46 research outputs found
A Review of Methods Employed to Identify Flicker Producing Sources
Because of increasing requirements of the present consumers and industrial units utilizing sensitive loads, there is need of good power quality in order to retain the power quality standards. Nowadays the study of the voltage flicker is becoming essential part of power quality studies. The flicker is typically the effect of a rapidly changing load which is large with respect to the short circuit ability of an electrical supply system. The inferior effects of voltage flicker include malfunctioning of power electronic equipment. Also it causes annoying effects to human. Hence detection of the flicker source is an essential step in the power quality assessment process. This paper delivers a review about methods used to identify flicker producing loads in accordance with IEC 61000-4-15. Once the report related to the disturbance place is known, an investigation and corrective action can be accordingly carried out. Also a method based upon Discrete Wavelet Transform and Artificial Neural Network is proposed to detect initial instance of occurrence of flicker
Automatic classification of power quality disturbances using optimal feature selection based algorithm
The development of renewable energy sources and power electronic converters in conventional power systems leads to Power Quality (PQ) disturbances. This research aims at automatic detection and classification of single and multiple PQ disturbances using a novel optimal feature selection based on Discrete Wavelet Transform (DWT) and Artificial Neural Network (ANN). DWT is used for the extraction of useful features, which are used to distinguish among different PQ disturbances by an ANN classifier. The performance of the classifier solely depends on the feature vector used for the training. Therefore, this research is required for the constructive feature selection based classification system. In this study, an Artificial Bee Colony based Probabilistic Neural Network (ABCPNN) algorithm has been proposed for optimal feature selection. The most common types of single PQ disturbances include sag, swell, interruption, harmonics, oscillatory and impulsive transients, flicker, notch and spikes. Moreover, multiple disturbances consisting of combination of two disturbances are also considered. The DWT with multi-resolution analysis has been applied to decompose the PQ disturbance waveforms into detail and approximation coefficients at level eight using Daubechies wavelet family. Various types of statistical parameters of all the detail and approximation coefficients have been analysed for feature extraction, out of which the optimal features have been selected using ABC algorithm. The performance of the proposed algorithm has been analysed with different architectures of ANN such as multilayer perceptron and radial basis function neural network. The PNN has been found to be the most suitable classifier. The proposed algorithm is tested for both PQ disturbances obtained from the parametric equations and typical power distribution system models using MATLAB/Simulink and PSCAD/EMTDC. The PQ disturbances with uniformly distributed noise ranging from 20 to 50 dB have also been analysed. The experimental results show that the proposed ABC-PNN based approach is capable of efficiently eliminating unnecessary features to improve the accuracy and performance of the classifier
Power Quality
Electrical power is becoming one of the most dominant factors in our society. Power
generation, transmission, distribution and usage are undergoing signifi cant changes
that will aff ect the electrical quality and performance needs of our 21st century industry.
One major aspect of electrical power is its quality and stability – or so called Power
Quality.
The view on Power Quality did change over the past few years. It seems that Power
Quality is becoming a more important term in the academic world dealing with electrical
power, and it is becoming more visible in all areas of commerce and industry, because
of the ever increasing industry automation using sensitive electrical equipment
on one hand and due to the dramatic change of our global electrical infrastructure on
the other.
For the past century, grid stability was maintained with a limited amount of major
generators that have a large amount of rotational inertia. And the rate of change of
phase angle is slow. Unfortunately, this does not work anymore with renewable energy
sources adding their share to the grid like wind turbines or PV modules. Although the
basic idea to use renewable energies is great and will be our path into the next century,
it comes with a curse for the power grid as power fl ow stability will suff er.
It is not only the source side that is about to change. We have also seen signifi cant
changes on the load side as well. Industry is using machines and electrical products
such as AC drives or PLCs that are sensitive to the slightest change of power quality,
and we at home use more and more electrical products with switching power supplies
or starting to plug in our electric cars to charge batt eries. In addition, many of us
have begun installing our own distributed generation systems on our rooft ops using
the latest solar panels. So we did look for a way to address this severe impact on our
distribution network. To match supply and demand, we are about to create a new, intelligent
and self-healing electric power infrastructure. The Smart Grid. The basic idea
is to maintain the necessary balance between generators and loads on a grid. In other
words, to make sure we have a good grid balance at all times. But the key question that
you should ask yourself is: Does it also improve Power Quality? Probably not!
Further on, the way how Power Quality is measured is going to be changed. Traditionally,
each country had its own Power Quality standards and defi ned its own power
quality instrument requirements. But more and more international harmonization efforts
can be seen. Such as IEC 61000-4-30, which is an excellent standard that ensures
that all compliant power quality instruments, regardless of manufacturer, will produce of measurement instruments so that they can also be used in volume applications and
even directly embedded into sensitive loads. But work still has to be done. We still use
Power Quality standards that have been writt en decades ago and don’t match today’s
technology any more, such as fl icker standards that use parameters that have been defi
ned by the behavior of 60-watt incandescent light bulbs, which are becoming extinct.
Almost all experts are in agreement - although we will see an improvement in metering
and control of the power fl ow, Power Quality will suff er. This book will give an
overview of how power quality might impact our lives today and tomorrow, introduce
new ways to monitor power quality and inform us about interesting possibilities to
mitigate power quality problems.
Regardless of any enhancements of the power grid, “Power Quality is just compatibility”
like my good old friend and teacher Alex McEachern used to say.
Power Quality will always remain an economic compromise between supply and load.
The power available on the grid must be suffi ciently clean for the loads to operate correctly,
and the loads must be suffi ciently strong to tolerate normal disturbances on the
grid
Reconfigurable power quality analyser
Electronic power supplies are found in almost all electrical equipment. They are
sensitive to power quality disturbances but they themselves are causers of interference.
This becomes more prominent with their wider use which means that these disturbances
have a tendency to aggravate in future. One of the results will be that additional losses will
occur and end-users will also be penalised for it by paying more. There is a need to revert
this tendency also in an effort to help lower pollution. Another consequence of
disturbances is the added difficulty that power grid operators will have to maintain the
network stable. Everyone would therefore benefit from more efficient electricity
consumption. A power quality disturbance can be measured with a power quality analyser
to help the technician find its cause. This is the first step to finding a solution to resolve the
disturbance.
The objective of this project was to implement digital signal processing algorithms
on a FPGA for the analysis of power quality disturbances. The motive for choosing the
FPGA was that it allowed a processor, used for lower demanding processing tasks, and
dedicated hardware, used for time-critical operations, to be integrated into a single
integrated circuit. The implementation of these algorithms in dedicated hardware permitted
obtaining high-resolution measurements and the exploitation of parallelism to increase the
quantity of information available to the user. The FPGA is a versatile component, ideal to
implement the reconfigurable power quality analyser that is upgradable in future.
The project resulted in the successful measurement of the fundamental frequency and
the magnitude of the signal at the input. The device was able to detect and measure
harmonic and inter-harmonic components. Positive and negative peak values were
measured and the root mean square value both for full-cycle and half-cycle were calculated
making stationary signal variation evaluation possible. Time aggregation of values was
also done. The generation of an internal signal made it possible for the comparison with the
input signal, resulting in event isolation for further verification and classification by the
controller
Comparison of Simulation Methods of Single and Multi-Bit Continuous Time Sigma Delta Modulators
Continuous time Sigma Delta Modulators (CT ΣΔMs) are a type of analog to digital converter (ADC) that are used in mixed signal systems to convert analog signals into digital signals. ADCs typically require antialiasing filter; however antialiasing filters are inherent in CT ΣΔMs, and therefore they require less circuitry and less power than other ADC architectures that require separate antialiasing filters. As a result, CT ΣΔM ADC architectures are preferred in many mixed signal electronic applications.
Because of the mixed signal nature of CT ΣΔMs, they can be difficult to simulate. In this thesis, various methods for simulating single-bit and multi-bit CT ΣΔMs are developed and these simulations include the bilinear transform or trapezoidal integration, impulse invariance transform, midpoint integration, Simpson’s rule, delta transform or Euler’s forward integration rule and Simulink modeling. These methods are compared with respect to speed which is given by the total simulation time, accuracy which is given by the signal to noise ratio (SNR) value and the simplicity of the simulation method. The CT ΣΔMs have been extended from first order up to fifth order with one, two and three bit quantizers. Also, the frequency domain analysis is done for all the orders of CT ΣΔMs.
The results show that the numerical integration methods are more accurate and faster than Simulink. However, CT ΣΔM simulations using Simulink are simpler because of the availability of the required blocks in Simulink. The overall comparison shows that the numerical integration methods can perform better than Simulink models. The frequency domain analysis proves the correctness of the use of numerical integration methods for CT ΣΔM simulations
Transients in Power Systems
Power system engineering largely focuses on steady state analysis. The main areas of power system engineering are power flow studies and fault studies - both steady state technologies. But the world is largely transient, and power systems are always subject to time varying and short lived signals. This technical report concerns several important topics in transient analyses of power systems. The leading chapter deals with a new analytical tool-wavelets-for power system transients. Flicker and electric are furnace transients are discussed in Chapters I1 and IV. Chapter 111 deals with transients from shunt capacitor switching. The concluding chapters deal with transformer inrush current and non simultaneous pole closures of circuit breakers. This report was prepared by the students in EE532 at Purdue University. When I first came to Purdue in 1965, Professor El-Abiad was asking for student term projects which were turned into technical reports. I have \u27borrowed\u27 this idea and for many years we have produced technical reports from the power systems courses. The students get practice in writing reports, and the reader is able to get an idea of the coverage of our courses. I think that the students have done a good job on the subject of transients in power systems
Power Quality Issues in Distributed Generation
This book deals with several selected aspects of electric power quality issues typically faced during grid integration processes of contemporary renewable energy sources. In subsequent chapters of this book the reader will be familiarized with the issues related to voltage and current harmonics and inter-harmonics generation and elimination, harmonic emission of switch-mode rectifiers, reactive power flow control in power system with non-linear loads, modeling and simulation of power quality issues in power grid, advanced algorithms used for estimating harmonic components, and new methods of measurement and analysis of real time accessible power quality related data