The modular multilevel converter (MMC) is currently one of the power converter topologies which has attracted more research and development worldwide. Its features, such as high quality of voltages and currents, high modularity and high voltage rating, have made the MMC a very good option for several applications including high-voltage dc (HVdc) transmission, static compensators (STATCOMs), and motor drives. However, its unique features such as the large number of submodules, floating capacitor voltages, and circulating currents require a dedicated control system able to manage the terminal variables, as well as the internal variables with high dynamical performance. In this paper, a review of the research and development achieved during the last years on MMCs is shown, focusing on the challenges and proposed solutions for this power converter still faces in terms of modeling, control, reliability, power topologies, and new applications.

Modular Multilevel Converters: Recent Achievements and Challenges

A modulation scheme for dual active bridge converter is proposed to achieve zero voltage switching (ZVS) and reduce the conduction loss in this article. To compromise the ZVS achievement and the conduction loss, optimized working modes are derived from different cases. Compared with dual phase shift and triple phase shift modulations, the modulation in this article can achieve ZVS in both the light load and the heavy load. Therefore, the switching loss in the light load can be reduced, and the efficiency in the light loads is improved. However, the converter cannot achieve seamless transient among the different optimized working modes, which may cause the transient oscillation in the mode transition. A modulation scheme employing closed-loop control by integrating different working modes is proposed. Furthermore, the seamless transition method among the different working modes is proposed, so the modulation scheme is very suitable to be used for wide battery voltage and wide load requirements. The conduction loss and peak current by using the proposed modulation scheme are compared with those of the previous modulation schemes. With the proposed modulation scheme, both the conduction loss and ZVS can be improved. Finally, a 1.2-kW experimental prototype has been built to verify the effectiveness of the proposed converter and the modulation scheme.

Modulation Scheme of Dual Active Bridge Converter for Seamless Transitions in Multiworking Modes Compromising ZVS and Conduction Loss

The rise of greenhouse gas levels in the atmosphere is a severe climate change concern. A significant part, such as CO2 emission, comes from internal combustion engine-driven vehicles, incited the automotive sector to focus more on the sustainable electric transportation system. However, electric vehicles face significant charging time, charging methods, and range anxiety challenges. To overcome these challenges, charging technologies for electric vehicle batteries play an essential role. Many types of electric vehicle charging topologies have been discussed in the literature and implemented in many practical applications. This paper presents a state of art criticism of advanced converter topologies and charging methodology for electric vehicle applications. Apart from the conventional topologies, this manuscript has covered the comparative criticism of the recently proposed EV charging technologies regarding charging methods, control strategies, and power levels. Further, this paper discussed the different onboard chargers with their power factor correction topologies, drawbacks, and required corrections. This manuscript provides the research directions for the academic and industrial communities. 

A comprehensive review on advanced charging topologies and methodologies for electric vehicle battery

Predicting the environmental economic dispatch problem for reducing waste nonrenewable materials via an innovative constraint multi-objective Chimp Optimization Algorithm

Medium-voltage dc (MVdc) grids are attractive for electric aircraft and ship power systems, battery energy storage system (BESS), fast charging electric vehicle (EV), etc. Such EV or BESS applications need isolated bidirectional MVdc to low-voltage dc (LVdc) or LVac converters. However, the existing Si-based solutions cannot fulfill the requirements of a high-efficiency and robust converter for MVdc grids. This article presents a 5-kV SiC-based universal modular solid-state transformer (SST). This universal current-source SST can interface either an LVac or LVdc grid with an MVdc grid in single-stage power conversion, while the conventional dual-active bridge (DAB) converter needs an additional inverter. The proposed SST module using 3.3-kV SiC MOSFET s and diodes is bidirectional and can serve as a building block in series or parallel for higher voltage higher power systems. The topology of each module is based on the soft-switching solid-state transformer (S4T) with reduced conduction loss, which features reduced electromagnetic interference electromagnetic interference (EMI) through controlled dv/dt, and high efficiency with full-range zero-voltage switching for main devices and zero-current switching for auxiliary devices. Operation principle of the modular S4T (M-S4T), capacitor voltage balancing control between the cascaded modules, design of components including a medium-voltage (MV) medium-frequency transformer (MFT) to realize a 50-kVA, 5-kV dc to 600 V dc or 480 V ac M-S4T are presented. Importantly, the MV MFT prototype achieves very low leakage inductance (0.13%) and 15-kV insulation with coaxial cables and nanocrystalline cores. The proposed universal modular SST is compared against the DAB solution and verified with dc–dc and dc–ac simulation and 4-kV experimental results. Significantly, the MV experimental results of a modular dc transformer with each module at MVdc are rarely covered in the literature and reported for the first time.

SiC-Based 5-kV Universal Modular Soft-Switching Solid-State Transformer (M-S4T) for Medium-Voltage DC Microgrids and Distribution Grids

This paper introduces the high-frequency link concept into the modular multilevel converter (MMC) topology, which can totally reduce the individual dc-link capacitors at the high-voltage side. The proposed converter, called isolated MMC, has basic triple ports of medium-voltage ac, medium-voltage dc, and low-voltage dc. Thus, it is especially suitable for hybrid dc and ac applications in power generation and transmission, such as solid-state transformer. The fundamental principle and applied control scheme of phase-shift pulsewidth modulation are presented in detail. The design of the voltage clamping circuit and analysis of duty loss are carried out. The experimental results are given to illustrate the efficient operation characteristics.

An Isolated Modular Multilevel Converter (I-M 2 C) Topology Based on High-Frequency Link (HFL) Concept

This article proposes a novel single-stage isolated cascade photovoltaic (PV) inverter topology based on a multibus dc collection. The PV power plant can be divided into many arrays, each of which supplies power to three cascaded isolated inverter units through a dc bus. This isolated inverter unit is composed of cascade isolated bridge cells (I-BCs) connected in input-parallel output-series (IPOS). Compared with a conventional two-stage isolated cascade PV converter, the proposed PV topology can totally eliminate the individual dc-link capacitors at the high-voltage (HV) side, which leads to extremely reduced system volume and eliminated the voltage-balancing control between the dc-link capacitors. This article, first, describes the basic principle and the carrier phase shift pulse-width modulation (CPS-PWM) applied to this topology and, then, analyzes the power balance constraints between the cascade three-phase units for the PV grid-connected system. Finally, the effectiveness of the novel topology is verified by the simulation and experimental results.

Novel High-Frequency Isolated Cascade PV Inverter Topology Based on Multibus DC Collection

In the medium-voltage AC/DC distribution networks with distributed renewable sources on islands, a multi-port receiver is the key factor for hybrid power conversion. However, the most used modular multilevel converter (MMC)-based multi-port converters (MCs) face the coordination and complexity challenges due to their double-stage control system and voltage-balancing control of capacitors. In particular, the control system is more unstable and complicated when the control of circulating currents is considered. In this paper, an isolated modular multilevel converter (I-MMC) is used as a receiver, and a unified coordinated control scheme based on the multiple modulation freedoms is proposed. Due to the voltage clamping of high-frequency transformers, there is no concern of the capacitors' voltage-balancing control. Based on the proposed single-stage control system, the unified coordinated control scheme solves the coordination problem of the MMC-based MCs. The multiple modulation freedoms corresponding to an AC port, two DC ports, and three-phase circulating currents can independently control respective targets. The control structure is simplified, while the control freedoms are ensured. Experimental results confirming the performance of the designed control system is shown.

/pdf/single-stage-control-system-of-i-mmc-based-island-mvdc-link-3h2nwb6n03.pdf

Single-Stage Control System of I-MMC-Based Island MVDC Link Receiver With Multiple Modulation Freedoms

Phase-shift Full-Bridge (PSFB) Converter Integrated Double-Inductor Rectifier with Separated Resonant Circuits (SRC) for 800V High-Power Electric Vehicles

This paper introduces a topology named bidirectional PSFB (B-PSFB) DC-DC converter, which can realize real seamless power transition by unified modulation strategy. The modulation strategy of the switches is given, and the working modes of the converter are discussed in detail. In buck mode, the Zero-Voltage-Switching (ZVS) of switches in the primary side is analyzed. In addition, A RCD clamping circuit is used to suppress the voltage oscillation and spike. The theoretical efficiency under different working conditions is given as well. Finally, a 2kW prototype of B-PSFB DC-DC converter is established to verify the performance of bidirectional power flow and seamless power transition.

A Bidirectional PSFB (B-PSFB) DC-DC Converter with Seamless Power Transition

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