International Journal of Engineering Trends and Technology (IJETT) – Volume 22 Number 8-April 2015
Renewable Energy Resources Connected In Grid
at the Distribution Level with High Power Quality
Enhancement
Mr.Manoj R. Gujar1, Mr.Ajit P. Chaudhari2, Mr.Girish K. Mahajan3
Department Name: Electrical, M.E. Student1, Associate Professor2, Associate Professor3
SSGB’s College of Engineering & Technology 1,2,3 Bhusawal, Jalgaon (India-425201)
Abstract— power quality problem is a big challenge for power
engineers as well as consulting engineers in recent times.
Renewable energy resources (RES) are connected in a grid at
distribution system by utilizing power electronic interfaces. The
power electronic devices create various power quality issues like
unbalance or nonlinear current and voltage, grid and load current
harmonics, load active and reactive power demand. In this paper
Renewable energy resources (RES) connected to the grid through a
grid interfacing inverter for power quality enhancement. The grid
interfacing inverter supplies power generated from RES to the grid
and compensate unbalance or nonlinear current and voltage, grid
and load current harmonics, load active and reactive power
demand. This new power quality enhancement concept is evidence
with simulation results carried out by MATLAB/Simulink.
Keywords — Grid interfacing inverter, Filter, Renewable
Energy Resources (RES), Distribution system, Power quality
enhancement.
voltage and current. The heavy use of electronic devices
create power quality problems. Electronic devices mainly
affect on voltage, current and frequency of the system.
Because of heavy use of electronic devices create various
power quality issues like unbalance or nonlinear current and
voltage, load current harmonics, load active and reactive
power demand. Because of such power quality issues increase
cost of electricity, which is affected on consumers and
supplies. So decrease cost of electricity, economic energy
supplies to consumers, increase power factor and compensate
the power quality issues like unbalance or nonlinear current
and voltage, load and grid current harmonics, load active and
reactive power requirement for that need of power quality
enhancement.
III. POWER QUALITY ISSUES AND RES
Power quality issue means deviation of the voltage, current
and frequency of the power system. The pure sinusoidal
I. INTRODUCTION
waveform of voltage and current is called Power quality.
Both electric utilities and end users of electric power are
Some important issues of power quality are power system
becoming increasingly concerned about the quality of electric
reliability, stability, efficiency, cost etc [5]. Renewable energy
power. Power quality is challenging issue in all over the world.
resources (RES) connected in the distribution system by
The energy demand increasing day by day, which can create
utilizing power electronic interfaces. The heavy use of power
problem for electric utilities and end users of electric power.
electronic devices create various power quality issues like
Increasing air pollution, global warming worry, decreasing
unbalance or nonlinear current and voltage, load and grid
fossil fuels and their increasing cost has made it necessary to
current harmonics, load active and reactive power
look towards Renewable Energy Sources (RES) as a future
requirement[1]. Other power quality issues are,
energy solution [1]. Renewable energy resources like solar,
fuel cell, photovoltaic energy sources, wind, etc. are largely
A. Over voltage /under voltage
merged into in power system for full fill increasing energy
The supply voltage rating above the rated voltage of the
demand. The Renewable energy resources (RES) connected at
system is called overvoltage and the supply voltage rating
distribution system. Due to the high penetration of Renewable
below the rated voltage is called under voltage. The overenergy resources, create issues of stability, voltage regulation
voltage and under voltage condition occur by environmental
and power quality of the power system [4].
phenomena such as direct or indirect lightening strikes on the
Renewable energy resources (RES) connected to the grid
grid. Such condition is rarely occurring and it can be reduced
through a grid interfacing inverter for power quality
using grid components[5],[4].
enhancement. The grid interfacing inverter supplies power
generated from RES to grid and compensate unbalance or
B. Voltage dips/Voltage sags
nonlinear current and voltage, load and grid current harmonics,
It is a short term reduction concept means it is reduced in
load active and reactive power demand [1].
fraction of a second to several second. The voltage dips are
II. NEED OF POWER QUALITY ENHANCEMENT being in two forms like swell and sag. When heavy load
disconnects from the system, then voltage swell is occurring
Power quality is very important and the main aspect of the
power system. Power quality mains sinusoidal waveform of
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and when heavy load connects specially motor to the system
then voltage sags is occurring.
C. Transients
It is very short duration short duration concept, but high
magnitude (up to several thousand volts) and its acceleration
time also fast. Transients occur due to lightening strokes or
switching of heavy and reactive loads in the grid.
D. Harmonics.
The heavy use of electronic devices create harmonics in
grid current. The deformity in sine wave of voltage and
current caused harmonics in the system. Every non-sinusoidal
waveform contains harmonics. The grid interfacing inverter
compensates load current harmonics.
IV. BASIC MODEL OF THE SYSTEM
interfaces. Heavy use of power electronic devices creates a
power quality issue like unbalance or nonlinear current and
voltage, load current harmonics. To reduce load current
harmonics by using filters. Mostly Active power filter are
used to compensate the load current harmonics and load
unbalance at distribution level[1].
C. Grid interfacing inverter
The grid interfacing inverter is one of the important aspect of
the system. It is a heart of the system. Generally, current
controlled voltage source inverter is used to interface the
Renewable energy resources in the distribution system. The
voltage source inverter is a key component of the system. The
voltage source inverter is powered electronic device and it
connect shunt or parallel to the system which is used to
generate sinusoidal voltage. The voltage source inverter is
connected Renewable energy resources (RES) to the grid this
is the main function of voltage source inverter. The power
generated by Renewable energy resources (RES) may be DC
voltages, then it convert AC voltages with the help of voltage
source inverter and connect to the grid. The voltage source
inverter compensates load active and reactive power
requirement of the system[1],[2],[4].
D. Renewable energy resources(RES)
The renewable energy sources connect to the grid by using
a voltage source inverter. The generated power of renewable
energy is supplied to voltage source inverter via a DC link.
The renewable energy sources may be solar, wind, fuel cell
and photovoltaic energy sources, etc[1]. are largely merged
into in power system for full fill increasing energy demand.
E. Control system.
Control system is key element of voltage source inverter.
The control diagram of grid interfacing inverter for 3-phase 4wire system is shown in figure 2 [1].
Fig-1 Basic block Diagram of System
A.
B.
C.
D.
E.
Distribution transformer
Filter
Grid interfacing inverter
Renewable energy resources
Control system
A. Distribution transformer
Distribution transformer is connected in series with line
which to be compensated. Distribution transformer is three
phase two winding transformer. A distribution transformer is
transformer that provide the final voltage transformation in
distribution system. It is one of the important component of
the system.
B. Filter
The filter is also one of the important components of the
system. The filter is interconnect with grid as shown in figure
1. The Renewable energy resources (RES) are connected in
the distribution system by utilizing power electronic
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Fig-2 Block diagram of grid interfacing inverter Control
The control is used for grid interfacing inverter for 3-phase 4wire distribution system. The four leg of inverter is used to
compensate the neutral current of the load. The main function
of this control is to regulate the power at the point of common
coupling (pcc) [2].
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The control of four leg inverter at three conditions, when the
power of renewable energy sources is zero, power of
renewable energy sources is less than the total load power and
power of renewable energy sources is greater than total load
power. This control performs the function at above three
conditions, power supplies at the point of common coupling
(PCC) in the distribution system. This control supplies active
power demand from the grid or to the grid [1]. If the load
connected to the point of common coupling is non linear,
unbalance or a combination of both, the given control
compensates the harmonics, unbalance and neutral current [2].
there is no current and Voltage flow from RES. In first mode
grid current is similar to the load current is shown in
simulation results.
V. SIMULATION AND RESULTS
The renewable energy system connected in a grid by using a
grid interfacing inverter modelled shown in figure 3. The grid
interfaces with 3-phase 4-wire distribution system, a
comprehensive simulation study is carried out using
MATLAB/Simulink. The current controlled voltage source
inverter strongly controlled and enhance power quality of
variable energy generated by renewable energy resources. It
obtains balance load current, grid voltage, grid current at unity
power factor. The simulation result carried out in two modes
of operation.
Fig-4 Grid voltage before t = 0.7s
Fig-5 Grid current before t = 0.7s
Fig-6 Load current before t = 0.7s
Fig-3 MATLAB simulation model of the system
The grid current is similar to the load current is shown in fig.5
and fig.6 of simulation results.
A. Modes of Operation.
Mode 1. No power generation from RES and no grid
interfacing inverter connected to the system.
In the first mode of operation, no power generation from
renewable energy resources (RES). The grid interfacing
inverter is not connected to the till time 0.7s. At the starting
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The above simulation results fig. 8,9,10 shows active and
reactive power flows of the grid, load and inverter, when the
grid interfacing inverter is not connected in the system. When
the grid interfacing inverter is not connected in the system
before t=0.7s then active power not injected by the inverter
from renewable energy resources (RES) is shown in fig.10.
The active power flow of load is high and reactive power flow
is low as shown in fig. 9.
Fig-7 Inverter current before t = 0.7s
Mode 2. Power generation from RES and Grid interfacing
inverter connected to the system.
This is the second mode of operation of simulation result. In
this mode Renewable energy resources generated power and
grid interfacing inverter is connected in the system. The result
carried out with the help of MATLAB/ Simulation after time t
= 0.7s. The grid interfacing inverter supplies load neutral
current, active and reactive power demand. It compensates
unbalance current and voltage.
Fig. 8 Active and reactive power flow of grid before t=0.7s
Fig-11. Compensate grid voltage after t = 0.7s.
Fig. 9 Active and reactive power flow of load before t=0.7s.
Fig-12 Compensate grid current after t = 0.7s.
Fig. 10 Active and reactive power flow of inverter before t=0.7s.
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Fig-13 Compensate load current after t = 0.7s.
Fig-17 Active and reactive power flow of inverter after t=0.7s.
The above simulation results fig. 15,16,17 shows active and
reactive power flows of the grid, load and inverter, when the
grid interfacing inverter is connected in the system. When the
grid interfacing inverter is connected in the system after t=0.7s
then active power injected by the inverter from renewable
energy resources (RES) is shown in fig.17. The active power
flow of grid at t=0. 7s is high and it slightly reduced at t=0.
85s and again high after t=0. 9s but reactive power flow of
grid is higher than the active power flow as shown in fig. 15.
The active power flow of load is high and reactive power flow
is low as shown in fig. 9.
Fig-14.Compensate inverter current after t =0.7s.
B. Total harmonic distortion (TDH) at Grid side and Load
side of the system.
The total harmonic distortion (THD) is challenging issue for
power quality. The active power filter performs functions and
reduced current harmonics from load & grid side. When the
inverter is not connected to the system before t=0.7s, then
harmonics in load and grid side current is high. After t=0.7s
inverter connected to the system then active power filter is
reduced harmonics in load and grid side current.
Fig-15 Active and reactive power flow of grid after t=0.7s.
Fig-16 Active and reactive power flow of load after t=0.7s.
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Fig. 18 Grid side THD before t=0.7s.
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The fig. 18 shows grid side THD before t=0.7s. The THD
magnitude takes at t=0.2s as shown in fig.18. At t=0.2 grid
side THD is 63.88%.
Fig. 21 Load side THD after t=07s.
Fig. 19 Grid side THD after t=0.7s.
The fig. 21 shows load side THD after t=0.7s. At t=0.8s THD
of load side is 64.06% is near about equal to the THD of load
side before t=0.7s.
The fig. 19 shows grid side THD before t=0.7s. The THD Need to check load side THD magnitude in different time. It
magnitude takes at t=0.8s as shown in fig.18. After t=0.7s. checks at t=0.3s before and after t=0.7s condition, the
grid interfacing inverter is connected to the system, then grid simulation results are shown below fig.22 and fig.23.
side harmonics are reduced. At t=0.8s grid side THD is 1.40%.
Fig. 20 Load side THD before t=07s.
Fig. 22 Load side THD before t=07s.
The fig. 20 shows load side THD before t=0.7s. At t=0.2s
THD of load side is 63.88%.
The fig. 22 shows load side THD before t=0.7s. At t=0.3s
THD of load side is 106.39%.
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when renewable energy resources connected in a grid at
distribution level. This paper is a presentation enhancement of
power quality with the help of grid interfacing inverter. The
simulation results are carried out by comprehensive use of
MATLAB/Simulink.
The
grid
interfacing
inverter
compensates unbalance current and voltage, load and grid
current harmonics, load active and reactive power requirement
and maintain grid side unity power factor.
REFERNCES
[1]
Fig. 23 Load side THD before t=07s.
The fig. 23 shows load side THD after t=0.7s. At t=0.3s THD
of load side is 64.14%.
TABLE
System
rating
THD(%)
Before
t=0.7s
THD(%)
After
t=0.7s
THD(%)
Grid side THD
63.88%
1.40%
Load side THD
106.39%
64.14%
11KV 50Hz
AC
Table-1. THD magnitude of grid side and load side Current.
VI. CONCLUSION
Power quality issues is a common problem in power industry
and also a big challenge for power engineers. The power
quality issue like unbalance current and voltage, load current
harmonics, load active and reactive power demand is not a
new issue for distribution system, but it’s challenging issues
ISSN: 2231-5381
MukhtiarSingh,VinodKhadkikar, Ambrish Chandra, and Rajiv
K.
Varma, ―Grid Interconnection of Renewable Energy Sources at the
Distribution Level With Power-Quality Improvement Features,‖ IEEE
Trans. Power Electron., vol. 26, no. 1, Jan. 2011.
[2] S. Syed Ahmed, N. Sreekanth, K. Siva Kumar-Power Quality
Improvement at Distribution Level for Grid Connected Renewable
Energy Sources,| ISSN : 2248-9622, Vol. 4, Issue 9( Version 5),
September 2014.
[3] M.Archana, Y.C.V.Kondaiah - Grid Interfacing Inverter of Renewable
Energy Sources to Improve the Power Quality in Distribution System,|
International Journal of Advanced Research in Electrical, Electronics
and Instrumentation Engineering Vol. 1, Issue 5, November 2012.
[4] SREYA GRACE MATHEW, FOSSY MARY CHACKO -POWER
QUALITY IMPROVEMENT IN A GRID CONNECTED
RENEWABLE ENERGY SYSTEM,| International Journal of Electrical,
Electronics and Data Communication, ISSN: 2320-2084 Volume-2,
Issue-10, Oct.-2014.
[5] NEHA KAUSHIK - POWER QUALITY, ITS PROBLEM AND
POWER QUALITY MONITORING, INTERNATIONAL JOURNAL
OF ELECTRICAL ENGINEERING & TECHNOLOGY (IJEET)
Volume 4, Issue 1, January- February (2013), pp. 46-57
[6] F. Blaabjerg, R. Teodorescu, M. Liserre, and A. V. Timbus, Overview
of control and grid synchronization for distributed power generation
systems,” IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1398–1409,Oct.
2006.
[7] Vikas khare, Dr. Savita Nema, Dr. Prashant baredar,” Power Quality
Disturbances in Grid Connected Solar System & Its Prevention”,
International Journal of Engineering and Innovative Technology
(IJEIT)Volume 1, Issue 5, May 2012.
[8] J. M. Guerrero, L. G. de Vicuna, J. Matas, M. Castilla, and J. Miret,- A
wireless controller to enhance dynamic performance of parallel inverters
in distributed generation systems| IEEE Trans. Power Electron., vol. 19,
no. 5, pp. 1205–1213, Sep. 2004
[9] P. Jintakosonwit, H. Fujita, H. Akagi, and S. OgasawaraImplementation and performance of cooperative control of shunt active
filters for harmonic damping throughout a power distribution
system|IEEE Trans. Ind. Appl., vol. 39, no. 2, pp.556–564, Mar./Apr.
2003.
[10] J. M. Carrasco, L. G. Franquelo, J. T. Bialasiewicz, E. Galván, R. C.P.
Guisado, M. Á. M.Prats, J. I. León, and N. M. Alfonso- Power
electronic systems for the grid integration of renewable energy sources:
A survey| IEEE Trans. Ind. Electron., vol. 53, no. 4, pp. 1002– 1016,
Aug. 2006.
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