Today, small distributed power generation (DG) systems are becoming more common as the need for electric power increases. Small DG systems are usually built close to the end-user and they take advantage of using different energy sources such as wind and solar. A few examples are hybrid cars, solar houses, data centers, or hospitals in remote areas where providing clean, efficient and reliable electric power is critical to the loads. In such systems, the power is distributed from the source side to the load side via power electronic converters in the system. At low and medium power applications, the task is often left to single phase inverters where they are the only interface between sources connected to DC bus and loads connected to an AC bus. Much has been done for the control of single phase inverters in the past years; however, due to the requirements of stand alone systems and the time-varying nature of the converter, its controller design is still quite difficult, and especially so if its critical functionality within the system is taken into consideration. Part of the challenge is also due to the fact that the load is not known at all time, further complicating the controller design. This thesis proposes a different method of control for single phase inverters used in low and medium power DG systems. The new control method takes advantage of the well-known DQ transformation and analysis mostly employed for three phase converters' analysis and control design. Providing a time-invariant model of single phase inverters is the main feature of DQ transformation. In addition to that, control design of the inverter in DQ frame becomes similar to those of DC-DC and three phase converters making it easier to achieve superior performance under different operation conditions while achieving a robust controller. The transformation requires at least two independent phases for each state variable in the system; thus a second phase must be created. This thesis proposes the creation of an imaginary circuit based on the real circuit of the inverter to provide the second required phase for transformation. The state variables of the imaginary circuit are obtained by differentiating the state variables of the main inviter's circuit. The differentiation can be implemented in DSP so there is no need for additional hardware in the system, making it more attractive and cost effective method. The DQ controller not only provides superior transient response, it also provides zero steady-state error as well as low output voltage THD under nonlinear load operation. The entire controller can be implemented in a digital control board which is becoming more common in power electronics converters within the past decade. Analysis and design of a DQ controller for a 2.5kW single phase full-bridge inverter is presented in this study with the final results implemented in a FPGA/DSP based digital controller board. / Master of Science

This thesis shows the implementation of a novel control scheme DC-DC converter. The converter is a phase-shifted full-bridge PWM converter that is designed to operate as a front stage of a power conversion system where the input is a variable low voltage high current source. The converter is designed to step-up the low voltage input to an acceptable level that can be inverted to a 120/240 VAC 60Hz voltage for residential power. A DSP based adaptive control model is developed, taking into account line variations introduced by the input source while providing very good load dynamics for the converter in both discontinuous and continuous conduction modes. The adaptive controller is implemented using two voltage sensors that read the input and the output voltages of the converter. The controller's bandwidth is comparable to current mode control, without the need for an expensive current sensor, yet providing the noise immunity seen in voltage mode controllers. The intended input source was a fuel cell but in its absence a DC supply is utilized instead. The system is simulated for both discontinuous and continuous conduction modes and implemented and demonstrated for the continuous conduction mode. The test results are shown to match the simulation results very closely. / Master of Science

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This Master s Dissertation is proposes the development of a charge management system of a bank of 16 lead-acid batteries with 7Ah load capacity, commonly used in Uninterruptible Power Supplies (UPS). This system aims to ensure that these batteries reach a full charge status faster than the conventional way. To this, it was chosen to make the modification of the pulsed current charging method, in order to reduce problems, such as elevation of bus voltage to return the energy to it, or dissipation of that energy in a resistance, resulting in lower system efficiency, inherent in the method taken as a basis when the battery power withdrawal interval occurs. For the development of the suggested charging system the static converter Full-Bridge Isolated with modulation Phase Shift was chosen. To implement the digital control as well as its practical development in the same laboratory the simplified modeling of this converter was made. The results of simulation and experimental to validate the method are presented. / Esta dissertação de mestrado tem como proposta o desenvolvimento de um sistema de gerenciamento de carga de um banco de 16 baterias de chumbo ácido, com capacidade de carga de 7Ah, comumente utilizado em Fontes Ininterruptas de Energia (UPS). Este sistema visa garantir que estas baterias cheguem a um estado de carga completo e de forma mais rápida que a convencional. Para isto, foi escolhido fazer a modificação do método de carga de corrente pulsada, com o objetivo de reduzir problemas inerentes do método tomado como base, quando ocorre o intervalo de retirada de energia da bateria, tais como: elevação da tensão do barramento ao retornar a energia para ele, ou, dissipar esta energia em uma resistência, o que acarreta em baixa eficiência do sistema. Para o desenvolvimento do sistema de carga sugerido foi escolhido o conversor estático Full-Bridge Isolado com modulação Phase Shift. Foi feita a modelagem simplificada deste conversor, para a implementação do controle digital, assim como o desenvolvimento prático do mesmo em laboratório. São apresentados os resultados de simulação e experimentais para validar o método.

Fluorescent lamps are in general driven by ac ballasting currents. The cyclic variation in arc discharging power results in light fluctuation at twice the frequency of the ac current. Light fluctuation may be intolerable when a steady light output is required in some particular applications. To eliminate light fluctuation, an electronic ballast with dc current is proposed to operate the fluorescent lamp at a constant power. The main power conversion of the electronic ballast employs the single-stage high-power-factor inverter, which is originated from a combination of the half-bridge resonant inverter and the buck-boost converter. With such a circuit configuration, the output power can be regulated by asymmetrical pulse-width-modulation. The ac output of the inverter is then rectified and filtered to provide the dc ballasting current. Driven by dc current, however, the fluorescent lamp emits electrons unilaterally from one end leading to wearing out of emission material on the cathode filament. To solve this problem, an inverter is integrated for commutation of the lamp electrodes. Furthermore, a preheating control is included to start the fluorescent lamps with zero glow-current. A prototype is designed and built for the OSRAM T5-80W fluorescent lamp. The dc operating characteristics of starting transient, light fluctuation, lighting spectra, color temperature as well as the light fluctuation are investigated from experiments. Experimental results also show that the electronic ballast is capable of high-power-factor, dimming capability and zero glow-current preheating.

The thesis is related to investigate characteristics and performance of a Z-source full bridge dc/dc converter which boosts the input voltage to a higher output voltage. Zsource structure increases the reliability of the converter according to current fed full bridge dc/dc converter and also reducing the complexity according to two stage design approach (boost followed by full bridge). Operating principles of the Z-source dc-dc converter is described by current and voltage waveforms of the components and mathematical expressions. Moreover, small signal models and transfer functions are derived for both continuous current mode (CCM) and discontinuous current mode (DCM) operations of the converter. Waveforms obtained, mathematical expressions, small signal models and transfer functions derived are confirmed by simulations. Performance of the converter and controller are both tested in laboratory prototype.

A worldwide awareness of the environment is accelerating fuel cell vehicle development. With respect to power electronics, special requirement is on the development of high efficiency, high voltage ratio bi-directional DC/DC converter for fuel cell energy system management. In this paper, two bi-directional DC/DC converters, which are developed for Ford Motor Company’s fuel cell vehicle, are compared from different aspects. Comparison is concentrated on the circuit topology and EMI performance. Emphasis is placed on soft-switch, hard-switch, synchronized rectification, auxiliary start-up winding and their effect on EMI performance in this kind of isolated bi-directional converter. Comparison includes circuits analysis and test result. The EMI test setup is described. EMI measurements are given and explained. EMI solutions for bi-directional DC/DC converter are discussed. An EMI filter is designed and final test result is given. / Master of Science

Tato práce se zabývá návrhem výkonového měniče určeného pro použití ve fotovoltaických systémech. Klíčovým je použití programovatelného hradlového pole (FPGA) pro realizaci řídicích funkcí. Do detailu jsou diskutovány aspekty návrhu spínaných měničů a na základě takto získaných poznatků je zkonstruován funkční vzorek měniče.

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The bi-directional dc/dc converter is a very popular and effective tool for alternative energy applications. One way it can be utilized is to charge and discharge batteries used in residential solar energy systems. In the day, excess power from the PV panels is used to charge the batteries. During the night, the charged batteries will power the dc bus for loads in the house such as home appliances. The dual active bridge (DAB) converter is very useful because of its high power capability and efficiency. Its symmetry is effective in transferring power in both directions. However, the DAB converter has drawbacks in the start-up stage. These drawbacks in boost mode include high in-rush current during start-up, and the fact that the high side voltage cannot be lower than the low side voltage. A popular existing method to alleviate this problem is the use of an active clamp and a flyback transformer in the circuit topology to charge the high side before the converter is switched into normal boost operation. The active clamp not only helps eliminate the transient spike caused by the transformer leakage, but also continues to be used during steady state. However, this method introduces a new current spike occurring when the converter transitions from start-up mode to boost mode. To alleviate this new setback, an additional transitional stage is proposed to significantly reduce the current spike without the use of any additional components. The converter is current-fed on the low side, and voltage-fed on the high side. A simple phase shift control is used in buck mode and PWM control is used during the boost mode for both the start-up mode and the normal boost operation. This thesis discusses the performance results of a 48-400 V dc/dc converter with 1000 W power output. / Master of Science

This thesis focuses on the design issues of the multiple-output boost full-bridge converter, which is constructed by cascading the boost regulator with the inductor-less full-bridge converter. The design of the boost regulator has been proposed briefly with component selection and compensator design. After that, the inductor-less full-bridge converter is analyzed extensively. In the first place, the operation principle of the inductor-less full-bridge converter is introduced. Later, the effect of parasitic resistance and inductance is analyzed in an L-R series circuit model as step-response, which relates the drop of output voltage to the load current. Then, the effects of the dc blocking capacitor for the unbalanced load condition and unbalanced duty cycle are tackled. The theoretical results are compared with the experimental results and the simulation results to verify the relationship between the output voltage drop and load current. The overall efficiency of the converter is tested under various conditions. The design of the planar transformer is critical to limit the profile of the converter and the leakage phenomenon. A planar transformer fit for the inductor-less full-bridge converter is designed and analyzed in 3D FEA software. An N-port transformer model is proposed to implement the inductance matrix into the leakage inductance matrix for circuit analysis. Based on this N-port model several measurements to extract the parameters in this model are proposed, where only the impedance analyzer is needed. Finally, the effects of trace layout and encapsulation on breakdown voltage in PCB are summarized from experimental results. / Master of Science