Optimization And Design Of Photovoltaic Micro-inverter

To relieve energy shortage and environmental pollution issues, renewable energy, especially PV energy has developed rapidly in the last decade. The micro-inverter systems, with advantages in dedicated PV power harvest, flexible system size, simple installation, and enhanced safety characteristics are the future development trend of the PV power generation systems. The double-stage structure which can realize high efficiency with nice regulated sinusoidal waveforms is the mainstream for the micro-inverter. This thesis studied a double stage micro-inverter system. Considering the intermittent nature of PV power, a PFC was analyzed to provide additional electrical power to the system. When the solar power is less than the load required, PFC can drag power from the utility grid. In the double stage micro-inverter, the DC/DC stage was realized by a LLC converter, which could realize soft switching automatically under frequency modulation. However it has a complicated relationship between voltage gain and load. Thus conventional variable step P&O MPPT techniques for PWM converter were no longer suitable for the LLC converter. To solve this problem, a novel MPPT was proposed to track MPP efficiently. Simulation and experimental results verified the effectiveness of the proposed MPPT. The DC/AC stage of the micro-inverter was realized by a BCM inverter. With duty cycle and frequency modulation, ZVS was achieved through controlling the inductor current bi-directional in every switching cycle. This technique required no additional resonant components and could be employed for low power applications on conventional full-bridge and half-bridge inverter topologies. Three different current mode control schemes were derived from the basic theory of the proposed technique. They were referred to as Boundary Current Mode (BCM), Variable Hysteresis Current Mode (VHCM), and Constant Hysteresis Current Mode (CHCM) individually in this paper with their advantages and disadvantages analyzed in detail. Simulation and experimental iv results demonstrated the feasibilities of the proposed soft-switching technique with the digital control schemes. The PFC converter was applied by a single stage Biflyback topology, which combined the advantages of single stage PFC and flyback topology together, with further advantages in low intermediate bus voltage and current stresses. A digital controller without current sampling requirement was proposed based on the specific topology. To reduce the voltage spike caused by the leakage inductor, a novel snubber cell combining soft switching technique with snubber technique together was proposed. Simulation and experimental waveforms illustrated the same as characteristics as the theoretical analysis. In summary, the dissertation analyzed each power stage of photovoltaic micro-inverter system from efficiency and effectiveness optimization perspectives. Moreover their advantages were compared carefully with existed topologies and control techniques. Simulation and experiment results were provided to support the theoretical analysis

Survey on Photo-Voltaic Powered Interleaved Converter System

Renewable energy is the best solution to meet the growing demand for energy in the country. The solar energy is considered as the most promising energy by the researchers due to its abundant availability, eco-friendly nature, long lasting nature, wide range of application and above all it is a maintenance free system. The energy absorbed by the earth can satisfy 15000 times of today’s total energy demand and its hundred times more than that our conventional energy like coal and other fossil fuels. Though, there are overwhelming advantages in solar energy, It has few drawbacks as well such as its low conversion ratio, inconsistent supply of energy due to variation in the sun light, less efficiency due to ripples in the converter, time dependent and, above all, high capitation cost. These aforementioned flaws have been addressed by the researchers in order to extract maximum energy and attain hundred percentage benefits of this heavenly resource. So, this chapter presents a comprehensive investigation based on photo voltaic (PV) system requirements with the following constraints such as system efficiency, system gain, dynamic response, switching losses are investigated. The overview exhibits and identifies the requirements of a best PV power generation system

A 1-MHz Series Resonant DC-DC Converter with a Dual-Mode Rectifier for PV Microinverters

The photovoltaic (PV) output voltage varies over a wide range depending on operating conditions. Thus, the PV-connected converters should be capable of handling a wide input voltage range while maintaining high efficiencies. This paper proposes a new series resonant dc-dc converter for PV microinverter applications. Compared with the conventional series resonant converter, a dual-mode rectifier is configured on the secondary side, which enables a twofold voltage gain range for the proposed converter with a fixed-frequency phase-shift modulation scheme. The zero-voltage switching turn-on and zero-current switching turn-off can be achieved for active switches and diodes, thereby, minimizing the switching losses. Moreover, a variable dc-link voltage control scheme is introduced to the proposed converter, leading to a further efficiency improvement and input-voltage-range extension. The operation principle and essential characteristics (e.g., voltage gain, soft-switching, and root-mean-square current) of the proposed converter are detailed in this paper, and the power loss modeling and design optimization of components are also presented. A 1-MHz 250-W converter prototype with an input voltage range of 17-43 V is built and tested to verify the feasibility of the proposed converter

Integrated Topologies And Digital Control For Satellite Power Management And Distribution Systems

This work is focused on exploring advanced solutions for space power management and distribution (PMAD) systems. As spacecraft power requirements continue to increase, paralleled by the pressures for reducing cost and overall system weight, power electronics engineers will continue to face major redesigns of the space power systems in order to meet such challenges. Front-end PMAD systems, used to interface the solar sources and battery backup to the distribution bus, need to be designed with increased efficiency, reliability, and power density. A new family of integrated single-stage power converter structures is introduced here. This family allows the interface and control of multiple power sources and storage devices in order to optimize utilization of available resources. Employing single-stage power topologies, these converters control power flow efficiently and cost-effectively. This is achieved by modifying the operation and control strategies of isolated soft-switched half-bridge and full-bridge converters--two of the most popular two-port converter topologies. These topologies are reconfigured and utilized to realize three power processing paths. These paths simultaneously utilize the power devices, allowing increased functionality while promising reduced losses and enhanced power densities. Each of the proposed topologies is capable of performing simultaneous control of two of its three ports. Control objectives include battery or ultra-capacitor charge regulation, solar array maximum power point tracking (MPPT), and/or bus voltage regulation. Another advantage of the proposed power structure is that current engineering design concepts can be used to optimize the new topologies in a fashion similar to the mother topologies. This includes component selection and magnetic design procedures, as well as achieving soft-switching for increased efficiency at higher switching frequencies. Galvanic isolation of the load port through high-frequency transformers provides design flexibility for high step-up/step-down conversion ratios. It further allows the converters to be used as power electronics building blocks (PEBB) with outputs connected in different series/parallel combinations to meet different load requirements. Utilizing such converters promises significant savings in size, weight, and costs of the power management system as well as the devices it manages. Chapter 1 of this dissertation provides an introduction to the requirements, challenges, and trends of space PMAD. A review of existing multi-port converter technologies and digital control techniques is given in Chapter 2. Chapter 3 discusses different PMAD system architectures. It outlines the basic concepts used for PMAD integration and discusses the potential for improvement. Chapters 4 and 5 present and discuss the operation and characteristics of three different integrated multi-port converters. Chapter 6 presents improved methods for practical digital control of switching converters, which are especially useful in complex multi-objective controllers used for PMAD. This is followed by conclusions and suggested future work

Control of distributed power in microgrids: PV field to the grid, islanding operation, and ultra-fast charging station.

Aquesta tesi explora el control de l'energia distribuïda en microxarxes (MG) i aborda diversos reptes relacionats amb el control, l'estabilitat, la compartició d'energia, el disseny del convertidor d'energia, la connexió a la xarxa, la càrrega ultraràpida i el subministrament d'energia renovable. El rendiment dels MG s'analitza tant en modes d'operació connectats a la xarxa com en illa, considerant diferents configuracions i escenaris de flux d'energia. La tesi se centra en diversos reptes clau, com ara maximitzar l'extracció d'energia de matrius fotovoltaiques (PV) en MG que utilitzen convertidors DC-DC, injectar potència MG excedent a la xarxa principal mitjançant inversors de font de tensió DC-AC (VSI) sota càrregues no lineals i desequilibrades, optimitzant el rendiment de MG i la compartició d'energia en mode illa mitjançant VSI, connectant-se a la xarxa principal en el punt d'acoblament comú (PCC) mitjançant transformadors de baixa freqüència (LFT) i transformadors d'estat sòlid (SST) i explorant topologies de convertidors de potència per ultra -càrrega ràpida de CC de vehicles elèctrics (EV). L'ús de SST en lloc de LFT pot millorar la capacitat de MG alhora que redueix el volum i el pes de l'arquitectura elèctrica MG. Aquesta tesi proporciona coneixements i solucions per abordar els reptes esmentats anteriorment, contribuint a l'avenç del control, l'estabilitat, la qualitat de l'energia i la integració eficient de les fonts d'energia renovables i la càrrega dels vehicles elèctrics.Esta tesis explora el control de la potencia distribuida en microrredes (MGs) y aborda diversos retos relacionados con el control, la estabilidad, el reparto de potencia, el diseño de convertidores de potencia, la conexión a la red, la carga ultrarrápida y el suministro de energías renovables. El rendimiento de las MG se analiza tanto en modo de funcionamiento conectado a la red como en modo aislado, considerando diferentes configuraciones y escenarios de flujo de potencia. La tesis se centra en varios retos clave, como la maximización de la extracción de energía de las matrices fotovoltaicas (FV) en las MG utilizando convertidores CC-CC, la inyección del excedente de energía de las MG en la red principal a través de inversores de fuente de tensión CC-CA (VSI) bajo cargas no lineales y desequilibradas, la optimización del rendimiento de las MG y del reparto de energía en modo aislado mediante VSI, la conexión a la red principal en el punto de acoplamiento común (PCC) mediante transformadores de baja frecuencia (LFT) y transformadores de estado sólido (SST), y la exploración de topologías de convertidores de potencia para la carga ultrarrápida en corriente continua de vehículos eléctricos (VE). El uso de SST en lugar de LFT puede mejorar la capacidad de la MG y, al mismo tiempo, reducir el volumen y el peso de la arquitectura eléctrica de la MG. Esta tesis aporta ideas y soluciones para abordar los retos mencionados, contribuyendo al avance del control de la MG, la estabilidad, la calidad de la energía y la integración eficiente de fuentes de energía renovables y la carga de vehículos eléctricos. Traducción realizada con la versión gratuita del traductor www.DeepL.com/TranslatorThis thesis explores the control of distributed power in microgrids (MGs) and addresses various challenges related to control, stability, power sharing, power converter design, grid connection, ultra-fast charging, and renewable energy supply. The performance of MGs is analysed in both grid-connected and islanded modes of operation, considering different configurations and power flow scenarios. The thesis focuses on several key challenges, including maximising power extraction from photovoltaic (PV) arrays in MGs utilizing DC-DC converters, injecting surplus MG power into the main grid via DC-AC voltage source inverters (VSIs) under nonlinear and unbalanced loads, optimising MG performance and power sharing in islanded mode through VSIs, connecting to the main grid at the point of common coupling (PCC) using low-frequency transformers (LFTs) and solid-state transformers (SSTs), and exploring power converter topologies for ultra-fast DC charging of electric vehicles (EVs). The use of SSTs instead of LFTs can enhance MG capability while reducing the volume and weight of the MG electrical architecture. This thesis provides insights and solutions to address the aforementioned challenges, contributing to the advancement of MG control, stability, power quality, and efficient integration of renewable energy sources and EV charging

Modeling And Design Of Multi-port Dc/dc Converters

In this dissertation, a new satellite platform power architecture based on paralleled three-port DC/DC converters is proposed to reduce the total satellite power system mass. Moreover, a fourport DC/DC converter is proposed for renewable energy applications where several renewable sources are employed. Compared to the traditional two-port converter, three-port or four-port converters are classified as multi-port converters. Multi-port converters have less component count and less conversion stage than the traditional power processing solution which adopts several independent two-port converters. Due to their advantages multi-port converters recently have attracted much attention in academia, resulting in many topologies for various applications. But all proposed topologies have at least one of the following disadvantages: 1) no bidirectional port; 2) lack of proper isolation; 3) too many active and passive components; 4) no softswitching. In addition, most existing research focuses on the topology investigation, but lacks study on the multi-port converter’s control aspects, which are actually very challenging since it is a multi-input multi-output control system and has so many cross-coupled control loops. A three-port converter is proposed and used for space applications. The topology features bidirectional capability, low component count and soft-switching for all active switches, and has one output port to meet certain isolating requirements. For the system level control strategy, the multi-functional central controller has to achieve maximal power harvesting for the solar panel, the battery charge control for the battery, and output voltage regulation for the dc bus. In order to design these various controllers, a good dynamic model of the control object should be obtained first. Therefore, a modeling procedure based on a traditional state-space averaging method is v proposed to characterize the dynamic behavior of such a multi-port converter. The proposed modeling method is clear and easy to follow, and can be extended for other multi-port converters. In order to boost the power level of the multi-port converter system and allow redundancy, the three-port converters are paralleled together. The current sharing control for the multi-port converters has rarely been reported. A so called “dual loop” current sharing control structure is identified to be suitable for the paralleled multi-port converters, since its current loop and the voltage loop can be considered and designed independently, which simplifies the multi-port converter’s loop analysis. The design criteria for that dual loop structure are also studied to achieve good current sharing dynamics while guaranteeing the system stability. The renewable energy applications are continuously demanding the low cost solution, so that the renewable energy might have a more competitive dollar per kilowatt figure than the traditional fossil fuel power generation. For this reason, the multi-port converter is a good candidate for such applications due to the low component count and low cost. Especially when several renewable sources are combined to increase the power delivering certainty, the multi-port solution is more beneficial since it can replace more separate converters. A four-port converter is proposed to interface two different renewable sources, such as the wind turbine and the solar panel, one bidirectional battery device, and the galvanically isolated load. The four-port converter is based on the traditional half-bridge topology making it easy for the practicing power electronics engineer to follow the circuit design. Moreover, this topology can be extended into n input ports which allow more input renewable sources. vi Finally, the work is summarized and concluded, and references are listed