Comparative Analysis of Multilevel-High-Frequency-Link and Multilevel-DC-Link DC–DC Transformers Based on MMC and Dual-Active Bridge for MVDC Application

Zhao, Biao; Song, Qiang; Li, Jianguo; Xu, X. P.; Liu, Wenhua

doi:10.1109/tpel.2017.2700378

Cited by 106 publications

(35 citation statements)

References 30 publications

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“…The SM voltages u cj (t) are calculated from (7) and (10). All of the SM voltages u cj (t) is also accurate.…”

Section: Type 3 Multilevel With the Inserted Slave Sm After Level Dromentioning

confidence: 99%

“…In response to the desire for clean and reliable energy, power electronic converters now play an important role in the power grid. Because of their relatively high modularity, flexibility, and expandability, modular multilevel converters (MMCs) [1][2][3][4][5] are regarded as one of the most promising modular multilevel techniques and have been widely used in high-voltage direct current (HVDC) transmission systems [6][7][8][9], medium-voltage direct current (MVDC) grids [10,11], and electric railway supplies [12]. The half-bridge sub-module (HBSM)-based MMC is the typical MMC topology, but it does not have DC fault blocking capability [13,14].…”

Section: Introductionmentioning

confidence: 99%

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Master–slave structure‐based capacitor voltage measuring technique for hybrid modular multilevel converters

Sun

Zhang

et al. 2018

IET Power Electronics

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The measurement of the capacitor voltage of each sub-module (SM) is a crucial part of achieving robust control of modular multilevel converters (MMCs). This study proposes a master-slave structure-based capacitor voltage measuring technique (MS-MT) for hybrid MMCs, in which the SM capacitor voltages are calculated using nine processes at the corresponding sampling instants according to the changing rule of the arm AC-side voltage and SM operation states. In MS-MT, the master sensor is used to measure the overall arm voltage while the slave sensor, which measures the full bridge, is used additionally to improve accuracy. Furthermore, MS-MT performs well even under pre-charging and DC short-circuit fault conditions, for the reason that a single SM short-circuit fault can be detected during above two conditions by comparing the voltages measured by the two sensors. Compared with the direct measuring technique, which has low measurement errors, and the overall measuring technique, which requires less hardware cost, MS-MT inherits both advantages. Finally, extensive simulation and experimental results validate the effectiveness of the proposed MS-MT. Nomenclature N SM number in every arm f c carrier frequency u c SM capacitor voltage u Hout output voltage of HBSM u Fout output voltage of FBSM U dc DC bus voltage of MMC u a , u b and u c MMC AC-side phase voltages u m_au measured upper arm AC-side voltage by the master sensor u m_auFs measured voltage of the slave SM in the upper arm S aui switching state of the ith SM in the upper arm of phase A i arm_au , i arm_al upper and lower arm currents T c sampling period S j switching state of the jth SM Δu ecj estimated voltage variation of the jth SM u cs measured voltage by the slave sensor ΔU ceb voltage drop caused by auxiliary circuit

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“…The SM voltages u cj (t) are calculated from (7) and (10). All of the SM voltages u cj (t) is also accurate.…”

Section: Type 3 Multilevel With the Inserted Slave Sm After Level Dromentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Master–slave structure‐based capacitor voltage measuring technique for hybrid modular multilevel converters

Sun

Zhang

et al. 2018

IET Power Electronics

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“…With the development of power electronics, voltage source converter based high voltage direct current transmission (VSC-HVDC) is widely used in scenarios such as the offshore wind power integration, asynchronous AC grids interconnection, multi-terminal HVDC/DC grid, etc. Compared with other VSCs, modular multilevel converters (MMCs) have many outstanding advantages such as low harmonic output, low losses and good scalability [1][2][3][4]. Up till now, MMC with half-bridge sub-modules (HBSMs) is one of the most promising HVDC topologies, and they have been widely used in high voltage and high power transmission projects, such as the three-terminal Nan'ao Project, the four-terminal Zhangbei Project and the fiveterminal Zhoushan Project [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

An Equivalent Calculation Method for Pole-to-Ground Fault Transient Characteristics of Symmetrical Monopolar MMC Based DC Grid

Zhang

et al. 2020

IEEE Access

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The pole-to-ground fault is one of the most typical faults in modular multilevel converters (MMCs) based DC grid. Analyzing the transient characteristics of fault voltages and currents is of great significance for fault identification, configuration of protection, and optimization of system parameters. This paper proposes an equivalent transient characteristics calculation method for pole-to-ground faults for symmetrical monopolar MMC based DC grid. Firstly, according to the mechanism of the pole-to-ground faults, the fault network and the steady-state network are formed. Then, the star-delta transformation is performed on modelling the MMCs in the fault network, which overcomes the problem that the number of the inserted sub-modules (SMs) in each arm is time-variant. Based on the discrete adjoint model, the prefault and faulted matrices describing the voltages and currents are established, and a general method for solving the transient voltages and currents is proposed. Finally, the proposed method is validated in a fourterminal symmetrical monopolar MMC based DC grid. The results show that the proposed method is of high accuracy, and is much more time efficient than time-domain simulation. INDEX TERMS Modular multilevel converter (MMC), symmetrical monopolar, DC grid, pole-to-ground fault, discrete adjoint model, voltage and current characteristics

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“…Recently, modular multilevel converters (MMCs) have become increasingly attractive for high-voltage and high-power applications owing to the excellent output voltage waveforms and high efficiency [1][2][3][4]. When MMC is used in high-voltage direct current (HVDC) transmission systems [5][6][7] and medium-voltage direct current (MVDC) grids [8,9], the DC short circuit fault is one of the serious failures. In the conventional MMC based on the halfbridge sub-module (HBSM), the fault current cannot be cut down by itself, because HBSM-based MMC (HBSM-MMC) does not have the DC fault blocking capability.…”

Section: Introductionmentioning

confidence: 99%

Improved hybrid modular multilevel converter with enhanced fault ride‐through capability and fast pre‐charging strategies

Sun

et al. 2019

IET Power Electronics

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This study proposes an improved hybrid modular multilevel converter (MMC) topology with enhanced fault ridethrough capability and fast pre-charging strategies. This improved MMC topology mainly consists of the half-bridge sub-modules (HBSMs), the modified series connected double sub-modules (MSDSMs), and the adjustable damping sub-module (ADSM). In the improved topology, in addition to being configured on the MMC AC-side, resistors are also configured in MSDSMs and ADSM, respectively, in the MMC. This type of resistance configuration based on the improved MMC topology benefits adjusting the value of the total equivalent current limiting resistance during the pre-charging process, leading to a higher pre-charging speed and a lower SM voltage drop risk. Three different pre-charging strategies can cope with changes in resistance configuration caused by the increasing number of SMs. Furthermore, the resistances in MSDSM and ADSM also help dissipate the energy caused by the DC short-circuit fault so that the fault ride-through capacity is enhanced. The simulation and experimental results validate the effectiveness of the proposed topology and the corresponding pre-charging strategies.

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Comparative Analysis of Multilevel-High-Frequency-Link and Multilevel-DC-Link DC–DC Transformers Based on MMC and Dual-Active Bridge for MVDC Application

Cited by 106 publications

References 30 publications

Master–slave structure‐based capacitor voltage measuring technique for hybrid modular multilevel converters

Master–slave structure‐based capacitor voltage measuring technique for hybrid modular multilevel converters

An Equivalent Calculation Method for Pole-to-Ground Fault Transient Characteristics of Symmetrical Monopolar MMC Based DC Grid

Improved hybrid modular multilevel converter with enhanced fault ride‐through capability and fast pre‐charging strategies

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