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

Electric Vehicle Charging Infrastructure: From Grid to Battery

The fast development of electric vehicles (EVs) provides significant opportunities to further utilize clean energies in the automotive. On-board chargers (OBCs) are widely used in EVs because of their simple installation and low cost. Limited space in the vehicle and short charging time require an OBC to be power-dense and highly efficient. Moreover, the possibility for EVs to deliver power back to the grid has increased the interest in bidirectional power flow solutions in the automotive market. This paper presents a comprehensive overview and investigation on the state-of-the-art solutions of bidirectional OBCs. It reviews the current status, including architectures and configurations, smart operation modes, industry standards, major components, and commercially available products. A detailed overview of the promising topologies for bidirectional OBCs, including two-stage and single-stage structures, is provided. Future trends and challenges for topologies, wide bandgap technologies, thermal management, system integration, and wireless charging systems are also discussed in this paper.

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A Review of Bidirectional On-Board Chargers for Electric Vehicles

2D group-III nitride materials have shown a great promise for applications in optoelectronic devices thanks to their thickness-dependent properties. However, the epitaxial growth of 2D group-III nitrides remains a challenge. In this work, epitaxial growth of 2D GaN with well-controlled lattice structures and bandgaps is achieved by plasma-enhanced metal organic chemical vapor deposition via effective regulation of plasma energy and growth temperature. The structure of graphene/2D GaN/Si heterostructures is carefully investigated by high-resolution transmission electron microscopy. The formation mechanism of the 2D GaN layer is clearly clarified by theoretical calculations. Furthermore, a bandgap for 2D GaN ranging from ≈4.18 to ≈4.65 eV varying with the numbers of layers is theoretically calculated and experimentally confirmed. 2D GaN with well-controlled lattice structure and bandgap holds great potential for the development of deep ultraviolet light-emitting diodes, energy conversion devices, etc.

Lattice Structure and Bandgap Control of 2D GaN Grown on Graphene/Si Heterostructures

Subject herein is a battery charging apparatus and a method that includes the inverter output danreul designed to be connected to the power supply network and are designed to be connected to rectifier input terminals and the battery. The apparatus includes an average means according to the current to the maximum current supplied by the power supply network and to control so calculated according to the maximum voltage for larger coefficient than a ratio between battery voltage rectified by the input current value obtained from the input end.

Fast charging device for an electric vehicle

A unique three-step short-circuit protection method is proposed for the 650-V enhancement mode (E-mode) gallium nitride high-electron mobility transistor (GaN HEMT). This method can quickly detect the short-circuit event, reduce gate voltage to enhance the device short-circuit capability, and turn off the device under fault after confirmation. Experimental results prove that with this method, the short-circuit fault detection time for E-mode GaN HEMT is shortened from 2  μ s to several tens of nanoseconds, and the device can be successfully protected from fatal failure under high dc bus voltage without mistriggering.

A Reliable Ultrafast Short-Circuit Protection Method for E-Mode GaN HEMT

With offline single-phase power supplies moving toward the megahertz switching frequency range, the converter's bus capacitor becomes the bottleneck of further improvement of power density. Partial constant power operation is effective in reducing the bus capacitance and capacitor current stress for low-power applications. However, its impact on circuit design and operation design has not been studied thoroughly. With the developed circuit operation and loss model, this paper presents design considerations and power loss analysis of megahertz ac/dc converters in partial constant power operation. An adaptive constant power control is also proposed, based on the developed models, to improve the light-load efficiency and power factor. A 65 W, megahertz critical conduction mode GaN-based ac/dc converter prototype has been developed to validate the analysis and circuit operation method. Compared with power factor correction (PFC) operation, partial constant power control exhibits an efficiency drop of less than 1%. However, a 50% reduction of bus capacitance can be realized. With the proposed adaptive constant power control, the light-load efficiency and power factor can be improved to be a level similar to the PFC operation. This paper ends with a discussion of the possibility of extending the proposed operation method to higher power applications.

Adaptive Constant Power Control of MHz GaN-Based AC/DC Converters for Low Power Applications

Electric vehicle (EV) chargers are traditionally isolated from the grid. Non-isolated chargers have great potential as they enable higher power density at lower cost. Integrated chargers have the potential to utilize existing onboard, high power-rated electronic components for Level 3 charging. Four possible non-isolated integrated charger topologies based on permanent magnet synchronous machine (PMSM) are introduced at the beginning of this paper. Then, the issue of common mode (CM) leakage current through the on-board filters is identified and analyzed. It is found that the leakage current could rise to dangerous levels and cause potential electric shocks to users. The negative influence and safety risks from the leakage current for different grounding systems are also discussed. Experimental results are presented to validate the leakage current analysis. Finally, possible mitigation techniques of the leakage current are discussed.

Leakage Current Issue of Non-Isolated Integrated Chargers for Electric Vehicles

With off-line power supplies moving towards MHz switching frequency range, the converter's bus capacitor becomes the bottleneck of further improvement of power density. Partial constant power operation is effective in reducing the bus capacitance and capacitor current stress for low power applications. However, its impact on circuit operation and circuit design have not been studied thoroughly. With the developed circuit operation and loss model, this paper presents design considerations and power loss analysis of MHz AC/DC converters in partial constant power operation. Based on the models, an adaptive constant power control is also proposed to improve the light load efliciency. A 70 W, MHz CrM GaN-based AC/DC converter prototype has been prototyped to validate the analysis and circuit operation method. Compared with PFC operation, partial constant power control exhibits an efficiency drop of less than 0.5 %, but a 50 % reduction of bus capacitance is realized. With the proposed adaptive constant power control, the light load efficiency can be improved by roughly 0.5 %, which is similar as PFC operation. At the end, the possibility of extending the proposed operation method to higher power applications is also discussed.

Adaptive constant power control and power loss analysis of a MHz GaN-based AC/DC converter for low power applications

Wide bandgap (WBG) devices allow power factor correction (PFC) circuits to operate at megahertz (MHz), which improves power density. In low-power applications, critical conduction mode (CrM) boost PFC circuits are widely used due to its simple structure and minimized turn-on loss. Compared with the kilohertz (kHz) operation, MHz PFC in CrM yields larger inductor valley current during the zero voltage or valley switching turn-on, and significant grid current zero-crossing distortion, both of which are not considered in conventional PFC behavioral models. As a result, the conventional PFC design tool shows substantial inaccuracy in the estimation of switching frequency, inductor current envelopes, and power loss. This article analyzes these issues and proposes an improved power loss model to aid the design of MHz CrM PFC. Experimental results are presented to validate the accuracy.

Power Loss Model for GaN-Based MHz Critical Conduction Mode Power Factor Correction Circuits

This paper presents a comprehensive analysis of the generation mechanism and suppression methods of common-mode (CM) touch current when employing semiconductor-based galvanic isolation (SGI). SGI achieves galvanic isolation by utilizing semiconductor switches to deliver differential-mode (DM) power during their on states while sustaining CM isolation voltage during their off states. In SGI converters, the touch current (TC) is generated as the switch output capacitance is charged by the CM voltage during each turn- on transient. The TC rises as the switching frequency increases, which limits the system power density. This process is modeled by the proposed high-frequency pulse current model and the low-frequency equivalent resistance-based average model. Passive TC suppression approaches are reviewed, and an active TC compensation method has been proposed. A 2-kW EV battery charger with a GaN-based Totem-pole power factor correction stage and an SGI-based dc/dc stage has been built and tested. The touch current has been effectively reduced by 27 dB. It allows the converter to operate at a higher switching frequency to achieve higher power density while meeting the safety standards’ touch current requirement.

Yue Zhang

Papers

Adaptive Constant Power Control of MHz GaN-Based AC/DC Converters for Low Power Applications

Leakage Current Issue of Non-Isolated Integrated Chargers for Electric Vehicles

Adaptive constant power control and power loss analysis of a MHz GaN-based AC/DC converter for low power applications

Power Loss Model for GaN-Based MHz Critical Conduction Mode Power Factor Correction Circuits

Semiconductor-Based Galvanic Isolation: Touch Current Suppression