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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]

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 FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is a promising candidate for high-/medium-voltage high-power applications such as medium voltage ac drives due to its modularity, reliability, and scalability. The main challenge of a conventional MMC is low-frequency operation. Capacitor voltage ripple is inversely proportional to the operating frequency. Hence, operating at low frequency necessitates employing large submodule capacitances to limit voltage ripple or the utilization of energy equalization modules (EEMs). The first option negatively affects converter lifetime, and the second option requires a large number of semiconductor devices and isolating transformers. In this article, a modified MMC topology with self-energy equalization is proposed to ensure converter operation with balanced capacitor voltages with low ripple during zero-/low-frequency conditions. Operating with balanced capacitor voltages with low ripple is achieved by maintaining the same energy level in the involved upper and lower arms. A low device count alternative to the EEMs approach is proposed in this work. Detailed illustration of the operational concept and design of the associated passive components is presented. The performance of the proposed medium voltage ac drive is elucidated through simulation and experimental results. [ABSTRACT FROM AUTHOR]

Conventional modular multilevel converters (MMCs) are widely used in high power applications due to their various astonishing advantages; however, they fail to achieve balanced capacitor voltage in DC operation. In this paper, a hybrid two‐stage modular DC–DC converter is proposed to solve the issue of unbalanced capacitor voltages. The proposed converter consists of a single‐phase half‐bridge MMC with half‐bridge submodules followed by a medium voltage valves‐based H‐bridge rectifier. The proposed converter is used in medium‐voltage applications such as feeding a DC‐load or interconnection between two DC grids of different voltage levels. The proposed configuration achieves successful DC–DC conversion with a low number of switches, a high conversion ratio with bidirectional power flow, low current stresses, soft switching across the second stage, and low switching losses. The operational concept and the control algorithm have been illustrated in detail. Finally, the effectiveness of the proposed DC–DC converter is evaluated based on simulation studies of MATLAB SIMULINK and a scaled‐down laboratory experimental test rig. [ABSTRACT FROM AUTHOR]