Modular Multilevel Converters Part-I: A Review on Topologies, Modulation, Modeling and Control Schemes

Abstract

Renewable power generation using photovoltaic is very interesting to be developed to deal with the problems of conventional energy sources and environmental issues. The photovoltaic power generation can operate both in stand-alone and grid-connected operations. This paper presents an application of the single-phase five-level common-emitter current-source inverter (CE-CSI) for grid connected photovoltaic system without batteries as energy storage system. In the proposed system, the five-level CE-CSI works generating a sinusoidal output current from photovoltaic system to be injected directly into the power grid. The transformer is used in the system to step-down the grid voltage to meet the voltage level of the photovoltaic system, and also works as a galvanic insulation between the power grid and the inverter system. Two conditions of the power grid voltage, i.e. a pure sinusoidal and a distorted power grid, are tested through computer simulation using PSIM software. Furthermore, experimental test result of the five-level inverter is also presented. The test results show that the five-level CE-CSI works well injecting a sinusoidal current into the power grid with low harmonic contents, and with unity power factor operation. The results also show that the distorted grid voltage affects the harmonic contents of the current injected by the inverter.

An Improved Repetitive Control for Circulating Current Restraining in MMC-MTDC

“…Assume that the topology of three-phase MMC is symmetric, and the AC current is allocated equally among three phases. So the relationships between circulating current and output current of upper arm and lower arm of x phase can be obtained from equation (3) as formula (4).…”

“…MMC is an attractive converter topology of VSC which consists of many sub-modules (SM). Comparing with traditional two-level topology and threelevel topology of VSC, MMC is superior because it has flexible expandability, lower switching frequency, higher power quality and better fault-handling ability due to its redundancy [3][4][5]. However, MMC has a well-known defect, that is, the circulating current which is caused by the energy imbalance among three phases.…”

A simplified space vector modulation implementation for modular multilevel converter by grouping submodules

“…However, on some occasions where the number of submodules (SMs) is small, the harmonic content and distortion rate of the output voltage are high when NLM is adopted. As for the high-frequency modulation methods, the carrier-based pulse width modulation (PWM) schemes [6] such as the carrier phase-shifted PWM and the carrier level-shifted PWM could be preferred in an MMC with any number of SMs [7][8][9][10][11]. However, when involving the achievement of better performances, for example, high DC voltage utilisation, these modulation schemes are very limited.…”

Fault Diagnosis and Reconfiguration of Multilevel Inverter Switch Failure-A Performance Perspective

“…Different multilevel inverter (MLI) topologies are explored and are reviewed in [1].The cascaded multilevel inverter with reduced number of switches are discussed [2].The CMLI eliminates the bulk transformers available in the multipulse inverters, clamping diode in the Diode Clamped MLI and the capacitors in Flying Capacitor MLI [3]. CMLI gets rid of the capacitor voltage balancing method, which is a major challenge in the Flying Capacitor Multilevel Inverter as; it needs very complex voltage balancing techniques [4].…”