INTEGRATED INSTANCE-BASED AND KERNEL METHODS FOR POWER QUALITY KNOWLEDGE MODELING

In this paper, an integrated knowledge discovery strategy for high dimensional spatial power quality event data is proposed. Real time, distributed measuring of the electricity transmission system parameters provides huge number of time series power quality events. The proposed method aims to construct characteristic event distribution and interaction models for individual power quality sensors and the whole electricity transmission system by considering feasibility, time and accuracy concerns. In order to construct the knowledge and prediction model for the power quality domain; feature construction, feature selection, event clustering, and multi-class support vector machine supervised learning algorithms are employed

A General Purpose Inverter Set-Up For Power Electronics Laboratory Experiments

A general purpose experimental set-up has been designed and implemented for students to carry out various experiments on inverters in the power electronics laboratories of universities, during a few hours of laboratory work. This is the first inverter setup that incorporates hardware and software control, as well as an optional user interface in a laboratory experimental set-up of a single multi-purpose inverter, thus making the system versatile and very practical for both undergraduate and graduate students. The system can be controlled either by a computer or through a liquid crystal display (LCD) and a keypad control unit, and it constitutes a low-cost alternative to relatively expensive commercial teaching sets. The computer provides a user friendly interface and easier control for laboratory environments equipped with computers. The LCD and keypad units eliminate the need for a computer, which makes this system usable in the laboratory as a standalone unit as well

Medium-Frequency Induction Melting Furnace as a Load on the Power System

The variable-frequency operation of the coreless induction melting furnace (IMF) has been investigated in detail both theoretically and experimentally. The time variations of the operational impedance value of the IMF, owing to the time-varying resonance frequency and crucible conditions, have been derived for typical melting cycles by using a variable parallel RLC model derived from extensive field measurements. The work coil and its crucible are supplied at variable frequency from a multipulse rectifier and a current-fed load-resonant inverter cascade. Uncharacteristic current harmonics caused by cross-modulation phenomenon across the alternating current ac-dc-ac link have been derived theoretically and verified by field tests. These theoretical results and extensive field measurements on a sample IMF installation have shown the following: 1) The major power quality problem of an IMF as a load on the power system is the injection of various characteristic and uncharacteristic current harmonics to the grid; 2) line currents on the supply side are nearly balanced; 3) flicker contribution is below the limits specified in the standards; 4) reactive power demand is relatively low and the variations in the magnitude and rate of change of active power are not drastic; and 5) no voltage sag and swell phenomena arising from furnace operation occur

A Selective Harmonic Amplification Method for Reduction of kVA Rating of Current Source Converters in Shunt Active Power Filters

This paper describes a new approach to the design of current-source converter (CSC)-based shunt active power filters (APFs) to reduce the converter kilovolt-ampere rating considerably. This design approach is called the selective harmonic amplification method (SHAM), and is based on the amplification of some selected harmonic current components of CSC by the ac-side filter, and the CSC control system specifically designed for this purpose. The proposed SHAM has been implemented on a CSC-based APF for the elimination of 11th and 13th current harmonics of 12-pulse rectifier loads supplied from a medium-voltage underground cable. Simulation and field test results have shown that SHAM can successfully be applied to a CSC-based APF for reduction of the converter kilovolt-ampere rating, thus making it a cost-competitive alternative to voltage-source-converter-based APFs traditionally used in industry applications

Field-Data-Based Modeling of Medium-Frequency Induction Melting Furnaces for Power Quality Studies

In this paper, the coreless medium-frequency induction melting furnace (IMF) system is represented by alternative field-data-based models, developed specifically for power quality studies. The IMF operation has been represented by a variable series RL circuit, to model the fundamental components of electrical quantities, and a shunt-connected current source, to model the generated harmonics and interharmonics over a typical melting cycle. Both the sinusoidal coding method applied to the major harmonics and interharmonics in the supply line currents obtained from field measurements and the raw data have been used in the developed models. It has been shown that the sinusoidal coding method can be used to satisfactorily represent the operation of the IMF system as seen from the supply terminals, with a minimum data storage requirement, and can be used to construct efficient IMF databases for power quality studies. The power quality problems of the IMF system, particularly the problematic time-varying interharmonic voltage distortion, and the interaction of those time-varying interharmonic currents with the passive shunt filter installations connected to the same bus have been investigated in detail, using the developed models

PQONT: A domain ontology for electrical power quality

Electrical power quality (PQ) data is a ubiquitous type of engineering data quantified as a set of PQ parameters, such as frequency, flicker, and harmonics, obtained from electricity transmission and distribution systems. For PQ problems detected as deviations from nominal power system behavior negatively affect the workings of governmental and industrial institutions, as well as the electronic equipment and the psychology of individual humans, several systems of varying complexities to measure and monitor PQ parameters have been developed in order to detect the problems and take the necessary countermeasures. Yet, the domain of PQ data still suffers from the lack of a common vocabulary to be shared by the involved parties. In this paper, a novel domain ontology for electrical PQ, called PQONT, is presented to fulfill this need. Relevant standards and regulations have been utilized extensively during the ontology building process. The proposed ontology also supports linguistic applications by providing a number of linguistic properties applicable to all of its concepts. This facility of the ontology is employed in a multilingual natural language based interface for PQ data collected through a nationwide PQ measurement system so that the data can be queried in a flexible way. The implementation details of the interface is presented with a couple of query examples to illustrate the contribution of the ontology to a real application. The future work includes the extension of PQONT to a more general power system ontology so that it can contribute to a wider range of applications in the power system domain

A new DC voltage balancing method for cascaded multilevel inverter based statcom

It has been mentioned in the literature that, among the multilevel inverter topologies used for STATCOM applications, the cascaded multilevel topology is the most advantageous and economical one. On the other hand, the main problem of this topology comes out to be the difficulty of sustaining the DC capacitors' mean voltages. This issue is very important for obtaining an output voltage with low THD and having equal device stresses. In this work, a new DC voltage balancing method (Selective-Swapping Algorithm) for cascaded multilevel inverter based STATCOM applications is investigated and the results are given. Moreover, these results are compared with the ones obtained for the other DC voltage equalization methods given in the literature