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2016 Technical Sessions

Monday-Tuesday, April 4-5 2016

Session T1: Modeling and Control

Monday, April 4, 1:30 P.M. - 3:30 P.M.
Session Chair: Prof. Rolando Burgos, Virginia Tech

  • T1: A New Constant On Time Current Mode Control with Ultrafast Load Transient Response Syed Bari, Qiang Li, Fred C Lee

  • Abstract: The paper presents a new current mode control using charge control concept to improve the performances of the constant on-time control. Currently, ripple-based current mode control is very widely used for its excellent small-signal property. The issue of this ripple-based current mode control is that when the inductor current ripple becomes small because of ripple cancellation effect for multiphase operation, control becomes very noise sensitive and create jittering at the output. These days constant on-time control is widely used for the VR applications for its higher light-load efficiency and higher bandwidth design capability. In the constant on-time control, current mode control based on inductor current ripple is very popularly used because of its very simple compensation. One issue of this ripple-based current mode constant on-time control is that, in the heavy load step up transient, inductor current increment becomes limited by on-time and minimum off-time ratio in each cycle, which can create large undershoot at the output. On the other hand, in the load step-down case, if load change occurs at the beginning of fixed Ton, large overshoot can occur at the output as well. For the multiphase operation case, limited pulse overlapping capability of different phases becomes an issue at heavy load step-up transient. In this paper, a new current mode control based on charge control concept is presented to solve these limitations of ripple-based current mode controls with simulation and test results to verify the concept.

  • T2: Low Frequency Common Mode Voltage Control for Systems Interconnected with Power Converters Fang Chen, Rolando Burgos, Dushan Boroyevich, Xuning Zhang

  • Abstract: DC system is promising in data centers and future homes. It can be interconnected with ac system through power converters. One typical case is connecting the 380 V dc grid to the single-phase ac utility through a transformerless two-stage ac/dc converter. In such configuration, the ac and dc system common mode (CM) quantities are coupled through the common ground. While the high frequency noise is filtered by passives, the dc and low frequency CM voltage also needs to be controlled for bipolar dc systems. In this paper, a passive floating filter is used to contain the high frequency noise within the converter. An active CM duty cycle injection method is proposed to suppress the low-frequency (e.g. double-line frequency) CM voltage ripple and generate symmetric dc bus voltage to the ground. The operation range is identified and the impact from voltage level and grounding scheme is analyzed. Detailed CM circuit is modeled. The CM transfer function is derived and verified by measurement to complete the control loop design. Design trade-off is provided. Experimental results validate the performance and stability of the CM voltage control. The control method is also generalized to three-phase cascaded converters.

  • T3: Model-Based Design of a Modular Multilevel Converter with Minimized Design Margins Niloofar Rashidi Mehrabadi, Rolando Burgos, Christopher Roy, Dushan Boroyevich

  • Abstract: A discrepancy between simulation and experimental results is inevitable due to their different sources of uncertainty, which are not usually incorporated at an early design stage. Therefore, design margins are used for design variables in order to generate reliable modeling and simulation-based designs. These margins are generally estimated using heuristic safety factors. In this paper, a design margin calculation procedure is proposed to minimize the allocated margin of the selected design specification when designing a converter in order to better utilize the converter's components. This procedure is based on probabilistic modeling and simulation, which take into account different sources of uncertainties.

  • T4: Capacitor Voltage Ripple Reduction for Modular Multilevel Converter with Over Modulation Yadong Lyu, Fred C. Lee, Qiang Li, Chen Li

  • Abstract: In this paper, a method of capacitor voltage ripple reduction for modular multilevel converter is proposed. In conventional control of MMC, capacitor voltage ripples consist of fundamental component and 2nd order component. That is because the module input power contains fundamental power and 2nd order power. With power flow analysis, the physical meaning is that this fundamental power is swapping between upper arm and lower arm, but the 2nd order power is delivered to the load. With this proposed method, both fundamental power and 2nd order power of module have been reduced dramatically. As a result, the capacitor voltage ripple can be reduced about 80%.

Session T2: GaN Devices and Applications

Monday, April 4, 4:00 P.M. - 5:30 P.M.
Session Chair: Prof. Qiang Li, Virginia Tech

  • T1: Comparison of Silicon, SiC and GaN Power Transistor Technologies with Breakdown Voltage Rating from 1.2 kV to 15 kV Sauvik Chowdhury, Zhibo Guo, Xueqing Liu, T. Paul Chow

  • Abstract: In recent years, different power transistors have been developed in silicon carbide (SiC) and gallium nitride (GaN) as replacements for silicon based IGBTs. This paper presents a simulation comparison of the static and dynamic performance of silicon IGBTs with different SiC and GaN based lateral and vertical power transistors (HEMT, MOSFET and IGBT) with breakdown voltage ratings between 1.2 kV to 15 kV. The strengths and weaknesses of different technologies which make them suitable at different voltage levels have been discussed.

  • T2: Design Consideration of MHz Active Clamp Flyback Converter with GaN Devices for Low Power Adapter Application Xiucheng Huang, Junjie Feng, Weijing Du, Fred C. Lee, Qiang Li

  • Abstract: With ever-increasing demands of smaller size, lighter weight for all forms of consumer electronics, efficient power conversion with higher operating frequency has always being pursued rigorously. This paper demonstrates high frequency, high efficiency and high power density design of active clamp flyback converter for adapter application. Both the primary and secondary switches are gallium nitride (GaN) devices which can significantly reduce the device related conduction and switching loss. The design procedures, including the selection of active clamping capacitor, optimization of flyback transformer, and EMI filter design, are presented in detail. A 65W (19.5V/3.3A) prototype of active clamp flyback front end converter is developed to verify the feasibility of the system design. The prototype efficiency is 1~2% higher than the state of art product and the power density (exclude case) is more than 40W/in3.

  • T3: A Novel High Efficiency System Architecture for Bi-directional On Board Battery Charger Bin Li, Fred C. Lee, Qiang Li, Zhengyang Liu

  • Abstract: CLLC bi-directional resonant converter is able to achieve soft switching for all devices, which makes it a great candidate for high frequency DC-DC converter. In order to make the converter working at its optimized point, a variable DC-link voltage is introduced so that the switching frequency can be fixed around resonant frequency. Four different candidates are evaluated and compared, including convention fixed DC-link voltage structure. The advantage of variable DC-link voltage is demonstrated. With this variable DC-link voltage, 1.2kV SiC devices are adopted as primary side switches to reduce conduction loss as well as switching loss. 650 GaN devices are used in parallel as secondary side switch to handle the high output current.

Session T3: SiC Devices and Applications

Tuesday, April 5, 8:00 A.M. - 9:30 P.M.
Session Chair: Prof. Dushan Boroyevich, Virginia Tech

  • T1: Modular Scalable Medium-voltage Impedance Measurement Unit Using 10 kV SiC MOSFET PEBBs Igor Cvetkovic, Zhiyu Shen, Marko Jaksic, Christina DiMarino, Fang Chen, Dushan Boroyevich, Rolando Burgos

  • Abstract: This paper describes the design and implementation of the first functional medium-voltage impedance measurement unit capable of characterizing in-situ source and load impedances of dc- and ac- networks (4160 V ac, 6000 V dc, 300 A, 2.2 MVA) in the frequency range from 0.1 Hz - 1 kHz. It comprises three power electronics building blocks, each built using SiC MOSFET H-bridges, features great reconfigurability, and allows both series and shunt perturbation injection in order to achieve accurate impedance characterization of the Navy's shipboard power systems. With extraordinary advantages featured by the power electronics building block modular concept, and unconventional power processing benefits offered by SiC semiconductors, development of the unit shown in this paper unquestionably enables both, improvement of the existing, and design of the future, stable and reliable electrical Navy shipboard platforms with advanced electrical energy generation and modern distribution architecture.

  • T2: Gate Driver Design for 1.7kV SiC MOSFET Module with Rogowski Current Sensor for Shortcircuit Protection Jun Wang, Zhiyu Shen, Christina DiMarino, Rolando Burgos, Dushan Boroyevich

  • Abstract: This paper shows a gate driver design for 1.7 kV SiC MOSFET module as well a Rogowski-coil based current sensor for effective shortcircuit protection. The design begins with the power architecture selection for better common-mode noise immunity as the driver is subjected to high dv/dt due to the very high switching speed of the SiC MOSFET modules. The selection of the most appropriate gate driver IC is made to ensure the best performance and full functionalities of the driver, followed by the circuitry designs of paralleled external current booster, Soft Turn-Off, and Miller Clamp. In addition to desaturation, a high bandwidth PCB-based Rogowski current sensor is proposed to serve as a more effective method for the shortcircuit protection for the high-cost SiC MOSFET modules.

  • T3: Design and Optimization of a High Performance Isolated Three-Phase AC/DC Converter Qiong Wang, Xuning Zhang, Rolando Burgos, Dushan Boroyevich, Adam White, Mustansir Kheraluwala

  • Abstract: This paper presents the design and optimization of a high performance isolated three-phase AC/DC converter that converts variable frequency 115 V AC voltage into isolated 28 V DC voltage for modern aircrafts. The main design target is to maximize converter rated power within given loss, size limits and operation requirements. A two-stage structure, consisting of an active front-end (AFE) converter and an isolated DC/DC converter, is employed. To complete the design and optimization of the multi-converter system, a hierarchical design and optimization approach has been developed to explore the system loss-size Pareto front with considerations of thermal management, EMI performance and power quality. Methods for component optimization and loss calculation are introduced. Based on the design results (system loss-size Pareto front), a Vienna rectifier and an LLC resonant converter were selected for AFE and DC/DC stage respectively. Finally, a 1.2 kW convection cooled prototype was built and experimentally tested. It achieved 97.1% full load efficiency and 22 W/inch3 power density. Compliance of EMI and power quality standard was experimentally verified.

Session T4: High Density Integration

Tuesday, April 5, 10:00 A.M. - 11:30 A.M.
Session Chair: Prof. Guo-Quan Lu, Virginia Tech

  • T1: Design of a High-Density, Diode-Less 1.2 kV, 90 A SiC MOSFET Half-Bridge Power Module Christina DiMarino, Wenli Zhang, Rolando Burgos, Dushan Boroyevich

  • Abstract: SiC devices with current ratings close to 100 A per chip have recently been released. These devices decrease the number of paralleled die needed in high-current power modules, thus increasing power density. By utilizing these devices in synchronous operation with the body diode used for dead time commutation, the external antiparallel diode can be eliminated. This mode reduces cost, and further increases the power density without sacrificing efficiency. In this work, a 1.2 kV, 90 A diode-less SiC MOSFET half-bridge module was designed, fabricated and tested. A survey of packaging materials and technologies was conducted, and the selections were based on the tradeoff between cost and performance. The fabricated module has low gate- and power-loop parasitic inductances (3 and 2.4 nH, respectively), and has more than twice the power density (7.8 W/mm3) and less than half of the switching loss (1.3 mJ) as similarly rated commercial half-bridge modules.

  • T2: Very High Frequency Integrated VR for Small Portable Devices Dongbin Hou, Fred C Lee, Qiang Li

  • Abstract: As today's small portable devices (smartphones, tablets, etc.) become lighter, thinner, quicker, and smarter, the voltage regulator for the processor is expected to be efficient, miniaturized, integrated, and placed closer to the processor. To power multi-core processors efficiently, dynamic voltage and frequency scaling (DVFS) were proposed to dramatically reduce power consumption by fast adapting voltage and frequency with respect to the power demand of each core. In this paper, a concept of very high frequency (tens of MHz) 3D integrated voltage regulator for small portable devices is proposed. A 20MHz inductor with NEC flake magnetic material is designed, fabricated and experimentally tested, featuring simple structure, small size, ultra-low profile, air-gap free, and lateral non-uniform flux.

  • T3: Omnidirectional Wireless Power Transfer for Portable Devices Junjie Feng, Qiang Li, Fred C.Lee

  • Abstract: Recently, wireless power transfer market is increasing rapidly due to its convenience. In the large growing market, low power devices, such as consumer electronics and mobile devices, share a large portion. In this paper, existing state-of-art wireless charging platforms for portable devices are classified and evaluated in this paper. Wireless power transfer system with omnidirectional flux is preferred than planar charging system due to its better user experience. FEA simulation is used to verify three dimensional flux distribution, however, it is very time-consuming. Therefore, numerical model to analyze the three dimensional flux is built in MATLAB. With simulation and calculation model, the limitations of existing omnidirectional wireless power transfer system is illustrated according to application. Omnidirectional wireless power transfer can only be achieved in limited area due to its transmitter coil structure. A new transmitter coil structure with omnidirectional wireless power transfer is proposed in this paper. The advantage of proposed system is demonstrated by numerical model and simulation. With this proposed coil structure, wireless power transfer system will be much more convenient due to its increased freedom for position and orientation of charging device.

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