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4. Modelling, design, control, and implementation of advanced isolated DC/DC converters for renewable energy applications.

Author

Wei, Yuqi, Luo, Quanming, Mou, Di, Zhao, Shuang, Liserre, Marco, and Mantooth, H. Alan

Subjects
ENGINEERS, INTEGRATED circuit design, ROBUST stability analysis, ELECTRIC power transmission, ELECTRICAL engineering, DC-to-DC converters
Abstract

This document discusses the increasing demand for high-efficient isolated DC/DC converters in renewable energy applications. It presents seventeen papers that cover various topics such as reducing switch count and current balancing, addressing voltage ringing issues, solving current unbalance problems, and optimizing converter design. The papers provide experimental results and propose innovative methods to improve the efficiency and performance of DC/DC converters in renewable energy applications. The document also includes three research papers related to power converters, including one on a prototype for NanoGrid applications, one on a new DC-DC bipolar resonance converter, and one on enhancing the stability of a DCMG cluster. The text also includes acknowledgments and biographies of the guest editors. [Extracted from the article]

Published
2024
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5. An adaptive synchronous rectifier driving strategy for unregulated LLC resonant converter.

Author

Wei, Yuqi, Li, Ziang, and Liu, Jinjun

Subjects
DC transformers, EQUALIZERS (Electronics), VOLTAGE, INDUSTRIAL applications, DIODES
Abstract

LLC resonant converters are widely adopted in many different industrial applications due to their high efficiency operation. To further improve LLC resonant converters' efficiency, the secondary unregulated diode rectifier is replaced by the synchronous rectifier (SR). In many applications, LLC converter is designed to operate at resonant frequency to maximize the system efficiency and act as a DC transformer (DCX). The SR driving signal is set as the same as the primary driving signal to work in an open‐loop mode. However, the resonant frequency will deviate due to the tolerance, working environment, and ageing effect of circuit components, which will lead to the degradation of the system efficiency and output voltage variation. Unfortunately, most of the existing techniques cannot be simply adopted in SR LLC DCX. Therefore, an adaptive SR driving strategy that can compensate the circuit components' variations is necessary for SR LLC DCX. Inan adaptive SR strategy based on the constant voltage gain characteristic at resonant frequency point is proposed. The proposed strategy is applicable for all different scenarios with easy implementation and low cost. [ABSTRACT FROM AUTHOR]

Published
2024
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16. Cryogenic Overcurrent Characteristic of GaN HEMT and Converter Evaluation

Author

Wei, Yuqi, Hossain, Md Maksudul, and Mantooth, H. Alan

Abstract

Cryogenic power electronics is regarded as the next step to improve the converter efficiency and power density. It is advantageous in many different applications, including aerospace, renewable energy, transportation and so on. Among all different semiconductors, gallium nitride (GaN) was found more advantageous with significant loss reduction at cryogenic temperature. In this paper, overcurrent test is performed and analyzed for a high-efficient commercial GaN high electron mobility transistor (HEMT). The experimental results demonstrate a significant improvement of the device overcurrent capability at cryogenic temperature (from 160 A at room temperature to 250 A at cryogenic temperature). The operating mechanisms behind the overcurrent test are investigated and discussed. Finally, a 5 kW GaN HEMT based cryogenic Buck converter is built and tested. Maximum efficiency of 98.5% is achieved at 1.5 kW output power and around 1% efficiency improvement can be achieved when compared to room temperature operation. Another GaN HEMT based four-switch Buck-boost converter is evaluated at cryogenic temperature, maximum efficiency improvement of 1.5% is observed when compared to room temperature.

Published
2024
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34. Self-Tuning Multiport Resonant DC/DC Converter Based on Actively-Controlled Inductors for Hybrid Storage System Integration

Author

Pereira, Thiago, Wei, Yuqi, Pascal, Yoann, Mantooth, H. Alan, and Liserre, Marco

Abstract

In the field of electric mobility, in particular heavy-duty electric vehicles and long-haul trucks, the energy systems are susceptible to transients with different amplitudes and dynamics due to the high power demand. With the combination of high power and long distances, the available battery technologies become insufficient as a single energy source for such a system. Thus, the integration of hybrid energy storage systems (HESSs) with different energy capabilities, such as fuel cells, battery packs, and supercapacitors, is highly required. In this context, for leveraging HESSs in an efficient way, a resonant multiwinding transformer-based converter is proposed to interconnect these different energy storage systems (ESSs) since the resonant converters are able to operate at a wider range of switching frequencies and, hence, a wider soft-switching range. However, due to the multiple resonant circuits and possible parameter deviations, the control capability might be compromised. Thus, a multiport resonant dc/dc converter embedded with variable inductors is proposed to enhance the power flow management among these different ESSs with reduced conversion stages. Further, the proposed concept can also improve the immunity to parameter deviations on the resonant by compensating for possible variations at the resonant frequencies. Finally, simulations and experimental results of a $\text{20} \;\text{kW}$ four-port resonant dc/dc converter embedded with variable inductors are shown to prove the effectiveness of the proposed concept.

Published
2023
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35. Comparisons and Evaluations of Silicon and Wide Band Gap Devices at Cryogenic Temperature

Author

Wei, Yuqi, Hossain, Md Maksudul, and Mantooth, H. Alan

Abstract

In this article, the static and dynamic characterizations for semiconductors with different materials, including silicon (Si), silicon carbide (SiC), and gallium nitride (GaN), are evaluated and compared at room temperature and cryogenic temperature (liquid nitrogen temperature). For static characterizations, the on-state resistance and threshold voltage are evaluated. For dynamic characterizations, the turn-on switching loss, turn-off switching loss, and dynamic on-state resistance (Rds(on)) are evaluated. The results demonstrate that Si and GaN based semiconductors have improved performances with lower on-state resistance and faster switching speed at low temperature operations. For SiC based semiconductors, the on-state resistance increases significantly at cryogenic temperature. The switching speed is reduced dramatically for the evaluated 1.2 kV SiC metal oxide semiconductor field effect transistors (MOSFETs) at cryogenic temperature. This makes it less attractive for cryogenic applications. For the evaluated 650 V and 900 V SiC MOSFETs, the switching speed remains almost unchanged at low temperature. GaN high electron mobility transistor (HEMT) demonstrates a fast turn-on switching speed at low temperature, where the device's dv/dt and di/dt are almost doubled when compared with room temperature. In addition, the dynamic Rds(on) of the evaluated GaN HEMTs also decreases at low temperatures. The evaluation results can serve as guidelines for cryogenic power electronics applications. Meanwhile, the future work for semiconductors cryogenic characterizations is discussed.

Published
2023
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40. Performance evaluation of NBA teams: A non-homogeneous DEA approach

Author

Yang, Min, Wei, Yuqi, Liang, Liang, Ding, Jingjing, and Wang, Xianmei

Subjects
ComputingMethodologies_SYMBOLICANDALGEBRAICMANIPULATION
Abstract

National Basketball Association (NBA) is one of the four major sports leagues in North America. The performance evaluation of NBA teams is an important reference for team managers. However, non-homogeneity issues exist on both inputs and outputs sides for NBA teams evaluations. For example, some teams do not have “high-level” players as inputs and some teams are not qualified to play in the playoffs with respect to “wins in the playoffs” as an output. The current paper extends the existing non-homogeneous DEA method to address the non-homogeneous structure of NBA teams in performance evaluation by splitting NBA teams into types of homogeneous sub-units. The sub-unit, in this paper, consists of empirical input subset and output subset which satisfies both atomic property and maximum property. In addition, our method yields a unique efficiency decomposition of sub-units of NBA teams in 2018–2019 season without the need for imposing any additional conditions which are needed in some prior relative researches. As a result, detailed performance improvement directions for all teams can be provided.

Published
2020
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