Search

• The faulty operation of MMC with hot-reserved SMs is analyzed. • NLM corrector based fault-tolerant strategy for high-voltage MMC is proposed. • The strategy features simplicity, low voltage stress and little influence scope. The reliable and consistent operations of modular multilevel converters (MMCs) under fault conditions are crucial for high-voltage and high-power applications. To strengthen the performances of MMCs under submodule (SM) faults, a fault- tolerant strategy based on the nearest level modulation (NLM) is proposed in this paper. According to the changed AC component in the faulty arm voltage, this method adds a corrector in NLM, which remedies the faulty arm voltage by adjusting the number of inserted SMs for the faulty arm. Then, the faulty operation can be recovered to the normal. The corrector is simple to realize and can effectively suppress the odd-order circulating currents. Under the proposed method, only the ripples of the capacitor voltages in the faulty arm rise. The average voltage stress on each capacitor is the same as that in normal operation since the rated capacitor voltage in the faulty arm has no rise. No measure and influence impose on healthy arms. With features of simplicity, low voltage stress and little influence scope, the proposed strategy is fit for high-voltage MMCs. The feasibility of the proposed strategy is verified by the simulation results with the professional tool Matlab/Simulink. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an extensive analysis of the influence of the DC voltage on the compensation performance of Static Var Generator (SVG). A method to design the DC voltage rated value is proposed according to the compensation performance. First, a required lowest value of the DC voltage for full compensation (a unity total power factor) is obtained by using the analysis of the equivalent circuit. For the situation where the DC voltage is smaller than the above-obtained lowest value, two basic options which are the sinusoidal modulation and the over modulation for the PWM control of SVG are considered. Then, the quantitative relationship between the DC voltage rated value and the compensation performance is detailed. In addition, the lowest value of the DC voltage in the SVG with a battery energy storage device is also obtained for the reactive and active output current. Based on the above analysis, the design of the DC voltage rated value for SVG is quite straight forward. Both simulation results and the hardware experimental results are finally presented to verify the validity of the analysis results and the proposed design method. [Copyright &y& Elsevier]

• The study of the combined operation of RSFCLs and DCCBs has shown effective protecting results. • Detailed models of the RSFCL and DCCB are built in this paper. • The influence of four kinds of different parameters on the fault clearing process are investigated. • Converters in the system remain unblocked, making the fast recovery of the system possible through DCCBs' reclosing. The high rate of rise and large amplitude of a dc fault current in MMC-MTDC system make its interruption difficult for DC Circuit Breakers (DCCBs). In order to tackle this issue, this paper proposes a combined operation of a Resistive-type Superconducting Fault Current Limiter (RSFCL) and a DCCB. By analyzing the fault current in a symmetrical monopole MMC-MTDC system, the effectiveness and necessity of adding a resistive type fault current limiting device into the system after fault is established. With detailed modeling of the RSFCL and DCCB including the quench and recovery processes of the RSFCL, their combined operation is investigated. The influence of different parameters, such as the maximum quench resistance of the RSFCL, the insertion time of the energy absorption branch in the DCCB, and the quench and recovery process of RSFCL, on the fault clearing process are investigated in detail. The effectiveness of the combined operation is verified by extensive simulations in PSCAD/EMTDC. The results indicate that the combination of RSFCLs and DCCBs can obtain a suppression rate of at least 25% on the peak value of the fault current. Besides, the energy that DCCBs need to absorb in their arresters has been reduced by more than 60%, and the total fault clearing time is also reduced. Furthermore, all the converters remain unblocked, making the fast recovery of MMC-MTDC system possible through DCCBs reclosing. It is concluded that the combination of RSFCLs and DCCBs provides an effective solution to handle short circuit faults in MMC-MTDC systems. [ABSTRACT FROM AUTHOR]

Modular Gravity Energy Storage (M-GES) systems are emerging as a pivotal solution for large-scale renewable energy storage, essential for advancing green energy initiatives. This study introduces innovative capacity configuration strategies for M-GES plants, namely Equal Capacity Configuration (EC) and Double-Rate Capacity Configuration (DR), tailored to optimize energy storage efficiency and stability. Through comprehensive MATLAB/Simulink simulations, we demonstrate each configuration's distinct power characteristics and operational advantages. Our findings reveal that while the EC configuration offers enhanced power accuracy and stability, it requires a larger number of units. In contrast, the DR configuration, characterized by fewer but larger units, shows a trade-off with reduced power stability. This paper contributes significantly to the field by presenting a first-of-its-kind comparative analysis of these configurations, offering insights into their practical applications and scalability. The proposed strategies and findings lay a foundation for future research and development in gravity energy storage systems, marking a step forward in pursuing sustainable and reliable energy solutions. [Display omitted] • Two typical unit capacity configuration strategies for M-GES power plants are proposed. • The unit scheduling method of the M-GES power plant is proposed. • The coordination control method is provided for each proposed configuration strategy. • Equal capacity configuration has better power accuracy but requires more units. • Double rate configuration needs fewer but larger units and less power stability. [ABSTRACT FROM AUTHOR]

This paper presents the first systematic study on power control strategies for Modular-Gravity Energy Storage (M-GES), a novel, high-performance, large-scale energy storage technology with significant research and application potential. Addressing the current research gap in M-GES power control technology, we propose two corresponding compensation modes and several power control strategies for Hybrid M-GES and M-GES. The effectiveness of these strategies is validated through simulations on the MATLAB/Simulink platform, including tests using sinusoidal power and feasibility verification based on a natural California load curve. Additionally, we analyze the normal and abnormal operating conditions of M-GES. In conclusion, the characteristics of the proposed control strategies are summarized, providing a guideline for further research. [Display omitted] • Modular-gravity energy storage (M-GES) power control system studied. • Two compensation modes and four control strategies are systematically studied and validated. • The center switching method with hysteresis control (CSM-H) excels in continuous compensation mode. • The center switching method with hysteresis control and dead zone (CSM-HD) excels in overlap compensation mode. • Based on the power control system proposed in this paper, the M-GES plant performs highly in natural power systems. [ABSTRACT FROM AUTHOR]

The limitation of existing point to point high-voltage DC connections for offshore wind farm transmission is that it does not support power exchange or trading between two or multiple DC systems. However, proposed by many researchers, interconnected voltage-source converter based multi-terminal high-voltage DC systems provide system redundancy, higher flexibility and capability of exchanging power between multiple areas. This paper presents a detailed review of several key technical and operational aspects of multi-terminal high-voltage DC systems for large scale offshore wind farm transmission. This review not only summarizes the development of high-voltage DC system technology in the past decades such as line-commutated converter based and traditional 2-level voltage-source converter based high-voltage DC technology, but also provides an overview of contemporary challenges and opportunities for multi-terminal high-voltage DC systems including modular multi-level converter technology, DC breakers and network topologies. A case study of a six-terminal MTDC system was carried out in order to better compare these different topologies in terms of transmission line capacities, total length of transmission line, capital cost, and running costs. [ABSTRACT FROM AUTHOR]