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Modular Multilevel Converter (MMC) has great application prospects for the flexible HVDC transmission, high-power motor drive and so on. In this paper, a discrete-time model of the MMC based on the virtual ergodic method is proposed for the typical MMC topology. First, the MMC topology is analyzed and its continuous-time model is established. Then, the state equation in the continuous-time model is...
Modular multilevel converter (MMC) is a promising topology of Voltage Source Converter based High voltage Direct Current (VSC-HVDC) system with many outstanding advantages such as low switching frequency, low voltage distortion and harmonics. Pre-charge process is one of the core issues of MMC based system, especially for the MMC with DC fault blocking capability. In this paper, considering a novel...
This paper discusses the active and reactive power control method for a modular multilevel converter (MMC) based grid-connected PV system. The voltage vector space analysis is performed by using average value models for the feasibility analysis of reactive power compensation (RPC). The proposed double-loop control strategy enables the PV system to handle unidirectional active power flow and bidirectional...
Multi-rate (MR) simulation is necessary for a system which contains both large and small time constraints. In the traditional MR real-time simulation of MMC, only the MMC valves are implemented on FPGA with a small time-step, while the rest parts are implemented on central processing units (CPU) with a large time-step. This paper presents a fully FPGA based MR real-time simulation of two MMC terminals...
The negative- and zero-sequence currents of a modular multilevel converter (MMC) under imbalanced ac-grid conditions increase the maximum voltage of the submodule (SM) capacitors, which should be kept below a maximum voltage limit. This paper investigates the impact of offset pulse-width modulation (OPWM) on the capacitor voltage of the MMC under imbalanced ac-grid conditions. It is demonstrated that...
Recently, modular multilevel converters (MMC) have attracted extensive research interest in the field of HVDC and motor drives. However in motor drives, it appears that the inherent problem of the fluctuation of capacitor voltage particularly at low frequencies limits its further application. This paper proposes a new back-to-back hybrid MMCs topology, of which one MMC is directly connected to the...
As the development and building of 220kV and 500kV Unified Power Flow Controller (UPFC) in Jiangsu grid of China, a higher requirement is put forward by power grid analysis on the accuracy of modelling and simulation. UPFC has different characteristics under different control strategies, and Modular Multilevel Converters (MMC) simulation is a difficult task. In order to study its dynamic characteristics,...
High-speed permanent magnet motors (HSPMMs) have gained ever-increasing interests in high speed direct-drive applications due to their advantages of high-power density, small size and high efficiency. However, the low stator inductance of the HSPMM causes large current ripple in the stator current, therefore brings additional iron loss. The Modular multilevel converter (MMC) increases both voltage...
The modular multilevel converter with series and parallel connectivity was shown to provide advantages in several industrial applications. Its reliability largely depends on the absence of failures in the power semiconductors. We propose and analyze a fault-diagnosis technique to identify shorted switches based on features generated through wavelet transform of the converter output and subsequent...
Multi-modular converters have proven to be one of the most suitable topology to be used in high and power applications. The modularity of these configurations offer several advantages, such as: high quality voltage, redundancy and high efficiency. In these converters, the series connection of modules increase the number of voltage levels, but also the floating voltage of modules with respect the neutral...
In the situation that the modular multilevel converter (MMC) needs to maintain a good current control performance within a wide scope of operations such as the intermittent new energy grid connection and electric locomotive, etc, this paper starts from the output current slope generated after the output voltage and system voltage of MMC converter are jointly acted on the equivalent coupling reactance...
This study proposed a novel protective action for converter side phase-to-ground fault of FB-MMC-based bipolar HVDC. The faulty converter is kept in operation during fault, and its dc-link voltage reference is set to zero in order to avoid serious overvoltage of the sub-module capacitors. This protective action was verified by simulation. The overcurrent and overvoltage of converter arms are moderate...
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...
High-speed models of facilities with AC generators and modular multilevel converters have been developed by using the methodology of system modeling by interconnected subsystems. The method of facility separation on parts by introducing in circuits virtual voltage sources has been implemented. Analysis of operation modes of considered systems was completed. Fast response of models was validated.
Three-phase three-wire shunt active power filter (SAPF) with traditional positive-sequence control can only compensate part of the nonlinear load current harmonics if the PCC voltage changes from balanced to unbalanced condition. Changes of both nonlinear load current harmonic components and equivalent circuit for modular multilevel converter based SAPF (MMC-SAPF) are analyzed in the paper. To solve...
Modular multilevel converters (MMC) have been at the heart of numerous research projects and publications over the last decade. This topology is particularly challenging when it comes to real-time simulation; it has thousands of power-switching devices, control signals, and differential equations to solve. This has led to various models with different levels of detail. Although, all models are equally...
Modular multilevel converter (MMC) has attracted great attention in the high voltage direct current (HVDC) transmission systems. Redundant submodules (SMs) are usually set to enhance the reliability of MMC. However, if some SMs break down, the arm energy is unbalanced and fundamental fluctuation appears in the DC current. This paper proposes an arm energy rebalancing control scheme to suppress the...
The modular multilevel converters become more and more popular in high power applications in recent years. The solution to make the MMC operate well under the submodule failure is a key technology to increase reliability of the MMC-based systems. In this paper, a fault tolerant control method based on the zero-sequence voltage injection is proposed to maintain stable line-to-line voltage under submodule...
Modular multilevel converter (MMC) is one of the recent developed converter for high power applications. However, the major drawback of this converter in variable speed drives is that the capacitor ripple voltage increases at lower speed, when the load torque remains constant. This ripple voltage can be reduced by reducing the dc-bus voltage at lower speeds, while the capacitor voltages are maintained...
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