Power electronics is an area of great need in many industry sectors from performance and mobile computing (data centers and cell phones) to renewable energy and electrified transportation. However it is an often overlooked area of study and is increasingly a bottleneck in the performance and cost of many systems. Power electronics is a surprisingly interdisciplinary field - it requires the knowledge and practice of analog and digital circuits (embedded system design), control theory, and signal processing. It also relies heavily on basic physics (E&M and semiconductor theory), material science, and a deep understanding of application requirements and the underlying modalities of energy generation, storage, distribution, and usage.
Our research combines solid-state circuit design (integrated circuits), embedded systems, and power electronics to address the growing needs of a variety of applications. These include photovoltaics, battery management for electric vehicles, low-voltage power delivery for portable electronics, and wireless power delivery. A main focus of our work is on increasing the power-density (or more generally reducing the size and cost) of power electronic circuits, while also maintaining high efficiency (low power loss) and meeting a variety of system specifications.This is important for portable electronics (say, your cell phone) as power electronic components are growing to dominate the overall board area and form factor. It is important for a variety of other applications (renewable energy and automotive) which are very cost sensitive, and (yes) increasingly sensitive to size and weight.
The coming decades will be very exciting in power electronics. There are a number of transformational advances underway in active devices, passive components, and underlying electronics integration that are positioned to revolutionize the way circuits are designed, as well as their achievable levels of integration and performance. These include the growing pervasiveness of wide bandgap semiconductor devices and ongoing exponential cost and performance scaling of silicon integrated circuits. The roadmap for high-density, integrated passive components (inductors and capacitors) is increasingly promising.
Our research is based on the premise that capacitors have historically been underutilized as core components in power electronic circuits. We work on new directions in switched capacitor dc-dc converters that can be resonated, soft-charged, or otherwise hybridized with (very small) inductors. Our contributions in this area have included integrated circuit implementations that achieve very high power density by shrinking or integrating key passive components, and operating at very high frequencies. This has required innovations in the circuit architecture, operating modes, and key circuit blocks such as level shifters, gate drivers, analog instrumentation, control and regulation, and digital signal processing. We have also worked on many application-specific examples including photovoltaics and battery management. Recent work has also completed a systematic comparison of a variety of common SC architectures in terms of active and passive component utilization, and other considerations such as control and regulation, balancing flying capacitor voltage states, the use of multiphase interleaving. Overall, we tend to approach electronics as a platform that can be used to address systemic limitations or application challenges, rather than as an end in itself.
A good overview of the hybrid-resonant switched capacitor space (kind of a review paper and a general perspective from our group): Pathways to mm-scale DC-DC converters: Trends, opportunities, and limitations, CICC 2018.
This paper provides a comparison framework (and relatively straightforward figure of merit for arbitrary dc-dc converter topologies). Aspects such as losses in magnetic components are discussed: Optimization and comparison of hybrid-resonant switched capacitor DC-DC converter topologies, COMPEL 2017.
This paper is a good example of a highly-integrated hybrid SC DC-DC converter. Details such as a startup (precharge) circuit and autotuning of the zero-current or zero-voltage switching state are included. A Highly-Integrated Series-Parallel Switched-Capacitor Converter with 12-Volt-Input and Quasi-Resonant Voltage-Mode Regulation, JESTPE 2018.
Integrated Power Electronics
High-density DC-DC converters
Theory, Control and Modelling
Hybrid Switched Capacitor Implementation
Kesarwani: [2015a], [2015b], [Rentmeister '16]
- Multiphase interleaving and bypass capacitance allocation for resonant switched capacitor converters: [Schaef '15], [Rentmeister '17]
- Flying capacitor multilevel (FCML) converters - voltage balance on flying capacitors and multilevel operation: [Kesarwani '15], [Rentmeister '17]
- Optimized topology comparison - Which SC topology is best when operated in a resonant or soft-charging mode? [Kiani '17]
- Multilevel VR - vertically stacked digital voltage domains with efficient power management hardware to regulate voltage levels: [Schaef '16], [Schaef '15]