This thesis work focuses on the study and improvement of single-stage power factor correction techniques. The generalized structures of the present pulse-width-modulation (PWM) integrated single-stage power factor correction (PFC) converters are presented. The typical PFC cells in the single-stage PFC converter are identified. After that, the necessary PFC condition is derived and verified to understand the principle of the single-stage PFC converters. As an example, the continuous current mode (CCM) current source single-stage PFC converter is studied. The circuit intuitions and design consideration of this converter are presented. Also, an improved current source single-stage PFC converter with a low-frequency auxiliary switch is proposed to overcome the problem of the previous converter. Experimental verification shows the improvement is effective. To evaluate single-stage PFC technique, a comparison study between the current source single-stage and the boost two-stage PFC converters is done in this thesis. It shows that for universal line application, due to the wide bus-capacitor voltage range, single-stage PFC converters have higher component ratings than two-stage PFC converters. This limits the application of single-stage PFC converter. Therefore, an interesting future work will be how to reduce the bus voltage range of single-stage PFC converters. / Master of Science

This dissertation presents the in-depth study and innovative solutions of the advanced integrated single-stage power-factor-correction (S2PFC) techniques, which target at the low- to medium-level power supplies, for wide range of applications, from power adapters and computers to various communication equipment. To limit the undesirable power converter input-current-harmonic's impact on the power line and other electronics equipment, stringent current harmonic regulations such as IEC 61000-3-2 have already been enforced. The S2PFC techniques have been proposed and intensively studied, in order to comply these regulations with minimal additional component count and cost. This dissertation provides a systematic study of the S2PFC input-current-shaping (ICS) mechanism, circuit topology generalization and variation, bulk capacitor voltage stress and switch current stress, converter design and optimization, and evaluation of the state-of-the-art S2PFC techniques with universal-line input. Besides, this presentation also presents the development of novel S2PFC techniques with a voltage-doubler-rectifier front end to both improve the performance and reduce the cost of S2PFC converters for (international voltage range) universal-line applications. The calculation and experimental results show that the proposed techniques offer a more cost-effective and efficient solution than industries' current practice, with universal-line input and converter power level up to 600 W. Finally, further improved technique is also presented with reduced filter inductor size and increased power density. / Ph. D.

The Lead-Acid battery has become the power source of several electron product. The major drawback is that it requires long charging time. This thesis is to design a programmable rapid charger and energy recovery scheme with DSP. Furthermore zero-voltage-switching(ZVS) capability of the adopted asymmetrical half-bridge topology enhances the power density of the charger. The energy recovery cell stores the negative pulse energy into DC bus capacitor temporarily to avoid unnecessary energy consumption in conventional schemes. This thesis is experimentally verified on 12V/7.5Ah nonspillable sealed-lead assembled batteries. According to experimental results, the charger can achieve the goal of rapid charge within 1 hour. Because of using the rapid charge algorithm, it can give different charging section depends on temperature and voltage of battery, and it can adjust the over-temperature and the over-voltage of battery to guarantee the battery be charged safely. In this thesis, a prototype module is implemented with mature protection condition. Some experiments are shown to verify the feasibility of the proposed scheme.

Renewable or sustainable energy (SE) sources have attracted the attention of many countries because the power generated is environmentally friendly, and the sources are not subject to the instability of price and availability. This dissertation presents new trends in the DC-AC converters (inverters) used in renewable energy sources, particularly for photovoltaic (PV) energy systems. A review of the existing technologies is performed for both single-phase and three-phase systems, and the pros and cons of the best candidates are investigated. In many modern energy conversion systems, a DC voltage, which is provided from a SE source or energy storage device, must be boosted and converted to an AC voltage with a fixed amplitude and frequency. A novel switching pattern based on the concept of the conventional space-vector pulse-width-modulated (SVPWM) technique is developed for single-stage, boost-inverters using the topology of current source inverters (CSI). The six main switching states, and two zeros, with three switches conducting at any given instant in conventional SVPWM techniques are modified herein into three charging states and six discharging states with only two switches conducting at any given instant. The charging states are necessary in order to boost the DC input voltage. It is demonstrated that the CSI topology in conjunction with the developed switching pattern is capable of providing the required residential AC voltage from a low DC voltage of one PV panel at its rated power for both linear and nonlinear loads. In a micro-grid, the active and reactive power control and consequently voltage regulation is one of the main requirements. Therefore, the capability of the single-stage boost-inverter in controlling the active power and providing the reactive power is investigated. It is demonstrated that the injected active and reactive power can be independently controlled through two modulation indices introduced in the proposed switching algorithm. The system is capable of injecting a desirable level of reactive power, while the maximum power point tracking (MPPT) dictates the desirable active power. The developed switching pattern is experimentally verified through a laboratory scaled three-phase 200W boost-inverter for both grid-connected and stand-alone cases and the results are presented.

<p> The thesis is concerned with the design, construction and evaluation of an analog to digital converter based on the "cascade" principle. However, this converter requires only one stage, instead of the usual one stage per bit required by conventional cascade converters. This reduction in the number of stages is achieved by storage in analog form, and by feeding the output of the stage back to its input via a switching network. An 8 bit converter that operates up to a clock frequency of 700KHz was built. The converter is shown to have promising possibilities as a low cost general purpose analog to digital converter. </p> / Thesis / Master of Engineering (MEngr)

This paper presents a single-stage inverter with variable frequency modulation (VFM) based on LLC resonant converter. And LLC converter is a common topology of dc/dc conversion. LLC resonant converter can achieve high efficiency and soft-switching performance. Since the dc gain curve of the single-resonant LLC converter is flat when the switching frequency is larger than the resonant frequency, namely fs>fr, an additional L-C series resonant branch is paralleled to the original resonant tank to introduce higher-order-harmonic resonant current and a zero-gain point to the gain curve. Higher-order-harmonics help to deliver power and the zero-gain point enlarges the gain range which improves output THD and reduces the switching frequency range. A 1.2 kW prototype is built to demonstrate the performance of the proposed inverter. Zero-voltage-switching (ZVS) and zero-current-switching (ZCS) are achieved on the primary side and secondary side, respectively. And 97.3% efficiency and 2.17% voltage THD are achieved at full load condition, while 97.2% efficiency and 3.2% voltage THD are achieved at half load condition. / M.S. / The inverter is widely used to connect renewable energy into the grid by converting dc to ac waveform, like photovoltaic (PV) technology. Basically, the two-stage topology is usually used. The inverter would consist of two stages working in high frequency, the first stage is dc/dc converter which can regulate the input voltage to the desired bus voltage for the second stage, and the second stage is dc/ac converter. The first stage works at a specific switching frequency, so it can be designed to achieve higher efficiency in dc/dc conversion. The second stage also works at high switching frequency and converts dc to ac commonly by using SPWM which changes the duty cycle ratio in a sinusoidal pattern. The single-stage inverter only has one stage working in high frequency while the second stage works at twice line frequency. The first stage converts dc to rectified ac waveform and the second stage unfolds it to ac. The topology of LLC resonant converter being applied for the first stage of the single-stage inverter has been proposed. This topology uses variable-frequency-modulation (VFM) which varying switching frequency on the primary side to output different voltage levels. And it achieves zero-voltage-switching (ZVS). However, LLC converter can hardly output very low voltage due to the flat voltage gain curve at high frequency. Also, LLC converter only transfers the fundamental harmonic component to the load. If the higher-order harmonic components help transfer power when the switching frequency equals the resonant frequency, the current shape will be more like a square wave and the peak of resonant current can be reduced. This thesis proposes a topology that has two L-C resonant branches in parallel for the resonant tank in the converter. And the paralleled resonant branches produce a zero-gain frequency point into the gain curve so that the gain range is enlarged within the reduced switching frequency range and 3rd harmonic component of the resonant current helps to transfer power so that the rms value of resonant current can also be reduced.

Let Knots be the abelian monoid of isotopy classes of knots S1 ⊂ S3 under connected sum, and let C be the topological knot concordance group of knots modulo slice knots. Cochran-Orr-Teichner [COT03] defined a filtration of C: C ⊃ F(0) ⊃ F(0.5) ⊃ F(1) ⊃ F(1.5) ⊃ F(2) ⊃ . . .The quotient C/F(0.5) is isomorphic to Levine’s algebraic concordance group AC1 [Lev69]; F(0.5) is the algebraically slice knots. The quotient C/F(1.5) contains all metabelian concordance obstructions. The Cochran-Orr-Teichner (1.5)-level two stage obstructions map the concordance class of a knot to a pointed set (COT (C/1.5),U). We define an abelian monoid of chain complexes P, with a monoid homomorphism Knots → P. We then define an algebraic concordance equivalence relation on P and therefore a group AC2 := P/ ~, our second order algebraic knot concordance group. The results of this thesis can be summarised in the following diagram: . That is, we define a group homomorphism C → AC2 which factors through C/F(1.5). We can extract the two stage Cochran-Orr-Teichner obstruction theory from AC2: the dotted arrows are morphisms of pointed sets. Our second order algebraic knot concordance group AC2 is a single stage obstruction group.

This thesis mainly presents the design and implementation of a flyback converter with single-stage power factor correction. In the beginning, we propose different power factor collection (PFC) techniques referring to the inductor current of converter under three kinds of operation modes. In the continuous mode, we adopt the nonlinear-carrier control (NLC). Then, in the discontinuous mode and boundary mode, voltage-follower control (VFC) and transition mode technique control (TM) are adopted respectively. As to the converter analysis, we derive and verify the results of a small-signal model and perform equivalent circuit analysis by state-space averaging method, loss-free resistor (LFR) model, averaging method for two-time-scale system (AM), and current injected equivalent circuit approach (CIECA). Results derived from the above-mentioned models are compared and verified to be accurate of the system model. Furthermore, the control function and element design are implemented by simulation. We perform a PI controller to achieve better power factor based on results of analysis of the time and frequency domains analysis. Finally, three sets of different hardware are fabricated and verified depending on measured result and theoretical simulation.

Carbon dioxide is a natural refrigerant that has been considered for certain refrigeration and air conditioning applications. The coefficient of performance (COP) of carbon dioxide cycles is low compared to classical vapor compression cycles. The aim of this portion of the thesis is to present a thermodynamic analysis of carbon dioxide cycles in order to evaluate the potential performance of a refrigeration cycle using carbon dioxide. A thermodynamic model for the cycle is proposed which can simulate the operation of a carbon dioxide refrigeration cycle. This model takes into account the practical effects of the thermo-physical properties of carbon dioxide as a refrigerant in a trans-critical cycle. One and two-stage compression processes were considered for comparison purposes. A sensitivity analysis has been conducted so that cycle performance can be estimated. The effect of cycle components on system capacity and cycle performance was investigated. The second portion of the thesis deals with the concept of reheat air conditioning, and looks at the performance of different reheat cycles. The thesis looks at reheat systems that utilize different placements of the reheat coil. The overall performance of these reheat systems is then calculated. These systems require no additional electric power to reheat the air after it is cooled and dehumidified in the evaporator. Instead, they use heat from the condenser heat exchanger to reheat the air during partial load conditions. Four different reheat configurations are discussed and analyzed to determine performance levels. Visual Basic programs were written for each of the four cycles to simulate the different configurations and to evaluate key performance parameters. Graphs were developed based on these programs, where critical variables were changed to monitor trends in coefficient of performance. The thermodynamic cycle of each reheat configuration is developed, with equations presented with figures depicting the cycles. Refrigerant 134a was used in the programs throughout the reheat section of the thesis. The reheat coefficient of performance is used as the basis for cycle comparison. The relative performance of the four cycles is illustrated in the figures and explained in the Results and Discussion section at the end of chapter 3.

This thesis presents a novel Zero Voltage Switching (ZVS) approach in a grid connected single-stage flyback inverter without using any additional auxiliary circuits. The soft-switching of the primary switch is achieved by allowing negative current from the grid-side through bidirectional switches placed on the secondary side of the transformer. Basically, the negative current discharges the MOSFET’s output capacitor thereby allowing turn-on of the primary switch under zero voltage. In order to optimize the amount of reactive current required to achieve ZVS a variable frequency control scheme is implemented over the line cycle. In addition, the bi-directional switches on the secondary side of the transformer have ZVS during the turn-on times. Therefore, the switching losses of the bi-directional switches are negligible. A 250W prototype has been implemented in order to validate the proposed scheme. Experimental results confirm the feasibility and superior performance of the converter compared to the conventional flyback inverter. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2012-07-06 16:24:13.385