Fault Characteristics and Control Strategies of Multiterminal High Voltage Direct Current Transmission Based on Modular Multilevel Converter

The modular multilevel converter (MMC) is an emerging voltage source converter topology suitable for multiterminal high voltage direct current transmission based on modular multilevel converter (MMC-MTDC). This paper presents fault characteristics of MMC-MTDC including submodule fault, DC line fault, and fault ride-through of wind farm integration. Meanwhile, the corresponding protection strategies are proposed. The correctness and effectiveness of the control strategies are verified by establishing a three-terminal MMC-MTDC system under the PSCAD/EMTDC electromagnetic transient simulation environment

GaN-Based Modular Multilevel Converter for Low-Voltage Grid Enables High Efficiency

Gallium Nitride (GaN) semiconductors with low inductance packages enable low switching losses and high efficiency. In this paper we present a compact arm PCB design with low loop inductance, allowing for fast and efficient switching. The PCB includes four full-bridge cells for a 7 kW Modular Multilevel Converter (MMC) for low-voltage grid applications

Zero phase sequence voltage injection for the alternate arm converter

The Alternate Arm Converter (AAC) is a voltage source converter being developed as an alternative to the Modular Multilevel Converter (MMC) for HVDC power transmission and reactive power compensation. Each Arm of the converter contains high voltage series IGBT Director Switches and full-bridge cells, which enables the VSC to ride through AC and DC network faults. This paper describes how the AAC can be optimised by modulating the converter terminal voltages with zerophase sequence triplen harmonic components. The optimisation reduces the ratio of the number of the full-bridge cells compared to the simpler Director Switches which offers a valuable improvement in footprint and efficiency

Estudi d'un convertidor MMC

L’objecte d’aquest treball és estudiar el funcionament de la topologia de convertidor multinivell Modular Multilevel Converter (MMC), analitzar el funcionament d’algunes de les tècniques de control més utilitzades i desenvolupar una estratègia per al control del corrent de branca

Design and implementation of 30kW 200/900V LCL modular multilevel based DC/DC converter for high power applications

This paper presents the design, development and testing of a 30kW, 200V/900V modular multilevel converter (MMC) based DC/DC converter prototype. An internal LCL circuit is used to provide voltage stepping and fault tolerance property. The converter comprises two five level MMC based on insulated gate bipolar transistors (IGBTs) and metal oxide semiconductor field effect transistor (MOSFET). Due to low number of levels, selective harmonic elimination modulation (SHE) is used, which determines the switching angles in such a way that third harmonic is minimized whereas the fundamental component is a linear function of the modulation index. In addition, instead of using an expensive control board, three commercial control boards are embedded. This is required to implement the sophisticated DC/DC converter control algorithm. Simulation and experimental results are presented to demonstrate the converter performance in step up and down modes

Modular multilevel converter based LCL DC/DC converter for high power DC transmission grids

This paper presents a modular multilevel converter (MMC) based DC/DC converter with LCL inner circuit for HVDC transmission and DC grids. Three main design challenges are addressed. The first challenge is the use of MMCs with higher operating frequency compared to common transformer-based DC/DC converters where MMC operating frequency is limited to a few hundred hertz due to core losses. The second issue is the DC fault response. With the LCL circuit, the steady state fault current is limited to a low magnitude which is tolerable by MMC semiconductors. Mechanical DC circuit breakers can therefore be used to interrupt fault current for permanent faults and extra sub-module bypass thyristors are not necessary to protect antiparallel diodes. Thirdly, a novel controller structure is introduced with multiple coordinate frames ensuring zero local reactive power at both bridges in the whole load range. The proposed controller structure is also expandable to a DC hub with multiple ports. Detailed simulations using PSCAD/EMTDC are performed to verify the aforementioned design solutions in normal and fault conditions

Modular multilevel converters: Recent applications [History]

The story of the modular multilevel converter (MMC) started with its invention by Prof. Rainer Marquardt in 2001. Since then, this new concept has been recognized as a milestone achievement in power electronics. MMCs have revolutionized the capabilities of power conversion technologies, particularly in high-voltage dc (HVdc) transmission systems

Simplified rail power conditioner based on a half-bridge indirect AC/DC/AC modular multilevel converter and a V/V power transformer

This paper presents a comprehensive study about a Simplified Rail Power Conditioner (SRPC) based on a half bridge indirect AC/DC/AC Modular Multilevel Converter (MMC) and a V/V traction power transformer. The proposed system with a half bridge MMC can decrease the costs, reduce the control complexity, and require less hardware devices in comparison with the rail power conditioner based on a full bridge indirect AC/DC/AC MMC. Moreover, the SRPC with a half bridge MMC is able to compensate current harmonics, reactive power, and the Negative Sequence Components (NSCs) of currents, which are caused by the unbalance loads between power grid phases. This paper explains the system architecture and its control algorithms based on a pulse width modulation and a proportional integral controller, which is used to control the compensation currents. The simulation results of the SRPC show the submodule voltage balancing control and the DC bus voltage control in order to verify its effectiveness. The compensation strategy based on the NSCs detection is described and evaluated through simulation results.Mohamed Tanta was supported by FCT (Fundacao para a Ciencia e Tecnologia) PhD grant with a reference PD/BD/127815/2016. This work has been supported by COMPETE: POCI-01-0145-FEDER-007043 and FCT within the Project Scope: UID/CEC/00319/2013.info:eu-repo/semantics/publishedVersio

Energy transfer analysis for capacitor voltage balancing of modular multilevel converters

Voltage balancing between sub-module (SM) capacitors is essential for reliable operation of the modular multilevel converter (MMC). To facilitate design and understanding of the balancing controllers, this study presents an energy transfer analysis for MMC, which explains how the energy can be independently transmitted from/to one phase, between the upper and lower arms, and among the SMs, of an MMC. Using this analysis, the variables which can be utilized to achieve capacitor voltage balancing are identified. Validity of this study has been verified by experimental results based on a three-phase MMC prototype