CPES Power Management Consortium - with Extended Scope of Work

CPES Power Management Consortium - with Extended Scope of Work 1. Objectives Power Management Consortium (PMC) is an outgrowth of the VRM mini-consortium initiated in 1997. The goal is to extend its research scope with a focus on developing pre-competitive technologies in the areas of power management for distributed power system architectures, EMI/EMC, power quality, AC/DC converters, DC/DC converters, POL converters in such applications as powering microprocessors, tablet, notebook, desktop, server, data center, networking products, telecom equipment, solid state lighting and other industrial and consumer electronic applications. 2. Scope of Work The scope of work is highlighted in the following. For detailed information, please refer to the PMC prospectus at: <http://www.cpes.vt.edu/public_files/pmc_prospectus_march2013.pdf>. High performance VRM/POL converters High frequency magnetics characterization and design High frequency modeling Digital control High efficiency power architectures for laptops, desktops and servers EMI Solid state lighting Power management for PV system Power management for battery system The scope of work remains essentially the same as before. With the advent of recent wideband-gap power devices such as gallium-nitride (GaN) devices and silicon carbide (SiC) devices, significant emphasis will be placed on the development of high-efficiency and highpower density switch-mode power supplies. This effort will be highly leveraged with the recent DOE award, Next Generation Power Electronics Manufacturing Innovation Institute (NGPEMII). CPES is in partnership with this multi-industry, multi-university collaborative program for a period of 5 years, where CPES Director Fred C. Lee serves as the Power Electronics Thrust Leader. Our role is to work with the wide-band-gap (WBG) manufacturing industry to explore the potential applications and impact of GaN and SiC devices in power conversion technologies. The increasing emphasis on WBG-related activities is to bring more synergy between NGPEMII and the CPES mini-consortium programs, namely Power Management Consortium (PMC), High Density Integration (HDI), and Renewable Energy and Nanogrids (REN). While the major GaN research activities will be placed within PMC, SiC is targeted at higher power applications and will be addressed with greater interest in the REN mini-consortium. 1

In the proposed GaN-based research in PMC, we will use two testbeds to demonstrate the benefits of GaN-based power converters: (a) High-frequency adapter with 30-40W/in 3 power density and above 92% efficiency (b) High-frequency Off-Line Distributed Power Systems with 200-300W/in 3 power density and above 96% efficiency The following description pertains to the GaN-based research to be conducted within PMC. 3. The State-of-The-Art Power Supplies Industry According to U.S. Electric Power Research Institute, power electronics solutions can save 1/3 of the world s electrical power consumption. However, the full potential of power electronics has not yet been realized due to its high costs and poor reliability resulting from the current practice of using custom-designed, non-standard components and labor-intensive manufacturing processes. In the 1980s, power electronics was considered to be a core enabling technology for all of the major corporations in U.S. In the 1990s, major corporations adopted an outsourcing strategy and spun off their power electronics divisions. What had been a captive market was transformed into a merchant market. Fewer resources were available to devote to technical advancements in power electronics. Consequently, innovative solutions were scarce, and products became commoditized and cost driven. Today, most of the industry is focused on the bottom line and little is spent on R&D, with resources mostly spent on development rather than research. It is clear that the next-generation power electronics technologies can only be defined and developed with a longer-term vision and effort. It is our mission to lead this effort within PMC, with your support and shared vision. 4. A Trend Towards More Distributed Power Systems With the ever-increasing current consumption and clock frequency, today s microprocessors are operating at very low voltages and continuously switching between the sleep-mode and wake-up mode at frequencies of up to several MHz in order to conserve energy. Under the support of the National Science Foundation Engineering Research Center (NSF ERC), together with 25 industry corporations, Fred Lee and his team [1] have proposed and developed a multiphase voltage regulator (VR) module as the point-of-load (POL) converters for new generations of Intel Pentium microprocessors. A total of 25 U.S. patented technologies have been developed over the past 15 years, encompassing power delivery architecture, modularity and scalability, control and sensing, current sharing, integrated magnetics, advanced packaging, and integration technologies. Today, every PC and server microprocessor in the world is powered with this multi-phase VR. These technologies have been further extended to high-performance graphical 2

processors, server chipset and memory devices, networks, telecommunications, and all forms of mobile electronics. Recently, CPES-PMC demonstrated a series of 3D-integrated POL converters using GaN devices [2-4]. Although it is questionable that low-voltage GaN can compete with low-voltage silicon MOSFET at low voltage, these exercises were set to demonstrate the benefits of higher frequency operation and its ability to reduce the volume of magnetics. At 2-5 MHz, the magnetic component can be readily integrated into PCB or other forms of substrate. These prototype converters can achieve high efficiency (~90%) at a much higher power density (1000W/in 3 ) than today s industry practice, as shown in Fig. 1. It is envisioned that similar impact can be achieved for front-end power processor with high-voltage GaN devices. (a) Discrete 4 phase VR products with 100W/in 3 power density (b) Integrated 4 phase GaN based VR with 1000W/in 3 power density and 90% efficiency Figure 1. Comparison between discrete VR products and integrated GaN based VR While POL technologies are rapidly advancing, the front-end converter, at the present time, is still a custom-designed product using discrete power semiconductor devices and bulk passive components. The operating frequency of the front-end converters is still limited to relatively low switching frequency, around 50-100 khz. Emerging GaN devices [5] have enabled a 10X increase in switching frequency [5-18]. CPES- PMC team has developed a 48V/12V DCX [6] and 400V/12V DCX [7] using GaN devices, operating at 1.6MHz and 1MHz, respectively as shown in Fig. 2. These two prototypes have demonstrated 900 W/in 3 @ 325W for 48V/12V DCX and 700 W/in 3 @ 1kW level for 400V/12V DCX. Furthermore, a bridgeless, totem-pole boost was developed, operating at 3

1MHz while achieving greater than 99% efficiency [14]. We believe that this high-frequency design will also gain significant size reduction in the EMI filter. Efficiency 0.98 0.97 0.96 0.95 0.94 0.93 0.92 0.91 0.9 0.89 0.88 0 5 10 15 20 25 30 35 40 45 Output Current (Io) (a) 48V to 12V operating at 1.6 MHz with 900W/in 3 power density (b) 400V to 12V operating at 1MHz with 700W/in 3 power density Figure 2. Prototypes of LLC resonant converter based DC/DC transformer (DCX) With guarded optimism, we believe it is reasonable to expect that the power density of the frontend converter unit can be made with dramatically increased power density, from 30-50W/in 3 today to 300-500W/in 3 in the future, while achieving an improved efficiency greater than 96%. Furthermore, with additional efforts to perfect this design process, it is envisioned that front-end power processing would be fully modularized in standard building blocks at low cost, as shown in Fig. 3. 4

Figure 3. DPS based on simple building blocks 5. Technology Demonstrations In the proposed effort, we will use two testbeds to demonstrate the benefit of DPS with GaNbased building blocks. These two testbeds are chosen for their potential economic impact. (a) High Density High Efficiency Adapter An adapter is highly driven by efficiency and power density for all forms of portable electronics. An adapter below 65W power level is chosen for the demonstration for its potential economic impact, with a wide range of applications covering a large section of mobile devices, including tablet, notebook, and many other portable electronics equipment. Today, most of the adapters are only operating at a relatively low frequency (<100 khz), with state-of-the-art efficiency up to 91.5%. However, the low-frequency operation limits the adapter power density at 8-11W/in 3. CPES-PMC team will develop a 65W proof-of-concept prototype adapter with GaN devices targeted at an operating frequency above 500 khz. It is anticipated that we will gain a 3-4X size reduction to achieve 30-40W/in 3 in power density with an efficiency of 92%. A possible alternative is to improve the efficiency to 94%, together with a 2X improvement in power density, depending on which is more appealing in the marketplace. In this project, we will collaborate with Transphorm to develop a GaN with targeted design for this application. (b) High Density Off Line Distributed Power Systems In this task, a 1kW data server power system will be demonstrated with GaN-based front-end converters including an EMI filter, a two-phase interleaved totem-pole bridgeless PFCs, and DCX, operating at 1 MHz to achieve 200-300W/in 3 power density and above 96% efficiency. The state-of-the-art industry product will be used as a benchmark to demonstrate efficiency and power density improvements. The chosen platform is sufficiently general and can be used in all 5

forms of switch-mode power supplies with applications ranging from computer, telecommunication, data centers, mobile electronics devices, and industrial and consumer electronics products. In this project, the PMC team will focus on the following aspects: 1) High-frequency driving circuit with noise immunity to high dv/dt and di/dt for both cascode and enhancement-mode GaN; 2) Evaluation of 600V GaN devices switching losses distribution under hard-switching and soft-switching conditions; 3) Investigation of various PWM and resonant soft-switching topologies not only for switching-loss reduction, but also for minimization of noises and stresses created when circuit parasitics interact with high dv/dt and high di/dt; 4) High-frequency GaN module packaging design with special attention on device packaging and circuit layout to minimize parasitics, including quantification of the effect of parasitics detrimental to switching performances; 5) Characterization of candidate high frequency (1-5MHz) magnetic materials for PFC inductor and DC/DC stage transformer; 6) Innovative magnetics design with preference for high-density, low-profile PCB winding design, if deemed suitable; inductor and transformer design with possibility to reduce loss at light load; distributed magnetic such as matrix transformer, with reduced winding losses and transformer leakage inductance; inverse coupled inductors for multi-phase PFC. Because of high-switching frequencies, both conducted and radiated EMI become more severe moving into the more highly sensitive frequencies bands. Hence, filter design and layout become a primary focus. A full EMI analysis will be performed through simulation and design targets set for the filters, etc. A topology study will be performed inclusive of packaging effects. Results will be used for a centralized EMI filter development. 6. Broader Impact Successful demonstration of GaN devices for the chosen applications will lead to widespread use of GaN devices to replace the predominant Si MOSFET devices for all forms of switchmode power supplies, including but not limited to computer, telecommunication, network products, PV inverters, battery chargers, and industry and consumer electronics. This project is aimed at the development of standardized modular building blocks, instead of custom-designed solutions suitable only for specific applications. This paradigm shift is accompanied by significant improvements in efficiency, power density and cost. Furthermore, the design and fabrication of a power conversion system with GaN-based modules would be aimed at the ease of manufacturing for volume and with less labor content in the assembly process. 6

References [1] X. Zhou, P. L. Wong, P. Xu, F.C. Lee and A.Q. Huang, Investigation of Candidate VRM Topologies for Future Microprocessors, IEEE Transactions on Power Electronics, Vol. 15, No. 6, Nov 2000, pp. 1172-1182. [2] Fred C. Lee, Qiang Li, Overview of Three-Dimension Integration for Point-of-Load Converters IEEE 28th Applied Power Electronics Conference, March. 2013. [3] S. Ji, D. Reusch, and F. C. Lee, High Frequency High Power Density 3D Integrated Gallium Nitride-Based Point of Load Module Design, IEEE Transactions on Power Electronics, vol. 28, no. 9, pp.4216-4226, September 2013. [4] Yipeng Su, Qiang Li, Fred C. Lee, Design and Evaluation of a High-Frequency LTCC Inductor Substrate for a Three-Dimensional Integrated DC/DC Converter, Special Issue: "Power Supply on Chip," IEEE Transactions on Power Electronics, September 2013, Volume 28, No. 9, pp. 4354-4364. [5] U. K. Mishra, P. Parikh, and Y. Wu, AlGaN/GaN HEMTs an overview of device operation and applications, proc. of the IEEE, vol. 90, no. 6, pp.1022-1031, Jun. 2002. [6] David Reusch, "High Frequency, High Power Density Integrated Point of Load and Bus Converters Ph.D. Dissertation, Virginia Tech, April 16, 2012. [7] Daocheng Huang, Shu Ji, Fred C. Lee, Matrix Transformer for LLC Resonant Converters, Applied Power Electronics Conference, 2013. [8] Xiucheng Huang; Zhengyang Liu; Qiang Li; Lee, F.C., "Evaluation and Application of 600 V GaN HEMT in Cascode Structure," IEEE Transactions on Power Electronics, vol.29, no.5, pp.2453,2461, May 2014. [9] Xiucheng Huang; Qiang Li; Zhengyang Liu; Lee, F.C., "Analytical Loss Model of High Voltage GaN HEMT in Cascode Configuration," IEEE Transactions on Power Electronics, vol.29, no.5, pp.2208,2219, May 2014 [10] Zhengyang Liu; Xiucheng Huang; Lee, F.C.; Qiang Li, "Package Parasitic Inductance Extraction and Simulation Model Development for the High-Voltage Cascode GaN HEMT," IEEE Transactions on Power Electronics, vol.29, no.4, pp.1977,1985, April 2014 [11] Liu, Zhengyang; Huang, Xiucheng; Zhang, Wenli; Lee, Fred C.; Li, Qiang, "Evaluation of high-voltage cascode GaN HEMT in different packages," Applied Power Electronics Conference and Exposition (APEC), 2014 Twenty-Ninth Annual IEEE, vol., no., pp.168,173, 16-20 March 2014. [12] Xiucheng Huang, Fred. C. Lee, Qiang Li, Weijing Du, High Frequency High Efficiency GaN Based Interleaved CRM Bi-directional Buck/Boost Converter with Coupled Inductor, CPES Conference 2014. 7

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