IRJET- Power Quality Improvement in Solar by using Fuzzy Logic Controller

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 05 Issue: 04 | Apr-2018 www.irjet.net p-ISSN: 2395-0072
© 2018, IRJET | Impact Factor value: 6.171 | ISO 9001:2008 Certified Journal | Page 1164
POWER QUALITY IMPROVEMENT IN SOLAR BY USING FUZZY LOGIC
CONTROLLER
S. Sakthitharani1, R. Sangeetha2, S. Subha3, G. Deivamani4.
1,2,3 Dept of Electrical and Electronics Engineering, Tamilnadu,India
4Assitant professor, Dept of Electrical and Electronics Engineering, Tamilnadu,India
---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - Photovoltaic(PV)systemsaregrid-connectedvia
an interfacing converterwhichoperateswithMaximumPower
Point Tracking (MPPT) controller in order to feed the grid by
the maximum allowable solar power. Nonlinear loads affect
the system power quality. Conventionally single-phase shunt
active power filter (APF) can be used to improve the power
quality in terms of current harmonics mitigation and reactive
power compensation. In this paper, thePVinterfacinginverter
is controlled using a predictive control technique to perform
both functions of power quality improvement in addition to
transferring the PV maximum power to the grid. A Fuzzy logic
control algorithm isappliedforMPPT. Theproposedtechnique
does not require an accurate system model and can easily
handle system nonlinearity. The system performance is
investigated using a MATLAB simulation model.
Index Terms—power quality, shunt APF, predictive
control, grid-connected PV systems, MPPT, Fuzzy logic
control.
1.INTRODUCTION
Harmonics is one of the power quality issues that
influence to a great extent transformer overheating, rotary
machine vibration, voltage quality degradation, destruction
of electric powercomponents,andmalfunctioningofmedical
facilities [1]. Power quality improvement has been given
considerable attention due to the intensive use of nonlinear
loads and the limitationsrequiredbyinternational standards
such as IEEE519-1992[2].Those limitations weresettolimit
the disturbancesandavoid majorproblemsinpowersystem.
Since linear and/or non-linearsingle-phaseloadsarerapidly
increasing,zerosequencecomponentandcurrentharmonics
are generated. This causes overheating of the associate
distribution transformers that may lead to a system failure,
especially inweak networks [3]-[5].Photovoltaic (PV)power
supplied to the utility grid is gaining more and more
visibility, while the world’s power demand is increasing.
Global demand of electrical energy is growing by high rate
due to the requirement of modern civilization. Recently,
energy generated from clean, efficient and environmentally
friendly sources has become one of the major challenges for
engineers and scientists. Among them, PV application has
received a great attention in research because it appears to
be one of the most efficient and effective solutions to this
environmental problem [6]. There are two topologies used
to connect the PV with the grid; two stages and single stage
PV system. A two stage is the traditional type and consists of
a CUK DC/DC converter direct coupled with PV array and a
grid connected universal bridge inverter. In single stage PV
system, the DC/AC inverter has more complex control goals;
Maximum Power Point Tracking (MPPT) and outputcurrent
control. Regardless its control complicity, single stage PV
system is more efficient and cheaperthantwostagessystem.
For connecting the PV system to the grid, there are three
widely used grid interactive PV systems; the centralized
inverter system, the string inverter system and the AC
modulator the Module Integrated Converter (MIC) system.
Among these, the MIC system offers “plug and play” concept
and greatly optimizes the energy yield [7].With these
advantages, the MIC concept has become the trend for the
future PV system development but challenges remain in
terms of cost, reliability and stability for the grid connection
[8].Conventionally single phase shunt active power
filter(APF) uses an inverter for harmonics elimination and
reactive power compensation [9]-[10].A grid connected PV
system with active power filtering feature has been
presented in [11][13].However, measuring the load current
is mandatory. In this paper, an inverter is used as a single-
phase shunt active power in addition to interfacing a power
of a photovoltaic (PV) as shown in Fig.1. Fuzzy Logic Control
(FLC) is used as a robust controller for MPPT; this control
technique can handle the model uncertainties in addition to
easily handle the nonlinearity. The single-phaseshuntactive
power filter (APF) uses a predictive control technique to
mitigate of the grid current harmonics and improve the
power factor. The proposed control strategy provides a
multifunction with a simple controller incorporating Phase
Locked Loop (PLL) independency, less sensors, ease of
practical implementation, and reduced system sizeandcost.
The proposed system performance is investigated for most
of the conditions using a MATLAB simulation model.
Fig. 1. Block diagram of a grid-connected PV unit

Fig.2. The overall system modelling including control
signal
II. PV SYSTEM MODELLING
The single-phase multi stage gridconnectedsystemisshown
in Fig. 2. It consists of a PV array followed by step up stage,
which feeds a predictive current controlled voltage source
inverter acts as an APF that feed s current into the single
phase grid and linear/non-linear single phase loads.
A. Photovoltaic Cell equivalent circuit
The traditional equivalent circuit of a solar cell is
represented by a current source in parallel with one or two
diodes. A single-diode PV cell model for m is illustrated in
Fig. 3, including four components:a photocurrentsource, Iph,
a diode parallel to the source, a series resistor, Rs, a shunt
resistor, Rsh. The DC current generated, Ip h, when the cell is
exposed to light varies linearly with solar irradiance [14].
The shunt resistance RSh is inversely related with shunt
leakage current to the ground. In general, the PV efficiencyis
insensitive to variation in RSh and the shunt-leakage
resistance can be assumed to approach infinity without
leakage current to ground. The net cell current of the cell is
the difference of the light-generated current, Iph, and the d
iode current, Id, as shown in Fig. 4. Equation (1) describes th
e I-V characteristic of the ideal photovoltaic cell.
where Ipv,cell is the current generated by the incident light (it
is directly proportional to the sun irradiation), I0,cell is the
leakage current, q is the Boltzmann constant
[1.60217646× K is the Boltzmann constant
[1.3806503× J/K],T is the temperature of the p-n
junction, and a is the diode identity constant
Fig: 3 Single-diode model of theoretical PV cell [5]
Practical arrays are composed of several connected
photovoltaic cells and the observation of the characteristics
at the terminals of the photovoltaic array requires the
inclusion of additional parameters to the basic equation (2):
where Ipv and I 0 are the photovoltaic and saturation
currents of the array and Vt = (NskT)/q is the thermal voltage
of the array with Ns cells connected in series.
The light generated current of the photovoltaic cell
depends linearly on the solar irradiation and is also
influenced by the temperature according to (3) [15]:
+
where Ipv,n is the light-gene rated current at the nominal
condition (usually 25◦
C and 10 00W/m2),∆T = T – Tn (being
Tand Tn the actual and nominal temperatures ), G [W/m2] is
the irradiation on the device surface, and Gn is the nominal
irradiation. The diode saturatio n current I0 and its
dependence on the temperature may be expressed by
equation (4) [16]:
where Eg is the band gap energy of the semiconductor (Eg
≈1.12 eV for the polycrystalline Si at 25◦
C [17]), andI0,nis the
nominal saturation current.
III.MODEL OF CUK CONVERTER
For grid-connected PV applications, two topologiesofthePV
energy conversion systems have been mostly presented;
known as one-stage and two stage systems. This paper
focuses on the two-stage PV energy conversion system,
because it offers an additional degree of freedom in the
operation of the system when compared with the one-stage
configuration, in addition to de creasing the global efficiency
of the combined system because of the connection of two
cascade stages. Therefore, by including a CUK converter
between the PV array and the inverter connected to the
electric grid, various control objectives are possible to track
concurrently with the PV system operation. Theconverteris
linked to the PV system with a filter capacitor Ctoreducethe
high frequency ripples due to transistor switching. The D C-
DC converter output is connected to the DC bus of the DC-AC
converter, as depicted in Fig.5, and produces a chopped
output voltage, therefore controls the average DC voltage
relation between its input and output. So the PV system and
the DC-AC converter are matching. The steady-state voltage
and current relations of the boost converter operating i n
continuous current mode are [19]: Fly-back transformer
includes an inductance Lm and an ideal transformer with a

turns ratio the leakage inductance and loses fly back
transformer are neglected here. But the leakage inductance
affect the switch and diode transitions .
The magnitude of Lm decides the boundary between
continuous and discontinuous current modes (CCM)and
(DCM).The series connection of switch with DC generator
result in pulsating input current[18].
IV.PROPOSED MPPT USING FUZZYLOGICCONTROL
In order to track the time varying maximum power point of
the solar array depending on its operating conditions of
insulations and temperature, the MPPT control technique
place an important role in the practical PV system. A variety
of MPPT schemes and several sensor-less approaches have
been proposed in the literatures [20].
This paper proposes MPPT control techniquewithFLC.thg
output power of PV arrays varies with weather conditions
;solar irradiation and atmospheric temperature. Therefore
,real time MPPT control forextracting maximum powerfrom
The PV panel becomes indispensable in PV generating
system[21]-[22].
MPPT using FLC gains several advantage of better
performance, robust and simple design. In addition, this
technique does not require the knowledge of the exact
model of the system and it can handle the nonlinearity . The
main parts of FLC; fuzzification ,rule-base , inference and
defuzzification ,are shown in fig,6.
MPPT using FLC provides bet performance robust and
simple design. The proposed FL-MPPT control shown in
fig7.it has two input and one output .the two FLC variables
are the error and change for error CE at sampled times j
defined by
(9)
(10)
(11)
Fig.4 Gird connected PV system with cuk converter
v
Where:
Efficiency of the cuk converter
D: DC-DC converter duty cycle
PV array output current
PV array output voltage
DC bus current (inverter side)
DC bus voltage (inverter side)
The fly back transformer provides isolation and also the
voltage ratios are multiplied by turns ratio. Where
are the PV power ,current and voltage
respectively at instant j .E(j) shows the if the load operating
point at the instant j is located on the left or on the maximum
power point on the p-v characteristicwhereitisequaltozero
at MPP. While the change of error CE(j)expressesthemoving
direction of the point where the control action duty cycle D
used for the tracking of the MPP by comparing with the saw
tooth waveform to generate a PWM signal for the fly-back
boost
Fig.5 Fuzzy Controller Diagram
For example, if the operating point is far to the left of the
MPP, that is E is PB, and CE is ZE, then it is required to
largely increase the duty ratio i.e., D should be PB to reach
the MPP. In the defuzzification stage, the fuzzy logic
controller output is converted from a linguistic variable to a
numerical variable still using a membership function. This
provides an analog signal that will control the power
converter to the MPP [24].
In this paper Madman’s fuzzy interface method ,with Max-
Min operation fuzzy combination has been used. The
membership function forthe variablesareshowninfig.7.The
control rules are indicated in table 1 with E and CE as input
and Das the output

Fig 6,membership function of (a) error E-(b)change of
error CE-(c) duty ratio D
V PROPOSED INVERTER CONTROL TECHNIQUES
The proposed system show in fig.8 consist of PV array, cuk
converter DC link capacitor ,and a universal bridge
connected at the PCC to a three phase grid through in
interface inductance . the compensator reference current is
calculated from the sensed grid current drawn by the
nonlinear and three phase loads connected to the grid. the
reference current is computed by using capacitor voltage
control[25].the compensation objectives is to compensate
for load current harmonics, reactive power compensation
and to regulate the DC bus doing bidirectional active power
exchange between the Dc side load/source and the power
system grid .
The compensation functions are executedsimultaneously
where a three phase nonlinear load are fed from both the
grid pv system. the performance is tested from thefollowing
cases:
Case 1: at normal conditions
Case 2: the load increases
Case 3: the solar irradiation decreases
Case 4: the atmospheric temperature increases.
The proposed control system block diagram is shown in
Fig. 7. Block diagram of the proposed control of inverter
Symb
ol
Values
Rated power 199 W
Rated voltage 26.3V
Rated current 7.6A
Open circuit voltage 32.9V
short circuit current 8.21A
Number of series cell 54
Number of parallel cell 1
Number of series module 1
Number of parallel
module
1
C PV module capacitor 4700µF
Tc Atmospherictemperature
Gn Solar irradiation 1000
W/
Vs Grid voltage in RMS 220V
DC references voltage 420 V
DC bus capacitor 3.0mF
Sampling frequency 3.2mH
Switching frequency 5µF
F Line frequency 50KHz
Table 3:Fly-back transformer parameters
Fig.8. the universal bridge is controlled with a predictive
control strategy.it requires the measurement of the grid
voltage and current at PCC and the inverter DC link voltage.
The measurement of the load current and the injected
inverter current are not required. The inverter references
current is extracted using DC-link capacitor voltage control
method. The DC-link voltage, , are subtracted from the
reference voltage, . A PI controller acts on the resultant
error the DC –link voltage is maintained constant and the
power balance between the grid, inverter ,and the load is
achieved as the capacitor compensate instantaneously the
difference between the grid and the load power[26]-[29].
Multiplication of the PI controller output with PCC per unit
voltage forms the grid current reference. Ideal voltage is
assumed. The reference and measured grid current and the
PCC voltage are used to predict the inverter reference
voltage required to force the actual current to track its
reference. The predictive current controller presented in
[27] is used to control the interfacing.
Power converter of the DG unit. The predicted converter
output voltage is expressed in terms of the reference and
actual grid current by
Where, is the interfacing inductance, is the sampling
time. (k) and (k) are the sinusoidal reference and the
measured grid current at the sampling instant k,
respectively. is the grid voltage.

The grid reference current (k) in (13) represents three
phase sinusoidal grid current. The introducedsamplingtime
delay is less significant sampling frequency is high (28).
T
herefore, the predictive control method proposed for the
multifunctional inverter can compensate both of the grid
current harmonics and reactive power required also
transfers the PV power, thus grid current become sinusoidal
and the DC bus are regulator during bidirectional active
power exchange between the DC side load source and the
grid. This method provides simple control algorithm
without a PLL, minimizes the number of sensor as the load
and inverter current are not measure, and provides ease of
piratical implementation.
VI PERFORMANCE INVESTIGATION OF THE
PROPOSED SYSTEM
The proposed system shown in Fig.2 is simulated using a
MATLAB/simulink model to investigateisperformances. The
system parameter are listed in table to and the high
frequency transformer parameter of the fly-back DC-DC
converter shown in Fig.5, are listed in table 3. The PCC
voltage is 220 v .The nonlinear load isrepresentedbya three
phase diode rectifier feeding an inductive load representing
a harmonic current producing a source. The resistance and
the inductions of the inverter coupling inductor, are
and respectively. DC link capacitor of 3.0 mF is
used. The reference voltage for this loop is sat at 420 v and
the inverter switching frequency f is 5 KHz.
Quantity Symbol Values
Inductance 28µH
DC resistance DCR primary 0.008
Ohms
DC
inductance
DCR
Secondary
0.472
Ohms
Self-Resonant
Frequency
SRF 360KHz
Saturation
current
10.5 A
Turns ratio Pri:Sec 1:12
The system performance is investigated for the following
cases:
Case 1: from 0.2 to 0.4 s; a single-phasenonlinearloadof250
W is fed from both the gird and the PV unit at solar
irradiation of 1000 W/m2 and an atmospheric temperature
of 25oC.
Case 2: at 0.4 s, the load increases to 400 W.
Case 3: at 0.6 s, the solar irradiation decreases to900 W/m2.
Case 4: at 0.8 sec, the temperature increases to 35oC.
The simulation results are shown in Fig. 9. The grid voltage
waveforms at the PCC, vs, are shown in Fig. 9(a).Typical non-
linear load current, iL, is shown in Fig. 9(b). Its total
harmonic distortion (THD) is 31 %. The invertercurrent, iinv,
injected at the PCC is shown in Fig. 9(c). As a result,
sinusoidal grid current, is, with near unity power factor is
achieved as shown in Fig. 9(d). The grid current THD is
compared before and aftercompensation.TheAPFimproves
the THD from 31% to 3.2% which comply with the IEEE Std.
519-1992. An almost steady DC-link voltage, Vdc, is shown in
Fig. 10. The load active and reactive powers PL, QL are
increased from 250 W to 400 W and from 50 VAR to 80 VAR
as shown Fig. 11(a). The active and reactive powers of the
grid are shown in Fig. (b), the grid active power, Ps are
increased from 130 W to 250 W while the grid reactive
power Qs maintained nearzero.Fig.11(c)presentsthepower
supplied by the PV unit which is almost maintainedat140W
with small variations duo to the change of solar irradiation
and atmospheric temperature
Fig.8.Simulation result: (a) grid voltage, v,(b) load
current, ,A(c) inverter current, , (A),and (d)grid
current, .
Fig 9.simulation results :Capacitor voltage ,

In this paper, a PV system is interfaced to the grid via a
multifunctional interfacing inverter. A MPPT fuzzy logic
controller is employed to feed the grid by the maximum
allowable PV power. A simple predictive current control
algorithm is used. The system performance is investigated
using a MATLAB/ Simulink model at different cases of load
variation, atmospheric temperature variation and solar
irradiation variation. The inverter achieves functions of
supplying the available power from the PV unit into the
loads in addition to improving the power quality in terms of
grid current THD and power factor. The results comply with
the limits of the IEEE Std. 519-1992.
REFERENCES
[1] R.D. Henderson, and P. J. Rose, ‘‘Harmonics: The effects
on power quality and transformers,’’ IEEE Transaction on
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532.
[2]IEEE Std. 519-1992, Recommended Practices and
Requirements for Harmonic Control in Electric Power
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[3]T.M. Gruzs, "A survey of neutral currents in three-phase
computerpower systems, Industry Applications, ," IEEE
Transaction on Industrial Electronics, Vol.26, No.4, Jul/Aug
1990, pp.719-725.
[4]F. Liu, X. Zhang, Z. Xie, P. Xu, and L. Chang, "Shunt active
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[5]B. Singh, and S. Sharma, "SRF theory for voltage and
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[6] T. Shimizu, O. Hashimoto, and G. Kimura, “A novel high
performance utility-interactive photovoltaic inverter
system.” IEEE Transaction on Power Electronics,Vol.18,No.
2, Feb. 2003, pp. 704–711.
[7] S. B. Kjær, J. K. Pedersen, and F. Blaabjerg, “A review of
single-phase grid-connected inverters for photovoltaic
modules,” IEEE Transaction on Industrial Applications, Vol.
41, No. 5, Sep./Oct. 2005, pp. 1292–1306.
[8] J. M. Carrasco, et.al., “power-electronic systems for the
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“Stud S.SAKTHITHARNI,
Dept of Electrical & Electronics
Engineering, Paavai Engineering
College, Namakkal, Tamilnadu”
“Stud S.SUBHA,
“Stud R.SANGEETHA,
G.DEIVAMANI.,M.E,
Assistant professor,
VII. CONCLUSION BIOGRAPHIES:

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