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ISSN (Online) 2395-2717
International Journal of Engineering Research in Electrical and Electronic
Engineering (IJEREEE)
Vol 3, Issue 9, September 2017
All Rights Reserved © 2017 IJEREEE 191
Islanding Detection and Resynchronization Mode
For Micro grid With UPQC Using Fuzzy Logic
Controller [1]
B.Vineela, [2]
T.Obulesu [1]
PG Scholar , [2]
Academic Assistant [1][2]
Dept. of EEE, JNTUA College Pulivendula, Andhra Pradesh, India
Abstract:-- :- A novel presentation of unified power quality conditioner (UPQC) is used for developing the dynamic
performance of grid connected DG based microgrid/microgeneration (μG) system as a custom power device has been
presented here. UPQC is an arrangement of two series and shunt inverters coupled side to side with the sharing of DC storage link
Capacitor. Series inverter is positioned between the point of common coupling (PCC) and source for minimizes the source side
interruptions: flicker voltage swell/sag, voltage unbalances by inserting voltages to attain preferred load level at before the PCC.
Shunt inverter is positioned at the PCC for minimizes the reactive power and harmonic troubles. This proposed system represents
the working of UPQCµG−IR in both islanding and reconnection mode of process for developing the power quality. This UPQCµG−IR
can even works in the incident of phase variation between grid and microgrid. The process of UPQC µG−IR in normal and
interruption methods are shown in MATLAB/SIMULINK.
Index Terms: Distributed generation (DG), intelligent islanding detection, microgrid, power quality, smart grid, unified power
Quality compensator (UPQC).
INTRODUCTION:
Now-a-days DG sources are performed as a microgrid
(μG) for supplying real/active power to the grid/load.
UPQC is introduced in a DG supported grid with micro
generation system as a power enhancing device to 1)
mitigate the true power transfer complexity; 2)
compensating the reactive power under islanded mode; 3)
control the current and voltage THD at PCC within
permissible limits. Seamless/Smooth operation for power
transfer is possible for islanding and reconnection/
resynchronization modes.
For improving system flexibility and improving
power quality, UPQC has been introduced in a grid
combined μG system, which is named as UPQC μG
.UPQC contains two active power filters (APF). One is
Shunt part (APFsh) positioned at the PCC. Another one
is series part (APFse) is positioned earlier than PCC and
in series with the source. The communication process
is placed between μG and UPQCμG are mentioned in
for islanded and reconnection modes of operation. In
this seamless operation of island and
reconnection/resynchronize modes with fewer sums of
switches without any interruptions, UPQCμG−IR is
preferred over normal UPQC. Advantages of
UPQCμG−IR are as follows
1) Voltage interruptions/sag/swell and reactive
current in the reconnected mode are compensated by
using UPQCμG−IR. The operation flexibility is
improved. 2) QH power at the loads is compensated during
islanded mode by using APFsh. 3) In both modes of operation, μG are always
interconnected with the load for providing active
power. Therefore UPQCμG−IR can be suggested in to the
system for reducing control difficulty of the DG
converter. 4) Islanding and resynchronization/reconnected modes are initiated as secondary control in a proposed system. 5) Any phase difference/phase jump conditions
between μG and grid has also been allowed in to the system.
Section II describes the operation principle of UPQCμG−IR
with different modes. Section III represents the
construction and rating issues. Section IV represents
island and resynchronization/reconnect mode of
techniques. By using MATLAB/SIMULINK Performance
of system UPQCμG−IR is verified.
ISSN (Online) 2395-2717
International Journal of Engineering Research in Electrical and Electronic
Engineering (IJEREEE)
Vol 3, Issue 9, September 2017
All Rights Reserved © 2017 IJEREEE 192
II. OPERATION PRINCIPLE
The combination of UPQCμG−IR with DG connected μG
system and grid is shown in Figure.1 (a). The interconnect and island mode detection system of process are possible by breaker switches for proper connection of μG with grid. Island and reconnected technique operations of UPQC
shows in .Figure.1 (b) and (c).The performance of
UPQCμG−IR is as follows.
A. Interconnected Mode
This interconnected mode shown in Figure.1 (b), it holds:
1) The distribution generation source delivers real /active power only to the grid, storage and load. 2) APFsh minimizes the reactive and harmonic (QH)
power of the non linear load at PCC with in permissible limits. 3) APFse minimizes the voltage sag/swell/interruptions at before PCC. 4) If any faults/errors occur, UPQC alerts the DG
converter for islanding with in preset time.
B. Islanded Mode
This islanded mode shown in Figure.1(c), it holds: 1) If any interruptions/grid failure occurs, APFse is removed
from the system by using switches and DG remains in
operation for supplying real/true power to the load. 2) The APFsh is used to control the non-active /reactive
power at PCC, if any linear or nonlinear loads placed.
3) After restoration of grid power, APFse is again reconnected in series with the source.
Figure.1 (a) Grid coupled micro
generation/microgrid with UPQCμG−IR, (b)
Interconnection mode of µG with UPQC, (c) Islanded
detection of µG with UPQC, (d) overall fundamental
working principle diagram of µG with
representations.
III. DESIGN AND RATING ISSUES
The necessary frequency illustration of the system
shown in Figure.1 (d) (1) represents voltage equation at
PCC and (2) represents current equation.
A. Shunt part of UPQCμG−IR(APFsh) Whenever voltage sag occurred in the source side, APFse is
comes into operation for compensate voltage sag by giving
required voltage and maintain zero- phase at PCC. APFsh is
used to compensate reactive power of the load by giving Ish
in quadrature to Vpcc. Figure. (2) Shows the phasor
diagrams at different conditions.
Represents the additional new source current and Ish represents the
additional active component current drawn by APFsh
ISSN (Online) 2395-2717
International Journal of Engineering Research in Electrical and Electronic
Engineering (IJEREEE)
Vol 3, Issue 9, September 2017
All Rights Reserved © 2017 IJEREEE 193
B. Series part of UPQCµG-IR (APFse)
The APFse is always coupled in series with the
source/grid and allows only real fundamental current
(Iloadfp) to the load current. Therefore, APFse current rating
is same as the primary real load current.
Voltage sag equation from figure. 2(c) and (d) is written
as
The highest injected voltage sag value will be considered
as Voltage evaluation of APFse, Thus
Assume that voltage sag is represented as k fraction of Vs
Therefore, the APFse VA rating can be expressed as
When =0, the real power of APFse can be expressed
as
Assume = = 0 for steady and in-phase operating
circumstances
The equation of supply current passed through series
transformer of APFse under compensation of voltage sag
from figure .2(e) can be written as
Thus, the transformer rating and its size is developed
on the highest compensated voltage sag value. The
APFse voltage rating is key for determining the
transformer size and compensation range of voltage sag
value.
C. Link Capacitor
This dc link storage capacitor is used to 1) maintain
proper steady state voltage at interruption conditions; 2)
serve non-active power to the utility side; 3) maintain
balanced load voltage by giving real /true power. The
preferred range of storage capacitor constructed on the
energy handling capacity. For continuous supply DG
energy storage has also been proposed and it is help to
lower the capacitor size.
IV.CONTROLLER DESIGN
For successful signal transfer between UPQCµG-IRand μG depends on proper designed control structure for compensating the sag/swell/interrupt/failure modes are
shown in Figure.(3).This proposed UPQCµG-IR controller contains following five elements:
1) Positive -Sequence Detection:
The positive sequence detector is used to determine the fundamental voltage amplitude, phase angle and
frequency at the measuring point. The generated Vpcc-ref
represents the Vsag-ref for APFse for voltage compensation.
2) Series part (APFse) control: The voltage interruption in the supply/grid side is compensated by APFse at PCC. It receives reference voltage
from PSD and generates proper compensating voltage.
3) Shunt part (APFsh) control:
ISSN (Online) 2395-2717
International Journal of Engineering Research in Electrical and Electronic
Engineering (IJEREEE)
Vol 3, Issue 9, September 2017
All Rights Reserved © 2017 IJEREEE 194
Shunt inverter control describes the following two
functions: 1) the QH powers are regulated 2) supply
required load power even in the incidence of voltage
interruptions. This compensating harmonic current and
the reactive power are calculated.
4) Intelligent Islanding Detection: The main object of interconnecting μG with distribution
grid is to keep the proper voltage during fault conditions,
detecting the isolated condition automatically during fault
and naturally reconnect the grid to μG after clearance of
fault. Islanding is detected by matching the source phase,
frequency and amplitude with rated values. Series APFse
improves system flexibility .By using this detection 95%
Voltage sag problems can be mitigated by injecting rated
voltage
Figure.3 (a) Basic structure of UPQCμG-IRController.
(b) Secondary control algorithm of UPQCμG-IR
5. Synchronization and Reconnection
Once the fault/error is cleared grid is again restored for
supplying proper power. A smooth reconnection operation
is achievable by phase variation between two buses are
minimized to zero. UPQCµG-IR performs reconnection even
in the case of phase variation between source/grid and the
PCC by using APFse. The most value of phase variation
placed on
the rating of APFse and level.
Assume = , the can be written as
= = ½ =
By using S3 and S4 breakers, reconnection and islanding techniques of operations are possible by active pulses from control model for on/off the switches. First three controllers represents the primary basic control of UPQC shown in Figure.3(a).The smooth performance of
UPQCµG-IRand μG is possible by level 2 secondary
control for automatic process of islanding detection and reconnection purpose shown in Figure.3(a).The secondary control algorithm of UPQCµG-IR shown in Figure.3(b).
V.FUZZY LOGIC CONTROLLER
Fuzzy logic controller (FLC) shown in Figure.4 has
been build for various applications: Process control,
Modeling, Estimation, Agriculture and various power
electronics fields. FLC is developed in the projected
system for receiving better results. FLC does not desire
mathematical functions, handle Non-linearity functions
easily, Contains simple linguistic variables for easy
understand and offers more flexibility etc.
Figure.4 Fuzzy logic controller (FLC)
Fuzzification is the translation of crisp inputs (measured
quantities) in to linguistic variables by applying membership
functions and these linguistic variables are stored in a
knowledge base system. FLC is planned by set of rules from
fuzzy rule base system as shown in below Figure.5
ISSN (Online) 2395-2717
International Journal of Engineering Research in Electrical and Electronic
Engineering (IJEREEE)
Vol 3, Issue 9, September 2017
All Rights Reserved © 2017 IJEREEE 195
Figure .5General control rule base table for FLC
FLC control table produces required linguistic
variables in the mode of output. The defuzzication
operation a conversion of linguistic variables into crisp
variables (reverse of fuzzification) by using membership
functions. The most generally used fuzzy inference
method is mamdani type fuzzy inference type.
VI.SIMULATION RESULTS:
The proposed method represents the grid connected micro
grid/micro generation (µG) system with UPQC designed in
MATLAB/SIMULINK by using FLC is shown below:
Figure .6Simulation model of grid coupled microgrid
with UPQC.
Figure.7Shows position of breaker switches
during sag/swell operation.
Here UPQC is coupled between load and grid side with
DG is designed by MATLAB simulink library
parameters. DG is designed by using renewable energy
generation plants with battery storage for additional
supply at peak load levels as shown in Figure.6. Both
island and interconnect modes indentified by switching
positions from 0 to 2 s. switching positions (0 for open
and 1 for close) are very significant for island and
reconnection modes. Above figure represents 0 to 0.3 for
normal period, 0.3 to 0.5 for sag period, 0.5 to 1.1 for
sag/interrupt period, 1.1to 1.4 shows Islanded period and
1.4 to 2 shows reconnected/resynchronized period.
1) Interconnected period: In this period DG provides bidirectional of real/true
power deliver to the source/grid and load side. In
forward flow mode, grid supplies necessary amount of
power to the storage and load which is not met by the
DG and in reverse flow mode, the DG supplies extra
amount of power to the source/grid and load side.
2) Islanded Period: Whenever voltage sag happened in the system, APFse
compensates up to certain limit and after it is
separated. The system comes into islanded mode, at
this condition the utility gets required continuous
supply from addition of isolated μG and Storage. APFsh
is always connected for controlling QH powers.
ISSN (Online) 2395-2717
International Journal of Engineering Research in Electrical and Electronic
Engineering (IJEREEE)
Vol 3, Issue 9, September 2017
All Rights Reserved © 2017 IJEREEE 196
3) Reconnection/Resynchronization period: After sag clearance, the phase variation between Vs and reduced to zero. By using control
algorithm
UPQCµG-IR reconnection signal to DG for reconnection
and switches are closed for continuous power supply from grid. FLC is implemented in this paper for getting less THD values for ripple free supply over normal PI control.
Figure.8 Shows wave forms of voltages at different
positions and conditions
Figure.9 Shows current waveforms at different positions
and conditions.
Difference between FLC and PI are represented by
THD.Below Figure.10 shows harmonic spectrum of
IPCC.
a) By using fuzzy logic controller
b) By using PI controller
THD value is 5.80% for FLC and 11.46% for PI
controller. Below Figure.11 shows Harmonic spectrum of
VPCC.
a) By using fuzzy logic controller
b) By using PI controller
ISSN (Online) 2395-2717
International Journal of Engineering Research in Electrical and Electronic
Engineering (IJEREEE)
Vol 3, Issue 9, September 2017
All Rights Reserved © 2017 IJEREEE 197
THD value is 20.59% for FLC and23.73% for PI
controller.
VII.CONCLUSION:
This paper represents the purpose of UPQCµG-IR with
Grid connected μG for detecting both resynchronization
and islanding method of operation by using control
method. DG always connected for providing continuous
active /real power to the load during islanded grid
condition. The procedure of UPQCµG-IR is used for
mitigating load side disturbances.
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