Abstract-- Microgrids are miniature versions of traditional grids.
They comprise of distributed energy resources like wind turbine, Photovoltaic, Storage devices like batteries and renewable resources of power systems. They can operate in two modes, viz. Connected mode, where they are connected to the Main grid; and island mode, where they are isolated from Main grid. While microgrids offer advantages like improved reliability, stability,and efficiency; their implementation poses different technical challenges specifically for protection of microgrid. It is essential to protect a micro grid in both the grid-connected and the island mode of operation against all different types of faults. This paper gives literature review for different challenges and protection of techniques for microgrid protection.
Frequency Scanning Techniques for Subsynchronous Resonance Screening AnalysisHardik Parikh, E.I.T.
Abstract—Subsynchronous Resonance (SSR) is a well known
phenomenon that is observed in the conventional energy
generation and wind farm sites. SSR is more prone to generation sites that are directly connected to the series compensated transmission lines. Series compensation is required to improve the voltage profile and reduce transmission losses of the transmission lines. The work presented here aims to highlight the potential causes, the system configurations and the methods that are used to identify SSR. The main focus of the poster is to outline frequency scan techniques that are based on the small
signal perturbation method. The analysis generally employs
Electro Magnetic Transient Program (EMTP). This technique
provides the spectrum of frequency response to resistance and reactance. Finally, based on that we deduce the damping
provided by the system, and thereby the SSR risk to the project.
PROTECTION OF MICROGRID FROM HIGH IMPEDANCE FAULT USING DIFFERENTIAL RELAYijiert bestjournal
As source of traditional energy is vanishes day by day,importance of microgrid increasing very effectively. In traditional generation and transmission of electrical power we have to rely on frequency and generation of power but in case of microgrid we have to depend on whether condition. Managing these systems to change of atmospheric condition becomes challenging . All study going on all over world related to microgrid protection of microgrid is one of them. Micro grids can either operate connected to the grid,or in the case of a grid fault,in an islanded mod e. Effect of high impedance fault is studied in this paper,by taking help of Matlab - Simulink�s SimPower Systems . We model a microgrid containing mix of renewable DG and one dispatch able source,we then simulate the HIF fault at one of the bus in both gri d - connect and island modes and analyze fault currents and voltage levels in order to determine how the protection scheme of the distribution network would need to be changed to facilitate microgrid functionality. We show that standard protection methods ar e insufficient and propose the use of digital relays which is different from traditional system.
These slides presents the different challenges and issues related to DG integration to Micro-grid distribution systems. The possible solutions are also presented. Later of the class I will try to upload the mathematical presentations and simulation results related to each protection scheme. However, your suggestions are always welcome.
Voltage Support and Reactive Power Control in Micro-grid using DGIJMER
Distribution Generators(DGs) are the renewable energy resource which can be connected to
the grid. When it is connected to the grid it should be operated with controlled voltage and reactive
power control. And in autonomous mode(i.e disconnected mode) it should operate in backup generation
mode. These DGs are connected towards the micro grid operation. The proposed control system
facilitates flexible and robust DG operational characteristics such as active/reactive power (PQ) or
active power/voltage (PV) bus operation in the grid- connected mode, regulated power control in
autonomous micro-grid mode, smooth transition between autonomous mode and PV or PQ grid
connected modes and vice versa, reduced voltage distortion under heavily nonlinear loading conditions,
and robust control performance under islanding detection delays. Evaluation results are presented to
demonstrate the flexibility and effectiveness of the proposed controller
Frequency Scanning Techniques for Subsynchronous Resonance Screening AnalysisHardik Parikh, E.I.T.
Abstract—Subsynchronous Resonance (SSR) is a well known
phenomenon that is observed in the conventional energy
generation and wind farm sites. SSR is more prone to generation sites that are directly connected to the series compensated transmission lines. Series compensation is required to improve the voltage profile and reduce transmission losses of the transmission lines. The work presented here aims to highlight the potential causes, the system configurations and the methods that are used to identify SSR. The main focus of the poster is to outline frequency scan techniques that are based on the small
signal perturbation method. The analysis generally employs
Electro Magnetic Transient Program (EMTP). This technique
provides the spectrum of frequency response to resistance and reactance. Finally, based on that we deduce the damping
provided by the system, and thereby the SSR risk to the project.
PROTECTION OF MICROGRID FROM HIGH IMPEDANCE FAULT USING DIFFERENTIAL RELAYijiert bestjournal
As source of traditional energy is vanishes day by day,importance of microgrid increasing very effectively. In traditional generation and transmission of electrical power we have to rely on frequency and generation of power but in case of microgrid we have to depend on whether condition. Managing these systems to change of atmospheric condition becomes challenging . All study going on all over world related to microgrid protection of microgrid is one of them. Micro grids can either operate connected to the grid,or in the case of a grid fault,in an islanded mod e. Effect of high impedance fault is studied in this paper,by taking help of Matlab - Simulink�s SimPower Systems . We model a microgrid containing mix of renewable DG and one dispatch able source,we then simulate the HIF fault at one of the bus in both gri d - connect and island modes and analyze fault currents and voltage levels in order to determine how the protection scheme of the distribution network would need to be changed to facilitate microgrid functionality. We show that standard protection methods ar e insufficient and propose the use of digital relays which is different from traditional system.
These slides presents the different challenges and issues related to DG integration to Micro-grid distribution systems. The possible solutions are also presented. Later of the class I will try to upload the mathematical presentations and simulation results related to each protection scheme. However, your suggestions are always welcome.
Voltage Support and Reactive Power Control in Micro-grid using DGIJMER
Distribution Generators(DGs) are the renewable energy resource which can be connected to
the grid. When it is connected to the grid it should be operated with controlled voltage and reactive
power control. And in autonomous mode(i.e disconnected mode) it should operate in backup generation
mode. These DGs are connected towards the micro grid operation. The proposed control system
facilitates flexible and robust DG operational characteristics such as active/reactive power (PQ) or
active power/voltage (PV) bus operation in the grid- connected mode, regulated power control in
autonomous micro-grid mode, smooth transition between autonomous mode and PV or PQ grid
connected modes and vice versa, reduced voltage distortion under heavily nonlinear loading conditions,
and robust control performance under islanding detection delays. Evaluation results are presented to
demonstrate the flexibility and effectiveness of the proposed controller
Presentation from the EPRI-Sandia Symposium on Secure and Resilient Microgrids: Practical Implementation of Microgrid Control, Protection, and Communications, presented by Scott Manson, SEL, Baltimore, MD, August 29-31, 2016.
The energy sector is moving into the era of distributed generation (DG) and microgrids
(MGs). The stability and operation aspects of converter-dominated DG MGs, however, are faced by
many challenges. To overcome these difficulties, this paper presents a new large-signal-based control
topology for DG power converters that is suitable for both grid connected and islanding modes of
operation without any need to reconfigure the control system and without islanding detection. To
improve MG stability and to guarantee stability and high performance of the MG system during sudden
harsh transients such as islanding, grid reconnection, and large load power changes, a nonlinear MG
stabilizer is proposed. We propose a novel control topology for microgrids which can work in both grid
connected and islanding modes without reconfiguration so it does not require islanding detection
technique, the controller is based on the concept of synchronverter In this paper, a radical step is taken
to improve the synchronverter as a self-synchronized synchronverter by removing the dedicated
synchronization unit
Control technique for single phase inverter photovoltaic system connected to ...jbpatel7290
In photovoltaic system connected to the grid, the main goal is to control the power that the inverter injects into the grid
from the energy provided by the photovoltaic generator. The power quality injected into the grid and the performance of the
converter system depend on the quality of the inverter current control. In this paper, a control technique for a photovoltaic
system connected to the grid based on digital pulse-width modulation (DSPWM) which can synchronize a sinusoidal output
current with a grid voltage and control the power factor is proposed. This control is based on the single phase inverter controlled
by bipolar PWM Switching and lineal current control. The electrical scheme of the system is presented. The approach is widely
explained. Simulations results of output voltage and current validate the impact of this method to determinate the appropriate
control of the system. A digital design of the control based on generator PWM using VHDL is proposed and implemented on
Field-Programmable Gate Array “FPGA”.
Types of islands in power systems with DR
Issues with unintentional islands
Methods of protecting against unintentional islands
Standard testing for unintentional islanding
Advanced testing of inverters for anti-islanding functionality
Probability of unintentional islanding
The future of anti-islanding protection
What is islanding ?
Consider the power network as shown in fig.1
Now if we disconnect the line AB from the infinite transmission grid there will be an isolated region . The D1, D2 are power sources (eg : inverter , solar power cells ). The power generated in this region is fed to the island only.
We see that there no longer is any control over the island voltage at the bus X . Also there is no mechanism here for control of frequency.
This state is referred to as islanding.
A transient current based micro grid connected power system protection scheme...IJECEIAES
Micro-grids comprise Distributed Energy Resources (DER’s) with low voltage distribution networks having controllable loads those can operate with different voltage levels are connected to the micro-grid and operated in grid mode or islanding mode in a coordinated way of control. DER’s provides clear environment-economical benefits for society and consumer utilities. But their development poses great technical challenges mainly protection of main and micro grid. Protection scheme must have to respond to both the main grid and micro-grid faults. If the fault is occurs on main grid, the response must isolate the DER’s from the main grid rapidly to protect the system loads. If the fault ocuurs within the micro-grid, the protection scheme must coordinate and isolates the least priority possible part of the grid to eliminate the fault. In order to deal with the bidirectional energy flow due to large numbers of micro sources new protection schemes are required. The system is simulated using MATLAB Wavelet Tool box and Wavelet based Multi-resolution Analysis is considered. Wavelet based Multi-resolution Analysis is used for detection, discrimination and location of faults on transmission network. This paper is discussed a transient current based micro-grid connected power system protection scheme using Wavelet Approach described on wavelet detailed-coefficients of Mother Biorthogonal 1.5 wavelet. The proposed algorithm is tested in micro-grid connected power systems environment and proved for the detection, discrimination and location of faults which is almost independent of fault impedance, fault inception angle (FIA) and fault distance of feeder line.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
In planning for Distributed Energy Resources (DER) in a microgrid, careful consideration must be taken to ensure the DER and microgrid are resilient during both grid-connected and islanded operation. There are many factors considered in the design of a microgrid, including the size of an existing DER, or the size of a new DER, the preferred DER/microgrid control technology and the material and labors costs. This paper discusses protection topics that need to be considered when analyzing microgrid voltage stability during fault conditions. Areas examined are fault contributions and voltage ride-though concerns with synchronous generators and inverter based DERs. A case study simulated on a real time power system simulator is presented in this paper.
Presentation from the EPRI-Sandia Symposium on Secure and Resilient Microgrids: Practical Implementation of Microgrid Control, Protection, and Communications, presented by Scott Manson, SEL, Baltimore, MD, August 29-31, 2016.
The energy sector is moving into the era of distributed generation (DG) and microgrids
(MGs). The stability and operation aspects of converter-dominated DG MGs, however, are faced by
many challenges. To overcome these difficulties, this paper presents a new large-signal-based control
topology for DG power converters that is suitable for both grid connected and islanding modes of
operation without any need to reconfigure the control system and without islanding detection. To
improve MG stability and to guarantee stability and high performance of the MG system during sudden
harsh transients such as islanding, grid reconnection, and large load power changes, a nonlinear MG
stabilizer is proposed. We propose a novel control topology for microgrids which can work in both grid
connected and islanding modes without reconfiguration so it does not require islanding detection
technique, the controller is based on the concept of synchronverter In this paper, a radical step is taken
to improve the synchronverter as a self-synchronized synchronverter by removing the dedicated
synchronization unit
Control technique for single phase inverter photovoltaic system connected to ...jbpatel7290
In photovoltaic system connected to the grid, the main goal is to control the power that the inverter injects into the grid
from the energy provided by the photovoltaic generator. The power quality injected into the grid and the performance of the
converter system depend on the quality of the inverter current control. In this paper, a control technique for a photovoltaic
system connected to the grid based on digital pulse-width modulation (DSPWM) which can synchronize a sinusoidal output
current with a grid voltage and control the power factor is proposed. This control is based on the single phase inverter controlled
by bipolar PWM Switching and lineal current control. The electrical scheme of the system is presented. The approach is widely
explained. Simulations results of output voltage and current validate the impact of this method to determinate the appropriate
control of the system. A digital design of the control based on generator PWM using VHDL is proposed and implemented on
Field-Programmable Gate Array “FPGA”.
Types of islands in power systems with DR
Issues with unintentional islands
Methods of protecting against unintentional islands
Standard testing for unintentional islanding
Advanced testing of inverters for anti-islanding functionality
Probability of unintentional islanding
The future of anti-islanding protection
What is islanding ?
Consider the power network as shown in fig.1
Now if we disconnect the line AB from the infinite transmission grid there will be an isolated region . The D1, D2 are power sources (eg : inverter , solar power cells ). The power generated in this region is fed to the island only.
We see that there no longer is any control over the island voltage at the bus X . Also there is no mechanism here for control of frequency.
This state is referred to as islanding.
A transient current based micro grid connected power system protection scheme...IJECEIAES
Micro-grids comprise Distributed Energy Resources (DER’s) with low voltage distribution networks having controllable loads those can operate with different voltage levels are connected to the micro-grid and operated in grid mode or islanding mode in a coordinated way of control. DER’s provides clear environment-economical benefits for society and consumer utilities. But their development poses great technical challenges mainly protection of main and micro grid. Protection scheme must have to respond to both the main grid and micro-grid faults. If the fault is occurs on main grid, the response must isolate the DER’s from the main grid rapidly to protect the system loads. If the fault ocuurs within the micro-grid, the protection scheme must coordinate and isolates the least priority possible part of the grid to eliminate the fault. In order to deal with the bidirectional energy flow due to large numbers of micro sources new protection schemes are required. The system is simulated using MATLAB Wavelet Tool box and Wavelet based Multi-resolution Analysis is considered. Wavelet based Multi-resolution Analysis is used for detection, discrimination and location of faults on transmission network. This paper is discussed a transient current based micro-grid connected power system protection scheme using Wavelet Approach described on wavelet detailed-coefficients of Mother Biorthogonal 1.5 wavelet. The proposed algorithm is tested in micro-grid connected power systems environment and proved for the detection, discrimination and location of faults which is almost independent of fault impedance, fault inception angle (FIA) and fault distance of feeder line.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
In planning for Distributed Energy Resources (DER) in a microgrid, careful consideration must be taken to ensure the DER and microgrid are resilient during both grid-connected and islanded operation. There are many factors considered in the design of a microgrid, including the size of an existing DER, or the size of a new DER, the preferred DER/microgrid control technology and the material and labors costs. This paper discusses protection topics that need to be considered when analyzing microgrid voltage stability during fault conditions. Areas examined are fault contributions and voltage ride-though concerns with synchronous generators and inverter based DERs. A case study simulated on a real time power system simulator is presented in this paper.
Modelling and Implementation of Microprocessor Based Numerical Relay for Prot...Kashif Mehmood
This paper includes the design and implementation of Numerical Relay that can protect the equipment against over-voltage, over-current and under voltage. Although, every power system is subjected to faults and these faults can severe damage to the power system. Therefore, it is necessary
to observe and resolve in time to avoid a large damage such as blackouts. For this purpose, there
should be some sensing devices, which give signals to the circuit breakers for preventing of power
system damages. The multipurpose relays have much importance role in power system for sensing
and measuring the amplitude of faults. Numerical relay provides settings of over-current, overvoltage and under voltage values. Simulations have been carried out using Proteus software along
with tested on hardware with Arduino Uno Microcontroller that proves the working and operation of
numerical relay.
An adaptive protection scheme to prevent recloser-fuse miscoordination in dis...iosrjce
IOSR Journal of Electrical and Electronics Engineering(IOSR-JEEE) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of electrical and electronics engineering and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in electrical and electronics engineering. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
The number of Power Electronic Converter(PECs) utilised in power systems throughout the world is increasing.
PECs are found in a huge range of applications, in power systems they are used to interface Distributed Generation (DG) to the main power system and for fault current limiting/interruption applications.
These PEC interfaces generally have a low tolerance to overcurrent and rely on extremely fast acting protection which is integral to the PECs’ control systems.
The widespread introduction of PEC-interfaced energy sources has both positive and negative implications for network protection.
Analysis and Implementation of Power Quality Enhancement Techniques in Hybrid...ijtsrd
With the growth in global warming, renewable energy based distributed generators DGs play a prominent role in power generation. Wind, solar energy, biomass, mini hydro, and the usage of fuel cells and microturbines will provide substantial impetus in the near future. Environmental friendliness, expandability, and flexibility have made distributed generation, powered by a variety of renewable and unconventional energy sources, an appealing alternative for building contemporary electrical systems. A microgrid is made up of a group of loads and dispersed generators that work together to form a single controlled system. Microgrids, as an integrated energy delivery system, may function in tandem with or independently of the main power grid. The microgrid idea reduces the number of reverse conversions in a single AC or DC grid while also making it easier to link variable renewable AC and DC sources and loads to power systems. The connectivity of DGs to the utility grid through power electronic converters has raised concerns regarding equipment safety and protection. The microgrid may be configured to fulfil the customers specific needs, such as greater local dependability, reduced feeder losses, local voltage support, greater efficiency via waste heat usage, voltage sag correction, or uninterruptible power supply. The performance of a hybrid AC DC microgrid system in grid tethered mode is examined in this paper. For the creation of a microgrid, a solar system, a wind turbine generator, and a battery are utilized. Control methods are also included to allow the converters to appropriately coordinate the AC sub grid with the DC sub grid. The MATLAB SIMULINK environment was used to achieve the findings. Tarun Jaiswal | Ashish Bhargava "Analysis and Implementation of Power Quality Enhancement Techniques in Hybrid AC/DC Microgrid" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-5 | Issue-5 , August 2021, URL: https://www.ijtsrd.com/papers/ijtsrd46296.pdf Paper URL: https://www.ijtsrd.com/engineering/electrical-engineering/46296/analysis-and-implementation-of-power-quality-enhancement-techniques-in-hybrid-acdc-microgrid/tarun-jaiswal
Protection Technique for Complex Distribution Smart Grid Using Wireless Token...Power System Operation
Distributed generation is expected to increase sharply
as more and more renewable are integrated to power system with
the realization of smart grid, consequently complex distribution
smart grid is given. The traditional protection devices cannot
be able to protect complex power system configuration due to
many fault current loops will feed the fault point. Relays based on
standalone decisions cannot provide reliable and correct action
when used on a complex distribution system. This paper proposes
new protection philosophy using wireless technology. Data
sharing among relays to obtain reliable and accurate decision are
introduced. Wireless Token Ring Protocol (WTRP) as a wireless
local area network (LAN) protocol inspired by the IEEE 802.4
Token Bus Protocol is used for data sharing. WTRP is selected
to improve efficiency by reducing the number of retransmissions
due to collisions. WTRP architecture and protocol are described
to verify operation. MATLAB simulation program is used to
simulate the data exchange protocol between relays in a ring for
a specified amount of time.
Dealing With Reactive Power in Islanded Micro Grid Corresponding Power Distri...ijtsrd
A Micro grid MG is a local energy system consisting of a number of energy sources e.g., wind turbine or solar panels among others , energy storage units, and loads that operate connected to the main electrical grid or autonomously. MGs provide flexibility, reduce the main electricity grid dependence, and contribute to changing large centralized production paradigm to local and distributed generation. However, such energy systems require complex management, advanced control, and optimization. Moreover, the power electronics converters have to be used to correct energy conversion and be interconnected through a common control structure is necessary. A classical droop control system is often implemented in MG. It allows correct operation of parallel voltage sourced converters in grid connection, as well as islanded mode of operation. However, it requires complex power management algorithms, especially in islanded MGs, which balance the system and improves reliability. The novel reactive power sharing algorithm is developed, which takes into account the parameters of the converter as apparent power limit and maximum active power. The developed solution is verified in simulation and compared with other known reactive power control methods. G. Amulya | Dr. S. V. D. Anil Kumar "Dealing With Reactive Power in Islanded Micro Grid-Corresponding Power Distribution in Hierarchical Droop Control using Photovoltaic System" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-5 , August 2019, URL: https://www.ijtsrd.com/papers/ijtsrd26498.pdfPaper URL: https://www.ijtsrd.com/engineering/electrical-engineering/26498/dealing-with-reactive-power-in-islanded-micro-grid-corresponding-power-distribution-in-hierarchical-droop-control-using-photovoltaic-system/g-amulya
Transforming Brand Perception and Boosting Profitabilityaaryangarg12
In today's digital era, the dynamics of brand perception, consumer behavior, and profitability have been profoundly reshaped by the synergy of branding, social media, and website design. This research paper investigates the transformative power of these elements in influencing how individuals perceive brands and products and how this transformation can be harnessed to drive sales and profitability for businesses.
Through an exploration of brand psychology and consumer behavior, this study sheds light on the intricate ways in which effective branding strategies, strategic social media engagement, and user-centric website design contribute to altering consumers' perceptions. We delve into the principles that underlie successful brand transformations, examining how visual identity, messaging, and storytelling can captivate and resonate with target audiences.
Methodologically, this research employs a comprehensive approach, combining qualitative and quantitative analyses. Real-world case studies illustrate the impact of branding, social media campaigns, and website redesigns on consumer perception, sales figures, and profitability. We assess the various metrics, including brand awareness, customer engagement, conversion rates, and revenue growth, to measure the effectiveness of these strategies.
The results underscore the pivotal role of cohesive branding, social media influence, and website usability in shaping positive brand perceptions, influencing consumer decisions, and ultimately bolstering sales and profitability. This paper provides actionable insights and strategic recommendations for businesses seeking to leverage branding, social media, and website design as potent tools to enhance their market position and financial success.
Hello everyone! I am thrilled to present my latest portfolio on LinkedIn, marking the culmination of my architectural journey thus far. Over the span of five years, I've been fortunate to acquire a wealth of knowledge under the guidance of esteemed professors and industry mentors. From rigorous academic pursuits to practical engagements, each experience has contributed to my growth and refinement as an architecture student. This portfolio not only showcases my projects but also underscores my attention to detail and to innovative architecture as a profession.
Dive into the innovative world of smart garages with our insightful presentation, "Exploring the Future of Smart Garages." This comprehensive guide covers the latest advancements in garage technology, including automated systems, smart security features, energy efficiency solutions, and seamless integration with smart home ecosystems. Learn how these technologies are transforming traditional garages into high-tech, efficient spaces that enhance convenience, safety, and sustainability.
Ideal for homeowners, tech enthusiasts, and industry professionals, this presentation provides valuable insights into the trends, benefits, and future developments in smart garage technology. Stay ahead of the curve with our expert analysis and practical tips on implementing smart garage solutions.
White wonder, Work developed by Eva TschoppMansi Shah
White Wonder by Eva Tschopp
A tale about our culture around the use of fertilizers and pesticides visiting small farms around Ahmedabad in Matar and Shilaj.
You could be a professional graphic designer and still make mistakes. There is always the possibility of human error. On the other hand if you’re not a designer, the chances of making some common graphic design mistakes are even higher. Because you don’t know what you don’t know. That’s where this blog comes in. To make your job easier and help you create better designs, we have put together a list of common graphic design mistakes that you need to avoid.
Book Formatting: Quality Control Checks for DesignersConfidence Ago
This presentation was made to help designers who work in publishing houses or format books for printing ensure quality.
Quality control is vital to every industry. This is why every department in a company need create a method they use in ensuring quality. This, perhaps, will not only improve the quality of products and bring errors to the barest minimum, but take it to a near perfect finish.
It is beyond a moot point that a good book will somewhat be judged by its cover, but the content of the book remains king. No matter how beautiful the cover, if the quality of writing or presentation is off, that will be a reason for readers not to come back to the book or recommend it.
So, this presentation points designers to some important things that may be missed by an editor that they could eventually discover and call the attention of the editor.
Top 5 Indian Style Modular Kitchen DesignsFinzo Kitchens
Get the perfect modular kitchen in Gurgaon at Finzo! We offer high-quality, custom-designed kitchens at the best prices. Wardrobes and home & office furniture are also available. Free consultation! Best Quality Luxury Modular kitchen in Gurgaon available at best price. All types of Modular Kitchens are available U Shaped Modular kitchens, L Shaped Modular Kitchen, G Shaped Modular Kitchens, Inline Modular Kitchens and Italian Modular Kitchen.
1. 1
Abstract-- Microgrids are miniature versions of traditional grids.
They comprise of distributed energy resources like wind turbine,
Photovoltaic, Storage devices like batteries and renewable
resources of power systems. They can operate in two modes, viz.
Connected mode, where they are connected to the Main grid; and
island mode, where they are isolated from Main grid. While
microgrids offer advantages like improved reliability, stability,
and efficiency; their implementation poses different technical
challenges specifically for protection of microgrid. It is essential
to protect a micro grid in both the grid-connected and the island
mode of operation against all different types of faults. This paper
gives literature review for different challenges and protection of
techniques for microgrid protection.
Index Terms-- Distributed energy resources; Distributed
generation; Microgrids; Micro Grid Central Control; Renewable
energy sources; Power Electronics
I. INTRODUCTION
ITH the development of renewable energy sources,
energy storage devices and distributed generation (DG)
the microgrid has attracted a lot attention. A micro grid
consists of a low to medium voltage network of small load
clusters with DG sources and controllable loads. Microgrids
can operate in an island mode or can be connected to the main
grid system. If a micro grid is connected to the main grid, it is
seen as a single aggregate load or source; when connected in
island mode it caters to considerably smaller loads and energy
sources. One of the potential advantages of a microgrid is that
it could provide a more reliable supply to customers by is
landing from the system in the event of a major disturbance.
As a distributed generator placed/situated close to the load, it
has the advantage of reducing transmission losses and
preventing network congestions [1,2]. Thus, distributed
energy resources can enhance system reliability and stability.
Micro grids offer advantages, such as: Improved energy
efficiency, improve power quality and reliability, minimized
overall energy consumption, reduced green- house gases and
pollutant emissions and cost efficient electricity infrastructure
replacement [1-4].
The paper is organized as follows. A complete review of
protection challenges for microgrids in Section II. In Section
III, Different protection schemes are discussed in depth which
also discusses limitations of protection techniques. The
experiment test bed setups are discussed in Section IV and
future development in the area of microgrid protection in
Section V. Finally, conclusions are drawn in Section VI.
II. KEY PROTECTION CHALLENGES FOR MICROGRID SYSTEM
A. Fault current level modification
Connection of a single large DER unit or a large number of
small DER units that use synchronous or induction generators
will alter the fault current level (FCL) as both types of
generator contribute to it. This change in FCL can disturb
coordination. A different scenario results when DER units are
connected to the Microgrid; due to the PE interface of these
interfaces (i.e. Inverters), the fault current is limited
electronically to typically twice the load current or even less
and hence an independent relay will not be able to distinguish
between normal operation and a fault condition. The severity
is more when there is hardly any increase in phase current in
case of a fault or failure. As fault current is not clearly
distinguishable from the operational current, some of the over
current (OC) relays will not trip; others that might respond
would take many seconds instead of responding in a fraction
of a second. The undetected fault situation can lead to high
voltages despite lower fault currents. Moreover, if the fault
remains undetected for long, it can spread out in the system
and cause damage to equipment [2].
The position of a fault point relative to a DG unit and a MV
system transformer also affects the operation of the protection
system. When a fault occurs downstream of the point of
common coupling (PCC), both the MV distribution system
and the DER will contribute to the fault current as shown in
Figure1. But the relay situated upstream of the DG will only
measure the fault current supplied by the upstream source. As
this is only one part of the actual fault current, the relays,
especially the ones with inverse time characteristics, may not
function properly resulting in coordination problems. When
the fault is between the MV bus and the Microgrid, then the
fault current from MV bus would not change significantly as,
generally a DER unit is contribution is quite small.
B. Device discrimination
In traditional power systems that have a generation source at
one end of the network, as the distance of the fault point from
the source increases, the fault current decreases [9]. This is
due to the increase of the impedance in proportion to the
distance from the source. This phenomenon is used for
discrimination of devices that use fault current magnitude. But
in case of an islanded microgrid with DER units, as the
maximum fault current is limited, so the fault level at
locations along the feeder will be almost constant. Hence, the
traditional current based discrimination strategies would not
Comprehensive Review of Protection Strategies
for Microgrids
H.M.Parikh, Student Member, IEEE, and W. L. Lee, Fellow, IEEE
W
2. 2
work. New device discrimination strategies are therefore
required to protect the system effectively.
C. Reduction in reach of impedance relays
The reach of an impedance relay is the maximum fault
distance that causes the relay to trigger in a certain impedance
zone, or in a certain amount of time. This maximum distance
corresponds to maximum fault impedance or a minimum fault
current that is detected [5]. In case of a fault that occurs
downstream of the bus where DER units are connected to the
utility network, the impedance measured by an upstream relay
will be higher than the real fault impedance (as seen from the
relay). This is equivalent to an apparently increased fault
distance and is due to increased voltage resulting from an
additional in feed at the common bus. As a consequence, this
will affect the grading of the relays and will cause delayed
triggering or no triggering at all. This phenomenon is defined
as under reaching of relay.
D. Bi-directionality and Reserve power flow
The power flow changes its direction in case of when local
generation exceeds the local consumption [2]. The reverse
power flow may hinder the working of directional relays as,
traditionally; radial distribution networks are designed for
unidirectional power flow. Moreover, reverse power flow also
means a reverse voltage gradient along a radial feeder. This
can cause power quality problems, result in violation of
voltage limits, and cause increased equipment voltage stress.
E. Sympathetic tripping
This phenomenon can occur due to unnecessary operation of a
protective device for faults in an outside zone, i.e., a zone that
is outside its jurisdiction of operation [3-6]. An unexpected
contribution from a DER can lead to a situation when a
bidirectional relay operates along with another relay, which
actually sees the fault, thus resulting in malfunctioning of the
protection scheme.
F. Islanding
The DER can create severe problems when a part of the DN is
islanded. This phenomenon is described as Loss of Mains
(LOM) or Loss of Grid (LOG). In case of LOM, the utility
supply neither controls the voltage nor the frequency. In most
of the cases, islanding is due to a fault in the network. If the
embedded generator continues supplying power despite the
disconnection of the utility, the fault might persist as the fault
will be fed by the DG [13]. The voltage magnitude gets out of
control in an islanded network as most of small embedded
generators and grid interfaces are not equipped with voltage
control. This can lead to unexpected voltage levels in case of
island operation. Frequency instability may be another result
of the lack of voltage control that poses a risk to electric
machines and drives.
III. REVIEW OF PROTECTION SCHEMES FOR MICROGRIDS
One of the major challenges of micro grid protection system
is that it must respond to both island and grid connected faults
[1,2]. In the first case the protection system should isolate the
smallest part of the micro grid when the fault occurs inside
(F3 and F4 in Fig.1) microgrid. In the second case the
protection system should isolate the micro grid as rapidly as
necessary to protect the micro grid loads from the main grid
when fault occur on MV side of distribution system (F1 and
F2 in Fig.1).
Fig.1. Different fault scenarios in microgrid
When different type of distributed resource connected to
micro grid and Utility grid, the DER contribute fault current to
the system and the contribution level depends on distribution
resource type. To ensure safe operation of micro grid the
protection equipment should be updated accordingly. It also
point out the importance of the “3S” (sensitivity, selectivity
and speed) requirements for different cases, which provides a
basis for the design criteria for the microgrid protection
system.
A. Intelligent communication protection scheme
Conventional protection systems cannot give reliable
protection for DER units, because there is limited capacity to
supply fault current. The solution can be achieved by using
DER units which have high fault current capability. This
scheme requires use of faster communication system which
has higher cost to benefit ratio. [5]
B. Differential protection scheme
The conventional differential protection cannot give the
reliable protection. The protection scheme for micro grid with
PE interfaced DER units cannot differentiate between fault
current and an overload current, which results in nuisance
tripping when system is overloaded. For proper clearing of
fault in an islanded microgrid and to ensure selectivity, it is
important that different distributed generators should
effectively communicate with each other. Use of evolving
distribution system version of pilot wire line differential
scheme is required for protection [5, 6].
C. Inverter control design
A protection scheme for an islanded microgrid is heavily
dependent on the type of the DER units. The PE interface of
DER actively limits the available fault current from units. This
has been demonstrated in [6,7] where two different controllers
i.e. one using 'dqo' coordinates and the other using three-phase
(abc) coordinates, are employed to control a standalone four
leg inverter supplying a microgrid. In both cases, the fault
current is quite small but its magnitude is different. Thus,
selection of a controller can be helpful for the protection
system.
3. 3
D. Voltage based detection techniques
A protection scheme that combines conventional over current
characteristics and under voltage initiated directional fault
detection with definite time delays is proposed in [8]. A large
depression in network voltage cannot be used alone for
detecting low levels of fault current in a microgrid as voltage
depression would not have sufficient gradient to discriminate
the protection devices. So measurement of some other
parameters is recommended. It is mentioned in [8] that simple
device discrimination can be achieved by current direction
along with definite time delays. The duration of delays is
proposed to be set on the basis of sensitivity of loads or
generation to under voltage. For setting up adequate
discrimination paths, selecting different delays for forward
and reverse direction flow of the fault current is
recommended. This scheme looks sound but the use of
communication channels for coordinating protection with
control and automation schemes can complicate the things.
The authors of [9] propose various voltage detection methods
to protect networks with a low fault current. One of the
suggested methods make use of the Clarke and Park
transformations to transform a set of instantaneous three
phase utility voltages into a synchronously rotating two axis
coordinate system. The resultant voltage is compared with a
reference value to detect the presence of the disturbance. In
case of an unsymmetrical fault, the utility voltage 'dq'
components have a ripple on top of the DC term[10]. Fault
detection in case of low fault current networks can be
achieved by making use of voltage source components. It is
possible to calculate the values of voltage source components
for different types of faults since the theory of the
interconnection of equivalent sequence networks in the event
of a fault.
E. Protection based on symmetrical and differential current
components.
An islanded microgrid can be protected against Single Line-
to-Ground (SLG) and Line-to-Line (LL) faults with a
protection strategy that makes use of symmetrical current
components [11]. Based on these facts, a symmetric approach
for protection of a microgrid is proposed in [11]. This scheme
makes use of differential and zero-sequence current
components as a primary protection for SLG faults and
negative-sequence current component as a primary protection
against LL faults. It is recommended that a threshold should
be assigned to each of the symmetrical current components to
prevent the microgrid protection from operating under
unbalanced load conditions. This threshold should be selected
carefully to avoid any mal-operation of relays.
F. Adaptive protection scheme
The dynamic structure of micro grid and their various
operating conditions require the development of adaptive
protection strategies. Adaptive protection is as “an online
activity that modifies the preferred protective response to a
change in system conditions or requirements in a timely
manner by means of externally generated signals or control
action”.
Fig.2. Centralized adaptive protection system for microgrid
There is a microgrid central controller (MCC) and
communication system in addition to elements shown in
Figure 1. Communication electronics make each CB with an
integrated directional OC electronic trip unit (relay) capable of
exchanging information with MCC. By polling individual
relays the MCC can read data (electrical values, status) from
CBs and if necessary modify a subset of the relay settings
(tripping characteristics) on the fly without any resetting
protection needs.
Adaptive protection schemes are presented as a solution for
microgrid protection both in grid connected as well as in
islanded mode. In an islanded microgrid, the adaptive
protection strategy can be used by assigning different trip
settings for different levels of fault current, which in turn are
linked to different magnitudes of system voltage drops
resulting from disturbance in the system.
Fig.3. Base case trip curve and tripping sequence with directional over
current protection
Fig.4. Base case and modified trip curves and a tripping sequence
4. 4
As discussed earlier, in an islanded microgrid with DER units,
the fault in the system can result in severe voltage depression
in the entire network (due to low impedances within the
network). In such a scenario, selectivity can't be assured using
voltage measurement alone. A possible solution could be the
use of a voltage restrained over current technique as proposed
in [12]. The scheme is shown in Figure 4. A large depression
in voltage (which happens mostly in case of short circuit as
opposed to overload) will result in the selection of a lower
current threshold. This would effectively move the time-
current characteristic down and thus the tripping time would
be reduced. In contrast to this, tripping times would be longer
during overloads, as small voltage depression would not be
able to switch the scheme to the lower setting. Thus the
system would retain the longer time setting corresponding
with long-term characteristics.
This scheme although appears to be sound, it has its
drawbacks. It is not clear how the scheme will perform if there
is a little difference in magnitude of voltage depression
resulting from short circuit and overload conditions. The
scheme seems to make use of the principle of relays with
inverse time characteristics, i.e., the larger is the fault current,
the smaller would be the response time. Also it will suffer
from a long clearing time in case of faults that cause small
voltage drop, thus posing the risk of fault current spreading in
the entire network.
IV. EXPERIMENTAL MICROGRIDS AND MICROGRID TEST-BEDS
Microgrids are likely to play a key role in the evolution of
smart grids. They could become prototypes for smart-grid
sites of the future. There are many variations in adopting the
microgrid architecture and design. However, they are
implemented with common perspectives such as reliability
and optimal integration of DGs. Recent developments are
discussed in [13].
The CERTS test bed – United States
UW microgrid – United States
Bronsbergen Holiday Park microgrid – Netherland
The Residential Microgrid of Am Steinweg in Stutensee
German
CESI RICERCA DER test microgrid – Italy
Kythnos island microgrid – Greece
University of Manchester microgrid energy storage
Laboratory prototype – UK
Laboratory scale microgrid – China
V. FUTURE WORK
Identifying the dependable control strategies and utilizing
them accordingly to further improve the system reliability.
It is important to research in more reliable, fast responding
islanding detection method for integrating to a microgrid
with MV grid.
Critical transition period (from grid connected mode to
islanded operation mode) for stable operation of a
microgrid.
The areas of transient stability performance, protection and
control strategies require implementation of new
technologies.
Implementation of common standard design protocols and
operating guidelines for microgrids.
VI. CONCLUSION
An extensive review of all major microgrids protection
schemes are presented in this paper comprehensively. All
main characteristics of adaptive protection scheme are
discussed. The covered protection methods are: Intelligent
communication protection scheme, The differential protection
scheme, Inverter control design, Voltage based detection
techniques, Protection based on symmetrical and differential
current components, adaptive protection scheme. Among all
discussed schemes, a recently proposed adaptive protection
scheme seems to be more reliable as it covers wide variety of
considerations. All other reviewed techniques are either
economically infeasible, or they do not satisfy all the
protection requirements. The paper successfully reviews range
of challenges, solutions and future developments in the field
of microgrid systems.
VII. REFERENCES
[1] A. Oudalova and A. Fidigattibfd, “Adaptive Network Protection in
MICROGRID,” 2011. Available:
www.microgrids.eu/documents/519.pdf
[2] N. Hatziargyriou, Microgrids: Architectures and Control, Wiley-IEEE
Press,2014,pp.1-7Available:
[3] Md R. Islam, H. A. Gabbar, Study of Micro Grid Safety & Protection
Strategies with Control System Infrastructures Smart Grid and
Renewable Energy, 2012, pp. 1-9 Available:
http://dx.doi.org/10.4236/sgre.2012.31001
[4] X.-P. WANG, Y. Li and Y.-Y. YU, “Research on the Relay Protection
System for a Small Laboratory-Scale Microgrid System,” Proceedings of
the 6th IEEE Conference on Industrial Electronics and Applications,
Beijing, 21-23 June 2011, pp. 2712-2716.
[5] B.Hussain, S.Sharkh, S.Hussain, M.Abusara,"Integration of distributed
generation into the grid: Protection challenges and solutions," 10th IET
International Conference on Developments in Power System Protection,
March/April 2010, pp. 1-5
[6] P. Anil Kumar, J. Shankar, Y. Nagaraju, “Protection issues in micro
grid” International journal of applied control, electrical and electronics
engineering (IJACEEE) vol. 1,May 2013, pp.1-12
[7] E. J. Ng and R. A. El-Shatshat, "Multi-Microgrid Control Systems," in
2010 IEEE Power and Energy Society General Meeting, Minneapolis,
Minnesota, 2010, pp. 1-6.
[8] G. Buigues, A. Dysko, V. Valverde, I. Zamora and E. Fernandez,
“Microgrid Protection: Technical Challenges and Existing Techniques,”
international Conference on Renewable Energies and Power Quality,
ICREPQ, March 2013
[9] R.M. Tumilty et aI., "Coordinated Protection, Control & Automation
Schemes for Microgrids", Int. Journal of Distributed Energy Resources,
vol. 3, 2007, pp. 225-241
[10] Wang, Xiao-ping, Yang Li, and Yong-yang Yu. "Research on the relay
protection system for a small laboratory-scale microgrid system."
Industrial Electronics and Applications (ICIEA), 2011 6th IEEE
Conference on. IEEE, 2011.
5. 5
[11] Miveh, Mohammad Reza, Sohrab Mirsaeidi, and Majid Gandomkar.
"Fundamental Key Issues and Analysis of Symmetrical Current
Components in Micro-Grids." IOSR Journal of Pharmacy (IOSRPHR),
Vol.2, Issue 4 (July2012), PP 09-16
[12] A.Oudalova, “Advanced Architectures and Control Concepts for MORE
MICROGRIDS,” 2011. Available:
www.microgrids.eu/documents/654.pdf
[13] N.W.A. Lidula, A.D. Rajapakse, “Microgrids research: A review of
experimental microgrids and test systems”- Renewable and Sustainable
Energy Reviews, Volume 15, Issue 1, January 2011, pp. 186–202