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Abstract Modular Multilevel Converters (MMCs) are promising candidates for high‐voltage high‐power applications. The main challenge of the MMCs is the zero‐frequency operation. To achieve a successful DC–DC conversion process with balanced capacitors’ voltages with limited voltage ripple, this paper suggests the employment of the conventional two‐leg half‐bridge submodule‐based MMC structure in conjunction with a single bidirectional high‐voltage (HV) valve across the low‐voltage side. In the suggested structure, the HV valve is controlled on and off to ensure energy equalization for the MMC arms. In addition, soft‐switching for the HV valve is proposed to reduce the switching losses. Detailed illustration and design of the proposed concept are presented. Simulation and experimentation results are elucidated to show the effectiveness of the proposed DC–DC hybrid MMC. The results showed efficient performance of the suggested converter.

Abstract In this work, a novel three‐phase unidirectional off‐board Electric Vehicles (EVs) fast charger is proposed. Each phase of the proposed converter consists of a two‐stage converter. The first stage is an AC–DC front‐end converter with power factor correction (PFC) control. The front‐end AC–DC converter is based on an isolated boost converter, which has a boosting capability and provides galvanic isolation. In this stage, parallel‐in parallel‐out isolated boost converter modules are employed in each phase. This enables sharing the current among modules to avoid implementing one module with a high current rating to meet the fast‐charging requirements. The multimodule option provides fault‐ride through capability for the proposed charger. The DC outputs of involved phases, that is, three isolated DC voltages, are fed to three cascaded DC–DC unidirectional buck converters. The charging terminals are used to charge the EV battery through a filter inductor with a charging current controller's aid. A detailed illustration of the suggested closed‐loop controllers is presented to ensure a successful operation for the proposed architecture. A simulation case study for a 25‐kW charger is presented. Finally, a 1‐kW prototype is implemented for experimental validation.

This study investigates and analyzes the effect of flux intensification due to the propeller shaft and rudder on the 3D mapped induced magnetic signature of marine vessels. The study was designed to extrapolate the 3D induced magnetic signature and to analyze the difference between signature components in two different cases: a vessel without propeller shaft or rudder and a vessel with the propeller shaft and rudder attached. Numerical modeling was conducted using full-scale vessel dimensions and finite-element analysis (FEA) modeling software. Measurements on a 1:100 properly scaled and designed physical scale model (PSM)were conducted in a magnetically clean area. To enrich the analysis, both signature components from the numerical evaluation and experimental measurements were 3D mapped. Both the scaling technique and scaling effect on magnetic signature were investigated. The signature measurements of the scaled vessel model were performed to verify the numerical model. Both the numerical and experimental results are both discussed and shown to be consistent. The extrapolated signature components revealed that the studied effect became prominent as the saliency of the 3D mapped signature components increased. Consequently, this effect increases the magnetic susceptibility of the vessel to detection or destruction. Finally, this study suggests solutions to reduce this effect.

Abstract Medium‐/High Voltage DC grids are interesting for the integration of renewable energy sources. DC‐DC conversion systems are highly needed for the development of DC grids. Recently, Modular Multilevel Converter (MMC) is the most promising technology for medium‐/high‐voltage applications, but employing the conventional MMC with DC output voltage leads to diversion in the Submodule (SM) capacitor voltages, that is energy drift. This paper proposes a modified modular multilevel DC‐DC converter with self‐energy equalization, which ensures successful DC‐DC conversion with balanced capacitors voltages. In the modified topology, clamping Insulated Gate Bipolar Transistors (IGBTs) are employed in each arm to enable parallel‐connection of the capacitors in the same arm. During the operation (equalization period), the parallel‐connected upper capacitors are connected to the parallel‐connected lower capacitors in each leg through a small limiting inductor to transfer energy between the arms to ensure balanced capacitor voltages. The proposed configuration, along with the operational concepts, mathematical analysis, and design, are presented. Finally, simulation and experimental results are presented for validation.

Abstract Nowadays, most of the converters used in high‐power high‐voltage (HV) applications are the conventional modular multilevel converters (MMC). However, in the case of DC‐DC conversion, an imbalance of the capacitor voltages occurs and the conventional MMC fails to operate correctly. This paper introduces an arm current reversal‐based modular multilevel DC‐DC converter, which successfully provides balance among the capacitor voltages while operating in DC‐DC conversion. The proposed configuration is used in medium voltage DC grids to feed DC loads or to interconnect between two DC grids of different voltage levels. The proposed converter is a two‐stage DC‐DC modular converter, which consists of a single‐phase half‐bridge MMC with half‐bridge submodules (HBMMC) followed by a single‐phase H‐bridge MMC with half‐bridge submodules (SMs). The operational concept of the proposed converter is based on reversing the arm current direction and reversing the output terminals with the help of the H‐bridge MMC stage, which ensures the same direction of the voltage at the load terminals. The proposed converter provides a high conversion ratio, bidirectional power flow, simple architecture, and a simple control scheme. Detailed illustrations, analysis, and design of the proposed converter are presented. Besides, MATLAB‐based and Opal RT‐based simulation results and experimental results are presented to validate the proposed configuration claims.

DC-AC Modular Multilevel Converter (MMC) is a promising candidate for high-power AC drive applications. The main challenge of operating the MMC in AC drive applications is its performance during low-frequency conditions, as high voltage ripple is associated with the low-frequency operation, which results in voltage stresses on the involved semiconductor devices. To keep capacitor voltages balanced and bounded in low-frequency operation, different techniques have been proposed in literature, which can be classified into software and hardware approaches. In this paper, a hybrid MMC with arm-interchange concept is proposed to ensure operating successfully during low-frequency conditions. The hybrid MMC consists of two-stages. The first stage is a front-end Integrated Gate Commutated Thyristor (IGCT)-based H-bridge converter, while the second stage is a Full-Bridge Sub-Module (FBSM)-based MMC, where FBSMs is able to generate positive, zero, and negative voltage states. Detailed illustration and design of the hybrid MMC are introduced. Simulation results of the proposed converter are presented to show the effectiveness during low-frequency and normal frequency conditions in AC drive applications. Finally, a scaled-down prototype is employed for experimental validation.

This paper presents small-signal modeling, stability analysis, and controller design of a non-isolated bidirectional hybrid-modular DC-DC Converter for DC grid applications. The DC-DC converter can be used to interconnect two different DC voltage levels in a medium-/high-voltage DC grid. Half-bridge Sub-Modules (SMs) and a high-voltage valve are the main components of the converter. The high-voltage valve can be implemented via employing series-connected Insulated-Gate Bipolar Transistors (IGBTs). Operation with zero voltage switching of the involved high-voltage valve is feasible, i.e., there is no concern pertinent to dynamic voltage sharing among the series-connected IGBTs. The power is transferred from one side to another through the involved SMs, where their capacitors are connected in series across the high-voltage side, while they are connected sequentially across the low-voltage side. In this paper, the state-space averaging technique is employed to derive the small-signal model of the presented converter for controller design. Closed-form expression of the duty cycle-to-inductor current transfer function is extracted. Comparison between simulation results of the small-signal model and the detailed circuit model is presented to authenticate the accuracy of the derived small-signal model. Finally, a scaled-down prototype is used to verify the accuracy of the small-signal model.