The power converters based on modular structure have gained importance for electric transportation applications including electric vehicles (EV), EV charging stations, railway traction, and electric ships. Modular multilevel converters (MMCs) are recognized as one of the promising topologies to improve the energy conversion efficiency and fault-tolerant ability of power conversion systems. This paper aims at a review of latest research contributions regarding the evolution of circuit topologies, operational challenges, control schemes and fault-tolerant strategies of the MMC. Finally, the current state of the art, opportunities and their further perspective of MMC in the electric transportation applications are addressed.

With the growing fleet of a new generation electric vehicles (EVs), it is essential to develop an adequate high power charging infrastructure that can mimic conventional gasoline fuel stations. Therefore, much research attention must be focused on the development of off-board DC fast chargers which can quickly replenish the charge in an EV battery. However, use of the service transformer in the existing fast charging architecture adds to the system cost, size and complicates the installation process while directly connected to medium-voltage (MV) line. With continual improvements in power electronics and magnetics, solid state transformer (SST) technology can be adopted to enhance power density and efficiency of the system. This paper aims to review the current state of the art architectures and challenges of fast charging infrastructure using SST technology while directly connected to the MV line. Finally, this paper discusses technical considerations, challenges and introduces future research possibilities.

This paper reviews the modern electric propulsion architectures and configurations for railway traction, which are currently in practice. The development and advancement of power electronics and digital controllers led to the standardization of the insulated gate bipolar transistor (IGBT)-based converter fed induction motor drives. This paper summarizes the state-of-the-art technology of IGBT-based rolling stock in terms of both power and control. Control hierarchy of traction system and drive control techniques are explored. Special emphasis has been put on the technologies, which can improve energy efficiency as well as reliability to develop high-speed rails and metro trains in the near future in both urban and suburban areas. Specific attention is given to power electronic transformer technologybased traction drives and on-board energy storage systems. In addition, advances in traction drive technology and widebandgap power devices are addressed. Finally, major issues faced in rolling stock including the challenges for further improvement are highlighted.

With the continual development of intellectualization and vehicle onboard communication networks, the cyber-physical security of modern electric vehicles (EVs) has captured paramount importance. Particularly, the powertrain and battery charging infrastructure are becoming more vulnerable to cyber-attacks owing to interconnectedness among the EVs in the intelligent traffic environment. Therefore, it urges the development of monitoring and diagnosis strategies to ensure secure and reliable power electronics systems for networked EVs. However, there is a lack of overview of the ramifications, detection, and mitigation approaches of cyber-attacks on battery charging infrastructure. This article aims to provide an overview of the latest research contributions regarding the evolution of battery charger architectures, control methods, electric vehicle supply equipment, charging protocols, communication channels, and their compliance from the perspective of cyber security. Furthermore, the potential impacts of sabotage cyber-attacks on various popular battery chargers are explored through case studies. Also, the latest hardware and software-intensive cyber-attack detection and countermeasure techniques are discussed and analyzed through case studies. Finally, distinct challenges and prospective research opportunities for establishing cyber-resilient EV battery charging systems are presented.

The modularity, fault-tolerability and voltage scalability features allow the modular multilevel converter (MMC) to be a promising topology for modern electric ship applications. Arm voltage and submodule (SM) capacitor voltage balancing controllers with conventional high-frequency modulation schemes are indispensable for reliable and stable operation of an MMC. This requires an additional external arm controller, and the control complexity increases for an MMC with a large number of SMs. Alternatively, the space-vector pulse width modulation (SVPWM) schemes provide more freedom in selecting the voltage vectors to achieve multiple objectives, thus eliminating the arm voltage balancing controller. In this paper, a simplified SVPWM implementation for an n-level MMC is proposed. This scheme utilizes all the available switching states and calculates switching timings by mapping to a two-level space-vector structure. The computational burden of the proposed scheme is independent of converter voltage level, therefore it is computationally efficient and well suited to the MMC with any number of SMs. Experimental results are presented to show the performance of an MMC system using the proposed scheme under steady-state, rapid acceleration and speed-reversal conditions.

Modular multilevel converters (MMCs) are emerging as a promising topology for medium/high-power applications. Aluminum electrolytic capacitors (AECs) are usually employed in MMCs as floating capacitors due to their high volumetric efficiency and low price. AECs gradually deteriorate over time due to electrolyte vaporization and for this reason, they have been recognized as one of the most fragile components in the converter. As they continue to age, the AEC's capacitance decreases and its equivalent series resistance (ESR) increases which can result in an increase of submodule (SM) capacitor voltage ripple, power loss, and could damage the operation of the MMC with prolonged use of the aged capacitors. To prevent such damage, monitoring the health of capacitors is an important step to enhance the reliability of the MMC by predictive maintenance. This paper presents a failure prediction scheme for SM capacitors in the MMC by monitoring the SM capacitor voltage oscillations. Detailed simulation studies are carried out for a five-level MMC in PLECS platform and verified experimentally. The estimated capacitance through simulations and experiments are in close agreement to that value measured using the LCR meter.