scispace - formally typeset
Search or ask a question
Author

Zichao Ye

Bio: Zichao Ye is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Switched capacitor & Capacitor. The author has an hindex of 14, co-authored 27 publications receiving 654 citations. Previous affiliations of Zichao Ye include University of Illinois at Urbana–Champaign.

Papers
More filters
Journal ArticleDOI
TL;DR: In this article, the authors present a 2-kW, 60-Hz, 450-V -to-240-V power inverter, designed and tested subject to the specifications of the Google/IEEE Little Box Challenge, which achieves a high power density of 216 W/in $3$ and a peak overall efficiency of 97.6%, while meeting the constraints including input current ripple, load transient, thermal, and FCC Class B EMC specifications.
Abstract: High-efficiency and compact single-phase inverters are desirable in many applications such as solar energy harvesting and electric vehicle chargers. This paper presents a 2-kW, 60-Hz, 450-V $ _{\text{DC}}$ -to-240-V $_{\text{AC}}$ power inverter, designed and tested subject to the specifications of the Google/IEEE Little Box Challenge. The inverter features a seven-level flying capacitor multilevel converter, with low-voltage GaN switches operating at 120 kHz. The inverter also includes an active buffer for twice-line-frequency power pulsation decoupling, which reduces the required capacitance by a factor of 8 compared to conventional passive decoupling capacitors, while maintaining an efficiency above 99%. The inverter prototype is a self-contained box that achieves a high power density of 216 W/in $^3$ and a peak overall efficiency of 97.6%, while meeting the constraints including input current ripple, load transient, thermal, and FCC Class B EMC specifications.

251 citations

Proceedings ArticleDOI
20 Mar 2016
TL;DR: In this article, the authors present a 2 kW, 60 Hz, 450 VDC to 240 VRMS power inverter, designed and tested subject to the specifications of the Google/IEEE Little Box Challenge.
Abstract: High efficiency and compact single phase inverters are desirable in many applications such as solar energy harvesting and household appliances. This paper presents a 2 kW, 60 Hz, 450 VDC to 240 VRMS power inverter, designed and tested subject to the specifications of the Google/IEEE Little Box Challenge. The inverter features a 7-level flying capacitor multilevel converter, with low-voltage GaN switches operating at 120 kHz, the highest switching frequency to date at this power level. The inverter also includes an active buffer for twice-line-frequency power pulsation decoupling, which reduces the required capacitance by a factor of eight compared to conventional passive decoupling capacitor, while maintaining an efficiency above 99%. The inverter prototype is a self-contained box that achieves a high power density of 216 W/in3 and a peak overall efficiency of 97.6% while meeting the constraints including input current ripple, load transient, thermal and EMC specifications.

83 citations

Proceedings ArticleDOI
01 Jul 2017
TL;DR: In this article, the authors investigated the origins of the voltage imbalance in practical implementations of flying capacitor multilevel (FCML) converters and presented corresponding solutions to solve the problem.
Abstract: Flying capacitor multilevel (FCML) converters are known to naturally balance the capacitor voltages through the use of phase-shifted pulse-width modulation. However, in practice, the capacitor voltages can still deviate and active balancing is often required. This work investigates the origins of the voltage imbalance in practical implementations of such converters and presents corresponding solutions. It is shown that the source impedance and the input capacitor can have a drastic impact on the flying capacitor voltages. Moreover, we also demonstrate that an FCML converter with an even number of levels has significantly better immunity to the presence of source impedance than one with an odd number of levels. It is also found that gate signal propagation delay mismatch from half-bridge gate drivers will lead to capacitor imbalance. An alternative gate drive power supply circuit is designed to address this problem. Lastly, variations of switches' on-resistance are found to have a small impact on the capacitor voltage balance.

75 citations

Journal ArticleDOI
TL;DR: A new hybrid/resonant SC converter topology, comprising two cascaded 2-to-1 ReSC converters, to address high-conversion-ratio applications and proposes a zero-voltage switching method to improve light-load efficiency.
Abstract: Resonant switched-capacitor (ReSC) converters have efficient utilization of both active and passive components, and hold the potential to achieve higher efficiency and higher power density than conventional switched-capacitor (SC) and magnetic-based converters. This article presents a new hybrid/resonant SC converter topology, comprising two cascaded 2-to-1 ReSC converters, to address high-conversion-ratio applications. The proposed cascaded resonant converter has a simple structure and operation principle and can achieve one of the best overall metrics among popular ReSC topologies. A 36-60-V input 4:1-fixed-ratio bus converter prototype for data center application is designed and constructed. We present detailed design guidelines and discussions to address practical challenges, such as component variations and interstage decoupling requirements. With 48-V input and operating at the typical zero-current switching mode of ReSC converters, the prototype achieves a peak efficiency of 98.85% (including gate drive loss) and a power density of 2500 W/in 3 , both of which are significantly higher than the state of the art. Furthermore, we propose a zero-voltage switching method to improve light-load efficiency. Through this control method, which greatly reduces the output capacitance loss, the prototype can maintain an efficiency above 97% starting from 3% of the rated load, with a peak of 99.0%.

75 citations

Journal ArticleDOI
TL;DR: A power factor correction (PFC) front end based on a seven-level flying capacitor multilevel (FCML) boost converter that features the use of low-voltage-rated transistors, reduced voltage stress, and high effective switching frequency on the filter inductor to significantly improve the power density of the PFC front end compared to conventional solutions.
Abstract: This paper presents a power factor correction (PFC) front end based on a seven-level flying capacitor multilevel (FCML) boost converter. Compared to the conventional two-level boost converter, the proposed seven-level FCML converter features the use of low-voltage-rated transistors, reduced voltage stress, and high effective switching frequency on the filter inductor. These characteristics of the FCML converter lead to drastic reduction in the filter inductor size while maintaining high efficiency and, therefore, significantly improve the power density of the PFC front end compared to conventional solutions. On the other hand, the small inductance imposes challenges on the PFC control. The dynamics of the seven-level FCML converter has been analyzed, and a feedforward control has been implemented to overcome these challenges. A hardware prototype is designed for universal ac input (90 to 265 Vac), 400-V dc output, and 1.5-kW power rating. Compared to existing solutions, the hardware prototype demonstrates improved efficiency and power density while maintaining high power factor and low THD. A power density of 219 W/in3 (490 W/in3 for the power stage) has been achieved, and a peak efficiency of 99.07% has been experimentally verified.

63 citations


Cited by
More filters
01 Jan 1992
TL;DR: In this paper, a multilevel commutation cell is introduced for high-voltage power conversion, which can be applied to either choppers or voltage-source inverters and generalized to any number of switches.
Abstract: The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<>

1,202 citations

Journal ArticleDOI
TL;DR: The UWBG semiconductor materials, such as high Al‐content AlGaN, diamond and Ga2O3, advanced in maturity to the point where realizing some of their tantalizing advantages is a relatively near‐term possibility.
Abstract: J. Y. Tsao,* S. Chowdhury, M. A. Hollis,* D. Jena, N. M. Johnson, K. A. Jones, R. J. Kaplar,* S. Rajan, C. G. Van de Walle, E. Bellotti, C. L. Chua, R. Collazo, M. E. Coltrin, J. A. Cooper, K. R. Evans, S. Graham, T. A. Grotjohn, E. R. Heller, M. Higashiwaki, M. S. Islam, P. W. Juodawlkis, M. A. Khan, A. D. Koehler, J. H. Leach, U. K. Mishra, R. J. Nemanich, R. C. N. Pilawa-Podgurski, J. B. Shealy, Z. Sitar, M. J. Tadjer, A. F. Witulski, M. Wraback, and J. A. Simmons

785 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a 2-kW, 60-Hz, 450-V -to-240-V power inverter, designed and tested subject to the specifications of the Google/IEEE Little Box Challenge, which achieves a high power density of 216 W/in $3$ and a peak overall efficiency of 97.6%, while meeting the constraints including input current ripple, load transient, thermal, and FCC Class B EMC specifications.
Abstract: High-efficiency and compact single-phase inverters are desirable in many applications such as solar energy harvesting and electric vehicle chargers. This paper presents a 2-kW, 60-Hz, 450-V $ _{\text{DC}}$ -to-240-V $_{\text{AC}}$ power inverter, designed and tested subject to the specifications of the Google/IEEE Little Box Challenge. The inverter features a seven-level flying capacitor multilevel converter, with low-voltage GaN switches operating at 120 kHz. The inverter also includes an active buffer for twice-line-frequency power pulsation decoupling, which reduces the required capacitance by a factor of 8 compared to conventional passive decoupling capacitors, while maintaining an efficiency above 99%. The inverter prototype is a self-contained box that achieves a high power density of 216 W/in $^3$ and a peak overall efficiency of 97.6%, while meeting the constraints including input current ripple, load transient, thermal, and FCC Class B EMC specifications.

251 citations

Journal ArticleDOI
Yanchao Li1, Xiaofeng Lyu1, Dong Cao1, Shuai Jiang2, Chenhao Nan2 
TL;DR: Through the proposed design methodology in this paper, power loss on switching devices and planar inductors can be minimized and detailed power loss analysis and breakdown provide hints for further efficiency improvement.
Abstract: Achieving high efficiency and high power density features of intermediate bus converter (IBC) in data center application is very critical. This paper proposes a nonisolated switched-tank dc–dc converter (STC) to meet the high requirement of IBC. The proposed STC has fixed voltage conversion ratio. Theoretical analysis provides the guideline for designing resonant tank and nonresonant tank as well as selecting proper deadtime for the proposed circuit. With resonant operation feature of the proposed circuit, zero current switching is realized on all switching devices to help the high-efficiency operation of the proposed converter. Through the proposed design methodology in this paper, power loss on switching devices and planar inductors can be minimized. In addition, detailed power loss analysis and breakdown provide hints for further efficiency improvement. Simulation has been performed to validate the operating principle of the proposed STC. A designed 6x STC (450 W nominal/600 W maximum) based on eGaNFETs is demonstrated. With 54 V typical input voltage, the output of the 6x STC is 9 V. The GaN-based prototype achieves a peak efficiency of 98.55%. Also, it achieves 97.18% efficiency and 750 W/in3 power density at 450 W.

120 citations

Journal ArticleDOI
TL;DR: In this paper, a high-efficiency, high-power-density buffer architecture is proposed for power pulsation decoupling in power conversion between dc and single-phase ac. In the proposed architecture, the main energy storage capacitor is connected in series with an active buffer converter across the dc bus.
Abstract: A high-efficiency, high-power-density buffer architecture is proposed for power pulsation decoupling in power conversion between dc and single-phase ac. We present an active decoupling solution that yields improved efficiency and reduced circuit complexity compared to existing solutions. In the proposed architecture, the main energy storage capacitor is connected in series with an active buffer converter across the dc bus. The series-stacked capacitor blocks the majority of the dc bus voltage to reduce the voltage stress on the buffer converter, such that fast, low-voltage transistors can be employed for the buffer converter. Moreover, the series capacitor provides the majority of the power pulsation decoupling through a wide voltage swing, and the buffer converter only needs to process a small fraction of the total power of the entire architecture, allowing a very small active circuit volume and very high system efficiency. The circuit operation and design constraints are analyzed in detail. In the proposed buffer architecture, the series stacking of a nearly lossless capacitor and a lossy converter presents a challenge of capacitor voltage balancing and power loss compensation. We propose a control scheme exploiting the small ripple in the bus voltage and dc input current to compensate for the power loss in the buffer converter while maintaining the voltage balance. Light-load techniques are also introduced to ensure that the buffer architecture meets strict ripple requirements while providing sufficient loss compensation. A 2-kW hardware prototype based on low-voltage GaN switches has been built to demonstrate the performance of the proposed solution. A power density of 25 W/cm $^3$ (410 W/in $^3$ ) by rectangular box volume and an efficiency above 98.9% across a wide load range has been experimentally verified.

118 citations