Control and Protection of MMC-Based HVDC Systems: A Review

The voltage source converter (VSC) based HVDC (high voltage direct current system) offers the possibility to integrate other renewable energy sources (RES) into the electrical grid, and allows power flow reversal capability. These appealing features of VSC technology led to the further development of multi-terminal direct current (MTDC) systems. MTDC grids provide the possibility of interconnection between conventional power systems and other large-scale offshore sources like wind and solar systems. The modular multilevel converter (MMC) has become a popular technology in the development of the VSC-MTDC system due to its salient features such as modularity and scalability. Although, the employment of MMC converter in the MTDC system improves the overall system performance. However, there are some technical challenges related to its operation, control, modeling and protection that need to be addressed. This paper mainly provides a comprehensive review and investigation of the control and protection of the MMC-based MTDC system. In addition, the issues and challenges associated with the development of the MMC-MTDC system have been discussed in this paper. It majorly covers the control schemes that provide the AC system support and state-of-the-art relaying algorithm/ dc fault detection and location algorithms. Different types of dc fault detection and location algorithms presented in the literature have been reviewed, such as local measurement-based, communication-based, traveling wave-based and artificial intelligence-based. Characteristics of the protection techniques are compared and analyzed in terms of various scenarios such as implementation in CBs, system configuration, selectivity, and robustness. Finally, future challenges and issues regarding the development of the MTDC system have been discussed in detail

A Signal Segmentation Approach to Identify Incident/Reflected Traveling-Waves for Fault Location in Half-Bridge MMC-HVDC Grids

This article presents a new systematic technique for identifying voltage traveling-waves (TWs) to determine the location of line faults in half-bridge modular multilevel converter-based high-voltage direct-current (HBMMC-HVDC) grids. In this technique, the buffered voltage signal frame around the fault-detection time is first scaled and then segmented via an optimization process. Finally, the incident/reflected TWs arrival times are obtained by executing a simple search algorithm on the reconstructed signal segments’ differences. This article describes how to use this technique in three forms of TW-based fault location schemes, including the single-ended scheme with known TW velocity, the double-ended scheme with known TW velocity, and the double-ended scheme with unknown TW velocity. The application results on a 4-terminal HBMMC-HVDC grid simulated with exact component models show the proposed technique’s high capability and accuracy in all the three TW-based fault-location schemes. According to these results, the average fault-location errors are less than 0.5% for all the schemes. The numerical results also confirm that the proposed technique maintains its excellent performance, even in the face of close to terminal faults with distances down to 4 km, faults with high resistances up to 450 Ω, and noisy signals with signal-to-noise ratios down to 55 dB. Moreover, the comparison results confirm that the proposed approach is more tolerant of measurement noise than the wavelet transform.©2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.fi=vertaisarvioitu|en=peerReviewed

Development of a hybrid offshore wind and wave energy system

The proposed research aims to fulfil the growing demand for sustainable energy solutions by developing a hybrid offshore wind-wave energy (HOWWE) system. The project intends to contribute to the optimisation of power outputs and the reduction of infrastructure costs by harnessing the potential of both sources individually and synergistically. Key performance indicators (KPIs), including output power optimization and the efficiency of control algorithms, serve as crucial metrics for assessing the project's success. This project is in line with global initiatives to shift to cleaner, more efficient energy sources. This research's novitiates are focused on overcoming significant development issues relating to efficiency and power output maximisation. To improve the system efficiency by integration using converters with the implementation of a maximum power-point tracking algorithm (MPPT). A comprehensive numerical model that includes the permanent magnet synchronous generator (PMSG), linear generator, and HOWWE system serves as a basic novitiate for achieving the hybrid system. The research's principal goals are twofold: First, create an analytical model that integrates numerical and analytical approaches, focusing on power modelling and various power calculation case studies. Second, to optimise offshore wind and wave energy output power, various control strategies such as feedback linearization (FBL), proportional integral derivative (PID), sliding-mode control (SMC), super-twisting algorithm (STA), and integral-based real twisting algorithm (IBRTA) will be investigated and evaluated. STA and IBRTA algorithms have been carefully tested in comparison to conventional PID, FBL, and SMC algorithms, confirming their efficiency in increasing power generation. In the case of wave energy, single point absorber (SPA) and multipoint absorber (MPA) solutions are investigated using real-time data. Furthermore, by developing MPPT techniques for both energy sources, the research contributes to the seamless integration of offshore wind-wave energy. Maximum power extraction is ensured by the use of voltage source converters (VSC) for both sources. The integration strategy, which employs VSC for AC-DC and voltage source inverter (VSI) for DC-AC, is tested using real-time data from the North West, Silverstone lightship and Greenwich lightship of the United Kingdom on a semi-submersible platform equipped with one PMSG and nine linear generators. The proposed system was successfully constructed and rigorously tested in MATLAB, with real-time data used to ensure accuracy and reliability in realistic situations. The findings of this study have the potential to considerably augment the field of HOWWE and contribute to the creation of long-term energy solutions for a cleaner and greener future