Edge-Oriented Graphene on Carbon Nanofiber for High-Frequency Supercapacitors

High-frequency supercapacitors are being studied with the aim to replace the bulky electrolytic capacitors for current ripple filtering and other functions used in power systems. Here, 3 D edge-oriented graphene(EOG)was grown encircling carbon nanofiber(CNF) framework to form a highly conductive electrode with a large surface area. Such EOG/CNF electrodes were tested in aqueous and organic electrolytes for high-frequency supercapacitor development. For the aqueous and the organic cell, the characteristic frequency at-45° phase angle was found to be as high as 22 and 8.5 k Hz, respectively. At 120 Hz, the electrode capacitance density was 0.37 and 0.16 m F cm^(-2) for the two cells. In particular, the 3 V high-frequency organic cell was successfully tested as filtering capacitor used in AC/DC converter, suggesting the promisingpotential of this technology for compact power supply design and other applications.

Transient Characteristics and Accommodative Current Limiting Strategy for Bidirectional Interlinking Converters in Hybrid AC/DC Microgrids

Bidirectional interlinking converter(BIC)is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids.However,the variety of control modes and flexible bidirectional power flow complicate the influence of AC faults on BIC itself and on DC sub-grid,which potentially threaten both converter safety and system reliability.This study first investigates AC fault influence on the BIC and DC bus voltage under different BIC control modes and different pre-fault operation states,by developing a mathematical model and equivalent sequence network.Second,based on the analysis results,a general accommodative current limiting strategy is proposed for BIC without limitations to specific mode or operation condition.Current amplitude is predicted and constrained according to the critical requirements to protect the BIC and relieving the AC fault influence on the DC bus voltage.Compared with conventional methods,potential current limit failure and distortions under asymmetric faults can also be avoided.Finally,experiments verify feasibility of the proposed method.

Analysis of Commutation Failure in Multi-Infeed HVDC System under Different Load Models

HVDC technology has been widely used in modern power system. On one hand, HVDC has the advantages of economy, high efficiency and strong controllability. While on the other hand, it makes the dynamic characteristics of the power system becoming more and more complex. That puts forward a new challenge to system stability and raises new questions for power system simulation. This paper focuses on the interaction between AC and DC systems, especially the problem of commutation failure caused by AC system fault. Based on the data of China Southern Power Grid, this paper calculates the fault regions that may cause commutation failure and calculates the system critical clearance time under different load models, analyzes the impacts of different load models on commutation failure and the stability of AC/DC hybrid system.

Analysis of the Transition Between Multiple Operational Modes for Hybrid AC/DC Microgrids

There are four basic operational modes for the hybrid AC/DC microgrid,including AC grid-connected while interconnecting,both off-grid while interconnecting,AC gridconnected without connection,and both off-grid without connection.How to achieve a seamless operational mode transition is an urgent technical need to overcome.First,this paper describes the typical structure of the hybrid microgrid,and places a detailed focus on the power balance and transition strategy.Secondly,it takes the master-slave control structure as an example,and designs the transition logic for different operational modes,and then a method for selecting the slack bus and transition time-sequence is proposed.Based on the different roles that the interlinking converter(IC)plays in the process of modes transition,a voltage-power(U-P)control method for a hybrid AC/DC microgrid is proposed,and the exchanged power is calculated based on the voltage deviation between the rating value and measured value.Finally,a control flowchart for the transition between the four operational modes in transition is designed.Using the PSCAD/EMTDC platform,this paper takes a typical seven-point microgrid structure as an example,the proposed transition strategy is carried out,and the results show that the transition method and time sequence can achieve smooth transition between different operational modes.

Recent advances in micro-supercapacitors for AC line-filtering performance:From fundamental models to emerging applications

Recently,micro-supercapacitors(MSCs)have undergone major development as next-generation micro-electrochemical energy storage devices for self-powered,integrated,and wearable systems,thanks to their excellent performance capability.In particular,their rapid frequency response characteristics make them potential candidates to replace conventional capacitors and function as alternating current(AC)line filters to rectify pulse energy or as current ripple filters in the kHz range.However,few papers have been published about the associated fundamental device components,architectures,and correct characterization of MSCs applied in filter applications.In addition,it is a huge challenge to achieve a balance between capacitance and frequency response,not yet to be overcome.This review comprehensively summarizes recent advances in MSCs for AC line-filtering,from fundamental mechanisms to appropriate characterization and emerging applications.Special attention is given to progress in microfabrication strategies,electrode materials,and electrolytes for high-frequency MSCs.We also present perspectives and insights into the development of MSCs in different frequency ranges for AC line-filtering applications.