1,994 research outputs found
International White Book on DER Protection : Review and Testing Procedures
This white book provides an insight into the issues surrounding the impact of increasing levels of DER on the generator and network protection and the resulting necessary improvements in protection testing practices. Particular focus is placed on ever increasing inverter-interfaced DER installations and the challenges of utility network integration. This white book should also serve as a starting point for specifying DER protection testing requirements and procedures. A comprehensive review of international DER protection practices, standards and recommendations is presented. This is accompanied by the identiïŹ cation of the main performance challenges related to these protection schemes under varied network operational conditions and the nature of DER generator and interface technologies. Emphasis is placed on the importance of dynamic testing that can only be delivered through laboratory-based platforms such as real-time simulators, integrated substation automation infrastructure and ïŹ exible, inverter-equipped testing microgrids. To this end, the combination of ïŹ exible network operation and new DER technologies underlines the importance of utilising the laboratory testing facilities available within the DERlab Network of Excellence. This not only informs the shaping of new protection testing and network integration practices by end users but also enables the process of de-risking new DER protection technologies. In order to support the issues discussed in the white paper, a comparative case study between UK and German DER protection and scheme testing practices is presented. This also highlights the level of complexity associated with standardisation and approval mechanisms adopted by different countries
Detection and Diagnosis of Motor Stator Faults using Electric Signals from Variable Speed Drives
Motor current signature analysis has been investigated widely for diagnosing faults of induction motors. However, most of these studies are based on open loop drives. This paper examines the performance of diagnosing motor stator faults under both open and closed loop operation modes. It examines the effectiveness of conventional diagnosis features in both motor current and voltage signals using spectrum analysis. Evaluation results show that the stator fault causes an increase in the sideband amplitude of motor current signature only when the motor is under the open loop control. However, the increase in sidebands can be observed in both the current and voltage signals under the sensorless control mode, showing that it is more promising in diagnosing the stator faults under the sensorless control operation
Islanding detection in three-phase and single-phase systems using pulsating high frequency signal injection
This paper analyzes the use of pulsating high frequency signal injection for islanding detection purposes. Active islanding detection using high frequency signal injection is an appealing option due to its reduced non-detection zone, reduced cost and ease of implementation. The use of a rotating high frequency signal has been reported and analyzed. However, this method can only be applied to three-phase systems. In this paper, the use of a pulsating high frequency signal injection is proposed. While it uses the same principles as rotating signal injection, it can be applied to both threephase and single-phase system
Detection of inter-turn faults in multi-phase ferrite-PM assisted synchronous reluctance machine
Inter-turn winding faults in five-phase ferrite-permanent magnet-assisted synchronous reluctance motors (fPMa-SynRMs) can lead to catastrophic consequences if not detected in a timely manner, since they can quickly progress into more severe short-circuit faults, such as coil-to-coil, phase-to-ground or phase-to-phase faults. This paper analyzes the feasibility of detecting such harmful faults in their early stage, with only one short-circuited turn, since there is a lack of works related to this topic in multi-phase fPMa-SynRMs. Two methods are tested for this purpose, the analysis of the spectral content of the zero-sequence voltage component (ZSVC) and the analysis of the stator current spectra, also known as motor current signature analysis (MCSA), which is a well-known fault diagnosis method. This paper compares the performance and sensitivity of both methods under different operating conditions. It is proven that inter-turn faults can be detected in the early stage, with the ZSVC providing more sensitivity than the MCSA method. It is also proven that the working conditions have little effect on the sensitivity of both methods. To conclude, this paper proposes two inter-turn fault indicators and the threshold values to detect such faults in the early stage, which are calculated from the spectral information of the ZSVC and the line currentsPeer ReviewedPostprint (published version
Fault Location in Grid Connected Ungrounded PV Systems Using Wavelets
Solar photovoltaic (PV) power has become one of the major sources of renewable energy worldwide. This thesis develops a wavelet-based fault location method for ungrounded
PV farms based on pattern recognition of the high frequency transients due to switching
frequencies in the system and which does not need any separate devices for fault location.
The solar PV farm used for the simulation studies consists of a large number of PV modules connected to grid-connected inverters through ungrounded DC cables. Manufacturers
report that about 1% of installed PV panels fail annually. Detecting phase to ground faults in ungrounded underground DC cables is also difficult and time consuming. Therefore, identifying ground faults is a significant problem in ungrounded PV systems because such earth
faults do not provide sufficient fault currents for their detection and location during system operation. If such ground faults are not cleared quickly, a subsequent ground fault on the healthy phase will create a complete short-circuit in the system, which will cause a fire hazard and arc-flashing. Locating such faults with commonly used fault locators requires costly external high frequency signal generators, transducers, relays, and communication devices as well as generally longer lead times to find the fault.
This thesis work proposes a novel fault location scheme that overcomes the shortcomings of the currently available methods. In this research, high frequency noise patterns are used to identify the fault location in an ungrounded PV farm. This high frequency noise is generated due to the switching transients of converters combined with parasitic capacitance
of PV panels and cables. The pattern recognition approach, using discrete wavelet transform (DWT) multi-resolution analysis (MRA) and artificial neural networks (ANN), is utilized to
investigate the proposed method for ungrounded grid integrated PV systems.
Detailed time domain electromagnetic simulations of PV systems are done in a real-time
environment and the results are analyzed to verify the performance of the fault locator. The fault locator uses a wavelet transform-based digital signal processing technique, which uses the high frequency patterns of the mid-point voltage signal of the converters to analyze the ground fault location. The Daubechies 10 (db10) wavelet and scale 11 are chosen as the appropriate mother wavelet function and decomposition level according to the characteristics of the noise waveform to give the proposed method better performance. In this study, norm values of the measured waveform at different frequency bands give unique features at different fault locations and are used as the feature vectors for pattern recognition. Then, the three-layer feed-forward ANN classifier, which can automatically classify the fault locations according to the extracted features, is investigated. The neural network is trained with the Levenberg-Marquardt back-propagation learning algorithm.
The proposed fault locating scheme is tested and verified for different types of faults, such as ground and line-line faults at PV modules and cables of the ungrounded PV system. These faults are simulated in a real-time environment with a digital simulator and the data is then analyzed with wavelets in MATLAB. The test results show that the proposed method
achieves 99.177% and 97.851% of fault location accuracy for different faults in DC cables and PV modules, respectively. Finally, the effectiveness and feasibility of the designed fault
locator in real field applications is tested under varying fault impedance, power outputs, temperature, PV parasitic elements, and switching frequencies of the converters. The results demonstrate the proposed approach has very accurate and robust performance even with
noisy measurements and changes in operating conditions
Multilevel Converters: An Enabling Technology for High-Power Applications
| Multilevel converters are considered today as the
state-of-the-art power-conversion systems for high-power and
power-quality demanding applications. This paper presents a
tutorial on this technology, covering the operating principle and
the different power circuit topologies, modulation methods,
technical issues and industry applications. Special attention is
given to established technology already found in industry with
more in-depth and self-contained information, while recent
advances and state-of-the-art contributions are addressed with
useful references. This paper serves as an introduction to the
subject for the not-familiarized reader, as well as an update or
reference for academics and practicing engineers working in
the field of industrial and power electronics.Ministerio de Ciencia y TecnologĂa DPI2001-3089Ministerio de EduaciĂłn y Ciencia d TEC2006-0386
Incremental learning for large-scale stream data and its application to cybersecurity
As many human currently depend on technologies to assist with daily tasks,
there are more and more applications which have been developed to be fit in one
small gadget such as smart phone and tablet. Thus, by carrying this small gadget
alone, most of our tasks are able to be settled efficiently and fast. Until the end
of 20th century, mobile phones are only used to call and to send short message
service (sms). However, in early 21st century, a rapid revolution of communiïżœcation technology from mobile phone into smart phone has been seen in which
the smart phone is equipped by 4G Internet line along with the telephone service
provider line. Thus, the users are able to make a phone call, send messages using
variety of application such as Whatsapp and Line, send email, serving websites,
accessing maps and handling some daily tasks via online using online banking,
online shopping and online meetings via video conferences. In previous years, if
there are cases of missing children or missing cars, the victims would rely on the
police investigation. But now, as easy as uploading a notification about the loss
on Facebook and spread the news among Facebook users, there are more people
are able to help in the search. Despite the advantages that can be obtained using
these technologies, there are a group of irresponsible people who take advanïżœtage of current technologies for their own self-interest. Among the applications
that are usually being used by almost Internet users and also are often misused
by cyber criminals are email and websites. Therefore, we take this initiative to
make enhancement in cyber security application to avoid the Internet users from
being trapped and deceived by the trick of cyber criminals by developing detecïżœtion system of malicious spam email and Distributed Denial of Services (DDoS) 377.1781.8781$0,1$+
iii
backscatter.
Imagine that a notice with a logo of Mobile Phone company is received by
an email informing that the customer had recently run up a large mobile phone
bill. A link regarding the bill is attached for him/her to find out the details.
Since, the customer thinks that the billing might be wrong, thus the link is
clicked. However, the link is directed to a webpage which displays a status that
currently the webpage is under construction. Then the customer closes the page
and thinking of to visit the website again at other time. Unfortunately, after
a single click actually a malicious file is downloaded and installed without the
customer aware of it. That malicious file most probably is a Trojan that capable
to steal confidential information from victimâs computer. On the next day, when
the same person is using the same computer to log in the online banking, all
of a sudden find out that his/her money is lost totally. This is one of a worst
case scenario of malicious spam email which is usually handled by cybersecurity
field. Another different case of cybersecurity is the Distributed Denial of Services
(DDoS) attack. Let say, Company X is selling flowers via online in which the
market is from the local and international customer. The online business of
Company X is running normally as usual, until a day before motherâs day, the
webpage of Company X is totally down and the prospective customers could not
open the webpage to make order to be sent specially for their beloved mother.
Thus, the customers would search another company that sells the same item. The
Company X server is down, most probably because of the DDoS attack where a
junk traffic is sent to that company server which makes that server could not
serve the request by the legitimate customers. This attack effect not only the
profit of the company, but also reputation damage, regular customer turnover
and productivity decline.
Unfortunately, it is difficult for a normal user like us to detect malicious spam 377$
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email or DDoS attack with naked eyes. It is because recently the spammers
and attacker had improved their strategy so that the malicious email and the
DDoS packets are hardly able to be differentiated with the normal email and
data packets. Once the Social Engineering is used by the spammers to create
relevant email content in the malicious spam email and when a new campaign
of DDoS attack is launched by the attacker, no normal users are capable to
distinguish the benign and malicious email or data packets. This is where my
Ph.D project comes in handy. My Ph.d is focusing on constructing a detection
system of malicious spam email and DDoS attack using a large number of dataset
which are obtained by a server that collect double-bounce email and darknet for
malicious spam email detection system and DDoS backscatter detection system,
respectively. As many up-to-date data are used during the learning, the detection
system would become more robust to the latest strategy of the cybercriminal.
Therefore, the scenario mentioned above can be avoided by assisting the user
with important information at the user-end such as malicious spam email filter
or at the server firewall. First of all, the method to learn large-scale stream
data must be solved before implementing it in the detection system. Therefore,
in Chapter 2, the general learning strategy of large-scale data is introduced to
be used in the cybersecurity applications which are discussed in Chapter 3 and
Chapter 4, respectively.
One of a critical criterion of the detection system is capable to learn fast because
after the learning, the updated information needs to be passed to user to avoid
the user from being deceived by the cybercriminal. To process large-scale data
sequences, it is important to choose a suitable learning algorithm that is capable
to learn in real time. Incremental learning has an ability to process large data
in chunk and update the parameters after learning each chunk. Such type of
learning keep and update only the minimum information on a classifier model. 377.1781.8781$0,1$+
Therefore, it requires relatively small memory and short learning time. On the
other hand, batch learning is not suitable because it needs to store all training
data, which consume a large memory capacity. Due to the limited memory, it is
certainly impossible to process online large-scale data sequences using the batch
learning. Therefore, the learning of large-scale stream data should be conducted
incrementally.
This dissertation contains of five chapters. In Chapter 1, the concept of inïżœcremental learning is briefly described and basic theories on Resource Allocating
Network (RAN) and conventional data selection method are discussed in this
chapter. Besides that, the overview of this dissertation is also elaborated in this
chapter. In Chapter 2, we propose a new algorithm based on incremental Radial
Basis Function Network (RBFN) to accelerate the learning in stream data. The
data sequences are represented as a large chunk size of data given continuously
within a short time. In order to learn such data, the learning should be carried
out incrementally. Since it is certainly impossible to learn all data in a short peïżœriod, selecting essential data from a given chunk can shorten the learning time. In
our method, we select data that are located in untrained or ânot well-learnedâ
region and discard data at trained or âwell-learnedâ region. These regions are
represented by margin flag. Each region is consisted of similar data which are
near to each other. To search the similar data, the well-known LSH method proïżœposed by Andoni et al. is used. The LSH method indeed has proven be able to
quickly find similar objects in a large database. Moreover, we utilize the LSH ÊŒs
properties; hash value and Hash Table to further reduced the processing time. A
flag as a criterion to decide whether to choose or not the training data is added in
the Hash Table and is updated in each chunk sequence. Whereas, the hash value
of RBF bases that is identical with the hash value of the training data is used to
select the RBF bases that is near to the training data. The performance results of 377$
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vi
the numerical simulation on nine UC Irvine (UCI) Machine Learning Repository
datasets indicate that the proposed method can reduce the learning time, while
keeping the similar accuracy rate to the conventional method. These results indiïżœcate that the proposed method can improve the RAN learning algorithm towards
the large-scale stream data processing.
In Chapter 3, we propose a new online system to detect malicious spam emails
and to adapt to the changes of malicious URLs in the body of spam emails by
updating the system daily. For this purpose, we develop an autonomous system
that learns from double-bounce emails collected at a mail server. To adapt to new
malicious campaigns, only new types of spam emails are learned by introducing an
active learning scheme into a classifier model. Here, we adopt Resource Allocating
Network with Locality Sensitive Hashing (RAN-LSH) as a classifier model with
data selection. In this data selection, the same or similar spam emails that
have already been learned are quickly searched for a hash table using Locally
Sensitive Hashing, and such spam emails are discarded without learning. On
the other hand, malicious spam emails are sometimes drastically changed along
with a new arrival of malicious campaign. In this case, it is not appropriate to
classify such spam emails into malicious or benign by a classifier. It should be
analyzed by using a more reliable method such as a malware analyzer. In order
to find new types of spam emails, an outlier detection mechanism is implemented
in RAN-LSH. To analyze email contents, we adopt the Bag-of-Words (BoW)
approach and generate feature vectors whose attributes are transformed based
on the normalized term frequency-inverse document frequency. To evaluate the
developed system, we use a dataset of double-bounce spam emails which are
collected from March 1, 2013 to May 10, 2013. In the experiment, we study the
effect of introducing the outlier detection in RAN-LSH. As a result, by introducing
the outlier detection, we confirm that the detection accuracy is enhanced on 377.1781.8781+
average over the testing period.
In Chapter 4, we propose a fast Distributed Denial of Service (DDoS) backscatïżœter detection system to detect DDoS backscatter from a combination of protocols
and ports other than the following two labeled packets: Transmission Control
Protocol (TCP) Port 80 (80/TCP) and User datagram Protocol (UDP) Port 53
(53/UDP). Usually, it is hard to detect DDoS backscatter from the unlabeled
packets, where an expert is needed to analyze every packet manually. Since it
is a costly approach, we propose a detection system using Resource Allocating
Network (RAN) with data selection to select essential data. Using this method,
the learning time is shorten, and thus, the DDoS backscatter can be detected
fast. This detection system consists of two modules which are pre-processing
and classifier. With the former module, the packets information are transformed
into 17 feature-vectors. With the latter module, the RAN-LSH classifier is used,
where only data located at untrained region are selected. The performance of the
proposed detection system is evaluated using 9,968 training data from 80/TCP
and 53/UDP, whereas 5,933 test data are from unlabeled packets which are colïżœlected from January 1st, 2013 until January 20th, 2014 at National Institute of
Information and Communications Technology (NICT), Japan. The results indiïżœcate that detection system can detect the DDoS backscatter from both labeled
and unlabeled packets with high recall and precision rate within a short time.
Finally, in Chapter 5, we discussed the conclusions and the future work of our
study: RAN-LSH classifier, malicious spam email detection system and DDoS
backscatter detection system
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