An enhanced islanding microgrid reactive power imbalance power and harmonic power sharing scheme

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AN ENHANCED ISLANDING MICROGRID REACTIVE POWER, IMBALANCE
POWER, AND HARMONIC POWER SHARING SCHEME
By
A
PROJECT REPORT
Submitted to the Department of electronics & communication Engineering in the
FACULTY OF ENGINEERING & TECHNOLOGY
In partial fulfillment of the requirements for the award of the degree
Of
MASTER OF TECHNOLOGY
IN
ELECTRONICS & COMMUNICATION ENGINEERING
APRIL 2016

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CERTIFICATE
Certified that this project report titled “AN ENHANCED ISLANDING MICROGRID
REACTIVE POWER, IMBALANCE POWER, AND HARMONIC POWER SHARING
SCHEME” is the bonafide work of Mr. _____________Who carried out the research under my
supervision Certified further, that to the best of my knowledge the work reported herein does not
form part of any other project report or dissertation on the basis of which a degree or award was
conferred on an earlier occasion on this or any other candidate.
Signature of the Guide Signature of the H.O.D
Name Name

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DECLARATION
I hereby declare that the project work entitled “AN ENHANCED ISLANDING MICROGRID
SCHEME” Submitted to BHARATHIDASAN UNIVERSITY in partial fulfillment of the
requirement for the award of the Degree of MASTER OF APPLIED ELECTRONICS is a record
of original work done by me the guidance of Prof.A.Vinayagam M.Sc., M.Phil., M.E., to the
best of my knowledge, the work reported here is not a part of any other thesis or work on the
basis of which a degree or award was conferred on an earlier occasion to me or any other
candidate.
(Student Name)
(Reg.No)
Place:
Date:

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ACKNOWLEDGEMENT
I am extremely glad to present my project “AN ENHANCED ISLANDING MICROGRID
SCHEME” which is a part of my curriculum of third semester Master of Science in Computer
science. I take this opportunity to express my sincere gratitude to those who helped me in
bringing out this project work.
I would like to express my Director, Dr. K. ANANDAN, M.A.(Eco.), M.Ed., M.Phil.,(Edn.),
PGDCA., CGT., M.A.(Psy.) of who had given me an opportunity to undertake this project.
I am highly indebted to Co-Ordinator Prof. Muniappan Department of Physics and thank from
my deep heart for her valuable comments I received through my project.
I wish to express my deep sense of gratitude to my guide
Prof. A.Vinayagam M.Sc., M.Phil., M.E., for her immense help and encouragement for
successful completion of this project.
I also express my sincere thanks to the all the staff members of Computer science for their kind
advice.
And last, but not the least, I express my deep gratitude to my parents and friends for their
encouragement and support throughout the project.

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ABSTRACT:
To address inaccurate power sharing problems in autonomous islanding microgrids, an
enhanced droop controlmethod through online virtual impedance adjustment is proposed. First, a
term associated with DG reactive power, imbalance power, or harmonic power is added to the
conventional real power-frequency droop control.
The transient real power variations caused by this term are captured to realize DG series
virtual impedance tuning. With the regulation of DG virtual impedance at fundamental positive
sequence, fundamental negative sequence, and harmonic frequencies, an accurate power sharing
can be realized at the steady state.
In order to activate the compensation scheme in multiple DG units in a synchronized
manner, a low-bandwidth communication bus is adopted to send the compensation command
from a microgrid central controller to DG unit local controllers, without involving any
information from DG unit local controllers. The feasibility of the proposed method is verified by
simulated and experimental results from a low-power three-phase microgrid prototype.

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INTRODUCTION:
In the case of islanding operation, the load demand must be properly shared by parallel
DG units. To facilitate the power sharing requirement without using any communications
between DG units, the real power–frequency and reactive power– voltage magnitude droop
control method has been developed.
In this control category, real power and reactive power in the power control loop are
calculated using low-pass filters (LPF). Accordingly, the major focus of droop control is the
sharing of averaged real and reactive power.
It has been pointed out that the real power sharing is always accurate, while the reactive
power sharing performance is dependent on the impedance of DG feeders. In addition, the droop
control method may cause some stability problems when DG feeders are mainly resistive.
To enhance the power sharing performance in a microgrid, various types of modified
droop control methods have been developed. In a DG unit is equipped with dominate inductive
virtual impedance. With this method, the reactive power sharing errors can be reduced. However,
in a weak islanding microgrid with higher existing feeder impedance, the virtual impedance
needs to be very large, and therefore, the power sharing dynamics can be affected.
To avoid the using of virtual impedance, a few alternatively methods have been
developed. In an interesting “Q-V dot droop” method was proposed. However, it can be seen
that the reactive power sharing errors can hardly be completely eliminated using the method in
especially in the case of a weak microgrid. Additionally, an improved droop control method was
proposed to realize the power sharing in proportion to DG power rating.

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Compared to the standard droop control method, the power sharing performance in is
improved via the measurement of point of common coupling (PCC) voltage. Furthermore,
virtual, real, and reactive power concept was introduced in to improve the stability of droop
control. Similarly, the concept of virtual frequency and virtual voltage magnitude concept was
also proposed to prevent instability operation of islanding microgrids.

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EXISTING SYSTEM:
Each DG system is comprised of a dc source, a pulse-width modulation (PWM) voltage
source inverter (VSI) and LC filters. Under normal mode of operation, the microgrid is
connected to the utility system at the point of common coupling (PCC) usually through a static
transfer switch (STS). In this mode, the two DG systems are controlled to provide local power
and voltage support for critical loads 1–3. This configuration reduces the burden of generation
and delivery of power directly from the utility grid and enhances the immunity of critical loads to
system disturbances in the utility grid.
When a utility fault occurs, the STS opens to isolate the micro and utility grids within
half a line frequency cycle. The two DG systems are now the sole power sources left to regulate
the load voltages and to supply uninterrupted power in a certain predetermined DG power
sharing scheme to all critical loads within the microgrid. Subsequently when the fault is cleared,
the microgrid has to be resynchronized with the utility grid before the STS can be reclosed to
return the system smoothly back to the grid-connected mode of operation.

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PROPOSED SYSTEM:
In this paper, an adaptive virtual impedance control method is applied to DG units in
islanding microgrids. The virtual impedance at fundamental positive sequence, fundamental
negative sequence, and harmonic frequencies are determined according to transient real power
variations. To activate small amount of transient power variations, a transient control term is
added to the conventional real power–frequency droop control. Through interactions between
real power variations and the virtual impedance regulation, a microgrid reactive power,
imbalance power, and harmonic power sharing errors can be compensated at the steady state.

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ADVANTAGES:
 Distributed generation.
 Renewable energy resource (RES).

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BLOCK DIAGRAM:
THREE PHASE
INVERTER
DRIVERCIRCUIT
PICCONTROLLER
WITH BUFFER
5V DC
12V DC
LC FILTER
LOAD
INPUT DC
SUPPLY
NON
LINEAR
LOAD

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TOOLS AND SOFTWARE USED:
 MPLAB – microcontroller programming.
 ORCAD – circuit layout.
 MATLAB/Simulink – Simulation

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APPLICATIONS:
 Distributed generation.
 Renewable energy resource (RES).

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CONCLUSION:
This paper discusses an enhanced power sharing scheme for islanding microgrids. The
proposed method utilizes the frequency droop as the link to compensate reactive, imbalance, and
harmonic power sharing errors. Specifically, the frequency droop control with additional
disturbance is used to produce some real power sharing variations. These real power variations
are used to adjust the DG unit virtual impedances at fundamental positive sequence, fundamental
negative sequence, and harmonic frequencies. With the interactions between the transient
frequency droop control and the variable DG virtual impedance, the impact of unknown feeder
impedances can be properly compensated and an accurate power sharing is achieved at the
steady state. Comprehensive simulated and experimental results from a low-voltage microgrid
prototype verified the effectiveness of the proposed scheme. Note that the same virtual
impedance is used at negative sequence fifth and positive sequence seventhharmonics, as
typically they are dominate harmonic components in an islanding microgrid. To realize better
compensation performance, independent harmonic power-sharing error compensation at each
harmonic order and each sequence can be developed in a similar way.
.

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REFERENCES:
[1] F. Blaabjerg, Z. Chen, and S. B. Kjaer, “Power electronics as efficient interface in dispersed
power generation systems,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1184–1194, May
2004.
[2] F. Blaabjerg, R. Teodorescu, M. Liserre, and V. A. 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.
[3] Y. W. Li and C. N. Kao, “An accurate power control strategy for powerelectronics-
interfaced distributed generation units operating in a lowvoltage multibus microgrid,” IEEE
Trans. Power Electron., vol. 24, no. 2, pp. 2977–2988, Dec. 2009.
[4] J. M. Guerrero, L. G. Vicuna, J. Matas, M. Castilla, and J. Miret, “Output impedance design
of parallel-connected UPS inverters with wireless load sharing control,” IEEE Trans. Ind.
Electron., vol. 52, no. 4, pp. 1126–1135, Aug. 2005.
[5] J. M. Guerrero, L. G. 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. 4, pp. 1205–1213, Sep. 2004

An enhanced islanding microgrid reactive power imbalance power and harmonic power sharing scheme

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An enhanced islanding microgrid reactive power imbalance power and harmonic power sharing scheme