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Excessive power loss is a major concern in high voltage and high power applications and is considered one of the main drawbacks of VSC-HVDC system when compared with traditional HVDC system based on thyristor technology. This is primarily caused by high switching loss associated with switching devices used in the VSC-HVDC. This issue can be largely addressed by using the emerging MMC-HVDC topology,...
Recently, multi-terminal DC (MTDC) system has received more attention in the power transmission areas. Development of modular structured power converter topologies has now enabled the power converter technology to attain high voltage high power ratings. Compared to current source converter technology, voltage source converters have several benefits including higher power quality, independent control...
The AC side Single Line to Ground (SLG) fault is one of the most frequent faults in power systems. And, in an HVDC system based on modular multilevel converter it calls for the fault ride through strategy to transmit maximum possible electricity during the fault to secure power system stability. It presents different characteristics of SLG faults at the voltage regulator side and the power dispatcher...
Circuit breakers are expected to be a vital element within any high capacity HVDC network. This paper examines the directional current breaking capacity requirements that might be seen on a typical HVDC grid, as required for the specification of backup protection. It is shown that there is a significant difference between the peak prospective fault currents observed when the current direction is analysed...
This paper addresses the limitation of current technologies in the interconnection between medium-voltage (MV) DC and high-voltage (HV) DC grids. One transformerless approach is proposed to achieve bidirectional high power transfer and high step up/down ratio, which can be configured to interface with different grids connection. The proposed technology integrates modular multilevel converter (MMC)...
This paper proposes a post-fault control technique for H-bridge multilevel modular converters (MMC), which in combination with a restoration framework, can achieve fast operation recovery in multi-terminal direct current (MTdc) networks under different dc fault types. The studied network consists of four voltage-source converters (VSC) for high voltage dc (HVdc) transmission. A meshed MTdc grid topology...
Modular Multilevel Converter (MMC) has recently become a popular multilevel topology for high-power applications. Conventionally, the circulating current between the legs of an MMC is an unwanted current that must be minimized in order to reduce the converter loading. In this paper the impacts of the circulating current in the MMC to the current ratings of power semiconductor devices are comprehensively...
The DC transmission system provides a cost effective solution for long distance power transmission compared to the AC transmission system. Hence, this has increased the emphasis on the development of the DC transmission system. Development of power converter with modular structure has now made it possible to achieve higher voltage and power level. This opens the possibility for further development...
In this paper, a novel topology of the HVDC converter is proposed for offshore wind farm applications. A combined structure of a voltage-source converter (VSC) and a 12-pulse diode rectifier is applied to the sending-end station on the offshore side and a hybrid topology of a VSC and 12-pulse SCR converters is employed for a receiving station. The VSC is used not only to control the high DC-link voltage,...
The Modular Multilevel Converter (MMC) based VSC HVDC is an increasingly popular technology worldwide for both engineering installation and academic research purposes over the years. A submodule serves as the basic unit for the MMC, and the typical topology of a submodule is a half bridge configuration. Normally, controllable power devices are used for switches in a submodule, and plastic module IGBT...
This paper presents the implementation of a scaled 4-terminal high-voltage direct current (HVDC) test-bed. The hardware construction, control scheme and communication architecture are described. The typical scenarios such as system start-up, station online recommission, power variation, online mode transition and station failure are emulated in the test-bed. A dc line current control is proposed to...
Small-signal state-space analysis of power system stability relies on linearized models where steady state operation corresponds to constant values of all state variables. Such models are available and commonly used for analysis of configurations with three-phase 2- or 3-level Voltage Source Converters (VSC). However, the Modular Multilevel Converter (MMC), which is emerging as a preferred topology...
Over the past years, modular multilevel converters (MMC) have been widely researched as a preferred option among voltage source converters for HVDC transmission system. The converter presents modularity to generate high number of output voltage levels by simple series connection of modules, resulting in higher reliability and easy failure management/maintenance. Synthesis of near sinusoidal output...
A transformer-less UPFC based on an innovative configuration of two cascaded multilevel inverters (CMIs) has been proposed recently, which is suitable for power flow control between two interconnected synchronous AC grids. The active power as well as the reactive power can be independently controlled by the new transformer-less UPFC. In addition, the semiconductor device ratings (SDPRs) for different...
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