Fang Luo

Bio: Fang Luo is an academic researcher from Stony Brook University. The author has contributed to research in topics: Power module & EMI. The author has an hindex of 25, co-authored 131 publications receiving 2141 citations. Previous affiliations of Fang Luo include Virginia Tech & Huazhong University of Science and Technology.

Dual active bridge based battery charger for plug-in hybrid electric vehicle with charging current containing low frequency ripple

Abstract: High power density is strongly preferable for the on-board battery charger of Plug-in Hybrid Electric Vehicle (PHEV). Wide band gap devices, such as Gallium Nitride HEMTs are being explored to push to higher switching frequency and reduce passive component size. In this case, the bulk DC link capacitor of AC-DC Power Factor Correction (PFC) stage, which is usually necessary to store ripple power of two times the line frequency in a DC current charging system, becomes a major barrier on power density. If low frequency ripple is allowed in the battery, the DC link capacitance can be significantly reduced. This paper focuses on the operation of a battery charging system, which is comprised of one Full Bridge (FB) AC-DC stage and one Dual Active Bridge (DAB) DC-DC stage, with charging current containing low frequency ripple at two times line frequency, designated as sinusoidal charging. DAB operation under sinusoidal charging is investigated. Two types of control schemes are proposed and implemented in an experimental prototype. It is proved that closed loop current control is the better. Full system test including both FB AC-DC stage and DAB DC-DC stage verified the concept of sinusoidal charging, which may lead to potentially very high power density battery charger for PHEV.

A review of SiC power module packaging: Layout, material system and integration

Abstract: Silicon-Carbide (SiC) devices with superior performance over traditional silicon power devices have become the prime candidates for future high-performance power electronics energy conversion. Traditional device packaging becomes a limiting factor in fully realizing the benefits offered by SiC power devices, and thus, improved and advanced packaging structures are required to bridge the gap between SiC devices and their applications. This paper provides a review of the state-of-art advanced module packaging technologies for SiC devices with the focuses on module layout, packaging material system, and module integration trend, and links these packaging advancements to their impacts on the SiC device performances. Through this review, the paper discusses main challenges and potential solutions for SiC modules, which is critical for future SiC applications.

Evaluation of the switching characteristics of a gallium-nitride transistor

Abstract: Gallium-nitride (GaN) technology for power conversion is maturing, with a growing need to evaluate the capabilities of GaN devices in high switching frequency and elevated ambient temperature operation. These capabilities may particularly benefit systems constrained by strict EMI standards, due to the possibility of significant size and weight reduction. An inductive load tester circuit has been developed for switching characterization of a GaN transistor (EPC1010) and a paired silicon diode (SBR10U200P5). Maximum measured switching speeds for hard switching turn-on and turn-off transitions were dv/dt (on) = 4 V/ns, di/dt (on) = 4.5 A/ns, and dv/dt (off) = 18 V/ns, di/dt (off) = 5 A/ns respectively. Total measured switching energy loss was Etot = 40 µJ under 100 V supply voltage and 15 A load current conditions, with little change with increase of transistor junction temperature from 25 °C to 100 °C. Zero-voltage switching reduced loss to only E tot = 6 µJ, thus enabling high switching frequency operation. As the switching pair of a silicon diode and an EPC1010 is not suitable in hard switching mode and high switching frequency operation due to high switching loss of the turn-on process, another tester was built. Here, two EPC1010 devices were used in a phase-leg configuration. The fastest switching speeds were dv/dt (on) = 21 V/ns, di/dt (on) = 9 A/ns, and dv/dt (off) = 20 V/ns, di/dt (off) = 2 A/ns respectively. Total measured switching energy loss was E tot = 11 µJ, under 100 V supply voltage and 15 A load current conditions.

Leakage Current Reduction in a Single-Phase Bidirectional AC–DC Full-Bridge Inverter

Abstract: The leakage current in grid-interface converter systems presents a considerable issue in regard to safety and efficiency. The full-bridge inverter is a well-accepted topology in single-phase power conversion applications. The high-frequency pulsewidth modulation (PWM) modulation schemes are normally applied to the full-bridge topology for smaller ac filter size, which, however, generates a high-frequency dc-side leakage current, resulting in an enormous negative impact on dc components, such as photovoltaic panels and energy storage elements. In this paper, a modified full-bridge inverter topology to reduce the dc-side leakage current as well as to mitigate the ac-side common-mode electromagnetic interference noise is presented. Several considerations are discussed, such as the PWM modulation and filter design. Compared to the other existing methods, the proposed solution provides a reliable performance for bidirectional operation, minimum additional components, low cost, and a simple design process.

Grid-Interface Bidirectional Converter for Residential DC Distribution Systems—Part 2: AC and DC Interface Design With Passive Components Minimization

Abstract: With the emerging installations of multitype renewable energy sources and energy storage elements, the dc electronic distribution systems in residential houses/buildings (dc nanogrid) are becoming an alternative future system solution, achieving a zero net-energy consumption and optimized power management. One of the critical components in such a dc system is the grid-interface bidirectional ac–dc power converter, namely the energy control center. Besides, the basic power conversion function, the system interface solution in grid-interface converter is important to successfully interconnect the ac and dc systems as well as fulfill the power quality and EMI regulation codes on both dc and ac sides. This paper presents a complete discussion of several aspects of system interface design for the grid-interface converter under both single-phase and three-phase system conditions. A passive plus active filter solution is proposed to accomplish the common-mode-related noises minimization as well as a dramatic reduction of the converter system volume.

DC Microgrids—Part II: A Review of Power Architectures, Applications, and Standardization Issues

Abstract: DC microgrids (MGs) have been gaining a continually increasing interest over the past couple of years both in academia and industry. The advantages of dc distribution when compared to its ac counterpart are well known. The most important ones include higher reliability and efficiency, simpler control and natural interface with renewable energy sources, and electronic loads and energy storage systems. With rapid emergence of these components in modern power systems, the importance of dc in today's society is gradually being brought to a whole new level. A broad class of traditional dc distribution applications, such as traction, telecom, vehicular, and distributed power systems can be classified under dc MG framework and ongoing development, and expansion of the field is largely influenced by concepts used over there. This paper aims first to shed light on the practical design aspects of dc MG technology concerning typical power hardware topologies and their suitability for different emerging smart grid applications. Then, an overview of the state of the art in dc MG protection and grounding is provided. Owing to the fact that there is no zero-current crossing, an arc that appears upon breaking dc current cannot be extinguished naturally, making the protection of dc MGs a challenging problem. In relation with this, a comprehensive overview of protection schemes, which discusses both design of practical protective devices and their integration into overall protection systems, is provided. Closely coupled with protection, conflicting grounding objectives, e.g., minimization of stray current and common-mode voltage, are explained and several practical solutions are presented. Also, standardization efforts for dc systems are addressed. Finally, concluding remarks and important future research directions are pointed out.

The 2018 GaN power electronics roadmap

Abstract: 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.

Review of Commercial GaN Power Devices and GaN-Based Converter Design Challenges

Abstract: Gallium nitride (GaN) power devices are an emerging technology that have only recently become available commercially. This new technology enables the design of converters at higher frequencies and efficiencies than those achievable with conventional Si devices. This paper reviews the characteristics and commercial status of both vertical and lateral GaN power devices, providing the background necessary to understand the significance of these recent developments. In addition, the challenges encountered in GaN-based converter design are considered, such as the consequences of faster switching on gate driver design and board layout. Other issues include the unique reverse conduction behavior, dynamic $R_{\mathrm {{ds}},\mathrm {{on}}}$ , breakdown mechanisms, thermal design, device availability, and reliability qualification. This review will help prepare the reader to effectively design GaN-based converters, as these devices become increasingly available on a commercial scale.