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.

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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

Wide-bandgap (WBG) transistors provide better switching performance and higher operating temperatures compared to state-of-the-art Si devices and are suited for high-frequency applications due to very short switching times. The main obstacle for implementation of WBG transistors at full potential is the high-frequency oscillation in voltage and current during switching transients. Oscillations arise from resonance due to parasitic and device inductances and capacitances. Introduction of WBG transistors depends on the elimination of these oscillations and their negative effect on the performance of power converters. Good layout practice is mandatory, but there is a limit to the reduction of these parasitics, and often, slowing of the semiconductor switching time must be applied. This article presents a simple methodology for the attenuation of the negative effects of WBG transistor high-frequency oscillations without increasing rise and fall times. The proposed methodology is based on determination of the source of feedback resonant frequency between gate and power loops using network analyzer measurement on printed circuit board and utilization of a tuned $RLC$ filter. Experimental application of the methodology shows a direct relationship between loop resonant frequency and voltage and current oscillations. The proposed method reduces power losses, high-frequency oscillations, and electromagnetic interference.

Wide-Bandgap Semiconductor HF-Oscillation Attenuation Method With Tuned Gate $RLC$ Filter

The present paper introduces a power supply system for Machine to Machine Modules and Fixed Cellular Terminals with discontinuous current consumption. The architecture proposed tries to solve the input high current peaks derived from the discontinuous current consumption of the PA. The final solution decreases the voltage supply ripple and current peak applied to the battery. The document also describes the problem and shows a practical implementation of the solution proposed.

Improvements of Power Supply Systems in Machine to Machine Modules and Fixed Cellular Terminals with Discontinuous Current Consumption

This paper proposes a more precise way of radiofrequency output power control and sensing for mobile base station transmitters without increasing the complexity of the AGC of their power amplifier in order to overcome the design adjustment problems and the production ones. The solution presented is based on measuring both the output power RF and the current consumption of the PA. The solution has been tested on commercial GSM triple-band fixed cellular terminals and prototypes of 3G power amplifiers.

Mixed RF Output Power Control for Low Power Transmitters in Mobile Cellular Terminals

Power electronic applications need high voltage and current ranges which are impossible to obtain with discrete devices. Parallelization technique is a solution to increase power converter current capacity. Current distribution problems may reduce device lifetime and cause converter malfunction. Parallelization requires a total control of circuit parasitic elements which depend on layout physical materials and dimensions. The objective of this article is to show, by electromagnetic (EM) model simulations, layout non ideal effects for power circuits, in order to understand and control circuit stray elements, especially parasitic inductances, and current distributions.

Analysis of impedance and current distributions in parallel IGBT design

In some power electronic applications, with high current and voltage ranges, discrete devices are not enough unless parallelization techniques are employed. IGBTs are one of the most common and widespread power electronic semiconductors, to make a parallel design with them, either as a discrete devices, dies, individual cells or power modules, it is necessary to know their static and dynamic behaviour. Besides, operation temperature, device parameter tolerances, driver circuit and power layout, as well as different parasitic inductance also affect its performance. The objective of this article is to show and model how all the aforementioned parameters affect the behaviour and performance of a parallelized IGBT, and highlight the design keys for a successful parallelized design.

Jose Ignacio Garate

Papers

Wide-Bandgap Semiconductor HF-Oscillation Attenuation Method With Tuned Gate $RLC$ Filter

Improvements of Power Supply Systems in Machine to Machine Modules and Fixed Cellular Terminals with Discontinuous Current Consumption

Mixed RF Output Power Control for Low Power Transmitters in Mobile Cellular Terminals

Analysis of impedance and current distributions in parallel IGBT design

Analysis and modelling of IGBTs parallelization fundamentals