A Study on Harmonic Reduction Scheme by the Advanced Auxiliary Voltage Supply

Diode rectifiers are very popular in industry. However, they include large low-order harmonics in the input current and do not satisfy harmonic current content restrictions. To reduce the harmonics to the power system, several methods have been introduced. It is heavy and expensive solution to use passive filters as the solution for high power application. Another solution for the harmonic filter is utilization of active filter, but is too expensive solution. Diode rectifiers with configurations using switching device have been introduced, but are very complicated. The combined 12-pulse diode rectifier with the square wave-auxiliary supply has been introduced. It has the advantages that auxiliary circuit is simple and inexpensive compared to other strategies. The advanced wave auxiliary voltage supply in this thesis is presented as a new solution. It shows the improved result for reducing THD compared to the case inserting a single phase square wave auxiliary voltage supply. Especially, for the case with a low load factor, it shows a outstanding improvement of THD. Theoretical analysis of the combined 12-pulse diode rectifier with the advanced auxiliary supply is presented and control methods of the auxiliary supply is proposed. The reduction in the input current harmonics is verified by simulation using software PSIM and experiment.제 1 장 서 론 제 2 장 고조파의 발생과 영향 2.1 고조파의 발생 2.1.1 고조파의 정의 2.1.2 고조파의 발생 2.1.3 고조파의 해석 2.2 고조파의 영향 2.2.1 발전장치 2.2.2 변압기 2.2.3 유도전동기 2.2.4 가변속 구동장치(variable speed drives) 2.2.5 조명장치 2.2.6 무정전 전원장치 2.2.7 전선(電線Cable) 2.2.8 계측장치 2.2.9 전화기 2.2.10 회로차단기 2.2.11 릴레이 2.2.12 커패시터 제 3 장 고조파 완화 및 저감 대책 3.1 3상 3선 배선시스템 3.1.1 위상이동(phase shifting) 3.1.2 능동필터(active filter) 3.2 3상 4선 배선시스템 3.2.1 zero sequence 변압기(zig-zag transforme 3.2.2 능동필터(active filter) 3.3 3상 AC 및 DC 구동장치용 표준 리액터 3.3.1 AC line 리액터 3.3.2 DC bus 리액터 3.3.3 AC line 리액터 & DC bus 리액터 3.4 3상 AC 및 DC 구동장치용 특수 리액터 3.4.1 광폭필터(wide spectrum filter) 3.4.2 이중리액터(duplex reactors) 3.5 수동 L-C필터(passive L-C filters) 3.6 위상이동 변압기(phase shifting transformer) 3.7 전자필터(electronic filter) 3.7.1 능동필터(active filter) 3.7.2 능동-수동필터(hybrid active-passive filter) 제 4 장 본 논문에서 제안하는 고조파 저감방식 4.1 기본개념 4.2 AVS(보조 전원장치)의 삽입 4.3 AVS의 개요 4.4 AVS의 동작원리 및 해석 제 5 장 시뮬레이션 및 검토 5.1 컴퓨터 시뮬레이션 다이어그램 5.2 시뮬레이션 결과 5.2 시뮬레이션 결과 검토 제 6 장 실험 및 검토 6.1 실험장치의 구성 6.2 실험 결과 검토 제 7 장 결 론 참고문

Design and Analysis of Stationary Reference Frame Controllers for Active Front End Converter

An active front end converter along with its associated control system has been the scope of this thesis. Relavant literature has been considered for identifying the operation and possible system implementations of this system with emphasis on its control. Different current- and voltage controllers have been studied and designed for simulation purposes. A discretized simulation model has been used to aid controller design. This simulation model has been used to investigate and compare the performance of the different controllers when employed in the stationary reference frame

Power Quality Improvement of Distributed Generation Integrated Network with Unified Power Quality Conditioner.

With the increased penetration of small scale renewable energy sources in the electrical distribution network, maintenance or improvement of power quality has become more critical than ever where the level of voltage and current harmonics or disturbances can vary widely. For this reason, Custom Power Devices (CPDs) such as the Unified Power Quality Conditioner (UPQC) can be the most appropriate solution for enhancing the dynamic performance of the distribution network, where accurate prior knowledge may not be available. Therefore, the main objective of the present research is to investigate the (i) placement (ii) integration (iii) capacity enhancement and (iv) real time control of the Unified Power Quality Conditioner (UPQC) to improve the power quality (PQ) of a distributed generation (DG) network connected to the grid or microgrid

Harmonic domain modelling and analysis of the electrical power systems of onshore and offshore oil and gas field /platform

This thesis first focuses on harmonic studies of high voltage cable and power line, more specifically the harmonic resonance. The cable model is undergrounded system, making it ideal for the harmonics studies. A flexible approach to the modelling of the frequency dependent part provides information about possible harmonic excitations and the voltage waveform during a transient. The power line is modelled by means of lumped-parameters model and also describes the long line effect. The modelling depth and detail of the cable model influences the simulation results. It compares two models, first where an approximate model which make use of complex penetration is used and the second where an Bessel function model with internal impedance is used. The both models incorporate DC resistance, skin effect and their harmonic performances are investigated for steady-state operating condition. The methods illustrate the impotance of including detailed representation of the skin effect in the power line and cable models, even when ground mode exists. The cable model exhibit lower harmonics comparable to overhead transmission lines due to strong influence of the ground mode. Due to the application of voltage source converter (VSC) technology and pulse width modulation (PWM) the VSC-HVDC has a number of potential advantages as compared with CSC-HVDC, such as short circuit current reduction, independent control of active power and reactive power, etc. With these advantages VSC-HVDC will likely be widely used in future oil and gas transmission and distribution systems. Modular multilevel PWM converter applies modular approach and phase-shifted concepts achieving a number of advantages to be use in HVDC power transmission. This thesis describes the VSC three-phase full-bridge design of sub-module in modular multilevel converter (MMC). The main research efforts focus on harmonic reduction using IGBTs switches, which has ON and OFF capability. The output voltage waveforms multilevel are obtained using pulse width modulation (PWM) control. The cascaded H-bridge (CHB) MMC is used to investigate for two-level, five-level, seven-level, nine-level converter staircase waveforms. The results show that the harmonics are further reduced as the sub-module converter increases. The steady-state simulation model of the oil platform for harmonic studies has been developed using MATLAB. In order to save computational time aggregated models are used. The load on the platforms consists of passive loads, induction motors, and a constant power load representing variable speed drives on the platforms. The wind farm consists of a wind turbine and an induction machine operating at fixed speed using a back-to-back VSC. Simulations are performed on system harmonics that are thought to be critical for the operation of the system. The simulation cases represent large and partly exaggerated disturbances in order to test the limitations of the system. The results show low loss, low harmonics, and stable voltage and current. With the developments of multilevel VSC technology in this thesis, multi-terminal direct current (MTDC) systems integrating modular multilevel converters at all nodes may be more easily designed. It is shown that self-commutated Voltage Source Converters (VSC) is more flexible than the more conventional Current Source Converter (CSC) since active and reactive powers are controlled independently. The space required by the equipment of this technology is smaller when compared to the space used by the CSCs. In addition, the installation and maintenance costs are reduced. With these advantages, it will be possible for several oil and gas production fields connected together by multi-terminal DC grid. With this development the platforms will not only share energy from the wind farms, but also provide cheaper harmonic mitigation solutions. The model of a multi-terminal hypothetical power system consisting of three oil and gas platforms and two offshore wind farm stations without a common connection to the onshore power grid is studied. The connection to the onshore grid is realized through a High Voltage Direct Current (HVDC) transmissions system based on Voltage Source Converter (VSC) technology. The proposed models address a wide array of harmonic mitigation solutions, i.e., (i) Local harmonic mitigation (ii) semi-global harmonic mitigation and (iii) global harmonic mitigation. In addition, a computationally-efficient technique is proposed and implemented to impose the operating constraints of the VSC and the host IGBT-PWM switches within the context of the developed harmonic power flow (HPF). Novel closed forms for updating the corresponding VSC power and voltage reference set-points are proposed to guarantee that the power-flow solution fully complies with the VSC constraints. All the proposed platform models represent (i) the high voltage AC/DC and DC/AC power conversion applications under balanced harmonic power-flow scenario and (ii) all the operating limits and constraints of the nodes and its host modular converter (iii) three-phase VSC coupled IGBT-PWM switches

Contribucions a l'estudi de rectificadors no controlats m-fàsics en condicions no equilibrades per unitats TRUs o ATRUs multi polsos

Tesi amb diferents seccions retallades per drets de l'editorThis doctoral thesis has been developed to provide a new point of view and a new approach to the analysis and study of uncontrolled bridge rectifiers. The methodology developed has been generalized to extend the study to an m-phase system, applicable for both balanced and unbalanced systems. It is possible to quickly obtain an analytical formulation to calculate the average voltage for balanced systems. However, there are multiple formulations for unbalanced systems, and, in general, it is not easy to be applied. For this reason, an easy-to-apply formulation has been determined to calculate the average voltage, using the perimeter of the convex polygon defined by the ends of the phase voltages of the power supplies. As the convexity condition is necessary for its application, it has been determined that this approach is related to one of the formulas proposed by Cauchy. This formula determines the average width of a convex body, which has made it possible to relate the average width to the average voltage and the convex body to the convex polygon defined by the maximum stresses. The relationship with vision systems also has been observed. The projections and average widths in a rotation are used, for example, to determine the section of bones, veins, and muscles, which is the basis of the Computed Tomography (CT) scan. It is important to highlight the close relationship between the Couchy formula and the application to the CT scan. However, the proposed method has some differences from Cauchy's. While the Cauchy formulation applies to a body that must be derivable at all points, the proposed formulation applies to a convex polygon with no equal derivative at the vertices since the derivatives are different from the right than from the left vertex. This new method, called the Phasorial Convex Hull Method, has been published in the article "Average value of DC-link output voltage in multi-phase uncontrolled bridge rectifiers under supply voltage balance and unbalance conditions". In the demonstration of the developed method, it has been observed that the instantaneous voltage is obtained before calculating the average voltage of the DC bus. Therefore, the voltage signature at the rectifier's output allows detailed studies of behavior in the voltage sag, unbalance operation, faults, etc. This new methodology for obtaining instantaneous voltage has been titled "Shadow Projection", presented in the article "New Methodology to Calculate DC Voltage Signature in N-Phases TRUs Under Supply Voltage Sags". Because rectifiers are usually coupled to Transformers or Autotransformers, the Thesis was believed to be linked to Transformer Rectifier Units (TRUs) and Auto-Transformer Rectifier Units (ATRUs) and a patent study has been done to see how the industry has evolved, studying some configurations. Formulations have been proposed for solutions for series, parallel and / or coupling connections. The joint study of the rectifying units with the Transformer or the Autotransformer opens the study to determine the line currents on the AC side. Therefore, if the study of voltages goes from AC sources to DC load, the study of currents goes from DC side to AC side. Solutions have been proposed for the study of 12-pulse rectifiers in three-winding TRUs, and for Delta-polygonal ATRUs. This study, yet to be published, allows obtaining simple equivalent circuits for complex systems. The effect on DC voltage when there are fused diodes producing a lack of open circuit has also been studied, the proposed method allows to determine the diode or diodes that are missing and need to be replaced. In this case, the article entitled “Open-Circuit fault diagnosis and maintenance in multi-pulse parallel and series TRU topologies” has been published. The method is based on signing the DC voltage at the output of the rectifier, starting the period according to the hourly index of the transformer for 12-18 pulses.Aquesta Tesi doctoral ha estat elaborada amb l’objectiu d’aportar una nova visió i un nou enfocament a l’anàlisi i a l’estudi de rectificadors en pont no controlats. La metodologia desenvolupada s’ha generalitzat per tal d’estendre l’estudi a un sistema m-fàsic, essent aplicable tant per sistemes equilibrats com per sistemes no equilibrats. És possible obtenir de forma senzilla una formulació analítica pel càlcul de la tensió mitja per a sistemes equilibrats (igual mòdul i desfasament), però hi ha múltiples formulacions per als sistemes desequilibrats (diferent mòdul i/o desfasament), i en general d’aplicació complexa. És per aquest motiu que s’ha determinat una formulació de fàcil aplicació que permet determinar la tensió mitja amb el perímetre del polígon convex definit pels extrems de les tensions de fase de les fonts d’alimentació dividit pel número “pi”. Com per la seva aplicació, la condició de convexitat és necessària, s’ha determinat que aquest plantejament té relació amb una de les fórmules proposades per Cauchy. Aquesta formula determina l’amplada mitja d’un cos convex, i s’ha relacionat l’amplada mitja amb el voltatge mig, i el cos convex amb el polígon convex definit per les tensions màximes. També s’ha observat la relació que té amb els sistemes de visió, i com a partir de les projeccions i amplades mitges en una rotació es pot determinar per exemple la secció dels ossos, venes i muscles, que és la base del TAC. S’ha de destacar la relació estreta que hi ha amb la fòrmula de Couchy i l’aplicació al TAC. No obstant, el mètode plantejat presenta algunes diferències amb el de Cauchy. Mentre que la formulació de Cauchy s’aplica a un cos que ha de ser derivable en tots els punts, la formulació que s’ha desenvolupat s’aplica a un polígon convex que no té igual derivada en els vèrtex, ja que són diferents des de la dreta que des de l’esquerra del vèrtex. Aquest nou mètode que s’ha denominat “Phasorial Convex Hull Method” ha estat publicat a l’article titulat: “Average value of the DC-link output voltage in multi-phase uncontrolled bridge rectifiers under supply voltage balance and unbalance conditions”. En la demostració del mètode desenvolupat s’ha observat que en pas previ a obtenir la tensió mitja del bus de continua, s’obté la tensió instantània, i per tant la signatura de la tensió a la sortida del rectificador, el que obre les portes a estudis detallats del comportament davant de sots de tensió, desequilibris, faltes, etc. Aquesta nova metodologia per obtenir la tensió instantània s’ha titulat com “Shadow Projection”, que ha estat presentada en un article, amb el títol "New Methodology to Calculate DC Voltage Signature in NPhases TRUs Under Supply Voltage Sags". Els rectificadors acostumen a anar acoblats a transformadors (TRUs) o a autotransformadors (ATRUs), pel que s’ha fet un estudis de patents, analitzant com la indústria ha anat evolucionat amb l’aplicació de diferents configuracions. En aquesta Tesi s’han proposat formulacions per configuracions tant sèrie com paral·lel, i/o amb bobina d’acoblament. L’estudi conjunt de les unitats rectificadores amb el transformador o amb l’autotransformador permet determinar tant el corrent CC com els corrents de línia CA, i l’estudi de les tensions va des de les fonts de CA a la càrrega de CC. Com a exemple s’ha fet un estudi detallat de rectificadors de 12 polsos en TRUs de tres debanats, i també ATRUs Delta-poligonal. Aquest estudi, pendent de publicació, permet l’obtenció de circuits equivalents senzills per sistemes complexos. També s’ha estudiat l’efecte sobre la tensió de CC quant hi ha díodes fosos produint una falta de circuit obert, el mètode proposat permet determinar el díode o díodes que estan en falta i cal canviar-los. En aquest cas s’ha publicat l’article titulat “Open-Circuit fault diagnosis and maintenance in multi-pulse parallel and series TRU topologies”, en el que es mostra el mètode d’identificació de díodes en circuit obert, basat en la signatura de la tensió de CC a la sortida del rectificador, per a configuracions de 12 i 18 polsos. Aquest mètode d’identificació de faltes permetrà estudis més amples de manteniment amb Machine Learning.Postprint (published version

Renewable Energy

Renewable Energy is energy generated from natural resources - such as sunlight, wind, rain, tides and geothermal heat - which are naturally replenished. In 2008, about 18% of global final energy consumption came from renewables, with 13% coming from traditional biomass, such as wood burning. Hydroelectricity was the next largest renewable source, providing 3% (15% of global electricity generation), followed by solar hot water/heating, which contributed with 1.3%. Modern technologies, such as geothermal energy, wind power, solar power, and ocean energy together provided some 0.8% of final energy consumption. The book provides a forum for dissemination and exchange of up - to - date scientific information on theoretical, generic and applied areas of knowledge. The topics deal with new devices and circuits for energy systems, photovoltaic and solar thermal, wind energy systems, tidal and wave energy, fuel cell systems, bio energy and geo-energy, sustainable energy resources and systems, energy storage systems, energy market management and economics, off-grid isolated energy systems, energy in transportation systems, energy resources for portable electronics, intelligent energy power transmission, distribution and inter - connectors, energy efficient utilization, environmental issues, energy harvesting, nanotechnology in energy, policy issues on renewable energy, building design, power electronics in energy conversion, new materials for energy resources, and RF and magnetic field energy devices