ISSN (Online) 2395-2717 Engineering (IJEREEE) Vol 3, Issue 9, … · 2018. 1. 18. · (APF sh)...

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.






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






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:






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






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.






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






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.

REFERENCES:

1. M. F. Conlan, S. K. Khadem and M. Baasu

“UPQC for power quality improvement in DG integrated

smart grid network”, 2012.

2. M. F. Conlan, S. K. Khadem and M. Baasu, “A

new placement and integration method of UPQC to

improve the PQ in DG network”, Sep. 2013.

3. S. P. Das, G. K. Dubay and M. Baasu

“Comparative evaluation of two models of UPQC for

suitable interface to enhance power quality” , 2007

4. L. G. Vicunna, J. Matas, M. Castila, J. C.

Vasqueez and

M. Guerrero “Hierarchical control of droop controlled AC

and DC microgrids”, Jan. 2011.

5. S.Baek, B. Baye, H. Kim, and B. Han

“Combined operation of unified power-quality

conditioner with distributed generation”, Jan. 2006.

6. M.F. Conlan, S. K. Khadem, and M. Baasu,

“Harmonic power compensation capacity of shunt active

power filter and its relationship with design parameters”

,2013.

7 P. Rodríguez, A. Luna, J. M. Guerrero, J. I.

Candelaa, and

J. Rocabert, “Intelligent connection agent for three-phase

grid-connected microgrids”, May 2008

8. F. Blabjerg, N. Mohan and J. Neelsen, “Control

strategies for dynamic voltage restorer compensating

voltage sags with phase jump”, 2001.

9. Y. Yaan and Z. Yaoo, “Seamless transfer of

single phase grid interactive inverters between grid-

connected and stand-alone modes,” Jun. 2010.

10. T. Yuo, S. Choii and H. Kim, “Indirect control of

current algorithm for utility interactive inverters in

distributed generation systems”, May 2008.

ISSN (Online) 2395-2717 Engineering (IJEREEE) Vol 3, Issue 9, … · 2018. 1. 18. · (APF sh)...

Documents

Transcript of ISSN (Online) 2395-2717 Engineering (IJEREEE) Vol 3, Issue 9, … · 2018. 1. 18. · (APF sh)...