Operational Reliability Model of Hybrid MMC Considering Multiple Time Scales and Multi-state Submodule

Feng, Fei; Yu, Jie; Dai, Wei; Yang, Zhifang; Zhao, Xingpan; Kamel, Salah; Fu, Guobin

doi:10.35833/mpce.2019.000227

Cited by 10 publications

(6 citation statements)

References 25 publications

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“…Assuming U dcM remains constant under the fault, substitute (3) and ( 4) into (2), then (2) is rewritten as: (5) Supposing that L equ = 0.5L and m = 0.9, the maximum upper arm SM capacitor voltage will be 1.52U dcM approximately. Considering a 10% ripple during the operation, this value may increase to 1.62U dcM .…”

Section: ) Negative Half-cycles Of Valve-side Ac Voltagementioning

confidence: 99%

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Application of MMC with Embedded Energy Storage for Overvoltage Suppression and Fault Ride-through Improvement in Series LCC-MMC Hybrid HVDC System

Zhang

2023

Journal of Modern Power Systems and Clean Energy

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The series line-commutated converter (LCC) and modular multilevel converter (MMC) hybrid high-voltage direct current (HVDC) system provides a more economical and flexible alternative for ultra-HVDC (UHVDC) transmission, which is the so-called Baihetan-Jiangsu HVDC (BJ-HVDC) project of China. In one LCC and two MMCs (1+2) operation mode, the sub-module (SM) capacitors suffer the most rigorous overvoltage induced by three-phase-to-ground fault at grid-side MMC and valve-side single-phase-to-ground fault in internal MMC. In order to suppress such huge overvoltage, this paper demonstrates a novel alternative by employing the MMC-based embedded battery energy storage system (MMC-BESS). Firstly, the inducements of SM overvoltage are analyzed. Then, coordinated with MMC-BESS, new fault ride-through (FRT) strategies are proposed to suppress the overvoltage and improve the FRT capability. Finally, several simulation scenarios are carried out on PSCAD/EMTDC. The overvoltage suppression is verified against auxiliary device used in the BJ-HVDC project in a monopolar BJ-HVDC system. Further, the proposed FRT strategies are validated in the southern Jiangsu power grid of China based on the planning data in the summer of 2025. Simulation results show that the MMC-BESS and proposed FRT strategies could effectively suppress the overvoltage and improve the FRT capability.

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Section: ) Negative Half-cycles Of Valve-side Ac Voltagementioning

confidence: 99%

“…As an alternative, MMC-based HVDC (MMC-HVDC) has many attractive features such as no commutation failure (CF) and potentially smaller footprint. However, compared with LCC-HVDC, the MMC-HVDC has several obstacles such as smaller power rating, higher installation cost, and higher loss [5].…”

Section: Introductionmentioning

confidence: 99%

Application of MMC with Embedded Energy Storage for Overvoltage Suppression and Fault Ride-through Improvement in Series LCC-MMC Hybrid HVDC System

Zhang

2023

Journal of Modern Power Systems and Clean Energy

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“…Redundancy levels for MMCs are determined based on topology, which requires the analysis of the failure distribution of the SMs. The exponential distribution is the most commonly used failure distribution [2]- [6], [14], [16], [21]- [22]. However, it assumes a constant failure rate and system operating availability over time.…”

Section: Introductionmentioning

confidence: 99%

MVDC MMC Redundancy Design Based on Availability and Cost Considering Submodule Degradation

Nam,

Cho,

Moon

et al. 2023

IEEE Access

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A modular multilevel converter (MMC) synthesizes output voltages by combining voltages from various submodules (SMs) connected in series; thus, it is ideal for high-voltage transmission and distribution ranging from tens to several hundreds of kilovolts. However, MMCs incur high costs and losses, thus necessitating reliable operation. Research has been conducted to assess and enhance MMC reliability. Prior studies have presumed an exponential distribution for the reliability of SMs, including redundancy, thus implying that the failure rate does not change over time. This assumption signifies a constant system availability for the converter station, regardless of time, thus presenting a limitation in adequately comprehending the breakdown impact caused by a failure of the converter station. Additionally, as no standard exists for determining redundancy in medium-voltage direct current (MVDC) systems, a methodology is required to establish a redundancy criterion during the design process. Particularly for MVDC systems, the impact of power outages must be evaluated by considering the cost of expected outages based on system availability, as the load is interconnected. As a solution, we propose a method to assess the tradeoff between system availability and cost for an MVDC MMC, employing the Weibull distribution-based SM failure rate. The L-BFGS algorithm calculates the optimal value of the availabilitycost function, and the number of redundant modules minimizing total operating cost is evaluated. Our case study determines the appropriate number of redundancy modules based on outage costs. The proposed methodology enables redundancy design that considers both reliability and operational costs, thus providing a practical solution to the problem of determining the number of redundant modules needed in MMCs.

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“…Increasingly, offshore wind farms are being built on a large scale and remote from the shore, where wind pow-er must then be collected by cables and transported to onshore grids across great distances [3]. Modular multilevel converter based high-voltage direct current (MMC-HVDC) has become the prevailed scheme for remote offshore wind farms [4], [5].…”

Section: Introductionmentioning

confidence: 99%

Impact of Different AC Voltage Control Modes of Wind-farm-side MMC on Stability of MMC-HVDC with Offshore Wind Farms

Lin,

Xue,

Lyu

et al. 2023

Journal of Modern Power Systems and Clean Energy

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Wind-farm-side modular multilevel converters (WFMMCs) used in modular multilevel converter based highvoltage direct current (MMC-HVDC) transmission systems must be able to control the AC grid voltage in offshore wind farms. Different AC voltage control strategies can significantly affect the dynamic characteristics of WFMMCs. However, existing studies have not provided a general methodology of controller parameter design, and few comparative studies have been conducted on control performance under varying operating conditions as well as the effects of different AC voltage control modes (AVCMs) on the stability of MMC-HVDCs with offshore wind farms. This paper provides a controller parameter design method for AVCMs, which is tested in various operating scenarios. Sequence impedance models of offshore wind farms and WFMMCs under different AVCMs are then developed. The effects of AVCMs on the small-signal stability of the interconnected system are then analyzed and compared using the impedance-based method. Finally, case studies are conducted on a practical MMC-HVDC system with offshore wind farms to verify the theoretical analysis.

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Operational Reliability Model of Hybrid MMC Considering Multiple Time Scales and Multi-state Submodule

Cited by 10 publications

References 25 publications

Application of MMC with Embedded Energy Storage for Overvoltage Suppression and Fault Ride-through Improvement in Series LCC-MMC Hybrid HVDC System

Application of MMC with Embedded Energy Storage for Overvoltage Suppression and Fault Ride-through Improvement in Series LCC-MMC Hybrid HVDC System

MVDC MMC Redundancy Design Based on Availability and Cost Considering Submodule Degradation

Impact of Different AC Voltage Control Modes of Wind-farm-side MMC on Stability of MMC-HVDC with Offshore Wind Farms

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