Design and Evaluation of High Efficiency Power Converters Using Wide-Bandgap Devices for PV Systems

The shortage of fossil resources and the need for power generation options that produce little or no environmental pollution drives and motivates the research on renewable energy resources. Power electronics play an important role in maximizing the utilization of energy generation from renewable energy resources. One major renewable energy source is photovoltaics (PV), which comprises half of all recently installed renewable power generation in the world. For a grid-connected system, two power stages are needed to utilize the power generated from the PV source. In the first stage, a DCDC converter is used to extract the maximum power from the PV panel and to boost the low output voltage generated to satisfy the inverter side requirements. In the second stage, a DC-AC inverter is used to convert and deliver power loads for grid-tied applications. In general, PV panels have low efficiency so high-performance power converters are required to ensure highly efficient PV systems. The development of wide-bandgap (WBG) power switching devices, especially in the range of 650 V and 1200 V blocking class voltage, opens up the possibility of achieving a reliable and highly efficient grid-tied PV system. This work will study the benefits of utilizing WBG semiconductor switching devices in low power residential scale PV systems in terms of efficiency, power density, and thermal analysis. The first part of this dissertation will examine the design of a high gain DC-DC converter. Also, a performance comparison will be conducted between the SiC and Si MOSFET switching devices at 650 V blocking voltage regarding switching waveform behavior, switching and conduction losses, and high switching frequency operation. A major challenge in designing a transformerless inverter is the circulating of common mode leakage current in the absence of galvanic isolation. The value of the leakage current must be less than 300mA, per the DIN VDE 0126-1-1 standard. The second part of this work investigates a proposed high-efficiency transformerless inverter with low leakage current. Subsequently, the benefits of using SiC MOSFET are evaluated and compared to Si IGBT at 1200 V blocking voltage in terms of efficiency improvement, filter size reduction, and increasing power rating. Moreover, a comprehensive thermal model design is presented using COMSOL software to compare the heat sink requirements of both of the selected switching devices, SiC MOSFET and Si IGBT. The benchmarking of switching devices shows that SiC MOSFET has superior switching and conduction characteristics that lead to small power losses. Also, increasing switching frequency has a small effect on switching losses with SiC MOSFET due to its excellent switching characteristics. Therefore, system performance is found to be enhanced with SiC MOSFET compared to that of Si MOSFET and Si IGBET under wide output loads and switching frequency situations. Due to the high penetration of PV inverters, it is necessary to provide advanced functions, such as reactive power generation to enable connectivity to the utility grid. Therefore, this research proposes a modified modulation method to support the generation of reactive power. Additionally, a modified topology is proposed to eliminate leakage current

A novel active gate driver for improving SiC MOSFET switching trajectory

The trend in power electronic applications is to reach higher power density and higher efficiency. Currently, the wide band-gap devices such as silicon carbide MOSFET (SiC MOSFET) are of great interest because they can work at higher switching frequency with low losses. The increase of the switching speed in power devices leads to high power density systems. However, this can generate problems such as overshoots, oscillations, additional losses, and electromagnetic interference (EMI). In this paper, a novel active gate driver (AGD) for improving the SiC MOSFET switching trajectory with high performance is presented. The AGD is an open-loop control system and its principle is based on gate energy decrease with a gate resistance increment during the Miller plateau effect on gate-source voltage. The proposed AGD has been designed and validated through experimental tests for high-frequency operation. Moreover, an EMI discussion and a performance analysis were realized for the AGD. The results show that the AGD can reduce the overshoots, oscillations, and losses without compromising the EMI. In addition, the AGD can control the turn-on and turn-off transitions separately, and it is suitable for working with asymmetrical supplies required by SiC MOSFETs.Postprint (author's final draft

FY 2005 Oak Ridge National Laboratory Annual Progress Report for the Power Electronics and Electric Machinery Program

The U.S. Department of Energy (DOE) and the U.S. Council for Automotive Research (composed of automakers Ford, General Motors, and DaimlerChrysler) announced in January 2002 a new cooperative research effort. Known as FreedomCAR (derived from ''Freedom'' and ''Cooperative Automotive Research''), it represents DOE's commitment to developing public/private partnerships to fund high-risk, high-payoff research into advanced automotive technologies. Efficient fuel cell technology, which uses hydrogen to power automobiles without air pollution, is a very promising pathway to achieve the ultimate vision. The new partnership replaces and builds upon the Partnership for a New Generation of Vehicles initiative that ran from 1993 through 2001. The Vehicle Systems subprogram within the FreedomCAR and Vehicle Technologies Program provides support and guidance for many cutting-edge automotive and heavy truck technologies now under development. Research is focused on understanding and improving the way the various new components of tomorrow's automobiles and heavy trucks will function as a unified system to improve fuel efficiency. This work also supports the development of advanced automotive accessories and the reduction of parasitic losses (e.g., aerodynamic drag, thermal management, friction and wear, and rolling resistance). In supporting the development of hybrid propulsion systems, the Vehicle Systems subprogram has enabled the development of technologies that will significantly improve fuel economy, comply with projected emissions and safety regulations, and use fuels produced domestically. The Vehicle Systems subprogram supports the efforts of the FreedomCAR and Fuel and the 21st Century Truck Partnerships through a three-phase approach intended to: (1) Identify overall propulsion and vehicle-related needs by analyzing programmatic goals and reviewing industry's recommendations and requirements, then develop the appropriate technical targets for systems, subsystems, and component research and development activities; (2) Develop and validate individual subsystems and components, including electric motors, emission control devices, battery systems, power electronics, accessories, and devices to reduce parasitic losses; and (3) Determine how well the components and subsystems work together in a vehicle environment or as a complete propulsion system and whether the efficiency and performance targets at the vehicle level have been achieved. The research performed under the Vehicle Systems subprogram will help remove technical and cost barriers to enable technology for use in such advanced vehicles as hybrid and fuel-cell-powered automobiles that meet the goals of the FreedomCAR Program. A key element in making hybrid electric vehicles practical is providing an affordable electric traction drive system. This will require attaining weight, volume, and cost targets for the power electronics and electrical machines subsystems of the traction drive system. Areas of development include: (1) Novel traction motor designs that result in increased power density and lower cost; (2) Inverter technologies involving new topologies to achieve higher efficiency and the ability to accommodate higher-temperature environments; (3) Converter concepts that employ means of reducing the component count and integrating functionality to decrease size, weight, and cost; (4) More effective thermal control and packaging technologies; and (5) Integrated motor/inverter concepts. The Oak Ridge National Laboratory's (ORNL's) Power Electronics and Electric Machinery Research Center conducts fundamental research, evaluates hardware, and assists in the technical direction of the DOE Office of FreedomCAR and Vehicle Technologies Program, Power Electronics and Electric Machinery Program. In this role, ORNL serves on the FreedomCAR Electrical and Electronics Technical Team, evaluates proposals for DOE, and lends its technological expertise to the direction of projects and evaluation of developing technologies. ORNL also executes specific projects for DOE. The following report discusses those projects carried out in FY 2004 and conveys highlights of their accomplishments. Numerous project reviews, technical reports, and papers have been published for these efforts, if the reader is interested in pursuing details of the work

Contribution to improve the EMI performance of electrical drive systems in vehicles with special consideration of power semiconductor modules

Diese Arbeit dient als Beitrag zur Verbesserung des EMV-Verhaltens elektrischer Antriebssysteme in Fahrzeugen, wobei der Fokus auf dem Leistungshalbleitermodul für die Automobilanwendung liegt. Für ein besseres und tieferes Verständnis der Quelle von leitungsgebundenen Störungen werden die EMV-Mechanismen und -Effekte im Zusammenhang mit dem Leistungsmodul im Antriebssystem durch Simulationen und Messungen untersucht. Der Einfluss der Diode Reverse Recovery Effekte auf das EMV-Verhalten wird quantitativ mit verschiedenen Lastströmen sowie mit verschiedenen Diodentypen, wie z.B. SiC-Schottky-Dioden, analysiert. Durch Simulationen wird der Einfluss des Leistungsmoduls auf das System untersucht; auf dieser Basis wird die Bedeutung verschiedener Faktoren innerhalb und außerhalb des Leistungsmoduls für das EMV-Verhalten bewertet. Zur Validierung der Simulationsergebnisse wird der Messaufbau für eine konventionelle EMV-Messung für die Automobilanwendung vorgestellt. Die Messergebnisse belegen, dass die Simulationsmodelle unter bestimmten Randbedingungen für zukünftige Leistungsmodulkonstruktionen zur EMV-Vorhersage verwendbar sind. Basierend auf dem Verständnis, wie es aus den Simulationen und Messergebnissen hergeleitet wurde, werden konkrete Optimierungskonzepte für ein inhärent störungsarmes Leistungsmodul entwickelt und realisiert. Dessen EMV-Verhalten sowie der Aufwand des Musterbaus aus Sicht des Leistungsmodulherstellers werden anhand verschiedenen Kriterien verglichen und bewertet. Außerdem wird das dynamische und Kurzschlussverhalten der Prototypen einschließlich der Stromverteilung zwischen den Halbleiterchips charakterisiert. In dieser Arbeit wird ein neuartiges Testverfahren vorgestellt, mit dem es möglich ist, das leitungsgebundene EMV-Verhalten von Leistungsmodulen abzuschätzen, ohne den gesamten Testaufbau wie bei einer konventionellen EMV-Messung zu erstellen. Diese Charakterisierung kann anschließend in der Phase der Inverterentwicklung verwendet werden, um ein geeignetes Modul auszuwählen und den erwarteten Aufwand zur Einhaltung der EMV Standards zu bewerten.This work serves as a contribution to improve the EMI performance of electrical drive systems in vehicles; the focus is on the power semiconductor module for automotive application. For a better and deeper understanding of the conducted EMI source, the conducted EMI mechanisms and effects in the drive system are investigated through simulations as well as measurements with special consideration of power modules: The influence of the diode recovery effects on the EMI performance is quantitatively analyzed with different load currents, as well as with different types of diodes, e.g. SiC Schottky barrier diode. Through the simulation, the influence coming from the power module to the system is clarified; the importance of different factors inside and outside of the power module regarding EMI performance are therefore evaluated. To validate the simulation results, the setup and test bench for a conventional EMI measurement for the typical automotive application are presented. Through the measurement results it is proven that the simulation models are usable under certain boundary conditions for future power module designs with regard to the EMI prediction. Based on the understanding and the conclusions from the simulation and measurement results, concrete EMI optimization concepts for an inherently low-interference power module are developed and realized. The EMI performance as well as the feasibility of the sample modules are compared and evaluated under different criteria from the power module manufacturer’s point of view. Besides, the dynamic and short-circuit performances of the sample modules, regarding to the current distribution on the semiconductor chips, are characterized. A novel test procedure is introduced in this work, by which it is possible to estimate the conducted EMI performance of power modules without building the whole test setup like in a conventional EMI measurement. This characterization can subsequently be used in the phase of converter development to select a suitable device and evaluate the expected effort to comply with EMI standards

A Low Temperature Co-fired Ceramic (LTCC) Interposer Based Three-Dimensional Stacked Wire Bondless Power Module

The objective of this dissertation research is to develop a low temperature co-fired ceramic (LTCC) interposer-based module-level 3-D wire bondless stacked power module. As part of the dissertation work, the 3-D wire bondless stack is designed, simulated, fabricated and characterized. The 3-D wire bondless stack is realized with two stand-alone power modules in a half-bridge configuration. Each stand-alone power module consists of two 1200 V 25 A silicon insulated-gate bipolar transistor (IGBT) devices in parallel and two 1200 V 20 A Schottky barrier diodes (SBD) in an antiparallel configuration. A novel interconnection scheme with conductive clamps and a spring loaded LTCC interposer is introduced to establish electrical connection between the stand-alone power modules to connect them in series to realize a half-bridge stack. Process development to fabricate the LTCC based 3-D stack is performed. In traditional power modules, wire bonds are used as a top side interconnections that introduce additional parasitic inductance in the current conduction path and prone to failure mechanism under high thermomechanical stresses. The loop inductance of the proposed 3-D half-bridge module exhibits 71% lower parasitic inductance compared to a wire bonded module. The 3-D stack exhibits better switching performance compared to the wire bonded counterpart. The measurement results for the 3-D stack shows 30% decrease in current overshoot at turn-on and 43% voltage overshoot at turn-off compared to the wire bonded module. Through measurements, it has been shown that the conducted noise reduces by 20 dB in the frequency range 20-30 MHz for the 3-D stack compared to the wire bonded counterpart. A simulation methodology using co-simulation techniques using ANSYS EM software tools is developed to predict EMI of a power module. Hardware verification of the proposed simulation methodology is performed to validate the co-simulation technique. The correlation coefficient between the measurement and simulation is found to be 0.73. It is shown that 53% of the variability in the simulation can be explained by the simulated result. Moreover, the simulated and measured amplitudes of the EMI spectrum closely match with each other with some variations due to round-off errors due to the FFT conversion

Resonant Behaviour of Pulse Generators for the Efficient Drive of Optical Radiation Sources Based on Dielectric Barrier Discharges

Dielectric barrier discharge (DBD) excimer lamps emit vacuum-UV optical radiation. This work presents novel methods for efficiently operating DBDs with short, high-voltage pulses. Transformer-less systems utilising SiC power semiconductor switches are presented. Pulse frequencies of up to 3.1 MHz and peak inverter efficiencies of 92 % were achieved. The work encloses both mathematical backgrounds of pulsed resonant circuits and practical implementation of low-inductive power stages

Characterization and evaluation of a 6.5-kV silicon carbide bipolar diode module

This work presents a 6.5-kV 1-kA SiC bipolar diode module for megawatt-range medium voltage converters. The study comprises a review of SiC devices and bipolar diodes, a description of the die and module technology, device characterization and modelling and benchmark of the device at converter level. The effects of current change rate, temperature variation, and different insulated-gate bipolar transistor (IGBT) modules for the switching cell, as well as parasitic oscillations are discussed. A comparison of the results with a commercial Si diode (6.5 kV and 1.2 kA) is included. The benchmark consists of an estimation of maximum converter output power, maximum switching frequency, losses and efficiency in a three level (3L) neutral point clamped (NPC) voltage-source converter (VSC) operating with SiC and Si diodes. The use of a model predictive control (MPC) algorithm to achieve higher efficiency levels is also discussed. The analysed diode module exhibits a very good performance regarding switching loss reduction, which allows an increase of at least 10 % in the output power of a 6-MVA converter. Alternatively, the switching frequency can be increased by 41 %.:1 Introduction 2 State of the art of SiC devices and medium-voltage diodes 2.1 Silicon carbide diodes and medium-voltage modules 2.2 Medium-voltage power diodes 3 Characterization of the SiC PiN diode module 37 3.1 Introduction 3.2 Experimental setup 3.3 Experimental results: static behaviour 3.4 Experimental results: switching behaviour 3.5 Comparison with 6.5-kV silicon diode 3.6 Oscillations in the SiC diode 3.7 Summary 4 Comparison at converter level 4.1 Introduction 4.2 Power device modelling 4.3 Determination of maximum converter power rating 4.4 Analysis 4.5 Increased efficiency through model predictive control 4.6 Summary 5 Conclusio