Study on overvoltage protection in HVDC LTT valve

Tanabe, S.; Kobayashi, Sumio; Sampei, M.

doi:10.1109/61.852982

Cited by 7 publications

(6 citation statements)

References 3 publications

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“…Moreover, one very important issue about the MMSC is that as previously mentioned and as will be further explained in this paper, the bidirectional switches operate with a very low switching frequency ( f i = 50 Hz). In other words, even though series-connected devices are required, these devices switch at very low frequencies and, thus, snubber circuits could be used, with tolerable losses, in order to guarantee a safe transient voltage balance among the semiconductor devices connected in series [49][50][51]. This way, the MMSC can operate in a safe and reliable fashion.…”

Section: Ac-ac MMC As a Series-connected Voltage Sourcementioning

confidence: 99%

New AC–AC Modular Multilevel Converter Solution for Medium-Voltage Machine-Drive Applications: Modular Multilevel Series Converter

et al. 2020

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Due to its scalability, reliability, high power quality and flexibility, the modular multilevel converter is the standard solution for high-power high-voltage applications in which an AC–DC–AC connection is required such as high-voltage direct-current transmission systems. However, this converter presents some undesired features from both structural and operational perspectives. For example, it presents a high number of components, which results in high costs, size, weight and conduction losses. Moreover, the modular multilevel converter presents problems dealing with DC-side faults, with unbalanced grid conditions, and many internal control loops are required for its proper operation. In variable-frequency operation, the modular multilevel converter presents some serious limitations. The most critical are the high-voltage ripples, in the submodule capacitors, at low frequencies. Thus, many different AC–AC converter solutions, with modular multilevel structure, have been proposed as alternatives for high-power machine-drive applications such as offshore wind turbines, pumped-hydro-storage systems and industrial motor drives. These converters present their own drawbacks mostly related to control complexity, operational limitations, size and weight. This paper introduces an entirely new medium-voltage AC–AC modular multilevel converter solution with many operational and structural advantages in comparison to the modular multilevel converter and other alternative topologies. The proposed converter presents high performance at low frequencies, regarding the amplitude of the voltage ripples in the submodule capacitors, which could make it very suitable for machine-drive applications. In this paper, an analytical description of the voltage ripples in the submodule capacitors is proposed, which proves the high performance of the converter under low-frequency operation. Moreover, the proposed converter presents high performance under unbalanced grid conditions. This important feature is demonstrated through simulation results. The converter solution introduced in this paper has a simple structure, with decoupled phases, which leads to the absence of undesired circulating currents and to a straightforward control, with very few internal control loops for its proper operation, and with simple modulation. Since the converter phases are decoupled, no arm inductors are required, which contributes to the weight and size reduction of the topology. In this paper, a detailed comparison analysis with the modular multilevel converter is presented based on number of components, conduction and switching losses. This analysis concludes that the proposed converter solution presents a reduction in costs and an expressive reduction in size and weight, in comparison to the modular multilevel converter. Thus, it should be a promising solution for high-power machine-drive applications that require compactness and lightness such as offshore wind turbines. In this paper, simulation results are presented explaining the behavior of the proposed converter, proving that it is capable of synthesizing a high-power-quality load voltage, with variable frequency, while exchanging power with the grid. Thus, this topology could be used to control the machine speed in a machine-drive application. Finally, experimental results are provided to validate the topology.

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Section: Ac-ac MMC As a Series-connected Voltage Sourcementioning

confidence: 99%

New AC–AC Modular Multilevel Converter Solution for Medium-Voltage Machine-Drive Applications: Modular Multilevel Series Converter

et al. 2020

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“…As the key equipment in ac/dc converter, the HVDC converter valves are exposed to various kinds of overvoltage [1]- [3] that rise rapidly and occupy a wide frequency range, and this would lead to converter valve damage during operation. Meanwhile, the electromagnetic interference [4]- [7] that caused by switching the converter valves periodically can cause radiative interference in MHz and conducted interference that propagates along the bus and transmission lines in kHz [8] to the adjacent communication and computer equipment system operations.…”

mentioning

confidence: 99%

Building and Analysis of Integrated Wideband Models for Key Components in HVDC Converter Valve Systems

Guan

et al. 2014

IEEE Trans. Electromagn. Compat.

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As the key devices of an HVDC transmission system, converter valves should bear different forms of overvoltage. Additionally, the wideband frequency electromagnetic noises caused by the switching of thyristor may impact the normal operation of the communication and control systems in an HVDC converter substation. Consequently, it is of great significance to build the model that is suitable for wide frequency range for the key components of converter valve system. Based on the elementary wideband model, the integrated wideband model is proposed and the estimation method for corresponding parameters is also addressed for different kinds of components in this paper. The theoretical analysis and simulation results show that the integrated wideband model has high accuracy and simplicity; it also can provide the results with rigorous passivity and specific physical meaning. As for the application, the proposed method is used to model the key components of an HVDC converter valve and proved to be correct and effective.

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“…V o and V g are the peak values of the voltage reference and of the grid voltage, respectively. Finally, in (4), ω o = 2πf o , ω i = 2πf i , and f o and f i are the load and grid frequency, respectively. A natural characteristic of the 3x3-MMSC due the series connection of its submodule strings between grid and load terminals is the fact that the grid voltage is distributed between the N capacitors of the N series-connected submodules of each string.…”

Section: Gridmentioning

confidence: 99%

“…In other words, in this example, f i = 50 Hz ̸ = f o = 10 Hz and, thus, there will be moments where the peak of the grid voltage will meet the valley of the load voltage reference for example. According to (4), in this case the instantaneous value of the voltage to be synthesized in series if the phase-A submodule string remained connected to phase A of the grid would be equal to |v sa | = V g + V o = 12 + 10 = 22 kV (if it happens before t = 3 s), which is a value obviously bigger than V g = 12 kV, which is the maximum voltage possible to be synthesized in series. Thus, the converter would lose control over the load voltage, and this voltage would diverge from its reference.…”

Section: Gridmentioning

confidence: 99%

“…The traditional solution available to reach increased voltage levels was to connect in series several semiconductor devices aiming at obtaining a stack capable to behave as a high voltage switch. However, small delays in the turn-on/turn-of time of the many devices in the stack could result in serious problems related to static and dynamic voltage sharing among these devices, which would then result in a solution with poor reliability [1][2][3][4][5][6]. This problem would be particularly critical in flexible voltagesource converters operating with high switching frequencies.…”

Section: Introduction 1backgroundmentioning

confidence: 99%

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Novel Converter Solutions with a Modular Multilevel Structure for High-Power Medium-Voltage Electrical Machine Drive Applications

Gontijo¹

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Study on overvoltage protection in HVDC LTT valve

Cited by 7 publications

References 3 publications

New AC–AC Modular Multilevel Converter Solution for Medium-Voltage Machine-Drive Applications: Modular Multilevel Series Converter

New AC–AC Modular Multilevel Converter Solution for Medium-Voltage Machine-Drive Applications: Modular Multilevel Series Converter

Building and Analysis of Integrated Wideband Models for Key Components in HVDC Converter Valve Systems

Novel Converter Solutions with a Modular Multilevel Structure for High-Power Medium-Voltage Electrical Machine Drive Applications

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