Fuzzybased Transformerless Single-Phase Universal Apf for Harmonic and Reactive Power Compensation

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 03 | Mar -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 344
FUZZYBASED TRANSFORMERLESS SINGLE-PHASE UNIVERSAL APF FOR
HARMONIC AND REACTIVE POWER COMPENSATION
D. Surendra1, S. M.rama sekhara reddy2
1PG Scholar, Dept. Of Electrical & Electronics Engineering, JNTUACEA, Anantapuramu, A.P., India
2Assistant professor, incharge HEAD, ,JNTUA College of Engineering, Kalikiri,, A.P., India
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ABSTRACT- In this paper, a universal active filter was
developed with fuzzy logic controller for harmonic and
reactive power compensation for single-phase systems
applications. APF can correct the power quality and
improve the reliability and stability on power utility. The
proposed system is a combination of parallel and series
active filters without transformer. It reduces the lower
order harmonics and thus effectively reduces total
harmonic distortion. Here we are using fuzzy logic
controller instead of using other controllers. The model of
the system is derived and it is shown that the circulating
current observed in the proposed active filter is an
important quantity that must be controlled. A complete
control system, including pulse width modulation (PWM)
techniques, is developed. The simulation was done by
using MATLAB/Simulink software.
INDEX TERMS: Optimum voltage angle, single-phase
configuration, total harmonic distortion, universal active
power filter (UAPF), Fuzzy logic controller.
I. INTRODUCTION
Sensitive loads are greatly affected by power-
quality (PQ) disturbances in the system. The Increased
NON- Linear loads today’s life increase the distortion
which causes Voltage Swell and sag. The strict
requirement of power quality at input ac mains and the
output load (sensitive loads) in the area of power line
conditioning is very important in power electronics.
Different equipments are used to improve the power
quality, e.g., transient suppressors, line voltage regulators,
uninterrupted power supplies, active filters, and hybrid
filters. The continuous proliferation of electronic
equipment either for home appliance or industrial use has
the drawback of increasing the non sinusoidal current into
power network. Thus, the need for economical power
conditioners for single-phase systems is growing rapidly.
Different mitigation solutions are currently proposed and
used in practice applications to work out the problems of
harmonics in electric grids.
There are many studies about harmonic
distortion with techniques to improve power quality and
compensate distorted signal. Usually, when a passive LC
(Inductor and Capacitor) power filter is connected in
parallel with the load, of parallel or series resonances
because of which the passive filter cannot provide a
complete solution it is used to eliminate current
harmonics. This compensation equipment has some
defects mainly related to the appearance. For eliminating
harmonic pollution in power systems, the active power
filter (APF) is a very suitable tool. APF has to respond
instantaneously and work with high control precision in
current tracking, since the load harmonics may be very
complicated and change randomly and quickly. Many
advanced control and signal-processing techniques have
been applied, such as pulse width modulation (PWM),
hysteresis band current control (HBCC), sliding-mode
control, fuzzy-logic control, neural-network theory, and
adaptive signal processing and etc.
Fig. 1. Single-phase UAPF: (a) conventional structure and
(b) transformer-less proposed structure.
Over the past few decades, the use of active
filtering techniques has became more attractive due to the
technological progress in power electronic switching
devices, enhanced numerical methods, and more efficient
control algorithms. The series active power filter (SAPF)
provides load voltage control eliminating voltage
disturbances, such as unbalance, sags, notches, flickers,
and voltage harmonics, so that a regulated fundamental
load voltage with constant magnitude is provided to the
load. The purpose of a parallel active power filter (PAPF)
is to absorb harmonic currents, compensate for reactive
power, and regulate the dc-bus voltage between both
active filters. The universal active power filter (UAPF)

which is a combination of both, is a versatile device that
operates as series and parallel active power filter.
It can simultaneously fulfill different objectives
like maintaining a sinusoidal voltage (harmonic free) at
the load, source current harmonics elimination, load
balance, and power factor correction. The cost and size
associated with the transformer makes undesirable such a
solution, mainly for office and home environments. This
paper proposes an universal active filter topology for
single-phase systems applications without transformer, as
shown in Fig. 1(b). A complete control system, including
pulse-width modulation (PWM) techniques, I developed.
Comparisons between the structures are made from
weighted total harmonic distortion (WTHD). The steady-
state analysis is also presented in order to demonstrate
the possibility to obtain an optimum voltage angle
reducing the current amplitude of both series and parallel
converters and, consequently, the total losses of the
system.
II. MODELING OF SYSTEM
The proposed configuration shown in Fig. 1(b)
comprise the grid ( ), internal grid inductance ( ),
load ( ), converters and with a capacitor bank
at the dc-link and filters ( , , and ) and ( ,
and ). Converter is composed of switches , ̅ , ,
and ̅ . Converter is composed of switches , ̅ , ,
and ̅ . The conduction state of all switches is represented
by a homonymous binary variable, where q = 1 indicates a
closed switch, while q = 0 an open one. The converter pole
voltages , , , and depend on the conduction
states of the power switches, that is
( ) ( )
( ) ( )
( ) ( )
( ) ( )
Where is the dc-link voltage.
From Fig. 1(b), the following equations can be derived:
( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
( ) ( )
( ) ( )
( ) ( )
Where p = d/dt, and is
calculated using the load model which can be linear or
nonlinear; and symbols r and l represent resistances and
inductances of the inductors , , , , and . The
circulating current is defined by
( ) ( )
The resultant circulating voltage model is
obtained by adding the above equations,
( )
The voltage is used to compensate for the circulating
current In the balanced case, filter inductors are equal
( and ) the circulating voltage model
becomes
[( ) ( ) ] ( )
Thus, it can be noted that to minimize the
circulating current , the voltage must be equal to ,
i.e,
( )
When ( ) the system model
becomes
( ) ( )
( ) ( )
( ) ( )
( ) ( )
( ) ( )
This model is similar to the model of the
conventional filter with an ideal transformer. Therefore,

we can use (converter ) to regulate the
load voltage and (converter ) to control
the power factor and harmonics of as in the
conventional filter.
TOTAL HARMONIC DISTORTION
The WTHD values for the standard [see Fig. 1 (a)]
and proposed [see Fig. 1(b)] configurations. The WTHD
has been computed by using
( ) √∑ ( ) ( )
Where is the amplitude of the fundamental component
is, is the amplitude of ith harmonic, and p is the number
of harmonics taken into consideration.
III. PWM CONTROL STRATEGY
The PWM strategy of the converters can be
directly calculated from the pole voltages , , , and
. Considering that , , and denote the reference
voltages requested by the controllers, it comes
( )
( )
( )
These equations are insufficient to determine the
four pole voltages , , , and . Introducing an
auxiliary variable and choosing , it can be
written as
( )
( )
( )
( )
Two methods are presented next in order to choose
Method A: General approach
In this manner, the reference voltage is
calculated by taking into account the maximum and
minimum value of the pole voltages, then
( )
( )
After is selected, all pole voltages are obtained
from (25) – (28). Then, can be chosen equal to ,
, or = ( )/2. Note that when
or is selected, one of the converter-leg operates with
zero switching frequency. On the other hand, operation
with generates pulse voltage cantered in the
sampling period that can improve the THD of voltages. The
maximum and minimum values can be alternatively used.
For example, during the time interval τ choose
and in the next choose . The interval τ can be
made equal to the sampling period (the smallest value) or
multiple of the sampling period to reduce the average
switching frequency. Once is chosen, pole voltages ,
, , and are defined from (25) – (28). Since the
pole voltages have been defined, pulse-widths , , ,
and can be calculated by
( )
( )
( )
( )
Alternatively, the gating signals can be generated
by comparing the pole voltage with a high-frequency
triangular carrier signal.
Method B: Local approach
In this case, the voltage is calculated by taking
into account its maximum and minimum values in the
series or shunt side. For example, if the series side is
considered (s=e), then = max ϑe and = min
ϑe with ϑe = { , 0} and if the shunt side (s=h) is
considered, then = max ϑh and = min ϑh
with ϑh = { + − , − − }.
Besides these voltages, voltage v x must also obey the
other converter side. Then, these limits can be obtained
directly from and from (3.35) and (3.36).
The algorithm for this case is given by
1) Choose the converter side to be the THD optimized and
calculate between , , or =
( )/2.
2) Calculate the limits and from (29) and (30).
3) Do = if > and = if < .

4) Do = .
5) Determine the pole voltage and the gating signal as in
previous method.
OVERALL CONTROL SYSTEM
Fig. 2 presents the control block diagram of the
system. The capacitor dc-link voltage ( = E) is
adjusted to a reference value by using the controller ,
which is a fuzzy logic controller. This controller provides
the amplitude of the reference current . For the power
factor and harmonic control, the instantaneous reference
current must be synchronized with voltage . This is
performed by the block GEN-g, from a phase-locked loop
(PLL) scheme. From the synchronization with eg and the
amplitude , the current is generated. The current
controller is implemented by using the controller
indicated by block which the input reference voltage
used to compose the PWM strategies for grid’s current
compensation.
Fig. 2. Control block diagram with FLC
The instantaneous reference load voltage can
be determined by using the rated optimized load angle
plus the information θg from block SYN and the defined
load amplitude . The block GEN-l uses the input
information to generate the desired reference load voltage
. From the difference between the voltages and the
block of control defined as generates the reference
voltage signal to be applied to the PWM strategies in
order to compensate for the load voltage. The homo-polar
current io is controlled by controller , that determines
voltage responsible to minimize the effect of the
circulating current , maintaining this current near to
zero. The controllers are of type double-sequence digital
controllers and all these reference voltages , , and
are applied to the PWM block to determine the conduction
states of the converter’s switches.
IV. FUZZY LOGIC CONTROLLER
In FLC, basic control action is determined by a set
of linguistic rules. These rules are determined by the
system. Since the numerical variables are converted into
linguistic variables, mathematical modeling of the system
is not required in FC. The FLC comprises of three parts:
fuzzification, interference engine and defuzzification. The
FC is characterized as i. seven fuzzy sets for each input and
output. ii. Triangular membership functions for simplicity.
iii. Fuzzification using continuous universe of discourse. iv.
Implication using Mamdani’s, ‘min’ operator. v.
Defuzzification using the height method.
Fig.3. Fuzzy logic controller
Fuzzification: Membership function values are assigned
to the linguistic variables, using seven fuzzy subsets: NB
(Negative Big), NM (Negative Medium), NS (Negative
Small), ZE (Zero), PS (Positive Small), PM (Positive
Medium), and PB (Positive Big). The Partition of fuzzy
subsets and the shape of membership CE(k) E(k) function
adapt the shape up to appropriate system. The value of
input error and change in error are normalized by an
input scaling factor.
Table I Fuzzy Rules
Change
in error
Error
NB NM NS Z PS PM PB
NB PB PB PB PM PM PS Z
NM PB PB PM PM PS Z Z
NS PB PM PS PS Z NM NB
Z PB PM PS Z NS NM NB
PS PM PS Z NS NM NB NB
PM PS Z NS NM NM NB NB
PB Z NS NM NM NB NB NB

In this system the input scaling factor has been
designed such that input values are between -1 and +1.
The triangular shape of the membership function of this
arrangement presumes that for any particular E(k) input
there is only one dominant fuzzy subset. The input error
for the FLC is given as
E(k) =
( ) ( )
( ) ( )
CE(k) = E(k) – E(k-1)
Inference Method: Several composition methods such as
Max–Min and Max-Dot have been proposed in the
literature. In this paper Min method is used. The output
membership function of each rule is given by the
minimum operator and maximum operator. Table 1 shows
rule base of the FLC.
Defuzzification: As a plant usually requires a non-fuzzy
value of control, a defuzzification stage is needed. To
compute the output of the FLC, „height‟ method is used
and the FLC output modifies the control output. Further,
the output of FLC controls the switch in the inverter. In
UPQC, the active power, reactive power, terminal voltage
of the line and capacitor voltage are required to be
maintained. In order to control these parameters, they are
sensed and compared with the reference values. To
achieve this, the membership functions of FC are: error,
change in error and output
Fig.4. Membership functions
The set of FC rules are derived from
u=-[αE + (1-α)*C]
Where α is self-adjustable factor which can regulate the
whole operation. E is the error of the system, C is the
change in error and u is the control variable. A large value
of error E indicates that given system is not in the
balanced state. If the system is unbalanced, the controller
should enlarge its control variables to balance the system
as early as possible. One the other hand, small value of the
error E indicates that the system is near to balanced state.
V. SIMULATION RESULTS
The proposed configuration was simulated using
PSIM software with the following circuit parameters:
1) Power system: 1.2 kVA;
2) Source frequency of : 60 Hz;
3) Harmonic frequency of : 180 Hz;
4) DC-bus voltage, : 130 Vdc and 250 Vdc;
5) Inductors filters, and : 7 mH;
6) Capacitor filter, : 70 μF;
7) Grid voltage, : 110 Vrms ± 20%;
8) Grid voltage, : 50Vrms and 100 Vrms ± 20%;
9) Load voltage, : 50Vrms and 100 Vrms ;
10) Linear load composed by: R = 5 Ω and L = 63 mH.
11) Nonlinear load composed by diode bridge rectifier
with: R = 5Ω, L = 75 mH.
The proposed configuration does not use a
transformer in the series connection and consist of four-
leg converter. The capacitors of the dc-bus voltage and the
switching frequency were, respectively, selected as C =
2200 μF and 10 kHz. In order to demonstrate the
feasibility of the proposed configuration, two different
kinds of simulated results are presented.
MATLAB RESULTS
With fuzzy logic controller
(a)
(b)

(c)
(d)
Fig. 9. Simulated results for a linear load: (a) voltage ( )
and current ( ) of the grid, (b) voltage ( ) and current
( ) of the load. (c) dc-bus voltage ( ), (d) voltages and
(a)
(b)
Fig. 10. Simulated results for a linear load: (a) currents of
converter ( and ) and circulating current ( ), (b)
currents of converter ( and ) and circulating current
( )
(a)
(b)
(c)
(d)
Fig. 11. Simulated results for a linear load with = −35◦:
(a) load ( ) and grid ( ) voltage, (b) voltages of the filters
capacitors and , (c) currents of converter ( and
) and circulating current ( ), (d) currents of converter
( and ) and circulating current ( )
(a)
(b)
(c)

(d)
Fig. 12. Simulated results for a nonlinear load: (a) voltage
( ) and current ( ) of the grid, (b) voltage ( ) and
current ( ) of the load. (c) dc-bus voltage ( ), and (d)
voltages and
(a)
(b)
Fig. 13. Simulated results for a nonlinear load: (a) currents
of converter ( and ) and circulating current ( ); (b)
currents of converter ( and ) and circulating current
( )
(a)
(b)
(c)
(d)
Fig. 14. Simulated results for a nonlinear load with =
−35◦: (a) load ( ) and grid ( ) voltage, (b) voltages of the
filters capacitors and , (c) currents of converter
( and ) and circulating current ( ), (d) currents of
converter ( and ) and circulating current ( )
VI. CONCLUSION
A suitable control strategy, including the PWM
technique has been developed for the proposed UAPF
along with the fuzzy logic controller. In this way, it has
been shown that the proposed configuration presents low
WTHD, whose value is, however, higher than that of
conventional configuration. Here we are using fuzzy logic
controller instead of using other controller. The proposed
transformer-less UAPF is controlled according to two
proposed PWM techniques objecting the elimination of
undesirable circulating current. The universal active
power filter (UAPF) which is a combination of both, is a
versatile device that operates as series and parallel active
power filter. It can simultaneously full fill different
objectives like maintaining a sinusoidal voltage (harmonic
free) at the load, source current harmonics elimination,
load balance, and power factor correction. So, by using
fuzzy logic controller in UPFC model will improve reactive
power injection and reduce THD content. The simulation
was done by using MATLAB/ SIMULINK software.
REFERENCES
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[5] H. Komurcugil and O. Kukrer, “A new control strategy
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[6] L. Asiminoaei, F. Blaabjerg, and S. Hansen, “Detection is
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Fuzzybased Transformerless Single-Phase Universal Apf for Harmonic and Reactive Power Compensation

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