56 research outputs found
CHARACTERIZATION OF NONLINEAR LOADS IN POWER DISTRIBUTION GRID
Electronic devices are complex circuits, consisting of analog, switching, and digital subsystems that require direct current (DC) for polarization. Since they are connected to the mains delivering alternating current (AC), however, AC-to-DC converters are to be introduced between the mains and the electronics to be fed. A converter is an electric circuit containing several subsystems, the most important being the switch-mode power supply, drawing power from the mains in pulses hence it is highly nonlinear. That happens, in reduced amplitude, even when the electronics to be fed is switched off. The process of AC-to-DC conversion is not restricted to feeding electronic equipment only. It is more and more frequently encountered in modern smart-grid facilities giving rise to the importance of the studies referred hereafter. The converter can be studied (theoretically or by measurements) as two-port network with reactive and nonlinear port-impedances. Characterization is performed after determining the port electrical quantities which are voltages and currents. Based on these data power and power quality parameters – power factor and total harmonic distortion- may be extracted. When nonlinear loads are present, one should introduce new ways of thinking into the considerations due to the existence of harmonics and related power components. In that way the power factor can be generalized to total or true power factor where the apparent power, involved in its calculations, includes all harmonic components. After introducing a wide range of definitions used in contemporary literature, here we describe our measurement set-up both as hardware and a software solution. The results reported unequivocally confirm the importance of the subject of characterization of small nonlinear loads to the grid having in mind their number which is rising without saturation seen in the near and even far future
Elektronski sistem za analizu polifaznih opterećenja baziran na FPGA
Electronic devices industry is characterized by a very dynamic growth. Such quick advancement is not recognized in other technological branches. It is exponential and it can be represented by Moore’s law, which describes long-term tendency: the number of active components integrated on circuit doubles every eighteen months, keeping constant production price. This trend stands almost fifty years, and it will stand in the near future. Moore’s law is closely related to electronic device’s properties: processor speed, memory capacity, resolution, etc. Exponential growth had immense impact on world economy and it led to significant changes in lifestyle. Consequently, electronic devices are cheaper and more available on the market. As a result, electronic equipment takes a bigger portion in overall power consumption.
Electronic devices are complex circuits, consisting active semiconductor components that require direct current for polarisation. Electric energy is delivered to end users using three-phase alternating current distribution. Three-phase distribution is suitable for electric power transfer; however it cannot be directly applied to electronic circuits. Alternating current must be converted to direct current, using AC/DC power converters. Converter is electric circuit containing transformer, or switch mode power supply drawing power from the mains in pulses hence it is nonlinear. It can be analysed as two-port network with reactive and nonlinear impedance. Characterisation of power converter is performed by means of determining electrical quantities, power and power quality parameters – power factor and total harmonic distortion.
In linear circuits, consisting of linear loads, the currents and voltages are sinusoidal and the power factor effect arises only from the difference in phase between the current and
voltage. When nonlinear loads are present one should introduce new quantities in the calculations emanated by the harmonics and related power components. Now the power factor can be generalized to a total or true power factor where the apparent power, involved in its calculations, includes all harmonic components. This is of importance in characterization and design of practical power systems which contain
non-linear loads such as rectifiers, and especially, switched-mode power supplies.
Phase difference between current and voltage, as well as harmonic distortion has negative impact on distribution system. Therefore, industry standards regulate the limits (minimum) of power factor. One of the most paradigmatic examples is personal computer that typically includes switched-mode power supply (SMPS) with output power ranging from 150 W to 500 W. SMPS with passive power correction factor (PFC) can achieve power factor of about 0.7–0.75, SMPS with active PFC – up to 0.99, while SMPS without any PFC has power factor of about 0.5–0.65 in the best.
Since the problem of distortion becomes ubiquitous, it can be either observed at the distribution system level, or one has to take local measurement of the properties of this kind of loads.
Measurement of power factor and distortion, however, usually requires dedicated equipment. For example, use of a classical ammeter will return incorrect results when attempting to measure the AC current drawn by a non-linear load and then calculate the power factor. A true RMS multimeter must be used to measure the actual RMS currents and voltages and apparent power. To measure the real power or reactive power, a wattmeter designed to properly work with non-sinusoidal currents must be also used.
Contemporary methods and algorithms for spectrum analysis are presented in this thesis. The basic definitions of parameters describing nonlinear loads in one-phase and three-phase circuits are introduced. Alternative definitions for reactive power and their calculation methods are elaborated. A new approach to polyphase load analysis is presented: system for nonlinear load characterization which is flexible, scalable, with advanced options.
The solution introduced in the thesis brings all benefits of virtual instrumentation, keeping main advantage of classical instrument – determinism in measurement. The hardware component of the system is implemented using field programming gate array (FPGA) in control of data acquisition. The software part is implemented in two stages, executing on real-time operating system and general purpose operating system. Described realization provides possibility for calculating a large number of parameters that characterize nonlinear loads, which is impossible using classical instruments. This is of great importance particularly in
calculation of alternate definitions of reactive power. The system is scalable; it can be upgraded in number of calculated parameters, as well as in number of independent measurement channels or functionality. The system is open; it can be modified to be a part of harmonic compensation circuitry or aimed for hardware-in-the-loop simulations. The system is flexible; it is implemented on different platforms for different purposes: as laboratory equipment for real time measurements (PXI controller equipped with PXI-7813R FPGA card and expansion chassis), as compact industrial device for real time operation (installed on programmable automation controller) or simple portable instrument equipped with computer interface. It consists of three subsystems: acquisition subsystem, real time application for parameter calculations and virtual instrument for additional analysis and data manipulation.
Acquisition subsystem consists of acquisition modules for A/D conversion, FPGA circuit and interface for computer or programmable automation controller. A/D resolution is 24-bit, with 50 kSa/s sampling rate and dynamic range ±300 V for voltages and ±5 A for currents. Function of FPGA circuit is acquisition control and harmonic analysis.
Real time application calculates power and power quality parameters deterministically and save calculated values on local storage. The application is executed on real time operating system.
Virtual instrument for additional analysis and data manipulation represents user interface of described system. It runs on general purpose operating system, physically apart from rest of the system. Communication is achieved by TCP/IP. Parameters and values obtained by means of acquisition and calculations are presented numerically and graphically.
The usage of the system is also described. Nonlinear single-phase (SMPS, LED, CFL) and three-phase loads are examined in order to present all possibilities of new system
Merenje snage po standardu IEEE 1459-2010 upotrebom rezonatorskih filterskih struktura
Liberalizacijom tržišta električne energije merenje električne snage i energije u nesinusoidalnim uslovima dobilo je veliki značaj. Ta tema je još uvek predmet aktivnih rasprava, tako da ne postoji neka generalizovana teorija koja se može uzeti kao osnova za potrebe obračuna, evaluacije kvaliteta energije, detekcije izvora harmonika i kompenzacije u energetskim sistemima. Kao posledica, postojeći standardi se odnose na sinusoidalne slučajeve i ne daju definiciju reaktivne energije (i/ili snage) u nesinusoidalnim uslovima. Slično, oni ne daju specifične zahteve za tačnost i odgovarajuće uslove testiranja u prisustvu harmonijskih izobličenja. Jedini standard koji se odnosi na ovu problematiku je IEEE Std. 1459-2010 koji ne daje definiciju reaktivne snage u nesinusoidalnim uslovima. Koncept ovog IEEE standarda je baziran na razdvajanju snage na fundamentalni i nefundamentalni deo. Ovaj prilaz separacije na fundamentalni i harmonijski deo može se primeniti na najbitnije veličine i može se iskoristiti kao indikator kvaliteta. U radu je prikazana jedna efikasna algoritamska struktura za računanje električnih veličina definisanih standardom IEEE 1459-2010. Struktura se sastoji od dva dekuplovana dela. Za estimaciju spektra napona i struje korišćena je efikasna metoda bazirana na paralelnoj strukturi rezonantnih filtera sa zajedničkom povratnom vezom. U drugom delu strukture se na osnovu poznatog spektra naponskog i strujnog signala računaju komponente snage i indikatori kvaliteta na osnovu definicija datih u standardu IEEE 1459-2010. Predloženi algoritam je pogodan za primene u realnom vremenu. Realizacijom virtualnog instrumenta baziranog na PC računaru i programskom paketu LabVIEW, u cilju procene performansi algoritma, izvršene su računarske simulacije i eksperimentalna merenja i dati njihovi rezultati.This paper proposes an accurate and computationally efficient implementation of the IEEE Std. 1459-2010 for power measurements. An implementation is based on digital resonators embedded in a feedback loop. In the first algorithm stage, the unknown signal harmonic parameters are estimated. By this, the voltage and current signals are processed independently of each other. In the second algorithm stage, the unknown power components are estimated (calculated) based on estimated spectra. To demonstrate the performance of the developed algorithm, computer-simulated data and laboratory testing records are processed. Simple LabView implementation, based on the point-by-point processing feature, demonstrates techniques modest computation requirements and confirms that the proposed algorithm is suitable for real-time applications
Modified walsh transform for harmonic assessment
Harmonic assessment at end users through energy meter is a part of power quality monitoring to determine harmonics contamination level in distribution network. Integration of harmonics extraction technique with energy meter requires two considerations which are measurement accuracy of the technique and its computational complexity to extract harmonics. These two aspects are main requirements for meter to support the execution of harmonics extraction since it is operated under low-cost microcontroller. In harmonic extraction of Fast Fourier Transform (FFT), the computation burden is quite high and requires additional hardware installation to support the algorithm’s operation. Therefore, this thesis presents a Modified Walsh Transform algorithm as an alternative harmonic extraction. The proposed algorithm consumes less arithmetic operations than FFT and suitable to be integrated into energy meter. This study involves with extracting distorted current signal into harmonic components, measuring the harmonics magnitude and calculating Root-Mean-Square (RMS), Total Harmonic Distortion (THD) and Distortion Power Factor (DPF) as well as computational analysis between FFT and Modified Walsh Transform algorithms. The result from simulation indicates that the proposed algorithm has 99% of accuracy percentage with more consistent result than FFT. Moreover, the arithmetic operation in Modified Walsh Transform is less than FFT to show that less computation burden consumed by the proposed algorithm. Meanwhile, a laboratory experiment has been conducted to demonstrate consideration of DPF in harmonics assessment and power factor measurement as complied in IEEE Std.1459-2010
Fault diagnosis and fault tolerant control of multiphase voltage source converters for application in traction drives
There is an increasing demand for vehicles with less environmental impact and higher fuel efficiency. To meet these requirements, the transportation electrification has been introduced in both academia and industry during last years. Electric vehicle (EV) and hybrid Electric vehicle (HEV) are two practical examples in transportation systems.
The typical power train in the EVs consists of three main parts including energy source, power electronics and an electrical motor. Regarding the machine, permanent magnet (PM) motors are the dominant choice for light duty hybrid vehicles in industry due to their higher efficiency and power density.
In order to operate the power train, the electrical machine can be supplied and controlled by a voltage source inverter (VSI). The converter is subjected to various fault types. According to the statistics, 38% of faults in a motor drive are due to the power converter. On the other side, the electrical power train should meet a high level of reliability.
Multiphase PM machines can meet the reliability requirements due to their fault-tolerant characteristics. The machine can still be operational with faults in multiple phases. Consequently, to realize a multiphase fault-tolerant motor drive, three main concepts should be developed including fault detection (FD), fault isolation and fault-tolerant control. This PhD thesis is therefore focused on FD and fault-tolerant control of a multiphase VSI.
To achieve this research goal, the presented FD and control methods of the power converter are thoroughly investigated through literature review. Following that, the operational condition of the multiphase converter supplying the electrical machine is studied.
Regarding FD methods in multiphase, three new algorithms are presented in this thesis. These proposed FD methods are also embedded in new fault-tolerant control algorithms. At the first step, a novel model based FD method is proposed to detect multiple open switch faults. This FD method is included in the developed adaptive proportional resonant control algorithm of the power converter. At the second step, two signal based FD methods are proposed. Fault-tolerant control of the power converter with the conventional PI controller is discussed. Furthermore, the theory of SMC is developed. At the last step, finite control set (FCS) model predictive control (MPC) of the five-phase brushless direct current (BLDC) motor is discussed for the first time in this thesis. A simple FD method is derived from the control signals. Inputs to all developed methods are the five-phase currents of the motor.
The theory of each method is explained and compared with available methods. To validate the developed theory at each part, FD algorithm is embedded in the fault-tolerant control algorithm. Experimental results are conducted on a five-phase BLDC motor drive. The electrical motor used in the experimental results has an in-wheel outer rotor structure. This motor is suitable for electric vehicles. At the end of each part, the remarkable points and conclusions are presentedHay una creciente demanda de vehículos con menor impacto ambiental y una mayor eficiencia de combustible. Para cumplir estos requisitos, la electrificación del transporte se ha introducido en la academia y la industria en los últimos años. Vehículos eléctricos y vehículos eléctricos híbridos son dos ejemplos prácticos en los sistemas de transporte.
El tren de potencia típico en los vehículos eléctricos se compone de tres partes principales, incluyendo la fuente de energía, la electrónica de potencia y un motor eléctrico. En cuanto a la máquina, de imán permanente motores son la opción dominante para vehículos híbridos ligeros en la industria debido a su mayor eficiencia y densidad de potencia.
Con el fin de operar el tren de potencia, la máquina eléctrica se puede suministrar y controlado por un inversor de fuente de tensión. El convertidor se somete a diversos tipos de fallos. Según las estadísticas, 38 % de las fallas en un motor se deben al convertidor de potencia. Por otro lado, el tren de potencia eléctrica debe cumplir con un alto nivel de fiabilidad.
Máquinas multifase PM pueden cumplir con los requisitos de fiabilidad debido a sus características de tolerancia a fallos. La máquina puede seguir siendo operativo con fallas en múltiples fases. En consecuencia, para realizar una unidad de motor de alta disponibilidad de múltiples fases, tres conceptos principales deben desarrollarse incluyendo la detección de fallos, el aislamiento de fallas y control tolerante a fallos. Por tanto, esta tesis doctoral se centra en la FD y control tolerante a fallos de un VSI multifase.
Para lograr este objetivo la investigación, los productos alimenticios y bebidas y métodos de control que se presentan del convertidor de potencia se investigan a fondo a través de revisión de la literatura. Después de eso, se estudió la condición operativa del convertidor de múltiples el suministro de la máquina eléctrica.
En cuanto a los métodos de FD en múltiples fases, tres nuevos algoritmos se presentan en esta tesis. Estos métodos FD propuestas también están integrados en los nuevos algoritmos de control con tolerancia a fallos. En el primer paso, se propone un método FD modelo novela basada detectar fallas múltiples del interruptor abierto. Este método FD está incluido en el algoritmo de control adaptativo desarrollado proporcional resonante del convertidor de potencia. En el segundo paso, se proponen dos métodos FD señal basada. Se discute el control tolerante a fallos del convertidor de potencia con el controlador PI convencional. Además, la teoría de la SMC se desarrolla. En el último paso, el control conjunto finito modelo de control predictivo del motor de cinco fases sin escobillas de corriente continua se discutió por primera vez en esta tesis. Un método FD sencilla se deriva de las señales de control. Las entradas a todos los métodos desarrollados son las corrientes de cinco de fase del motor.
La teoría de cada método se explica y se compara con los métodos disponibles. Para validar la teoría desarrollada en cada parte, FD algoritmo está incorporado en el algoritmo de control tolerante a fallos. Los resultados experimentales se llevan a cabo en una unidad de motor BLDC de cinco fases. El motor eléctrico usado en los resultados experimentales tiene una estructura de rotor exterior en las cuatro ruedas. Este motor es adecuado para los vehículos eléctricos. Al final de cada parte, se presentan los puntos notables y conclusione
Identification of loss models from measurements of the magnetic properties of electrical steel sheets
Numerical simulations of electrical machines require good knowledge of the magnetic properties of the materials they are made of. The magnetic cores of these machines are made of electrical steel sheets, the magnetic properties of which are nonlinear and hysteretic. Moreover, the behavior of the magnetic flux density and the magnetic field strength of such materials depends on the form of the supply.
In the Laboratory of Electromechanics, there are several projects which aim to model correctly the behavior of the electrical steel sheet (hysteresis, stress-dependency, losses, etc.) when used in electrical machines. For this purpose, numerical models are developed and built in an in-house finite element program package. However, knowledge of the material properties and the parameters of loss models are necessary and needs to be measured. This work is proposed to measure the magnetization curves and specific losses of an electrical steel sheet. The measurements were carried out using a device specially designed for this purpose and adequate programs for field control. The measurements were conducted under rotating and alternating magnetic fields at different fundamental frequencies and amplitudes. The results of the measurements consisted of a large amount of data that has been analyzed, processed and presented in an appropriate manner. Moreover, the parameters of the loss models were estimated from the measurements through identification procedures that have been written and constructed in MATLAB software. The conclusions of this work provide the basis for a better understanding of the parameters needed to improve loss models
Power meter based on Red Pitaya developement system
V zadnjem času lahko opazimo veliko porast nelinearnih bremen, ki v tokokrogih povzročajo višje harmonske komponente, le-te so v splošnem nezaželene in škodljive. Velik poudarek se zato daje na analizo razmer v takšnih tokokrogih.
Vse dostopnejši in zmogljivejši postajajo razvojni sistemi. Eden takšnih je Red Pitaya, ki je integrirano merilno vezje z odprtokodno programsko opremo. V nalogi je predstavljen postopek razvoja aplikacije analizatorja električne moči z Red Pitayo.
V drugem poglavju so podane različne definicije veličin v tokokrogih z nesinusnimi razmerami. V tretjem poglavju so podani in primerjani postopki za merjenje frekvence, efektivne vrednosti ter faznega premika med tokom in napetostjo. V četrtem poglavju je predstavljena izbrana razvojna platforma in postopek razvoja novih aplikacij za njo. V petem poglavju je predstavljena izdelana aplikacija in implementacija izbranih algoritmov. Za analizo so izbrani postopki diskretne Fouriereve transformacije. V šestem poglavju je zmogljivost izdelane aplikacije primerjana z laboratorijskim instrumentom.
Rezultati meritev z razvito aplikacijo so zadovoljivo točni, izpolnjeni so tudi zadani cilji, saj je aplikacija enostavna za uporabo in omogoča dober pregled razmer v tokokrogu.Non-linear loads are responsible for producing unwanted higher current harmonics in power systems. Because they are becoming increasingly more common, there is currently high emphasis given on precision power analysis.
Development systems are also becoming more powerful and accessible. One of those is Red Pitaya, which is an open-source-software measurement tool. In this thesis the process of developing power analyzer application for Red Pitaya is presented.
Definitions for electrical power in nonsinusoidal conditions are listed in second chapter. In third chapter different procedures for measuring frequency, RMS value and phase difference of voltage and current are compared. In fourth chapter process of developing new applications and selected development platform is presented. In fifth chapter implementation of selected algorithms and developed application are presented. Discrete Fourier transform algorithms were selected for power analysis. Performance of developed application is compared with precision laboratory instrument in chapter six.
Performance of developed application meets objectives because it is satisfactory accurate, easy to use and provides good overview of conditions in measured system
Electrical impedance spectroscopy for real-time monitoring of the life cycle of graphene nanoplatelets filters for some organic industrial pollutants
This article proposes an approach for smart monitoring of the life cycle of innovative graphene-haled filters for water remediation in the presence of pollutants. The measurement technique is based on suitable figures of merit that analyze the time variation of the electrical impedance frequency spectrum. The proposed study considers the remediation of two toxic industrial pollutants, such as the acetonitrile and the 2,4-dichlorophenol. The contribution of this article is twofold. The first is the demonstration of a reliable monitoring setup that is able, for the selected use cases, to correlate in real time the behavior of the electrical impedance of the filter to its status, defined as "absence of pollutants" and/or "saturation." The second contribution is the proposal of suitable figures of merit, based on measurement of the impedance frequency spectrum, able to increase the measurement sensitivity and the reliability and to mitigate some sources of uncertainty typically associated with these kinds of setups and measurements. Results show that the proposed graphene-based filters combine very good filtering capability and high sensitivity of the electrical impedance to the considered pollutants. These results suggest further investigations with other pollutants and the potential use of this technique for the predictive maintenance of the water filters in industrial applications, by endowing the graphene filters of smart sensing devices
Electric Vehicle Powertrain Integrated Charging
Batterieelektrische Fahrzeuge benötigen ein im Fahrzeug eingebautes Ladegerät, um die Energie aus dem Wechselstromnetz für die Gleichstrom- Batterie aufzubereiten. Integriertes Laden ist eine Methode der Integration von Ladefunktionalität in die Antriebsstrangkomponenten, welche während des Parkens außer Betrieb sind, mit dem Ziel, Kosten, Gewicht und Volumen des Ladegerät zu sparen. Das Laden ohne die Sicherheitsmaßnahme einer galvanischen Trennung im Ladegerät ist möglich mit zusätzlichen Maßnahmen gegen elektrischen Schlag, z.B. mit einer Fehlerstromerkennung und entsprechenden Trenneinrichtung. Im Stand der Technik wurden 33 integrierte Ladekonzepte gefunden und bezüglich Antriebsstrangnutzung, benötigte Komponenten, Drehmoment der elektrischen Maschine und Wirkungsgrad verglichen.
Im Rahmen dieser Arbeit wird ein neues galvanisch getrenntes integriertes Ladekonzept beschrieben, mit dem Ziel, die Effizienz zu verbessern und gleichzeitig auftretendes Drehmoment in der Maschine zu vermeiden. Der Antriebsstrang wird als DC/DC-Wandler mit der elektrischen Maschine als Transformator im Stillstand genutzt. Berechnungen zeigen eine maximale Effizienz von 88%. Ansätze zur Verbesserung des Wirkungsgrads und zur Integration des Energieflusses im Bordnetz werden in dieser Arbeit vorgeschlagen und diskutiert. Allerdings muss der Rotorkäfig geöffnet werden, um ein Drehmoment während des Laden zu vermeiden. Dies stellt einen ähnlichen Aufwand dar wie die Darstellung eines separaten Ladegeräts. Somit ist dieses Konzept aus heutiger Sicht wegen niedriger Effizienz und hoher Kosten gegenüber einem separaten Ladegerät nicht konkurrenzfähig.
Zwei Ladekonzepte ohne galvanische Trennung, die eine sechsphasige elektrische Maschine als in Serie geschaltete Hoch- und Tiefsetzsteller nutzen, werden im Rahmen der Arbeit vorgestellt und bezüglich der benötigten Komponenten, der Effizienz und des Drehmoments des Maschine ausgearbeitet. Die Antriebsstrangverluste werden für die Ladebedingungen mit Gleichströmen analysiert, basierend auf neuen Materialcharakterisierungen für die angewendete Belastung. Es wurden Wirkungsgrade bis zu 93% demonstriert und auch in theoretischen Berechnungen mit einer maximalen Abweichung von ±1% zum experimentellen Befund bestätigt. Zum Schutz gegen elektrischen Schlag bei nicht isolierten Ladekonzepten werden drei Konzepte für eine Fehlerstrommessung präsentiert und anhand von Messergebnissen analysiert. Siliziumkarbid-Inverter-Technologien zeigen in Kombination mit diesen Ladekonzepten Wirkungsgrade, die vergleichbar zu herkömmlichen separaten Ladegeräten sind, und weisen dabei deutlich geringere Kosten auf
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