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The integration of renewable energy sources in Medium-/High-voltage DC grids has called up continuous research to develop DC-DC conversion systems. This paper presents a hybrid modular multilevel DC-DC converter topology which successfully overcomes the issue of capacitors voltage imbalance during DC-DC conversion. In the proposed topology, single MMC leg is employed with half-bridge submodules in the upper arm and full-bridge submodules in the lower arm along with soft-switched high-voltage valves. The proposed hybrid modular multilevel converter has inherited arm energy equalization with the help of the parallel connectivity of involved arms’ capacitors. During the equalization period, the series-connected upper arm capacitors are connected in parallel to the series-connected lower arm capacitors to transfer the energy between the involved arms which results in operating with balanced capacitors voltages. The proposed modular DC-DC converter is a bidirectional converter which allows power flow from high-voltage side to low-voltage side and vice versa, i.e., it can be operated successfully as a DC transformer. The operational concept of the proposed configuration, control strategy, and parameters design are presented. Simulation results are presented along with experimental results of a scaled-down prototype to validate the proposed approach. Simulation and experimental results show the viability of the suggested approach.

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.

Multilevel inverters have been widely used in various applications, as they provide output voltage with better quality, lower dv/dt, and lower Total Harmonic Distortion (THD). Multilevel inverter such as Neutral Point Clamped (NPC) inverter uses a large number of semiconductor devices (IGBTs and diodes) which negatively affects the inverter cost and efficiency. Recently, a three-level (3L) F-type inverter has been proposed with lower switch voltage stresses, cost, and losses compared to 3L T-type and NPC inverters. This paper proposes a five-level (5L) F-type inverter as an extension for the 3L F-type inverter. Like a 5L NPC inverter, the voltages of the involved dc-link capacitors should be kept at a certain voltage level. To achieve that, buck-boost converter-based Equalization Channels (ECs) are employed. To show the pros and cons of the 5L F-type inverter, a comparison between the proposed inverter and other existing multilevel inverters has been held. The numerical assessment also shows that the proposed architecture has a lower kVA rating and losses than the conventional 5L NPC inverter. Finally, different Simulation and experimental results of the proposed 5L F-type inverter are presented. The presented results show the viability of the proposed converter.

Due to the severe impacts of climatic change, many recent developments in air cleaning systems have received an increasing attention. The best solution for expelling pollutant particles, met in industrial and commercial applications, is the electrostatic precipitator (ESP). One of the key components in the ESP system is the high-voltage power supply. Many recent studies have proven that the sectionalization of industrial ESPs enhances their particle collection efficiency. Consequently, this paper proposes a new modular switched-capacitor voltage multiplier-based multi-module high-voltage pulse power supply. In the proposed configuration, the two different patterns of output pulse are adopted. The proposed scheme is characterized by its modular structure and its capability of providing two isolated high-voltage pulse generators for each two ESP bus sections from one low-voltage AC source with an adjustable repetition rate, a controllable pulse width, and the desired values of the base and pulse voltages. A detailed illustration and simulation results are presented for the proposed approach. A comparative study is presented to elucidate the advantages of the proposed topology in contrast with the existing topologies. Finally, a -1.2-kV, 0.36-kW experimental setup has been built to show the viability of the proposed concept.

Central and string inverters are the most common technologies in PV integrated systems. The central inverter technology is simple and cheap, but its generated power is greatly reduced during Partial Shading Condition (PSC). In string inverter technology, higher power can be extracted during PSC, but multi-inverters are needed. To keep the system simple and cheap, a cost-effective solution,namely, String Optimizers Circuits (SOCs)-based PV system has been recently proposed, where central converter is employed along with SOCs (SOC for each string). The SOC is responsible for controlling its string current to ensure operating at the string GMP. In this paper, a closed-loop string current controller is presented to enhance the performance of the SOCs-based PV system. To test the effectiveness of the proposed controller, the system is simulated under different PSCs. The simulation results of the open-loop and proposed closed-loop approaches have been compared to show the effectiveness of the proposed control approach, where it provides a significant improvement in tracking accuracy under different PSCs. Circuit analysis and component design of the SOC-based PV system are highlighted. Finally, an assessment of the SOC-based PV system compared to other existing technologies is presented to show the effectiveness of the SOC-based system.

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.

Summary: DC‐DC converters play a vital role in the integration of renewable energy sources. Modular multilevel converter (MMC) has emerged as a highly promising option for high‐voltage high‐power applications, for DC‐AC and DC‐DC conversion, thanks to its distinctive characteristics. An inherent limitation of using traditional MMC in DC‐DC conversion is the occurrence of arm energy drift, leading to imbalanced voltages across capacitors of submodules (SMs). Many approaches have been presented in the literature to address the energy drift issue during DC‐DC conversion process. In this paper, a novel bidirectional hybrid modular multilevel DC‐DC converter with balanced arm energy has been proposed. The proposed converter consists of one high‐voltage valve and two legs. Each leg is equipped with half‐bridge submodules (HB‐SMs) in the upper arm and full‐bridge submodules (FB‐SMs) in the lower arm. The proposed architecture enables the parallel connection between series‐connected capacitors of the upper arm and series‐connected capacitors of the lower arm during the equalization period. The parallel connectivity enables the energy transfer between the upper and lower arms in the same leg, hence preventing energy drift issues. A detailed illustration of converter operational concept, mathematical analysis, design, and efficiency estimation are presented. The presented simulation and experimental results show the bidirectional power flow ability and the promising behavior of the proposed converter during normal operating conditions with balanced arm energy. Finally, a comparison between the proposed converter and other existing topologies has been made to show the superiority of the proposed converter over the other alternatives. The proposed converter has a lower count of insulated gate bipolar transistors (IGBTs) and eliminates the usage of isolating transformers when compared to the energy equalization modules approach. In addition, unlike the other alternatives, the proposed converter has a DC fault blocking capability. [ABSTRACT FROM AUTHOR]

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.

Saudi Arabia's obesity prevalence is 19.2% among men and 21.4% among women. Treatment includes lifestyle modifications, medication, and bariatric surgery. Procedures reach up to 1200 annually in our center. Porto-mesenteric venous thrombosis associated with venous mesenteric ischemia and bowel necrosis is a rare complication that necessitates an early workup and management. A 29-year-old Saudi male underwent laparoscopic sleeve gastrectomy. Post-surgery, he experienced abdominal pain, nausea, and vomiting, exacerbated by eating and smoking. Abdomen computed tomography scans revealed engorged portal veins, congested mesenteric veins, and small bowel thickening. He underwent exploratory laparoscopy shifted to laparotomy with resection of an infarcted omentum and 1 m of jejunal small bowel loop, and was discharged postoperatively after 7 days. Porto-mesenteric venous thrombosis is a rare complication after laparoscopic sleeve gastrectomy, requiring early diagnosis and appropriate treatment. Patients present with non-specific symptoms, necessitating high suspicion for computed tomography recommendations. [ABSTRACT FROM AUTHOR]

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.

Modular multilevel converter (MMC)-based AC motor drives are emerging trend-research. They ease medium-/high-voltage handling in high-power applications with reduced footprint and life-cycle costs. A known challenge concerning their operation is the zero-/low-speed operating condition. The recent techniques proposed to improve operation during that interval, implement complex hardware/software approaches. To cope with this issue, this paper proposes multiphase machines for MMC-based AC-drives. Among several advantages regarding the power splitting, multiphase machines provide additional degrees of freedom compared with their three-phase counterparts. Novel exploitation to these additional degrees of freedom is proposed in this paper by injecting a secondary current component in the load current with specific magnitude and frequency during zero-/low-speed intervals enabling the motor to function duly. Since the control of these secondary components is already inherited in the current controller structure of any multiphase machine, no additional algorithms or sensors will be required. In this paper, a three-level five-phase MMC-based distributed winding induction machine drive system for medium-/high-voltage applications is investigated during low-speed operation as well as starting from standstill to rated speed. Two different control options are proposed using capacitor voltage measurements or under sensorless operation in order to reduce the cost and complexity in the case of a high number of MMC levels. The experimental results have been obtained with a downscaled drive system to verify the proposed solution.

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.