298 research outputs found

    Improving multiphase induction-heating systems: several configurations and resonant control show promise

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    This article presents a new configuration for multiphase induction-heating (IH) systems and their control schemes. Instead of using separate voltage inverters to supply the required current to the inductors in each phase, we specifically configured the inverters to reduce the number of power switches. A modification of the inverter-setting parameters ensured the proper operation of the system. We obtained the best references through a specific optimization procedure and tested several solutions for neutral current minimization, including a new arrangement of the coils. In addition, proportional-resonant (PR) controllers allowed us to achieve current control in the different phases. We developed the application on a reduced-power, three-phase coupled resonant test bench, which provided simulation and experimental results

    A new space-vector-modulation algorithm for a three-level four-leg NPC inverter

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    For power conversion systems interfaced to 4-wire supplies, four-leg converters have become a standard solution. A four-leg converter allows good compensation of zero-sequence harmonics and full utilization of the dc-link voltage. These are very important features when unbalanced and/or non-linear loads are connected to the system. This paper proposes a 3D-SVM algorithm and provides a comprehensive analysis of the algorithm implemented on a three-level, four-leg NPC converter. The algorithm allows a simple definition of the different switching patterns and enables balancing of the dc-link capacitor voltages using the redundancies of the converter states. A resonant controller is selected as the control strategy to validate the proposed SVM algorithm in a 6kW experimental rig

    Power Electronics in Renewable Energy Systems

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    Advanced Energy Harvesting Technologies

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    Energy harvesting is the conversion of unused or wasted energy in the ambient environment into useful electrical energy. It can be used to power small electronic systems such as wireless sensors and is beginning to enable the widespread and maintenance-free deployment of Internet of Things (IoT) technology. This Special Issue is a collection of the latest developments in both fundamental research and system-level integration. This Special Issue features two review papers, covering two of the hottest research topics in the area of energy harvesting: 3D-printed energy harvesting and triboelectric nanogenerators (TENGs). These papers provide a comprehensive survey of their respective research area, highlight the advantages of the technologies and point out challenges in future development. They are must-read papers for those who are active in these areas. This Special Issue also includes ten research papers covering a wide range of energy-harvesting techniques, including electromagnetic and piezoelectric wideband vibration, wind, current-carrying conductors, thermoelectric and solar energy harvesting, etc. Not only are the foundations of these novel energy-harvesting techniques investigated, but the numerical models, power-conditioning circuitry and real-world applications of these novel energy harvesting techniques are also presented

    Advance control of multilevel converters for integration of distributed generation resources into ac grid

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    Premi extraordinari doctorat curs 2011-2012, àmbit d’Enginyeria IndustrialDistributed generation (DG) with a converter interface to the power grid is found in many of the green power resources applications. This dissertation describes a multi-objective control technique of voltage source converter (VSC) based on multilevel converter topologies, for integration of DG resources based on renewable energy (and non-renewable energy)to the power grid. The aims have been set to maintain a stable operation of the power grid, in case of di erent types of grid-connected loads. The proposed method provides compensation for active, reactive, and harmonic load current components. A proportional-integral (PI) control law is derived through linearization of the inherently non-linear DG system model, so that the tasks of current control dynamics and dc capacitor voltage dynamics become decoupled. This decoupling allows us to control the DG output currents and the dc bus voltage independently of each other, thereby providing either one of these decoupled subsystems a dynamic response that signi cantly slower than that of the other. To overcome the drawbacks of the conventional method, a computational control delay compensation method, which delaylessly and accurately generates the DG reference currents, is proposed. The rst step is to extract the DG reference currents from the sensed load currents by applying the stationary reference frame and then transferred into synchronous reference frame method, and then, the reference currents are modi ed, so that the delay will be compensated. The transformed variables are used in control of the multilevel voltage source converter as the heart of the interfacing system between DG resources and power grid. By setting appropriate compensation current references from the sensed load currents in control circuit loop of DG link, the active, reactive, and harmonic load current components will be compensated with fast dynamic response, thereby achieving sinusoidal grid currents in phase with load voltages while required power of loads is more than the maximum injected power of the DG resources. The converter, which is controlled by the described control strategy, guarantees maximum injection of active power to the grid continuously, unity displacement power factor of power grid, and reduced harmonic load currents in the common coupling point. In addition, high current overshoot does not exist during connection of DG link to the power grid, and the proposed integration strategy is insensitive to grid overload.La Generació Distribuïda (DG) injectada a la xarxa amb un convertidor estàtic és una solució molt freqüent en l'ús de molts dels recursos renovables. Aquesta tesis descriu una técnica de control multi-objectiu del convertidor en font de tensió (VSC), basat en les topologies de convertidor multinivell, per a la integració de les fonts distribuïdes basades en energies renovables i també de no renovables.Els objectius fixats van encaminats a mantenir un funcionament estable de la xarxa elèctrica en el cas de la connexió de diferents tipus de càrregues. El mètode de control proposat ofereix la possibilitat de compensació de les components actives i reactives de la potencia, i les components harmòniques del corrent consumit per les càrregues.La llei de control proporcional-Integral (PI) s’obté de la linearització del model inherentment no lineal del sistema, de forma que el problema de control del corrent injectat i de la tensió d’entrada del convertidor queden desacoblats. Aquest desacoblament permet el control dels corrents de sortida i la tensió del bus de forma independent, però amb un d’ells amb una dinàmica inferior.Per superar els inconvenients del mètode convencional, s’usa un retard computacional, que genera les senyals de referència de forma acurada i sense retard. El primer pas es calcular els corrents de referència a partir de les mesures de corrent. Aquest càlcul es fa primer transformant les mesures a la referència estacionaria per després transformar aquests valors a la referència síncrona. En aquest punt es on es poden compensar els retards.Les variables transformades son usades en els llaços de control del convertidor multinivell. Mitjançant aquests llaços de control i les referències adequades, el convertidor és capaç de compensar la potencia activa, reactiva i els corrents harmònics de la càrrega amb una elevada resposta dinàmica, obtenint uns corrents de la xarxa de forma completament sinusoïdal, i en fase amb les tensions.El convertidor, controlat amb el mètode descrit, garanteix la màxima injecció de la potencia activa, la injecció de la potencia reactiva per compensar el factor de potencia de la càrrega, i la reducció de les components harmòniques dels corrents consumits per la càrrega. A més, garanteix una connexió suau entre la font d’energia i la xarxa. El sistema proposat es insensible en front de la sobrecarrega de la xarxaAward-winningPostprint (published version

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

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    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

    Modular platform for research in microgrids

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    The present Ph.D. thesis has been developed following an Industrial Ph.D. program and verses on developing a commercial piece of equipment for teknoCEA, a spin-off company from CITCEA-UPC. The thesis is centered on developing power electronics-based emulation systems for research in microgrids. Lately, the use of power electronics-based emulation systems is drawing substantial attention in the field of microgrids because their characteristics substantially facilitate research in laboratory facilities. First, the suitability of different topologies for implementing an emulation platform is analyzed. The focus is set on the topologies adjustability to implement various types of emulation systems. The analysis determines the most appropriate number of legs for the platform. A comparative analysis is done between two-level and multi-level topologies to determine their suitability based on different aspects. Moreover, the analysis confirms the usefulness of wide-bandgap semiconductors for this type of application. Next, a control structure is proposed together with its implementation in a low-cost microcontroller based on a modular software architecture. The control strategy based on fractional proportional resonant controllers for AC emulation systems provides a control system with high control bandwidth while keeping a low computational cost. The control strategy for DC emulation systems is provided to reach a fast transient response and immunity to external disturbances, which is key for good emulation of electric systems. The modular software architecture provides a software framework easily adjustable to the needs of multiple emulation systems. That allows the implementation of the multiple control strategies with minimum changes. Additionally provides a graphical representation of the software architecture from a static and dynamic point of view. Last, the reliability of the proposed platform is assessed based on the reliability curves provided in the literature. The reliability analysis is centered on the semiconductors and capacitors. It provides evidence that emulation systems typical currents and voltages clearly affect their reliability. For the capacitors reliability assessment, a thermal modeling methodology is proposed to overcome the limitations of standard approximations. The methodology is based on anisotropic modeling of the capacitor winding. Finally, the reliability analysis establishes the guidelines to assess the platform reliability if a given mission profile is provided.La present tesi doctoral s'ha dut a terme seguint un programa de doctorat industrial. La tesi exposa el desenvolupament d'un equip comercial per a teknoCEA, una spin-off del CITCEA-UPC. La tesi es centra en el desenvolupament d'emuladors basats en electrònica de potència per recerca en el camp de les microxarxes. Darrerament, l'ús d'emuladors s'ha estès ja que les seves característiques faciliten molt la recerca en laboratoris. En primer lloc, s'analitza la idoneïtat de diferents topologies per implementar una plataforma d'emulació. El focus recau en la capacitat de diferents topologies per ajustar-se a la implementació de múltiples sistemes d'emulació. L'anàlisi determina el número òptim de branques. Un anàlisi comparatiu entre topologies dos nivells i multinivell permet determinar-ne la idoneïtat en funció de diferents aspectes. A continuació, es proposa una estructura de control juntament amb la seva implementació en un microcontrolador de baix cost a partir d'una arquitectura de programari modular. L'estratègia de control basada en controladors FPR (fractional proportional resonant) per a emuladors de corrent altern, proporciona un sistema de control amb un gran ample de banda amb un baix cost computacional. L'estratègia de control proposada per emuladors de corrent continu proporciona una resposta transitòria ràpida i elevada immunitat a pertorbacions, aspecte clau per a una bona emulació de sistemes elèctrics. L'arquitectura de programari modular proporciona un marc de programari fàcilment ajustable a les necessitats de múltiples emuladors. Això permet la implementació de les múltiples estratègies de control amb canvis mínims. A més, ofereix una representació gràfica de l'arquitectura del programari tant des d'un punt de vista estàtic com dinàmic. Finalment, s'avalua la fiabilitat de la plataforma a partir de les corbes de fiabilitat disponibles a la bibliografia científica. L'anàlisi es centra en els semiconductors i condensadors i proporciona evidència que els corrents i les tensions típics en emuladors afecten la seva fiabilitat. Per a l'avaluació de la fiabilitat dels condensadors, es proposa una metodologia de modelització tèrmica que permet superar les limitacions de les metodologies emprades típicament en la bibliografia científica. La metodologia es basa en el modelatge del bobinat del condensador com un element anisòtrop. Per últim, l'anàlisi de fiabilitat estableix les pautes per avaluar la fiabilitat de la plataforma en el cas que es proporcioni un perfil d'operació determinat.Postprint (published version

    Design and Implementation of a Multi-port Solid State Transformer for Flexible Der Integration

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    Conventional power system includes four major sections, bulk generation, transmission network, distribution network, and loads. The main converter in the conventional electric grid is the low-frequency passive transformer providing galvanic isolation and voltage regulation for various voltage zones. In this configuration, small-scale renewable energy resources are generally connected to the power system at low voltage zones or inside microgrids. Recent developments in the design of power electronic elements with higher voltage and power ratings and medium/high frequency enable making use of solid state transformer at different voltage levels in the distribution system and microgrid design. In this work, the concept of a Multi-Port Solid State Transformer (MPSST) for distribution network application is introduced. MPSST provides a compact, integrated and galvanically isolated multi-port node for microgrid and distribution applications and reduces the number and size of the converters in the concept of efficient smart distribution systems. A new architecture for distribution systems integrating distributed generation (DG) at different voltage zones using MPSST is proposed, studied and simulated. The developed concept interconnects different voltage types and levels using one compact converter with a centralized control logic. In addition, a general method is developed and mathematically analyzed to provide active and reactive power support using the local alternative power sources through MPSST. MPSST is a combination of high-frequency power electronic converters and a multi-winding high-frequency transformer. The total size of the MPSST is dramatically smaller than the conventional transformers with the same voltage and power rating. MPSST also enables online measurement and data collection and active control of the parameters at all connected ports. A two-layer control technique, which is a combination of duty cycle control and a modified phase shift control is used to regulate the voltage and power flow of the different ports. Since the converter has several independent and dependent variables, a transfer matrix between variables of the converter is calculated and used in system control. Finally, the implementation process of the converter including, component selection, modeling, software development, and transformer design is presented and the first prototype of the MPSST is developed and tested in the lab. Chapter five includes the hardware test results and the discussion and comparison of the results with the design expectations

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

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    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

    A Simple Braking Method for Six-phase Induction Motor Drives with Unidirectional Power Flow in the Base-speed Region

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    Induction motor drives supplied from diode front-end rectifiers are commonly used in industrial applications due to their low cost and reliability. However, the two-quadrant operation of such a topology makes the regenerative braking impossible. Braking resistors can be used to dissipate the braking power and provide enhanced braking capability, but additional hardware is then necessary. Alternatively, the braking power can be dissipated within the inverter/motor by control software reconfiguration. In this scenario, the additional degrees of freedom of multiphase drives can be used to increase the system losses without disturbing the flux and torque production. Experimental results confirm the possibility to enhance the braking capability of six-phase drives with only few changes in the control scheme
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