Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

/pdf/the-2018-gan-power-electronics-roadmap-2iunv619fh.pdf

The 2018 GaN power electronics roadmap

With the number of electric vehicles (EVs) on the rise, there is a need for an adequate charging infrastructure to serve these vehicles. The emerging extreme fast-charging (XFC) technology has the potential to provide a refueling experience similar to that of gasoline vehicles. In this article, we review the state-of-the-art EV charging infrastructure and focus on the XFC technology, which will be necessary to support the current and future EV refueling needs. We present the design considerations of the XFC stations and review the typical power electronics converter topologies suitable to deliver XFC. We consider the benefits of using the solid-state transformers (SSTs) in the XFC stations to replace the conventional line-frequency transformers and further provide a comprehensive review of the medium-voltage SST designs for the XFC application.

Extreme Fast Charging of Electric Vehicles: A Technology Overview

A comprehensive procedure for the derivation of optimal, full-operating-range zero voltage switching (ZVS) modulation schemes for single-phase, single-stage, bidirectional and isolated dual active bridge (DAB) ac-dc converters is presented. The converter topology consists of a DAB dc-dc converter, receiving a rectified ac line voltage via a synchronous rectifier. The DAB comprises primary and secondary side full bridges, linked by a high-frequency isolation transformer and a series inductor. ZVS modulation schemes previously proposed in the literature are either based on current-based or energy-based ZVS analyses. The procedure outlined in this paper for the calculation of optimal DAB modulation schemes (i.e., combined phase-shift, duty-cycle, and switching frequency modulation) relies on a novel, more accurate, current-dependent charge-based ZVS analysis, taking into account the amount of charge that is required to charge the nonlinear parasitic output capacitances of the switches during commutation. Thereby, the concept of “commutation inductance(s)” is shown to be an essential element in achieving full-operating-range ZVS. The proposed methods are applied to a 3.7 kW, bidirectional, and unity power factor electric vehicle battery charger which interfaces a 400 V dc-bus with the 230 Vac, 50-Hz utility grid. Experimental results obtained from a high-power-density, high-efficiency converter prototype are given to validate the theoretical analysis and practical feasibility of the proposed strategy.

/pdf/optimal-zvs-modulation-of-single-phase-single-stage-851jvg7dpg.pdf

Optimal ZVS Modulation of Single-Phase Single-Stage Bidirectional DAB AC–DC Converters

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

The integration of solar photovoltaic (PV) into the electric vehicle (EV) charging system has been on the rise due to several factors, namely continuous reduction in the price of PV modules, rapid growth in EV and concerns over the effects of greenhouse gases. Despite the numerous review articles published on EV charging using the utility (grid) electrical supply, so far, none has given sufficient emphasis on the PV charger. With the growing interest in this subject, this review paper summarizes and update all the related aspects on PV–EV charging, which include the power converter topologies, charging mechanisms and control for both PV–grid and PV-standalone/hybrid systems. In addition, the future outlook and the challenges that face this technology are highlighted. It is envisaged that the information gathered in this paper will be a valuable one-stop source of information for researchers working in this topic.

Electric vehicles charging using photovoltaic: Status and technological review

This paper presents a combined phase-shift and frequency modulation scheme of a dual–active-bridge (DAB) ac–dc converter with power factor correction (PFC) to achieve zero voltage switching (ZVS) over the full range of the ac mains voltage. The DAB consists of a half bridge with bidirectional switches on the ac side and a full bridge on the dc side of the isolation transformer to accomplish single-stage power conversion. The modulation scheme is described by means of analytical formulas, which are used in an optimization procedure to determine the optimal control variables for minimum switch commutation currents. Furthermore, an ac current controller suitable for the proposed modulation scheme is described. A loss model and measurements on a 3.3-kW electric vehicle battery charger to connect to the 230  $\text{V}_\text{rms}$  / 50-Hz mains considering a battery voltage range of 280–420 V validate the theoretical analysis.

Combined Phase-Shift and Frequency Modulation of a Dual-Active-Bridge AC–DC Converter With PFC

This paper presents a single-phase bidirectional isolated AC-DC converter with Power Factor Correction (PFC) consisting of a half-bridge on the AC side and a full-bridge on the DC side to accomplish single-stage power conversion. The converter applies a new control scheme combining phase-shift and frequency modulation to achieve Zero-Voltage-Switching (ZVS) over the full range of the AC line voltage. Compared to the conventional boost PFC approach, the proposed converter eliminates high frequency harmonic distortions on the mains due to the inherently integrated LC input filter stage. The operating principle in AC-to-DC and DC-to-AC under ZVS conditions by means of analytical considerations are provided. Simulation results and a detailed loss model of a 3.3 kW electric vehicle battery charger to connect to the 230 V rms / 50 Hz mains considering a battery voltage range of 280 V to 430 V validate the theoretical analysis. The converter can also be used as a submodule in a Cascaded H-Bridge Converter (CHB) for medium or high voltage applications.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/06397479.pdf

Single-phase single-stage bidirectional isolated ZVS AC-DC converter with PFC

The paper presents a novel modeling approach of the power flow in a bidirectional dual active bridge DC-DC converter. By using basic superposition principles, the mathematical distinction of cases is avoided in the modeling process of high-frequency transformer currents for different types of modulation. The generalized model is used in an optimization of converter losses of a 3.3 kW electric vehicle battery charger with an input voltage of 400 V and a battery voltage range of 280 V to 420 V. Besides the commonly used control variables such as phase-shift and clamping intervals, also the variation of switching frequency is considered in the optimization process. The optimal modulation including frequency variation leads to an increase of converter efficiency up to 8.6% using IGBTs and 17.8% using MOSFETs in the most critical point compared to phase-shift modulation at fixed switching frequency.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/06869826.pdf

Generalized modeling and optimization of a bidirectional dual active bridge DC-DC converter including frequency variation

This paper presents the detailed analysis, optimisation and hardware realisation of an ultra-fast charging station with a split grid storage battery which enables to recharge electric vehicles (EVs) in less than 10 minutes. The station consists of a T-type AC-DC grid interface connected to the 400 V low voltage AC grid, a DC-DC dual active bridge (DAB) isolation stage, a stationary storage battery and a high power multi-phase interleaved buck converter for charging operation. The operating principle of the converter systems is briefly explained and the analytical loss models of the components are derived which are used in an optimisation procedure to evaluate the pareto front limits in terms of efficiency and power density for the DAB isolation stage and the high power charger. By introducing a split storage battery, beneficial conditions for the semiconductor devices are achieved so that the losses of the high power charger can be reduced by approximately 35 % with respect to a standard solution without a split as will be shown in the paper.

Ultra-fast charging station for electric vehicles with integrated split grid storage

/pdf/generalized-modeling-and-optimization-of-a-bidirectional-2ufr96id52.pdf

Felix Jauch

Papers

Combined Phase-Shift and Frequency Modulation of a Dual-Active-Bridge AC–DC Converter With PFC

Single-phase single-stage bidirectional isolated ZVS AC-DC converter with PFC

Generalized modeling and optimization of a bidirectional dual active bridge DC-DC converter including frequency variation

Ultra-fast charging station for electric vehicles with integrated split grid storage

Generalized Modeling and Optimization of a Bidirectional Dual Active Bridge DC-DC Converter Including Frequency Variation