Transformerless Microinverter with Low Leakage Current Circulation and Low Input Capacitance Requirement for PV Applications

The inevitable depletion of limited fossil fuels combined with their harmful footprint on the environment led to a global pursuit for alternative energy sources that are clean and inexhaustible. Renewable energies such as wind, biomass and solar are the best alternative energy candidates, with the latter being more suitable for GCC countries. Besides, the energy generated from photovoltaic (PV) modules is one of the elegant examples of harnessing solar energy, as it is clean, pollutant-free and modular. Furthermore, recent advances in PV technology, especially grid-connected PV systems revealed the preeminence of using multiple small inverters called (Microinverters) over using the conventional single inverter configuration. Specifically, the break-even cost point can be reached faster and the system modularity increases with microinverters usage. Nonetheless, due to microinverter’s small ratings designers prefer transformerless designs because transformer removal achieves higher efficiency and power density. However, the transformer removal results in loss of galvanic isolation that leads to dangerous leakage current circulation that affects system safety. Another issue with microinverters is that since they are installed outside their bulky DC-Link electrolytic capacitor lifetime deteriorates the system reliability because electrolytic capacitor failure rate increases as temperature increases. Moreover, the DC-Link capacitor is used to decouple the 2nd order power harmonic ripples that appear in single-phase systems. Thus, the objective of this thesis is to design an efficient transformerless microinverter that has low leakage current circulation and low input capacitance requirement with a minimum number of active switches. In other words, the objective is to increase the safety and the reliability of the system while maintaining the high efficiency. Eventually, the configuration selected is the transformerless differential buck microinverter with LCL filter and it is modeled with passive resonance damping and active resonance damping control

Emerging Converter Topologies and Control for Grid Connected Photovoltaic Systems

Continuous cost reduction of photovoltaic (PV) systems and the rise of power auctions resulted in the establishment of PV power not only as a green energy source but also as a cost-effective solution to the electricity generation market. Various commercial solutions for grid-connected PV systems are available at any power level, ranging from multi-megawatt utility-scale solar farms to sub-kilowatt residential PV installations. Compared to utility-scale systems, the feasibility of small-scale residential PV installations is still limited by existing technologies that have not yet properly address issues like operation in weak grids, opaque and partial shading, etc. New market drivers such as warranty improvement to match the PV module lifespan, operation voltage range extension for application flexibility, and embedded energy storage for load shifting have again put small-scale PV systems in the spotlight. This Special Issue collects the latest developments in the field of power electronic converter topologies, control, design, and optimization for better energy yield, power conversion efficiency, reliability, and longer lifetime of the small-scale PV systems. This Special Issue will serve as a reference and update for academics, researchers, and practicing engineers to inspire new research and developments that pave the way for next-generation PV systems for residential and small commercial applications

Power Converters in Power Electronics

In recent years, power converters have played an important role in power electronics technology for different applications, such as renewable energy systems, electric vehicles, pulsed power generation, and biomedical sciences. Power converters, in the realm of power electronics, are becoming essential for generating electrical power energy in various ways. This Special Issue focuses on the development of novel power converter topologies in power electronics. The topics of interest include, but are not limited to: Z-source converters; multilevel power converter topologies; switched-capacitor-based power converters; power converters for battery management systems; power converters in wireless power transfer techniques; the reliability of power conversion systems; and modulation techniques for advanced power converters

Power Converter of Electric Machines, Renewable Energy Systems, and Transportation

Power converters and electric machines represent essential components in all fields of electrical engineering. In fact, we are heading towards a future where energy will be more and more electrical: electrical vehicles, electrical motors, renewables, storage systems are now widespread. The ongoing energy transition poses new challenges for interfacing and integrating different power systems. The constraints of space, weight, reliability, performance, and autonomy for the electric system have increased the attention of scientific research in order to find more and more appropriate technological solutions. In this context, power converters and electric machines assume a key role in enabling higher performance of electrical power conversion. Consequently, the design and control of power converters and electric machines shall be developed accordingly to the requirements of the specific application, thus leading to more specialized solutions, with the aim of enhancing the reliability, fault tolerance, and flexibility of the next generation power systems

A review on power electronics technologies for power quality improvement

Nowadays, new challenges arise relating to the compensation of power quality problems, where the introduction of innovative solutions based on power electronics is of paramount importance. The evolution from conventional electrical power grids to smart grids requires the use of a large number of power electronics converters, indispensable for the integration of key technologies, such as renewable energies, electric mobility and energy storage systems, which adds importance to power quality issues. Addressing these topics, this paper presents an extensive review on power electronics technologies applied to power quality improvement, highlighting, and explaining the main phenomena associated with the occurrence of power quality problems in smart grids, their cause and effects for different activity sectors, and the main power electronics topologies for each technological solution. More specifically, the paper presents a review and classification of the main power quality problems and the respective context with the standards, a review of power quality problems related to the power production from renewables, the contextualization with solid-state transformers, electric mobility and electrical railway systems, a review of power electronics solutions to compensate the main power quality problems, as well as power electronics solutions to guarantee high levels of power quality. Relevant experimental results and exemplificative developed power electronics prototypes are also presented throughout the paper.This work has been supported by FCT-Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017 and by the FCT Project newERA4GRIDs PTDC/EEIEEE/30283/2017

Quasi impedance source based high power medium voltage converter for grid integration of distributed energy sources

The next generation of Power Electronics systems would need to be able to work at higher power levels, higher switching frequencies, compact size, and higher ambient temperatures, as well as should have improved energy efficiency than existing Silicon (Si) devices. As a result, new wide bandgap semiconductor technologies must be introduced to address Si's physical limitations. Silicon Carbide (SiC) devices are becoming popular because of their outstanding properties that address all the requirements of the next generation Power Electronics system. On the other hand, the converter topology still plays a major role in deciding the overall system performance. Hence the major objective of this dissertation is to devise new multilevel quasi impedance source (qZS) based converter topologies using SiC devices to achieve a compact, highly efficient, and modular solution for grid integration of Solar PV Energy Source to the utility grid. Other objectives include modification in the PWM methods to address the problem of unequal power-sharing in Solar PV multilevel converters. By using qZS as the front-end power converter several different power converter topologies have been developed and presented in this dissertation. The detailed design, modulation, loss analysis, and control have been developed for multi module cascaded structure. Level-shifted PWM technique is developed at first for two cascaded modules which are similar to the standard Phase opposed disposed Pulse width modulation (PODPWM). However, this control method cannot be directly applied to a higher number of modules. For more than two cascaded modules a unified combined hybrid PWM technique is developed and presented. During normal balanced operation, the power among the modules is unequal. To address the unequal power sharing problem, further modification in the PWM technique is done called the Carrier rotation technique. For providing the isolation between the low voltage PV panels and the high voltage AC grid, a modified Inverter topology, and a new modulation technique is developed. The presented technique, however, is limited to a single module, and more research is needed to implement for cascaded structure. Front-end qZS based single-stage DC-AC-DC converter is developed as an alternative of one of the most popular conventional dual active bridge (DAB) converter. The proposed converter offers reduced component count while maintaining the continuous input current. The detailed operation, modulation technique, simulation, and experimental result are presented to show the superiority of the developed qZS Cascaded Multilevel Converter. The developed power converter has strong commercialization potentia

Emerging Power Electronics Technologies for Sustainable Energy Conversion

This Special Issue summarizes, in a single reference, timely emerging topics related to power electronics for sustainable energy conversion. Furthermore, at the same time, it provides the reader with valuable information related to open research opportunity niches

Emerging Power Electronics Technologies for Sustainable Energy Conversion

This Special Issue summarizes, in a single reference, timely emerging topics related to power electronics for sustainable energy conversion. Furthermore, at the same time, it provides the reader with valuable information related to open research opportunity niches

Wide-bandgap semiconductor based power converters for renewable energy systems

The demand for low carbon economy and limited fossil resources for energy generation drives the research on renewable energy sources and the key technology for utilisation of renewable energy sources: power electronics. Innovative inverter topologies and emerging WBG semiconductor based devices at 600 V blocking class are the enabling technologies for more efficient, reliable and accessible photovoltaic based electricity generation. This thesis is concerned with the impact of WBG semiconductor based power devices on residential scale PV inverter topologies in terms of efficiency, volume reduction and reliability. The static and dynamic characterisation of the Si and WBG based devices are carried out, gate drive requirements are assessed and experimental performance comparison in a single phase inverter is discussed under wide range of operating conditions. The optimisation of GaN HEMT based single phase inverter is conducted in terms of converter efficiency, switching frequency and converter volume. The long term mission-profile based analysis of GaN and Si based devices is conducted and impact of WBG devices under low and high switching frequency conditions in terms of power loss and thermal loading are presented. Finally, a novel five-level hybrid inverter topology based on WBG devices is proposed, simulated and experimentally verified for higher power applications