This paper provides a comprehensive review and analyses on the state-of-the-art and future trends for high-power conductive on-board chargers (OBCs) for electric vehicles. To provide a global context, a summary of global charging standards and electric vehicle (EV) related trends are presented, which demonstrates momentum toward the OBCs with higher power rating. High-power OBCs are either unidirectional or bidirectional, and they have either an integrated or non-integrated system architecture. Non-integrated high-power OBCs are studied both from industry and academia, and the former are used to illustrate the current state of the art. The latter are classified on the basis of the converter design approach, studied for their principle of operation, and compared over power density, weight, efficiency, and other metrics. In addition to non-integrated OBCs, recent advancements in propulsion-machine integrated OBC solutions are also presented. Other integrated OBC techniques, such as system integration with the EV's auxiliary power module and wireless charging systems, are also discussed. Finally, future charging strategies and functionalities in charging infrastructures are addressed, and global OBC trends are summarized.

Global Trends in High-Power On-Board Chargers for Electric Vehicles

This paper overviews the silicon carbide (SiC) technology. The focus is on the benefits of SiC based power electronics for converters and systems, as well as their ability in enabling new applications. The challenges and research trends on the design and application of SiC power electronics are also discussed

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Overview of Silicon Carbide Technology: Device, Converter, System, and Application

Electric vehicle (EV) adoption continues to rise, yet EV sales still represent a small portion of vehicle sales in most countries. An expansion of the dc fast-charging (DCFC) network is likely to accelerate this revolution toward sustainable transportation, giving drivers more flexible options for charging on longer trips. However, DCFC presents a large load on the grid, which can lead to costly grid reinforcements and high monthly operating costs—adding energy storage to the DCFC station can help mitigate these challenges. This article performs a comprehensive review of DCFC stations with energy storage, including motivation, architectures, power electronic converters, and detailed simulation analysis for various charging scenarios. The review is closely tied to current state-of-the-art technologies and covers both academic research contributions and real energy storage projects in operation around the world.

A Comprehensive Review of DC Fast-Charging Stations With Energy Storage: Architectures, Power Converters, and Analysis

This article 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 have put this growing architecture in the spotlight, as it has drawn the attention of different research groups recently. The following provides an insightful discussion regarding the topologies that enable these architectures and their regulatory requirements, besides their features and level of development. In addition, 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.

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Bipolar DC Power Conversion: State-of-the-Art and Emerging Technologies

Data centers use more than 1.5% of all electricity in China and the U.S., with continuing growth. This paper reviews the power hierarchy levels within modern data centers. It considers energy consumption and power electronics challenges across all levels of a data center, including building distribution, dc architectures, and conversion down to the board level. Power electronics plays a central role throughout the hierarchy, and emerging approaches are described. Strategies that enhance center energy efficiency, both in terms of overall center operation and in terms of computation performance, are discussed.

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Data center challenges and their power electronics

Three-phase power factor correction rectifiers are an essential area of power electronics, supplying a direct current load with tens of kilowatts, or more, from the public three-phase mains and achieving sinusoidal input currents. In many applications, isolation is required between the mains and the load, for example, due to safety reasons or different grounding schemes. This paper describes the modulation, design, and realization of a buck–boost-type, unity-power-factor, isolated matrix-type, dual-active-bridge, three-phase rectifier. It uses a circuit similar to a conventional dual-active-bridge converter, but employs a direct matrix converter to connect the high-frequency transformer's primary winding to the mains. A soft-switching modulation scheme is proposed and comprehensively analyzed, deriving closed-form solutions and numerical optimization problems to calculate switching times that achieve minimal conduction losses. Based on this analysis, the design of an 8-kW 400-V rms three-phase ac to 400-V dc prototype is discussed, striving for the highest possible efficiency. Using 900-V SiC mosfet s and a transformer with an integrated inductor, a power density of ${\text{4}}\; {\text{kW}\cdot \text{dm}^{-3}}$ ( ${\text{66}}\; {\text{W}\cdot \text{in}^{-3}}$ ) is achieved. Measurement results confirm an ultrahigh full-power efficiency of 99.0% at nominal operating conditions and 98.7% at 10% lower input voltage.

99% Efficient Isolated Three-Phase Matrix-Type DAB Buck–Boost PFC Rectifier

With the increasing use of photovoltaic systems, a large demand for efficient, power-dense and lightweight grid-interface inverters is arising. Accordingly, new concepts like multi-level converters, which are able to reduce the converter losses while still keeping a low construction volume, have to be investigated. The hybrid seven-level topology analyzed in this paper comprises an active neutral point clamped stage, followed by a flying capacitor stage. Compared to a pure flying capacitor converter, the combination of these two stages allows to save more than half of the capacitor volume, while still having the same requirement for the output filter stage, and hence, the same output filter volume. Moreover, the topology employs low-voltage devices and ensures low conduction and switching losses, resulting in a higher efficiency. The principle of operation of the system is briefly reviewed, and based on a detailed component modeling, an efficiency vs. power density optimization is carried out, for which switching loss measurements of state-of-the-art 200 V semiconductors are performed. From the optimization, a high-efficiency design is selected and the practical hardware realization is discussed. The simulation and optimization results are then verified by realizing an all-silicon 99.35% efficient three-phase seven-level system, featuring a volumetric power density of 3.4 kW/dm
 3
 (55.9 W/in
 3
), a gravimetric power density of 3.2 kW/kg, and fulfilling CISPR Class A EMI requirements. Finally, it is shown that an all-silicon realization with next generation silicon switches can achieve 99.5% efficiency with the same hardware, and 99.6% with commercial state-of-the-art GaN switches.

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All-silicon 99.35% efficient three-phase seven-level hybrid neutral point clamped/flying capacitor inverter

DC power distribution systems for data centers, industrial applications, and residential areas are expected to provide higher efficiency, higher reliability, and lower cost compared to ac systems and have been an important research topic in recent years. In these applications, an efficient power factor correction (PFC) rectifier, supplying the dc distribution bus from the conventional three-phase ac mains, is typically required. This paper analyzes the three-phase, buck-type, unity power factor SWISS Rectifier for the realization of an ultrahigh-efficiency PFC rectifier stage with a 400-V rms line-to-line ac input voltage and a 400-V dc output voltage. It is shown that the mains current total harmonic distortion of the rectifier can be improved significantly by interleaving two converter output stages. Furthermore, the dc output filter is implemented using a current-compensated integrated common-mode coupled inductor, which ensures equal current sharing between the interleaved half bridges and provides common-mode electromagnetic interference (EMI) filter inductance. Based on a theoretical analysis of the coupled inductor's magnetic properties, the necessary equations and the design procedure for selecting semiconductors, magnetic cores, the number of turns, and the EMI filter are discussed. Based on these results, an ultrahigh-efficient 8-kW 4-kW $\cdot$ dm $^{-3}$ (66-W $\cdot$ in $^{-3}$ ) laboratory-scale prototype converter using 1.2-kV SiC MOSFETs is designed. Measurements taken on the prototype confirm a full power efficiency of $\text{{99.16}{\%}}$ and a peak efficiency of $\text{{99.26}{\%,}}$ as well as the compliance to CISPR 11 Class B conducted emission limits.

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99.3% Efficient Three-Phase Buck-Type All-SiC SWISS Rectifier for DC Distribution Systems

Due to the increasing power consumption of data centers, efficient dc power distribution systems have become an important topic in research and industry over the last years and according standards have been adopted. Furthermore the power consumed by telecommunication equipment and data centers is an economic factor for the equipment operator, which implies that all parts of the distribution system should be designed to minimize the life cycle cost, i.e. the sum of first cost and the cost of the power conversion losses. This paper demonstrates how semiconductor technology, chip area, magnetic component volumes and switching frequency can be selected based on life cycle cost, using analytical and numerical optimizations. A three-phase buck-type PFC rectifier with integrated active filter for 380V dc distribution systems is used as an example system, which shows that a peak efficiency of 99% is technically and economically feasible with state-of-the-art SiC MOSFETs and nanocrystalline or ferrite cores. Measurements taken on an 8 kW, 4 kWdm-3 hardware prototype demonstrate the validity and feasibility of the design.

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99% Efficient three-phase buck-type SiC MOSFET PFC rectifier minimizing life cycle cost in DC data centers

This paper describes a new modulation concept for the uni- and bidirectional SWISS rectifier, which mitigates ac input current distortions at the mains voltage sector boundaries. An analytical model is derived and compared to simulations, which allows an estimation of the distortion's magnitude from design parameters, showing that these distortions increase the input current total harmonic distortion (THD) significantly. A modification of the original circuit topology is proposed, which decouples the operation of SWISS Rectifier's active third-harmonic current injection network and its dc–dc converter switches. An algorithm is presented which allows the calculation of a temporary pulse width modulation for the SWISS Rectifier's current injection network to mitigating the distortions. The concept is verified for both power flow directions and for operation with unsymmetrical and distorted mains voltages by measurement results taken on a bidirectional 7.5-kW SWISS Rectifier prototype. An ac input current THD of 1.3% results for symmetric sinusoidal mains voltages and 1.4% and 1.6% for operation with distorted and unsymmetrical mains voltages.

Lukas Schrittwieser

Papers

99% Efficient Isolated Three-Phase Matrix-Type DAB Buck–Boost PFC Rectifier

All-silicon 99.35% efficient three-phase seven-level hybrid neutral point clamped/flying capacitor inverter

99.3% Efficient Three-Phase Buck-Type All-SiC SWISS Rectifier for DC Distribution Systems

99% Efficient three-phase buck-type SiC MOSFET PFC rectifier minimizing life cycle cost in DC data centers

Novel SWISS Rectifier Modulation Scheme Preventing Input Current Distortions at Sector Boundaries