La presente tesis estudia, propone y realiza sus principales aportaciones en el campo del control para el convertidor CC/CA de tres niveles, sobre la topología denominada Neutral-Point-Clamped, aunque se puede extender a otras topologías y/o número de niveles. Se presenta una metodología de modelado que emplea funciones de conmutación de fase, el operador de promediado y la transformación D-Q, tal que los modelos obtenidos en el dominio D-Q contienen una información completa sobre la dinámica del sistema. La estrategia de conmutación se puede entender como una extensión de la estrategia PWM senoidal de dos a tres niveles. Esta estrategia es simple y no realiza el control de ninguna de las variables del sistema. En esta tesis, el controlador se encarga de regular todas las variables del sistema, incluido el equilibrio del bus de continua. Este es un enfoque diferente del convencional, donde el equilibrio del bus de continua se consigue mediante la elección adecuada de los estados redundantes del convertidor en la estrategia de conmutación, mientras que el resto de variables se regulan a través del controlador. Para la realización del controlador, se propone la técnica de control lineal multivariable LQR (Linear Quadratic Regulator), complementada con la técnica de control no lineal adaptativo denominada programación de ganancia (Gain Scheduling). Se presenta, además, una metodología de cálculo del controlador. Este control es versátil, abierto y adaptable. En cualquier caso, el controlador se puede adaptar a las necesidades concretas de cada aplicación. El cálculo del controlador se realiza mediante simulación con MatLab-Simulink. Los modelos matemáticos que emplean las funciones de conmutación del convertidor son aquellos que ofrecen un mejor compromiso entre velocidad de simulación y precisión. Para validar el control propuesto, se ha diseñado y construido un equipo experimental donde el controlador se ha mostrado aplicable, útil y eficaz en la regulación de las distintas cargas y aplicaciones experimentadas, incluso con carga no lineal, bajo diferentes condiciones de trabajo y variables a controlar, tanto en régimen permanente como en procesos transitorios. La rapidez y calidad de la respuesta transitoria es comparable a la de otros sistemas de control publicados. Es especialmente interesante el excelente control conseguido del equilibrio del bus de continua. Además, la robustez del control permite cancelar el error estacionario aunque diferentes parámetros del sistema presenten desviaciones significativas respecto los valores esperados. El uso de la programación de ganancia junto con la técnica LQR se ha mostrado muy efectivo, puesto que permite realizar diferentes tipos de control. Se ha comprobado la congruencia entre simulaciones y resultados experimentales obtenidos, lo que valida los modelos de simulación empleados y el proceso de diseño del controlador mediante simulación. / This dissertation study, propose and carry out the main contributions in the field of three-level inverter control, using the topology Neutral-Point-Clamped, although results can be extended to other topologies and/or number of levels. A procedure for modelling is presented, based on line-switching functions, moving average operator and D-Q transformation. Then, the obtained models in D-Q frame contain complete information about system dynamics. Switching strategy is simple and can be considered as an extension of two-level sinusoidal PWM to three level. The system variables are not controlled by the switching strategy. In this work, all the system variables are controlled by the regulator, including DC-link balance. This control approach is different than the conventional one, where DC-link balance is achieved by means of a proper selection of redundant states in the switching strategy, and the other variables are controlled by the regulator. The regulator is based on the multivariable linear control technique LQR (Linear Quadratic Regulator), in combination with the non-linear adaptive control technique Gain Scheduling. Moreover, a methodology for the calculation of the controller is presented. This controller is versatile, open and adaptable. However, the controller can be built depending on the concrete specifications of each application. The controller is calculated by means of simulation using MatLab-Simulink. The mathematical models based on the switching functions of the converter give the best trade-off between simulation speed and precision. In order to validate the proposed controller, an experimental prototype has been designed and implemented. Experimental results show that the controller is useful and effective for the regulation of different loads and applications, even with non-linear loads, different operation points and variables to control, in steady-state and transitory operation. Dynamic response speed and quality are similar to other control systems in the literature. The DC-link balance control achieved is specially interesting. Furthermore, steady-state error is cancelled due to the robustness of the controller, even though significant deviation of different system parameters are present. The use of Gain-Scheduling in combination with LQR is effective, allowing the calculation of regulators with different control strategies. Good agreement between simulations and experimental results has been found. This result validates simulation models and the design method for the controller, based on simulations.

Pulse width modulation (PWM) voltage source converters (VSC) are one type of motor drives that have become popular because they enable precise control of speed and torque in medium voltage motors. However, these drives are known to have adverse effects on the insulation system particularly on conductive armour tape (CAT) and semi-conductive stress grading tape (SGT). These tapes, which are crucial components of the insulation system, control the surface electrical stresses in the stator slot and in the end portion of the form-wound coils outside the grounded stator. The material properties of CAT and SGT and the methods by which they are applied on form-wound motor coils are traditionally designed for power frequency, or a 60 Hz sinusoidal voltage. However, because of the high frequencies associated with the repetition rate and the fast rise time of the PWM pulses, elevated electrical and thermal stresses develop in these tapes, which can lead to premature insulation failure. Little research has been conducted with respect to understanding the mechanism of dielectric heating as a function of frequency and repetitive pulse characteristics. The material characterization of CAT and SGT is a vital part of an investigation of the performance of the stress relief system at high frequencies. In this study, the anisotropic dielectric properties of CAT and SGT have been measured in dc and ac and in low and high electric fields. The laboratory experiments for determining the material characteristics are discussed and the results analyzed. According to the ac space charge limited field (SCLF) theory, the maximum ac tangential component of the electric field in a nonlinear resistive SGT on medium voltage form-wound motor coils can be predicted from the field dependent electrical conductivity and the frequency. However, the SCLF theory cannot predict the total electric field (vector sum of the tangential and normal components) in the air adjacent to the surface of the tapes. Simulations of the electric field using a finite element method (FEM), is one of the best ways of finding the resultant electric field distribution in the air space adjacent to the SGT. However, prior to this study, researchers simplified the modelling of the stress relief system to avoid the convergence problems that develop due to the nonlinearity of the SGT conductivity as a function of the electric field, and also because of the geometry and dimensions of the tapes when their depths are orders of magnitude smaller than the other dimensions associated with form-wound coils. For modelling the stress grading (SG) system at power frequency and at the rated voltage, the dc isotropic conductivity of the SGT and CAT has also been extensively investigated. However, relatively little work has been done with respect to the ac electrical behaviour of these materials and dc modelling cannot reflect the effects of high-frequency stresses on the machine insulation. In this study, comprehensive transient FEM modelling has been developed in order to simulate the insulation system with nonlinear field dependent materials. The actual dimensions of the components are applied in the model, and the appropriate material parameters for the FEM simulations are extracted from the experimental test results. One crucial point that has not been considered in previous studies is the effect of the component of the electric field that is normal to the surface of the coil. In most studies, only the tangential component of the electric field is considered; however, in this study, both components and the resultant electric field are computed. The surface tangential field is calculated with reference to the gradient of the surface potential as measured with an electrostatic voltmeter. It is shown that this technique can provide a reasonable estimate for the tangential field along the SG system, but not without limitations, which are discussed in detail. Based on laboratory work and analytical analysis, this research has successfully determined the relationship between the thermal effect of the PWM voltage and the other repetitive fast pulses, such as square wave and impulse voltages. The influence of the pulse characteristics on the development of stresses has also thoroughly investigated, and the results are presented. A coupled electric and thermal model that incorporates the finite element method (FEM) is used as a means of studying thermal stresses and determining appropriate remedies. However, using transient analysis as an approach for finding the temperature profile associated with high repetitive impulses (1-10 kHz) and fast rise times (~200 ns) is both difficult and impractical. According to these considerations, an alternative method has been developed from stationary analyses based on two sinusoidal voltages of different frequencies. The frequency and amplitude of these sinusoids are measured relative to the switching frequency, signal power, and nonlinearity of the system, and the results of the simulation are then verified experimentally, thus showing the efficacy of this method. This research also concluded that a capacitive SG system with conductive foil embedded in the groundwall insulation can be a practical alternative to a conventional SGT of form-wound coils in inverter fed motors. The performance of the capacitive SG scheme is independent of frequency and can therefore provide the required mitigation of the stress caused by repetitive fast pulses. The results of the evaluation of this system with respect to qualification tests demonstrate the effectiveness of the system.

A repetitive control method for output voltage control of a three phase uninterruptible power supply (UPS) with isolation transformer is investigated. In the method voltage control loop is employed in the stationary dq frame. The controller eliminates the periodic errors on the output voltages due to inverter voltage nonlinearity and load disturbances. The controller design and implementation details are given. The controller is implemented on a 5-kVA UPS prototype which is constructed in laboratory. Linear and nonlinear loads for balanced and unbalanced load operating conditions are considered. The steady-state and dynamic performance of the control method are investigated in detail. The theory of the control strategy is verified by means of simulations and experiments.

A method for high performance output voltage control of a four-leg inverter based three-phase transformerless UPS is proposed. Voltage control loop is employed and the method employs stationary frame resonant filter controllers for the fundamental and harmonic frequency components. A capacitor current feedback loop provides active damping and enhances the output voltage dynamic performance. The controller design and implementation details are given. Linear and nonlinear loads for balanced and unbalanced load operating conditions are considered. The steadystate and dynamic performance of the UPS are investigated in detail. A scalar PWM method with implementation simplicity and high performance is proposed and implemented. The control and PWM methods are proven by means of theory, simulations, and experiments.

The study designs and constructs a three-phase to three-phase direct AC&ndash / AC matrix converter based surface mounted permanent magnet synchronous motor (PMSM) drive system. First, the matrix converter topologies are analyzed and the state-space equations describing the system have been derived in terms of the input and output variables. After that, matrix converter commutation and modulation methods are investigated. A four-step commutation technique based on output current direction provides safe commutation between the matrix converter switches. Then, the matrix converter is simulated for both the open-loop and the closed-loop control. For the closed-loop control, a current regulator (PI controller) controls the output currents and their phase angles. Advanced pulse width modulation and control techniques, such as space vector pulse width modulation and field oriented control, have been used for the closed-loop control of the system. Next, a model of diode-rectified two-level voltage source inverter is developed for simulations. A comparative study of indirect space vector modulated direct matrix converter and space vector modulated diode-rectified two-level voltage source inverter is given in terms of input/output waveforms to verify that the matrix converter fulfills the two-level voltage source inverter operation. Following the verification of matrix converter operation comparing with the diode-rectified two-level voltage source inverter, the simulation model of permanent magnet motor drive system is implemented. Also, a direct matrix converter prototype is constructed for experimental verifications of the results. As a first step in experimental works, filter types are investigated and a three-phase input filter is constructed to reduce the harmonic pollution. Then, direct matrix converter power circuitry and gate-driver circuitry are designed and constructed. To control the matrix switches, the control algorithm is implemented using a DSP and a FPGA. This digital control system measures the output currents and the input voltages with the aid of sensors and controls the matrix converter switches to produce the required PWM pattern to synthesize the reference input current and output voltage vectors, as well. Finally, the simulation results are tested and supported by laboratory experiments involving both an R-L load and a permanent magnet synchronous motor load. During the tests, the line-to-line supply voltage is set to 26 V peak value and a 400 V/3.5 kW surface mounted permanent magnet motor is used.

Pulse width modulation (PWM) rectifiers are extensively used in battery charger, regulated dc voltage source, UPS systems, ac line conditioner and motor drives. The conventional control schemes for these rectifiers require PLL, transformations, and input voltage sensing, which increase the cost and complexity of the controller. Simple control schemes based on resistance emulation control are developed in this thesis work for different PWM boost rectifiers. Modeling, analysis and design methods for these rectifier systems are presented. The effect of computational delay involved in digital implementation on the performance of the above rectifier systems is studied. A single-switch boost rectifier system is presented, which operates in DCM and in CCM for an output power less than and greater than 50% rated load, respectively, exploiting the best features of both the operating modes. A generalized feedforward control is presented to improve the dynamic response of output voltage of single-phase boost rectifiers against input voltage, load current and reference voltage disturbances. Feedforward control requires additional voltage and/or current measurements. A state observer is presented for estimating the inductor current of a buck rectifier, and two disturbance observers are presented to estimate the input voltage and the load current of a boost rectifier. These observers eliminate the need of additional sensors for implementing the feedforward control. The resistance emulation control is extended to four-wire PWM rectifier. Two control methods are presented. The first method makes the input currents of the rectifier proportional to their respective input voltages, while the second one balances its input currents even under unbalanced input voltage condition. A detailed analysis of line and neutral current distortions of four-wire converter is presented. A three-carrier based PWM scheme is presented, which significantly reduces the neutral current of the rectifier compared to conventional PWM scheme, when three single-phase inductors are used, and considerably reduces both line and neutral current distortions, when a three-limb inductor is used. A regenerative test setup containing two back-to-back connected three-phase PWM converters is presented for testing high-power converters in the active and reactive power circulation mode. The proposed scheme considerably reduces the cost of testing, and hence, the overall production cost of the converters compared to load-bank testing. A mathematical model is presented for the above system. A suitable control method is presented to control the two converters of the back-to-back system. A new PWM scheme is presented, which considerably reduces the requirement of the dc bus voltage of the back-to-back system compared to conventional PWM schemes. All theoretical predictions are experimentally validated. The experimental results are presented.

The major achievements of this work are based on two categories: (A) introduction of an advanced simulation technique in both time domain and frequency domain, and (B) realistic and reliable models for converters applicable to analysis of alternative transmission systems. The proposed modeling-methodology using a combination of model quadratization and quadratic integration (QMQI) is demonstrated as a more robust, stable, and accurate method than previous modeling methodologies for power system analyses. The quadratic-integration method is free of artificial numerical-oscillations exhibited by trapezoidal integration (which is the most popularly used method in power system analyses). Artificial numerical oscillations can be the direct reason for switching malfunction of switching systems. However, the quadratic-integration method has a natural characteristic to eliminate fictitious oscillations with great simulation accuracy. Also, model quadratization permits nonlinear equations to be solved without simplification or approximation, leading to realistic models of nonlinearities. Therefore, the QMQI method is suitable for simulations of network systems with nonlinear components and switching subsystems. Realistic and reliable converter models by the application of the QMQI method can be used for advanced designs and optimization studies for alternative transmission systems; they can also be used to perform a comprehensive evaluation of the technical performance and economics of alternative transmission systems. For example, the converters can be used for comprehensive methodology for determining the optimal topology, kV-levels, etc. of alternative transmission systems for wind farms, for given distances of wind farms from major power grid substations. In this case, a comprehensive evaluation may help make more-informed decisions for the type of transmission (HVAC, HVDC, and LFAC) for wind farms.

This thesis presents the preliminary work in the development of a biomimetic actuation mechanism for prosthetic and wearable robotic hand applications. This work investigates the use of novel artificial muscle technology, namely, shape memory alloys. The mechanism developed is based on the combination of compliant tendon cables and one-way shape memory alloy wires that form a set of agonist–antagonist artificial muscle pairs for the required flexion/extension or abduction/adduction of the finger joints. For the purpose of this thesis, an anthropomorphic four degree of freedom artificial testbed was developed with the same kinematic properties as the human finger. Hence, the size, appearance and kinematic architecture of the index finger were efficiently and practically mimicked. The biomimetic actuation scheme was implemented on the anthropomorphic artificial finger and tested, in an ad-hoc fashion, with a simple microcontroller-based pulse width modulated proportional derivation (PWD-PD) feedback controller. The tests were done to experimentally validate the performance of the actuation mechanism as emulating the natural finger’s joints movement. This thesis details the work done for the finger design process as well as the mechanisms and material used to achieve the actuation and control objectives. The results of the experiments done with the actuation platform are also presented.

Pulse width modulation (PWM) voltage source converters (VSC) are one type of motor drives that have become popular because they enable precise control of speed and torque in medium voltage motors. However, these drives are known to have adverse effects on the insulation system particularly on conductive armour tape (CAT) and semi-conductive stress grading tape (SGT). These tapes, which are crucial components of the insulation system, control the surface electrical stresses in the stator slot and in the end portion of the form-wound coils outside the grounded stator. The material properties of CAT and SGT and the methods by which they are applied on form-wound motor coils are traditionally designed for power frequency, or a 60 Hz sinusoidal voltage. However, because of the high frequencies associated with the repetition rate and the fast rise time of the PWM pulses, elevated electrical and thermal stresses develop in these tapes, which can lead to premature insulation failure. Little research has been conducted with respect to understanding the mechanism of dielectric heating as a function of frequency and repetitive pulse characteristics. The material characterization of CAT and SGT is a vital part of an investigation of the performance of the stress relief system at high frequencies. In this study, the anisotropic dielectric properties of CAT and SGT have been measured in dc and ac and in low and high electric fields. The laboratory experiments for determining the material characteristics are discussed and the results analyzed. According to the ac space charge limited field (SCLF) theory, the maximum ac tangential component of the electric field in a nonlinear resistive SGT on medium voltage form-wound motor coils can be predicted from the field dependent electrical conductivity and the frequency. However, the SCLF theory cannot predict the total electric field (vector sum of the tangential and normal components) in the air adjacent to the surface of the tapes. Simulations of the electric field using a finite element method (FEM), is one of the best ways of finding the resultant electric field distribution in the air space adjacent to the SGT. However, prior to this study, researchers simplified the modelling of the stress relief system to avoid the convergence problems that develop due to the nonlinearity of the SGT conductivity as a function of the electric field, and also because of the geometry and dimensions of the tapes when their depths are orders of magnitude smaller than the other dimensions associated with form-wound coils. For modelling the stress grading (SG) system at power frequency and at the rated voltage, the dc isotropic conductivity of the SGT and CAT has also been extensively investigated. However, relatively little work has been done with respect to the ac electrical behaviour of these materials and dc modelling cannot reflect the effects of high-frequency stresses on the machine insulation. In this study, comprehensive transient FEM modelling has been developed in order to simulate the insulation system with nonlinear field dependent materials. The actual dimensions of the components are applied in the model, and the appropriate material parameters for the FEM simulations are extracted from the experimental test results. One crucial point that has not been considered in previous studies is the effect of the component of the electric field that is normal to the surface of the coil. In most studies, only the tangential component of the electric field is considered; however, in this study, both components and the resultant electric field are computed. The surface tangential field is calculated with reference to the gradient of the surface potential as measured with an electrostatic voltmeter. It is shown that this technique can provide a reasonable estimate for the tangential field along the SG system, but not without limitations, which are discussed in detail. Based on laboratory work and analytical analysis, this research has successfully determined the relationship between the thermal effect of the PWM voltage and the other repetitive fast pulses, such as square wave and impulse voltages. The influence of the pulse characteristics on the development of stresses has also thoroughly investigated, and the results are presented. A coupled electric and thermal model that incorporates the finite element method (FEM) is used as a means of studying thermal stresses and determining appropriate remedies. However, using transient analysis as an approach for finding the temperature profile associated with high repetitive impulses (1-10 kHz) and fast rise times (~200 ns) is both difficult and impractical. According to these considerations, an alternative method has been developed from stationary analyses based on two sinusoidal voltages of different frequencies. The frequency and amplitude of these sinusoids are measured relative to the switching frequency, signal power, and nonlinearity of the system, and the results of the simulation are then verified experimentally, thus showing the efficacy of this method. This research also concluded that a capacitive SG system with conductive foil embedded in the groundwall insulation can be a practical alternative to a conventional SGT of form-wound coils in inverter fed motors. The performance of the capacitive SG scheme is independent of frequency and can therefore provide the required mitigation of the stress caused by repetitive fast pulses. The results of the evaluation of this system with respect to qualification tests demonstrate the effectiveness of the system.

Η παρούσα διπλωματική εργασία έχει ως αντικείμενο την μελέτη και τη μοντελοποίηση ενός υβριδικού συστήματος, που αποτελείται από φωτοβολταϊκά και κυψέλες καυσίμου τα οποία τροφοδοτούν ένα μικροδίκτυο. Το φορτίο το οποίο καλείται το σύστημα να καλύψει είναι 30kW και 15kVar. Για τη μοντελοποίηση του συστήματος χρησιμοποιείται το πρόγραμμα σχεδίασης και προσομοίωσης ηλεκτρικών συστημάτων PSCAD. Στην εργασία αυτή το ενδιαφέρον επικεντρώνεται στη συμπεριφορά του συστήματος στη μόνιμη κατάσταση λειτουργίας και στη συμπεριφορά σε κάποια μεταβατατικά φαινόμενα. Τα μεταβατικά φαινόμενα που εξετάζονται είναι τα εξής: - Συμπεριφορά συστήματος σε μεταβολές της ηλιοφάνειας. - Απόκριση συστήματος σε μεταβολές του φορτίου. - Τριφασικό και μονοφασικό βραχυκύκλωμα με τη γη στη γραμμή. Στο κεφάλαιο 1 γίνεται αναφορά στις ανανεώσιμες πηγές, στην εξέλιξή και στην προοπτική τους στο μέλλον. Στη συνέχεια περιγράφονται τα διάφορα είδη των υβριδικών συστημάτων και γίνεται αναφορά για τη διεσπαρμένη παραγωγή και τα μικροδίκτυα. Στο κεφάλαιο 2 περιγράφεται η λειτουργία των φωτοβολταϊκών κυττάρων, παρουσιάζονται οι I-V και P-V χαρακτηριστικές και στη συνέχεια ακολουθεί αναλυτική περιγραφή του μοντέλου της φωτοβολταϊκής συστοιχίας που θα χρησιμοποιήσουμε στην προσομοίωση στο PScad. Στο κεφάλαιο 3 περιγράφεται η λειτουργία των κυψελών καυσίμων και παρουσιάζονται τα διάφορα είδη κυψελών που υπάρχουν στις μέρες μας. Εν συνεχεία ακολουθεί αναλυτική περιγραφή της λειτουργίας της κυψέλης καυσίμου πολυμερούς ηλεκτρολυτικής μεμβράνης PEM FC καθώς αυτό το είδος των κυψελών καυσίμου χρησιμοποιούμε στο σύστημά μας. Τέλος, κατασκευάζεται το μοντέλο της PEM FC και ακολουθεί η αναλυτική περιγραφή του μοντέλου. Στο κεφάλαιο 4 γίνεται αναφορά στους dc/dc μετατροπείς ανύψωσης τάσης και στις περιοχές λειτουργίας τους. Εν συνεχεία γίνεται διαστασολόγηση του ανυψωτή τάσης και παρουσιάζεται το σύστημα ελέγχου του. Επίσης μελετάται η λειτουργία του ανυψωτή ως ανιχνευτή του σημείου μέγιστης ισχύος της φωτοβολταϊκής συστοιχίας και γίνεται προσομοίωση των κυψελών και της φωτοβολταϊκής συστοιχίας με τους dc/dc μετατροπείς που χρησιμοποιούνται. Στο κεφάλαιο 5 ακολουθεί η περιγραφή της λειτουργίας των μονοφασικών και τριφασικών αντιστροφέων DC/AC και παρουσιάζεται αναλυτικά η στρατηγική της διαμόρφωσης εύρους παλμών (PWM). Τέλος, γίνεται υπολογισμός των τιμών του φίλτρου που τοποθετείται στην έξοδο του αντιστροφέα και στη συνέχεια προσομοιώνεται και μελετάται το μοντέλο του αντιστροφέα που χρησιμοποιούμε στο σύστημά μας. Στο κεφάλαιο 6 γίνεται η πλήρη προσομοίωση του συστήματος. Περιγράφονται επίσης και τα μοντέλα του φορτίου, του Μ/Σ, του δικτύου και της μηχανής παραγωγής σφαλμάτων. Τέλος, παρουσιάζονται και περιγράφονται τα αποτελέσματα των μελετών που πραγματοποιούνται στο σύστημα (απόκριση συστήματος σε κανονικές συνθήκες, απόκριση συστήματος για μεταβολή της ηλιοφάνειας, μελέτη συστήματος στη μεταβολή του φορτίου, προσομοίωση συστήματος για σφάλματα στη γραμμή). / The current diploma thesis presents the study and simulation of a hybrid system, which consists of a Photovoltaic Array (PV) and a Fuel Cell stack (FC), which supports a microgrid. The critical load that the system supports is 30kW and 15kVar. For the system modelling the program of designing and simulation of electric systems PSCAD is used. At this project the interest is focused in the behavior of system in the permanent situation of operation and in the behavior in certain transient phenomena. The transient phenomena that are examined are the following: - Behavior of the system in variations in solar insolation. - System’s response to variations of the load. - Fault analysis (single line to ground and three-phase line to ground short circuit). In Chapter 1 there is a description of renewable energy sources, their development and prospects in the future. Afterwards, the different kinds of hybrid systems are mentioned and there is a reference in distributed generation and microgrids. In Chapter 2 the function of photovoltaic cells and different kinds of photovoltaic technologies are described. Furthermore, I-V and P-V characteristic are presented and then follows an analytical description of the photovoltaic model that we use in our simulation in PScad. In Chapter 3 , the function of the Fuel Cells is described and the different kinds of fuel cells are presented. Afterwards, there is an analytical description of the proton exchange membrane fuel cells (PEM FC) as we use this kind of FC in our system. Finally, the PEM FC model is constructed and an analytical description of the model is made. The Chapter 4 entails information for the dc/dc boost converters and their operating modes. Subsequently the control system of the dc/dc boost converter is presented. Finally, the utilization of the boost converter as a maximum power point tracker is examined and the simulation of the FV and PV with the boost converter is presented. In Chapter 5 there is a description of the function of the single-phase and three-phase dc/ac inverters and the technique of the pulse-width modulation (PWM) is presented. Finally, the value of the output filter of the inverter is calculated and then the model of the dc/ac inverter, which we use in our system, is simulated. In Chapter 6 there is a simulation of the whole system. Furthermore, the models of the load, the transformer and the fault generator are described. Finally, the results of the simulations for which the system was tested is presented (system response to normal conditions, system response to changes in the insolation, System’s response to variations of the load, system response to grid faults).