As an important renewable energy source, the scale of wind energy utilization is growing rapidly worldwide in recent decades. The increasing capacity of both onshore and offshore wind power generation calls for higher requirements for the power level and reliability of generators and converters. Compared to the traditional three-phase wind power generation, multiphase wind power generation systems have obvious advantages in low-voltage high-power operation, enhanced fault-tolerant ability and increased degrees of control freedom, which help them gaining increasing popularity in modern wind power generation. This paper presents an overview on the multiphase energy conversion of wind power generation and introduces the pertinent technology advances, including the design of multiphase wind turbine generators, multiphase converter topologies, modeling and control of multiphase generators. Besides, this paper offers prospects of novel solutions brought by the redundant control freedom in multiphase system to cope with some difficult technical problems, such as Common-Mode Voltage (CMV) suppression, Low Voltage Ride Through (LVRT), and vibration & noise reduction.

A review of multiphase energy conversion in wind power generation

The global concern with power quality is increasing due to the penetration of renewable energy (RE) sources to cater the energy demands and meet de-carbonization targets. Power quality (PQ) disturbances are found to be more predominant with RE penetration due to the variable outputs and interfacing converters. There is a need to recognize and mitigate PQ disturbances to supply clean power to the consumer. This article presents a critical review of techniques used for detection and classification PQ disturbances in the utility grid with renewable energy penetration. The broad perspective of this review paper is to provide various concepts utilized for extraction of the features to detect and classify the PQ disturbances even in the noisy environment. More than 220 research publications have been critically reviewed, classified and listed for quick reference of the engineers, scientists and academicians working in the power quality area.

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Comprehensive Review on Detection and Classification of Power Quality Disturbances in Utility Grid With Renewable Energy Penetration

Advanced dielectric polymers for energy storage

An electrostatic capacitor has been widely used in many fields (such as high pulsed power technology, new energy vehicles, etc.) due to its ultrahigh discharge power density. Remarkable progress has been made over the past 10 years by doping ferroelectric ceramics into polymers because the dielectric constant is positively correlated with the energy storage density. However, this method often leads to an increase in dielectric loss and a decrease in energy storage efficiency. Therefore, the way of using a multilayer structure to improve the energy storage density of the dielectric has attracted the attention of researchers. Although research on energy storage properties using multilayer dielectric is just beginning, it shows the excellent effect and huge potential. In this review, the main physical mechanisms of polarization, breakdown and energy storage in multilayer structure dielectric are introduced, the theoretical simulation and experimental results are systematically summarized, and the preparation methods and design ideas of multilayer structure dielectrics are mainly described. This article covers not only an overview of the state-of-the-art advances of multilayer structure energy storage dielectric but also the prospects that may open another window to tune the electrical performance of the electrostatic capacitor via designing a multilayer structure.

Recent Advances in Multilayer-Structure Dielectrics for Energy Storage Application.

The large-scale application of wind power and photovoltaic power solves the energy crisis and alleviates the environmental problems caused by the use of conventional energy. However, they are at risk of being randomly tripped from the network when faced to voltage sag and severe fault events, which will lead to a sudden reduction of active power output and also complicates fault recovery process of the whole system. Moreover, it may also aggravate failures and lead to large-scale power outages, which stimulates a growing interest in analyzing the low-voltage ride-through (LVRT) capabilities of the renewable energy systems (RES) and improving the performance through developing various mathematical models and analysis tools. In this paper, a systematical overview of cause, classification of voltage sag phenomena and voltage sag emulating techniques is presented, and four voltage sag generators (VSGs) are discussed and compared, which include generator based-VSG, shunt impedance based-VSG, transformer based-VSG and full converter based-VSG. Furthermore, a closed-loop detection platform based on real-time digital simulator (RTDS) for the converter controller of a permanent magnet synchronous generator (PWSG) set is introduced, to investigate the LVRT performance of the WT system under grid voltage sag conditions. Finally, the application of VSG in RES are presented and the future research directions are also discussed.

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Cause, Classification of Voltage Sag, and Voltage Sag Emulators and Applications: A Comprehensive Overview

Introducing high-permittivity nano-fillers into a dielectric polymer is a practical way to enhance the permittivity of nanocomposite dielectrics. However, this normally leads to a decrease in the breakdown strength, which has limited the development of electrostatic capacitors. In this work, silica (SiO2) coating and polydopamine (PDA) surface modification methods were combined for enhancement of the breakdown strength; we prepared poly(vinylidene fluoride) (PVDF) based composite dielectrics doped using double core-shell structure BaTiO3 nano-particles (BT NPs) and nano-fibers (NFs) (PDA-SiO2@BT NPs/PVDF or PDA-SiO2@BT NFs/PVDF). Then, the contributions of the double-layer core-shell structure and filler shape to improving the energy storage performance of the dielectrics were systematically discussed. The results show that the synergy between the silica and PDA effectively increased the breakdown strength. Furthermore, the dielectric properties and energy storage properties of the PVDF-based dielectrics with various double core-shell filler (PDA-SiO2@BT NPs or PDA-SiO2@BT NFs) contents were also investigated. Compared with the particles, appropriate introduction of the PDA-SiO2@BT NFs could more preferentially improve the energy storage characteristics. It was found that 1.0 vol.% PDA-SiO2@BT NFs/PVDF exhibited a high energy storage density of 14.7 J/cm
 3
 with an efficiency of 68%. This research provides a promising avenue for enhancing the energy storage capability of PVDF-based nanocomposite dielectrics.

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Yu Feng

Papers

Cause, Classification of Voltage Sag, and Voltage Sag Emulators and Applications: A Comprehensive Overview

Enhanced Energy Storage Characteristics in PVDF-Based Nanodielectrics With Core-Shell Structured and Optimized Shape Fillers