The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

DC microgrids (MGs) have been gaining a continually increasing interest over the past couple of years both in academia and industry. The advantages of dc distribution when compared to its ac counterpart are well known. The most important ones include higher reliability and efficiency, simpler control and natural interface with renewable energy sources, and electronic loads and energy storage systems. With rapid emergence of these components in modern power systems, the importance of dc in today's society is gradually being brought to a whole new level. A broad class of traditional dc distribution applications, such as traction, telecom, vehicular, and distributed power systems can be classified under dc MG framework and ongoing development, and expansion of the field is largely influenced by concepts used over there. This paper aims first to shed light on the practical design aspects of dc MG technology concerning typical power hardware topologies and their suitability for different emerging smart grid applications. Then, an overview of the state of the art in dc MG protection and grounding is provided. Owing to the fact that there is no zero-current crossing, an arc that appears upon breaking dc current cannot be extinguished naturally, making the protection of dc MGs a challenging problem. In relation with this, a comprehensive overview of protection schemes, which discusses both design of practical protective devices and their integration into overall protection systems, is provided. Closely coupled with protection, conflicting grounding objectives, e.g., minimization of stray current and common-mode voltage, are explained and several practical solutions are presented. Also, standardization efforts for dc systems are addressed. Finally, concluding remarks and important future research directions are pointed out.

/pdf/dc-microgrids-part-ii-a-review-of-power-architectures-69j8nn2rpd.pdf

DC Microgrids—Part II: A Review of Power Architectures, Applications, and Standardization Issues

Wind power is the most reliable and developed renewable energy source over past decades. With the rapid penetration of the wind generators in the power system grid, it is very essential to utilize the maximum available power from the wind and to operate the wind turbine (WT) at its maximal energy conversion output. For this, the wind energy conversion system (WECS) has to track or operate at the maximum power point (MPP). A decent variety of publication report on various maximum power point tracking (MPPT) algorithms for a WECS. However, making a choice on an exact MPPT algorithm for a particular case require sufficient proficiency because each algorithm has its own merits and demerits. For this reason, an appropriate review of those algorithms is essential. However, only a few attempts have been made in this concern. In this paper, different available MPPT algorithms are described for extracting maximum power which are classified according to the power measurement i.e. direct or indirect power controller. Merits, demerits and comprehensive comparison of the different MPPT algorithms also highlighted in the terms of complexity, wind speed requirement, prior training, speed responses, etc. and also the ability to acquire the maximal energy output. This paper serves as a proper reference for future MPPT users in selecting appropriate MPPT algorithm for their requirement.

A review of conventional and advanced MPPT algorithms for wind energy systems

The modern electric power systems are going through a revolutionary change because of increasing demand of electric power worldwide, developing political pressure and public awareness of reducing carbon emission, incorporating large scale renewable power penetration, and blending information and communication technologies with power system operation. These issues initiated in establishing microgrid concept which has gone through major development and changes in last decade, and recently got a boost in its growth after being blessed by smart grid technologies. The objective of this paper is to presents a detailed technical overview of microgrid and smart grid in light of present development and future trend. First, it discusses microgrid architecture and functions. Then, smart features are added to the microgrid to demonstrate the recent architecture of smart grid. Finally, existing technical challenges, communication features, policies and regulation, etc. are discussed from where the future smart grid architecture can be visualized.

Enhancing smart grid with microgrids: Challenges and opportunities

Microgrids have been widely studied in the literature as a possible approach for the integration of distributed energy sources with energy storage systems in the electric network. Until now the most used configuration has been the ac microgrid, but dc-based microgrids are gaining interest due to the advantages they provide over their counterpart (no reactive power, no synchronization, increasing number of dc devices, etc.). Therefore, hybrid ac/dc microgrids are raising as an optimal approach as they combine the main advantages of ac and dc microgrids. This paper reviews the most interesting topologies of hybrid ac/dc microgrids based on the interconnection of the ac and dc networks and the conventional power network. After performing a description and analysis of each configuration, a comparative evaluation has been performed to highlight the most important features of each one. The future trends identified during the study also show that several features such as the scalability, modeling or design require further research towards the integration of hybrid microgrids in the power network.

Hybrid ac/dc microgrids—Part I: Review and classification of topologies

Microgrids are a suitable, reliable and clean solution to integrate distributed generation into the mains grid. Microgrids can present both AC and DC distribution lines. The type of distribution conditions the performance of distribution line and implies different features, advantages and disadvantages in each case. This paper analyses, in detail, all this parameters for AC and DC microgrids in order to identify and describe the available alternatives for building and configuring a microgrid. Elements and issues involved in the implementation and development, such as protections, power converters, economic analysis, and availability are discussed and described. This analysis constitutes a tool for selecting a suitable configuration of a microgrid adapted to the needs in each situation. In addition, the paper provides a picture of the current situation of microgrids, and identifies and proposes future research lines.

AC and DC technology in microgrids: A review

A large number of factors such as the increasingly stringent pollutant emission policies, fossil fuel scarcity and their price volatility have increased the interest towards the partial or total electrification of current vehicular technologies. These transition of the vehicle fleet into electric is being carried out progressively. In the last decades, several technological milestones have been achieved, which range from the development of basic components to the current integrated electric drives made of silicon (Si) based power modules. In this context, the automotive industry and political and social agents are forcing the current technology of electric drives to its limits. For example, the U.S Department of Energy’s goals for 2020 include the development of power converter technologies with power densities higher than 14.1 kW/kg and efficiencies greater than 98%. Additionally, target price of power converters has been set below $3.3/kW. Thus, these goals could be only achieved by using advanced semiconductor technologies. Wide-bandgap (WBG) semiconductors, and, most notably, silicon carbide (SiC) based power electronic devices, have been proposed as the most promising alternative to Si devices due to their superior material properties. As the power module is one of the most significant component of the traction power converter, this work focuses on an in-deep review of the state of the art concerning such element, identifying the electrical requirements for the modules and the power conversion topologies that will best suit future drives. Additionally, current WBG technology is reviewed and, after a market analysis, the most suitable power semiconductor devices are highlighted. Finally, this work focuses on practical design aspects of the module, such as the layout of the module and optimum WBG based die parallelization, placement and Direct Bonded Copper (DBC) routing.

Power module electronics in HEV/EV applications: New trends in wide-bandgap semiconductor technologies and design aspects

A novel adaptative maximum power point tracking algorithm for small wind turbines

As worldwide awareness about global climate change spreads, green electronics are becoming increasingly popular as an alternative to diminish pollution. Thus, nowadays energy efficiency is a paramount characteristic in electronics systems to obtain such a goal. Harvesting wasted energy from human activities and world physical phenomena is an alternative to deal with the aforementioned problem. Energy harvesters constitute a feasible solution to harvesting part of the energy being spared. The present research work provides the tools for characterizing, designing and implementing such devices in electronic systems through their equivalent structural models.

https://www.mdpi.com/2079-9292/8/5/486/pdf

Energy Harvesting Technologies and Equivalent Electronic Structural Models—Review

Loss reduction in converters is one of main targets in power electronics to obtain higher efficiency and lower thermal stress, which can enhance the lifetime of devices. This paper presents a variable switching frequency technique for switching loss reduction in a three-phase voltage source inverter, obtaining similar output current quality as that of a space vector pulse width modulation (SVPWM) algorithm. This type of optimization has not been applied for a three-phase system before. Simulation and experimental results are also shown. The output current ripple rms value of three-phase SVPWM is used as the optimization constraint. Results of the optimization of the switching losses with quality constraints in the switching frequency as the variable are presented for different load angles and compared with classical SVPWM. Experimental results show that this technique can save up to nearly $19\%$ in switching losses with similar total harmonic distortion of the output current, concluding that converter losses are reduced without reducing output current quality.

Jose Ignacio Garate

Papers

AC and DC technology in microgrids: A review

Power module electronics in HEV/EV applications: New trends in wide-bandgap semiconductor technologies and design aspects

A novel adaptative maximum power point tracking algorithm for small wind turbines

Energy Harvesting Technologies and Equivalent Electronic Structural Models—Review

Three-Phase VSI Optimal Switching Loss Reduction Using Variable Switching Frequency