB (positive big) as
shown in Table 1.
III. WORKING PRINCIPLE OF SHUNT ACTIVE FILTER
Active filters are designed using passive and active
components, and require an outside power source. Operational
amplifiers are used in design of active filter [4]. These can
have high reactive power and quality factor, and can achieve
resonance without using inductors. However, their higher limit
is limited by the bandwidth of the amplifiers used in that
system. Filters having multiple elements are usually
constructed as a sequence network. These can be designed as a
continuation of the L, T and π format of filters. More elements
are required when it is desired to improvise some parameters
of the filter like stop-band rejection, slope of transition from
pass band to stop band.
Fig. 6: Block Diagram Representation for Proposed SAPF
Control Strategy
A three-phase system connected with an inverter load has
been considered to study the operation of the SAPF. It has
been concluded that due to the characteristics change of power
electronics loads the Total Harmonic Distortion of source
current and terminal voltage fall below the IEEE-519 standard
and in main APF system is used to inject a current with equal
magnitude but opposite in phase to harmonic current to get a
pure sinusoidal current waveform in phase with the supply
voltage [7]. Fig. 6 shows the control strategy for proposed
method. The main component of the Active Power Filter is the
IGBT based Voltage Source Inverter. A dc capacitor is used to
deliver power for the inverter circuit. For the desired operation
of APF, capacitor voltage should be minimum of 150 % of
maximum line to line supply voltage.
A. Harmonic Loop
To eliminate harmonic resonances, the HAFU is proposed to
operate as variable conductance at harmonic frequencies as
follows:
i∗h = G∗ ec (3)
where,
i∗h represents the harmonic current command. The
conductance command.
G∗ is a variable gain which has to be provide damping for
all harmonic frequencies.
using SRF transformation [9] Harmonic voltage component eh
is obtained where a phase-locked loop (PLL) is used to
determine the fundamental frequency of the power system. In
the SRF, the basic component becomes a dc value, and other
harmonic components are still ac values[10]. Therefore,
harmonic voltage component can be extracted from graph by
using high pass filters. After transferring back to a three-phase
system, the harmonic current command i∗h is obtained by
multiplying eh and the conductance command G∗.
415V
50Hz
Harmonic
Loads
Distribu
-tion
Transfor
-mer
Detection
Unit
Fuzzy Logic
Controller
and
Selectivity
DC Side
Voltage
Control
Strategy
4-leg
SVPWM
Inverter
IF Ig
Iref
Vc
Source Delta Star PCC
International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 22 Issue 2 – MAY 2016.
147
The conversion of three axes frame to two axes frame is done
by using Park’s and Clarke’s transformation as shown below
𝑖𝑐𝑎𝑖𝑐𝑏𝑖𝑐𝑐
= 2/3
1 0 1\√2
−1\2 √3\ 1\√2
−1\2 −√3\2 1\2√2
𝑖𝐿𝑎𝑖𝐿𝑏𝑖𝐿𝑐
𝑖𝐿𝑎𝑖𝐿𝛽
= 𝑐𝑜𝑠(𝜔𝑡) −𝑠𝑖𝑛(𝜔𝑡)𝑠𝑖𝑛(𝜔𝑡) 𝑐𝑜𝑠(𝜔𝑡)
𝑖𝐿𝑑𝑖𝐿𝑞
B. Current Regulator
The current command i∗ is consisted of i∗h and i∗f . Based on
the current command i∗ and the measured current i, the voltage
command v∗ can be derived by using a proportional controller
as follows:
v∗ = Kc (i∗ − i) (6)
where,
Kc is a proportional gain. According to the voltage
command v∗, space-vector pulse width modulation (PWM) is
employed to synthesize the required output voltage of the
inverter. The computational delay of digital signal processing
is equal to one sampling delay T, and PWM delay
approximates to half sampling delay T/2. Hence, the
proportional gain Kc can be simply evaluated from both open-
loop and closed-loop gains for suitable stability margin and
current tracking capability[11].
IV. RESULT ANALYSIS
A summary of the simulation values is presented in Table 2.
Since inverter power is the main factor in this comparison, the
following quantities were taken into account: harmonic
mitigation efficiency considered by measuring the current
THD after connection of harmonic compensation device, the
voltage value on the capacitor at the dc-side of the inverter,
the RMS current flowing through the inverter in steady state
operation of the device. These quantities allow determining
the inverter power.
Table 2: Test System Specifications
S. No. Parameters Values
1 Three Phase Source Voltage 415 V
2 Frequency 50 Hz
3 DC Capacitor 5000 µF
4 Diode Resistance 1 mΩ
5 DC Link Voltage 500 V
6 Rectifier Load 10 Ω, 60 mH
The results obtained in simulations show that the pure active
filter provides the best harmonic mitigation efficiency. It
decreased the THD of the system current from near 25% to
3%, which is considerably low regarding no switching
frequency filter installed, and thus the ripple also contributes
to the harmonic distortion [13].
Fig. 7: Non Linear Load (Rectifier) model for SAPF system
According to IEEE std. 519-1992 [31], voltage THD is limited
to 5%, and individual distortion should be below 4%. Thus,
THD∗ is set in the range of 3% and 5%. If Vs,h and Rs are
neglected, voltage THD at E, due to harmonic current load I,
can be expressed as follows:
𝑇𝐻𝐷1 = 1\𝐼1 𝐼2∞
ℎ−2
= 𝐼𝑟𝑚𝑠
𝐼1,𝑟𝑚𝑠
2
− 1
Nevertheless, ability to compensate current distortion is only
slightly worse and should be sufficient for most applications.
It is measured that all the presented topologies provide
satisfactory current harmonic compensation. The dc-voltage
value of both hybrid filters is 3.5 times lower then the dc-
voltage of an active power filter.
Fig. 8: Fuzzy control for Power Filter System
100......
100%
1
22
3
2
2
1
,
V
VVV
V
VTHD
NRMSh
V
(5)
(4)
International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 22 Issue 2 – MAY 2016.
148
This is because, in order to create any current flowing
through the line inductor, the dc-voltage needs to be higher
than the maximum voltage on the ac-side of the inverter [14].
The inverter currents vary considerably between the presented
topologies. Fig. 7 shows the fuzzy control scheme for
proposed system. Some fundamental component is also
necessary to feed the dc capacitor[15], in order to maintain the
inverter in operation, and thus a real current is used by the
APF.
A. SIMULATION OUTPUT
i) Output Waveform for Without SAPF System
Fig. 9: Load voltage without using Active Filter
Fig. 10: Load current without using Active Filter
Fig. 11: Harmonic spectrum for load current without SAPF
ii) Output Waveform for With SAPF System
Fig. 12: Output Graph for Phase Voltage at PCC
Fig. 13: Phase Voltage when breaker is in on Condition
Fig. 14: Phase Current when Breaker is in on Condition
International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 22 Issue 2 – MAY 2016.
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Fig. 15: Inverter Output Voltage for Compensation
Fig. 16: Output Voltage across the DC Capacitor
Fig. 17: Output Graph for Voltage after Compensation
Fig. 18: Load Side Voltage Graph after Compensation
Fig. 19: Harmonic Spectrum Graph after Compensation
However it is reduced by the harmonic component (5th
harmonic), which flows through the active filter as shown in
Fig. 19.The overall inverter power, which roughly determines
the cost of the harmonic mitigation device, is an important
factor in cost-sensitive applications[17]. Low inverter power
rating rapidly improves the profitability of the investment in
harmonic compensation. In presented comparison the pure
active power filter requires the largest inverter, which apparent
power is 46% of the load apparent power[18].
V. CONCLUSION
In this paper an active power filter with SVPWM based on
fuzzy logic was analyzed and simulated. The main goal was to
find a solution, which has as profitable relationship between
the accuracy and cost, as possible. Current distortion was
mitigated sufficiently by the all proposed devices, meeting
IEEE-519 limits. However, as it was proved in this paper,
there is a great difference in inverter sizes between these
topologies. According to above presented simulations and
practical experiments, active device connected between the
elements of the shunt passive filter is the most advantageous
topology. It ensures proper harmonic mitigation with minimal
initial costs, which frequently is crucial factor in cost-sensitive
applications. In addition, in high power applications, this shunt
active power filter topology can be used as an upgrade to the
existing passive filter improving its performance and
cancelling its serious drawbacks.
ACKNOWLEDGEMENT
The Author are grateful for the valuable comments and
suggestions for the reviewers. The valuable comments and
suggestions will enhance the strength and significance of this
paper.
International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE)
ISSN: 0976-1353 Volume 22 Issue 2 – MAY 2016.
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