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Considering the increasing amounts of renewable energy generation and energy storage required to meet ambitious environmental goals, it is clear that the next generation of power grids will be dominated by converter-connected devices. In addition, the increasing share of loads connected via power electronics and the general transition to non-synchronous grids with distributed generators make dc microgrids an attractive future alternative. However, achieving optimal utilization of distributed generators in such cases is a complex task, as the performance depends on both the grid and control design. In this paper, we consider such a case where the optimal utilization of distributed generators is achieved by optimal power sharing while taking into account the grid topology, the available generators, and the way they are controlled. For the latter, we consider a droop-based decentralized control scheme whose primary objective is to achieve voltage regulation in the allowable operating range. A novel mixed-integer optimization approach is proposed to identify the optimal converter size and location in the network so that the microgrid can operate safely and with optimal use of the available resources. Time-domain simulations are used to validate the proposed approach and demonstrate its robustness to uncertainty in generator availability. [ABSTRACT FROM AUTHOR]

The application of energy storage in offshore renewable generation systems allows managing the intrinsic uncertainty of the resources and improving the utilization factor of the electrical network. Optimal storage design algorithms generally have to evaluate the behavior of the whole system thousands times before converging to the optimal solution and the reliability of the results obviously depends on the quality of input data. On the other hand, the utilization of simplified storage models in the design stage can reduce the simulation time drastically, while still providing useful information. The goal of this paper is to evaluate the applicability of a methodology for sizing the energy storage system in a hybrid wind and wave farm, which is based on fluid models. The description and performance of thismodeling approachwill be introduced and compared to standard design procedures based on extensive simulations. Advantages and limitations of each approach will be underlined and the impact of input data quality will be discussed. [ABSTRACT FROM AUTHOR]

The future success of wave energy in the renewable energy mix depends on the technical advancements of the specific components and systems, on the grid access availability and, ultimately, on the economical profitability of the investment. Small and remote islands represent an ideal framework for wave energy exploitation, due both to resource availability and to the current high cost of electricity that mostly relies on diesel generation. Energy storage can be the enabling technology to match the intermittent power generation from waves to the energy needs of the local community. In this paper real data from La Palma, in the Canary Islands, are used as a basis for the considered test case. As a first step the study quantifies the expected power production from Wave Energy Converter (WEC) arrays, based on data from the Lifesaver point absorber developed by Fred. Olsen. Then, a stochastic optimization approach is applied to evaluate the convenience of energy storage introduction for reducing the final cost of energy and to define the corresponding optimal rating of the storage devices. [ABSTRACT FROM AUTHOR]

The fifth paper [[5]], entitled "AC-DC Converters for Electrolyzer Applications: State of the Art and Future Challenges", presents a comprehensive review of currently used AC-DC converters for alkaline and proton exchange membrane electrolyzers in power grid or wind energy conversion systems. It includes a silicon-controlled rectifier forced shutdown control strategy and a three-loop control strategy, which greatly reduces the silicon-controlled rectifier shutdown time and ensures the reliability of local load power supply. With the rapid progression of renewable energies into grids, grid-connected systems are increasing dramatically around the world. [Extracted from the article]

Wave energy is nowadays one of the most promising renewable energy sources; however, wave energy technology has not reached the fully-commercial stage, yet. One key aspect to achieve this goal is to identify an effective control strategy for each selected Wave Energy Converter (WEC), in order to extract the maximum energy from the waves, while respecting the physical constraints of the device. Model Predictive Control (MPC) can inherently satisfy these requirements. Generally, MPC is formulated as a quadratic programming problem with linear constraints (e.g., on position, speed and Power Take-Off (PTO) force). Since, in the most general case, this control technique requires bidirectional power flow between the PTO system and the grid, it has similar characteristics as reactive control. This means that, under some operating conditions, the energy losses may be equivalent, or even larger, than the energy yielded. As many WECs are designed to only allow unidirectional power flow, it is necessary to set nonlinear constraints. This makes the optimization problem significantly more expensive in terms of computational time. This work proposes two MPC control strategies applied to a two-body point absorber that address this issue from two different perspectives: (a) adapting the MPC formulation to passive loading strategy; and (b) adapting linear constraints in the MPC in order to only allow an unidirectional power flow. The results show that the two alternative proposals have similar performance in terms of computational time compared to the regular MPC and obtain considerably more power than the linear passive control, thus proving to be a good option for unidirectional PTO systems. [ABSTRACT FROM AUTHOR]

Ocean waves are a promising source of renewable energy. In this paper, we briefly introduce the characteristics of ocean wave energy and summarize the principles of harvesting ocean energy by wave energy converters. We also review the prototypes or commercial devices deployed in real sea between 2005 and July 2016. In addition, we present the concept of a wave-to-wire model as a framework to systematically review and compare control strategies for wave energy conversion systems, with a focus on the numerical and experimental validation. [ABSTRACT FROM AUTHOR]

The rising integration of offshore wind energy into the electric grid provides remarkable opportunities in terms of environmental sustainability and cost efficiency. However, it poses challenges to power quality (PQ) caused by variable operational events and power electronic devices used in wind turbines. This renders early-stage disturbance detection and classification tools critical for managing grid systems with renewable energy sources. While existing reviews specialize in the monitoring measures of partial PQ events, this survey offers a deeper understanding by further exploring root causes and disturbance locations, followed by a critical discussion of emerging algorithmic solutions. In contrast with generalists' stances on PQ, this work delves into the impact of offshore wind energy on PQ events and their early diagnosis. Moreover, the principles and applications of synchronized waveform measurement, a promising measurement technology for detection and classification processes, are highlighted. Then, evaluation metrics for detection and classification algorithms are discussed for the first time. Finally, a novel system-wide monitoring framework is proposed given the need for holistic assessment frames in this field. This review not only illustrates the challenges and future research directions in the level of algorithms, measurements, and frameworks, but can also serve as a guideline for real-time disturbance analysis of offshore wind power grid connection and integration. [Display omitted] • Review of power quality events sensitive to offshore wind energy penetration. • Structured view on power quality disturbance monitoring: events, collection locations, and standards. • Detailed survey of algorithmic advances for disturbance detection and classification. • Critical view of the advantages and applications of synchronized waveform measurements in power quality analysis. • Evaluation guidelines: algorithmic performance and system-wide assessment. [ABSTRACT FROM AUTHOR]

Abstract The purpose of this paper is to highlight the most demanding aspects of grid interconnection of marine energy installations while at the same time providing an updated overview and comparative analysis of the connection requirements of eight European Grid Codes. Therefore, the major issues related to marine energy installations will be summarized as well as the requirements of this type of generation. Besides, the extent to which current Grid Codes include marine energy technologies will be analysed jointly with the need of harmonization of different Grid Codes into a generalised European grid code. Apart from this, several future trends of marine energy technology and its interconnection will be provided for the final discussion. Highlights • Capacity limits and critical power quality issues where not originally planned. • Impacts: limited dispatchability, electrical grid stress, high penetration effects. • Long submarine cables reduce precise voltage or reactive power control capability. • European Grid codes compared: only in UK and Germany offshore treated separately. • ENTSO-E effort for harmonization by setting common requirements for grid connection. [ABSTRACT FROM AUTHOR]