The use of power converters is very important in maximizing the power transfer from renewable energy sources such as wind, solar, or even a hydrogen-based fuel cell to the utility grid. An LCL filter is often used to interconnect an inverter to the utility grid in order to filter the harmonics produced by the inverter. Although there is an extensive amount of literature available describing LCL filters, there has been a gap in providing a systematic design methodology. Furthermore, there has been a lack of a state-space mathematical modeling approach that considers practical cases of delta- and wye-connected capacitors showing their effects on possible grounding alternatives. This paper describes a design methodology of an LCL filter for grid-interconnected inverters along with a comprehensive study of how to mitigate harmonics. The procedures and techniques described in this paper may be used in small-scale renewable energy conversion systems and may be also retrofitted for medium- and large-scale grid-connected systems.

Modern power systems face different challenges such as the ever-increasing electrical energy demand, the massive growth of the renewable energy with distributed generations, the large-scale internet of things (IoT) devices adaptation, the emerging cyber-physical security threats, and the main goal of maintaining the system’s stability and reliability. These challenges pose extreme pressure on finding advanced technologies and sustainable solutions for secure and reliable operations of the power system. The blockchain is one of the recent technologies that have gained lots of attention in different applications including smart grid for its uniqueness and decentralized nature. In the last few years, this technology grew a momentum specifically with the cryptocurrencies’ industry such as the Bitcoin and Etherium. Blockchain’s applications in the smart grids could offer many innovative and affordable solutions to some of the challenges that the future and the current smart grids will be facing. This paper reviews different prospects, advantages, approaches, and technical challenges of utilizing the blockchain technology in the smart grid, as well as presents frameworks for key smart grid blockchain-based applications; more specifically, it is shown that how the blockchain can be used as the smart grid’s cyber-physical layer.

This paper presents a new operational strategy for a small scale wind farm which is composed of both fixed and variable speed wind turbine generator systems (WTGS). Fixed speed wind generators suffer greatly from meeting the requirements of new wind farm grid code, because they are largely dependent on reactive power. Integration of flexible ac transmission systems (FACTS) devices is a solution to overcome that problem, though it definitely increases the overall cost. Therefore, in this paper, we focuses on a new wind farm topology, where series or parallel connected fixed speed WTGSs are installed with variable speed wind turbine (VSWT) driven permanent magnet synchronous generators (PMSG). VSWT-PMSG uses a fully controlled frequency converter for grid interfacing and it has abilities to control its reactive power as well as to provide maximum power to the grid. Suitable control strategy is developed in this paper for the multilevel frequency converter of VSWT-PMSG. A real grid code defined in the power system is considered to analyze the low voltage ride through (LVRT) characteristic of both fixed and variable speed WTGSs. Moreover, dynamic performance of the system is also evaluated using real wind speed data. Simulation results clearly show that the proposed topology can be a cost effective solution to augment the LVRT requirement as well as to minimize voltage fluctuation of both fixed and variable speed WTGSs.