Browsing by Author "Yu, Jianghui"
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- DC Fault Current Analysis and Control for Modular Multilevel ConvertersYu, Jianghui (Virginia Tech, 2016-11-28)Recent research into industrial applications of electric power conversion shows an increase in the use of renewable energy sources and an increase in the need for electric power by the loads. The Medium-Voltage DC (MVDC) concept can be an optimal solution. On the other hand, the Modular Multilevel Converter (MMC) is an attractive converter topology choice, as it has advantages such as excellent harmonic performance, distributed energy storage, and near ideal current and voltage scalability. The fault response, on the other hand, is a big challenge for the MVDC distribution systems and the traditional MMCs with the Half-Bridge submodule configuration, especially when a DC short circuit fault happens. In this study, the fault current behavior is analyzed. An alternative submodule topology and a fault operation control are explored to achieve the fault current limiting capability of the converter. A three-phase SiC-based MMC prototype with the Full-Bridge configuration is designed and built. The SiC devices can be readily adopted to take advantage of the wide-bandgap devices in MVDC applications. The Full-Bridge configuration provides additional control and energy storage capabilities. The full in-depth design, controls, and testing of the MMC prototype are presented, including among others: component selection, control algorithms, control hardware implementation, pre-charge and discharge circuits, and protection scheme. Systematical tests are conducted to verify the function of the converter. The fault current behavior and the performance of the proposed control are verified by both simulation and experiment. Fast fault current clearing and fault ride-through capability are achieved.
- Design of a 10 kV SiC MOSFET-based high-density, high-efficiency, modular medium-voltage power converterMocevic, Slavko; Yu, Jianghui; Fan, Boran; Sun, Keyao; Xu, Yue; Stewart, Joshua; Rong, Yu; Song, He; Mitrovic, Vladimir; Yan, Ning; Wang, Jun; Cvetkovic, Igor; Burgos, Rolando; Boroyevich, Dushan; DiMarino, Christina; Dong, Dong; Motwani, Jayesh Kumar; Zhang, Richard (IEEE, 2022-03)Simultaneously imposed challenges of high-voltage insulation, high dv/dt, high-switching frequency, fast protection, and thermal management associated with the adoption of 10 kV SiC MOSFET, often pose nearly insurmountable barriers to potential users, undoubtedly hindering their penetration in medium-voltage (MV) power conversion. Key novel technologies such as enhanced gatedriver, auxiliary power supply network, PCB planar dc-bus, and high-density inductor are presented, enabling the SiC-based designs in modular MV converters, overcoming aforementioned challenges. However, purely substituting SiC design instead of Sibased ones in modular MV converters, would expectedly yield only limited gains. Therefore, to further elevate SiC-based designs, novel high-bandwidth control strategies such as switching-cycle control (SCC) and integrated capacitor-blocked transistor (ICBT), as well as high-performance/high-bandwidth communication network are developed. All these technologies combined, overcome barriers posed by state-of-the-art Si designs and unlock system level benefits such as very high power density, high-efficiency, fast dynamic response, unrestricted line frequency operation, and improved power quality, all demonstrated throughout this paper.
- High-Frequency Design Consideration and EMI Mitigation in SiC-based Multilevel ConvertersYu, Jianghui (Virginia Tech, 2022-05-23)Medium Voltage (MV) power conversion systems are essential in high power applications to address the increasing demand of energy and the increasing penetration of renewable energy sources. MV power electronics converters are the key elements for power conversion in MV systems and are the focus of this study. Multilevel converter topologies are promising topologies in MV applications because of their reduced voltage stress on devices, excellent output quality, reduced semiconductor losses, lower common mode voltage among other advantages. However, they may suffer from the large number of switching devices and capacitors, as well as the need to regulate capacitor voltages. SiC MOSFETs can achieve higher switching speeds, higher switching frequencies, higher voltage ratings, higher operation temperatures compared to traditional Si devices. They have shown promise to increase the efficiency and power density of the converters, but may suffer from higher voltage overshoots, increased Electromagnetic Interference (EMI) emission and so on. In SiC-based multilevel converters, the features of multilevel topologies, and the features of SiC MOSFETs are coupled together. The benefits, challenges, and solutions of using SiC MOSFETs in multilevel converters are studied explicitly in this work. With the high switching speeds and high switching frequencies of SiC MOSFETs, and the large number of switches and capacitors in multilevel topologies, SiC-based multilevel converters need to be studied while considering high-frequency voltage and current behaviors and the interactions among them at different locations. Firstly, the use of SiC-based multilevel converter in the high-speed motor drive application is explored. A three-phase inverter is designed and built employing five-level Stacked Multicell Converter topology and SiC MOSFETs. The benefits and challenges of using multilevel converter topology and using SiC MOSFETs for this application are explored. A fitting topology is selected, and a prototype is designed, both with attentions paid to deal with the high switching speeds of SiC MOSFETs. The inverter is verified through experiments to meet all specifications with a high efficiency. Then a unique type of converter, converters with Integrated Capacitor Blocked Transistor (ICBT) cells are studied. Unlike the traditional methods, there are no fast-developing voltage unbalances, or high cell capacitor voltage ripples in ICBT-based converters. The ideal operation principle is analyzed and verified by the simulation results. Then the impacts of non-idealities on the operation are analyzed, and a control method is proposed for this type of converter. The operation and control of ICBT-based converters are verified by experimental results to achieve low cell capacitor voltage ripples and excellent voltage balance in Medium Voltage high power applications. Lastly, the conducted EMI emission in SiC-based multilevel converters are studied. Four SiC-based multilevel converters are studied, with the focus on the power circuit in one converter and the auxiliary circuits in the other three converters. The complexity of noise generation and propagation in multilevel converters is presented. The conducted EMI disturbances are experimentally evaluated, analyzed, and effectively mitigated in all four cases.