Center for Power Electronics Systems

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Zero-current transition PWM converters
(United States Patent and Trademark Office, 1996-01-23)
A zero-current transition pulse-width modulated (ZCT-PWM) d.c.-d.c. converter allows minority-carrier semiconductor devices such as, for example, bipolar junction transistors (BJTs), insulated gate bipolar transistors (IGBTs), MOSFET controlled thyristors (MCTs), and gate turn-off thyristors (GTOs), to be used as switches for high-power, high frequency applications. The ZCT-PWM converter comprises a shunt resonant branch inserted into a conventional PWM converter circuit. The resonant branch comprises a resonant inductor (Lr), a resonant capacitor (Cr), an auxiliary switch (S1), and an auxiliary diode (D1). The resonant branch is only active during a relatively short switching time in order to create a zero-current switch condition for the main pulse-modulating switch (S) without substantially increasing voltage or current stresses.
Center Program Snapshot (April 2009)
Center for Power Electronics Systems (Virginia Tech. Center for Power Electronics Systems, 2009-04)
With the widespread use of power electronics technology, the United States would be able to cut electrical energy consumption by 33 percent. The energy savings, by today’s measure, is equivalent to the total output of 840 fossil fuel-based generating plants. This would result in enormous economic, environmental and social benefits. The engineers of the Center for Power Electronics Systems (CPES) are working to make electric power processing more efficient and more exact in order to achieve these benefits. The effort requires close collaboration with industry and with researchers across universities and fields of endeavor. Electrification is considered the greatest engineering feat of the 20th century by the National Academy of Engineering. The dream of CPES engineers is to take electricity to the next step and develop power processing systems of the highest value to society.
Center Program Snapshot
Lee, Fred C.; Boroyevich, Dushan (Virginia Tech, 2009-04)
This book provides a comprehensive introduction to CPES research, education,and outreach.
CPES : 10-Year Progress Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2010-04)
A major strength of CPES is its ability to use a wealth of existing resources and industrial collaboration. Virginia Tech, the University of Wisconsin-Madison (UW), and Rensselaer Polytechnic Institute (RPI) are the nation’s leaders in power electronics and advanced power semiconductor materials and devices. These three universities have combined forces with North Carolina A&T State University (NCA&T) and the University of Puerto Rico-Mayagüez (UPRM), which are institutions with solid reputations in the quality of their undergraduate engineering programs as well as their power electronics and related research. Virginia Tech brings expertise in high-frequency power conversion devices and circuit technologies, power electronics packaging, and systems integration. The University of Wisconsin has expertise in industrial and utility-grade power conversion, electric machines and motor drives, and industrial controls. RPI’s expertise involves novel discrete power semiconductor materials, process techniques, power devices, and smart power ICs. North Carolina A&T contributes knowledge of nonlinear control, neural networks, and fuzzy logic-based intelligent control, and the University of Puerto Rico-Mayagüez has expertise in controls and electric machines. The resources and expertise of researchers from each of these institutions have contributed to the success of the Center. CPES industry members have been the critical key in our success. From the beginning, industry members have been enthusiastic and involved, helping shape goals and contributing to the management of the ERC. Since 1998, CPES research goals have evolved and the collaborations with industry and university researchers have strengthened. CPES succeeded in changing the technology of power electronics, while increasing knowledge and participation in the field. As we graduate from the NSF ERC program, we look forward to building on our global collaboration and changing the way electricity is used.
CPES Center Brochure (April 2011)
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2011-04)
The Center for Power Electronics Systems is a $4 million/year research center dedicated to improving electrical power processing and distribution that impact systems of all sizes –from battery-operated electronics to vehicles to regional and national electrical distribution systems. Our mission is to provide leadership through global collaborative research and education for creating electric processing systems of the highest value to society. CPES has a worldwide reputation for its research advances, work with industry to improve the entire field, and its many talented graduates. From 1998- 2008, CPES served as an Engineering Research Center (ERC) for the NSF. A collaboration of five universities and many industrial firms, the CPES ERC was the largest-ever collaboration of power electronics researchers. During the ERC period, CPES developed the IPEM, a standardized off-the-shelf module that has revolutionized power electronics. Today, we are building on that foundation so that power electronics can fulfill its promise and reduce energy use while helping electronics-based systems grow in capability.
CPES : Mini-Consortium Brochure
Center for Power Electronics Systems (Virginia Tech. Center for Power Electronics Systems, 2011-04)
The CPES mini-consortium model provides a unique mechanism for all participants in power electronics – including industry competitors – to pool efforts to address their common challenges and develop pre-competitive Advances. Companies and organizations join CPES as a Principal Plus Member and choose the mini-consortium option. Annual membership fees are $50,000. Research results generated within a miniconsortium are shared among its members, and intellectual properties developed under the CPES industry consortium are shared among all Principal-level members as described on the next page. The research and IP benefits are only part of what makes the mini-consortium effective. The distinctive feature of the model is discussion among all participants, which then shapes and guides research toward overcoming the major barriers in the field. Competitive plans and technologies are protected, yet participants can discuss their mutual technical problems. Miniconsortium interactions take place in the quarterly review meetings.
2012 CPES Annual Report
Center for Power Electronics Systems (Virginia Tech. Center for Power Electronics Systems, 2012)
The Center for Power Electronics Systems at Virginia Tech is a research center dedicated to improving electrical power processing and distribution that impact systems of all sizes – from battery – operated electronics to vehicles to regional and national electrical distribution systems. Our mission is to provide leadership through global collaborative research and education for creating advanced electric power processing systems of the highest value to society. CPES, with annual research expenditures about $4-5 million US dollars, has a worldwide reputation for its research advances, its work with industry, and its many talented graduates. From its background as an Engineering Research Center for the National Science Foundation during 1998 - 2008, CPES has continued to work towards making electric power processing more efficient and more exact in order to reduce energy consumption. Power electronics is the “enabling infrastructure technology” that promotes the conversion of electrical power from its raw form to the form needed by machines, motors and electronic equipment. Advances in power electronics can reduce power conversion loss and in turn increase energy efficiency of equipment and processes using electrical power. This results in increased industrial productivity and product quality. With widespread use of power electronics technology, the United States would be able to cut electrical energy consumption by 33 percent. This energy savings in the United States alone is estimated to be the equivalent of output from 840 fossil fuel based generating plants. This savings would result in enormous economic, environmental and social benefits.
2013 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2013)
The CPES industrial consortium is designed to cultivate connectivity among researchers in academia and industry, as well as create synergy within the network of industry members. The CPES industrial consortium offers: The best mechanism to stay abreast of technological developments in power electronics; The ideal forum for networking with leadingedge companies and top-notch researchers; The CPES connection provides the competitive edge to industry members via: Access to state-of-the-art facilities, faculty expertise, top-notch students; Leveraged research funding of over $4-10 million per year; Industry influence via Industry Advisory Board and research champions; Intellectual properties with early access for Principal Plus and Principal members via CPES IPPF (Intellectual Property Protection Fund); Technology transfer made possible via special access to the Center’s multi-disciplinary team of researchers, and resulting publications, presentations and intellectual properties; Continuing education opportunities via professional short courses offered at a significant discount. The CPES industrial consortium offers the ideal forum for networking with leading-edge companies and top-notch researchers and provides the best mechanism to stay abreast of technological developments in power electronics.
2014 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2014)
Over the past two decades, CPES has secured research funding from major industries, such as GE, Rolls-Royce, Boeing, Alstom, ABB, Toyota, Nissan, Raytheon, and MKS, as well as from government agencies including the NSF, DOE, DARPA, ONR, U.S. Army, and the U.S. Air Force, in research pursuing high-density system design. CPES has developed unique high-temperature packaging technology critical to the future powerelectronic industry. In the HDI mini-consortium, the goal of high power density will be pursued following two coupled paths, both leveraging the availability of wide-bandgap power semiconductor, as well as high-temperature passive components and ancillary functions. The switching frequency will be pushed as high as component technologies, thermal management, and reliability permit. At the same time, the maximum component temperatures will be pushed as high as component technologies, thermal management, and reliability permit. The emergence of wide‐bandgap semiconductors such as Silicon Carbide (SiC) and Gallium Nitride (GaN) makes it possible to realize power switches that operate at frequency beyond 5 MHz and temperature beyond 200° C. As the switching frequency increases, switching noise is shifted to higher frequency and can be filtered with small passive components, leading to improved power density. Higher operating temperatures enable increased power density and applications under harsh environments, such as military systems, transportation systems, and outdoor industrial and utility systems.
A diffusion-viscous analysis and experimental verification of defect formation in sintered silver bond-line
Xiao, Kewei; Ngo, Khai D. T.; Lu, Guo-Quan (Cambridge University Press, 2014-04-01)
The low-temperature joining technique (LTJT) by silver sintering is being implemented by major manufacturers of power electronic devices and modules for bonding power semiconductor chips. A common die-attach material used with LTJT is a silver paste consisting of silver powder (micrometer- or nanometer-sized particles) mixed in organic solvent and binder formulation. It is believed that the drying of the paste during the bonding process plays a critical role in determining the quality of the sintered bond-line. In this study, a model based on the diffusion of solvent molecules and viscous mechanics of the paste was introduced to determine the stress and strain states of the silver bond-line. A numerical simulation algorithm of the model was developed and coded in the C++ programming language. The numerical simulation allows determination of the time-dependent physical properties of the silver bond-line as the paste is being dried with a heating profile. The properties studied were solvent concentration, weight loss, shrinkage, stress, and strain. The stress is the cause of cracks in the bond-line and bond-line delamination. The simulated results were verified by experiments in which the formation of bond-line cracks and interface delamination was observed during the pressure-free drying of a die-attach nanosilver paste. The simulated results were consistent with our earlier experimental findings that the use of uniaxial pressure of a few mega-Pascals during the drying stage of a nanosilver paste was sufficient to produce high-quality sintered joints. The insight offered by this modeling study can be used to develop new paste formulations that enable pressure-free, low-temperature sintering of the die-attach material to significantly lower the cost of implementing the LTJT in manufacturing.
2015 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2015)
In its efforts to develop power processing systems to take electricity to the next step, CPES has developed research expertise encompassing five technology areas: (1) power conversion technologies and architectures; (2) power electronics components; (3) modeling and control; (4) EMI and power quality; (5) high density integration. These technology areas target applications that include: (1) Power management for information and communications technology; (2) Point-of-load conversion for power supplies; (3) Vehicular power conversion systems; (4) Renewable energy systems. In 2015, CPES sponsored research totaled approximately $2.2 million. The following abstracts provide a quick insight to the current research efforts.
2016 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2016)
In its effort to develop power processing systems to take electricity to the next step, CPES has cultivated research expertise encompassing five technology areas: (1) power conversion technologies and architectures; (2) power electronics components; (3) modeling and control; (4) EMI and power quality; and (5) high density integration. These technology areas target applications that include: (1) Power management for information and communications technology; (2) Point-of-load conversion for power supplies; (3) Vehicular power converter systems; and (4) High-power conversion systems. In 2016, CPES sponsored research totaled approximately $2.1 million. The following abstracts provide a quick insight to the current research efforts.
Structural Resemblance Between Droop Controllers and Phase-Locked Loops
Zhong, Qing-Chang; Boroyevich, Dushan (IEEE, 2016)
It is well known that droop control is fundamental to the operation of power systems and now the parallel operation of inverters, while phase-locked loops (PLLs) are widely adopted in modern electrical engineering. In this paper, it is shown at first that droop control and PLLs structurally resemble each other. This bridges the gap between the two communities working on droop control and PLLs. As a result, droop controllers and PLLs can be improved and further developed via adopting the advancements in the other field. This finding is then applied to operate the conventional droop controller for inverters with inductive output impedance to achieve the function of PLLs, without having a dedicated synchronization unit. Extensive experimental results are provided to validate the theoretical analysis.
Optimal trajectory control for LLC resonant converter for LED PWM dimming
(United States Patent and Trademark Office, 2016-03-01)
Pulse width modulation is provided for controlling a resonant power converter, particularly for dimming of light emitting diode arrays without loss of efficiency. Dynamic oscillation due to the beginning of a pulse width modulated pulse burst is limited by shortening of the first and/or last pulse of a pulse bust such that the first pulse of a subsequent pulse burst close to or to connect with a full load steady-state voltage/current trajectory of the power converter. Pulse shortening made be made substantially exact to virtually eliminate dynamic oscillation but substantial reduction in dynamic oscillation is provided if inexact or even performed randomly.
Optimal trajectory control for LLC resonant converter for soft start-up
(United States Patent and Trademark Office, 2016-04-19)
By setting switching instants of a switching circuit of a resonant power converter based on current in a resonant circuit reaching a current limit of a current limitation band, soft start-up of the power converter can be achieved to avoid or limit electrical stress with full control over a trade-off between time required to settle to a full load steady-state mode of operation and the amount of electrical stress permitted while soft start up switching frequency is automatically optimized.
Iaverage current mode (ACM) control for switching power converters
(United States Patent and Trademark Office, 2016-05-17)
Providing a fast current sensor direct feedback path to a modulator for controlling switching of a switched power converter in addition to an integrating feedback path which monitors average current for control of a modulator provides fast dynamic response consistent with system stability and average current mode control. Feedback of output voltage for voltage regulation can be combined with current information in the integrating feedback path to limit bandwidth of the voltage feedback signal.
Method and apparatus for driving a power device
(United States Patent and Trademark Office, 2016-12-27)
Aspects of the disclosure provide a circuit for driving a power switch. The circuit includes a first circuit configured to provide a charging current to charge a control terminal of the power switch, a second circuit configured to provide a discharging current to discharge the control terminal of the power switch, and a control circuit configured to provide control signals to the first circuit and the second circuit to activate/deactivate the first circuit and the second circuit. At least one of the charging current and the discharging current ramps from a first level to a second level at a rate.
2017 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2017)
In its effort to develop power processing systems to take electricity to the next step, CPES has cultivated research expertise encompassing five technology areas: (1) power conversion technologies and architectures; (2) power electronics components; (3) modeling and control; (4) EMI and power quality; and (5) high density integration. These technology areas target applications that include: (1) power management for information and communications technology; (2) point-of-load conversion for power supplies; (3) vehicular power converter systems; and (4) high-power conversion systems. In 2016, CPES sponsored research totaled approximately $2.4 million. The following abstracts provide a quick insight to the current research efforts.
Two-stage multichannel LED driver with CLL resonant circuit
(United States Patent and Trademark Office, 2017-01-10)
In a two-stage power converter providing voltage regulation in a first stage, zero voltage switching (ZVS) is provided in switches in an unregulated, constant frequency second stage of a two-stage power converter by an inductor of a CLL resonant circuit connected in parallel with both a series connection of an external inductor and a primary winding of one or more transformers connected in series and an output of the switching circuit so that the output capacitances of the switches can be charged and discharged, respectively, by current in the parallel-connected inductor and independently of current in the magnetizing inductance of the transformer. Therefore, the magnetizing inductance of the transformer can be made sufficiently large to balance currents delivered to respective loads as is particularly desirable for driving a plurality of unbalanced LED strings independently of the value of the parallel-connected inductor which is desirably small.
High frequency integrated point-of-load power converter with embedded inductor substrate
(United States Patent and Trademark Office, 2017-02-07)
A low profile power converter structure is provide wherein volume is reduced and power density is increased to approach 1 KW/in3 by at least one of forming an inductor as a body of magnetic material embedded in a substrate formed by a plurality of printed circuit board (PCB) lamina and forming inductor windings of PCB cladding and vias which may be of any desired number of turns and may include inversely coupled windings and which provide a lateral flux path, forming the body of magnetic material from high aspect ratio flakes of magnetic material which are aligned with the inductor magnetic field in an insulating organic binder and hot-pressed and providing a four-layer architecture comprising two layers of PCB lamina including the embedded body of magnetic material, a shield layer and an additional layer of PCB lamina, including cladding for supporting and connecting a switching circuit, a capacitor and the inductor.

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