Christopher Barth

Bio: Christopher Barth is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Capacitor & Inverter. The author has an hindex of 16, co-authored 25 publications receiving 956 citations.

A 2-kW Single-Phase Seven-Level Flying Capacitor Multilevel Inverter With an Active Energy Buffer

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.

A High Power Density Series-Stacked Energy Buffer for Power Pulsation Decoupling in Single-Phase Converters

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.

Enhancing Microinverter Energy Capture With Submodule Differential Power Processing

Abstract: Differential power processing (DPP) is a power electronics system architecture that configures dc–dc converters in parallel with the PV string to improve its power yield. The parallel nature of the DPP architecture brings a number of benefits, such as low converter power rating and low power losses, all of which make DPP especially suitable for submodule-level maximum power point tracking (MPPT). Meanwhile, microinverters typically perform only module-level MPPT and do not address power losses due to uncompensated submodule mismatch. In this paper, we introduce DPP converters into a microinverter system to improve its energy capture by recovering power losses due to submodule mismatch. The control method to interface DPP converters with a microinverter for submodule MPPT is presented and the tradeoff between tracking accuracy and control overhead is analyzed. A small-footprint DPP converter is designed. A digitally assisted windowed sensing technique is also implemented to address the challenge of precise current sensing. Altogether, the proposed solution seamlessly integrates DPP into the existing microinverter design. To demonstrate the effectiveness of the proposed solution, a hardware prototype has been built and tested with an off-the-shelf commercial microinverter. The improvement in energy capture with DPP converters has been experimentally verified.

Design and control of a GaN-based, 13-level, flying capacitor multilevel inverter

Abstract: Multilevel topologies are an appealing method to achieve higher power density inverters for both mobile and stationary systems. This work discusses the design and development of a 13-level, flying capacitor multilevel (FCML) inverter. Operating from an 800 V bus, this inverter requires switches with a voltage blocking capability of less than 80 V. A 120 kHz switching frequency is enabled through the use of GaN FETs and the development of custom integrated switching cells, which reduce commutation loop inductance and allow for a modular design. Additionally, the frequency multiplication effect of FCML inverters allows the output inductor of the inverter to be made exceptionally small (4.7 μH) while maintaining a 0.7 % THD due to the 1.44 MHz effective inductor ripple frequency.

A 2 kW, single-phase, 7-level, GaN inverter with an active energy buffer achieving 216 W/in3 power density and 97.6% peak efficiency

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.

Multi-level conversion : high voltage choppers and voltage-source inverters

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.<>

Ultrawide-Bandgap Semiconductors: Research Opportunities and Challenges

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

A 2-kW Single-Phase Seven-Level Flying Capacitor Multilevel Inverter With an Active Energy Buffer

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.

Low-Frequency Power Decoupling in Single-Phase Applications: A Comprehensive Overview

Abstract: This paper presents a literature overview of all techniques proposed until the submission of this paper in terms of mitigating power oscillation in single-phase applications. This pulsating energy is the major factor for increasing the size of passive components and power losses in the converter and can be responsible for losses or malfunctioning of the dc sources. Reduction of power ripple at twice the fundamental frequency is one of the key elements to increase power converter density without lack of dc stiffness. Pulsation reduction is achieved by incorporating control techniques or auxiliary circuitries with energy storage capability in reactive elements to avoid this oscillating power to propagate through the converter, creating what is called as single-phase power decoupling. The topologies are divided as: rectifiers, inverters, and bidirectional. Among them, it is possible to classify as isolated and nonisolated converters. The energy storage method may be classify as: capacitive and inductive. For the power decoupling technique, it is convenient to divide as control and topology. The power decoupling technique may be implemented as series or parallel with respect to the ac, dc or link side. This paper represents the best reference on this topic.

A Distributed Approach to Maximum Power Point Tracking for Photovoltaic Submodule Differential Power Processing

Abstract: This paper presents the theory and implementation of a distributed algorithm for controlling differential power processing converters in photovoltaic (PV) applications. This distributed algorithm achieves true maximum power point tracking of series-connected PV submodules by relying only on local voltage measurements and neighbor-to-neighbor communication between the differential power converters. Compared to previous solutions, the proposed algorithm achieves reduced number of perturbations at each step and potentially faster tracking without adding extra hardware; all these features make this algorithm well-suited for long submodule strings. The formulation of the algorithm, discussion of its properties, as well as three case studies are presented. The performance of the distributed tracking algorithm has been verified via experiments, which yielded quantifiable improvements over other techniques that have been implemented in practice. Both simulations and hardware experiments have confirmed the effectiveness of the proposed distributed algorithm.