Lclr filter design and modelling for harmonic mitigation in interconnected micro grid system

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 04 Issue: 04 | April-2015, Available @ http://www.ijret.org 706
LCLR FILTER DESIGN AND MODELLING FOR HARMONIC
MITIGATION IN INTERCONNECTED MICRO GRID SYSTEM
D. S. Sargar1
, C. L. Bhattar2
1
P.G. Scholar, Department of Electrical Engineering, Rajarambapu Institute of Technology, Maharashtra, India
2
Assistant Professor, Department of Electrical Engineering, Rajarambapu Institute of Technology, Maharashtra,
India
Abstract
Today many people are attracted towards distribution generation (DG) because of low energy cost power supply, local
generation, highly reliable system, supply with good power quality. Increasing attention and investment in renewable energy that
is DG energy sources give rise to rapid development of high penetration renewable energy sources like solar energy, wind energy,
hydro energy. Out of this most important and best is the solar energy. There are multiple ways to interface PV arrays with the
power grid, but in there is problem of power quality. Today’s important concern of the power system is the power quality in case
of renewable energy sources. The power quality improvement in the interconnected micro grid systems and grid interconnection
with Distribution Generation (DGs) is the challenging task and to overcome the power quality problem passive filters are the best
and cost effective solution. In this paper the LCLR filter is implemented between inverter and grid. The complete system consists
of photovoltaic cell (PV), DC-DC boost converter, DC-AC inverter, LCLR filter and the grid. This paper also consists of complete
MATLAB simulation of PV cell, DC-DC boost converter and inverter with LCLR filter.
Key Words: Renewable energy, PV module, DC-DC boost converter, DGs, LCLR filter, power quality, micro grid
(MG) and THD
--------------------------------------------------------------------***----------------------------------------------------------------------
1. INTRODUCTION
Nowadays the cost of fuel increased due to increasing
demand of fuel and use of it, but the fuels are exhaustible in
nature so in the future they will be completely vanished in
one day. Other reasons are the tremendous increase in
population and global warming. The best solution for to
reduce the fuel cost and reduce unlimited use of fuel and to
save the fuel for future is the use of renewable energy
sources for the generation of electrical energy. Some best
renewable energy sources for generation of electricity are:
(1) Wind energy (2) solar energy (3) Tidal energy (4) Hydro
energy [1]. The distribution generation (DGs) means the use
of renewable energy sources for generation of electricity and
electricity generation is local and own generation. In these
the solar energy and wind energy sources are the very
popular energy sources because of its availability and
suitability. That is in the distribution system electrical
energy is generated using wind mill, solar panel with DC-
DC converter and DC-AC converter i.e. inverter with its
suitable controlling system [1]. The main objectives of use
renewable energy sources are: i) provide low cost energy
with local generation ii) Reduce the cost of conventional
energy sources. iii) Provide good quality power supply. The
power quality is obtained using the various power quality
improvement devices and equipment’s like DSTATCOM
(distribution static compensation), DVR (dynamic voltage
restorer), filters (active and passive), and zigzag
transformers, etc. For the grid interconnection of renewable
energy sources with power grid or micro grid is done using
inductor in past cases [2] and in recently LCL (Inductor (L)-
Capacitor (C)- Inductor (L)) filters are used [2]-[5].
The higher order harmonic attenuation of LCL filter allows
the use of lower order switching frequencies to find the
harmonic limitations and these harmonic constraints are
defined by IEEE standards. IEEE 1233 standard is for power
quality definitions [6]. IEEE 519 standard is for harmonic
control in electrical power system [7]. The higher-order
LCLR filter has been used in place of the traditional single L
i.e. only one inductor in series with line for getting the ripple
free the output currents at output of the inverter which is
formed by using IGBTs or MOSFETs as power electronic
devices. The LCLR filter achieves the higher harmonic
reduction along with simple design, the overall weight and
size of the LCLR filter is reduced due to appropriate design
and modelling. In addition LCLR filter does not produce
very high voltage drop across it. LCLR filters have been
used in between inverters connected with renewable energy
sources with pulse width modulation techniques (PWM) for
inverters.
In this paper detailed description about LCLR filter
modeling, designing procedure is given. The objective of
this paper is to carry out the detailed study about modeling
and designing of LCLR filter for inverter with renewable
energy sources as solar (PV panel). The MATLAB
simulation of PV model with boost converter and full bridge
inverter with LCLR filter is done with MATLAB Simulink
software. The proposed block diagram is shown in fig-1.

_______________________________________________________________________________________
Fig-1: Proposed Block Diagram of Inverter with LCLR Filter
.
2. PV MODULE AND BOOST CONVERTER
2.1 PV Module (Photovoltaic Cell)
PV solar energy is a best, clean, renewable energy with a
long service life and high reliability. But because of its high
cost, energy contribution is not as much of as other energy
sources. It is therefore important to have effective and
flexible models. In the photovoltaic (PV) system the solar
energy is converted into electrical energy using
semiconductor device to generate the charge. Two
parameters are very important in the PV systems that are
temperature (T in ºC) and solar irradiation is nothing but the
light intensity which is in watt per meter square; W/m2
. The
equivalent electrical circuit of PV cell is shown in fig-2,
which consists of semiconductor diode D, series resistance
 sR , shunt resistance is  shR , current flowing through
diode ( dI ) and scI is short circuit current and I is the
current of PV
Fig -2: PV cell Equivalent Electrical Circuit.
Under the standard conditions solar radiation 1000 W/m2
and temperature 250
C is considered [8].
By applying Kirchhoff’s Current Law (KCL) to circuit
which is given by,
shdph IIII  (1)
Now, the shunt current is given by equation
0
.
r
sc
rph
I
I
II  (2)
The diode current dI and the diode characteristics is given
by
 










1. ..
.
st
s
NVn
RIV
sd eII (3)
The shunt current is given by,
 
p
s
sh
R
RIV
I
.
 (4)
The equation of thermal voltage is given by
q
TK
Vt
.
 (5)
Where, K is Boltzmann constant, T is temperature and q is
the charge [16].
The output voltage of the PV cell is depends upon the
number cells connected in series with each other. Adding
cells in series will increase the voltage. In the proposed

_______________________________________________________________________________________
system single cell PV gives output voltage 21.07V DC and
by increasing seven series cells then output voltage become
147.49V DC. The PV module model is done in the
MATLAB Simulink Soft wares with considering table-1
parameters. The PV curve and IV curve are shown in fig-3
and fig-4 respectively [17, 18].
Fig -3: IV curve of PV cell
Fig -4: PV curve of PV cell
The single PV cell output voltage output voltage
which is 21.07V DC shown in fig-5 and seven cell PV
output voltage is shown in fig-6 which is near about
147.49V DC.
Fig-5: One PV cell output voltage (21.07V)
Fig -6: Seven PV cell output voltage (147.49V).
2.2 DC-DC Boost Converter
DC-DC Boost converters are used to convert DC non-
uniform voltage from the PV cell to required fixed high
level regulated or uniform DC voltage. In addition the boost
converter boosts the voltage level from low to high. The
boost converter circuit consists of input DC voltage from PV
cell, Inductor (L_boost) for boosting, IGBT with pulse
generator for getting the suitable control output, diode,
capacitor (C_boost) and load resistance R [9]. In this paper
seven PV cells produces 147.49V DC, but using this
147.49V boost converter boost the DC voltage up to 312V
DC. The parameters of DC-DC boost converter are
calculated using following equations-
Fig-7:Simulation model of DC-DC boost converter
(a) Duty Cycle: Duty cycle (D) of the boost converter is
intended by considering converter efficiency (η) 95%, for
the more sensible results of the duty cycle efficiency is
added in duty cycle [10]. Mathematical expression for duty
cycle is given by,
D =
out
in
V
V
× η (6)
(b) Inductor Selection: To finding good inductor value
equation (7) is used, di is the ripple current [11]
outs
inoutin
boost
Vfdi
VVV
L



)(
; mH
Vout
Vin
Idi 2 (7)
(c) Capacitor Selection: To select best capacitor value
equation (8) is used. [11-12]

_______________________________________________________________________________________
dVf
DI
C
s
boost


 F (8)
Where,
dV is the ripple voltage
  21
dI
D
I
dV 


(d) Resistance Selection: The resistance value is
calculating using following equation,
out
out
I
V
R  (9)
Fig-8: DC-DC Boost Converter Output Voltage (312V DC)
3. LCLR FILTER MODELLING
A. Per Phase Equivalent Circuit Modelling of LCLR Filter
The per phase equivalent model of LCLR filter is fully
described in case of its modeling and designing. Fig-9
shows the per phase model of LCLR filter. L, C, L and R are
the important parameters, 1L is the inverter side inductor,
2L is the grid side inductor, C is the capacitor and R is the
damping resistance. The capacitor C is connected in series
with resistance R.
Fig-9: Per Phase Model of LCLR Filter
The resistance R is connected to avoid the damping in the
circuit. iV is the inverter side voltage i.e. output voltage of
the inverter, gV is the grid side voltage, iI is the inverter
output current, cI is the current flowing through capacitor
and gI is the grid current.
The three phase model of the LCLR is shown in the fig-10.
Fig-10: Three phase model of LCLR Filter.
Transfer function of LCLR filter i.e. transfer function of
LCLR filter with damping resistance
Fig-11: Per Phase model of LCLR filter for finding TF
By applying Kirchhoff’s Voltage Law to loop1 we get
equation,
    0
1
1  IgIiRIgIi
CS
SIiLVi (10)
By applying Kirchhoff’s Voltage Law to loop2 we get
equation,
  02
1
)(  SIgLIiIg
CS
IiIgRVg (11)
Vg=0 because grid voltage assumed to be ultimate so to
dumping out all harmonic frequencies we set the Vg=0
02  SIgL
CS
Ii
CS
Ig
RIiRIg (12)
0
1
2
1












 Ii
CS
RIgSL
CS
R (13)
By some manipulation we get Ii i.e. inverter side current
Ig
RCS
CSLRCS
Ii 








1
12 2
(14)
From equation (10)

_______________________________________________________________________________________
01  RIgRIi
CS
Ig
CS
Ii
SIiLVi (15)
IgR
SC
IiR
SC
SLVi 












11
1 (16)
Putting value of Ii from equation (14) in the equation (16)
  
 
 Ig
CS
RCS
Ig
RCS
RCSCSL
CS
RCSCSL
Vi
1
1
1211 22





(17)
By solving brackets we get,
 
 
 
Ig
CS
RCS
Ig
RCSCS
RCSCSLRCSSCRSRCLCSLSRCLSCLL
Vi
1
1
1221121 22223223242





(18)
By taking denominator as CS
 
 
 
Ig
CS
RCS
Ig
CS
RCSCSLRCSSCRSRCLCSLSRCLSCLL
RCSVi
2
22223223242
1
1221121
1




(19)
Now by cancelling plus and minus terms we get,
     
1
2121211 23
SLLRCSLLCSLL
Ig
RCSVi 

 (20)
Now by rearranging terms we get important transfer
function
  )21(2121
1
23
LLSLLCRSLCLS
SCR
Vi
Ig


 (21)
 
  )21(2121
1
23
LLSLLCRSLCLS
SCR
Vi
Ig
SHLCLR


 (22)
B. Frequency Response of LCLR filter
To know the frequency response of the LCLR filter
system essentials to find transfer function of the filter. The
transfer function of the LCLR which is the compensation
characteristics of the filter and given by
i
g
LCLR
V
I
H  ,
where gI is the grid current and iV inverter output voltage,
in this case grid side voltage is assumed to be an idyllic
voltage. Equation (23) gives the transfer function of LCLR
with damping resistance. [12]
 
   SLLSLLCRSCLL
CRS
SHLCLR
21
2
21
3
21
1


 (23)
The filter parameter values are achieved from filter design
procedure which is shown in table-2. Response of filter is
shown in the Bode plot of LCLR with damping resistance in
fig-12
Fig-12: Bode plots of the LCLR filter showing response of
filter with damping resistance.
The insertion of resistance in series with capacitor
affects the frequency response of the LCLR filter which is
easily observed in the fig-12. Without series resistance very
high gain spikes are present in the magnitude Bode plot.
When series resistance with capacitor inserted in filter then
gain spike in the magnitude plot is almost reduced which
smoothing the overall current response, in addition the series
resistance plays important role in the filter to damp out the
oscillations and its value is very small so very less voltage
drop will occurs.
4. FILTER DESIGN PROCEDURE
A. Methodical Filter Design
Some important characteristics of filters must be considered
in the designing of LCLR filter, such characteristics are: (i)
filter size (ii) filter design (iii) amount of current ripple (iv)
cost of the filter (v) switching attenuation performance of
the filter. In case of the only LCL filter there is chance of
resonance due to the reactive power requirement and
because of this capacitor of filter will interfere with grid
resistance; therefore must add passive component as like
resistor in series with the capacitor. The passive component-
resistance is added in series with capacitor to smooth the
current ripples. The active components can be used to solve
these problems.
The important parameters required for the filter design are:
phV : Phase voltage of inverter output
LLV : Line to line voltage of inverter output
P : Rated active power
DCV : DC voltage from renewable energy sources i.e. input
voltage to the inverter
swf : Switching frequency of the inverter
gf : Grid frequency
g : Grid angular frequency

_______________________________________________________________________________________
resf : Resonance frequency
m : Inverter modulation factor
ak : Desired attenuation constant
Firstly need to find base values of the system so that
filter values is in percentage of base values, the base
capacitance  bC and base impedance  bZ which are
given by,
P
E
Z n
b
2
 (24)
bg
b
Z
C

1
 ; gg f 2 (25)
In the normal power system, it is supposed that highest
variation of power factor in grid is 5 %, when this value
multiplied by base capacitance value to get capacitance
value i.e. bCC 05.0 . The design factor greater than 5%
can used to compensate the reactance of the filter which is
inductive reactance [13]. The highest ripple of the current at
output of the inverter is given by
  sw
DC
L mTm
L
V
I  1
3
2
1
max (26)
swT : Is the switching time of the inverter and m :
modulation factor depends upon which PWM technique
used by the inverter. It is seen that highest peak to peak
current distortion occurs at 5.0m , therefore inductor
maximum current given by
1
max
6 Lf
V
I
sw
DC
L  (27)
Where, 1L is the inductor of inverter side. For the maximum
rated current consider 10% ripple in current. Rated
maximum current given by,
maxmax 1.0 IIL  (28)
Where
phV
P
I
3
2
max  (29)
Therefore 1L is given by,
max
1
6.0 If
V
L
sw
DC
 (30)
The LCLR filter minimizes current distortion to very low
level so ripple value will be below 2 %. The relation
between harmonic current of inverter and the grid is given
by,
 
    a
swbi
g
k
xCLrhi
hi


 2
111
1

(31)
Where ak is the desired attenuation factor of the inverter
and r is the constant which is ratio of grid side inductor
 2L to the inverter side inductor  1L and equation (32)
gives its relation.
12 rLL  (32)
Fig-13: Implemented System of Inverter with LCLR filter.

_______________________________________________________________________________________
The scheming for the various values of r any can assess
transfer of filter at specific resonance frequency which
depends on the nominal impedance of the grid. [14]
The value of grid side inductor in terms of desired
attenuation factor is given by,
2
2
2
1
1
sw
a
C
k
L


 (33)
The resistance (R) in series with capacitor (C) compensates
the part of ripples in the switching frequency to avoid the
resonance of the LCLR filter. The resonance frequencies in
terms of LCLR filter parameters given in,
CLL
LL
res
21
21 
 (34)
The range of resonance frequency should satisfy
swresg fff 5.010  (35)
The resistance value should be one third of capacitor
impedance at the resonance frequency [15]. The equation
(36) gives the value of resistance of LCLR filter.
C
R
res3
1
 (36)
Table-1: PV Cell Parameters
PARAMETER SYMBOLS VALUE
Temperature T 25+273.15 0
C
Irradiance (p. u.) IrrG  1 W/m2
Nominal Irradiance Ir0 1000 W/m2
Boltzmann Constant K 1.38e-3
Charge q 1.6e-19 C
Emission coefficient n 1.36
Open circuit voltage Voc 21.3 V
Short circuit current Isc 3.8 A
Table-2: DC-DC Boost Converter Parameters
PARAMETERS SYMBOLS VALUE
Duty Cycle D 0.575962
Boost Inductor L_boost 0.0019 H
Boost Capacitor C_boost 0.0044 F
Load Resistance R 16.4211 Ω
Table-3: System Parameters
Phase Grid Voltage Vg 230V
DC Link Voltage VDC 312V
Nominal Power P 5 KW
Grid Frequency
gf 50 Hz
Switching Frequency
swf 15 KHz
Modulation Factor M 0.05
Attenuation Factor
aK 0.2
Table-4: LCLR Filter Parameters
Inverter Side Inductor L1 1.9729 mH
Grid Side Inductor L2 0.04495 mH
Capacitor of Filter C 15.043 µF
Damping Resistance R 0.5694 Ω
6. SIMULATION RESULTS AND DISCUSSION
A. Inverter controller and LCLR Filter
The model of Inverter with LCLR is done using MATLAB
in Simulink Power System Tool Box shown in fig.13. The
LCLR filter plays very important role in the Power Quality
Improvement and better interconnection of renewable
energy sources inverter with grid. For the inverter dqo
algorithm is used for the power quality improvement which
reduces THD to very low level. dqoMeans the direct-
quadrature-zero transformation is mathematical
transformation which rotates the reference frame of three
phase systems. The dqo transformation decreases three AC
quantities (phases a, b, c) to two DC quantities so that
simplified calculations can be done with DC quantities.
These are done to simplify the calculations for control of the
any three phase inverters.
B. Inverter Without LCLR Filter
Without LCLR filter inverter output current contains
harmonics. The Fig-14 shows the inverter output voltage
(230V) and fig-15(a), (b) and (c) shows phase a, b and c
currents respectively and fig-16 shows inverter output
current of combined phases a, b and c (0.015A). THD of the
system is very high which is up to 50.38%. In this case
current is much distorted so in the power system it is very
dangerous and harmful. The Fig-17 shows THD analysis of
the current.
Fig-14: Inverter output voltage without LCLR Filter (230V)

_______________________________________________________________________________________
Fig-15(a), 15(b), 15(c): Inverter output Current without
LCLR Filter of phase a, b and c respectively.
Fig-16: Inverter output Current without LCLR Filter of
combined phases a, b and c (0.015A).
Fig-17: THD analysis of Inverter output Current without
LCLR Filter.
C. Inverter With LCLR Filter
With the LCLR filter the THD of the system is reduced to
very low level which improves the power quality.
Fig-18: Inverter output active, reactive power, Voltage and
Current with LCLR Filter.
Fig-18 shows the inverter output voltage (230V), current
(0.6A); these quantities are nearly sinusoidal from the
MATLAB simulation results. Means the total harmonic
distortion percentage is almost reduced. Fig-19 shows the
THD analysis of the current and THD of the system is only
0.94%.
Fig-19: THD analysis of Inverter output current with LCLR
filter
7. CONCLUSIONS
In this paper LCLR filter is designed
systematically with grid connected inverter system. The
inverter is fed by renewable energy sources as PV cell and
generates required DC voltage; these papers also proposes
DC-DC Boost Converter for regulating the voltage of PV
cell and boost the voltage level up to optimal required
voltage for inverter. The very cheap LCLR filter with grid
connected inverter reduces system THD and it is found that
proposed LCLR filter meets THD within prescribed range
which is up to 0.94 % therefore power quality would be
improved as well as grid interconnection of inverters with
renewable energy sources is done bitterly.

_______________________________________________________________________________________
ACKNOWLEDGEMENT
I would like to thank Prof. C. L. Bhattar for his valuable
guidance and support. I also thanks to Prof. A. R. Thorat Sir
HOP and Prof. H.T. Jadhav HOD of Electrical department at
Rajarambapu Institute of Technology, Sakhrale, Islampur
for their guidance.
REFERENCES
[1]. Aleksandr Reznik, Marcelo Godoy Simoes, Ahmed
Al-Durra and S. M. Muyeen, “LCL Filter
Design and Performance Analysis for Grid-
Interconnected Systems,” IEEE Trans. Ind. Appl.,
vol.50, no.2, pp. 1225-1232 Mar/April. 2014
[2]. F. Bouchafaa, D. Beriber, and M. S. Boucherit,
“Modeling and control of a grid connected PV
generation system,” in Proc. 18th MED Conf. Control
Autom., 2010, pp. 315–320
[3]. Singh Bhim, Jayaprakash P, Somayajulu TR, Kothari
DP. “Reduced rating VSC with a zig-zag transformer
for current compensation in a three-phase four wire
distribution system,’’ IEEE Trans Power Deliv 2009;
24 (1): 249.
[4]. Singh Bhim, Jayaprakash P, Kothari DP. “A T-
connected transformer and three leg VSC based
DSTATCOM for power quality improvement,” IEEE
Trans Power Electron 2008; 23 (6):2710–8.
[5]. Zaveri Tejas, Bhalja Bhavesh, Zaveri Naimish.
“Comparison of control strategies for DSTATCOM in
three-phase, four-wire distribution system for power
quality improvement under various source voltage and
load conditions,” Electr. Power Energy Syst 2012; 43:
582–94.
[6]. IEEE 1233 standard for power quality definitions.
[7]. IEEE 519 standard for harmonic control in electrical.
[8]. KHELIF Messa oud, M'RAOUI Abdelhamid, MALEK
Ali. “Simulation optimization and performance
analysis of an analog, easy to implement, perturb and
observe MPPT technique to be used in a 1.5 KW p
photovoltaic system,” Centre de Development des
Energies Renouvelables, CDER, 16340, Algiers,
Algeria.
[9]. Sajib Chakraborty, Saila Ishrat Annie and M. A.
Razzak. “Design of Single-Stage Buck and Boost
Converters for Photovoltaic Inverter Applications,”
3rd Inter. Conf. on Informatics, Electron & Vision
2014.
[10]. http://www.scribd.com/doc/53012897/slva372b/access
ed on July, 2013.
[11]. R. O. Caceres, I. Barbi, “A boost dc-ac converter:
Analysis, design, and experimentation,’’ IEEE Trans.
Power Electron., vol. 14, no. 1, pp. 134--141, 1999
[12]. Ravish R. Singh, “Electrical Networks,” Tata
McGraw-Hill Publication, first edition, 2008.
[13]. V. H. Prasad, “Average current mode control of a
voltage source inverter connected to the grid:
Application to different filter cells,” M.S. thesis, Dept.
Elect. Eng., Virginia Polytech. Inst. State Univ.,
Blacksburg, VA, USA, 1997.
[14]. Y. Tang, S. Member, P. C. Loh, P. Wang, and F. H.
Choo, “Generalized Design of High Performance
Shunt Active Power Filter With Output LCL Filter,”
IEEE Transactions on Industrial Electronics, vol. 59,
no. 3, pp. 1443-1452, 2012.
[15]. S. V. Araújo, A. Engler, B. Sahan, V. U. Kassel, F.
Luiz, and M. Antunes, “LCL filter design for grid-
connected NPC inverters in offshore wind turbines,” in
Proc. 7th Int. Conf. Power Electron., 2007, pp. 1133–
1138.
[16]. M.G. Villalva, J.R. Gazoli, E. Ruppert “Modeling and
Circuit Based Simulation of Photovoltaic Arrays”,
Brazilian Journal of Power Electronics, Vol. 14, No. 1,
pp. 35-45, 2009.
[17]. C. Osorio. Matlab-Simulink models, Math works.
[18]. http://ecee.colorado.edu/~ecen2060/matlab.html.
BIOGRAPHIES
Dhananjay S. Sargar received the
B.E degree in Electrical engineering
from Annasaheb Dange College of
Engineering and Technology Ashta,
Sangli, Maharashtra, India in 2013.
Currently he is pursuing M.Tech in
Electrical (Power System) at
Rajarambapu Institute of Technology,
Sakhrale (Islampur), Maharashtra, India. His area of interest
includes Power quality improvement and Renewable Energy
sources.
Chandrakant L. Bhattar received
the B.E. degree in electrical
engineering from Government College
of Engineering, Karad, India, in 2008,
and the M.Tech. Degree in electrical
power system from Government
College of Engineering, Amravati,
India in 2011 He is currently working
as an Assistant Professor in Electrical Engineering
Department, Rajarambapu Institute of Technology,
Maharashtra, India. His research interests are Power Quality
and Application of Power Electronics in Power System and
Smart Grid.

Lclr filter design and modelling for harmonic mitigation in interconnected micro grid system

More Related Content

What's hot (19)

Viewers also liked (19)

Similar to Lclr filter design and modelling for harmonic mitigation in interconnected micro grid system (20)

More from eSAT Journals (20)

Recently uploaded (20)

Lclr filter design and modelling for harmonic mitigation in interconnected micro grid system