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The modular multilevel converter (MMC) has become the most promising converter technology for high power applications. However, to get more number of levels in the output voltage, a conventional MMC requires large number of submodules. The main technical challenges of an MMC, with a large number of submodules, are the requirement of large number of semiconductor switches, submodule capacitors and...
In this paper, an asymmetric mixed MMC topology of multilevel converter for bipolar HVDC transmission systems is introduced. Among the existing MMC topologies for the bipolar HVDC systems, the asymmetric mixed MMC topology provides the benefits of: a lower number of submodule cells, fewer switching devices and lower conduction losses. Furthermore, the HVDC based on asymmetric mixed MMC can be flexibly...
This paper develops an alternate arm converter (AAC) high-voltage direct current (HVDC) terminal model that is compatible with the existing benchmark models of modular multilevel converter (MMC) based HVDC and dc-grid benchmark models. The developed model is a first step towards an AAC-based point-to-point transmission system and the future development of multi-converter, multiterminal benchmark models...
A transformer-less Modular Multilevel DC-DC converter for High Voltage Direct Current (HVDC) applications is proposed in this paper. This topology is suitable for interfacing two HVDC links at different voltage levels using only conventional half bridge submodules. The uniqueness of the proposed converter is in its symmetry in performance in the event of reversal of polarity of one of the DC links...
The hybrid high voltage direct current (Hybrid HVDC) system based on line commutated converter (LCC) and modular multilevel converter (MMC) is a feasible solution for long distance bulk power transmission. In order to handle the dc-side short-circuit fault, two kinds of methods can be adopted. The first one is to replace half-bridge sub-modules (HBSMs) with full-bridge SMs or clamp-double SMs which...
With the rapid development of voltage source converter (VSC) based high voltage direct current (HVDC) transmission technology, the HVDC grid will be an effective solution for large-scale renewable energy generations integration. The modular multilevel converter (MMC) is one the most promising topology for HVDC and DC grid presently. The precharge of the MMCs and start-up of DC grid are essential problems...
A novel isolated high step-up gain DC-DC conversion system for HVDC grid-connected PV power generation applications is proposed in this paper. The proposed system has a distributed MPPT and centralized step-up DC-DC configuration. By employing distributed MPPT converter, high power losses caused by partial shading of the PV arrays can be reduced significantly. Modular scheme is adopted for the centralized...
In recent years, significant progress has been made in HVDC transmission by the advent of voltage-source-converter (VSC) technology using modular multilevel converters. There is increasing demand to interconnect the existing HVDC lines into meshed HVDC grids for better renewable energy penetration. In this paper, a series of power electronic topologies, all based on the front-to-front VSC structure,...
This paper presents a voltage regulated step up Marx DC-DC converter suitable for HVDC offshore wind farm applications. This configuration has the capability to generate a variable high voltage adding controllability to the standard Marx converter with a fixed gain. For voltage control, an auxiliary controlled buck-boost converter was combined with the Marx converter to regulate the output voltage...
This paper proposes a DC-DC modular multilevel converter (MMC) topology for MVDC and HVDC applications that does not require ac transformers or coupled inductors. The DC-DC MMC comprises two dc-dc subconverters that are interlinked in a symmetric manner, whereby the modulated ac voltages remain isolated from the dc terminals. This enables a substantial reduction in converter size, weight, capital...
An HVDC system based on a Cockcroft-Walton (CW-HVDC) topology is presented and a novel strategy is proposed to analyze and control the converter. In the connection to the grid the CW-HVDC uses a 3×2 matrix converter. The CW-HVDC voltage state-space vectors are derived and used to control the AC currents, guaranteeing nearly unitary power factor in the connection to the grid. Sliding mode controllers...
The isolated modular DC-DC converter (IMDCC) is a new topology designed to connect high-voltage direct current (HVDC) lines with different voltage levels, which ties two DC grids by using two modular multilevel converters (MMCs) via a medium-frequency transformer. Due to the large value of capacitance in the IMDCC, proper precharge strategies before the start-up are significant for the safety and...
This paper analysis starts from the typical architecture of high-frequency solid-state transformer (HF-SST), which is the core power part of Energy Internet, and studies the key technology and control scheme of main circuit of bidirectional dc/dc converter and cascaded H-bridge converter. Based on the complex structure, in dc/dc stage, the uniform-discretization control strategy is proposed to simplify...
The business case for MMC-HVDC is becoming popular in power transmission systems. Despite their superior potential compared to the AC and LLC-HVDC technologies, MMC-MTDC grid is yet to be efficiently realised in practice. Operation, control and modelling in such VSC-based schemes are arguably the most challenging research and development problems that academia and industry are presently engaged in...
A new topology of energy router with multiple isolated HVAC ports is proposed in this paper. The topology is composed of several modular multilevel converters (MMC) and a cascaded multi-active bridge (MAB) converter. With this topology, distribution lines with the same voltage level can be connected together and switched seamlessly, even though the voltage amplitude, phase angle and earthing points...
This paper investigates a Solid State Transformer (SST) based DC microgrid architecture, addressing the design and control of the multiple SST power conversion stages and the power management strategy required for its integration with other microgrid elements, such as storage devices and local distributed generation. The advantages of a SST in relation to conventional low frequency transformers are...
this paper explains internal capacitor energy balancing and circulating current control of Modular Multi-level Converters (MMCs). MMCs are considered as one of the promising multilevel converter topologies especially in high voltage applications such as HVDC transmission system. Circulating current is a unique feature in MMC, it arises from capacitor voltage differences between the three phases. The...
The VSC-HVDC system performance has the most competitive and new feasible solution for integration of high wind penetration at offshore sites for efficient power transmission. This paper presents an overview of various control strategy for power converters and the plan of services in VSC-HVDC transmission. For long distance transmission line, reactance limits the transfer capability of high voltage...
The widely used Line Commutated Converter (LCC) suffers from commutation failure which might cause severe economic and secure consequence. The recently proposed Modular Multilevel Converter (MMC) HVDC is expected to be an alternative solution. However, the half bridge MMC (HBMMC) cannot interrupt the short current caused by DC transmission line fault, which have stunted the engineering practice of...
This paper presents a novel hybrid modular multilevel voltage source converter suitable for HVDC applications. It has the advantages of other modular multilevel topologies and can be made more compact making it attractive for offshore stations and city infeed applications. The Operating principle of the converter and internal energy management are discussed with simulation results from a scaled medium...
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