Electrification has been a key component of technological progress and economic development since the industrial revolution. It has improved living conditions, spurred innovation, and increased efficiency across all sectors of our economy and all aspects of our lives. During the coming decades, electrification is expected to reach further and deeper into the transportation, building, and industry sectors, mainly motivated by the energy transition to a zero-carbonemission-based economy to mitigate climate change.

This paper provides a detailed analysis of the power electronics solutions enabling bipolar dc grids. The bipolar dc grid concept has proven to be more efficient, flexible and higher in quality than the conventional unipolar one. However, despite its many features, these systems still have to overcome their issues with asymmetrical loading to avoid voltage imbalances, besides meeting regulatory and safety requirements that are still under development. Advances in power electronics and the large-scale deployment of dc consumer appliances has put this growing architecture in the spotlight, as it has drawn the attention of different research groups recently. The following pages provide an insightful discussion regarding the topologies that enable these architectures, their regulatory requirements besides their features and level of development. Additionally, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.

Modules with series and parallel connectivity add new features and operation modes to modular multilevel converters (MMCs). Compared to full- and half-bridges, the series/parallel modules allow sensorless module balancing and reduce conduction loss with the same semiconductor area. However, in high-voltage applications with limited switching rates, the sensorless operation of the series/parallel modules suffers from large charge-balancing currents. This paper introduces a series/parallel module variant with a small port inductor. The port inductor suppresses the charge-balancing current despite low switching rates. We also propose a carrier-based modulation framework and show the importance of the carrier assignment in terms of efficiency and balancing. The proposed module and the modulation method are verified on a lab setup with module switching rates down to 200 Hz. The module voltages are kept within a narrow band with the charge-balancing currents below 5% of the arm current. The experimental results show practicality and advantages of the new series/parallel modules in high-voltage MMC applications.

The increasing power levels handled by electric vehicle dc fast chargers will impose additional challenges to the switching devices in order to cope with the efficiency requirements. A cost-effective alternative to achieve highly efficient power conversion is through the partial-power conversion concept. This paper validates the advantages of a step-down Type II partial-power converter (PPC), based on the phase-shifted full-bridge converter, for EV Fast Chargers. By exploiting the reduced voltage range of an EV battery pack along with the reduced power ratio for a Type II PPC, an extremely efficient charging process can be achieved. The concept is validated with the development of a 7 kW demonstrator, hence realistic efficiency measurements are obtained. Results indicate the effectiveness of charging a battery by merely handling 13.32% of the power provided to it, with a peak efficiency of 99.11%.