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In high-voltage applications, the magnitude of total semiconductor losses (on-state and switching) determines the viability of modular-type multilevel converters. Therefore, this paper presents a new cell arrangement that aims to lower total semiconductor loss of the modular multilevel converter (MMC) to less than that of the half-bridge modular multilevel converter (HB-MMC). Additional attributes of the proposed cell are: it eliminates the protective thyristors used in conventional half-bridge cells that deviate part of the dc-fault current away from the antiparallel diode of the main switch when the converter is blocked during a dc short-circuit fault, and it can facilitate continued operation of the MMC during cell failures without the need for a mechanical bypass switch. Thus, the MMC that uses the proposed cell retains all advantages of the HB-MMC such as full modularity of the power circuit and internal fault management. The claimed attributes of the proposed cell are verified using illustrative simulations and reduced scale experimentations. Additionally, this paper provides brief and critical discussions that highlight the attributes and limitations of popular MMC control methods and different MMC cells structures proposed in the literature, considering the power electronic system perspective. [ABSTRACT FROM AUTHOR]

Hybrid multilevel converters are contemplated in an attempt to optimize the performance of voltage source converters in terms of magnitude of semiconductor losses and converter footprint, and to achieve additional features such as dc short circuit proof, which is essential for a high integrity multiterminal HVDC grid. Therefore, this paper considers an emerging hybrid cascaded converter that offers the dc side short circuit proof feature at reduced loss and footprint compared to the existing multilevel and other hybrid converters. Its operating principle, modulation, and capacitor voltage balancing strategies are described in detail. Furthermore, hybrid converter scalability to high voltage applications is investigated. The validity of the modulation and capacitor voltage strategy presented are confirmed using simulation and experimentation. The hybrid cascaded converter is extendable to a large number of cells, making it applicable to high voltage applications, and operation is independent of modulation index and power factor. On these ground, the converter is expected to be applicable for both real and reactive power applications. [ABSTRACT FROM AUTHOR]

This article presents an isolated high-frequency (HF) multiport dc–dc converter for photovoltaics (PV) interfacing systems. In the proposed multiport converter, an HF transformer with multiple input windings and single output winding is utilized. Each input port is based on a proposed two-quadrant inverter topology, which connects a PV module to the HF transformer. The output port is tied to a dc bus using a rectifier. The proposed two-quadrant inverter topology prevents current flow from the ac side to the dc side. This action prevents circulating currents between different ports. Each two-quadrant inverter is controlled to harvest maximum power from its associated PV module. The analysis and operation scenarios of the proposed multiport converter are discussed. PSCAD/EMTDC software package is used to simulate the proposed PV interfacing system to investigate the operation of the proposed multiport converter topology and to examine the dynamic system behavior. In addition, an experimental prototype is developed to validate the operation scenarios of the proposed multiport dc–dc converter and to examine the performance of the presented PV interfacing system. [ABSTRACT FROM AUTHOR]