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This paper presents an improved cascaded DC-DC resonant converter for offshore windfarms. The improvements are reduced losses and the number of components. The topology is based on the Marx principle where charged capacitors are charged in parallel and discharged in series to achieve the voltage transformation. The four inductors of the converter are designed to resonate with the capacitors to create...
The AC/AC single-phase/single-phase Modular Multilevel Converter (MMC) presents very interesting features for the realization of a Medium Frequency Power Electronic Transformer for traction applications, in AC-fed or multisystem railway rolling stock, like locomotives, Electric Multiple Units (EMU), high-speed units, and so on. Aiming to maximize the output frequency of the converter, i.e. the operating...
The multilevel converters have advantages of low voltage stresses of the switches and possible reduction of size of the passive components. Input-series output-series (ISOS) configuration of the converter enable the utilization of low voltage rating switches in converters with high input voltage and high output voltage in applications that requires galvanic isolation. While multilevel topology offers...
A modular-multilevel (MMC) DC/DC converter is proposed in this paper, which can be deployed to inter-connect DC grid of different voltage levels, especially in the new energy sources such as wind power and solar power grid connection. Its key features include: 1) step-up and step-down operation. 2) bidirectional power flowing. 3) bi-directional fault blocking similar to a DC breaker. The operation...
Modular Multilevel Converter (MMC) topology is an interesting solution for number of medium and high voltage applications. Key advantages over another multilevel topologies include flexibility of scaling in voltage and simple implementation of redundancy. In this publication control of DC-DC MMC is discussed. Analyzed converter consists of six branches connected in double wye structure. It enables...
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...
Modular Multilevel Converter (MMC) has served as a promising Voltage Source Converter (VSC) for High Voltage Direct Current (HVDC) applications. In this paper, a new MMC Submodule (SM) topology called Modified Switched Capacitor Sub-Module (MSCSM) is proposed. The MSCSM is able to block the DC fault using the power electronics semiconductor diodes due to its intelligent configuration without the need...
This paper compares several multilevel topologies (3L-NPC, 3L-TNPC, 5L-ANPC and 5L-SMC converters) as an alternative to the 2L converter for low voltage applications, using low voltage IGBT modules. The comparative evaluations are made considering figures of merit such as the total losses and their power loss distribution, the amount of devices of each converter, the maximum output power, the harmonic...
In this paper we study the modeling and control of an interleaved DC-DC multilevel topology that exhibits a high-voltage gain and a minimum ripple point design. In this configuration, the current ripple cancelation point can be arbitrarily defined according to a desired specification, which represents an advantage with respect to classical topologies whose minimum ripple point is constrained (e.g...
Due to the increase of electrical power transferred in various fields, the multilevel voltage-source-inverters (VSI) gained high popularity during the last decade. Their ability to produce low harmonic distortion waveforms and reduced power losses led to the development of a large number of solutions and control methods. This paper presents some five-level (5L) VSI topologies with their main features...
A fifth and seventh order harmonic elimination scheme for IM drive with a multilevel dodecagonal voltage space vector structure using a single DC source is proposed in this work. Single DC source requirement makes four quadrant operation of the drive system simpler compared to the multilevel do-decagonal structures presented in literatures before. The space vector structure consists of six concentric...
The interleaved multilevel DC-DC converters have advantages of low voltage stress of the switches and diodes and reduction of filter size. Particularly series input parallel output (ISOP) configuration is well suited for high output voltage and large output current application but input series output series (ISOS) configuration enable the utilization of low voltage rating switches in high voltage...
The current from an electrical arc furnace (EAF) in a steel plant is highly unsymmetrical, i.e. it comprises a large amount of negative sequence. This causes problems with the voltage stability in the capacitor submodules for a static synchronous compensator (STATCOM), when implemented using the modular multilevel converter (M2C) concept. In order to counteract the uncontrollability of the capacitor...
A three-phase dual active bridge (DAB) converter with three-level phase-legs is analyzed, showing an increased soft-switching region and a reduction in rms current in the ac-link for unequal input and output voltages compared to the conventional two-level circuit. Furthermore, a comparison of the semiconductor losses is carried out for different three-level inverter implementations using commercially...
The complex topology of the Modular Multilevel Converter (MMC) requires some additional controllers to keep its functionalities. One of the important requirements on the MMC control is to balance the energy stored in the distributed capacitors in the arms on the three legs. However, due to the superimposed internal DC and AC power flows in the converter, the energy stored in the arms contains intrinsic...
In this paper we investigate limitations of delta connected multilevel STATCOMs based on chain links of H bridge cells/modules in compensation of positive sequence reactive and/or negative sequence currents. Particular attention is paid on the effect of grid voltage imbalance on balance of arm capacitor voltages and required supplementary zero and/or negative sequence current injections.
The trend in wind turbines has shown an ongoing power rating growth, reaching sizes up to 10 MW. Multilevel converters have therefore become a favourable solution for Multi-MW Wind Energy Conversion Systems (WECSs), due to high efficiency, reliability, controllability and the ability to reach high power/voltage ratings. Moreover, stringent grid codes to regulate the connection of WECSs to the electrical...
In this paper, a comparison of the energy storage requirements is performed for the modular multilevel converter (MMC) with half-bridge and full-bridge submodules as well as for the alternate arm converter (AAC). Concerning the AAC, the operational mode with overlap period is taken into account and an analytical relation between the overlap angle and the modulation index is presented. This ensures...
In order to stabilize the grid frequency in case of sudden loss of power generation, an injection of real power is needed. For this, a Static Var Compensator (SVC) can be combined with ultracapacitors, forming a grid frequency stabilizer. To prove the feasibility of this novel combination, the paper shows the realization of a 1 MW class test rig for full-size modules. Single modules are tested using...
This paper investigates different compensation methods for neutral point potential deviation based on modular multilevel single star neutral point clamped bridge converter. Theoretical analysis indicates injecting an offset for a cell can effectively decrease this deviation, so this research presents different offset-based compensation techniques, and evaluates their output performance. Besides, this...
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