Nowadays wind turbines are generally required to offer ancillary services similar to those
provided by conventional generators. One of the most important services wind turbines must offer is
to stay connected to the grid in fault situations delivering the reactive current specified in the recent
grid codes. In this paper, FACTS solutions for fixed speed wind farms such as DVR (Dynamic
Voltage Restorer) are presented as well as classic control and crowbar solutions for variable speed
wind turbines.
POWER QUALITY IMPROVEMENT AND FAULT RIDE THROUGH OF GRID CONNECTED WIND ENE...Bharadwaj S
This work tries to improve the power quality by compensating reactive power with Active Power Filters and also to analyze Fault Ride Through of Grid connected wind energy conversion systems.
Distributed Generation generally refers to power generation at the point of end user or
customer. Distributed Generation is gaining worldwide acceptance due to it’s a number of benefits.
Distributed Generation eliminates the cost and complexity and reduces the chances of inefficiency
which occur in the transmission and distributed network [1]. Basically electricity produced is
generated at large generating stations which is then send at high voltages through the transmission
lines to the load centers and then through local distribution network distributed to the customers at
distribution level voltage. In present scenario there is an increase in demand which is creating gap
between demand and supply to fulfill this gap distributed generation can plays the significant role.
The main reason for the need of distributed generation is it is clean and continuous. Distributed
generation means generating power on site not centrally. Distributed generation is the best way for
rural electrification. This paper will discuss the importance and benefits of Distributed Generation in
near future
POWER QUALITY IMPROVEMENT AND FAULT RIDE THROUGH OF GRID CONNECTED WIND ENE...Bharadwaj S
This work tries to improve the power quality by compensating reactive power with Active Power Filters and also to analyze Fault Ride Through of Grid connected wind energy conversion systems.
Distributed Generation generally refers to power generation at the point of end user or
customer. Distributed Generation is gaining worldwide acceptance due to it’s a number of benefits.
Distributed Generation eliminates the cost and complexity and reduces the chances of inefficiency
which occur in the transmission and distributed network [1]. Basically electricity produced is
generated at large generating stations which is then send at high voltages through the transmission
lines to the load centers and then through local distribution network distributed to the customers at
distribution level voltage. In present scenario there is an increase in demand which is creating gap
between demand and supply to fulfill this gap distributed generation can plays the significant role.
The main reason for the need of distributed generation is it is clean and continuous. Distributed
generation means generating power on site not centrally. Distributed generation is the best way for
rural electrification. This paper will discuss the importance and benefits of Distributed Generation in
near future
In the modern power system the reactive power compensation is one of the main issues, the transmission of active power requires a difference in angular phase between voltages at the sending and receiving points (which is feasible within wide limits), whereas the transmission of reactive power requires a difference in magnitude of these same voltages (which is feasible only within very narrow limits). The reactive power is consumed not only by most of the network elements, but also by most of the consumer loads, so it must be supplied somewhere. If we can't transmit it very easily, then it ought to be generated where it is needed." (Reference Edited by T. J. E. Miller, Forward Page ix).Thus we need to work on the efficient methods by which VAR compensation can be applied easily and we can optimize the modern power system. VAR control technique can provides appropriate placement of compensation devices by which a desirable voltage profile can be achieved and at the same time minimizing the power losses in the system. This report discusses the transmission line requirements for reactive power compensation. In this report thyristor switched capacitor is explained which is a static VAR compensator used for reactive power management in electrical systems.
Seminar Topic For Electrical and Electronics Engineering (EEE)
These slides present at an introduction level about the demand side management and demand response in smart micro-grid system. Later mathematical modelling and detail on optimization techniques will be covered.
Demand Side Management” means the actions of a Distribution Licensee, beyond the customer's meter, with the objective of altering the end-use of electricity
Renewable Energy Sources are being used in Off-Grid mode. By integrating all these sources to a common point energy efficiency can be improved and frequent dynamic faults can be avoided. This approach needs to implement smart grid and technologies.
Design factors; Limitations; Modern trends; Electrical
Engineering Materials; Space factor; Choice of Specific
Electric and Magnetic loadings; Thermal Considerations;
Heat flow; Temperature rise; Insulating Materials; Properties;
Rating of Machines; Various Standard Specifications ;
MicroGrid and Energy Storage System COMPLETE DETAILS NEW PPT Abin Baby
A microgrid is a localized grouping of electricity generation, energy storage, and loads that normally operates connected to a traditional centralized grid (macrogrid). This single point of common coupling with the macrogrid can be disconnected. The microgrid can then function autonomously. Generation and loads in a microgrid are usually interconnected at low voltage. From the point of view of the grid operator, a connected microgrid can be controlled as if it were one entity.
Microgrid generation resources can include fuel cells, wind, solar, or other energy sources. The multiple dispersed generation sources and ability to isolate the microgrid from a larger network would provide highly reliable electric power. Produced heat from generation sources such as micro turbines could be used for local process heating or space heating, allowing flexible trade off between the needs for heat and electric power.
Deregulated electricity markets. The role of the ISO. Processes and systems.ETRM Systems Group
Processes run from an independent system operator (ISO) in deregulated energy markets. From physical dispatching to economic dispatching. Load forecasting. Power network operation. Day ahead markets. Ancillary services markets. SCADAs. Metering. The whole process is represented.
Low voltage ride through control of modular multilevel converter based hvdc s...Ghazal Falahi
Low Voltage Ride Through (LVRT) is an important grid requirement for Voltage Source Converter (VSC) based HVDC links. This paper studies the performance of the modular multilevel converter (MMC) VSC based HVDC systems during faults or voltage dips and proposes a new control strategy to improve the LVRT performance. The proposed algorithm controls the system to generate the required active and reactive powers that are calculated mathematically based on the ratings of the MMC-HVDC system and LVRT requirements. The injected active and reactive power values obey the LVRT guidelines and are adaptable to different grid codes. The mathematical calculations are presented and EMTDC/PSCAD simulation evaluates the performance of the proposed method.
A Hybrid Control Scheme for Fault Ride-Through Capability using Line-Side Con...Suganthi Thangaraj
As the wind power installations are increasing in number, Wind Turbine Generators (WTG) are required to have Fault Ride-Through (FRT) capabilities. Lately developed grid operating codes demand the WTGs to stay connected during fault conditions, supporting the grid to recover faster back to its normal state. In this paper, the generator side converter incorporates the maximum power point tracking algorithm to extract maximum energy from wind turbine system. A hybrid control scheme for energy storage systems (ESS) and braking choppers for fault ride-through capability and a suppression of the output power fluctuation is proposed for permanent-magnet synchronous generator (PMSG) wind turbine systems. During grid faults, the dc-link voltage is controlled by the ESS instead of the line-side converter (LSC), whereas the LSC is exploited as a STATCOM to inject reactive current into the grid for assisting in the grid voltage recovery. A simple model of the proposed system is developed and simulated in MATLAB environment. The effectiveness of the system is validated through extensive simulation results
In the modern power system the reactive power compensation is one of the main issues, the transmission of active power requires a difference in angular phase between voltages at the sending and receiving points (which is feasible within wide limits), whereas the transmission of reactive power requires a difference in magnitude of these same voltages (which is feasible only within very narrow limits). The reactive power is consumed not only by most of the network elements, but also by most of the consumer loads, so it must be supplied somewhere. If we can't transmit it very easily, then it ought to be generated where it is needed." (Reference Edited by T. J. E. Miller, Forward Page ix).Thus we need to work on the efficient methods by which VAR compensation can be applied easily and we can optimize the modern power system. VAR control technique can provides appropriate placement of compensation devices by which a desirable voltage profile can be achieved and at the same time minimizing the power losses in the system. This report discusses the transmission line requirements for reactive power compensation. In this report thyristor switched capacitor is explained which is a static VAR compensator used for reactive power management in electrical systems.
Seminar Topic For Electrical and Electronics Engineering (EEE)
These slides present at an introduction level about the demand side management and demand response in smart micro-grid system. Later mathematical modelling and detail on optimization techniques will be covered.
Demand Side Management” means the actions of a Distribution Licensee, beyond the customer's meter, with the objective of altering the end-use of electricity
Renewable Energy Sources are being used in Off-Grid mode. By integrating all these sources to a common point energy efficiency can be improved and frequent dynamic faults can be avoided. This approach needs to implement smart grid and technologies.
Design factors; Limitations; Modern trends; Electrical
Engineering Materials; Space factor; Choice of Specific
Electric and Magnetic loadings; Thermal Considerations;
Heat flow; Temperature rise; Insulating Materials; Properties;
Rating of Machines; Various Standard Specifications ;
MicroGrid and Energy Storage System COMPLETE DETAILS NEW PPT Abin Baby
A microgrid is a localized grouping of electricity generation, energy storage, and loads that normally operates connected to a traditional centralized grid (macrogrid). This single point of common coupling with the macrogrid can be disconnected. The microgrid can then function autonomously. Generation and loads in a microgrid are usually interconnected at low voltage. From the point of view of the grid operator, a connected microgrid can be controlled as if it were one entity.
Microgrid generation resources can include fuel cells, wind, solar, or other energy sources. The multiple dispersed generation sources and ability to isolate the microgrid from a larger network would provide highly reliable electric power. Produced heat from generation sources such as micro turbines could be used for local process heating or space heating, allowing flexible trade off between the needs for heat and electric power.
Deregulated electricity markets. The role of the ISO. Processes and systems.ETRM Systems Group
Processes run from an independent system operator (ISO) in deregulated energy markets. From physical dispatching to economic dispatching. Load forecasting. Power network operation. Day ahead markets. Ancillary services markets. SCADAs. Metering. The whole process is represented.
Low voltage ride through control of modular multilevel converter based hvdc s...Ghazal Falahi
Low Voltage Ride Through (LVRT) is an important grid requirement for Voltage Source Converter (VSC) based HVDC links. This paper studies the performance of the modular multilevel converter (MMC) VSC based HVDC systems during faults or voltage dips and proposes a new control strategy to improve the LVRT performance. The proposed algorithm controls the system to generate the required active and reactive powers that are calculated mathematically based on the ratings of the MMC-HVDC system and LVRT requirements. The injected active and reactive power values obey the LVRT guidelines and are adaptable to different grid codes. The mathematical calculations are presented and EMTDC/PSCAD simulation evaluates the performance of the proposed method.
A Hybrid Control Scheme for Fault Ride-Through Capability using Line-Side Con...Suganthi Thangaraj
As the wind power installations are increasing in number, Wind Turbine Generators (WTG) are required to have Fault Ride-Through (FRT) capabilities. Lately developed grid operating codes demand the WTGs to stay connected during fault conditions, supporting the grid to recover faster back to its normal state. In this paper, the generator side converter incorporates the maximum power point tracking algorithm to extract maximum energy from wind turbine system. A hybrid control scheme for energy storage systems (ESS) and braking choppers for fault ride-through capability and a suppression of the output power fluctuation is proposed for permanent-magnet synchronous generator (PMSG) wind turbine systems. During grid faults, the dc-link voltage is controlled by the ESS instead of the line-side converter (LSC), whereas the LSC is exploited as a STATCOM to inject reactive current into the grid for assisting in the grid voltage recovery. A simple model of the proposed system is developed and simulated in MATLAB environment. The effectiveness of the system is validated through extensive simulation results
Fault Ride-Through of DFIG Wind Turbine by DVR Using Synchronous Reference Fr...theijes
The International Journal of Engineering & Science is aimed at providing a platform for researchers, engineers, scientists, or educators to publish their original research results, to exchange new ideas, to disseminate information in innovative designs, engineering experiences and technological skills. It is also the Journal's objective to promote engineering and technology education. All papers submitted to the Journal will be blind peer-reviewed. Only original articles will be published.
The papers for publication in The International Journal of Engineering& Science are selected through rigorous peer reviews to ensure originality, timeliness, relevance, and readability.
A Review on Optimization Techniques for Power Quality Improvement using DSTAT...ijtsrd
As demand for electricity has risen exponentially, power production and transmission are affected by scarce energy, environmental constraints and other losses. Soft computing methods to fix the sag, swell and disruption of the supply voltage in the distributed device. At present, a broad variety of highly versatile controls that leverage on newly available power electronics components are evolving for custom power applications. Control electronic equipment intended to improve the stability and efficiency of electricity flows in low voltage distribution networks. The control algorithm is used to derive the fundamental weighted value of the active and reactive power components. Using a digital signal processor, DSTATCOM is built and its output as a DSTATCOM is found to be satisfactory for different types of loads. Amit Radhakrishna Parhad | Pramod Kumar Rathore "A Review on Optimization Techniques for Power Quality Improvement using DSTATCOM (Neural Network Approach)" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-5 | Issue-4 , June 2021, URL: https://www.ijtsrd.compapers/ijtsrd42403.pdf Paper URL: https://www.ijtsrd.comengineering/electrical-engineering/42403/a-review-on-optimization-techniques-for-power-quality-improvement-using-dstatcom-neural-network-approach/amit-radhakrishna-parhad
International Refereed Journal of Engineering and Science (IRJES) is a peer reviewed online journal for professionals and researchers in the field of computer science. The main aim is to resolve emerging and outstanding problems revealed by recent social and technological change. IJRES provides the platform for the researchers to present and evaluate their work from both theoretical and technical aspects and to share their views.
www.irjes.com
Optimization Technique for Power Quality Improvement using DSTATCOM Neural Ne...ijtsrd
As the power demand has been increasing rapidly, power generation and transmission are being affected due to limited resources, environmental restrictions and other losses. soft computing the techniques of correcting the supply voltage sag, swell and interruption in a distributed system. At present, a wide range of very flexible controllers, which capitalize on newly available power electronics components, are emerging for custom power applications. Power electronic based equipment aimed at enhancing the reliability and quality of power flows in low voltage distribution networks. A control algorithm is used for the extraction of the fundamental weighted value of active and reactive power components. Using digital signal processor the DSTATCOM is developed and its performance of DSTATCOM is found to be satisfactory for various types of loads. Hareram Mishra | Manju Gupta | Dr. Anuprita Mishra "Optimization Technique for Power Quality Improvement using DSTATCOM (Neural Network Approach) – A Review" 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/ijtsrd45219.pdf Paper URL: https://www.ijtsrd.com/engineering/other/45219/optimization-technique-for-power-quality-improvement-using-dstatcom-neural-network-approach- – -a-review/hareram-mishra
This document proposes a photovoltaic (PV) based single-phase dynamic voltage restoration (DVR) device, it eliminates both sag and swell voltage and compensates for power. The proposed system requires a power source to compensate for the sag/swell voltage. This system has found a simple topology for the DVR that uses PV with two DC-DC boosts converters as the DC power source for the dynamic voltage conservator. The DC/DC boost converter powered by the PV generator is used to increase the voltage to meet the DC bus voltage requirements of the single-branch voltage source inverter (VSI). This system uses renewable energy; saves energy accordingly and supplies power to critical/sensitive loads. The control method used in this work is a Sliding Mode Control (SMC) method and relies on a phase locked loop (PLL) used to control the active filter. The effectiveness of the suggested method is confirmed by the MATLAB/Simulink® simulation results and some prototype experiments. These results show the capacity of the proposed DC link control.
IMPLEMENTATION OF FUZZY CONTROLLED PHOTO VOLTAIC FED DYNAMIC VOLTAGE RESTORER...Wireilla
Power Quality(PQ) has become an area of concern in the electrical distribution system. Dynamic Voltage Restorer(DVR) restores load voltage to a nominal balanced sinusoidal voltage, when the source voltage has harmonic distortions, sag, swell and unbalances. In this paper a Photo Voltaic(PV) fed DVR is proposed to mitigate PQ problems. The PV system can supply the maximum power to the load at a particular operating point known as Maximum Power Point (MPP), at which the entire PV system operates with maximum efficiency. A Fuzzy Controller based MPPT is implemented to generate the optimal voltage from the photovoltaic system by modulating the duty cycle applied to the boost converter. The DVR is implemented using a Fuzzy Logic Controller based voltage source inverter with Photovoltaic system. The test system has been simulated and the efficacy of the proposed PV based Fuzzy controlled DVR is compared with Proportional Integral (PI) controlled DVR.
Implementation of Fuzzy Controlled Photo Voltaic Fed Dynamic Voltage Restorer...ijfls
Power Quality(PQ) has become an area of concern in the electrical distribution system. Dynamic Voltage
Restorer(DVR) restores load voltage to a nominal balanced sinusoidal voltage, when the source voltage
has harmonic distortions, sag, swell and unbalances. In this paper a Photo Voltaic(PV) fed DVR is
proposed to mitigate PQ problems. The PV system can supply the maximum power to the load at a
particular operating point known as Maximum Power Point (MPP), at which the entire PV system operates
with maximum efficiency. A Fuzzy Controller based MPPT is implemented to generate the optimal voltage
from the photovoltaic system by modulating the duty cycle applied to the boost converter. The DVR is
implemented using a Fuzzy Logic Controller based voltage source inverter with Photovoltaic system. The
test system has been simulated and the efficacy of the proposed PV based Fuzzy controlled DVR is
compared with Proportional Integral (PI) controlled DVR.
Photo Voltaic Cell Integrated DVR for Power Quality ImprovementIJMTST Journal
Grid integration of distributed energy resources (DERs) is increasing rapidly. Integration of various types of energy storage technologies like batteries, ultra capacitors (UCAPs), superconducting magnets and flywheels to support intermittent DERs, such as solar and wind, in order to improve their reliability is becoming necessary. Of all the energy storage technologies UCAPs have low energy density, high power density and fast charge/discharge characteristics. They also have more charge/discharge cycles and higher terminal voltage per module when compared to batteries. All these characteristics make UCAPs ideal choice for providing support to events on the distribution grid which require high power for short spans of time. UCAPs have traditionally been limited to regenerative braking and wind power smoothing applications. The major contribution of this dissertation is in integrating UCAPs for a broader range of applications like active/reactive power support, renewable intermittency smoothing, voltage sag/swell compensation and power quality conditioning to the distribution grid. Renewable intermittency smoothing is an application which requires bi-directional transfer of power from the grid to the UCAPs and vice-versa by charging and discharging the UCAPs. This application requires high active power support in the 10s-3min time scale which can be achieved by integrating UCAPs through a shunt active power filter (APF) which can also be used to provide active/reactive power support. Temporary voltage sag/swell compensation is another application which requires high active power support in the 3s-1min time scale which can be provided integrating UCAPs into the grid through series dynamic voltage restorer (DVR). All the above functionalities can also be provided by integrating the UCAPs into a power conditioner topology.
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.
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.
Improving Stability of Utility-Tied Wind Generators using Dynamic Voltage Res...IJMTST Journal
The generation of electricity using wind power is significantly increasing and has received considerable attention in recent years. One important problem with the induction generator based wind farms is that they are vulnerable to voltage disturbances and short circuit faults. Any such disturbance may cause wind farm outages. Since wind power contribution is in considerable percentage, such outages may lead to power system stability issues and also violate the grid code requirements. Thus, improving the reliability of wind farms is essential to maintain the stability of the system. The proposed strategy is to use Dynamic Voltage Restorer (DVR), which is one of the promising devices to compensate the voltage disturbance and to improve the stability of the system. It provides the wind generator with the fault ride through capability and improves the reliability of the system. Fuzzy Logic controller is used as a controller in order to control the dc link voltages and to reduce the harmonics. Simulation results for a 2 MW wind turbine are presented, especially for asymmetrical grid faults. They show the effectiveness of the DVR in comparison to the low voltage ride-through of the DFIG using a crowbar that does not allow continuous reactive power production. Extensive simulation results are included to illustrate the operation of DVR and fault compensation.
Improved Control Strategy for Low Voltage Ride Through Capability of DFIG wit...ecij
This paper deals with a protection and control strategy to enhance the low voltage ride through capability of a wind turbine driven doubly fed induction generator (DFIG). As the wind power penetration continues to increase, wind turbines are required to provide Low Voltage Ride-Through (LVRT) capability. Crowbars are commonly used to protect the power converters during voltage dips and their main drawback is that the DFIG absorbs reactive power from the grid during grid faults. According to emergency grid code requirements, wind farms should have the ability to stay connected and continue generation under external voltage failure conditions, that is, wind turbines have to keep in connection with grid and own continue reactive power supply. This paper proposes a hysteresis current control strategy for the crowbar protection
and a reactive power control to satisfy the grid code requirements. Consequently, the dynamic model of double fed wind turbines is established to study the transient behavior of DFIG. Simulation results are presented to show the effectiveness of the proposed control scheme.
Sag mitigation in distribution system by using Dynamic voltage Restorer (DVR)IJERA Editor
Power quality is most important concern in the current age. It’s now a day’s necessary with the refined devices, where performance is very perceptive to the quality of power supply. Power quality crisis is an incidence manifest as a typical voltage, current or frequency that results in a failure of end use equipments. One of the major crises dealt here is the power sag. Perceptive industrial loads and distribution networks suffer from different types of service interruptions and outages which results in a major financial loss. To improve the power quality, custom power-devices are used. The device considered in this work is Dynamic Voltage Restorer. This paper shows modelling, analysis and simulation of a DVR test systems using MATLAB.
I have considered single line to ground fault for linear load. The role of DVR is to “compensate load voltage” is examined during the different fault conditions like voltage sag, single phase to ground faults.
Similar to LOW VOLTAGE RIDE - THROUGH CAPABILITY OF WIND FARMS (20)
A NEW DATA ENCODER AND DECODER SCHEME FOR NETWORK ON CHIPEditor IJMTER
System-on-chip (soc) based system has so many disadvantages in power-dissipation as
well as clock rate while the data transfer from one system to another system in on-chip. At the same
time, a higher operated system does not support the lower operated bus network for data transfer.
However an alternative scheme is proposed for high speed data transfer. But this scheme is limited to
SOCs. Unlike soc, network-on-chip (NOC) has so many advantages for data transfer. It has a special
feature to transfer the data in on-chip named as transitional encoder. Its operation is based on input
transitions. At the same time it supports systems which are higher operated frequencies. In this
project, a low-power encoding scheme is proposed. The proposed system yields lower dynamic
power dissipation due to the reduction of switching activity and coupling switching activity when
compared to existing system. Even-though many factors which is based on power dissipation, the
dynamic power dissipation is only considerable for reasonable advantage. The proposed system is
synthesized using quartus II 9.1 software. Besides, the proposed system will be extended up to
interlink PE communication with help of routers and PE’s which are performed by various
operations. To implement this system in real NOC’s contains the proposed encoders and decoders for
data transfer with regular traffic scenarios should be considered.
A RESEARCH - DEVELOP AN EFFICIENT ALGORITHM TO RECOGNIZE, SEPARATE AND COUNT ...Editor IJMTER
Coins are important part of our life. We use coins in a places like stores, banks, buses, trains
etc. So it becomes a basic need that coins can be sorted, counted automatically. For this, there is
necessary that the coins can be recognized automatically. Automated Coin Recognition System for the
Indian Coins of Rs. 1, 2, 5 and 10 with the rotation invariance. We have taken images from the both
sides of coin. So this system is capable to recognizing coins from both sides. Features are taken from the
images using techniques as a Hough Transformation, Pattern Averaging etc.
Analysis of VoIP Traffic in WiMAX EnvironmentEditor IJMTER
Worldwide Interoperability for Microwave Access (WiMAX) is currently one of the
hottest technologies in wireless communication. It is a standard based on the IEEE 802.16 wireless
technology that provides a very high throughput broadband connections over long distances. In
parallel, Voice Over Internet Protocol (VoIP) is a new technology which provides access to voice
communication over internet protocol and hence it is becomes an alternative to public switched
telephone networks (PSTN) due to its capability of transmission of voice as packets over IP
networks. A lot of research has been done in analyzing the performances of VoIP traffic over
WiMAX network. In this paper we review the analysis carried out by several authors for the most
common VoIP codec’s which are G.711, G.723.1 and G.729 over a WiMAX network using various
service classes. The objective is to compare the results for different types of service classes with
respect to the QoS parameters such as throughput, average delay and average jitter.
A Hybrid Cloud Approach for Secure Authorized De-DuplicationEditor IJMTER
The cloud backup is used for the personal storage of the people in terms of reducing the
mainlining process and managing the structure and storage space managing process. The challenging
process is the deduplication process in both the local and global backup de-duplications. In the prior
work they only provide the local storage de-duplication or vice versa global storage de-duplication in
terms of improving the storage capacity and the processing time. In this paper, the proposed system
is called as the ALG- Dedupe. It means the Application aware Local-Global Source De-duplication
proposed system to provide the efficient de-duplication process. It can provide the efficient deduplication process with the low system load, shortened backup window, and increased power
efficiency in the user’s personal storage. In the proposed system the large data is partitioned into
smaller part which is called as chunks of data. Here the data may contain the redundancy it will be
avoided before storing into the storage area.
Aging protocols that could incapacitate the InternetEditor IJMTER
The biggest threat to the Internet is the fact that it was never really designed. For e.g., the
BGP protocol is used by Internet routers to exchange information about changes to the Internet's
network topologies. However, it also is among the most fundamentally broken; as Internet routing
information can be poisoned with bogus routing information. Instead, it evolved in fits and start,
thanks to various protocols that have been cobbled together to fulfill the needs of the moment. Few
of protocols from them were designed with security in mind. or if they were sported no more than
was needed to keep out a nosy neighbor, not a malicious attacker. The result is a welter of aging
protocols susceptible to exploit on an Internet scale. Here are six Internet protocols that could stand
to be replaced sooner rather than later or are (mercifully) on the way out.
A Cloud Computing design with Wireless Sensor Networks For Agricultural Appli...Editor IJMTER
The emergence of exactitude agriculture has been promoted by the numerous developments within
the field of wireless sensing element actor networks (WSAN). These WSANs offer important data
for gathering, work management, development of crops, and limitation of crop diseases. Goals of
this paper to introducing cloud computing as a brand new way (technique) to be utilized in addition
to WSANs to any enhance their application and benefits to the area of agriculture.
A CAR POOLING MODEL WITH CMGV AND CMGNV STOCHASTIC VEHICLE TRAVEL TIMESEditor IJMTER
Carpooling (also car-sharing, ride-sharing, lift-sharing), is the sharing of car journeys so
that more than one person travels in a car. It helps to resolve a variety of problems that continue to
plague urban areas, ranging from energy demands and traffic congestion to environmental pollution.
Most of the existing method used stochastic disturbances arising from variations in vehicle travel
times for carpooling. However it doesn’t deal with the unmet demand with uncertain demand of the
vehicle for car pooling. To deal with this the proposed system uses Chance constrained
formulation/Programming (CCP) approach of the problem with stochastic demand and travel time
parameters, under mild assumptions on the distribution of stochastic parameters; and relates it with a
robust optimization approach. Since real problem sizes can be large, it could be difficult to find
optimal solutions within a reasonable period of time. Therefore solution algorithm using tabu
heuristic solution approach is developed to solve the model. Therefore, we constructed a stochastic
carpooling model that considers the in- fluence of stochastic travel times. The model is formulated as
an integer multiple commodity network flow problem. Since real problem sizes can be large, it could
be difficult to find optimal solutions within a reasonable period of time.
Sustainable Construction With Foam Concrete As A Green Green Building MaterialEditor IJMTER
A green building is an environmentally sustainable building, designed, constructed and
operated to minimise the total environmental impacts. Carbon dioxide (CO2) is the primary
greenhouse gas emitted through human activities. It is claimed that 5% of the world’s carbon dioxide
emission is attributed to cement industry, which is the vital constituent of concrete. Due to the
significant contribution to the environmental pollution, there is a need for finding an optimal solution
along with satisfying the civil construction needs. Apart from normal concrete bricks, a clay brick,
Foam concrete is a new innovative technology for sustainable building and civil construction which
fulfills the criteria of being a Green Material. This paper concludes that Foam Concrete can be an
effective sustainable material for construction and also focuses on the cost effectiveness in using
Foam Concrete as a building material in replacement with Clay Brick or other bricks.
USE OF ICT IN EDUCATION ONLINE COMPUTER BASED TESTEditor IJMTER
A good education system is required for overall prosperity of a nation. A tremendous
growth in the education sector had made the administration of education institutions complex. Any
researches reveal that the integration of ICT helps to reduce the complexity and enhance the overall
administration of education. This study has been undertaken to identify the various functional areas
to which ICT is deployed for information administration in education institutions and to find the
current extent of usage of ICT in all these functional areas pertaining to information administration.
The various factors that contribute to these functional areas were identified. A theoretical model was
derived and validated.
Textual Data Partitioning with Relationship and Discriminative AnalysisEditor IJMTER
Data partitioning methods are used to partition the data values with similarity. Similarity
measures are used to estimate transaction relationships. Hierarchical clustering model produces tree
structured results. Partitioned clustering produces results in grid format. Text documents are
unstructured data values with high dimensional attributes. Document clustering group ups unlabeled text
documents into meaningful clusters. Traditional clustering methods require cluster count (K) for the
document grouping process. Clustering accuracy degrades drastically with reference to the unsuitable
cluster count.
Textual data elements are divided into two types’ discriminative words and nondiscriminative
words. Only discriminative words are useful for grouping documents. The involvement of
nondiscriminative words confuses the clustering process and leads to poor clustering solution in return.
A variation inference algorithm is used to infer the document collection structure and partition of
document words at the same time. Dirichlet Process Mixture (DPM) model is used to partition
documents. DPM clustering model uses both the data likelihood and the clustering property of the
Dirichlet Process (DP). Dirichlet Process Mixture Model for Feature Partition (DPMFP) is used to
discover the latent cluster structure based on the DPM model. DPMFP clustering is performed without
requiring the number of clusters as input.
Document labels are used to estimate the discriminative word identification process. Concept
relationships are analyzed with Ontology support. Semantic weight model is used for the document
similarity analysis. The system improves the scalability with the support of labels and concept relations
for dimensionality reduction process.
Testing of Matrices Multiplication Methods on Different ProcessorsEditor IJMTER
There are many algorithms we found for matrices multiplication. Until now it has been
found that complexity of matrix multiplication is O(n3). Though Further research found that this
complexity can be decreased. This paper focus on the algorithm and its complexity of matrices
multiplication methods.
Malware is a worldwide pandemic. It is designed to damage computer systems without
the knowledge of the owner using the system. Software‟s from reputable vendors also contain
malicious code that affects the system or leaks information‟s to remote servers. Malware‟s includes
computer viruses, spyware, dishonest ad-ware, rootkits, Trojans, dialers etc. Malware detectors are
the primary tools in defense against malware. The quality of such a detector is determined by the
techniques it uses. It is therefore imperative that we study malware detection techniques and
understand their strengths and limitations. This survey examines different types of Malware and
malware detection methods.
SURVEY OF TRUST BASED BLUETOOTH AUTHENTICATION FOR MOBILE DEVICEEditor IJMTER
Practical requirements for securely demonstrating identities between two handheld
devices are an important concern. The adversary can inject a Man-In- The-Middle (MITM) attack to
intrude the protocol. Protocols that employ secret keys require the devices to share private
information in advance, in which it is not feasible in the above scenario. Apart from insecurely
typing passwords into handheld devices or comparing long hexadecimal keys displayed on the
devices’ screen, many other human-verifiable protocols have been proposed in the literature to solve
the problem. Unfortunately, most of these schemes are unsalable to more users. Even when there are
only three entities attempt to agree a session key, these protocols need to be rerun for three times.
So, in the existing method a bipartite and a tripartite authentication protocol is presented using a
temporary confidential channel. Besides, further extend the system into a transitive authentication
protocol that allows multiple handheld devices to establish a conference key securely and efficiently.
But this method detects only the outsider attacks. Method does not consider the insider attacks. So,
in the proposed method trust score based method is introduced which computes the trust values for
the nodes and provide the security. The trust score is computed has a positive influence on the
confidence with which an entity conducts transactions with that node. Network the behavior of the
node will be monitored periodically and its trust value is also updated .So depending on the behavior
of the node in the network trust relation will be established between two nodes.
GLAUCOMA is a chronic eye disease that can damage optic nerve. According to WHO It
is the second leading cause of blindness, and is predicted to affect around 80 million people by 2020.
Development of the disease leads to loss of vision, which occurs increasingly over a long period of
time. As the symptoms only occur when the disease is quite advanced so that glaucoma is called the
silent thief of sight. Glaucoma cannot be cured, but its development can be slowed down by
treatment. Therefore, detecting glaucoma in time is critical. However, many glaucoma patients are
unaware of the disease until it has reached its advanced stage. In this paper, some manual and
automatic methods are discussed to detect glaucoma. Manual analysis of the eye is time consuming
and the accuracy of the parameter measurements also varies with different clinicians. To overcome
these problems with manual analysis, the objective of this survey is to introduce a method to
automatically analyze the ultrasound images of the eye. Automatic analysis of this disease is much
more effective than manual analysis.
Survey: Multipath routing for Wireless Sensor NetworkEditor IJMTER
Reliability is playing very vital role in some application of Wireless Sensor Networks
and multipath routing is one of the ways to increase the probability of reliability. More over energy
consumption is constraint. In this paper, we provide a survey of the state-of-the-art of proposed
multipath routing algorithm for Wireless Sensor Networks. We study the design, analyze the tradeoff
of each design, and overview several presenting algorithms.
Step up DC-DC Impedance source network based PMDC Motor DriveEditor IJMTER
This paper is devoted to the Quasi Z source network based DC Drive. The cascaded
(two-stage) Quasi Z Source network could be derived by the adding of one diode, one inductor,
and two capacitors to the traditional quasi-Z-source inverter The proposed cascaded qZSI inherits all
the advantages of the traditional solution (voltage boost and buck functions in a single stage,
continuous input current, and improved reliability). Moreover, as compared to the conventional qZSI,
the proposed solution reduces the shoot-through duty cycle by over 30% at the same voltage boost
factor. Theoretical analysis of the two-stage qZSI in the shoot-through and non-shoot-through
operating modes is described. The proposed and traditional qZSI-networks are compared. A
prototype of a Quasi Z Source network based DC Drive was built to verify the theoretical
assumptions. The experimental results are presented and analyzed.
SPIRITUAL PERSPECTIVE OF AUROBINDO GHOSH’S PHILOSOPHY IN TODAY’S EDUCATIONEditor IJMTER
The paper reflects the spiritual philosophy of Aurobindo Ghosh which is helpful in today’s
education. In 19th century he wrote about spirituality, in accordance with that it is a core and vital part
of today’s education. It is very much essential for today’s kid. Here I propose the overview of that
philosophy.At the utmost regeneration of those values in today’s generation is the great deal with
education system. To develop the values and spiritual education in the youngers is the great moto of
mine. It is the materialistic world and without value redefinition among them is the harder task but not
difficult.
Software Quality Analysis Using Mutation Testing SchemeEditor IJMTER
The software test coverage is used measure the safety measures. The safety critical analysis is
carried out for the source code designed in Java language. Testing provides a primary means for
assuring software in safety-critical systems. To demonstrate, particularly to a certification authority, that
sufficient testing has been performed, it is necessary to achieve the test coverage levels recommended or
mandated by safety standards and industry guidelines. Mutation testing provides an alternative or
complementary method of measuring test sufficiency, but has not been widely adopted in the safetycritical industry. The system provides an empirical evaluation of the application of mutation testing to
airborne software systems which have already satisfied the coverage requirements for certification.
The system mutation testing to safety-critical software developed using high-integrity subsets of
C and Ada, identify the most effective mutant types and analyze the root causes of failures in test cases.
Mutation testing could be effective where traditional structural coverage analysis and manual peer
review have failed. They also show that several testing issues have origins beyond the test activity and
this suggests improvements to the requirements definition and coding process. The system also
examines the relationship between program characteristics and mutation survival and considers how
program size can provide a means for targeting test areas most likely to have dormant faults. Industry
feedback is also provided, particularly on how mutation testing can be integrated into a typical
verification life cycle of airborne software. The system also covers the safety and criticality levels of
Java source code.
Software Defect Prediction Using Local and Global AnalysisEditor IJMTER
The software defect factors are used to measure the quality of the software. The software
effort estimation is used to measure the effort required for the software development process. The defect
factor makes an impact on the software development effort. Software development and cost factors are
also decided with reference to the defect and effort factors. The software defects are predicted with
reference to the module information. Module link information are used in the effort estimation process.
Data mining techniques are used in the software analysis process. Clustering techniques are used
in the property grouping process. Rule mining methods are used to learn rules from clustered data
values. The “WHERE” clustering scheme and “WHICH” rule mining scheme are used in the defect
prediction and effort estimation process. The system uses the module information for the defect
prediction and effort estimation process.
The proposed system is designed to improve the defect prediction and effort estimation process.
The Single Objective Genetic Algorithm (SOGA) is used in the clustering process. The rule learning
operations are carried out sing the Apriori algorithm. The system improves the cluster accuracy levels.
The defect prediction and effort estimation accuracy is also improved by the system. The system is
developed using the Java language and Oracle relation database environment.
Software Cost Estimation Using Clustering and Ranking SchemeEditor IJMTER
Software cost estimation is an important task in the software design and development process.
Planning and budgeting tasks are carried out with reference to the software cost values. A variety of
software properties are used in the cost estimation process. Hardware, products, technology and
methodology factors are used in the cost estimation process. The software cost estimation quality is
measured with reference to the accuracy levels.
Software cost estimation is carried out using three types of techniques. They are regression based
model, anology based model and machine learning model. Each model has a set of technique for the
software cost estimation process. 11 cost estimation techniques fewer than 3 different categories are
used in the system. The Attribute Relational File Format (ARFF) is used maintain the software product
property values. The ARFF file is used as the main input for the system.
The proposed system is designed to perform the clustering and ranking of software cost
estimation methods. Non overlapped clustering technique is enhanced with optimal centroid estimation
mechanism. The system improves the clustering and ranking process accuracy. The system produces
efficient ranking results on software cost estimation methods.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Automobile Management System Project Report.pdfKamal Acharya
The proposed project is developed to manage the automobile in the automobile dealer company. The main module in this project is login, automobile management, customer management, sales, complaints and reports. The first module is the login. The automobile showroom owner should login to the project for usage. The username and password are verified and if it is correct, next form opens. If the username and password are not correct, it shows the error message.
When a customer search for a automobile, if the automobile is available, they will be taken to a page that shows the details of the automobile including automobile name, automobile ID, quantity, price etc. “Automobile Management System” is useful for maintaining automobiles, customers effectively and hence helps for establishing good relation between customer and automobile organization. It contains various customized modules for effectively maintaining automobiles and stock information accurately and safely.
When the automobile is sold to the customer, stock will be reduced automatically. When a new purchase is made, stock will be increased automatically. While selecting automobiles for sale, the proposed software will automatically check for total number of available stock of that particular item, if the total stock of that particular item is less than 5, software will notify the user to purchase the particular item.
Also when the user tries to sale items which are not in stock, the system will prompt the user that the stock is not enough. Customers of this system can search for a automobile; can purchase a automobile easily by selecting fast. On the other hand the stock of automobiles can be maintained perfectly by the automobile shop manager overcoming the drawbacks of existing system.
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
Quality defects in TMT Bars, Possible causes and Potential Solutions.PrashantGoswami42
Maintaining high-quality standards in the production of TMT bars is crucial for ensuring structural integrity in construction. Addressing common defects through careful monitoring, standardized processes, and advanced technology can significantly improve the quality of TMT bars. Continuous training and adherence to quality control measures will also play a pivotal role in minimizing these defects.
Forklift Classes Overview by Intella PartsIntella Parts
Discover the different forklift classes and their specific applications. Learn how to choose the right forklift for your needs to ensure safety, efficiency, and compliance in your operations.
For more technical information, visit our website https://intellaparts.com
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
LOW VOLTAGE RIDE - THROUGH CAPABILITY OF WIND FARMS
1. Scientific Journal Impact Factor (SJIF): 1.711
International Journal of Modern Trends in Engineering
and Research
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e-ISSN: 2349-9745
p-ISSN: 2393-8161
LOW VOLTAGE RIDE - THROUGH CAPABILITY OF
WIND FARMS
Rekha G Padaki1,
Murugesh Dodakundi 2
, Anand Layadgundi 3
1
Assistant Professor, Dept. of studies in EEE, University BDT College of Engineering,
Davangere, Karnataka, India
2, 3
PG Scholar, Dept. of studies in EEE, University BDT College of Engineering,
Davangere, Karnataka, India
Abstract: Nowadays wind turbines are generally required to offer ancillary services similar to those
provided by conventional generators. One of the most important services wind turbines must offer is
to stay connected to the grid in fault situations delivering the reactive current specified in the recent
grid codes. In this paper, FACTS solutions for fixed speed wind farms such as DVR (Dynamic
Voltage Restorer) are presented as well as classic control and crowbar solutions for variable speed
wind turbines.
Keyword: Wind Turbine, Generator, Grid, Facts, DVR, Crowbar.
I. INTRODUCTION
Wind energy is available and clean source of energy that has been used to generate electrical power.
The focus on electrical power generated from wind energy has been noticeably increased due to the
environmental problems that fossil fuels make. Global warming and greenhouse emissions are the
main harmful results of fossil fuel consumption. United States wind power has been quickly spread
and wind generation installed capacity for 2014 is increasing. It has reached approximately 50 (GW)
of power according to the U.S Department of Energy (DOE) and the American Wind Energy
Association (AWEA) and according to the report prepared by the U.S. Department of Energy with
contributions from the National Renewable Energy Laboratory (NREL), the wind energy installed
capacity by 2030 will be around 20% of the total capacity. Wind power integration to the grid has
limitations and standards that have to be followed. Standards for wind integration to the grid are
addressed in the Institute of Electrical and Electronics Engineers (IEEE), North American Electric
Reliability Corporation (NERC) and by different utility companies.
Wind power integration to the grid has different difficulties and problems due to the variation of the
wind speed which results in fluctuation of the wind generated power that leads to fluctuations in
voltage and frequency. Grid faults also one of the problems that wind turbine control should take into
consideration. Wind turbines should be properly controlled to overcome the grid faults that lead to
voltage and frequency drop. It has to have a fault right through capabilities or as it is called voltage
ride through to protect the turbine generator form accelerating and damaging mechanical part due to
instability that increases vibration and stress on the mechanical parts like the speed conversion
system (gear box). Generator acceleration also leads to over current and overvoltage in the DC bus of
the electrical conversion system that makes the mechanical system unstable and might damage the
electrical converter.
Several countries have achieved relatively high levels of wind power penetration as following in
below table (Collection from Wikipedia). Some 80 percent of the global wind power market is now
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centered in just four countries - which reflect the failure of most other nations to adopt supportive
renewable energy policies. Future market growth will depend in large measure on whether additional
countries make way for renewable energy sources as they reform their electricity industries.
II. PHASE LOCKED LOOP (PLL)
Low Voltage Ride-Through capability (LVRT) is required by TSO's for connecting wind farms in
power systems as it is defined in the main grid codes. Wind farms must remain connected and
actively contribute to system stability during a wide range of network fault scenarios.
LVRT requirements differ according to the dynamic characteristics of the power system concerned.
Smaller power systems, with little or no interconnection, are prone to frequency instability, and
hence, their codes typically emphasize the provision of active power.
1.1 LVRT in fixed speed wind farms:
Fixed speed wind turbines were dominant in the 1990s. Until 1996 they represented 100% of the
wind turbines installed in Spain. Today, they represent less than 20%. Fixed speed wind farms are
composed of squirrel induction generators coupled directly to the grid. Consequently, the only ways
to control them are either to adjust the pitch angle of the turbine blades and thereby their
aerodynamic efficiency (Cp) or by varying the voltage applied to the stator.
The mechanical power input stays approximately constant during the voltage dip. However the
torque developed by the stator decreases, since it is proportional to the applied voltage squared. As
consequence, the energy not absorbed by the grid is accumulated as rotational kinetic energy in the
turbine. Pitch control is considered when studying LVRT capability. Blade pitch actuators are
powerful to fully pitch the blades within a fraction of a second when necessary. However it has to be
taken into account that it is necessary to apply big dynamic forces. Consequently, blade pitch control
is not the most convenient way to offer LVRT capabilities. Other alternative to avoid speed
instability is to employ an active stall strategy. Once the fault is detected, the pitch is regulated
toward a stall position in order to reduce aerodynamic torque.
The most commonly suggested LVRT-strategy for fixed speed wind farms is the application of
FACTS devices such as: Static Var Compensators (SVC’s), Static Synchronous Compensators
(STATCOM’s) or Dynamic Voltage Restorers (DVR’s).
Here the application of Dynamic Voltage Restorer (DVR) for restoring the voltage level at the wind
farm terminals under fault conditions is studied explaining its structure and control. It is important to
notice that in this case DVR is protecting not a critical load but a critical source of power sensitive to
voltage dips. Here, power flows in different direction.
1.2 Phase-Locked Loop (PLL)
The mentioned special devices for complying the grid codes such as DVR, STATCOM, DFIG
(Doubly Fed Induction Generator) converters and any power electronic converter that manages
reactive power actively, need all the information related with the synchronization of the input voltage
angle.
In order to mitigate the voltage dip, it is not only needed its precise detection but also to track the
phase angle of the fundamental AC voltage. This reference signal can be obtained by the Phase-
Locked Loop (PLL). A PLL is a device for tracking periodic signals in order to obtain frequency
characteristics. It should provide frequency value and phase of an input voltage.
A PLL is simply a servo system, which controls the phase of its output signal in such a way that the
phase error between output phase and reference phase reduces to a minimum.
As it can be seen in Fig.2 that represents the functional block diagram of a PLL and according to,
PLL contains three basic components:
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a phase detector (PD)
a loop filter
a voltage - controlled oscillator (VCO), whose frequency is controlled by an external voltage
Figure 2: Block diagram of an analog PLL
III. DYNAMIC VOLTAGE RESTORER (DVR)
Dynamic voltage restorer is a Static Var device that has applications in a variety of transmission and
distribution systems. It is a series compensation device, which protects sensitive electric load from
power quality problems such as voltage sags, swells, unbalance and distortion through power
electronic controllers that use voltage source converters (VSC). The first DVR was installed in North
America in 1996 - a 12.47 kV system located in Anderson, South Carolina. Since then, DVRs have
been applied to protect critical loads in utilities, semiconductor and food processing. Today, the
dynamic voltage restorer is one of the most effective PQ devices in solving voltage sag problems.
The basic principle of the dynamic voltage restorer is to inject a voltage of required magnitude and
frequency, so that it can restore the load side voltage to the desired amplitude and waveform even
when the source voltage is unbalanced or distorted. Generally, it employs a gate turn off thyristor
(GTO) solid state power electronic switches in a pulse width modulated (PWM) inverter structure.
The DVR can generate or absorb independently controllable real and reactive power at the load side.
In other words, the DVR is made of a solid state DC to AC switching power converter that injects a
set of three phase AC output voltages in series and synchronism with the distribution line voltages.
Dynamic voltage restorer is a series connected device designed to maintain a constant RMS voltage
across a sensitive load. The structure of DVR is shown in Fig.3.
Figure 3: Schematic diagram of DVR
VOLTAGE CONTROL
OSCILLATOR
LOOP
FILTER
PHASE
DETECT
Input
Signal
VCO
Output
Phase
Error
Static
Phase Error
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The DVR consists of:
a. Voltage Source Converter (VSC): Voltage Source Converter converts the dc voltage from the
energy storage unit to a controllable three phase ac voltage. The inverter switches are normally fired
using a sinusoidal Pulse Width Modulation scheme.
b. Injection Transformer: Injection transformers used in the DVR plays a crucial role in ensuring
the maximum reliability and effectiveness of the restoration scheme. It is connected in series with the
distribution feeder.
c. Passive Filters: Passive Filters are placed at the high voltage side of the DVR to filter the
harmonics. These filters are placed at the high voltage side as placing the filters at the inverter side
introduces phase angle shift which can disrupt the control algorithm.
d. Control system / Energy storage device: Examples of energy storage devices are dc capacitors,
batteries, super-capacitors, superconducting magnetic energy Storage and flywheels. The capacity of
energy storage device has a big impact on the compensation capability of the system. Compensation
of real power is essential when large voltage sag occurs.
IV. BASIC OPERATION OF DFIG
The DFIG wind turbines use wound rotor induction generators, where the rotor winding is fed
through a back-to-back variable frequency and amplitude PWM converter. The variable frequency
rotor voltage permits the adjustment of the rotor speed to match the optimum operating point at any
practical wind speed. The variable frequency converter consists of a rotor side converter (RSC) and a
grid side converter (GSC) and only handles rotor power. Consequently the control of the machine
can be carried out with a converter that is sized for a power around 25%-30% of the rated power of
the turbine. As compared to variable speed turbines that use full power converter connected to the
stator, the converter of the DFIG is lower cost and lower sized. The main objective of the RSC is to
control the DFIG stator active power, speed and reactive power. While the GSC keeps the voltage of
DC link constant.
Figure 5: Basic operation of DFIG
A DFIG system is essentially a wound rotor induction generator with slip rings, the stator directly
connected to the grid and the rotor interfaced through a back-to-back partial scale power converter.
The DFIG is doubly fed by means that the voltage on the stator is applied from the grid and the
voltage on the rotor is induced by the power converter. The converter consists of two conventional
voltage source converters (rotor-side converter RSC and grid-side converter GSC) and a common
link DC-bus, as illustrated in Fig. 5.
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It contains two protection circuits, a DC-chopper and an AC-crowbar to avoid DC-link over-voltages
during grid faults. The chopper module is not essential for fault ride-through operation but it
increases the normal range of DFIG operation by smoothing the DC-link voltage during heavy
imbalances of active power on rotor- and line-side converter. Theoretically converters and choppers
could be designed to withstand even terminal short-circuits but economic considerations normally
limit to a lower rating.
Following deep voltage sags caused by grid short circuits the rotor currents and thus the RSC
currents rise rapidly. The DC short circuit component on the stator side appears on the rotor side as
an alternating current with high initial peak. When the current exceeds a certain limit the IGBTs will
be stopped to protect the converter but the current and thus the energy continues to flow into the DC-
link through the freewheeling diodes leading to fast voltage increase. To keep the DC voltage below
the upper threshold first the chopper is switched on by IGBT switches. Depending on the level of
energy flow into the DC link and the chopper design this measure may be successful in most cases.
When the DC voltage is maintained by the chopper the RSC goes back into operation following a
few milliseconds and the DFIG can be controlled again even if it is operating on a low voltage level.
However, in extreme situations the DC voltage may increase further. As the next line of protection
the crowbar is fired and the rotor is short-circuited. The crowbar firing is triggered by the DC-
voltage. The characteristic operating modes of the RSC and the crowbar during FRT are shown in
Fig. 6. When the crowbar is switched on the wind turbine operates as a slip-ring asynchronous
machine. After a short transient period the machine becomes a reactive power consumer which is
counterproductive in respect of the grid voltage support as required by the grid codes. However, the
crowbar is switched on only for a time period of 60-120 ms, because the crowbar thyristor switches
used in many applications will not interrupt the currents before their zero-crossing, the exact
interruption time is not predictable. Therefore, between crowbar interruption and RSC
resynchronization a possible time slot with open rotor circuits characterized as mode 3 in Fig.6 can
exist.
Figure 6: Operation modes of DFIG Converter during FRT
V. DFIG CROWBAR SCHEME
The function of the conventional crowbar protection system when a short circuit occurred the RSC is
disabled and bypassed , at the same time external resistors is coupled via the slip rings to the rotor
winding instead of the converter as shown in Fig. 7, so the controllability of active and reactive
power gets unfortunately lost.
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Figure 7: DFIG crowbar scheme
The crowbar implemented in the DFIG model has been presented in figure 6. It consists of a diode
bridge and a controlled crowbar resistor, able to be connected with a power electronic switch. During
the voltage dip situation, the high rotor currents will be diverted through the crowbar protecting the
rotor side converter. While crowbar is working, DFIG is acting as a squirrel cage induction
generator. In this section the effect of the crowbar resistance on rotor currents is analyzed, see Fig. 8.
It is proven how high values of crowbar resistance damp rotor currents more than low values. On the
other hand, electromagnetic torque will fluctuate more as long as the crowbar resistance decreases.
The crowbar system used in modern wind turbines is based on a three-phase series resistance
controlled by power electronics. The crowbar system is activated during over-current on the rotor
windings or/and over-voltage on the DC link. Most of the time, these atypical values appear after a
short circuit close to the wind farm. The steps involved during the activation and the deactivation of
the crowbar system by the circuit breakers (CB) are summarized:
Disconnection of the rotor windings from the RSC.
Insertion of the three-phase resistance in series to the rotor windings.
Disconnection of the crowbar system from the rotor windings.
Reconnection of the RSC to the rotor windings.
If the voltage at the DC link or/and the current at the rotor windings are at a normal levels, the
operation returns to its normal, however, if not, the activation of the crowbar system can be restarted
(the second activation is undesirable). Considering more restrictive grid codes, the use of DC-
Chopper system in the DC-link is also recommended to avoid the reinsertion of the crowbar system
to enable the reestablishment of the terminal voltage control by the RSC. The DC-Chopper is a
thyristor controlled resistance, in which the unbalance of electrical power injection into the power
system by the GSC and the electrical power injected into the DC-link by the RSC is dissipated.
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Figure 8: Rotor currents with different crowbars applied
The crowbar resistance values are referred to the rotor resistance of the laboratory machine. Hence, 1
p.u. equals 1.8 Ω. During the recovery of the voltage, it can be seen that the higher value of the
crowbar resistance, the bigger variation of the rotor current. The reason is simple: when high value of
the crowbar resistance is used, rotor currents are small in comparison when lower crowbar
resistances are used. Once the crowbar is disconnected, the machine control has to re-assume DFIG
control. In this situation, if rotor currents are very low due to high crowbar resistances, the machine
control will try to recover the set point by increasing rotor currents. In any case, it can be seen how
currents rise in the moment of the crowbar activation. This increasing on the current value is lower
than without crowbar, and the rotor can withstand currents slightly higher than the nominal for a
short time due to its relatively large thermal constant.
The effect of the crowbar resistance on the electromagnetic torque must be analyzed as well. Fig. 9
shows how the fluctuation of the electromagnetic torque depends also on the crowbar resistance.
Figure 9: Electromagnetic torque with different crowbars applied
Torque fluctuations are more noticeable for low crowbar resistances but the difference is not
significant. Thus, the main design factor will be the current waveform. Considering the previously
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exposed facts and the obtained results, the crowbar resistor is set to a value of 1 p.u. By setting the
crowbar resistor to 1 p.u, the comparison between different locking times is presented. The chosen
values have been 150 ms in one case.
Note that, as it was introduced above, some control actions must be taken for the reconnection of the
RSC. In this case, the reference signals for the active and reactive power during the voltage dip are
set to the instantaneous actual value. When the crowbar is released, the reference signals are slowly
directed to the original set point. In figures 10, 11 and 12 the results are shown.
Figure 10: Rotor current with different crowbar locking-times
Figure 11: Reactive power with different crowbar locking-times
9. International Journal of Modern Trends in Engineering and Research (IJMTER)
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Figure 12: Electromagnetic torque with different crowbar locking-times
VI. CONCLUSION
Wind turbines must participate in the increase of power system stability. One of the most important
facts is their ability to withstand voltage dips. Fixed Speed wind turbines do not fulfill the grid codes
by themselves. FACTS devices such as DVR are needed in this task. Variable Speed Wind Turbines
are more flexible offer in reactive power control. In this seminar, it has been shown how crowbar
devices act when facing voltage dips.
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