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Chen, Baifeng. "High-efficiency Transformerless PV Inverter Circuits." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/56686.
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With worldwide growing demand for electric energy, there has been a great interest in exploring photovoltaic (PV) sources. For the PV generation system, the power converter is the most essential part for the efficiency and function performance. In recent years, there have been quite a few new transformerless PV inverters topologies, which eliminate the traditional line frequency transformers to achieve lower cost and higher efficiency, and maintain lower leakage current as well.
With an overview of the state-of-the-art transformerless PV inverters, a new inverter technology is summarized in the Chapter 2, which is named V-NPC inverter technology. Based this V-NPC technology, a family of high efficiency transformerless inverters are proposed and detailly analyzed. The experimental results demonstrate the validity of V-NPC technology and high performance of the transformerless inverters.
For the lower power level transformerless inverters, most of the innovative topologies try to use super junction metal oxide semiconductor field effect transistor(MOSFET) to boost efficiency, but these MOSFET based inverter topologies suffer from one or more of these drawbacks: MOSFET failure risk from body diode reverse recovery, increased conduction losses due to more devices, or low magnetics utilization. By splitting the conventional MOSFET based phase leg with an optimized inductor, Chapter 3 proposes a novel MOSFET based phase leg configuration to minimize these drawbacks. Based on the proposed phase leg configuration, a high efficiency single-phase MOSFET transformerless inverter is presented for the PV micro-inverter applications. The PWM modulation and circuit operation principle are then described. The common mode and differential mode voltage model is then presented and analyzed for circuit design. Experimental results of a 250 W hardware prototype are shown to demonstrate the merits of the proposed MOSFET based phase-le and the proposed transformerless inverter.
New codes require PV inverters to provide system regulation and service to improve the distribution system stabilization. One obvious impact on PV inverters is that they now need to have reactive power generation capability. The Chapter 4 improves the MOFET based transformerless inverter in the Chapter 3 and proposed a novel pulse width modulation (PWM) method for reactive power generation. The ground loop voltage of this inverter under the proposed PWM method is also derived with common mode and differential mode circuit analyses, which indicate that high-frequency voltage component can be minimized with symmetrical design of inductors. A 250-W inverter hardware prototype has been designed and fabricated. Steady state and transient operating conditions are tested to demonstrate the validity of improved inverter and proposed PWM method for reactive power generation, high efficiency of the inverter circuit, and the high-frequency-free ground loop voltage.
Besides the high efficiency inverter circuit, the grid connection function is also the essential part of the PV system. The Chapter 5 present the overall function blocks for a grid-connected PV inverter system. The current control and voltage control loop is then analyzed, modeled, and designed. The dynamic reactive power generation is also realized in the control system. The new PLL method for the grid frequency/voltage disturbance is also realized and demonstrate the validity of the detection and protection capability for the voltage/frequency disturbance.
At last, a brief conclusion is given in the Chapter 6 about each work. After that, future works on device packaging, system integration, innovation on inverter circuit, and standard compliance are discussed.Ph. D.
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Becker, Martin Gerhard. "Transformerless series dip/sag compensation with ultracapacitors." Thesis, Stellenbosch : University of Stellenbosch, 2004. http://hdl.handle.net/10019.1/16256.
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Thesis (MScIng)--University of Stellenbosch, 2004.ENGLISH ABSTRACT: This thesis covers the development of a transformerless series dip compensator. Of all known power quality problems, voltage dips are the greatest reason for concern. Series injection dip compensators offer the advantage of only having to compensate for the decrease in supply voltage during a dip. This results in significant reduction in converter ratings and energy storage requirements. The aim of this thesis was to take up previous developments and combine them with new technologies to maximize their functionality. The new design was implemented with ultracapacitors to offer a maintenance-free device lifespan of 20 years. As they are very expensive, a new topology was introduced in this thesis to maximize their use so that they become viable for industry. Furthermore, a new method of daisy chaining switches was introduced to minimize costs involved in controlling them. A single-phase compensator, with this new topology and the new way of controlling switches, was designed and built according to specifications stated by Eskom. This ultracapacitor-based dip compensator was tested with a dip generator, developed by the University of Stellenbosch for different load currents. The experimental results confirmed simulations made with identical parameters. This thesis presents a reliable and cost effective solution for dip compensation.
AFRIKAANSE OPSOMMING: Hierdie tesis dek die ontwikkeling van ’n transformatorlose duik kompenseerder. Van al die bekende toevoerkwaliteit probleme wek duike in die spanning die meeste kommer. Serie-injeksie kompenseerders het die voordeel dat hulle net kompenseer vir die verlies in die toevoerspanning tydens die duik. Dit het ’n beduidende vermindering in die omsetterkenwaardes en energiestoorvereistes tot gevolg. Hierdie tesis mik om vorige soortgelyke ontwikkelings op te volg en te verbeter met nuwe tegnologie om die funktionliteit te maksimeer. Die ontwerp is geimplementeer met ultrakapasitore wat die onderhoudsvrye toestel ‘n leeftyd van 20 jaar toelaat. Omdat ultrakapasitore so duur is moes ‘n nuwe topologie onwikkel word om die gebruik van ultrakapasitore meer ekonomies aantreklik te maak. Daar is ook ‘n nuwe manier van skakelaar beheer ontwikkel wat toelaat dat baie skakelaars oor een optise veesel beheer kan word. ‘n Enkel fase dip kompensaeerder is toe onwikkel en gebou volgens Eskom se spesifikasies. Die ultrakapasitor gebaseerde omsetter is getoets met ‘n dip generator wat deur die Universiteit van Stellenbosch ontwikkel is. Die praktiese resultate bevestig die simulasies wat gedoen is met dieselfe parameters. Hierdie tesis lei tot ‘n betroubaare en ekonomiese oplossing vir duik kompensasie.
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Visser, Abraham Johannes. "Transformerless series dip/sag compensation with a multilevel cascaded inverter." Thesis, Stellenbosch : Stellenbosch University, 2001. http://hdl.handle.net/10019.1/52592.
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Thesis (MScEng)--University of Stellenbosch, 2001.ENGLISH ABSTRACT: This thesis covers the development of a multilevel cascaded inverter for the purpose of costeffective transformerless series dip compensation. Of all known power quality problems, voltage dips are the greatest reason for concern. Dips/sags occur more frequently than outages and therefore tend to be more costly for industry as modem technical equipment becomes all the more sensitive to the quality and reliability of supply. A number of devices already exist to compensate for this problem, but the cost of most of these systems does not always justify the financial losses they compensate for. All of these systems are using transformers and/or large filter components that contribute to the size, price and losses to quite a large extent. Series injection dip compensators offer the advantage of only having to compensate for the decrease in supply voltage during a dip. This results in a significant reduction in the converter ratings and energy storage requirements compared to conventional uninterruptible power supplies or shunt injection power quality devices. Existing inverter topologies, including multilevel inverters, were therefore studied and compared as possible solutions for cost-effective transformerless series dip compensation. On the basis of these considerations the multilevel cascaded inverter seems to be the most cost-effective option. The relatively low harmonic content of its unfiltered output also eliminates the need for a large output filter. A single-phase dip compensator, with this topology, was designed and built according to specifications stated by Eskom, the main utility in South Africa. Batteries as energy storage and automotive MOSFETs as switching components, proved to be most cost-effective options for the specified power ratings. Control algorithms for dip compensation with the multilevel inverter were also developed. Some of these algorithms are based on existing techniques, but two new algorithms were also developed to implement force commutation of the thyristors and to share the power dissipation in the dip compensator. Simulations indicated that these algorithms could be suitable and sufficient for their application. This dip compensator with its control algorithms was tested with a dip generator, developed at the University of Stellenbosch, for different types of loads. The experimental results confirmed the simulations and showed a very good performance for the specified conditions. An optimised design of this dip compensator will make it a cost-effective solution for dip compensation.
AFRIKAANSE OPSOMMING: Hierdie tesis dek die ontwikkeling van 'n multivlakwisselrigter, in kaskade, met koste-effektiewe transformatorlose duik kompensasie as mikpunt. Van al die bekende toevoerkwaliteit probleme wek duike in die spanning die meeste kommer. Duike kom meer gereeld voor as kragonderbrekings en neig daarom om 'n groter onkoste te wees vir die industrie soos wat moderne tegnologiese toerusting al hoe meer sensitief raak vir die kwaliteit en betroubaarheid van die toevoer. 'n Aantal toestelle wat vir hierdie probleem kompenseer bestaan reeds, maar die koste van hierdie stelsels regverdig nie altyd die finansiële verliese wat hulle moet elimineer nie. Al hierdie stelsels gebruik transformators en/of groot filter komponente wat grootliks bydra tot die grootte, prys en verliese van hierdie stelsels. Serie-injeksie kompenseerders het die voordeel dat hulle net kompenseer vir die verlies in die toevoerspanning tydens die duik. Dit het 'n beduidende vermindering in die omsetterkenwaardes en energiestoorvereistes tot gevolg in vergelyking met ononderbroke kragbronne (UPS) of newe-injeksie toevoerkwaliteit toestelle. Daarom IS bestaande wisselrigtertopologië, insluitende multivlakwisselrigters, bestudeer en vergelyk as moontlike oplossings vir koste-effektiewe serie duik-kompensasie. Van al hierdie moontlikhede lyk die multivlakwisselrigter, in kaskade, na die mees koste-effektiewe opsie. Die relatiewe lae harmoniese inhoud van sy ongefilterde uittree elimineer die behoefte aan 'n groot uittreefilter. 'n Enkelfase duik kompenseerder, met hierdie topologie, is ontwerp en gebou volgens die spesifikasies wat vasgestel is deur Eskom, die hoof elektriese kragvoorsiener in Suid-Afrika. Dit het geblyk dat batterye, en MOSFETte uit die motorbedryf, die mees koste-effektiewe opsies bied vir onderskeidelik die energiestoor en skakelkomponente. Beheeralgoritmes VIr duik kompensasie met die multivlakwisselrigter is ook ontwikkel. Sommige van hierdie algoritmes is gebaseer op bestaande tegnieke, maar twee nuwe algoritmes is ook ontwikkel vir die kommutering van die tiristors en die deling van die drywingsverkwisting in die duik kompenseerder. Simulasies dui aan dat hierdie algoritmes geskik en voldoende kan wees vir hulle toepassing. Hierdie duik kompenseerder met sy beheeralgoritmes is getoets vir verskillende tipes laste met 'n duikgenerator wat ontwikkel is by die Universiteit van Stellenbosch. Die eksperimentele resultate bevestig dit wat verkry is uit die simulasies en wys 'n goeie werkverrigting vir die gespesifiseerde kondisies. 'n Geoptimeerde ontwerp van hierdie duik kompenseerder sal dit 'n koste-effektiewe oplossing maak vir duik kompensasie.
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Sharma, Ronald. "Single-phase transformerless unipolar switched inverters for utility-connected photovoltaic applications." University of Southern Queensland, Faculty of Engineering and Surveying, 2007. http://eprints.usq.edu.au/archive/00004120/.
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[Abstract]: The disadvantages of using solar energy are its capital cost (which is about A$6/W), in comparison to that of conventional sources of energy (which is about A$1.80/W), and its conversion efficiency, which in commercially available Photovoltaic (PV) systems is less than 20%. Consequently, for utility connected PV generation to become a viable alternative energy source, its efficiency needs to be improved, its cost reduced, and the quality of power supplied by the inverters must meet stringent standards.This dissertation describes the research work carried out to optimise the conversion efficiency and to minimise the cost of a single-phase, hysteretic current controlunipolar switched inverter system, for use as an interface between solar panels and the grid network. The 1 kW (peak power) PV system being considered does not useenergy storage batteries and the inverter output is connected to the grid supply without the use of a power transformer. Improvements in the efficiency of such aninverter system often come at the expense of the quality of its output power and an increase in cost. However, in the proposed inverter system the harmonics of theoutput current has been improved without compromising its overall efficiency or its cost. An improvement in power quality has been achieved using a novel AC splitinductorfilter network that reduces electromagnetic interference, prevents unwanted operation of the inverter switches, attenuates switching frequency harmonics,minimises low frequency harmonics and provides an average value of the inverter output current necessary for the removal of DC offset currents.An improvement in inverter efficiency and a reduction in cost has been achieved by omitting the 50 Hz power transformer (transformerless) and by optimising theinverter current control strategies. In Australia, some power supply authorities permit transformerless PV inverters of less than 10 kW rating to be connected to their supply system. However, avoiding the use of transformers can lead to magnitudes of DC offset current outside the limits specified by Australian Standard 4777.2, 2005 being injected into the grid supply. In this project a new cost effective DC offset current controller that removes DC offset current from the output of the inverter has been realised. This result translates into two primary benefits; firstly, a saving of about20% in the cost of the power transformer and in the cost of providing additional solar panels to overcome transformer power losses, and secondly the DC offset controller can also be utilised in inverter applications where power transformers are used, to prevent distortion of the magnetising current.The novel design procedure proposed in this thesis for a current controller takes into account intentional and unintentional switching circuit delays, and yields higherefficiencies without sacrificing power quality or increasing the cost of the inverter system. The inclusion of the effect of circuit delays in the design procedure issignificant as it is shown that delay not only has an adverse effect on the performance of the current controller but also on the efficiency and the power quality of the inverter system.Of paramount importance for the successful completion of this project was the relationship between switching circuit delays and the level of low frequencyharmonics generated by unipolar switched inverters. Theoretical analysis is developed to show why circuit delays, inverter DC input voltage and the inductanceof the current loop, are responsible for low frequency harmonics in unipolar switched and not in bipolar switched inverters. It has also been established that unipolarswitched inverters can be designed to operate within the limits specified by the Australian Standard 4777.2, 2005 and that the low frequency harmonics can be maintained at acceptable levels.For a current controller using unipolar switching, the choice of only one of four equivalent switching combinations of the inverter switches leads to suppression of switching noise, and prevents unwanted switching without the need for additional filters. Results are presented to demonstrate the unique advantage of unipolarswitching over bipolar switching.
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Fraser, Malcolm E. "Power factor-corrected transformerless three-phase PWM converter for UPS applications." Thesis, Loughborough University, 1996. https://dspace.lboro.ac.uk/2134/33002.
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This thesis describes the research of a new transformerless three phase PWM converter for uninterruptible power supplies (UPS) applications. The removal of the bulky three phase transformer in larger power UPS can provide a significant saving in weight and cost of the overall system. The converter consists of a new four-wire rectifier coupled with a four-wire inverter via a dc bus. The supply and load neutral may be connected together without any neutral current flowing into the utility regardless of the load on the inverter. This allows the load to be at the same potential as the utility. The rectifier, inverter and complete UPS and control system are described in detail and simulation results are used extensively to back up the theory. An experimental prototype of the four-wire rectifier provides further confirmation of the principles. A further proposal to digitize the system is given. This would reduce the size of the required control circuit and simplify the hardware requirements.
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Lam, Chi Seng. "Over-operating voltage and stability study of a transformerless-coupled dynamic voltage restorer." Thesis, University of Macau, 2005. http://umaclib3.umac.mo/record=b1445894.
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Photong, Chonlatee. "A current source inverter with series AC capacitors for transformerless grid-tied photovoltaic applications." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/13128/.
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The Current Source Inverter (CSI) is one of the simplest power converter topologies that can convert DC to AC and feed power generated from photovoltaic (PV) cells into the AC grid with a single power conversion stage over the whole PV voltage range. The CSI also provides smooth DC current which is one of the requirements of the PV cells as well as preventing reverse current using unidirectional switches. However, the CSI operates with low efficiency at lower PV voltages, which is where the PV cells produce maximum output power. This low efficiency is caused by large differences in voltage levels between the PV side and the grid side across the converter. This thesis presents an alternative topology to the three-phase CSI by connecting an AC capacitor in series with each AC phase line of the CSI circuit. The presence of the series AC capacitors in the CSI topology allows the AC voltage levels to be adjusted to match the voltage levels of the PV cells. Therefore, the CSI with series AC capacitors is able to operate with optimal DC-AC voltage levels. Performance of the proposed topology is evaluated in comparison to the standard CSI and five other converter topologies based on transformerless circuit concepts selected from those already available in the market and suitable converters discussed in the literature. All converter topologies were modeled and simulated with the SABER simulation software package. The CSI with series AC capacitors prototype was constructed in order to validate the feasibility of the proposed topology and the performance of the proposed topology in comparison to the standard CSI. Simulation results show that the CSI with series AC capacitors provides improved efficiency and better input/output power quality in comparison to the standard CSI. The proposed topology also achieves the lowest output line current distortion, lowest voltage stress across the circuit components and lowest estimated cost of power semiconductors when compared to all considered topologies. Experimental results are also presented to validate the simulation results.
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Ozkan, Ziya. "Leakage Current And Energy Efficiency Analyses Of Single Phase Grid Connected Multi-kva Transformerless Photovoltaic Inverters." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614236/index.pdf.
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In order to inject solar power to the utility grid, among various types of inverters, Grid Connected Transformerless Solar Inverters (GCTSI) are mostly preferred for residential or commercial applications. This preference is because of the high energy efficiency and low cost due to the absence of a line frequency or a high frequency transformer. Peak value of the efficiency characteristics of GCTSIs can reach 98%, which are selected topology, component optimization, switching strategy and operating condition dependent. In spite of the attractive energy efficiency characteristics of GCTSIs, due to the lack of galvanic isolation, these inverters are vulnerable to leakage currents, which are prohibitive for the safety and the maintenance reasons. The purpose of this research is to analyze GCTSIs in terms of their leakage current and energy efficiency characteristics. In the research, the leakage current mechanisms of GCTSIs are identified and grid connected solar inverters are classified in terms of their leakage current characteristics including the GCTSIs. In addition to the existing ones, several novel topologies are proposed enriching the family of GCTSIs. The leakage current and the inductor current ripple performances of GCTSI topologies are analyzed and evaluated by detailed simulations for 3 kVA and 10 kVA single-phase systems. In addition, the energy efficiency characteristics of GCTSIs are investigated in these power levels by making use of Calculated Average Power Per Switching Cycle (CAPPSC) method. The efficiency studies with CAPPSC method provide design guidelines and comparison of the GCTSI topologies in terms of their energy efficiency characteristics.
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Zanetti, Francesco. "Analisi teorica e sperimentale di uno schema di controllo per convertitori fotovoltaici monofase di tipo transformerless." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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Il tema centrale dell’elaborato è lo studio dell’efficienza e del THD di due inverter monofase di tipo transformerless indicati comunemente con la sigla H6; uno è stato realizzato in silicio e l’altro in carbonato di silicio Nel primo capitolo è stato presentato il classico impianto fotovoltaico domestico, le normative che lo riguardano e le problematiche tecniche che lo caratterizzano; nel secondo capitolo invece sono state illustrate le varie tecniche di modulazione che è possibile attuare con la struttura dell’inverter H6 e si sono riportate anche le principali caratteristiche del nuovo materiale; il silicio carbonato. Nel terzo capitolo si è riportato l’intero programma di simulazione costruito con i tools di Matlab; Simulink e Plecs. Sono state riportate anche le principali ipotesi adottate per lo studio preliminare del progetto del sistema di misura. Il quarto capitolo è stato dedicato invece alle simulazioni che sono state svolte per identificare le possibili problematiche dell’impianto sia durante la fase di avviamento che in condizioni di regime. Nel quinto capitolo si è descritto il processo di discretizzazione necessario per implementare il codice utilizzato nelle simulazioni sui dispositivi elettronici; che per funzionare richiedono delle grandezze digitali in ingresso. Il sesto capitolo è stato incentrato sulla realizzazione e sul collaudo del banco di misura; mentre nel settimo capitolo si sono elencati i risultati delle prove sperimentali ottenuti. L’elaborato termina con le conclusioni tratte dai dati, che confermano l’alta efficienza del dispositivo realizzato in SiC rispetto a quello realizzato in Si e forniscono ulteriori informazioni sugli andamenti del THD sia per armoniche di ordine basso che quelle in alta frequenza.
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Salem, Qusay [Verfasser]. "A transformerless H-bridge inverter as a bidirectional power flow controller in a microgrid based P/V droop control / Qusay Salem." Ulm : Universität Ulm, 2020. http://d-nb.info/1208767070/34.
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Patrao, Herrero Iván. "Concepción e integración en microrredes residenciales de inversores multinivel sin transformador de aislamiento con extracción simultánea de la máxima potencia de múltiples generadores fotovoltaicos." Doctoral thesis, Editorial Universitat Politècnica de València, 2015. http://hdl.handle.net/10251/52023.
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[EN] Multilevel inverters are being used in high-power applications, but the use of those topologies in small-power photovoltaic power plants presents some advantages. In this Thesis it is proposed a transformerless grid-connected single-phase photovoltaic inverter topology, called NPC+GCC, based on a multilevel topology.
The characteristics of the NPC+GCC are of great interest for grid-connected transformerless inverters. It is demonstrated that that topology generates a very low capacitive leakage current, which is well below the limits stablished by the DIN VDE 0123-1-1 norm.
The NPC+GCC topology permits the connection of a pair of photovoltaic sources on its input, getting the maximum power of both sources simultaneously. The efficiency of the power electronic converter is very high, since cascaded power stages are not used. This feature is of great interest in photovoltaic generation in urban areas because of the partial shadowing of the photovoltaic modules. Partial shadowing significantly deteriorates the energy harvesting. The double maximum power point tracking of the NPC+GCC reduces the effects of partial shadowing.
Moreover, the inverter has been designed for working in distributed generation microgrids, an upcoming scenario. The main features of the inverter, transformerless and with a double maximum power point tracking, are especially relevant for power generation in the context of microgrids.
The design has been validated by means of the construction and experimental study of an NPC+GCC converter with a nominal power of 5kW.[ES] Los inversores multinivel se utilizan de forma habitual en aplicaciones de gran potencia, pero la aplicación de las topologías multinivel en la generación fotovoltaica de pequeña potencia presenta algunas ventajas de interés. Se propone una topología de inversor fotovoltaico monofásico de inyección a red sin transformador, basada en las topologías multinivel, llamada NPC+GCC. Esta topología presenta características de gran interés para su uso como inversor sin transformador directamente conectado a la red eléctrica. Se estudia su tensión de modo común, y cómo esta genera una corriente de derivación capacitiva que se mantiene muy por debajo de los límites permitidos por la normativa. La topología NPC+GCC permite la conexión de dos generadores fotovoltaicos en su entrada, sobre los que efectuará una búsqueda del punto de máxima potencia de manera totalmente independiente y con un elevado rendimiento y fiabilidad, ya que no utiliza convertidores conectados en cascada para realizar esta función. Esta característica es de especial interés para la generación fotovoltaica en entornos urbanos, pues frecuentemente aparecen sombreados parciales sobre los módulos fotovoltaicos, que pueden deteriorar significativamente el aprovechamiento energético. El doble seguimiento del punto de máxima potencia permite reducir la influencia del sombreado parcial. Además, el inversor está diseñado para funcionar en microrredes de generación distribuida, adaptando así la generación fotovoltaica al nuevo escenario que está naciendo en la actualidad. Las principales características del inversor (sin transformador y con doble seguimiento del punto de máxima potencia) son de especial relevancia para la generación en el entorno de microrredes. El diseño se ha validado mediante la construcción y experimentación de un convertidor NPC+GCC de potencia nominal 5kW.
[CAT] Els inversors multinivell s'utilitzen de forma habitual en aplicacions de gran potència, però l'aplicació de les topologies multinivell en la generació fotovoltaica de petita potència presenta alguns avantatges d'interès. Proposem una topologia d'inversor fotovoltaic monofàsic d'injecció a xarxa sense transformador, basada en topologies multinivell, anomenada NPC+GCC. Aquesta topologia presenta característiques de gran interès per l'ús com a inversor sense transformador directament connectat a la xarxa elèctrica. N'estudiem la tensió de mode comú, i com aquesta genera un corrent de derivació capacitiu que es manté molt per davall dels límits permesos per la normativa. La topologia NPC+GCC permet la connexió de dos generadors fotovoltaics en l'entrada, sobre els quals efectuarà una cerca del punt de màxima potència de manera totalment independent i amb una elevada eficiència i fiabilitat, ja que no usa convertidors connectats en sèrie per a dur a terme aquesta funció. Aquesta característica és d'interès especial per a la generació fotovoltaica en entorns urbans, ja que freqüentment apareixen ombrejats parcials als mòduls fotovoltaics, que poden deteriorar significativament l'aprofitament energètic. El doble seguiment del punt de màxima potència permet reduir la influència de l'ombrejat parcial. A més, l'inversor està dissenyat per a funcionar en microxarxes de generació distribuïda, i així la generació fotovoltaica s'adapta al nou escenari que està naixent en l'actualitat. Les principals característiques de l'inversor (sense transformador i amb doble seguiment del punt de màxima potència) són d'especial rellevància per a la generació en l'entorn de microxarxes. El disseny ha sigut validat per mitjà de la construcció i l'experimentació d'un convertidor NPC+GCC de potència nominal 5kW.
Patrao Herrero, I. (2015). Concepción e integración en microrredes residenciales de inversores multinivel sin transformador de aislamiento con extracción simultánea de la máxima potencia de múltiples generadores fotovoltaicos [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/52023
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Jank, Henrique. "Circuito auxiliar para equilíbrio da tensão e redução da corrente do ponto central do barramento CC aplicado a uma UPS sem transformador." Universidade Federal de Santa Maria, 2016. http://repositorio.ufsm.br/handle/1/8592.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoThis work proposes the use of an auxiliary circuit to perform the voltage balancing and reduce the low frequency currents of the DC Bus center point of a three-phase transformerless UPS. The Bus voltage unbalance may occur due to the connection of unbalanced loads and non-idealities of the circuit and may impair the quality of the UPS output voltage. The low frequency current components occur due to the connection of non-linear or unbalanced loads. With the occurrence of these currents, there is an increase in the DC Bus voltage ripple, making it necessary to use a DC Bus with significant capacitance values. Moreover, these currents should increase the losses in the capacitor and deteriorate its lifespan. Thus, it is proposed the use of an auxiliary circuit comprising a switching branch and an inductor, whose function is to reduce the harmonic content from the currents flowing through the central point of the capacitive divider, in addition to ensuring the balancing of the DC Bus voltages. It is carried out the design of a three-phase transformerless UPS and the proposed auxiliary circuit, besides the design of its control systems. Simulation and experimental results demonstrate the procedures developed over this work and validate the functionality of the proposed circuit with respect to its purpose.
Este trabalho propõe a utilização de um circuito auxiliar para realizar o equilíbrio de tensão e redução das correntes de baixa frequência do ponto central do barramento CC de uma UPS trifásica sem transformador. O desequilíbrio de tensão do barramento pode ocorrer devido a conexão de cargas desequilibradas e não-idealidades do circuito e podem prejudicar a qualidade da tensão de saída da UPS. Já as componentes de corrente em baixa frequência ocorrem devido à conexão de cargas não-lineares ou desequilibradas. Com a ocorrência dessas correntes, há um aumento na ondulação de tensão do barramento CC, tornando necessário a utilização de expressivos valores de capacitância. Além disso essas correntes devem aumentar as perdas nos capacitores e deteriorar sua vida útil. Dessa forma, propõe-se a utilização de um circuito auxiliar composto por um braço de interruptores e um indutor, cuja função é reduzir o conteúdo harmônico proveniente das correntes que circulam pelo ponto central do divisor capacitivo, além de assegurar o equilíbrio das tensões do barramento CC. É realizado o dimensionamento de uma UPS trifásica sem transformador e do circuito auxiliar proposto, bem como o projeto dos sistemas de controle dos mesmos. Resultados de simulação e experimentais comprovam os procedimentos desenvolvidos ao longo do trabalho, bem como validam a funcionalidade do circuito proposto com relação a sua finalidade.
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Finamor, Gustavo Andres. "Inversor fotovoltaico não isolado NPC intercalado." Universidade Federal de Santa Maria, 2016. http://repositorio.ufsm.br/handle/1/8585.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThroughout the twentieth century, the supply of electricity, mainly obtained from fossil fuels like oil and coal, it has supported the growth and transformation of the world economy. In the early years of this century, the scenario has changed to a new reality, the need for sustainable development. In other words, the challenge is to gradually replace the traditional sources of electricity from renewable energy sources, in which the solar photovoltaic energy has highlighted. Photovoltaic inverters may be constituted in different ways, presenting in recent decades a high research progress. The main study efforts focus on getting high efficiency, high power density and high reliability, to increase the overall performance of the photovoltaic installation. In this direction, this Master Thesis aims to propose, analyze, design and implement a single-phase grid-tied photovoltaic inverter, which provides high efficiency and high power density. This circuit is called Transformerless Photovoltaic Interleaved Multilevel NPC Inverter , that use uncoupled inductors, Gallium Nitride power transistors and employs interleaving strategy beside the LCL filter, synthesizing 9 levels. Are introduced studies on the operation, modulation and design methodology of power stages, considering the static performance. Results are presented for the 1 kW, in order to support the validity of the proposed topology in conjunction with the standard aspects, especially in relation to THD (Total Harmonic Distortion) of grid current, leakage current, efficiency and power density.
Durante todo o século XX, a oferta de energia elétrica, obtida principalmente a partir dos combustíveis fósseis como petróleo e o carvão mineral, deu suporte ao crescimento e as transformações da economia mundial. Já nos primeiros anos do século atual, o cenário mudou para uma nova realidade, a necessidade do desenvolvimento sustentável. Em outras palavras, o desafio é substituir gradativamente as fontes tradicionais de energia elétrica por fontes de energia renovável, onde a energia solar fotovoltaica tem destaque. Os conversores eletrônicos para sistemas fotovoltaicos, também chamados de inversores, podem ser constituídos de diversas maneiras, apresentando nas últimas décadas um acentuado progresso de pesquisa. Os principais esforços de estudo tem se concentrado em obter alto rendimento, alta densidade de potência e alta confiabilidade, de modo a aumentar o desempenho global da instalação fotovoltaica. Neste horizonte, esta dissertação tem por objetivo propor, analisar, projetar e implementar um inversor fotovoltaico monofásico, para aplicação conectada à rede, de alto rendimento e alta densidade de potência. Esta estrutura é denominada de Inversor Fotovoltaico NPC Multinível Intercalado sem Transformador , que utiliza indutores não acoplados, interruptores de Nitreto de Gálio e emprega a técnica interleaving junto ao filtro LCL, sintetizando 9 níveis. No decorrer do trabalho são introduzidos estudos relativos à operação, modulação, metodologia de projeto e estágios de potência, estabelecendo critérios, enquanto considera a performance estática. São apresentados resultados, observando a potência de 1 kW, com a finalidade de corroborar a validade da topologia proposta juntamente as normativas e aspectos que norteiam a aplicação, especialmente com respeito à THD (Total Harmonic Distortion) da corrente da rede, corrente de fuga, rendimento e densidade de potência.
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Giacomini, Julian Cezar. "Desenvolvimento de um inversor fotovoltaico trifásico não isolado conectado à rede elétrica." Universidade Federal de Santa Maria, 2015. http://repositorio.ufsm.br/handle/1/8560.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThis Master Thesis presents the development of a grid-connected transformerless three-phase photovoltaic inverter. The Neutral Point Clamped (NPC) three-level inverter was chosen for implementation. The grid connection is made with a modified LCL filter (MLCL), where the common point of the output filter capacitors is connected directly to the dc bus central point (neutral point). The MLCL filter reduces the leakage current of photovoltaic system and attenuates the current harmonics injected in the grid. A passive damping of MLCL filter resonance peak was employed in order to avoid instability in the grid connection. In this sense, this Master Thesis contributes proposing a passive damping design method which is based not only on the stability requirement, but also considers the leakage current of photovoltaic system, once that passive damping impacts on the high frequency components of voltage on parasitic capacitance. Therefore, based on leakage current limit and current loop stability, a range for the damping resistance was obtained. The control system of the threephase inverter was developed in a synchronous reference frame (dq0), where the proper alignment with the grid voltage reference vector allows the independent control of active and reactive power inject in the grid. Simulation and experimental results are shown to evaluate the inverter performance and to validate the theoretical analysis.
Esta Dissertação de Mestrado apresenta o desenvolvimento de um inversor fotovoltaico trifásico não isolado conectado à rede. A topologia desenvolvida foi a de um inversor trifásico três níveis com ponto neutro grampeado (NPC Neutral Point Clamped). A conexão com a rede é feita através de um filtro LCL modificado (LCLM), que possui o ponto comum dos seus capacitores conectado ao ponto central do barramento CC do inversor. O filtro LCLM possui a finalidade de reduzir a corrente de fuga do sistema fotovoltaico ao mesmo tempo em que atenua os harmônicos de corrente injetados na rede. De modo a evitar problemas de instabilidade da malha de corrente do inversor, um sistema de amortecimento passivo do pico de ressonância do filtro LCLM foi empregado. Neste sentido, esta Dissertação de Mestrado contribui propondo um método de projeto do amortecimento passivo que se baseia não somente no critério de estabilidade, mas que também considera a corrente de fuga do sistema fotovoltaico, uma vez que o amortecimento impacta na atenuação das componentes de alta frequência da tensão sobre a capacitância parasita dos módulos fotovoltaicos. Com isso, uma faixa de valores para a resistência de amortecimento foi obtida a partir do limite permitido para a corrente de fuga e da estabilidade da malha de corrente. O sistema de controle do inversor trifásico foi desenvolvido com base no sistema de coordenadas síncronas dq0, cujo correto alinhamento com o vetor de referência das tensões da rede permite o controle independente das potências ativa e reativa injetadas na rede. Resultados experimentais e de simulação são apresentados de modo a comprovar o desempenho do inversor trifásico.
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Raji, Atanda Kamoru. "Performance evaluation and improvement of grid-connected technology." Thesis, Cape Peninsula University of Technology, 2012. http://hdl.handle.net/20.500.11838/1198.
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Dissertation (DTech(Electrical Engineering))--Cape Peninsula University of Technology, 2012The confluence of the limited resources of fossil fuels (e.g. coal, oil and natural gas), environmental degradations leading to climate change, security of supplies and fossil fuels high costs have demanded a tremendous efforts on humanity to seek for a sustainable and unlimited natural energy sources. Amongst these renewable energy sources stands out solar energy because of its ubiquitousness. Solar energy is converted to DC electricity by the photovoltaic effect. Photovoltaic (PV) power systems installed in commercial and industrial buildings are a good example of distributed power generation. Here the energy consumption and production match and thus electricity taken from the grid during daytime peak hours can be reduced. This is beneficial as the transmission losses in the grid are avoided and also transmission need is reduced. The cost effectiveness of a solar energy system has hindered its wide adoption and deployment in terms of the initial capital cost even though it has a zero energy cost and very minimal operating and maintenance costs. Different governments have instituted many financial incentives for fast adoption of PV systems for both residential and commercial applications. However, all these incentives are not sustainable in the longer term forecast. For PV system to attain grid parity requires more than unsustainable approach of many governments providing time limited subsidies. The technical solution to the problem is to reduce the overall system cost through technical innovations. One such method is the adoption of transformerless inverter technology as the grid interface system. Transformerless inverter topology provides galvanic isolation through innovative inverter topology and switching strategies that eliminates problems created by not employing the service of transformer.
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Dai, Min. "Control of power converters for distributed generation applications." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1124329850.
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Bonnin, Xavier. "Alimentation électrique des dispositifs de décharge à barrière diélectrique." Phd thesis, Toulouse, INPT, 2014. http://oatao.univ-toulouse.fr/13645/1/bonnin.pdf.
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Les dispositifs DBD se répandent dans un grand nombre d’applications industrielles. Utilisés depuis plus de 150 ans pour la production d’ozone afin de décontaminer l’eau à grande échelle, ils ont depuis la fin du XXème siècle investi les domaines du traitement de surface polymère, du dépôt de couche mince sur substrat et de l’émission lumineuse pour la décontamination ainsi que la médecine. Ces dispositifs sont mis en oeuvre avec un générateur électrique dont les caractéristiques impactent fortement la qualité de la décharge. Ce travail s’inscrit en partie dans le cadre du développement d’une application de traitement de surface à pression atmosphérique. Il aborde la problématique de l’augmentation de la vitesse de dépôt de couche mince au travers des paramètres de l’alimentation électrique. Plus précisément, ce travail s’intéresse aux apports d’une alimentation en courant rectangulaire et aborde également les problématiques liées à la conception et à la fabrication de ce convertisseur. En particulier, une grande attention est portée sur l’étude du transformateur élévateur, car au travers de ses éléments parasites capacitifs, ce dernier peut limiter le transfert de puissance entre la source électrique et le dispositif DBD. Un deuxième aspect de cette étude consiste à entrevoir l’intérêt que revêtent deux convertisseurs statiques dédiés à l’alimentation de dispositifs DBD. Le premier consiste en une alimentation résonante en régime de conduction discontinue dont la particularité est de posséder trois degrés de liberté (fréquence, tension d’entrée et largeur d’impulsion), ce qui lui confère un intérêt exploratoire. Le second convertisseur consiste en une alimentation résonante haute tension et haute fréquence permettant l’éviction du transformateur élévateur, et mettant en oeuvre des interrupteurs au nitrure de gallium (GaN) afin d’atteindre une fréquence de fonctionnement supérieure au mega-Hertz avec un faible niveau de pertes.
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Figueredo, Ricardo Souza. "Corrente de fuga em inversores monofásicos sem transformador para conexão de sistemas fotovoltaicos à rede de distribuição de energia elétrica: análise e proposta de filtro passivo integrado de modo comum e diferencial." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/3/3143/tde-20072016-092205/.
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Este trabalho apresenta um estudo sobre a corrente de fuga de modo comum em inversores monofásicos sem transformador utilizados para a conexão de sistemas fotovoltaicos (FV) à rede de distribuição de energia elétrica. O estudo se concentra em inversores do tipo fonte de tensão que empregam a topologia em ponte completa. A partir da adequada modelagem do sistema (rede, conversor e módulo fotovoltaico) identifica-se e quantifica-se a contribuição das tensões de modo comum e modo diferencial para a corrente de fuga. Conclui-se que a tensão de modo comum de alta frequência produzida pelo inversor, que depende da estratégia de modulação por largura de pulso (PWM Pulse Width Modulation) empregada, fornece a maior contribuição para produção da corrente de fuga. Esse estudo mostra que os inversores sem transformador, com topologia em ponte completa e modulação que produz tensão de saída com três níveis, necessitam de medidas adicionais para a minimização da corrente fuga quando aplicados em sistemas fotovoltaicos conectados à rede. Algumas soluções propostas na literatura para a minimização da corrente de fuga baseadas em topologias modificadas e filtros de modo comum são listadas e discutidas. Neste trabalho é proposto um filtro integrado de modo comum e modo diferencial com amortecimento passivo de baixas perdas, para minimizar a corrente de fuga produzida por um inversor monofásico sem transformador. Um exemplo de aplicação do filtro proposto é apresentado juntamente com seu procedimento de projeto, resultados de simulação e experimentais que validam a proposta. Além disso, a influência da variação da indutância da rede elétrica e da capacitância parasita do sistema fotovoltaico no comportamento do filtro proposto é analisada. A influência da variação da indutância da rede no comportamento do sistema de controle e o impacto da corrente de modo comum no projeto dos indutores do lado do conversor também são analisados.This paper presents a study on the common mode leakage current in single-phase transformerless inverters for grid-connected photovoltaic (PV) systems. The study focuses on voltage source inverters (VSI) employing the full-bridge topology. The common mode and differential mode voltages that contribute to the leakage current are identified and quantified from the analysis of the system model (utility grid, converter and PV module). The system model analysis shows that the high frequency common mode voltage produced by the inverter, which depends on the Pulse Width Modulation (PWM) strategy, is the main source contributing to the leakage current. This work shows that transformerless inverters employing the full-bridge topology and a modulation strategy that produces a three-level output voltage require some leakage current minimization strategy when they are employed in grid-connected PV systems. Some solutions proposed in the literature for leakage current minimization based on modified topologies and common mode filters are listed and discussed. In this dissertation an integrated common and differential filter with low loss passive damping is proposed to minimize the leakage current produced by a single-phase transformerless PV inverter. An application example of the proposed filter is presented with design procedure, simulation and experimental results validating the proposal. Additionally, the influence of grid inductance and PV module parasitic capacitance variations on the behavior of the proposed filter is analyzed. The behavior of the control system considering the grid inductance variation and the impact of the common mode current on the converter side inductors design are also analyzed.
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Lin, Po Heng, and 林柏衡. "D-Σ Digital Control Based Transformerless UPS." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/71290810850960375136.
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碩士國立清華大學
電機工程學系
103
In most uninterruptible power supply (UPS) systems, transformers are incorpo-rated for galvanic isolation to reduce circulating current. However, the use of trans-formers increases cost and size of a system. In addition, heat generated during opera-tion lowers the stability and reduces the longevity of power components. A trans-fomerless UPS system regulates the power flow between dc link and utility and stabilizes the output voltage. Rather than the conventional abc to dq frame transformation, the division-summation(D-Ʃ) digital control is adopted instead so that the calculation process can be greatly simplified. This research presents a transformerless UPS systems which includes a power factor corrector (PFC) and a voltage source inverter(VSI). For the PFC, a three-phase three-wire full-bridge inverter is adopted while a three-phase four-wire full-bridge inverter is adopted for the VSI. Microprocessor RX62T is incorporated in both cir-cuits to implement the proposed control law. The main contributions of this research are summarized as follows: First, The circulation current is suppressed effectively. Large circulating current flowing through the common ground of the PFC and the VSI due to different switching states is observed. To reduce the circulating current, synchronization of: a) the switching states between the two circuits and b) the input voltage of the PFC and the output voltage of the VSI have been implemented. Secondly, both ac harmonic voltage and inductance variation are taken into account in the control law derivation of the D-Ʃ digital control, allowing a sinusoidal output current even in the presence of harmonic-contaminated grid voltage. Meanwhile, core size can be greatly reduced with the consideration of wide inductance variation. Thirdly, total harmonic distortion of the output voltage can be effectively reduced by incorporating a repetitive control in the D-Ʃ digital control based voltage tracking control. Finally, the feasibility of the proposed control scheme has been verified by the measurements from the implemented transformerless UPS system.
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Chang, Chien Shih-Chun, and 張簡士俊. "Analysis of Transformerless Solar Power Generation System." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/21801579740646301804.
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碩士國立高雄海洋科技大學
微電子工程研究所
103
The grid-connected power converter is used as an interface between the solar cell array and utility grid. The grid-connected power converter converts the DC power generated from the solar cell array to an AC power injected into the utility grid. However, a parasitic capacitor is induced between the terminals of solar cell array and ground, and it will result in a leakage current while a high-frequency pulse voltage is generated by the grid-connected power converter. The leakage current will result in the problems of safety, electromagnetic interference (EMI), current distortion and extra power loss. In general, an isolation transformer is used to solve the problems of leakage current. However, the isolation transformer will result in bulky volume, high cost, and poor efficiency. Several grid-connected power converters have been developed for the transformerless solar power generation system to solve the problems of leakage current. The developed grid-connected power converters can be divided into circuit decoupling topology and common-mode voltage clamped topology. In this thesis, the transformerless solar power generation system is discussed, and computer simulation is made to verify the performance of transformerless solar power generation system.
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HUNG, CHIH-YI, and 洪誌翊. "Study of Transformerless Multi-Level Solar Power Generation System." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/39831480023057081207.
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碩士國立高雄海洋科技大學
微電子工程研究所
104
In this thesis a transformerless multi-level solar power generation system is developed. The transformerless multi-level solar power generation system is composed of a solar cell array, a DC-DC boost converter, an isolation switch set, and a full-bridge DC-AC inverter. The unipolar pulse-width modulation(PWM) is used in the full-bridge DC-AC inverter to attenuate the ripple of output current. To suppress the leakage current of full –bridge DC-AC inverter using unipolar PWM, the circuit isolation method is used by integrating the isolation switch set between the solar cell array and the utility. The isolation switch set will separate the solar cell array and the utility under the free-wheeling operation mode of full-bridge DC-AC inverter to block the path of leakage current. The isolation switch set can also determine the DC bus voltage of full-bridge DC-AC inverter. When the absolute value of utility voltage is lower than the voltage of solar cell array, the DC bus of full-bridge DC-AC inverter is directly connected to the solar cell array through the isolation switch set and DC-DC boost converter will turns off to reduce power consumption. On the contrary, the isolation switch set connects the DC bus of full-bridge DC-AC inverter to the output of DC-DC boost converter while the absolute value of utility voltage is higher than the voltage of solar cell array. Accordingly, the transformerless multi-level solar power generation system will generate a five-level voltage. In addition, partial power of solar cell array is converted to AC power through only the full-bridge DC-AC inverter such that the power efficiency is advanced. A prototype is developed to validate the performance of the transformerless multi-level solar power generation system.
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Hsieh, Chu-Hsiu, and 謝竹修. "Design and Implementation of a Transformerless Dynamic Voltage Restorer." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/58315538267707839582.
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碩士國立成功大學
電機工程學系碩博士班
94
Conventional dynamic voltage restorer can help solve the under-voltage problem, yet for the over-voltage problem, its efficiency was seen limited. Therefore, in this thesis, a transformerless dynamic voltage restorer is proposed, where the power angle, power factor and mains voltage variation were all taken into considerations. With the appropriate control made in this proposed approach, the method not only helped compensate the under-voltage phenomenon, but also owned the capability of correcting the mains over-voltage problem. In the mean time, with the assistance of the proposed system, the voltage variation disturbance can be also better alleviated. To validate the effectiveness of such a method, a prototype circuit was simulated, implemented and tested. From those test results revealed, they helped consolidate the feasibility of the method in maintaining the voltage stability at demand side. This outcome can be also provided as the reference for electric power quality improvement study.
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Denniston, Nicholas Aaron. "High Gain Transformerless DC-DC Converters for Renewable Energy Sources." Thesis, 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-05-7778.
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Renewable energy sources including photovoltaic cells, fuel cells, and wind turbines require converters with high voltage gain in order to interface with power transmission and distribution networks. These conversions are conventionally made using bulky, complex, and costly transformers. Multiple modules of single-switch, single-inductor DC-DC converters can serve these high-gain applications while eliminating the transformer.
This work generally classifies multiple modules of single-switch, single-inductor converters as high gain DC-DC converters transformers. The gain and efficiency of both series and cascade configurations are investigated analytically, and a method is introduced to determine the maximum achievable gain at a given efficiency. Simulations are used to verify the modeling approach and predict the performance at different power levels. Experimental prototypes for both low power and high power applications demonstrate the value of multiple module converters in high gain DC-DC converters for renewable energy applications.
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Liu, Tsung-Hsien, and 劉宗憲. "Common-Mode Current Reduction for Transformerless Grid-Connected Photovoltaic Inverters." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/88554855466969352699.
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碩士國立臺灣科技大學
電機工程系
97
This thesis proposes a novel inductance-capacitance filter to improve the common-mode current for transformerless grid-connected photovoltaic (PV) inverters. Reduction of the voltage of PV negative electrode with respect to ground is then resulted to avoid shortening the service life of PV array and harming the personnel safety. A boost-type dc-dc converter is introduced to boost the PV array voltage from 560V to 670V on output side of PV array for inverter input. The three-phase full-bridge inverter designed uses voltage space vector pulse-width modulation to convert dc-link voltage to three-phase alternating current for grid-connection. In this thesis, a 32-bit digital signal processor is adopted as the control core for reducing the circuit complexity. The Powersim simulation software is used to analyse the suppression effect of the proposed inductance-capacitance filter. A 10 kW prototype of transformerless grid-connected three-phase PV inverter is built. Experimental results show that the voltage of PV negative electrode to ground is reduced from 1,793V to 181V, and the corresponding common-mode current is reduced from 253 mA to 99 mA, respectively. The proposed inductance-capacitance filter is better than current passive techniques in the suppression effect of common-mode current. Thus it is applicable for transformerless grid-connected photovoltaic inverters.
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Soong, Theodore. "A Transformerless High Step-up DC-DC Converter For DC Interconnects." Thesis, 2012. http://hdl.handle.net/1807/32626.
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The proliferation of distributed energy resources (DER)s has prompted interest in the expansion of DC power systems. The technological limitations that hinder the expansion of DC power systems are the absence of DC circuit breakers and high step-up/high step-down DC converters for interconnecting DC systems.
This thesis presents a transformerless high step-up DC-DC converter intended for use as an interconnect between DC systems. The converter is required to operate at medium to high voltage (>1kV) and provide high voltage gain (>5).
This work details the steady state operation and dynamic model of the proposed converter. The component ratings are identified and converter design limitations are investigated. A 100V:1kV/4kW prototype is produced to verify the analytic steady state model and measure efficiency. An experimental efficiency of 90% was achieved at a step-up ratio of 1:10, however efficiency at low power is limited due to the need to circulate power.
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Lee, Chao-Han, and 李昭翰. "Modeling and Analysis of a Novel Transformerless Voltage Quadrupler DC Converter." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/79496616728732104978.
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碩士國立清華大學
電機工程學系
99
High voltage DC converters are widely used in various applications to provide a high output DC voltage. However, the existing voltage doubler is not sufficient for some much higher voltage applications. Although, one can cascade more stages to achieve the desired voltage level, however, the resulting complex topology will result in less efficiency and reliability. Hence, the major motivation of this thesis is to propose a high efficiency voltage quadrupler DC converter. In fact, the major contributions of this thesis may be summarized as follows. First, a single stage transformerless voltage quadrupler DC converter is proposed for achieving much higher voltage gain, less voltage stress of switches and higher efficiency. In addition, the proposed converter possesses automatic current sharing capability without adding any extra component. Second, mathematical model of the proposed converter is derived and fundamental characteristics of the new converter are analyzed. Third, a 400W rating prototype with 25V input and 400V output is constructed for verifying the feasibility of the prototype converter. It is seen that the voltage stress of the active switches and the diodes are equal to quarter and half of the output voltage respectively. The resulting efficiency can be maintained above 93% as the load is varied from 120W to 400W, and the highest efficiency of 95% is achieved at 120W. Both simulation and experimental results indeed verify the effectiveness of the proposed converter. Finally, the extended isolated version of proposed quadrupler converter is also presented in this thesis.
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Chen, Yi-Chang, and 陳怡成. "Power Integrated Circuit Design of 110V AC/5V DC Transformerless Converter." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/43029311838957060170.
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碩士國立交通大學
電機與控制工程系
90
A design of 110V AC/5V DC transformerless converter power integrated circuit is proposed. Three design scheme of converter are proposed and their structures are categorized into two types. For the typeⅠdesign, only one stage of AC/DC converter is employed. This scheme is simpler, but the output voltage ripple is wholly the same as the traditional full-wave rectifier. For the typeⅡdesign, two scheme are proposed. The first scheme contains only one stage too. The output voltage ripple is reduced a lot. However, the power dissipation is very large (7.5W). The second scheme add one more DC/DC converter to reduce the power dissipation and to improve the output voltage ripple. The design uses no transformer and inductance. The output rating 5V+10%~ 5V-10%and 100mA.The power transfer efficiency is 40%.
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Su, Wen Tao, and 蘇文韜. "Design of a Gallium Nitride Transistor based Transformerless Single-Phase Inverter." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/gmn66x.
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Tsai, Meng-Hung, and 蔡孟衡. "Development of a Small Vertical Axis Wind Generation System with Transformerless Inverter." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/52631745968383788581.
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碩士健行科技大學
電機工程系碩士班
103
This thesis focuses on development of a small vertical axis wind generation system with transformerless inverter. Firstly, the PSIM software package was used to simulate the whole system architecture, and then according to the simulation results as a basis for measurement systems and program control parameters adjustment. The AC power of wind turbine output was rectified into DC power, the perturbation and observation method was adapted to control the high-gain boost DC converter for maximum power point tracking to keep the maximum power output of small vertical axis wind turbine at different wind speed. Finally, the DC power was transformed into AC power by a single-phase full-bridge with transformerless inverter for grid connected control. The wind turbine mathematics model was built from experimental data of wind tunnel laboratory for PSIM software simulation and analysis. Based on simulation results, a digital signal processor (DSP, TMS320F28335) was used to implement a 300W grid-connected small-scaled vertical axis wind power generation system prototype to verify the theory.
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Lin, Bing Syuan, and 林稟軒. "Design of Transformerless Single-Phase PV Inverters with Balanced Capacitor-Clamping Voltages." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/64712491007040054596.
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Hagar, Abdelrahman. "A New Family of Transformerless Modular DC-DC Converters for High Power Applications." Thesis, 2011. http://hdl.handle.net/1807/29738.
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This thesis presents a new family of converters for high power interconnection of dc buses with different voltage levels. Proposed converters achieve high voltage dc-dc conversion without an intermediate ac conversion stage. This function is implemented without series connection of active switches, or the use of isolation transformers. The salient features of proposed converters are (i) design and construction simplicity, (ii) low switching losses through soft turn-on and soft turn-off, (iii) single stage dc-dc conversion without high-current chopping, (iv) modular structure, (v) equal voltage sharing among the converter modules.
Three converter circuits are investigated. The first performs unidirectional power transfer from a dc bus with higher voltage to a dc bus with lower voltage. The second performs unidirectional power transfer from a dc bus with lower voltage to a dc bus with higher voltage. Both converters are suitable for interconnecting single pole dc buses with same polarity, or double pole dc buses. A third converter is also presented which performs the function of either the first or the second converter with polarity reversal. The third converter is suitable for interconnecting single pole dc buses with different polarities, or double pole dc buses. By hybrid integration of the proposed three converters, the thesis also investigates other topologies for bidirectional power transfer between two dc buses.
Proposed converters operate only in discontinuous conduction mode and exhibit soft switching operation for the active and passive switches. A common feature between the proposed converters is the self current turn-off for the active switches at zero voltage. This allows the use of thyristors as active switches alleviating their reverse recovery losses. For each converter topology, the structure is presented, its operation principle is explained and a complete set of design equations are derived. Comparisons are performed on high-power and high-voltage design examples. The merits and limitations of each converter are concluded. Practical considerations regarding components selection, loss analysis, filter design and the non-idealities of the circuits are studied. Experimental implementation of scaled-down laboratory prototypes is presented to provide a proof of concept and validate the operation principle of the proposed converter topologies.
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Chen, Meng-Liang, and 陳孟良. "Design and Implementation of a Single-phase Transformerless Grid-connected Photovoltaic Generation System." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/55307129830202610798.
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碩士健行科技大學
電機工程系碩士班
103
This thesis focuses on design and implementation of a single-phase transformerless grid-connected photovoltaic generation system. A 1.14kW photovoltaic generation system model was built by Powersim (PSIM) software. The simulation and analysis results were used to design the control algorithms and programs for system testing. First,we observed the output characteristics of solar cell, the perturb-and-observe method was adopted to control the boost DC chopper for maximum power point tracking. Finally, the current control method was adopted to control a new single-phase full-bridge inverter for grid connected control to convert DC/AC power and connect to the grid. A digital signal processor (DSP, TMS320F28335) was applied to implement 1kW prototype single-phase transformerless grid-connected photovoltaic generation system. Experiment was then conducted to verify the theory.
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"A Double Grounded Transformerless Photovoltaic Array String Inverter with Film Capacitors and Silicon Carbide Transistors." Doctoral diss., 2014. http://hdl.handle.net/2286/R.I.25847.
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abstract: A new photovoltaic (PV) array power converter circuit is presented. The salient features of this inverter are: transformerless topology, grounded PV array, and only film capacitors. The motivations are to reduce cost, eliminate leakage ground currents, and improve reliability. The use of Silicon Carbide (SiC) transistors is the key enabling technology for this particular circuit to attain good efficiency.
Traditionally, grid connected PV inverters required a transformer for isolation and safety. The disadvantage of high frequency transformer based inverters is complexity and cost. Transformerless inverters have become more popular recently, although they can be challenging to implement because of possible high frequency currents through the PV array's stay capacitance to earth ground. Conventional PV inverters also typically utilize electrolytic capacitors for bulk power buffering. However such capacitors can be prone to decreased reliability.
The solution proposed here to solve these problems is a bi directional buck boost converter combined with half bridge inverters. This configuration enables grounding of the array's negative terminal and passive power decoupling with only film capacitors.
Several aspects of the proposed converter are discussed. First a literature review is presented on the issues to be addressed. The proposed circuit is then presented and examined in detail. This includes theory of operation, component selection, and control systems. An efficiency analysis is also conducted. Simulation results are then presented that show correct functionality. A hardware prototype is built and experiment results also prove the concept. Finally some further developments are mentioned.
As a summary of the research a new topology and control technique were developed. The resultant circuit is a high performance transformerless PV inverter with upwards of 97% efficiency.Dissertation/Thesis
Doctoral Dissertation Electrical Engineering 2014
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Zhan, Shi-Hung, and 詹士鋐. "Design and Implementation of a Single-Phase H-bridge Zero Voltage Rectifier Grid-connected Transformerless Inverter." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/29515365474239612020.
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碩士健行科技大學
電機工程所
101
This thesis focuses on design and implementation of a single-phase H-bridge zero voltage rectifier grid-connected transformerless to overcome common-mode voltage variable and leakage current problems of the grid-connected transformerless inverter. First, the common-mode voltage characteristics of various transformerless inverters were simulated and verified, then a 1kW single-phase H-bridge zero voltage rectifier grid-connected transformerless inverter was implemented. All the control methods were finished by software to reduce the cost and improve the reliability of the system. In this thesis, the control algorithms of the proposed system was simulated and analyzed by the Psim software first. The current control method was adopted to control the single-phase full-bridge inverter for grid connection function and the zero-voltage status was used to control the full-bridge rectifier to obtain a fixed common mode voltage for suppressing leakage current of the inverter. A digital signal processor (DSP, TMS320F28335) was used to implement a 1kW, 110V, 60Hz, prototype single-phase H-bridge zero voltage rectifier grid-connected transformerless inverter. Experiment then was conducted to justify the analysis. The prototype inverter conversion efficiency can reach 94.9%.
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Ελευθεράκης, Γεώργιος. "Μελέτη και κατασκευή μονοφασικού αντιστροφέα τύπου Η5 για φωτοβολταϊκά συστήματα." Thesis, 2013. http://hdl.handle.net/10889/6014.
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Η παρούσα διπλωματική εργασία πραγματεύεται τη μελέτη και την κατασκευή ενός μονοφασικού αντιστροφέα Η5, ο οποίος χρησιμοποιείται ευρέως σε τοπολογίες αντιστροφέων χωρίς μετασχηματιστή για τη διασύνδεση φωτοβολταϊκών πλαισίων με το δίκτυο χαμηλής τάσης. Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών.
Σκοπός της διπλωματικής αυτής εργασίας είναι να καταστεί σαφής η λειτουργία του αντιστροφέα Η5 μέσω της θεωρητικής ανάλυσής του. Ακόμη, σκοπός της εργασίας αυτής είναι να γίνει κατανοητός ο λόγος για τον οποίο ο αντιστροφέας Η5 βρίσκει μεγάλη εφαρμογή και προτιμάται έναντι άλλων τοπολογιών αντιστροφέων στα φωτοβολταϊκά συστήματα ισχύος της τάξης των 5-20 kW.
Αρχικά, παρουσιάζεται η ανάγκη εκμετάλλευσης της ηλιακής ενέργειας και περιγράφονται εν συντομία τα φωτοβολταϊκά στοιχεία που αποτελούν καθοριστικό ρόλο στον τομέα αυτό. Στη συνέχεια, περιγράφονται τα φωτοβολταϊκά συστήματα, οι τρόποι διασύνδεσής τους με το δίκτυο χαμηλής τάσης καθώς και οι τοπολογίες αντιστροφέων χωρίς μετασχηματιστή.
Ακολούθως, παρατίθεται η θεωρητική ανάλυση και η προσομοίωση του αντιστροφέα Η5 καθώς και η σύγκρισή του με την τοπολογία πλήρους γέφυρας.
Τέλος, αναλύεται η διαδικασία υλοποίησης κάθε σταδίου του μονοφασικού αντιστροφέα τύπου Η5 και παρατίθενται παλμογραφήματα και μετρήσεις που προέκυψαν από τα πειράματα που διενεργήθηκαν μετά την ολοκλήρωση της κατασκευής σε εργαστηριακό περιβάλλον.This thesis deals with the design and construction of a single-phase H5 inverter, which is widely used in transformerless inverter topologies to interconnect PV modules to the low voltage grid. The study was prepared in the Laboratory of Electromechanical Energy Conversion, Department of Electrical and Computer Engineering, University of Patras. The aim of this thesis is to clarify the operation of the H5 inverter through theoretical analysis. Moreover, the aim of this work is to illustrate the reason why the H5 inverter finds wide application and is preferred over other transformerless inverter topologies in photovoltaic power systems in the range of 5-20 kW. Initially, is presented the need to exploit solar energy and are described shortly PV modules which form a key role in this area. Then, takes place a description of photovoltaic systems, the interconnection ways to the low voltage grid as well different transformerless topologies. Thereafter,is presented the theoretical analysis and simulation of H5 inverter and its comparison with the full-bridge topology. Finally, is analyzed the implementation process of every step of the single-phase H5 inverter,while some graphs and measurements obtained from the experiments carried out after the copletion of H5 inverter's construction in a lab environment are cited.
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"High Gain DC-DC and Active Power Decoupling Techniques for Photovoltaic Inverters." Doctoral diss., 2017. http://hdl.handle.net/2286/R.I.46225.
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abstract: The dissertation encompasses the transformer-less single phase PV inverters for both the string and microinverter applications. Two of the major challenge with such inverters include the presence of high-frequency common mode leakage current and double line frequency power decoupling with reliable capacitors without compromising converter power density. Two solutions are presented in this dissertation: half-bridge voltage swing (HBVS) and dynamic dc link (DDCL) inverters both of which completely eliminates the ground current through topological improvement. In addition, through active power decoupling technique, the capacitance requirement is reduced for both, thus achieving an all film-capacitor based solution with higher reliability. Also both the approaches are capable of supporting a wide range of power factor.
Moreover, wide band-gap devices (both SiC and GaN) are used for implementing their hardware prototypes. It enables the switching frequency to be high without compromising on the converter efficiency. Also it allows a reduced magnetic component size, further enabling a high power density solution, with power density far beyond the state-of-the art solutions.
Additionally, for the transformer-less microinverter application, another challenge is to achieve a very high gain DC-DC stage with a simultaneous high conversion efficiency. An extended duty ratio (EDR) boost converter which is a hybrid of switched capacitors and interleaved inductor technique, has been implemented for this purpose. It offers higher converter efficiency as most of the switches encounter lower voltage stress directly impacting switching loss; the input current being shared among all the interleaved converters (inherent sharing only in a limited duty ratio), the inductor conduction loss is reduced by a factor of the number of phases.
Further, the EDR boost converter has been studied for both discontinuous conduction mode (DCM) operations and operations with wide input/output voltage range in continuous conduction mode (CCM). A current sharing between its interleaved input phases is studied in detail to show that inherent sharing is possible for only in a limited duty ratio span, and modification of the duty ratio scheme is proposed to ensure equal current sharing over all the operating range for 3 phase EDR boost. All the analysis are validated with experimental results.Dissertation/Thesis
Doctoral Dissertation Electrical Engineering 2017