Power balancing and dc fault ride through in DC grids with dc hubs and wind farms

Acknowledgment This project was funded by European Research Council under the Ideas program in FP7; grant no 259328, 2010.Peer reviewedPostprin

Full Bridge MMC Converter Optimal Design to HVDC Operational Requirements

This project is funded by RTE, Paris, FrancePeer reviewedPostprin

Dynamic Modelling of VSCs in a dq Rotating Frame for Pole-to-Pole dc Fault Study

Financial support from European Research Council in FP7 grant no 259328, 2010 is acknowledged.Peer reviewedPostprin

Segmentation of Fuzzy and Touching Cells Based on Modified Minimum Spanning Tree and Concave Point Detection

In order to segment fuzzy and touching cell images accurately, an improved algorithm is proposed based on minimum spanning tree (MST) and concave point detection. First, the cell images are smoothed and enhanced by a Gaussian filter. Then, the improved minimum spanning tree algorithm is used to segment the cell images. The MST algorithm is modified from three aspects, namely, weight function of edges, difference function of internal and inter region, and threshold function and parameter k. Furthermore, the problem of cell touching is solved by means of concave point detection. According to the rugged topography of touching cells, the concave points are found from the concave regions in the touching cell images, which are used to find the separation points quickly and accurately. Experimental results indicate that the new algorithm is ideal and effective

Distributed Power balance and damping control for high power multiport LCL DC hub

This project is funded by European Research Council in FP7; grant no 259328, 2010 and EPSRC grant no EP/K006428/1, 2013.Peer reviewedPostprin

Analysis of wide-band oscillation of hybrid MMC interfacing weak AC power system

The wide-band oscillation of the hybrid MMC induced by excessive power infeed under weak AC power system integration is analyzed in this paper. A closed-loop state-space-based time-domain small-signal model is firstly established to investigate the instability problem. Different from the findings in two-level VSCs or half-bridge MMCs, the root locus analysis and participation factor analysis in this paper reveals that the oscillation frequency and involved control loops are highly related to the operation status. When hybrid MMC operates as a rectifier, a low-frequency oscillation is observed with the d-channel control loop mainly participated. In contrast, a high-frequency oscillation occurs with a q-channel control loop mainly involved when the hybrid MMC operates as an inverter. This wide-band oscillation phenomenon is explored with the aid of two simplified loop-gain-based s-domain models, which are derived referring to the selective modal analysis approach. To suppress the oscillation, sensitivity analysis regarding the impact of parameters on the phase margin is conducted to recognize effective parameter adjustment methods. The analysis results are validated by detailed electromagnetic simulations

Comparative study of small-signal stability under weak AC system integration for different VSCs

Voltage source converters (VSCs) with self-commutation ability are suitable to interconnect weak AC systems. This paper conducts a comparative study of the small-signal stability characteristics for three typical VSCs, namely, the two-level VSCs (TL-VSCs), the half-bridge modular multilevel converters (HB-MMCs) and the hybrid MMCs (HY-MMCs),underweak AC system integration with special consideration on both inverter and rectifier operation. The frequency responses based on impedance models are compared using the frequency-domain analysis. The oscillation frequencies and mainly participated state variables of the unstable modes are compared using root locus and participation factor analysis in time-domain. Proper parameter retuning approaches for stability enhancement are proposed. The above analysis is adequately validated by electromagnetic simulations

CausalVLR: A Toolbox and Benchmark for Visual-Linguistic Causal Reasoning

We present CausalVLR (Causal Visual-Linguistic Reasoning), an open-source toolbox containing a rich set of state-of-the-art causal relation discovery and causal inference methods for various visual-linguistic reasoning tasks, such as VQA, image/video captioning, medical report generation, model generalization and robustness, etc. These methods have been included in the toolbox with PyTorch implementations under NVIDIA computing system. It not only includes training and inference codes, but also provides model weights. We believe this toolbox is by far the most complete visual-linguitic causal reasoning toolbox. We wish that the toolbox and benchmark could serve the growing research community by providing a flexible toolkit to re-implement existing methods and develop their own new causal reasoning methods. Code and models are available at https://github.com/HCPLab-SYSU/CausalVLR. The project is under active development by HCP-Lab's contributors and we will keep this document updated.Comment: CausalVLR: A Toolbox and Benchmark for Visual-Linguistic Causal Reasoning. https://github.com/HCPLab-SYSU/CausalVL

Low Energy Protection System for DC Grids Based on Full Bridge MMC Converters

This project is funded by RTE, Paris, France. D. Jovcic and W. Lin are with the School of Engineering, University of Aberdeen, AB24 3UE, U.K. ( [email protected], [email protected]). S. Nguefeu and H. Saad are with the Réseau de Transport d’Electricité, Paris 92932, France ([email protected], [email protected] )Peer reviewedPostprin

A cascaded converter interfacing long distance HVDC and back-to-back HVDC systems

This paper proposes a cascaded converter dedicated to long-distance HVDC infeed and asynchronous back-to-back interconnection of receiving grids. The cascaded converter is consisted of MMCs in series and parallel connection, meeting the high DC voltage and power demand of HVDC system. It realizes hierarchical feeding and asynchronous interconnection of receiving grids, optimizing the multi-infeed short circuit ratio and improving the flexibility of the receiving grids. The topology and operating characteristics of the cascaded converter are introduced in detail. The multi-infeed short-circuits ratio (MISCR) and the maximum power infeed of the cascaded converter based HVDC systems are analyzed. Various feasible operating modes with online switching strategies of the cascaded converter are studied to improve the operational flexibility of the system. The simulation results verify the effectiveness of the control strategy of the HVDC system embedding the cascaded converter. The DC faults clearing strategy and operating modes switching strategies are also validated