A New Simulation Modeling for Nonlinear Current Control in Single Phase Grid Connected PV System

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 04 Issue: 07 | July -2017 www.irjet.net p-ISSN: 2395-0072
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A New Simulation Modeling for Nonlinear Current Control in Single
Phase Grid Connected PV System
Dhananjay P. Labde1, Mrs. Pranita Chavan2, Anantkumar N. Pimpale3
1 M. E Student, Dept. of EE ,YTIET, Karjat , Maharashtra, India
2HOD , Dept. of EE,YTIET, Karjat, Maharashtra, India
3Lecturer, Dept. of ExTc ,YTGOI, Karjat, Maharashtra, India
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Abstract - Many Schemes generated better results in
nonlinear current control scheme for single phase grid
connected PV systems. But its controller design is a
tedious work. This Paper describes methodology in design
of a nonlinear current control scheme in single phase grid
connected photovoltaic systems. The designed model uses
partial feedback linearization technique to control the
maximum power delivered to the load. The generated
nonlinear reference input current calculation is done by
using Lyapunov function. Function produced gives
stability in internal dynamic changes of PV system. The
performance of system tested on simulation software for
parameters like change in atmospheric conditions. A
comparison with traditional controllers is also done for
verification with respective of its designed parameters.
Keywords :- Partial feedback linearization, Lyapunov
function, Grid connected PV System.
1. INTRODUCTION
The issue of energy saving & energy conservation is prime
concern in electrical power system. Researchers start
taking interest in efficient use of renewable energy
sources & improvement in its implementation techniques.
Apart from the different renewable energy sources,
photovoltaic systems are prime renewable energy source.
PV cells are pollution & noise free sources of energy. Due
to increasing demand in energy, government in developing
countries like India also shown keen interest to individual
solar power plants. PV system used in a solar cell
connected in array like structure. Major advantage of
integrating PV system in array format is that they can be
interfaced with energy converter system easily. The use of
PV system can be found in both AC converters as well as
DC inverters. The topology has easier controller design as
the two converters have independent control goals and
architectures. Yet, the system has poor efficiency, due to a
large number of devices, excessive size, heavy weight, and
high cost. [1]
As intermittent PV generation varies with changes in
atmospheric conditions and due to the high initial
investment and reduced life time of PV system as
compared to traditional sources, it is essential to extract
maximum power from PV systems. For this proper
controllers have to be included, to achieve the desired
performance under disturbances like changes in
atmospheric conditions, changes in load demands or
external faults within the system. This can be performed
by regulating the switching signal of the inverter, i.e., if a
proper controller is applied through the inverter switches.
The current controlling techniques are intended for
providing stability, low steady state error, fast transient
response and low harmonic distortion [1,2].
The controller design model includes both linear &
nonlinear techniques. PID, PI, PR, repetitive controllers are
the linear techniques. While predictive, deadbeat,
hysteresis controllers are some of the nonlinear
controllers.
The problem with linear controllers is on the equilibrium
conditions they are unable to provide stable linear output
over a fixed set of operating points. This can be solved by
use of nonlinear controllers. The complexity of design of
nonlinear controllers is more than linear for
implementation. When we connect photovoltaic systems
in grid manner, they used to posses nonlinear behavior.
This behavior is due to the variation of solar irradiance
and nonlinear switching functions of the inverters. For
controlling such non linear systems, first we can make the
system linear, and then control it with any linear
techniques [2].
Solution to this problem is use of partial feedback
linearization technique. Feedback linearization is a
straight forward way to design nonlinear controller since
it transforms a nonlinear system by cancelling the
inherent non linearity’s within the system and then, linear
controllers can be employed to design the controller for
linearized system. The technique can be implemented for
single phase and three phase supply systems. For
completely nonlinear or partially linear systems this
method is not applicable.[5]
This paper work focuses on improvement of internal
stability of a PV system. The controller design for
transferring maximum power to the loads is also
discussed. The proposed controller design compared with
existing controllers by analyzing the output in real time
system. The model simulated on the practical simulator

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
models on various atmospheric conditional parameters. In
this paper we discuss design of an efficient current
controller through partial feedback linearization to control
the current injected into the grid. It also includes the
stability of internal dynamics through the formulation
Lyapunov function and the calculation of sinusoidal
reference current. The design with PI controllers provides
rapid changes in dynamics response & unstable in various
atmospheric conditions. The difficulty of using a PI
controller is the necessity of tuning the gain with changes
in atmospheric conditions [3].This problem also overcome
in the model by proposing a new current control scheme.
The performance of current control scheme tested under
various atmospheric conditions to produce stable gain
value.
2. LITURATURE SURVEY
Previously implemented schemes in design of current
controller of PV system had some advantages &
drawbacks. A comparative analysis of all implemented
schemes also done as literature survey. All the techniques
implemented in recent past few years.
In 2016 Radwan & Rady proposed power synchronization
control (PSC) scheme for single phase grid connected CSC
based PV generators. They proposed a small signal model
with PSC scheme to investigate system stability,
interaction with grid & controller design parameters.
Synchronization of PSC with the grid in different operating
conditions was great advantage of the method. But it fails
to describe direct control of injected ac current through
inverter & self current limiting feature.
In 2015 ICPICC, J. Thomas & D. Jose used partial feedback
linearization current control technique for grid connected
PV system. Problem of tuning of controller with varying
atmospheric conditions can be easily solved by using this
technique. They tracked grid & reference current for
consideration of irradiation level change with PI & PR
controllers. [5]
Mahmood , Pota , Hossain & Roy presented a robust partial
feedback linearization scheme for stabilization on three
phase grid connected PV systems , in 2014. The scheme
ensures uncertainty in PV system model for matching
conditions. In another paper they proposed back stepping
controller design for sharing active & reactive power on
three phase grid connected PV systems. A constant
amount of power stored with cascaded control structure &
DC link voltage controller. Power flow balanced with the
help of incremental conductance method. It guarantee of
acting current control with unity or less power
factor.[4,17]
H. Agazadeh & H. M. Kojabadi suggested a standalone
system of PV generation with MPPT with changing
irradiance & ambient temperature. They used SPWM
scheme of inverters to reduce harmonics. MATLAB
simulink model shows feasible & effective output. [6]
3. PROBLEM IDENTIFICATION
Fallowing problems identified in the literature review of
the system. The problem solution method discussed
below.
1) Nonlinear Coordinate Transformation and its
partial Linearization
2) Internal Dynamic stability of a Grid Connected PV
System
3) Control Law for a Grid-Connected PV System
4) MPPT calculation & algorithm
4. METHODOLOGY
In PV cell characteristics diode current & output current of
PV cell given as
ION IS VPV RS IPV [4.1] IPV IL [
exp [α (VPV+ RSIPV ) ]-1 ]– )
[4.2]
It is seen that light generated current due to solar
irradiance & saturation current varies by temperature. It
is given by
[4.3]
* + ( ) [4.4]
When number of PV module connected together then for
grid connection integrated module current is
* * ( )+ +
[4.5]
For single phase grid connected inverters MPPT points
after inverter stage can be tracked as
̇ [4.6]
̇ [4.7]
4.1 Partial feedback linearization and partial
linearizability of PV system
Mathematical modeling equations for for nonlinear
performance of the grid connected PV systems expressed
below.
̇ [4.8]
[4.9]
[4.10]
[ ] [4.11]

[ ] [4.12]
[4.13]
Equation [4.13] shows that current should be controlled in
terms of its nonlinear transformation. Consider the
following nonlinear coordinate transformation:
[4.14]
Two possible transformation conditions are
[4.15]
[4.16]
On satisfaction of these conditions linearized system
transformation equation expressed as
̇ [4.17]
Where A & B are linearized system transformation
matrices.
5. CASE STUDY
Fig. 1 Case study of Partial feedback linearization
We referred evaluated system by M. A.. Mahmood, Pota &
Hossain . They tested their performance of designed
controller on a practical system. Reference current
obtained from PV system module is actually from MPPT.
Angular part of the change in current obtained from PLL.
Partial feedback linearization block equations obtained
from these blocks. Combination of the input implemented
through an inverter which uses PWM scheme. Fallowing
section gives considered values of implemented system
controller.
Switching frequency of inverter considered to be 10KHz.
PV array module consist of 5 strings which gives 2.8735
rated current on 43.5 V for parallel & 14.37A current with
217.5V for series connection. Hence power generated is
3.125kW. Passive component like dc link capacitor is of
value 400uF, line resistance 0.1ohm, & inductance 10mH.
Grid voltage is 240V with frequency 50Hz.
For standard atmospheric conditions solar irradiation
considered as 1kw-1 on 298K temperature. Some
fluctuation obtained on these condition posses nonlinear
characteristics. Here grid current fallowed by reference
current at MPPT point. Inverter switches perform
regulation on a proper control scheme. [1,2]
Changing atmospheric conditions has different effect.
Generally there are changes in working cell temperature &
solar irradiation. This results in change in voltage, current
& power. Partially shaded condition will reduce output
current giving change in operating point. Hardware of PV
module responds in 1.05S to 1.15S. But when weather
remains cloudy or shaded & irradiation changes up to
700W-1, response time increases up to 1.25S. MPP will
select different operating point keeping grid voltage same.
The noticeable thing is that conventional PI controllers
unable to track reference current in situations like change
in atmospheric conditions, change in load & fault
occurrences in various parts of the system. [1,2]
These test parameters considered for Australian
conditions. Hence for capacity of 2kW of load, conditions
are fulfilled & excess power taken to the grid. For grid line
impedance is to be considered as 0.12+j0.35 ohm km-1. A
designed controller should be capable of maintaining
stability under these changing conditions. Faults in system
may occur depending on load demand making controller
unstable.
For unit time period system supposed to be in ideal
conditions. A conventional PI controller can track current
only for unit time period. For variation in load, power
delivered in grid also changes. Instances at which power
delivered in grid, load consideration also taken in account.

6. PROPOSED SYSTEM
Fig.2 Power GUI for single phase grid connected PV
system
Power GUI has initial steady state voltage & current
settings. Here we have not used machine load flow.
Proposed system is linear time invariant which has a fixed
impedance keeping frequency constant i.e. 50Hz.
Computation of RLC parameters also done for inverter
design. For grid parameters conductor size with skin effect
taken in consideration .Our proposed simulation model
designed in MATLAB which is shown in fig. 3.Proposed
model has inbuilt MPPT response.
Fig.3 Proposed simulation model
In proposed model PV array system considered with
respect to irradiance & & ambient temperature. Further
DC power conversion into AC power is performed by
inverter. MPPT track reference voltage. P & O method used
to track MPP point means current controlled for stability
of controller by PWM scheme.
Fig.4 Implemented PV array module
Specification for PV array given below
S= irradiance level= 1000 W/Sq.m
Tamb= Ambient temperature= 250C
Tref= Reference temperature= 550C
Isc= short circuit current = 2.02 A
Voc= Open circuit voltage = 86.8 V
Im= Maximum current = 1.93A
Vm= Maximum voltage= 70.4V

Fig.5 Implemented inverter module
Implemented inverter module consists of 6mH inductor
with 4700uF DC link capacitor. An ideal IGBT with anti
parallel diode used for switching & regulation of current. A
1000uF capacitor improves power factor with respect to
load variation.
7. RESULT & DISCUSSION
Before adjustment of MPP, current from MPP is maximum
in time interval of 0.2S to 0.5 S but unstable. This time is
taken by PV system to initialize. It settles downs to 1.5A
after 0.5S. Voltage at this time is 86.8V. Simulation Carried
out for unit time period as shown in fig. 5 & fig.6.
Fig.5 Controlled input power from PV array
Even after applying it to the grid voltage level boost to
173V. Nonlinear current reduces to 0 after 0.4 S. This time
is linearizing time taken by controller to be linearize &
stable completely. The system tested for default line
parameters of grid. If system uploaded on hardware
module response time for linearizing output would be in
range of 1.4 S to 1.5 S.
Fig.6 Controlled unstable current by inverter
Fig.7 Boost voltage after inverter
8. CONCLUSION
PV generation has significant impact of irradiation & PV
cell temperature on stability of grid connected systems. It
is challenge to develop an accurate model for dynamic
behavior of PV generators under changing atmospheric
conditions, variation in load & fault tolerances. Proposed
model has capability of representing system response for
various irradiance & ac grid voltages for small as well as
large power. The software response time of model found
to be 0.4S. Accuracy of proposed model compared with
other models for partial linearization. Model found to be
accurate on line parameters of grid under steady state &
LTI systems. Hysteresis , skin effect of line conductors &
operating frequency ranging from 50Hz to 60Hz has less
effect on power loss in grid.
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ACKNOWLEDGEMENT
I would like to express my deepest appreciation to all
those who provided me the possibility to complete this
paper. A special thanks to Mr. Tushar Mandlik & Sprinkle
Enterprises who help to collect simulation data regarding
solar characteristics & implementation on grid.
BIOGRAPHIES
Dhananjay P. Labde currently
pursuing M.E. in Electrical
Power System in YTIET
Karjat, Maharashtra (India).
Mr. A. N. Pimpale received M.
Tech degree in digital
communication from RGPV
Bhopal (India). He has 7 years
of teaching experience in
Electronics & Electrical
Engineering. Currently he is
working as a technical trainer
in Sprinkle Enterprises.
Mrs Pranita Chavan currently
working as a HOD in
Electrical department YTIET
Karjat, Maharashtra (India).
She has 10 years of
experience in Electrical
engineering stream.

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