Since 2002, the department of electricity at Uppsala university has pushed the Lysekil project. The project has a number of wave energy converters installed in the sea southwest of Lysekil. The purpose of this work is to design, build and test a DC-DC converter, which will later be used as a necessary part of the grid connection of a wave energy converter. Since a wave energy converter does not generate electricity at a constant frequency, it is not possible to use a gearbox. Instead, power is rectified and, if there are several wave power energy converters, are put together with the others before it is inverted and transformed to the correct voltage level, and finally connected to the grid [1]. The designed DC-DC converter is a converter of the type "inverting buck-boost", i.e. a converter that can both lower and raise the voltage, and inverts the polarity of the output. Although the voltage in normal circumstances will only be increased, the simulations showed that the efficiency and cost of components did not differ much between a "boost" and "buck-boost" converter, thus considered flexibility to be able to lower the voltage if needed. The project also includes a small part to the construction of a bridge rectifier, but as the most difficult moment in the project is the DC-DC converter, the greatest focus will be there.

This thesis presents an electrical system analysis of a wave energy converter (WEC) for the objective of grid connection. To transfer the enormous amount of power from waves to the load centers, efficient power electronic systems are essential. This thesis includes the modeling of a buoy–translator dynamics and the modeling of a linear permanent magnet generator along with simulation and experimental validation. Diode bridge rectifiers are considered for rectification to avoid the complex linear generator control at the input side. To reduce the size and the cost of energy storage elements, DC voltage regulation is done using a DC/DC converter. To achieve smooth and high power, many WECs need to be connected to a common DC link. A neutral point clamped inverter is considered for the DC/AC conversion due to its advantages over conventional topologies. Various pulse width modulation schemes are tested for the inverter to choose the optimum PWM method. The harmonics in the inverter output voltage is derived numerically and compared with simulation and experiment to understand the effect of dead-time in the inverter operation. Depending on the load current drawn from the inverter, the voltages in the two input capacitors of a three-level neutral point clamped inverter deviates from equilibrium unless the neutral point is grounded. To avoid this voltage imbalance as well as to regulate the DC link voltage a dual output boost converter with pulse delay control is proposed. The modeling, simulation and experiments show an improvement in the compensation voltage using pulse delay control compared to the previously proposed methods in the literature. The synchronous current control and the grid connection of the three-level converter have been accomplished in the laboratory.  Finally, the three-level power converter system has been tested with a linear permanent magnet generator at Lysekil to analyze the controller requirements.

This Bachelor’s degree thesis has been performed on behalf of Upplands Lokaltrafik. The thesis aims to suggest a design of a stand-alone renewable power supply system for the bus stops in Uppland. Because of reorganization of Upplands Lokaltrafik and a change in the electricity act they now have to make the decision of either having the future bus stops connected to the electricity grid, with the requirement of installing an electricity meter at each bus stop, or to implement an off grid solution. Upplands Lokaltrafik has a goal of doubling the number of passengers until 2020 and as a part of reaching this goal the bus stops will be designed with electrical features. This thesis also aims to investigate the electricity demand for these future bus stops. The result of the study shows that a connection to the electricity grid and installation of an electricity meter means an investment cost of approximately 83 500 SEK or 123 500 SEK depending on how far cables have to be drawn. The solution with a photovoltaic system with a 180 Wp solar panel would result in an installation cost of 18 500 SEK, which would be both cheaper and more sustainable for the future. However, a photovoltaic system means higher maintenance and a higher risk of destruction. Depending on choice of batteries and the slope of solar panels, both maintenance and risk of vandalization could be diminished.

Orientador: Carlos Alberto Canesin / Banca: Falcondes Jose Mendes de Seixas / Banca: Dionizio Paschoareli Junior / Banca: Ernane Antônio Alves Coelho / Banca: José Demisio da Silva / Resumo: Uma das importantes aplicações dos sistemas inversores está associada ao fornecimento de energia elétrica. Com este foco destacam-se o fornecimento para cargas críticas, o fornecimento em áreas desprovidas dos usuais sistemas de transmissão e distribuição e aplicações com multi-fontes primárias de energia, incluindo-se neste caso, as aplicações para geração distribuída, com possibilidade de conectividade com a rede elétrica de distribuição ou, com o paralelismo entre estruturas isoladas. Atualmente, topologias e filosofias de controle que atendam as características das aplicações supracitadas são de interesse técnico e científico. Neste sentido, a possibilidade de paralelismo entre inversores sem interconexão do controle tem se mostrado atrativa à medida que se exigem sistemas distribuídos e adaptáveis às variações paramétricas do circuito. Entretanto, problemas de estabilidade e resposta dinâmica devem ser solucionados para garantir a confiabilidade de tais sistemas. Sendo assim, neste trabalho inicialmente é realizada a modelação em espaço de estados de sistemas compostos por inversores cuja filosofia de controle esteja embasada nas curvas P- e Q-V. Com esta modelação, tornam-se possíveis avaliações de estabilidade e resposta dinâmica através dos autovalores da matriz de estados. Propõe-se assim a busca da estabilidade dos sistemas com melhores respostas dinâmicas através de alterações nos valores da matriz de estados, resultando-se em autovalores que representem parâmetros de desempenho otimizados. Obviamente que alterações na matriz de estados estão associadas a alterações na planta, contudo, alterações em parâmetros físicos não são interessantes, uma vez que não são simples de serem obtidas na prática. Sendo assim, são propostas alterações nas constantes que definem as inclinações das curvas de controle P- e Q-V... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: One of main applications of inverter systems is associated to electrical energy supply. With this focus it emphasizes the supply of energy to critical loads, the supply of energy to areas devoid of the usual transmission and distribution systems of energy and the use of primary energy in multi-fonts applications, including in this case, distributed generation applications with grid connectivity or, parallelism in stand alone applications. Currently, topologies and control philosophies capable to assure the applications characteristics above mentioned are in technical and scientific interests. In this way, the possibility of inverter parallelism with no control interconnection has showed attractive, since distributed systems and adaptable systems to parametric variations are mandatory nowadays. However, stability troubles and inadequate dynamic responses must be solved to ensure reliability of these systems. So, in this work is performed the state space modeling of systems set by inverters whose control philosophy is based on P- and Q-V curves. With this modeling it becomes possible evaluations of stability and dynamic response through state matrix eigenvalues. Thus, it proposes to assure the systems stability and better dynamic responses through changes on state matrix values, resulting in eigenvalues that represent optimized performance parameters. Obviously those variations in state matrix are associated with plant variations, however, physical parameters variations are not interesting, seeing that it is not simple to be obtained in practical situations. In face of this are proposed variations in constants that define the slopes of P- and Q-V curves. These slopes intervene directly on state matrix values and consequently in systems eigenvalues. The variations on constants are not performed randomly, nevertheless based on evolutionary algorithm capable to search values that represent...(Complete abstract click electronic access below) / Doutor

The recent growth expectation of the participation of solar-photovoltaic energy sources in the power generation matrix has significantly increased the number of grid-connected systems. For connection to power grid, it is essential to use a dc-ac converter, which is able to suit the characteristics of the power provided by the photovoltaic modules to grid parameters. This dissertation presents a project proposal of a 2 kW single phase dc-ac converter for connecting a 311 V dc bus to a 220 Vrms ac bus of a microgrid. The proposed converter is bidirectional and allows, when necessary, the power flow from ac to dc bus. The study shows, through simulation and prototype implementation in the laboratory, that with the application of an appropriate control strategy it is possible to control the direction of power flow, as well as properly modulating the current flowing between two buses, dc, powered by photovoltaic panels and the battery bank, and the ac, at grid side. The prototype had a yield of about 91% and has injected electric current with low harmonic content (THDi less than 5%). / A recente expectativa de crescimento da participaÃÃo da energia solar-fotovoltaica na matriz de geraÃÃo de energia elÃtrica aumentou significativamente o nÃmero de conexÃes desses sistemas à rede elÃtrica. Para que a interligaÃÃo com a rede elÃtrica convencional seja possÃvel, à indispensÃvel a utilizaÃÃo de conversores CC/CA, capazes de adequar as caracterÃsticas da energia disponibilizada pelos mÃdulos fotovoltaicos aos padrÃes da rede. Esta dissertaÃÃo apresenta uma proposta de projeto de conversor CC/CA de 2 kW para conexÃo de dois barramentos de uma microrrede, um CC em 311 V e outro CA em 220 Vrms. O conversor proposto à bidirecional e permite, quando necessÃrio, o fluxo de energia elÃtrica do barramento CA para o CC. O estudo realizado mostra, atravÃs de simulaÃÃes e de implementaÃÃo de protÃtipo em laboratÃrio, que com a aplicaÃÃo de uma estratÃgia de controle adequada à possÃvel controlar o sentido do fluxo de potÃncia do conversor, assim como modular apropriadamente a corrente que flui entre dois barramentos, o CC, alimentado por painÃis fotovoltaicos e por banco de baterias, e o barramento CA, do lado da rede elÃtrica. O protÃtipo desenvolvido apresentou rendimento de cerca de 91% e forneceu corrente elÃtrica de baixo conteÃdo harmÃnico (THDi menor que 5%).

Wave power is a renewable energy source with great potential, which is why there are more than a hundred ongoing wave power projects around the world. At the Division of Electricity, Uppsala University, a point-absorber type wave energy converter (WEC) has been proposed and developed. The WEC consists of a linear synchronous generator placed on the seabed, connected to a buoy floating on the surface. Power is absorbed by heave motion of the buoy, and converted into electric energy by the generator. The point-absorber WEC must be physically much smaller than the wavelength of the incoming waves, and can therefore not be scaled to very high power levels. Instead, the total power output is boosted by increasing the number of WECs, connecting them in wave power farms. To transfer the electric energy to the grid, an intermediate marine substation is proposed, where an AC/DC/AC conversion step is performed. Within this PhD-work, a full-scale offshore marine substation has been designed, constructed and experimentally evaluated. The substation is rated for grid-connection of seven WECs to the local 1kV-grid, and is placed on the seabed 3km off the coast at a depth of 25m. Various aspects of the substation design have been considered, including the mechanical and electrical systems, the WEC electrical interface, offshore operations and the automatic grid connection control system. A tap change circuit and different multilevel topologies have also been proposed. This dissertation has an experimental approach, validating a major part of the work with lab results. The final substation electrical circuit has been tested at rated grid voltage with a fluctuating input power source. The efficiency has been measured and the implemented functions are verified. Offshore operations have been successfully carried out and offshore wave farm data is expected in the nearby future.

Κατά τη διάρκεια των τελευταίων δεκαετιών, το διεθνές ενδιαφέρον για την φωτοβολταϊκή μετατροπή της ηλιακής ακτινοβολίας αυξάνει συνεχώς. Έχει δοθεί ιδιαίτερη σημασία στην ανάπτυξη φωτοβολταϊκών συστημάτων για την σύνδεσή τους με το δίκτυο, έτσι ώστε να αξιοποιείται η ηλιακή ακτινοβολία για παραγωγή ηλεκτρικής ενέργειας με τον καλύτερο δυνατό τρόπο. Στην παρούσα εργασία γίνεται μελέτη των φωτοβολταϊκών συστημάτων παραγωγής ηλεκτρικής ενέργειας και σκοπός αυτής είναι η κατασκευή ενός συστήματος μετατροπής συνεχούς τάσης σε εναλλασσόμενη για τη διασύνδεση μιας πηγής συνεχούς τάσης με το μονοφασικό δίκτυο. Το σύστημα αυτό αποτελείται από ένα ηλεκτρονικό μετατροπέα ισχύος διπλής βαθμίδας. Το πρώτο τμήμα είναι ένας μετατροπέας συνεχούς τάσης σε συνεχή τάση υψηλότερης τιμής. Συγκεκριμένα, ο μετατροπέας αυτός ανυψώνει την τάση του φωτοβολταϊκού συστήματος του Εργαστηρίου στα 400V. Στη συνέχεια υπάρχει το δεύτερο τμήμα, αποτελούμενο από το σύστημα μετατροπής συνεχούς τάσης σε εναλλασσόμενη, το οποίο μετατρέπει την εισερχόμενη συνεχή τάση των 400V σε εναλλασσόμενη τάση συχνότητας 50 Hz και ενεργού τιμής 220V. Η διπλωματική αυτή εργασία πραγματοποιήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών, υπό την επίβλεψη του Ομότιμου Καθηγητή Δρ.-Μηχ. Αθανασίου Σαφάκα. Αρχικά, αναλύεται η αρχή λειτουργίας των ηλιακών κυττάρων και περιγράφονται οι υπάρχουσες τεχνολογίες τους. Έπειτα γίνεται αναφορά στα φωτοβολταϊκά συστήματα και τους τρόπους που μπορεί να χρησιμοποιηθούν, δηλαδή συνδεδεμένα με το δίκτυο ή αυτόνομα. Στη συνέχεια, αναφέρονται και αναλύονται διάφορες τεχνικές συγχρονισμού μετατροπέων με το μονοφασικό δίκτυο και τρόποι ρύθμισης της ενεργού και αέργου ισχύoς που παρέχεται από τις πηγές ενέργειας στο δίκτυο. Παρατίθενται στοιχεία του μετατροπέα συνεχούς τάσης σε συνεχή και γίνεται η μελέτη του μονοφασικού αντιστροφέα που πρόκειται να κατασκευαστεί. Επιπρόσθετα γίνεται προσομοίωση του συστήματός στο λογισμικό MATLAB/Simulink. Συγκρίνεται η λειτουργία του αντιστροφέα με τη μέθοδο παλμοδότησης SPWM (Ημιτονοειδής Διαμόρφωση του Εύρους Παλμών) με διπολική και μονοπολική τάση εξόδου και παρουσιάζονται αποτελέσματα της προσομοίωσης για παραλληλισμό του συστήματος με το δίκτυο και προσφορά ισχύος από πηγή συνεχούς τάσης προς το δίκτυο. Αναλύονται τα τεχνικά χαρακτηριστικά του αντιστροφέα που κατασκευάστηκε, καθώς και ο τρόπος κατασκευής των απαραίτητων κυκλωμάτων για την οδήγηση του. Τέλος, παρατίθενται πειραματικά αποτελέσματα από τη λειτουργία του συστήματος. / During the last decades, the international interest in the photovoltaic conversion of solar radiation is increasing. Special attention has been given to the development of photovoltaic systems for their connection to the utility grid, in order to use solar radiation for electricity generation in the best possible way. In this diploma thesis, the photovoltaic power generation is studied and the purpose of this work is to construct a single phase grid connected dc/ac converter system in order to connect a dc voltage source to the grid. This system consists of a dual-stage electronic power converter. The first part is a dc-dc converter, which converts a source of direct current (dc) from one voltage level to another, with an output voltage greater than its input voltage. Specifically, the dc/dc converter increases the voltage of the photovoltaic system, which is installed on the laboratory, to 400V DC. The second part consists of a dc/ac inverter, which converts the incoming voltage of 400V DC to 220V AC at 50Hz. The work presented on this diploma thesis was carried out at the Laboratory of Electromechanical Energy Conversion, Department of Electrical and Computer Engineering, University of Patras, under the supervision of Emeritus Professor Dr.-Ing. Athanasios Safacas. Initially, the working principle of solar cells is analysed and its current technologies are described. Then, reference is given to the photovoltaic systems and their applications, i.e. stand-alone PV systems and grid-connected PV systems. Next, reference and analysis are given to the various grid synchronization techniques for single phase inverter systems and control methods to regulate the active and reactive power supplied from sources of energy into the grid. Data are presented about the dc/dc converter and the study of the single-phase inverter to be constructed. Additionally, the system is simulated with MATLAB/Simulink software and the simulation results of the specific system are presented. A comparison of the operation of the inverter is made using sinusoidal pulse width modulation technique (“SPWM”) with bipolar and unipolar output voltage and simulation results of the grid connected converter system are presented. The technical characteristics of the constructed inverter and the design of its necessary integrated circuits are analysed. Finally, experimental results from the operation of the grid connected dc/ac inverter are presented.

Η παρούσα διπλωματική εργασία πραγματεύεται τη μελέτη και κατασκευή ενός τριφασικού αντιστροφέα και το συγχρονισμό-σύνδεση αυτού με το τριφασικό δίκτυο. Η εργασία εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Σκοπός της εργασίας αυτής είναι η μελέτη και η κατασκευή ενός τριφασικού αντιστροφέα, ο οποίος θα συνδεθεί με το τριφασικό δίκτυο και θα αποτελέσει μέρος ενός συστήματος με πηγή ενέργειας μία συστοιχία κυψελών καυσίμου (fuel cells) και ενός μετατροπέα ανύψωσης συνεχούς τάσης σε συνεχή, με διαδοχική αγωγή δύο παράλληλων κλάδων (interleaved boost converter). Η είσοδος του τριφασικού αντιστροφέα συνδέεται στην έξοδο του μετατροπέα ανύψωσης συνεχούς τάσης σε συνεχή, με διαδοχική αγωγή δύο παράλληλων κλάδων, ο οποίος τροφοδοτεί τον αντιστροφέα με σταθερή τάση 80 V. Στην έξοδο του αντιστροφέα πρόκειται να συνδεθεί ένα φίλτρο LC για την αποκοπή των υψίσυχνων σημάτων της τάσης και στη συνέχεια ένας τριφασικός μετασχηματιστής, ο οποίος προσφέρει γαλβανική απομόνωση και ανυψώνει την τάση στην επιθυμητή τιμή, που είναι και η τιμή της τάσης του δικτύου. Καταρχάς έγινε θεωρητική μελέτη των ανανεώσιμων πηγών ενέργειας, του τριφασικού αντιστροφέα, του φίλτρου LC, του τριφασικού μετασχηματιστή, καθώς και μεθόδων συγχρονισμού με το δίκτυο. Επίσης έγινε μελέτη με το πρόγραμμα εξομοίωσης MATLAB/Simulink της διασύνδεσης του αντιστροφέα με το δίκτυο. Τέλος ακολούθησε η κατασκευή της διάταξης και η διεξαγωγή πλήθους πειραματικών δοκιμών. / The present diploma thesis deals with the design and manufacture of a three-phase inverter to synchronize and connect to the three-phase grid. This work was developed in the Laboratory of Electromechanical Energy Conversion at the Department of Electrical Engineering and Computer Technology of the School of Engineering in the University of Patras, Greece. The purpose of this thesis is the design and manufacture of a three-phase inverter, which will be connected to the three-phase grid and will be part of a system with source of energy a fuel cell stack and an interleaved boost converter, with two parallel branches. The input of the three-phase inverter is connected to the output of the interleaved boost converter with two parallel branches, which feeds the inverter with a dc voltage of 80 V. The output of the inverter is connected to an LC filter, in order to cut off the high frequency voltage signals and subsequently a three-phase transformer, which provides galvanic isolation and lifts the voltage to the appropriate value, which is the voltage value of the grid. At first a theoretical study of the renewable sources of energy, the three-phase inverter, the LC filter, the three-phase transformer, as well as the methods of synchronization with the grid was made. Study was also made with the simulation program MATLAB/Simulink at the interface of the inverter to the grid. Finally the construction of the device followed and numerous experimental trials were conducted.

Made available in DSpace on 2014-06-11T19:30:51Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-03-01Bitstream added on 2014-06-13T21:01:25Z : No. of bitstreams: 1 godoy_rb_dr_ilha.pdf: 3494392 bytes, checksum: 572327823a0ebf4a37a2c4352c009edc (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Uma das importantes aplicações dos sistemas inversores está associada ao fornecimento de energia elétrica. Com este foco destacam-se o fornecimento para cargas críticas, o fornecimento em áreas desprovidas dos usuais sistemas de transmissão e distribuição e aplicações com multi-fontes primárias de energia, incluindo-se neste caso, as aplicações para geração distribuída, com possibilidade de conectividade com a rede elétrica de distribuição ou, com o paralelismo entre estruturas isoladas. Atualmente, topologias e filosofias de controle que atendam as características das aplicações supracitadas são de interesse técnico e científico. Neste sentido, a possibilidade de paralelismo entre inversores sem interconexão do controle tem se mostrado atrativa à medida que se exigem sistemas distribuídos e adaptáveis às variações paramétricas do circuito. Entretanto, problemas de estabilidade e resposta dinâmica devem ser solucionados para garantir a confiabilidade de tais sistemas. Sendo assim, neste trabalho inicialmente é realizada a modelação em espaço de estados de sistemas compostos por inversores cuja filosofia de controle esteja embasada nas curvas P- e Q-V. Com esta modelação, tornam-se possíveis avaliações de estabilidade e resposta dinâmica através dos autovalores da matriz de estados. Propõe-se assim a busca da estabilidade dos sistemas com melhores respostas dinâmicas através de alterações nos valores da matriz de estados, resultando-se em autovalores que representem parâmetros de desempenho otimizados. Obviamente que alterações na matriz de estados estão associadas a alterações na planta, contudo, alterações em parâmetros físicos não são interessantes, uma vez que não são simples de serem obtidas na prática. Sendo assim, são propostas alterações nas constantes que definem as inclinações das curvas de controle P- e Q-V... / One of main applications of inverter systems is associated to electrical energy supply. With this focus it emphasizes the supply of energy to critical loads, the supply of energy to areas devoid of the usual transmission and distribution systems of energy and the use of primary energy in multi-fonts applications, including in this case, distributed generation applications with grid connectivity or, parallelism in stand alone applications. Currently, topologies and control philosophies capable to assure the applications characteristics above mentioned are in technical and scientific interests. In this way, the possibility of inverter parallelism with no control interconnection has showed attractive, since distributed systems and adaptable systems to parametric variations are mandatory nowadays. However, stability troubles and inadequate dynamic responses must be solved to ensure reliability of these systems. So, in this work is performed the state space modeling of systems set by inverters whose control philosophy is based on P- and Q-V curves. With this modeling it becomes possible evaluations of stability and dynamic response through state matrix eigenvalues. Thus, it proposes to assure the systems stability and better dynamic responses through changes on state matrix values, resulting in eigenvalues that represent optimized performance parameters. Obviously those variations in state matrix are associated with plant variations, however, physical parameters variations are not interesting, seeing that it is not simple to be obtained in practical situations. In face of this are proposed variations in constants that define the slopes of P- and Q-V curves. These slopes intervene directly on state matrix values and consequently in systems eigenvalues. The variations on constants are not performed randomly, nevertheless based on evolutionary algorithm capable to search values that represent...(Complete abstract click electronic access below)

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / A geraÃÃo de energia elÃtrica que combina o desenvolvimento humano com menos impactos ambientais e menos poluiÃÃo à um item fundamental no inÃcio deste sÃculo. Assim, a principal motivaÃÃo da caminhada atual à o desenvolvimento de novas topologias de sistemas descentralizados de fornecimento de energia. O objetivo à desenvolver um conversor bidirecional com alto ganho tensÃo, que à projetado para operar em dois modos: boost e buck. A topologia apresentada permite a transferÃncia bidirecional de energia, o que em algumas situaÃÃes, à transferida para o barramento CC, ou para um banco de baterias. O conversor à projetado para um potÃncia de 2 kW. à apresentado o desenvolvimento teÃrico e experimental do projeto para os dois modos de operaÃÃo. A fim de validar a proposta, sÃo apresentados resultados experimentais, para uma potÃncia de 1 kW. Os resultados foram satisfatÃrios e seu rendimento global de 93%. O protÃtipo foi testado em condiÃÃes diferentes que podem ser encontradas no dia-a-dia. / The achievement of energy generation which combines human development with less environment pollution impact is a key item in the premises of this century. Thus the main motivation of the present walk is the development of new topologies for decentralized supply systems. The objective is to develop a bidirectional converter with high voltage gain, which is designed to operate in two modes: step-up (boost) and step down (buck). The presented topology enables to bidirectional energy transfer, which in some situations it is returned to the load DC bus, formed by a back of batteries. The converter is designed for 2 kW linear load power. If is presented theoretical development and experimental designs for the two operation modes. In order to validate the proposal, it is presented experimental results, from 1 kW laboratory prototype are presented as well and 93% overall efficiency. The prototype was tested in different conditions that may be found daily.