In this paper, the principle of modularity is used to derive the different multilevel voltage and current source converter topologies. The paper is primarily focused on high-power applications and specifically on high-voltage dc systems. The derived converter cells are treated as building blocks and are contributing to the modularity of the system. By combining the different building blocks, i.e., the converter cells, a variety of voltage and current source modular multilevel converter topologies are derived and thoroughly discussed. Furthermore, by applying the modularity principle at the system level, various types of high-power converters are introduced. The modularity of the multilevel converters is studied in depth, and the challenges as well as the opportunities for high-power applications are illustrated.

Modular Multilevel Converters for HVDC Applications: Review on Converter Cells and Functionalities

Photovoltaic (PV) energy has grown at an average annual rate of 60% in the last five years, surpassing one third of the cumulative wind energy installed capacity, and is quickly becoming an important part of the energy mix in some regions and power systems. This has been driven by a reduction in the cost of PV modules. This growth has also triggered the evolution of classic PV power converters from conventional singlephase grid-tied inverters to more complex topologies to increase efficiency, power extraction from the modules, and reliability without impacting the cost. This article presents an overview of the existing PV energy conversion systems, addressing the system configuration of different PV plants and the PV converter topologies that have found practical applications for grid-connected systems. In addition, the recent research and emerging PV converter technology are discussed, highlighting their possible advantages compared with the present technology. Solar PV energy conversion systems have had a huge growth from an accumulative total power equal to approximately 1.2 GW in 1992 to 136 GW in 2013 (36 GW during 2013) [1]. This phenomenon has been possible because of several factors all working together to push the PV energy to cope with one important position today (and potentially a fundamental position in the near future). Among these factors are the cost reduction and increase in efficiency of the PV modules, the search for alternative clean energy sources (not based on fossil fuels), increased environmental awareness, and favorable political regulations from local governments (establishing feed-in tariffs designed to accelerate investment in renewable energy technologies). It has become usual to see PV systems installed on the roofs of houses or PV farms next to the roads in the countryside. Grid-connected PV systems account for more than 99% of the PV installed capacity compared to

An Overview of Recent Research and Emerging PV Converter Technology

Photovoltaic (PV) energy has grown at an average annual rate of 60% in the last five years, surpassing one third of the cumulative wind energy installed capacity, and is quickly becoming an important part of the energy mix in some regions and power systems. This has been driven by a reduction in the cost of PV modules. This growth has also triggered the evolution of classic PV power converters from conventional single-phase grid-tied inverters to more complex topologies to increase efficiency, power extraction from the modules, and reliability without impacting the cost. This article presents an overview of the existing PV energy conversion systems, addressing the system configuration of different PV plants and the PV converter topologies that have found practical applications for grid-connected systems. In addition, the recent research and emerging PV converter technology are discussed, highlighting their possible advantages compared with the present technology.

Grid-Connected Photovoltaic Systems: An Overview of Recent Research and Emerging PV Converter Technology

Silicon carbide (SiC) switching power devices (MOSFETs, JFETs) of 1200 V rating are now commercially available, and in conjunction with SiC diodes, they offer substantially reduced switching losses relative to silicon (Si) insulated gate bipolar transistors (IGBTs) paired with fast-recovery diodes. Low-voltage industrial variable-speed drives are a key application for 1200 V devices, and there is great interest in the replacement of the Si IGBTs and diodes that presently dominate in this application with SiC-based devices. However, much of the performance benefit of SiC-based devices is due to their increased switching speeds ( di/dt, dv/ dt), which raises the issues of increased electromagnetic interference (EMI) generation and detrimental effects on the reliability of inverter-fed electrical machines. In this paper, the tradeoff between switching losses and the high-frequency spectral amplitude of the device switching waveforms is quantified experimentally for all-Si, Si-SiC, and all-SiC device combinations. While exploiting the full switching-speed capability of SiC-based devices results in significantly increased EMI generation, the all-SiC combination provides a 70% reduction in switching losses relative to all-Si when operated at comparable dv/dt. It is also shown that the loss-EMI tradeoff obtained with the Si-SiC device combination can be significantly improved by driving the IGBT with a modified gate voltage profile.

An Experimental Investigation of the Tradeoff between Switching Losses and EMI Generation With Hard-Switched All-Si, Si-SiC, and All-SiC Device Combinations

Soft magnetic materials are key to the efficient operation of the next generation of power electronics and electrical machines (motors and generators). Many new materials have been introduced since Michael Faraday's discovery of magnetic induction, when iron was the only option. However, as wide bandgap semiconductor devices become more common in both power electronics and motor controllers, there is an urgent need to further improve soft magnetic materials. These improvements will be necessary to realize the full potential in efficiency, size, weight, and power of high-frequency power electronics and high-rotational speed electrical machines. Here we provide an introduction to the field of soft magnetic materials and their implementation in power electronics and electrical machines. Additionally, we review the most promising choices available today and describe emerging approaches to create even better soft magnetic materials.

http://science.sciencemag.org/content/sci/362/6413/eaao0195.full.pdf

Soft magnetic materials for a sustainable and electrified world

This paper investigates the switching behavior of normally OFF silicon carbide (SiC) JFETs in an inverter for a motor drive. The parasitic ringing caused by different parasitic effects is analyzed. Two different methods, the use of an RC snubber and the use of suppression ferrite component, are investigated for dampening the parasitic oscillations. It is found that applying a ferrite bead not only dampens the parasitic oscillations, but also results in significantly lower switching losses. Furthermore, it is shown that the capacitive coupling between SiC devices in the bridge leg and heat sinks significantly deteriorates the JFETs' switching performance. The effect of two substrates, an insulated metal substrate and a printed circuit board, on the capacitive coupling is investigated. A method in which the use of two separate heat spreaders minimizes the capacitive coupling, thus, exploiting the full potential of fast SiC JFETs is proposed.

Improving SiC JFET Switching Behavior Under Influence of Circuit Parasitics

Power electronics is a key technology for the efficient conversion, control, and conditioning of electric energy from the source to the load. In this paper, the potential of power electronics for energy savings in four major application fields, buildings and lighting, power supplies, smart electricity grid, and industrial drives, is investigated. It is shown that by wider adoption of power electronics in these areas, the current European Union electricity consumption could be reduced by 25%. The technology challenges for exploiting this potential for all the four areas are identified in the paper.

Power Electronics Enabling Efficient Energy Usage: Energy Savings Potential and Technological Challenges

https://repository.tudelft.nl/islandora/object/uuid:e1ff3160-1158-4bad-8e5d-23b740237c7f/datastream/OBJ/download

Estimating battery lifetimes in Solar Home System design using a practical modelling methodology

Using the newly developed enhancement-mode Galium-Nitride-on-Silicon (eGaN) devices with high conductivity and very fast switching speed a breakthrough in switching performance can be achieved. Multi-megahertz switching frequency capability will significantly reduce the size of passive components, adding the cost benefits and increasing the integration level and power density. As to date, the use of GaN devices in power converters is still in its infancy, but its widespread application is a near reality. PV converter industry is one of the areas which would greatly benefit from the new GaN technology. The most important requirements for a PV converter, efficiency and cost effectiveness, can both be addressed with improved switching devices. This paper presents a performance comparison of a PV module integrated DC-DC converter based on commercially available GaN and Si power devices. The presented results show that the first generation of GaN devices outperforms the best in class Si devices. Since GaN is immature technology, further improvements will be seen in the years to come.

Comparison of Si and GaN power devices used in PV module integrated converters

https://repository.tudelft.nl/islandora/object/uuid%3A71e33863-97ba-4488-a0c4-21ee7ebc41a6/datastream/OBJ/download

Exploring the boundaries of Solar Home Systems (SHS) for off-grid electrification: Optimal SHS sizing for the multi-tier framework for household electricity access

Jelena Popovic-Gerber

Papers

Improving SiC JFET Switching Behavior Under Influence of Circuit Parasitics

Power Electronics Enabling Efficient Energy Usage: Energy Savings Potential and Technological Challenges

Estimating battery lifetimes in Solar Home System design using a practical modelling methodology

Comparison of Si and GaN power devices used in PV module integrated converters

Exploring the boundaries of Solar Home Systems (SHS) for off-grid electrification: Optimal SHS sizing for the multi-tier framework for household electricity access