Our group’s research is in the area of energy conversion systems, where we explore the design, control, and analysis of power electronics systems, and their use in achieving efficient and reliable energy conversion, generation, and use. Our current research areas are shaped by the emerging trends of new and increased electrified loads (e.g, transportation, data centers), renewable energy resources & grid storage, and space-constrained systems (e.g, smart phones, vehicles, medical devices, sensors, etc.). Common to these applications is the need for highly efficient electric power management, as well as overall small physical size, which demand solutions that greatly surpass that available through conventional means. Our ongoing research spans from power levels of hundreds of kilowatts for grid energy storage and transportation, to low-voltage integrated circuits that process power down to a few milliwatts. We seek out challenges where innovative solutions can have great societal impact. As outlined below, we strive to achieve improved energy conversion through innovations in fundamentally better power electronics systems, as measured by efficiency, size, cost, and reliability. Moreover, we seek to improve performance in a wide variety of systems (e.g., data centers, electric vehicles, renewable energy, consumer electronics) through innovative applications of electronics. Finally, our research is highly interdisciplinary, where we collaborate with researchers in a number of related areas, such as: circuits, electric machines, cloud computing, mechanical engineering, controls, and material science at Illinois as well as numerous other institutions (e.g., Stanford, University of Arkansas, Howard University, MIT, KTH Royal Institute of Technology).
New Power Electronics Architectures with Extreme Efficiency and Power Density
Much of our research focuses on the development of fundamentally new power electronics architectures that can achieve both extreme efficiency and miniaturization, with greatly improved performance over the state-of-the-art. To achieve this goal, we seek to leverage recent advances in semiconductor devices such as GaN transistors, the increased computational power available for digital control of power converters, and the performance enhancements made possible by CMOS integration and advanced packaging to develop power conversion systems with record-breaking power density and efficiency.
Hybrid Switched-Capacitor Converters
Hybrid Switched-Capacitor Converter with 3D Printed Heatsink
We are presently exploring power converter architectures that leverage the greatly superior (100-1000x) energy density of capacitors compared to inductors and transformers. However, conventional methods for utilizing capacitors alone for power conversion (i.e., switched-capacitor converters) suffer from poor efficiency and regulation, which to date has limited their widespread adoption outside of certain niche areas. Over the last several years, we have been investigating a new class of hybrid power converters, which combine the best features of capacitive and inductive power conversion to simultaneously achieve both high efficiency and power density. We have demonstrated a theoretical framework for analyzing such converter topologies [1], which has already seen widespread use by other research groups. Recently, we expanded on this work to develop advanced control techniques [2] which enable a wider range of converters to benefit from this hybrid technology, culminating in our most recent prototype which achieved a record-breaking power density of 1011 W/in^3, approximately 5x higher than comparable recently reported best-in-class research prototypes. Our ongoing research explores the modeling, control, and design of high-performance hybrid switched-capacitor power converters, with applications in on-chip CMOS power management, compact high-voltage generation, auxiliary power management for electric vehicles, and ultra-high efficient power converters for consumer electronics (e.g., USB Type C chargers).
Multi-level Converters
2 kW 7-Level Flying Capacitor Inverter with GaN Transistors
We are investigating new multi-level converters for dc-ac, ac-dc, and dc-dc power conversion. By combining new circuit topologies, digital control methods and new semiconductor devices (such as GaN and SiC transistors), we are attempting to push the frontier in efficiency and size for inverters and rectifiers in a wide range of applications, from solar inverters and electric aircrafts to server power supplies. To date, we have demonstrated the most compact flying capacitor multi-level inverter in the field [3], and are currently developing prototypes with the goal of greatly surpassing the performance of our initial prototype. Some applications that we are applying these converters include: inverters for renewable energy generation, bidirectional converters for grid storage, compact motor drives for electric vehicles.
Partial Power Processing
Our group is one of the leaders in the field of partial power processing converters (also referred to as diffential power processing). In these types of converters, only a fraction of the overall system power is processed by power converters, where the rest of is transferred without loss through the inherent system architecture. Initially we successfully demonstrated this concept in solar photovoltaic systems [4] and we have recently demonstrated its effectiveness in data center power delivery, with the highest ever reported data center power delivery of 99.8% [5]. We are currently investigating partial power processing systems for solar photovoltaic systems, data center power delivery, battery management, and thermoelectric power generation.
Applications of Innovative Power Electronics Systems
Panel embedded power electronics to increase energy capture and diagnostics capabilities
In addition to the development of fundamentally new techniques for converting electrical energy, a strong focus of our research program is the application of power electronics in a variety of areas related to energy. Below, we briefly list some areas where we are pursuing research.
Photovoltaic Energy Systems
Over the last several years, our group has explored techniques for increasing the energy output of solar
PV systems through PV panel embedded power converters, and ultra-high efficiency inverters for connecting solar panels to the grid. We recently developed low-cost, high-efficiency dc-dc converters that fit into an existing junction box of off- the-shelf PV panels, and worked with our industry partner SolarBridge Technologies to verify the concept at scale. Our solution combined a custom low-power control method [6] which achieved a 10x improvement in accuracy/speed over conventional techniques with a new system architecture [7] that enabled up to 30% increase in energy capture, and greatly reduced standby/control losses compared to state-of-the-art.
Extreme Efficiency Data Center Power Delivery
Datacenter represent one of the fastest growing electrical loads on the grid today, and already consumes several percent of the U.S. electricity. In today’s systems, a significant portion (up to 30%) of the energy in datacenters is wasted in various power conversion steps, as the electric power flows from the high voltage AC input to the low voltage DC supply of the servers. We are addressing this challenge through the development of new power delivery architectures with extreme efficiency. To date we have demonstrated 99.8% efficiency for a small-scale prototype, and are currently scaling this up to larger system. We are also investigation practical considerations such as software and hardware integration, and hot-swapping. This work is supported by Google, Texas Instruments, and the National Science Foundation.
Electric Vehicles
104 W dc-dc step-down converter, suitable for consumer electronics applications.
The trend of transportation electrification is only in its infancy. Thanks to the superior efficiency, performance, and reliability of electric drive systems, vehicles ranging from personal cars and construction vehicles, to ships and airplanes are seeing an ever increasing rate of electrification. Our research focuses on accelerating this trend, by developing more efficient, more compact, and more reliable power electronic systems for electric vehicles. Our research here spans from battery management and chargers to high density motor drive systems (inverters) for vehicles (cars, off-highway vehicles, and airplanes). We work closely with our collaborators in electric machines and advanced thermal management to achieve system-level performance improvements.
Consumer Products
Power converters for consumer products consume a large portion of the electricity generated in the world. Products ranging from computers, laptops and smartphone chargers to flatscreen TVs and appliances, most modern products require
several power converters to operate. Our goal is to improve the efficiency and reduce the cost of these systems through innovations in circuits, control, and packaging. Our work here spans from chip-scale power converters in smartphones to UBS Type C charger for laptops, and larger power converter up to several kW.